ATLAS OF GROUND-WATER RESOURCES IN PUERTO RICO 
AND THE U.S. VIRGIN ISLANDS
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 94-4198
I Prepared in cooperation with the
U.S. ENVIRONMENTAL PROTECTION AGENCY
ATLAS OF GROUND-WATER RESOURCES IN PUERTO RICO AND THE U.S. VIRGIN ISLANDS
By Thalia D. Veve and Bruce E. Taggart (editors)
U.S. GEOLOGICAL SURVEY
Water-Resources Investigations Report 94-4198
Prepared in cooperation with the
U.S. ENVIRONMENTAL PROTECTION AGENCY
San Juan, Puerto Rico 
1996
U.S. DEPARTMENT OF THE INTERIOR 
BRUCE BABBIT, Secretary
U.S. GEOLOGICAL SURVEY 
Gordon P. Eaton, Director
For additional information write to:
Caribbean District Chief 
U.S. Geological Survey 
GSA Center
651 Federal Drive, Suite 400-15 
San Juan, Puerto Rico 00965
Copies of this report can be purchased from:
U.S. Geological Survey
Earth Science Information Center
Open-File Reports Section, MS 517
Box 25286, Denver Federal Center
Denver, CO 80225
CONTENTS 
__         
Abstract............................................................................................................_^
Acknowledgement......................................................._^
1.0 Introduction................................................................................................................................................... 1
Thalia D. Veve
1.1 Purpose and scope...............................................................................................................................!
1.1.A Location and major geographic features...........................................................................................2
1.1.B Population and estimated ground-water use.....................................................................................2
1.1.C Geologic setting.................................................................................................................................3
1.1.D Hydrogeology ....................................................................................................................................3
1.1.E Ground-water levels and movement.................................................................................................. 3
1.1.F Soil permeability.................................................................................................................................3
1.2 Description of the area..........................................................................................................................3
1.3 General land-use patterns in Puerto Rico and the U.S. Virgin Islands .................................................6
1.3.A North Coast Area...............................................................................................................................6
1.3.B South Coast Area ..............................................................................................................................6
1.3.C West Coast Area ...............................................................................................................................6
1.3.D East Coast Province..........................................................................................................................8
1.3.E East Central Area..............................................................................................................................8
1.3.F Puerto Rico Offshore Islands: Isla de Culebra and Isla de Vieques..................................................8
1.3.G U.S. Virgin Islands.............................................................................................................................8
2.0 Ground-water resources areas in Puerto Rico............................................................................................11
2.1 North Coast Area ................................................................................................................................ 11
2.1.1 Aguadilla-Hatillo Region........................................................................................................... 12
Patrick Tucci
2.1.1.A Location and major geographic features .....................................................................12
2.1.1.B Population and estimated ground-water use............................................................... 13
2.1.1.C Geologic setting........................................................................................................... 14
2.1.1.D Hydrogeology..............................................................................................................16
2.1.1.E Ground-water levels and movement............................................................................17
2.1.1.F Soil permeability ..........................................................................................................18
2.1.2 Arecibo-Manati Region.............................................................................................................20
Angel Roman-Mas
2.1.2.A Location and major geographic features.....................................................................20
2.1.2.B Population and estimated ground-water use...............................................................20
2.1.2.C Geologic setting...........................................................................................................20
2.1.2.D Hydrogeology..............................................................................................................21
2.1.2.E Ground-water levels and movement............................................................................22
2.1.2.F Soil permeability ..........................................................................................................22
2.1.3 Vega Baja-Toa Baja Region.....................................................................................................30
Fernando Gomez-Gomez and Thalia D. Veve
2.1.3.A Location and major geographic features .....................................................................30
2.1.3.B Population and estimated ground-water use...............................................................30
2.1.3.C Geologic setting........................................................................................................... 33
2.1.3.D Hydrogeology.............................................................................................................. 34
2.1.3.E Ground-water levels and movement ...........................................................................37
2.1.3.F Soil permeability.......................................................................................................... 38
2.1.4 Bayamon-Loiza Region............................................................................................................40
Jose M. Rodriguez and Thalia D. Veve
2.1.4.A Location and major geographic features..................................................................... 40
2.1.4.B Population and estimated ground-water use............................................................... 40
2.1.4.C Geologic setting ..........................................................................................................42
2.1.4.D Hydrogeology..............................................................................................................44
2.1.4.E Ground-water levels and movement ...........................................................................46
2.1.4.F Soil permeability ..........................................................................................................47
2.2 South Coast Area ...............................................................................................................................49
2.2.1 Santa Isabel-Patillas Region.................................................................................................... 50
Orlando Ramos-Gines
2.2.1 .A Location and major geographic features..................................................................... 50
2.2.1.B Population and estimated ground-water use............................................................... 51
2.2.1.C Geologic setting ..........................................................................................................53
2.2.1.D Hydrogeology..............................................................................................................54
2.2.1.E Ground-water levels and movement ...........................................................................56
2.2.1.F Soil permeability.......................................................................................................... 57
2.2.2 Juana Diaz-Ponce Region .......................................................................................................59
Orlando Ramos-Gines
2.2.2.A Location and major geographic features..................................................................... 59
2.2.2.B Population and estimated ground-water use............................................................... 59
2.2.2.C Geologic setting .......................................................................................................... 61
2.2.2.D Hydrogeology..............................................................................................................62
2.2.2.E Ground-water levels and movement........................................................................... 64
2.2.2.F Soil permeability.......................................................................................................... 65
2.2.3 Penuelas-Guanica Region .......................................................................................................66
Orlando Ramos-Gines
2.2.3.A Location and major geographic features..................................................................... 66
2.2.3.B Population and estimated ground-water use............................................................... 67
2.2.3.C Geologic setting ..........................................................................................................68
2.2.3.D Hydrogeology..............................................................................................................69
2.2.3.E Ground-water levels and movement........................................................................... 71
2.2.3.F Soil permeability.......................................................................................................... 73
2.3 West Coast Area................................................................................................................................. 75
2.3.1 Anasco region ..........................................................................................................................76
Thalia D. Veve
2.3.1.A Location and major geographic features..................................................................... 76
2.3.1 .B Population and estimated ground-water use............................................................... 77
2.3.1.C Geologic setting ..........................................................................................................78
2.3.1.D Hydrogeology..............................................................................................................79
2.3.1.E Ground-water levels and movement ...........................................................................81
2.3.1.F Soil permeability.......................................................................................................... 82
Contents 
iii
2.3.2 Guanajibo Region.....................................................................................................................83
Thalia D. Veve
2.3.2.A Location and major geographic features .....................................................................83
2.3.2.B Population and estimated ground-water use ...............................................................84
2.3.2.C Geologic setting...........................................................................................................85
2.3.2.D Hydrogeology ..............................................................................................................87
2.3.2.E Ground-water levels and movement............................................................................89
2.3.2.F Soil permeability...........................................................................................................90
2.3.3 Lajas Region.............................................................................................................................91
Robert P. Graves
2.3.3.A Location and major geographic features .....................................................................91
2.3.3.B Population and estimated ground-water use ...............................................................92
2.3.3.C Geologic setting...........................................................................................................93
2.3.3.D Hydrogeology ..............................................................................................................94
2.3.3.E Ground-water levels and movement............................................................................95
2.3.3.F Soil permeability...........................................................................................................96
2.4 East Coast Area..................................................................................................................................97
2.4.1 Naguabo-Maunabo Region.......................................................................................................98
Angel Roman-Mas
2.4.1.A Location and major geographic features .....................................................................98
2.4.1.B Population and estimated ground-water use ...............................................................99
2.4.1.C Geologic setting......................................................................................................... 100
2.4.1.D Hydrogeology ............................................................................................................101
2.4.1.E Ground-water levels and movement..........................................................................103
2.4.1.F Soil permeability......................................................................................................... 104
2.5 East Central Area.............................................................................................................................. 105
2.5.1 Aguas Buenas-Juncos Region ...............................................................................................106
Juan C. Puig
2.5.1.A Location and major geographic features ...................................................................106
2.5.1.B Population and estimated ground-water use .............................................................107
2.5.1.C Geologic setting......................................................................................................... 108
2.5.1.D Hydrogeology............................................................................................................ 109
2.5.1.E Ground-water levels and movement..........................................................................111
2.5.1.F Soil permeability......................................................................................................... 112
2.6 Puerto Rico Offshore Islands............................................................................................................113
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico.................................................................114
Thalia D. Veve and Angel Roman-Mas
2.6.1.A Location and major geographic features ...................................................................114
2.6.1.B Population and estimated ground-water use............................................................. 114
2.6.1.C Geologic setting......................................................................................................... 117
2.6.1.D Hydrogeology ............................................................................................................117
2.6.1.E Ground-water levels and movement..........................................................................122
2.6.1.F Soil permeability......................................................................................................... 122
3.0 Ground water-resources areas in the U.S. Virgin Islands......................................................................... 125
3.1 U.S. Virgin Islands............................................................................................................................ 125
3.1.1 St. Thomas and St. John, U.S. Virgin Islands........................................................................ 126
Robert P. Graves
3.1.1.A Location and major geographic features................................................................... 126
3.1.1.B Population and estimated ground-water use............................................................. 126
3.1.1.C Geologic setting ........................................................................................................ 129
3.1.1.D Hydrogeology............................................................................................................ 130
3.1.1.E Ground-water levels and movement......................................................................... 131
3.1.1.F Soil permeability........................................................................................................ 131
3.1.2 St. Croix, U.S. Virgin Islands.................................................................................................. 133
Zelda Chapman Bailey
3.1.2.A Location and major geographic features................................................................... 133
3.1.2.B Population and estimated ground-water use............................................................. 134
3.1.2.C Geologic setting ........................................................................................................ 136
3.1.2.D Hydrogeology............................................................................................................ 137
3.1.2.E Ground-water levels and movement......................................................................... 137
3.1.2.F Soil permeability........................................................................................................ 137
4.0 Present and potential ground-water problems in Puerto Rico and the U.S. Virgin Islands....................... 141
4.1. North Coast Area............................................................................................................................. 142
4.1.1 Aguadilla-Hatillo Region......................................................................................................... 142
4.1.2 Arecibo-Manatf Region .......................................................................................................... 142
4.1.3 Vega Baja-Toa Baja Region................................................................................................... 142
4.1.4 Bayamon-Loiza Region.......................................................................................................... 143
4.2 South Coast Area ............................................................................................................................. 143
4.2.1 Santa Isabel-Patillas Region.................................................................................................. 143
4.2.2 Juana Diaz-Ponce Region ..................................................................................................... 143
4.2.3 Penuelas-Guanica Region ..................................................................................................... 143
4.3 West Coast Area............................................................................................................................... 144
4.3.1 Anasco Region....................................................................................................................... 144
4.3.2 Guanajibo Region .................................................................................................................. 144
4.3.3 Lajas Region .......................................................................................................................... 144
4.4 East Coast Area................................................................................................................................ 144
4.4.1 Naguabo-Maunabo Region.................................................................................................... 144
4.5 East Central Area ............................................................................................................................. 144
4.5.1 Aguas Buenas-Juncos Region............................................................................................... 144
4.6 Puerto Rico Offshore Islands............................................................................................................ 145
4.6.1 Isla de Culebra and Isla de Vieques ...................................................................................... 145
4.7 U.S. Virgin Islands............................................................................................................................ 145
4.7.1 St. Thomas and St. Johns...................................................................................................... 145
4.7.2 St. Croix ................................................................................................................................. 145
5.0. Selected references................................................................................................................................. 147
iv 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
FIGURES 
____
1.0 Introduction
1.1-1 
Index map for sections of the Atlas and ground-water resources
areas in Puerto Rico and the U.S. Virgin Islands ........................................................2
1.2-1 
Location map of Puerto Rico and the U.S. Virgin Islands in the Caribbean ................3
1.2-2 Physiographic provinces of Puerto Rico......................................................................4
1.2-3 General geology of Puerto Rico and the U.S. Virgin Islands .......................................5
1.3-1 
General land use in Puerto Rico in 1977.....................................................................7
1.3-2 General land use in St. John and St. Thomas, U.S. Virgin Islands .............................9
1.3-3 General land use in St. Croix, U.S. Virgin Islands.....................................................10
2.0 Ground-water resources areas in Puerto Rico 
2.1 North Coast Area
2.1.1 Aguadilla-Hatillo Region
2.1.1 .A-1 
Location and major geographic features in the Aguadilla-Hatillo region,
Puerto Rico................................................................................................................ 12
2.1.1.B-1 Approximate well locations in the Aguadilla-Hatillo region, Puerto Rico.................... 13
2.1.1.C-1 
Generalized surficial geology in the Aguadilla-Hatillo region, Puerto Rico................ 15
2.1.1.D-1 
Hydrogeologic section in the Aguadilla-Hatillo region, Puerto Rico...........................16
2.1.1 .E-1 
Altitude of water-level surface and direction of ground-water flow during
November 1984 in the Aguadilla-Hatillo region, Puerto Rico ....................................17
2.1.1.F-1 
Soil associations and permeability in the Aguadilla-Hatillo region, Puerto Rico........ 19
2.1.2 Arecibo-Manatf Region
2.1.2.A-1 
Location and major geographic features in the Arecibo-Manatf region,
Puerto Rico................................................................................................................23
2.1.2.B-1 Approximate well locations in the Arecibo-Manati region, Puerto Rico .....................24
2.1.2.C-1 
Generalized surficial geology in the Arecibo-Manati region, Puerto Rico..................25
2.1.2.C-2 Generalized aquifer thickness and hydraulic conductivity in the Arecibo- 
Manati region, Puerto Rico........................................................................................26
2.1.2.D-1 Transmissivity in the Arecibo-Manati region, Puerto Rico .........................................27
2.1.2.E-1 
Composite potentiometric surface of the upper aquifer of the years
1965 and 1987 in the Arecibo-Manati region, Puerto Rico........................................28
2.1.2.F-1 
Soil associations and permeability in the Arecibo-Manatf region, Puerto Rico..........29
2.1.3 Vega Baja-Toa Baja Region
2.1.3.A-1 
Location and major geographic features in the Vega Baja-Toa Baja region,
Puerto Rico................................................................................................................31
2.1.3.B-1 Approximate well locations in the Vega Baja-Toa Baja region, Puerto Rico .............32
2.1.3.C-1 
Generalized surficial geology in the Vega Baja-Toa Baja region, Puerto Rico..........33
2.1.3.D-1 Approximate altitude of the bottom of the freshwater aquifer in the Vega
Baja-Toa Baja region, Puerto Rico............................................................................34
2.1.3.D-2 Transmissivity estimates at selected wells and the regionalized aquifer 
transmissivity distribution as obtained through model calibration for the 
freshwater part of the coastal aquifer in the Vega Baja-Toa Baja region, 
Puerto Rico................................................................................................................35
2.1.3.D-3 Approximate location of wells sampled for dissolved-solids
concentration in the Vega Baja-Toa Baja region, Puerto Rico.................................. 36
2.1.3.E-1 Altitude of water-level surface and direction of ground-water flow
during February 1983 in the Vega Baja-Toa Baja region, Puerto Rico..................... 37
2.1.3.F-1 
Soil associations and permeability in the Vega Baja-Toa Baja region,
Puerto Rico...............................................................................................................39
2.1.4 Bayamon-Lofza Region
2.1.4.A-1 
Location and major geographic features in the Bayamon-Lofza region,
Puerto Rico............................................................................................................... 41
2.1.4.B-1 Approximate well locations in the Bayamon-Loiza region, Puerto Rico.................... 42
2.1.4.C-1 
Generalized surficial geology in the Bayamon-Lofza region, Puerto Rico ................ 43
2.1.4.D-1 Altitude of the top of Cibao Formation in the Bayamon-Loiza region,
Puerto Rico............................................................................................................... 44
2.1.4.D-2 Transmissivity in the northern Bayamon-Loiza region, Puerto Rico ......................... 45
2.1.4.E-1 Altitude of the water-level surface and direction of ground-water flow
during 1971 in the Bayamon-Lofza region, Puerto Rico........................................... 46
2.1.4.F-1 
Soil associations and permeability in the Bayamon-Loiza region, Puerto Rico ........ 48
2.2 South Coast Area
2.2.1 Santa Isabel-Patillas Region
2.2.1 .A-1 
Location and major geographic features in the Santa Isabel-Patillas region,
Puerto Rico ...............................................................................................................50
2.2.1 .B-. Approximate well locations in the Santa Isabel-Patillas region, Puerto Rico ............ 52
2.2.1 .C-1 
Generalized surficial geology in the Santa Isabel-Patillas region, Puerto Rico......... 53
2.2.1 .D-1 
Altitude of the top of the bedrock unit in the Santa Isabel-Patillas region,
Puerto Rico............................................................................................................... 54
2.2.1 .D-2 Average hydraulic conductivity in the Santa Isabel-Patillas region, Puerto Rico ...... 55
2.2.1 .E-1 
Composite altitude of the water-level surface and direction of ground-water
flow during 1986 and 1987 in the Santa Isabel-Patillas region, Puerto Rico............ 56
2.2.1 .F-1 
Soil associations and permeability in the Santa Isabel-Patillas region,
Puerto Rico............................................................................................................... 57
2.2.2 Juana Dfaz-Ponce Region
2.2.2.A-1 
Location and major geographic features in the Juana Diaz-Ponce region,
Puerto Rico...............................................................................................................59
2.2.2.B-1 Approximate well locations in the Juana Diaz-Ponce region, Puerto Rico................ 60
2.2.2.C-1 
Generalized surficial geology in the Juana Dfaz-Ponce region, Puerto Rico............ 61
2.2.2.D-1 Aquifer thickness in the Juana Diaz-Ponce region, Puerto Rico............................... 62
2.2.2.D-2 Average hydraulic conductivity estimates in the Juana Diaz-Ponce region,
Puerto Rico...............................................................................................................63
2.2.2.E-1 Altitude of water-level surface and direction of ground-water flow during
1980 in the Juana Dfaz-Ponce region, Puerto Rico.................................................. 64
2.2.2.F-1 
Soil associations and permeability in the Juana Dfaz-Ponce region,
Puerto Rico............................................................................................................... 65
2.2.3 Penuelas-Guanica Region
2.2.3.A-1 
Location and major geographic features in the Penuelas-Guanica region,
Puerto Rico...............................................................................................................66
Contents
2.2.3.B-1 Approximate well locations in the Pefiuelas-Guanica region, Puerto Rico............... 67
2.2.3.C-1 
Generalized surficial geology in the Pefiuelas-Guanica region, Puerto Rico ........... 68
2.2.3.D-1 
Aquifer thickness in the Pefiuelas-Guanica region, Puerto Rico.............................. 69
2.2.3.D-2 Regional distribution of apparent hydraulic conductivity in the Pefiuelas- 
Guanica region, Puerto Rico .....................................................................................70
2.2.3.E-1 Altitude of water-level surface and direction of ground-water flow during
February 1976 in the Pefiuelas-Guanica region, Puerto Rico...................................71
2.2.3.E-2 Water-level contour during February 1968 and direction of ground-water
flow in the Penuelas-Guanica, Puerto Rico...............................................................72
2.2.3.F-1 
Soil associations and permeability in the Penuelas-Guanica region,
Puerto Rico................................................................................................................73
2.3 West Coast Area
2.3.1 Anasco Region
2.3.1 .A-1 
Location and major geographic features in the Afiasco area, Puerto Rico................76
2.3.1 .B-1 
Approximate well locations in the Afiasco region, Puerto Rico..................................77
2.3.1 .C-1 
Generalized surficial geology in the Anasco region, Puerto Rico ..............................78
2.3.1 .D-1 
Locations of seismic-refraction survey cross sections and well in the
Afiasco region, Puerto Rico.......................................................................................79
2.3.1 .D-2 Aquifer thickness cross section obtained from seismic-refraction velocity
profiles survey and well information in the Afiasco region, Puerto Rico....................80
2.3.1 .E-1 
Composite altitude of water-level surface for September 1981 and
February 1982, and direction of ground-water flow during September
1981 in the Anasco region, Puerto Rico....................................................................81
2.3.1 .F-1 
Soil associations and permeability in the Anasco region, Puerto Rico ......................82
2.3.2 Guanajibo Region
2.3.2.A-1 
Location and major geographic features in the Guanajibo region, Puerto Rico ........83
2.3.2.B-1 Approximate well locations in the Guanajibo region, Puerto Rico .............................84
2.3.2.C-1 
Generalized surficial geology in the Guanajibo region, Puerto Rico..........................85
2.3.2.C-2 Locations of cross section and wells in the Central Guanajibo valley,
Puerto Rico................................................................................................................86
2.3.2.D-1 Approximated depth to bedrock in the Central Guanajibo valley, Puerto Rico ..........87
2.3.2.D-2 Apparent aquifer transmissivity in the Central Guanajibo valley, Puerto Rico...........88
2.3.2.E-1 Altitude of water-level surface and direction of ground-water flow during
June 1980 in the Central Guanajibo valley, Puerto Rico...........................................89
2.3.2.F-1 
Soil associations and permeability in the Guanajibo region, Puerto Rico..................90
2.3.3 Lajas Region
2.3.3.A-1 
Location and major geographic features in the Lajas region, Puerto Rico ................91
2.3.3.B-1 Approximate well locations in the Lajas region, Puerto Rico.....................................92
2.3.3.C-1 
Generalized surficial geology in the Lajas region, Puerto Rico .................................93
2.3.3.D-1 Aquifer thickness in the Lajas region, Puerto Rico ....................................................94
2.3.3.D-2 Transmissivity in the Valle de Lajas area, Puerto Rico..............................................94
2.3.3.E-1 
Potentiometric surface and direction of ground-water flow during March
1986 in the Lajas region, Puerto Rico .......................................................................95
2.3.3.F-1 
Soil associations and permeability in the Lajas region, Puerto Rico .........................96
vi 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.4 East Coast Area
2.4.1 Naguabo-Maunabo Region
2.4.1 .A-1 
Location and major geographic features in the Naguabo-Maunabo
region, Puerto Rico ...................................................................................................98
2.4.1 .B-1 
Approximate well locations in the Naguabo-Maunabo region, Puerto Rico............... 99
2.4.1.C-1 
Generalized surficial geology in the Naguabo-Maunabo region, Puerto Rico......... 100
2.4.1.D-1 Aquifer thickness in the Naguabo-Maunabo region, Puerto Rico............................ 101
2.4.1 .D-2 Regional distribution of hydraulic conductivity in the Naguabo-Maunabo
region, Puerto Rico ................................................................................................. 102
2.4.1 .E-1 Altitude of water-table surface and direction of ground-water flow in the
Naguabo-Maunabo region, Puerto Rico.................................................................. 103
2.4.1 .F-1 
Soil associations and permeability in the Naguabo-Maunabo region,
Puerto Rico............................................................................................................. 104
2.5 East Central Area 
2.5.1 Aguas Buenas-Juncos Region
2.5.1 .A-1 
Location and major geographic features in the Aguas Buenas-Juncos
region, Puerto Rico ................................................................................................. 106
2.5.1.B-1 
Approximate well locations in the Aguas Buenas-Juncos region, Puerto Rico ....... 107
2.5.1.C-1 Generalized surficial geology in the Aguas Buenas-Juncos region, Puerto Rico.... 108
2.5.1.D-1 
Depth to bedrock in the Aguas Buenas-Juncos region, Puerto Rico....................... 109
2.5.1 .D-2 Regionalized apparent transmissivity values in the Aguas Buenas-Juncos
region, Puerto Rico ................................................................................................. 110
2.5.1 .E-1 
Altitude of water-level surface and direction of ground-water flow during
March 1988 in the Aguas Buenas-Juncos region, Puerto Rico............................... 111
2.5.1 .F-1 
Soil associations and permeability in the Aguas Buenas-Juncos region,
Puerto Rico............................................................................................................. 112
2.6 Puerto Rico Offshore Islands
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico
2.6.1 .A-1 
Locations and major geographic features in Isla de Culebra and Isla de
Vieques, Puerto Rico .............................................................................................. 115
2.6.1 .B-1 
Approximate well locations in Isla de Culebra and Isla de Vieques,
Puerto Rico .............................................................................................................116
2.6.1 .C-1 
Generalized surficial geology in Isla de Culebra and Isla de Vieques,
Puerto Rico............................................................................................................ 118
2.6.1 .C-2 Hydrogeologic section of the aquifer in the Esperanza valley, Isla de
Vieques, Puerto Rico .............................................................................................. 119
2.6.1 .D-1 
Distribution of aquifer hydraulic conductivity values in the Esperanza
valley, Isla de Vieques, Puerto Rico........................................................................ 120
2.6.1 .D-2 Altitude of base of the Esperanza valley alluvial aquifer, Isla de Vieques,
Puerto Rico............................................................................................................. 121
2.6.E-1 
Altitude of water-level surface and direction of ground-water flow during
April 1983 in the Esperanza valley aquifer, Isla de Vieques, Puerto Rico .............. 123
2.6.F-1 
Soil associations and permeability in Isla de Culebra and Isla de Vieques,
Puerto Rico............................................................................................................. 124
3.0 Ground water-resources areas in the U.S. Virgin Islands 
3.1 U.S. Virgin Islands
3.1.1 St. Thomas and St. John, U.S. Virgin Islands
3.1.1 .A-1 
Location major geographic features in St. Thomas and St. John,
U.S. Virgin Islands................................................................................................... 127
3.1.1.B-1 Approximate well locations in St. Thomas and St. John, U.S. Virgin Islands ..........128
3.1.1.C-1 
Generalized surficial geology in St. Thomas and St. John, U.S. Virgin Islands.......129
3.1.1.D-1 
Principal aquifers in St. Thomas and St. John, U.S. Virgin Islands.........................130
3.1.1 .E-1 
Altitude of water-level surface and direction of ground-water flow during
September 11, 1987, in St. Thomas and St. John, U.S. Virgin Islands................... 131
3.1.1 .F-1 
Soil associations and permeability in St. Thomas and St. John, U.S.
Virgin Islands........................................................................................................... 132
3.1.2 St. Croix, U.S. Virgin Islands
3.1.2.A-1 
Location and major geographic features in the Kingshill aquifer, St. Croix,
U.S. Virgin Islands................................................................................................... 133
3.1.2.B-1 
Clusters of well fields and location in St. Croix, U.S. Virgin Islands ........................135
3.1.2.C-1 
Generalized surficial geology in St. Croix, U.S. Virgin Islands ................................136
3.1.2.D-1 Transmissivity estimates at selected wells in the regionalized transmissivity 
distribution as obtained through model calibration in St. Croix, U.S. 
Virgin Islands........................................................................................................... 138
3.1.2.E-1 
Altitude of water-level surface and direction of ground-water flow during
July 1987 in St. Croix, U.S. Virgin Islands...............................................................139
3.1.2.F-1 
Soil associations and permeability in St. Croix, U.S. Virgin Islands ........................140
TABLES
1.0 Introduction
1.1 .C-1 
Geologic time scale for that period of geologic time pertaining to geologic
formations occurring in Puerto Rico and the U.S. Virgin Islands.................................3
2.0 Ground-water resources areas in Puerto Rico 
2.1 North Coast Area
2.1.1 Aguadilla-Hatillo Region
2.1.1.B-1 
Population for the Aguadilla-Hatillo region, Puerto Rico............................................14
2.1.1.B-2 Ground-water withdrawals and estimated population served during 1983
for the Aguadilla-Hatillo region, Puerto Rico..............................................................14
2.1.1 .F-1 
Thickness, permeability, and available water capacity for the soil associations
in the Aguadilla-Hatillo region, Puerto Rico...............................................................18
2.1.2 Arecibo-Manati Region
2.1.2.B-1 
Population for the Arecibo-Manati region, Puerto Rico .............................................20
2.1.2.B-2 Ground-water withdrawals and estimated population served during 1983
for the Arecibo-Manati region, Puerto Rico ...............................................................21
2.1.2.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Arecibo-Manati region, Puerto Rico.................................................................22
2.1.3 Vega Baja-Toa Baja Region
2.1.3.B-1 
Population for the Vega Baja-Toa Baja region, Puerto Rico..................................... 30
2.1.3.B-2 Ground-water withdrawals during 1987 in the Vega Baja-Toa Baja region, 
Puerto RicoSO
2.1.3.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Vega Baja-Toa Baja region, Puerto Rico........................................................ 38
2.1.4 Bayamon-Loiza Region
2.1.4.B-1 
Population for the Bayamon-Lofza region, Puerto Rico............................................ 40
2.1.4.B-2 Ground-water withdrawals and estimated population served during 1987
for the Bayamon-Lofza region, Puerto Rico.............................................................. 41
2.1.4.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Bayamon-Loiza region, Puerto Rico............................................................... 47
2.2 South Coast Area
2.2.1 Santa Isabel-Patillas Region
2.2.1 .B-1 
Population for the Santa Isabel-Patillas region, Puerto Rico..................................... 51
2.2.1 .B-2 Ground-water withdrawals and estimated population served during 1983
for the Santa Isabel-Patillas region, Puerto Rico...................................................... 51
2.2.1 .F-1 
Thickness, permeability, and available water capacity for the soil associations
in the Santa Isabel-Patillas region, Puerto Rico........................................................ 58
2.2.2 Juana Dfaz-Ponce Region
2.2.2.B-1 
Population for the Juana Dfaz-Ponce region, Puerto Rico........................................ 60
2.2.2.B-2 Ground-water withdrawals and estimated population served during 1983
for the Juana Dfaz-Ponce region, Puerto Rico ......................................................... 60
2.2.2.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Juana Dfaz-Ponce area, Puerto Rico.............................................................. 65
2.2.3 Penuelas-Guanica Region
2.2.3.B-1 
Population for the Penuelas-Guanica region, Puerto Rico........................................ 67
2.2.3.B-2 Ground-water withdrawals and estimated population served during 1983
for the Penuelas-Guanica region, Puerto Rico ......................................................... 67
2.2.3.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Penuelas-Guanica region, Puerto Rico........................................................... 74
2.3 West Coast Area
2.3.1 Anasco Region
2.3.1.B-1 
Population for the Anasco region, Puerto Rico .........................................................77
2.3.1 .B-2 Ground-water withdrawals and estimated population served during 1982 for
the Anasco region, Puerto Rico............................................................................... 77
2.3.1 .F-1 Thickness, permeability, and available water capacity for the soil associations
in the Anasco region, Puerto Rico ............................................................................ 82
2.3.2 Guanajibo Region
2.3.2.B-1 
Population for the Guanajibo region, Puerto Rico.....................................................84
2.3.2.B-2 Ground-water withdrawals for public-water supply by municipio for 1980,
1981, and 1982, in the Guanajibo region, Puerto Rico............................................. 84
2.3.2.B-3 Ground-water withdrawals and estimated population served during 1982
for the Guanajibo region, Puerto Rico....................................................................... 85
Contents 
vii
2.3.2.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Guanajibo region, Puerto Rico .......................................................................90
2.3.3 Lajas Region
2.3.3.B-1 
Population for the Lajas region, Puerto Rico .............................................................92
2.3.3.B-2 Ground-water withdrawals for public supply during 1983 in the Lajas
region, Puerto Rico....................................................................................................92
2.3.3.D-1 Transmissivity of the alluvial aquifer estimated from specific-capacity data..............94
2.3.3.F-1 Thickness, permeability, and available water capacity for the soil associations
in the Lajas region, Puerto Rico ................................................................................96
2.4 East Coast Area 
2.4.1 Naguabo-Maunabo Region
2.4.1 .B-1 
Population of the Naguabo-Maunabo region, Puerto Rico ........................................99
2.4.1 .B-2 Ground-water withdrawals and estimated population served during 1983
for the Naguabo-Maunabo region, Puerto Rico.......................................................100
2.4.1 .F-1 Thickness, permeability, and available water capacity for the soil associations
in the Naguabo-Maunabo region, Puerto Rico........................................................104
2.5 East Central Area 
2.5.1 Aguas Buenas-Juncos Region
2.5.1.B-1 
Population of the Aguas Buenas-Juncos region, Puerto Rico................................. 107
2.5.1 .B-2 Ground-water withdrawals and estimated population served during 1982
for the Aguas Buenas-Juncos region, Puerto Rico..................................................108
2.5.1 .F-1 
Thickness, permeability, and available water capacity for the soil associations
in the Aguas Buenas-Juncos region, Puerto Rico...................................................112
2.6 Puerto Rico Offshore Islands
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico
2.6.1.B-1 
Population for Islade Culebra and Islade Vieques, Puerto Rico............................ 117
2.6.1 .B-2 Ground-water withdrawals and estimated population served during 1986
for Isla de Culebra and Isla de Vieques, Puerto Rico..............................................117
2.6.1 .F-1 Thickness, permeability, and available water capacity for the soil associations
in Isla de Culebra and Isla de Vieques, Puerto Rico...............................................122
3.0 Ground water-resources areas in the U.S. Virgin Islands 
3.1 U.S. Virgin Islands
3.1.1 St. Thomas and St. John, U.S. Virgin Islands
3.1.1 .B-1 
Ground-water withdrawals and estimated population served during 1983-84
for St. Thomas and St. John, U.S. Virgin Islands....................................................126
3.1.1 .F-1 Thickness, permeability, and available water capacity for the soil associations
in St. Thomas and St. John, U.S. Virgin Islands......................................................132
3.1.2 St. Croix, U.S. Virgin Islands
3.1.2.B-1 
Ground-water withdrawals and estimated population served during 1985
for St. Croix, U.S. Virgin Islands 1985.....................................................................134
3.1.2.B-2 Average daily ground-water withdrawals from municipal well fields during
September to November 1990, St. Croix, U.S. Virgin Islands.................................134
3.1.2.F-1 Thickness, permeability, and available water capacity for the soil associations
in St. Croix, U.S. Virgin Islands ...............................................................................137
CONVERSION FACTORS, ABBREVIATED WATER- 
QUALITY UNIT, AND AGENCY ABBREVIATIONS
Multiply
inch (in.) 
foot (ft) 
mile (mi)
square mile (mi2)
gallon (gal) 
gallon (gal) 
million gallons (Mgal)
foot per day (ft/d)
foot squared per day (ft2/d)
cubic feet per second (ft3/s)
gallon per minute (gal/min)
million gallons per day (Mgal/d)
gallons per day (gal/d)
inch per hour (in/hr)
inch per year (in/yr)
inch per inch (in/in)
gallon per minute per foot [(gal/min)/ft]
Abbreviated water-quality unit
microgram per liter (|ig/L)
Agency Abbreviations
Puerto Rico Aqueduct and Sewer Authority (PRASA)
Puerto Rico Department of Natural and Environmental Resources (PRDNER)
U.S. Geological Survey (USGS)
By
Length
25.4
0.3048
1.609
Area
2.590
Volume
3.785
0.003785
3,785
Flow
0.3048
0.09294
0.02832
0.06308
0.04381
0.003785
25.4
25.4
25.4
0.2070
To obtain
millimeter
meter
kilometer
square kilometer
liter
cubic meter
cubic meter
meter per day 
meter squared per day 
cubic meter per second 
liter per second 
cubic meter per day 
cubic meter per day 
millimeter per hour 
millimeter per year 
millimeter per millimeter 
liter per second per meter
viii 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
By Thalia D. Veve and Bruce E. Taggart (editors)
Abstract
This atlas presents an overview of the ground-water 
resources of the main island of Puerto Rico; two of its 
larger offshore islands, Isla de Culebra and Isla de 
Vieques; and the three principal islands of the U.S. 
Virgin Islands, St. Thomas, St. John, and St. Croix. The 
atlas 
presents 
the 
most 
important 
ground-water 
information available for these islands, and is written for 
water managers and the general public. It describes, 
through the use of maps, graphs, and hydrogeologic 
sections, 
the 
most 
important 
aspects 
of 
the 
geohydrology, ground-water flow system, and ground- 
water withdrawals for the principal aquifers in these 
islands. Most of the information presented in the atlas is 
from published reports, although unpublished data from 
ongoing studies by the U.S. Geological Survey were 
used to prepare parts of the atlas. This report provides 
a useful compilation of information concerning major 
aquifers in Puerto Rico and the U.S. Virgin Islands and 
provides a first step in gaining a general knowledge of 
these aquifers. More detailed information is available 
from the primary sources referenced in the report.
The atlas contains an introductory section and 15 
sections describing the ground-water resources of 12 
regions within the 7 ground-water areas of the main 
island of Puerto Rico, Isla de Culebra and Isla de 
Vieques (described in a single section of the atlas), and 
the U.S. Virgin Islands (St. Thomas and St. John are 
described in one section of the atlas and St. Croix in 
another), and a concluding section describing present 
and potential problems related to the development of 
ground-water resources. Information presented in each 
of 15 descriptive sections of the atlas include the (1) 
location and major geographic features of the area 
covered by that section, (2) population and estimated 
ground-water use within the area, (3) geologic setting,
(4) hydrogeology of the area, (5) ground-water levels 
and 
movements, 
and 
(6) 
a description 
of soil 
permeabilities.
Acknowledgement
The U.S. Geological Survey, Caribbean District 
wishes to acknowledge the contribution of Thalia D. 
Veve to the completion of this report. Without her vision 
and persistence in the face of overwhelming obstacles 
this report would never have been completed.
1.0 Introduction
This atlas, prepared by the U.S. Geological Survey 
(USGS) in cooperation with the U.S. Environmental 
Protection Agency (EPA), presents an overview of the 
ground-water resources of the main island of Puerto 
Rico, the offshore islands of Culebra and Vieques, and 
St. Thomas, St. John, and St. Croix in the U.S. Virgin 
Islands.
1.1 Purpose and Scope
The atlas was prepared to meet the need for a 
single publication that presents an overview of the 
ground-water resources of these areas that can be used 
by planners, managers, and personnel of various 
Federal, Commonwealth, and local agencies. The atlas 
is based largely on published reports that have been 
prepared during the last 70 years. It does not present a 
comprehensive description of all that is known about the 
ground-water resources of these areas, but it does 
describe 
the 
most 
important 
aspects 
of 
the 
geohydrology, ground-water flow system, water use, and 
water-supply or water-quality problems that could affect
the future development of water from the principal 
aquifers. The aquifers selected for description in this 
report are those that are important sources of water for 
public and domestic water supply.
The main island of Puerto Rico was divided in five 
ground-water areas: 
the North Coast, South Coast, 
West Coast, East Coast, and East Central (fig. 1.1-1). 
The North Coast area is underlain by limestone aquifers 
that are the most productive aquifers in Puerto Rico. 
These limestone aquifers cover an area of about 600 
square miles (mi2) and are as much as 5,600 feet thick. 
For purposes of this report, the North Coast area was 
divided into four regions. From west to east they are the 
Aguadilla-Hatillo, the Arecibo-Manatf, the Vega Baja-Toa 
Baja, and the Bayamon-Lofza regions.
The South Coast area is underlain by an alluvial 
aquifer that averages about 3 miles wide and is about 
200 to 300 feet thick in the eastern half, and includes 
alluvial valleys cut into Tertiary age limestones in its 
western half. For purposes of this report, this area was 
divided into three regions. From east to west the areas 
are the Santa Isabel-Patillas, the Juana Diaz-Ponce, 
and the Penuelas-Guanica regions.
The West Coast area includes four small alluvial 
valleys separated by ridges composed of volcanic rocks, 
limestone, and some intrusive rocks. The Lajas valley is 
included in this area, although the origin of this valley 
differs from that of the other valleys in that it is believed 
to have been formed by block faulting. For purposes of 
this report, the West Coast area was divided into three 
regions. From north to south they are the Anasco, the 
Guanajibo, and the Lajas regions.
The East Coast area consists of a discontinuous 
narrow coastal plain and includes several alluvial river 
valleys. It extends from the Rfo Grande in the north to 
Maunabo in the south. However, due to a paucity of 
published data for the northern part of the area, only the 
area between Maunabo and Naguabo is described in 
this report (Naguabo-Maunabo region).
The East Central area, which describes the Aguas 
Buenas-Juncos region is characterized by mostly 
mountainous terrain and is underlain by volcanic rocks, 
intrusive rocks, a few interbedded limestones, and 
isolated alluvial deposits in river valleys. Although some 
wells produce ground water from highly fractured 
volcanic and intrusive rocks, these rocks are important 
aquifers only locally, and are not described in this report. 
The Caguas-Juncos alluvial valley, the largest in Puerto 
Rico is located within the East Central area.
The three largest of Puerto Rico's offshore islands 
are Isla de Vieques, Isla de Culebra, and Isla de Mona 
(fig. 1.1-1). Isla de Culebra and Isla de Vieques lie to 
the east and Isla de Mona to the west of Puerto Rico. 
Isla de Vieques is underlain by mixed volcanic and 
intrusive rocks, with some small areas underlain by 
limestone and alluvial deposits near the coast. Isla de 
Culebra is underlain mainly by mixed volcanic rocks with 
some small areas underlain by alluvium near the coast. 
Isla de Vieques and Isla de Culebra are described in one 
section of this report. Isla de Mona is an uninhabited 
island underlain by carbonate rocks and is bounded by a 
low-lying coastal plain along its south coast. 
A few 
shallow wells have been dug on the island, but little is 
known about the ground-water resources of the area. 
The hydrology of Isla de Mona is not described in this 
report.
1.0 Introduction
The U.S. Virgin Islands (fig. 1.1-1) include the 
islands of St. Croix, St. Thomas, and St. John. St. Croix 
is underlain by mixed volcanic and intrusive rocks, and 
carbonate rock with some small areas underlain by 
alluvium. St. Thomas and St. John are underlain mostly 
by layered volcanic rocks with some small areas 
underlain by carbonate rock and alluvium.
Information presented in each of these descriptive 
sections of the atlas include (1) the location and major 
geographic features of the area covered by that section, 
(2) population and estimated ground-water use within 
the area, (3) geologic setting, (4) hydrogeology of the
area, (5) ground-water levels and movements, and (6) a 
description of soil permeabilities. The amount of detail 
presented in each of these sections for a particular area 
is dependent upon the quality and quantity of published 
data available for that area.
1.1.A Location and Major Geographic 
Features
This section of the report includes a general 
topographic map showing the areal 
extent and 
boundaries of the area, major streams, and cultural 
features. 
The 
brief 
text 
describes 
prominent 
geomorphic features in the area.
1.1.B Population and Estimated 
Ground-Water Use
This section describes the population of the area, 
presents a map showing approximate locations of 
known wells, and principal uses of ground water in the 
area. Population data for the area are from the 1980 
and 1990 Census of population and housing (U.S. 
Department of Commerce, 1982). 
Water-use data 
presented are generally for the years 1981-82 and were 
obtained from various USGS reports. The well location 
maps were compiled from the USGS Ground-Water Site 
Inventory, an electronic database maintained in the
USGS Caribbean District for Puerto Rico and the U.S. 
Virgin Islands.
Population data are available by municipio (county) 
subdivisions, which provides an accurate means of 
calculating population over specific aquifer areas. 
Unfortunately, water-use data are not available by 
municipio subdivisions. In areas where specific studies 
have determined the use of water from a particular 
aquifer, information is given. Insofar as possible, all the 
information in this section is presented by municipio in 
order to facilitate the comparison of data with other 
sections of the report.
67°15'
67W
45'
30'
15"
66W
45'
30'
15'
65W
45'
64°30'
18°30'
15'
18°00'
17°45'
 O
Area of limited ground-water availability. 
Not described in this report.
2.1 NORTH COAST AREA
ATLANTIC OCEAN
Isla de Culebra
67°55' 
67°50'
Isla de 
Mona
18°10
18°05
2.2 SOUTH COAST AREA
Area of limited ground-water availability. 
Not described in this report.
St. Thomas
3.1.1
PUERTO RICO
OFFSHORE ISLANDS
St. John
U.S. VIRGIN 
ISLANDS
2.4 EAST COAST AREA
2.3 WEST COAST AREA
10 
20
30 KILOMETERS
CARIBBEAN SEA
2.5 EAST CENTRAL AREA
10
20
30 MILES
St. Croix
Figure 1.1-1 Index map for sections of the Atlas and ground-water resources areas in Puerto Rico and the U.S. Virgin Islands (the numbers correspond to the section of the report in which each area is described).
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
1.1.C Geologic Setting
This section includes a map showing the surficial 
geology and describes prominent rock types within the 
area. Information presented on the geologic formations 
include age, composition, and thickness. The age of 
geologic formations are presented in terms of the 
Geologic Time Scale (Palmer, 1983), which assigns 
formal names to specific ranges of geologic time (table 
1.1.C-1).
1.1. D Hydrogeology
In this section, the formations that constitute major 
aquifers are identified and described. 
Hydraulic 
characteristics for each of the major aquifers in the area 
are described. 
This section generally includes two 
maps: a map of hydraulic conductivity or transmissivity 
(the rate of flow of water through a unit cross section of 
one square foot of a porous rock or sediment), and a 
map showing aquifer thickness or depth to bedrock. 
Hydrogeologic cross sections are included where 
aquifer thickness or depth to bedrock maps are not 
available.
Table 1.1. C-l Geologic Time Scale for that period of geologic time pertaining to geologic 
formations occurring in Puerto Rico and the U.S. Virgin Islands (from Palmer, 1983)
[Ma, millions of years]
1.1.E Ground-Water Levels and 
Movement
This section presents a map showing ground-water 
levels and direction of ground-water flow. Factors such 
as rainfall and ground-water development that affect 
ground-water levels are also described in this section.
1.1.F Soil Permeability
This section 
presents 
a 
map 
showing 
soil 
associations and their corresponding permeabilities. 
The source of data for these maps is the soil surveys of 
the U.S. Department of Agriculture, Soil Conservation 
Service. General characteristics of the soil associations 
and ranges of permeability based on published
permeability values for the soil series comprising each 
soil association are described in this section. Significant 
differences among soil associations are also described.
1.2 Description of the Area
Puerto Rico and the U.S. Virgin Islands are located 
in the northeastern Caribbean Sea between latitudes 
17°40'N and 18°35'N, and longitudes 64°30'W and 
68°00'W (fig. 1.2-1). Puerto Rico is the smallest of the 
Greater Antilles and, together with its associated 
offshore islands, has a total area of 3,435 mi2 . The U.S. 
Virgin Islands include the three main islands of St. 
Thomas, St. John, and St. Croix with a combined area 
of 133 mi2.
Age (Ma)
Era
Period
Epoch
0. 
- 
0.01 
Cenozoic
0.01 - 
1.0
1.6 - 
3.4
3.4 - 
5.3
5.3 - 
11.2
11.2 - 16.6
16.6 - 23.7
23.7 - 30.0
30.0 - 36.6
36.6 - 40.0
40.0 - 52.0
52.0 - 57.8
57.8 - 63.6
63.6 - 66.4
66.4 - 97.5 
Mesozoic
97.5 - 144
144. 
- 163
163. 
- 187
187. 
-208
208. 
- 230
230. 
- 240
240. 
- 245
Quaternary
Tertiary 
Neogene
Paleogene
Cretaceous
Jurassic
Triassic
Holocene
Pleistocene
Pliocene 
Late
Early
Miocene 
Late
Middle
Early
Oligocene 
Late
Early
Eocene 
Late
Middle
Early
Paleocene 
Late
Early
Late
Early
Late
Middle
Early
Late
Middle
Early
93°
27° I
24°
21'
18°
15°
12°
90° 
87° 
84° 
81° 
78° 
75° 
72° 
69° 
66° 
63° 
60°
NORTH AMERICA
VJ5=*
4-^
0 
100 200 300 KILOMETERS
I    H  h   .
0 
100 
200 
300 MILES
\ BAHAMAS 
<"\ 
*^v
ATLANTIC OCEAN
PUERTO RICO
AND THE 
U.S. VIRGIN ISLANDS
-
CARIBBEAN SEA
. 
 _» 
 ^ 
v
^J\^
SOUTH AMERICA
Figure 1.2-1 Location map of Puerto Rico and the U.S. Virgin Islands in the Caribbean.
1.2 Description of the Area
The main island of Puerto Rico has three principal 
physiographic areas: the alluvial coastal plains, karst, 
and the central mountainous interior (fig. 1.2-2). Land- 
surface elevations range from mean sea level at the 
coast to 4,389 feet above mean sea level in Cerro Punta
at Jayuya. In the offshore islands of Puerto Rico, the 
highest elevation is in Isla de Vieques where Monte 
Pirata, at the extreme west end of the island, attains an 
elevation of 988 feet above mean sea level.
St. Thomas and St. John are characterized by 
steep topography. The highest land-surface elevations 
of these two islands are 1,556 feet above mean sea 
level in St. Thomas and 1,277 feet above mean sea 
level in St. John (Gomez-Gomez and others, 1984b, p.
409). St. Croix is characterized by low rolling hills. The 
highest peak in St. Croix is in the Northside Range, 
where the land-surface elevation is as high as 1,088 feet 
above mean sea level.
67°15'
67W
45'
30'
15'
66W
45'
65°30'
ATLANTIC OCEAN
18°30'
15'
18°00'
CARIBBEAN SEA
17-45-
10
20
30 KILOMETERS
10
20
30 MILES
EXPLANATION
PHYSIOGRAPHIC PROVINCE
I 
| 
ALLUVIAL COASTAL PLMNS
| 
| 
KARST
| 
| 
CENTRAL MOUNTAINOUS INTERIOR
Modified from de-Galinanes, 1977
Figure 1.2-2 Physiographic provinces of Puerto Rico.
4 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Puerto Rico and the U.S. Virgin Islands are of 
volcanic origin. 
The mountainous interior of Puerto 
Rico, its offshore islands, and the U.S. Virgin Islands are 
composed mainly of a mixture of volcanic and 
sedimentary rocks (fig. 1.2-3). 
The volcanic rocks 
include lava, tuff, breccia, and tuffaceous breccia. The 
sedimentary 
rocks 
include 
siltstone, 
sandstone, 
conglomerate, and limestone. Intrusive rocks crop out
in several places in the central mountainous interior, 
especially in the southeastern corner and the western 
central part of Puerto Rico. These intrusive rocks also 
crop out in Isla de Culebra and Isla de Vieques. They 
consist mainly of granodiorite, quartz diorite, and diorite. 
Minor quantities of quartz porphyry, gabbro, and 
amphibolite are also present. A large serpentinite and 
chert deposit crops out in southwestern Puerto Rico.
The Puerto Rico central mountainous interior is 
flanked by limestone deposits of Tertiary age and by 
clastic sediments of Quaternary age. 
The most 
extensive limestone deposits in Puerto Rico are along 
the north coast in a band that extends from the 
northwestern corner of the island to the Rio Grande de 
Lofza in the northeastern corner. 
This band has a 
maximum width of 14 miles (Monroe, 1980a, p. 20). In
this area along the north coast, a mature karst has 
developed by dissolution of the limestone. 
The 
limestone deposits in the southern part of the island are 
less extensive and karst features are not as well 
developed. Limestone rocks similar to those in Puerto 
Rico are also present in some areas of Isla de Mona, 
Isla de Vieques, and St. Croix. Clastic sediments that 
underlie Puerto Rico consist predominately of poorly
67°15'
67W
45'
30
64°30'
18"30'
15'
18'00'
17°45'  
ATLANTIC OCEAN
PUERTO RICO
Isla de Culebra
U.S. VIRGIN 
ISLANDS
Isla de Vieques
Isla de Mona
EXPLANATION
GENERAL GEOLOGY
CARIBBEAN SEA
Qs 
QUATERNARY SURFICIAL DEPOSITS 
Tm 
I 
MIOCENE DEPOSITS
OLIGOCENE DEPOSITS
Tki 
INTRUSIVE IGNEOUS ROCKS
10 
20 
30 KILOMETERS
Modified from Monroe, 1980a
Figure 1.2-3 General geology of Puerto Rico and the U.S. Virgin Islands.
1.2 Description of the Area
sorted mixtures of gravel, sand, and finer materials 
(Quinones-Marquez and others, 1984b, p. 367). These 
sediments lie along the north and south coastal plains 
and in river valleys along the east and west coasts of 
Puerto Rico. 
In Isla de Vieques, Isla de Culebra, St. 
Thomas, and St. John clastic sediments are present in 
small areas along the coast and within the small river 
valleys incised by the intermittent streams. In St. Croix, 
deposits of clastic sediments are more extensive.
Average annual rainfall in Puerto Rico is 70 inches. 
Rainfall varies geographically and is much more 
abundant in the northern part of the island than in the 
southern part, because the latter lies in a rain shadow 
caused by the central mountain range, which forces the 
northeasterly trade winds to rise and precipitation to fall 
on the windward slopes. Annual rainfall ranges from 
about 30 inches in the western end of the south coast 
area valleys to about 160 inches near the top of El 
Yunque (Colon-Dieppa and Torres-Sierra, 1991, p. 475). 
Rainfall also varies seasonally. 
The driest month is 
February and the wettest months are September and 
October.
Average annual precipitation is 45 inches at St. 
Thomas and St. John, and 40 inches at St. Croix 
(Gomez-Gomez and others, 1984, p. 409). 
Annual 
rainfall on St. Thomas and St. John ranges from about 
40 to 60 inches (Colon-Dieppa and Torres-Sierra, 1991, 
p. 521). In St. Croix, rainfall patterns are more variable. 
Annual 
rainfall 
averages 
about 
50 
inches 
in 
northwestern St. Croix and about 20 inches on the 
eastern end of the island (Colon-Dieppa and Torres- 
Sierra, 1991, p. 521). Wet and dry seasons are not 
sharply defined but patterns are similar to those in 
Puerto Rico. Annual evapotranspiration averages about 
45 inches in Puerto Rico and 39 inches in the U.S. 
Virgin Islands (Gomez-Gomez and Heisel, 1980, p. U1).
1.3 General Land-Use Patterns 
in Puerto Rico and the U.S. 
Virgin Islands
The most recent generalized land-use map for 
Puerto Rico was produced by the Puerto Rico 
Department of Natural and Environmental Resources 
(Editorial Cordillera, 1984). The 1977 land-use data has
been entered into the Caribbean District Geographic 
Information System and used to produce a generalized 
land-use map for Puerto Rico (fig. 1.3-1). 
This map 
gives only a general idea of the dominant land uses in 
the area. For the U.S. Virgin Islands, farmland maps 
produced by the U.S. Department of Agriculture have 
been used. 
These maps show only two land uses: 
agricultural and residential. The industrial category has 
been added using USGS topographic maps. The 
description that follows has been generalized for the 
purpose of this report.
1.3.A North Coast Area
Agriculture is the predominant land use; largely as 
pasture and small, family-owned farms. Farmland 
occupies much of the high, rolling plain in the northern 
third of the western part of the area and the floodplain of 
the Rfo Culebrinas. To the east, farmland predominates 
where there are small flats or blanket sand filled valleys 
between limestone hills. Large-scale farming occurs on 
the flood plains of the Rfo Grande de Arecibo and Rfo 
Grande de Manatf. Sugarcane was once the principal 
crop in these floodplains. Pineapples are grown on the 
blanket sands along Highway 2.
Forests occupy most of the karst uplands, which 
are relatively inaccessible, particularly the area adjacent 
to the Rfo Guajataca, and in the southwestern and 
southeastern North Coast area. 
Wetlands are not 
extensive in the western portion of the area. However, 
large coastal wetlands are common on the coastal plain 
between Camuy and Manatf.
Most residential areas are near the coast in the 
towns of Aguadilla, Isabela, Quebradillas, Camuy, 
Hatillo, Arecibo, Manatf, Barceloneta, Toa Baja, Dorado, 
and the San Juan metropolitan area. While these urban 
centers have expanded considerably in recent years, 
they still occupy a small percentage of the land in the 
western and central portions of the North Coast area. 
The only exception to this trend is along the coastal 
plain from Bayamon to Carolina, where about 90 
percent of the land use is residential or urban. Smaller 
towns and villages are located inland.
Industrial development is not extensive in the 
western part of the North Coast area, occurring mainly 
in association with military bases and urban areas.
Industrial areas are primarily concentrated in the urban 
areas along Highway 2 between Arecibo and Manatf 
and between Bayamon to Carolina near Catano and 
along the Bahia de San Juan.
Residential, 
commercial, 
and 
industrial 
development will probably continue along the more level 
coastal areas throughout the North Coast area, 
especially near Guaynabo and Bayamon, as the 
population in these areas increases and expands into 
farm land. Changes in land use are unlikely in the more 
inaccessible karst areas.
1.3.B South Coast Area
Historically, the South Coast area has been one of 
the most important agricultural areas in the island. 
As 
in other agricultural areas in Puerto Rico, sugarcane 
was the principal crop for many years. 
However, 
sugarcane is being replaced by vegetables. 
The 
eventual replacement of the sugarcane fields by 
vegetable crops and the associated changes from 
furrow to drip irrigation may decrease the water demand 
for agriculture in an area that depends largely on its 
ground-water resources. This change from furrow to 
drip irrigation will also affect the recharge patterns to the 
alluvial aquifer. Farming is the major activity within the 
alluvial valleys between 
Penuelas 
and 
Guanica. 
Sugarcane production and pastures for dairy cattle have 
been the most important agricultural activities in this 
area, with fruits and vegetables generally planted on a 
small scale.
Forest constitutes the largest land-use category in 
the mountains in the South Coast area, with agriculture 
(bananas, citrus fruit, coffee, vegetables, and other 
crops) a minor land-use category in the region. 
A 
xerophytic forest dominates the limestone hills along the 
coast near Guanica. 
Wetlands, consisting of both 
estuarine and palustrine marsh environments, are 
common along the coast throughout the South Coast 
area.
Industrial and urban land use in the South Coast 
area is most developed between Juana Dfaz and 
Guanica, due to the availability of water sources. The 
major urban centers in this area are concentrated in the 
mountains, although rural communities are common 
throughout the South Coast area. 
A major industrial
center occupies the lower Tallaboa valley, east of 
Ponce. The Commonwealth Oil Refinery Company was 
established in the entire lower part of this valley. Other 
heavy industries were established between Ponce and 
Guanica in the 1960's. However, many of them ceased 
operations in the early 1980's, leaving their physical 
structures behind. A salt industry was also established 
in this area, which obtains its product from the 
evaporation of seawater.
1.3.C West Coast Area
The principal land-use category in the West Coast 
area is agriculture. 
According to Dfaz and Jordan 
(1987), sugarcane has been the major crop in the 
Anasco valley in the past. 
In recent years, however, 
sugarcane cultivation has decreased. In 1985, almost 
all of the Central Guanajibo valley was under cultivation 
with sugarcane, with some cultivation of vegetables and 
to pasture. 
In 1972, 19,000 acres of sugarcane were 
irrigated in the Valle de Lajas for agricultural purposes 
(Anderson, 1977, p. 3). The next most important land- 
use category in the Valle de Lajas is pasture, which 
accounted for 3,500 acres.
Large areas are covered by forest in the hills to the 
north and northwest of the Central Guanajibo valley. 
Forested areas are also common in the hills surrounding 
the Valle de Lajas. Small coastal wetlands are found 
near the Central Guanajibo valley. 
The Laguna 
Cartagena and the Bahfa de Boqueron located in the 
Valle de Lajas, are surrounded by small wetlands.
Major residential areas account for a small 
percentage of land use in the West Coast area. 
Principal urban centers include Mayaguez, Anasco, 
Cabo Rojo, San German, Lajas, and Boqueron. 
Frequent flooding of West Coast area valleys has 
prevented the establishment of residential communities 
in low-lying areas. 
Consequently, the principal urban 
centers have been built in elevated regions adjacent to 
the valleys and in their upper reaches, where the effects 
of flooding are less severe.
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
18°30'
15'
18W
17°45'
67°55' 
67°50'
18°05'
Isla de Mona
67°15'
 i 
67W
45'
30'
15'
66W
45' 
30'
ATLANTIC OCEAN
65°15'
  I 
Isla de Culebra
EXPLANATION
LAND USE 1977
Isla de Vieques
CARIBBEAN SEA
0 
5 
10 KILOMETERS
0
10 MILES
[.:...! AGRICULTURE, PASTURE, FALLOW FIELDS
^H FOREST, RANGELAND
^H WATER BODIES
I 
I 
MANGROVE, SWAMPS
^H NON-PRODUCTIVE LAND (ROCK, REEFS, SAND)
I 
I 
RESIDENTIAL AREAS
I^H RECREATIONAL AREAS, PUBLIC USE, MILITARY AREAS
^H COMMERCIAL, INDUSTRIAL
^H MINES, QUARRIES AND SAND, AND GRAVEL EXTRACTION SITES
^H COMMUNICATIONS, TRANSPORTATION, PORTS
Modified from Puerto Rico Department of Natural and Environmental Resources, Land-Use Database, 1977
Figure 1.3-1 General land use in Puerto Rico in 1977.
1.3 General Land-Use Patterns in Puerto Rico and the U.S. Virgin Islands 
7
1.3.D East Coast Area
Historically, the cultivation of sugarcane has been 
the dominant land use in the alluvial valleys and 
adjacent highlands of the East Coast area. Sugar mills, 
to process the sugarcane, were the only sizable 
industry. 
Within the last 15 years, an oil refinery, 
pharmaceutical plants, and light industries, as well as 
urban areas, have developed. 
These industries and 
other agricultural activities such as dairy, livestock, and 
vegetable farms are replacing the sugarcane economy 
in the area. 
Industrial and urban development is 
concentrated around the towns of Humacao and 
Yabucoa.
1.3.E East Central Area
In the last several decades, the East Central area 
has changed from a predominantly agricultural land-use 
base to industrial, commercial, and residential land 
uses. 
Of particular interest is the rapid increase in 
urbanization in the city of Caguas. Over 90 percent of 
the Caguas valley falls within the industrial and high- 
density residential land-use categories. In recent years, 
the city of Caguas has served as a residential suburb of 
the San Juan metropolitan area. The main agricultural 
land-use category 
has changed from sugarcane 
cultivation to dairy farms. 
Although the towns of 
Gurabo, Juncos, and Las Piedras also have grown, the 
changes in these areas are less dramatic than the 
changes in the vicinity of Caguas. The northeastern and 
southern parts of the East Central area contain the 
largest forested areas, including the northwestern 
extremity of the Caribbean National Forest of El 
Yunque.
1.3.F Puerto Rico Offshore Islands: 
Isla de Culebra and Isla de Vieques
The interior of Isla de Culebra is primarily used for 
pasture. The rest of the island is covered by brush or 
secondary growth forest (fig. 1.3-1). The town of Dewey 
and surrounding areas are residential and commercial. 
A number of individual homes and small resorts are 
scattered throughout the island. 
The Penfnsula 
Flamenco on the northwest corner of Isla de Culebra 
was once used as a gunnery impact area by the U.S. 
Navy. This area has been designated a wildlife refuge.
A large part of Isla de Vieques is devoted to military 
use. 
The eastern quarter of the island serves as a 
gunnery impact area. Adjacent to the impact area, and 
encompassing an additional fourth of the island, is 
Camp Garcfa, a U.S. Marine Corps training facility. The 
western quarter of the island is also under military 
control. About half of this area is covered by brush, with 
the rest covered by grassland and leased for grazing. 
There are a number of ammunition bunkers in the area, 
a few of which are still in use.
Residential land use is concentrated in areas of Isla 
de Vieques not under military control, particularly 
around the town of Isabel Segunda on the north coast 
and Esperanza on the south coast. There is some light 
industrial development at Isabel Segunda and on a 
peninsula near Ensenada Honda. 
Small grazing 
enterprises occupy the non-residential and the non- 
military areas of the island.
1.3.G U.S. Virgin Islands
St. Thomas is an urban island (fig. 1.3-2). Charlotte 
Amalie, the only city, occupies a relatively small area on 
the south coast. However, in at least six other areas on 
the island, the density of housing and commercial areas 
approaches that in Charlotte Amalie. 
Residential 
subdivisions 
are 
present 
throughout 
the 
island. 
Agricultural usage is minimal. There are a few small 
areas in pasture and devoted to truck farming. 
The 
remainder of the land is covered by brush and 
secondary forest.
Two-thirds of St. John is a National Park (fig. 1.3-2). 
There are some private holdings in the Park area, 
mostly individual residences. The Park land and much 
of the privately owned land outside the Park is in brush 
and secondary forest. 
The village of Cruz Bay and 
vicinity make up a lightly populated urban area on the 
western end of the island. The same is true of Coral 
Bay, on the eastern end of the island.
In the past, nearly all of St. Croix was under 
sugarcane or cotton cultivation, or was in pasture. 
Agricultural usage has declined, but some land is still 
used for pasture (Jordan, 1975, p. 1; fig. 1.3-3). 
Although about one third of St. Croix has soil suitable for 
agriculture, only about 5,000 acres are under cultivation. 
The remainder of the island is generally undeveloped, 
except for about 2,000 acres of urban or industrial 
areas.
8 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
18°25'
20'
65W
55'
50'
45'
ATLANTIC 
OCEAN
ST. THOMAS
ST. JOHN
EXPLANATION
LAND USE
AGRICULTURAL
RESIDENTIAL
OTHER
VIRGIN ISLANDS NATIONAL PARK BOUNDARY
CARIBBEAN SEA
      - 
EPHEMERAL STREAM 
  
TOWN
0 
1 
2 KILOMETERS
I 
I 
0 
1 
2 MILES
64°40'
Modified from U.S. Department of Agriculture, 1982
Figure 1.3-2 Generalized land use in St. John and St. Thomas, U.S. Virgin Islands.
1.3 General Land-Use Patterns in Puerto Rico and the U.S. Virgin Islands 
9
64°50'
45'
40'
64°35'
17°45'
17°40'
ST. CROIX
CARIBBEAN SEA
FREDERIKSTED
CARIBBEAN SEA
0 
1 
2 KILOMETERS
i 
II_____,
I 
I 
I
0 
1 
2 MILES
EXPLANATION
AGRICULTURAL 
___j 
RESIDENTIAL 
|^| 
INDUSTRIAL 
|^| 
OTHER
    EPHEMERAL STREAM
  
TOWN
Modified from U.S. Department of Agriculture, 1982
Figure 1.3-3 Generalized land use in St. Croix, U.S. Virgin Islands.
10 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.0 GROUND-WATER RESOURCES AREAS IN PUERTO RICO
2.1 North Coast Area
2.0 Ground-Water Resources Areas in Puerto Rico 
11
2.1.1 AGUADILLA-HATILLO REGION
By Patrick Tucci
2.1.1 .A Location and Major Geographic 
Features
The Aguadilla-Hatillo region covers about 400 mi2 
in the westernmost part of the North Coast area. The 
region extends about 37 miles from the west end of the 
island to the approximate position of the divide between 
the Rfo Camuy and the Rfo Grande de Arecibo (fig.
2.1.1 .A-1). The region is bordered on the south by rocks 
of the volcanic island core, on the west by the Mona 
Passage, and on the north by the Atlantic Ocean. 
Rolling plains and karst features dominate the central 
and northern areas. The municipios of Rincon, Aguada, 
Aguadilla, Isabela, Quebradillas, Camuy, and Hatillo are 
located along the coast, and the municipios of Moca, 
San Sebastian, and Lares are located inland (fig. 
2.1.1.A-1).
The coast is lined by cliffs that, in places, rise more 
than 200 feet above mean sea level. Much of the south 
portion of the region is marked by an escarpment of 
several hundred feet cut by the Rfo Culebrinas. The 
northern third of the region is a rolling plain that lies from 
about 200 to 400 feet above mean sea level, and is 
bounded on the north by sea cliffs and on the south by 
karst landforms. 
Two northward flowing rivers cut
67'15'
10'
across the karst area. The Rfo Guajataca flows through 
a deep canyon formed by the collapse of a cave system, 
and the Rfo Camuy flows, in part, through a cave system 
and, in part, through a canyon formed by the collapsed 
parts of a cave. Lago Guajataca, in the east central part 
of the region, is a large, man-made reservoir used for 
public-water supply.
6630'
18°30'
25'  
20'
1815'  
ATIANTIC OCEAN
SENATORIAL DISTRICT NUMBER
M ^ - \ 
L^vrv n-v 
A> kj; .UVM Bt.vA;^!':^^^
U 
f*lrt' I -f°t.-T-3.t.^\
AGUADILLA- 
HATILLO REGION
01234 KILOMETERS
Base from U.S. Geological Survey
Puerto Rico e Islas Limftrofes, 1:240,000, 1952
Figure 2.1.1.A-1 Location and major geographic features in the Aguadilla-Hatillo region, Puerto Rico. 
12 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2. 1 . 1 .B Population and Estimated 
Ground-Water Use
The population of the Aguadilla-Hatillo region was 
about 257,000 in 1980 and 282,000 in 1990, an increase 
of about 9 percent (U.S. Department of Commerce, 
1982, 1991; Gomez-Gomez and others, 1984; table
2.1.1.B-1). About 74 percent of the population lives on 
farms and in rural communities, and the remainder (26 
percent) lives in urban areas. The largest municipio is 
Aguadilla, which had a total population of about 55,000 
in 1980 and 59,000 in 1990 (table 
2.1.1.B-1).
Ground-water pumpage for domestic use is limited, 
because most water for public supply is obtained from 
Lago Guajataca. About 25 Mgal/d of water from Lago 
Guajataca was used for public supply in 1983 (Gomez- 
Gomez and others, 1984). Ground water withdrawn in 
1983 
totalled 
about 
2 
Mgal/d, 
and 
supplied 
approximately 12 percent of the population (1980
population estimate; table 2.1.1.B-2). 
A rural water- 
supply system in the municipio of Lares uses about 0.01 
Mgal/d of ground water. About 6,000 gal/d of ground 
water was pumped for industrial use in the municipio of 
Aguadilla. 
The approximate location of public-supply 
and industrial wells are shown in figure 2.1.1 .B-1.
67°15'
10'
05'
67°00'
55'
50'
45'
40'
35'
66°30'
ATLANTIC OCEAN
18°30'
MONA 
PASSAGE
25'
20'
EXPLANATION
EXTENT OF COASTAL AQUIFER AREAS 
Limestone and coastal alluvial deposits
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
01234 KILOMETERS
I 1   '   ,  , 
01234 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.1.1.B-1 Approximate well locations in the Aguadilla-Hatillo region, Puerto Rico.
2.1.1 Aguadilla-Hatillo Region 
13
Table 2.1.1.B-1 Population for the Aguadilla-Hatillo region, Puerto Rico 
(U.S. Department of Commerce, 1982, table 1; U.S. Department of Commerce, 
1991, table 1)
MUNICIPIO
Aguadilla
Moca
Isabela
San Sebastian
Quebradillas
Lares
Camuy
Hatillo
Total
TOTAL
54,606
29,185
37,435
35,690
19,728
26,743
24,884
28,958
257,229
1980 population
URBAN
22,039
3,960
12,087
10,619
3,770
5,224
3,680
5,019
66,398
RURAL
32,567
25,225
25,348
25,071
15,958
21,519
21,204
23,939
190,831
1990 population
TOTAL
59,335
32,926
39,147
38,799
21,425
29,015
28,917
32,703
282,267
2.1.l.C Geologic Setting
Sedimentary rocks are the predominant rock type in 
the 
Aguadilla-Hatillo region. 
They unconformably 
overlie volcanic rocks (fig. 2.1.1.C-1). The sedimentary 
rock formations dip northward toward the Atlantic Ocean 
at an average angle of 3 to 4 degrees. The following 
description is summarized from Monroe (1980a).
The sedimentary rocks, predominately limestone 
and calcareous clays of Tertiary age, are probably as 
much as 5,000 to 6,000 feet thick at the Atlantic 
coastline. 
The basal San Sebastian Formation of 
Tertiary age is primarily a clay in the eastern part of the 
region, but contains gravel and cobbles in the western 
part. The San Sebastian Formation ranges in thickness 
from near zero to about 300 feet. The five overlying 
formations (Lares Limestone, Cibao Formation, Aguada 
Limestone, 
Aymamon 
Limestone, 
and 
Camuy 
Formation) are predominately limestone, marls, or 
calcareous clays deposited in a shallow sea, when sea 
level altitude was higher than in recent geologic times.
The Lares Limestone, overlying the San Sebastian 
Formation, consists primarily of a fine- to medium- 
grained limestone. In the western part of the Aguadilla- 
Hatillo region, the Lares Limestone grades laterally into
clastic beds indistinguishable from the San Sebastian 
Formation. The Lares Limestone ranges in thickness 
from near zero to about 1,000 feet in this region.
The Cibao Formation overlies the Lares Limestone 
and is made up of interbedded calcareous clay, 
limestone, sandy clay, and sand and gravel. 
In the 
Aguadilla-Camuy region, the Cibao Formation typically 
is composed of beds of chalk, marl, and calcareous clay. 
The Cibao Formation contains significant amounts of 
sand and gravel near the municipio of San Sebastian, 
and contains limestone in the lower part of the formation 
in the Rfo Camuy area. The Cibao Formation is about 
650 feet thick in the Aguadilla-Hatillo region.
The Aguada Limestone, overlying the Cibao 
Formation, consists primarily of limestone containing 
chalky beds in the lower part and nearly pure, indurated 
limestone in the upper part. The Aguada Limestone is 
about 300 feet thick in the Aguadilla-Hatillo region.
The Aymamon Limestone overlies the Aguada 
Limestone and consists of a very pure limestone 
containing almost no sand or clay. 
In the Aguadilla- 
Hatillo region, the Aymamon 
Limestone can 
be
Table 2.1.1.B-2 Ground-water withdrawals and estimated population served during 
1983 for the Aguadilla-Hatillo region, Puerto Rico 
[Mgal/d, million gallons per day;  , no data available]
1 Use and supplier
Estimated 
population served
Average ground- 
water withdrawals 
(Mgal/d)
I. Domestic Use
2A. Puerto Rico Aqueduct and Sewer Authority
1. Aguadilla
2. Moca
3. Isabela
4. San Sebastian
5. Quebradillas
6. Lares
7. Camuy
8. Hatillo
4B. Community Systems
1. Lares 
4II. Industrial Use
1. Aguadilla
112
4334
0.058
0.007
0.273
Subtotal
14,399
10,138
29,904
632
0.561
0.953
1.852
0.095
0.006
Total
30,536
1.953
1 Municipios not listed under some specific use do not withdraw ground water for the subject use.
2 Modified from data reported by Gomez-Gomez and others, 1984.
3 Based on a water consumption of 63 gallons per person per day.
4 Modified from data reported by a written communication of the Puerto Rico Department of Health.
separated into two members. The lower member has 
been extensively altered, recrystallized, and solution 
riddled by percolating ground water. The upper member 
is predominately a chalk interbedded with limestone. 
The total thickness of the Aymamon is about 600 feet in 
this region.
The Camuy Formation is predominately limestone 
with sand. The lower members of the Camuy Formation 
consist of chalk or chalky limestone, and contain 
appreciable quantities of quartz sand. 
The upper 
member of the Camuy Formation is a mixture of chalk, 
limestone, and calcareous sandstone. 
The total 
thickness of the Camuy Formation in this region ranges 
from about 350 to 550 feet.
The Aguadilla-Hatillo 
region 
has 
more 
karst 
features per square mile than any other part of the north 
coast limestone (Giusti, 1978, p. 9). The greatest karst 
development is in the Aymamon Limestone and the 
Lares Limestone. Areas of little or no karst development 
are primarily limited to the outcrop area of the Cibao and 
San Sebastian Formations. 
Relatively little karst has 
developed on the Camuy Formation. 
The Camuy 
Formation forms a rolling plain of 100 to 600 feet above 
mean sea level in most of its outcrop area. Tertiary and 
Quaternary blanket sands are widespread and overlie 
large areas of the Aymamon Limestone and the Camuy 
Formation.
14 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
67°15'
10'
05'
67W
18°30'  
25'
20'
55'
ATLANTIC OCEAN
50'
45'
40'
35'
66°30'
MONA 
PASSAGE
01234 KILOMETERS
i ii ii ___
01234 MILES
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
LANDSLIDE DEPOSITS
BLANKET DEPOSITS
CAMUY FORMATION
AYMAMON LIMESTONE
AGUADA LIMESTONE
CIBAO FORMATION
LARES LIMESTONE
SAN SEBASTIAN FORMATION J
PLUTONIC ROCKS
Holocene 
and
QUATERNARY
I QUATERNARY 
J 
TERTIARY
Miocene
and 
Oligocene
Eocene 
to Lower 
Cretaceous
VOLCANIC AND
VOLCANICLASTIC
ROCKS
RESERVOIR
A' LINE OF SECTION-Location of cross section 
shown in figure 2.1.1.D-1
-   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TERTIARY 
CRETACEOUS
PERENNIAL STREAM 
TOWN OR CITY
Modified from Briggs and Akers, 1965
Figure 2.1.1.C-1 Generalized surficial geology in the Aguadilla-Hatillo region, Puerto Rico.
2.1.1 Aguadilla-Hatillo Region 
15
2.1.1.D Hydrogeology
The water-table aquifer, consisting of the saturated 
parts of the Aguada and Aymamon Limestones (fig. 
2.1.1.D-1), is the primary source of ground water in the 
Aguadilla-Hatillo region. 
Localized areas of confined 
ground water may be present within water-bearing 
zones of the Cibao Formation and Lares Limestone; 
however, the extent of these zones in the Aguadilla- 
Hatillo region is unknown. Extensive artesian zones, if
present, will likely be located east of the Rfo Guajataca. 
Less is known about the hydrogeology of the Aguadilla- 
Hatillo region than in other areas of the North Coast.
The areal extent and thickness of the water-table 
aquifer is controlled by the location of the top of the 
Cibao Formation and the location of the saline- 
freshwater interface, which forms the base of the 
aquifer. 
The maximum thickness of the water-table 
aquifer is approximately 450 feet, about 4 miles inland
from the Atlantic Ocean south of Isabela (Jesus 
Rodrfguez-Martmez, U.S. Geological Survey, written 
communication, 1991). 
The aquifer is generally less 
than 100 feet thick at distances of 2 miles or less from 
the coast, due to the presence of saline water with 
depth.
Hydraulic-conductivity values of the limestones 
along the north coast generally are smaller in the 
Aguadilla-Hatillo region than in other regions of the 
North Coast. Limestones in this region may be an order
of magnitude less permeable than limestones in the 
area immediately to the east. 
Guisti (1978, p. 25) 
estimated hydraulic-conductivity values of the Lares 
Limestone, Cibao Formation, Aguada Limestone, and 
Aymamon Limestone to be 0.6, 1.4, 5.7, and 57 feet per 
day (ft/d), respectively. 
Analysis of specific-capacity 
tests of wells in the region result in similar estimates of 
hydraulic-conductivity values. Cavernous zones in the 
limestones, encountered during drilling of test wells, 
may indicate localized areas of significantly greater
MEAN SEA LEVEL
300
POTENTIOMETRIC SURFACE
Modified from Giusti and Bennett, 1976
0 
1 
2 
KILOMETERS
I_____i 
, 
i______,
I 
l 
I
0 
1 
2 
MILES
Tea 
| 
CAMUY FORMATION
Tay 
| 
AYMAMON LIMESTONE
Ta 
| 
AGUADA LIMESTONE
~TfcI CIBAO FORMATION
EXPLANATION
Tcm 
| CIBAO FORMATION (Including Montebello
Limestone Member)
Q__I LARES LIMESTONE
I 
SAN SEBASTIAN FORMATION AND VOLCANICS
I
WATER-TABLE AQUIFER
ARTESIAN AQUIFER ? 
(EXTENT UNCERTAIN)
WELL
Figure 2.1.1.D-1 Hydrogeologic section in the Aguadilla-Hatillo region, Puerto Rico (line of section shown in figure 2.1.1.C-1).
16 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
hydraulic conductivity. The transmissivity of the water- 
table aquifer generally is less in this region than in other 
regions of the North Coast area, because of the low 
hydraulic conductivity and the relatively thin saturated 
thickness. Transmissivity values generally are less than 
5,000 ft2/d, and range from less than 0.1 ft2/d where the 
aquifer pinches out to about 10,000 ft2/d in areas where 
the saturated thickness of the Aymamon Limestone and
depth to saline water is greatest. Parts of the Aguada 
and Aymamon Limestones and all of the Camuy 
Formation are above the water table, and are not part of 
the aquifer in this region.
The amount of recharge to the ground-water 
system in the region is unknown. Estimated recharge in 
a geologically similar region near Barceloneta is about 
60 Mgal/d (Torres-Gonzalez, 1985, p. 26).
2.1.1 .E Ground-Water Levels and 
Movement
Ground-water flow in the Aguadilla-Hatillo region is 
from recharge areas in the karstic highlands in the 
center of the North Coast area towards coastal areas to 
the north and west and towards the Rfo Culebrinas to 
the south (fig. 2.1.1 .E-1). The water-table map shown in 
figure 2.1.1.E-1 is for the wet season in November and
December 1984. 
Water levels during that time were 
somewhat higher than average annual water levels; 
however, the shape of the water-table contours and the 
overall pattern of ground-water flow are probably similar 
throughout the year. 
Because of the relatively small 
number of wells available for water-level measurements, 
the water-table map should be considered only a 
generalized representation of the water table from which 
overall patterns of ground-water flow can be estimated.
67°15'
10'
05'
67W
55'
50'
45'
40'
35'
66°30'
ATLANTIC OCEAN
18°30'
MONA 
PASSAGE
25'
20'
EXPLANATION
669
01234 KILOMETERS
4 MILES
\ \
EXTENT OF COASTAL AQUIFER AREAS 
Limestone and coastal alluvial deposits
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
WATER-LEVEL CONTOUR-Shows altitude
of water level in feet. Contour interval is variable.
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
WELL LOCATION AND WATER-LEVEL ALTITUDE- 
Shows well location and measured water-level altitude 
in tightly cased well. Datum is mean sea level
TOWN OR CITY
Modified from Tucci and Martinez, 1995
Figure 2.1.1.E-1 Altitude of water-level surface and direction of ground-water flow during November 1984 in the Aguadilla-Hatillo region, Puerto Rico.
2.1.1 Aguadilla-Hatillo Region 
17
Locally, ground water also flows to the Rfo 
Guajataca and Rfo Camuy. 
This component of flow is 
not 
apparent 
on 
the 
water-table 
surface 
map 
(fig. 2.1.1.E-1), because of the large scale of the map 
and the scarcity of water-level measurements in wells 
near the rivers. Giusti (1978, p. 35) estimated that from 
about 30 to 40 percent of the total flow of the lower parts 
of the Rfo Camuy and Rfo Guajataca is base flow, which 
is the ground-water contribution to the stream. 
The 
Quebrada de los Cedros, in the extreme northwestern 
part of the region, is usually dry and flows only after 
prolonged rainfall (Giusti, 1978, p. 34). 
This small 
stream provides a small amount of ground-water 
recharge by leakage through the streambed following 
rainstorms.
The amount of ground water discharging directly to 
the sea is unknown. A large spring located just 600 feet 
inland of the coastline in Aguadilla had an average 
discharge of 1.1 ft3/s from December 1982 through 
January 1984 (Guzman-Rfos, 1988, p. 11). 
Several 
offshore springs have been documented, or their 
existence 
inferred, 
by 
remote-sensing techniques 
(Percious, 1971; Blume and others, 1981), but their 
discharge is unknown.
Several tributaries on the north side of the Rfo 
Culebrinas originate as springflow from the escarpment 
on the southern edge of the Aguadilla-Hatillo region. 
The total amount of this springflow and the total amount 
of ground-water discharge along the southern boundary 
of the region are unknown.
2.1.1.F Soil Permeability
Soil development can be divided physiographically 
into five areas: 
coastal plain, flood plain, limestone 
upland, 
volcanic 
upland, 
and 
upland 
valley 
(fig. 2.1.1.F-1). 
These areas are characterized by 
different morphology and parent material upon which 
soils developed. Coastal plain soils are developed on 
level to gently sloping surfaces. Five soil associations 
are developed on the coastal plain; permeability for 
these soils ranges from 0.60 to 20.00 in/hr (table 
2.1.1.F-1). Two soil associations are developed on the 
nearly level flood plains, and these are prone to frequent 
flooding. Soil permeability of the flood plain generally is 
less than that in the coastal plain, and ranges from 0.06 
to 2.00 in/hr. The four soil associations on limestone 
uplands tend to be thinner than those in other areas 
(table 2.1.1.F-1) and rock outcrops are common. 
Slopes are moderate to very steep in these uplands, 
and soil permeability ranges from 0.60 to 20.00 in/hr. 
The four soil associations on volcanic uplands are 
developed on gently sloping to steep slopes, and 
permeability ranges from 0.60 to 2.00 in/hr. The two soil 
associations in upland valleys may be on sloping to very 
steep areas or on ridgetops, and permeability ranges 
from 0.06 to 2.00 in/hr.
The most permeable soils (2.00 to 20.00 in/hr) in 
the Aguadilla-Hatillo region are developed along the 
coast, but are of limited extent (fig. 2.1.1 .F-1). The least 
permeable soils (0.06 to 0.60 in/hr) are found on flood 
plains or upland valleys. Most of the region is covered 
by soils of moderate permeability, ranging from 0.6 to 
2.00 in/hr.
Table 2.1.1.F-1 Thickness, permeability, and available water capacity for soil associations 
in the Aguadilla-Hatillo region, Puerto Rico (Modified from Gierbolini, 1975; Acevedo, 1982)
Area and soil association
Coastal Plain
Bejucos-Jobos
G uerrero-Carrizales- Jobos
Coto-Aceitunas
Almirante-Espinosa-Vega Alta
Bayamon-Matanzas
Flood Plains
Coloso-Toa
Toa-Coloso-Bajura
Limestone Uplands
Colinas-Soller
Limestone Outcrop-San Sebastian
Rock-Tanama-San Sebastian
Soller-San German-Rock Outcrop
Volcanic Uplands
Voladora-Moca
Caguabo-Mucara
Consumo-Humatas
Humatas-Los Guineos-Alonso
Upland Valleys
Moca-Perchas
Colinas-Naranjo-Juncal
Thickness 
(inches)
42 to 75
55 to 72
55 to 60
65 to 75
64 to 70
42 to 65
60 to 63
60 to 63
60 to 63
10 to 60
25 to 60
Oto55
16 to 55
10 to 25
18 to 62
50 to 60
18 to 27
50 to 56
56 to 62
56 to 60
58 to 60
Oto60
Permeability 
(inch per hour)
0.60
2.00
2.00
0.60
0.60
0.60
0.06
0.06
0.06
0.60
0.60
0.60
0.60
6.00
0.60
0.60
0.60
0.60
0.60
0.06
0.06
0.60
to 20.00
to 20.00
to 20.00
to 2.00
to 6.00
to 6.00
to 2.00
to 2.00
to 2.00
to 20.00
to 2.00
to 2.00
to 2.00
to 20.00
to 2.00
to 2.00
to 2.00
to 2.00
to 2.00
to 2.00
to 0.60
to 2.00
Available water 
capacity 
(inch per inch)
0.04 to 0.20
0.05 to 0.1 5
0.04 to o.20
0.10 to 0.20
0.06 to 0.20
0.06 to 0.20
0.1 2 to 0.20
0.1 2 to 0.20
0.1 2 to 0.20
0.05 to 0.25
0.09 to 0.25
0.1 5 to 0.20
0.1 5 to 0.20
0.05 to 0.25
0.05 to 0.24
0.1 5 to 0.24
0.05 to 0.1 7
0.10 to 0.18
0.10 to 0.18
0.09 to 0.20
0.1 5 to 0.24
0.09 to 0.20
18 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
67°15'
10'
05'
67W
18°30'
25'
20'
55'
ATLANTIC OCEAN
50'
45'
40'
35'
66°30'
MONA 
PASSAGE
01234 KILOMETERS
E-1
EXPLANATION
SOIL ASSOCIATIONS
COASTAL PLAINS
A-1 BEJUCOS-JOBOS
A-3 GUERRERO-CARRIZALES-JOBOS
B-1 COTO-ACEITTJNAS
B-2 ALMIRANTE-ESPINOSA-VEGA ALTA
B-3 BAYAMON-MATANZAS
FLOOD PLAINS 
E-1 COLOSO-TOA 
E-3 TOA-COLOSO-BAJURA
LIMESTONE UPLANDS 
C-1 COLINAS-SOLLER
C-2 LIMESTONE OUTCROP-SAN SEBASTIAN 
C-3 ROCK OUTCROP-TANAMA-SAN SEBASTIAN 
C-5 SOLLER-SAN GERMAN-ROCK OUTCROP
VOLCANIC UPLANDS 
F-1 VOLADORA-MOCA 
M-1 CAGUABO-MUCARA 
N-1 CONSUMO-HUMATAS 
N-4 HUMATAS-LOS GUINEOS-ALONSO
UPLAND VALLEYS 
T-1 MOCA-PERCHAS 
U-1 COLINAS-NARANJO-JUNCAL
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.60 
FROM 0.60 TO 2.00 
FROM 0.60 TO 6.00 
FROM 2.00 TO 20.00
SOIL ASSOCIATION BOUNDARY
01234 MILES
\ \
-- --   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
Modified from Gierbolini, 1975; Acevedo, 1982
Figure 2.1.1.F-1 Soil associations and permeability in the Aguadilla-Hatillo region, Puerto Rico.
2.1.1 Aguadilla-Hatillo Region 
19
2.1.2 ARECIBO-MANATI REGION
By Angel Roman-Mas
2.1.2.A Location and Major Geographic 
Features
The Arecibo-Manatf region is located in the west- 
central part of the North Coast area. 
The Arecibo- 
Manatf region extends 23 miles from the western 
drainage divide between the Rio Camuy (fig. 2.1.1.A-1) 
and Rfo Grande de Arecibo to the eastern drainage 
divide, 2 miles east of the Rfo Grande de Manatf (fig. 
2.1.2.A-1). 
The southern boundary is the contact 
between the limestone belt and the undifferentiated 
lower Tertiary and Cretaceous rocks of the island core. 
The northern boundary is the Atlantic Ocean. 
The 
Arecibo-Manatf region is comprised of three major 
drainage basins, the Rfo Grande de Arecibo, Rfo 
Tanama, and Rfo Grande de Manatf. The Rfo Grande 
de Arecibo and the Rfo Grande de Manatf flow 
northward from the island's mountainous core into 
entrenched valleys and discharge to the Atlantic Ocean. 
The Rfo Tanama, a principal tributary of the Rfo Grande 
de Arecibo, flows to the northeast.
The valley floors of the Rfo Grande de Arecibo and 
Rfo Grande de Manatf have gently sloping surfaces 
ranging in elevation from mean sea level to about 80 
feet above mean sea level at the contact with the 
limestones. In contrast, the elevation of the limestones 
range from about 1,200 feet above mean sea level in the 
southern part of the region to a few tens of feet above 
mean sea level in the coastal lowlands. 
The most 
prominent feature of the coastal lowland is the Cano 
Tiburones, a sea level swamp that was largely drained 
for agriculture in 1949.
The major population centers in the Arecibo-Manatf 
region 
are 
the 
cities 
of 
Arecibo, 
Manatf, 
and 
Barceloneta. Industrial development in the region has 
mainly focused on the establishment of pharmaceutical 
industries that form one of the largest pharmaceutical 
manufacturing centers in the world. Urban and industrial 
development has been concentrated within a few miles 
of the coast, because of the nearly inaccessible karst 
terrain further inland.
2.1.2.B Population and Estimated 
Ground-Water Use
The total population within the Arecibo-Manatf 
region was about 253,000 in 1980 (U.S. Department of 
Commerce, 1982). 
However, total population of the 
municipios 
overlying 
the 
aquifer areas 
(Arecibo, 
Barceloneta, Ciales, Florida, and Manatf) totalled about 
166,000. About 53 percent of the population in these 
municipios lives in the urban areas. The remainder of 
the population (47 percent) lives in small villages, rural 
communities, and on farms. 
Population in these 
municipios increased by about 8 percent in 1990 (Puerto 
Rico Planning Board, written communication, 1991). 
The 1980 and 1990 population distribution in all the 
municipios within this region is shown in table 2.1.2.B-1. 
The total ground-water pumpage for the region was 
about 25 Mgal/d in 1983. The Puerto Rico Aqueduct 
and Sewer Authority public-water supplies accounted for 
76 percent (18.5 Mgal/d) of the total ground-water 
withdrawals in the region. 
The estimated population 
served was about 139,000 (table 2.1.2.B-2). Well 
location or well fields furnishing water for the different 
uses are shown on figure 2.1.2.B-1. In this report, 
domestic use refers to public-water supply and self- 
supplied users.
The major industries in the Arecibo-Manatf region 
obtain water from wells. 
Pumping for industrial use 
accounts for about 17 percent (4.2 Mgal/d) of the total 
ground water withdrawn. Most of the ground water used 
for industrial purposes comes from the deep artesian 
limestone aquifer. 
Agriculture accounted for about 
seven percent of the total ground-water withdrawal in 
1983 (1.7 Mgal/d); agricultural use occurs mostly in the 
Arecibo area where ground water has been used for rice 
irrigation (Roman-Mas, 1988).
Table 2.1.2.B-1 Population for the Arecibo-Manati region, Puerto Rico (U.S. Department of 
Commerce, 1982, table 1; Puerto Rico Planning Board, written communication, 1991)
1980 population
MUNICIPIO
Adjuntas
Arecibo
Barceloneta
Ciales
Florida
Jayuya
Manatf
Orocovis
Utuado
Total
TOTAL
18,786
86,766
18,942
16,211
7,232
14,722
36,562
19,332
34,505
253,058
URBAN
5,239
48,779
4,502
3,582
3,641
3,588
17,347
1,256
11,113
99,047
RURAL
13,547
37,987
14,440
12,629
3,591
11,134
19,215
18,076
23,392
154,011
1990 population
TOTAL
19,451
93,385
20,947
18,084
8,689
15,527
38,692
21,158
34,980
270,913
2.1.2.C Geologic Setting
Sedimentary rocks, predominately limestones of 
Tertiary age, are the principal rocks in the Arecibo- 
Manatf region (fig. 2.1.2.C-1). These limestones rest on 
a volcanic base of Early Cretaceous to middle Eocene 
age and range in thickness from near zero, where they 
abut the volcanic rocks of the island core, to nearly 
6,000 feet at the coastline (fig. 2.1.2.C-2, a). The San 
Sebastian Formation is the base of the Tertiary rock 
sequence. 
In the Arecibo-Manatf region the San 
Sebastian Formation is predominately clay, sandy-clay, 
and sandy limestone derived from sediment carried by 
major rivers to the sea and deposited along a former 
coastline. 
The five formations overlying the San 
Sebastian Formation are mostly limestones deposited in 
shallow seas (Monroe, 1976 and 1980a). They are the
Lares Limestone, Cibao Formation, Aguada Limestone, 
Aymamon Limestone, and Quaternary deposits.
The Lares Limestone overlies the San Sebastian 
Formation and consists of a nearly pure limestone 
containing abundant reef-forming organisms. The Cibao 
Formation, overlying the Lares Limestone, consists of 
many members having a heterogeneous lithology 
varying from limestone to sand, to clay and clayey sand. 
In the Arecibo-Manatf region, the Montebello Limestone 
Member of the Cibao Formation, a thick reefal type 
deposit, overlies the Lares Limestone. 
In turn, the 
Montebello Limestone Member is overlain by calcareous 
clay and sand considered to be typical of the upper 
Cibao Formation. The Aguada Limestone overlies the 
Cibao Formation and is a nearly pure limestone 
probably 
deposited 
in 
a 
fringing 
reef-backreef
20 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Table 2.1.2.B-2 Ground-water withdrawals and estimated population served 
during 1983 for the Arecibo-Manati region, Puerto Rico
[Mgal/d, million gallons per day;  , no data available]
1 Use and supplier
2I. Domestic Use
1. Arecibo
2. Barceloneta
3. Florida
4. Ciales
5. Manati
3II. Industrial Use
1. Arecibo
2. Barceloneta
3. Manatf
Estimated 
population 
served
64,705
20,326
8,264
6,739
38,671
Subtotal 
138,695
 
 
 
Average 
ground-water 
withdrawals 
(Mgal/d)
6.623
3.725
1.073
0.763
6.379
18.563
0.044
2.845
1.750
Subtotal
3II. Agricultural Use
1. Arecibo
2. Barceloneta
3. Manati
4.639
1.629
0.045
0.052
Subtotal
1.726
Total 
138,695
24.928
1 Municipios not listed under some specific use do not withdraw ground water for the 
subject use.
2 Modified from data reported by Gomez-Gomez and others, 1984.
3 Modified from Industrial Ground-Water Inventory, November-December 1985.
environment. The Aymamon Limestone, overlying the 
Aguada Limestone, is also a reef deposit but differs in 
that much of the Aymamon Limestone is more of a chalk 
than a crystalline limestone. The Quaternary deposits 
overlies the Aymamon Formation and are present only 
in scattered patches in the Arecibo-Manatf region. The 
Quaternary deposits consist of sandy and silty clays and 
muck deposits.
The limestones of the Arecibo-Manatf region have 
undergone 
significant 
karstification 
since 
their 
deposition. 
Prominent karst features in this region 
include mogotes, cockpits with steep-walled ridges, and 
steep-sided canyons. The extent of karst development 
depends on the composition of the limestone. 
The 
Cibao Formation, where it is composed of calcareous 
clay and sandy clay, as in the southeastern part of the 
region, is the only formation in the Arecibo-Manatf 
region with little or no karst development.
Alluvial, blanket sand, swamp, and beach deposits 
of Quaternary age overlie the limestone formations 
throughout the region (fig. 2.1.2.C-1). 
Among these 
surficial deposits, the alluvial and blanket sand deposits 
play important roles in the hydrogeology of the region. 
During Pleistocene time, a sea-level stand at more than 
300 feet below present sea level, resulted in downward 
erosion and deepening of the Rio Grande de Arecibo 
and Rfo Grande de Manatf valleys. Subsequent rises in 
sea level caused river transported sediments to be 
deposited 
within 
these 
valleys, 
filling 
them 
to 
approximately their present level (Gomez-Gomez, 1984, 
p. 14; Quinones-Aponte, 1986b, p. 13). 
The alluvial 
deposits are composed of moderately well sorted, 
stratified sand, gravel, silt, and clay (Briggs, 1968). The 
thickness of alluvial deposits within the Rio Grande de 
Arecibo valley average about 130 feet thick (fig. 
2.1.2.C-2, a) in the southeastern part of the valley 
(Quinones-Aponte, 1986b, p. 13). In the Rfo Grande de 
Manatf valley (fig. 2.1.2.C-2, b), alluvial deposits could 
be as thick as 300 feet (Gomez-Gomez, 1984, p. 14). 
The rivers also deposited blanket sands, which are 
composed of quartz and clay in greatly varying 
proportions (Briggs, 1966, p. 60).
2.1.2.D Hydrogeology
The Aymamon and Aguada Limestones are the 
principal geologic units comprising the water-table 
aquifer in the Arecibo-Manati region. The alluvium in 
the river valleys is hydraulically connected to the 
limestones and, although locally semi-confined by clays, 
particularly in the Rfo Grande de Arecibo valley, is 
considered to be part of the water-table aquifer in the 
region. Blanket sand deposits, although low yield water- 
bearing units (aquicludes), are important recharge 
media to the water-table aquifer underneath.
The artesian aquifer formed by the Lares Limestone 
and Montebello Limestone Member of the Cibao 
Formation is confined by the upper member of the Cibao 
Formation overlying the Montebello Limestone Member, 
although water-table conditions exist in their outcrop 
area. The confining layer pinches out towards the south 
(fig. 2.1.2.C-2, a), causing both the water-table and 
artesian aquifers to behave as water-table aquifers and 
to be 
hydraulically connected (Jesus Rodrfguez- 
Martfnez, 
U.S. 
Geological 
Survey, 
written
communication, 1991). Recently collected lithologic and 
hydrogeologic information indicates that the Lares 
Limestone and Montebello Limestone Member have a 
good hydraulic connection. Artesian conditions in both 
limestones extend beyond the western limit of the 
Arecibo-Manatf region. 
East of the Rfo Grande de 
Manatf, the Montebello Limestone Member pinches out 
and is replaced by the Rfo Indio Limestone and the 
Quebrada Arenas Limestone Members of the Cibao 
Formation. 
The replacement of the Montebello 
Limestone Member with these members of the Cibao 
Formation may be at the eastern limit of the Montebello 
artesian 
zone. 
Artesian 
conditions 
have 
been 
documented in the Lares Limestone beyond the eastern 
limit of the region (Rodrfguez-Martfnez and others, 
1992). Although artesian conditions occur in the Lares 
Limestone and the various limestone members of the 
Cibao Formation throughout the entire North Coast 
area, the artesian system is most productive in the 
Arecibo-Manatf region. 
The relative thickness of the 
limestone formations, the associated karst development, 
the larger recharge area, and the large potentiometric 
heads in the area probably account for the productive 
artesian conditions already documented.
The hydraulic conductivity of the limestones in the 
Arecibo-Manatf region varies widely. 
In general, the 
older the rocks, the lower the hydraulic conductivity. 
Giusti and Bennett (1976, p. 23) estimated the average 
hydraulic conductivity of the Lares Limestone to be 0.7 
ft/d; the Montebello Limestone, 9.4 ft/d; the Aguada 
Limestone, 87 ft/d; and the Aymamon Limestone, 535 
ft/d (fig. 2.1.2.C-2, c). Hydraulic conductivity appears to 
be closely related to the depositional environment, type 
of depositional material, and the extent of secondary 
permeability. The highest hydraulic conductivity values 
occur in the rocks closest to the surface, where the 
effects of solution by recharge waters are most effective. 
Giusti and Bennett (1976, p. 21) showed that hydraulic 
conductivity in the Aymamon Limestone decreases with 
depth from approximately 2,800 ft/d near the surface to 
about 2.8 ft/d over about a 1,000 feet depth range (fig. 
2.1.2.C-2, d). Hydraulic conductivity for the Rio Grande 
de Arecibo alluvium may range from 25 to 40 ft/d 
(Quinones-Aponte, 1986b, p. 22) while the Rio Grande 
de Manatf ranges from 20 to 30 ft/d (Gomez-Gomez, 
1984, p. 30).
2.1.2 Arecibo-Manatf Region 
21
Transmissivity values in the water-table aquifer 
were 
estimated 
from 
specific-capacity test 
data 
(Sigfredo Torres-Gonzalez, U.S. Geological Survey, 
written communication, 1991). Transmissivity increases 
from less than 100 ft2/d at the contact between the water 
table and the artesian aquifers to more than 100,000 
ft2/d immediately west of Barceloneta (fig. 2.1.2.D-1).
Yields to wells tapping the water-table aquifer range 
from 7 to more than 2,000 gal/min (Gomez-Gomez, 
1986). Yields of 1,000 gal/min or more can be obtained 
from the Aymamon Limestone and from the alluvium in 
the river valleys. The Aguada, Montebello Limestone 
Member of the Cibao Formation, and Lares Limestones, 
comprising the limestone water-table aquifer, usually 
yield less than 100 gal/min. Maximum yields to wells are 
from the Aguada Limestone and the upper part of the 
Montebello Limestone Member where it is artesian. 
Wells tapping cavernous-limestone zones can yield over 
100 gal/min. 
In artesian zones where the Montebello 
Limestone Member and Lares Limestone are tapped by 
wells, yields range from 500 to 1,000 gal/min or more. 
Yields, however, are not due to the high permeability of 
these rocks in the artesian zones but to the high 
pressure heads driving the systems.
2.1.2.E Ground-Water Levels and 
Movement
The water-table surface map 
(fig. 2.1.2.E-1) 
represents the elevation of the water table in the 
limestone aquifer at the end of the wet season in 
December 1984. Water levels range from a few feet 
below mean sea level in the Cano Tiburones area to 
more than 500 feet above mean sea level near the 
south-central limit of the limestones. Ground-water flow 
originating in the Montebello Limestone Member of the 
Cibao Formation at an elevation of 500 feet moves 
north, through the Aguada Limestone, to elevations of 
100 feet or less in the Aymamon Limestone. Hydraulic 
gradients associated with this ground-water flow are 
steeper in the Aguada Limestone than in the Aymamon 
Limestone.
Ground-water flow is generally from the interior of 
the island to the sea in the Arecibo-Manati region. Flow 
in the water-table aquifer is influenced by coastal 
wetlands, drainage canals, and the two major rivers that
are deeply incised into the limestones. Ground water 
moves from the limestone units northward into the 
coastal plain alluvium, discharging from the alluvium into 
the rivers. 
Ground water also discharges as springs 
issuing from the limestone walls of the valleys or from 
the contact between limestone and alluvium on the 
valley floors. In the lower reach of the Rio Grande de 
Arecibo, the river losses water to the alluvial aquifer, and 
that water may discharge at springs in the Cano 
Tiburones.
When first drilled, 
heads 
in the Montebello 
Limestone Member of the Cibao Formation were as 
much as 400 feet above sea level. Well location or well 
fields furnishing water for the different uses are shown 
on figure 2.1.2.B-1. Withdrawals and possible leakage 
to 
the 
water-table 
aquifer, 
through 
improperly 
constructed wells, has caused major head declines in 
the industrial area where withdrawals from the artesian 
aquifer are concentrated. Discharge from the artesian 
aquifer probably is diffused by upward leakage through 
the overlying limestones to the sea floor and offshore 
(Guisti and Bennett, 1976).
2.1.2.F Soil Permeability
The infiltration rate of the soil zone is an important 
factor in assessing either recharge to the underlying 
aquifer 
or 
the 
vulnerability 
of 
the 
aquifer 
to 
contamination from certain land-use or waste-disposal 
practices. Soil-zone permeability as determined by the 
U.S. 
Department of Agriculture (Acevedo, 
1982) 
provides an estimate of the water infiltration rate when 
the soil is saturated. Generalized infiltration rates (fig. 
2.1.2.F-1) are derived from soil permeability data 
(Acevedo, 1982; table 2.1.2.F-1). The values shown in 
table 2.1.2.F-1 and figure 2.1.2.F-1 are those of the soil 
zone with the lowest infiltration rate, usually the B 
horizon that is 3 to 5 feet below land surface in the deep 
soils of the Arecibo-Manatf region. 
The overlying A 
horizon usually is much more permeable.
The most permeable soils, those developed on 
cemented sand dunes along the coast, are of limited 
extent. 
Infiltration rates are high, often exceeding 20 
in/hr. In contrast, the deep muck deposits of the Cano 
Tiburones are the least permeable soils in the region 
and have infiltration rates as low as 0.06 in/hr. At depth,
these 
soils 
are 
underlain 
by 
a 
dense, 
nearly 
impermeable clay. Infiltration rates for the greater part of 
the region range from 0.6 to 2.0 in/hr. 
Although 
infiltration rates are similar, the soils are diverse ranging 
from deep soils developed on river flood-plain alluvium, 
blanket sand deposits, and adjacent limestones, to thin 
soils and often bare rock in highly developed karst 
areas.
Table 2.1.2.F-1 Thickness, permeability, and available water capacity for the soil 
associations in the Arecibo-Manati region, Puerto Rico (Modified from Acevedo, 1982)
Area and soil association
Humid Coastal Plains
Algarrobo-Corozo-Arecibo
Guerrero-Carrizales-Jobos
Almirante-Espinosa-Vega Alta
Bayamon-Matanzas
Rock Outcrop-Tanama-San Sebastian
Soller-San German-Rock Outcrop
Tiburones-Palmar-Garrochales
Toa-Coloso-Baj u ra
Moca-Perchas
Humid Upland Valleys
Colinas-Naranjo-Juncal
Mucara-Caguabo
Humid Uplands
Mucara-Morado-Maraguez
Humatas-Naranjito-Consumo
Humatas-Los Guineos-Alonso
Humatas-Maricao-Los Guineos
Maricao-Los Guineos
Pellejas-Lirios-lngenio
Thickness 
(inches)
Oto99
Oto60
Oto70
Oto65
Oto55
Oto25
Oto84
Oto63
Oto60
Oto60
Oto27
Oto60
Oto60
Oto62
Oto62
Oto62
Oto62
Permeability 
(inch per hour)
0.06 to 0.20
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.06 to 0.20
0.06 to 0.20
0.06 to 0.20
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
Available 
water capacity 
(inch per inch)
0.02 to 0.20
0.04 to 0.20
0.06 to 0.20
0.06 to 0.20
0.1 5 to 0.20
0.05 to 0.25
0.1 5 to 0.20
0.1 2 to 0.20
0.1 5 to 0.24
0.09 to 0.20
0.05 to 0.1 7
0.05 to 0.1 7
0.10 to 0.20
0.10 to 0.20
0.10 to 0.20
0.10 to 0.20
0.06 to 0.21
22 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
6650'
1830'  
45'
6610'
ATLANTIC OCEAN
Pta Patmas Alias
J**| *%, 
fj Pta Manati
ARECIBO- 
MANATI 
REGION
SENATORIAL DISTRICT NUMBER
Base from U.S. Geological Survey
Puerto Rico e Is las Limftrofes, 1:240,000, 1952
Figure 2.1.2.A-1 Location and major geographic features in the Arecibo-Manati region, Puerto Rico.
2.1.2 Arecibo-Manati Region 
23
66°50'
45'
40'
35'
30'
25'
20'
15'
66°10'
18°30'
25'
20'
15'
ATLANTIC OCEAN
EXPLANATION
I 
I 
EXTENT OF SEDIMENTARY ROCKS- 
Limestone and coastal alluvial deposits
BHB 
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR OR LAGOON
  -    - -    DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
  
-    -    BOUNDARY BETWEEN MUNICIPIOS
          PERENNIAL STREAM
O 2 
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
01234 KILOMETERS
I   ,   '      
01234 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.1.2.B-1 Approximate well locations in the Arecibo-Manati region, Puerto Rico.
24 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°50'
45'
40'
35'
30'
25'
20'
15'
66°10'
18°30'  
25'
20'
15'
ATLANTIC OCEAN
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
LANDSLIDE DEPOSITS
BLANKET DEPOSITS
Holocene
and 
Pleistocene
QUATERNARY
QUATERNARY 
TERTIARY
CAMUY FORMATION 
AYMAMON LIMESTONE 
AGUADA LIMESTONE 
CIBAO FORMATION 
LARES LIMESTONE 
SAN SEBASTIAN FORMATION 
PLUTONIC ROCKS
Miocene
and 
Oligocene
TERTIARY
VOLCANIC AND
VOLCANICLASTIC
ROCKS
Eocene
to Lower
Cretaceous
TERTIARY 
CRETACEOUS
RESERVOIR OR LAGOON
J A' L|NE °f SECTION-Location of cross section 
shown in figure 2.1.2.C-2
-   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
   PERENNIAL STREAM
TOWN OR CITY
01234 KILOMETERS
I     \ '    
01234 MILES
Modified from Briggs and Akers, 1965
Figure 2.1.2.C-1 Generalized surficial geology in the Arecibo-Manati region, Puerto Rico.
2.1.2 Arecibo-Manati'Region 
25
SEA LEVEL
(c)
3,000 -
4,000 -
5,000
6,000
VERTICAL EXAGGERATION X 6.6 
Modified from Torres-Gonzalez, 1985 
DISTANCE FROM SHORELINE, IN MILES
0 
1 
2 MILES
I 
I 
I
Modified from Gomez-Gomez, 1984
1 MILE
1,600
VERTICAL EXAGGERATION X 10
Modified from Guisti and Bennett. 1976
DISTANCE FROM SHORELINE, IN MILES
(535) Number in parentheses is 
hydraulic conductivity, in 
feet per day
DIAGRAMMATIC GEOLOGIC SECTION SHOWING HYDRAULIC CONDUCTIVITY 
OF PRINCIPAL ROCK UNITS
EXPLANATION
(a) AQUIFER THICKNESS
(b) THICKNESS OF ALLUVIAL DEPOSITS IN THE 
RIO GRANDE DE ARECIBO VALLEY
(c) AVERAGE HYDRAULIC CONDUCTIVITY SHOWN IN 
(c) OF LIMESTONE IN THE ARECIBO-MANATI 
AREA OF THE AYMAMON LIMESTONE WITH DEPTH
(d) CHANGES IN THE AVERAGE HYDRAULIC CONDUCTIVITY
(d)
10,000
1,000
100
10
.o 
o 
oZi
0.1
0.01
\ 
i 
I 
l 
I 
l 
1
i 
i 
r 
\
MID-POINT OF SCREENED 
OR OPEN INTERVAL
l 
l 
I 
l 
l 
l 
1 
l 
l 
l 
I
0 
400 
800 
1,200 
1,600 
2,000 
2,400 
DEPTH BELOW PROJECTED SURFACE OF AYMAMON LIMESTONE, IN FEET
Modified from Guisti and Bennett, 1976
VARIATIONS IN HYDRAULIC CONDUCTIVITY WITH DEPTH
Figure 2.1.2.C-2 Generalized aquifer thickness and hydraulic conductivity in the Arecibo-Manati region, Puerto Rico (lines of section shown in figure 2.1.2.C-1).
26 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°50'
45'
40'
35'
30'
25'
20'
15'
66°10'
18°30'
25'
20'
15'
ATLANTIC OCEAN
24,000 
(
~ 
19'000 *6,000
90,000 
'BARCELONETA?
EXPLANATION
EXTENT OF SEDIMENTARY ROCKS- 
Limestone and coastal alluvial deposits
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR OR LAGOON
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
36,000 
APPARENT AQUIFER TRANSMISSIVITY-
  
Shows well location and apparent
transmissivity, in feet squared per day
  
TOWN OR CITY
01234 KILOMETERS
h-'       !           .
01234 MILES
Modified from Torres-Gonzalez, 1995
Figure 2.1.2.D-1 Transmissivity in the Arecibo-Manati region, Puerto Rico.
2.1.2 Arecibo-Manati Region 
27
66°50'
45'
40'
35'
30'
25'
20'
15'
66°10'
18°30'
25'
20'
15'
ATLANTIC OCEAN
EXPLANATION
EXTENT OF SEDIMENTARY ROCKS- 
Limestone and coastal alluvial deposits
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR OR LAGOON
WATER-LEVEL CONTOUR-Shows altitude 
of water level in feet. Hachures indicate 
depression. Contour interval is variable. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
WELL LOCATION AND WATER-LEVEL ALTITUDE- 
Shows well location and measured water-level altitude, 
in feet, in a tightly cased well. Datum is mean sea level
TOWN OR CITY
01234 KILOMETERS
I      , '    
01234 MILES
Modified from Torres-Gonzalez, 1995
Figure 2.1.2.E-1 Composite potentiometric surface of the upper aquifer of the years 1965 and 1987 in the Arecibo-Manati region, Puerto Rico.
28 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°50'
45'
40'
35'
30'
25'
20'
15'
66°10'
18°30'
25'
20'
15'
ATLANTIC OCEAN
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
A-2 ALGARROBO-COROZO-ARECIBO 
A-3 GUERRERO-CARRIZALES-JOBOS 
B-2 ALMIRANTE-ESPINOSA-VEGA ALTA 
B-3 BAYAMON-MATANZAS 
C-3 ROCK OUTCROP-TANAMA-SAN SEBASTIAN 
C-5 SOLLER-SAN GERMAN-ROCK OUTCROP 
D-3 TIBURONES-PALMAR-GARROCHALES 
E-3 TOA-COLOSO BAJURA
HUMID UPLAND VALLEYS
T-1 MOCA-PERCHAS
U-1 COLINAS-NARANJO-JUNCAL
HUMID UPLANDS 
M-1 MUCARA-CAGUABO 
M-4 MUCARA-MORADO-MARAGUEZ 
N-3 HUMATAS-NARANJITO-CONSUMO 
N-4 HUMATAS-LOS GUINEOS-ALONSO 
N-5 HUMATAS-MARICAO-LOS GUINEOS 
N-6 MARICAO-LOS GUINEOS 
0-2 PELLEJAS-LIRIOS-INGENIO
SOIL PERMEABILITY, IN INCHES 
PER HOUR
| 
FROM 0.06 TO 0.20 
I 
FROM 0.60 TO 2.00
SOIL ASSOCIATION BOUNDARY
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
01234 KILOMETERS
I      ,      
01234 MILES
Modified from Acevedo 1982; Boccheciamp, 1978
Figure 2.1.2.F-1 Soil associations and permeability in the Arecibo-Manati region, Puerto Rico.
2.1.2 Arecibo-Manatf Region 
29
2.1.3 VEGA BAJA-TOA BAJA REGION
By Fernando Gomez-Gomez and Thalia D. Veve
Table 2.1.3.B-1 Population for the Vega Baja-Toa Baja region, Puerto Rico 
(U.S. Department of Commerce, 1982, table 1; U.S. Department of Commerce, 
1991, table 1)
2.1.3.A Location and Major Geographic 
Features
The Vega Baja-Toa Baja coastal aquifer area 
extends across a 9-miles wide segment of the North 
Coast area (fig. 2.1.3.A-1). It is bounded to the north by 
the Atlantic Ocean, to the west by the Rfo Cibuco, to the 
east by the Rfo de La Plata, and to the south by a karst 
tableland (fig. 2.1.3.A-1). Along the coast, sand dunes 
form an almost continuous ridge, except where the 
ridge has been breached by the Rfo Cibuco and Rfo de 
La Plata. 
The coastal dune ridge has an average 
elevation of about 30 feet above mean sea level and 
reaches its maximum elevation of 65 feet at Dorado. 
The dune ridge is less than 2-miles wide, draining to the 
ocean along its northern slope and to the coastal plain 
along its southern slope. 
The karst tableland is 
generally defined within the 170 feet topographic 
contour and is about 
3-miles wide. This tableland has 
become the principal area of urban development, and 
also contains the major highway connecting the San 
Juan metropolitan area to the western part of the island. 
High relief topography, dominated by numerous ridges 
and sinks typical of an immature karst, occurs south of 
the tableland. The tableland is dissected to the east 
and west by northward flowing streams that form a well 
developed alluvial plain, extending inland as much as 6 
miles from the coast. 
Little urban development has 
taken place within the alluvial plain except for a 0.25 mi2 
urban area within the town limits of Toa Baja. 
The 
municipio of Toa Baja, parts of suburban developments 
on the coastal plain, and parts of Vega Baja are within 
the flood plain of the Rfo Cibuco and Rfo de La Plata. 
The headwaters of both streams lie within the island's 
volcanic-rock interior (southern parts of the Vega Baja- 
Toa Baja region) and have a combined drainage area of 
240 mi2 at the point where they enter the coastal aquifer 
areas. 
Most of this drainage area is within the 
watershed of the 62-miles long Rfo de La Plata, which 
has its headwaters at an elevation of 2,960 feet.
2.1.3.B Population and Estimated 
Ground-Water Use
In 1980, the combined population in the municipios 
of Dorado and Vega Alta was about 54,200 (U.S. 
Department of Commerce, 1982). In the 1990 Census 
(U.S. Department of Commerce, 1991), the population 
within these municipios was 65,318. This represents an 
increase of 17 percent from 1980 to 1990. In 1980, 38 
percent of the population in the municipios of Dorado 
and Vega Alta resided within the urban limits of both 
municipios. The remainder of the population resided 
within 
suburban 
communities 
(table 
2.1.3.B-1). 
According to the 1980 census, 97 percent of the 
housing units in the municipios of Dorado, Toa Baja, 
Toa Alta, Vega Baja, and Vega Alta (approximately 
14,800 houses) were served from public-water supply. 
However, only 38 percent of the housing units were 
served by public sewers.
Public-water supply within this geographic region is 
provided principally by ground water. 
In 1983, there 
were 24 public-supply wells yielding 
12 Mgal/d. 
Because the Vega Baja-Toa Baja coastal aquifer area 
public-water 
supply 
distribution 
system 
is 
interconnected to the east with the San Juan 
metropolitan area and to the west with Manatf, part of 
the well production could have been transferred outside 
the region. 
In addition, during 1990 a major public- 
supply 
distribution 
pipeline 
was 
completed 
that 
connected Dorado with the Enrique Ortega filtration 
plant. 
This filtration plant is part of the San Juan 
Metropolitan area public-water supply and provides 
approximately 55 Mgal/d from Lago de La Plata. Since 
1983, approximately seven public-water supply wells 
have been taken out of production, either as a result of 
contamination 
with 
organic 
chemicals 
(principally 
trichloroethylene and tetrachloroethylene) or saltwater 
encroachment. 
The production lost from these wells 
has been offset by increasing withdrawals from, and the
1980 population
MUNICIPIO
Aibonito
Barranquitas
Cayey
Ciales
Cidra
Corozal
1 Dorado
Morovis
Naranjito
Toa Alta
Toa Baja
1 Vega Alta
Vega Baja
Total
TOTAL
22,167
21 ,639
41 ,099
16,211
28,365
28,221
25,511
21,142
23,633
31,910
78,246
28,696
47,115
413,955
URBAN
9,331
3,618
23,305
3,582
6,069
5,889
10,203
2,637
2,849
4,427
1,992
10,582
18,233
102,717
RURAL
12,836
18,021
17,794
12,629
29,532
22,332
15,308
18,505
20,784
27,483
76,254
18,114
28,882
318,474
1990 population
TOTAL
24,971
25,605
46,553
18,084
35,601
33,095
30,759
25,288
27,914
44,101
89,454
34,559
55,997
491,981
1 Municipio having geographic limits entirely within the limestone belt.
rehabilitation of, the remaining wells, as well as the 
construction of new wells. Ground-water withdrawals of 
13 Mgal/d in 1991, from a total of 20 public-supply wells, 
is equal to that estimated for 1983. 
Ground-water 
withdrawals for commercial, industrial, and agricultural 
use could represent less than 2.0 Mgal/d in 1991 
(Senen Guzman-Rios, U.S. Geological Survey, written 
communication, 1991; table 2.1.3.B-2). This indicates 
that between 1983 and 1991 total withdrawals from the 
coastal 
aquifer 
area 
have 
remained 
essentially 
unchanged. Ground-water withdrawals for irrigation of 
rice in the vicinity of the Rfo Cibuco, which accounted 
for approximately 3 Mgal/d in 1983, were discontinued 
in 1985. The approximate location of wells in the Vega 
Baja-Toa Baja region is shown on figure 2.1.3.B-1.
Table 2.1.3.B-2 Ground-water withdrawals during 
1987 in the Vega Baja-Toa Baja region, Puerto Rico 
[Mgal/d, million gallons per day; <, less than]
Water-use category
Public-water supply
Irrigation
Industrial
Commercial
Agricultural
Domestic
Mining
Ground-water 
withdrawals (Mgal/d)
12.10
<3.30
1.00
0.40
0.20
<0.05
0.50
Total
<17.55
30 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
6625'
20'
66 05
18°30'  
25'  
20'  
15'  
10'
18°05'  
SENATORIAL DISTRICT NUMBER
01234 KILOMETERS
VEGA BAJA 
TOA BAJA 
REGION
CAR1BBEANSEA
Figure 2.1.3.A-1 Location and major geographic features in the Vega Baja-Toa Baja region, Puerto Rico.
2.1.3 Vega Baja-Toa Baja Region 
31
66°25'
20'
15'
10'
66°05'
18°30'
25'
20'
15'
10'
18°05'
ATLANTIC OCEAN
EXTENT OF SEDIMENTARY ROCKS- 
LJmestone and coastal alluvial deposits
^>/Hk
V>J"'\V @V'^X'
Ll/'& 
is^Lac/N. \] 
" ^* 
)T !a Plata 
«
* 
' K-x 
<>
.fflf '.' ^^_v_"-
firl/^j- 
\
%f \ Hio Quests 
-
NARANJrtO 
<^ ^ 
It \ \ ~A'1
"V^ c\ f\"-7 (1^^;&
'V VI 7 4'v^-'^ 
jfe ^ > ::-^Csa ^ <
^^| 
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR OR LAGOON
  -    - -    DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
  
-    -    BOUNDARY BETWEEN MUNICIPIOS
          SOUTHERN LIMIT OF KARST TABLELAND
          PERENNIAL STREAM
01234 KILOMETERS
01234 MILES
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.1.3.B-1 Approximate well locations in the Vega Baja-Toa Baja region, Puerto Rico. 
32 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66'25'
20'
18'30'  
25'  
20'
15'
10'
18°05'
15'
ATLANTIC OCEAN
10
66°05'
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
LANDSLIDE DEPOSITS
BLANKET DEPOSITS
Holocene 
f QUATERNARY
and 
Reistocene
1 QUATERNARY 
| 
TERTIARY
CAMUY FORMATION 
AYMAMON LIMESTONE 
AGUADA LIMESTONE 
CIBAO FORMATION 
LARES LIMESTONE 
SAN SEBASTIAN FORMATION 
PLUTONIC ROCKS
Miocene
and 
^ TERTIARY 
Oligocene
VOLCANIC AND
VOLCANICLASTIC
ROCKS
^H 
RESERVOIR OR LAGOON
-    -  -   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
   
- 
PERENNIAL STREAM 
  
TOWN OR CITY
BARRANQUITAS
1234 KILOMETERS
3 
4 MILES
Eocene
to Lower
Cretaceous
TERTIARY 
CRETACEOUS
Modified from Briggs and Akers, 1965
Figure 2.1.3.C-1 Generalized surficial geology in the Vega Baja-Toa Baja region, Puerto Rico.
2.1.3.C Geologic Setting
Sedimentary rocks of Tertiary age underlie the 
coastal aquifer areas in the Vega Baja-Toa Baja region 
(fig. 2.1.3.C-1). They are the San Sebastian Formation 
and 
Lares 
Limestone 
of 
Oligocene 
age; 
the 
Mucarabones Sand, the Rio Indio Limestone, the 
Quebrada Arenas Limestone, the Miranda Sand 
Member, and the unnamed upper members of the Cibao 
Formation of Miocene to Oligocene age; and the Cibao 
Formation, Aguada Limestone, Aymamon Limestone, 
and Camuy Formation of Miocene age. Following are 
brief summaries of the lithology of these geologic units 
arranged in order from oldest to youngest.
The San Sebastian Formation consists of a sandy 
carbonaceous clay, locally containing pebbles and 
cobbles 
of older volcanic 
rocks, 
and 
beds 
of 
fossiliferous-earth limestone. Outcrops are mainly in the 
southeastern perimeter of the Cretaceous-Tertiary 
contact.
The Lares Limestone overlies the San Sebastian 
Formation and consists entirely of calcareous clay in the 
coastal aquifer areas of the Vega Baja-Toa Baja region. 
The Mucarabones Sand, overlying the Lares Limestone, 
is a cross-bedded fine- to medium-grained sand 
containing lenses of fossiliferous sandy limestone and 
sandy clay. The Rio Indio Limestone Member of the 
Cibao Formation overlies the Mucarabones Sand and 
consists of chalky fragmented limestone, weakly bedded 
to massive, and locally glauconitic. 
The Quebrada 
Arenas Limestone Member of the Cibao Formation, 
overlying the Rio Indio Limestone Member, is a finely 
crystalline to dense limestone locally containing grains 
of quartz sand and abundant fossil molds. 
Its main 
exposure is in the drainage basin of the Rio Lajas. The 
Miranda Sand Member of the Cibao Formation overlies 
the Quebrada Arenas Limestone Member and consists 
of angular to subangular fine- to coarse-grained quartz 
sand in a noncalcareous silty clay matrix. Exposures 
near Vega Alta contain sand and gravel that grade 
upward into fossiliferous sand. Only minor exposures 
of the Miranda Sand Member (less than 0.5 mi2) have 
been mapped and lie within the Rio Lajas drainage 
basin. 
The unnamed upper member of the Cibao 
Formation, overlying the Miranda Sand Member, is 
considered to be typical of the Cibao Formation 
lithology, consisting of beds of calcareous clay, earthy
2.1.3 Vega Baja-Toa Baja Region 
33
66°25'
20'
15'
10'
18°30'
25'
18°20'
66°05'
01234 KILOMETERS 
\-^- 
01234 MILES
Cienaga Prieta 
DORADO
CIALES
x ^ JrV/Cx <#/ ^ V~A ' A
MOROVIS)* 
\ \ ) 
f e 66*25' [ 
S 
S\ 
V/8-30'      '    |   -    
EXTENT OF SEDIMENTARY ROCKS- 
Limestone and coastal alluvial deposits
RESERVOIR OR LAGOON
SUBSURFACE CONTOUR-Shows estimated altitude 
of bottom of freshwater aquifer, in feet below sea level. 
Contour interval is variable. Datum is mean sea level
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
SOUTHERN LIMIT OF KARST TABLELAND
TOWN OR CITY
ID 
\.
25'
18°20'
___ __ --^i-  100   
  200 ' 
VEGA BAJA
S
0
0
1234 KILOMETERS
I 
I 
I 
I
l 
l 
1 
2
I 
3
4 MILES
Modified from Gomez-Gomez and Torres-Sierra, 1988
Figure 2.1.3.D-1 Approximate altitude of the bottom of the freshwater aquifer in the Vega Baja-Toa Baja region, Puerto Rico. 
34 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
limestone, and marl. The Aguada Limestone overlies the 
unnamed upper member of the Cibao Formation and 
consists of hard calcarenite alternating with chalky and 
rubbly limestone. The Aymamon Limestone, overlying 
the Aguada Limestone, is a very pure fossiliferous 
limestone, massive to thick bedded. 
The Camuy 
Formation overlies the Aymamon Limestone and consists 
of chalk and limestone, commonly somewhat sandy and 
ferruginous. The Camuy Formation is found in isolated 
outcrops near the coast of less than 0.25 mi2.
Unconsolidated deposits, regionally referred to as 
blanket sands, cover most flat areas throughout the 
outcrop 
areas 
of 
the 
Aguada 
and 
Aymamon 
Limestones. 
These deposits are thought to be of 
Quaternary to Tertiary age and to have an irregular 
thickness, typically not greater than 100 feet. 
Along 
stream valleys, alluvial deposits known to be as much as 
280 feet thick in the Rio Cibuco drainage basin and as 
much as 100 feet thick near the Rfo de La Plata near Toa 
Baja, interfinger with swamp and marsh deposits of the 
coastal plain. In the coastal plain area, between the Rfo 
Cibuco and Rfo de La Plata, the unconsolidated swamp 
and marsh deposits are typically less than 60 feet thick. 
Along the edges of the coastal plain, Pleistocene age 
silica sand deposits form most of the ridge of the coastal 
terrace deposits. Silica sand deposits are also found as 
terrace deposits along the northern perimeter of the karst 
tableland. 
These deposits are locally mined for the 
manufacture of glass (Briggs, 1965).
2.1.3.D Hydrogeology
Fresh ground water occurs within the carbonate 
rocks of Miocene and Oligocene age at areas generally 
inland of latitude 18°25'. Seaward of this latitude, ground 
water occurs mainly as a lens of freshwater above 
saltwater. 
Along a north-south line at approximately 
longitude 66°19', the depth to the bottom of this 
freshwater lens varies from about 300 feet at its inland 
point to about 100 feet at the coast (fig. 2.1.3.D-1). Since 
1960, ground-water withdrawals from the coastal aquifer 
areas have increased significantly. 
In 
1960, total 
withdrawals were estimated to be less than 2.6 Mgal/d. 
During 1991, ground-water withdrawals were estimated 
to be 15 Mgal/d. About 95 percent of this amount was 
withdrawn within an area that has a transmissivity greater 
than 10,000 ft2/d (fig. 
2.1.3.D-2). 
Transmissivity is 
estimated to be as high as 150,000 ft2/d.
66°25'
20'_
15'
66°05'
18°30
18°20'
01234 KILOMETERS
i 
i 
i 
i
01234 MILES
Cienaga Prieta 
DORADO
EXPLANATION
EXTENT OF SEDIMENTARY ROCKS- 
LJmestone and coastal alluvial deposits
LINE OF EQUAL APPARENT TRANSMISSIVITY 
IN FEET SQUARED PER DAY-Contour interval 
is variable
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
SOUTHERN LIMIT OF KARST TABLELAND
2,400 
APPARENT AQUIFER TRANSMISSIVITY- 
Shows well location and apparent 
transmissivity, in feet squared per day
Modified from Gomez-Gomez and Torres-Sierra, 1988
Figure 2.1.3.D-2 Transmissivity estimates at selected wells and the regionalized aquifer transmissivity distribution as obtained through 
model calibration for the freshwater part of the coastal aquifer in the Vega Baja-Toa Baja region, Puerto Rico.
Ground water within the confined aquifer, consisting 
of the Lares Limestone and Mucarabones Sand Member 
of the Cibao Formation (Rodriguez-Martmez, 1991), 
flows beneath the karst tableland and coastal plain. The 
total thickness of both units is unknown; however, the 
thickness of carbonate strata corresponding to the Lares 
Limestone penetrated by a test well near the coast 
(latitude 18°27'01", longitude 66°18'22") was 500 feet. A 
preliminary estimate of the transmissivity of the confined 
aquifer is 1,000 ft2/d (Fernando Gomez-Gomez and 
Sigfredo Torres-Gonzalez, U.S. Geological Survey, 
written communication, 1991). 
Potential for ground- 
water development from the artesian aquifer in this part 
of the Vega Baja-Toa Baja coastal aquifer area is limited 
by the depth at which freshwater is found (1,700 feet 
below land surface on the coastal plain north of Vega 
Alta), the lower quality of the ground water (dissolved- 
solids concentrations greater than 500 mg/L), and the 
availability of freshwater from the coastal water-table 
aquifer (fig. 2.1.3.D-3).
2.1.3 Vega Baja-Toa Baja Region 
35
66°25'
20'
15'
10'
66°05'
18°30'
25'
20'
15'
10'
18°05'
ATLANTIC OCEAN
Laguna 
Tortuguero
DORADO BEACH #5 DORADO
: *v S 
  
, Cienaga ftfete
/ SABANA HOYOS #1
HIGUILLAR"
TOA BAJA
VEGAALtA 4\
EXPLANATION
I ^-1 
EXTENT OF SEDIMENTARY ROCKS- 
'   ' 
Limestone and coastal alluvial deposits
^^| 
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR OR LAGOON
------- 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
HIGUILLAR
SOUTHERN UMITOF KARST TABLELAND 
PERENNIAL STREAM
SAMPLING SITE 
TOWN OR CITY
01234 KILOMETERS
I 
' 
. ' 
'i       
01234 MILES
Figure 2.1.3.D-3 Approximate location of wells sampled for dissolved-solids concentration in the Vega Baja-Toa Baja region, Puerto Rico.
36 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°25'
20'
15'
10'
18'30'
25'
18°20'
66°05'
01234 KILOMETERS
I 1       .    
01234 MILES
EXPLANATION
EXTENT OF SEDIMENTARY ROCKS- 
Limestone and coastal alluvial deposits
RESERVOIR OR LAGOON
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly cased well 
during February 1983. Contour interval is 
variable. Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
PERENNIAL STREAM
SOUTHERN LIMIT OF KARST TABLELAND
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
18°20
Modified Gomez-Gomez and Torres-Sierra, 1988
Figure 2.1.3.E-1 Altitude of water-level surface and direction of ground-water flow during February 1983 in the Vega Baja-Toa Baja 
region, Puerto Rico.
2.1.3.E Ground-Water Levels and 
Movement
Regional ground-water flow in the coastal water- 
table upper aquifer is generally toward the ocean coast 
in the Vega Baja-Toa Baja region (fig. 2.1.3.E-1). 
A 
smaller flow component, estimated at less than 3 ft3/s, 
discharges toward the Rio Cibuco, Rio Indio, and Rio de 
La Plata (Gomez-Gomez and Torres-Sierra, 1988). 
Under pre-development conditions (prior to 1930), most 
aquifer discharge may have been to the Cienaga Prieta. 
Aquifer discharge to this marsh was estimated, by use of 
a digital ground-water flow model, to be 15 ft3/s under 
pre-development conditions, and decreased to about 4 
ft3/s in 1985 (Gomez-Gomez and Torres-Sierra, 1988). 
Between 1960 and 1970, withdrawals increased from 
about 3 Mgal/d to about 13 Mgal/d. During this same 
period, the potentiometric surface throughout the coastal 
plain could have declined by as much as 10 feet 
(Gomez-Gomez and Torres-Sierra, 1988). Most of this 
drawdown could have resulted from increased aquifer 
withdrawals. 
However, in about 1960, a drainage 
channel was dredged from Cienaga Prieta to the Rfo 
Cibuco and part of the decline in the water table could 
have been caused by dewatering the marsh.
Regional ground-water flow in the confined lower 
aquifer is toward the east (Fernando Gomez-Gomez 
and Sigfredo Torres-Gonzalez, U.S. Geological Survey, 
written communication, 1991). The head in the lower 
aquifer was determined to be about 190 feet above 
mean sea level at a test well drilled about 0.5 miles east 
of Laguna Tortuguero, and about 10 feet above mean 
sea level at the possible regional discharge area located 
12 miles east of the Rio de La Plata.
Rainfall recharge to the upper aquifer occurs 
throughout the outcrop areas of the carbonate units. In 
1983, rainfall recharge constituted about 85 percent of 
total aquifer recharge (average of 7 inches of rainfall 
recharge per year), and seepage from the Rio Cibuco 
contributed about 6 ft3/s (Gomez-Gomez and Torres- 
Sierra, 1988). Throughout the outcrop area of the lower 
aquifer, the estimated annual rainfall recharge rate is 
about 4 inches (Fernando Gomez-Gomez and Sigfredo 
Torres-Gonzalez, 
U.S. 
Geological 
Survey, 
written 
communication, 1991).
2.1.3 Vega Baja-Toa Baja Region 
37
2.1.3.F Soil Permeability
The dominant soil associations overlying the 
aquifers in this region are the Almirante-Espinosa-Vega 
Alta, 
Bayamon-Matanzas, 
Almirante-Vega 
Alta- 
Matanzas, 
Rock 
outcrop-Tanama-San 
Sebastian, 
Tanama-Colinas-Soller, 
Tiburones-Palmar-Garrocha- 
les, and the Toa-Coloso-Bajura (fig. 2.1.3.F-1). 
Also 
present to a minor extent are the Algarrobo-Corozo- 
Arecibo, Martin Pena-Saladar-Hydraquents, and the 
Pandura-Lirios. These soil associations belong to the 
humid coastal plains category, except for the Pandura- 
Lirios association, which is present in the humid 
uplands.
The 
Almirante-Espinosa-Vega Alta, 
Bayamon- 
Matanzas, and the Almirante-Vega Alta-Matanzas soil 
associations are composed of deep, gently sloping to 
sloping, well drained and clayey soils (Acevedo, 1982, p. 
3; and Boccheciamp, 1978, p. 5). 
The Almirante- 
Espinosa-Vega Alta association is mainly located on 
limestone hills and on terraces along the coast. The 
Bayamon-Matanzas soils overlie small valleys between 
limestone hills and on the coastal plains. The Almirante- 
Vega Alta-Matanzas association is located on terraces 
and alluvial fans of the coastal plain. These soils formed 
mainly in clayey sediments of mixed origin and organic 
materials. 
The soils that form the Rock Outcrop- 
Tanama-San Sebastian association, found in the 
uplands, are described as rock outcrop and shallow to 
deep, sloping to very steep, well drained, clayey soils 
(Acevedo, 1982, p. 4). 
The Tanama-Colinas-Soller 
association is composed of shallow to moderately deep, 
moderately-to very-steep, well drained soils of the humid 
mountainous areas (Boccheciamp, 1978, p. 5). These 
soils are formed mainly in clayey materials weathered 
from the limestone. The Tiburones-Palmar-Garrochales 
association is composed of deep, nearly level, poorly 
drained, acid mucky soils (Acevedo, 1982, p. 4) that 
overlie flats and depressional areas along the coast and 
form in organic material. 
The Toa-Coloso-Bajura 
association is formed by deep, nearly level, well-to 
poorly-drained, loamy to clayey soils (Acevedo, 1982, p. 
4)-
The Algarrobo-Corozo-Arecibo soil association is 
composed of deep, gently sloping, excessively drained 
and well drained, sandy soils (Acevedo, 1982, p. 3). 
The Pandura-Lirios soil association is composed of 
shallow to deep, moderately- to very-steep, well drained 
soils of the humid mountainous areas (Boccheciamp, 
1978, p. 4). 
These soils formed in the residuum of 
granitic rock that is part of the San Lorenzo Batholith. 
The Martin Pena-Saladar-Hydraquents is composed of 
deep, nearly level, very-poorly drained soils in low 
depressions 
and 
lagoons 
of 
the 
coastal 
plain 
(Boccheciamp, 1978, p. 6).
In general, soil permeability ranges from 0.60 to 
2.00 in/hr throughout most of the Vega Baja-Toa Baja 
region. Only the Algarrobo-Corozo-Arecibo, Tiburones- 
Palmar-Garrochales, 
and 
Toa-Coloso-Bajura 
associations on the humid coastal plains and the Mabf- 
Rio Arriba and Moca-Perchas associations in the humid 
upland valleys have lower permeabilities, ranging from 
0.06 to 0.20 in/hr. These associations coincide mainly 
with the alluvium deposits along the main rivers in the 
region. 
All of the soil associations have very low 
available water capacities ranging from 0 to 0.25 in/in. 
Soil thicknesses range from 0 to 99 inches. 
Table 
2.1.3.F-1 summarizes the information on thickness, 
permeability, and available water capacity for all the soil 
associations present in this drainage area including the 
ones not overlying the aquifers.
Table 2.1.3.F-1 
Thickness, permeability, and available water capacity for the soil 
associations in the Vega Baja-Toa Baja region, Puerto Rico (Modified from Gierbolini, 1975)
Area and soil association
Thickness 
(inches)
Permeability 
(inch per hour)
Available 
water capacity 
(inch per inch)
Humid Coastal Plains
Algarrobo-Corozo-Arecibo
Guerrero-Carrizales-Jobos
Almirante-Espinosa-Vega Alta
Bayamon-Matanzas
Almirante-Vega Alta-Matanzas
Rock Outcrop-Tanama-San Sebastian
Tanama-Colinas-Soller
Martin Pena-Saladar-Hydraquents
Tiburones-Palmer-Garrochales
Swamps-Marshes
Toa-Coloso-Bajura 
Humid Upland Valleys
Mabi-Rio Arriba
Moca-Perchas
Colinas-Naranjo-Juncal 
Humid Uplands
Mucara-Caguabo
Mucara-Morado-Maraguez
Humatas-Naranjito-Consumo
Humatas-Los Guineos-Alonso
Pandura-Lirios 
Semiarid Uplands
Descalabrado
Oto99
Oto60
Oto70
Oto65
Oto70
Oto55
Oto60
Oto63
Oto84
Oto60
0.06 to 0.20
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.06 to 0.20
too variable to be
0.06 to 0.20
Oto99 
Oto60 
Oto60
Oto 30 
Oto60 
Oto60 
Oto62 
Oto60
Oto 17
0.06 to 0.20 
0.06 to 0.20 
0.60 to 2.00
0.63 to 2.00 
0.60 to 2.00 
0.60 to 2.00 
0.60 to 2.00 
0.60 to 2.00
0.60 to 2.00
0.02 to 0.20 
<0.04 to 0.20 
0.06 to 0.20 
0.1 Oto 0.20 
0.06 to 0.20 
0.00 to 0.20 
0.09 to 0.25 
0.12 to 0.20 
0.15 to 0.20 
estimated
0.15 to 0.20
0.15 to 0.20 
0.15 to 0.24 
0.09 to 0.20
0.05 to 0.17 
0.05 to 0.17 
0.10 to 0.18 
0.1 Oto 0.20 
0.02 to 0.20
0.1 Oto 0.20
38 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°25'
20'
18°30'  
25'
20'
15'
10'
18°05'
15'
ATLANTIC OCEAN
10'
66°05'
M-1
NARANJITO
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.20 
FROM 0.60 TO 2.00
SOIL ASSOCIATION BOUNDARY
N-6
-------- DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
  
TOWN OR CITY
M-1 
COMERIO
BARRANQUITAS
CIDRA
M-1
AIBONITO
CAYI
01234 KILOMETERS
01234 MILES
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS
A-2 ALGARROBO-COROZO-ARECIBO
A-3 GUERRERO-CARRIZALES-JOBOS
B-2 ALMIRANTE-ESPINOSA-VEGA ALTA
B-3 BAYAMON-MATANZAS
B-4 ALMIRANTE-VEGA ALTA-MATANZAS
C-3 ROCK OUTCROP-TANAMA-SAN SEBASTIAN
C-4 TANAMA-COLINAS-SOLLER
C-5 SOLLER-SAN GERMAN-ROCK OUTCROP
D-1 MARTfN PENA-SALADAR-HYDRAQUENTS
D-3 TIBURONES-PALMAR-GARROCHALES
E-2 SWAMPS-MARSHES
E-3 TOA-COLOSO-BAJURA
HUMID UPLANDS
M-1 MUCARA-CAGUABO 
M-4 MUCARA-MORADO-MARAGUEZ 
N-3 HUMATAS-NARANJITO-CONSUMO 
N-4 HUMATAS-LOS GUINEOS-ALONSO 
0-3 PANDURA-LJRIOS
HUMID UPLAND VALLEYS 
S-2 MABl'-Rl'O ARRIBA 
T-1 MOCA-PERCHAS 
U-1 COLINAS-NARANJO-JUNCAL
SEMIARID UPLANDS 
R-1 DESCALABRADO
Modified from Boccheciamp, 1977 and 1978
Figure 2.1.3.F-1 Soil associations and permeability in the Vega Baja-Toa Baja region, Puerto Rico.
2.1.3 Vega Baja-Toa Baja Region 
39
2.1.4 BAYAMON-LOIZA REGION
By Jose M. Rodriguez and Thalia D. Veve
2.1.4.A Location and Major Geographic 
Features
The Bayamon-Lofza region covers about 280 mi2 in 
the eastern North Coast area. It is bounded to the north 
by the Atlantic Ocean, to the west and south by the 
drainage basin divide of the Rfo de Bayamon, and to the 
east and south by the drainage basin divide of the lower 
Rio Grande de Loiza (below Lago Loiza). Included in the 
Bayamon-Loiza region are the Rio Bayamon, Rio 
Piedras, and lower Rio Grande de Loiza drainage basins 
(fig. 2.1.4.A-1). The San Juan metropolitan area is not 
only the principal population center of the Bayamon- 
Loi'za region, but also of all Puerto Rico.
The northern section of the Bayamon-Lofza region 
consists of a coastal plain composed of deposits of 
sand, silt, clay, and sand muck overlying limestone 
formations, which form the principal aquifer. 
The 
elevation of the land surface in the coastal plain ranges 
from mean sea level to about 100 feet above mean sea 
level. 
An almost continuous strip of swamps and 
lagoons lies near the coast. 
The principal coastal 
lagoons are Laguna San Jose, Laguna La Torrecilla, and 
Laguna de Pinones. The southern part of the region is 
comprised mostly of the foothills of the inner uplands, 
which range in elevation from about 100 to 1,300 feet 
above mean sea level.
The principal streams flowing through the region are 
the Rfo Bayamon and Rfo Piedras which flow north, and 
the Rfo Grande de Lofza which flows northeast. The Rfo 
Bayamon has its headwaters in the mountainous interior 
of the island and flows across a wide alluvial valley 
surrounded by swamp deposits near the coast. The Rfo 
Piedras, a relatively short river that has its headwaters in 
the foothills, flows across a wide alluvial plain and 
discharges into Bahfa de San Juan. The Rfo Grande de
Lofza, with headwaters in the interior of the island 
(section 2.5), is the primary source of water filling Lago 
Lofza (the principal water-supply reservoir for the San 
Juan metropolitan area), on its course to the Atlantic 
Ocean.
2.1.4.B Population and Estimated 
Ground-Water Use
The Bayamon-Lofza region includes the San Juan 
metropolitan area, which is comprised of the capital city 
of San Juan, 
and the municipios of Bayamon, 
Guaynabo, Carolina, and Catano (fig. 2.1.4.B-1). It also 
includes the municipios of Trujillo Alto, Lofza, and 
Canovanas. A small area of the municipio of Cidra falls 
within the southern limits of the Bayamon-Lofza region. 
The population of the region was about one million in 
1980 (table 2.1.4.B-1), which represented 26 percent of 
the population of Puerto Rico. 
In 1990, there was a 
slight increase in population of 7 percent to a total of 
about 1.1 million. 
About 89 percent of the total 
population of the Bayamon-Lofza region live in urban 
areas, and the remaining 11 percent live in rural areas. 
The municipios with the greatest percentage of rural 
population are Lofza and Canovanas.
Estimated total ground-water withdrawals of 0.94 
Mgal/d (table 2.1.4.B-2), were a small fraction of the total 
of about 158 Mgal/d of surface water distributed for 
public-water supply in the Bayamon-Lofza region in 
1987 (Puerto Rico Aqueduct and Sewer Authority, 1988). 
Ground-water withdrawals for public use accounted for 
0.17 Mgal/d during 1987. 
Public-water supply wells 
located throughout the San Juan metropolitan area were 
in stand-by status most of the time, and were activated 
only during emergency situations (fig. 2.1.4.B-1).
Table 2.1.4.B-1 Population for the Bayamon-Loiza region, Puerto Rico (U.S. Department 
of Commerce, 1982, table 1; U.S. Department of Commerce, 1991, table 1)
MUNICIPIO
Bayamon
Canovanas
Carolina
Catano
Cidra
Guaynabo
Lofza
San Juan
Trujillo Alto
Total
TOTAL
196,206
31 ,880
165,954
26,243
28,365
80,740
20,867
434,849
51 ,389
1 ,036,493
1980 population
URBAN
185,087
7,260
147,835
26,243
6,069
60,706
3,932
424,600
41,141
902,873
RURAL
11,119
24,620
18,119
0
22,296
20,036
16,935
10,249
10,248
133,622
1990 population
TOTAL
220,262
36,816
177,806
34,587
35,601
92,886
29,307
437,745
437,745
1,126,130
Estimated ground-water withdrawals for industrial, 
agricultural, and domestic use were 0.59, 0.14, and 0.04 
Mgal/d, respectively. 
Industrial wells are located 
principally in the coastal plain, but most agricultural and 
domestic wells are located south of Trujillo Alto and 
Carolina.
40 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
6610'
18'25'
20'
15'
AEROPUERTO INTERNACIONAL
ATLANTIC OCEAN
' C X
<   
...   _ V7?i'
^-^r 
~-'^*%
0 12 3 ^ KILOMETERS 
01234 MILES
SENATORIAL DISTRICT NUMBER
ATLANTIC OCEAN
BAYAMON-LOfZA I 
REGION
CARIBBEAN SEA
Base from U.S. Geological Survey
Puerto Rico e Islas LJmftrofes, 1:240,000, 1952
Table 2.1.4.B-2 Ground-water withdrawals and estimated 
population served during 1987 for the Bayamon-Loiza 
region, Puerto Rico
[Mgal/d, million gallons per day;  , no data available]
1 Use and supplier
I. Public Use
1 . San Juan
2. Bayamon
3. Carolina
Subtotal
II. Industrial Use
1. San Juan
2. Bayamon
3. Carolina
Subtotal
2II. Agricultural Use
1. Carolina
2. TrujilloAlto
3. Canovanas
Subtotal
IV. Domestic Use
1. Carolina
2. TrujilloAlto
Subtotal
Total
2Estimated 
population 
served
529
1,692
529
2,750
...
...
 
 
 
 
 
...
...
 
--_
2,750
Average 
ground- water 
withdrawals 
(Mgal/d)
0.03
0.11
0.03
0.17
0.22
0.25
0.12
0.59
0.08
0.03
0.03
0.14
0.01
0.03
0.04
0.94
1 Municipios not listed under some specific use do not 
withdraw ground water for the subject use.
2 Based on a water consumption of 63 gallons per person per 
day.
Figure 2.1.4.A-1 Location and major geographic features in the Bayamon-Loiza region, Puerto Rico.
2.1.4 Bayamon-Loiza Region 
41
66°10'
18°25'
20'
15'
05'
SAN JUAN
66°00'
ATLANTIC OCEAN
55'
65°50'
EXPLANATION
EXTENT OF UPPER AND LOWER AQUIFERS 
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR OR LAGOON
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
0 12 34 KILOMETERS 
01234 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1990
2.1.4.C Geologic Setting
Volcanic rocks, consolidated sedimentary rocks, 
and unconsolidated Quaternary surficial deposits are 
the three major rock types that occur within the 
Bayamon-Lofza region (fig. 2.1.4.C-1). Volcanic rocks 
of Cretaceous age are the most abundant rock type, and 
are exposed in more than half the region. They are 
composed of volcanic tuff, breccia and lava, associated 
sandstone, siltstone and limestone, and some intrusive 
igneous rocks. These volcanic rocks contain little water 
except in weathared and fractured zones. Consolidated 
sedimentary rocks of Tertiary age overlie the volcanic 
rocks in the northern part of the Bayamon-Lofza 
region. 
They are composed of consolidated gravel, 
sand and clay, and calcareous rocks ranging from marl 
to 
indurated 
limestone. 
The 
sedimentary 
rock 
formations have a seaward dip of four to six degrees, 
and are mostly exposed near Bayamon. Unconsolidated 
surficial deposits overlie the sedimentary rocks in the 
San Juan to Carolina area.
The consolidated sedimentary rocks have been 
differentiated into five formations in the Bayamon-Lofza 
region. 
In ascending order these formations are: the 
San Sebastian Formation of Oligocene age, the 
Mucarabones Sand and Cibao Formation of Oligocene 
to Miocene age, and the Aguada Limestone and 
Aymamon Limestone of Miocene age (Monroe, 1980a, 
p. 9).
The San Sebastian Formation is composed of 
cross-bedded to massive beds of sand, sand and 
gravel, and sandy clay, with some thin beds of 
sandstone and sandy limestone (Anderson, 1976, p. 
9). 
The thickness of the San Sebastian Formation 
ranges from 165 to 330 feet, attaining its maximum 
thickness in the western part of the area and becoming 
thinner to the east. 
In the San Juan area, the San 
Sebastian Formation becomes indistinguishable from 
the overlying Mucarabones Sand and Quaternary 
deposits.
Figure 2.1.4.B-1 Approximate well locations in the Bayamon-Loiza region, Puerto Rico.
42 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°10'
05'
66W
55'
65°50'
18°25'
20'
15'
ATLANTIC OCEAN
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
LANDSLIDE DEPOSITS
BLANKET DEPOSITS
Holocene
and 
Pleistocene
QUATERNARY
1 QUATERNARY 
J 
TERTIARY
AYMAMON LIMESTONE 
AGUADA LIMESTONE 
CIBAO FORMATION 
SAN SEBASTIAN FORMATION 
PLUTONIC ROCKS
Miocene
and 
f TERTIARY 
Oligocene
VOLCANIC AND
VOLCANICLASTIC
ROCKS
Eocene
to Lower
Cretaceous
TERTIARY 
CRETACEOUS
RESERVOIR OR LAGOON
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
01234 KILOMETERS 
01234 MILES
Modified from Briggs and Akers, 1965
The Mucarabones Sand overlies the San Sebastian 
Formation and interfingers eastward with the lower part 
of the overlying Cibao Formation. 
East of the Rfo 
Bayamon, the Mucarabones Sand is composed of 
coarse sand interbedded with sandy limestone, coarse 
sandy clay, and lenses of gravel (Monroe, 1980a, p. 27). 
Near San Juan, the Mucarabones Sand appears to thin 
to less than 300 feet, from a maximum thickness of 
about 400 feet near Bayamon (Monroe, 1980a, p. 27).
The Cibao Formation overlies the Mucarabones 
Sand and 
is composed of interlensing beds of 
calcareous clay, limestone, sandy clay, sand, and gravel 
(Monroe, 1980a, p. 29). 
The thickness of the Cibao 
Formation in the city of Bayamon is about 160 feet.
The 
Aguada 
Limestone 
overlies 
the 
Cibao 
Formation and is a hard thick-bedded to massive 
calcarenite, and dense limestone interbedded with 
chalky limestone and marl (Briggs and Akers, 1965). 
Studies by Monroe (1973) indicate that the lower part of 
the Aguada Limestone intertfingers with the upper part 
of the Cibao Formation eastward from the city of 
Bayamon. 
The thickness of the Aguada Limestone 
seems to range from about 80 to 260 feet in most of the 
area.
The Aymamon Limestone overlies the Aguada 
Limestone and consists mainly of thick-bedded to 
massive, commonly quartz free, very pure limestone 
(Monroe, 1980a, p. 53). 
This formation is largely 
covered throughout the area by unconsolidated surficial 
deposits. The thickness of the Aymamon Limestone is 
estimated to be as much as 2,000 feet at the coastline 
(Kaye, 1959).
The surficial deposits of Quaternary age cover the 
Tertiary age formations in the northern part of the region. 
These surficial deposits consist of alluvial deposits, 
blanket sands, beach and dune sands, and swamp 
deposits. The thickness of the surficial deposits is about 
100 feet in the San Juan coastal areas.
Figure 2.1.4.C-1 Generalized surficial geology in the Bayamon-Loiza region, Puerto Rico.
2.1.4 Bayamon-Loiza Region 
43
66°10'
05'
66W
55'
65°50'
18'27'30"
25'
22'30"
18°20'
01234 KILOMETERS
h^     '     
01234 MILES
EXPLANATION
EXTENT OF UPPER AND LOWER AQUIFERS 
RESERVOIR OR LAGOON
SURFACE CONTOUR-Shpws estimated altitude 
of the top of Cibao Formation, in feet 
below or above mean sea level. Contour 
interval is 100 feet
18°27'
18°22'30"
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
Laguna 
La Torrecilla
TRUJILLQ 
ALTO
01234 KILOMETERS
18°2
Modified from Anderson, 1976
Figure 2.1.4.D-1 Altitude of the top of the Cibao Formation in the Bayamon-Loiza region, Puerto Rico.
2.1.4.D Hydrogeology
Two principal water-bearing units are present in the 
Bayamon-Loiza region: an upper water-table aquifer 
comprised of sedimentary rocks of Tertiary age and 
surficial deposits of Quaternary age; and a lower 
confined aquifer comprised mainly of sedimentary rocks 
of Tertiary age. 
The two units are separated by the 
upper member of the Cibao Formation, which acts as a 
confining unit.
The upper aquifer occurs in the uppermost rocks 
overlying the upper member of the Cibao Formation, the 
Aguada and 
Aymamon 
Limestones, 
and 
alluvial 
deposits. The Aguada and Aymamon Limestones are 
eroded and covered with alluvial deposits, and the upper 
part of the Cibao Formation becomes thinner near San 
Juan. As a consequence, the available freshwater in the 
upper aquifer around San Juan largely resides in 
surficial deposits. 
For the most part, according to 
Rodrfguez-Martfnez (1991, p. 12), the upper aquifer is 
absent in the San Juan metropolitan area, and where 
present, is thin and contains brackish water. 
The 
thickness of the upper aquifer is limited by the location 
of the saline-freshwater interface and the top of the 
Cibao Formation (fig. 2.1.4.D-1).
44 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°10'
05'
66W
55'
65°50'
r27'30"  
25'
22'30"
18°20'
01234 KILOMETERS
I 1     '    i 
01234 MILES
EXPLANATION
DISTRIBUTION OF AQUIFER TRANSMISSIVITY. 
IN FEET SQUARED PER DAY
18°22'30
&ANOVANAS/ 
f- 
\
Less than 500' 
500 to 1,000 
1,000 to 3,000 
3,000 to 5,000
RESERVOIR OR LAGOON
TRIUJILLO
' ALTO ^ 
Rfr^
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
SAN JUAN
Laguna 
La Torrecillc:
CAROLINA CANOVANAS
TRUJILLO 
^ ALTO
Lago Las 
A Curias
18°27'3iO"   
18°25'   
Modified from Ingrid Padilla, U.S. Geological Survey, written communication, 1991
Figure 2.1.4.D-2 Transmissivity in the northern Bayamon-Loiza region, Puerto Rico.
The transmissivity of the upper aquifer ranges from 
less than 500 to more than 3,000 ft2/d (Ingrid Padilla, 
U.S. Geological Survey, written communication, 1991; 
fig. 2.1.4.D-2). 
Higher transmissivity values are 
measured west of the Canal del Rfo de Bayamon in the 
Toa Baja-Vega Baja region.
The lower aquifer occurs in the Mucarabones Sand 
and minor limestone lenses within the Cibao Formation 
(Rodriguez-Martmez, 1991, p. 15). The lower aquifer is 
confined from Bayamon to San Juan, but east of Rio 
Piedras, the formations that comprise this hydrologic 
unit pinch out. The transmissivity of the lower aquifer 
ranges from less than 150 to 2,000 ft2/d (Anderson, 
1976, p. 18). The quality of water in the lower aquifer 
ranges between fresh to brackish in the San Juan 
metropolitan area (Rodriguez-Martmez, 1991, p.15).
Some wells south of Trujillo Alto and Carolina yield 
water from the volcanic rocks in small quantities. The 
water that may be available in the volcanic bedrock 
flows through cracks and fissures in the weathered 
zones.
2.1.4 Bayamon-Loiza Region 
45
66°10'
05'
66W
55'
65°50'
°27'30"
25'
22'30"
18°20'
01234 KILOMETERS 
h^           
01234 MILES
EXPLANATION
EXTENT OF UPPER AND LOWER AQUIFERS 
RESERVOIR OR LAGOON
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly cased well. 
Contour interval is variable. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
01234 KILOMETERS
i 
i
2.1.4.B Ground-Water Levels and 
Movement
Regional ground-water flow in the upper and lower 
aquifers within the Bayamon-Loiza region is northward 
from surficial exposures of the formations of Tertiary 
age, where the recharge occurs, to eventually discharge 
into swamps and lagoons along the coast (fig. 
2.1.4.E-1). Ground water also moves locally towards 
the main stream systems of the Rfo Bayamon, Rio 
Piedras, and Rfo Grande de Lofza.
Higher ground-water levels are observed during the 
rainy season, which occurs from August through 
November and from April to May, than during the dry 
season. The difference between the highest and the 
lowest water-level 
altitude 
during 
1987 
in 
one 
observation well near Catano and another near San 
Juan was about 4 and 9 feet, respectively.
Recharge to the water-bearing formations in the 
area is primarily from rainfall, but also from infiltration of 
streamflow. 
In the highly urbanized San Juan 
metropolitan area another possible source of recharge 
to the aquifer is leakage from water and sewer lines 
(Anderson, 1976, p. 15). According to Anderson (1976, 
p. 27), the Rio Bayamon recharges the alluvium and the 
Tertiary age aquifers when ground-water levels are low, 
generally from January to April. During the rest of the 
year the aquifer either is in balance with the stream or 
contributes water to it.
Modified from Anderson, 1976
Figure 2.1.4.E-1 Altitude of water-level surface and direction of ground-water flow during 1971 in the Bayamon-Loiza region, Puerto Rico.
46 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.1.4.F Soil Permeability
The soil associations overlying the aquifers in the 
Bayamon-Loiza region belong to the humid coastal 
plains group (fig. 2.1.4.F-1). These soil associations are 
Catano-Aguadilla, 
Almirante-Vega 
Alta-Matanzas, 
Martin Pena-Saladar-Hydraquents, Swamps-Marshes, 
Coloso-Toa-Bajura, and Toa-Coloso-Bajura.
The dominant soil association in the Bayamon- 
Loiza region is the Almirante-Vega Alta-Matanzas, 
which covers most of the west and west central parts of 
the aquifer area. 
The soils of this association are 
described by Boccheciamp (1978, p. 5) as deep, gently 
sloping, well drained soils of clayey texture on terraces 
and alluvial fans of the coastal plain. The Almirante- 
Vega Alta-Matanzas association ranges in thickness 
from near zero to 84 inches and has a permeability of 
0.60 to 2.00 in/hr.
The second important soil association is the 
Coloso-Toa-Bajura, which covers most of the eastern 
part of the aquifer. This association is composed of 
deep, moderately well- to poorly-drained, nearly level 
soils on flood plains (Boccheciamp, 1977, p. 3). The 
Coloso-Toa-Bajura association is derived from fine- to 
moderately-fine textured sediment of mixed origin. The 
dominant permeability values in this association range 
from 0.06 to 0.20 in/hr, although the Toa series within 
the Coloso-Toa-Bajura association has a permeability of 
0.60 to 2.00 in/hr. Thickness of soils in the Coloso-Toa- 
Bajura association ranges from near zero to 70 inches.
Other soil associations are not extensive in the 
region. The Swamps-Marshes association covers the 
northeast, in areas adjacent to the San Jose, La
Torrecilla, and Pinones lagoons. These are deep, very 
poorly drained soils in the coastal plains, whose 
characteristics are too variable to be estimated. The 
Martm Pena-Saladar-Hydraquents association occupies 
the area surrounding the Bahia de San Juan. These 
soils are deep, nearly level, and very poorly drained. 
They are located in low depressions and lagoons of the 
coastal plains, and permeability generally ranges from 
0.60 to 2.00 in/hr. 
In the Martm Pena series, a 
permeability at a depth of 18 inches decreases to less 
than 0.06 in/hr. Thickness of soils in the Martm Pena- 
Saladar-Hydraquents association ranges from near zero 
to 63 inches. The Toa-Coloso-Bajura soil association 
overlies the alluvial deposits located along the Rio de 
Bayamon in the northwestern part of the upper aquifer. 
This association has a dominant permeability of 0.06 to 
0.20 in/hr, although the upper 16 inches in the Coloso 
series has a permeability of 0.20 to 0.60 in/hr, and the 
Toa series has a permeability of 0.60 to 2.00 in/hr. 
Thickness of soils in the Toa-Coloso-Bajura association 
range from near zero to 70 inches. 
The Catano- 
Aguadilla soil association is present in a fringe bordering 
the coast in the northeastern part. This soil association 
has the greatest permeability of any within the region 
(>20 in/hr); however, the upper 8 inches in the Aguadilla 
series have a permeability of 6 to 20 in/hr. Thickness of 
these soils ranges from near zero to 64 inches.
Thickness, 
permeability, 
and available water- 
capacity values are listed for all the soil associations 
present within 
the 
Bayamon-Lofza 
region 
(table 
2.1.4.F-1). 
Soil associations present in the upland 
areas south of the coastal aquifer areas and their 
characteristics are included in table 2.1.4.F-1.
Table 2.1.4.F-1 
Thickness, permeability, and available water capacity for the soil
associations in the Bayamon-Loiza region, Puerto Rico (Modified from Boccheciamp, 1977 and
1978)
[>, more than]
Area and soil association
Thickness 
(inches)
Permeability 
(inch per hour)
Available water 
capacity 
(inch per inch)
Humid Coastal Plains 
Catano-Aguadilla 
Almirante-Vega Alta-Matanzas 
1 Martm Pena-Saladar-Hydraquents 
1 Swamps-Marshes 
Coloso-Toa-Bajura 
Toa-Coloso-Bajura
Humid Upland Valleys 
Mabi-Rfo Arriba
Humid Uplands
Mucara-Caguabo
Caguabo-Mucara-Naranjito
Los Guineos-Humatas-Lirios
Humatas-Naranjito-Consumo
Los Guineos-Guayabota-Rock Land
Oto64 
Oto84 
Oto63
Oto70 
Oto70
OtoGO
OtoSO 
Oto40 
OtoGO 
OtoGO 
OtoGO
>20.00 
0.03 to 0.05 
0.60 to 2.00 
0.10 to 0.20 
0.60 to 2.00 
0.12 to 0.20 
too variable to estimate
0.06 to 0.20 
0.12 to 0.20 
0.06 to 0.20 
0.12 to 0.20
0.06 to 0.20
0.63 to 2.00 
0.60 to 2.00 
0.60 to 2.00 
0.60 to 2.00 
0.06 to 0.20
1 High water table
0.15 to 0.20
0.05 to 0.17 
0.05 to 0.19 
0.10 to 0.20 
0.10 to 0.20 
0.15 to 0.20
2.1.4 Bayamon-Lofza Region 
47
66°10'
05'
18°25'
20'
15'
66W
ATLANTIC OCEAN
55'
65°50'
01234 KILOMETERS
i 
II II ______
01234 MILES
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
A-4 CATANO-AGUADILLA 
B-4 ALMIRANTE-VEGA ALTA-MATANZAS 
D-1 MARTfN PENA-SALADAR-HYDRAQUENTS 
D-2 SWAMPS-MARSHES 
E-2 COLOSO-TOA-BAJURA 
E-3 TOA-COLOSO BAJURA
HUMID UPLANDS
M-1 MUCARA-CAGUABO
M-2 CAGUABO-MUCARA-NARANJITO
N-2 LOS GUINEOS-HUMATAS-LIRIOS
N-3 HUMATAS-NARANJITO-CONSUMO
N-7 LOS GUINEOS-GUAYABOTA-ROCK LAND
HUMID UPLAND VALLEYS 
S-2 MABI-RI'O ARRIBA
SOIL PERMEABILITY, IN INCHES 
PER HOUR
I 
FROM 0.06 TO 0.20
| 
FROM 0.60 TO 2.00
'^ | 
MORE THAN 20
I 
TO VARIABLE TO ESTIMATE
SOIL ASSOCIATION BOUNDARY
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
Modified from Boccheciamp, 1977 and 1978
Figure 2.1.4-F-l Soil associations and permeability in the Bayamon-Loiza region, Puerto Rico.
48 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2 South Coast Area
2.2 South Coast Area 
49
2.2.1 SANTA ISABEL-PATILLAS REGION
By Orlando Ramos-Gines
2.2.1.A Location and Major 
Geographic Features
The Santa Isabel-Patillas region covers 
about 90 mi2 and is located in the South 
Coast area of Puerto Rico. It is bounded to 
the north by the Cordillera Central, to the 
west by the Rio Descalabrado drainage basin 
divide, to the east by the Rio Grande de 
Patillas drainage basin divide, and to the 
south by the Caribbean Sea. A coastal 
alluvial plain is the major geographic feature 
within this region. This coastal plain abuts 
the Cordillera Central to the north, which 
reaches elevations of as much as 1,600 feet 
above mean sea level, and the Caribbean 
Sea to the south (fig. 2.2.1 .A-1). The region 
includes several small rivers: the Rio Grande 
de Patillas, 
Rfo Nigua of Arroyo, 
Rfo 
Guamanf, Rio Seco, Rfo Nigua of Salinas, 
Rfo Jueyes, Rfo Cayures, Rfo Coamo, Rfo 
Cuyon, Rfo Lapa, and Rfo Descalabrado. 
Most of the original vegetation has been 
removed 
for 
agricultural 
purposes. 
Nevertheless, a few mangrove swamps 
remain scattered along the coast. A complex 
irrigation-canal system constructed between 
1914 and 1916 transfers water from Patillas, 
Coamo, Guayabal, and Carite lakes to the 
many farms in the region. The principal 
population centers in the Santa Isabel- 
Patillas region are Patillas, Arroyo, Guayama, 
Salinas, Santa Isabel, and Coamo.
ATLANTIC OCEAN
SANTA ISABEL-PATILLAS 
REGION
CARIBBEAN SEA
66°30'
25'
20'
15'
10'
66°00'
65°55'
05'
18°00'  
17°55'
A Punta Guilarte
royo - - , 
rrote 
/
CARIBBEAN SEA
*k!
' Cayos Caribes 
Cayos de Barca
Cayos de Caracoles
Punta Ola Grande
Cayos Cabezazos o
Base from U.S. Geological Suivey
Puerto Rico e Istes Limftrofes, 1:240,000,1952
Figure 2.2.1.A-1 Location and major geographic features in the Santa Isabel-Patillas region, Puerto Rico.
50 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Pumping for agricultural use represented about 64 
percent (25.8 Mgal/d) of the total ground-water 
withdrawn in the region in 1983. About 35 percent of the 
total water used for irrigation was supplied from ground- 
water sources; the remaining 65 percent was supplied 
by streamflow through an irrigation canal and lake 
system. 
It is expected that agricultural water supply 
from streamflow areas west of the Rfo Jueyes will 
decrease after 1991, as a result of the conversion from 
furrow to drip irrigation.
2.2. l.B Population and Estimated 
Ground-Water Use
The population of the Santa Isabel-Patillas region 
was about 152,000 in 1980 (U.S. Department of 
Commerce, 1982). 
The population in the region 
increased about 6 percent by 1990 resulting in a 
population of about 162,000 (U.S. Department of 
Commerce, 1991). About 61 percent of the population 
lives in rural areas and about 39 percent in urban areas 
(table 2.2.1.B-1).
Total ground-water withdrawals in the Santa Isabel- 
Patillas region in 1983 were about 40 Mgal/d, of which 
approximately 9.4 Mgal/d were for domestic use (table 
2.2.1.B-2). 
The Puerto Rico Aqueduct and Sewer 
Authority was the major single user, pumping about 9.2 
Mgal/d. Private wells and a small community system in 
the municipio of Santa Isabel, which pumped about 
7,000 gal/min, account for the other 0.2 Mgal/d. 
Ground-water withdrawals represent about 24 percent 
of the total water for domestic use in this region. 
Approximate location and use of wells are shown on 
figure 2.2.1.B-1.
Table 2.2.1.B-1 Population for the Santa Isabel-Patillas region, Puerto Rico 
(U.S. Department of Commerce, 1982, table 1; U.S. Department of Commerce, 
1991, table 1)
Table 2.1.1.B-2 Ground-water withdrawals and estimated population served during 
1983 for the Santa Isabel-Patillas region, Puerto Rico 
[Mgal/d, million gallons per day;  , no data available]
1980 population
MUNICIPIO
Arroyo
Coamo
Guayama
Patillas
Salinas
Santa Isabel
Total
TOTAL
17,014
30,822
40,183
17,774
26,438
19,854
152,085
URBAN
8,432
12,851
21,097
3,172
6,220
6,948
58,720
RURAL
8,579
17,971
19,086
14,602
20,218
12,906
93,362
1990 population
TOTAL
18,910
33,837
41,588
19,633
28,335
19,318
161,621
1.
3
3
3
1 Use and supplier
Domestic Use
2 A. Puerto Rico Aqueduct and Sewer Authority
1. Patillas
2. Arroyo
3. Guayama
4. Salinas
5. Santa Isabel
6. Coamo
Subtotal
3 B. Community Systems
41. Santa Isabel
Subtotal
4 C. Private Supplies
1. Guayama
2. Salinas
3. Santa Isabel
Subtotal
II. Industrial Use
1 . Salinas
2. Santa Isabel
Subtotal
III. Agriculture Use
1. Patillas
2. Arroyo
3. Guayama
4. Salinas
5. Santa Isabel
Subtotal
IV. Commercial Use
1 . Santa Isabel
Subtotal
Total
Estimated 
population 
served
13,011
18,900
6,890
27,912
20,711
122
87,546
111
111
4 111
4 285
4 2,500
2,896
...
...
...
 
...
...
...
...
...
 
136,358
Average 
ground-water 
withdrawals 
(Mgal/d)
1.0
0.9
0.7
3.5
3.1
0.001
9.21
0.007
0.007
0.007
0.018
0.16
0.185
3.35
1.44
4.79
0.09
1.2
2.64
9.1
12.72
25.75
0.009
0.009
39.95
1 Municipios not listed under some specific use do not withdraw ground water for the subject use.
2 Modified from data reported by Gomez-Gomez and others, 1984.
3 Modified from data reported by a written communication of the Puerto Rico Department of Health.
4 Based on a water consumption of 63 gallons per person per day.
2.2.1 Santa Isabel-Patillas Region 
51
66°30'
25'
20'
15'
10'
05'
18°00'
17°55'
05' 
66°00' 
65°55'
EXPLANATION
I 
I 
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
-    -  -   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
  
-    -    BOUNDARY BETWEEN MUNICIPIOS
PERENNIAL STREAM 
_.. _ ._ EPHEMERAL STREAM
TUNNEL
LOCATION AND NUMBER OF WELLS 
AT SITE WHEN MORE THAN ONE 
WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
CARIBBEAN SEA
01234 KILOMETERS
01234 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.2.1.B-1 Approximate well locations in the Santa Isabel-Patillas region, Puerto Rico.
52 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.l.C Geologic Setting
The geology of the Santa Isabel-Patillas region 
consists of three basic lithologic units. They are, in 
ascending order, the volcanic-volcaniclastic rocks, the 
Juana Dfaz Formation of Oligocene age, and the alluvial 
deposits (fig. 2.2.1.C-1).
The volcanic-volcaniclastic and sedimentary rocks 
of Eocene to Cretaceous age are intensely faulted and 
constitute almost 67 percent of the Santa Isabel-Patillas
region (the uplands), and underly the Quaternary alluvial 
deposits. According to Monroe (1980a), these rocks are 
composed of tightly cemented limestone, sandstone and 
siltstone, tuff breccia, lava, granodiorite, and quartz 
diorite.
The Juana Diaz Formation of Oligocene age, 
unconformably overlies the volcanic-volcaniclastic and 
sedimentary rocks and is highly variable in lithologic 
character, consisting of conglomeratic sandstone and 
conglomerate, calcareous arenite, and minor limestone
in the Santa Isabel-Patillas region. 
The thickness of 
Juana Dfaz Formation ranges from 600 to more than 
2,400 feet (Monroe, 1980a) and generally thins from 
east to west.
The 
Ponce 
Formation 
of 
Miocene 
age 
unconformably overlies the Juana Dfaz Formation and 
consists of a tightly cemented, very pale orange to 
grayish-orange 
limestone, 
generally 
containing 
abundant molds of mollusks and corals (Monroe, 
1980a). Small exposures are observed in the western 
Santa Isabel-Patillas region.
The 
alluvial 
deposits 
of 
Quaternary 
age 
unconformably overlap the Juana Diaz Formation and 
are composed of layers or lenses of unconsolidated to 
poorly consolidated clay, sand, gravel, and rounded to 
angular boulders. 
They coalesce to form a gently 
southward sloping coastal alluvial plain of highly variable 
thickness, due to extensive bedrock faulting. 
These 
deposits are hydrogeologically the most important 
lithologic unit in the Santa Isabel-Patillas region.
66°30'
25'
20'
15'
10'
05'
66W
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
PONCE LIMESTONE 
JUANA Dl'AZ FORMATION 
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
05
18W
01234 KILOMETERS
Holocene 
and
Pleistocene
)
} 
Miocene 
and 
Oligocene
Eocene
to Lower
Cretaceous
QUATERNARY
TERTIARY
TERTIARY 
CRETACEOUS
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
EPHEMERAL STREAM 
TUNNEL 
TOWN OR CITY
01
4 MILES
17°55'
CARIBBEAN SEA
Modified from Briggs and Akers, 1965
Figure 2.2.1.C-1 Generalized surficial geology in the Santa Isabel-Patillas region, Puerto Rico.
2.2.1 Santa Isabel-Patillas Region 
53
2.2.l.D Hydrogeology
The alluvial deposits of Quaternary age are the 
most important lithologic unit in the Santa Isabel-Patillas 
region, containing its only sizeable aquifer. This aquifer 
is generally under water-table conditions, although 
flowing-artesian 
conditions 
have 
been 
observed 
throughout the area. Aquifer thickness may range from
zero at the edge of the bedrock-alluvial contact to about 
3,000 feet in the vicinity of Santa Isabel (fig. 2.2.1.D-1). 
East of the Rfo Jueyes and west of the Rfo Coamo, 
aquifer thickness decreases to no more than 300 feet 
along the shore. The aquifers in the fractured volcanic 
and plutonic rocks sustain very low yields. 
Thermal 
springs near Coamo are used as thermal water pools for 
recreation.
Hydraulic conductivities, ranging from 100 to 300 
ft/d, occur near Santa Isabel, Salinas, and Guayama 
(fig. 2.2.1 .D-2). Elsewhere, hydraulic conductivity is less 
than 
100 ft/d and decreases toward the coast. 
Transmissivity in the Santa Isabel-Patillas region is 
highly variable. The highest values, as great as 80,000 
ft2/d, occur in the area between the Rfo Coamo and Rfo 
Jueyes, due to an increase in aquifer thickness.
Transmissivities as high as 40,000 ft2/d are observed 
between the Rfo Cayures and the approximate divide 
between the Rfo Nigua of Salinas and Rfo Seco. 
Transmissivity values in this area increase seaward and 
toward the interfluvial area. West of the Rfo Coamo and 
east of the approximate divide between the Rfo Salinas 
and Rfo Seco, transmissivity values range from 1,000 to 
30,000 ft2/d.
66°30'
25"
20
15'
10'
05'
66W
65°55'
05'
18°00
17°55"
EXPLANATION
50
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
SUBSURFACE CONTOUR-Shows estimated 
altitude of the top of the bedrock unit, 
in feet below and above sea level. 
Contour interval is variable
APPARENT FAULT TRACE
-------- DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
PERENNIAL STREAM 
EPHEMERAL STREAM 
TUNNEL
TOWN OR CITY
s
CARIBBEAN SEA
01234 KILOMETERS
01234 MILES
Modified from Renken and others, 1991
Figure 2.2.1.D-1 Altitude of the top of the bedrock unit in the Santa Isabel-Patillas region, Puerto Rico.
54 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66'30'
25'
20'
15'
10'
05'
66°00'
65°55'
05'
18'00'
17°55'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
_  100    LINE OF EQUAL HORIZONTAL HYDRAULIC 
CONDUCTIVITY, IN FEET PER DAY-Dashed 
where approximated. Contour interval is variable
-------- 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
PERENNIAL STREAM
01234 KILOMETERS
1234 MILES
CARIBBEAN SEA
Modified from Bennett, 1976
Figure 2.2.1.D-2 Average hydraulic conductivity in the Santa Isabel-Patillas region, Puerto Rico.
2.2.1 Santa Isabel-Patillas Region 
55
2.2.1.E Ground-Water Levels and 
Movement
Ground-water levels in the Santa Isabel-Patillas 
region range from 150 to 200 feet above mean sea level 
near the bedrock-alluvial contact to a few feet above 
mean sea level near the coast (fig. 2.2.1.E-1). 
Accordingly, ground-water flows seaward. 
Where 
confined conditions occur, ground-water levels may be
as high as 10 feet above land surface (Vicente 
Quinones-Aponte, 
U.S. 
Geological 
Survey, 
oral 
communication, 1987). 
Ground-water levels may 
fluctuate as much as 10 feet as a result of seasonal 
changes.
Sources of aquifer recharge may vary throughout 
the region. Seepage from rivers and irrigation canals 
represent the major source of ground-water recharge.
Aquifer recharge from precipitation represents only 
about 10 percent of the mean annual rainfall in the 
region (Vicente Quinones-Aponte, 
U.S. Geological 
Survey, oral communication, 1987). 
In the Patillas to 
Salinas region, aquifer recharge depends primarily on 
conveyance losses from water diverted from Lago 
Guamanf and Lago Carite through the Canal de 
Guamanf and Canal de Patillas. A preliminary ground- 
water flow simulation of the area has shown that if
diversion from Lago Guamanf ceases and actual 
ground-water pumpage is sustained, the aquifer will 
undergo an abrupt decrease in water levels (Sigfredo 
Torres-Gonzalez, 
U.S. 
Geological 
Survey, 
oral 
communication, 1987). West of the Rio Jueyes, aquifer 
recharge comes primarily from streamflow leakage. In 
general, ground-water discharges to streams in the 
upland areas and near the coast.
66°30'
25'
20'
15'
10'
05'
66°00'
65°55'
05'
18W
17°55'
EXPLANATION
100
/,
PERENNIAL STREAM
_..._ _ 
EPHEMERAL STREAM 
-<  ( 
TUNNEL
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly 
cased well. Contour interval is 
variable. Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
  
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
CARIBBEAN SEA
01234 KILOMETERS
01234 MILES
Modified from Torres-Gonzalez and Gomez-Gomez, 1987; Quinones-Aponte and Gomez-Gomez, 1987; Rodriguez-del-Rfo and Gomez-Gomez, 1987
Figure 2.2.1.E-1 Composite altitude of water-level surface and direction of ground-water flow during 1986 and 1987 in the Santa Isabel-Patillas region, 
Puerto Rico.
56 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.l.F Soil Permeability
The principal soils overlying the aquifer areas in the 
Santa Isabel-Patillas region are the Coamo-Guamani- 
Vives, 
the 
Jacana-Amelia-Fraternidad, 
and 
the 
Constancia-Jacaguas-San Anton (fig. 2.2.1.F-1). 
The 
Coamo-Guamanf-Vives is composed of deep, well- 
drained, nearly level to strongly sloping soils on terraces 
and alluvial fans (Boccheciamp, 1977, p. 4). 
Its
permeability ranges from 0.60 to 2.00 in/hr (table 
2.2.1.F-1). 
The soils composing the Jacana-Amelia- 
Fraternidad 
soil 
association 
are 
described 
as 
moderately deep and deep, well drained and moderately 
well drained, nearly level to strongly sloping. They are 
located on terraces, alluvial fans, and foot slopes and 
their permeability ranges from 0.60 to 2.00 in/hr. These 
clayey soils are highly suitable for agricultural use.
66°30'
25'
20'
15'
10
05'
66W
65°55'
05'
18W
17°55'
EXPLANATION
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.20 
FROM 0.20 TO 0.60 
FROM 0.60 TO 2.00 
TOO VARIABLE TO ESTIMATE
SOIL ASSOCIATION BOUNDARY
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS
D-2 SWAMPS-MARSHES
E-2 COLOSO-TOA-BAJURA 
SEMIARID COASTAL PLAINS
G-1 FRATERNIDAD-PASO SECO
H-1 COAMO-GUAMANf-VIVES
J-1 CONSTANCIA-JACAGUAS-SAN ANT6N 
HUMID UPLANDS
M-1 MUCARA-CAGUABO
M-3 CAGUABO-MUCARA-QUEBRADA
N-2 LOS GUINEOS-HUMATAS-LIRIOS
N-5 HUMATAS-MARICAO-LOS GUINEOS
O-1 PANDURA-ROCK LAND-PATILLAS
SEMIARID UPLANDS 
R-2 DESCALABRADO-GUAYAMA 
R-3 CALLABO 
R-6 DESCALABRADO 
R-7 JACANA-AMELIA-FRATERNIDAD
CARIBBEAN SEA
01234 KILOMETERS
01234 MILES
Modified from Bocheciamp, 1977; Gierbolini, 1979; Gilberto Acevedo, Soil Conservation Service, written communication, 1990
Figure 2.2.1.F-1 Soil associations and permeability in the Santa Isabel-Patillas region, Puerto Rico.
2.2.1 Santa Isabel-Patillas Region 
57
Table 2.2.1.F-1 Thickness, permeability, and available water capacity for the soil associations 
in the Santa Isabel-Patillas region, Puerto Rico (Modified from Gierbolini, 1979; Boccheciamp, 
1977; and Gilberto Acevedo, Soil Conservation Service, written communication, 1990) 
[>, more than]
Area and soil association
Humid Coastal Plains 
Swamp-Marshes 
Coloso-Toa-Bajura 
Semiarid Coastal Plains
Fraternidad-Paso Seco
Coamo-Guamanf-Vives
Constancia-Jacaguas-San Anton
Humid Uplands
Mucara-Caguabo
Caguabo-Mucara-Quebrada
Los Guineos-Humatas-Lirios
Humatas-Maricao-Los Guineos
Pandura-Rock Land-Patillas
Semiarid Uplands
Descalabrado-Guayama
Callabo
Descalabrado
Jacana-Amelia-Fraternidad
Thickness 
(inches)
0
0
0
0
0
0
0
0
0
0
0
0
0
Permeability 
(inch per hour)
Available water 
capacity 
(inch per inch)
too variable to be estimated 
to >72 
0.06 to 2.00 
0. 1 0 to 0.20
to
to
to
to
to
to
to
to
to
to
to
to
50
20
65
30
60
60
72
48
26
13
17
50
0.06 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.20 to 0.60
0.20 to 0.60
0.15 to 0.18
0.10 to 0.15
0.08 to 0.1 4
0.05 to 0.1 7
0.06 to 0.1 7
0.08 to 0.20
0.12 to 0.16
0.05 to 0.1 4
0.10 to 0.1 5
0.10 to 0.15
0.10 to 0.20
0.10 to 0.18
58 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.2 JUANA DIAZ-PONCE REGION
By Orlando Ramos-Gines
2.2.2.A Location and Major Geographic 
Features
The Juana Dfaz-Ponce region covers about 80 mi2 
and includes the municipios of Ponce, Juana Dfaz, and 
Villalba. It is bounded to the north by the drainage basin 
divide in the Cordillera Central, to the west by the Rfo 
Canas drainage basin divide, to the east by the Rfo 
Jacaguas drainage basin divide, and to the south by the 
Caribbean 
Sea 
(fig. 
2.2.2.A-1). 
Steep 
volcanic 
mountains rising to as much as about 4,500 feet above 
mean sea level, eroded limestone hills, and a coastal 
alluvial plain are the predominant types of landforms in 
the region. The coastal alluvial plain covers about 80 
percent of the municipal boundaries of Juana Dfaz and 
about 40 percent of the Ponce municipal limits. The 
most important surface-water features in this region are 
the Rfo Canas, the Rfo Portugues, the Rfo Bucana, the 
Rfo Inab6n, the Rfo Jacaguas, and the Lago Toa Vaca. 
From Punta Cucharas inland to the valley of the Rfo 
Canas, limestone hill forms constitute most of the 
southwestern part of the Juana Dfaz-Ponce region 
(McClymonds, 1972, p. 2). There are numerous stream 
diversions, canals, and storage lakes in the Juana Dfaz- 
Ponce region that are used principally for agriculture 
(McClymonds, 1972, p. 13). 
Ponce is the principal 
population center in this region.
2.2.2.B Population and Estimated 
Ground-Water Use
The population of the Juana Dfaz-Ponce region 
was about 253,000 in 1980 (U.S. Department of 
Commerce, 1982). Population in the region increased 
by about 1.3 percent by 1990, resulting in a population 
of about 256,000 (U.S. Department of Commerce, 
1991). However, the municipio of Ponce experienced a 
decrease in population from a total of 189,046 in 1980 to 
187,749 in 1990. About 74 percent of the population of 
the Juana Dfaz-Ponce region lives in urban areas and 
about 26 percent lives in rural areas (table 2.2.2.B-1).
ATIANTIC OCEAN
JUANA DIAZ- 
PONCE 
REGION
CARIBBEAN SEA
66°40'
35'
30'
25'
20'
15'
66°10'
05'
18°00'
SENATORIAL DISTRICT NUMBER
Penoncillo 
Gata Islet 
Pta Carenero * 
Cayo Cardona
CARIBBEAN SEA
01234 KILOMETERS
0 
1
4 MILES
Base from US. Geological Survey
Puerto Rico e Islas Utnrtrofes, 1:240,000.1952
Figure 2.2.2.A-1 Location and major geographic features in the Juana Diaz-Ponce region, Puerto Rico.
2.2.2 Juana Diaz-Ponce Region 
59
Table 2.2.2.B-1 Population for the Juana-Diaz Ponce region, Puerto Rico (U.S. Department 
of Commerce, 1982, table 1; U.S. Department of Commerce, 1991, table 1)
1980 population
MUNICIPIO
Juana Dfaz
Ponce
Villalba 
Total
TOTAL
43,505
189,046
20,734
253,285
URBAN
10,469
161,739
3,469
175,677
RURAL
33,036
27,307
17,265
77,608
1990 
population
TOTAL
45,198
187,749
23,559
256,506
In 1983, ground-water withdrawals averaged about 
25 Mgal/d, of which 13.1 Mgal/d was for domestic use, 
11.7 Mgal/d was for agricultural use, and about 0.1 
Mgal/d was for private and commercial use (table 
2.2.2.B-2). 
The Puerto Rico Aqueduct and Sewer 
Authority was the major single user, pumping about 13 
Mgal/d. Private wells for domestic use were only found 
in the municipio of Juana Dfaz and pumped about 0.03 
Mgal/d. 
An estimated 38 percent of the total water 
demand for domestic use in the region was supplied by 
ground water.
Average ground-water withdrawals for agriculture 
durind 1983 were 11.7 Mgal/d. 
In the municipio of 
Juana Dfaz, the total water use for agricultural purposes 
during 1983 was approximately 23 Mgal/d of which 32 
percent was obtained from ground-water sources. The 
remaining 68 percent was supplied by streamflow 
through the Canal de Juana Dfaz irrigation system. In 
the municipio of Ponce, 43 percent of the water used for 
agricultural purposes was supplied from ground water. 
About 0.06 Mgal/d were pumped for commercial use. 
Approximate locations and uses of wells are shown on 
figure 2.2.2.B-1.
Table 2.2.2.B-2 
Ground-water withdrawals and estimated 
population served during 1983 for the Juana Diaz-Ponce 
region, Puerto Rico
[Mgal/d, million gallons per day;  , no data available]
66°40'
35'
30'
25'
20'
15'
66°10'
1 Use and supplier
Estimated 
population 
served
Average 
ground-water 
withdrawals 
(Mgal/d)
I. Domestic Use
2 A. Puerto Rico Aqueduct and 
Sewer Authority
1 . Juana Dfaz
2. Ponce
Subtotal
4 B. Private Supplies
1 . Juana Dfaz
Subtotal
4 II. Agriculture Use
1 . Juana Dfaz
2. Ponce
Subtotal
4 III. Commercial Use
1 . Juana Dfaz
Subtotal
Total
37,467
62,678
100,145
3 460
460
 
 
 
 
100,605
3.4
9.6
13.0
0.03
0.03
7.2
4.4
11.7
0.06
0.06
24.8
1 Municipios not listed under some specific use do not withdraw 
ground water for the subject use.
2 Modified from data reported by Gomez-Gomez and others, 1984.
3 Based on a water consumption of 63 gallons per person per day.
4 Based on a ground-water survey conducted during March 1986.
05'
18W
CARIBBEAN SEA
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM 
EPHEMERAL STREAM
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL
TOWN OR CITY
01234 KILOMETERS
1
4 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.2.2.B-1 Approximate well locations in the Juana Diaz-Ponce region, Puerto Rico.
60 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.2.C Geologic Setting
The geology of the Juana Diaz-Ponce region 
consists of four basic lithologic types. Among these are 
a suite of volcaniclastic, volcanic, 
plutonic, 
and 
limestone rocks of Early Cretaceous to Eocene age; the 
Juana Diaz Formation of Oligocene to Miocene age; the 
Ponce Limestone of Miocene age; and alluvial deposits 
of Quaternary age (fig. 2.2.2.C-1).
The suite of Early Cretaceous to Eocene age rocks 
are exposed in the interior upland portions of the Juana
Dfaz-Ponce region and are composed of volcanic and 
volcaniclastic-plutonic 
rocks, 
tightly 
cemented 
limestone, tylaceous sand and siltstone, tuff breccia, 
lava, granodiorite, and quartz diorite (Monroe, 1980a). 
These rocks are intensely faulted and are structurally 
complex.
The Juana Dfaz Formation unconformably overlies 
the suite of Early Cretaceous to Eocene rocks toward 
the south and consists of limestone in the upper part of 
the formation and a basal conglomerate of pebbles, 
cobbles, 
and boulders 
in the lower part. 
It 
is
continuously exposed, except in alluvium-filled valleys, 
and rests on an eroded and highly irregular surface of 
the older volcaniclastic-plutonic rocks (Monroe, 1980a, 
p. 67).
The Ponce Limestone unconformably overlies the 
Juana Dfaz Formation and consists of a tightly 
cemented 
very 
pale 
orange 
to 
grayish-orange 
limestone, generally containing abundant molds of 
mollusks and corals (Monroe, 
1980a). 
It too is 
continuously exposed throughout the Juana Dfaz-Ponce 
region, except where covered by alluvium.
The Quaternary alluvial deposits unconformably 
overlie the Juana Dfaz Formation and Ponce Limestone. 
These deposits consist of poorly bedded and poorly 
sorted gravel, sand, silt, and some clay. In general, the 
amount of gravel diminishes seaward with increasing 
amounts of silt and clay. 
The thickness of alluvium 
deposit exposures in the Juana Dfaz-Ponce region 
range from about 200 to 2,000 feet, though much of this 
thickness may be due to faulting (Gomez-Gomez and 
Heisel, 1980).
66°40'
35'
30'
25'
20'
15'
66°10'
05'
18W
c 
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
LANDSLIDE DEPOSITS 
PONCE LIMESTONE
JUANA Dl'AZ 
FORMATION
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
QUATERNARY
Miocene
and 
I TERTIARY 
Oligocene
Eocene 
to Lower 
f CRETACEOUS 
Cretaceous
PERENNIAL STREAM 
EPHEMERAL STREAM
TOWN OR CITY
01234 KILOMETERS
I    "-T
0 
1
4 MILES
CARIBBEAN SEA
Modified from Briggs and Akers, 1965
Figure 2.2.2.C-1 Generalized surficial geology in the Juana Diaz-Ponce region, Puerto Rico.
2.2.2 Juana Diaz-Ponce Region 
61
2.2.2.D Hydrogeology
The principal aquifer in the Juana Dfaz-Ponce 
region is under water-table conditions in the alluvial 
deposits, although flowing-artesian conditions have 
been observed (McClymonds, 1972, p. 19). 
Aquifer 
thickness increases toward the coast to about 300 feet 
(fig. 2.2.2.D-1). 
In upper valley areas where the 
alluvium 
is 
thinner, 
ground-water seepage 
from 
fractures within the bedrock are an additional source of
ground-water recharge. 
In 
general, 
the 
Ponce 
Limestone seems to yield more water to wells than the 
alluvial aquifer in the upper valley areas. The aquifer in 
the fractured volcanic and plutonic rock is a locally 
important source of water. The highest well yield in this 
aquifer, about 200 gal/min, is in the upper Rfo Portugues 
(McClymonds, 1972, p. 
18). 
Numerous springs, 
particularly on formation outcrops, flow in the Juana 
Diaz-Ponce region. 
Two thermal springs flow in the
upper Rio Portugues, and one was developed and used 
for hot baths (McClymonds, 1972, p. 18).
Hydraulic-conductivity values in the alluvial aquifer 
ranged from 0.1 to 100 ft/d, increasing from east to west 
toward Ponce and decreasing from the center of the 
valley toward the shore where amounts of silt and clay 
increase significantly (fig. 2.2.2.D-2). As a result, most 
of the deeper water is protected from direct seawater 
encroachment (McClymond, 1972, p. 5). 
The Ponce
Limestone in the upper valley area may have hydraulic- 
conductivity values as high as 300 ft/d (Fernando 
Gomez-Gomez, 
U.S. 
Geological 
Survey, 
oral 
communication, 1987). 
Transmissivity values of the 
alluvial aquifer near the town of Ponce could be as high 
as 10,000 ft2/d. 
Transmissivity values in the Juana 
Dfaz-Ponce region increase from east to west toward 
the Rio Canas and decrease seaward.
66°40'
35'
30'
25'
20'
15'
66°10'
05'
18°00'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
_  100    LINES OF EQUAL THICKNESS-Shows average 
saturated thickness, in feet. Dashed where 
approximated.Contour interval is variable
   ------ 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
PERENNIAL STREAM 
EPHEMERAL STREAM 
TOWN OR CITY
01234 KILOMETERS
0 
1
4 MILES
CARIBBEAN SEA
Modified from Bennett, 1976
Figure 2.2.2.D-1 Aquifer thickness in the Juana Diaz-Ponce region, Puerto Rico.
62 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°40'
35'
30'
25'
20'
15'
66°10'
05'
18W
CARIBBEAN SEA
EXPLANATION
I 
... 
I 
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
    
25     LINE OF EQUAL HYDRAULIC CONDUCTIVITY, 
IN FEET PER DAY-Dashed where approximated. 
Contour interval is variable
-       --  
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
          
PERENNIAL STREAM
  --     
EPHEMERAL STREAM
  
TOWN OR CITY
01234 KILOMETERS
I  "-r-1   ",  L ,    ,
01234 MILES
Modified from Bennett, 1976
Figure 2.2.2.D-2 Average hydraulic conductivity estimates in the Juana Diaz-Ponce region, Puerto Rico.
2.2.2 Juana Dfaz-Ponce Region 
63
2.2.2.E Ground-Water Levels and 
Movement
Ground-water levels in the Juana Dfaz-Ponce 
region range from more than 100 feet above mean sea
(fig. 2.2.2.E-1). 
Accordingly, ground-water flows 
seaward. Ground-water levels may fluctuate as much 
as 20 feet seasonally.
Seepage from ponds, streams, and irrigation
recharge 
to 
the 
alluvium, 
whereas 
precipitation 
contributes only about 30 percent (McClymonds, 1972, 
p. 15). The quantity of ground water flowing into the 
alluvial aquifer from the bedrock is probably small 
compared to the flow in the alluvium. 
In general,
and near the coast. Commonly, streamflow that has not 
been diverted seeps into the alluvial aquifer during dry 
periods. As a result, only peak discharges reach the 
sea. Small springs issuing from bedrock fractures flow 
to streams and maintain the flow throughout the year
level in the upper valley areas to zero near the coast 
canals represents about 70 percent of ground-water 
ground-water discharges to streams in the upland areas 
(McClymonds, 1972, p. 5).
66°40'
35'
30'
25'
20'
15'
66°10'
05'
18'00'
EXPLANATION
-700
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly cased well. 
Contour interval is variable. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
EPHEMERAL STREAM 
TOWN OR CITY
01234 KILOMETERS
01
4 MILES
CARIBBEAN SEA
Modified from Colon-Ramos and Colon-Dieppa, 1981
Figure 2.2.2.E-1 Altitude of water-level surface and direction of ground-water flow during 1980 in the Juana Diaz-Ponce region, Puerto Rico.
64 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.2.F Soil Permeability
The most prominent soil associations overlying the 
aquifers within this region are the Constancia-Jacaguas- 
San Anton, Fraternidad-Paso Seco, and the Aguilita- 
Tuque (fig. 2.2.2.F-1). The Constancia-Jacaguas-San 
Anton soil association is composed of nearly level, 
poorly- and well-drained, neutral to moderately alkaline,
loamy and clayey soils that grade from deep to shallow 
over sand and gravel (Gierbolini, 1979, p. 5) These 
soils were formed over the river flood plains and are 
subject to flooding. 
The Fraternidad-Paso Seco soil 
association is composed of gently sloping to strongly 
sloping, moderately well drained, neutral to moderately 
alkaline, clayey soils that are deep or moderately deep 
to sand and gravel (Gierbolini, 1979, p. 5). They have
been developed on terraces, alluvial fans, and foot 
slopes on the coastal plain. The soils in the Aguilita- 
Tuque soil associations are described by Gierbolini 
(1979, p. 4) as steep and very steep, well drained, 
moderately alkaline, loamy and clayey soils that have 
gravel and pebbles over limestone. They are present on 
foot slopes, side slopes, and hilltops on the limestone 
uplands.
Almost all the soil associations in this region have 
moderate soil permeabilities ranging from 0.06 to 2.00 
in/hr (table 2.2.2.F-1). 
The Fraternidad-Paso Seco 
association, occurring on the upper valley west of Rio 
Portugues, has the lowest permeabilities in the whole 
area, ranging from 0.06 to 0.20 in/hr. As a result, small 
ponds to store water for irrigation occur within this soil 
association. In general, soils occurring within the Juana 
Diaz-Ponce region are suitable for agricultural use.
66°40'
35'
30'
25'
20'
15'
66°10'
Table 2.2.2.F-1 Thickness, permeability, and available water 
capacity for soil associations in the Juana Diaz-Ponce region, 
Puerto Rico (Modified from Gierbolini, 1979)
18*10'
Area and soil association
Thickness 
(inches)
Permeability 
(inch per hour)
Available 
water capacity 
(inch per inch)
Semiarid Coastal Plains
Fraternidad-Paso Seco 
OtoGO 
0.06 to 0.20 
0.06 to 0.18 
Constancia-Jacaguas-San Anton 
Oto65 
0.60 to 2.00 
0.08 to 0.14 
Aguilita-Tuque 
Oto60 
0.60 to 2.00 
0.07 to 0.10
Humid Uplands
Caguabo-Mucara-Quebrada 
Oto60 
0.60 to 2.00 
0.06 to 0.17 
Humatas-Maricao-Los Guineos 
Oto72 
0.60 to 2.00 
0.12 to 0.16
Semiarid Uplands
CallabO 
Oto27 
0.60 to 2.00 
0.12 to 0.16
05'
18W
EXPLANATION
SOIL ASSOCIATIONS
SEMIARID COASTAL PLAINS
G-1 FRATERNIDAD-PASO SECO
J-1 CONSTANCIA-JACAGUAS-SAN ANTON
L-1 AGUILITA-TUQUE
HUMID UPLANDS
M-3 CAGUABO-MUCARA-QUEBRADA 
N-5 HUMATAS-MARICAO-LOS GUINEOS
SEMIARID UPLANDS 
R-3 CALLABO
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.20 
FROM 0.60 TO 2.00
SOIL ASSOCIATION BOUNDARY
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
01234 KILOMETERS
1
4 MILES
CARIBBEAN SEA
Modified from Gieitolini, 1979
Figure 2.2.2.F-1 Soil associations and permeability in the Juana Diaz-Ponce region, Puerto Rico.
2.2.2 Juana Dfaz-Ponce Region 
65
2.2.3 PENUELAS-GUANICA REGION
By Orlando Ramos-Gines
2.2.3.A Location and Major Geographic 
Features
The 
Penuelas-Guanica 
region 
is 
located 
in 
southwestern Puerto Rico, about 15 miles west of Ponce 
(fig. 2.2.3.A-1). 
It covers an area of 30 mi2 and is 
bounded to the north by the Cordillera Central, reaching 
elevations of 3,600 feet above mean sea level, to the 
west by the Rfo Loco drainage basin divide, to the east 
by the Rfo Tallaboa drainage basin divide, and to the 
south by the Caribbean Sea. The Penuelas-Guanica 
region includes the municipios of Penuelas, Guayanilla, 
Yauco, and a portion of Guanica. 
The Penuelas- 
Guanica region includes the drainage basins of the Rfo 
Tallaboa, Rfo Macana, Rfo Guayanilla, Rfo Yauco, and 
Rfo Loco. Limestone hills, alluvium filled valleys, and 
coastal plains are the most typical landforms that occur 
within the region. 
The limestone hills, reaching 
elevations of as much as 1,100 feet above mean sea 
level, flank the alluvial valleys of the Pefiuelas-Guanica 
region to the north, east, and west. The alluvial valley 
floors reach elevations of as much as 150 feet above 
mean sea level and slope gently toward the coast to 
elevations slightly above mean sea level. The Bosque 
Estatal de Guanica, a tropical xerophitic forest (a forest 
composed of plants structurally adapted to grow under 
very dry or desert conditions) included in the Biosphere 
Reserve Program of the United Nations, is located in the 
southwestern part of the region. The principal population 
centers in the Penuelas-Guanica region are Penuelas, 
Guayanilla, Yauco, and Guanica.
ATLANTIC OCEAN
PENUEUVS-GUANICA REGION
CARIBBEAN SEA
66°55'
50
66°30'
01234 KILOMETERS
' 
' 
  
CARIBBEAN SEA
18°00' -
17°55' -
Base from U.S. Geological Survey
Puerto Rico e Islas LJmftrofes, 1:240,000, 1952
Figure 2.2.3.A-1 Location and major geographic features in the Penuelas-Guanica region, Puerto Rico.
66 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.3.B Population and Estimated 
Ground-Water Use
The population of the Penuelas-Guanica region was 
about 96,500 in 1980 (U.S. Department of Commerce, 
1982). From 1980 to 1990 population increased by 10 
percent 
to 
about 
106,000 
(U.S. 
Department 
of 
Commerce, 1991). About 64 percent of the population in 
this region live in rural areas, whereas only 36 percent of 
the population live in urban areas (table 2.2.3.B-1). 
Surface water has been the major water source for the 
Penuelas-Guanica region. In 1983, public-water supply 
in the municipio of Penuelas came exclusively from 
surface-water sources.
Table 2.2.3.B-1 
Population for the Penuelas-Guanica region, Puerto Rico (U.S. 
Department of Commerce, 1982, table 1; U.S. Department of Commerce, 1991, table 1)
Total ground-water withdrawals in 1983 were about 
8.82 Mgal/d (table 2.2.3.B-2). The Puerto Rico Aqueduct 
and Sewer Authority was the major single user, pumping 
about 5.2 Mgal/d, which provided water to 43 percent of 
the population in the area for domestic use. 
Ground- 
water use for agriculture was about 41 percent (3.62 
Mgal/d) of the total pumpage in 1983. About 30 percent 
of the total water demand for irrigation came from 
ground-water sources; the remaining 70 percent was 
diverted from streamflow. Approximate locations of wells 
are shown on figure 2.2.3.B-1.
1980 population
MUNICIPIO
Penuelas
Guayanilla
Yauco
Guanica 
Total
TOTAL
19,116
21 ,050
37,742
18,799
96,707
URBAN
4,235
6,163
14,594
9,628
34,620
RURAL
14,881
14,887
23,148
9,171
62,087
1990 
population
TOTAL
22,515
21,581
42,058
19,984
106,138
66°55'
50'
45'
40'
35'
66°30'
Table 2.2.3.B-2 Ground-water withdrawals and estimated population served 
during 1983 for the Penuelas-Guanica region, Puerto Rico 
[Mgal/d, million gallons per day;  , no data available]
1 Use and supplier
Estimated
population
served
Average 
ground-water 
withdrawals
(Mgal/d)
10'
I. Domestic Use
2 A. Puerto Rico Aqueduct and Sewer Authority
1. Penuelas
2. Guayanilla
3. Yauco
4. Guanica
Subtotal
II. Agriculture Use
1. Penuelas
2. Guayanilla
3. Guanica
Subtotal
III. Commercial Use
14,339
3 7,334
20,003
41,676
 
...
...
1.3
0.5
3.4
5.2
0.17
0.95
2.5
05'
3.62
18W
Total 
41,676
8.82
1 Municipios not listed under some specific use do not withdraw ground water for the 
subject use.
2 Modified from data reported by Gomez-Gomez and others, 1984.
3 Based on a water consumption of 63 gallons per person per day.
17°55'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM 
TROPICAL FOREST LIMITS 
DRAINAGE TUNNEL
LOCATION AND NUMBER OF WELLS AT 
SITE WHEN MORE THAN ONE WELL 
PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL
TOWN OR CITY
01234 KILOMETERS
CARIBBEAN SEA
01
4 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.2.3.B-1 Approximate well locations in the Penuelas-Guanica region, Puerto Rico.
2.2.3 Penuelas-Guanica Region 
67
2.2.3.C Geologic Setting
The geology of the Penuelas-Guanica region 
consists of four basic lithologic units. They are: a suite of 
volcaniclastic, volcanic, plutonic, and limestone rocks of 
Early Cretaceous to Eocene age; the Juana Dfaz 
Formation of Oligocene to Miocene age; the Ponce 
Limestone of Miocene age; and alluvial deposits of 
Quaternary age.
The suite of Early Cretaceous to Eocene age rocks 
in the uplands consists of tuffaceous sand and siltstone, 
tuff breccia, lava, granodiorite, and quartz diorite 
(Monroe, 1980a) (fig. 2.2.3.C-1). These rocks are 
intensely faulted and are structurally complex.
The Juana Dfaz Formation overlies the suite of 
Early Cretaceous to Eocene age rocks and crops out in 
upper valley areas (Monroe, 1980a). 
It consists of a 
stratified chalky, clayey, white to very pale orange 
limestone in the upper part of the formation and of sand, 
gravel, and cobbles of various types of volcanic rocks, 
and very fossiliferous mudstone in the lower part. It is 
continuously exposed, except in alluvium-filled valleys, 
and rests on an eroded and highly irregular surface of 
the older volcaniclastic-plutonic rocks (Monroe, 1980a).
The Ponce Limestone, overlying the Juana Dfaz 
Formation, is a very pale to grayish-orange, tightly 
cemented, and fossiliferous limestone. It is continuously 
exposed throughout the Juana Dfaz-Ponce region, 
except where covered by alluvium (section 2.2.2).
The Quaternary alluvium in the river valleys and 
coastal plains unconformably overlies the Juana Dfaz 
Formation and Ponce Limestone and is the most 
important lithologic unit in the Penuelas-Guanica region, 
because it contains the most productive aquifers. These 
deposits are composed of layers or lenses of poorly 
consolidated clay, silt, sand, gravel, and boulders. 
In 
general, particles decrease in size toward the coast 
where the amount of silt and clay is higher. Beach and 
swamp deposits of Quaternary age are scattered along 
the shore (fig. 2.2.3.C-1).
66°55'
50'
45'
40'
35'
66°30'
10'
05'
18W
17°55'
EXPLANATION
Tunnel from
[ n
} 
Miocene 
and
BEACH DEPOSITS
SWAMP DEPOSITS
ALLUVIAL DEPOSITS 
J
PONCE LIMESTONE
JUANA Dl'AZ FORMATION 
J 
Oligocene
PLUTONIC ROCKS 
} 
_ 
] 
Eocene
VOLCANIC AND 
f 
to Lower 
>
VOLCANICLASTIC 
Cretaceous
ROCKS 
> 
>
RESERVOIR
------ DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
       PERENNIAL STREAM
Holocene
and 
\ QUATERNARY 
Pleistocene
TERTIARY
TERTIARY 
CRETACEOUS
  EPHEMERAL STREAM 
DRAINAGE TUNNEL
CARIBBEAN SEA
01234 KILOMETERS
I '           
01234 MILES
Modified from Briggs and Akers, 1965
Figure 2.2.3.C-1 Generalized surficial geology in the Penuelas-Guanica region, Puerto Rico.
68 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.3.D Hydrogeology
The principal aquifers in the Penuelas-Guanica 
region occur in the alluvial deposits under water-table 
conditions. 
The thickness of alluvial deposits range 
from less than 1 foot along the valley sides to more than 
200 feet along existing stream courses (fig. 2.2.3.D-1). 
Hydraulic-conductivity values were estimated from 
specific-capacity tests of wells in the Rfo Loco and Rfo 
Yauco valleys (fig. 2.2.3.D-2). 
In these valleys, the 
hydraulic-conductivity values could be as high as 300 
feet, decreasing seaward with increasing silt and clay 
content. The transmissivity of the alluvial aquifer in the 
Penuelas-Guanica region may, in general, increase 
inland and streamward as aquifer hydraulic conductivity 
increases (Bennett,1976).
Aquifers in both the Ponce Limestone and the 
Juana Dfaz Formation may yield more water in upper 
valley areas. 
Estimates 
of apparent 
hydraulic 
conductivity at wells tapping the aquifer in the Ponce 
Limestone and the Juana Dfaz Formation range from 
2.7 to about 270 ft/d (Bennett, 1976, p. 17).
66°55'
50'
45'
40'
35'
66°30'
10'
05'
18W
17°55'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
LINES OF EQUAL AQUIFER THICKNESS-Shows 
aquifer thickness, in feet. Dashed where 
approximated Contour interval is variable
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TROPICAL FOREST LIMITS 
PERENNIAL STREAM 
EPHEMERAL STREAM 
DRAINAGE TUNNEL 
TOWN OR CITY
01234 KILOMETERS
CARIBBEAN SEA
4 MILES
Modified from McClymonds, 1967; Crooks and others, 1968; Grossman and others, 1972
Figure 2.2.3.D-1 Aquifer thickness in the Penuelas-Guanica region, Puerto Rico.
2.2.3 Penuelas-Guanica Region 
69
66°55'
50'
45'
40'
10'
05'
18W
17°55'
CARIBBEAN SEA
35'
EXPLANATION
DISTRIBUTION OF AQUIFER HYDRAULIC 
CONDUCTIVITY, IN FEET PER DAY
66°30'
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TROPICAL FOREST LIMITS 
PERENNIAL STREAM 
EPHEMERAL STREAM 
DRAINAGE TUNNEL
TOWN OR CITY
01234 KILOMETERS 
h^           
01234 MILES
Modified from Bennett, 1976; Quinones-Aponte, 1986a
Figure 2.2.3.D-2 Regional distribution of apparent hydraulic conductivity in the Penuelas-Guanica region, Puerto Rico.
70 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.3.E Ground-Water Levels and 
Movement
Ground-water levels in the alluvial deposits range 
from 1 00 feet above mean sea level in the upper valley 
areas to near mean sea level along the coast (fig. 
2.2.3.E-1). In the Rio Guayanilla, Rio Macana, and Rio 
Tallaboa, ground-water levels are as high as 40 feet 
above mean sea level in upper valley areas during 
average dry periods (fig. 2.2.3.E-1) and 10 feet above 
mean sea level during very dry years (fig. 2.2.3.E-2). 
Ground-water levels in the upper parts of the Rio Yauco 
and Rfo Loco valleys are as high as 100 feet above 
mean sea level during dry periods and 25 feet above 
mean sea level during droughts. 
Average seasonal 
ground-water level fluctuations in the Penuelas-Guanica 
region are as high as 40 feet in the Rio Yauco valley. 
Throughout the Rfo Yauco valley, ground-water levels 
fluctuated from 10 to 36 feet below land surface during 
1975 
to 
1985 
(Quinones-Aponte, 
1986b, 
p. 
8). 
Seasonal 
ground-water 
level 
fluctuations 
in 
the 
Penuelas-Guanica region are affected by pumpage. 
The water table is generally at its lowest level during 
February.
Ground-water recharge and discharge in the 
Penuelas-Guanica region vary throughout the year in 
response to precipitation, pumping, and streamflow 
diversions. 
Greater stream seepage into the aquifer 
was observed in upper valley areas during low 
streamflow conditions (Grossman and others, 1972, p. 
48; Quinones-Aponte, 1986b, p. 8), although streams 
are generally gaining, rather than loosing, water in lower 
reaches. 
Aquifer recharge from stream seepage is 
affected by the regulation of streamflow at headwaters 
and diversions to irrigation channels in the Rfo Tallaboa, 
Rio Yauco, and Rfo Loco valleys. Aquifer recharge by 
rainfall in the Penuelas-Guanica region is minimal, 
because of high evapotranspiration rates and low rainfall 
frequency, intensity, and duration. Ground-water flows 
predominantly toward the sea, from recharge to 
discharge areas, following the general topography and 
drainage of the alluvial valley floors.
66°55'
10'
05'
18W
17°55'
50'
T~
45'
40'
~T
35'
66°30'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly cased well. 
Contour interval is variable. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TROPICAL FOREST LIMITS 
PERENNIAL STREAM 
EPHEMERAL STREAM 
DRAINAGE TUNNEL 
TOWN OR CITY
CARIBBEAN SEA
01234 KILOMETERS
I '           
01234 MILES
Modified from Gomez-Gomez and Heisel, 1976
Figure 2.2.3.E-1 Altitude of water-level surface and direction of ground-water flow during February 1976 in the Penuelas- 
Guanica region, Puerto Rico.
2.2.3 Penuelas-Guanica Region 
71
66°55'
50'
45'
40'
35'
66°30'
10'
05'
18W
17°55'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly cased well. 
Contour interval is variable. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TROPICAL FOREST LIMITS 
PERENNIAL STREAM
EPHEMERAL STREAM 
DRAINAGE TUNEL
TOWN OR CITY
CARIBBEAN SEA
J___________i____
01234 KILOMETERS
I ii ii ___
01234 MILES
Modified from Gomez-Gomez and Heisel, 1976
Figure 2.2.3.E-2 Water-level contour during February 1968 and direction of ground-water flow in the Penuelas-Guanica 
region, Puerto Rico.
72 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.2.3.F Soil Permeability
The most prominent soil associations overlying the 
aquifer areas in the Pehuelas-Guanica region are 
Aguilita-Tuque, Constancia-Jacaguas-San Anton, and 
the Fraternidad-Aguirre-Cartagena (fig. 2.2.3.F-1). The 
Aguilita-Tuque soils are steep to very steep, well 
drained, moderately alkaline, loamy and clayey soils 
with some gravel and pebbles (Gierbolini, 1979). These 
soils occupy foot slopes, side slopes, hilltops, and 
overlie the limestone and alluvial deposits in the Rfo 
Tallaboa valley. The Constancia-Jacaguas-San Anton 
association overlies the alluvial deposits in the Rfo 
Guayanilla valley and coastal plain. They are nearly 
level, deep to shallow, somewhat poorly- to well- 
drained, neutral to moderately alkaline, loamy and 
clayey soils. These clayey to loamy soils are the best 
for farming in the area. Both the Aguilita-Tuque and the 
Constancia-Jacaguas-San Anton soil associations have 
permeabilities ranging from 0.60 to 2.00 in/hr (table 
2.2.3.F-1). The Fraternidad-Aguirre-Cartagena soils are 
moderately well drained to poorly drained, nearly level 
to sloping, 
calcareous alluvial 
soils. 
This soil 
association has the lowest permeability for this region 
ranging from 0.06 to 0.20 in/hr.
66°55'
50'
45'
40'
35'
66°30'
10'
05'
18W
17'55"
EXPLANATION
         SOIL ASSOCIATION BOUNDARY
_.    .   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
CARIBBEAN SEA
SOIL ASSOCIATIONS
SEMIARID COASTAL PLAINS
G-2 FRATERNIDAD-AGUIRRE-CARTAGENA 
G-3 FE-GUANICA-AGUIRRE 
J-1 CONSTANCIA-JACAGUAS-SAN ANTON 
L-1 AGUILITA-TUQUE
HUMID UPLANDS
M-1 CAGUABO-MUCARA
M-3 CAGUABO-MUCARA-QUEBRADA
N-1 CONSUMO-HUMATAS
N-5 HUMATAS-MARICAO-LOS GUINEOS
SEMIARID UPLANDS
R-4 DESCALABRADO-JACANA-SAN GERMAN 
R-6 DESCALABRADO
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.20 
FROM 0.20 TO 0.80 
FROM 0.60 TO 2.00
01234 KILOMETERS
4 MILES
Modified from Gierbolini, 1979; Carter, 1965
Figure 2.2.3.F-1 Soil associations and permeability in the Pefiuelas-Guanica region, Puerto Rico.
2.2.3 Pefiuelas-Guanica Region 
73
Table 2.2.3.F-1 
Thickness, permeability, and available water capacity for the soil 
associations in the Pefiuelas-Guanica region, Puerto Rico (Modified from Gierbolini, 1979)
Area and soil association
Semiarid Coastal Plains
Fraternidad-Aguirre-Cartagena
Fe-Guanica-Aguirre
Constancia-Jacaguas-San Anton
Aguilita-Tuque
Humid Uplands
Caguabo-Mucara
Caguabo-Mucara-Quebrada
Consumo-Humatas
Humatas-Maricao-Los Guineos
Semiarid Uplands
Descalabrado-Jacana-San German
Descalabrado
Thickness 
(inches)
Oto70
Oto56
Oto65
Oto60
Oto36
Oto60
Oto60
Oto72
Oto28
Oto20
Permeability 
(inch per hour)
0.06 to 0.20
0.06 to 0.20
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
Available 
water capacity 
(inch per inch)
0.10 to 0.18
0.12 to 0.18
0.08 to 0.1 4
0.11 to 0.1 4
0.03 to 0.1 7
0.03 to 0.1 7
0.09 to 0.1 8
0.12 to 0.16
0.08 to 0.1 7
0.09 to 0.11
74 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3 West Coast Area
2.3 West Coast Area 
75
2.3.1 ANASCO REGION
By Thalia D. Veve
2.3.1.A Location and Major Geographic 
Features
The Afiasco region is located on the west coast 
area of Puerto Rico between latitudes 18°20'N and 
18°05'N and longitudes 67°15'W and 66°45'W. The 
two principal river basins in the region are the 
Rio Grande de Afiasco and the Rfo Yaguez (fig. 
2.3.1.A-1).
The Rfo Grande de Afiasco originates near the 
Cordillera Central, flows west, and discharges into 
the Bahfa de Afiasco. 
The upper reaches of the 
basin contain four reservoirs connected by pipelines; 
the Lago Toro, Lago Prieto, Lago Guayo, and Lago 
Yahuecas. The Rio Grande de Afiasco alluvial valley 
covers an area of approximately 18 mi2. 
It is 
bounded by hills to the north, east, and south, and by 
Bahfa de Afiasco to the west. The two prominent 
mountain ranges are the Cadena de San Francisco 
and the Atalaya mountains to the north, and the 
Colinas de Uroyan to the southeast. The tributaries 
of the Rfo Grande de Afiasco that flow into the lower 
valley are the Rfo Daguey and the Rfo Cafias. The 
Cafio La Puente and Cano Boquilla are smaller 
streams within the valley.
The Rfo Yaguez originates near the town of 
Maricao, flows west, and discharges into the Bahfa 
de Mayaguez. The Rfo Yaguez alluvial valley covers 
an area of about 2 mi2. The valley is bounded by hills 
to the north, east, and south, and by Bahfa de 
Mayaguez to the west.
Elevations within the alluvial valleys range from 
mean sea level to 65 feet above mean sea level. The 
highest elevation in the mountains located within the 
Afiasco region is Monte Guilarte in the Cordillera 
Central at 3,953 feet above mean sea level.
The two principal population centers in the Afiasco 
region are the town of Afiasco and the city of Mayaguez. 
Afiasco is located upstream of the confluence between 
the Rfo Daguey and Rfo Grande de Afiasco. Mayaguez 
is located on the coast and is much larger than Afiasco, 
covering almost all of the Rfo Yaguez alluvial valley.
ATLANTIC OCEAN
CARIBBEAN SEA
67°10'
05'
67°00'
55'
50'
66*45'
18°20'
15'
01234 KILOMETERS
' 
' 
' 
'
01234 MILES
Base from U.S. Geological Suivey
Puerto Rico e Islas LJmftrofes, 1:240,000,1952
Figure 2.3.1.A-1 Location and major geographic features in the Afiasco region, Puerto Rico.
76 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.l.B Population and Estimated 
Ground-Water Use
The population of the Anasco region totalled 180,480 
in 1980 (U.S. Department of Commerce, 1982; table 
2.3.1.B-1). It grew by 5 percent from 1980 to 1990, when 
the total population was 189,583 (U.S. Department of 
Commerce, 1991). The towns overlying the aquifer areas 
are 
Mayaguez and Anasco, 
which 
in 
1980 
had 
populations of 96,193 and 23,274, respectively. A large 
portion of Mayaguez lies within the Guanajibo region 
(section 2.3.2).
Ground-water use within the Anasco region is limited 
(table 2.3.1.B-2). No public-supply wells were reported 
for the municipio of Anasco from 1980 to 1982 by Torres-
Sierra and Aviles (1986), or in 1983 by Gomez-Gomez 
and others (1984). 
Public-supply wells reported by 
Torres-Sierra and Aviles (1986) and Gomez-Gomez and 
others (1984) for the municipio of Mayaguez are located 
outside the Anasco region or inland from the alluvial 
valley of the Rio Yaguez. Public-water supply within the 
region originated entirely from surface-water sources 
during 1980 to 1983.
Data from the Ground-Water Site Inventory (U.S. 
Geological Survey, written communication, 1990) identify 
several agricultural and industrial wells in the Rfo Grande 
de Anasco lower valley (fig. 2.3.1 .B-1). In the Rio Yaguez 
valley, there are also several industrial and domestic 
wells.
Table 2.3.1.B-1 Population for the Anasco region, Puerto Rico (U.S. Department of 
Commerce, 1982, table 1; U.S. Department of Commerce, 1991, table 1)
1980 population
MUNICIPIO
Adjuntas
Anasco
Lares
Las Marias
Maricao
Mayaguez
Total
TOTAL
18,786
23,274
26,743
8,747
6,737
96,193
180,480
URBAN
5,239
5,646
5,224
799
1,390
82,968
101,266
RURAL
13,547
17,628
21,519
7,948
5,347
13,225
79,214
1990 
population
TOTAL
19,451
25,234
29,015
9,306
6,206
100,371
189,583
67°10'
05'
67W
55'
50'
66°45'
Table 2.3.1.B-2 Ground-water withdrawals and estimated 
population served during 1982 for the Anasco region, Puerto 
Rico (Torres-Sierra and Aviles, 1986) 
[Mgal/d, million gallons per day]
18°20'
15'
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM
LOCATION AND NUMBER OF WELLS AT 
SITE WHEN MORE THAN ONE WELL 
PRESENT
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
01234 KILOMETERS
I ii ii ___
01234 MILES
ADJUNTAS
From U.S. Geological Survey Ground-Water Site Inventory Database, 1990
1 Use
I. Domestic Use
1. Adjuntas
2. Anasco
3. Lares
4. Las Marfas
5. Maricao
6. Mayaguez
II. Commercial Use
1. Adjuntas
2. Anasco
3. Lares
4. Las Marfas
5. Maricao
6. Mayaguez
III. Industrial Use
1. Adjuntas
2. Anasco
3. Lares
4. Maricao
5. Mayaguez
Estimated 
population 
served
3,016
5,367
6,296
1,634
803
27,182
Subtotal 
44,218
151
274
401
101
42
2,169
Subtotal 
3,138
3
18
6
6
86
Subtotal 
119
Total 
47,475
Average 
ground-water 
withdrawals 
(Mgal/d)
0.71
1.01
1.07
0.3
0.16
6.35
9.6
0.03
0.07
0.08
0.02
0.01
0.92
1.13
0.00
0.05
0.00
0.01
1.93
1.99
12.72
Municipios not listed under some specific use do not withdraw 
ground water for the subject use.
Figure 2.3.1.B-1 Approximate well locations in the Anasco region, Puerto Rico.
2.3.1 Anasco Region 
77
2.3.l.C Geologic Setting
Volcanic and volcaniclastic rocks of Cretaceous 
age, most of which were formed or deposited in a marine 
environment, are present throughout the Anasco region 
(fig. 2.3.1.C-1). Small patches of plutonic rocks crop out 
in the upper reaches of the basin. In the Rio Grande de 
Anasco valley, these volcanic and volcaniclastic rocks
are unconformably overlain by alluvial deposits of 
Quaternary age. 
The alluvial fill in the valley is 
composed of clay, silt, and sand with localized gravel 
deposits. Thin corridors of alluvium have been deposited 
along the course of the Rfo Grande de Anasco. Swamp 
deposits are present over relatively large areas of the 
valley. 
Beach deposits are extensive along the coast, 
extending inland as far as 6 miles.
Seismic surveys were used to locate and describe 
the subsurface materials in the lower Rio Grande de 
Anasco valley (Diaz and Jordan, 1987). The surface of 
the volcanic rocks underlying the valley is deeply incised 
to depths of about 350 feet below present mean sea 
level, indicating that the Rio Grande de Anasco cut 
deeply into the valley floor during these lower sea levels. 
A zone of clay, interbedded with limestone, is present in
the central part of the valley along the ancient incision. 
The interbedded clay and limestone layer is about 250 
feet thick. Alluvial deposits of Quaternary age, which 
have 
a thickness of as 
much 
as 
100 feet, 
unconformably overlie the clay and limestone zone 
and the volcanic and volcaniclastic bedrock.
67°10'
05'
67W
55'
50'
66°45'
18°20'
15'
LAS MARIAS
N 
LARES
\m
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
RESERVOIR
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
Holocene
and 
\ QUATERNARY 
Pleistocene J
Eocene
to Lower 
L 
TERTIARY 
Cretaceous 
CRETACEOUS
PERENNIAL STREAM 
TOWN OR CITY
Bahfa 
<"*»  -J
de 
Mayaguez
MAYAGUEZ
01234 KILOMETERS
01234 MILES
MARICAO
ADJUNTAS
V--
XV_\
Modified from Briggs and Akers, 1965
Figure 2.3.1.C-1 Generalized surficial geology in the Afiasco region, Puerto Rico.
78 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3. l.D Hydrogeology
The principal water-bearing units within the lower 
Rio Grande de Anasco valley are the alluvium and the 
underlying limestone beds (Diaz and Jordan, 1987). 
Seismic refraction surveys performed in the lower Rio 
Grande de Anasco valley reveal a saturated zone of 
alluvium which ranges in thickness from 50 to 100 feet 
(figs. 2.3.1.D-1 and 2.3.1.D-2; Di'az and Jordan, 1987). 
The zone between the volcanic and volcaniclastic rocks
and the alluvium is composed of hard clay interbedded 
with soft limestone and is as much as 250 feet thick. The 
amount of ground water available in the Anasco region 
is unknown. No ground-water studies have been 
conducted in the Rio Yagiiez alluvial valley.
The alluvial deposits have very low permeability, 
due to the predominance of fine-grained materials in 
them. Permeability is higher where beds of sand and 
gravel occur locally within the alluvial deposits. Yields of
100 to 150 gal/min have been documented at wells that 
tap these sand and gravel beds (Di'az and Jordan, 1987) 
and are directly proportional to the extent the well 
penetrates the layer. 
The more sand or gravel 
penetrated, the higher the yield.
A shallow aquifer formed by limestone rocks is the 
principal source of ground water in the Anasco region. 
Yields of 500 gal/min have been documented from this 
rock unit (Di'az and Jordan, 1987). The limestone beds
have a maximum thickness of 50 feet. 
The only 
transmissivity value for the aquifers in the Anasco region 
was reported from a pumping test performed on well 7 
(fig. 2.3.1.D-1), which penetrated 50 feet of limestone. 
This test gave an estimated transmissivity of 2,150 ft2/d 
(Di'az and Jordan, 1987, p. 30). 
The hydraulic 
connection between the limestone and the alluvium is 
poor.
67°10'
05'
67W
55'
50'
66°45'
18°20'
15'
67°10'
67°07'30"
EXPLANATION
Bahia
de 
Mayaguez
MAYAGUEZ
01234 KILOMETERS 
I 1           
01234 MILES
EXTENT OF ALLUVIAL DEPOSITS
LINE OF SECTION- 
Shown in figure 2.3.1.D-2
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
WELL AND DESIGNATION 
TOWN OR CITY
Modified from Diaz and Jordan, 1987
Figure 2.3.1.D-1 Location of seismic-refraction survey cross sections and well in the Anasco region, Puerto Rico (line of section shown in figure 2.3.1.D-2).
2.3.1 Anasco Region 
79
A
60 n
SEA LEVEL - 
60 
120 
180 
240 
300 -
500 FEET
SEA LEVEL
240
300
360
100 FEET
_I
B
LU 
LU 
LL
Z
EVATION,
3
LU
60
SEA LEVEL
60
120
180 
240
300
360
SEA LEVEL
300
500 FEET
_I
100 FEET
EXPLANATION
| 
SOIL AND ALLUVIUM
^ SATURATED ALLUVIUM
H HARD CLAY AND SOFT LIMESTONE
H EARLY TERTIARY AND CRETACEOUS ROCKS
100 FEET
_I
Modified from Dfaz and Jordan, 1987
Figure 2.3.1.D-2 Aquifer thickness cross section obtained from seismic -refraction velocity profiles surveys and well information in the Anasco region, Puerto Rico 
(location of section shown in figure 2.3.1.D-1).
80 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.1.E Ground-Water Levels and 
Movement
The recharge to the alluvium in the lower Rfo 
Grande de Afiasco valley is almost entirely derived from 
direct rainfall (Dfaz and Jordan, 1987, p. 31). 
The 
average annual precipitation at the Mayaguez Airport 
located at the lower valley areas was 68 inches for the 
period of 1973-82. 
Because it lies in a rain shadow, 
rainfall at the airport may average 10 to 20 inches less
than that in the central part of the valley. The sources of 
recharge to the limestone aquifer are unknown. 
However, Dfaz and Jordan (1987, p. 31) suggest that 
recharge to this aquifer could originate in the overlying 
alluvium in places where the clay layer is absent and 
where in contact with the volcanic rocks.
Ground-water levels in the lower valley range from 
0 feet near the coast to about 30 feet above mean sea 
level in the upper reaches of the valley (fig. 2.3.1.E-1).
Ground water flows toward the sea and discharges to 
the Rfo Grande de Anasco. 
Ground water also 
discharges to the Cano La Puente and Cano Boquilla, 
where 
swamp 
and 
marsh 
conditions 
prevail. 
Fluctuations in ground-water levels between dry and wet 
seasons average about 1 foot in most places. Dfaz and 
Jordan (1987, p. 27) state that this small degree of 
variation indicates a low permeability of the alluvium.
The hydraulic gradient steepens in the vicinity of the 
Mayaguez Airport (Dfaz and Jordan, 1987; fig. 2.3.1.E- 
1). This rapid change in gradient may be caused by a 
change in the composition of the alluvium from finer to 
coarser sediments.
67°10'
67°05'
67W
66=55'
66°50"
66°45'
67°10'
67°07'30"
18°20'
Mayaguez
MAYAGUEZ
01234 KILOMETERS
i 
i 
i 
i 
i_____
0 
1
4 MILES
0
0
1 
2 KILOMETERS
I 
I
i 
I 
1 
2 MILES
EXPLANATION
15
    15    
EXTENT OF ALLUVIAL DEPOSITS
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly 
cased well during September 3 1981 
(wet season). Contour interval is 
variable. Datum is mean sea level
WATER-LEVEL CONTOUR-Shows altitude 
of water level in feet in tightly 
_ 
cased well during February 11,1982 
(dry season). Contour interval is 
variable. Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
-    -   --  DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
Modified from Di'az and Jordan, 1987
Figure 2.3.1.E-1 Composite altitude of water-level surface for September 1981 and February 1982, and direction of ground-water flow during September 1981 
in the Anasco region, Puerto Rico.
2.3.1 Anasco Region 
81
2.3.l.F Soil Permeability
The soil associations present over the lower Rio Grande 
de Anasco valley are the Coloso-Toa, and the Consumo- 
Humatas associations (fig. 2.3.1.F-1). 
The Coloso-Toa 
almost entirely covers the valley. 
The Coloso-Toa 
association is described by Gierbolini (1975, p. 7) as nearly 
level, loamy soils that are porous. This association is derived 
from the underlying limestone and volcanic rocks and has a 
moderate permeability: values range from 0.60 to 2.00 in/hr. 
The Consumo-Humatas covers the southern part of the 
valley near Carlo Boquilla. 
The Consumo-Humatas 
association is described as strongly leached, sticky, and 
plastic soils underlain by thick layers of weathered rock. 
Most of these soils occur on steep side slopes. 
This
association also has moderate permeabilities ranging from 
0.60 to 2.00 in/hr. 
The available water capacity of both 
associations is very low. The water holding capacity values 
for the Coloso-Toa association range from 0.11 to 0.14 in/in 
of soil, and for the Consumo-Humatas association from 0.09 
to 0.18. The thickness of both soil associations ranges from 
near zero to 60 inches.
Other associations that are present in the Anasco region 
but overlying the volcanic rocks that surround the Rfo 
Grande de Anasco valley are the Caguabo-Mucara, the 
Humatas-Maricao-Los 
Guineos, 
and the 
Nipe-Rosario 
associations. The characteristics of these associations are 
shown in table 2.3.1.F-1.
Table 2.3.1.F-1 Thickness, permeability, and available water capacity for the 
soil associations in the Anasco region, Puerto Rico (Modified from Gierbolini, 
1975)
Area and soil association
Coloso-Toa
Consumo-Humatas
Caguabo-Mucara
Humatas-Maricao-Los Guineos
Nipe-Rosario
Thickness 
(inches)
OtoGO
OtoGO
Oto22
OtoGO
OtoSO
Permeability 
(inch per hour)
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
2.00 to 6.00
Available 
water capacity 
(inch per inch)
0.11 to 0.14
0.09 to 0.1 8
0.03 to 0.1 7
0.09 to 0.1 8
0.11 to 0.13
67°10'
05'
67W
55'
50'
66°45'
18°20'
15'
j 
X
LAS MARIAS
LARES
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
E-1 COLOSO-TOA
HUMID UPLANDS
M-1 CAGUABO-MUCARA
N-1 CONSUMO-HUMATAS
N-5 HUMATAS-MARICAO-LOS GUINEOS
P-1 NIPE-ROSARIO
SOIL PERMEABILITY, 
IN INCHES PER HOUR
| 
FROM 0.60 TO 2.00 
^H 
FROM 2.00 TO 6.00
MAYAGUEZ
01234 KILOMETERS
I ii ii ___
01234 MILES
N-1
SOIL ASSOCIATION BOUNDARY
  DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
ADJUNTAS
Modified from Carter, 1965; Gierbolini, 1975
Figure 2.3.1.F-1 Soil associations and permeability in the Anasco region, Puerto Rico.
82 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.2 GUANAJIBO REGION
By Thalia D. Veve
2.3.2.A Location and Major Geographic 
Features
The Guanajibo region, located on the west coast of 
Puerto Rico, covers an area of approximately 146 mi2. 
The principal population centers in the Guanajibo region 
are San German, Hormigueros, Cabo Rojo, and 
Mayagiiez (fig. 2.3.2.A-1).
The Guanajibo region is characterized by a broad 
alluvial valley (the Central Guanajibo valley) covering 
about 29 mi2. This valley is bounded on all sides by 
hills, except to the northwest, where it is bounded by the 
Mona Passage. 
At the coast, the Guanajibo valley 
extends northward joining the Rfo Yaguez valley. 
A 
barrier of low-lying hills almost completely separates the 
Central Guanajibo Valley from the coast. These hills 
form a ridge called the Cordillera Sabana Alta that 
reaches its greatest elevation in the east. West of these 
hills, the shore features a fringe of beach and swampy 
terrain. 
A large coastal lagoon, Laguna Joyuda, 
dominates the west-central coast areas.
The Central Guanajibo valley measures 18 miles in 
length along its east-west axis, with a width ranging from 
6 miles in the east to 12 miles in the west. The Central 
Guanajibo valley has an area of about 25 mi2. 
Elevations within the valley range from mean sea level 
at the coast to about 200 feet above mean sea level. 
Hills surrounding the valley reach maximum elevations 
of 1,968 feet above mean sea level in the Cordillera 
Central.
The major river in the region is the Rfo Guanajibo, 
flowing to the west-northwest. 
It originates along the 
western side of the Cordillera Central and flows to the 
sea on the west coast, south of Mayagiiez. The principal 
tributaries to the Rfo Guanajibo are the Rfo Rosario, Rfo 
Duey, Rfo Hoconuco, Rfo Cam, Rfo Cupeyes, Rfo 
Cruces, and Rfo Flores, draining to the south- 
southwest, and the Rfo Viejo, draining to the west- 
northwest.
ATLANTIC OCEAN
CARIBBEAN SEA
67°10'
05'
67°00'
66°55'
10'
18°05'
MAYAGUEZ
Pta Guanajibo
£oAM
ftttuM&pr*
Pta Arenas
Pta Ostiones
_ 
Pu«tt__,
.nta Carener0.£ <* 
Pta LA Mela <*^
laniquiHa
Base from U.S. Geological Survey
Puerto Rico e Islas Umftrofes, 1:240,000, 1952
SENATORIAL DISTRICT NUMBER
01234 KILOMETERS
4 MILES
Figure 2.3.2.A-1 Location and major geographic features in the Guanajibo region, Puerto Rico.
2.3.2 Guanajibo Region 
83
2.3.2.B Population and Estimated 
Ground-Water Use
The total population of the municipios within the 
Guanajibo region in 1980 was about 204,000 (table 
2.3.2.B-1; 
U.S. Department of Commerce, 
1982). 
Between 1980 and 1990 the population increased by 7 
percent 
to 
about 
218,000 
(U.S. 
Department 
of 
Commerce, 1991). 
However, a large portion of the
population in the municipios of Mayaguez and Maricao 
is outside the Central Guanajibo valley.
Ground-water 
withdrawals 
in 
Cabo 
Rojo, 
Hormigueros, Mayaguez, and San German totalled less 
than 5.9 Mgal/d in 1982 (table 2.3.2.B-2; Torres-Sierra 
and Aviles, 1986). According to Torres-Sierra and Aviles 
(1986), no ground water was withdrawn in the municipio 
of Mayaguez from 1980 to 1982. 
However, Gomez-
Gomez and others (1984), reported a withdrawal of 0.45 
Mgal/d of ground water for 1981 in that municipio.
During the 1980's, ground water was the only 
source of water for public supply in Cabo Rojo and 
Hormigueros. Public-water supply in Mayaguez is from 
surface-water sources, while in San German both 
surface and ground water contribute in meeting public- 
water demands.
Public-supply sources provided less than 5.46 
Mgal/d for domestic use, while community systems 
supplied less than 0.43 Mgal/d (table 2.3.2.B-3). Water 
used for industry, agriculture (livestock), and commerce 
totalled less than 0.27, 0.25, 0.62 Mgal/d, respectively. 
Approximate well locations by use are shown in figure 
2.3.2.B-1.
Table 2.3.2.B-1 Population for the Guanajibo region, Puerto Rico (U.S. 
Department of Commerce, 
1982, table 
1; 
U.S. Department of 
Commerce, 1991, table 1)
1980 population
MUNICIPIO
Cabo Rojo
Hormigueros
Maricao
Mayaguez
Sabana Grande
San German 
Total
TOTAL
34,045
14,030
6,737
96,193
20,207
32,922
204,134
URBAN
10,292
12,031
1,390
82,968
7,435
13,054
127,170
RURAL
23,753
1,999
5,347
13,225
12,772
19,868
76,964
1990 
population
TOTAL
38,521
15,212
6,206
100,371
22,843
34,962
218,115
Table 2.3.2.B-2 Ground-water withdrawals for public-water 
supply by municipio for 1980, 1981, and 1982 in the 
Guanajibo region, Puerto Rico (Torres-Sierra and Aviles, 1986) 
[Mgal/d, million gallons per day]
Total ground-water withdrawal 
(Mgal/d)
MUNICIPIO
Cabo Rojo
Hormigueros
Maricao
Mayaguez
Sabana Grande
San German
Total
1980
3.72
0.98
0.01
0.00
0.37
1.02
6.10
1981
3.28
1.21
0.00
1 0.45
0.44
1.40
6.78
1982
2.75
1.29
0.00
0.00
0.51
1.54
6.09
1 Value given in Gomez-Gomez and others (1984) for 
1981.
67°10'
05'
67W
66°55'
10'
1805'
Bahia
de 
Mayaguez
^.Jtyuda ^ m ^ p ,1
n -O^CA^ )}
li/ 
-&'k-<a^3*«-^
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM
LOCATION AND NUMBER OF WELLS AT SITE 
WHEN MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL 
TOWN OR CITY
0 12 34 KILOMETERS 
01234 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.3.2.B-1 Approximate well locations in the Guanajibo region, Puerto Rico.
84 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Table 2.3.2.B-3 Ground-water withdrawals and estimated population 
served during 1982 for the Guanajibo region, Puerto Rico (Torres-Sierra 
andAviles, 1986) 
[Mgal/d, million gallons per day;  , no data available; <, less than]
Use
Estimated
population
served
I. Domestic Use
A. Public Supply
1. Cabo Rojo
2. Hormigueros
3. Maricao
4. Mayaguez
5. Sabana Grande
6. San German
B. Community Systems
1. Cabo Rojo
2. Hormigueros
3. Maricao
4. Mayaguez
5. Sabana Grande
6. San German
II. Commercial Use
1. Cabo Rojo
2. Hormigueros
3. Maricao
4. Mayaguez
5. Sabana Grande
6. San German
III. Industrial Use
1. Cabo Rojo
2. Hormigueros
3. Maricao
4. Mayaguez
5. Sabana Grande
6. San German
IV. Agricultural Use (livestock)
1. Cabo Rojo
2. Hormigueros
3. Mayaguez
4. Sabana Grande
5. San German
28,419
13,397
19,653
23,634
Subtotal 
167,455
5,626
633
4,335
9,288
Subtotal
36,679
Subtotal
Subtotal
Average 
ground-water 
withdrawals
(Mgal/d)
1.94
0.84
2 <1 .49
<5.46
0.22
0.03
0.18
2 <0.37
<0.43
0.28
0.04
2 <0.07 
2 <0.23
<0.62
0.03
0.01
2 <0.03 
2 <0.20
<0.27
0.13
0.01
2 <0.04 
2 <0.07
67°10'
10'
18°05'
Bahia
de 
Mayaguez
2.3.2.C Geologic Setting
There are four major lithologically distinct rock groups 
present in the Guanajibo region (fig. 2.3.2.C-1). They are: 
the Bermeja Complex of Jurassic to Early Cretaceous 
age; a suite of volcanic, volcaniclastic, plutonic, and 
sedimentary rocks of Late Cretaceous age; limestone 
formations of Late Cretaceous age; and alluvial deposits 
of Quaternary age.
The 
Bermeja 
Complex 
of 
Jurassic 
to 
Early 
Cretaceous age (Montgomery and others, 1994) consists 
primarily of serpentinite, amphibolite, basalt, and chert. It 
is highly deformed and metamorphism has destroyed 
most primary textures, bedding, and lithological relations. 
It is most extensively exposed in the southwestern part of 
the Guanajibo region.
05'
67W
66°55'
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
LAGOON
Holocene
and 
Pleistocene
Eocene
to Lower
Cretaceous
QUATERNARY
TERTIARY 
CRETACEOUS
  DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM
LINE °.F SECTION-Location of section 
shown in figure 2.3.2.C-2
01234 KILOMETERS
4 MILES
Modified from Briggs and Akers, 1965
Subtotal
<0.25
Total 
104,985
<7.03
1 Municipios not listed under a specific use did not withdraw water for that use.
2 Includes both surface- and ground-water sources.
Figure 2.3.2.C-1 Generalized surficial geology in the Guanajibo region, Puerto Rico.
2.3.2 Guanajibo Region 
85
The suite of volcanic, volcaniclastic, plutonic, and 
sedimentary rocks of Late Cretaceous age predominate 
in the mountains surrounding the Central Guanajibo 
valley (fig. 2.3.2.C-2). 
Subsequent to their formation 
these rocks were folded and faulted (Colon-Dieppa and 
Quinones-Marquez, 
1985), and then subjected to 
extreme weathering 
and 
erosion. 
The 
Central 
Guanajibo valley largely lies within an anticline that has
been breached by erosion and is bounded in part by 
faults (Mattson, 
1960, p. 321; Colon-Dieppa and 
Quinones-Marquez, 1985, p. 10).
The limestone formations of Late Cretaceous age in 
the Central Guanajibo valley include the Penones 
Limestone, Cotui Limestone, Parguera Limestone, and 
Melones Limestone (Curet, 1986; Volckmann, 1984b
and 1984c). While these various formations vary in 
coloration, they are generally massive to thick-bedded 
limestones rich in mollusk fossils. These formations 
overlie the Bermeja Complex and various of the 
volcanic, volcaniclastic, plutonic, and sedimentary rocks.
Alluvial deposits of Quaternary age overlie volcanic 
and volcaniclastic rocks in the southwestern Guanajibo
region and the Bermeja Complex in the Central 
Guanajibo valley (Mattson, 1960; Colon-Dieppa and 
Quinones-Marquez, 1985, p. 18). Clay predominates in 
the surface of the alluvium. These surficial clay deposits 
in the alluvium are generally underlain by sand lenses 
and, at greater depths, gravel lenses within the clay-rich 
alluvium.
Modified from Colon-Dieppa and Quinones-Marquez, 1985
SAND
GRAVEL
CLAY
EXPLANATION
LIMESTONE 
BASALT
1
PRASA 
PUERTO RICO AQUEDUCT 
GROUND-WATER SURFACE 
AND SEWER AUTHORITY
Figure 2.3.2.C-2 Locations of cross section and wells in the Central Guanajibo valley, Puerto Rico (location of 
cross section shown in figure 2.3.2.C-1).
86 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.2.D Hydrogeology
Ground water within the Central Guanajibo valley 
occurs in the limestone formations underlying the 
alluvium and in the sand and gravel lenses within the 
alluvium. 
Where volcanic rocks are highly fractured, 
limited amounts of ground water can be withdrawn. 
Limestone formations and sand and gravel lenses within 
the alluvium are concentrated in the western and 
southwestern parts of the Central Guanajibo valley. 
Clay, a nearly impermeable material, is more abundant 
in alluvial deposits in the northern and eastern
Guanajibo region than in the Central Guanajibo valley. 
The alluvium is about 70 feet thick and the limestone is 
more than 200 feet thick in the Central Guanajibo valley 
and is thickest near Cabo Rojo, where the bedrock lies 
at 500 feet below land surface. These deposits become 
thinner toward the north and west, where they are less 
than 100 feet thick (fig. 2.3.2.D-1).
Aquifer 
characteristics 
in 
the 
southwestern 
Guanajibo region have been estimated from data on 
driller's logs. Yields to wells average from 280 to 660 
gal/min (Colon-Dieppa and Quinones-Marquez, 1985, p.
48). Maximum yields range from 75 to 1,100 gal/min 
and specific capacities from 2.4 to 40 gal/min per foot of 
drawdown 
(Colon-Dieppa 
and 
Quinones-Marquez, 
1985, p. 40). Transmissivities ranging from 670 to 6,000 
ft2/d were estimated from the specific capacities of the 
Puerto Rico Aqueduct and Sewer Authority wells drilled 
in the southwestern part of the Central Guanajibo valley 
(fig. 2.3.2.D-2; Colon-Dieppa and Quinones-Marquez, 
1985, p. 40). The aquifer in the Central Guanajibo valley 
is composed of limestone with some sand and gravel. 
Apparent transmissivity estimates for two wells in Cabo 
Rojo differed by one order of magnitude from 11,000 to
1,600 ft2/d, in spite of being close together. The water 
bearing unit here consists primarily of fractured volcanic 
rock or limestone. 
The difference in performance 
between these two wells may be explained by 
differences in the degree of fracturing of the water 
bearing unit around them.
67°10'
05'
67W
66°55'
67°07'30"
67°02'30"
Bahia
de 
Mayaguez
10'
18°05'
SUBSURFACE CONTOUR-Shows depth to bottom 
of aquifer below land surface, in feet. Dashed 
where approximated. Contour interval is 100 feet. 
Depth referred to 1:20,000 U.S. Geological Survey 
topographic maps
01234 KILOMETERS
01234 MILES
EXTENT OF ALLUVIAL DEPOSITS 
-------- 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
LAGO°N 
          
PERENNIAL STREAM
  
TOWN OR CITY
Modified from Colon-Dieppa and Quinones-Marquez, 1985
Figure 2.3.2.D-1 Approximate depth to bedrock in the Central Guanajibo valley, Puerto Rico.
2.3.2 Guanajibo Region 
87
10'
18°05'
67°10'
05'
67W
66°55'
67°07'30"
67=02'30"
Bahia
de 
Mayaguez
01234 KILOMETERS
I ii ii __
01234 MILES
SABANA 
GRANDE
EXPLANATION
I  ]
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
1,600 
APPARENT AQUIFER TRANSMISSIVITY- 
  ' 
Shows well location and apparent
transmissivity, in feet squared per day
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
Modified from Colon-Dieppa and Quinones-Marquez, 1985
Figure 2.3.2.D-2 Apparent aquifer transmissivity in the Central Guanajibo valley, Puerto Rico.
88 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.2.E Ground-Water Levels and 
Movement
Aquifer recharge to the Guanajibo region originates 
principally along the contact between the alluvium and 
the igneous rocks. Direct recharge from rainfall is not 
believed to occur throughout the valley since clay covers
almost the entire surface. In the few places where more 
permeable materials (limestone or sand and gravel) 
reach the surface, rainfall may recharge the aquifer. 
Annual rainfall in the lower part of the valley averages 56 
inches, and in the upper reaches of the basin, annual 
rainfall ranges from 70 to 100 inches (Colon-Dieppa and 
Quinones-Marquez, 1985, p. 6 and 20).
Ground-water levels within the Central Guanajibo 
valley range from 16 feet above mean sea level west of 
Hormigueros to 115 feet above mean sea level north of 
San German (fig. 2.3.2.E-1). Ground water moves from 
the surrounding hills to the center of the valley and then 
moves towards the coast following the general 
topography of the region. The water-table gradient
generally is about 14 ft/mi (Colon-Dieppa and Quinones- 
Marquez, 1985).
67°10'
05'
67°00'
66°55'
10'
18°05'
67°07'30"
05'
67°02'30"
Bahia
de 
Mayaguez
HORMIGUEROS
0
0
1 
2
I 
l
1
KILOMETERS
i 
2 
MILES
  CAEO ROJO
- 
^AN
" ''XOtRJVlAN^
~\
x\^''
EXPLANATION
 115-
0 
1 
2
3 4 KILOMETERS
i 
i____
0 
1
4 MILES
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly 
cased well. Contour interval is variable. 
Datum is mean sea level
GENERALIZED DIRECTION 
OF GROUND-WATER FLOW
------   
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
Modified from Colon-Dieppa and Quinones-Maiquez, 1985
Figure 2.3.2.E-1 Altitude of water-level surface and direction of ground-water flow during June 1980 in the Central Guanajibo 
valley, Puerto Rico.
2.3.2 Guanajibo Region 
89
2.3.2.F Soil Permeability
The soil association overlying the Guanajibo region 
is the Coloso-Toa (fig. 2.3.2.F-1). This association is 
described by Gierbolini (1975, p. 7) as nearly level, 
porous soils that are loamy throughout. 
Scattered 
ponded areas are present in these soils that are 
frequently flooded 
and, 
subsequently, 
subject to 
sediment deposition. 
These soils were formed in 
sediments derived from limestone and volcanic rocks. 
The 
Coloso-Toa 
association 
has 
moderate 
permeabilities ranging from 0.60 to 2.00 in/hr (table 
2.3.2.F-1). Depth from surface ranges from near zero to 
60 inches and available water capacity ranges from 0.11 
to 0.14 in/in of soil.
67°10'
05'
67W
66°55'
10'
Table 2.3.2.F-1 Thickness, permeability, and available water capacity for 
the soil associations in the Guanajibo region, Puerto Rico (Modified from 
Gierbolini, 1975)
Area and soil association
Humid Coastal Plains
Coloso-Toa
Voladora-Moca
Humid Uplands
Caguabo-Mucara
Consumo-Humatas
Nipe-Rosario
Semiarid Uplands
Descalabrado
Descalabrado-Jacana-San German
Thickness 
(inches)
OtoGO
Oto64
Oto22
OtoGO
OtoSO
Oto20
Oto34
Permeability 
(inch per hour)
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
2.00 to 6.00
0.60 to 2.00
0.20 to 0.60
Available 
water capacity 
(inch per inch)
0.11 to 0.14
0.11 to 0.1 7
0.03 to 0.1 7
0.09 to 0.1 8
0.11 to 0.13
0.09 to 0.1 6
0.03 to 0.1 6
18°05'
1MARICAO
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
E-1 COLOSO-TOA 
F-1 VOLADORA-MOCA
HUMID UPLANDS 
M-1 CAGUABO-MUCARA 
N-1 CONSUMO-HUMATAS 
P-1 NIPE-ROSARIO
SEMIARID UPLANDS 
R-1 DESCALABRADO 
R-4 DESCALABRADO-JACANA-SAN GERMAN
SOIL PERMEABILITY, 
IN INCHES PER HOUR
B 
FROM 0.20 TO 0.60 
| 
FROM 0.60 TO 2.00 
H 
FROM 2.00 TO 6.00 
     SOIL ASSOCIATION BOUNDARY
SABANA 
GRANGE
~R-4
-    -   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
  
TOWN OR CITY
01234 KILOMETERS
I ii ii ___
01234 MILES
Modified from Gierbolini, 1975; Gilberto Acevedo, Soil Conservation Service, written communication, 1990
Figure 2.3.2.F-1 Soil associations and permeability in the Guanajibo region, Puerto Rico.
90 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.3 LAJAS REGION
By Robert P. Graves
2.3.3.A Location and Major Geographic 
Features
The most prominent geographic feature of the 76 
mi2 Lajas region is the Valle de Lajas (fig. 2.3.2.A-1). 
The valley, oriented along an east-west axis, is 
approximately 18 miles long and ranges from 1 to 3 
miles wide. The valley is open at both ends, draining 
into the Rio Loco and Bahfa de Guanica to the east and 
Bahfa de Boqueron to the west. Foothills on the north 
and south sides of the valley rise to a maximum 
elevation of 980 and 820 feet above mean sea level, 
respectively. The elevation of the central valley floor 
varies from mean sea level to about 43 feet above mean 
sea level along the east-west drainage divide that is 
located 6.5 miles east of Bahfa de Boqueron. North and 
south of the central valley floor, the land surface rises to 
elevations of as much as 164 feet above mean sea level 
at the base of the bordering foothills.
Surface-water flow in the Valle de Lajas is both 
natural and man-induced. Natural streams that flow out 
of the foothills into the Valle de Lajas are small and 
ephemeral. Man-induced surface-water flow is evident 
in a gravity-fed irrigation canal that extends westward 
from Lago Loco to Bahfa de Boqueron along the base of 
the northern foothills. 
Further, drainage canals have 
been constructed within the valley. 
The principal 
drainage canal extends east-west along the southern 
edge of the valley and the direction of flow is controlled 
by the central drainage divide in the valley. Surface- 
water bodies within the Valle de Lajas include Laguna 
Cartagena and a mangrove swamp near Bahfa de 
Boqueron.
ATLANTIC OCEAN
CARIBBEAN SEA
67°10'
67°00'
66°55'
18°05'  
18°00'
17°55'  
l^^yy Isla Guayacan 
Pta Toc6n
CARIBBEAN SEA
01234 KILOMETERS
Base from U.S. Geological Survey
Puerto Rico e Islas LJmftrofes, 1:240,000, 1952
Figure 2.3.3.A-1 Location and major geographic features in the Lajas region, Puerto Rico.
2.3.3 Lajas Region 
91
2.3.3.B Population and Estimated 
Ground-Water Use
The total population of the municipios within the 
Lajas region increased from about 74,000 in 1980 to 
84,000 in 1990 (U.S. Department of Commerce, 1982 
and 1991), an increase of 13 percent (table 2.3.3.B-1). 
However, the population within the Lajas region 
drainage basin was estimated to be approximately 
30,000 in 1980; the majority living in the town of Cabo 
Rojo. In general, ground-water use in the Lajas region is 
limited. 
High concentrations of dissolved solids in 
ground water make it unsuitable for most uses (Graves, 
1991). 
Daily ground-water pumpage in 1986 for 
municipal, domestic, and agricultural supply was 0.79, 
0.16, and 2.00 Mgal/d, respectively (Graves, 1991). The 
locations of wells supplying water for these uses are 
shown in figure 2.3.2.B-1. 
Ground-water withdrawals 
from public-supply wells are shown by municipio in table 
2.3.3.B-2. These totals include water withdrawn from 
wells that are located in the Lajas region.
Table 2.3.3.B-1 
Population for the Lajas region, Puerto Rico (U.S. 
Department of Commerce, 1982, table 1; U.S. Department of Commerce, 
1991, table 1)
1980 population
MUNICIPIO
Cabo Rojo
Guanica
Lajas
Total
TOTAL
34,045
18,799
21 ,236
74,080
URBAN
10,292
9,628
4,275
26,175
RURAL
23,753
9,171
16,961
49,885
1QQO
population
TOTAL
38,521
19,984
23,271
83,766
67°10'
05'
67W
66°55'
18°05'
18W
Table 2.3.3.B-2 Ground-water withdrawals for public 
supply during 1983 in the Lajas region, Puerto Rico 
[Mgal/d, million gallons per day]
MUNICIPIO
Average ground- 
water withdrawals 
(Mgal/d)
17'55'
Cabo Rojo
Lajas
Guanica
Total
2.84
0.79
1 12.3
15.93
1 Modified from McClymonds (1967) and Graves 
(1991).
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM
O 
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
	MORE THAN ONE WELL PRESENT
O 
PUBLIC-SUPPLY WELL
® 
INDUSTRIAL WELL
© 
AGRICULTURAL WELL
  
DOMESTIC WELL
  
TOWN OR CITY
01234 KILOMETERS
i 
i 
i 
i 
i____
0 
1
4 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.3.3.B-1 Approximate well locations in the Lajas region, Puerto Rico.
92 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.3.C Geologic Setting
A simplified description of the geology of the Lajas 
region follows. The four major lithologically distinct rock 
groups present in the Lajas region are the Bermeja 
Complex of Jurassic to Early Cretaceous age; a suite of 
volcanic, volcaniclastic, plutonic, and sedimentary rocks 
of Late Cretaceous age; limestone formations of Late 
Cretaceous to Tertiary age; and alluvial deposits of 
Quaternary age (fig. 2.3.3.C-1).
The Bermeja Complex of Jurassic to Early 
Cretaceous age (Schellekers and others, 1990) consists 
primarily of serpentinite, amphibolite, basalt, and chert. 
It is highly deformed and metamorphism has destroyed 
most 
primary textures, 
bedding, 
and 
lithological 
reactions. It is most extensively exposed in the southern 
part of the Lajas region in the Sierra Bermeja.
The basement rock under the central Valle de Lajas 
is igneous rock (quartz diorite or andesite; Graves, 
1991). The volcanic, volcaniclastic, 
plutonic, 
and 
sedimentary rocks outcrop on the ridges to the north of 
the valley (Volckmann,1984a).
Limestone of Tertiary and Cretaceous age and 
quartz sand deposits of Tertiary age are found locally in 
the 
surrounding 
ridges. 
The 
limestone 
deposits 
described by Volckmann (1984a) in the Lajas region are 
the Guanajibo Formation, Ponce Limestone, Sabana 
Grande 
Formation, 
Cotuf 
Limestone, 
Melones 
Limestone, and the Parguera Limestone. The quartz 
sand deposits consist of extremely angular, moderately 
sorted, quartz grains and minor amounts of hematite, 
limonite, or clay.
Alluvial deposits of Holocene and Pleistocene age 
fill the valley and consist mainly of silt and clay and have 
fine sand lenses grading into sand and gravel fan 
deposits on the north and south sides of the valley. 
Results of test drilling in the Valle de Lajas revealed that 
the alluvial deposits can exceed 210 feet in thickness 
(Graves, 1991).
67°10'
05'
6700'
66°55'
18°05'
18°00'
17°55'
_i  *.. *.* v W ^ ^P
htO-/ ^^°A- (\
CARIBBEAN SEA 
EXPLANATION
GUANICA
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS 
BLANKET DEPOSITS
Holocene
and 
Pleistocene
QUATERNARY
LAGOON
-   DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PONCE LIMESTONE 
] Miocene 
f 
and
MARINE SEDIMENTARY ROCKS
J Oligocene
PERENNIAL STREAM
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
BERMEJA COMPLEX 
_J__________
Eocene
to Lower
Cretaceous
Jurassic
to Early
Cretaceous
TERTIARY 
CRETACEOUS
H A' LINE OF SECTION-Location of 
section shown in figure 2.3.3.D-1
TOWN OR CITY
01234 KILOMETERS
4 MILES
Modified from Briggs and Akers, 1965
Figure 2.3.3.C-1 Generalized surficial geology in the Lajas region, Puerto Rico.
2.3.3 Lajas Region 
93
2.3.3.D Hydrogeology
The principal aquifer in the Lajas region is a 
nonhomogeneous, 
anisotropic 
confined 
aquifer 
comprised of alluvial deposits. The upper confining unit 
of the aquifer consists of clay deposits. 
The alluvial 
deposits are in hydraulic connection with underlying 
limestone deposits or quartz-sand deposits; however, it 
is suspected that because of the difference in rock type, 
significant differences could exist between the hydraulic 
characteristics of these geologic units. Because of this,
the 
underlying 
sedimentary 
deposits 
could 
be 
considered a distinct aquifer. Geohydrologic data for the 
sedimentary deposits in the Valle de Lajas are available 
for only two deep test wells. Therefore, only the alluvial 
aquifer will be discussed here.
There are few data available delimiting the 
thickness of the alluvial aquifer or its upper clay 
confining unit throughout the valley. 
Test drilling 
indicates that the top of the alluvial aquifer ranges from 
27 to 90 feet below land surface and the base of the
aquifer is at depths greater than 210 feet (Graves, 1991; 
fig. 2.3.3.D-1).
Hydraulic characteristics have been determined 
only for the alluvial aquifer. Aquifer tests and specific- 
capacity tests completed by Graves (1991) indicate 
aquifer transmissivities ranging from 670 to 8,020 ft2/d 
and a storage coefficient of 9.3 x 10~4 (fig. 2.3.3.D-1 and 
table 2.3.3.D-1).
Table 2.3.3.D-1 Transmissivity of the alluvial 
aquifer estimated from specific-capacity data 
(estimates based on method by Meyer, 1963) 
[ft2/d, feet squared per day; [(gal/min)/ft], gallons per minute 
per foot of drawdown]
Well number 
Specific capacity 
(fig. 2.3.3.D-2) 
[(gal/min)/ft]
30 
31
36 
45
53
71
73 
100
102
103
105
6 
20
25 
9
5
5
7
2
3
3
Transmissivity 
(ffrd)
1,740 
7,350
8,020 
2,406
1,340
1,340
7,500 
2,005
670
935
935
67°10'
05'
67W
66°55'
18°05'
QUATERNARY AGE 
) H^L
UNDIFERENT1ATED 
/ XnTj\/IAL
V 
ALLUVIAL DEPOSITS 
/ ^S^
AGE SEDIMENTARY ROCK
_
IGNEOUS ROCK
700
800
900
3 KILOMETERS
3 MILES
18W
17°55'
VERTICAL SCALE GREATLY EXAGGERATED
Alluvial clay 
deposits
Alluvial sand 
deposits
Alluvial gravel
and pebble deposits
Type of alluvial 
deposits unknown
EXPLANATION
Claystone 
^^ 
Sandstone 
^1
Siltstone 
^H
Gravel and 
   
pebbles 
^|
Fossiliferous 
limestone
Calcarenite
Argillaceous 
limestone
Limestone
Igneous rock
_ _ Estimated
lithostratigraphic 
contact
Figure 2.3.3.D-1 Aquifer thickness in the Lajas region, Puerto Rico (line of section 
shown in figure 2.3.3.C-1).
CARIBBEAN SEA
GUANICA
EXPLANATION
|105
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
APPARENT AQUIFER TRANSMISSIVITY- 
Shows well location and apparent 
transmissivity, in feet squared per day
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
01234 KILOMETERS
01
34 MILES
Figure 2.3.3.D-2 Transmissivity in the Valle de Lajas area, Puerto Rico.
94 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.3.3.E Ground-Water Levels and 
Movement
The altitude of the potentiometric surface of the Lajas 
region alluvial aquifer is more than 50 feet above mean 
sea level in the northern and southern parts of the valley, 
about 12 feet above mean sea level in the central part of 
the valley, and is approximately at mean sea level near 
Bahia de Boqueron. 
The main direction of horizontal 
ground-water flow is from the foothills toward the center of 
the valley and then, either east to the Bahia de Guanica or 
west to Bahia de Boqueron (fig. 2.3.3.E-1).
Although long-term fluctuations in the potentiometric 
surface of the Valle de Lajas alluvial aquifer cannot be 
evaluated because of the lack of historical data, seasonal 
fluctuations in the potentiometric surface are evident. 
Water-level data collected from 1981 to 1986 indicate that 
heads generally begin to decline in December or January 
and reach a low in June, July, or August. Recovery of the 
potentiometric surface usually begins in September.
The Valle de Lajas alluvial aquifer is recharged by 
streamflow and rainfall. Anderson (1977) estimated the 
annual recharge to the aquifer to be about 2 inches. Most 
of this recharge is through the coarse-grained alluvial fan 
deposits that lie near the edge of the alluvial valley. In the 
central part of the valley, recharge to the aquifer from 
rainfall is limited by the less permeable clays near the 
surface of the alluvial deposits.
Ground-water discharge can occur through pumpage, 
evapotranspiration, and subsurface seepage. Subsurface 
seepage occurs at Laguna Cartagena, along the extensive 
drainage canal system in the Valle de Lajas, and at the 
mangrove 
swamp 
at 
Boqueron 
(Anderson, 
1977). 
Subsurface seepage also occurs in the form of base flow 
to Bahfa de Boqueron in the western part of the valley and 
to the Rio Loco and Bahia de Guanica in the eastern part 
of the valley.
67°10*
05"
67W
66°55'
18°05'
18W
17°55'
CARIBBEAN SEA
GUANICA
EXPLANATION
 30 - -
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
WATER-LEVEL CONTOUR-Shows potentiometric 
surface, in feet. Contour interval variable. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
01234 KILOMETERS
01
4 MILES
Modified from Graves, 1991
Figure 2.3.3.E-1 Potentiometric surface and direction of ground-water flow during March 1986 
in the Lajas region, Puerto Rico.
2.3.3 Lajas Region 
95
2.3.3.F Soil Permeability
Soils in the Lajas region are of three types. The 
most prominent soil types in the valley are the 
Fraternidad-Aguirre-Cartagena 
and 
Fe-Guanica- 
Aguirre soil associations that have a slow soil 
permeability of 0.06 to 0.20 in/hr (fig. 2.3.3.F-1). The 
Fraternidad-Aguirre-Cartagena association is described 
by Carter (1965, p. 5) as moderately well drained to 
poorly drained, nearly level to sloping, calcareous 
alluvial soils. 
The Fe-Guanica-Aguirre association is 
described as moderately well drained to poorly drained, 
nearly level, saline-alkali and nonsaline alluvial soils. 
The third soil type is the Bahfa-Guayabo-Sosa soil 
association which has rapid soil permeabilities ranging 
from 5.00 to 10.00 in/hr. This association is described 
as well drained to excessively drained, level to sloping, 
sandy soils.
Table 2.3.3.F-1 Thickness, permeability, and available water capacity for soil 
associations in the Lajas region, Puerto Rico (Modified from Carter, 1965)
Soils in the ridges surrounding the Valle de Lajas 
are also of three types. The most prominent soil types 
in the ridges are the Descalabrado-Jacana-San German 
and Guayama-Aguilita-Amelia soil associations which 
have moderately slow soil permeabilities ranging from 
0.20 to 0.60 in/hr. 
The third soil type is the 
Descalabrado 
soil, 
which 
has 
moderate 
soil 
permeabilities 
ranging 
from 
0.60 
to 
2.00 
in/hr. 
Thickness and available water for each one of the soils 
in this area are shown in table 2.3.3.F-1.
67°10'
05'
67W
66°55'
18°05'
18°00'
Area and soil association
Semiarid Coastal Plains
Fraternidad-Aguirre-Cartagena
Fe-Guanica-Aguirre
Bahfa-Guayabo-Sosa
Semiarid Uplands
Descalabrado
Descalabrado-Jacana-San German
Guayama-Aguilita-Amelia
Thickness 
(inches)
Oto70
Oto56
Oto50
Oto12
Oto12
Oto46
Permeability 
(inch per hour)
0.06
0.06
5.00
0.60
0.20
0.20
to
to
to
to
to
to
0.20
0.20
10.00
2.00
0.60
0.60
Available 
water capacity 
(inch per inch)
0.16 to 0.18
0.1 2 toO.
0.00 to 0.
0.07 to 0.
0.07 to 0.
0.08 to 0.
18
13
,17
17
,17
1755'
CARIBBEAN SEA
EXPLANATION
SOIL ASSOCIATIONS
SEMIARID COASTAL PLAINS
G-2 FRATERNIDAD-AGUIRRE-CARTAGENA
G-3 FE-GUANICA-AGUIRRE
K-1 BAHI'A-GUAYABO-SOSA 
SEMIARID UPLANDS
R-1 DESCALABRADO
R-4 DESCALABRADO-JACANA-SAN GERMAN
R-5 GUAYAMA-AGUILITA-AMELIA
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.20
FROM 0.20 TO 0.60
FROM 0.20 TO 0.80
FROM 0.60 TO 2.00
FROM 5.00 TO 10.00
SOIL ASSOCIATION BOUNDARY
TOWN OR CITY
Modified from Carter, 1965; Gierbolini, 1975; Gilberto Acevedo, Soil Conservation Service, written communication, 1990
Figure 2.3.3.F-1 Soil associations and permeability in the Lajas region, Puerto Rico.
96 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.4 East Coast Area
2.4 East Coast Area 
97
2.4.1 NAGUABO-MAUNABO REGION
By Angel Roman-Mas
2.4.1.A Location and Major Geographic 
Features
Prominent geographic features of the 150 mi2 
Naguabo-Maunabo region are the Sierra de Luquillo 
and Sierra de Cayey mountain ranges, that form the 
inland backbone of the province, and three coastal 
alluvial valley systems in the vicinity of Humacao- 
Naguabo, Yabucoa, and Maunabo. Within a few miles, 
steep mountain slopes give way to a series of broad, 
relatively flat alluvial valleys separated from one 
another by steep, narrow bedrock ridges. 
Swamps 
and lagoons are prominent coastal features in the 
alluvial valleys, which comprise about one-third of the 
Naguabo-Maunabo region and contain the principal 
aquifers, major cities, industrial development, and most 
of the population and agriculture.
The 
Humacao-Naguabo 
basin 
covers 
approximately 91 mi2, of which the alluvial valleys 
occupy 36 mi2. There are six distinct drainage basins 
within these alluvial valleys ranging in elevation from 
300 to 500 feet above mean sea level. 
The Rfo 
Humacao and Rio Blanco are the major drainage 
basins, and the Rio Candelero, Rfo Anton Ruiz, Rio 
Santiago, and Quebrada Fronteras are the minor 
drainage basins. 
The interconnected alluvium-filled 
valleys of these six basins range in elevation from 
mean sea level to 160 feet above mean sea level. A 
forested wetland and several brackish water lagoons 
are located near the mouth of the Rfo Anton Ruiz. 
Non-forested 
wetlands 
are 
present 
in 
coastal 
depressions (fig. 2.4.1.A-1).
The Yabucoa alluvial valley occupies 7 mi2 of the 
45 mi2 occupied by the Yabucoa basin. The area is 
surrounded by hills ranging from 100 to 2,000 feet 
above mean sea level, except to the east where it is 
bounded by the Caribbean Sea. There are numerous 
streams in the area, including the Rfo Guayanes (the 
principal stream in the region), Rfo del Ingenio, and 
Cano de Santiago (fig. 2.4.1.A-1).
The Maunabo basin covers about 10 mi2, of 
which 3.5 mi2 is the alluvial valley. 
The area is 
surrounded by hills ranging from 200 to 1,600 feet 
above mean sea level, except to the east where it is 
bounded by the Caribbean Sea. The area is drained 
by the Rfo Maunabo, which has its headwaters at 
Cerro La Torrecilla. Tributaries of the Rfo Maunabo 
head in the foothills to the north and south of the 
alluvial valley.
ATLANTIC OCEAN
NAGUABO-MAUNABO 
REGION
CARIBBEAN SEA
66W
65°45'
18°00'
iaya d« Humacao 
** 
\fCayo Santiago
-
CARIBBEAN 
SEA
Puerto Maunabo 
Cabo Mala Pascua
4, KILOMETERS
4 MILES
Base from U.S. Geological Survey
Puerto Rico e Islas Limftrofes, 1.240,000,1952
Figure 2.4.1.A-1 Location and major geographic features in the Naguabo-Maunabo region, Puerto Rico.
98 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.4.l.B Population and Estimated 
Ground-Water Use
The total population of the Naguabo-Maunabo 
region increased from about 110,000 in 1980 to about 
127,000 in 1990 (table 2.4.1.B-1), an increase of 15 
percent. Ground water supplies about 34 percent of 
the population water-supply needs. Domestic water 
use was about 56 gallons per person per day. In 1983, 
approximately 3.8 Mgal/d of ground water was 
pumped in the region; nearly all from the alluvial 
aquifers (fig. 2.4.1.B-1 and table 2.4.1.B-2). A minor 
amount of water for domestic use was obtained from 
plutonic and volcanic rock aquifers in the mountains. 
About 55 percent of ground-water withdrawals were 
for domestic use, 32 percent for industrial use, and 13 
percent for agricultural use.
The Humacao-Naguabo basin accounts for 61 
percent of the total population within the region. About 
35 percent of the population live in urban areas; the 
remaining 65 percent live in rural areas (table 
2.4.1.B-1; 
U.S. Department of Commerce, 1982, 
p. 53-4 and 53-6). The population in the Humacao- 
Naguabo basin increased from about 67,000 in 1980 
to about 78,000 in 1990 (U.S. Department of 
Commerce, 1991), an increase of about 16 percent 
(table 2.4.1.B-1). In 1983, ground-water withdrawals 
were approximately 0.90 Mgal/d, of which 0.14 Mgal/d
were for domestic use (table 2.4.1.B-2). The aquifers 
provided water to only 3.9 percent of the population. 
Industrial use was about 0.62 Mgal/d and was limited 
to a group of pharmaceutical and light industries 
located in the vicinity of Humacao. Agricultural uses 
(livestock and sugarcane) were about 0.14 Mgal/d.
The population by 1980 within the Yabucoa and 
Maunabo basins was 31,425 and 11,813, respectively 
(table 2.4.1.B-1). The populations of Yabucoa and 
Maunabo 
increased 
by 
16 
and 
4.5 
percent 
respectively by 1990. 
Most of the population in 
Yabucoa (78 percent) and Maunabo (75 percent) live 
in rural areas. 
Ground-water withdrawals in the 
Yabucoa basin were about 2.3 Mgal/d in 1983. 
Ground water provides about 78 percent of the water 
demand for domestic use in this area. 
About 1.4 
Mgal/d of the total was withdrawn by the Puerto Rico 
Aqueduct and Sewer Authority for domestic use (table 
2.4.1.B-2). The pharmaceutical, oil refinery, and light 
industries located in the Yabucoa basin withdraw 
about 0.6 Mgal/d. In addition, about 0.4 Mgal/d were 
pumped for agricultural 
use, 
mainly sugarcane 
irrigation. 
In the Maunabo basin, ground-water 
withdrawals were 0.61 
Mgal/d 
by 
1983 
(table 
2.4.1.B-2). 
The Puerto Rico Aqueduct and Sewer 
Authority accounted for all ground-water withdrawals 
in the Maunabo basin.
Table 2.4.1.B-1 Population for the Naguabo-Maunabo region, Puerto Rico (U.S. 
Department of Commerce, 1982, table 1; U.S. Department of Commerce, 1991, 
table 1)
1980 population
MUNICIPIO
Humacao
Maunabo
Naguabo
Yabucoa 
Total
TOTAL
46,134
11,813
20,617
31 ,425
109,989
URBAN
19,147
2,987
4,135
6,797
33,066
RURAL
26,987
8,826
16,482
16,482
76,923
1990 
population
TOTAL
55,203
12,347
22,620
36,483
126,653
66W
65°45'
18W
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
BOUNDARY BETWEEN MUNICIPIOS 
PERENNIAL STREAM
LOCATION AND NUMBER OF WELLS AT SITE 
WHEN MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL
TOWN OR CITY
CARIBBEAN 
SEA
0123
4 KILOMETERS
0 
1
4 MILES
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.4.1.B-1 Approximate well locations in the Naguabo-Maunabo region, Puerto Rico.
2.4.1 Naguabo-Maunabo Region 
99
Table 2.4.1.B-2 Ground-water withdrawals and estimated population served during 
1983 for the Naguabo-Maunabo region, Puerto Rico 
[Mgal/d, million gallons per day;  , no data available]
1 Use and supplier
Estimated
population
served
I. Domestic Use
2 A. Puerto Rico Aqueduct and Sewer 
Authority
Average 
ground-water 
withdrawals
(Mgal/d)
1. Maunabo 
2. Yabucoa 
3. Humacao
3 B. Community Systems 
1. Naguabo
3 C. Private Supplies 
1. Humacao
3 1 1. Industrial Use 
1. Yabucoa 
2. Humacao
3 III. Agricultural Use 
1. Yabucoa 
2. Humacao 
3. Naguabo
10,872 
24,129 
1,918
Subtotal 
36,919 
120
Subtotal 
120 
4 572
Subtotal 
572
Subtotal
Subtotal
Total 
37,61 1
0.610 
1.370 
0.100
2.080 
0.010
0.010 
0.036
0.036
0.600 
0.619
1.219
0.360 
0.115 
0.020
0.495
3.840
1 Municipios not listed under some specific use do not withdraw ground water for the 
subject use.
2 Modified from Gomez-Gomez and others, 1984.
3 Modified from a written communication of the Puerto Rico Department of Health.
4 Based on a water consumption of 52 gallons per person per day.
66W
65°45'
2.4.l.C Geologic Setting
The geology of the Naguabo-Maunabo region is 
described in terms of two basic lithologic types: the 
Eocene to lower Cretaceous plutonic and volcanic 
bedrock outcropping in the mountains and underlying 
the alluvial deposits in the valleys; and the Holocene 
and Pleistocene age alluvial deposits filling the valleys 
(fig. 2.4.1.C-1). 
Small areas of swamp and beach 
deposits are associated with coastal alluvial deposits.
The plutonic rocks are mostly granodiorite and 
quartz diorite of the San Lorenzo Batholith, frequently 
veined with calcite. The volcanic bedrock is a mixture 
of medium- to thick-bedded volcaniclastic tuff, breccia, 
sandstone, and conglomerate, as well as andesitic 
lava flows. Much of the volcanic rock was deposited in 
the sea and, during quiescent conditions, was 
interbedded with limestone (McGonigle, 1978 and 
1979; Rogers and others, 1979).
18W
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
LAGOON
------- DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
CARIBBEAN 
SEA
jr
PERENNIAL STREAM 
TOWN OR CITY
s
0 12 34 KILOMETERS 
01234 MILES
Modified from Briggs and Akers, 1965
Figure 2.4. l.C-1 Generalized surficial geology in the Naguabo-Maunabo region, Puerto Rico.
100 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
The alluvial deposits are composed of poorly 
sorted clay, silt, and sand. In the Humacao-Naguabo 
basin, the alluvial deposits range in thickness from 
near zero at the bedrock-alluvium contact to more than 
160 feet near the coast (Graves, 1989, p. 15). The 
maximum thickness of the alluvium in the Yabucoa 
basin is unknown, but probably exceeds 180 feet 
(Anders, 1971, p. 15). Clean sand beds, as thick as 
50 feet, were reported in this area by Anders (1971, p. 
15). In the Maunabo basin, the alluvial deposits are 
estimated to be as much as 200 feet thick (Adolphson 
and others, 1977, p. 5).
2.4.l.D Hydrogeology
The principal aquifers in the Naguabo-Maunabo 
region are in the alluvial deposits that fill the valleys. 
These aquifers are under water-table conditions, but 
are influenced by the delayed yield of water from clay 
beds 
present 
within 
them 
and 
by 
anisotropy 
characterized by a horizontal component of hydraulic 
conductivity that is several times larger than the 
vertical component. 
These aquifers may range in 
thickness from near zero at the bedrock-alluvium 
contact to 200 feet near the coast and toward the 
central part of the valleys (fig. 2.4.1 .D-1). The aquifers 
in the fractured volcanic and plutonic rocks are 
discussed only briefly in this report because of their 
very low yields, although locally they may represent an 
important water source.
Based on data from Anders (1971), Adolphson 
and others (1977), and Graves (1989), the hydraulic 
conductivity of the bedrock and the alluvial-bedrock 
contact area is estimated at about 5 ft/d throughout the 
region. Average hydraulic conductivity for the alluvial 
deposits is estimated at about 10 ft/d (fig. 2.4.1.D-2). 
Observed differences in the hydraulic conductivity for 
the alluvium result from aerial and vertical variability in 
sediment particle size. 
In 
addition, 
hydraulic 
conductivity values along the major rivers are usually 
high. 
Within the Humacao-Naguabo basin a minor 
increase in hydraulic conductivity to 20 ft/d is observed
along the Ri'o Humacao, Ri'o Blanco, Rfo Santiago, 
and the lower part of the Ri'o Anton Ruiz. 
In the 
Yabucoa basin, hydraulic conductivity is also about 20 
ft/d along the major streams (Ri'o Guayanes and Ri'o 
del Ingenio). 
Along the Maunabo basin, hydraulic 
conductivity averages 100 ft/day (Adolphson and 
others, 1977). Along the major tributaries to the Ri'o 
Maunabo and other streams in the Maunabo basin, 
hydraulic conductivity ranges from 50 to 75 ft/d (fig. 
2.4.1.D-2).
Apparent 
transmissivity 
values 
within 
the 
Humacao-Naguabo basin range from about 600 to 
2,000 ft2/d (Graves, 1989). 
In the Yabucoa basin, 
apparent transmissivity can be as high as 7,000 ft2/d. 
Transmissivity values as high as 20,000 ft2/d were 
calculated for areas adjacent to the Ri'o Maunabo, due 
to large values of hydraulic conductivity.
66W
65°45'
18°00'
EXPLANATION
[.. .' 
I 
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
_ -100- - 
LINES OF EQUAL AQUIFER THICKNESS-Shows 
aquifer thickness, in feet. Dashed where 
approximated. Contour interval is variable
-------- DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
rc-
PERENNIAL STREAM 
TOWN OR CITY
CARIBBEAN 
SEA
0 12 34 KILOMETERS 
01234 MILES
Modified from Graves, 1989; Robison and Anders, 1973; Adolphson and others, 1977
Figure 2.4.1.D-1 Aquifer thickness in the Naguabo-Maunabo region, Puerto Rico.
2.4.1 Naguabo-Maunabo Region 
101
66W
65°45'
18°00'
EXPLANATION
DISTRIBUTION OF AQUIFER HYDRAULIC 
CONDUCTIVITY, IN FEET PER DAY
___ 
LAGOON
------ 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
01234 KILOMETERS 
01234 MILES
Modified from Graves, 1989; Robison and Anders, 1973; Adolphson and others, 1977
Figure 2.4.1.D-2 Regional distribution of hydraulic conductivity in the Naguabo-Maunabo region, Puerto Rico.
102 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66W
65°45'
2.4. l.E Ground-Water Levels and 
Movement
Ground-water levels in the plutonic and volcanic 
rocks in the mountains and uplands follow the 
topography. The water-table surface lies within 50 to 
100 feet below land surface in the ridges and at or 
near land surface in the valleys. 
Ground-water 
discharge from the plutonic and volcanic rocks 
maintains stream base flow in the mountain and 
upland areas. The contribution to ground water from 
the volcanic and plutonic rocks to the alluvial aquifers 
is relatively small compared to the total quantity of 
ground water in the valleys.
Water levels within the alluvial aquifers of the 
Naguabo-Maunabo region vary from 100 feet above 
mean sea level near the bedrock-alluvium contact to 
near mean sea level in coastal areas (fig. 2.4.1.E-1). 
Although the water table fluctuates seasonally due to 
rainfall, pumpage has caused major overall declines in 
the Yabucoa and Maunabo basins. The water table is 
generally at its lowest elevation during the dry months 
of March and April and at its highest elevation in 
September.
Ground water in the alluvial aquifers flows east in 
the Humacao-Naguabo and Yabucoa basins, and 
southeast in the Maunabo basin, towards the coast. 
Ground water may flow toward or away from streams, 
depending on the hydraulic gradient between the 
stream and the adjacent aquifer. Within the Humacao- 
Naguabo basin, a considerable amount of ground 
water discharges to the rivers in the upper reaches of 
the alluvial valleys; whereas in the lower reaches, the 
alluvial aquifer is recharged by streamflow losses 
(Graves, 1989, p. 20). 
In the lower-most reaches, 
swampy areas and lagoons serve as aquifer discharge 
zones (Graves, 1989, p. 48). 
In contrast, rivers in the 
Yabucoa and Maunabo alluvial valleys drain the 
alluvial aquifer. 
According to the water budget 
presented by Anders (1971, p. 38) and Adolphson and 
others (1977, p. 17), discharge from the alluvial 
aquifers into the streams represents 27 and 50 
percent of the annual river flow in Yabucoa and 
Maunabo basins, respectively.
18°00'
EXPLANATION
-wo
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet m tightly cased well. 
Contour interval is variable. Datum is 
mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
CARIBBEAN 
SEA
0123
4, KILOMETERS
4 MILES
Modified from Graves, 1989; Collar and others, 1990; Adolphson and others, 1977
Figure 2.4.1.E-1 
Altitude of water-table surface and direction of ground-water flow in the 
Naguabo-Maunabo region, Puerto Rico (data for the Naguabo to Humacao alluvial valleys are from 
March 1984, for the Yabucoa valley from April 1990, and for the Maunabo valley from June 1974).
2.4.1 Naguabo-Maunabo Region 
103
2.4.1.F Soil Permeability
Soils 
in 
the 
mountain 
and 
upland 
areas 
associated with plutonic rocks, the Pandura-Rock 
Land-Patillas and the Los Guineos-Humatas-Lirios soil 
associations, some of the soils associated with 
volcanic 
rocks, 
such 
as the 
Caguabo-Mucara- 
Naranjito, have permeabilities of 0.6 to 2.0 in/hr. Other 
soils in the mountain and upland areas (Los Guineos- 
Guayabota-Rock 
Land 
soil 
association) 
have 
permeabilities (0.06 to 0.2 in/hr) similar to the soils in 
the valleys (fig. 2.4.1.F-1 and table 2.4.1.F-1).
Soils in the alluvial valleys are generally less 
permeable than those in the mountains and upland 
areas. 
Soils of high permeability occur along the 
edges of the alluvial valleys in the San Lorenzo 
Batholith. 
Finer grained and less permeable soils 
predominate in the centers of the valleys and 
throughout the valleys where surrounded by volcanic 
rocks.
North of the Rio Humacao, in the Humacao and 
Naguabo basin, the Caguabo-Mucara-Naranjito soil 
association overlies the alluvial aquifer. Permeability 
for these clayey soils ranges from 0.60 to 2.0 in/hr. 
South of the Rfo Humacao and in the northern part of 
the Yabucoa basin, the Pandura-Rock Land-Patillas 
soil association overlies the aquifer. Permeability of 
soils in this association ranges from 0.6 to 2.00 in/hr. 
The Catano-Aguadilla soil association overlies the 
alluvial aquifer near the coast in the Humacao- 
Naguabo and Yabucoa basins. Permeability of these 
sandy soils, ranges from 6 to more than 20 in/hr. A 
Swamp-Marshes soil association has developed at the 
mouth of the Rio Anton Ruiz. Permeability of this soil 
association is too variable to be estimated. Within the 
Humacao-Naguabo 
basin, 
the 
Coloso-Toa-Bajura 
association overlies most of the valley area. However, 
south of the Rio Maunabo, the Descalabrado- 
Guayama association overlies the valley. Permeability 
for this soil association ranges from 0.6 to 2.0 in/hr.
Table 2.4.1.F-1 Thickness, permeability, and available water capacity for the soil associations 
in the Naguabo-Maunabo region, Puerto Rico (Modified from Boccheciamp, 1977; Gilberto 
Acevedo, Soil Conservation Service, written communication, 1990) 
[ <, less than]
Area and soil association
Thickness 
(inches)
Permeability 
(inch per hour)
Available water 
capacity (inch 
per inch)
Humid Coastal Plains 
Catano-Aguadilla 
Swamps-Marshes 
Coloso-Toa-Bajura
Humid Uplands
Caguabo-Mucara-Naranjito 
Los Guineos-Humatas-Lirios 
Los Guineos-Guayabota-Rock Land 
Pandura-Rock Land-Patillas
Semiarid Uplands
Descalabrado-Guayama
Humid Upland Valleys
Mabf-Rfo Arriba-Cayagua
0 to 72 
< 20.00 
< 0.03
Too variable to be estimated 
0 to 72 
0.06 to 0.20 
0.10 to 0.20
Oto72
Oto72
Oto60
Oto72
0.60 to 2.00
0.60 to 2.00
0.06 to 0.20
0.60 to 2.00
0.10 to 0.18
0.08 to 0.20
0.1 5 to 0.20
0.05 to 0.1 4
Oto26
Oto60
0.60 to 2.00
0.20 to 0.60
0.10 to 0.15
0.15 to 0.20
66W
65°45'
18W
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
A-4 CATANO-AGUADILLA 
D-2 SWAMPS-MARSHES 
E-2 COLOSO-TOA-BAJURA
HUMID UPLANDS
M-2 CAGUABO-MUCARA-NARANJITO
N-2 LOS GUINEOS-HUMATAS-URIOS
N-7 LOS GUINEOS-GUAYABOTA-ROCK LAND
O-1 PANDURA-ROCK LAND-PATILLAS
SEMIARID UPLANDS
R-2 DESCALABRADO-GUAYAMA
HUMID UPLAND VALLEYS
S-1 MABI'-RI'O ARRIBA-CAYAGUA
CARIBBEAN 
SEA
SOIL PERMEABILITY, IN 
INCHES PER HOUR
FROM 0.06 TO 0.20
FROM 0.20 TO 0.60
FROM 0.60 TO 2.00
MORE THAN 20
TOO VARIABLE TO ESTIMATE
SOIL ASSOCIATION BOUNDARY
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
0 12 34 KILOMETERS 
0 
1 
2
4 MILES
Modified from Boccheciamp, 1977
Figure 2.4.1.F-1 Soil associations and permeability in the Naguabo-Maunabo region, Puerto Rico.
104 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.5 East Central Area
2.5 East Central Area 
105
2.5.1 AGUAS BUENAS-JUNCOS REGION
By Juan C. Paig
2.5.1.A Location and Major Geographic 
Features
The East Central area (the Aguas Buenas-Juncos 
region) coincides with the upper Rfo Grande de Lofza 
basin, an area of about 210 mi2 (fig. 2.5.1.A-1) This 
drainage basin encloses the Caguas and the Gurabo- 
Juncos valleys, which contain the only significant 
aquifer in the area. 
These valleys, which have a 
surface area of approximately 35 mi2, is surrounded 
by high mountains reaching elevations of as much as 
1,074 feet above mean sea level in the northeast and 
903 feet above mean sea level in the southeast.
The two major valleys in the Aguas Buenas- 
Juncos region are: (1) the nearly circular-shaped 
Caguas valley to the west, covering an area of about 
16.6 mi2; and (2) the elongate Gurabo-Juncos valley 
to the east, covering an area of about 18.5 mi2 (fig. 
2.5.1.A-1). 
These valleys are connected along a 
3,500 feet reach of the Rfo Grande de Lofza just 
upstream of Lago Lofza. The Caguas valley has an 
average diameter of about 4 miles. The Caguas valley 
floor is steep and irregular and has a maximum 
elevation of about 490 feet above mean sea level 
south of Caguas and a minimum elevation of about 
145 feet above mean sea level near Lago Lofza. In 
contrast, the Gurabo-Juncos valley floor is a flat, 
narrow plain about 12 miles long and from 0.5 to 1.5 
miles wide. 
The Gurabo-Juncos valley has a 
maximum elevation of about 360 feet above mean sea 
level at the eastern boundary and a minimum 
elevation of about 145 feet above mean sea level near 
Lago Lofza.
The principal streams in the Caguas valley are 
the Rfo Grande de Lofza, flowing from south to north 
along the central parts; the Rfo Turabo, flowing from 
west to east in the southwest part of the valley; the Rfo 
Caguitas, flowing from west to east in the northern part 
of the valley; and the Rfo Bairoa, flowing from west to 
east along the northwest part of the valley. Two main 
streams flow through the Gurabo-Juncos valley: the 
Rfo Gurabo flows from east to west along the center of 
the valley, and the lower reach of the Rfo Valenciano 
which flows from south to north near Juncos. 
All 
streams and creeks eventually discharge into Lago 
Lofza, which is located in the lowest point in the basin 
at the northern boundary.
ATLANTIC OCEAN
CARIBBEAN SEA
66"05'
66°00'
55'
65°50'
10'
18°05'
SENATORIAL DISTRICT NUMBER
01234 KILOMETERS
1  
0
1 
2
3
4 MILES
I
I 
I
Base from U.S. Geological Survey
Puerto Rico e Islas Limitrofes, 1:240,000,1952
Figure 2.5.1.A-1 Location and major geographic features in the Aguas Buenas-Juncos region, 
Puerto Rico.
106 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.5.1.B Population and Estimated 
Ground-Water Use
Population of the Aguas Buenas-Juncos region is 
concentrated principally in the municipios of Aguas 
Buenas, Caguas, Gurabo, Juncos, Las Piedras, and 
San Lorenzo. The population totaled about 244,000 in 
1980 (U.S. Department of Commerce, 1982). A 16 
percent increase in population was recorded from 
1980 to 1990 (U.S. Department of Commerce, 1991), 
when the population for the region totaled about 
282,000 (table 2.5.1.B-1). The municipio of Caguas 
accounts for nearly 50 percent of the total population 
within the region. 
About 49 percent of the total 
population of the Aguas Buenas-Juncos region live in 
urban areas, the remaining 51 percent live in rural 
areas (table 2.5.1.B-1).
Most wells in the Caguas-Juncos valley are 
screened in the alluvial deposits (fig. 2.5.1.B-1). 
These deposits constitute the main aquifer in the 
region. Yields to wells in the Caguas-Juncos valley 
are variable, but pumping rates of up to 310 gal/min 
have been observed. 
Ground-water withdrawal for 
public supply has been reduced from 3.71 Mgal/d in 
1986 to about 2.6 Mgal/d in 1988, because the Puerto 
Rico Aqueduct and Sewer Authority inactivated eight 
of their public-supply wells in this region (table 
2.5.1.B-2). 
The 
estimated 
total 
ground-water 
withdrawal at 22 active wells on dairy farms averaged 
about 0.27 Mgal/d from 1986 to 1988. 
Withdrawal 
from eight industrial wells averaged about 0.13 
Mgal/d. Withdrawals from domestic and commercial 
wells were low, averaging about 0.07 Mgal/d. 
The 
total ground-water withdrawal for all water uses was 
about 4 Mgal/d in 1986 and 1987, but decreased to 3 
Mgal/d in 1988 (Puig and Rodriguez, 1992).
Table 2.5.1.B-1 
Population 
for the Aguas Buenas-Juncos region, 
Puerto Rico (U.S. Department of Commerce, 1982, table 1; U.S. 
Department of Commerce, 1991, table 1)
1980 population
MUNICIPIO
Aguas Buenas
Caguas
Gurabo
Juncos
Las Piedras
San Lorenzo 
Total
TOTAL
22,429
117,959
23,574
25,397
22,412
32,428
244,199
URBAN
3,766
87,214
7,645
7,851
4,857
8,880
120,213
RURAL
18,66
30,745
15,929
17,546
17,555
23,548
123,986
1990 
population
TOTAL
25,424
133,447
28,737
30,612
27,896
35,163
281,279
Public-water supply during 1986 in the Aguas Buenas- 
Juncos region was distributed as follow: 
local surface 
water, 10.6 Mgal/d; local ground water, 3.7 Mgal/d; and 
basin transfers, 4.5 Mgal/d from Guaynabo and 2.8 Mgal/d
from Humacao; for a total of 21.6 Mgal/d. 
However, 
about 80 Mgal/d are transferred from the Lago Loiza to 
the San Juan metropolitan area for public-water supply.
66°05'
66°00'
55'
65°50'
10'
18°05'
AGUAS 
BUENAS
01234 KILOMETERS
I   H-
EXPLANATION
^^B 
EXTENT OF ALLUVIAL DEPOSITS 
^^B 
RESERVOIR
 ------- 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
  
-    -    
BOUNDARY BETWEEN MUNICIPIOS
          
PERENNIAL STREAM
LOCATION AND NUMBER OF WELLS 
AT SITE WHEN MORE THAN ONE 
WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURAL WELL 
DOMESTIC WELL
O
®
©
0 
1
34 MILES
TOWN OR CITY 
I
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.5.1.B-1 Approximate well locations in the Aguas Buenas-Juncos region, Puerto Rico.
2.5.1 Aguas Buenas-Juncos Region 
107
Table 2.5.1.B-2 Ground-water withdrawals and estimated population 
served during 1986 for the Aguas Buenas-Juncos region, Puerto Rico 
[Mgal/d, million gallons per day;  , no data available]
1 Use
I. Public Use
1. Caguas
2. Juncos
3. Gurabo
4. Aguas Buenas
5. Las Piedras
II. Domestic Use
1. Caguas
2. Gurabo
III. Industrial Use
1. Caguas
2. Gurabo
IV. Agricultural Use
1. Caguas
2. Gurabo
3. Juncos
4. Las Piedras
Estimated 
population 
served
3,650
15,360
17,320
460
1,630
Subtotal 
38,420
...
...
Subtotal
...
 
Subtotal
...
 
...
...
Subtotal
Total 
38,420
Average 
ground-water 
withdrawals 
(Mgal/d)
0.26
2.34
0.83
0.05
0.23
3.71
0.04
0.03
0.07
0.08
0.05
0.13
0.08
0.04
0.08
0.07
0.27
4.18
1 Municipios not listed under some specific use do not withdraw ground water 
for the subject use or data is not available.
2.5.l.C Geologic Setting
The group of rocks constituting the basement and 
flanks of the Aguas Buenas-Juncos region is made up 
largely of volcaniclastics, lavas, intrusives, minor 
amounts of metamorphic rock of Late Cretaceous to 
early Tertiary age and locally minor amounts of 
limestone of early Tertiary age (Puig and Rodrfguez, 
1993). 
This rock complex is overlain by Holocene 
surface deposits, 
mainly of alluvial origin 
(fig. 
2.5.1.C-1).
The volcanic rocks are the most abundant rocks 
in the study area. The Late Cretaceous and rocks of 
early Tertiary age are highly faulted, and locally folded. 
The volcaniclastic and other consolidated rock groups 
are of little hydrologic importance, because they do 
not have the necessary permeability to serve as 
water-bearing units. 
Water in fractures within the 
volcanic rocks is the source for water discharge in 
perennial and ephemeral low-flow springs.
The surface deposits are predominantly alluvial in 
origin and consist of varying lithologies, which reflect 
both the changing nature of the source material and the 
dynamics of the fluvial history of the rivers that drain the 
enclosing basin. The alluvial sediments are composed 
of poorly sorted clay, silt, and sand. 
In the vicinity of 
Caguas, the alluvial sediments range in thickness from 
near zero at the bedrock-alluvium contact, to more than 
150 feet in the center of the valley, and are mostly 
composed of silt, clay, and fine-grained sand, with
subordinate amounts of gravel and coarse-grained 
sand. 
Alluvial sediments in Gurabo and Juncos thin 
toward the western and eastern ends of the valley and 
toward the northern and southern edges of the valley, 
and have a maximum thickness of about 160 feet. The 
amount of gravel and coarse sand in the alluvium is 
greater in the Gurabo-Juncos valley than in the Caguas 
valley. 
The principal aquifer in the Aguas Buenas- 
Juncos region is in the alluvial deposits that fill these 
valleys.
66°05'
66W
55'
65°50'
10'
18°05'
AGUAS 
BUENAS
V.,
Holocene 
and
Pleistocene
Eocene
to Lower
Cretaceous
01234 KILOMETERS
h-H  .      
01234 MILES
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
RESERVOIR
-------- DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
QUATERNARY
TERTIARY 
CRETACEOUS
PERENNIAL STREAM 
TOWN OR CITY
Modified from Briggs and Akers, 1965
Figure 2.5.1.C-1 Generalized surficial geology in the Aguas Buenas-Juncos region, Puerto Rico.
108 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°05'
66
65°50'
2.5.l.D Hydrogeology
The Caguas and the Gurabo-Juncos alluvial 
valleys aquifer of the Aguas Buenas-Juncos region is 
under water-table conditions, but is influenced by the 
delayed yield of water from clay beds and by 
anisotropy characterized by a horizontal component of 
hydraulic conductivity that is several times higher than 
the vertical component. 
This aquifer may range in 
thickness from near zero at the bedrock-alluvium 
contact to about 130 feet toward the central part of the 
Caguas valley and to about 140 feet along the Rfo 
Gurabo flood plain (fig. 2.5.1.D-1). The aquifers in the 
fractured volcanic and plutonic rocks have very low 
yields, although locally they may represent a viable 
water source.
The transmissivity of the alluvial aquifer can 
range from less than 66 ft2/d to a maximum of 4,770 
ft2/d (Puig and Rodriguez, 1993; fig. 2.5.1.D-2). Along 
the main stream channels, transmissivity values are 
usually higher. The area along the Rfo Bairoa appears 
to have the highest transmissivities in the Caguas 
valley. 
Within the Gurabo-Juncos valley, higher 
transmissivity values occur along the Rio Gurabo.
10'
18°05'
01234 KILOMETERS
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
_  j00    SUBSURFACE CONTOUR-Shows depth to bottom 
of the aquifer below land surface. Dashed where 
approximated Contour interval is variable. 
Depth referred to 1:20,000 U.S. Geological Survey 
topographic maps
-    -  --  
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
4 MILES
PERENNIAL STREAM 
TOWN OR CITY
Modified from Puig and Rodriguez, 1992
Figure 2.5.1.D-1 Depth to bedrock in the Aguas Buenas-Juncos region, Puerto Rico.
2.5.1 Aguas Buenas-Juncos Region 
109
66°05'
66°00'
55'
65°50'
66°05'
66°00'
55'
65°50'
10'
18°05'
01234 KILOMETERS
EXPLANATION
DISTRIBUTION OF AQUIFER TRANSMISSIVITY, 
IN FEET SQUARED PER DAY
| 
| 
< 1,000
BH 
1,000-2,000
|^H 
2,000 - 3,000
I^H 
3,000 - 4,000
RESERVOIR
------ 
DRAINAGE DIVIDE THAT LIMITS
BOUNDARY OF AREA
01234 MILES
PERENNIAL STREAM 
TOWN
Modified from Puig and Rodnguez, 1993
Figure 2.5.1.D-2 Regionalized apparent transmissivity values in the Aguas Buenas-Juncos region, Puerto Rico.
110 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
66°05'
66W
55'
65° 50'
2.5.1.E Ground-Water Levels and 
Movement
Regional ground-water movement in the Caguas 
valley differs from that of the Gurabo-Juncos valley. In 
the Caguas valley, 
ground water moves from 
southwest to northeast in the southern part and from 
west to east in the northern part. 
In the Gurabo- 
Juncos valley, the regional ground-water movement is 
along flow paths from the northern and southern 
boundaries of the aquifer toward the Rfo Gurabo (fig. 
2.5.1.E-1). Low ground-water levels for the year are 
usually in April and normally correspond to the end of 
a period of low rainfall. High ground-water levels are 
usually during November and December, at the end of 
the wet season.
In the Aguas Buenas-Juncos region, streams and 
aquifers are generally hydraulically well connected, 
and flow through valleys where the water-table may be 
lower than the stream stage, promoting recharge of 
the aquifer from the streams. Nevertheless, seepage 
studies in the Caguas-Juncos valley indicate that 
water flowing out of the streams to the aquifer 
eventually discharges back to the stream, causing a 
net stream gain (Puig and others, 1989; Puig and 
Rodrfguez, 1990).
66°05'
66°00'
55'
65°50'
10'
18°05'
   30
01234 KILOMETERS
I '           
01234 MILES
EXTENT OF ALLUVIAL DEPOSITS 
RESERVOIR
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly 
cased well. Contour interval is 5 feet. 
Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
-        -   
DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
PERENNIAL STREAM 
TOWN OR CITY
Modified from Puig and others, 1989: Puig and Rodn'guez. 1990
Figure 2.5.1.E-1 Altitude of water-level surface and direction of ground-water flow during March 
1988 in the Aguas Buenas-Juncos region, Puerto Rico.
2.5.1 Aguas Buenas-Juncos Region 
111
2.5.l.F Soil Permeability
Soils in the mountains and upland areas that are 
associated with volcanic and volcaniclastic rocks are 
moderately permeable ranging from 0.6 to 2.0 in/hr 
(fig. 2.5.1.F-1). These soil associations include the 
Caguabo-Mucara, 
Caguabo-Mucara-Naranjito, 
Los 
Guineos-Humatas-Lirios, 
and 
Humatas-Naranjito- 
Consumo. 
The soils associated with plutonic rocks, 
the Pandura-Rock Land-Patillas and the Pandura- 
Lirios, also have moderate permeabilities, ranging 
from 0.6 to 2.0 in/hr.
Soils in the alluvial valley are generally less 
permeable than those in upland areas and in the 
mountains. 
Within the valley, soils with high 
permeability are in the southern part of Caguas and 
along the southern edge of the Gurabo-Juncos 
valley. In most of the Caguas and Gurabo area, the 
Mabi-Rio Arriba soil association overlies the alluvial
aquifer 
(fig. 2.5.1.F-1). The permeability of these 
clayey 
soils ranges from 0.06 to 0.2 in/hr. Between 
Gurabo and Juncos, and along the upstream section 
of 
the Rio Gurabo, the Coloso-Toa-Bajura soil 
association 
overlies 
most of the 
aquifer 
(fig. 
2.5.1.F-1). 
The permeability of soils 
in this 
association also ranges from 0.06 to 0.2 in/hr 
(table 2.5.1.F-1). In the remaining part of the valley, 
along the southeast and northeast end, the Mabi-Rio 
Arriba-Cayagua soil association dominates. The 
permeability of this soil association ranges from 0.2 to 
0.6 in/hr (fig. 2.5.1.F-1). A wedge of the Caguabo- 
Mucara-Naranjito soil association along the eastern 
boundary of the valley has higher permeabilities that 
vary from 0.6 to 2.0 in/hr (fig. 2.5.1 .F-1).
Table 2.5.1.F-1 Thickness, permeability, and available water capacity for the 
soil associations in the Aguas Buenas-Juncos region, Puerto Rico (Modified 
from Boccheciamp, 1977)
Area and soil association
Humid Coastal Plains
Coloso-Toa-Baj u ra
Humid Upland Valleys
Mabi-Rfo Arriba-Cayagua
Mabi-Rfo Arriba
Humid Uplands
Mucara-Caguabo
Caguabo-Mucara-Naranjito
Los Guineos-Humata-Lirios
Humatas-Naranjito-Consumo
Maricao-Los Guineos
Pandura-Rock Land-Patillas
Pandura-Lirios
Thickness 
(inches)
0 to 0.60
0 to 0.10
0 to 0.99
0 to 0.32
0 to 0.38
0 to 0.60
0 to 0.60
0 to 0.60
0 to 0.48
0 to 0.50
Permeability 
(inch per hour)
0.06 to 0.20
0.20 to 0.60
0.06 to 0.20
0.63 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
0.60 to 2.00
Available water 
capacity 
(inch/inch)
0.10 to 0.20
0.03 to 0.20
0.1 5 to 0.20
0.10 to 0.17
0.08 to 0.20
0.08 to 0.20
0.10 to 0.20
0.10 to 0.20
0.05 to 0.1 4
0.05 to 0.1 5
66°05'
66°00'
55'
65°50'
10'
18°05'
AGUAS 
BUENAS
M-2
PIEDRAS
SOIL PERMEABILITY, IN { 
INCHES PER HOUR
FROM 0.06 TO 0.20 
FROM 0.20 TO 0.60 
FROM 0.60 TO 2.00
  SOIL ASSOCIATION BOUNDARY
  DRAINAGE DIVIDE THAT LIMITS 
BOUNDARY OF AREA
TOWN OR CITY
01234 KILOMETERS
I  ,  '       
01234 MILES
EXPLANATION
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
E-2 COLOSO-TOA-BAJURA
HUMID UPLANDS
M-1 MUCARA-CAGUABO
M-2 CAGUABO-MUCARA-NARANJITO
N-2 LOS GUINEOS-HUMATAS-LIRIOS
N-3 HUMATAS-NARANJITO-CONSUMO
N-6 MARICAO-LOS GUINEOS
O-1 PANDURA-ROCK LAND-PATILLAS
0-3 PANDURA-LIRIOS
HUMID UPLAND VALLEYS
S-1 MABI'-RI'O ARRIBA-CAYAGUA 
S-2MABI-RIO ARRIBA
Modified from Boccheciamp, 1977 and 1978
Figure 2.5.1.F-1 Soil associations and permeability in the Aguas Buenas-Juncos region, Puerto Rico.
112 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
2.6 Puerto Rico Offshore Islands
2.6 Puerto Rico Offshore Islands 
113
2.6.1 ISLA DE CULEBRA AND ISLA DE VIEQUES, PUERTO RICO
By Thalia D. Veve and Angel Roman-Mas
2.6.1.A Location and Major Geographic 
Features
The islands of Isla de Culebra and Isla de Vieques 
lie a few miles off the eastern coast of Puerto Rico (fig. 
2.6.1.A-1). 
Isla de Culebra, the smaller of the two 
islands with an area of about 10 mi2 , is 7 miles long and 
5 miles wide. The island of Isla de Vieques covers an 
area of about 20 mi2 and is approximately 18 miles long 
and 3 miles wide. There are no perennial streams on 
either island.
Isla de Culebra contains an east-west trending 
ridge with an average elevation of about 300 feet above 
mean sea level in the northern part of the island. The 
highest peak along this ridge and on the island is the 
640 feet high Monte Resaca. The land slopes steeply 
from the crest of the ridge northward to the coast. To the 
south, the slope is steep near the peaks becoming less 
steep below an elevation of 200 feet above mean sea 
level, where southward trending valleys separated by 
low ridges continue to the coast. The larger of these 
valleys contain alluvium in small embayments where 
they reach the coast. Intermittent stream channels drain 
the valleys on the south side of the ridge. An interior 
valley located in east central Isla de Culebra contains a 
relatively extensive area of alluvium in its upper reaches. 
A northwest to southeast trending ridge, ranging from 
300 to 440 feet above mean sea level, forms the 
western part of Isla de Culebra. The ridge is separated 
from the remainder of the island by a low saddle 
between Ensenada Honda and Bah fa Flamenco. The 
principal population center on Isla de Culebra is the 
town of Culebra, located west of Ensenada Honda.
Isla de Vieques is dominated by a 250 to 500 feet 
high east-west trending ridge stretching the length of the 
island. Monte Pirata, at the west end of Isla de Vieques, 
is the highest point on the island with an elevation of 988 
feet above mean sea level. With the exception of Monte
Pirata, the topography is gentle, consisting of relatively 
broad valleys separated by rounded hills trending 
seaward from the central ridge. The Resolucion valley, 
which cuts completely across Isla de Vieques, isolates 
Monte Pirata topographically from the rest of the island. 
In the south central part of the island, east of Esperanza, 
several valleys coalesce to form an alluvial coastal plain 
about 0.5 miles wide and 5 miles long. Several of the 
larger drainage basins in south-central Isla de Vieques 
have streams with intermittent flow. The most important 
of these streams are the Quebradas Mina, Pilon, and 
Urbano. These intermittent streams discharge into the 
south coastal plain during rain events. 
The principal 
population centers on Isla de Vieques are Isabel 
Segunda on the north coast and 
Esperanza on the 
south coast. About three-fourths of the island's territory 
is used by the Atlantic Fleet Weapons Training Facility, 
under the jurisdiction of the U.S. Department of 
Defense.
2.6.1.B Population and Estimated 
Ground-Water Use
Isla de Culebra had a permanent population of 
1,265 in 1980 (U.S. Department of Commerce, 1982; 
table 2.6.1.B-1). In 1990, the total population was 1,542 
(U.S. 
Department 
of 
Commerce, 
1991), 
which 
represents an increase of 22 percent. In recent years, 
the island has become a popular tourist area and 
location for vacation homes. The transient population 
may equal that of the permanent population, especially 
during the winter months.
Public-water supply on Isla de Culebra comes from 
a desalination plant that yields more than 0.1 Mgal/d 
(Turner, 1991, p. 1, 21). At present, this plant meets the 
water needs of Isla de Culebra. 
In 1982 total of 
0.05 
Mgal/d 
were 
withdrawn 
from 
ground-water 
sources (Torres-Gonzalez, 1989), supplementing the 
desalination plant yields. 
In 1982, ground water
supplied about 0.03 Mgal/d of water for domestic 
purposes and 0.01 Mgal/d for commercial uses (table 
2.6.1.B-2). 
Based on the 1980 census, an estimated 
742 persons were served by public supply. About 523 
persons used self-supplied water that probably came 
from community operated purification plants not owned 
by the Puerto Rico Aqueduct and Sewer Authority or 
from private wells. There are a few shallow private wells 
on the island (fig. 2.6.1 .B-1) dug in the coastal areas that 
yield brackish water used for watering cattle.
In 1980, the population of Isla de Vieques consists 
of a civilian population of 7,662 (table 2.6.1.B-1), a 
permanent staff population at the U.S. Marine facilities 
at Camp Garcia of a few hundred, and a transient 
population at Camp Garcfa that may swell to several 
thousand during training exercises. From 1980 to 1990, 
the civilian population of Isla de Vieques increased by 12 
percent to 8,602.
Until 1977, ground water supplied both the civilian 
and military population as well as minor industrial,
commercial, 
and 
agricultural 
demands 
(Torres- 
Gonzalez, 1989). Water for civilian use was obtained 
from four well batteries in the alluvial coastal plain near 
Esperanza on the south coast. Water for military use 
was withdrawn from three wells tapped 
in 
the 
Resolucion valley in western Isla de Vieques. 
Small 
industries either used private wells or used the public 
supply. Agriculture (mainly cattle) relied primarily on dug 
wells.
Ground-water withdrawals have been stopped in 
the Resolucion valley, and operation of the well field in 
the Esperanza valley was discontinued in 1978 as a 
result of increasing salinity and maintenance problems 
(Torres-Gonzalez, 1989). In 1977, a pipeline was laid 
from eastern Puerto Rico to Isla de Vieques. Since that 
time, the water needs of both the civilian and military 
population are being supplied by the pipeline, which 
obtains its water from the Rio Blanco filtration plant in 
eastern Puerto Rico. 
In 1989, about 500,000 gal/d of 
potable water were pumped through the pipeline to Isla 
de Vieques (Torres-Gonzalez, 1989).
Table 2.6.1.B-1 Population for Isla de Culebra and Isla de Vieques, Puerto 
Rico (U.S. Department of Commerce, 1982, table 1; U.S. Department of 
Commerce, 1991, table 1)
1980 population
MUNICIPIO
Isla de Culebra 
Isla de Vieques
Total
TOTAL
1,265 
7,662
8,927
URBAN
938 
2,330
3,268
RURAL
327 
5,332
5,659
1990 
population
TOTAL
1,542 
8,602
10,144
114 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
65°35'
18°20'
ATLANTIC OCEAN
ISLA DE CULEBRA
ISLA DE VIEQUES
CARIBBEAN SEA
18° 17'30"
65°20' 
65° 17'30"
ATLANTIC OCEAN
65°15'
ISLA DE CULEBRA
Cayo Norte
Isla Culebrita
CARIBBEAN SEA
2 MILES
65°32'30"
65°30'
65°27'30"
65°25'
65°22'30"
65°20'
65°17'30"
18°07'30"
18°05'00"
ISLA DE VIEQUES
CAJ6
CARIBBEAN SEA
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON 
      
EPHEMERAL STREAM
  
TOWN
2 MILES
Base from U.S. Geological Survey
Puerto Rico e Isla Limflrofes, 1:120,000,1961
Figure 2.6.1.A-l Locations and major geographic features in Isla de Culebra and Isla de Vieques, Puerto Rico.
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico 
115
65° 35'
65°32'30"
18°20'
18°17'30"
65°20' 
65° 17'30"
ATLANTIC OCEAN
65°15'
ISLA DE CULEBRA
0 
1 
2 KILOMETERS
Isla Culebrita
Sardinerall 
CARIBBEAN SEA
2 MILES
65°30'
65°27'30"
65°25'
65°22'30"
65°20'
65° 17'30"
18°07'30"
18°05'00"
ISLA DE VIEQUES
o 
1 
2 KILOMETERS
CARIBBEAN SEA
0
1
2 MILES
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON 
    
    EPHEMERAL STREAM
O3 
LOCATION AND NUMBER OF WELLS AT SITE 
WHEN MORE THAN ONE WELL PRESENT
O 
PUBLIC-SUPPLY WELL
© 
AGRICULTURAL WELL
  
DOMESTIC WELL
  
TOWN
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 2.6.1.B-1 Approximate well locations in Isla de Culebra and Isla de Vieques, Puerto Rico.
116 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Table 2.6.1.B-2 Ground-water withdrawals and estimated population served 
during 1982 for Isla de Culebra and Isla de Vieques, Puerto Rico (Modified from 
Torres-Sierra and Aviles, 1986; Gomez-Gomez and others, 1984) 
[Mgal/d, million gallons per day;  , no data available, <, less than]
1 Use and supplier
I. Domestic Use
A. Puerto Rico Aqueduct and Sewer Authority
1 . Isla de Culebra
2. Isla de Vieques
Subtotal
1 B. Community Systems
1. Isla de Culebra
2. Isla de Vieques
Subtotal
II. Agriculturall Use (livestock)
1. Islade Culebra
2. Isla de Vieques
Subtotal
III. Commercial Use
1 . Isla de Culebra
2. Isla de Vieques
Subtotal
Total
Estimated 
population 
served
742
7,114
7,856
523
548
1,071
...
 
 
...
 
...
8,927
Average 
ground-water 
withdrawals 
(Mgal/d)
0.03
2<0.01
0.03
0.02
0.02
0.04
0.02
<0.01
<0.03
0.01
0.05
0.06
0.16
1 Includes water from desalination plants.
2 Sigfredo Torres-Gonzalez, U.S. Geological Survey, written communication, 1989.
2.6.l.C Geologic Setting
Isla 
de 
Culebra and 
Isla 
de 
Vieques are 
geologically associated with Puerto Rico. They were 
separated from the main island by fairly recent drowning 
of a more extensive Puerto Rico land mass during the 
melting of the late Pleistocene ice sheets of North 
America and Europe in the Holocene (Monroe, 1980a, 
p. 30).
The rocks of Isla de Culebra are primarily volcanic 
and plutonic rocks of Late Cretaceous age (fig. 
2.6.1 .C-1). Andesite lava, lava breccia, and tuffs are the 
dominant volcanic rocks. These rocks were intruded by 
diorite and diorite porphyry. These plutonic type rocks
crop out in the north-central part of the island. Earth 
movements have fractured these rocks and formed in a 
joint pattern. Some faulting is also present, with major 
faulting aligned in a northwest-southeast direction. 
Alluvium, predominately composed of silt and clay with 
minor quantities of sand and gravel, was subsequently 
deposited in the few existing river valleys near the coast. 
On the coast, alluvium interfingers with coral, beach, 
and mangrove deposits. Alluvium is also found in the 
high valley of east-central Isla de Culebra.
The 
rocks comprising 
Isla de Vieques 
are 
predominately plutonic (fig. 2.6.1.C-1). 
Quartz-diorite 
and granodiorite underlie most of the western half of the 
island. 
These plutonic rocks are part of the San
Lorenzo-Humacao 
Batholith 
that 
crops 
out 
in 
southeastern Puerto Rico. Volcanic rocks predominate 
in the eastern part with small patches of plutonic rocks 
cropping out in the east-central area. 
The rocks of 
volcanic origin are sandstones, breccias, and tuffs, most 
of which were deposited in a marine environment. 
Minor beds of marine limestone are locally interbedded 
with these rocks. Small areas of soft clayey Tertiary 
limestone are present in the easternmost part of Isla de 
Vieques and on the headlands in the vicinity of Puerto 
Mosquito on the south coast. The only major alluvial 
deposits underlie the coastal plain east of Esperanza. 
Small alluvial deposits are present at the north and 
south ends of the Resolucion valley and in the larger 
valleys of both the north and south coasts. The alluvium 
of the southern coastal plain east of Esperanza is 
composed primarily of sand and occasional lenses of 
fine gravel interbedded with beds of clay and occasional 
beds of limestone. These deposits range in thickness 
from near zero to 90 feet (Torres-Gonzalez, 1989; fig. 
2.6.1.C-2). Alluvium in the Resolucion valley and the 
larger valleys that head in the plutonic rocks is 
composed of beds of sand with some clay. The alluvium 
in the valleys that head in the volcanic rocks is primarily 
a mixture of clay and angular rock fragments with 
occasional lenses of sand and angular gravel. Beach 
and dune sand is present in the coastal embayments, 
covering an area of more than 0.5 mi2 in the west 
(Torres-Gonzalez, 1989).
2.6.l.D Hydrogeology
Although scarce, ground water in Isla de Culebra is 
known to occur in alluvial deposits and in the volcanic 
and plutonic rocks. Alluvial deposits are located along 
major stream valleys that reach the coast. The alluvium 
is mostly composed of silt and clay with limited 
quantities of sand and gravel. 
Fractures and joints 
within the volcanic and plutonic rock formations store 
water in small quantities. Most of these fractures and 
joints diminish in number and size with depth and pinch 
out at about 300 feet below land surface. Water-table 
conditions prevail in the bedrock aquifer. By comparing 
changes in water levels with records of pumpage and 
estimates of recharge, the specific yield for the bedrock 
aquifer was estimated as less than one percent (Jordan 
and Gilbert, 1976, p. 16).
The most important aquifers in Isla de Vieques are 
alluvial deposits in the Esperanza and Resolucion 
valleys. Another, less important, source of ground water 
is found in the Playa Grande area. Of these aquifers, 
only the Esperanza valley aquifer has been studied in 
detail (Torres-Gonzalez, 1989).
The Esperanza valley covers about 10 mi2 and 
extends from Ensenada Sombe near the town of 
Esperanza towards the east to Bah fa Tapon. 
The 
alluvium in this valley consists of a mixture of sand, silt, 
and clay, with increasing clay content at depth; overlies 
volcanic bedrock and marine sedimentary deposits; and 
contains a clay layer 5 feet thick at about 25 feet below 
land surface (Torres-Gonzalez, 1989). Inland, the entire 
aquifer behaves as a water-table aquifer. However, as 
the clay layer becomes more clearly defined near the 
coast, the alluvial deposits above the clay layer behave 
as a strongly anisotropic water-table aquifer, while those 
below the clay layer behave as an artesian aquifer 
(Torres-Gonzalez, 1989). Hydraulic-conductivity values 
range from 1 ft/d inland to 40 ft/d near the coast, where 
sand content is greater (fig. 2.6.1.D-1). 
Aquifer 
thickness increases towards the sea reaching a depth of 
about 70 feet below land surface at the coast (fig. 
2.6.1.D-2). 
Depth to bedrock also increases towards 
the sea reaching a maximum of about 90 feet below sea 
level (fig. 2.6.1.D-2). Transmissivity increases from east 
to west and ranges from 200 ft2/d at the eastern limit of 
the aquifer to 2,000 ft2/d in the western limit (Torres- 
Gonzalez, 1989).
The Resolucion valley covers an area of 8 mi2 and 
extends from the northwest corner of Isla de Vieques to 
east of the Isla de Vieques Airport. 
Geophysical 
surveys revealed that the Resolucion valley is similar to 
the Esperanza valley in that alluvium thickness 
averages 30 feet, with a clay unit located 20 to 30 feet 
below land surface. An estimated 200,000 gal/d may be 
pumped from this aquifer (Torres-Gonzalez, 1989).
The Playa Grande area covers about 5 mi2 and is 
located on the south coast, to the west of Esperanza 
valley. 
Water-table conditions prevail in this aquifer. 
The aquifer yielded 50,000 gal/d of water up to 1965 
(Henry Anderson, U.S. Geological Survey, written 
communication, 1972; Torres-Gonzalez, 1989).
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico 
117
18°20'
18" 17'30"
65°20' 
65° 17'30"
ATLANTIC OCEAN
65°15'
ISLA DE CULEBRA
Cayo Norte
Isla Culebrita
Playa
Sardinerall 
CARIBBEAN SEA
2 MILES
65°35'
65°32'30"
65°30'
65°27'30"
65'25'
65°22'30"
65°20'
65" 17'30"
18°07'30"
18°05'00"
ISLA DE VIEQUES
EXPLANATION
BEACH DEPOSITS 
SWAMP DEPOSITS 
ALLUVIAL DEPOSITS
Holocene
and 
Pleistocene
QUATERNARY
LAGOON
A ' LINE OF SECTION-Location of section 
shown in figure 2.6.1.C-2
\ 
Miocene 
MARINE SEDIMENTARY ROCK > 
and 
} TERTIARY
1 
2 KILOMETERS
CARIBBEAN SEA
  EPHEMERAL STREAM 
TOWN
1
2 MILES
PLUTONIC ROCKS
VOLCANIC AND
VOLCANICLASTIC
ROCKS
Oligocene
Eocene 
I 
TERTIARY 
to Lower 
^ 
CRETACEOUS 
Cretaceous
Modified from Briggs and Akers, 1965; Torres-Gonzalez, 1989
Figure 2.6.1.C-1 Generalized surficial geology in Isla de Culebra and Isla de Vieques, Puerto Rico. 
118 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
MEAN 
SEA LEVEL
10 -
Modified from Torres-Gonzalez, 1989
.40 KILOMETERS
I 
.25 MILES
EXPLANATION
COLLUVIUM, MOSTLY 
SAND, SILT AND CLAY
MOSTLY CLAY, WITH 
ROCK FRAGMENTS
HARD BROWN CLAY
FINE SAND, SOME ROCK 
FRAGMENTS, AND CLAY (Clay 
fraction increases with depth)
GRAY CLAY 
BEDROCK
POTENTIOMETRIC SURFACE 
June 6,1984
------ MEAN SEA LEVEL
1
WELL
Figure 2.6.1.C-2 Hydrogeologic section of the aquifer in the Esperanza valley, Isla de Vieques, Puerto Rico (line of section shown in figure 2.6. l.C-1).
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico 
119
65°20'
65°17'30"
65°15'
18°07'30"  
18°06'15"
ISLA DE CULEBRA
ATLANTIC OCEAN
Cayo de 
Luis Pena
Playa 
Sardinera II
0 
1 
2 KILOMETERS
CARIBBEAN SEA
\ESPERAN
ISLA DE VIEQUES
ISABEL 
SEGUNDA
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
DISTRIBUTION OF AQUIFER HYDRAULIC 
CONDUCTIVITY, IN FEET PER DAY
PLAYA GRANGE
MONTE PIRATA
CARIBBEAN SEA
0 
1 
2 KILOMETERS
  
    EPHEMERAL STREAM
18'07'30"
18°05'00" 
-
Modified from Torres-Gonzalez, 1989
Figure 2.6.1.D-1 Distribution of aquifer hydraulic conductivity values in the Esperanza valley, Isla de Vieques, Puerto Rico. 
120 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
65°20'
65°17'30"
65°15'
18°07'30"
18°06'15"
18°07'30"
18°05'00"
ISLA DE CULEBRA
ATLANTIC OCEAN
0 
1 
2 KILOMETERS
i 
i
CARIBBEAN SEA
\ESPERAN
ISLA DE VIEQUES
^ r
CAt(lP GARCJ
EXPLANATION
^ 
N
ESrERANZA
MONXTip?RATAV PLAYAGR^D^
S 
- 
- 
<
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
STRUCTURE CONTOUR-Shows altitude 
of base of the alluvial aquifer 
in feet. Contour interval is variable. 
Datum is mean sea level.
_. _. _ EPHEMERAL STREAM 
  
TOWN
CARIBBEAN SEA
18°10\ -
Modified from Torres-Gonzalez, 1989
Figure 2.6.1.D-2 Altitude of base of the Esperanza valley alluvial aquifer, Isla de Vieques, Puerto Rico.
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico 
121
2.6.l.E Ground-Water Levels and 
Movement
The only source of recharge for the aquifers of Isla 
de Culebra is direct rainfall. Annual rainfall on Isla de 
Culebra averaged approximately 32 inches from 1961 to 
1970 (Jordan and Gilbert, 1976). 
However, recharge 
from rainfall only occurs during storms that last two to 
four days. Such storms take place only two to three 
times a year. About one percent of the rainfall infiltrates 
to the aquifer during these events. 
Annual recharge 
ranges from 0 to 6.8 percent of annual rainfall (Jordan 
and Gilbert, 1976). A relation between water levels and 
rainfall events exists; after rainstorms, water levels rise 
for several months (fig. 2.6.1.E-1). This is caused by a 
thick layer of soil or fine grained alluvium that acts as a 
reservoir and that releases water at a slow rate. This 
reservoir system occurs in the alluvium and underlying 
saprolite of the high valley that lies at the eastern end of 
the dioritic rocks in north-central Isla de Culebra. The 
yield of bedrock wells in the valley is due to the reservoir 
system. Water-table conditions prevail in the bedrock 
aquifer. 
Each stream drainage basin constitutes a 
separate aquifer with a ground-water divide impeding 
movement between basins. 
The depth to the water 
table beneath the hills may be 100 feet or more, but in 
the lower part of the valleys may be less than 10 feet. 
The water flows towards the sea, but little water is 
discharged to the sea because it mostly evaporates 
from the water table. In coastal embayments, the water 
table usually is 1 to 2 feet above mean sea level. 
Because of the low heads and the proximity to the sea, 
salt water encroachment is common.
On Isla de Vieques, the long-term annual rainfall 
average is 45 inches (Torres-Gonzalez, 1989). The 
western part of the island receives about twice as much 
precipitation as the eastern part. Recharge rates have 
been estimated to range from three to five percent of 
annual rainfall. Sources of recharge to the Esperanza 
valley aquifer are direct rainfall and infiltration from 
ephemeral streams during storms through the alluvial
fans in the vicinity of the bedrock-alluvium contact. The 
clay layer found at a depth of 25 feet limits the amount 
of water that can recharge the lower part of the aquifer, 
especially near the coast. 
The water-table elevation 
ranges from 100 feet above mean sea level near the 
inland part of the coastal plain to about 5 feet near the 
coast (fig. 2.6.1.E-1). The hydraulic gradient is steep 
near Camp Garcia and becomes less steep towards 
Esperanza.
In the Resolucion valley, the water table ranges 
from about 30 feet below land surface in the inland part 
of the alluvial deposit to about 10 feet below land 
surface near the coast. Recharge is from rainfall on the 
sandy soil and by infiltration from streams during wet 
weather. Ground-water movement on Isla de Vieques is 
generally towards the sea.
2.6. l.F Soil permeability
On Isla de Culebra, the soil cover is homogeneous 
and only one soil association, the Descalabrado- 
Guayama, is present. This association is described by 
Boccheciamp (1977) as composed of shallow, well 
drained, strongly sloping to very steeply sloping soils 
derived from the underlying volcanic rocks. 
Its 
permeability is moderate and ranges from 0.6 to 2.0 
in/hr. The Descalabrado-Guayama association is also 
present on Isla de Vieques and covers the eastern half 
of the island.
The Esperanza and Resolucion valleys on Isla de 
Vieques are overlain principally by the Swamps- 
Marshes and the Coamo-Guamanf-Vives associations 
(fig. 2.6.1.F-1). The Swamps-Marshes association is 
present near the coast in the Esperanza valley and in 
the northwestern corner of the Resolucion valley. It also 
covers most of the Playa Grande area. The soils in this 
association are generally deep, poorly drained, sandy or 
clayey, and contain organic material derived from 
decaying mangrove trees. 
Characteristics of the 
Swamps-Marshes association are too variable to be 
estimated. 
The Coamo-Guamanf-Vives association
covers the northernmost reaches of the Esperanza 
valley and the central and eastern parts of the 
Resolucion valley. These soils are described as deep, 
well drained, nearly level to strongly sloping soils on 
terraces and alluvial fans (Boccheciamp, 1977). These 
soils were formed from sediment derived from limestone 
and volcanic rocks, and their permeability ranges from 
0.6 to 2.0 in/hr increasing with depth to more than 20 
in/hr in the Guamanf series. 
Small areas of these 
valleys are overlain by the Pandura-Rock Land-Patillas 
association. This association is composed of shallow, 
well drained, steep and very steep soils derived from the 
underlying plutonic rocks; permeability is moderate (0.6 
to 2.0 in/hr) but increases to rapid (6.00 to 20.00 in/hr) 
with depth in both the Pandura and Patillas series.
Available water capacity values and depth from the 
surface for each of the associations in Isla de Culebra 
and Isla de Vieques are given in table 2.6.1.F-1. The 
available water capacity of these soils is very low, less 
than 3 in/in in all the associations. 
The deepest 
associations are the Pandura-Rock Land-Patillas and 
the Coamo-Guamanf-Vives. These associations reach 
a depth of 50 feet below surface. The Descalabrado- 
Guayama association is the shallowest of the four 
associations, with a maximum depth of 19 feet below 
land surface.
Table 2.6.1.F-1 Thickness, permeability, and available water capacity for 
the soil associations in Isla de Culebra and Isla de Vieques, Puerto Rico 
(Modified from Boccheciamp, 1977)
[<, less than]
Area and soil association
Thickness 
Permeability 
(inches) 
(inch per hour)
Available 
water capacity 
(inch per inch)
Humid Coastal Plains
Swamps-Marshes 
Semiarid Coastal Plains
Coamo-Guamanf-Vives 
Humid Uplands
Pandura-Rock Land-Patillas 
Semiarid Uplands
Descalabrado-G uayama
too variable to be estimated
0 to 50 
0.60 to 2.00 
<0.05 to 0.16
0 to 48 
0.60 to 2.00 
0.05 to 0.14
Oto19 
0.60 to 2.00 
0.10 to 0.15
122 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
65°20'
65° 17'30"
65°15'
18°07'30"  
18°06'15"
18°07'30'
18°05'00
ISLA DE CULEBRA
ATLANTIC OCEAN
Cayo de 
Luis Pena
Playa 
Sardinera II
0 
1 
2 KILOMETERS
CARIBBEAN SEA
ESPERANZA
1 KILOMETERS
ISLA DE VIEQUES
;, 
I Laguna 
? Anones
Laguna 
- \Yanuel
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LAGOON
WATER-LEVEL CONTOUR-Shows altitude of 
water level, in feet in tightly cased well during 
April 1983. Dashed where approximated. Contour 
interval is variable. Datum is mean sea level
Laguna 
Playa Grande
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
CARIBBEAN SEA
1 
2 KILOMETERS
i 
i
18°ia
Modified from Torres-Gonzalez, 1989
Figure 2.6.1.E-1 Altitude of water-level surface and direction of ground-water flow during April 1983 in the Esperanza valley aquifer, Isla de Vieques, Puerto Rico.
2.6.1 Isla de Culebra and Isla de Vieques, Puerto Rico 
123
65°20'
65~17'30"
65°35'
65°32'30"
65°30'
18°20'
18° 17'30"
65°15'__________
ISLA DE CULEBRA
Cayo Norte
Isla Culebrita
Cayo de 
Luis Peria
0 
1 
2 KILOMETERS
I___i 
i____
0 
1 
2 MILES
Playa 
Sardinera II
65°27'30"
65°25'
65°22'30"
65°20'
65° 17'30"
18°07'30"
18°05'00"
ISLA DE VIEQUES
EXPLANATION
R-2
1 
2 KILOMETERS
SOIL PERMEABILITY, IN 
INCHES PER HOUR
FROM 0.60 TO 2.00
TOO VARIABLE TO ESTIMATE
SOIL ASSOCIATION BOUNDARY 
TOWN
2 MILES
SOIL ASSOCIATIONS
HUMID COASTAL PLAINS 
D-2 SWAMPS-MARSHES
SEMIARID COASTAL PLAINS 
H-1 COAMO-GUAMANl'-VIVES
HUMID UPLANDS 
0-1 PANDURA-ROCK LAND-PATILLAS
SEMIARID UPLANDS 
R-2 DESCALABRADO-GUAYAMA
Modified from Boccheciamp, 1977
Figure 2.6.1.F-1 Soil associations and permeability in Isla de Culebra and Isla de Vieques, Puerto Rico.
124 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
3.0 GROUND-WATER RESOURCES AREAS IN THE U.S. VIRGIN ISLANDS
3.1 U.S. VIRGIN ISLANDS
3.0 Ground-Water Resources Areas in the U.S. Virgin Islands 
125
3.1.1 ST. THOMAS AND ST. JOHN, U.S. VIRGIN ISLANDS
By Robert P. Graves
3.1.1.A Location and Major Geographic 
Features
St. Thomas, the second largest of the three 
principal 
islands of the 
U.S. 
Virgin 
Islands, 
is 
approximately 14 miles long and 2 to 3 miles wide, and 
has an area of 32 mi2 (fig. 3.1.1.A-1). Charlotte Amalie 
is the only city on the island, however, St. Thomas is so 
densely populated that the whole island could be 
considered urban.
The land surface of St. Thomas is almost entirely 
sloping and extends seaward from a central ridge, that is 
800 to 1,200 feet above mean sea level and runs the 
length of the island (Jordan and Cosner, 1973). The 
slopes, which commonly exceed 35 degrees, are 
dissected by numerous stream channels of steep 
gradient. The general appearance of St. Thomas is a 
panorama of steep interstream spurs and rounded 
peaks (Jordan and Cosner, 1973). 
Flat land in St. 
Thomas is confined to the Charlotte Amalie area and a 
few small alluvial-filled embayments. The only variation 
in the general topography is in the upper valley of 
Turpentine Run in eastern St. Thomas. This valley has 
rolling hills in a basin surrounded by steep slopes and 
sharp ridges. Streamflow on St. Thomas is generally 
intermittent, however, Bonnes Resolution Gut, on the 
north side of the island and Turpentine Run Gut, on the 
southeast, have perennial reaches. Turpentine Run Gut 
base flow consists predominantly of sewage effluent 
(Santiago-Rivera and Colon-Dieppa, 1986).
St. John, the smallest of the three principal islands 
of the U.S. Virgin Islands, is about 6 miles long and 3 
miles wide, and has an area of 19 mi2 , of which 
approximately two-thirds is the Virgin Islands National 
Park (fig. 3.1.1.A-1). 
St. John is composed of a main 
eastward trending ridge with steep slopes that descend 
to the sea to the north (Cosner, 1972). In contrast, the 
south side of the ridge has several prominent spur
ridges that extend southward. The highest point on the 
island is 1,277 feet above mean sea level (Cosner, 
1972). 
Flat land on St. John is confined to small, 
isolated coastal embayments. 
The largest drainage 
basins on St. John are Reef Bay Gut and Fish Bay Gut, 
which together drain 1.77 mi2 (Cosner, 1972). 
Other 
basins are Coral Bay Gut and Guinea Gut with 1.69 and 
0.72 mi2 of drainage, respectively. Guinea Gut is the 
only stream considered to be perennial on St. John.
St. John has two small population centers and 
these are Cruz Bay (the largest) on the west end and 
Coral Bay near the east end. Because a large portion of 
the island is part of the Virgin Islands National Park, 
residences are confined to the two population centers. 
St. John does not have an airport and is accessed only 
by ferry service from St. Thomas.
3.1.1.B Population and Estimated 
Ground-Water Use
The total population of St. Thomas in 1990 was 
48,166. 
About 43 percent of the population is 
concentrated in the Charlotte Amalie subdistrict and 19 
percent in the Tutu subdistrict. 
The remaining 38 
percent is divided among the Northside, Eastend, 
Southside, Westend, and Water Island 
subdistricts. 
However, the entire island can be considered a single 
urban complex.
The demand for freshwater on St. Thomas exceeds 
the available supply. 
Ground water is an important 
resource in the U.S. Virgin Islands (fig. 3.1.1.B-1), and 
provides about 18 percent of the total freshwater supply 
in all the islands. However, on St. Thomas, ground water 
supplies only about one percent or 0.35 Mgal/d of the 
estimated 3.5 
Mgal/d 
of freshwater used 
(table 
3.1.1.B-1; Torres-Sierra and Dacosta, 1987). 
The 
remainder of the freshwater supplies in St. Thomas 
come from desalinated seawater, estimated at 2.5
Mgal/d; and rainfall runoff to cisterns estimated at 0.65 
Mgal/d. However, ground-water production is increasing 
on St. Thomas; during 1991, the U.S. Virgin Islands 
Water and Power Authority completed a new well field in 
the Charlotte Amalie area that has an estimated yield of 
0.136 Mgal/d.
The total population of St. John in 1990 was 3,504. 
As on St. Thomas, St. John has been divided into 
subdistricts. The largest subdistrict is Cruz Bay which 
has 70 percent of the population; the smallest districts 
are Central, Coral Bay, and Eastend which had 18, 10, 
and 2 percent of the population, respectively.
Ground-water use on St. John is minimal; ground- 
water discharge is equal to only 0.30 Mgal/d (table 
3.1.1.B-1). 
Freshwater is predominantly supplied by 
rainwater collected from rooftop catchment systems. 
Ground-water use in the Cruz Bay area consists of 0.10 
Mgal/d from the nearby Susannaberg well field (fig. 
3.1.1.B-1). 
The 
ground-water 
supplies 
from 
the 
Susannaberg well field are stored in a water tank to 
serve as backup supplies for the public-water supply 
system. 
The remaining 0.10 Mgal/d of ground water 
used on St. John is from wells located in the Virgin 
Islands National Park and from private well owners 
located throughout the island.
Table 3.1.1.B-1 
Ground-water withdrawals and estimated population served 
during 1983-84 for St. Thomas and St. John, U.S. Virgin Islands 
[Mgal/d, million gallons per day;  , no data available]
1 Use and supplier
1 Estimated
population
served
Average 
ground-water 
withdrawals
(Mgal/d)
St. Thomas
I. Domestic Use
II. Commercial Use
2,884
0.15
0.20
Subtotal 
2,884 
St. John
I. Domestic Use
A. U.S. Virgin Islands Water and Power Authority 
2,395 
B. Private Supplies
0.35
0.20
0.10
Subtotal 
2,395
0.30
Total
5,279
0.65
1 Based on a water consumption of 52 gallons per person per day.
2 Modified from Torres-Sierra and Dacosta, 1987.
126 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
ATLANTIC OCEAN
CARIBBEAN SEA
ST. JOHN
ST. THOMAS
18°25'
65°00'
55'
50'
45'
64°40'
20'
0 
1 
2 KILOMETERS
i 
ii____
2 MILES
ATLANTIC OCEAN
ST. JOHN
ST. THOMAS
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS 
LIMIT BETWEEN SUBDISTRICTS 
EPHEMERAL STREAM
Figure 3.1.1.A-1 Locations and major geographic features in St. Thomas and St. John, U.S. Virgin Islands.
3.1.1 St. Thomas and St. John, U.S. Virgin Islands 
127
18°25'
65°00'
55'
50'
45'
64°40'
20'
ST. JOHN
ST. THOMAS
0 
1 
2 KILOMETERS
I 
ii___
0 
1 
2 MILES
EXPLANATION
EXTENT OF ALLUVIAL DEPOSITS
BOUNDARY BETWEEN SUBDISTRICTS 
EPHEMERAL STREAM
LOCATION AND NUMBER OF WELLS AT SITE WHEN 
MORE THAN ONE WELL PRESENT
PUBLIC-SUPPLY WELL 
INDUSTRIAL WELL 
AGRICULTURALWELL 
DOMESTIC WELL
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 3.1.1.B-1 Approximate well locations in St. Thomas and St. John, U.S. Virgin Islands.
128 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
3.1.1.C Geologic Setting
The geology of St. Thomas and St. John is similar 
(fig. 3.1.1.C-1). 
The islands are underlain by mildly 
deformed Cretaceous volcanic rock and limestone that 
were intruded and contact metamorphosed by dioritic 
plutons during Late Cretaceous or early Tertiary time
(Donnelly, 1959). Volcanic rock is the predominant rock 
type on St. Thomas and St. John. The oldest volcanic 
rock is the Water Island Formation, which consists 
predominantly of 
lava flows 
and flow breccias. 
Overlying the Water Island Formation is the Louisenhoj 
Formation, which was extruded from a volcanic center 
and is a combination of very coarse reworked cone
debris and fine-grained tuff. 
Near the base of the 
Louisenhoj Formation is a conglomerate composed 
chiefly of rock from the Water Island Formation. 
Overlying the Louisenhoj Formation is the Outer Brass 
Limestone which consists of 200 to 600 feet of thin- 
bedded graphitic silicified radiolarian limestone. 
The 
youngest rock exposed on St. Thomas and St. John is
the Tutu Formation, which is composed of angular 
debris derived from the Louisenhoj Formation and minor 
limestone debris. Locally, small alluvial deposits, which 
range from Pleistocene to Holocene age, lie in the valley 
of Turpentine Run and the larger coastal embayments.
18°25'
65°00'
55'
50'
45'
64'40'
20'
ATLANTIC OCEAN
ST . JOHN
SUSANNABERG 
WELL FIELD
ST. THOMAS
ALLUVIAL DEPOSITS
EXPLANATION
\ Recent \ QUATERNARY
Lower Tertiary 
1 
TERTIARY 
PLUTONIC ROCKS 
\ 
to 
L 
TO
Lower Cretaceous 
CRETACEOUS
0 
1 
^ KILOMETERS
TUTU FORMATION 
OUTER BRASS LIMESTONE 
LOUISENHOJ FORMATION 
WATER ISLAND FORMATION
Albian
to 
\ CRETACEOUS 
Lower Cretaceous
2 MILES
     -    LIMIT BETWEEN SUBDISTRICTS 
    EPHEMERAL STEAMS
Modified from Donnelly, 1959
Figure 3.1.1.C-1 Generalized surficial geology in St. Thomas and St. John, U.S. Virgin Islands.
3.1.1 St. Thomas and St. John, U.S. Virgin Islands 
129
3.1.1.D Hydrogeology
Ground water in St. Thomas and St. John is under 
water-table conditions in the volcanic rock, limestone, 
and alluvial deposits. The availability of ground water 
from the limestone and alluvial aquifers is limited 
because of their small areal extent. Consequently, the 
fractured volcanic rock aquifers are the principal source 
of ground water (fig. 3.1.1.D-1).
The volcanic rock consists of regolith, transition 
zone, and bedrock. The regolith is a highly weathered
65°00'
volcanic material that occurs as saprolite or very friable 
and highly weathered volcanic rock. 
The transition 
consists of shattered to highly fractured volcanic rock 
underlying the regolith, and contains areas of highly 
weathered volcanics that grade upward to saprolite. 
The volcanic bedrock is a dense, indurated and locally 
contains horizontal and vertical fractures.
In the volcanic rock aquifers, ground water is 
principally in the fractured and highly shattered transition 
zone. The regolith overlying the transition zone has an
55'
overall low permeability that limits yields. 
However, 
when the regolith is saturated, it acts as an excellent 
storage reservoir and contributes considerable water to 
the underlying transition zone (Jordan and Cosner, 
1973). 
Ground water is found in fractures within the 
underlying bedrock; however, yields are negligible. 
Deep wells, completed into the transition zone and the 
underlying bedrock, have never had higher yields than 
wells completed only in the transition zone.
Well yields from the transition zone are dependent 
on saturated thickness, abundance of fractures, and the
50'
density of the highly shattered zones. Aquifer yields in 
the transition zone may range from 21,000 to 72,000 
gal/d.
Wells completed into the aerially limited limestone 
aquifers are capable of short term yields of 150,000 
gal/d and sustained yields of 50,000 gal/d (Jordan and 
Cosner, 1973). Where the alluvial deposits are found to 
be saturated, aquifer yields to wells as high as 43,000 
gal/d can occur.
45'
64°40'
18°25'
20'
ATLANTIC OCEAN
ST. JOHN
lTTLE NORTH 
'--» \ 
SIDE
, 
\ <CHARLOTTC 
...^
L J 
AMALJE 
j iKINGS -
ST. THOMAS
0 
1 
2 KILOMETERS 
0 
1 
2 MILES
EXPLANATION
HH 
LIMESTONE AQUIFERS
|B 
FRACTURED VOLCANIC ROCK AQUIFERS
HH 
ALLUVIAL AQUIFERS
- -    -    
LIMIT BETWEEN SUBDISTRICTS
  
-     
EPHEMERAL
Modified from Donnelly, 1959
Figure 3.1.1.D-1 Principal aquifers in St. Thomas and St. John, U.S. Virgin Islands.
130 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
3. 1 . 1 . E Ground-Water Levels and 
Movement
Because of the complexity of the fractured volcanic 
rock, limestone, and alluvial aquifers, an islandwide 
potentiometric map of either St. Thomas or St. John has 
not been completed. 
Potentiometric maps covering 
small areas have been completed by Jordan and Cosner
(1973) and Graves and Gonzalez (1988). In general the 
water-table surface on St. Thomas and St. John 
parallels the topography. Ground-water movement is 
down gradient and perpendicular to the topographic 
contours towards the sea (fig. 3.1.1.E-1). Depending on 
the location, the water table can range from within a few 
feet of land surface to as deep as 120 feet below land 
surface (Jordan and Cosner, 1973).
3.1.1.P Soil Permeability
Soils on St. Thomas and St. John are of two types, 
the 
Cramer-lsaac 
and 
Dorothea-Victory-Magens 
associations (fig. 3.1.1.F-1, table 3.1.1.F-1), each of 
which have a soil permeability of 0.63 to 2.0 in/hr (Rivera 
and others, 1979). The Cramer-lsaac association is the 
predominant soil association that covers all of St. John 
and approximately 80 percent of St. Thomas. These soil
associations, when dry, are coarsely granular, because 
clay and silt particles have a tendency to clump (Jordan 
and Cosner, 1973). Prolonged saturation is necessary 
before the granules break down and weld together. As a 
result, the soil has a high permeability until well 
saturated, but once saturated, the soil becomes poorly 
permeable and retains water in the pore spaces 
between particles. Any excess water is shed.
65°00'
55'
50'
45'
64°40'
18°25'
20'
64°51'15"
64°52'30"
EXPLANATION
   30    
EXTENT OF ALLUVIAL DEPOSITS
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet in tightly cased well. 
Contour interval is variable. Datum is 
mean sea level
GENERALIZED DIRECTION OF GROUND 
WATER FLOW
  -    EPHEMERAL STREAM
0 
1 
2 KILOMETERS
I 
ii
I 
I 
I
0 
1 
2 MILES
Modified from Graves and Gonzalez, 1988
Figure 3.1.1.E-1 Altitude of water-level surface and direction of ground-water flow during September 11, 1987, in St. Thomas and St. John, U.S. Virgin Islands.
3.1.1 St. Thomas and St. John, U.S. Virgin Islands 
131
The typical soil zone will absorb about 2 inches of 
water before some water is shed or moves to the 
underlying bedrock (Jordan and Cosner, 1973). 
Fully 
saturated, the soil will probably retain 3 inches of water 
per foot of depth.
The capacity of the soil to hold large volumes of 
water, the infrequency of major rainstorms, and a high 
evapotranspiration rate, reduce ground-water recharge 
and storm runoff. 
Thickness, 
permeability, and 
available water capacity values for both soil associations 
are shown on table 3.1.1 .F-1.
Table 3. 1.1.F-1. Thickness, permeability, and available water capacity for the soil 
associations in the St. Thomas and St. John, U.S. Virgin Islands (Modified from 
Rivera and others, 1979)
Area and soil association
Cramer-lsaac 
Dorothea- Victory-Magens
Thickness 
(inches)
Oto36 
Oto84
Permeability 
(inch per hour)
0.63 to 2.00 
0.63 to 2.00
Available water capacity 
(inch per inch)
0.1 5 to 0.20 
0.10 to 0.20
18"25'
65°00'
55'
50'
45'
64°40'
20'
ATLANTIC OCEAN
ST. JOHN
ST. THOMAS
0 
1 
2 KILOMETERS
i 
ii 
I
I 
I
0 
1 
2 MILES
EXPLANATION
SOIL ASSOCIATIONS
5 CRAMER-ISAAC
6 DOROTHEA-VICTORY-MAGENS
SOIL PERMEABILITY INCHES 
PER HOUR
I 
FROM 0.63 TO 2.00 INCHES PER HOUR 
      SOIL ASSOCIATION BOUNDARY
Modified from Rivera and others, 1979
Figure 3. 1.1.F-1 Soil associations and permeability in St. Thomas and St. John, U.S. Virgin Islands.
132 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
3.1.2 ST. CROIX, U.S. VIRGIN ISLANDS
By Zelda Chapman Bailey
3.1.2.A Location and Major Geographic 
Features
(fig. 
3.1.2.A-1). Total land area is about 82 mi2 . St. Croix 
lies about 40 miles south of St. Thomas and St. John, and 
about 60 miles east-southeast of Puerto Rico. Christiansted
St. Croix, the largest of the U.S. Virgin Islands, is 
and Fredricksted are the principal population centers, but a 
about 20 miles long and 5 miles wide at its widest point 
number of villages are scattered throughout the island.
ATLANTIC OCEAN
ST. CROIX
CARIBBEAN SEA
17"45'
17°40'
64'50'
45'
40"
64'35'
CARIBBEAN SEA
ST. CROIX
CARIBBEAN SEA
EXPLANATION
^B 
EXTENT OF MARL, ALLUVIUM 
^^ 
AND LIMESTONE DEPOSITS
^| 
LAGOON OR POND
    EPHEMERAL STREAM
  
TOWN
0 
1 
2 KILOMETERS
I 
il
I 
I 
I
0 
1 
2 MILES
Modified from Gill, 1991
Figure 3.1.2.A-1 Location and major geographic features in the Kingshill aquifer, St. Croix, U.S. Virgin Islands.
3.1.2 St. Croix, U.S. Virgin Islands 
133
The northwestern part of St. Croix is a rugged 
mountainous area called the Northside Range, which 
runs from the west end of the island to Salt River Bay. 
Elevations generally range from 600 to 800 feet above 
mean sea level, although two peaks are higher than 
1,000 feet. 
Steep, deeply entrenched valleys extend 
from the central ridge. 
To the north and west, the 
mountains slope directly to the sea. The mountains are 
bounded by a gently rolling plain to the south. 
Eastward, the plain broadens and is marked by rounded 
limestone hills and broad valleys. East of Christiansted, 
the mountainous East End Range has peaks that reach 
800 feet in elevation above mean sea level and are 
more rounded.
Headwaters of the major streams of the island (fig. 
3.1.2.A-1) originate in the Northside Range (Jordan, 
1975, p. 10). These streams were once perennial, but 
now flow only when recharged by rainfall. The River Gut 
system, which includes Adventure and Bethlehem Guts, 
drains about 11 mi2. Jolly Hill and Salt River Guts drain 
about 4 and 4.5 mi2 , 
respectively. 
Creque and 
Caledonia Guts each drain about 1 square mile.
3.1.2.B Population and Estimated 
Ground-Water Use
The population of St. Croix in 1985 was about 
54,000, more than triple the population in 1960. The 
population is concentrated in the two cities, Fredricksted 
(population 4,350) and Christiansted (population 3,700), 
and in a number of villages and housing developments 
located primarily on the central lowland. 
About 60 
percent of the population is served by public-water 
supply, which derives water primarily from desalination 
plants. Ground water furnishes about 10 percent of the 
freshwater for public supply throughout the island. The 
remaining population is self supplied, either from rainfall 
collected from rooftops or from ground water. 
Total 
ground-water pumpage in 1985 (table 3.1.2.B-1) was
about 1.3 Mgal/d (Torres-Sierra, 1987). 
About 59 
percent of ground-water withdrawals were for public 
supply (0.22 Mgal/d) and domestic self-supplied (0.55 
Mgal/d). Commercial ground-water usage was about 26 
percent (0.34 Mgal/d) of the total, and industrial usage 
was almost 15 percent (0.19 Mgal/d).
A pipeline between the two principal cities on St. 
Croix is connected to saltwater desalination plants at 
Christiansted and to well fields at Adventure, Barren 
Spot, Concordia, Fairplain, Golden Grove, Negro Bay, 
La Grange, and Mahogany Road (fig. 3.1.2.B-1). Other 
wells supply individual villages. 
A large number of 
privately owned wells are used for domestic and 
commercial supplies.
Pumping from municipal and commercial well fields 
in 1967 was about 0.9 Mgal/d (Jordan, 1975, p. 42). 
Prior to 1967, pumping had been as much as 1.28 
Mgal/d, but the Golden Grove and Manning well fields 
were taken out of production due to the closing of a 
sugar factory. Pumping from the Mahogany Road well 
field was reduced by 30 percent because of saltwater 
encroachment, and pumping from the Adventure well 
field was reduced by 90 percent because of low ground- 
water levels. Demand for water increased the pumping 
at the other well fields, and in 1990, ground-water 
withdrawals from the municipal well fields totalled 1.13 
Mgal/d, an increase from the 0.22 Mgal/d pumped in 
1985 (table 3.1.2.B-2).
Table 3.1.2.B-1 Ground-water withdrawals and estimated population served during 
1985 for St. Croix, U.S. Virgin Islands (Modified from Torres-Sierra, 1987) 
[Mgal/d, million gallons per day;  , no data available]
Use and supplier
1. Domestic Use
1 A. Virgin Islands Water and Power Authority
B. Private Supplies (wells or purchased) 
Subtotal
Estimated 
population 
served
30,000
2 24,000
54,000
Average 
ground-water 
withdrawals 
(Mgal/d)
0.22
0.55
0.77
II. Industrial Use
Commercial Use
0.19
0.34
Total
54,000
1.30
1 Supply supplemented with 1.9 Mgal/d of desalinated sea water.
2 Population supplied supplements ground water with rain water.
Table 3.1.2.B-2 Average daily ground-water withdrawals from 
municipal well fields during September to November 1990, St. 
Croix, U.S. Virgin Islands (Data from daily operational sheets of 
the Virgin Islands Water and Power Authority)
Well Field
Pumpage 
(gallons per day)
Barren Spot
Concordia
Fairplain
Adventure, Golden Grove, Negro 
Bay, and areas north of Alexander 
Hamilton Airport
Prosperity,
Little La Grange, Fredericks 
Haab, and Mahogany Road
291,900
261,700
417,200
158,600
Total
1,129,400
134 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
64"50'
45'
40
64°35'
17°45'
17°40'
CARIBBEAN SEA
ST. CROIX
CARIBBEAN SEA
1 
2 KILOMETERS
i 
I_____
\ 
\ 
1 
2 MILES
EXPLANATION
I 
. 
I 
EXTENT OF MARL, ALLUVIUM 
t*-  *1 
AND LIMESTONE DEPOSITS
LAGOON OR POND
  
     EPHEMERAL STREAM
PUBLIC-SUPPLY WELL FIELDS
LOCATION AND NUMBER OF DOMESTIC WELLS 
AT SITE WHEN MORE THAN ONE WELL PRESENT
TOWN
From U.S. Geological Survey Ground-Water Site Inventory Database, 1991
Figure 3.1.2.B-1 Clusters of well fields and location in St. Croix, U.S. Virgin Islands.
3.1.2 St. Croix, U.S. Virgin Islands 
135
3.1.2.C Geologic Setting
The mountainous areas of the northwestern and 
eastern ends of St. Croix are composed largely of 
fractured and deformed rocks of volcanic origin or of 
sedimentary rocks derived by the erosion of older 
volcanic rocks. The volcanic rocks are the Caledonic, 
Judith Fancy, Cane Valley, and Allandale Formations of 
Cretaceous age (fig. 3.1.2.C-1). These formations are
primarily metamorphosed tuffs (Cederstrom, 
1950, 
p. 16). 
Two areas have small intrusions of plutonic 
rocks; gabbro in the northwest and diorite in the east. 
Stream valleys cut into the volcanic rocks are filled with 
alluvium in the coastal areas. The alluvium is composed 
mostly of clay and silt, and contains some thin beds or 
lenses of sand and gravel. 
Alluvium in the valleys 
draining the gabbro intrusion is composed largely of 
sand.
During Oligocene and Miocene time, a volcanic ash 
was deposited between the mountain masses in what 
was probably a graben in a larger St. Croix island mass. 
Coarse- and fine-grained alluvial material from the 
northwestern mountains was also carried into the 
graben 
and 
interfingered 
with 
the volcanic ash 
(Cederstrom, 1950). 
This material, consisting of 
alluvial-deposited, calcareous conglomerate in outcrop 
and blue clay in the subsurface, are together called the 
Jealousy Formation, 
and exceeds 
1,400 feet 
in
thickness. The Jealousy Formation is overlain by the 
calcareous mud and reef deposits of the Kingshill 
Limestone, which has a maximum thickness of about 
450 feet.
Fine-grained Quaternary alluvium mantles the 
coastal lowland. Alluvium in the River Gut drainage, 
containing considerable deposits of sand and gravel, 
cuts across the Kingshill Marl. 
In other valleys, the 
alluvium generally is composed of silt and clay and 
contains occasional lenses of sand and gravel.
64°50'
45'
40'
64°35'
CARIBBEAN SEA
ST. CROIX
17°45'
EXPLANATION
CARIBBEAN SEA
17°40'
2 KILOMETERS
i 
l 
1 
2 MILES
SURFICIAL DEPOSITS
/
JEALOUSY FORMATION 
KINGSHILL LIMESTONE 
CALEDONIC FORMATION 
JUDITH FANCY FORMATION 
CANE VALLEY FORMATION 
ALLANDALE FORMATION 
PLUTONIC ROCKS
LAGOON OR POND 
EPHEMERAL STREAM 
TOWN
Recent j QUATERNARY
Miocene
and 
^ TERTIARY 
Oligocene
Upper 
Cretaceous f CRETACEOUS
Modified from Whetten, 1966
Figure 3.1.2.C-1 Generalized surficial geology in St. Croix, U.S. Virgin Islands.
136 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
3.1.2.D Hydrogeology
Recharge to the ground-water system in St. Croix is 
small because of the low storage capacity of the 
aquifers (Jordan, 1975, p. 9). 
Only about one to six 
percent of annual rainfall may reach the water table and 
recharge the aquifers (Jordan, 1975, p. 43). 
The 
eastern third of the island usually receives less than 30 
inches of rain annually. This low rainfall, coupled with 
high evapotranspiration, results in infrequent recharge to 
the aquifers and often there is no recharge over periods 
of a year or more. Flow is rare in the ephemeral streams 
of the area. 
Ground-water quality is generally poor 
because 
mineral 
salts 
are 
concentrated 
by 
evapotranspiration. 
In contrast, the northwestern 
quarter of the island receives as much as 50 or more 
inches of rain annually. 
Aquifers in this area are 
recharged several times a year, and the recharge is 
reflected in ground-water discharge that maintains flow 
in perennial reaches of several streams in the Northside 
Range.
Fractured volcanic rock aquifers underlie eastern 
and northwestern St. Croix. Permeability is low in these 
aquifers, consisting of openings along joints and 
fractures. The greatest permeability occurs where these 
openings have been enlarged by weathering and 
dissolution. 
Ground water from the fractured rock 
aquifer has the lowest mineral salts content of any 
ground water on the island.
The principal aquifer on St. Croix is in the Kingshill 
Limestone (fig. 3.1.2.C-1). The quality of water in this 
aquifer is poor. Transmissivity is variable in the Kingshill 
aquifer, ranging from between 50 and 4,000 ft2/d (fig. 
3.1.2.D-1). The saturated thickness of the aquifer in 
1968 was as much as 200 feet (Robison, 1972). Water 
is obtained from solutioned and fractured limestone 
lenses and reef deposits in the Kingshill Limestone. 
Sand- and gravel-filled stream channels in the eastern 
part of the Kingshill Marl are the important water-bearing 
units. Buried alluvial fans that are water bearing in the 
Kingshill Marl are located where several present-day 
streams flow from the Northside Range onto the central 
lowlands. The quality of ground water in the Kingshill
aquifer is affected by residual water trapped in the 
lagoonal muds originally deposited. 
Dissolved-solids 
concentrations range from about 500 mg/L to more than 
1,000 mg/L. 
Mineral salts carried into the aquifer by 
recharge and concentrated in the soil zone by 
evapotranspiration also contribute to the poor quality of 
the water in the aquifer.
Alluvium is deposited in the valleys of several 
streams that originate in the Northside Range and cross 
south-central St. Croix. 
In general, these alluvial 
deposits are too thin or clayey to be significant aquifers, 
but act as reservoirs that recharge the underlying 
Kingshill Marl. Only along the lower reaches of River 
Gut (fig. 3.1.2.A-1) are the alluvial deposits of sufficient 
extent and thickness to be of importance as an aquifer. 
The water from the alluvium of the central lowlands 
resembles a mixture of water from the Kingshill aquifer 
and from the fractured rock aquifer of the Northside 
Range in quality. In the upper reaches of River Gut, thick 
water-bearing alluvial deposits are associated with 
dioritic rocks that were intruded into the volcanic rocks. 
Elsewhere, the alluvial deposits generally fill coastal 
embayments at the mouths of streams. These alluvial 
deposits act as a recharge reservoir for the underlying 
fractured rock aquifer.
Well yields from the volcanic aquifers are generally 
inadequate for public supply, but may provide water for 
domestic use. 
The Kingshill aquifer is capable of 
yielding several hundred gal/min if wells were drilled 
through the entire saturated thickness, but the quality of 
water would be poor (Robison, 1972, p. 3). Wells in 
joints, isolated beds of limestone or sand and gravel 
within the marl yield 5 to 10 gal/min. Wells in the reef- 
associated limestone may yield between 10 and 300 gal/ 
min (Jordan, 1975, p. 21). 
The Kingshill Marl is the 
principal aquifer supplying the Barren Spot and 
Concordia well fields. The alluvium, although too thin to 
provide much water in most areas, is the principal 
aquifer supplying the Adventure and Fairplain well fields. 
Well yield from the more productive areas of alluvium 
are between 10 and 50 gal/min (Jordan, 1975, p. 21).
3.1.2.E Ground-Water Levels and 
Movement
The ground-water surface in the fractured rock 
water-table aquifers of the East End and Northside 
Ranges is about 200 feet below land surface and 
generally follows the topography of the land surface. At 
the base of the mountains and in the mountain valleys, 
the water surface is about 50 feet below land surface. 
Ground-water levels were as much as 160 above mean 
sea level in 1962 (Jordan, 1975, p. 23).
The 
Kingshill 
aquifer 
is 
under 
water-table 
conditions. Water levels ranged from mean sea level to 
100 feet above mean sea level in July 1987 (fig. 
3.1.2.E-1). 
In general, ground-water levels and 
movement are controlled by the major valleys and 
movement is toward and down the valleys to the sea.
Water levels declined 20 feet or more in the 
mountains between 1940 and 1967, which probably 
explains a concurrent reduction in strearnflow during the 
same period (Jordan, 1975, p. 24). Water levels have 
continued to decline and were about 5 feet lower in 1987 
than in 1967 (Torres-Gonzalez, 1991).
3.1.2.F Soil Permeability
Soil associations (fig. 3.1.2.F-1) developed on 
steep or strongly sloping areas include Descalabrado- 
Jacana and Cramer-lsaac, formed on volcanic rock; 
Aguilita-Fredensborg-Sion, formed on marly limestone; 
and Southgate-Parasol, formed on weathered granitic 
rock and alluvial fans (U.S. Department of Agriculture, 
1970, p. 3-5). These soils are well drained but thin, and 
the areas covered are useful primarily for pasture or 
woodland. 
Permeability of these soil associations 
ranges from 0.2 to 2.0 in/hr (table 3.1.2.F-1).
Nearly level to gently sloping areas are covered by 
the Fraternidad-Aguirre-Glynn and Cornhill-Coamo-San 
Anton associations. These associations form on alluvial 
fans and flood plains, and range from well- to poorly- 
drained. 
Cornhill-Coamo-San Anton soils are suited 
only for pasture or woodland. The Fraternidad-Aguirre- 
Glynn soils are the only soils suited to agriculture, but 
are limited to certain crops. Permeability of these soil 
associations ranges from 0.06 to 0.60 in/hr.
Table 3.1.2.F-1 Thickness, permeability, and available water capacity for the soil 
associations in St. Croix, U.S. Virgin Islands (Modified from U.S. Department of 
Agriculture, 1970)
Area and soil association
Descalabrado-Jacana
Aguilita-Fredensborg-Sion
Fraternidad-Aguirre-Glynn
Southgate-Parasol
Cramer-lsaac
Cornhill-Coamo-San Anton
Thickness 
(inches)
Oto36
Oto20
OtoGO
OtoGO
Oto72
OtoGO
Permeability 
(inches per hour)
0.20 to 0.60
0.60 to 2.00
0.06 to 0.20
0.20 to 0.60
0.60 to 2.00
0.20 to 0.60
Available water 
capacity 
(inches per inches)
0.10 to 0.20
0.10 to 0.20
0.10 to 0.20
0.10 to 0.20
0.1 5 to 0.20
0.10 to 0.20
3.1.2 St. Croix, U.S. Virgin Islands 
137
64°35'
17°45'
17°40'
ST. CROIX
CARIBBEAN SEA
NORTHSOE RANGE 
(,
EAST END RANGE
CHRISTIANSTED
EXPLANATION
EXTENT OF MARL, ALLUVIUM 
AND LIMESTONE DEPOSITS
LAGOON OR POND
CARIBBE4NS
LINE OF EQUAL APPARENT TRANSMISSIVITY-ln feet 
squared per day. Contour interval is variable. Datum is 
mean sea level
EPHEMERAL STREAM 
LOCATION OF AQUIFER TEST 
TOWN
0 
1 
2 KILOMETERS
I 
I
Modified from Torres-Gonzalez, 1991
Figure 3.1.2.D-1 Transmissivity estimates at selected wells in the regionalized transmissivity distribution as obtained through model calibration in St. Croix, U.S. Virgin Islands.
138 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
64°50'
40'
64°35'
17°45'
17°40'
ST. CROIX
EXPLANATION
   30   
EXTENT OF MARL, ALLUVIUM 
AND LIMESTONE DEPOSITS
LAGOON OR FOND
WATER-LEVEL CONTOUR-Shows altitude 
of water level, in feet. Contour interval 
is variable. Datum is mean sea level
GENERALIZED DIRECTION OF GROUND- 
WATER FLOW
0 
1 
2 KILOMETERS
I 
II____. 
I      I     I 
0 
1 
2 MILES
     -  
EPHEMERAL STREAM
TOWN
Modified from Torres-Gonzalez, 1991
Figure 3.1.2.E-1 Altitude of water-level surface and direction of ground-water flow during July 1987 in St. Croix, U.S. Virgin Islands.
3.1.2 St. Croix, U.S. Virgin Islands 
139
64°50'
45'
40'
17°45'
17°40'
CARIBBEAN SEA
64°35'
ST. CROIX
CARIBBEAN SEA
1 
2 KILOMETERS
I 
I
I 
I 
1 
2 MILES
EXPLANATION
SOIL PERMEABILITY, IN INCHES 
PER HOUR
FROM 0.06 TO 0.20 
FROM 0.20 TO 0.60 
FROM 0.60 TO 2.00
SOIL ASSOCIATION BOUNDARY 
TOWN
SOIL ASSOCIATIONS
1 DESCALABRADO-JACANA
2 AGUILITA-FREDENSBORG-SION
3 FRATERNIDAD-AGUIRRE-GLYNN
4 SOUTHGATE-PARASOL
5 CRAMER-ISAAC
7 CORNHILL-COAMO-SAN ANTON
Modified from Rivera and others, 1975; Gilberto Acevedo, Soil Conservation Service, written communication, 1990
Figure 3.1.2.F-1 Soil associations and permeability in St. Croix, U.S. Virgin Islands.
140 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
4.0 PRESENT AND POTENTIAL GROUND-WATER PROBLEMS IN 
PUERTO RICO AND THE U.S. VIRGIN ISLANDS
4.0 Present and Potential Ground-Water Problems in Puerto Rico and the U.S. Virgin Islands 
141
4.0 PRESENT AND POTENTIAL GROUND-WATER PROBLEMS IN 
PUERTO RICO AND THE U.S. VIRGIN ISLANDS
In this concluding section, present or potential 
problems related to ground water are discussed. 
Common 
problems 
include ground-water demand 
versus 
potential 
for 
development, 
possible 
contamination 
sources, 
sea-water 
encroachment, 
natural concentration of minerals in ground water, and 
consequences of ground-water development.
4.1 NORTH COAST AREA
4.1.1 Aguadilla-Hatillo Region
The Aguadilla-Hatillo region contains some of the 
most highly developed karst features on Puerto Rico. 
The presence of abundant sinkholes and solution 
cavities provide for rapid infiltration of any contaminants 
and very little, if any, attenuation of contaminants. Five 
active 
municipal 
landfills 
were 
reported for the 
Aguadilla-Hatillo region in 1977, and all of these landfills 
were developed in or adjacent to sinkholes, which would 
provide a direct pathway for leachate to enter the 
ground-water system (Torres-Gonzalez and Gomez- 
Gomez, 1982). 
Karst features also provide potential 
pathways for contaminants, 
such 
as 
agricultural 
chemicals 
and 
petroleum 
products 
from 
leaking 
underground storage tanks (for example from gasoline 
station tanks), to enter the ground-water system.
Existing demand for water in the Aguadilla-Hatillo 
region is met primarily by water from Lago Guajataca. 
Additional urban and tourist-industry growth will result in 
additional demands for water, some of which could be 
supplied by ground water. However, because of the 
relatively thin aquifer, the potential for additional ground- 
water development is limited. Drilling of water-supply 
wells is expensive because of the great depth to the 
water table over much of the region. Also, yields to
wells may be low unless a particularly productive zone is 
penetrated. 
Additional pumping near coastal areas, 
where the freshwater lens is thin, could induce inland 
movement 
of 
saline 
water 
and 
subsequent 
contamination of wells.
An additional problem in the Aguadilla-Hatillo region 
is the generally limited knowledge of the hydrogeologic 
system. Knowledge of such factors as aquifer hydraulic 
properties, depth to the water table, water quality, 
stream-aquifer relations, and areas of existing or 
potential contamination is essential in assessing the 
potential for additional ground-water development and 
contamination.
4.1.2 Arecibo-Manati Region
Ground water from the upper unconfined and lower 
artesian is suitable for drinking and most other uses 
throughout the Arecibo-Manati region; and development 
of the ground-water resources in the region has 
increased dramatically since the early 1970's. Pumpage 
from both aquifers increased from less than 8 Mgal/d in 
1970 to more than 18 Mgal/d in 1982, of which the lower 
aquifer supplied about 5 Mgal/d. Yields of the upper 
aquifer are rapidly approaching a rate beyond which 
extensive 
sea-water 
encroachment 
could 
occur. 
Competition 
for 
ground 
water 
among 
industries, 
municipios, and agriculture is intense in the region and is 
expected to increase in the future.
The saltwater encroachment of sea water as the 
result of lowered water levels in the upper aquifer has 
affected public-supply wells completed in the limestone 
near the edge of the flood plain of the Rfo Grande de 
Manati (Gomez-Gomez, 
1984). 
Similar saltwater 
encroachment problems have been reported in wells at 
Central Cambalache in the flood plain of the Rio Grande 
de Arecibo.
There are two known cases of ground-water 
contamination affecting the upper aquifer in the region. 
Both are related to organic compounds from the 
industrial area along Highway 2 near Cruce Davila. In 
one case, a public water-supply well was contaminated 
by backflow of organic wastes from a nearby injection 
well (Angel Class-Cacho, U.S. Geological Survey, 
written communication, 1982). In the other case, water 
in a small area of the upper aquifer at Barceloneta was 
contaminated as a result of an accidental spill of carbon- 
tetrachloride (Zack and others, 1987a, p. 441). 
In the 
latter case, organic compounds were detected in a 
shallow injection well injecting organic compounds into 
the saline parts of the Aymamon Limestone.
Two industrial injection wells were drilled into the 
Lares Limestone in the late 1960's. 
Both wells are 
located near Cruce Davila in the Highway 2 industrial 
area. One of the wells was used to inject acid waste and 
the other, mentioned previously, was used to inject 
organic wastes. Neither well is currently being used for 
injection. 
The high potentiometric surface overlying 
freshwater in the Lares Limestone, about 400 feet above 
mean sea level, could result in contamination of the 
upper or lower aquifers if the casings in these wells are 
ever breached by corrosion.
Drainage in karst areas is mostly underground and 
the abundance of sinkholes provides easy access for 
contaminants to reach the aquifers. Sinkholes, which 
are numerous in the Arecibo-Manati region, have been 
used in the past for disposal of liquid and solid wastes 
by individuals and industries. In addition, at least three 
municipal landfills in the region were located in 
sinkholes. Sources of contaminants to the upper aquifer 
in the region include effluent from septic tanks and, in 
the more densely populated rural areas, effluent from 
sewage treatment plants.
4.1.3 Vega Baja-Toa Baja Region
Through the end of 1992, the only problem that has 
affected use of ground water in the Vega Baja-Toa Baja 
region was the discovery in 1983 of organic solvents at a 
public water-supply well in the vicinity of an industrial 
park at Vega Alta (Guzman-Rfos and Quinones- 
Marquez, 1984). The principal solvents detected were 
trichloroethylene (TCE) and tetrachloroethylene (PCE) 
in concentrations as high as 480 and 776 jj.g/L, 
respectively. Since 1983, five public water-supply wells 
have been closed, resulting in a yield loss of about 2 
Mgal/d. 
This loss has been offset by increasing 
withdrawals in other wells and the construction of new 
wells in unaffected areas. 
The extent of aquifer 
contamination by volatile organics having a total 
concentration of 10 jj,g/L or more was determined to be 
about 2 mi2 in 1985 (Bechtel Environmental, Inc., 1990).
The slow increase in dissolved-solids concentration 
that may result from saltwater encroachment along the 
coastal part of the aquifer could also become a major 
problem in the near future (Gomez-Gomez and Torres- 
Sierra, 1988). In general, all wells located northward of 
the karst tableland and within the coastal plain yield 
ground water that has dissolved-solids concentrations 
greater than 350 mg/L, and several major production 
wells have been abandoned as a result of increased 
salinity.
Although an assessment on the effect of septic tank 
infiltration to the aquifer has not been made, rapid 
population growth since 1980 and the relatively low 
percentage of housing units served by public sewers 
indicates that septic tank effects could become a 
problem in the foreseeable future. The soils that overlie 
the karst tableland, consisting principally of residuum 
deposits derived from weathering of the limestone rocks, 
have poor permeability. As a result, most septic tanks at
142 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
areas underlain by blanket sands deposits are sited 
within near-surface exposures of carbonate rocks. The 
1980 census estimated that there were approximately 
9,860 housing units within Vega Alta and Dorado which 
were not connected to public sewage treatment 
facilities. Total nitrogen generated from this number of 
housing units could be about 240 tons per year based 
on an average of 3.6 persons per housing unit and 17 
grams of nitrogen produced per person per day (17 
grams of nitrogen represents the average protein 
consumption per person in United States).
4.1.4 Bayamon-Loiza Region
Urban and industrial development are reducing the 
recharge areas of the aquifers in the Bayamon-Lofza 
region due to the construction of buildings and paving of 
the open land. This decrease in recharge area affects 
the ground-water supply and could result in additional 
salt-water intrusion to the aquifers. The channelization 
of rivers may also reduce the recharge to the aquifers 
and affect local ground-water levels.
The water-use demand in the Bayamon-Lofza 
region is met principally with surface water from Lago 
Lofza and Lago La Plata. 
Due to the finite saturated 
thickness and low transmissivity of the aquifers in the 
Bayamon-Lofza region the development potential of 
aquifers to meet additional water demand is limited.
Leaky underground tanks and sewer lines are a 
potential 
source 
of 
ground-water 
contamination, 
especially in highly urbanized and industrial areas such 
as the San Juan metropolitan area. Contamination of 
the aquifers from industrial and domestic waste disposal 
practices is a potential problem in the region. Three 
landfills are located within the region, including the 
largest one on the island, which is located near Bahfa de 
San Juan. 
In the southern part of the region where 
farmland dominates, livestock waste disposal may 
represent 
a 
potential 
ground-water contamination 
problem.
4.2 SOUTH COAST AREA
4.2.1 Santa Isabel-Patillas Region
The quality of ground water in the Santa Isabel- 
Patillas region makes it suitable for most uses. 
Dissolved solids concentration range from 130 to 2,500 
mg/L, increasing toward the coast where seawater 
encroachment occurs. Seawater intrusion and use of 
fertilizers 
and 
pesticides 
in 
agriculture 
represent 
potential ground-water quality problems in the region. 
Although seawater intrusion has not been detected in 
the Santa Isabel-Patillas region, the potential exists for 
coastal areas in the vicinity of Bahfa Jobos and between 
Rfo Descalabrado and Rfo Jueyes (Dfaz, 1974, p. 23- 
24; Giusti, 1971, p. 24). Application of large quantities of 
fertilizers and pesticides represents a potential source of 
ground-water 
contamination. 
However, 
samples 
collected by the U.S. Geological Survey have shown no 
contamination in the aquifer with either fertilizers or 
pesticides. 
A reconnaissance sampling for organic 
compounds 
conducted 
in 
1983 
indicated 
no 
contamination with organics in the alluvial aquifer 
(Guzman-Rfos and Quinones-Marquez, 1985a and 
1985b).
Simulations of ground-water flow have shown that 
east of the Rfo Jueyes, ground-water levels may decline 
if aquifer recharge from irrigation canal systems is 
diminished and actual 
ground-water pumpage 
is 
maintained (Sigfredo Torres-Gonzalez, U.S. Geological 
Survey, written communication, 
1987). 
Seawater 
intrusion may result from ground-water level declines. 
West of the Rfo Jueyes, the drip-irrigation system could 
diminish net recharge to the aquifer. 
Changes from 
furrow to drip irrigation are expected to reduce aquifer 
recharge by as much as 30 percent. 
Drip-irrigation 
implies a reduction in the ground-water demand in 
relation to furrow irrigation. 
However, according to a 
recent survey, ground-water pumpage in the region 
remains about the same (Orlando Ramos-Gines and 
Angel Roman-Mas, U.S. Geological Survey, written 
communication, 1987).
Streamflow represents the major source of ground- 
water recharge in the area west of the Rfo Jueyes 
(Ramos-Gines, 1993). 
Use of Streamflow as a water 
source results in reduction of ground-water recharge, 
which in turn could cause an abrupt decline of the 
ground-water levels and possible seawater intrusion.
4.2.2 Juana Diaz-Ponce Region
The alluvial aquifer in the Juana Dfaz-Ponce region 
generally has good-quality water, but its suitability for 
particular uses may be affected by water from 
underlying formations. Ground-water samples collected 
in 
the 
region 
show 
that 
the 
dissolved-solids 
concentration from the upper part of the alluvial aquifer 
may have increased as a result of mixing with water 
from either the Ponce Limestone or the Juana Dfaz 
Formation. Consequently, ground-water development in 
the upper valley areas is limited, although the thickness 
of the alluvium 
and 
permeability are adequate. 
Additional development of ground water may be 
possible closer to the coast line. 
Although seawater 
intrusion has not been detected in the Juana Dfaz- 
Ponce region in recent years, inadequate management 
of ground-water withdrawals could result in overpumping 
the aquifer and subsequent seawater intrusion. Stream 
water development may need to be limited in the Juana 
Dfaz-Ponce region because Streamflow is a major 
source of ground-water recharge. Reduction of ground- 
water recharge from Streamflow may result in an abrupt 
decline of the ground-water levels and subsequent 
seawater intrusion.
The large quantities of fertilizers and pesticides 
used in agricultural areas represent another potential 
source of ground-water contamination. 
However, 
samples collected by the U.S. Geological Survey have 
shown no contamination in the aquifer by fertilizers or 
pesticides. 
A reconnaissance sampling for organic 
compounds conducted in 1983 indicate the presence of 
methylene chloride extractable and tetrachloroethylene 
in two of four wells sampled in the region (Guzman-Rfos 
and Quinones-Marquez, 1985a and 1985b).
4.2.3 Penuelas-Guanica Region
Although available ground-water resources in the 
Penuelas-Guanica region seem to be adequate to 
supply the present water needs, the aquifer is sensitive 
to changes in recharge patterns. Results of simulations 
made with electric analog and digital ground-water flow 
models 
indicate 
that 
diminished 
ground-water 
availability and seawater intrusion problems may occur if 
recharge into the aquifer decreases markedly (Bennett, 
1976, p. 70-71; Quinones-Aponte, 1986b, p. 31). These 
studies indicate that aquifer recharge is very sensitive to 
Streamflow conditions and seepage from irrigation 
channels. As Streamflow increases by releasing more 
water from headwater reservoirs, aquifer recharge also 
increases. Furrow irrigation is another major source of 
aquifer recharge, and any decrease in this recharge 
source could result in future lower water levels if ground- 
water withdrawals remain the same.
Ground water in the Penuelas-Guanica region is 
suitable for most uses. Dissolved-solids concentrations 
in water within the alluvial aquifer range from 160 to 260 
mg/L in the Tallaboa Valley (Grossman and others, 
1972, p. 81), from 200 to 450 mg/L in the Guayanilla- 
Yauco Valleys and coastal plain (Crooks and others, 
1968, p. 51), and from 130 to 800 mg/L in the Rfo Loco 
Valley (McClymonds, 
1967, 
p. 40). 
In general, 
dissolved-solids concentrations increase toward the 
coast. Near the limestone hills, ground water is slightly 
higher in dissolved-solid concentrations (Grossman and 
others, 1972, p. 82). Seawater encroachment in lower 
valley areas and coastal plains may affect the suitability 
of ground water as total dissolved solids increase from 
250 mg/L to seawater concentrations. Wells in coastal 
areas may yield water that ranges from fresh (shallow 
wells) to brackish (seawater upconing due to heavy 
pumpage) to salty (deep wells). 
For instance, any 
attempt to use and divert most of the river water within 
the valley could produce an inland advance of the salt- 
water wedge, because Streamflow seepage into the 
aquifer is the major source of aquifer recharge 
(Grossman and others, 1972, p. 101). Seawater also 
may intrude into the aquifer through streambeds if lower 
streams reaches are channelized in order to provide 
better local drainage and to accelerate flood runoff
4.0 Present and Potential Ground-Water Problems in Puerto Rico and the U.S. Virgin Islands 
143
(Grossman and others, 1972, p. 98). 
Waste-water 
discharges to streams also could affect ground-water 
quality through stream seepage. A reconnaissance 
sampling for organic compounds conducted in 1983 
found no detectable contamination with organics at 
public water-supply wells 
in 
the alluvial 
aquifer 
(Guzman-Rios, and Quinones-Marquez, 1985a and 
1985b).
4.3 WEST COAST AREA 
4.3.1 Anasco Region
Di'az and Jordan (1987) documented evidence of 
inland movement of saltwater in 1981 and 1982. 
Saltwater was reaching the alluvium through Cano La 
Puente and Cano Boquilla. 
High concentrations of 
chloride were detected in water samples from swamp 
and marsh areas near these two streams, probably due 
to high evapotranspiration rates that characterize these 
areas. 
Chloride concentrations of 100 mg/L were 
detected in water samples as far as 1.5 miles inland in 
the Cano La Puente area during June 1981, and as far 
as 1.8 miles inland in February 1982 (Di'az and Jordan, 
1987, p. 41).
Another 
potential 
ground-water 
problem 
is 
contamination 
from 
septic-tank 
effluents 
where 
residential areas overlie the aquifers. 
In the Anasco 
region, where about 43 percent of all residential units 
use a septic tank or cesspool (U.S. Department of 
Commerce,1982), major residential areas are located 
over the lower valley aquifer.
Although ground-water use in this region is limited, 
ground-water quality is generally suitable for most uses, 
and is within the U.S. Environmental Protection Agency 
limits for drinking water (U.S. Environmental Protection 
Agency, 1976; Diaz and Jordan, 1987, p. 42).
4.3.2 Guanajibo Region
According to Colon-Dieppa and Quinones-Marquez 
(1985, p. 42), ground-water in the central Guanajibo 
Valley is generally suitable for most uses, including 
irrigation. 
High concentrations of sulfate and nitrates 
were detected in samples from two wells in the valley. 
In 1967, a sample obtained from a well had sulfate
concentrations that exceeded the secondary maximum 
contaminant levels (U.S. 
Environmental Protection 
Agency, 1976). 
Another well, showed similar results, 
exceeding 
the 
recommended 
U.S. 
Environmental 
Protection 
Agency drinking standards for sulfate 
concentrations in 1980. Both of these wells are located 
downstream from urban areas, which suggests that they 
were affected by domestic contamination (Colon-Dieppa 
and Quinones-Marquez, 1985, p. 42).
The San German municipal landfill cover material is 
very permeable and leached substances from the landfill 
have contaminated an adjacent creek that drains to the 
Rio Guanajibo (Torres-Gonzalez and Gomez-Gomez, 
1982, p. 115). 
This represents a potential source of 
contamination for the ground-water resources of the 
region.
4.3.3 Lajas Region
The development of ground-water supplies in the 
Lajas region could be limited due to the high mineral 
content of the ground water. Samples were collected 
from 20 wells in the Lajas Valley and analyzed for 
principal cations and anions, iron, manganese, barium, 
and aluminum. Water samples from 19 of these wells 
had dissolved-solids or chloride concentrations that 
exceeded the secondary maximum contaminant levels 
for drinking water standards of 500 and 250 mg/L, 
respectively (U.S. Environmental Protection Agency, 
1973). 
Samples from 
13 of the 20 wells 
had 
concentrations of dissolved iron or manganese that 
exceeded the secondary maximum contaminant level for 
drinking water standards of 0.3 and 0.05 mg/L, 
respectively (U.S. Environmental Protection Agency, 
1986).
The high concentration of dissolved solids found in 
most of the samples was due primarily to high 
concentrations of sodium and chloride ions. An analysis 
of 75 ground-water samples collected from wells located 
throughout the valley had chloride concentrations 
ranging from 20 to 6,760
4.4 EAST COAST AREA
4.4.1 Naguabo-Maunabo Region
The development of surface-water supplies in the 
Naguabo-Maunabo 
region 
are 
limited 
because 
topography precludes the construction of reservoirs in 
the upper stream reaches, and sewage contamination 
inhibits development in the lower reaches. 
Future 
development will probably rely on ground water for 
industrial, agricultural, and domestic supply. 
Large- 
scale ground-water development will be limited to the 
alluvial aquifers that are presently the most developed.
Ground-water development in the upland areas will 
be small because yields to wells generally range from 5 
to 50 gal/min. The development of agriculture in the 
upland areas represents a potential non-point source of 
pollution to these aquifers from fertilizers, herbicides, 
and insecticides and point-source pollution by waste 
from dairy-cattle farms. 
The location of municipal 
landfills in the upland areas represents additional point 
sources of pollution to the aquifer. 
Pollution of the 
aquifer from this latter source is generally limited in areal 
extent.
The low transmissivity of the alluvial aquifer within 
the Humacao-Naguabo area limits its potential for 
development. 
This contrasts with the fact that large 
industrial and urban development is planned for the 
region. 
In addition, the effects of any future ground- 
water development on lagoons and wetlands in the 
region should be evaluated. 
These lagoons and 
wetlands, which depend on ground water as their major 
water source, have been recognized by the PRDNER as 
areas of great ecological importance. Other aspects of 
ground-water resources that need to be considered in 
the 
Humacao-Naguabo area are: 
(1) 
potential 
contamination from the Humacao municipal landfill 
(Torres-Gonzalez, and Gomez-Gomez, 1982, p. 71); (2) 
seawater encroachment, 
particularly 
in 
the 
area 
between the Rio Anton Ruiz and Rio Santiago; (3) high 
concentrations of iron and manganese in the ground 
water; (4) potential contamination of the aquifer by 
industrial spills; and (5) potential contamination from 
river seepage (Torres-Gonzalez and Gomez-Gomez, 
1982).
The potential for additional development of the 
alluvial aquifer in the Yabucoa valley seems to be 
promising in terms of water availability. Nevertheless, 
any industrial spill from the oil refinery could impair the 
potential for future development. Saltwater intrusion into 
the aquifer probably occurs along the ship channel and 
port facilities at the refinery and near the mouths of the 
Rfo Guayanes and Cano de Santiago. Both streams are 
contaminated by sewage effluent. 
Additional ground- 
water development could cause a reversal in the 
ground-water gradient along the streams, thus inducing 
infiltration of seawater or contaminated water from the 
streams. Excessive pumping could draw seawater into 
the aquifer in the coastal area. The presence of high 
concentrations of iron and manganese in the ground 
water locally affects the suitability of the water for some 
uses.
The alluvial aquifer of the Maunabo valley has 
potential for additional development. 
Potential and 
existing problems are similar to those of the Yabucoa 
Valley: potential contamination by infiltration of sewage 
effluent from the Rio Maunabo or seawater near the 
river mouth; seawater encroachment as the result of 
excessive pumpage; and local water-quality problems 
due to naturally occurring iron and manganese.
4.5 EAST CENTRAL AREA
4.5.1 Aguas Buenas-Juncos Region
Analyses of ground water from the area indicate 
localized 
water-quality 
problems, 
including 
high 
concentrations of iron and manganese and selected 
volatile organic compounds. The use of underground 
tanks that store fuel or other substances within the 
Caguas and Gurabo-Juncos valleys is a threat to 
ground-water quality. 
Livestock waste is commonly 
disposed of on the land surface and, in some instances, 
into ponds excavated in the unsaturated zone directly 
above the water-table aquifer. These wastes may leach 
into the aquifer. The use of agricultural chemicals in the 
area also is a potential source of ground-water 
contamination.
144 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
Municipal landfills constitute a potential source of 
ground-water contamination in the Aguas Buenas- 
Juncos region, particularly landfills that are located near 
or within the alluvial valley boundaries. There are five 
landfills in the region, of which three have been closed. 
One of the closed landfills is the old Juncos landfill, 
which has been included in the U.S. Environmental 
Protection 
Agency 
"National 
Priority 
List" 
of 
contaminated sites for clean-up purposes.
The public wastewater disposal and treatment 
systems may also be a source of contamination. For 
example, in the city of Caguas, urban sewer pipes and 
the wastewater treatment plants lie directly above the 
aquifer and any leakage could introduce wastewater into 
the aquifer. Many communities that are not connected 
to the public sewer system use septic tanks or sewer 
trenches or discharge untreated wastewater directly into 
nearby creeks or streams. 
Production wells located 
near areas of contaminated or poor-quality water may 
not produce water suitable for public supply unless the 
water undergoes extensive treatment.
Much of the available surface water of the Aguas 
Buenas-Juncos region flows into Lago Lofza and is 
exported to San Juan (about 80 Mgal/d). If a ground- 
water supply is developed near streams, the hydraulic 
gradient from the river into the aquifer will increase, 
which would induce seepage from the river. This would 
improve well yield and decrease streamflow. However, 
a minimum river flow is necessary to sustain the 
required inflow into Lago Loi'za reservoir. 
It might be 
difficult to maintain the required inflow during droughts if 
the amount of induced seepage from the river to the 
aquifer is large.
4.6 PUERTO RICO OFFSHORE 
ISLANDS
4.6.1 Isla de Culebra and Isla de 
Vieques
The fractured rock aquifer of Isla de Culebra is 
considered a set of independent aquifers: the aquifer in 
each drainage basin is separated from the aquifer in 
adjacent basins by a ground-water divide. 
Although 
ground-water resource is scarce, existing or potential 
pollution of an aquifer, therefore, will usually affect a 
single basin. The ground water on Isla de Culebra is 
rich in mineral concentrations, which, in most cases, 
exceed EPA standards for drinking water. 
Dissolved- 
solids concentration range from 500 to 1,000 mg/L. This 
condition is a result of airborne particulates that fall in 
the land surface and infiltrate the aquifer during periods 
of recharge, evapotranspiration in the soil zone, and the 
limited amount of recharge. The most serious potential 
threat to ground water on Isla de Culebra are effluents 
from septic tanks. The effluents can quickly infiltrate 
through the thin soil and saprolite zone and enter the 
fractured bedrock aquifer 
in 
a nearly unfiltered, 
unaltered state. The greater the concentration of septic 
tanks in an area, the greater the potential threat to the 
aquifer.
On Isla de Vieques, although ground water is more 
abundant and alluvial deposits are more extensive than 
on Isla de Culebra, evapotranspiration affects ground- 
water quality. High sodium concentrations in the ground 
water due to overpumpage may limit its use for 
agricultural purposes (Torres-Gonzalez, 1989). Septic 
tank effluents pose the same potential threat to the 
fractured rock aquifers on Isla de Vieques as on Isla de 
Culebra. On that part of Isla de Vieques underlain by 
plutonic rocks, the soil and saprolite zone is thicker than
in the area underlain by volcanic rocks. 
However, 
because the soil is more permeable in areas of saprolite 
than in areas that have the Pandura-Rock Land-Patillas 
association, the rate of movement of septic-tank 
effluents would still pose a threat to the aquifer.
Some sea water encroachment has occurred in the 
Puerto Rico Aqueduct and Sewer Authority well field in 
the alluvial aquifer at Esperanza on the south coast of 
Isla de Vieques because of over pumping. The alluvial 
aquifer at the north end of the Resolucion valley also is 
susceptible to sea water encroachment. Withdrawals in 
excess of 0.40 Mgal/d could induce saline water 
intrusion and, during a drought, saline water intrusion 
could occur at pumpages as low as 0.20 Mgal/d (Torres- 
Gonzalez, 1989, p. 35).
4.7 U.S. VIRGIN ISLANDS 
4.7.1 St. Thomas and St. Johns
Ground water has been polluted by sewage effluent 
on St. Thomas. High concentrations of fecal coliform 
and fecal streptococci bacteria have been found in water 
from wells on both islands (Zack and others, 1987b). An 
estimated 20,000 to 25,000 people use septic tanks. 
The thin soil zone, usually less than 2 feet thick, is not 
capable of filtering the effluent wastes. 
The effluent 
either escapes to the surface or enters the open joints 
and fractures of the bedrock and, subsequently, the 
ground-water reservoir.
Residents on St. John also rely upon septic tanks 
for sanitary waste disposal. As the same hydrogeologic 
conditions prevail on St. John as on St. Thomas, 
effluents from septic tanks can pose the same hazard to 
the ground water on St. John.
4.7.2 St. Croix
The major issues of concern for ground-water 
supplies are (1) the growing population and tourism that 
increase the demand for water, (2) contamination by 
hazardous wastes, septic tanks, and leaky sewage lines 
and infiltration of sewage treatment plant discharges, 
and (3) saltwater intrusion (Troester, 1988).
The Kingshill Marl provides most of the ground 
water for St. Croix, but the overall quality is poor. The 
water exceeds the EPA secondary drinking water 
standards for dissolved solids and chloride; median 
concentrations 
are 
1,440 
mg/L 
and 
560 
mg/L, 
respectively (Zack and others, 1987b, p. 489). Reverse 
osmosis has been used as a means of improving the 
quality of water from this aquifer. 
Excessive ground- 
water pumping from the Kingshill aquifer, particularly 
near the coast, has caused saltwater upconing and 
encroachment (Zack and others, 1987b, p. 489), which 
further degrades the water quality.
Contamination 
by 
fecal 
coliform 
and 
fecal 
streptococci bacteria are common in the aquifers (Zack 
and others, 1987b, p. 491). 
Septic-tank effluent is a 
problem in the Kingshill aquifer where residential 
housing 
is concentrated. 
The effluent is often 
inadequately filtered by the thin soil, and contamination 
can become widespread in areas of fractured rock 
aquifers. 
Breakdowns or overloads in the sewage- 
treatment plants generally result in a discharge of 
effluent to dry streambeds, which are major ground- 
water recharge areas. 
This practice increases the 
potential for effluent to contaminate the aquifers (Zack, 
and others, 1987b, p. 492).
Solid waste has been deposited for many years in 
the vicinity of Krause Lagoon, but the effect on the 
underlying Kingshill aquifer is minor because water in 
the aquifer is brackish, and the ground-water gradient 
causes mixing of better quality water from inland.
4.0 Present and Potential Ground-Water Problems in Puerto Rico and the U.S. Virgin Islands 
145
146 
Atlas of Ground-Water Resources in Puerto Rico and the U.S. Virgin Islands
5.0 SELECTED REFERENCES
5.0 Selected References 
147
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