Hydrogeology of South-Central St. Croix, U.S. Virgin Islands By Robert P. Graves U.S. GEOLOGICAL SURVEY Water-Resources Investigations Report 93-4162 Prepared in cooperation with the U.S. VIRGIN ISLANDS WATER AND POWER AUTHORITY San Juan, Puerto Rico 1995 U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary U.S. GEOLOGICAL SURVEY Gordon P. Eaton, Director For additional information write to: District Chief U.S. Geological Survey GSA Center 651 Federal Drive, Suite 400-15 Guaynabo, 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................................................................................................................................................^ 1 Introduction..............................................................................................^^ 1 Approach..........................................................................................................._^ Description of the area.........................................................................................................................................4 Geology ..............................................................................................................................................................^ Ground-water hydrology.................................................................................................................................... 10 Ground water occurrence and movement............................................................................................ 10 Hydraulic characteristics of the aquifer............................................................................................... 15 Water Quality ..................................................................................................................................................^ Summary ............................................................................................................................................................32 References.......................................................................................................................................................... 33 ILLUSTRATIONS 1. Map showing location of study area, wells, and well fields in south-central St. Croix, U.S. Virgin Islands ..............................................................................................................2 2. Bar graph showing mean monthly rainfall for Beth Upper New Works Station, St. Croix, U.S. Virgin Islands 1982-91...................................................................................4 3. Bar graphs showing monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1989 through September 1992, and mean-monthly rainfall 1982-91 ...........................................................................................................9 4-6. Graphs showing: 4. Daily mean ground-water levels in selected wells at the Adventure well field, and monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, March 1990 through September 1992............................................................ 11 5. Daily mean ground-water levels in selected wells at the Golden Grove well field, and monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1989 through September 1992........................................................................ 12 6. Daily mean ground-water levels in wells VIWAPA 02, Fairplains, and VIWAPA 23A, Barren Spot, and monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1989 through September 1992.............................. 13 Contents 7. Map showing configuration of the water table in south-central St. Croix, U.S. Virgin Islands, July 1987........................................................................................................... 14 8. Diagrams showing major constituents in ground water from wells in the Adventure and Golden Grove well fields, St. Croix, U.S. Virgin Islands......................................... 17 9. Diagrams showing major constituents in ground water from wells in the Fairplains and Barren Spot well fields, St. Croix, U.S. Virgin Islands.............................................. 17 TABLES 1. Description of test holes drilled during 1989 in south-central St. Croix, U.S. Virgin Islands...............................................................................................................................5 2. Well name and site identification number of wells drilled in south-central St. Croix, U.S. Virgin Islands ..............................................................................................................8 3. Estimated transmissivity from specific capacity for selected wells at the Adventure well field, St. Croix, U.S. Virgin Islands......................................................................... 15 4. Chemical analyses of ground-water samples from wells in south-central St. Croix, U.S. Virgin Islands ............................................................................................................ 18 5. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's municipal wells in the Adventure well field, St. Croix..........................................................................................................22 6. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's municipal wells in the Golden Grove well field, St. Croix....................................................................................................24 7. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's municipal wells in the Fairplains well field, St. Croix...........................................................................................................27 8. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's municipal wells in the Barren Spot well field, St. Croix........................................................................................................ 28 IV Hydrogeology of South-Central St. Croix, U.S. Virgin Islands CONVERSION FACTORS, ABBREVIATED WATER-QUALITY UNITS, AND ACRONYMS Multiply By To obtain inch 25.4 millimeter foot 0.3048 meter foot squared per day ' 0.09290 meter squared per day gallon per minute 0.06308 liter per second gallon per minute per foot 0.2070 liter per second Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = 5/9 (°F - 32) Abbreviated water-quality units used in this report: microgram per liter (jig/L) milligram per liter (mg/L) microsiemen per centimeter at 25 °C (|iS/cm) Acronyms used in this report: National Oceanic and Atmospheric Administration (NOAA) U.S. Geological Survey (USGS) U.S. Virgin Islands (USVI) U.S. Virgin Islands Water and Power Authority (VIWAPA) 1 The standard unit for transmissivity is cubic foot per day per square foot times foot of an aquifer thickness [(ft3/d)/ft2]ft. In this report, the mathematically reduced form, foot squared per day (ft2/d), is used for convenience. Conversion Factors, Abbreviated Water-Quality Units, and Acronyms Hydrogeology of South-Central St. Croix, U.S. Virgin Islands By Robert P. Graves Abstract The subsurface geology of south-central St. Croix consists of alluvium and underlying carbonate rocks. Ground water occurs under water-table conditions in the alluvial deposits, the post-Kingshill Carbonates, and the Kingshill Limestone deposits. These deposits are hydraulically connected and are considered to be a single hydrologic unit. Depending on the location, depth to the top of the water-table aquifer can range from 5 to 68 feet below land surface. The top of the Jealousy Formation is considered to be the bottom of the water-table aquifer and lies from 85 to more than 120 feet below land surface. Well yields in south- central St. Croix ranged from less than 5 gallons per minute to 80 gallons per minute. Aquifer specific capacity at selected wells ranged from 1 to 14 gallons per minute per foot of drawdown. Aquifer transmissivity estimated from specific capacity ranged from 180 to 3,300 feet squared per day. Ground water in south-central St. Croix is of the sodium-chloride type. Ground-water samples collected from selected wells had chloride concentrations ranging from 67 to 4,400 milligrams per liter, and dissolved solids concentrations ranging from 619 to 7,540 milligrams per liter. Depending on location, connate water or saltwater intrusion are suspected of being the source of sodium chloride in the ground water of the study area. INTRODUCTION Freshwater is a scarce and expensive commodity on St. Croix, U.S. Virgin Islands (USVI). To meet the demand for drinking water, all available sources of water are used including ground water, water collected in rooftop-rainfall catchments, and desalinated seawater. Freshwater supply on St. Croix is provided to residents by the Virgin Islands Water and Power Authority (VIWAPA) from a combination of sources, primarily ground water and desalinated seawater. The high cost of desalination ($16.00 per one thousand gallons of water produced, 1991) has prompted VIWAPA to consider increasing their water supplies through additional ground- water development, primarily in the south-central part of the island. The extent to which ground-water resources in this area can be further developed will depend, in large part, on the hydrogeology of the area, about which relatively little is known. Recognizing the need for a better understanding of the hydrogeology of the area, the U.S. Geological Survey, in cooperation with VIWAPA, initiated a study of the ground-water resources of south- central St. Croix in 1989. This study, which is described herein, focused on four areas where wells existed and some geologic, lithologic, and hydrologic data were available. These areas, the Adventure, Golden Grove. Faiiplains, and Barren Spot well fields (fig. 1). were studied in detail but the knowledge of the hydrogeologic system in these areas was used to provide insight into the hydrogeology and ground-water resources throughout south-central St. Croix. Introduction 1 64°49'15" 64°48' 17°43' 17°41'45" \ / \ ' "/rV.A/"^ -\ ' \ /. v - jLwe V !>,H :^^ J-*v- '/'" ' V^kVi \ *' % V *~ - r> ' Is ^RS* v^ ' \ s . " > 1 v ' ".-""^ 't^1 * v ^ - f. / K ','--v-- MoA - V - ' ADVENTURE \ IV I VS * BETHLEHEM ADVENTURE v 4 » WELL FIELD V V\ \ ,."v '«* ",. f4 IS -' BETH UPPER .. NEW WORKS M STATION CARIBBEAN SEA BASE FROM USGS TOPOGRAPHIC MAP CHRISTIANSTED. V.I.. AND FREDERIKSTED, V.I. QUADRANGLES, 1982. CONTOUR INTERVAL 20 FEET, DOTTED LINES REPRESENT 10-FOOT CONTOURS. EXPLANATION 29 © WELL SITE AND SITE DESIGNATION Figure 1. Location of study area, wells, and well fields in south-central St. Croix, U.S. Virgin Islands. 2 Hydrogeology of South-Central St. Croix, U.S. Virgin Islands 64 46'45" 64'45'30" 17°43' 17'41'45" CARIBBEAN SEA BASE FROM USGS TOPOGRAPHIC MAP CHRISTIANSTED, V.I , AND FREDERIKSTED, V.I. QUADRANGLES, 1982. CONTOUR INTERVAL 20 FEET, DOTTED LINES REPRESENT 10-FOOT CONTOURS EXPLANATION 29 © WELL SITE AND SITE DESIGNATION Figure 1. Location of study area, wells, and well fields in south-central St. Croix, U.S. Virgin lslands~(Continued Introduction 3 This report summarizes the results of a study conducted between January 1989 and September 1992, to define the hydrogeology of selected lands in south-central St. Croix. The objectives of this study were to determine: 1. the occurrence and movement of ground water, 2. aquifer characteristics, and 3. ground-water quality in the area. APPROACH The objectives of this investigation were addressed primarily by analyses of data collected during test-hole drilling by VTWAPA. From April to August 1989, VIWAPA drilled 28 test holes (table 1). Of these test holes, 10 were completed as observation wells, 15 were completed as municipal water wells, and 3 were back- filled and abandoned. Of the 10 observation wells completed, 5 were instrumented by the USGS with continuous water-level recorders. These water-level monitoring sites were in operation from March 1990 until September 1992. Of the 15 municipal water wells completed, specific capacity tests to determine aquifer transmissivity were conducted on 4 wells and all wells were sampled for water-quality analysis. The test-hole drilling for this program was completed using the reverse- air circulation drilling method with an open-center reverse-air drill bit (Graves, 1992). Data used in this report include data from these test holes and wells and data from 13 VIWAPA wells completed prior to this investigation (table 2). Two of the existing VIWAPA wells were instrumented with continuous water-level recorders during January 1989, and 11 of the existing wells were sampled for water-quality analysis. The locations of all wells used in this study are shown in figure 1. Well numbers, names, and site identification numbers for these wells are given in table 2. The well numbers in table 2 apply only to this report. However, the site-identification numbers conform with the established USGS Ground-Water Site Inventory numbering system (Mathey, 1990). The site-identification number does not change and can be used to reference a specific well in other USGS publications. Information regarding well- construction data and lithologic information for the 28 test-holes drilled by VIWAPA in 1989 is given in table 1. DESCRIPTION OF THE AREA South-central St. Croix has been characterized as undulating lowlands with rounded hills (Cederstrom, 1950). Surface drainage out of the area is by way of Bethlehem and River Guts, two ephemeral streams that flow only in response to heavy rainfall (fig. 1). The mean annual air temperature recorded by the National Oceanic and Atmospheric Administration (NOAA) from 1982 to 1991 for St. Croix was 79.4 degrees Fahrenheit (U.S. Department of Commerce, 1982 to 1991). Mean-annual rainfall recorded by NOAA from 1982 to 1991 at the Beth Upper New Works Station (fig. 1) was 40.66 inches. Mean-monthly rainfall between 1982 and 1991 ranged from 1.48 inches in February to 6.48 inches in November (fig. 2). Monthly rainfall during this study (January 1989 to September 1992) ranged from less than 1 inch to more than 14 inches and differed substantially from the mean-monthly rainfall in some months (fig. 3). ^ 5 < 1 LJJ M ON Figure 2. Mean-monthly rainfall for Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1982-91. (Data from the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 1982 to 1991) Hydrogeology of South-Central St. Croix, U.S. Virgin Islands Table 1. Description of test holes drilled during 1989 in south-central St. Croix, U.S. Virgin Islands [fig, figure; mm-dd-yy, month-day-year; in, inches; ft-blsd, feet below land surface datum; gal/min, gallons per minute; VIWAPA, Virgin Islands Water and Power Authority; <, less than; ?, indicates that contact is uncertain; NA, data not available] o a (D Well number Date Diameter (see drilled of fig Well name (mm-dd- casing 1) (see table 2) yy) (in) 1 VIWAPA 1, Adventure 04-19-89 4 (Observation Well) 2 VIWAPA 2, Adventure 04-21-89 4 (Observation Well) 3 VIWAPA 2A, Adventure 04-25-89 6 (Municipal Water Well) 4 VIWAPA 3, Adventure 04-28-89 4 (Observation Well) 5 VIWAPA 4, Adventure 05-01-89 4 (Observation Well) 6 VIWAPA 5, Adventure 05-05-89 6 (Municipal Water Well) 7 VIWAPA 6, Adventure 05-06-89 6 (Municipal Water Well) 8 VIWAPA 7, Adventure 05-11-89 6 (Municipal Water Well) 9 VIWAPA 8, Adventure 05-12-89 NA Depth of Depth test of Screen Estimated hole casing interval yield (ft- (ft- (ft- (gal/ Subsurface material blsd) blsd) blsd) min) (ft-blsd) 127 60 60-80 5 Topsoil Kingshill Limestone Jealousy Formation 100 20 20 - 40 25 Topsoil Alluvial deposits Kingshill Limestone 60 20 20 - 60 20 Topsoil Alluvial deposits Kingshill Limestone 110 50 50-90 < 5 Topsoil Alluvial deposits Kingshill Limestone Jealousy Formation 100 40 40-80 < 5 Topsoil Alluvial deposits Kingshill Limestone 100 20 20 - 80 50 Topsoil Alluvial deposits Kingshill Limestone 100 20 20 - 80 25 Topsoil Alluvial deposits Kingshill Limestone 100 20 20 - 80 30 Topsoil Alluvial deposits Kingshill Limestone 100 TEST HOLE NA Topsoil BACK FILLED Alluvial deposits Kingshill Limestone 0 - 08 - 108 - 0 - 06 - 43 - 0 - 06 - 43 - 0 - 06 - 24 - 107 - 0 - 08 - 35 - 0 - 08 - 43 - 0 - 07 - 45 - 0 - 05 - 13 - 0 - 05 - 10 - 08 108 127 06 43 100 06 43 60 06 24 107 110 08 35 100 08 43 100 07? 45 100 05? 13 100 05? 10 100 >< Q. O (Q (D O_ O (Q O (D Si. o> p O (5" Table 1. Description of test holes drilled during 1989 in south-central St. Croix, U.S. Virgin Islands-Continued [fig, figure; mm-dd-yy, month-day-year; in, inches; ft-blsd, feet below land surface datum; gal/min, gallons per minute; VIWAPA, Virgin Islands Water and Power Authority; <, less than; ?, indicates that contact is uncertain; NA, data not available] Well number (see fig Well name 1) (see table 2) Date Diameter drilled of (mm-dd- casing yy) (in) Depth of test hole (ft- blsd) Depth of casing (ft- blsd) Screen interval (ft- blsd) Estimated yield (gal/ min) Subsurface material (ft-blsd) 10 VIWAPA 9, Adventure 05-15-89 NA 11 VIWAPA 10, Adventure 05-16-89 NA 12 VIWAPA 11, Adventure 05-17-89 4 (Observation Well) 13 VIWAPA 12, Adventure 05-18-89 (Observation Well) 15 VIWAPA 17, Adventure 06-09-89 (Observation Well) 16 VIWAPA 18, Adventure 06-13-? (Municipal Water Well) 17 VIWAPA 19, Adventure 06-15-89 6 (Municipal Water Well) 18 VIWAPA 20, Adventure 06-19-89 6 (Municipal Water Well) 21 VIWAPA 13, Golden 05-22-! Grove (Municipal Water Well) 22 VIWAPA 14, Golden 05-25-! Grove (Observation Well) 90 70 110 20 TEST HOLE BACK FILLED TEST HOLE BACK FILLED 20 - i 90 20 20 - 120 30 100 20 40 - 55 NA NA 100 20 20 - 80 55 95 10 10-40 < 5 25 100 20 20 - 80 50 100 20 20 - 95 60 30 - 115 30 20-40 < 5 55 - 75 Topsoil 0-05 Kingshill Limestone 05 - 90 Topsoil 0 - 10? Kingshill Limestone 10 - 70 Topsoil 0 - 10? Kingshill Limestone 10 - 96 Jealousy Formation 96 - 100 Topsoil 0-05 Kingshill Limestone 05 - 100 Topsoil 0-05 Alluvial deposits 05 - 15 Kingshill Limestone 15 - 95 Topsoil 0 - 05? Alluvial deposits 05 - 17 Kingshill Limestone 17 - 85 Jealousy Formation 85 - 90 Topsoil 0 - 07? Alluvial deposits 07 - 25 Kingshill Limestone 25 - 98 Jealousy Formation 98 - 100 Topsoil 0 - 05? Alluvial deposits 05 - 17 Kingshill Limestone 17 - 98 Jealousy Formation 98 - 100 Topsoil 0 - 06? Alluvial deposits 06 - 57 Kingshill Limestone 57 - 120 Topsoil 0 - 06? Alluvial deposits 06 - 50 Kingshill Limestone 50 - 100 Table 1. Description of test holes drilled during 1989 in south-central St. Croix, U.S. Virgin Islands-Continued [fig, figure; mm-dd-yy, month-day-year; in, inches; ft-blsd, feet below land surface datum; gal/min, gallons per minute; VIWAPA, Virgin Islands Water and Power Authority; <, less than; ?, indicates that contact is uncertain; NA, data not available] Well number Date Diameter (see drilled of fig Well name (mm-dd- casing 1) 23 24 i (see table 2) yy) (in) VIWAPA 15, Golden 05-30-89 6 Grove (Municipal Water Well) VIWAPA 16, Golden 06-06-89 6 Grove (Municipal Water Well) Depth of Depth test of Screen Estimated hole casing interval yield (ft- (ft- (ft- (gal/ Subsurface material blsd) blsd) blsd) min) (ft-blsd) 100 31 31 - 92 20 Topsoil Alluvial deposits Kingshill Limestone 110 30 30 - 100 25 Topsoil Alluvial deposits Kingshill Limestone 0 05 50 0 05 55 - 05 - 50 - 100 - 05 - 55 - 110 25 VIWAPA 21, Golden Grove (Municipal Water Well) 06-21-89 Topsoil 0 Alluvial deposits 05 Kingshill Limestone 45 o (D V> O 5' 5' D 2. (D 3 D) 26 VIWAPA 21A, Golden 06-23-89 4 Grove (Observation Well) 36 VIWAPA 23, Barren 08-12-89 6 Spot (Municipal Water Well) 37 VIWAPA 23A, Barren 08-08-89 4 Spot (Observation Well) 38 VIWAPA 24, Barren 06-30-89 6 Spot (Municipal Water Well) 39 VIWAPA 24A, Barren 07-05-89 6 Spot (Municipal Water Well) 40 VIWAPA 25, Barren 06-27-89 6 Spot (Municipal Water Well) 100 15 15 - 70 60 Topsoil Alluvial deposits Kingshill Limestone 120 80 80 - 120 50 Topsoil Post-Kings hi 11 Carbonates 110 70 70 - 110 80 Topsoil Post-Kingshill Carbonates 110 70 70 - 110 80 Topsoil Post-Kingshill Carbonates 120 80 80 - 120 35 Topsoil Post-Kingshill Carbonates 110 70 70 - 110 70 Topsoil Alluvial deposits Kingshill Limestone 0 - 05 - 55 - 0 - 02 - 0 - 01 - 0 - 01 - 0 - 03 - 0 - 05 - 20 - 05 55 100 02 120 01 110 01 110 03 120 05 20 110 Table 2. Well name and site identification number of wells drilled in south-central St. Croix, U.S. Virgin Islands [*, indicates well drilled by the Virgin Islands Water and Power Authority (VIWAPA) during 1989, wells without this designation completed prior to 1989; DPW, Department of Public Works] Well number (see figure I* 2* 3* 4* 5* 6* 7* 8* 9* 10* 11* 12* 13* 14 15* 16* 17* 18* 19 20 21* 22* 23* 24* 25* 26* 27 28 29 30 31 32 33 34 35 36* 37* 38* 39* 40* 41 Well 1) VIWAPA 1 VIWAPA 2 VIWAPA 2A VIWAPA 3 VIWAPA 4 VIWAPA 5 VIWAPA 6 VIWAPA 7 VIWAPA 8 VIWAPA 9 VIWAPA 10 VIWAPA 11 VIWAPA 12 VIWAPA 14 VIWAPA 17 VIWAPA 18 VIWAPA 19 VIWAPA 20 VIWAPA 1/DPW 1 VIWAPA 6/DPW 6 VIWAPA 13 VIWAPA 14 VIWAPA 15 VIWAPA 16 VIWAPA 21 VIWAPA 21A VIWAPA 1 VIWAPA 2 VIWAPA 6 VIWAPA 7 VIWAPA 9 VIWAPA 3A VIWAPA 5 VIWAPA 6 VIWAPA 7 VIWAPA 23 VIWAPA 23A VIWAPA 24 VIWAPA 24A VIWAPA 25 VIWAPA 31 name , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Adventure , Golden Grove , Golden Grove , Golden Grove , Golden Grove , Golden Grove , Golden Grove , Golden Grove , Golden Grove , Fairplains , Fairplains , Fairplains , Fairplains , Fairplains , Barren Spot , Barren Spot , Barren Spot , Barren Spot , Barren Spot , Barren Spot , Barren Spot , Barren Spot , Barren Spot , Barren Spot Site identification number 174304064484600 174303064481100 174303064481101 174308064482800 174311064482601 174304064481900 174304064482000 174311064481100 174306064484701 174321064485400 174318064490300 174329064483000 174328064482000 174311064482900 174316064480800 174313064481100 174307064481000 174309064481100 174247064475800 174243064475100 174240064475600 174237064474900 174247064475700 174244064475500 174247064475700 174247064475701 174225064471700 174225064472000 174225064471900 174229064471600 174231064471900 174323064454600 174329064454700 174331064453800 174316064453800 174327064454600 174319064454401 174319064454400 174332064453400 174316064454300 174315064454000 8 Hydrogeology of South-Central St. Croix, U.S. Virgin Islands JFMAMJJASOND 1989 1990 1991 JFMAMJJAS 1992 Figure 3. Monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1989 through September 1992, and mean-monthly rainfall 1982-91. (Data from the U.S. Department of Commerce, National Oceanic and Atmospheric Administration, 1982 through September 1992) GEOLOGY The subsurface geology of south-central St. Croix consists of alluvium and underlying carbonate rocks. The carbonate deposits consist of the Jealousy Formation of Eocene to middle Miocene age, the Kingshill Limestone of Miocene to Pliocene age (Gerhard, Frost, and Curth, 1978), and post-Kingshill Carbonates of Pliocene and younger age (Gill and Hubbard 1986). Using this stratigraphic nomenclature the results of the test-hole drilling in south-central St. Croix revealed the following: ALLUVIAL DEPOSITS-sand and gravel with cobbles and boulders, locally with thin lenses of silt and clay. The alluvial deposits are localized and not laterally extensive. A 5- to 8-foot thick topsoil overlies the alluvial deposits. The alluvial deposits range in thickness from 8 to 51 feet. Depth to the top of the alluvial deposits ranges from 5 to 8 feet below land surface. Depth to the bottom of the alluvial deposits ranges from 10 to 57 feet below land surface. POST-KINGSHILL CARBONATES a shallow water carbonate deposit which is dominantly a benthic foraminiferal packstone, with significant quantities of reef and skeletal clasts (Gill and Hubbard, 1986). Locally, these deposits were interbedded with clay, crushed coarse- grained coral fragments, and conglomerates of washed out limestone boulders and volcanic gravel, cobbles, and boulders. The top of the post-Kingshill Carbonates was near land surface and this unit commonly was overlain by only a 1- to 3-foot thick topsoil. Deposits of the post- Kingshill Carbonates were localized and were penetrated only in test holes drilled in the Barren Spot well field (fig. 1, table 1). Test-hole drilling indicated that the depth to the bottom of these deposits exceeded 120 feet below land surface, at some sites. Geology KINGSHILL LIMESTONE-a deep-water carbonate deposit of relatively soft, white to buff marl, which is locally fractured (Gill and Hubbard, 1986) with iron and manganese oxide stains common in the fracture zones. The Kingshill Limestone generally was overlain by a 5- to 8-foot thick layer of topsoil or alluvium. Where the bottom of the Kingshill Limestone was penetrated by test holes, this unit had a thickness that ranged from 68 to 100 feet. Depth to the top of the Kingshill Limestone ranged from 5 to 57 feet below land surface. Depth to the bottom of the Kingshill Limestone ranged from 107 to more than 120 feet below land surface. JEALOUSY FORMATION-a deep-water deposit of bluish-gray clay which contains a rich planktonic foraminiferal assemblage (Gill and Hubbard, 1986). The Jealousy Formation underlies the Kingshill Limestone. The top of the Jealousy Formation was from 85 to 108 feet below land surface in the test holes drilled during this study. However, data from other wells in the area indicate that the depth to the top of the Jealousy Formation exceeds 120 feet below land surface in places. The thickness of the Jealousy Formation has been estimated to exceed 1,400 feet (Gill and Hubbard, 1986). GROUND-WATER HYDROLOGY Fresh ground water is not plentiful in St. Croix, but it exists in sufficient quantities in some areas to be a source of water for public supply. Most of the fresh ground water exists at relatively shallow depths in unconsolidated surficial deposits or in relatively shallow limestone deposits. Ground Water Occurrence and Movement Ground water occurs under water-table conditions in the alluvial, post-Kingshill Carbonates, and Kingshill Limestone deposits. Where the alluvial deposits are saturated, they are considered to be hydraulically connected to the post-Kingshill Carbonates and Kingshill Limestone deposits and thus these thin units are considered a single hydrologic unit. The top of the Jealousy Formation, which underlies all of south-central St. Croix, is considered to be the bottom of this hydrologic unit. The water table fluctuates seasonally in response to rainfall variation and can fluctuate daily in wells located near pumping wells. Depth to the water table ranges from approximately 5 to 36 feet below land surface in the Adventure well field (fig. 4); 13 to 43 feet below land surface in the Golden Grove well field (fig. 5); 20 to 26 feet below land surface in the Fairplains well field (fig. 6); and 57 to 68 feet below land surface in the Barren Spot well field (fig. 6). The general direction of ground-water flow in south- central St. Croix is south-southeast toward the coast (Torres-Gonzalez and Rodriguez del Rio, 1990) (fig. 7). The elevation of the water table can range from approximately 140 feet above mean sea level in the northern part of the study area to less than 5 feet above mean sea level near the coast. The quantity of water recharging the water-table aquifer in south-central St. Croix has been estimated to be approximately 3 percent of annual rainfall (Robison, 1972). Jordan (1973) reported that aquifer recharge in the USVI is infrequent and probably occurs only after periods of heavy rainfall or a series of lesser rains. He believed that because of relatively low annual rainfall and high average annual temperatures, most recharge occurred after major rainstorms which produced more than 2 inches of rain. Evidence of the occurrence of recharge following a major rainstorm and the infrequency of aquifer recharge is evident when water-table fluctuations are compared to rainfall records (figs. 4, 5, and 6). During this study, substantial increases in ground-water levels were recorded only after three heavy rainfall events in September 1989 (14.24 inches), October 1990 (13.16 inches), and May 1992 (10.90 inches). 10 Hydrogeology of South-Central St. Croix, U.S. Virgin Islands op Q a o: 10 20 30 10 20 30 40 VIWAPA 17, ADVENTURE USGS OBSERVATION WELL 174316064480800 MAMJJ ASOND 1990 JFMAMJJ ASOND 1991 JFMAMJJAS 1992 i i i I i i i i I I i i I I I I I I I I I I I I I r VIWAPA 03, ADVENTURE USGS OBSERVATION WELL 174308064482800 MAMJJ ASOND 1990 JFMAMJJASOND 1991 JFMAMJJAS 1992 10 20 30 15 10 VIWAPA 02, ADVENTURE USGS OBSERVATION WELL 174303064481100 MAMJJ ASOND 1990 JFMAMJJ ASOND 1991 JFMAMJJAS 1992 § g BETH UPPER NEW WORKS STATION ST. CROIX, U.S. VIRGIN ISLANDS MAMJJ ASOND 1990 1,1.1.1.1.1.1.1.1.1. JFMAMJJ ASOND 1991 JFMAMJJAS 1992 Figure 4. Daily mean ground-water levels in selected wells at the Adventure well field and monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, March 1990 through September 1992. Ground-Water Hydrology 11 LL OCD LLJ CO 10 I I I I I 20 g Q 30 LLJ 40 2 50 VIWAPA 21A, GOLDEN GROVE USGS OBSERVATION WELL 174247064475701 I V JFMAMJJ ASONDJFMAMJJ ASONDJFMAMJJ ASONDJFMAMJJ AS 1989 1990 1991 1992 VIWAPA 06 / DPW 06, GOLDEN GROVE USGS OBSERVATION WELL 174243064475100 JFMAMJJ ASOND JFMAMJJ ASON OIJ FMAMJJ ASOND 35 15 10 1989 1990 1991 JFMAMJJAS 1992 .M.I.1.1,1.1.1.1.1. BETH UPPER NEW WORKS STATION ST. CROIX, U.S. VIRGIN ISLANDS JFMAMJJ ASONDJFMAMJJ ASOND 1989 1990 JFMAMJJASOND 1991 JFMAMJJAS 1992 Figure 5. Daily mean ground-water levels in selected wells at the Golden Grove well field and monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1989 through September 1992. 12 Hydrogeology of South-Central St. Croix, U.S. Virgin Islands cr=j GO 6 58 60 62 63 VIWAPA 23A, BARREN SPOT USGS OBSERVATION WELL 174319064454401 JFMAMJ JASON D J FMAMJJ ASOND 1989 1990 JFMAMJ JASOND 1991 JFMAMJJ AS 1992 24 28 JFMAMJ JASOND 1989 J FMAMJJ ASOND JFMAMJ JASOND 1991 JFMAMJJAS 1992 Z 00 < I = O JFMAMJ JASOND 1989 BETH UPPER NEW WORKS STATION ST. CROIX, U.S. VIRGIN ISLANDS J FMAMJJ ASOND 1990 JFMAMJ JASOND 1991 JFMAMJJAS 1992 Figure 6. Daily mean ground-water levels in wells VIWAPA 02, Fairplains, and VIWAPA 23A, Barren Spot, and monthly rainfall at Beth Upper New Works Station, St. Croix, U.S. Virgin Islands, 1989 through September 1992. Ground-Water Hydrology 13 64'48' 64'45'30" 44'17" 17'43' -r /Srv -^ v /i; s . ^' ^Ww*' V«r U -*,- **&%* 2r -~J &$* -**<& ''*&?, *.$**»# . .., .' /- ^ /:- . ' *, *^ek.»-^t*i :> ^ >. t"")ji>* f ' \~- - '^^ " ' * ''-'Sx-^'M-*- «i;^'-''vfi''' \ < ?> ' S \ ^tj i ' ,-««.- ' ' " ^>. -.^:,^^,, X5jS:-->5..> " -^- -/?, '/ ^X- ^. , . .-' Vt ' »» -.» ,' ^W^'^^^\'^^\^ J* V\ L . ^ ' , CARIBBEAN SEA BASE FROM USGS TOPOGRAPHIC MAP CHRISTIANSTED, V.I.. AND FREDERIKSTED, V.I. QUADRANGLES, 1982. CONTOUR INTERVAL 20 FEET. DOTTED LINES REPRESENT 10-FOOT CONTOURS. EXPLANATION LINE OF EQUAL WATER-TABLE ALTITUDE, IN FEET ABOVE MEAN SEA-LEVEL Interval is variable. All contours are approximately located. DIRECTION OF GROUND-WATER FLOW Figure 7. Configuration of the water table in south-central St. Croix, U.S. Virgin Islands, July 1987. (Adapted from Torres-Gonzalez and Rodriguez del Rio, 1990) 14 Hydrogeology of South-Central St. Croix, U.S. Virgin Islands Hydraulic Characteristics of the Aquifer The ground-water development potential of an aquifer is dependent upon hydraulic characteristics of transmissivity and storage coefficient. Transmissivity is a measure of the ability of the aquifer to transmit water and is defined as the product of the hydraulic conductivity and the aquifer thickness. The storage coefficient is the volume of water an aquifer releases from or takes into storage per unit surface area of the aquifer per unit change in head. During this study, aquifer transmissivities in south- central St. Croix were estimated to range from 180 to 3,300 feet squared per day. Transmissivity values for wells located in the Adventure well field were determined from four specific capacity tests. The specific capacity values determined from these tests ranged from 1 to 14 gallons per minute per foot of drawdown (table 3). The specific capacity values were converted to transmissivity using a method described by Meyer (1963), that relates well diameter, specific capacity, and the aquifer storage coefficient to aquifer transmissivity. Aquifer storage coefficients were not determined from field tests for this report, but rather are assumed to be typical water-table storage coefficients, which range from 0.1 to 0.3 (Lohman, 1979). The specific capacity/aquifer transmissivity relation developed by Meyer (1963) assumes a water-table storage coefficient of 0.1. The variation in aquifer transmissivity values in the Adventure well field can be explained by the presence or absence of intersecting fracture zones within the Kingshill Limestone. Where the density of fracture zones increase, the aquifer transmissivity will increase. Field tests to determine specific capacity were conducted only in the Adventure well field. However, well yield was estimated for all 28 test holes drilled in 1989 (table 1). The test to estimate well yield was completed by forcing, at a constant rate, compressed air through the drill pipe and measuring continuous flow out of the test hole. Results of this testing indicated somewhat higher potential aquifer yields in the Barren Spot well field, where yields of 35 to 80 gallons per minute were measured, than in the other well fields. Yields of less than 5 to 60 gallons per minute and less than 5 to 80 gallons per minute were measured in the Adventure and Golden Grove well fields, respectively. No wells were drilled or specific capacity tests conducted in the Fairplains well field for this study. However, Torres-Gonzalez (1991) indicated that aquifer transmissivity in the Fairplains area ranged from 3,000 to 4,000 feet squared per day. The relatively wide range of yields in the study area probably is due to the nonhomogeneity of the aquifer material. High yields in the Post Kingshill are due to the primary depositional porosity of the shallow-water limestone deposits and interlayered conglomerates and Table 3. Estimated transmissivity from specific capacity for selected wells at the Adventure well field, St. Croix, U.S. Virgin Islands (Estimates based on method described by Meyer, 1963) [(gal/min)/ft, gallons per minute per foot of drawdown; ft2/d, feet squared per day] Well name VIWAPA 05, Adventure VIWAPA 14, Adventure VIWAPA 18, Adventure VIWAPA 19, Adventure Specific capacity [(gal/min)/ft] 2 1 1 14 Transmissivity (ft2/d) 420 180 180 3,300 Length of test (hours) 19 19 20 20 Ground-Water Hydrology 15 volcanics, as well as to subsequent diagenetic changes within the limestone. Generally, where the Post Kingshill is tapped by wells, the yields will be consistently high. In the Kingshill Limestone high yields are common only in areas where there is a high density of intersecting fracture zones. The range of yields in the alluvial deposits are limited by the thin (10- to 30-foot), saturated thickness of the deposits. In areas where the thickness of the saturated alluvial deposits is greater, the yields probably are greater. WATER QUALITY In order to describe the quality of ground water in south-central St. Croix, 33 samples were collected from 25 wells and analyzed for common cations and anions and trace metals (table 4). Results of these analyses indicated that the ground water in the Golden Grove, Fairplains, and Barren Spot well fields was predominantly a sodium- chloride type water (Piper, 1953; figs. 8 and 9). In the Adventure well field, the ground-water type was mixed; no one cation or anion exceeded 50 percent of the total milliequivalents of cations or anions. In an island setting, ground water that is a sodium chloride type water commonly is considered to contain a mixture of freshwater and seawater (Gomez-Gomez, 1984). The source of the seawater could be from the lateral migration of seawater from the ocean through the aquifer, from the upconing of saline water as a result of excessive pumping, or from the presence of connate seawater which has not been completely flushed out of the aquifer. To help identify the source of the sodium chloride in ground water in south-central St. Croix, ; ground-water samples were collected monthly from selected wells in each well field and analyzed for chloride concentration and specific conductance (tables 5, 6,7, and 8). If the seasonal variations in the chloride concentrations are small, connate water is the most likely source of the sodium chloride; assuming that pumping at the well fields is relatively constant. If the variations are large, sodium chloride is most likely the source of upconing or lateral migration (intrusion) of seawater which changes with the seasonal water-level fluctuations in the aquifer, and the related movement of the saltwater- freshwater interface. In the Adventure and Golden Grove well fields, it is suspected that connate water is the source of saltwater, whereas in the Fairplains and Barren Spot well fields it is suspected that intrusion is the source of saltwater. In the Adventure and Golden Grove well fields, relatively small seasonal variations in chloride concentration indicate that connate water might be the principle source of the chloride. In the Adventure well field, the ranges of seasonal variation in chloride concentrations in samples collected from June 1990 to September 1992, from wells 6, 7, 16, 18, and 19 were 66, 292, 14, 22, and 14 milligrams per liter (mg/L), respectively (table 5). In the Golden Grove well field, the variations in chloride concentrations in samples collected from August 1990 to September 1992, from wells 1, 13, 15, 16, and 21 was 70, 80, 84, 68, and 56 mg/L,VesrJectively (table 6). With the exception of the significant change in chloride concentration in water from well 7 in the Adventure well field (292 mg/L), the relatively small seasonal variation in chloride concentrations and the relatively large water- level fluctuations of as much as 20 feet in the two well fields indicate that connate ground water probably is the predominant source of the sodium chloride. The seasonal variation in chloride concentration of 292 mg/L in well 7 of the Adventure well field might indicate possible upconing of saltwater into the Adventure well field at that site. In the Fairplains and Barren Spot well fields the greater seasonal variations in chloride concentrations indicate that seawater intrusion into the aquifer might be the principal source of the chloride. In the Fairplains well field, the variation in chloride concentrations in samples collected from June 1991 to September 1992, from wells 7 and 8 were 290 and 710 mg/L, respectively (table 7). In the Barren Spot well field, the variations in chloride concentrations in samples collected from August 1990 to September 1992, from wells 3A, 5,6,7, 25, 24,23, and 31 was 94, 220, 112, 94, 162, 250, 82, and 164 mg/L, respectively (table 8). The greater seasonal variations in chloride concentrations, and relatively small seasonal water-level fluctuations (approximately 6 feet) indicates that seawater intrusion could be the principal source of chloride in water from wells in these two well fields. 16 Hydrogeology of South-Central St. Croix, U.S. Virgin Islands CONSTITUENTS ADVENTURE WELL FIELD GOLDEN GROVE WELL FIELD Ca K Mg Na Cl C0 3 HC0 3 S0 4 Calcium Potassium Magnesium Sodium Chloride Carbonate Bicarbonate Sulfate Figure 8. Diagrams showing major constituents in ground water from wells in the Adventure and Golden Grove well fields, St. Croix, U.S. Virgin Islands. Values shown are percent of total milliequivalents per liter. Numbers refer to wells in table 2. CONSTITUENTS FAIRPLAINS WELL FIELD BARREN SPOT WELL FIELD Ca K Mg Na Cl C03 HC03 S04 Calcium Potassium Magnesium Sodium Chloride Carbonate Bicarbonate Sulfate Figure 9. Diagrams showing major constituents in ground water from wells in the Fairplains and Barren Spot well fields, St. Croix, U.S. Virgin Islands. Values shown are percent of total milliequivalents per liter. Numbers refer to wells in table 2. Water Quality 17 < Q. Table 4. Chemical analyses of ground-water samples from wells in south-central St. Croix, U.S. Virgin Islands [fig, figure; mm-dd-yy, month-day-year; (iS/cm, microsiemens per centimeter at 25 degrees Celsius; deg °C, degrees Celsius; mg/L, milligrams per liter; VIWAPA, Virgin Islands Water and Power Authority; DPW, Department of Public Works] igeology of South-Cer Well number (see Well fig 1 name and :? table 1) O 3. p. c J° <35 5T Q)3 Q. VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA DPW 1 VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA 2A 05 06 07 14 18 19 20 Adventure Adventure Adventure Adventure Adventure Adventure Adventure Adventure 3 6 7 8 14 16 17 18 Date (mm-dd-yy) 03-11-91 03-12-91 03-12-91 03-11-91 04-17-91 03-11-91 07-31-91 03-11-91 Spe- cific con- duct- ance (labor- atory value) (U,S/cm) 1, 2, 2, 1, 1, 1, 1, 1, 870 020 030 600 700 430 810 660 P H (field value) ( stand- ard units) 7.3 7.1 7.3 7.3 7.3 7.2 7.3 7.3 Temper- ature (deg 26 27 26 27 25 26 29 26 °C) .5 .0 .5 .0 .5 .5 .0 .5 Hard- ness (mg/L as CaC0 3 ) 330 360 310 190 270 320 230 230 Alka- linity (labor- atory value) (mg/L as CaC0 3 ) 597 648 634 553 528 494 577 566 Calcium, dis- solved (mg/L as Ca) 56 57 45 35 42 60 39 44 Magne- sium, dis- solved (mg/L as Mg) 45 52 47 24 40 42 32 28 Sodium dis- solved (mg/L as Na) 290 330 350 290 260 190 290 290 Golden Grove 13 13 15 15 16 16 21 21 01 06 07 09 3A 05 06 07 23 23 24 24 25 25 31 31 Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Fairplains Fairplains Fairplains Fairplains Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot 19 21 21 23 23 24 24 25 25 27 29 30 31 32 33 34 35 36 36 38 38 40 40 41 41 02-12-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 01-10-91 01-10-91 01-10-91 01-10-91 01-25-91 01-28-91 01-28-91 01-25-91 04-16-90 01-28-91 04-16-90 01-25-91 04-16-90 01-25-91 01-28-91 07-24-91 1, 1, 1, 2, 1, 2, 1, 1, 1, 12, 5, 3, 2, 3, 3, 2, 2, 3, 3, 4, 3, 3, 2, 3, 930 990 630 480 360 220 440 950 820 600 970 830 320 860 010 440 760 380 670 260 690 680 760 997 400 8.3 7.1 7.1 7.1 7.1 7.1 7 .1 7.2 7.1 7.0 7 .2 7.2 7.4 7.5 7.7 7.7 7 .7 7.5 7.6 7.6 7.6 7.5 7.5 7.7 7.3 28 27 27 28 27 28 27 28 27 27 27 27 28 27 27 27 26 28 26 27 27 27 25 25 27 .0 .0 .0 .0 .5 .5 .5 .0 .0 .5 .5 .5 .0 .5 .0 .5 .5 .0 .0 .5 .0 .5 .5 .0 .5 390 400 280 410 340 400 290 390 420 3,400 1,200 550 380 170 110 110 130 130 150 280 210 260 140 160 320 537 510 449 587 488 557 480 509 527 278 504 560 539 541 596 561 559 546 566 504 549 531 559 426 508 75 70 48 75 66 71 52 71 77 660 220 110 68 43 25 28 34 32 37 69 54 60 35 25 79 50 55 38 53 42 54 40 52 55 420 150 67 50 16 11 10 12 13 15 25 19 27 12 24 31 280 270 250 410 180 350 200 270 230 1,400 800 620 370 780 620 510 570 720 750 870 740 740 550 170 610 Table 4. Chemical analyses of ground-water samples from wells in south-central St. Croix, U.S. Virgin Islands-Continued [fig, figure; mm-dd-yy, month-day-year; mg/L, milligrams per liter; VIWAPA, Virgin Islands Water and Power Authority; DPW, Department of Public Works] Well number (see Well fig 1 name and Date table 1) (mm-dd-yy) Water Quality VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA DPW 1 VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA 2A 05 06 07 14 18 19 20 Adventure Adventure Adventure Adventure Adventure Adventure Adventure Adventure 3 6 7 8 14 16 17 18 03-11-91 03-12-91 03-12-91 03-11-91 04-17-91 03-11-91 07-31-91 03-11-91 Potas- sium, dis- solved (mg/L as K) 0 1 .4 .4 .6 .5 .6 .2 .4 .7 Sulfate, dis- solved (mg/L as S04 ) 94 86 84 94 53 71 84 92 Chlo- ride, dis- solved (mg/L as Cl) 230 260 260 150 200 150 220 170 Fluo- ride, dis- solved (mg/L as F) 0.80 .80 .80 .90 .60 .50 1.00 .70 Silica, dis- solved (mg/L as Si02 ) 43 44 41 44 41 48 41 45 Dis- solved solids (mg/L) 1,120 1,220 1,210 970 954 859 1,050 1,010 Golden Grove 13 13 15 15 16 16 21 21 01 06 07 09 3A 05 06 07 23 23 24 24 25 25 31 31 Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Fairplains Fairplains Fairplains Fairplains Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot 19 21 21 23 23 24 24 25 25 27 29 30 31 32 33 34 35 36 36 38 38 40 40 41 41 02-12-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 01-10-91 01-10-91 01-10-91 01-l'0-91 01-25-91 01-28-91 01-28-91 01-25-91 04-16-90 01-28-91 04-16-90 01-25-91 04-16-90 01-25-91 01-28-91 07-24-91 1 1 1 1 1 1 6 3 2 1 9 8 5 6 8 9 8 6 12 5 12 8 .9 .1 .7 .1 .9 .1 .7 .2 .2 .0 .5 .5 .4 .0 .8 .5 .8 .6 .5 .0 .5 .0 .7 .0 .6 100 86 75 140 51 110 65 91 87 450 290 240 190 250 200 130 130 200 220 290 240 230 130 39 230 270 300 210 400 140 350 160 290 240 4400 1600 860 350 780 510 380 480 670 700 880 720 760 470 67 650 .60 .20 .50 .30 .40 .20 .50 .20 .30 .10 .30 .90 .10 .70 .80 1.00 1.00 .20 .70 .30 .80 .10 .90 .80 .90 44 47 39 58 39 54 39 48 40 36 38 38 38 27 26 23 26 32 27 33 27 34 26 26 27 1, 140 1, 140 930 1,490 813 1,320 845 1,130 1,050 7,540 3, 400 2,270 1,390 2,230 1,760 1,420 1,590 2, 000 2,100 2, 480 2,140 2,180 1,560 619 1, 940 Table 4. Chemical analyses of ground-water samples from wells in south-central St. Croix, U.S. Virgin Islands-Continued [fig, figure; mm-dd-yy, month-day-year; mg/L, milligrams per liter; |J.g/L, micrograms per liter; VIWAPA, Virgin Islands Water and Power Authority; DPW, Department of Public Works; , indicates data not available; <, less than] 0 geology of South- § sl to o 3yc to '< <35' ii[ Q. (0 Well number (see Well fig I name and table 1) VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA DPW 1 VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA 2A Adventure 05 Adventure 06 Adventure 07 Adventure 14 Adventure 18 Adventure 19 Adventure 20 Adventure Golden Grove 13 Golden Grove 13 Golden Grove 15 Golden Grove 15 Golden Grove 16 Golden Grove 16 Golden Grove 21 Golden Grove 21 Golden Grove 01 Fairplains 06 Fairplains 07 Fairplains 09 Fairplains 3A Barren Spot 05 Barren Spot 06 Barren Spot 07 Barren Spot 23 Barren Spot 23 Barren Spot 24 Barren Spot 24 Barren Spot 25 Barren Spot 25 Barren Spot 31 Barren Spot 31 Barren Spot 3 6 7 8 14 16 17 18 19 21 21 23 23 24 24 25 25 27 29 30 31 32 33 34 35 36 36 38 38 40 40 41 41 Date (mm-dd-yy) 03-11-91 03-12-91 03-12-91 03-11-91 04-17-91 03-11-91 07-31-91 03-11-91 02-12-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 01-10-91 01-10-91 01-10-91 01-10-91 01-25-91 01-28-91 01-28-91 01-25-91 04-16-90 01-28-91 04-16-90 01-25-91 04-16-90 01-25-91 01-28-91 07-24-91 Nitro- gen, N02 +N0 3 dis- solved (mg/L as N) __ -- __ -- -- 1.2 -- 2.7 2.8 3.2 3.3 -- _- -- -- 5.2 6.1 5.2 6.3 Man- Iron, ganese dis- dis- solved solved (|lg/L (|lg/L as Fe) 3 10 10 3 6 5 9 5 12 3 3 10 3 10 3 9 3 20 10 10 10 10 10 10 10 20 10 200 10 40 10 14 20 as Mn) 2 10 10 1 2 6 1 1 1 1 1 10 1 10 1 1 1 100 10 30 340 10 10 10 10 10 10 10 10 10 10 23 10 Barium dis- solved (ug/L as Ba) 27 100 100 31 21 40 24 39 48 46 32 100 20 100 21 47 42 400 100 100 100 100 100 100 100 100 100 100 100 100 100 110 100 Alumi- nium dis- solved (ug/L as Al) <10 15 12 10 <10 20 <10 10 <10 10 12 10 <10 10 14 <10 <10 <10 <10 11 <10 10 <10 10 <10 10 11 <10 20 Arsenic dis- solved (ug/L as As) 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 3 1 -- 1 -- 1 1 1 1 Cadmium dis- solved (ug/L as Cd) 1 1 1 2 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 -- 1 -- 1 1 1 1 Chro- mium dis- solved (ug/L as Cr) 1 1 1 1 1 1 1 1 1 1 1 1 1 6 1 1 1 1 1 2 2 -- 2 -- 1 1 1 1 Table 4. Chemical analyses of ground-water samples from wells in south-central St. Croix, U.S. Virgin Islands-Continued [fig, figure; mm-dd-yy, month-day-year; |lg/L, micrograms per liter; VIWAPA, Virgin Islands Water and Power Authority; DPW, Department of Public Works; , indicates data not available] o Well number (see Well fig 1 name and Date table 1) (mm-dd-yy) VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA DPW 1 VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA VIWAPA 2A 05 06 07 14 18 19 20 Adventure Adventure Adventure Adventure Adventure Adventure Adventure Adventure 3 6 7 8 14 16 17 18 03-11-91 03-12-91 03-12-91 03-11-91 04-17-91 03-11-91 07-31-91 03-11-91 Mer- cury dis- solved (jig/L as Hg) 0.2 .9 .3 .1 .1 .2 .1 .2 Sel- nium dis- solved (jig/L as Se) 1 1 2 2 2 2 1 3 Silver dis- solved (u.g/L as Ag) 1 1 1 1 1 1 1 1 Lead dis- solved (u.g/L as Pb) 1 1 1 1 1 1 1 1 Golden Grove 13 13 15 15 16 16 21 21 01 06 07 09 3A 05 06 07 23 23 24 24 25 25 31 31 Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Golden Grove Fairplains Fairplains Fairplains Fairplains Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot Barren Spot 19 21 21 23 23 24 24 25 25 27 29 30 31 32 33 34 35 36 36 38 38 40 40 41 41 02-12-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 04-17-90 01-22-91 01-10-91 01-10-91 01-10-91 01-10-91 01-25-91 01-28-91 01-28-91 01-25-91 04-16-90 01-28-91 04-16-90 01-25-91 04-16-90 01-25-91 01-28-91 07-24-91 .1 .3 .1 .8 .1 1.6 .2 .1 .1 .1 .1 .1 .1 .2 .3 .1 .2 .1 3 4 4 9 6 4 4 3 3 6 5 3 2 5 5 3 1 4 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 1 1 1 1 1 1 1 1 1 2 1 1 Table 5. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's (VIWAPA) municipal wells in the Adventure well field, St. Croix Hydrogeology of Soul 1 sL 0) o o. c 0) 5: 5' 5T £U Q. (A [mm-dd-yy, month-day-year; mg/L, milligrams per liter; |iS/cm, microsiemens per centimeter at 25 degrees Celsius; NA, SWL, static water level; WP-WLNA, well pumping-water level not available] WELL VIWAPA 6, Adventure Date (mm-dd-yy) 12-13-89 12-13-89 01-11-90 01-19-90 01-31-90 02-05-90 02-23-90 02-26-90 03-16-90 03-26-90 04-27-90 06-01-90 06-27-90 06-26-90 08-01-91 08-29-91 09-27-91 10-30-91 12-03-91 02-08-92 02-05-92 03-13-92 04-28-92 05-29-92 07-02-92 07-28-92 09-15-92 Chloride concen- tration (mg/L) NA NA NA NA NA NA NA NA NA NA NA NA NA 292 NA 256 268 276 280 300 276 280 272 280 NA 274 234 Specific con- ductance (field value )lS/cm) 2,500 2,500 NA NA 1, 650 NA 1, 820 1, 900 NA 1,790 1, 840 NA NA 2,040 NA 2,090 2,030 2,090 2,080 2, 060 2,010 2,030 2, 030 2, 100 2,070 1, 890 2, 060 Water level (in feet below land surface) Comments 27 .65 27.65 27 .34 26.45 17.60 NA 50.19 39.57 35.45 40.65 19.33 18.25 18.69 NA 17.38 26.42 26.97 NA NA NA NA NA 51 .23 50.74 50.46 58.05 58.61 PWL PWL PWL PWL PWL SWL PWL PWL PWL PWL SWL SWL SWL WP-WLNA SWL PWL PWL WP-WLNA WP-WLNA WP-WLNA WP-WLNA WP-WLNA PWL PWL PWL PWL PWL data not available; PWL, pumping water level; WELL VIWAPA 7, Adventure Specific con- Chloride ductance Date (mm-dd-yy) 12-13-89 01-11-90 01-19-90 01-31-90 02-15-90 02-23-90 03-16-90 03-26-90 04-27-90 06-01-90 06-27-90 08-01-91 08-29-91 09-26-91 10-30-91 12-03-91 01-08-92 02-04-92 03-13-92 04-28-92 05-29-92 07-02-92 07-28-92 09-15-92 concen- tration (mg/L) NA NA NA NA NA NA NA NA NA NA NA NA 176 188 206 206 468 450 220 NA 216 224 214 NA (field value )lS/cm) 1,210 NA NA 1, 650 1, 600 1,490 1,010 NA 2,050 NA NA NA 1,810 1,710 1,780 1,790 2, 630 2,560 1,820 NA 1, 870 1,860 1,700 NA Water level (in feet below land surface) Comments 11.53 12.45 12.49 12.25 13.27 33.05 29.23 29.22 12.28 12.30 12.42 12 . 85 NA NA NA NA NA NA 50.81 21 .08 47 .19 47 . 69 NA 21.06 PWL PWL PWL PWL SWL PWL PWL PWL SWL SWL SWL SWL WP-WLNA WP-WLNA WP-WLNA WP-WLNA WP-WLNA WP-WLNA WP-WLNA SWL PWL PWL WP-WLNA SWL I) £ o s CO j ^ CO 1 &> rt ? bD C 'S, S3 CX- [ < > b~ 1 '3 C3 O C C3 'S O O s s -i£ CO i . =1.2 fe J3 "u > > ex TJ £ .c - IS £ d > » ^ >% n'. "6 ^ S *^ 0) 3 C 0) 1 «. CD rH rtjis H £> 1 1 i_3 l| 0 M 3 IS ^ vo rH SS J5j {s H 1 1 !_} !_} Hj^ co 4-> G 0) 0 O 0) M rH SO QJ 0) 4-J O T5 tc -LJ > C 0) rH c 4H (C Q) -H (1) (1) (C j_| S rH ' 4H ,£! rH rj CO O 0) -H 0 T5 _ <4H 1 C rH QJ g -H G (C 0) 3 o O O -LJ -H rH \ QJ U O MH (C co CO T3 QJ T5 1 G -H C O iH QJ -H J O O 4-1 \ i 1 G (tf tT1 r^ O iH £ U 0 -LJ ">, !>i QJ 1 4-J T5 (ft TI5 Q 1 g ' CO -LJ C QJ £ O O ^_, ® M rH SO QJ QJ 4-J O TS rO 4J > G QJ rH C 4H rO QJ -r-l QJ QJ (C }-i S rH ' 4H ,£! rH rj co O QJ -H O T) MH 1 G rH QJ £ -H G rO (D 3 O O O -LJ -H rH \ QJ O O 4H rO CO CX !3 "-^ > d. 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Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's (VIWAPA) municipal wells in the Golden Grove well field, St. Croix [DPW, Department of Public Works; mm-dd-yy, month-day-year; mg/L, milligrams per liter; |iS/cm, microsiemens per centimeter at 25 degrees Celsius; NA, data not available; SWL, static water level; PWL, pumping water level; WP-WLNA, well pumping-water level not available] >logy of South o Q. (A WELL VIWAPA 21, Golden Grove Date (mm-dd-yy) 02-22-90 03-16-90 03-26-90 04-17-90 05-29-90 06-26-90 08-07-90 08-28-90 10-04-90 11-01-90 11-26-90 01-03-91 02-05-91 03-04-91 03-25-91 05-01-91 06-17-91 08-01-91 08-29-91 09-25-91 10-24-91 12-03-91 01-08-92 02-05-92 03-13-92 04-30-92 05-27-92 06-26-92 07-28-92 09-15-92 Chloride concen t ration (mg/L) NA NA NA NA NA NA NA 284 NA 234 NA 250 NA 245 248 254 256 290 270 270 286 276 290 280 268 260 276 268 270 280 Specific con- ductance (field value )lS/cm) 1, 710 NA 1,730 1, 790 1,750 NA 1,800 2,140 1, 630 1,100 1,250 NA 1,780 1,780 1, 810 1,720 1,770 1, 910 1, 930 1, 940 1, 940 1,880 NA NA 1, 920 1, 890 1, 900 1, 970 1,850 1,990 Water level (in feet below land surface) 40 39 37 38 34 35 35 42 39 30 26 27 29 30 31 32 34 32 38 37 38 35 36 37 44 44 42 40 41 42 .80 .80 .47 .24 .24 .87 .92 .13 .87 .44 .67 .39 .69 .84 .47 .61 .10 .90 .67 .91 .05 .67 .31 .07 .00 .27 .24 .44 .16 .07 Comments PWL PWL PWL PWL SWL SWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL Table 7. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's (VIWAPA) municipal wells in the Fairplains well field, St. Croix [mm-dd-yy, month-day-year; mg/L, milligrams per liter; |0,S/cm, microsiemens per centimeter at 25 degrees Celsius; NA, data not available; WP-WLNA, well pumping- water level not available; PWL, pumping water level; SWL, static water level] WELL VIWAPA 7, Date (mm-dd-yy) 06-27-91 07-25-91 08-29-91 09-25-91 10-23-91 01-07-92 02-04-92 03-12-92 04-30-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) 850 780 800 NA NA NA NA 1,070 848 NA 870 850 NA Specific con- ductance (field value (J,S/cm) 3,920 3,750 3,850 NA NA NA NA 4,530 4, 050 NA 4,080 4, 060 NA Fairplains Water level (in feet below land surface) NA 48.52 48.59 25.82 28.89 48.12 48.13 48.12 48.11 3.15 48.13 48.12 4.63 Comment s WP-WLNA PWL PWL SWL SWL PWL PWL PWL PWL SWL PWL PWL SWL WELL --VIWAPA 8, Date (mm-dd-yy) 06-18-91 07-25-91 08-28-91 09-25-91 10-23-91 12-03-91 01-07-92 02-04-92 03-12-92 04-30-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) 1,390 1,490 1,550 NA 1,530 1, 608 1, 670 1, 650 1,700 2,050 1,372 1, 698 NA 1,340 Specific con- ductance (field value US/cm) 5, 640 5,700 6,080 NA 5,830 5, 890 6,110 6, 110 6,430 7, 170 5,240 6,450 NA 5,480 Fairplains Water level (in feet below land surface) 55.51 60.41 62.97 27.03 61.44 63.93 63.23 64.06 57.48 30.48 24.90 29.40 NA 24.98 Comments PWL PWL PWL SWL PWL PWL PWL PWL PWL PWL PWL PWL No Access PWL 0 QJ Hydrogeology of South-Central CO p o. c (O5' 5T Q)3Q. W Table 8. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's (VIWAPA) municipal wells in the Barren Spot well field, St. Croix [mm-dd-yy, month-day-year; mg/L, milligrams per liter; |j.S/cm, microsiemens per centimeter at 25 degrees Celsius; NA, data not available; WP-WLNA, well pumping- water level not available; PWL, pumping water level; SWL, static water level] WELL VIWAPA 3A, Date (mm-dd-yy) 02-26-90 03-26-90 04-25-90 05-21-90 06-25-90 08-06-90 08-29-90 10-04-90 10-30-90 11-19-90 12-27-90 02-06-91 03-05-91 03-25-91 05-02-91 06-20-91 07-24-91 08-27-91 09-23-91 10-22-91 11-25-91 01-09-92 02-04-92 03-12-92 04-27-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) NA NA NA NA NA NA 780 NA 874 NA 796 NA NA NA 820 800 798 810 NA 780 792 850 NA NA 850 840 836 860 870 Specific con- ductance (field value (as/cm) 3,520 3, 140 3, 370 3,540 NA 3, 460 3, 830 2, 690 3, 150 3, 830 NA 3, 900 NA NA 3,540 3, 800 3, 830 3, 940 NA 3, 930 3, 940 3, 940 NA NA 4,050 4,090 4, 030 4, 110 4, 100 Barren Spot Water level (in feet below land surface) NA NA NA 63.37 60.26 66.32 66.02 66.50 62.82 58. 92 64 .44 65 .25 47.90 65.38 65.13 65.86 67 . 65 66.15 65.32 65.30 65.23 66. 05 59.73 62.61 62.79 62.94 62 .72 62.12 62.98 Comment s WP-WLNA WP-WLNA WP-WLNA PWL SWL PWL PWL PWL PWL PWL PWL PWL SWL PWL PWL PWL PWL PWL SWL PWL PWL PWL SWL SWL PWL PWL PWL PWL PWL WELL VIWAPA 5, Barren Spot Date (mm-dd-yy) 12-13-89 02-26-90 02-26-90 03-26-90 04-25-90 05-21-90 06-25-90 08-06-90 08-29-90 10-04-90 10-30-90 11-19-90 12-27-90 02-06-91 03-05-91 03-25-91 05-02-91 06-20-91 07-24-91 08-27-91 09-23-91 10-22-91 11-25-91 01-09-92 02-04-92 03-12-92 04-27-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) NA NA NA NA NA NA NA NA NA NA 508 NA 500 NA NA 704 484 510 504 520 500 510 522 522 546 516 516 506 510 NA 500 Specific con- ductance (field value (iS/cm) NA 2, 620 NA 2, 800 NA 2,790 2,780 2,790 2, 880 2, 830 2, 840 2,860 NA 2, 880 NA 2,890 2, 810 2, 970 3, 000 3,060 3,090 3,050 3, 090 3, 080 3,090 3,070 3,080 3, 100 3,040 NA 3,030 Water level (in feet below land surface) 72.42 70.14 70.16 70.74 77.12 77.55 79.83 79.29 79.10 78. 97 76.81 77.04 79.23 77.15 67.95 76.68 77 .02 77.74 77 .95 78.22 76.72 77 .43 77.66 78.08 77.49 78.33 78.85 79.05 78.62 68.10 78.52 Comments PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL SWL SWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL SWL PWL Table 8. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's municipal wells in the Barren Spot well field, St. Croix-Continued [mm-dd-yy, month-day-year; mg/L, milligrams per liter; (iS/cm, microsiemens per centimeter at 25 degrees Celsius; NA, data not available; PWL, pumping water level; SWL, static water level] WELL VIWAPA 6, Q) fl? oc £. 5' Date (mm-dd-yy) 07-05-90 07-05-90 08-06-90 08-29-90 10-04-90 10-30-90 11-19-90 12-27-90 02-06-91 03-05-91 03-25-91 05-02-91 06-20-91 07-24-91 08-27-91 09-23-91 10-22-91 11-25-91 01-09-92 02-04-92 03-12-92 04-27-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) NA NA NA 304 NA 416 NA NA NA NA 384 320 354 354 342 368 340 350 340 354 330 318 NA NA NA NA Specific con- ductance (field value (iS/cm) 2,019 2,019 2,019 2,090 2, 115 2,300 2,325 NA 2,328 NA 2,356 2,294 2,366 2,347 2,375 2,470 2,384 2,375 2,380 2,390 2,280 2,330 NA NA NA NA Barren Spot Water level (in feet below land surface) 76.63 76.63 78.81 76.55 76.39 75.07 75.24 75.30 75.28 74 .77 75.14 75.95 76.28 76.46 76.58 75.92 75.94 76.06 76.44 76.28 76.72 76.79 76.05 75.76 75.13 75.71 Comment s PWL PWL PWL PWL PWL PWL PWL PWL PWL SWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL SWL SWL SWL WELL VIWAPA 7, Barren Spot Date (mm-dd-yy) 05-21-90 06-25-90 08-06-90 08-29-90 10-04-90 10-30-90 11-19-90 12-27-90 02-06-91 03-05-91 03-25-91 05-01-91 06-20-91 07-24-91 08-27-91 09-23-91 10-22-91 11-25-91 01-09-92 02-04-92 03-12-92 04-27-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) NA NA NA 458 NA 480 NA 436 NA NA NA 490 520 530 524 478 NA 460 468 450 440 436 NA 448 442 454 Specific con- ductance (field value US/cm) 2,835 2,565 2,477 2, 470 1, 936 2,562 2, 602 NA NA NA NA 2,716 2, 839 2,717 2, 889 2,792 NA 2, 688 2, 630 2,560 2,540 2, 610 NA 2,580 2,520 2, 620 Water level (in feet below land surface) 55.42 55.58 55.47 55.27 52.84 54.41 54.88 54.52 55.04 52.45 55.58 53.32 55.64 58.15 55.77 55.63 52.46 55.66 55.78 55.82 55.96 55.32 53.11 53.74 53.73 53.69 Comments PWL PWL PWL PWL PWL PWL PWL PWL PWL SWL PWL PWL PWL PWL PWL PWL SWL PWL PWL PWL PWL PWL SWL PWL PWL PWL Table 8. Chloride concentration, specific conductance, and water levels for the U.S. Virgin Islands Water and Power Authority's municipal wells in the Barren Spot well field, St. Croix-Continued Hydrogeology of Sout 3- 3 S_ (/) po. c j° 5: 5' 5T 0) Q. W [mm-dd-yy, month-day-year; mg/L, milligrams per liter; jiS/cm, microsiemens per centimeter at 25 degrees Celsius; NA, available; PWL, pumping water level; SWL, static water level; USGS, U.S. Geological Survey] Date (mm-dd-yy) 12-13-89 01-11-90 01-30-90 02-26-90 03-15-90 03-26-90 04-16-90 05-25-90 06-25-90 08-06-90 08-29-90 10-04-90 10-30-90 11-19-90 12-27-90 02-06-91 03-05-91 03-25-91 05-02-91 06-20-91 06-24-91 08-27-91 09-23-91 10-22-91 11-25-91 01-09-92 02-04-92 03-12-92 04-27-92 05-28-92 07-01-92 07-27-92 09-14-92 WELL VIWAPA 25, Specific con- Chloride ductance concen- (field tration value (mg/L) |lS/cm) NA 1,130 NA NA NA NA NA 3,000 NA NA NA NA NA 3,350 NA 3,140 NA 3,520 NA 3,410 672 1,920 NA 2,470 NA NA NA 2,640 NA NA NA 2,740 NA NA NA NA 534 2,940 570 3,090 580 3,060 562 3,160 572 3,380 580 3,250 590 3,250 576 3,170 580 3,160 568 3,070 514 3,060 514 3,060 534 3,020 540 2,960 510 3,020 Barren Spot, Water level (in feet below land surface) 52.06 52.12 53.33 53.43 53.60 52.31 53.75 57.62 58.41 67.01 59.70 59.20 58.78 56.20 56.57 55.32 54.94 55.16 57.59 57.98 58.18 58.32 57.45 57.51 57.72 58.17 57.98 58.16 57.93 58.27 57.96 57.83 57.99 (USGS-22) Comments PWL PWL PWL PWL SWL SWL PWL PWL PWL PWL PWL PWL SWL PWL PWL PWL SWL SWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL data not available; WP-WLNA WELL VIWAPA 24, Date (mm-dd-yy) 12-13-89 01-11-90 01-30-90 02-26-90 03-15-90 03-26-90 04-16-90 05-21-90 06-25-90 08-06-90 08-29-90 10-04-90 10-30-90 11-19-90 12-27-90 02-06-91 03-05-91 03-25-91 05-02-91 06-20-91 07-24-91 08-27-91 09-23-91 10-22-91 11-25-91 01-09-92 02-04-92 03-12-92 04-27-92 05-28-92 07-01-92 07-27-92 09-14-92 Chloride concen- tration (mg/L) NA NA NA NA NA NA NA NA NA NA NA NA 674 NA 678 NA NA 726 NA 700 682 704 NA 900 900 738 740 700 676 650 674 690 680 Barren Spot, Specific con- ductance (field value |lS/cm) 2,500 NA 3,800 NA NA NA 3, 850 NA NA NA NA NA 3,280 3,560 NA 1,250 NA 3,500 NA 3,560 3, 490 3, 610 NA 4, 320 4,430 3, 690 3, 680 3, 630 3,530 3,530 NA 3,580 3,530 , well pumping-water level not (USGS-23) Water level (in feet below land surface) 56.99 56.70 56.83 56.51 57.21 56.89 57.38 64.00 60.55 58.79 67.20 66.85 64.00 57.70 69.75 67.46 58.40 66. 65 NA 70.73 70.40 NA 57.95 58.70 58. 93 63.05 62.67 63.04 62.81 63.08 62.73 62.54 62.85 Comments PWL PWL PWL SWL PWL PWL "PWL PWL SWL PWL PWL PWL PWL PWL PWL PWL SWL PWL WP-WLNA PWL PWL WP-WLNA SWL PWL PWL PWL PWL PWL PWL PWL PWL PWL PWL CO