SITE REMEDIATION AND SUPPLEMENTAL INVESTIGATION PROGRAM
ESSO TUTU SERVICE STATION
TUTU, ANNA'S RETREAT, ST. THOMAS, U.S.V.I.
February 1995
Prepared for:
Esso Caribbean and South America
396 Alhambra Circle
Coral Gables, FL 33134
Prepared by:
Forensic Environmental Services, Inc.
623 North Pottstown Pike
Exton, Pennsylvania 19341
TUT 
OO7 
.184.1
*65009*
65009
SITE REMEDIATION AND SUPPLEMENTAL INVESTIGATION PROGRAM
ESSO TUTU SERVICE STATION
TUTU, ANNA'S RETREAT, ST. THOMAS, U.S.V.I.
Eage
1.0 
INTRODUCTION
1.1 
Preface 
1-1
1.2 
Site Description 
1-3
1.3 
Remedial Objectives 
1-4
2.0 
EXISTING SITE CONDITIONS
2.1 
Site-Specific Hydrogeology 
2-1
2.1.1 
Geology 
2-1
2.1.2 
Ground-Water Hydrology 
2-3
2.2 
Vadose Zone Soil Quality 
2-5
22.1 
Underground Storage Tanks/Pump Island 
2-5
2.2.2 
North Oil/Water Separator 
2-6
2.2.3 
Other Potential Source Areas 
2-8
2.3 
Ground-Water Quality 
2-9
2.3.1 
North Oil/Water Separator 
2-10
2.3.2 
Underground Storage Tanks/Pump Island 
2-11
2.3.3 
Phase-Separated Hydrocarbons 
2-12
2.3.4 
Regional Ground-Water Quality 
2-13
3.0 
PROPOSED REMEDIAL PROGRAM
3.1 
Conceptual Model 
3-1
3.2 
Vadose Zone Remediation 
3-1
3.3 
Saturated Zone Remediation 
3-3
4.0 
SUPPLEMENTAL 1NVESTIGATION/PRE-DESIGN ACTIVITIES
4.1 
Vadose Zone Remediation 
4-1
4.2 
Saturated Zone Remediation 
4-2
S.O 
IMPT.FMENTATION SCHEDULE
5.1 
Tentative Implementation Schedule 
5-1
TUT 
007
1842
LIST OF FIGURES
Following Page
1-1 
Area Map 
1-3
1-2 
Site Map 
1-3
2-1 
Water Table Elevation Map, Shallow Wells, 4/94 
2-3
2-2 
Soil Sample Locations, Soil Tech Tank Removal, 6/8/89 
2-5
2-3 
Soil Boring Location Map 
2-6
2-4 
Soil Sample Location Map, Oil/Water Separators 
2-7
2-5 
Ground-Water Isoconcentration Map, Total BTEX in ug/L, 4/94 
2-9
2-6 
Ground-Water Contaminant Distribution, Chlorinated Compounds in ug/L, 4/94 
2-10
3-1 
Conceptual Hydraulic Capture Zones 
3-3
LIST OF TABLES
Following Page
2-1 
Summary of Ground-Water Elevation Data 
2-3
2-2 
Summary of Soil Data, Soil Tech Tank Removal Samples 
2-5
2-3 
Summary of Soil Analytical Results, BB&L Soil Borings 
2-6
2-4 
Summary of Soil Analytical Data North Oil/Water Separator 
2-7
2-5 
Summary of Ground-Water Analytical Results 
2-9
2-6 
Chlorinated VOC Statistical Analysis 
2-13
5-1 
Tentative Implementation Schedule 
5-1
TUT 
007
SECTION 1.0
INTRODUCTION
1.1 
Preface
Anna's Retreat (Tutu) is located on the eastern end of Saint Thomas, United States Virgin
Islands. The Tutu area can be best characterized as a densely populated mixed residential,
commercial and industrial area. This history of diverse land use'has exerted significant stresses on
the localized ground-water regime (aquifer). 
The most significant of these stresses is the
degradation of ground-water quality as a result of anthropogenic activities (e.g.., residential and
commercial septic systems, improper handling and disposal of waste oils/hazardous materials,
unpermitted discharges to storm sewers, commercial and industrial operations, etc.). As a result of
these variable and widespread sources, the upper Tutu aquifer basin has experienced a
cumulative/progressive reduction in regional ground-water quality.
The Tutu area of Saint Thomas has been the focus of an ongoing Environmental Protection
Agency (EPA) directed investigation subsequent to July 1987. EPA's investigative activities were
precipitated as a result of the detection of volatile organic compounds in several potable water wells
located within the upper (northern) portion of the Tutu aquifer basin. Specifically, sampling
conducted by Weston in July 1987, on behalf of the EPA, identified the presence of synthetic
chlorinated organic compounds (halocarbons) and aromatic hydrocarbons at variable concentrations
and in sporadic locations within a number of ground-water production wells in the Tutu area.
Subsequent to July 1987, periodic water quality sampling of potable wells has been conducted by
the EPA. Additionally, site inspections, document reviews, and sampling activities have been
implemented in an attempt to identify potentially responsible parties (PRPs).
1-1
TUTURAP2.TUTU#2
In 1992 EPA directed the Tutu Environmental Investigation Committee (TEIC), comprised
of Texaco Caribbean, Inc. and Esso Standard Oil, to implement a joint hydrogeologic investigation
within the Tutu area. In an attempt to characterize the extent and sources of ground-water
contamination, ground-water monitoring wells were installed, soil/ground-water samples were
collected, and aquifer hydraulic information was obtained. Findings from this investigation were
presented by Geraghty & Miller in a Technical Memorandum (Tech Memo II) dated May 1993.
This investigation program represented the first step in the iterative process through which a
comprehensive Remedial Investigation/Feasibility Study (RI/FS) for the Tutu area would be
developed.
To address data voids identified in Tech Memo II, Geraghty and Miller developed elements
of a Phase II Remedial Investigation program in 1993. This program was submitted to EPA in
December 1993, and subsequently approved and implemented in 1994. Findings of the Phase II
/—N 
Remedial Investigation were presented in draft form in an October 1994 report.
In addition to global Remedial Investigation activities, several PRPs have conducted site-
specific investigations. Specifically, Esso has commissioned several site investigations of the Tutu
service station. These investigations have been implemented in phases and include the following
significant tasks:
• 
assessment of soil quality beneath the former location of the site's gasoline storage tanks
(samples collected during tank replacement activities 1989);
• 
investigation of the stations subsurface waste oil and oil/water separator piping systems;
• 
determination of environmental conditions adjacent to potential on-site source areas
including: the gasoline dispenser island; former location of hydraulic lifts; oil/water
separators; and existing gasoline storage tank field;
• 
characterization of hydrogeologic conditions beneath and adjacent to the site; and
• 
determination of ground-water quality on site as well as up- and downgradient of the
station.
1-2
TUTURAP2.TUTLW2
1845
This document serves to provide a concise summary of environmental conditions at and
proximal to the Esso service station, and to propose a remedial action program in accordance with
conditions of the Administrative Order On Consent (AOC) signed by Esso Standard Oil and Texaco
Caribbean, Inc. in 1992. The collection and analysis of supplemental environmental data proposed
in conjunction with this program will be implemented, to the extent possible, to conform with the
EPA approved Quality Assurance Project Plan (QAPP) developed by Geraghty & Miller for Phase I
and Phase II Remedial Investigation activities.
1.2 
Site Description
The Esso Tutu station is located adjacent to the Four Winds Plaza on Smith Bay Road (Route
38), south of the intersection with Route 384 (Figure 1-1). The station presently operates as a
gasoline retail facility, but in the past also conducted limited vehicle maintenance and repair
activities. Gasoline at the station is stored in two on-site underground storage tanks (USTs) located
in the southeastern corner of the property (Figure 1-2). The USTs are each 10,000-gallon capacity
and contain regular unleaded and super unleaded product. Gasoline is dispensed to vehicles from
the pump island located approximately 50 feet north of the USTs.
Structures on the service station property include a service building, an enclosed
garage/storage area, two open garage areas, and a garage enclosed by a steel cage (Figure 1-2). The
service building is located in the central portion of the site and is used for the storage of station
records and retail products (one-quart oil cans, windshield fluid, etc.). Also within the building are
vacant rooms which had previously served as vehicle maintenance bays prior to termination of
repair activities and building renovations.
The enclosed garage/storage area (located in the southern portion of the site) is currently
used for the storage of supplies and equipment related to ongoing environmental studies. Materials
contained within this area include a ground-water treatment system, health and safety equipment,
1-3
TUTURAP2.TUTU#2 
. 
TUT 
OO7 
1846
EPA REGION II
SCANNING TRACKING SHEET
DOC ID # 65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 1-1
AREA MAP
(Page: TUT 007 1847)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
EPA REGION II
SCANNING TRACKING SHEET
DOC ID #65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 1-2
SITE MAP
(Page: TUT 007 1848)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
and sampling tools. The enclosed garage/storage area is locked and secured to prevent public
access.
Open garages (including the caged garage) are present at the Esso Tutu station in the
southwestern corner of the site. The open garage areas, which are not currently used by Esso Tutu
personnel, had previously served as vehicle repair bays and/or storage areas. Within these areas are
two abandoned subsurface oil/water separators, designated as the "south oil/water separator" and
the "north oil/water separator". Historically, the north oil/water separator received waste oil
generated in the service bays previously located in the existing service building. The south
oil/water separator received both waste oil and storm water generated in service bays previously
located along the southern and western boundaries of the site.
13 
Remedial Objectives
The primary objectives of the proposed remedial action program have been developed in
accordance with the 1992 Administrative Order On Consent and include the following:
• 
remove phase-separated hydrocarbons, if any, from the saturated zone;
• 
abate residual sources, to the extent feasible, in the unsaturated zone that are or might
have an impact on ground-water quality; and
• 
capture and remediate, if feasible, the soluble-phase aromatic hydrocarbons (benzene,
toluene, ethylbenzene, and xylene) and semi-volatile compounds emanating from the
subject property.
TUTURAP2.TUTU#2 
fy-j-
1-4
T*i *.._
OO7
SECTION 2.0
EXISTING SITE CONDITIONS
Investigative studies at the Esso Tutu station have characterized site environmental
conditions in both the vadose and saturated zones. Specifically, the following studies have
provided quantitative information regarding site conditions:
• 
UST replacement activities performed by Soil Tech, Inc. and documented in "Final
Report, Lab Analysis of Soil for Tank Replacement", dated January 1990.
• 
Site characterization activities conducted by Blasland, Bouck & Lee (BB&L) during
the period of November 1993 through April 1994.
• 
Remedial investigation activities performed by Geraghty & Miller from February to
May 1994.
Presented below is a summary of the physical and chemical characteristics of subsurface
soils and ground water at the Esso Tutu site as defined in the above-referenced studies.
2.1 
Site-Specific Hydrogeology
2.1.1 
Geology
The geologic sequence at the Esso Tutu station, from the ground surface down, consists
of fill and unconsolidated Quaternary deposits, overlying volcanic units of Mesozoic and
Cretaceous age. The fill material at the Esso Tutu station varies in thickness from 2-3 feet at the
northern property boundary to approximately 8-10 feet in the southern portion of the site. This
layer consists primarily of a fine sand /silt/clay matrix surrounding angular rock fragments. In
certain areas, such as the southwestern corner of the site, in the vicinity of the open garages, the
fill material incorporates cobbles and boulders.
2-1
TUTURAP3.TUTU#2
TUT 
007 1S50
Beneath the fill are unconsolidated Quaternary alluvial and colluvial deposits and
weathered bedrock. These sediments range in thickness from two feet in the northern portion of
the site to approximately 6-8 feet in the southwestern corner of the property. The Quaternary
deposits can best be characterized as a poorly sorted mixture of clay, sift, sand, gravel and
cobbles. This material was derived from upland areas and transported to the valley by gravity
and surface runoff. Lying beneath the Quaternary deposits is a zone of weathered bedrock
(saprolite) that grades into competent rock. The weathered bedrock is composed of dense silt
and clay, and in some instances has retained original structure and fracture fabric.
Bedrock in the vicinity of the Esso Tutu station consists of two volcanic formations: the
Water Island Formation and the Louisenhoj Formation. The Water Island Formation is
composed primarily of basaltic flows and breccias. It is unconformably overlain by the
Louisenhoj Formation which consists of pyroclastic to ep»W»*tie <u»gite aadesite tuffs and
breccias. 
Locally, the base of the Lcpiseshog:-.Formation consists of the Cabes Point
Conglomerate, which contains welt rottndii SB* well sorted pebfetes and cobbles or the older
Water Island Formation (Dqiwe%1959 and 1966).
Stratographic infonrortWli obtained at the Esso Tutu site awHeaSes that depth to
competent bedrock varies from five feet along the northern property boundary to 18 feet in the
southwestern portion of the site. Because geologic logs of the area do not differentiate between
the two bedrock units, and since the contact between the two formations is ill-defined in the
study area, to date, it has not been definitively concluded whether the shallow bedrock beneath
the Esso Tutu station is the Water Island or the Louisenhoj Formation.
2-2
TUTURAP3.TUTU*2 
.y-j- O07
2.1.2 
Ground-Water Hydrology
Site hydraulic conditions have been ascertained through the collection and evaluation of
data from shallow and deep monitoring wells installed at, and proximal to, the Esso Tutu station.
Specifically, two depth intervals have been studied: a shallow interval (10-35 feet) and a deep
interval (65-85 feet).
Ground-water elevation data and field observations indicate that the shallow portion of
the aquifer is present under unconfined conditions. Depth to the water table beneath the Esso
Tutu site ranges from 11 feet to 20 feet , with ground water generally flowing to the south-
southeast under a gradient of 0.025 (Table 2-1, Figure 2-1). An area of perched ground water is
present in the southwestern portion of the site, in the vicinity of the north oil/water separator and
well SW-7. This perched zone is likely manifested by a permeability gradient between fill
material and saprolite strata. Depth to water in the perched zone, as measured in well SW-7, is
approximately 9 feet.
Information from geologic logs and pumping tests conducted in the Tutu area indicate
that the 65-85 foot interval represents a deeper zone within the water table aquifer, not a separate
water bearing system. Ground-water flow in the 65-85 foot interval is generally to the south
under a gradient of 0.04. Depth to ground water in monitoring wells screened in this deeper
zone ranges from 12.21 feet (DW-2) to 24.80 feet (MW-12D).
Vertical hydraulic gradient information obtained from three shallow/deep well clusters
proximal to the Esso Tutu station (MW-8/ DW-1, SW-6/DW-2, and MW-10/MW-10D), suggest
a slight downward gradient ranging between 0.0035 to 0.01. The vertical gradient of ground-
water flow at each well cluster was calculated by dividing the difference of the water level
elevation in the well cluster by the vertical separation of the mid-points of the well screens (or
open rock intervals).
2-3
TUTURAP3.TUTU#2
TUT 
OO7 1852
TABLE 2-1
SUMMARY OF GROUND-WATER ELEVATION DATA
TUTU AREA MONITORING WELLS
Tutu Esso Service Station
St. Thomas, USVI
Top-of Casing
Elevation (ft)
Ground-Water
Elevation (ft)
Ground-Water
Elevation (ft)
'Corrected ground-water elevation as a result of NAPL presence.
"Elevation measurement is approximate. No ground water elevation level has been calculated.
Top-of-casing elevations are referenced to Mean Sea Level (MSL).
Elevations from MW-9 through MW-12D and all CHT wells were obtained between April 7 and April 11, 1994.
EPA REGION II
SCANNING TRACKING SHEET
DOC ID # 65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 2-1
WATER TABLE ELEVATION MAP SHALLOW
WELLS, 4/94 (Page: TUT 007 1854)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
Single-well hydraulic conductivity tests indicate that the permeability of the shallow
fracture system below the Esso Tutu station ranges from 1.55 x 10"4 ft/min to 4.61 x 10"6 ft/min.
Calculated hydraulic conductivity values for the deep fracture system at well location DW-1 was
1.01 x 10"5 ft/min. Specific results from these tests are presented below:
Monitoring Well 
Calculated Hydraulic Conductivity
SW-1 
5.47 xlO"6*/™,,
SW-3 
4.61 xlO'6^
MW-8 
1.55xl0^ft/min
DW-1 
1.01xlO'5ft/min
The range in calculated hydraulic conductivity values is consistent with field
observations and geologic conditions. Field data obtained during well development, ground-
water sampling, and slug testing indicated that recharge to monitoring wells SW-1 and SW-3
was extremely slow. In comparison, data from MW-8 indicated that ground-water recharge in
this portion of the aquifer is greater, confirming the higher calculated hydraulic conductivity
value. This degree of variability in aquifer permeability is common in bedrock media, where
ground-water flow is restricted primarily to fractures, bedding planes, and formation contacts.
Monitoring wells which intersect portions of the bedrock that are highly fractured can exhibit
greater permeability (all other parameters held constant). The site-specific slug test data indicate
that the fracture density in the southern portion of the service station site is low, thereby
restricting ground-water flow downgradient from the station property.
Hydraulic conductivity data, in conjunction with ground-water gradient information,
indicate that ground-water velocity in the area of the Esso Tutu station is relatively slow.
Averaging the hydraulic conductivity for the shallow monitoring wells, and assuming an
effective porosity of 0.15, produces a calculated ground-water velocity of 0.013 feet/day (4.7
feet/year).
2-4
TUTURAP3.TUTU#2
TUT 
OO7 .1855
2.2 
Vadose Zone Soil Quality
Soil quality investigations have been performed at the Esso Tutu station to characterize
vadose zone conditions proximal to suspected source areas. A total of 59 samples have been
collected during these studies and submitted for laboratory analysis. Based upon these data, two
areas within the unsaturated zone at the Esso Tutu station have been identified as a residual source
for VOC contamination: 1) the area west of the north oil/water separator; and 2) proximal to the
underground storage tanks and pump island. All remaining'areas of the site, including those
adjacent to the south oil/water separator, subsurface waste oil/storm water piping, and the former
hydraulic lift/automobile repair areas demonstrated non-detectable to very low levels of target
constituents, and do not warrant additional investigation or remediation.
2.2.1 Underground Storage Tanks/Pump Island
Analytical data characterizing vadose zone soils in the vicinity of the gasoline USTs and
pump island were obtained by Soil Tech in 1989 (concurrent with UST replacement activities) and
BBL in 1993. Soil Tech obtained 13 samples from the UST excavation during the removal and
subsequent installation of new tanks (Figure 2-2). Data from the 13 samples indicated the presence
of aromatic hydrocarbons and select semi-volatile organic compounds (Table 2-2). Aromatic
hydrocarbons were observed at their highest concentrations in samples obtained from the floor of
the excavation, generally at a depth of 11-12 feet below grade (the approximate top of competent
bedrock). Samples collected from excavation sidewails demonstrated non-detectable concentrations
of BTEX constituents.
Semi-volatile organic compounds including naphthalene, fiuorene, and phenanthrene were
detected in the UST excavation at concentrations ranging to a maximum of 45 mg/Kg. The spatial
2-5
TUTURAP3.TUTU#2 
TUT 
Q07
TABLE 2-2
SUMMARY OF SOIL DATA
SOIL TECH TANK REMOVAL SAMPLES
June 8,1989
Tutu Esso Service Station
St. Thomas, USVI
TP-1
TP-2 
TP-3 TP-4 TP-5 TP-6 TP-7 TP-8 TP-9
•9 J TP-10 | TP-11 TP-12
;-x-x-x-x-x-x-x-x-x*x-Xtt-x-x-x*x-X':-x-x*x-x*x-x-x-x-x-:-:*X'X-x-x*x^
:x:x:X:::X:X.x:x:xa::x:x:x::.ra^
TP-1 3
Benzene
<0.006
<0.028
0.23 J
0.002 J
1.1
<23
<0.006
0.093
<0.006 
0.003 J
<0.006 
<0.006
<0.006
Toluene
<0.006
<0.028
5.2
<0.006
<0.72
180
<0.006
<0.029
<0.006
<0.006
<0.006
<0.006
<0.006
Ethyl benzene
<0.006
<0.028
2.1
0.005 J
55
0.005 J
0.52
<0.006
0.009
<0.006
<0.006
<0.006
Xylenes
<0.006
1.6 E
31 E
<0.006
<0.72
540
0.3 E
0.22
<0.006
<0.006
<0.006
<0.006
<0.006
Acetone
<0.012
<0.057
0.014
<47
0.029
<0.057
0.005 J
<0.012
<0.012
<0.012
0.11
2-Butanone
Naphthalene
<0.012
<0.057
0.4 BJ
3.6 BJ
19 B
<0.012
<0.057
<0.012 
0.005 J
<0.012 
<0.012
0.004 J
ND
ND
32 E
ND
9
45E
0.3 J
1.1
ND
0.19 J
ND
ND
ND
2-Methylnaphthalene
0.11 J
0.68 J
45 E
ND
43E
1.1
0.14 J
0.18 J
ND
ND
ND
Acenaphthene
ND
ND
0.4 J
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
Fluorene
ND
0.18 J
1.4
ND
ND
1.7
0.29 J
0.29 J
ND
ND
ND
ND
ND
Phenanthrene
ND
0.12 J
1.1
ND
0.37 J
1.3
0.16 J
0.18J
ND
ND
ND
ND
ND
Anthracene
ND
ND
0.13 J
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
Fluoranthracene
ND
ND
0.12 J
ND
ND
0.16 J
ND
ND
ND
ND
ND
ND
ND
Pyrene
ND
ND
0.21 J
ND
ND
0.25 J
ND
ND
ND
ND
ND
ND
ND
DI-n-Butylphthalate
0.069 BJ
ND
ND
ND
ND
ND
ND
ND
0.063 BJ
0.094 BJ
ND
0.033 BJ
0.04BJ
Butylbenzylphthalate
ND
ND
ND
ND
ND
ND
ND
ND
ND
0.31 J
ND
ND
ND
Bis (2-Ethylhcxyl) Phalate
0.28 BJ
ND
0.4 BJ
ND
0.11 BJ
0.38 BJ
ND
ND
ND
0.36 BJ
ND
ND
ND
Lead
ND
ND
0.2
ND
ND
0.1
ND
ND
ND
ND
ND
ND
ND
Arsenic
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
Chromium
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
Selenium
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
ND
00
O!
•--J
Notes:
ND = Not Detected
E = Estimated value above instrument calibration range
B = Compound detected in blank
J = Estimated value below minimum detection limit
TPH = Total Petroleum Hydrocarbons
EPA REGION II
SCANNING TRACKING SHEET
DOC ID #65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 2-2
SOIL SAMPLE LOCATIONS SOIL TECH TANK
REMOVAL, 6/8/89 (Page: TUT 007 1858)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18TH FLOOR
NEW YORK, NY 10007
distribution of semi-volatile organic compounds mimicked that identified for BTEX constituents.
Due to the limited thickness of unconsolidated deposits, if any, and the proximity of the water table
beneath the present/former location of the USTs, no vadose zone remediation is proposed for this
area. Rather, remediation in this area will be facilitated through hydraulic control and aqueous-
phase treatment.
Soil sampling activities conducted by BBL in 1993 incorporated the drilling of three soil
borings (SW-1 through SW-3; Figure 2-3) and the collection /analysis of four discrete soil samples.
Results of the volatile organic analyses (Table 2-3) indicated thai BTEX constituents were present
in shallow soils adjacent to the dispenser island (sample SW-3, 0-2 feet). Total BTEX constituents
were identified at concentrations ranging from 0.066 mg/Kg (benzene) to 1.7 mg/Kg (xylene).
However, the 6-8 foot sample interval of boring SW-3 did not demonstrate detectable levels of
aromatic compounds, indicating that the vertical extent of impacted soil in this area is limited to
shallow depths. Samples obtained from soil borings SW-1 (8-10 feet) and SW-2 (6-8 feet)
demonstrated the absence of BTEX constituents, thereby confirming the laterally confined nature of
aromatic hydrocarbons detected by Soil Tech in the UST area.
Chlorinated volatile organic compounds were not detected in any of the samples
collected by Soil Tech during UST replacement activities or in the soil boring samples collected by
BBL.
2.2.2 North Oil/Water Separator
Soil quality proximal to the north oil/water separator was characterized through the
collection of samples in 1993. Analytical data obtained during this investigation demonstrated the
presence of soils impacted by volatile organic compounds and base neutral constituents. Data
2-6
TUTURAP3.TUTU#2 
TUT 
OO7 
1B5C?
TABLE 2-3
SUMMARY OF SOIL ANALYTICAL RESULTS
BB&L SOIL BORINGS
Tutu Esso Station
St. Thomas, USVI
Bis (2-ethylhexyl) phthafate
I?"o
Note*:
MA - Not Analyzed
Volatile organic analysis conducted using EPA Method 8240; base neutrals analyzed by Method 8270; TPH analysis by Method 8015 (GC-FIO).
EPA REGION II
SCANNING TRACKING SHEET
DOC ID #65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 2-3
SOIL BORING LOCATION MAP
(Page: TUT 007 1861)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18TH FLOOR
NEW YORK, NY 10007
indicate that impacted soils were limited to the area immediately surrounding the former north
oil/water separator effluent pipe.
Volatile organic compounds were detected at their highest concentrations in samples SS-1,
SS-3, SS-7 and SS-8, all collected from the eastern portion of the effluent pipe excavation (Table 2-
4 and Figure 2-4). Compounds detected at the highest concentrations included toluene,
ethylbenzene, and xylenes, with a maximum reported total aromatic hydrocarbon concentration of
142.3 mg/Kg. Other volatile organic compounds detected in this area included 1,2-dichloroethene,
trichloroethene, tetrachloroethene, and 1,1,1-trichloroethane. "The highest reported individual
concentration was 3.2 mg/Kg of 1,2-dichloroethene at a depth of three feet in sample SS-3.
Data indicate that the extent of BTEX and chlorinated volatile organic compounds is limited
to the area adjacent to the western end of the north oil/water separator. Although the vertical extent
of BTEX impacted soil is not completely defined, data obtained from sidewalls of the trench (which
extended to a depth of approximately five feet) demonstrate a significant decrease in concentration
and therefore a limited lateral distribution. Data from samples SS-4, SS-5 and SS-6 (Figure 2-4) all
demonstrated BTEX levels significantly lower than the maximum concentrations reported.
Analytical data also indicated that the horizontal and vertical extent of chlorinated volatile
organic contamination is substantially defined. Samples SS-1 and SS-6 (separated by a distance of
approximately 15 feet), both demonstrated the absence of chlorinated volatile organics, thereby
defining the eastern and western extent of chlorinated impact. Samples SS-4 and SS-5 (separated
by a distance of approximately 5 feet) substantially define soil impact south and north of the former
north separator effluent pipe, respectively, with reported concentrations of individual chlorinated
compounds less than 0.15 mg/Kg. Sample SS-1, obtained at a depth of 9 feet, demonstrated non-
detectable levels of chlorinated compounds.
2-7
TUTURAP3,TUTU#2 
TUT 
Q07
TABLE 2-4
SUMMARY OF SOIL ANALYTICAL DATA
NORTH OIL/WATER SEPARATOR
Tutu Esso Station
St. Thomas, USVI
1,1,1-Trichloroethane
1,2-Dichlorobenzene
mg/kg
NA
2.8
0.84
<2
<0.38
<0.77
1.4
Naphthalene
mg/kg
NA
29
11
22
<0.38
19
23
Fluorene
mg/kg
NA
3.4
1.4
2.6
<0.38
1.4
1.6
Phenanthrene
mg/kg
NA
9.7
4.5
8.1
<0.38
4.3
6.1
Anthracene
mg/kg
NA
<2.4
0.92
<2
<0.38
<0.77
1.2
Fluoranthrene
mg/kg
NA
3.1
1.2
2.4
<0.38
1.1
1.5
Pyrene
mg/kg
NA
15
6.5
9
<0.38
5.7
8
Benzo (a) anthracene
mg/kg
NA
5.8
2.3
4.3
<0.38
2.1
2.8
Chrysene
mg/kg
NA
5.1
3.6
<0.38
1.9
2.4
Bis (2-ethylhexyl) phthalate
mg/kg
NA
19
8.3
11
<0.38
6.7
9.2
Di-n-octyl phthalate
mg/kg
NA
<2.4
<2
<0.38
<0.77
<0.77
Benzo (b) fluoranthrene
mg/kg
NA
6.1
3.8
<0.38
2.5
Benzo (a) pyrene
mg/kg
NA
3.2
0.97
<2
<0.38
0.88
1.1
Benzo (ghi) perylene
mg/kg
NA
7.7
1.6
3.4
<0.38
1.4
1.9
Gasoline Range
mg/kg
NA
5,000
3,000
3,000
<8
4,000
5,000
Kerosene Range
mg/kg
NA
<4,000
<1,000
<1,000
<8
<1,000
<1,000
Diesel Range
mg/kg
NA
<4,000
<1,000
<1,000
<8
< 1,000
<1,000
Notes:
NA= Not Analyzed
Volatile organic analysis conducted by EPA Method 8240; base neutrals analysed by EPA Method 8270; TPH analysis conducted by Method 8015 (GC-FID).
TUT 
OO7 1863
EPA REGION II
SCANNING TRACKING SHEET
DOC ID #65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 2-4
SOIL SAMPLE LOCATION MAP OIL /WATER
SEPARATORS (Page: TUT 007 1864)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
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290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
Laboratory data demonstrate the presence of semi-volatile organic compounds and total
petroleum hydrocarbons (TPH) in soils west of the north oil/water separator (Table 2-4). The
presence and distribution of semi-volatile compounds and TPH mimics that of the aromatic
compounds. In general, the highest levels were reported in the eastern portion of the excavation, at
a depth of 3 feet. Samples collected at greater depths, and at locations more distant from the
separator, contained lower levels of target constituents. Laboratory fingerprinting for TPH indicated
the presence of gasoline-range hydrocarbons at concentrations ranging from below detection (SS-6)
to 5,000 mg/Kg (SS-3 and SS-8). Kerosene range hydrocarbons and diesel range hydrocarbons
were not detected in any of the soil samples.
2.2.3 
Other Potential Source Areas
As the above-referenced data indicate, residual contamination remains in the vadose
zone soils adjacent to the north oil/water separator and the dispenser island. In addition to
collecting environmental samples in these areas, discrete soil samples were collected adjacent to
the south oil/water separator (Sample SS-9, Figure 2-4) and beneath the former location of the
hydraulic lifts/automobile repair area (Samples SB-1, SS-la and SS-2a, Figure 2-4). As
demonstrated in Table 2-3, the five soil samples collected from these locations were
characterized by the absence of volatile organic compounds. Sample SS-9 did demonstrate a
minor concentration of one semi-volatile compound (0.94 mg/Kg of Di-n-octyl phthalate) and
the 10 - 12 and 12-14 foot sample intervals from SB-1 were characterized by gasoline range
TPH concentrations of 400 and 70 mg/Kg, respectively. It is important to note that the TPH
concentrations decreased with increasing depth at SB-1. Based upon field observations and these
empirical data, the south oil/water separator, as well as the former hydraulic lift and automobile
repair areas, were eliminated as potential sources for ground-water contamination.
2-8
TUTURAP3.TUTU#2 
JUT 
OO7 1865
23 
Ground-Water Quality
Data regarding the presence and spatial distribution of soluble-phase contaminants in
ground water proximal to the Esso Tutu station were obtained from on-site and adjacent
monitoring wells. Specifically, wells SW-1, SW-2, SW-3, and SW-7 (Table 2-5, Figure 2-5) are
located on site immediately adjacent to potential source areas. Shallow well MW-8 and deep
well DW-1 are positioned along the upgradient property boundary of the Esso Tutu station. In
addition, five shallow and two deep wells (located within 100 feet of the station property) were
incorporated into the monitoring array to evaluate the potential for ground-water quality impact
resulting from operation of the Esso station. These wells, and their locations relative to the
station property are summarized below:
Well Designation 
Relative Location
CHT-2 
southwest and downgradient of both the north and south
oil/water separators
CHT-3 
south and immediately downgradient of the USTs
CHT-4 
northwest and upgradient of the site
CHT-7D 
south and downgradient of the USTs
MW-9 
southwest of the north oil/water separator and due west
of the south oil/water separator
M W-10 
south and downgradient of the USTs
M W-1OD 
south and downgradient of the USTs
Based upon analytical data obtained from a total of IS monitoring wells sampled by
BBL (April 1994), and confirmed through Phase II RI sampling by Geraghty & Miller (June
1994); a commingled aromatic hydrocarbon plume exist straddling a perched water zone and the
shallow portion of the aquifer beneath and immediately adjacent to the Esso Tutu station.
2-9
TUTURAP3.TUTU#2 
TUT 
007 
1866
TABLE 2-5
SUMMARY OF GROUND-WATER ANALYTICAL RESULTS
Tutu Esso Service Station and Adjacent Areas
St. Thomas, U.S.V.I.
SW-1
5W-2
SW-3
SW-4
sw-s
SW4
SW-7
DW-1
Page 1 of 2
DW-2
Benzene
pg/L
3700
1400
550 J
12000
10000 J
<5
<5
<5
160
99J
<5
<5
Toluene
pg/L
1800
1800
360 J
3400
3200 J
<5
<5
<5
16
<100
<5
Ethylbenzene
pg/L
2000
1000
<1000
2200
4100 J
<5
<5
<5
110
<100
Xvtenes (total)
pg/L
8100
4000
1800 J
10300
22000 J
<5
<5
<5
171
82
Methyl Terl Butyl Ether
ugA.
42000
52000
35000 J
110000
89000 J
10
6.3 J
<5
<50
<50
1600
1500 J
19
16 J
21
19 J
TCE
ug/L
<250*
<250'
<1000"
<250*
<1000*
<5
4J
<5
2J
<5
<5
<100
15
10 J
5J
PCE
pg/L
<250*
<250*
<1000*
<250"
<1000*
18
15 J
4J
<5
<100
62
42 J
14
18
1.2-DCE (total)
pg/L
<250*
<250*
<1000*
<250*
<1000*
46
38J
4J
<5
<5
<100
130
92 J
33
43
Vinl Chloride
pg/L
<500*
<500'
<1000'
<500*
<1000*
<100
j iBtiljg
Gasoline Range
mg/L
120
25
NA
310
NA
NA
NA
NA
NA
NA
NA
Kerosene Range
mg/L
<4
<4
NA
<40
NA
NA
NA
NA
<4
NA
NA
NA
Diesel/02 Range
<4
NA
<40
NA
NA
NA
NA
<4
NA
NA
NA
Naphthalene
ug/L
60
<100
1300
1000 J
60
96J
Fluorene
pg/L
<4
<2
40
40 J
<2
<2
<2
4J
<2
Phenanthrene
pg/L
40
32 J
<2
<2
<2
3J
<2
<2
Anthracene
pg/L
<50
<2
Pytene
Mg/l
<2
8J
<2
<2
<2
2J
<2
Chrysene
pg/L
9J
Benzo(a)pyrene
pg/L
0.3
0.7
<50
0.3
Benzofg, h, ijperylene
pg/L
1.4
<50
<5
1.4
c
Benzo(b)fluoranthrene
pg/L
2.1
<50
0.5
Calcium
mg/L
39.5
NA
14.3 J
91.3
86.2 J
NA
44.6
NA
52.9
NA
85.7
85
82.5 J
48.5
45
NA
242
Iron
mg/L
5.7
MA
14.1
98
108
NA
5.1
NA
18.6
NA
20.3 J
17.5
14.8 J
222
1.1
NA
3.1
Total Suspended Solids
mg/L
120
NA
284
2820
324
NA
117
NA
182
NA
159
260
783
18
NA
15
Carbon Dioxide
mg/L
835
1190
NA
1020
NA
533
NA
543
NA
752
NA
858
NA
566
NA
577
NA
Dissolved Oxygen
mg/L
7.6
3.2
NA
5.2
NA
2.4
NA
9.5
NA
2.7
NA
NA
NA
1.9
NA
--
TABLE 2-5 (continued)
SUMMARY OF GROUND-WATER ANALYTICAL RESULTS
Tutu Esso Service Station and Adjacent Areas
St. Thomas, U.S.V.I.
CHT-2
CHT-3
CHT-4
CHT-7D
MW-8
MW-9
MW-10
MW-10D
Page 2 of 2
MW-12D
Analytical Parameter | Units
4/11/94
4/11/94 
6/1/94
4/11/94
4/11/94 
6/2/94
4/7/94
6/3/94
4/7/94
4/8/94I 4/8/94 D J 5/31/94
4/8/94 I 5/31/94
4/8/94 
5/20/94
Benzene
UO/L
1900
1700
<5
<5
<5
11
<5
<5
<25
<5
<5
Toluene
ug/l
<5
<50
180
<5
<5
<25
<5
<5
Ethylbenzene
MO/L
<5
1500
1800
<5
<5
<5
39
<5
<25
<5
<5
o-Xylenes
van.
<5
1153
2000
<5
<5
<5
<5
<5
<25
<5
Methyl Tert Butyl Ether
ng/t
870
15000
13000
14
28 J
10
17 J
450
420
430
340 J
130
170 J
39
360 J
TCE
pg/L
<5
<50*
<100*
16
14
10
10 J
<5
14
12
18 J
11
14 J
<5
9J
PCE
<5
<50*
<100*
50
50
36
32
38J
<5
22
19
34J
39
48J
<5
33J
1,2-DCE (total)
ng/t
<50*
<100*
150
140
91
89
88J
<5
57
51
76 J
100
110 J
<5
67 J
Vinyl Chloride
pg/L
<100*
<100*
17
16
<25
Gasoline Range
mg/L
69
NA
NA
NA
5.1
NA
NA
NA
Kerosene Range
mg/L
NA
<4
NA
NA
NA
NA
NA
DieseW»2 Range
Naphthalene
mg/L
NA
NA
NA
NA
NA
pg/L
260
310
NA
Fluorene
MBA
<2
6J
<2
<2
<2
Phenanthrene
pg/L
<2
4J
<2
<2
<2
<2
<2
<2
<2
Anthracene
pg/L
<20
Pyrene
H8A
<2
<20
<2
<2
<2
<2
' <2
<2
Chrysene
pg/L
<20
Benzo(a)pyrene
pg/L
<20
<2
Benzo(fl.h,i)perylene
PQfl-
<20
Benzo(b)fluoranthrene
<20
<3^tilit:V^ttt:Cnit«»«)aty::;ig
Calcium
mg/L
MA
NA
NA
NA
44
NA
60.8
NA
NA
NA
31.2
NA
38.6
NA
30.6
Iron
mg/L
MA
NA
NA
NA
0.1
NA
49.7
NA
NA
NA
1.4
NA
0.6
NA
0.3
Total Suspended Solids
mg/L
NA
NA
12300
NA
NA
NA
478
NA
NA
NA
45
NA
NA
Carbon Dioxide
mg/L
623
834
NA
552
523
NA
572
NA
640
511
551
NA
516
NA
40
NA
Dissolved Oxygen
mg/L
2.1
NA
2.9
3.4
NA
NA
1.9
2.1
NA
2.5
NA
4.7
NA
NA = Not Analyzed 
R = Rejected 
J = Estimated Value
'Elevated chlorinated organic detection limit as a result of aromatic hydrocarbon concentrations.
H-
CO
TABLE 2-5 - ADDENDUM
SUMMARY OF GROUND-WATER QA/QC SAMPLES
APRIL 1994
H-ill
0-
••0
Tutu Esso Service Station and Adjacent Areas
St. Thomas, U.S.V.I.
Addendum
Analytical Parameter
Benzene
Toluene
Ethylbenzene
o-Xylenes
m&p-Xylenes
Methyl Tert Butyl Ether
TCE
PCE
1,2-DCE (total)
Vinyl Chloride
Total
TB
Units 
(4/8/94) (4/14/94)
TB
EB
EB
Bailer 
Pump
pg/L
pg/L
pg/L
pg/L
pg/L
pg/L
pg/L
pg/L
pg/L
pg/L
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
<5
Gasoline Range
Kerosene Range
Diesel/#2 Range
mg/L
mg/L
mg/L
Naphthalene
Fluorene
Phenanthrene
Anthracene
Pyrene
Chrysene
Benzo(a)pyrene
Benzo(g,h,l)perylene
Benzo(b)fluoranthrene
Calcium
Iron
Total Suspended Solids
Carbon Dioxide
Dissoived Oxygen
pg/L
pg/L
P9/L
pg/L
pg/L
pg/L
pg/L
pg/L
pg/L
NA
NA
NA
NA
NA
NA
<A
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
<50
<5
<5
<1
<3
NA
NA
NA
NA
NA
NA
NA
NA
NA
mg/L
mg/L
mg/L
mg/L
mg/L
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
NA
EPA REGION II
SCANNING TRACKING SHEET
DOC ID #65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 2-5
GROUNDWATER ISOCONCENTRATION MAP
TOTAL BTEX IN UG/L, 4/94
(Page: TUT 007 1870)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
Aromatic hydrocarbons and semi-volatile compounds emanate from the area of the north
oil/water separator; and the vicinity of the pump island. Table 2-5 summarizes ground-water
analytical data, while maps depicting the distribution of aromatic hydrocarbons and synthetic
chlorinated compounds are presented as Figures 2-5 and 2-6, respectively.
2.3.1 
North Oil/Water Separator
The distribution of aromatic hydrocarbons associated with the north oil/water separator
is characterized by the presence of BTEX, MTBE and select semi-volatile organic compounds.
Data from SW-7 demonstrate the presence of BTEX constituents at individual concentrations
ranging from a minimum of 16 ug/L (toluene) to a maximum of 230 ug/L (xylene). MTBE was
detected at a concentration of 1,600 ug/L in well SW-7. Semi-volatile compounds detected in
this well included naphthalene, phenanthrene, pyrene, and chrysene. Naphthalene was detected
at the highest concentration (60 ug/L), while the remaining semi-volatile compounds were
present at concentrations equal to or less than 4 ug/L.
Although soluble-phase aromatic hydrocarbons are present in the ground water proximal
to the north oil/water separator, data from adjacent wells indicate that the spatial distribution of
the plume is limited, confined primarily to the perched water zone proximal to SW-7. Total
BTEX concentrations at wells CHT-2 and MW-9, both located 20-30 feet southwest of SW-7,
were less than or equal to 50 ug/L. Additional data from wells CHT-2 and MW-9 has
demonstrated the absence of semi-volatile compounds, with the exception of fluorene (5 ug/L at
MW-9), and a significant decrease in MTBE concentrations.
Ground-water quality data obtained from SW-7 (screened in the perched water horizon)
by BBL, and subsequently by Geraghty & Miller, have demonstrated the absence of chlorinated
volatile organic compounds (Table 2-5). These data indicate that chlorinated compounds present
2-10
TUTURAP3.TUTU#2 
TUT 
OO7 1871
EPA REGION II
SCANNING TRACKING SHEET
DOC ID #65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 2-6
GROUNDWATER CONTAMINANT
DISTRIBUTION CHLORINATED IN UG/L, 4/94
(Page: TUT 007 1872)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
in soils in the vicinity of the north oil/water separator have not impacted the saturated zone.
Chlorinated compounds were absent in well MW-9, while ground water obtained from well
CHT-2 demonstrated a concentration of 1,2-dichloroethene of 6 ug/L (Figure 2-6). It is
important to note that 1,2-dichloroethene was detected in well CHT-4 (located upgradient of
wells CHT-2, MW-9, and the Esso station) at a concentration of 150 ug/L.
23.2 
Underground Storage Tanks/Pump Island
Similar to the distribution of aromatic hydrocarbons observed proximal to the north
oil/water separator, soluble constituents detected in the vicinity of the site underground storage
tanks and dispenser island were characterized by the presence of BTEX, MTBE, and PAHs.
Based upon the observed spatial distribution and constituent concentration gradients, it has been
concluded that this plume originates from the area adjacent to the dispenser island. The highest
concentrations of total BTEX constituents (27,000 ug/L) was detected in well SW-3, located
immediately downgradient of the dispenser island. Concentrations of total BTEX constituents
decreased south of the dispenser island with the downgradient extent of the plume defined by the
absence of aromatic hydrocarbons in monitoring wells MW-10 and MW-10D (located
approximately 50 feet south of the Esso Tutu property line and USTs). MTBE was detected in
monitoring wells proximal to the USTs and pump island with reported concentrations ranging
from 42,000 ug/L (SW-1) to 110,000 ug/L (SW-3). Similar to the BTEX distribution, data
regarding MTBE concentrations demonstrated a significant decrease in concentration south
(downgradient) of the dispenser island.
Of the 18 monitoring wells sampled by BBL, four demonstrated the presence of semi-
volatile organic compounds (SW-1, SW-3, SW-7, and CHT-3, Table 2-5). Semi-volatile organic
compounds detected included naphthalene, fluorene, phenanthrene, anthracene, and pyrene. Of
2-11
TUTURAP3.TUTU#2 
TUT
OO7 1873
these compounds, naphthalene was detected at the highest concentration (1300 ug/L in well SW-
3), the remainder of the compounds were detected at concentrations less than, or equal to, 40
ug/L. Ground-water samples from wells CHT-2, SW-2 and MW-10 demonstrated the absence of
semi-volatile compounds, thereby defining the spatial distribution of ground-water quality
impact from these compounds. 
These data indicate that the aromatic and semi-volatile
constituents exhibit a consistent spatial distribution, confirming a common source area.
Ground-water analytical data demonstrated the absence of chlorinated organic
compounds in both on-site and off-site monitoring wells positioned downgradient of potential
VOC source areas on the Esso service station (Figure 2-6). Specifically chlorinated compounds
were not detected in well MW-9 (downgradient of the north oil/water separator and immediately
adjacent to the south oil/water separator), well SW-7 (immediately downgradient of the north
oil/water separator), and wells SW-1, SW-2, and SW-3 (downgradient of the dispenser island
and USTs).
2.3.3 
Phase-Separated Hydrocarbons
Phase-separated hydrocarbons have been detected sporadically on and immediately
adjacent to the Esso service station property. Geraghty & Miller detected floating product in
monitoring wells MW-9 and MW-9S during the period September through November 1992.
Specifically, well MW-9 was characterized by a product sheen on only one occasion, while well
MW-9S demonstrated the presence of phase-separated hydrocarbons on four occasions
(September 17, September 28, October 28, and November 16, 1992), ranging in thickness from a
sheen to 0.11 foot. Subsequent measurements in these two wells have demonstrated the absence
of a free-floating product layer. Monitoring well SW-7, located on the station property, has also
sporadically demonstrated the presence of phase-separated hydrocarbons. This well exhibited
2-12
TUTURAP3.TUTU#2
TUT 
OO7 1874
the presence of 0.01 foot of product on December 20, 1993 (shortly after installation); two
subsequent measurements demonstrated the absence of phase-separated liquids in this well.
Floating product has not been detected at any of the remaining on-site monitoring wells.
23.4 
Regional Ground-Water Quality
As previously stated, chlorinated compounds were not detected in ground-water samples
collected downgradient of potential VOC source areas on the service station property. In
contrast, chlorinated compounds have been detected in the regional ground-water flow field both
upgradient and downgradient of the service station (Figure 2-6). The most important
characteristic with regard to the presence of these compounds in the environment, is the
consistency in their absolute concentrations and relative weight percent ratios upgradient and
downgradient of the Esso service station property. Tetrachloroethene (PCE), trichloroethene
(TCE), and 1,2-dichloroethene (DCE) demonstrate consistent concentrations and relative weight
percent ratios in monitoring wells north (upgradient) and south (downgradient) of the service
station. For example absolute concentrations of PCE, TCE, and DCE in wells CHT-4 and CHT-
7D (Table 2-6) are almost identical, as are the relative weight percent ratios of the individual
constituents. If a statistical comparison is made between the relative weight percent ratios of
PCE, TCE and DCE for those wells upgradient and downgradient of the service station, an
excellent correlation is observed which exhibits minimal variability (e.g., 0.05 for PCE and 0.05
for DCE). These data indicate that there is no statistical increase in the concentration of
chlorinated volatile organic compounds downgradient of the Esso station when compared to
regional ground-water quality.
TUTURAP3.TUTU#2
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oo
TABLE 2-6
CHLORINATED VOC STATISTICAL ANALYSIS
Tutu Esso Service Station
St. Thomas, USVI
CHT-4 (upgradient)
CHT-7D (downgradient)
MW-8 (upgradient)
MW-10 (downgradient)
MW-10D (downgradient)
Average Relative Weight %
Coefficient of Variability
Tetrachloroethene
Concentration
(ug/L)
50
50
32
22
39
Relative
Weight %•
23.1
24.5
24.6
23.6
26
24.4
0.05
Trichloroethene
Concentration
(ug/L)
16
14
9
14
11
Relative
Weight %
7.4
6.9
6.9
15.1
7.3
8.72
0.41
1,2-Dichloroethene
Concentration
(ug/L)
150
140
89
57
100
Relative
Weight %
69.5
68.6
68.5
61.3
66.7
66.92
0.05
H-
0?
SECTION 3.0
PROPOSED REMEDIAL PROGRAM
3.1 
Conceptual Model
Based upon available, site-specific, empirical soil and ground-water quality data,
remedial activities at the Esso Tutu station are presently anticipated to incorporate the following
objectives:
• 
remove phase-separated hydrocarbons, if any, from the saturated zone;
• 
abate residual sources, to the extent feasible, in the unsaturated zone adjacent to the
dispenser island and north oil/water separator; and
• 
capture and remediate, if feasible, the aromatic hydrocarbons emanating from the
dispenser island and north oil/water separator.
Although the collection of supplemental design data is required through on-site pilot
testing, the current conceptual design of the remedial action program incorporates soil vapor
extraction to address potential residual source areas in the vadose zone, and a combination of air
sparging and fluid extraction to capture and mitigate the presence of dissolved and phase-
separated hydrocarbons from the saturated zone. Final design specifications may vary pending
results from pre-design studies (Section 4.0) and initial system operation.
3.2 
Vadose Zone Remediation
As previously noted, the absence of a significant quantity of unconsolidated deposits and
the proximity of the water table preclude vadose zone remediation in the former/present location
of the site USTs. The conceptual plan for remediating soils in the vadose zone adjacent to the
north oil/water separator and dispenser islands employs soil vapor extraction. 
Although pilot
tests have not been completed to date, physical characteristics of both the subsurface materials
3-1
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and site contaminants indicate that vapor extraction will prove to be an effective vehicle for
reducing contaminant concentrations. The vapor extraction system will be used to treat soils in-
situ, eliminating physical and logistical concerns associated with excavating soils proximal to, or
beneath, building structures. It is anticipated that horizontal extraction trenches/piping, as
opposed to vertical extraction wells, will be installed in the two areas demonstrating soil impact.
One extraction trench will most likely be installed within the existing excavation
adjacent to the north oil/water separator. This trench will likely extend to a depth of six to seven
feet below grade and maintain its present length. The trench will be lined with a perforated PVC
pipe and backfilled with crushed stone. A solid section of PVC pipe will extend to the ground
surface to facilitate the connection of the drain pipe to a vacuum manifold. The surface of the
trench will be sealed with a layer of asphalt to eliminate short circuiting of the vapor extraction
system. A soil vapor extraction trench, installed adjacent to the gasoline dispenser island, will be
constructed in a similar fashion. It is presently anticipated that this trench, at a minimum, will
extend the length of the dispenser island at a distance of approximately ten feet from, and
parallel to, the island.
The two extraction trenches will be connected to a centralized vacuum pump via solid
PVC piping installed below grade. A moisture "drop out" or extraction vessel will be utilized to
eliminate water and paniculate damage to the vacuum pump. It is anticipated that treatment of
the off-gas will be required initially. This treatment will most likely be provided through
portable vapor phase carbon canisters, pending review of 
pre-design data, applicable
regulations, and discussions with Department of Planning and Natural Resources (DPNR ).
Based upon preliminary information obtained from DPNR, construction and operation of a vapor
extraction system will require two permits: 1) an Earth Change Permit, to facilitate the
installation of subsurface piping; and 2) an Air Discharge Permit or de minimis waiver.
3-2
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System effectiveness monitoring will be provided through periodic influent and effluent
sampling, as well as the collection of in-situ soil samples at the point in time at which the system
influent concentrations exhibit an asymptotic minimum. The specific schedule for collection of
monitoring samples will be developed subsequent to completion of pilot scale testing.
3.3 
Saturated Zone Remediation
It is presently anticipated that the saturated zone remediation system will incorporate the
extraction of ground water from three areas utilizing four existing monitoring wells (MW-9, SW-
7, SW-1 and CHT-3). Based upon available aquifer hydraulic data, each extraction well will be
pumped at a rate of 0.50 - 1.0 gallons per minute (gpm). Extraction of ground water at a rate of
0.50 - 1.0 gpm will produce a capture zone which extends an estimated 20 to 30 feet in a lateral
direction and approximately ten feet downgradient (downgradient stagnation point from each
recovery well). The combined effect of withdrawing ground water from these four wells is
presently anticipated to establish hydraulic control over the distribution of aromatic and semi-
volatile constituents emanating from the Esso Tutu station (Figure 3-1). Increased accuracy
regarding the dimensions of the true capture zone will be possible subsequent to the
implementation of a short duration pumping test in several of the identified wells.
Based upon available liquid level data, it is not anticipated that the volume of phase-
separated hydrocarbons, if present, will justify the installation of a dedicated/automated NAPL
extraction system. Liquid level measurements will be obtained from site monitoring wells on a
periodic basis to evaluate the presence/absence and accumulation rate of phase-separated
hydrocarbons. Initially, any accumulation of NAPL will be manually extracted from both
monitoring and/or recovery wells through hand bailing. Hydrocarbon product will be stored on
site in a fifty-five gallon drum for eventual off-site disposal.
3-3 
T.
TUTURAP4.TUTU#2 
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°°7 
J.S79
EPA REGION II
SCANNING TRACKING SHEET
DOC ID # 65009
DOC TITLE/SUBJECT:
TUTU WELLS SUPERFUND SITE
FIGURE 3-1
CONCEPTUAL HYDRAULIC CAPTURE ZONES
(Page: TUT 007 1880)
THIS DOCUMENT IS OVERSIZED AND CAN BE
LOCATED IN THE ADMINISTRATIVE RECORD FILE
AT THE
SUPERFUND RECORDS CENTER
290 BROADWAY, 18™ FLOOR
NEW YORK, NY 10007
Extracted ground water will be pumped from the extraction wells to an on-site treatment
system. The treatment system will consist of an air stripper and liquid-phase granular activated
carbon (GAC) canisters, and will be installed in a secured building, located along the southern
perimeter of the site. Preliminary designs indicate that the air stripper will be one foot in
diameter, have a packed height of approximately 8 -10 feet, and an overall height of
approximately 14 feet. Ground-water effluent from the air stripper will be passed through two
GAC canisters prior to discharge. The canisters, each 55 gallons in size, will be used as
polishing devices to ensure that discharge requirements are satisfied. This treatment technology
has been utilized successfully at the site to treat ground water generated during well development
and sampling activities performed as part of the RI, and has demonstrated the ability to reduce
volatile organic compound concentrations below Federal Drinking Water Standards.
At present, it is expected that treated ground water will be transferred, via an
underground pipe, to the storm sewer, located approximately 80 feet west of the treatment area.
Based upon preliminary discussions with DPNR, the Department of Public Works (DPW), and
the Water and Power Authority (WAPA), treatment and discharge of extracted ground water will
require the following permits: 1) a NPDES permit; and 2) a utility connection permit. The
necessity to obtain an air discharge permit, as opposed to a de minimis waiver, will be evaluated
based upon influent data obtained during proposed pump testing activities.
The primary purpose for incorporating air sparging into the proposed remedial action
program is to increase dissolved oxygen concentrations within the contaminant plume boundaries,
thereby stimulating biodegradation of hydrocarbon compounds. It has been demonstrated that
biodegradation is one of the most effective and efficient means of achieving mass reduction of
soluble-phase aromatic hydrocarbons. The primary mechanism for the breakdown of hydrocarbons
is aerobic degradation, therefore the limiting factor, with respect to the rate of biodegradation, is the
amount of dissolved oxygen available for microbial activity. 
Numerous case studies have
TUTURAP4TUTU#2 
TUT 007 1881
demonstrated the dramatic impact that elevating dissolved oxygen concentrations can have on the
time required to reduce plume mass. It is presently anticipated that air sparging will be conducted
in wells either upgradient and/or adjacent to the proposed recovery wells (e.g., SW-2, SW-3, and
MW-9S).
3-5
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007 
1832
SECTION 4.0
SUPPLEMENTAL EWESTIGATION/PRE-DESIGN ACTIVITIES
Supplemental data collection activities will be required to formulate detailed design
specifications for both the ground-water withdrawal and soil vapor extraction programs. It is
important to note that these data are not required to determine if these technologies will
effectively abate the presence of volatile and semi-volatile organic compounds at the site. Soil
vapor extraction and ground-water sparging/extraction have been proven successful and efficient
with respect to removing the same contaminants from a large number of analogous sites.
Supplemental data regarding soil vapor extraction rates, ground-water extraction rates, vapor and
liquid-phase influent concentrations, zones of capture, and mass loading rates are required to
more accurately design a cost-efficient treatment system.
4.1 
Vadose Zone Remediation
Requisite activities related to the final design of the unsaturated zone remediation
program will involve vacuum tests at well locations SW-3 and SW-7 to measure air flow rates,
document areas of influence, and quantify influent concentrations. Data from these two wells
will be utilized to size a vacuum blower and estimate vapor phase carbon saturation rates.
The vacuum tests will involve the application of negative pressure to each extraction
well, while monitoring the pressure differential in adjacent monitoring wells. It is estimated that
a series of step tests will be performed with varying degrees of vacuum exerted on either well
SW-3 or SW-7. Each step test will last approximately one hour. Tests will be terminated when
data indicate that a steady-state pressure distribution has been obtained. Test results will be
utilized to determine optimal extraction rates and predict radii of influence. Vapor samples will
4-1
TUTURAP5.TUTU#2
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TUT 
00/
be collected for subsequent laboratory analysis to quantify the concentrations of organic
constituents in the influent gas stream.
4.2 
Saturated Zone Remediation
The primary activity required to develop a final design for the ground-water extraction and
air sparging system is the completion of a series of 2-4 hour step pumping tests. Data from these
tests will be used to quantify aquifer characteristics such that an effective and efficient system can
be designed to establish hydraulic control in the area of the aromatic hydrocarbon and semi-volatile
organic contamination.
The step tests will be performed at monitoring wells SW-1, SW-7, and MW-9. It is
expected that 2-3 tests will be conducted at each well, with extraction rates ranging from 0.25 gpm
to 1.0 gpm. Tests will be performed sequentially so that stresses to the saturated zone can be
isolated. In addition, the aquifer will be allowed to recover to 80% of its original elevation prior to
commencement of the subsequent tests.
Data obtained from the aquifer tests will be analyzed using one or more of the methods
described by Theis (1935), Cooper and Jacob (1946), and Boulton and Streltsova (1976). The data
will be evaluated to determine the capacity of the aquifer to yield water and to define sustainable
extraction rates for operation of the ground-water collection system.
Other than the collection of supplemental data regarding the concentration of dissolved
oxygen and carbon dioxide from select site monitoring wells, no additional data is required to
develop and implement an air sparging system.
4-2
TUTURAP5.TUTIM2 
TUT 
OO7 1884
SECTION 5.0
IMPLEMENTATION SCHEDULE
5.1 
Tentative Implementation Schedule
Based upon our present understanding of site conditions, and assuming that unexpected
delays are not encountered as a result of: agency review (EPA and DPNR); permitting; off-site
access; weather; or procurement of equipment, a tentative schedule has been developed for the
implementation of the remedial action program at the Esso Tutu station (Table 5-1).
5-1
TUTURAP6.TUTU#2
cH
TABLE 5-1
Tentative Implementation Schedule
Tutu Esso Service Station
St. Thomas, USVI
Task
EPA Review of Site Remediation/Supplemental Investigation Report
Scheduling of Supplemental Data Collection Activities
Implementation of Supplemental Data Collection Activities
Z" 
'»*
Laboratory Analysis of Site Samples
Final Design of Ground-Water/Vapor Extraction Systems
EPA Review of Final System Design Specifications and Proposed Monitoring Schedule
Procurement of Applicable and Appropriate Permitts
Procurement of Equipment
Scheduling of System Installation
Installation of Remediation Systems
System Startup and Calibration
Initial Phase of System Operation and Monitoring
Total Estimated Schedule (Weeks)
Time in Weeks
(Following Submittal of Report to EPA)
4
3
2
2
4
4
8*
8*
3
3
1
2
36
* - Tasks implemented concurrently