FINAL
REPORT ON RESULTS OF SOIL GAS SURVEY,
TUTU, ST. THOMAS, U. S. VIRGIN ISLANDS
December 18, 1987
Prepared for:
TEXACO CARIBBEAN, INC.
Prepared by:
GEOSCIENCE CONSULTANTS, LTD.
HEADQUARTERS
500 Copper Avenue, NW
Suite 200
Albuquerque, New Mexico 87102
(505) 842-0001
FAX (505) 842-0595
WESTERN REGION OFFICE
5000 Birch Street
West Tower. Suite 3000
Newport Beach. CA 92660
(714) 476-3650
EASTERN REGIONAL OFFICE
1109 Spring Street
Suite 706
Silver Spring. Maryland 20910
(301) 587-2088
FAX (301) 587-2086
o 1 -J-
*64455*
64455
TABLE OF CONTENTS
1.0 EXECUTIVE SUMMARY . . . . . . . . . . . . . . . . . . . . . . . 
1
2.0 LOCATION AND HYDROGEOLOGIC BACKGROUND . . . . . . . . . . . . . 
3
2.1 LOCATION AND PURPOSE OF STUDY . . . . . . . . . . . . . . 
3
2.2 REGIONAL GEOLOGY . . . . . . . . . . . . . . . . . . . . . 
6
2.3 REGIONAL HYDROLOGY . . . . . . . . . . . . . . . . . . . . 
6
3.0 METHODS OF STUDY . . . . . . . . . . . . . . . . . . . . . . . 
8
3.1 SOIL GAS SURVEY . . . . . . . . . . . . . . . . . . . . . 
8
3.2 AUXILIARY HYDROGEOLOGIC STUDIES . . . . . . . . . . . . . 
11
4.0 RESULTS OF SOIL GAS SURVEY . . . . . . . . . . . . . . . . . . 
12
4.1 PETROLEUM HYDROCARBONS . . . . . . . . . . . . . . . . . . 
12
4.1.1 Service Station Site . . . . . . . . . . . . . . . 
16
4.1.2 Other Areas With Hydrocarbon Concentration Above
Background Levels . . . . . . . . . . . . . . . . . 
16
4.2 CHLORINATED HYDROCARBONS . . . . . . . . . . . . . . . . . 
21
5.0 PROBABLE MIGRATION PATHWAYS . . . . . . . . . . . . . . . . . . 
25
5.1 GROUND-WATER DATA . . . . . . . . . . . . . . . . . . . . 
25
5.2 BEDROCK FRACTURE SYSTEMS . . . . . . . . . . . . . . . . . 
25
6.0 CONCLUSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . 
28
7.0 REFERENCES CITED . . . . . . . . . . . . . . . . . . . . . . . 
30
LIST OF FIGURES
FIGURE 2-1 TOPOGRAPHIC MAP SHOWING LOCATION OF TUTU
SERVICE STATION, ST. THOMAS . . . . . . . . . . .
FIGURE 2-2 MAP OF CENTRAL TUTU AREA, ST. THOMAS, SHOWING
TUTU SERVICE STATION AND NEARBY FACILITIES . . . .
FIGURE 4-1 CONCENTRATIONS OF TOTAL PETROLEUM HYDROCARBONS IN
SOIL GAS ON TUTU SERVICE STATION SITE . . . . . .
FIGURE 4-2 CONCENTRATIONS OF TOTAL PETROLEUM HYDROCARBONS IN
SOIL GAS IN THE TUTU AREA, UPPER TURPENTINE
RUN BASIN . . . . . . . . . . . . . . . . . . . .
FIGURE 4-3 CONTOURS OF TOTAL PETROLEUM HYDROCARBON
CONCENTRATIONS IN SOIL GAS, TUTU AREA,
UPPER TURPENTINE RUN BASIN . . . . . . . . . . . .
FIGURE 4-4 CONCENTRATIONS OF PCE IN SOIL GAS IN THE
TUTU AREA, UPPER TURPENTINE RUN BASIN . . . . . .
FIGURE 5-1 ORIENTATIONS OF MAJOR FRACTURE SYSTEMS IN THE
TUTU AREA, UPPER TURPENTINE RUN BASIN . . . . . .
4
5
17
18
19
22
27
1014
LIST OF TABLES
TABLE 4-1 CONCENTRATIONS OF PETROLEUM HYDROCARBONS IN
SOIL GAS, TUTU AREA . . . . . . . . . . . . . . . . . . . 
13
TABLE 4-2 CONCENTRATIONS OF CHLORINATED HYDROCARBONS
IN SOIL GAS, TUTU AREA . . . . . . . . . . . . . . . . . 
23
LIST OF APPENDICES
APPENDIX A TRACER RESEARCH CORPORATION REPORT OF ANALYTICAL
RESULTS
APPENDIX B FIELD SYSTEM QUALITY ASSURANCE AUDIT OF OPERATIONAL
PROCEDURES
1.0 EXECUTIVE SUMMARY
During November 1987, Geoscience Consultants, Ltd. (GCL) conducted a soil
gas investigation in the vicinity of the Tutu service station of Texaco
Caribbean, Inc., in St. Thomas, U. S. Virgin Islands. The survey results
show a zone of significantly elevated total hydrocarbon concentrations
(up to 690,000 micrograms per liter [ug/1] as benzene) in soil gas
beneath the southwestern part of the service station site and beneath
adjacent roadways west and south of the station. These values indicate
the presence of hydrocarbons within the unsaturated soil zone. Another
zone of moderately high soil gas total hydrocarbon values (up to 2,600
ug/1) was found 300 to 800 feet southwest of the station, within a
topographic low beneath the southern part of the Four Winds Shopping
Center parking lot. Moderately elevated total hydro-carbon values (up to
3,000 ug/1) were also found adjacent to an Esso service station near the
southern end of the Four Winds Shopping Center parking lot. 
Soil gas
hydrocarbons in these areas are probably a result of vaporization from
hydrocarbons present in ground water.
A topographically high area around Tillett Gardens, an area of small
shops, in which a relatively great depth to ground water (about 25 feet)
and shallow depth to bedrock (about 5 feet) prevented adequate soil gas
analysis, lies between the two mapped zones of elevated hydrocarbon
values. Based on the soil gas analysis alone, it is therefore impossible
to determine with certainty whether the two zones are parts of a single
hydrocarbon plume or constitute two separate plumes. 
The presence of
benzene, toluene and other hydrocarbons in the Tillett water well, which
is located between the two zones, indicates that these compounds are
present in ground water in at least part of the area where soil gas
mapping was not feasible.
GCL also performed analyses for chlorinated compounds in soil gas at
selected points in the vicinity of the Tutu service station and Tillett
Gardens. 
Measurable concentrations of tetrachloroethylene (PCE) were
found at all points sampled for chlorinated compounds, with the highest
concentrations in soil gas near the LAGA building northeast of the Tutu
1
101&
service station. The LAGA building, where PCE is known to have been used
extensively in the past, is a possible source of the chlorinated hydro-
carbons.
2.0 LOCATION AND HYDROGEOLOGIC BACKGROUND
2.1 LOCATION AND PURPOSE OF STUDY
During November 1987, Geoscience Consultants LTD. (GCL) conducted a soil
gas survey in the vicinity of the Tutu service station of Texaco Carib-
bean, Inc. 
The purpose of the survey was to determine the range and
spatial distribution of hydrocarbons present in the soil gas at the
service station site, and to map the approximate extent of any hydrocar-
bon plume that might be encountered during the survey.
The Tutu service station is located at 18*20'3r North, 64*53'14" West,
in Anna's Retreat Estate, St. Thomas, U. S. Virgin Islands (Figure 2-1).
The station is on the northeast corner of the intersection of Highway 38
and Highway 384, on the eastern slope of the upper Turpentine Run basin.
Nearby facilities include an auto parts store and garage north of the
station, a fire station and the LAGA building (formerly a cloth manufac-
turing plant, now a public schools maintenance facility) uphill to the
northeast of the station, and Tillett Gardens, a courtyard of small shops
and a restaurant, south of the station (Figure 2-2). 
The Four Winds
Shopping Center lies in a topographically low area along the axis of the
upper Turpentine Run basin, west of the Tutu service station and Tillett
Gardens.
Elevated concentrations of hydrocarbons, including benzene, toluene, and
several chlorinated compounds, have been detected in water wells in the
upper Turpentine Run basin (Geraghty and Miller, 1983, p. 73-74). The
highest reported concentrations of benzene and toluene have been found in
water from the Tillett well, located 250 feet south of the Texaco station
and 300 feet northeast of an Esso service station (Figure 2-2}. 
In
August 1987, water samples from the Tillett well contained 1300 to 1400
parts per billion (ppb) of benzene and approximately 33 to 56 ppb of
toluene (C. Dolan, EPA Region II, written communication). 
High con-
centrations of tetrachloroethyl ene (PCE) and other chlorinated compounds
have also been found in the Tillett well.
TUT 003 1018
64°54'W
64°53'W
64°52'W
r^^'^e'tM^^C
TUTU SERVICE STATION
-18°21'N
=*«-18° 20' N
-18°19'N
Base from USGS Eastern St.Thomas 7.5 minute quadrangle.
FIGURE 2-1
TOPOGRAPHIC MAP SHOWING LOCATION OF TUTU SERVICE STATION, ST.THOMAS.
RAMSAY
MOTORS
LAGA
BUILDING
•*<^AUTO REPAIR
GARAGES
CONS.
AUTO
PARTS
FIRE
STATION-0
FENCE LINE (APPROX)
RETAINING WALL
FOUR
MINOS
SHOPPING
CENTER
VETERINARY
C L I N I C 
TILLETT 
*
GARDENS
AND
SMALL
SHOPS
© TILLLTT WELL
WELL©
——
PARKING
(SMALL BUSINESSES AND
HOUSING IN THIS
AREA NOT SHOWN)
VITELCO
(TELEPHONE
COMPANY)
ESSO
SERVICE STATION
AND AUTO REPAIR
FIGURE 2-2
MAP OF CENTRAL TUTU AREA, ST. THOMAS. 
.,
SHOWING TEXACO TUTU SERVICE STATION AND NEARBY FACILITIES.
5
2.2 REGIONAL GEOLOGY
The lithology of the Virgin Islands consists dominantly of volcanic
rocks, including spilites (albitized basalts), keratophyres (extrusive
igneous rocks containing albite and mafic minerals), andesites, and vol-
canic breccias and conglomerates derived from the igneous rocks. 
The
Louisenhoj Formation, which comprises the bedrock material throughout the
upper Turpentine Run basin, consists dominantly of augite andesite tuff
and associated volcanic breccias (Donnelly, 1966). 
The Louisenhoj
Formation is tentatively dated as Albian (late Early Cretaceous) in age
(Donnelly, 1966). The Louisenhoj Formation rocks in the vicinity of Tutu
have been extensively deformed and fractured by tectonic activity during
Late Cretaceous and Tertiary time.
2.3 REGIONAL HYDROLOGY
The upper Turpentine Run basin contains one of the most productive and
heavily used aquifers on the island of St. Thomas. Stevens and others
(1981) list 26 water wells in the Tutu area, and new wells have been
completed since their report was prepared. In 1983, Geraghty and Miller
estimated that "current pumpage in the upper basin may approach or exceed
the estimated safe yield of 300,000 gpd [gallons per day] calculated by
the USGS [U. S. Geological Survey]" (p. 68).
Ground water pumped from the upper Turpentine Run basin is derived
primarily from fracture zones in the underlying Louisenhoj bedrock. To
assure adequate supply, wells in the basin are comnonly drilled to depths
of 100 feet or more, although the water table is generally no more than
20 to 30 feet deep in the central part of the basin. 
Significant
drawdowns occur in many wells due to pumping and seasonal water table
fluctuations.
Ground water in the upper Turpentine Run basin contains total dissolved
solids (TDS) of 700 to 1,800 milligrams per liter (mg/1), consisting
dominantly of bicarbonate, sodium and chloride (Geraghty and Miller,
1983, p. 73, 76). Limited data from deep wells suggests that TDS
concentration tends to increase with depth in the aquifer (Geraghty and
Miller, 1983). Geraghty and Miller also report nitrate concentrations in
excess of 10 mg/1 (as nitrogen) from Virgin Islands Housing Authority
(VIHA) wells 1 and 2, which are located approximately 800 feet northeast
of the Tutu station, and elevated levels of chlorinated hydrocarbons in
well VIHA-1.
3.0 METHODS OF STUDY
Work performed by GCL at the Tutu service station site to date has
included a preliminary site investigation, a soil gas survey, and limited
hydrogeologic studies as judged appropriate for interpretation of the
soil gas data. The results of the preliminary site investigation were
reported in Section 3.3 of the Work Plan for Soil Gas Survey, Texaco
Service Station, Tutu, St. Thomas, U. S. Virgin Islands, and were used in
preparation of that work plan. The methods and results of the soil gas
survey and associated hydrogeologic studies are described in this report.
3.1 SOIL GAS SURVEY
The soil gas survey at the Tutu site was conducted during November 2-
18, 1987. 
This task consisted of soil gas sampling at points on the
service station site and in nearby areas, and on-site analysis of the
soil gas for selected hydrocarbons using a gas chromatograph (GC) owned
and operated by Tracer Research Corporation (Tracer) of Tucson, Arizona.
The gas chromatograph was equipped with detectors capable of identifying
total and aromatic hydrocarbons and halogenated compounds, using flame
ionization detector (FID) and electron capture detector (BCD) techniques.
Soil gas sampling and analysis were performed as described in the Work
Plan for Soil Gas Survey and Quality Assurance Project Plan for Soil Gas
Survey dated October 1987, as approved by and with amendments requested
by the U.S. Environmental Protection Agency Region II (USEPA) and the
Virgin Islands Department of Planning and Natural Resources (DPNR) during
discussions in the field.
The sampling and analysis were conducted in accordance with standardized
procedures which have been used by GCL and Tracer at numerous sites.
Soil gas samples were collected by driving a 2-cm diameter hollow
galvanized steel probe to the sampling depth and evacuating 5 to 10
liters of soil gas from immediately above the drive point with a vacuum
pump. 
A syringe was inserted through the silicone evacuation line to
collect a 10-milliliter gas sample for immediate on-site analysis.
Withdrawal of the sample from the evacuation line and its injection and
analysis in the GC were performed by an experienced Tracer chemist.
8
The initial soil gas sampling grid consisted of 20 points located on the
service station property, and 3 points located north and east of the
station which were selected in order to define background hydrocarbon
values. Samples at each point were taken from a depth of 5 feet below
the ground surface and from the greatest depth achievable by hand
driving of the probe, if greater than 5 feet. Samples were analyzed for
total hydrocarbons, excluding methane. 
Since the methane peak on the
chromatogram normally includes the peaks of ethane and propane as well,
the resulting "total hydrocarbon" values thus include only concentrations
of molecules containing 4 or more carbon atoms, which typically comprise
the major constituents of commercial gasoline and similar petroleum
products. 
Additionally, an effort was made to quantify the amounts of
benzene, toluene, ethyl benzene and xylene (BTEX) in the soil gas;
however, it was found that the OV-101 column employed for the FID work
failed in most cases to distinguish the individual BTEX constituents.
The OV-101 column has been used by GCL and Tracer in numerous soil gas
investigations, and in previous cases has adequately defined all BTEX
constituents.
Because a zone of high hydrocarbon values was identified in the south-
western portion of the station site, the sampling grid was extended to
the west and south in order to determine the extent of the hydrocarbon
plume. 
Due to the need to avoid water lines, sewer lines, underground
electrical lines, and other cultural features, the points of the extended
grid were not spaced as regularly as had been anticipated in the work
plan. 
Probes were driven to the greatest depth attainable, which was
generally about 5 feet, and a single sample was taken from the maximum
depth achieved at each point. The sampling grid was extended southward
and westward to the southern part of the Four Winds Shopping Center
parking lot (see Section 4.1.2 of this report). Samples were analyzed
for total hydrocarbons and BTEX using the OV-101 column.
During the last few days of the hydrocarbon survey, the USEPA representa-
tive at the site requested that another column be employed in an attempt
to better quantify individual BTEX constituents in the soil gas. Texaco
1024
Caribbean concurred with the request, and discussions were held with
chemists from Tracer and from Camp Dresser and McKee Federal Programs
Corporation (CDM-FPC) to identify an appropriate column. The Carbopak
AT-1000 column, a much slower column than the OV-101, was selected.
During calibration of the system, it became apparent that the full-length
AT-1000 column was unsuitable for field use because of its excessive
retention time. 
The AT-1000 column required as much as an hour to
analyze one sample, as compared with about 5 minutes for the OV-101.
After a few attempts, the column was cut to a length of 1.5 feet (from
its original 6-foot length), which shortened the run time to about 15
minutes, and was used to analyze a single sample taken from the vicinity
of the underground storage tanks (USTs) at the Tutu service station. The
column proved capable of quantifying benzene at this location, but
toluene, ethyl benzene and xylene, if present, were still undeterminable
due to interference by other peaks on the chromatogram. 
Due to the
excessive run times required to obtain results that were little better
than those obtained with the OV-101, no further attempts were made to use
the AT-1000 column. 
The soil gas survey is intended as a preliminary
screening tool to define the approximate extent of any hydrocarbons
identified in the soil zone. 
The use of total hydrocarbon values is
adequate to perform that task.
Although chlorinated compounds in significant quantities were considered
unlikely to have resulted from activities at the Tutu service station,
their presence in ground water is a matter of concern. 
GCL therefore
conducted a limited soil gas sampling program which was intended to
determine whether these compounds could have come from the Texaco
station. 
Sampling for Schlorina^ed hydrocarbons was performed
pojnts near the Tutu station an^pyrgrtTffirTrnm tho Tjiiett water
in which some of the compounds have been detected. 
Analyses were
performed using the electron capture detector. 
The soil gas sample
collection procedure was identical to that used in sampling for
petroleum components.
10
TUT 003 102S
3.2 AUXILIARY HYDROGEOLOGIC STUDIES
During the soil gas survey, GCL also conducted limited investigations
into the local hydrogeologic setting in order to better define potential
flow paths of hydrocarbons in the subsurface. 
GCL hydrogeologists
measured static water level in wells close to the Tutu site, determined
major fracture orientations in nearby exposures of bedrock, and recorded
other topographic and geologic data relevant to potential migration
pathways.
11
4.0 RESULTS OF SOIL GAS SURVEY
4.1 PETROLEUM HYDROCARBONS
The results of FID analyses for petroleum hydrocarbons for each soil gas
point analyzed are presented in Table 4-1. Copies of all results, as
recorded and supplied by the on-site chemist, are included in Appendix A
of this report. Copies of chromatograms annotated by the on-site chemist
will be made available, as required, in a supplement to this report.
Background concentrations were established based on analyses at three
points (Background 1, Background 2, and the Drift Point) located north
and northeast of the station. 
These points were in areas considered
unlikely to be affected by any hydrocarbons which might have resulted
from activities at the station. 
Total hydrocarbon concentrations in
these locations ranged from <0.01 ug/1 to 0.9 ug/1. At the Drift Point,
repeat samples were taken daily by inserting separate soil gas probes
within an area of less than 100 square feet, to determine whether soil
gas values varied significantly over time. 
Daily samples taken at the
Drift Point varied between 0.1 and 0.9 ug/1, with the highest value
recorded at a depth of 4 feet, which was achieved on only one day. For
drift samples taken at depths of 2 to 2.5 feet, total hydrocarbon
concentrations varied from 0.1 to 0.4 ug/1, indicating temporal variation
by up to a factor of 4 in soil gas hydrocarbon values.
The soil gas survey identified three zones in which concentrations of
total hydrocarbons (excluding methane) were significantly in excess of
background concentrations. These were:
• the southwestern portion of the Tutu station site and the
adjacent roadways
• the southern part of the Four Winds Shopping Center parking lot
• adjacent to the Esso service station at the southern end of the
Four Winds parking lot
It was not possible to verify with certainty whether these three zones in
fact represent portions of the same hydrocarbon plume, or whether they
12
TABLE 4-1
CONCENTRATIONS OF PETROLEUM HYDROCARBONS IN SOIL GAS, TUTU AREA
(All concentration values In mlcrograms per liter)
LOCATION
Background 1
Background 2
A-l
A-2
A-2
A-2A
A-2A
A-3
A-3.5
A-4
A-4
B-l
B-2
B-2
B-3
B-3
B-3. 5
B-4
B-4-C
B-4-C
B-4-C
C-l
C-2
C-3
C-4
C-4
D-l
0-2
D-3
D-4
F-l
F-l
F-2
F-3
F-4
DEPTH
5
4
5
4.5
8.5
4.5
7
5
5
4.5
5.5
5
5
8.5
5
8
5
5
5
5
7
5
5
5
4
7
4.5
2.5
5
4
4.5
6
4.5
6.5
6.5
DATE
11/06/87
11/06/87
11/04/87
11/04/87
11/04/87
11/05/87
11/05/87
11/05/87
11/05/87
11/05/87
11/05/87
11/04/87
11/04/87
11/04/87
11/04/87
11/04/87
11/04/87
11/04/87
11/05/87
11/06/87
11/06/87
11/05/87
11/05/87
11/05/87
11/04/87
11/04/87
11/05/87
11/05/87
11/05/87
11/04/87
11/10/87
11/10/87
11/10/87
11/10/87
11/10/87
BENZENE
<0.01
<0.01
<230
I
I
<0.01
I
I
1
<0.01
1
I
I
1
I
I
1
<0.02
<0.01
<0.01
<0.01
I
I
I
<0.09
<0.9
<0.01
I
<0.01
<0.09
<0.02
<0.02
<0.02
<0.02
<0.02
TOLUENE
<0.01
<0.01
<260
I
I
<0.01
<13
<13
<13
<0.01
<0.3
<510
1
I
I
I
<26
<0.02
<0.01
<0.01
<0.01
<130
<130
<0.5
<0.1
<1
<0.01
<0.5
<0.01
0.5
<0.02
<0.02
<0.02
<0.02
<0.02
ETHYL
BENZENE
<0.02
<0.02
<280
<280
<280
<0.01
<14
<14
<14
<0.01
<0.3
<570
<280
<280
<280
4,000
<28
<0.03
<0.01
<0.02
<0.02
<130
<140
<0.6
<0.1
<1
<0.01
<0.6
<0.01
<0.1
<0.03
<0.03
<0.03
<0.03
<0.03
XYLENES
<0.01
<0.01
<260
<260
<260
<0.01
<13
<13
<13
<0.01
<0.3
<530
<260
<260
<260
<110
<27
<0.03
<0.01
<0.01
<0.01
<130
<130
<0.5
<0.1
<1
<0.01
<0.5
<0.01
<0.1
<0.02
<0.02
<0.02
<0.02
<0.02
TOTAL HYDROCARBONS
(WITHOUT CH4)
0.2
<0.01
38.000
110,000
690.000
<0.01
7,600
4,600
3.600
<0.01
68
610,000
280,000
220.000
35,000
120,000
6,400
<0.02
0.1
<0.01
0.5
130,000
72,000
1.000
<0.09
1.700
8
1.000
<0.01
4
0.06
<0.02
0.07
0.4
0.2
I « Interference with adjacent peaks
T£XC\TABLE4-1.PRN
13
1.0.
TABLE 4-1 (Continued)
LOCATION
F-4
F-5
F-6
F-7
F-8
F-9
F-10
F-ll
F-12
F-13
F-14
F-15
F-16
F-17
F-18
F-19
F-20
F-21
F-22
T-l
T-l
T-2
T-2
T-3
T-5
T-6
T-7
T-7
T-8
T-10
T-ll
T-12
T-13
T-14
T-15
DEPTH
9.5
5.5
6
3.5
6
2
5.5
4
3.5
5.5
2
2.5
6
5
3.5
5
6
6
6
5
7
5
7
4
4
2.5
5
5.5
2
3
5
3.5
4.5
5.5
3.5
DATE
11/10/87
11/10/87
11/10/87
11/11/87
11/11/87
11/12/87
11/12/87
11/12/87
11/12/87
11/12/87
11/12/87
11/13/87
11/13/87
11/14/87
11/14/87
11/14/87
11/14/87
11/14/87
11/14/87
11/09/87
11/09/87
11/09/87
11/09/87
11/09/87
11/06/87
11/09/87
11/09/87
11/09/87
11/09/87
11/09/87
11/09/87
11/09/87
11/09/87
11/12/87
11/12/87
BENZENE
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
I
I
0.4
0.02
I
<0.02
<0.02
<0.02
<0.02
I
<0.02
<0.02
<0.02
<0.01
<0.02
<0.02
<0.02
<0.2
<0.01
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
TOLUENE
<0.02
<0.02
<0.02
<0.03
<0.03
<0.02
<6
<0.5
<0.1
<0.02
<12
<0.02
<0.02
<0.03
0.07
<5
<0.03
<0.03
<0.03
<0.01
<0.02
<0.02
<0.02
<0.2
<0.01
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
ETHYL
BENZENE
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<7
<0.5
<0.1
<0.03
<14
<0.03
<0.03
<0.03
<0.03
<6
<0.03
<0.03
<0.03
<0.01
<0.02
<0.02
<0.02
<0.3
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.03
<0.03
XYLENES
<0.02
<0.02
<0.02
<0.03
<0.03
<0.02
<6
<0.5
<0.1
<0.02
<13
<0.03
<0.03
<0.03
<0.03
<6
<0.03
<0.03
<0.03
<0.01
<0.02
<0.02
<0.02
*0.3
<0.01
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
TOTAL HYDROCARBONS
(WITHOUT CH4)
0.3
0.2
0.4
10
2
6
2.600
120
40
7
3.000
43
11
33
0.2
1.800
26
1
0.2
<0.01
<0.02
<0.02
<0.02
230
0.6
<0.02
<0.02
10
0.9
10
3
0.4
5
2
0.02
I • Interference with adjacent peaks
TEXCXTABLE4-1 .UIC1
14
TUT
TABLE 4-1 (Concluded)
LOCATION
T-16
T-17
T-17
T-18
T-19
T-19
T-20
2-1
1-2
2-4
2-5
Drift 1
Drift 2
Drift 3
Drift 4
Drift 5
Drift 6
Drift 6
Drift 7
DEPTH
5.5
6
6
5.5
6
10
4.5
5
3.5
6
5
4
2.5
2
2
2.5
2
2
2
DATE
11/13/87
11/13/87
11/14/87
11/13/87
11/13/87
11/13/87
11/14/87
11/11/87
11/11/87
11/11/87
11/11/87
11/04/87
11/05/87
11/06/87
11/09/87
11/11/87
11/12/87
11/13/87
11/14/87
BENZENE
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
<0.02
I
I
I
I
<0.02
<0.01
<0.01
<0.01
<0.02
<0.02
<0.02
<0.02
TOLUENE
<0.02
<0.02
<0.03
<0.02
<0.02
<0.02
<0.03
<7
<52
<26
<5
<0.02
<0.01
<0.01
<0.01
<0.03
<0.02
<0.02
<0.03
ETHYL
BENZENE
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<7
<58
<29
<6
<0.03
<0.01
<0.02
<0.01
<0.03
<0.03
<0.03
<0.03
XYLENES
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<0.03
<7
<54
<26
<5
<0.03
<0.01
<0.01
<0.01
<0.03
<0.02
<0.03
<0.03
TOTAL HYDROCARBONS
(WITHOUT CH4)
0.4
0.2
<0.02
0.4
0.2
2
0.2
4.000
28.000
12,000
A£M
ODU
0.9
0.1
0.2
0.2
0.4
0.4
0.2
0.4
interference with adjacent peaks
TEXCUABLE4-1.WK1
15
are entirely separate, because lithologic and hydrologic conditions in
the intervening area prevented adequate soil gas analysis (see Section
4.1.2).
4.1.1 Service Station Site
Soil gas hydrocarbon values measured on and immediately adjacent to the
Tutu service station site are shown in Figure 4-1. In cases where a hole
was sampled at two different depths, both concentration values are shown,
but the value from the greater depth was used in mapping the concentra-
tion contours. 
In all holes except B-2, the deeper point yielded the
higher value; in B-2 the values determined at 5 feet and 8.5 feet were
similar.
A zone of hydrocarbon concentrations significantly higher than background
levels is centered southwest of the underground storage tanks and extends
southward and westward beneath the highways adjacent to the station
property (Figure 4-2; Zone I, Figure 4-3). 
Elevated hydrocarbon con-
centrations were found consistently at depths of about 5 feet and at
depths of about 8 feet (maximum depth of probe penetration) in the
central part of this area; however, at some points along the station
boundaries (A-4, A-2A, C-4) hydrocarbon concentrations appear to increase
significantly with depth between 4 feet and 8 feet.
There was no evidence of significant hydrocarbon presence along the
northern and eastern boundaries of the station site. The value of 1,700
ug/1 recorded in hole C-4 near the north boundary of the station is
probably a result of hydrocarbon vapors migrating from the adjacent oil
separator pit. Movement of hydrocarbons east of the station area would
be inhibited by the steep southwestward topographic and water table
gradients.
4.1.2 Other Areas With Hydrocarbon Concentration Above
Background Levels
An attempt was made to trace the zone of elevated hydrocarbon concentra-
tions to the south across Highway 38 from the Tutu station. However, no
16
O.-M
•', ir
A-4
i © (4.5X0.01
(5.5) 68
1,000
UNDERGROUND STORAGE^TANKS
(5) 35,000
(8) 120,000
T\(5) 4,600
(4.5) 110.000 
(5) 280,000'
(8.5) 690,000 (8.5) 220,000 [1
(2.5) 1.000 i
m 
I
.5)
(7) 7,600
/(6) 12,000
D-1
/©(4.5) 8A.
- 
/
LEGEND
H -]0= SAMPLE POINT
(5) = DEPTH (FEET)
o ,000 = TOTAL HYDROCARBONS IN
K 
ug/1 AS BENZENE
(3.5) 28.000
HIGHWAY 38
Vi 
/ I
/ © / I
(5) 4,000/
FIGURE 4-1
CONCENTRATIONS OF TOTAL PETROLEUM HYDROCARBONS IN SOIL GAS ON TUTU SERVICE STATION SITE
BACKGROUND 2
0.01
BACKGROUND
0.2
RAMSAY
MOTORS
LAGA
BUILDING
REPAIR
GARAGES
• DRIFT POINT
0.1-0.9
FENCE LINE (APPROX)
FOUR
WINDS
SHOPPING
CENTER
AND
SMALL
SHOPS
PARKING 7~>0
(SMALL BUSINESSES AND
HOUSING IN THIS
AREA NOT SHOWN)
SAMPLE POINT AND TOTAL HYDROCARBON VALUE
VALUES LESS THAN 0.1 NOT SHOWN EXCEPT AT
BACKGROUND POINTS FOR POINTS ON TEXACO
SERVICE STATION SITE SEE FIGURE 4-1
SERVICE STATION 2.0QQ
AND AUTO REPAIR
FIGURE 4-2
CONCENTRATIONS OF TOTAL PETROLEUM HYDROCARBONS IN SOIL GAS IN THE TUTU AREA. UPPER
TURPENTINE RUN BASIN. ALL CONCENTRATIONS IN MICROGRAMS PER LITER. REPORTED AS
18
RAMSAY
MOTORS
LAGA
BUILDING
AUTO REPAIR
GARAGES
AUTO
PARTS
FENCE LINE (APPROX)
RETAINING WALL
VETERINARY
FOUR
WINDS
SHOPPING
CENTER
TILLETT 
*
GARDENS
AND
SMALL
SHOPS
(SMALL BUSINESSES AND
HOUSING IN THIS
AREA NOT SHOWN)
C^VITELCO
(TELEPHONE
COMPANY)
SAMPLE POINT.FOR IDENTIFICATION
SEE FIGURE 4-2
APPROXIMATE CONTOUR OF EQUAL
CONCENTRATION. VALUES IN MICROGRAMS
PER LITER. CONTOUR INTERVAL IS 1
ORDER OF MAGNITUDE
(I.e., A FACTOR OF 10). CONTOURS
DASHED WHERE POORLY CONSTRAINED
BY DATA.
/ S 
ESSO
SERVICE STATION
AND AUTO REPAIR
FIGURE 4-3
CONTOURS OF TOTAL PETROLEUM HYDROCARBON CONCENTREmwc
IN SOIL GAS. TUTU AREA, UPPER TURPENTINE RUN BAS TUT
19
values of hydrocarbons in excess of background levels were detected in
the area between the Tillett well and the north boundary of the Tillett
property at Highway 38, except at points under the sidewalk and under a
traffic island (points T-3 and T-7, Figure 4-2). Topographically, the
northern part of the Tillett property, southeast of the retaining wall
shown in Figure 2-2, is 10 to 15 feet higher than the land surface at the
service station, and it was not possible to achieve depths greater than
about 5 feet in placing the soil gas probes because of the presence of
bedrock at that depth. 
Ground water is at a depth of about 25 to 30
feet beneath the Tillett property, and thus is 20 feet or more below the
greatest depth of probe penetration. Therefore, the possible presence of
petroleum hydrocarbons at depths too great to be sampled beneath the
Tillett property could not be determined.
South of the Tillett well, detectable concentrations of hydrocarbons were
found in the southern part of the Four Winds Shopping Center parking lot,
near the Esso station and locally along the east side of Highway 38
(Zones II and III, Figure 4-3). Although most of the constituents
identified appear to be petroleum components, there was some admixture of
other compounds (up to about 5 ug/1 as benzene in some holes) which
appear to have a different origin. Since significant concentrations of
halogenated compounds were found in holes near this area, it is possible
that the unidentified constituents identified by the FID represent some
of the halogenated compounds.
It was possible to identify and map Zones II and III southwestward to and
beyond the Esso service station at the south end of the Four Winds
parking lot, even though bedrock in much of the area prevented probe
penetration to depths greater than about 5 feet (Figure 4-3). South and
west of the Esso station, increased soil gas hydrocarbon concentrations
were found, relative to those which were found immediately north of the
station. The soil gas survey was terminated at this location, because of
20
the presence of Increased hydrocarbon concentrations probably attribut-
able to a different source. Tracing of any soil gas plume not potential-
ly attributable to the Texaco station was outside the scope of the work
plan.
4.2 CHLORINATED HYDROCARBONS
Because chlorinated hydrocarbons have been identified in water samples
from the Tillett well and other wells in the Tutu area, a limited number
of soil gas points were sampled and analyzed for chlorinated compounds.
These points were located in the vicinity of the Tillett well, on and
adjacent to the Texaco service station, and near the LAGA building
(Figure 4-4). Samples were analyzed for:
• methylene chloride (dichloromethane)
• chloroform (trichloromethane)
• trichloroethane (TCA)
• carbon tetrachloride (tetrachloromethane)
• trichloroethylene (TCE)
• tetrachloroethylene (PCE)
Results of the chlorinated hydrocarbon analyses are listed in Table 4-2.
No significant concentration of any chlorinated compound was identified
in hole H-9, located on the Texaco station, in the center of the known
petroleum hydrocarbon plume. Methylene chloride (6 ug/1) was identified
in soil gas beneath the property north of the Texaco service station,
and TCA was identified at several locations, with the largest value (10
ug/1) being recorded in hole H-6, south of the Tillett well.
PCE was detected in all nine of the holes sampled for chlorinated com-
pounds. The lowest PCE concentration (0.02 ug/1) was found at the Texaco
station; the highest (170 ug/1) was found adjacent to the loading dock at
the LAGA building. 
PCE was also identified at points near the Tillett
well, although benzene and toluene, known to exist in the well water, had
21
RAMSAY
MOTORS
LAGA
BUILDING
REPAIR
GARAGES
FENCE LINE (APPROX)
RETAINING WALL
FOUR
MINOS
SHOPPING
CENTER
VETERINARY
CLIN'C 
TILLETT 
*
GARDENS
AND
SMALL
SHOPS
© TILLETT WELL
WELL©
—--^.
PARKING
(SMALL BUSINESSES AND
HOUSING IN THIS
AREA NOT SHOWN)
VITELCO
(TELEPHONE
COMPANY)
SAMPLE POINT SHOWING
IDENTIFICATION NUMBER AND PCE
CONCENTRATION IN MICROGRAMS
PER LITER
ESSO
SERVICE STATION
AND AUTO REPAIR
FIGURE 4-4
CONCENTRATIONS OF PCE IN SOIL GAS IN THE TUTU AREA, UPPER TURPF.NTTNF RUN
TABLE 4-2
CONCENTRATIONS OF CHLORINATED HYDROCARBONS IN SOIL GAS, TUTU AREA
(All concentration values in micrograms per liter)
SAMPLE
DEPTH
DATE
METHYLENE
CHLORIDE
CHLOROFORM 
TCA
CARBON
TETRACHLORIDE
TCE
PCE
H-l
H-2
H-3
H-4
H-5
H-6
H-7
H-8
H-9
3
3.5
4
3.5
4
4.5
5
5
5.5
11/17/87
11/17/87
11/17/87
11/17/87
11/17/87
11/17/87
11/17/87
11/17/87
11/17/87
<0.9
<0.9
<0.09
<0.09
<0.2
<30
<0.9
6
<0.09
<0.006
<0.006
<0.0006
<0.0006
<0.001
<0.2
<0.006
<0.006
< 0.0006
0.02
0.05
<0.0002
0.005
<0.0004
10
0.04
<0.002
< 0.0002
<0.0005
<0.0005
<0. 00005
<0. 00005
<0.0001
<0.02
<0.0005
<0.0005
<0. 00005
<0.004
0.5
< 0.0004
<0.0004
0.05
<0.1
0.6
0.3
<0.0004
1
42
0.4
0.8
6
16
170
1
0.02
23
TEXC\TABLE4-2.PRN
1038
not been detectable at the same points. The greater volatility of the
chlorinated compounds relative to the petroleum components explains the
comparative ease with which they can be traced in soil gas, assuming both
are present in ground water.
No attempt was made to delineate the boundaries of any chlorinated
hydrocarbon plume, which is likely to be a really extensive. PCE has been
found in water from a Virgin Islands Housing Authority well approximately
600 feet northeast of the LAGA building, as well as in the Tillett well
and one of the Four Winds water wells (Geraghty and Miller, 1983, p. 74;
C. Dolan, ERA Region II, written communication). A possible source of
the PCE is the LAGA building, presently used as a public schools office
and service facility. The LAGA building formerly housed a cloth factory,
closed about 1981, in which tetrachloroethylene (also known as perchloro-
ethylene, or "perk") is reported to have been used extensively. Unsub-
stantiated verbal reports of local residents indicate that the "perk" may
have been disposed of to the ground surface near the building.
24
5.0 PROBABLE MIGRATION PATHWAYS
5.1 GROUND-WATER DATA
The water table In the upper Turpentine Run basin is generally within 30
feet or less of the ground surface, and is influenced by the local
topography.
During November 1987 the static water levels were measured by GCL in the
Tillett well and the eastern Four Winds well. 
The western Four Winds
well was not measurable because it lacked an adequate port for insertion
of the water level probe. 
Water levels were 23.2 feet below top of
casing in the Tillett well, and 14.0 feet in the eastern Four Winds well.
Taking into account the difference in well head elevations (approximately
28 feet), this indicates a difference of about 19 feet in water-table
elevations at the two wells, and a water-table gradient of about 0.076,
if the Four Winds well is assumed to be directly downgradient from the
Tillett well. The gradient along the valley axis may be less than this
figure, whereas that on the eastern slope may be greater. 
It is not
known whether the Tillett and Four Winds wells intersect the same
fracture zone, or zones which are hydraulically connected.
5.2 BEDROCK FRACTURE SYSTEMS
Most ground water in the upper Turpentine Run basin is contained within
fracture systems of the Louisenhoj bedrock. 
Only minimal flow is
expected in the matrix of this fine-grained volcanic unit. Observations
of the soil profile, where it is exposed in road cuts and construction
excavations, indicated that the zone of significant weathering extends to
only about 6 feet below the surface in most areas, with fractured bedrock
below that level. These observations were confirmed by the difficulty
encountered in driving soil gas probes deeper than about 5 or 6 feet in
most of the study area. 
Consequently, the direction of local ground-
water flow will be strongly influenced by the orientation of the bedrock
fracture systems through which the water is moving.
25
Bedrock fracture orientations are not consistent throughout the upper
Turpentine Run basin. Orientations measured on outcrops exposed west of
the Four Winds Shopping center (west side of valley) and east of the
Seventh-Day Adventist Church and School (east side of valley) are shown
schematically in Figure 5-1. There are major fracture systems striking
north-northeast on both sides of the valley; however, those on the west
side of the valley dip to the southeast, while these on the east side dip
to the northwest. Consequently, these two systems differ by about 60* in
actual fracture orientation. 
It is not known whether there is an abrupt
transition along a defined boundary between these two systems at some
point within the valley, or whether the orientation of the fractures
rotates gradually from one position to the other as one moves across the
valley.
26
003 104.
RAMSAY
MOTORS/
LAGA
BUILDING
REPAIR
GARAGES
CONS.
AUTO
PARTS
RETAINING WALL
FOUR
MINOS
SHOPPING
CENTER
VETERINARY
CLINIC
TILLETT
GARDENS
AND
SMALL
SHOPS
© TILLETT WELL
(SMALL BUSINESSES AND
HOUSING IN THIS
AREA NOT SHOWN)
STRIKE AND DIP OF MAJOR FRACTURE
SYSTEM
VITELCO
(TELEPHONE
COMPANY)
STRIKE AND DIP OF SUBSIDIARY
FRACTURE SYSTEM
/ 
ESSO
fsERVICE STATION
AND AUTO REPAIR
STRIKE OF VERTICAL FRACTURE
SYSTEM
ROUTE OF STORM SEWER DRAINING
CENTRAL PART OF VALLEY
FIGURE 5-1
ORIENTATIONS OF MAJOR FRACTURE SYSTEMS
IN THE TUTU AREA, UPPER TURPENTINE RUN BAS'W
27 
T
•i 04:
6.0 CONCLUSIONS
The soil gas survey conducted by Texaco Caribbean, Inc., and GCL in the
Tutu area of St. Thomas identified a zone of elevated petroleum hydrocar-
bon values in the subsurface on the southwestern part of the Texaco Tutu
service station site (Zone I). The very high soil gas hydrocarbon values
in this area (up to 690,000 ug/1) indicate the probability that hydrocar-
bons have migrated through the unsaturated soil zone, leaving large
residual concentrations. The source of the hydrocarbons appears to be
the USTs at the Texaco station.
Elevated hydrocarbon values were traced southward to the south side of
Highway 38 and westward to the center of Highway 384. Points located on
the west side of Highway 384 indicate no significant hydrocarbon presence
in that area. Due to elevated bedrock and greater depth to water (25 to
30 feet), it was not possible to determine the extent of petroleum
hydrocarbon presence in the vicinity of the Tillett well, in which the
presence of benzene and toluene has been reported in ground water. The
same constraints limited complete mapping of the hydrocarbon plume on the
south side of Highway 38 across from the Texaco service station.
Moderately elevated concentrations of hydrocarbons were found in soil gas
beneath the southern part of the Four Winds Shopping Center parking lot
(Zone II) and adjacent to the Esso station (Zone III), 300 to 800 feet
downgradient from the Texaco station. The hydrocarbons encountered in
soil gas in this zone are probably derived by volatilization from a plume
of hydrocarbons moving with the ground water in the upper Turpentine Run
aquifer. 
However, based on the soil gas data, it was not possible to
determine with certainty whether Zones I, II and III are discontinuous or
whether they in fact represent parts of a single plume. 
It is not
possible to delineate such a plume by soil gas methods beneath the
bedrock high which underlies the Tillett property. Other direct methods
of sampling ground water and vadoze zone will be required to define the
relationship between the two areas of elevated soil gas concentrations.
28
Elevated levels of PCE were found in much of the study area, and other
chlorinated hydrocarbons were found in some locations. 
The source of
these compounds appears to be northeast of the Texaco service station,
and is possibly the LAGA building, where PCE is known to have been used
extensively in the past.
29
TUT 003 1044
7.0 REFERENCES CITED
Donnelly, T. W., 1966, Geology of St. Thomas and St. John, U. S. Virgin
Islands, in Hess, H. H., ed., Caribbean Geological Investigations:
Geological Society of American Memoir 98, p. 85 - 176.
Geraghty and Miller, Inc., 1983, Report on Current Groundwater Conditions
in the U. S. Virgin Islands, unpublished report prepared for the
Government of the U. S. Virgin Islands, 80 p.
Stevens, K. £., Gomez, P., and Alicea, J., 1981, Water Wells in the U. S.
Virgin Islands: 
Part One, St. Thomas: 
U. S. Geological Survey
Open-File Report 82-82.
TEXC/SOILGAS.RPT
30
TUT 003 104!
APPENDIX A
TRACER RESEARCH CORPORATION REPORT OF
ANALYTICAL RESULTS
6EOSCIENCE CONSUL TflNTS/TEXflCO/TUTU,
VIRGIN ISLRNDS
Ethyl
Tracer Research Corporation
Total
Samp 1 e
S6-R1
S6-R2
S6-R2
S6-R2R
S6-R2R
S6-R3
S6-R3.5
S6-R4
S6-R4
SG-B1
?6-B2
SG-B2
SG-B3
S6-B3
S6-B3.5
> S6--B4
*_ S6-B4C
S6-B4C
S6-B4C
SCs-BGl
S6-BG2
S6-C1
S6-C2
S6-C3
S6-C 1
S6-C4
S6-D2
-D3
r£ -04
,. 
r-l-1l
'-O3
Depth Oate
5'
4.5'
8.5'
4.5'
7'
5'
5'
4.5'
5.5'
5'
5'
8.5'
5'
Q'
5'
5'
5*
Cj »
7"
5'
5'
5'
5'
4'
2.5'
5'
4.5'
6'
4.5'
6.5'
6.5'
11 /O4
1 1/04
1 1 /OH
11/05
11/05
11/05
1 1 /OS
11/05
11 /O5
11 /O4
11 /O4
11 /O4
11/04
11 /O4
11 /OS
1 1/04
1 I/OS
11/06
11 /O6
11/06
11 /O6
11/05
11/05
11/05
1 1/04
11/04
1 1 /OS
11 /OS
1 1 /OS
11/04
11/10
11/10
1 1 / 1 0
1 1/10
1 1/1O
Benzene
f.ug/1)
<230
I
I
<o.oi
I
I
I
<O.01
I
I
I
I
I
I
I
<O.02
<O.01
<0.01
<0.01
<0.01
<0.01
I
II
<O.09
<O.9
<O.01
I
<O.01
<O.O9
<O.02
<0.02
<0.02
<O.02
<:o.02
Toluene
fug/1 )
<260
I
I
<O.O1
<O.O1
<51O
I
I
I
I
<2£
<0.02
<O.O1
<0.01
<O.O1
<O.O1
<O.O1
<13O
<130
<O.S
<0. 1
<0.01
<O.S
•ro.oi
0.5
<O.O2
<0.02
<O.O2
<0.02
<O.O2
Benzene
Cug/1)
<290
<28O
<2SO
<O.O1
<0.01
<0.3
<570
<280
<280
<280
4,OOO
<2S
<O.03
<O.01
<0.02
<O.02
<O.02
<O.O2
<130
<140
<0. 1
<O.01
<0.6
<O.01
<O. 1
<O . 03
<O.03
<O.03
<O.03
<O.03
My l»nes-
Cug/13
<26O
<26O
<2t.O
<0.01
<O.O1
<O.3
<530
<26O
<260
<260
<27
<O.03
<O.O1
<O.01
<0.01
<O.01
<O.O1
<130
<13O
<O.5
<O. 1
<O.O1
<0.5
<O.O1
<O. 1
<O.O2
<O.O2
<O.02
<O.O2
<O.O2
Hydroc. u/
Cug/1)
38 ,OOO
110.OOO
690,000
<0.01
7.60O
4.600
3,600
<0.01
BB
61O.OOO
280, OOO
220,000
35.OOO
120.OOO
6,400
<O.O2
0.1
<0.01
0.5
0.2
<O.O1
1 30 . OOO
72 , OOO
l.OOO
<0 . O9
1.70O
8
1,000
<O.01
4
0.06
<O.O2
O.O7
0.4
0.2
jj
at ions:
i rit«>rf" *t-*ric« with adjacent, peaks
not an
Rnalyzed by M. Kr-ct*nb»rg
Checked by M. Krotonberg
GEDSCIENCE CONSULTflNTS/TEXFtCO/TUTU. VIRGIN ISLflHDS
Ethyl
B»nz»n» 
Toluene 
B*rizs-ri* 
Xyl*ns-;
Samp Is- 
D*ptr, Dat* 
Cag/l) 
Ojg/1> 
Cug/O 
Cug/l!)
Tracer Research Corporation
Total
Hydroc.u/o CH4
(ug/1>
SSF-04
SGF-05
S6F-06
SGF-0?
SGF-03
SGF-09
SGF-10
SGF-11
SGF-12
SGF-13
SGF-14
SGF-15
JGF-16-
SGF-1?
SGF-1S
*• 
SGF-1 9
ro 
SGF-2Q
SGF-21
S6F-22
SGT-O1
5GT-01
SGT-02
SGT-O2
SGT-G3
SGT-05
SGT-O6
SGT-0?
SGT-O?
SGT-O8
SGT-10
~ ;GT-U
C JGT-12
"•' £.GT-13
O 
SGT- 1 4
,!- 
SGT-15
9. 5'
5.5'
f
3.5'
&'
2'
5.5'
4'
3.5'
5.5'
-> »
27s '
61
5'
3.5'
5f
6'
6'
6'
5'
7'
5'
?'
*'
A'
2.5'
5'
5.5'
2'
3'
5'
3.5'
•<>.5'
5.5'
3.5'
11/10
1 1 / 1 0
1 1/1O
11/11
11/11
11/12
1 1/12
1 1/12
11/12
11/12
11/12
11/13
1 1/13
1 1/14
1 1/14
1 1/14
1 1/14
1 1/14
11/14
11 /O9
11/09
11/09
11 /O9
1 1 /O9
11 /O6
11/09
11/09
11/09
11/09
11/09
11 /O9
11 /O9
11 /O9
11/12
11/12
<O.O2
<O.02
<0 . 02
<O.02
<O.O2
<0.02
I
I
O.4
0.02
I
<0.02
<0.02
<O.02
<0.02
I
<O.02
<O.02
<O.02
<O.O1
<O.O2
<O.02
<O.O2
<0.2
<O.O1
<O.O2
<O.O2
<O.O2
<O.O2
<O.O2
<O.O2
<O.02
<O.O2
<O.O2
<O.O2
<0.02
<O.02
<O.O2
<O.03
<O.O3
<O.O2
<6
<0.5
<0.1
<0.02
<12
<0.02
<0.02
*:0.03
O.07
<5
V0.03
<O.O3
<O.O3
<0.01
<0.02
<O.02
<0.02
<0.2
<O.O1
<O.02
<O.O2
<O.02
<O.02
<O.O2
<O.02
<0.02
<0.02
<O.O2
<O.02
<0.03
<0.03
<0.03
<O.O3
<O.O3
<O.O3
<7
<0.5
<0. 1
<0.03
<14
<O.O3
<0.03
<O.O3
<O.O3
<6
<O.O3
<O.D3
<0.03
<0.01
<0.02
<O.02
<0.02
<0.3
<O.O2
<0.02
<0.02
<O.O2
<O.02
<0.02
<O.O2
<O.O2
<O.O2
<O.O3
<O.O3
<0.02
<O.O2
<O.02
<O.O3
<O.03
<0.02
<6
<0.5
<0.1
<O.O2
<13
<0.03
<O.03
<O.03
<O.O3
<6
<O.O3
<O.03
<O.03
<O.01
<0.02
<O.O2
<0.02
<0.3
<O.01
<O.O2
<0.02
<0.02
<O.O2
<O.O2
<O.O2
<0.02
<0.02
<O.O2
<0.02
0.3
O.2
O.4
10
26
2.60O
120
40
7
3,OOO
43
11
33
0.2
i.eoo
26
1
0.2
<0.01
<0.02
<O.O2
<O.O2
230
O.6
<O.O2
<0.02
1O
O.9
1O
3
O.4
5
2
0.02
Notat ions:
I 
interfereric* uiith adjacent peaks
Nfl 
not. ari«lyz*d
finalyzc-d by M.
Chs-ct-ed by M. Krctc-nbe-rg
Proofed bu L.
GEOSCIENCE CONSULTflNTS/TEXflCO/TUTU, VIRGIN ISLRNDS
Ethyl 
Total
Benzene Toluene Benzene Xylenes; Hydroc.u/o CH4
Sample 
Depth Date (ug/U Cug/15 
Cog/I) 
Cug/1) 
Cug/li
Tracer Research Corporation
SGT-16
SGT-17
SGT-1?
SGT-18
SST-19
SI3T-19
S6T-2O
SeZ-Ol
SGZ-02
S6Z-04
SG2-O5
Drift 1
Drift 2
Drift a
Drift -1
> 
Drift 5
U> 
Drift. 6
Drift 6
5.5'
t.'
6'
5.5'
6'
10'
1.5'
S*
3.5'
6'
5*
4"
2.5'
2*
2'
2.5'
2*
2'
1 1/13
11/13
11/14
11/13
11/13
11/13
11/11
11/11
11/11
1 1/11
11/11
1 1 /CH
11/05
1 1/O6
1 1 /O9
11/11
1 1/12
1 1/13
<0.02
<0.02
<O.02
<0.02
<0.02
<0.02
<O.02
I
I
I
I
<0.02
<0.01
<0.01
<0.01
<O.02
<0.02
<0.02
<0.02
<0.02
<O.D3
<O.O2
<O.O2
<0. 02
<0.03
<7
<52
<26
<5
<O.O2
<O.01
<O.O1
<O.O1
<0.03
<0.02
<0.02
<O.D3
<O.O3
<0.03
<O.O3
<0.03
<O.O3
<0.03
<7
<58
<29
<6
<O.O3
<0.01
<0.02
<O.01
<O.O3
<O.O3
<0.03
<0.03
<O.O3
<0.03
<O.O3
<O.O3
<O.O3
<D.O3
<7
<54
<26
<5
<O.O3
<O.D1
<0.01
<0.01
<D.O3
<O.O2
<D.03
0.1
O.2
<0.02
O.1
0.2
2
0.2
4.000
28, ODD
I 2.0OO
660
O.9
O. I
O.2
0.2
0.4
O.4
0.2
Drift 7
<O.02
<0.03
<O.O3
<0.03
0.4
Notations:
I 
interference with adjacent peaks
MR 
not •ana I yzed
Analyzed by M. Krotenberg
Checked by M. Krotenberg
Proofed bi_| L. Laplander-
GEOSCIENCE CONSULTflNTS/TEXfiCO/TUTU, VIRGIN ISLRNDS
Tracer Research Corporation
SaiTiple 
Depth
SGH-O1
SGH-02
SGH-03
SGH-O4
SSH-05
SGH-06
SC-H-O7
SGH-O6
S6H-O9
=>'
3.5'
3.5'
4.5'
5'
5'
5.5'
1
1
1
1
1
1
1
1
1
Date
1/17
1/17
1/17
1/17
1/17
1/17
1/1?
1/1?
1/1?
CH2C12
Cug/1)
<0
<O
<O
<0
<O
.09
.09
.2
.9
6
.09
CHC13
Cug/lJ
<O.O06
<O.OO6
<O.OOO6
<O.OOO6
<O.OO1
<O.2
<O.OO6
<0 . OO6
<:o.ooo6
TCfl
Cug/l>
0
0
<0
0
<0
0
<0
<0
.02
.OS
.0002
.005
io
.04
.002
.OOO2
CC14
Cug/1)
<O.OOO5
<O.OOO5
<O.OOOO5
<O.OOOO5
<O.OOO1
<0.02
<O.OOO5
<o . ooos
<O.OOOO5
TCE
Cug/O
<O.OO4
0.5
<O.OOO4
O.O5
0.6
0.3
PCE
Cug/1)
1
o.e
6
16
170
1
O.O2
Notations:
Nfl
not ana 1 ijz»d
uith adjacent peaks
Rn«lyred by M. Krotenberg
Checked by M. Krotenberg
Proof ed bu L . I .-in 1 f,t-,,4&<-
APPENDIX B
FIELD SYSTEM QUALITY ASSURANCE AUDIT
OF OPERATIONAL PROCEDURES
T U V
FIELD SYSTEM AUDIT OF
OPERATIONAL PROCEDURES, SOIL GAS INVESTIGATION
AT TEXACO TUTU SERVICE STATION,
TUTU, ST. THOMAS, U.S. VIRGIN ISLANDS
Introduction
On November 6, 1987, a Field System Audit of the work being conducted by
Geoscience Consultants, Ltd. (GCL) and Tracer Research Corporation (TRC)
at the Tutu service station of Texaco Caribbean, Inc., on the island of
St. Thomas, was performed by the GCL Quality Assurance (QA) Officer,
Randall T. Hicks. The Field System Audit was conducted on the third day
of soil gas sampling and analysis conducted by GCL and TRC at the Tutu
site. 
Observations, recommendations, and corrective actions performed
during the Field System Audit are described in this report.
Project History and Procedures
Texaco Caribbean, Inc. has contracted with GCL to conduct a soil gas
investigation at the Tutu site in St. Thomas, U.S. Virgin Islands. The
Tutu survey is designed to determine the levels of hydrocarbons which are
found in soil gas from the areas surrounding underground storage tanks at
the facility, to determine if a release has occurred from the tanks, and
to assist in the definition of any soil or ground water contamination
plumes.
Soil gas hydrocarbon values are determined by inserting a steel probe
into the soil, withdrawing soil gas by use of a vacuum pump, and analyz-
ing the gas for hydrocarbons using an on-site gas chromatograph (GC).
Detailed descriptions for sampling and analytical procedures are in
GCL's Work Plan and Quality Assurance Project Plan for the Tutu site
(October 1987).
B-l
Field sampling and analytical procedures commenced at the Tutu site on
November 3, 1987.
Purpose of Field Svsten Audit
The Field System Audit was conducted to verify that procedures described
in the Work Plan (WP) and Quality Assurance Project Plan (QAPP) were
being adhered to in the field at the Tutu site, to determine whether any
procedures required modification based on experience in the field, and to
recommend any other procedural changes in field activities that might be
necessary or desirable to improve the final work product.
Field Observations
No major technical problems were found with the work performed at the
Tutu site. 
It was determined that significant difficulty exists using
the current column and detector (OV-101 Column, Flame lonization Detec-
tor) in the GC, as called for in the approved Work Plan and QAPP, to
quantify benzene and toluene in soil gas. This could be the result of
one of two situations:
Benzene and toluene have selectively been flushed or bio-
degraded in the vadose zone, even in areas with significant
total hydrocarbons as detected by the FID.
Benzene and toluene are obscured by interference peak(s) and
therefore not quantifiable with the presently used column in
the GC.
In order to resolve this problem and to quantify the presence or absence
of benzene and toluene in soil gas it was recommended, based on discus-
sions between GCL, TRC, EPA and CDM-FPC (J. Appel - GCL; A.A. Gutierrez
- GCL; 
Dan Evans - TRC; John Mihalich - CDM-FPC; Jim Ockalini-
CDM - Boston), that a Carbopak 1000 column that will have a much longer
retention time and allow a clean determination of the presence or
B-2
absence of benzene and toluene be used at the Tutu site. It was agreed
by all concerned that if this procedure failed to identify and quantify
benzene and toluene, these constituents would be considered absent in
soil gas. It must be noted, however, that this can be the case even
though these constituents may be present in ground water, due to the
biodegradation and flushing of the vadose zone and restriction of ground
water to fractured bedrock. Furthermore it must be noted that, although
the individual constituents have not been detected, the plume mapping
using total hydrocarbons and detectable halocarbons on the electron
capture detector (ECD) has been extremely successful over the majority of
the site.
The principal technical problems were not encountered with the site work,
but instead, with the site Work Plan and QAPP. Portions of the plans are
not appropriate for actual site conditions. Other portions of the plans
do not significantly add to accomplishing the goals of the project or
were not being done routinely by TRC, and we recommended deletion of
these practices from the QAPP and Work Plan. These recommended changes
are summarized in Table 1.
Conclusions and Recommendations
The Field System Audit indicated that not all the procedures described in
the WP and QAPP are followed exactly as planned previously due to site-
specific conditions. The reasons for these discrepancies are valid and
summarized in Table 1. Since the proposed changes to the Work Plan and
QAPP tend to improve the quality and/or speed at which data can be
collected during the project, it is recommended that the revised proce-
dures, presently in use, be continued during further sampling and
analysis and be incorporated into the Work Plan and QAPP for the Tutu
site.
B-3
'TUT 
OO3 1.054
GCL is confident that the procedural revisions to the QAPP described in
this report will result in improved data quality and a better final work
product.
B-4
TEXC\TUTUAUD.RPT
TABLE 1
RECOMMENDATIONS FOR CHANGES TO WORK PLAN AND QAPP
RECOMMENDED CHANGE 
JUSTIFICATION FOR THE CHANGE
Remove Russ Erbes from TRC.
Do not employ PID Detectors in the
Gas Chromatograph to conform with
actual practice.
Utilize a Carbopack 1000 column on
selected samples.
Reference to NBS Standards should
be deleted.
The purpose of the control point
should be stated in more detail.
Indicate that 'preliminary'
evaluation of data is conducted in
the field.
Utilize a 'one-point' Calibration
for the GC. not a three point
calibration as described. Justify
the adequacy of this calibration
which is presently being used in
the field.
Schleyer and Hicks will serve adequately for
TRC.
High humidity coupled with high levels of
hydrocarbons will result in operational problems
(clouding the window).
BTEX concentrations were not determined with
existing columns.
Standards are prepared by Chem Services. Inc
pursuant to procedures outlined in Appendix fi.
P-5.
It was unclear to field personnel. The control
point is utilized to test for variability in
analysis due to factors not related to any
contamination (e.g., weather conditions, smog,
etc.)
Any statistical tests, detailed mapping and
correlation of sol gas data with other hydro-
geologic features will be conducted after all
data are assembled into a logical format
The one-point calibration is appropriate for
soil gas surveys.
1 (Q)
Figure 2-1 (Q)
2(0)
p.8(WP)
Appendix B, p.5 (Q)
5(0)
7(0)
(Q)
6(0)
7(0)
The text addressing sample splits
should be re-written for clarity.
Appendix A should be ratified to
read Tracer Research Corporation
Methods of Operation for Soil Gas
Analyses Using TRC's Mobile
Laboratory and Probe Driver.
Appendix B should be modified
throughout to reflect Actual Site
Procedures.
Delete references to a second
sample for each point to conform to
actual practice.
Only one sample is taken from each point After
10 samples, a selected point is repeated,
sampled and analyzed.
The title may suggest that the methods dis-
cussed will be used at Tutu. Most of the
specific methods were modified to suit this
remote location.
Although this could not be fully anticipated,
site conditions dictated special methods not
described in the appendix (e.g., driving probes
by hand, refrigeration of the standards).
It is not done and is not necessary.
p.9 (O)
AppendU A (Q)
Appendix B (Q)
Appendix B, p.1 (Q)
'Observations' should be made by
GCL staff not TRC.
GCL staff is in a better position and it is
GCL's responsibility to describe the she
conditions for each sample point.
B-5
Appendix B. p.3 (Q)
O03 
It'56
TABLE 1 (CONTINUED)
RECOMMENDED CHANGE
Obtain QA data on Chem Services Inc
standards.
Dlute field standards should be
refrigerated.
The water used to prepare the
standard should be analyzed daily.
Primary standards may be kept at
the site to conform with actual
practice.
The syringe blank procedure should
reflect field practice.
System blanks may be run daily to
conform with actual practice.
Syringes and other equipment may be
baked for 1/2 hour at BO'C rather
than overnight at 70* to conform
with actual practice.
JUSTIFICATION FOR THE CHANGE
No data are provided.
During field work variation of the standard was
significant when not refrigerated.
Distied water from grocery stores has been
found to contain hydrocarbons or halocarbons at
other locations.
No technical reason for keeping such standards
off site was presented by site personnel.
Field method is equivalent. A 10 ml syringe is
filled with Nitrogen 2. Then a •micro* syringe
is used to obtain a sample from the 1st syringe,
the smaler sample Is analyzed.
System blanks after every 10 samples Is exces-
sive and not necessary to assume quality of
analytical results.
The level of 'Cleaning* is sufficient.
Appendix B. p.6 (Q)
Appendix B, p.6 (Q)
Appendix B. p.6 (Q)
Appendix B. p.7 (Q)
Appendix B. p.8, p. 12
(Q)
Appendix B, p.8, p.14
(Q)
Appendix B. p.9. p. 12
(Q)
note: (Q) - QAPP
(WP) « Work Plan
B-6
TUT