TEXACO CARIBBEAN INC. 
us. VIRGIN ISLANDS
PRODUCTS YOU CAN TRUST
RECEIVED
FH: 
, SKI
A. 
1 <JRR
CDM-FPC, NYC
The Honorable Alan D. Smith
C o m m i o O i o n c r o f Planning a n d M u C u r A l R a o o u r c o o
179 Alcona & Welgunst
St. T h o m a o . USUI 
00807
Dear Sir:
Please find attached revised pages to—b-c -incxHrtcd tnte the Final
Report on Results of Soil Gas Survey, Tutu, St. Thomas, U.S.V.I.,
which was submitted to the Department of Planning and Natural
Resources and the U. S. Environmental Protection Agency by
Texaco Caribbean Inc. These pages incorporate changes agreed upon
by representatives of the Department of Planning and Natural
Resources, U. S. Environmental Protection Agency and
Texaco Caribbean Inc. during a meeting held on January 12, 1988 in
St. Thomas.
The changes made also include aii the pending points addressed ITT
Ms. Caroline Kwan's letter of February 1, 1988.
Very truly yours,
William Hroch
Representative
A t t a o h m d n t C
cc: Ms. Caroline Kwan - USEPA Region II w/2 attachments
TU"
P,O. BOX 1458, FREDERIKSTEO, ST. CROIX, V.I, OOS40 (S09) 772-0104
P.O. BOX 3740, CHARLOTTE AMALIE, ST. THOMAS. V.I. OOS01 («09) 77-VlOjl
*64457*
64457
FINAL
REPORT ON RESULTS OF SOIL GAS SURVEY,
TUTU, ST. THOMAS, U. S. VIRGIN ISLANDS
December 18. 1987
Revised January 25, 1988
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
1247
Caribbean concurred with the request, and discussions were held with
chemists from Tracer and from the ERA oversight contractor 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 6 chlorinated hydrocarbons was performed at 9
points near the Tutu station and upgradient from the Tillett water well,
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 
Page Revised 1/25/88
are entirely separate, because lithologic and hydrologic conditions in
the Intervening area prevented adequate soil gas analysis (see Section
4.1.3).
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 may be
inhibited by the steep southwestward topographic and water table gra-
dients.
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 
Page Revised 1/25/88
003 
124V
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 below top of casing in the
eastern Four Winds well. 
Top of casing at the Tillett well is about 1
foot above the ground surface, while that of the Four Winds well is even
with the ground surface. Taking into account the difference in well head
elevations (approximately 28 feet, as measured by tape and Brunton
compass), 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 
Page Revised 1/25/88
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FIGURE 5-1
ORIENTATIONS OF MAJOR FRACTURE SYSTEMS
IN THE TUTU AREA, UPPER TURPENTINE RUN BASIN.