^^rGERAGHTY
'& MILLER, INC.
nvironmental Services
Ground Water 
Engineering 
Hydrocarbon 
Remediation 
Education
January 24, 1994
Caroline Kwan
U.S. Environmental Protection Agency
Region n
26 Federal Plaza, Room 737
New York, New York 10278
Re: 
Addendum to 
Appendix A - Soil Gas Survey Procedures, Phase II Remedial
Investigation (RI) Work Plan, Tutu Wells Site, St. Thomas, U.S. Virgin Islands.
Dear Ms. Kwan:
As discussed in our January 21, 1993 meeting, Geraghty & Miller, Inc. has prepared this
letter addendum to clarify the soil gas procedures presented in Appendix A of the Phase II
Remedial Investigation (RI) Work Plan, Tutu Wells Site, St. Thomas, U.S. Virgin Islands
(Geraghty & Miller, Inc. 1993). 
The U.S. Environmental Protection Agency's (USEPA)
comments on Appendix A were presented in a draft letter to Ms. Ana Gloria Ramos, Tutu
Environmental Investigation Committee (TEIC) Designated Coordinator, received on January
12, 1994. The specific responses or revisions to USEPA's concerns are presented below.
A revised Appendix A (Revision 1.0) has been prepared based on your comments.
Revision 1.0 of Appendix A (enclosed) supersedes and replaces the original version. Please
include Revision 1.0 in Appendix A of Volume 2 of the Phase II RI Work Plan (Geraghty &
Miller, Inc. 1993).
• 
Page 3 - Geraghty & Miller defines a soil-gas "hot spot" as a location that has a
soil-gas concentration that is an order of magnitude (10 times) greater than
surrounding soil-gas values for other locations within the immediate area. These
hot-spot areas may warrant further investigation.
TUT 
006 
1290
201 West Passaic Street, 3rd Floor • Rochelle Park, New Jersey 07662* (201) 909-0700 • FAX (201) 909-0567/0568
*64749*
64749
OERAGHTY & MILLER, INC.
• 
Page 4 - If a location contains concrete that is greater than 1 foot, the sample
location will be relocated or abandoned. The drill cannot penetrate concrete or
asphalt greater than 1 foot in thickness.
• 
Pages 4 and 5 - The volume of the sample syringe is 500 ul.
• 
Page" 5 - The sample syringe, teflon tubing and hosing apparatus will be purged
with air between each sampling location. An air blank sample will be collected
from this apparatus to determine that no cross-contamination is occurring.
• 
Page 5 - Yes. Sample probes will be purged with air before each new sampling
location.
We hope this clarifies the soil gas procedures to your satisfaction. If you have any
questions, please call.
Sincerely,
GERAGHTY & MILLER, INC.
c: 
Ana Gloria Ramos, TEIC
Paul Ryan, Texaco
Sally Odlund, CDM
JJ:nr
PR0013.»«-WP2/012494.1tr
Thomas V. Danahy 
//
Senior Scientist/Project Manager
Daniel A. Nachman
Vice President/Project Officer
TUT 
OO6 
1291
APPENDIX A
SOIL GAS SURVEY PROCEDURES
TUTU WELLS SITE
ST. THOMAS, U.S. VIRGIN THOMAS
Revision 1.0, January 1994
GERAGHTY 6? MILLER, INC 
TUT °06 
1292 
G
APPENDIX A
SOIL GAS SURVEY
TUTU WTCI^LS srns
ST. THOMAS. U.S. VIRGIN THOMAS
INTRODUCTION
A soil-gas survey will be conducted at the Curriculum Center (former LAGA building)
and the Virgin Islands Housing Authority (VIHA) maintenance area to identify potential sources
of volatile organic compounds (VOCs) in soil. The study will be conducted in accordance with
details outlined in Section 7.1.3 (Soil-Gas Surveys) of the Phase n Remedial Investigation (RI)
Work Plan. VOCs detected by a soil-gas survey can originate directly from VOCs in the soil
or from VOCs diffused upward into the soil atmosphere from ground water. Soil-gas surveys
provide a qualitative indication of VOCs in the unsaturated zone, rather than a quantitative
'"""^ 
indication of VOCs in the soil or the ground water, because site-specific factors (such as paving,
geology, distribution properties of VOCs, depth to water, soil moisture, and the geochemistry
of the unsaturated sediments) can affect soil-gas concentrations. Although many soil gas surveys
have been undertaken by various investigators at several facilities in the Tutu area, previously
conducted soil-gas surveys have had mixed results due to these factors. Therefore, interpretation
of the soil-gas survey results requires an understanding of the data and their limitations, as well
as knowledge of the site geology. Additional sampling and laboratory analyses of the soil and
ground water can confirm the presence and quantify the concentration of VOCs identified by the
soil-gas survey.
A Photovac 10S50 portable Gas Chromatograph (GC) will be used to determine the
presence or absence of VOCs in soil vapor samples collected at the Curriculum Center (former
LAGA building) and the VIHA maintenance area. A Photovac 10SSO GC will be used for its
ability to separate and quantify selected VOCs. Results can be obtained from the GC within 20
^^ 
to 30 minutes. Compound identification and approximate concentrations are provided; however,
only those compounds for which the instrument is initially calibrated can be identified and
quantified. Therefore, prior to the study, the GC will be calibrated with air standards for
GERAGHTY & MILLER, INC. 
TUT °°6 
1293 
0
r^ 
3
benzene, toluene, xylene, trichloroethene, tetrachloroethene, cis-l,2-dichloroethene, and
trans-l,2-dichloroethene. Each of these standards will be prepared by introducing a known
volume of the compound into a 1-liter (L) Tedlar bag that has previously been filled with
organic-free air.
SURVEY GRID
The soil-gas survey will be conducted on an unbiased rectilinear grid pattern established
initially on a 40-foot spacing. As "hot spots" are encountered, the grid will be reduced to 20-
foot spacing, as needed. The survey will be conducted in the areas to the north and west of the
Curriculum Center (former) LAGA building. These areas include the former LAGA loading
dock area and the area adjacent to the former LAGA dry cleaning room. The survey will also
include the areas to the north and west of the VIHA maintenance garage. Areas to be
investigated at the Curriculum Center and VIHA maintenance garage are shown on Figure 7-1
'' 
' 
of the Phase n RI Work Plan. The soil-gas survey results will be summarized on a map
delineating the approximate areal extent and the concentrations of VOCs detected. This map will
be used to evaluate potential sources and to identify optimal locations for monitoring wells at
the Curriculum Center and VIHA facilities, as appropriate.
A soil-gas "hot spot" is defined, for the purposes of this survey, as a location that has
a soil-gas concentration that is an order of magnitude (10 times) greater than surrounding soil-
gas values for other locations within the immediate area. The highest soil gas value within a
"hot spot" will be identified as the focus for possible further investigation. The exact
concentration of soil gas can vary, depending on soil type, initial concentration, soil moisture,
and depth to groundwater; therefore, an exact concentration is not useful for determination of
hot spots.
CALIBRATION
f~^
Prior to the initiation of the soil-gas survey, the GC will be calibrated with air standards
of site-specific compounds. Standards will be made for each compound by introducing known
GERAGHTY<S? MILLER, INC. 
TUT 
°°6 
1294
volumes of each compound into a 1-L Tedlar bag that has been previously filled with organic-
free air. The amounts of each compound injected into the Tedlar bag are based on the following
formula:
amount of compound added in microliters (ul) = (A x 760 mm/Hg)/p
where A = concentration of the compound, parts per million by volume (ppmv)
p = vapor pressure of the compound, in millimeters of mercury (mm/Kg)
For each initial calibration, the standards will be injected into the GC five times. An
average response factor will be obtained by dividing the concentration of the standard by the
average area under the peak from the five injections.
SAMPLING PROCEDURE
A rotary hammer drill with a 1 1/2-inch bit will be used to obtain access to the soil
beneath asphalt and cement, if present. If the asphalt or cement is believed to be thicker than
1 foot, which is generally the case around the loading docks, then no attempt will be made to
core through it. The location will either be relocated or abandoned. A 1/2-inch diameter
borehole in the soil will be created with a slide hammer and solid rod assembly. These
boreholes will be approximately 3 feet in depth. The solid rod will be removed and a 1/4-inch
diameter hollow, stainless-steel rod will be inserted. A 1/8-inch Teflon tube will be contained
inside the stainless-steel tube. The Teflon tube will extend outside of the hollow, stainless-steel
tube. Midway down the exposed tubing is a stainless-steel tee through which syringe samples
will be taken. A nail inserted into the lower end of the Teflon tubing will prevent clogging of
the assembly as it is lowered into the borehole. The nail will then be disengaged, and the top
of the borehole will be sealed around the stainless-steel rod with drill cuttings.
A pumping time study will then be conducted to determine the appropriate evacuation
time(s) for soils at the Tutu Wells Site. In this study, the Teflon tubing is attached to a
diaphragm pump and the borehole is evacuated for 1 minute. A 300-ul sample is collected
GERAGHTY6? MILLER, INC. 
TUT 
°°6 
i295
5
through the stainless-steel tee with a gas-tight syringe (the maximum capacity of the syringe is
500 ul), and then the pump is shut off. The sample is injected into the portable GC for analysis.
This procedure is repeated until five samples, at 1 minute intervals, are collected. The pumping
time to be used at the Tutu Wells Site will correspond to the time when the highest
concentrations of VOCs are detected. If compounds are not detected in the first borehole, the
procedure will be repeated. If compounds are not detected by the third borehole, a pumping
time of 2 minutes will be used. Care will be taken to ensure that at least two probe volumes
will be purged, prior to sampling at each new location.
The sample syringe, teflon tubing, and hosing apparatus will be purged with air in
between each sampling location. An air blank sample will be collected as discussed below from
this apparatus to determine that no cross-contamination is occurring.
COMPOUND IDENTIFICATION AND QUANTTTATION
The GC will identify all peak areas greater than 0.1 volt seconds (VS) as unknowns. The
GC operator will then match the retention times of the most recent standard with the unknowns.
If the retention times match, the VOCs will be identified and quantified by multiplying the area
(in VS) of the VOCs by the response factor calculated from the initial calibration. The final
concentration will be reported in parts per million (ppm).
BLANKS
Blanks will be run to determine if there is carryover from previous samples and
standards. The blanks will be one of the following: GC blanks, syringe blanks, or equipment
blanks. A GC blank will be run at the start of each day's sampling to ensure a steady baseline.
This is done by starting a GC analysis without injecting a sample. Syringe blanks will be
analyzed following the completion of the calibration runs by injecting 500 ul of ambient air into
the GC (500 ul is the maximum capacity of the syringe). Syringe blanks will also be analyzed
periodically during the day. VOC contamination detected in the syringe will be cleaned from
the syringe by using a methanol and organic-free water rinse. Equipment blanks of the sampling
r-co A/-U-TV £f K/TTI i CD ivu~ 
TUT 
°06 
1296
GERAGHTY & MILLER, INC.
/*•> 
•
 
6
apparatus (i.e., tubing and hose) will be analyzed following every sample where a positive result
is obtained. Equipment blanks are collected by removing the sampling assembly from a
borehole and running the pump for a few minutes to draw ambient air through the system. An
air sample is collected from the stainless-steel equipment and analyzed with the GC. If VOCs
are detected in the equipment blank sample, the sampling equipment will be decontaminated by
purging the equipment with the sampling pump until the VOCs is no longer detected.
QUALITY CONTROL
In addition to the calibration analyses, duplicate analyses will be run once every ten
samples. Continuing calibration analyses will be performed as required, or a minimum of once
every 2 hours, by injecting 300 ul of the standard into the GC. A syringe blank will be run
after every calibration check. The retention time of each compound will then be checked for
peak drift by comparing the new retention time with the one from the previous standard analysis.
1 
A fresh standard will be prepared at the beginning of each day to update the average response
factors.
PR0013.*«*-WPl/120393.^jp
TUT 
006 1297 
^
GERAGHTYfi? MILLER, INC. 
W