SDMS Document
99981
Explanation of Significant Differences (ESD)
Tutu Wells (GW)
Remedial Design 
'
St. Thomas, Virgin Islands
Work Assignment No.: 008-RDRD-021D
Prepared for:
U.S. Environmental Protection Agency
290 Broadway
New York, New York 10007-1866
Prepared by:
CDM Federal Programs Corporation
125 Maiden Lane - 5th Floor
New York, New York 10038
EPA Work Assignment No.
EPA Region
Contract No.
CDM Federal Programs Corporation
Document No.
Prepared by
Site Manager
Telephone Number
EPA Remedial Project Manager
Telephone Number
Date Prepared
008-RDRD-021D
II
68-W-98-210
3220-008-CO-EPOU-03948
CDM
Mr. Demetrios Klerides
(212) 785-9123
Ms. Caroline Kwan-Appleman
(212) 637-4275
April 15, 2003
tutuOOSltr.wpd - 4/15/03
Explanation of Significant Differences
TUTU WELLS SITE
ST. THOMAS, U.S. VIRGIN ISLANDS
Region 2
U. S. Environmental Protection Agency
April 2003
INTRODUCTION
In accordance with Section 117(c) of the Comprehensive
Environmental Response, Compensation, and Liability
Act (CERCLA), and Section 300.435(c)(2)(i) of the
National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), if the Environmental Protection
Agency (EPA) selects a remedial action and, thereafter,
it determines there is a significant change required with
respect to that action, an explanation of the significant
differences and the reasons for such changes must be
published.
EPA issued a Record of Decision (ROD) in 1996 with
regard to the Tutu Wells Superfund site (Site). The
remedy selected in the ROD included four property-
specific clean-ups, Site-wide containment and treatment
of contaminated groundwater at the source areas and
leading edges of contaminant plume, and cleanup of
contaminated soils at the property now occupied by
Virgin Islands Department of Education Curriculum
Center.
This Explanation of Significant Differences (ESD)
describes the modifications to the cleanup remedy set
forth in the ROD for Site-wide groundwater and the
Curriculum Center. These changes resulted from pre-
design investigations and design analyses.
The changes to the cleanup plan, as presented in this
ESD, are not considered by EPA and the Virgin Islands
Department of Planning and Natural Resources (DPNR)
to have fundamentally altered the remedy selected in the
ROD. The remedy remains protective of human health
and the environment and complies with federal and state
requirements that were identified in the ROD.
This ESD will become part of the Administrative Record
file for the Site. The entire Administrative Record for the
Site includes, among other things, the ROD and other
relevant documents. These documents are available for
review at the following locations:
EPA Virgin Islands Coordinator's Office
U.S. EPA Region 2
Caribbean Environmental Division
The Tunick Building
1336 Beltjen Road, Suite 102
St. Thomas, USVI 00808
Contact: Jim C. Casey
(340)714-2333
Department of Planning and Natural Resources
Division of Environmental Protection Agency
Cyril E. King Airport
St. Thomas, USVI 08802
Contact: Annette Roebuck
(340) 774-3320
Hours: Mon. - Fit, 9 AM - 4 PM
U.S. Environmental Protection Agency
290 Broadway, 18th Floor
New York, NY 10007-1866
Contact: Record Center
(212)637-4308
Hours: Mon. - Fri. 9 AM - 5 PM
Should there 
be any questions 
regarding 
this
Explanation of Significant Differences, please contact
Caroline Kwan, Remedial Project Manager at (212) 637-
4275 or Kwan.Caroline@epamail.epa.gov.
SUMMARY 
OF 
SITE 
HISTORY
CONTAMINATION PROBLEMS
AND
The Tutu Wells Site is located in the upper Turpentine
Run basin in east central St. Thomas, VI at the Estate
Anna's Retreat section of the island. The Turpentine
Run is an intermittent stream that traverses the length of
the basin and generally flows from north to south
following Route 38. The Site is surrounded by hills to the
west, north and east.
Numerous commercial establishments, including gas
stations, car repair shop, a shopping center, a dry
cleaner, fast food restaurants, etc., line the major roads
in the area. Private homes and multi-family housing,
such as the Virgin Islands Housing Authority (VIHA)
buildings, occupy the less heavily traveled roads. The
numerous water supply wells located in the Turpentine
Run basin are owned by the VIHA, water purveyors, and
private entities. The wells formerly supplied water for
domestic and commercial purposes.
According to 1990 census data, approximately 9,100
people live in the Tutu subdistrict of St. Thomas. The
Tutu subdistrict, also known as Anna's Retreat, covers
1.5 square miles and is second to Charlotte Amalie in
population density on St. Thomas, containing about 20
percesnt of the island's population.
In 1987, EPA tested several wells in the area after
reports of a strong, unpleasant odor from the water.
These wells, several of which were major commercial
well suppliers of public drinking water, were found to
have elevated concentrations of gasoline, chlorinated
organic compounds, and chlorinated volatile organic
compounds (VOCs). As a result, DPNR closed 13
commercial and 5 private wells in the Tutu area.
Additional sampling of over 100 wells resulted in a 1988
Superfund 
removal 
action 
to address 
potential
immediate threats posed by the Site and additional wells
were disconnected. 
Affected residents were either
connected to non-contaminated public water or provided
with water via a local water hauler.
On February 1, 1992, EPA proposed the Site for
placement on the National Priorities List, EPA's list of
significant sites that qualify for long-term cleanup. From
1992 to 1995, EPA lead an extensive Remedial
Investigation/Feasibility Study (RI/FS) at the Tutu Wells
Site. The purpose of the investigation was to determine
the nature and extent of contamination in Site soils and
groundwater, and evaluate possible cleanup options.
EPA determined that actual or threatened releases of
hazardous substances from the Site, if not addressed,
may pose a risk to public health or the environment.
Results identified areas of groundwater contamination
(i.e., groundwater plumes) in the Turpentine Run Aquifer,
which underlies the Site. Two of the plumes contain
petroleum-related contaminants. Two others contain
chlorinated volatile organic compounds (CVOCs), mainly
tetrachloroethene (PCE), trichloroethene (TCE), and cis-
1,2-dichloroethene (1,2-DCE). Together, the various
plumes overlap to form a large area of groundwater
contamination that has significantly impacted regional
groundwater quality.
Results also identified the property currently occupied by
the Curriculum Center as a main source of the CVOC
contamination in groundwater. These contaminants,
mainly PCE, TCE, and 1,2-DCE, are associated with dry
cleaning solvents that were historically used at the Site
as part of commercial textile manufacturing operations.
It was further determined that significant amounts of
CVOCs are present in the subsurface behind the
Curriculum Center, within the unsaturated fractured
bedrock (also referred to as "soils"), which may act as a
continuing source of groundwater contamination.
SELECTED REMEDY
The Record of Decision (ROD) for the Site, dated
August 5, 1996, described EPA's selected remedy to
clean up the soil and groundwater contamination at the
Site. 
The remedy include four property-specific
cleanups, Site-wide groundwater cleanup, and cleanup
of soils at the Curriculum Center.
Property-Specific Remedies
EPA ordered six responsible parties to design and
implement soil and groundwater cleanups at four
properties located within the Site. 
The selected
remedies for these four property locations were outlined
in the ROD. EPA issued a separate Administrative
Order (AO) to each of the following six responsible
parties: Texaco Caribbean, Inc.; ESSO Standard Oil
S.A., Limited; Western Auto Supply Co. and Four Winds
Plaza Partnership; and L'Henri, Inc. and The Cyril V.
Francois Associates. They represent two gas stations,
an auto supply store, and a dry cleaner in Tutu, which
are sources of chemical leaks into the soils and/or
Turpentine Run Aquifer underlying the Site.
The purpose of these property-specific, mini-cleanups is
source control. By ordering the responsible parties to
remove 
hazardous 
soils 
and 
treat 
the 
most
contaminated groundwater at these four source
locations, further contamination of the Turpentine Run
Aquifer can be prevented. All of the cleanups required
under the AOs are either complete or underway.
Site-wide Groundwater Remedy
The groundwater remedy also called for Site-wide
containment and treatment of contaminated groundwater
at the source areas and the leading edges of
contaminant plumes. The following groundwater cleanup
activities were included in the 1996 ROD for Site-wide
groundwater:
• 
Install two groundwater recovery wells to control
CVOC contaminant source areas.
• 
Install three groundwater recovery wells to control
movement of groundwater plumes.
• Construct a central groundwater treatment facility to
treat the extracted groundwater to meet applicable
discharge/end-use criteria.
• Allow low-level groundwater contamination to
naturally attenuate.
• 
Conduct semi-annual groundwater monitoring to track
changes in groundwater movement and quality.
• 
Implement 
institutional 
controls 
to 
prohibit
unauthorized use of groundwater and installation of
new wells.
Curriculum Center Soils Remedy
The preferred remedy also included cleanup of soils at
the Virgin Islands Department of Education Curriculum
Center. The following is a list of the 1996 ROD cleanup
activities for the Curriculum Center property:
• 
Excavation of contaminated soils, followed by either
off-Site disposal, or treatment by soil vapor extraction
(SVE) and redepositing of the treated soil on-Site.
• 
In-situ (in place) SVE treatment of contaminated
bedrock areas and soils not suitable for excavation.
• Thermal oxidation treatment of SVE offgas.
• 
Institutional controls in the form of Government
controls and/or proprietary controls 
to place
limitations on property usage (e.g., for commercial or
industrial use only).
DESCRIPTION OF SIGNIFICANT DIFFERENCES AND
THE REASONS FOR THOSE DIFFERENCES
EPA conducted a pre-design investigation of the
Curriculum Center soils and Site-wide groundwater from
August 1998 to November 1999. The purpose of the
investigation was to further define the nature and extent
of CVOC contamination in soil and groundwater, and to
collect hydrologic and geologic information to be used in
the Remedial Design.
Site-wide Groundwater Findings and Remedy
Modifications
As part of the pre-design groundwater investigation, EPA
conducted the following activities:
• Groundwater sampling of existing groundwater
monitoring and supply wells to determine the current
location and distribution of CVOC groundwater
contamination.
• Aquifer testing to obtain additional hydraulic data
and evaluate aquifer response to pumping.
• Groundwater modeling to assist in refining
extraction and monitoring well locations and
estimating remedial pumping rates.
• Installing new monitoring wells at critical locations
for use during the aquifer testing and for long-term
groundwater monitoring.
Based upon the results of the pre-design investigation
and subsequent design analyses, EPA approved the
following modifications to the selected cleanup remedy
defined in the ROD:
• The recovery well configuration for the Northern
CVOC Plume was refined according to the results of
the pre-design investigation.
• Monitored natural attenuation will be initially
implemented for the Southern CVOC Plume in lieu of
recovery wells. Existing groundwater data indicate
that the CVOC plume is steadily contracting and its
leading edge is not advancing. Use of the recovery
wells has been retained by EPA as a contingency,
which would be implemented in the future, if
warranted based upon long-term 
groundwater
monitoring results.
• Two smaller-size groundwater treatment plants will
be constructed proximal to recovery well clusters,
rather than one centralized plant. This approach is
more feasible, considering the existing Site
development/use and the distance between recovery
well clusters.
• 
Enhancement of the groundwater extraction and
treatment remedy at the Curriculum Center source
area will be investigated, following its implementation,
to address the significant CVOC contamination
identified at approximately 80 to 120 feet below
ground surface. 
Without enhancement, it is
estimated that this groundwater treatment system will
need to operate in excess of 30 years. A pilot study
will be performed to evaluate the feasibility of using
enhanced anaerobic bioremediation to supplement
this remedy.
Curriculum Soil Findingsand Remedy Modifications
EPA performed shallow and deep exploratory borings
and collected soil and rock samples, both around and
beneath the Curriculum Center building. Prior to drilling
through the floor, old process pipes were vacuum
cleaned, and samples of the removed material were
collected. 
Soil gas samples were also collected.
Although soil sampling did not reveal any contamination
in the soil, the results of the investigation indicated that
a residual CVOC contamination source is present within
the unsaturated fractured bedrock behind the Curriculum
Center building.
Based on the results of the pre-design investigation,
EPA performed a pilot study to assess the feasibility of
using SVE for remediating the CVOC contamination
from this area and to provide a basis for the design of a
full scale SVE system. An extended (5-day) and 15
short-term (up to 4 hours each) performance tests were
conducted. Based on the results of the SVE Pilot Study,
it was determined that appreciable CVOC mass can be
extracted from the unsaturated zone using SVE.
Approximately 40 pounds of CVOCs were removed from
the unsaturated zone during the 5-day test.
Based upon the results of the pre-design investigation
and subsequent design analyses, EPA approved the
following modifications to the selected cleanup remedy
defined in the ROD:
• 
Excavation is not required, because the shallow,
overburden soils are not contaminated above the
ROD cleanup goals.
• Activated 
carbon, 
followed 
by 
potassium
permanganate is more feasible than thermal
oxidation for SVE offgas treatment.
• 
Standard, performance-based cleanup criteria will be
used in lieu of the ROD soil cleanup goals (SSLs).
The ROD SSLs are not appropriate for application in
a fractured bedrock setting, because contaminants
are non-uniformly distributed in the rock fractures,
and rock sample analyses will not provide an
accurate representation 
regarding 
how much
contamination is present. The performance-based
cleanup criteria are generally based upon the net
reduction of contaminants in soil gas. Remedial
progress will routinely be evaluated by collecting soil
gas 
samples 
and field 
measurements from
permanent vapor monitoring points screened within
the contaminated area and from the SVE system.
AFFIRMATION
DETERMINATIONS
OF 
STATUTORY
All components of this design have been reviewed by
EPA and the Virgin Islands Department of Planning and
Natural Resources (DPNR). The design also conforms
to all DPNR permit requirements.
PUBLIC PARTICIPATION ACTIVITIES
In accordance with the NCP, a formal public comment
period is not required when issuing an ESD. EPA is
announcing the availability of this ESD in several local
newspapers. In addition, as noted above, questions
regarding this ESD may be directed to Caroline Kwan as
specified above.
SUPERFUND OMBUDSMAN
U.S. EPA, Region 2 has designated an ombudsman as
a point-of-contact for community concerns and questions
about the federal Superfund Program in New York, New
Jersey, Puerto Rico and the U.S. Virgin Islands. To
support this effort, the Agency has established a 24-
hour, toll-free number that the public can call to request
information, 
express their 
concerns 
or register
complaints about Superfund. 
The Ombudsman for
EPA's Region 2 office is:
George Zachos
U.S. EPA, Region 2
2890 Woodbridge Ave., MS-211
Edison, New Jersey 08837
(732)321-6621
Toll Free (888) 283-7626
For general information about the Superfund program,
visit our website at:
http://www.epa.gov/region02/superfund/superfund.htm