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TABLE OF CONTENTS
Record of Decision Amendment
Dover Gas Light Co. Superfund Site
DECLARATION iii
DECISION SUMMARY 1
Introduction 1
Site Description and Background 1
Community Participation and Information Availability 2
Summary of Original Remedy 3
Rationale for Changing Remedy Selected in 1994 ROD 3
Remedial Action Objectives for the Soil 5
Description of the Alternatives 6
Evaluation of Alternatives 8
Comparison of Alternatives 11
Selected Remedy: Performance Standards 11
Statutory Determinations .18
Documentation of Significant Changes 20
RESPONSIVENESS SUMMARY '.. 21
11
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DECLARATION
Site Name and Location
Dover Gas Light Co. Superfund Site
Dover, Kent County, Delaware
Statement of Basis and Purpose
This decision document modifies the Record of Decision (ROD) signed on August 16,
1994, for the Dover Gas Light Site (Site), in Dover, Kent County, Delaware. The revised remedy
was selected in accordance with the requirements of the Comprehensive Environmental
Response, Compensation, and Liability Act of 1980, as amended (CERCLA), 42 U.S.C. §§ 9601
et seq.. and, to the extent practicable, the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), 40 C.F.R. Part 300. This decision document explains the factual and
legal basis for modifying the remedy for this Site. The information supporting this remedial
action decision is contained in the Administrative Record file for this Site.
The Delaware Department of Natural Resources and Environmental Control, on behalf of
the State of Delaware, concurs with the selected remedy.
Assessment of the Site
Pursuant to duly delegated authority, I hereby determine, pursuant to Section 106 of
CERCLA, 42 U.S.C. § 9606, that actual or threatened releases of hazardous substances,
pollutants or contaminants from this Site, if not addressed by implementing the response action
selected in this Record of Decision Amendment, may present an imminent and substantial
endangerment to public health, welfare, or the environment.
Description of the Selected Remedy
This ROD Amendment modifies the original selected remedy which addressed soil
contamination at the location of a former coal gas plant and ground water contamination in the
Columbia Aquifer associated with the former coal gas plant. This ROD Amendment specifically
modifies the portion of the selected remedy which addresses the contaminated soil. The principal
threats associated with this portion of the Site are the heavily contaminated soils that are in and
around the remains of former gas holders which are buried on-site and the non-aqueous phase
liquid (NAPL) coal gas waste that sits on top of a clay lens in the top several feet of the
Columbia Aquifer underneath the former location of the coal gas plant (the contaminated
material below the former coal gas holders was originally going to be excavated and is now
being included in the ground water remedy).
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The selected remedy includes the following major components:
Remedial actions selected in this ROD Amendment:
Excavation and off-site thermal destruction of the contaminated soil inside the
buried bottoms of the former gas holders
• Use of soil vapor extraction (SVE) to treat contaminated soil in several areas
outside the former gas holders
• Paving the parking lot which is the location of the former coal gas plant
Including the upper several feet of the Columbia Aquifer at the location of a
former coal gas plant in the ground water remedy for this Site.
Remedial actions remaining from the original selected remedy:
• Testing for, and removal of, any pumpable NAPL and hydraulic containment of
the area with residual NAPL
Natural attenuation with monitoring of the portion of the ground water plume that
only contains dissolved contamination.
Declaration of Statutory Determinations
The selected remedy is protective of human health and the environment, complies with
Federal and State requirements that are legally applicable or relevant and appropriate to the
remedial action and is cost-effective. This remedy utilizes permanent solutions and alternative
treatment (or resource recovery) technologies to the maximum extent practicable, and it satisfies
the statutory preference for remedies that employ treatment that reduces toxicity, mobility, or
volume as a principal element.
Because this remedy will result in hazardous substances remaining on-site above
health-based levels, a review will be conducted within five years after commencement of
remedial action to ensure that the remedy continues to provide adequate protection of human
health and the environment. Such reviews will be conducted every five years thereafter until EPA
determines that the cleanup levels set forth in the amended ROD have been achieved, or that the
hazardous substances remaining at the Site do not prevent unlimited use and unrestricted
exposure at the Site.
_
Abraham Ferdas, Acting Director Date
Hazardous Site Cleanup Division
Region III
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DECISION SUMMARY
Introduction
The U.S. Environmental Protection Agency (EPA), following consultation with the
Delaware Department of Natural Resources and Environmental Control (DNREC), is issuing this
Record of Decision Amendment (ROD Amendment) to address contaminated soil at the Dover
Gas Light Co. Site (Site) in Dover, Kent County, Delaware. EPA selected this remedial action in
accordance with the Comprehensive Environmental Response, Compensation, and Liability Act
of 1980 (CERCLA), as amended, 42 U.S.C. §§ 9601 et seq., and the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP), 40 CFR Part 300. The decision for this Site is
based on the Administrative Record which contains all of the supporting documentation for this
ROD Amendment.
On August 16, 1994, the Environmental Protection Agency (EPA) issued a ROD for this
Site formally outlining how EPA would address the Site contamination. The ROD discussed two
areas of the Site: the location of the former coal gas plant containing soil contamination and
ground water contamination resulting from the operation and disposal practices at the plant.
The ROD was based, in part, on a future land use assumption that permitted on-site
construction. After the clean-up decision, EPA was made aware of a legally binding agreement
between Chesapeake Utilities Corporation and the State of Delaware that restricted the future use
of the Site because of the contamination. Because of this agreement, Chesapeake proposed
modifying the soil cleanup to take the restricted future land use into account.
Based on its review of the submitted information and the views of the community
gathered from several public meetings held on April 30, 1997 and September 9, 1997, EPA is
issuing this ROD Amendment to change the way the soils from the former coal gas plant will be
cleaned up. This ROD Amendment describes the revised selected remedy for the soils and
explains why EPA is changing the selected remedy.
EPA is the lead agency for response activities at the Site. DNREC is the support agency
for this response action.
Site Description and Background
The Dover Gas Light Site is in Kent County, Delaware, within the City of Dover. It
occupies the western half of the city block bounded by New Street, Bank Lane, North Street, and
Governor's Avenue (see Figure 1). From 1859 to 1948 the Site was used for the production of
gas from coal through a process known as coal gasification. The gas was used primarily for
lighting and cooking purposes. During this time, various buildings, gas holders, and storage areas
used in the gasification process were located on the Site.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 1 December 1997
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When the plant was closed in 1948. all the structures, except for one, were demolished.
Much of the plant was removed, but sections of the tanks and other process equipment containing
coal oil and/or coal tar were buried on-site. The remaining building was used by the Delaware
State Museum for storage until it was destroyed by a fire in 1982. The Site is currently an
unpaved parking area used by the Delaware State Museum and other nearby businesses. Site
topography is generally flat.
The size of the former coal gas plant is approximately one acre while the size of the
Superfund Site is approximately 23 acres due to the spread of contamination in the ground water.
Only the plant area itself has contamination from the coal gas process in soil near the surface.
Contamination was first discovered at the Site in 1984 when the Delaware Development
Office conducted studies in preparation for the construction of a Family Court building. Remains
of the coal gasification plant were found buried on-site and oily soil samples yielded significant
contamination levels. As a result, DNREC installed and sampled 16 monitoring wells on and
near the Site at varying depths below the ground surface.
The shallow ground water beneath and to the southeast of the former plant location was
contaminated with several volatile organic compounds (VOCS) including benzene, toluene,
ethylbenzene, and xylenes, (collectively known as BTEX), and polynuclear aromatic
hydrocarbons (PAHs) such as naphthalene and acenaphthylene. A portion of the ground water
contained an oily layer of contamination called a non-aqueous phase liquid or NAPL.
EPA then proposed to put the Site on the National Priorities List (NPL) in January 1987.
The Site was formally added to the NPL in October 1989.
For more information on the Site description, Site risks, and enforcement and community
relations activities conducted prior to August 1994, refer to pages 1-10 of the Record of Decision
issued on August 16, 1994.
Community Participation and Information Availability
The Focused Feasibility Study and Proposed Plan to modify the ROD were released to
the public for comment on August 29, 1997. These two documents (and other relevant
documents) were made available to the community in the information repositories maintained at
the following locations:
U.S. EPA Region 3, Docket Room Dover Public Library
Mrs. Anna Butch (3HW11) 45 South State Street
841 Chestnut Building, 9th floor Dover, DE 19901
Philadelphia, PA 19107 (302) 736-7030
(215)566-3157
Dover Gas Light Site Decision Summary
Record of Decision Amendment 2 December 1997
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The notice of availability for these documents was published in the Delaware State News
on August 29. 1997 and the Dover Post on September 3, 1997. In addition, a public meeting was
held on September 9, 1997. At this meeting representatives from EPA answered questions about
conditions at the Site and the remedial alternatives under consideration. The public comment
period on the Proposed Plan was held from August 29, 1997 to September 29, 1997. A response
to the comments received during this period is included in the Responsiveness Summary, which
is part of this ROD Amendment. These activities were undertaken by EPA as pan of its public
participation responsibilities under Section 117(a) of the CERCLA and Section 300.435(c)(2)(ii)
oftheNCP.
The Administrative Record includes all documents such as data analyses, public
comments, meeting transcripts, and other relevant information upon which the selection of the
response action was based. In accordance with Section 300;825(a)(2) of the NCP, this ROD
Amendment has become part of the Administrative Record.
Summary of Original Remedy
EPA's original selected remedy for the Dover Gas Light Superftmd Site addressed the
former coal gas plant soils and the ground water. It involved installing one line of ground water
recovery wells at the downgradient edge of the non-aqueous phase liquid (NAPL) contamination
area and other recovery wells within the NAPL area to remove any mobile NAPLs; allowing the
portion of the ground water plume that only contains dissolved contamination to attenuate
naturally to the ground water clean-up levels; excavating contaminated soils at the location of the
former coal gas plant and incinerating the soils off-site. The total estimated present worth cost of
EPA's original selected remedy was $13,200,000. See the August 16, 1994 ROD for a complete
description of the original selected remedy. Note that the cost estimate in the ROD was
$6,000,000 ($3,300,000 for the soil cleanup and $2,700,000 for the ground water cleanup). This
soil cost estimate was revised based on new soil volume calculations using soil boring and
contaminant concentration information obtained since the ROD was issued (see the
Administrative Record for more information).
Rationale for Changing Remedy Selected in 1994 ROD
On August 16, 1994, EPA, with the concurrence of DNREC, issued a Record of Decision
(ROD) which described the clean-up method for the Dover Gas Light Site. The cleanup method
contained two major components. One component addressed soil contamination at the location of
the former coal gas plant, the other addressed the ground water contamination
For the soil, the ROD required that the surface soil be cleaned up to protect the health of
the museum workers and that the subsurface soil (including the first few feet of soil below the
ground water table) be cleaned up to protect construction workers during a planned museum
expansion.
Dover Gas Light Site Decision Summary
Record of Decision Amendment . 3 December I99~
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Originally, as stated in the November 1993 Proposed Plan, EPA proposed cleaning the soil
to a level such that no building restrictions would be required. In this way. any type of
development allowed by the "Institution & Office" zoning designation could occur. In response
to discussions with the State, in which the State indicated that it may expand the museum and
that a school would not be built, EPA selected soil clean-up levels that would allow a museum
expansion but not a school.
During negotiations with the parties which were financially responsible for the cleanup
(which included the Chesapeake Utilities Corporation, State of Delaware, and General Public
Utilities Corporation), Chesapeake and the State informed EPA of the 1986 agreement to limit
future development of the property and allow it to be used only as a parking lot. Other aspects of
the agreement included Chesapeake's purchase of another piece of property for the State and
compensation to the State for environmental work the State had performed at the Site.
In light of the agreement, Chesapeake and the State claimed that EPA's mandated cleanup
was overly protective and costly because the State could not build on the property.
In 1995, Chesapeake submitted a focused feasibility study proposing a different clean-up
strategy for the soil which would require less soil removal and take into account a new future
land use assumption. Data collected by Chesapeake in preparation for the soil excavation
supports Chesapeake's view that a cleanup involving less soil removal could be protective of
human health and the environment given that no further development will occur at the Site.1
Information obtained from the local citizens at a public meeting held on April 30, 1997
and from the local public officials indicated a lot of support for changing the future land use
assumption at the Site. Following the meeting, Chesapeake revised its focused feasibility study
adding soil vapor extraction (SVE) to the cleanup to address some of the soil contamination
while using excavation to address only the soil contained inside the former gas holders. The
NAPL material in the ground water at the location of the former coal gas plant (which would
have been excavated under the original remedy) would be pumped, if possible, and disposed of
off-site.
As a result of the support to change the future land use assumption and the new soil data
that shows the soil to be less contaminated than originally thought, EPA is proposing to change
the clean-up plan. Part of this change involves modifying the overall clean-up goals at the Site.
Originally, EPA's goal was to clean the Site to a point where future subsurface construction
could take place. Now EPA is proposing only to clean the Site to the extent that the ground water
is protected and to use institutional controls to prevent subsurface construction in the future. EPA
is also proposing to protect the museum workers, not by soil excavation as in the original clean-
up plan, but by paving the parking lot to prevent contact with any contaminated soil.
'in 1996, Chesapeake performed over 20 soil borings in a grid pattern throughout the location of the
former coal gas plant to determine exactly what areas required excavation under the August 16, 1994 ROD.
Samples were collected at four depths in each boring. The data showed that the NAPL material was not as wide-
spread as originally thought based on the data collected during the Remedial Investigation.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 4 December 199'
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EPA evaluates three alternatives in this ROD Amendment to address the soil
contamination. The first alternative is the current clean-up plan that involves extensive
excavation and allows future property development. The second alternative involves just
excavating the gas holders and using SVE to address soil contamination outside of the gas
holders, and the third alternative involves excavating the inside of the gas holders and, to a
limited extent, the soil just outside of the gas holders. The second and third alternatives also
include paving the Site for a parking lot and limiting future development.
EPA's review of the alternatives found Chesapeake's SVE proposal to offer the required
protectiveness of human health and the environment at the Site at a substantially reduced cost,
and with fewer impacts to the local community. As a result, EPA's selected remedy for this Site
is to address the soil contamination with a combination of SVE and excavation. In the next
section, each of the three alternatives considered by EPA to address the soil contamination is
described in detail.
Remedial Action Objectives for the Soil
The August 16, 1994 ROD stated that:
All remedial action shall be conducted in accordance with CERCLA, the NCP,
the performance standards, including the remedial action objectives and clean-up
goals set forth herein.
The ROD went on to list six remediation goals for the Site (pages 15-16). The sixth goal stated:
[One remediation goal is] to return the soil at the former coal gas plant to a
condition where (1) it can either be used consistently with its "Institutional &
Office" zoning designation with no other restrictions or it can be used for the
museum expansion, (2) construction can safely take place, and (3) it no longer is a
continuing source of unacceptable levels of contamination to ground water....
Each soil alternative identifies the specific contaminant clean-up criteria that
apply to that alternative.
This continues to be the goal for remedial Alternative #2 below. However, due to current
land use restrictions, this remediation goal is being changed to:
The remediation goal of the soil cleanup is to (1) prevent the soil contamination
from being a continuing source of ground water contamination, (2) prevent
unacceptable exposure to surface soil contamination by museum workers, and (3)
ensure that current land use restrictions are kept in place.
This goal applies to the soil above the water table at the location of the former coal gas plant. In
the August 16, 1994 ROD, the extent of soil remediation went down to the top of a clay lens that
was two to four feet below the top of the water table. As a result of this change in extent of soil
Dover Gas Light Site Decision Summary
Record of Decision Amendment 5 December 1997
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remediation, the top portion of the ground water aquifer is being added to the ground water
remediation described in the August 16, 1994 ROD. This area is considered part of the NAPL
area and attempts will be made to remove any pumpable NAPL.
Description of the Alternatives
EPA evaluated three alternatives to address the soil contamination. The first alternative
was the original clean-up plan that involved extensive excavation and allowed future property
development. The second alternative involved just excavating the gas holders and using SVE to
address soil contamination outside of the gas holders, and the third alternative involved
excavating the inside of the gas holders and, to a limited extent, the soil just outside of the gas
holders. The second and third alternatives also included paving the Site for a parking lot and
limiting future development.
NOTE: Since EPA is only changing the cleanup for the contamination at the location of
the former coal gas plant, only the portion of the clean-up plan for that area is described below.
To. address the complete Site, each alternative would be coupled with the ground water cleanup
that is currently in the ROD and is not being changed.
Alternative # 1: The Original Remedy (Extensive Soil Excavation)
The goal of this alternative would be to return the former coal gas plant to a condition
where it can be used for a museum expansion and/or a parking lot (or use with similar exposure
to the soil subject to EPA approval) and to protect the museum workers from any contaminated
soil. It would involve excavating soil that exceeds contaminant-specific soil clean-up goals
which are listed in the ROD (see Figure 2 for the estimated area of excavation). Two sets of
criteria were developed: one set for the surface soil to protect the museum workers and one set
for the subsurface soil to protect future construction workers.
Besides being protective of people in direct contact with the soil, the soil clean-up levels
would also be protective of ground water (the contaminated soils act as a continuing source of
contamination to the ground water). The subsurface soil criteria would apply from the two-foot
depth to a clay lens identified during the remedial investigation that is at various depths ranging
from 14 to 18 feet below the ground surface. By removing contamination to this depth (which is
several feet below the water table), a significant amount of NAPL material would be removed.
The total estimated capital cost of this alternative is $10,500,000. There are no operation
and maintenance (O&M) costs associated with this alternative, so the present worth cost of this
alternative is also $10,500,000. Combined with the estimated present worth cost of the ground
water cleanup of $2,700,000, the overall estimated Site clean-up cost is $13,200,000.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 6 December 199'
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Alternative #2: Gas Holder Excavation and Soil Vapor Extraction (SVE)
Since there is no longer a need to protect a future construction worker due to the
limitations on future land use, the goal of this alternative would be to protect museum workers
from surficial soil contamination and to prevent the soil contamination from being a potential
and/or continuing source of ground water contamination. To protect the museum workers from
exposure to soil contamination, the parking lot would be paved, thereby preventing contact with
any contamination. As an added benefit, the pavement would also decrease the amount of
infiltrating rain water, reducing the potential for contamination to migrate to the ground water.
Under this alternative, the tar-filled soil contained in the gas holders would be excavated2
and shipped off-site for thermal treatment. Heavy contamination outside the gas holders would
be addressed by SVE (see Figure 2). SVE would remove the more volatile contaminants (which
are also the most mobile in ground water) and would increase the biodegradation of contaminants
in the soil by pulling more oxygen below the surface. The SVE system would continue to operate
until it was no longer removing contamination and was no longer aiding subsurface
biodegradation.
The top several feet of the ground water aquifer which contains NAPL material would be
addressed as part of the ground water cleanup rather than excavated as in the original clean-up
plan. This alternative also includes institutional controls (for example, the existing agreement
between the State of Delaware and Chesapeake) to prevent future development of the former coal
gas plant location in a way that could harm the public.
The estimated capital cost of this alternative is $1,300,000. The present worth cost of the
O&M portion of this alternative is $200,000.3 The total estimated present worth cost of this
alternative is $1,500,000. Combined with the estimated present worth cost of the ground water
cleanup of $2,700,000, the overall estimated Site cleanup cost is $4,200,000.
Alternative #3: Modified Soil Excavation
This alternative is the same as Alternative #2 except that the soil contamination just
outside the gas holders would be excavated and incinerated off-site rather than addressed by SVE
(see Figure 2).
The cost of this alternative is $3,000,000 (there are no O&M costs associated with this
alternative). Combined with the estimated present worth cost of the ground water remedy of
$2,700,000, the overall estimated Site clean-up cost is $5,700,000.
2The gas holders are approximately 8-10 feet in depth.
3The O&M cost estimate is based on operating the SVE system for four years with NAPL being recovered
from the SVE wells for two years.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 7 December 199 "
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Evaluation of Alternatives
The above alternatives were evaluated in detail to determine which would be the most
effective in achieving the goals of Superfund. EPA uses nine criteria to evaluate alternatives.
These criteria are summarized in Table 1. The first two criteria (overall protection of human
health and the environment and compliance with ARARs [applicable and relevant and
appropriate requirements]) are threshold criteria. The selected cleanup must meet both of these
threshold criteria (unless an ARAR waiver is invoked). The next five criteria (long-term
effectiveness and permanence; reduction of toxicity, mobility, or volume through treatment;
short-term effectiveness; implementability; and cost) are the primary balancing criteria. The
remaining two criteria (state and community acceptance) are referred to as modifying criteria.
The following is a brief comparative analysis of each alternative against the nine
evaluation criteria.
Overall Protection of Human Health and the Environment
All three alternatives provide for the overall protection of human health and the
environment. With the change in the future land use assumption from a museum expansion to a
parking lot, there is no longer a concern about construction worker exposure to the deeper soil
contamination. However, the deeper soil contamination continues to act and/or potentially could
act as a significant source of ground water contamination.
Each of the alternatives addresses the deeper soil as a source of ground water
contamination, but in varying degrees. Each alternative removes the worst contamination (that
being in the gas holders). However, Alternative #1 removes significantly more contamination
than the other two alternatives for several reasons: 1) since the goal of the original cleanup was to
protect against construction worker exposure to the deeper soil contamination, the clean-up
criteria were lower than required to protect the ground water at this Site, and 2) the required
excavation extended into the top several feet of the water table to remove the NAPL material that
is perched on top of a clay lens.
Alternatives #2 and #3 would address the NAPL material on the clay lens by adding it to
the rest of the ground water cleanup which includes attempts to remove any mobile NAPL. EPA
has determined that this would adequately protect the ground water because it would reduce
and/or eliminate the possibility of the NAPL migrating to parts of the aquifer which currently are
not heavily contaminated with NAPL material, and although the remaining residual NAPL would
continue to contribute to ground water contamination, the dissolved ground water plume in the
vicinity of the NAPL would be captured in the containment wells that are part of the ground
water cleanup.
Alternative #3 addresses the vadose zone (the portion of soil between the ground surface
and the water table) soil contamination in the same manner as Alternative #1 except the limits of
excavation would be significantly reduced since the goal of Alternative #3 is to only protect
ground water rather than future construction workers.
Dover Gas Lighi Site Decision Summary
Record of Decision Amendment 8 December 1997
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Alternative #2 addresses the vadose zone soil contamination that is outside the gas
holders through SVE which would remove the most volatile and mobile contaminants that can
most easily migrate, not only to the ground water, but in ground water.
Compliance with ARARs (Applicable and Relevant and Appropriate Requirements)
Each alternative meets this threshold criterium. The major ARARs associated with these
alternatives are the National Historic Preservation Act (NHPA), the Resource Conservation and
Recovery Act (RCRA), and Delaware's Hazardous Substance Cleanup Act (HSCA). Many
requirements of the NHPA were met during the remedial investigation and feasibility study
(RI/FS) through cultural resource surveys. As part of Alternatives #1 and #3, a data recovery
operation would be done at the beginning of the excavation to gather archaeological information
(the size of the recovery step would vary due to differences in the scope of the excavations).
Alternative #2 may also require a data recovery step or may only require further work (but less
intrusive) to mitigate impacts to cultural resources.
Some of the excavated soil may be RCRA-hazardous waste due to the teachability of
benzene. If so, on-site treatment by stabilization would likely be necessary to render the waste
non-hazardous. If any of the waste is considered a RCRA-hazardous waste, all on-site treatment,
storage, and handling practices would be done according to RCRA regulations. Some additional
stabilization might also be required in Alternative #1 because of the potential high water content
of some of the soil. For Alternative #1, the main requirement of HSCA as it relates to this Site is
that the clean-up criteria must be equal to or below the criteria provided by DNREC for
compliance with HSCA. For Alternatives #2 and #3, the main requirement is that the land-use
restrictions contained in these alternatives must be added to the deed of the property that is the
location of the former coal gas plant.
Due to the SVE, Alternative #2 may require emission controls to meet State and Federal
air regulations (for a complete list of the ARARs which apply to the soils portion of the selected
remedy, see Table 2).
Long-Term Effectiveness and Permanence
Alternative #1 offers the greatest degree of long-term effectiveness and permanence
because it removes and destroys the most contamination and allows a wider range of uses of the
land than the other two alternatives. Most of the waste is also destroyed in Alternatives #2 and #3
because of the excavation of the gas holders coupled with the off-site thermal destruction of the
waste.
Reduction of Toxicity, Mobility, or Volume Through Treatment
Each alternative offers significant reductions in toxicity, mobility, and volume through
treatment. Under each alternative, the most contaminated soil, contained in the gas holders,
would be removed and would undergo thermal treatment that would destroy the contamination.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 9 December I99~
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Alternative #1 offers the largest reduction of toxicity, mobility, or volume through
treatment because it has the largest volume of soil removal, followed by Alternative #3. In
Alternative #2, SVE will remove the most mobile contaminants from the vadose zone soil.
Alternatives #2 and #3 will remove any mobile NAPL below the water table by addressing this
area along with the ground water remedy. Once any contamination is removed from the soil it
would be disposed of properly according to State and Federal regulations.
Short-Term Effectiveness
Each alternative will create significant short-term impacts. The excavated soil will be
hauled off-site, increasing truck traffic in Dover. The potential exists for adverse air emissions to
come from the excavation pit. Precautions will be taken to minimize such emissions. The
excavation will, at a minimum, use most of the parking area at the museum and may disrupt
museum operations. Alternative #2 ranks best by far regarding short-term effectiveness because
it involves the least amount of excavation.
Implementability
Each alternative is implementable, but Alternative #2 is much easier to implement than
the other two because the excavation is confined to the gas holders. The walls of the gas holders
provide the stability necessary to ensure there is not a cave-in. Alternatives #1 and #3 would
require shoring of the sides of the excavation pit or sloped sides that would require significant
increases in the amount of excavated soil.
Since Alternative #2 requires the least amount of excavation, more of the Site is available
for equipment staging and soil stabilization (to treat RCRA-hazardous soils). In a small, confined
site such as this one, available work space is an important consideration.
Cost
The costs for the Site are directly proportional to how much soil is excavated. As a result,
Alternative #2 ($1,500,000) is the least costly followed by Alternative #3 ($3,000,000). Both of
these alternatives are much less costly than Alternative #1 ($10,500,000). Note that the original
estimate for Alternative #1 in the August 16,1994 ROD was $3,300,000. The new estimate of
$10,500,000 is based on data collected since that ROD was issued. To obtain the overall
estimated Site clean-up cost for each alternative, add the estimated present worth cost of the
ground water cleanup ($2,700,000) to each of the figures cited above.
State Acceptance
DNREC, on behalf of the State of Delaware, has concurred with EPA's selection of
Alternative #2 to address the soil contamination at the Site (see attached letter).
Dover Gas Light Site Decision Summary
Record of Decision Amendment 10 ' December 1997
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Community Acceptance
From views expressed by the community at EPA's April 30, 1997 public meeting and by
the City of Dover, there is considerable support for EPA to change the future land use
assumption at the Site. Also, there were no negative comments received regarding EPA's
preferred alternative (Alternative #2) at the September 9, 1997 public meeting. Alternative #2
does the most in limiting disruption near the Site, maximizing parking availability, and reducing
cost which appear to be the major issues to the local community.
Comparison of Alternatives
Most of the comparison of alternatives hinges on how much soil will be excavated.
Excavation of more soil does provide a higher degree of overall protection of human health and
the environment, as well as better long-term effectiveness and permanence and greater reduction
in toxicity, mobility, and volume through treatment. However, short-term impacts and the clean-
up cost are directly proportional to the amount of soil excavation.
Each alternative provides for the overall protection of human health and the environment
and complies with ARARS, yet Alternative #2 does so with the least cost and the least impact to
the local community while still offering a significant degree of long-term effectiveness and
permanence and reduction of toxicity, mobility, and volume through treatment. Therefore, EPA
has determined the Alternative #2 is the selected remedy.
Selected Remedy: Performance Standards
Below are the performance standards for the selected remedy described in this ROD
Amendment. In order to have a complete set of performance standards for the soil cleanup in this
ROD Amendment, a number of performance standards from the original remedy are repeated
here. Their inclusion here does not necessarily mean that they do not apply as well to the ground
water remedy that is described in the August 16, 1994 ROD which is still in effect except as
modified by this ROD Amendment. The performance standards included from the August 16,
1994 ROD are shown in italics. The performance standards from the August 16, 1994 ROD that
are being eliminated or replaced are shown below in "strikeout". Also note that one performance
standard (1.1.7) has been added to the ground water to further define the NAPL area based on the
data collected during the remedial design and due to changes in the soil cleanup.
1.1. NAPL Area
1.1.7. The NAPL area is approximately defined by the area shown in Figure 1.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 11 December I99~
-------
2.1 Soil Excavation
2. 1 . 1 . All soil in the area shown in Figure 4 that contains contaminant levels above those
iisico i n i crioniitiiicc oiuJiOAFO £ . *? snail DC cxcuV^HCci.
- 2.1.2. The depth of the excavation shall not exceed the top of the clay lens located at an
average depth of 14 to 20 feet below ground surface. In areas of the former coal gas plant that do
not have this clay lens, the excavation shall not go below the depth the lens would have been
expected to be found (i.e., the depth of lowest adjacent lens in the 14 to 20 foot range).
2. 1.3. The excavation shall be performed in such a manner as to minimize the release of
contaminants to the atmosphere.
2. 1. 4. Steps shall be taken to avoid structural or other damage to the museum, the streets,
the cemetery, or the church property during excavation.
-------
2.2.3. Excavated soil that contains contaminant levels above the levels listed in
Performance Standard 2.4 shall be treated off-site by thermal destruction. Thermal destruction
includes, but is not limited to, incineration at a hazardous waste incinerator, destruction at a
resource recovery unit such as a cement kiln or utility boiler, and low temperature thermal
dcsorption with off-gas incineration. The choice of-treatmcnt facility is subject to EPA approval.
Soil that must be excavated but is not a RCRA-hazardous waste and is only slightly
contaminated, may be landfillcd at an acceptable disposal facility subject to EPA approval. The
contfljninzint Tcvcis ociow wnicn son msy DC mnuiiii sn&ii DC determined cttinn^ rcnicui&i ocsi^n
and subject to EPA approval.
2.2.4. Contaminated debris shall either be cleaned at the Site or treated in the same
manner as the soil. Decontaminated debris may be backfilled at the Site. Any on-site debris
cleaning shall be performed in such a way as to prevent unacceptable discharge of contaminants
from the Super fund Site. Residue or waste from any debris cleaning operation shall be disposed
of off-site in accordance with all appropriate Federal and State regulations.
2.2.5 Excavated soil shall be treated off-site by thermal destruction. Thermal destruction
includes, but is not limited to, incineration at a hazardous waste incinerator, destruction at a
resource recovery unit such as a cement kiln or utility boiler, and low temperature thermal
desorption with off-gas incineration. The choice of treatment facility is subject to EPA approval.
Soil that must be excavated but is not a RCRA-hazardous waste and is only slightly
contaminated, may be landfilled at an acceptable disposal facility subject to EPA approval. The
contaminant levels below which soil may be landfilled shall be determined during remedial
design and subject to EPA approval.
2.3. Cultural Resource Recovery
2.3.1. Prior to any excavation and removal of contaminated soil, a cultural resource data
recovery operation shall be performed. This operation shall be performed in accordance with
substantive requirements of the National Historic Preservation Act, as amended.
2.3.2 Prior to any excavation and removal of contaminated soil and installation of the
SVE system, steps shall be taken to ensure compliance with the substantive requirements of the
National Historic Preservation Act, as amended. The steps may include, but not be limited to, a
data recovery step at the gas holders, consideration of piping locations to avoid adverse impacts
to cultural resources, consideration of the aesthetics of the SVE treatment equipment, and
consideration of cultural resources in the design of the parking lot.
2.4. Soil Clean-up Criteria
2.4. 1 . Below arc the soil clean-up criteria that apply to the soil from a depth of two feet
below ground surface to the clay lens that is located at an approximate depth of 14 to 20 feet;
- a. benzene - h?56 - ppm
- b. toluene - 28,000 - ppm
Dover Cos Light Site Decision Summary-
Record of Decision Amendment 13 December 1 99"
-------
- — u :• eirry t Benzene ; —
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2.5. Institutional Controls
2.5.3. The dced(s) of property that requires excavation as part of this ROD shall be
modified to give notice to the public of past land disposal and of the fact that releases and threats
0i rciC33C3 01 n&z&rQotis suD3uinccs n&vc sriGCtCQ tnc rcspcctivG pflrccis. iNoticc sriaii 211 so DC
placed on the dccd(3) that states that the soil clean-up criteria were not developed to allow
unrestricted use of the land, but that they were developed to safely allow expansion of the
museum and use as a parking area, as long as uncxcavatcd, yet contaminated, subsurface soil
docs not become surface soil.
2.5.4. The deed(s) of property that requires excavation as part of this ROD Amendment
shall be modified to give notice to the public of past land disposal and of the fact that releases
and threats of releases of hazardous substances have affected the respective parcel(s). Notice
shall also be placed on the deed(s) that states that there exists a contract between the current
owner (State of Delaware) and Chesapeake Utilities Corporation that prohibits development of
the parking area of the Delaware State Museum. If uses of the location of the former coal gas
plant other than as a parking lot are contemplated in the future, a human health risk assessment
must be submitted by the Site owner. The risk assessment, subject to EPA's approval, must show
that the planned uses provide for the overall protection of human health and the environment or
Dover Gas Light Site Decision Summary'
Record of Decision Amendment 14 December / 99 '
-------
state additional remedial actions which shall be undertaken prior to a change in land use which
would provide for the overall protection of human health and the environment.
2.6. Soil Vapor Extraction System
2.6.1. Soil vapor extraction shall be applied to the areas of the location of the former coal
gas plant shown in Figure 2, Alternative #2. Note that six SVE wells for the largest area have
already been installed.
2.6.2. The SVE system shall be operated in such a manner as to ensure that there are no
untreated zones within the areas depicted in Figure 2, Alternative #2.
2.6.3. The SVE wells and any piping (between the wells or between the emissions control
equipment and the wells) shall be installed underground in such a manner as to allow a parking
lot to be constructed on top. Vaults shall be installed around the wells, flush with the ground or
pavement surface, to protect the wells and any piping and instrumentation from vehicular traffic.
2.6.4. The emissions from the SVE systems shall be treated with granulated activated
carbon (GAC) to prevent, to the maximum extent practicable, the transfer of contaminants to the
air. The design and operation of the system shall include monitoring, and/or other features, to
demonstrate the successful control of the SVE emissions.
2.6.5. The SVE system shall continue to operate until NAPL recovery operations are
completed and until the monitoring of extracted vapors (both contaminants and carbon dioxide)
indicate that the SVE system is both removing only insignificant amounts of contaminants and
no longer aiding in subsurface biodegradation. The remedial design, subject to EPA approval,
shall outline the specific compounds to be monitored to determine when the SVE system can be
turned off and shall specifically outline the vapor levels at which the system can be turned off.
Due to the fact that vapor levels typically increase if the system is not operated for a period of
time, the system must be restarted after sitting idle for one winter. If the system continues to
meet the criteria established during the remedial design to allow the system to be turned off, the
system can be taken out of service. If the vapor levels rebound, the system must again be
operated (until the vapors meet the criteria established during the remedial design to allow the
system to be turned off) and then allowed to sit through one winter. This process will continue
until such a time as the vapors due not exceed the criteria after restarting the system.
2.6.6. Once the SVE system has been shut down for the last time, the SVE wells shall be
abandoned according to DNREC regulations to prevent them from being a conduit of
contamination to the subsurface.
2.7. Parking Lot
2.7.1. A parking lot, paved with asphalt, shall be constructed at the location of the former
coal gas manufacturing plant. The parking lot shall cover the approximate area shown in
Figure 2, Alternative #2.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 15 December 199~
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2.7.2. The parking lot shall be designed in accordance with local regulations and standard
design parameters for paving and traffic control. The parking lot shall also be designed in
compliance, as necessary, with the National Historic Preservation Act. The parking lot designer
shall discuss the design parameters with the property owner prior to initiation of the design. The
property owner shall be allowed to review and comment on the design at appropriate times as
determined by EPA. The design is subject to EPA's approval. Since the City of Dover has
expressed a desire to potentially lease a portion of this parking lot from the property owner,
efforts shall be made during the design to reach agreement on this issue with the City of Dover
and the property owner. However, these efforts shall not result in increased parking lot
construction costs (unless mutually agreed to by all parties involved in the design) and shall not
cause a delay in the construction schedule.
3.1. Operations and Maintenance Plan
3.1.1. An operations and maintenance plan shall be developed and implemented for the
ground-water recovery system. The plan shall include a list of all vendor-required maintenance
activities.
3.1.2. The plan shall include a list of potential operations and maintenance problems and
their proposed solution.
3.1.3. The plan shall include a list of all required inspections and general guidelines for
the inspections.
3.1.4. The plan shall include operating instructions.
f
3.1.5. The plan shall include reporting requirements and forms.
3.1.6. The plan shall include health and safety requirements.
3.1.7. The plan shall include a monitoring plan for the emissions from the ground-water
treatment system.
3.1.8. The plan shall include a -waste management plan describing how treatment wastes
and/or recovered NAPLs will be disposed of.
3.1.9. Performance standards 3.1.1 to 3.1.8 are the minimum requirements of the
operation and maintenance plan. The plan, including all of the appropriate information, shall be
submitted to EPA for approval.
3.1.10. All requirements of the approved plan shall be carried out.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 16 December 199'
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3.2. Erosion Control Plan
3.2.1. An erosion control plan shall be developed and implemented which outlines
procedures to be used to control transport of soil and sediment due to erosion, to the maximum
extent practicable and in accordance with the ARARs in Table 2, for all activities which present
the potential for transporting soils or sediments. This plan shall also include procedures to be
used to properly control and discharge stormwater from the construction areas.
3.2.2. This plan shall be developed in accordance with State and local regulations and
shall be submitted to EPA for approval.
3.3. Participate Air Emissions
3.3.1. All remedial work shall be done in such a manner as to minimize transport of
airborne paniculate emissions.
3.3.2. As part of the remedial action health and safety plan, levels of paniculate
considered to pose an unacceptable health risk shall be developed along with monitoring
requirements to measure paniculate counts.
3.3.3. Air monitoring shall be done at appropriate times to ensure protectiveness of
human health.
3.3.4. If the air monitoring results indicate that paniculate counts are high enough that
EPA concludes that unacceptable health risks are posed to people on-site or off-site, appropriate
measures shall be taken to reduce the paniculate count to safe levels off-site, and either to
reduce the paniculate count to safe levels on-site or to protect the workers through personal
protective equipment.
3.4. Waste Management Plan
3.4.1. A waste management plan shall be developed, submitted to EPA for approval, and
implemented to handle any other wastes generated during remedial design or remedial action
that have not previously had waste management performance standards set. The plan shall
outline how all Federal, State, and local regulations will be complied with.
3.5. ARARs
3.5.1. The selected remedy shall attain, at a minimum, all chemical, location, and action
specific ARARs listed in Table 2 unless a statutory waiver is invoked by EPA.
3.6. Utility Worker Risk Assessment
3.6.1. A risk assessment shall be prepared to determine if utility workers would be at risk
from installation and/or repair work to underground utilities at the location of the former coal gas
Dover Gas Light Site Decision Summary
Recordof Decision Amendment .17 December 1997
-------
plant in areas where the soil contamination is not being addressed by other parts of the selected
remedy. The risk assessment in the remedial investigation shall be used as a guide for this risk
assessment. The risk assessment shall be submitted to EPA for approval.
3.6.2. If the above risk assessment shows that the workers would be at risk, the proper
utility companies shall be notified to take additional precautions to ensure the safety of their
workers. EPA shall also determine at that time if other remedial measures are necessary to
protect any utility workers. This could involve extra SVE wells or excavation.
Statutory Determinations
EPA's primary responsibility at Superfund sites is to undertake remedial actions that are
protective of human health and the environment. In addition, Section 121 of CERCLA,
42 U.S.C. § 9621, establishes several other statutory requirements and preferences. These
requirements specify that when complete, the selected remedial action for each site must comply
with applicable or relevant and appropriate environmental standards established under Federal
and state environmental laws (ARARs) unless a statutory waiver is invoked. The selected remedy
must also be cost effective and utilize treatment technologies or resource recovery technologies
to the maximum extent practicable. Finally, the statute includes a preference for remedies that
permanently and significantly reduce the volume, toxicity or mobility of hazardous substances.
The following sections discuss how the selected remedy for this portion of the Site meets these
statutory requirements.
Protection of Human Health and the Environment
The selected remedy provides overall protection of human health and the environment. It
protects human health by:
• Paving the parking lot to prevent contact with contaminated surface soils which
may pose a threat to museum workers after long-term exposure.
• Removing highly concentrated levels of contamination from the soil to help
reduce the possibility of the Frederica aquifer becoming contaminated and thereby
unusable as a drinking water source.
• Ensuring that there is no nature construction at the Site which would pose a health
threat to construction workers.
The selected remedy will protect the environment by removing most of the soil
contamination that can be a continuing source of contamination to ground water, a natural
resource.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 18 December 1997
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Compliance with Applicable or Relevant and Appropriate Requirements
The selected remedy, Alternative #2, shall attain all action, location, and chemical
specific applicable or relevant and appropriate requirements for the Site which are listed in
Table 2. Also included in the table are criteria, advisories, or guidance to be considered (TBCs)
for the implementation of this remedy. Compliance with the air emission regulations for the SVE
system will ensure that cross media transfers of contaminants that are harmful to the public do
not occur.
The substantive requirements of the National Historic Preservation Act, as amended,
(NHPA) shall be met. Measures shall be taken to mitigate any adverse impacts to cultural
resources that are included or eligible for inclusion on the National Register of Historic Places.
Also, consideration will be given to the design of the SVE equipment housing and the parking lot
to ensure compliance with the NHPA. The soil excavation, piping installation, and the treatment
plant construction are examples of portions of the remedial action that have the potential to
impact cultural resources. Measures will be taken to minimize and/or mitigate any adverse
impacts.
Cost-Effectiveness
Cost was a major factor in selecting the new remedy for the soil contamination at the Site.
Alternative #2 meets each of the threshold criteria, as do the other alternatives, but meets them at
a substantially reduced cost. Alternative #2 represents a $9.2 million savings from the original
remedy (Alternative #1). As a result, Alternative #2 affords overall effectiveness proportionate to
the cost and is the most cost effective alternative.
Utilization of Permanent Solutions and Alternative Treatment Technologies to the
Maximum Extent Practicable
EPA has determined that the selected remedy (Alternative #2) provides the best trade-off
in terms of long-term effectiveness and permanence; reduction in toxicity, mobility, or volume
achieved through treatment; short-term effectiveness; implementability; and cost; as well as
considering the statutory preference for treatment as a principal element and considering State
and community acceptance.
Alternative #2 provides for destruction of the vast majority of the contamination in the
soil through thermal destruction. If an industrial boiler is used to destroy the waste, the energy
value of the contamination will be recovered. If a commercial thermal desorption company is
used to treat the soil, the soil can be reused. The contamination removed by the SVE system will
also likely be destroyed thermally (through regeneration of carbon used to absorb the
contamination in the off-gas from the SVE system).
Dover Gas Light Site Decision Summary-
Record of Decision Amendment 19 December 1997
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Preference for Treatment as a Principal Element
EPA has determined that the heavy deposits of coal tar and any NAPLs are principal
threat wastes meaning that the material includes or contains hazardous substances, pollutants, or
contaminants that act as a reservoir for migration of contamination to, for example, ground
water. These principal threats are being treated as part of the selected remedy. The heavy
deposits of coal tar will be excavated and incinerated off-site. Any mobile NAPLs that exist in
the upper portion of the water table, below the location of a former coal gas plant, will be
extracted from the ground water and undergo treatment.
Documentation of Significant Changes
The only significant change to the selected remedy in comparison to EPA's preferred
alternative described in the August 29, 1997 Proposed Plan is the addition of the utility worker
risk assessment. This addition is in response to a question EPA received at the Proposed Plan
public meeting. During the remedial investigation, EPA evaluated potential risks to utility
workers away from the location of the former coal gas plant, but not at or near the location of the
former coal gas plant. EPA anticipated at the time the original ROD was issued, that information
gained from the extensive excavation of Site soils would provide information as to the
contaminant levels at or near the streets adjacent to the location of the former coal gas plant.
Since extensive excavation is no longer occurring, there remains the need to evaluate potential
risks to utility workers digging into soil at and immediately adjacent to the location of the former
coal gas plant.
Dover Gas Light Site Decision Summary
Record of Decision Amendment 20 December I99~
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RESPONSIVENESS SUMMARY
This Responsiveness Summary for the Dover Gas Light Co. Site has been prepared to
respond to comments received by EPA, both oral and written, regarding changes to the selected
remedy which EPA originally proposed on August 29, 1997 in a Proposed Remedial Action Plan
(Proposed Plan). A number of the comments addressed below where received at a public meeting
which EPA held on September 9, 1997 to discuss the proposed changes. Other comments
received at the public meeting, but which did not relate to the proposed changes, are not
addressed in the Responsiveness Summary. However, they were addressed at the public meeting.
a transcript of which can be found in the Administrative Record.
The responses are divided into two groups: those that were received at the public meeting
and those that were received in writing.
Comments from the Public Meeting
1. A question was asked about the nature of the contaminants and the potential harm to
humans that the contaminants could cause.
EPA's RESPONSE: The soil contamination can be divided into two major classes of
chemicals: BTEX (benzene, toluene, ethylbenzene, and xylenes) which is a component of
gasoline and PAHs (polynuclear aromatic hydrocarbons) which can be found in coal tar, roofing
tar, and asphalt. Both of these classes of chemicals can cause carcinogenic and non-carcinogenic
impacts to humans. See pages 5-10 of the August 16, 1994 ROD for a detailed description of the
risks posed by the Site contamination.
2. A question was asked about whether construction such as road repair work to streets
adjacent to the Site would present a hazard.
EPA's RESPONSE: The Site does not present a hazard to workers performing road repair
work. However, workers installing and/or repairing utilities underground at the location of the
former coal gas plant may need to take extra safety precautions while performing their work. In
response to this issue, a performance standard has been added to the ROD Amendment which
addresses this potential. A risk assessment shall be performed during the remedial design to
determine if utility workers would be at risk, and if so, either further remedial actions shall be
required or the proper utility companies shall be notified to take additional precautions to ensure
the safety of their workers.
3. A question was asked about whether there would be air emissions from the soil vapor
extraction (SVE) system and how they would be treated.
EPA's RESPONSE: The emissions from the SVE system will be treated by passing the
vapor stream through granulated activated charcoal (GAC) which will absorb the contaminants.
Dover Gas Light Site Responsiveness Summary
Record of Decision Amendment 21 December I997
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A two-stage system will be employed to ensure that contaminants are not released to the
environment.
.4. A question was asked about whether the SVE system would require an air permit.
EPA's RESPONSE: A permit will not be required for the SVE system because permits
are not required for work performed entirely at a Superfund site. However, the technical
requirements of the laws and regulations governing air pollution will be met to ensure the overall
protection of human health and the environment.
5. A question was asked about the length of operation of the SVE system.
EPA's RESPONSE: EPA estimates that the SVE system will operate no longer than five
years. However, it will operate until the performance standards identified in this ROD
Amendment have been achieved.
6. A question was asked about what the SVE system would look like and if it would
cause any obstructions in the parking lot.
EPA's RESPONSE: The SVE system consists of wells and equipment to extract air from
the ground through these wells, as well as air treatment equipment. The system will also include
piping to connect the wells and the extraction equipment. The wells and the piping will be
underground, but the extraction and treatment equipment will occupy a small area of the parking
lot.
7. A question was asked about whether the contaminants have an odor.
EPA's RESPONSE: The contaminants do have an odor. For example, one of the
contaminants is naphthalene which is an ingredient in moth balls.
8. A question was asked about whether EPA is assured that someone will accept the
waste after it is excavated, and in particular whether Clean Earth of New Castle (a thermal
treatment facility for soils) has been approved to treat the waste.
EPA's RESPONSE: The contaminated soil that will be excavated is not an unusual waste
stream. There are many disposal facilities in the United States that could handle this waste.
EPA's review and approval of a plan to dispose of the waste at a particular facility will take place
during the remedial design. The selected remedy does allow for the on-site treatment of the soil
(for example, the stirring in of charcoal to absorb benzene) to ensure the soil is not a hazardous
waste as define by RCRA (the Resource Conservation and Recovery Act) which may allow
Clean Earth to treat the soil.
9. A question was asked about what contaminants would be left at the Site after the
cleanup.
Dover Gas Light Site Responsiveness Summary
Record of Decision Amendment 22 December 199?
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EPA's RESPONSE: The same type of contaminants present at the Site today will be
present at the Site once the cleanup is complete. However, the volume and levels of
contamination will be significantly reduced by the cleanup. The contamination remaining at the
Site will not pose a threat to human health or the environment once the cleanup is complete as
long as the land is used in accordance the Performance Standards outlined in this ROD
Amendment.
Written Comments
10. One commentor stated that it was not necessary to treat the small areas at the north
and south ends of the Site using SVE. Information was provided to support the commentor's
claim that these areas were not sufficiently contaminated to warrant SVE.
EPA's RESPONSE: EPA has reviewed the submitted information which includes boring
logs for soil borings that were done during the remedial design (after the August 16, 1994 ROD).
EPA continues to believe that the two small areas at the north and south ends of the Site (near
B-19 at the north end and near the east entrance to the museum at the south end [see Figure 2])
warrant remediation using SVE.
At the north end, the presence of contamination is indicated by the HNu readings
(showing the presence of organic vapors) and the coal tar odor at boring B-19. While this boring
may be close to or within the influence of other SVE wells, it is at best near the outer edge.
EPA's experience with SVE, especially when there are variations in the geology as at this Site, is
that zones of influence of SVE wells are anything but symmetrical. By placing an SVE well at
the location of B-19, there will be no question that this area will undergo treatment.
At the south end, the presence of contamination is indicated by the very high HNu
readings (showing the presence of organic vapors) and the strong coal tar odor at boring B-7
(data collected during the remedial investigation). Although other nearby borings did not show
these same types of readings, the contamination indicated by boring B-7 warrants remediation.
Both of these areas are closer to potential exposure points than the large middle area of
the Site. The south end is near the museum which has a basement and the north end is near the
street where underground utility work may take place.
23
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TABLE 1
EPA Criteria For Evaluating Alternatives
Threshold Criteria
• Overall Protection of Human Health and the Environment: Describes how an
alternative achieves and maintains protection of human health and the environment, and
how risks to human health and the environment are eliminated, reduced, or controlled
through treatment, engineering controls, or institutional controls.
• Compliance with ARARs: Addresses whether an alternative will meet all of the
applicable or relevant and appropriate requirements (ARARS) of Federal and State
environmental laws and/or justifies invoking a waiver.
Primary Balancing Criteria
• Long-Term Effectiveness and Permanence: Considers the ability of the cleanup to
maintain reliable protection of human health and the environment over time once clean-
up goals have been met.
• Reduction of Toxicity, Mobility, or Volume Through Treatment: Describes the
performance of the treatment technologies that may be employed in an alternative.
• Short-Term Effectiveness: Examines the effectiveness of an alternative in protecting
human health and the environment during the construction and implementation of the
cleanup, until the desired clean-up levels are achieved.
• Implementability: Evaluates the technical and administrative feasibility of an alternative
and the availability of required materials and services.
• Cost: Considers the capital, as well as operation and maintenance (O&M) costs of an
alternative.
Modifying Criteria
• State Acceptance: Indicates whether the state agency, based on its review of the proposed
remedy, concurs with, opposes, or has no comment regarding the clean-up plan.
• Community Acceptance: A measure of the community's general acceptance of the
clean-up plan.
24
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TABLE 2
Applicable or Relevant and Appropriate Requirements (ARARs)
And To Be Considered Material (TBCs) for the Soil Portion of the Selected Remedy
Dover Gas Light Co. Superfund Site
ARAR or TBC
1. CHEMICAL SPECIFIC - Air
Delaware Ambienl Air Quality
Standards
II. LOCATION SPECIFIC
National Historic Preservation
Act of 1966, as amended
Delaware Regulations Governing
Hazardous Substance Cleanup
III. ACTION SPECIFIC
A. Water
Slate of Delaware Regulations
Governing the Construction of
Water Wells. January 20. 1987
General Pretreatmenl Regulations
Legal Citation
Title 7, Delaware Code, Ch
60, Regulation 3, Section 6003
36C.F.R. §§ 800.4(b-c).
800.4(e). 800.5(e), 800.9
Delaware Regulations
Governing Hazardous
Substance Cleanup, Section
8.10
Stale of Delaware Regulations
Governing the Construction of
Water Wells, January 20. 1987
Sections 3, 4, 5. 6. 7. 8. 9, 10
40C.F.R. §8 403.5, 403.6(c-e)
ARAR
Class
Applicable
Applicable
Relevant and
Appropriate
Applicable
Applicable
Requirement Synopsis
Establishes ambient air quality standards.
Requires remedial action to take into account
effects on properties included on or eligible
for the National Register of Historic Places.
Institutional Controls must be recorded on the
deed.
Contain requirements governing the location,
design, installation, use, disinfection,
modification, repair, and abandonment of all
wells and associated pumping equipment.
Standards for discharge to POTW
Applicability to
Selected Remedy
1
Applicable for potential releases from SVE, excavation work, or other
remedial actions.
Steps must be taken (including possible data recovery step prior to soil
excavation) to mitigate adverse impacts lo cultural resources eligible lor
the National Register of Historic Places from the soil excavation or the
installation of the SVE system.
Only substantive requirements must be met.
The land-use restrictions contained in this ROD Amendment must he
added to the deed of the property that is the location of the former coal
gas plant.
Installation of any monitoring and recovery wells and (he abandonment
of wells shall meet all substantive requirements.
Applicable should any extracted ground water and/or condensed water
vapor from the SVE system be discharged lo a POTW.
25
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ARAR or TBC
B. Air
Control of Air Emissions from
Air Strippers al Super fund
Ground Water Sites, June IS,
1989 (EPA OSWER Directive
9355.0-28)
Delaware Regulations Governing
the Control of Air Pollution
C. Sediments/Solids
Delaware Sediment and
Slormwater Regulations
January 23. 1991
D. Waste Handling and
Disposal
Standards Applicable to
Generators of Hazardous Waste
Standards fur Owners and
Operators of Hazardous Waste
Treatment. Storage, and Disposal
Facilities (TSDF)
RCRA Requirements fur Use and
Management of Containers
RCRA Requirements for Tank
Systems
Legal Citation
No Legal Citation
Delaware Regulations
^Governing the Control of Air
Pollution Regulations
Numbers 2. 19, and 24
Delaware Sediment and
Slormwater Regulations
January 23. 1991
Sections 3. 6.9, 10. II. and 15
Delaware Regulations
Governing Hazardous Waste,
§§262.1
-------
ARAR or TBC
RCRA Requirements for Tank
Systems
RCRA Requirements for Waste
Piles
RCRA Requirements for Waste
Piles
Identification and Listing of
Hazardous Wastes
Legal Citation
EPA Regulations,
40C.F.R. §§264.190-1%,
264.198-199
Delaware Regulations
Governing Hazardous Waste.
§§264.251,264.254.264.256-
257, 264.258(a)
EPA Regulations,
40C.F.R. §§264.251-254
Delaware Regulations
Governing Hazardous Wastes,
§§261.20-24,264.31.261.33
ARAR
Class
Applicable
Applicable
Applicable
Applicable
Requirement Synopsis
Requirements for storage or treatment of
hazardous waste in lank systems.
Requirements for storage or treatment of
hazardous waste in waste piles.
Requirements for storage or treatment of
hazardous waste in waste piles.
Identifies solid wastes which are regulated as
hazardous wastes.
Applicability to
Selected Remedy
Applicable for onsile treatment systems and temporary storage tanks
containing hazardous wastes.
Applicable for on-site storage and/or treatment of excavated soil if the
soil is a hazardous waste.
Applicable for on-sile storage and/or treatment of excavated soil it (he
soil is a hazardous waste.
Use to determine which materials to be disposed of are hazardous
wastes.
27
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FIGURE 1
Dover Gas Light Super-fund Site
Record of Decision Amendment - December 1997
Government
Complex
W* BRANCH
Approximate Limits of Ground
Water Plume
£7777771 Approximate Limits of NAPL
Contamination
Former Coal Gas Plant
MAP NOT TO SCALE
-------
Figure 2
Soil Cleanup Areas
Record of Decision Amendment - December 1997
ALTERNATIVE #1: Soil Excavation
Location of Former
High-Pressure Tanks
Location of Former
Gas Holding Tank
Johnson
Building
Delaware
State
Museum
Estimated Limit of Excavation
o>
IB
CD
New Street
ALTERNATIVE *2: Soil Excavation and Soil Vapor Extraction (SVE)
XIMIIIiUXilll
t
Approximate Area of Paving
Inside of Gas
Holding Tank to
be Excavated
Boring •
(B-19) .
Approximate
Area of SVE
Location of Former
Gas Holding Tank..
Location of Former . •* "
High-Pressure Tanks •-
New Street
Approximate Area of SVE
I
i
!
k
Johnson
Building
Delaware
State
Museum
i
CO
ALTERNATIVE 43: Modified Soil Excavation
t
Approximate Area of Paving
Boring (B-19)
Location of Former
High-Pressure Tanks
Location of Former
Gas Holding Tan
Johnson
Building
Delaware
State
Museum
Estimated Limit of Excavation
2
j£
ra
CD
New Street
-------
t
S--'£ _- F D £_-.'. - => £
*1-1 £'•* ~, - Ni-'_,=>A,_ P:;c^P-;C5
4 Esvi RCN VE*. : At. Co>.*.-=C-
DIVISION OF AIR a WASTE MANAGEMENT
: -=• -_r 89 Kings Highway
EC-D.= Dover, Delaware 19901
October 8, 1997
Abraham Ferdas, Acting Direaor (3HWOO)
Hazardous Waste Management Division
Environmental Proteaion Agency Region III
841 Chestnut Street
Philadelphia, Pennsylvania 19107
RE: Dover Gas Light Site
Proposed Plan
Dear Mr.Ferdas:
The State of Delaware concurs with EPA's revised Proposed Plan for the Dover Gas Light
Site dated August 1997. The plan calls for the following:
• Limited excavations of on-site contaminated soils.
• On site soil vapor extraaion.
• Containment of non-aqueous phase liquids in ground water.
• Monitoring of dissolved contaminants in groundwater.
If you have any questions, please do not hesitate to call me.
Sincerely,
Nicholas A. Di Pasquale
Direaor
NAD:SFJ:nm
st|97061
DE 057 I ••>
Christophe A.G. Tulou, Secretary, DNREC
N.V. Raman, Manager, DNREC
Jamie H. Rutherford, Program Manager, DNREC
Stephen F. Johnson, Project Manager, DNREC
Peter Ludzia, EPA
Randy Sturgeon, EPA
0*
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