PB94-963923
EPA/ROD/R03-94/186
November 1994
EPA Superfund
Record of Decision:
Dover Gas Light Superfund Site,
Dover, DE,
8/16/94
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EPA REGION 3
AUGUST 1994
RECORD OF DECISION
DOVER GAS LIGHT SUPERFUND SITE
DOVER, KENT COUNTY, DELAWARE
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RECORD OF DECISION
DOVER GAS LIGHT SITE
omGrrw.
(RGd)
DECLARATION.
SITE NAME AND LOCATION.
Dover Gas Light Site,
Dover, Kent County, Delaware
STATEMENT OF BASIS AND PURPOSE
This decision document presents the selected remedial action
for the Dover Gas Light Site (Site), in Dover, Kent County,
Delaware, which was chosen in accordance with the requirements of
the Comprehensive Environmental Response, Compensation, and
Liability Act of 1980 (CERCLA), as amended, 42 U.S.C. SS 9601 et
sea., an~, 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 selecting the remedy for this Site. The information
supporting this remedial action decision is contained in the
Administrative Record file for this Site.
The State of Delaware has concurred on the selected remedy.
as stated in its August 2, 1994, letter (see Attachment A of this
Record of Decision).
ASSESSMENT OF THE SITE
The Site is highly contaminated and this contamination is
mainly the result of approximately 100 years of operation of a
coal gas plant. Pursuant to duly delegated authority, I hereby
determine, pursuant to Section 106 of CERCLA, 42 U.S.C. S 9606,
that actual or threatened releases of hazardous substances from
this Site, if not addressed by implementing the response action
selected in this Record of Decision (ROD), may present an
immirient and substantial endangerment to public health, welfare,
or the environment.
DESCRIPTION OF THE SELECTED REMEDY
The selected remedy addresses both the ground water and soil
adversely impacted by the contamination at the Site. This is the
final remedy for the Site. The selected remedy for the ground
water includes hydraulic containment of an area containing non-
aqueous phase liquids (NAPLs), removal of any accessible and
pumpable NAPLs, and natural attenuation of the portion of the
plume containing only dissolved contaminants. In the future, if
EPA determines that attainment of maximum contaminant levels
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Dover Gas Liaht Superfund Site Record of D~
(MCLs) or non-zero maximum contaminant level goals (MCLGs) in the
NAPL area is technically impracticable from an engineering
perspective, then EPA will invoke the "technical
impracticability" ARAR (applicable or relevant and appropriate
requirement) waiver, to the extent required by law.
For the soil, Site-specific clean-up criteria have been
developed. Soils at the location of the former coal gas plant
that do not meet these criteria will be excavated and treated
off-site usinq commercia+ly available thermal destruction
facilities. The total 'estimated present worth cost of this
remedy is $6,000,000. .
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 (or a waiver will be justified for any Federal
and State applicable or relevant and appropriate requirements
that cannot be met); 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 reduce toxicity, mobility, or volume as their
principal element. '
Because this remedy will result in hazardous substances
remaining on-site in the ground water above health-based levels
and in soil above levels which allow for unrestricted use, CERCLA
requires that a review be conducted within five years after'
remedial action is initiated 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 clean-up levels set
forth in this ROD have been achieved, or that the hazardous
substances remaining on the Site do not prevent unlimited use and
unrestricted exposure.
~~~.
JAf Peter H. Kostmayer
~' Reg~onalAdministrator
RegJ.on III
i . /t . , y
Date
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Dover Gas Uah! Superfund Site Record of Decision
DECISION SUMMARY
SITE DESCRIPTION AND BACKGROUND
The Dover Gas Light Site is located in Kent County, .
Delaware,withinthe City of Dover, and occupies the western half
of the city block bounded by New Street, Bank Lane, Nqrth 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 period, various
buildings, gas holders, and storage areas used in the
gasification process were located on the Site.
When the plant was closed in 1948, the structures, except
for the original retort building, were demolished. Much of the
plant was removed, but sections of the tanks and other process
equipment containing coal oil, coal tar, coke, and possibly acid,.
were buried on-site. The original retort 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 itself has/ contamination, from the coal gas process
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,
the Delaware Department, of Natural Resources and Environmental
Control (DNREC) installed and sampled 16 monitoring wells on and
in the vicinity of the Site at varying depths below ground
surface. The shallow ground water at and to the southeast of the
location of the former coal gas plant was found to be
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.
The Site was subsequently proposed for inclusion on the
National Priorities List (NPL) in January 1987 and was finalized
on the NPL in October 1989. Ip July 1990, Chesapeake utilities
Corporation, a potentially responsible party (PRP) at the Site,
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Dover Gas Light Superfund Site Record of Decision
entered into an Administrative Order on Consent with EPA and
.DNREC to conduct a remedial investigation and feasibility study
(RIfFS) at the site. The purpose of the RIfFS was to determine
the nature and extent of contamination at the Site, and to
screen, develop, and evaluate potential clean-up options.
HISTORY OF OTHER ENFORCEMENT ACTIVITIES
DNREC is currently negotiating an agreement under the
State's Hazardous Substance Cleanup Act (HSCA) with Capitol
Cleaners & Launderers to perform an RIfFS that includes an
investigation of a former dry cleaning establishment that has
contributed to the ground-water contamination at the site.
DNREC's Underground Storage Tank (UST) Program directed a project
to remove underground storage tanks at this location.
, Chesapeake utilities has filed a civil action for
'contribution under CERCLA against Capitol for reimbursement of
. its costs incurred at the Site. .
HIGHLIGHTS OF COMMUNITY PARTICIPATION
Pursuant to Section 113(k) (2) (B) (i-v) of the comprehensive
Environmental Response, Compensation and Liability Act of 1980
(CERCLA), as amended 42 U.S.C. S 9613(k) (2) (B) (i-v), a Proposed
Remedial Action Plan (Proposed Plan), and its supporting
documentation, was released to the public for comment on
February 2, 1994. The notice of availability of these documents
was published in The Delaware State News and the Dover Post on
February 2, 1994. A public comment period on the,documents was
originally held from February 2, 1994 to March 4, 1994, and due
to a request, was extended to April 4, 1994. In addition, a
public meeting was held on February 17, 1994, at DNREC's
Richardson and Robbins Building. At this meeting,
representatives ,from EPA answered questions about conditions at
the site and the remedial alternatives under consideration.
Responses to the comments received during the public comment
period, including those expressed verbally at the public meeting,
are included in the Responsiveness Summary, which is part of this
Record of Decision (ROD). This ROD presents the selected
remedial action for the Dover Gas Light site in Dover, Kent
County, Delaware,chosen in accordance with CERCLA and the
National oil and Hazar~ous Substances Pollution Contingency Plan
(HCP), 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. The Administra~ve Record file is
located at the EPA Administrative Record Room in Region III's
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Dover'Gas Uatrt Superfund Site Record of Decision
Philadelphia office,at the Dover Public Library, and at the
state Library of Delaware (also located in Dover).
SUMMARY OF SITE CHARACTERISTICS,
. ,
Geoloqically, the site is underlain by the unconfined
Columbia aquifer which is composed of coarse sand and gravel with
thin, discontinuous low-permeability clay and clay/silt layers at
varying depths. The Columbia aquifer extends to approximately 58
to 65 feet below ground surface (BGS) and is underlain by the
Frederica, Cheswold, and Piney Point aquifers. These three
aquifers are separated by silty sand/clay layers that form
aquitards which inhibit downward migration of contamination in
the ground water. The City of Dover uses ,the Cheswold and Piney.
Point aquifers, the deeper of the four aquifers, for its drinking
water supply. Ground-water flow from the Site moves in a
southeasterly direction towards the st. Jones River. The water
table in the area is'generally found at 8 to 15 feet BGS.
The Dover Gas Light RI included soil and ground-water
sampling, water sampling from the Tar Branch (formerly a drainage
ditch or stream which was enclosed in a concrete culvert in the
1930's), and surface water and sediment sampling in the st. Jones
River~ An aerial photography and a historical map investigation
was performed to identify and locate features that existed at the
Site during its operation. An inventory was conducted to,
identify potential sources for ground-water and soil
contamination other than the former coal gas plant.
In order to determine the degree of hydraulic connection
between the Frederica and Cheswold aquifers beneath the Site,
aquifer tests were conducted. Prior to the RI, aquifer tests,
'were'performed to determine the hydraulic connection between the.
Columbia aquifer and the two lower aquifers. Finally, an in-
depth archaeological assessment was conducted to evaluate the
potential presence of significant cultural resources at the Site.
The soils investigation revealed that the former plant soils
are contaminated with BTEX at concentrations as high as 4,890
parts per million (ppm) and with PARs at concentrations as high
as 26,000 ppm. The highest concentrations were found in the
vicinity of former gas holders, tanks, and storage areas of the
coal gas plant and were located in the 8 to 16 foot interval BGS.
However, elevated levels of PARs and BTEX were found in one soil
sample within two feet of the surface, and low levels of PARs
were found as deep as 57 feet BGS near the bottom of the Columbia
aquifer. During soil borings, black streaks with coal tar odors
and oily substances with fuel odors were found in many borings.
Soil contamination extended approximately 800 feet from the
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Dover Gas Liaht Superfund Site Record of Decision
former plant to the east and southeast. Elevated levels of BTEX,
as high as 12 ppm, and PAHs, as high as 8,000 ppm and similar to
soil contamination at the former plant location were found
primarily in the 25 to 50 foot interval BGS. See Figure 2 for
selected soil sample results.
Ground water has been impacted by the same classes of
contaminants as the soil (i.e., BTEX and PAHs). The BTEX and PAH
contamination were found to be highest in an area which includes
the former plant and extends to the east and southeast
approximately 1,600 feet. The levels of BTEX were as high as
3,310 parts per billion (ppb) and the levels of PAHs were as
4,611 ppb at the former plant location. Away from the former
plant, the levels of BTEX were as high as 8,350 ppb and the
levels of PAHs as high as 8,330 ppb. Vertically, the ground-
water contamination has had an impact only on the Columbia
aquifer to any great extent, though very low levels of benzene
were found in two monitoring wells in the Frederica aquifer. The
clay layers within the Columbia aquifer have helped limit the
downward migration of PAHs. The Cheswold and Piney Point
aquifers below the Frederica aquifer have not been impacted by
the Site. See Figure 3 for selected ground~water sample results.
The high levels of ground-water and soil contamination plus
field observations indicate that layers of both dense non-aqueous
phase liquids (DNAPLs) and light non-aqueous phase liquids
(LNAPLs) are present. At MW-4, located at the northwest corner
of Governor's-Avenue and Water streets, an oil coating has been
observed on the inside of a well casing. Soil data from the
plant shows that a source of non-aqueous phase liquid (NAPL)
exists. The soil data and boring logs away from the plant also
indicate .the presence of a NAPL and/or neavy contamination. At
MW-6 (located just east of a former dry cleaner between
Governor's Avenue and State Street, see Figure 1), "product" was
reported in the staining section of the drilling log at 46 feet
BGS. "Moderate" odors were also reported from 46 feet BGS to 60
feet BGS. A soil sample from 45 to 57 feet BGS had approximately,
140 ppm total PAHs. Data collected between the former plant and
MW-6 indicated a continuouslayer(s) of DNAPL from the plant to
at least as far as MW-6. At MW-6, the contamination problem is
compounded by the potential presence of a tetrachloroethylene or
perchloroethylene (PCE) DNAPL (see discussion in paragraph
below). The PCE could increase the solubility and mobility of
the PAHs thus allowing the PAHs to migrate further and faster.
The investigation of contaminants associated with the former
coal gas plant (BTEX and PAHs) uncovered widespread contamination
of another class of compounds called chlorinated organic
compounds such as PCE, trichloroethene (TCE), 1,1-dichloroethene,
and 1,2-dichloroethene. In soils (but below the water ~able),
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Dover Gas Liaht Superfund Site Record of Decision
these compounds are present at concentrations as high as 32 ppm
and extend as far as 1,600 feet from the former coal gas plant
to the southeast (near Water and Federal streets). In ground
water, the chlorinated contaminants are highest (47 ppm maximum)
downgradient of the former coal gas plant at MW-6 and extend at
least 2,50'0 feet to the east near the st. Jones River (see Figure
1). The chlorinated compounds have also been detected upgradient
and to the north (hydraulically side-gradient) of the former coal
gas plant (see Figure 1). EPA has determined from data examined
to date that the former coal gas plant is not the source of this
chlorinated organic contamination. .
There are undoubtedly two or more sources of this
chlorinated organic contamination. It appears that the source of
the greatest contamination is a former dry cleaning establishment
,located at 411 South Governor's Avenue (as discussed in detail in
the "Scope and Role of the Remedial Action" section below, the
State is investigating this contamination). Both leaking
underground storage tanks (USTs) and a spill during a 1989 fire
are likely sources of the heavy chlorinated contamination in the
vicinity of MW-6. The level of PCE is high enough to indicate
the presence of a DNAPL. The dry cleaner also had several
leaking USTs which were used to store fuel oil. These USTs have
undoubtedly contributed to the BTEX and PAH contamination in the
ground water as discussed above. ,All of the tanks have been. '
emptied and removed.
Vertically, the chlorinated contamination has behaved
similar to the BTEX and PAH contamination. The clay layers
within the Columbia have helped limit the downward 'migration, but
have not completely contained it as chloririated contamination has
been detected in several Frederica aquifer wells.
SUMMARY OF SITE RISKS
A baseline risk assessment was prepared to assess the
potential human health and environmental impacts that may result
from exposure to contaminants associated with the Site in the
absence of active remediation. A risk assessment is typically
composed of two parts: (1) the human health risk assessment that
examines current and potential future threats to the public and.
(-2) 'the environmental risk assessment that examines current and
potential future threats to environmental receptors such as
plants, aquatic life, and wildlife. In order for a site to pose
a current or potential future risk to a human or environmental
receptor, a complete exposure pathway must be established. A
complete exposure pathway consists of the following components:
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Dover Gas UQht Superfund Site Record of Decision
1.
A source or mechanism for contaminants to be released
to the environment.
2.
A medium through which contaminants may be transported
such as water, soil, sediment, or air.
3.
A point of actual or potential exposure or contact for
humans or environmental receptors.
4.
A route or mechanism such as ingestion, inhalation, or
dermal contact for exposure at the contact point. .
CUrrent and potential future exposure scenarios were evaluated
for complete exposure pathways which met the above criteria.
For the environmental portion of the risk assessment, a
survey of the area near the Site showed that the only potentially
impacted environmental receptors were in the st. Jones River.
The RIfFS showed that contaminants associated with or like those
associated with the Site are not currently adversely impacting
the st. Jones River. Although contaminants (PAHs, VOCs, other
semi-volatile organic compounds, metals, and pesticides) detected
in the sediments in the st. Jones River include some which are
similar to those found at the Site, they may be attrib~ted to
other urban sources in the area. The environmental assessment
concluded that the sediments were not toxic to test organisms
and, therefore, present no threat to environmental receptors in
the St. Jones River. However, contaminants in the ground water
from the Site could migrate and then discharge into the st. Jones
River and pose a threat in the future to aquatic receptors.
For the human health portion of the risk assessment, current
and potential future exposure pathways for eight potential
receptors were evaluated. The following is a list of the
potential receptors: .
L
Adult resident living over the ground-water plume and
near the former coal gas plant
Child resident living over the ground-water plume and
near the former coal gas plant
Adult museum visitor
Child museum visitor
Worker washing a truck using contaminated ground water
Museum worker
Construction worker
utility repairman
2.
3.
4.
5.
6.
7.
8.
The representative list of receptors was developed by examining
the current and potential future activities that could occur in
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Dover Gas UQht Superfund Site Record of Decision
areas that currently are or could become contaminated by the
Site. .
Several exposure pathways were examined for most of the
above receptors. For the adult and child residents the following
pathways were examined: (1) drinking contaminated ground water,
(2) showering (for adults) or bathing (for children) with
contaminated ground water, (3) watering the lawn' with
contaminated ground water, (4) ingesting of fish from the
st. Jones River, and (5) wading in contaminated water in the
st. Jones River. Each of these pathways is a hypothetical future
pathway. CUrrently there are no private drinking water wells in
Dover near the Site, and the municipal water supply wells are not
contaminated. Exposure to Site-related contamination in the
st. Jones'River could only occur once the ground-water plume
migrates to the river. Currently Site-related contamination has,
only migrated to the vicinity of Federal Street which is two or
more blocks from the river.
For the adult and child museum visitor, exposure to
contamination in shallow soils from the location of the former
coal gas plant was examined. This exposure is a current pathway.
For the worker washing a truck, exposure to contamination from
ground water was examined. This is only a potential future.
p~thway because there is no current use of the contaminated
ground water. For the museum worker, exposure to contamination
from shallow soil contamination during a normal working day and
exposure to contamination from subsurface soils while planting
trees around the museum was examined. .
For the construction worker, exposure to contamination in
subsurface soils during construction projects both at the
location of the former coal gas plant and nearby was examined.
This is a potential future pathway only because there are
currently no subsurface construction projects in areas of
contaminated soil. For the utility repairman, exposure to
contamination in subsurface soils at the location of the former
coal gas plant during the repair of underground utilities was
examined (see Table 1 for a list of exposure assumptions).
The human health risk assessment was divided into two.
categories of impacts: carcinogenic and non-carcinogenic or .
systemic. Many contaminants cause both types of impacts.
Remedial action is generally warranted when the calculated
carcinogenic risk level exceeds lx10-4 (meaning that one .
additional person out of 10,000 is at risk of developing cancer
caused by a lifetime of exposure to contaminants at a site) under
current or future conditions for any of the evaluated exposure
scenarios. Remedial action is also generally warranted if the
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Dover Gas Liaht Superfund Site Record d Decision
calculated non-carcinogenic Hazard Index' exceeds 1.0 under
current or future conditions for any of the evaluated exposure
scenarios. The actual or potential risk is calculated by .
mUltiplying an intake factor (calculated from all of the exposure
assumptions) by a cancer potency factor or CPF2 (for carcinogenic
risks) and by a reference dose or Rf~ (for non-carcinogenic
risks) and by the concentration of each contaminant for each
exposure pathway.~
. 'The potential for health effects resulting from exposure to
non-carcinogenic compounds is estimated by comparing an estimated
dose to an acceptable level, or reference dose. If this ratio
exceeds 1.0, there is a potential health risk associated with
exposure to that chemical. The ratios can be added for exposures
to multiple contaminants. The sum, known as the Hazard.Index, is .
not a mathematical prediction of the severity of toxic effects,
but rather a numerical indicator of the transition from
acceptable to unacceptable levels.
2CPFs, also known as slope factors, have been developed by
EPA's carcinogenic Assessment Group for estimating excess
lifetime cancer risks associated with exposure to potentially
carcinogenic chemicals. CPFs, which are expressed in units of
(mg/kg~body weight/day)-', are derived from the results of human
epidemiological studies or chronic animal bioassays to which
animal-to-human extrapolation and uncertainty factors have been
applied.
3An RfD is a toxicity value used to estimate the potential
for adverse non-carcinogenic health effects. The model to .
determine RfDs from the dose-response assessment assumes that
there is a concentration for non-carcinogens below which there is
little potential for adverse health effects over a lifetime of
exposure. The RfD is designed t~ represent this threshold level.
The RfD is calculated from the highest chronic exposure level
that did not cause adverse effects (the no-observed-adverse-
effect level, or NOAEL) in animals. The NOAEL is divided by a
factor to account for any uncertainty such as using data on
animals to predict effects on humans and an allowance for
sensitive individuals. uncertainty factors range from 1 to
10,000, based on the confidence level associated with the data.
The resulting RfD (mg/kg-body weight/day) is used to quantify the
risk. .
4The concentration value used here is the 95% upper
confidence limit (UCL) for the arithmetic mean of the levels of
each contaminant found in the samples taken from the appropriate
media in each area. This particular concentration value is a
statistical estimate of the highest average concentration.
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Dover Gas Uaht Superfund Site Record of Decision
- Table 2 provides a summary of the non-carcinogenic risks,
and Table 3 provides a summary of the carcinog~nic risks. Each
table shows the separate contribution of the coal gas plant- -
related contaminants (BTEX, PAHs, and metals) and non-coal gas
plant-related contaminants (chlorinated volatile organic
compounds) as well as the total risks for all contaminants of
concern. Significant risks are or could be caused by the
chlorinated compounds alone. In general, however, any-
remediation at the Dover Gas Light Site will be triggered by
exceedances of 1x10-4 for carcinogenic risks or 1.0 for non-
carcinogenic risks for the BTEX and/or the PAHs only (the coal
gas plant- or site-related contaminants)~
The risks caused by contaminants associated with the former
coal gas plant (BTEX, PABs, and metals) exceed the acceptable
target Hazard Index of 1.0, for non-carcinogenic risks, for four
of the eight receptors that were evaluated (as shown in Table 2),
and exceed the acceptable target of 1x10-4, for carcinogenic
risks, for two of the eight receptors that were evaluated (as
shown in Table 3). For those scenarios involving the use of
ground water, the chlorinateq VOCs associated with the former dry
cleaning operation often contributed greatly to the overall risk
caused by all of the contaminants present in the ground water.
For example, the carcinogenic risks associated with the
chlorinated VOCs were two to three orders of magnitude greater
than the risks associated with the contaminants from the former
coal gas plant.
It is important to note that there are no unacceptable risks
associated with current use scenarios. All unacceptable risks
are associated with future use scenarios involving the
installation of a Columbia aquifer water supply well or
construction at the location of the former coal gas plant.
Benzene was the largest contributor to the risks caused by -
contaminants from the. former coal gas plant primarily through
exposure to ground water.
It should be noted that if the soil is never remediated and
construction takes place, the contaminated subsurface soil may
become the top soil. If this were to happen, then the risks
predicted to occur in 95 out of 100 sets of samples. The use of
the 95% UCL produces an estimate of risks for the "Reasonable
Maximum Exposure" (RME) scenario. The 95% UCL is used to account
for the fact that the actual number of samples is relatively
small to accurately predict the average. This method of
calculating risks is designed to provide a conservative estimate
and makes the underestimation of actual risks highly unlikely.
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Dover GIIS Liaht Superfund Site Record of Decision
associated with the museum worker and visitors would be
underestimated.
In conclusion, the risk assessment shows that actual or
threatened releases of hazardous substances from this Site, if
not addressed by the selected remedy, may present a current or
potential threat to public health or welfare.
SCOPE AND ROLE OF REMEDIAL ACTION
As discussed in the section above, the results of the risk
assessment showed that there are two major areas of the Site
which require remediation: (1) the soils at the location of the
former coal gas plant and (2) ground water. In general,
remediation at the Dover Gas Light Site will be triggered by
exceedances of 1xl0-4 for carcinogenic risks or 1.0 for non-
carcinogenic risks for the BTEX and/or the PAHs only (the coal
gas plant- or site-related contaminants). .
Once EPA determines from the risk assessment that remedial
action is necessary at a.site, EPA characterizes waste on-site. as
either a principal ,threat waste or a low level threat waste. The
concept of principal threat waste and low level threat waste as
developed by EPA in the NCP is applied on a site-specific basis
when characterizing source material. "Source material'" is
defined as material that includes or contains hazardous
substances, pollutants, or contaminants that acts as a reservoir
for migration of contamination to ground water, to surface water,
to air, or that acts as a source for direct exposure. Source
materials are considered to be principal threat wastes when they
contain high concentrations of toxic compounds (e.g., several
orders of magnitude above levels that allow for unrestricted use
and unlimited exposure) or are highly mobile and generally cannot
be reliably contained. .
From the results of the RI/FS, EPA considers the heavy
deposits of coal tar and NAPLs to be principal threat waste
meaning that the material includes or contains hazardous
substances, pollutants, or contaminants that acts as a reservoir
for migration of contamination to, for example, ground water.
Generally, EPA expects to use treatment to address principal
threat waste as opposed to containment.
originally, EPA proposed that the, Dover Gas Light Site
(which is defined by the BTEX and PAH soil and ground-water
contamination resulting from operation and demolition of the
former coal gas plant, see Figure 1) be addressed .in two operable
units. The first operable unit would have addressed soil
contamination at the location of the former coal gas plant and
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Dover Gas Uaht SUD8rfund Site Record of Decision
ground-water contamination within the area defined as the Site
(see Figure 1). The second operable unit would have addressed
potential soii contamination at the location of the former dry
cleaning establishment at 411 South Governor's Avenue which may
be continually contributing to ground-water contamination. The
reason the former dry cleaner became part of the Superfund
project was that although it was not included in the original
scope of the project, it would not have been possible to clean up
the ground water without addressing soil contamination at the.
former dry cleaner. .
In the. Proposed Plan, EPA stated that the goal for the
ground water was to return it to its beneficial use as drinking
water. The Proposed Plan also stated, however, that "it is
unlikely that a pump-and-treat system without enhancements could
remediate the portions of the ground water containing a DNAPL to
levels that would allow human consumption." Due to comments
received during the public comment period expressing concern
about trying to achieve a remedial goal that was likely
unachievable, especially in an aquifer that has only a very
remote possibility of being used for drinking water, EPA has
modified its goals regarding.the ground water at the Site.
Section 300.430(a) (1) (iii) of the NCP discuss EPA's
expectations for cleanups at Superfund sites. For ground water,
"EPA"' expects to return usable ground waters to their beneficial
uses wherever practicable,. wi thin a time frame that is reasonable
given the particular circumstances of the site. When restoration
of ground water to beneficial uses is not practicable, EPA
expects to prevent further migration of the plume, prevent
exposure to the contaminated ground water, and evaluate further
risk reduction." [Section 300.430(a) (1) (iii) (F) of the NCP] In
order to determine whether ground water is usable as drinking
water, EPA relies on a classification system. By applying the
"Guidelines for Ground-Water Classification under the EPA Ground-
Water Protection Strategy," EPA has determined that the Columbia
aquifer at the Dover Gas Light site is a Class IIB aquifer,
meaning that it is a potential source of drinking water. As a
result EPA's gen&ral expectation would be to return the Columbia
aquifer to a condition where it can be used as a source of
drinking water. However, EPA has determined that in the NAPL
area, due to the presence of free phase product and due to the
high number of contaminants which has driven the clean-up
criteria down (see the fOllowing section for a discussion about
the specific clean-up goals for the ground water), returning the
Columbia aquifer to a drinkable condition is not practicable.5
SOther Site-specific conditions which entered into EPA's
determination included the low yield of the aquifer, the location
11
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DoverGes Uaht Superfund Site Record of Decision
Therefore, in the NAPL area, EPA's goal is to remove as much
free-phase product as possible and to prevent the continued
migration of contaminants from the NAPL area. In the area(s) of
the plume containing only dissolved contamination, the goal
remains to return the ground water to its beneficial use.
One commenter suggested that use of the "technical
impracticability" ARAR (applicable or relevant and appropriate
requirements) waiver6 be evaluated due to the problems associated
with remediating the ground water. Although EPA has determined
that it is not practicable to return the NAPL area to drinking
water condition, it may be possible for a groundwater.
remediation system to attain most, if not all, of the Maximum
Contaminant Levels (MCLs) under the Safe Drinking Water Act,
which are ARARs, for the contaminants of concern. Listed below
are the particular MCLs that are ARARs for this Site:
benzene
toluene
styrene
xylenes
trichloroethene
tetrachloroethene (PCE)
.1,1-dichloroethene
1,2-dichloroethene
.vinyl chloride.
benzo(a) anthracene
5
1000
100
10000
5
5
7
70
2
0.1
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
of the Site in an urban area (both of which make innovative
technologies extremely difficult to implement), the low
solubility and mobility of. some of the contaminants of concern
(the PAHs) , the resistance of some of the more toxic PAHs to
bioremediation, the difficulty of detecting all of the pools of
DNAPLs, and the .poor history to date of traditional pump-and-
treat systems in remediating DNAPLs to levels safe to drink.
. 6ARARs are Federal and state environmental requirements that
a selected remedy must attain for on-site actions. The NCP
provides certain instances where ARARs may be waived. Sections
300.430(f) (1) (ii) (C) (1-6) of the NCP outline six different ARAR
waivers, including the interim measure waiver, the equivalent
standard of performance waiver, the ,greater risk to human health
and the environment waiver, the technical impracticability
waiver, the inconsistent application of state standard waiver,
and the Fund-balancing waiver. The technical impracticability
waiver may be invoked when it is not possible from an engineering
perspective to achieve the ARAR. The selected remedy must still
provide for the overall protection of human health and the
environment even if an ARAR waiver is invoked by EPA.
12
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Dover Gas LiQht SuPerfund Site Record of Decision
benzo(k)fluoranthene
benzo(a)pyrene
0.2
0.2
ppb
ppb
Some of the MCLs such as the ones for toluene and the
xylenes are high enough that, coupled with the high mobility of
the compounds, that MCLs should be attained. Others, such as the
one for PCE which is present in the ground water at extremely
high levels, will likely not be attained. However, it is EPA's .
policy not to grant "technical impracticability" ARAR waivers for
ground water without either a field demonstration (i.e., try to
remediate first) or an extensive investigation during the RIfFS
showing that MCLs can not be attained. Since the RIfFS did not
adequately address whether MCLs could be attained and since no
attempts have been made to date to remediate the plume, EPA is
not in a position to invoke the "technical impracticability" ARAR
waiver. However, in each of the ground water remediation
alternatives described in the "Summary of Remedial Alternatives"
section below, the same pump-and-treat systems would be required
whether a "technical impracticability" waiver is invoked or not.
In this ROD, EPA is selecting the final remedial action for
' this Site. The remedy will attain ground water ARARs or a waiver
will be invoked in the future through the issuance of an
Explanation of Significant Differences if attainment of ground-
water ARARs is determined by EPA to be technically impracticable.
Alternatives GW-1 to GW-4 are tne same alternatives that were
presented in the Proposed Plan except for the addition, in
Alternatives GW-2 tp GW-4, of this potential ARAR waiver and
several other minor changes. A new alternative, GW-S, has been
added in response to public comment.
D~e to the presence of the chlorinated, organic contamination
in the ground water which is no~ from the former coal gas plant,
achievement of the ground-water remediation goals for BTEX and
PAHs would not, in and of itself, return the ground water to its
beneficial use. Therefore, the chlorinated organics in the
ground water must be remediatedas well. However, since EPA is
modifying its remedial goals for the NAPL area as discussed
above, there is no need to remediate the soils of the 'former dry
cleaner as part of this Superfund project. Continued leaching of
contaminants to the ground water from this soil will not.
interfere with the remedy for this portion of the Superfund Site
(i.e., hydraulic containment of the NAPL area). However, the
. soils at the former dry cleaner may present a health ris~ and, as
discussed in the Proposed Plan, will be addressed by DNREC.
DNREC is negotiating an agreement with Capitol Cleaners &
Launderers (the owner of the South Governor's Avenue location) to
perform an RIfFS, under the State's Hazardous Substance Cleanup
Act (HSCA), of two existing or former dry cleaners that are
13
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Dover Gas Liaht Superfund Site Record at Decision
suspected of causing or contributing to the chlorinated organic
ground-water contamination.
Originally in the Proposed Plan, EPA's goal for the former
coal gas plant was to remediate the soil to such an extent as to
allow for future construction of facilities allowed by the
"Institutional & Office" zoning designation. This necessitated
the proposal of clean-up goals that would allow the construction
of a school with a playground. The Proposed Plan also
acknowledged that the Delaware state Museum is currently planning
an expansion. Soil clean-up goals that are protective of museum
workers and visitors and construction workers are not as
stringent as those necessary for the protection of children at a
school. In response to comments that the soil clean-up criteria
in the Proposed Plan were based on an unlikely future land use
and were therefore too stringent, EPA has added a new
I alternative, S-3, that has soil clean-up criteria that were
developed assuming that the only land use for the former coal gas
plant would be for the.museum expansion and a parking lot.
Alternative S-2 retains the soil clean-up criteria that allow the
former coal gas location to be used as a school.
In both of the above soil alternatives, the remediation of
the former coal gas plant must allow for future construction
which usually involves some intrusive work. Therefore,
containment of the soils "in place"(for example, by capping the
site to prevent rain water infiltration and to prevent direct
contact with contaminated soils) would not be a viable remedial
option. If the soils are only contained in place, intrusive
construction would ruin any containment structure (such as the
cap that was described in the Feasibility study) allowing the
soils to pose an unacceptable risk to human health and the.
environment.
REMEDiAL ACTiON OBJECTiVES AND CLEAN-UP GOALS
FOR GROUND WATER AND SOiL
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 Risk Assessment indicates that the carcinogenic and non-
carcinogenic risks associated with the Site exceed acceptable
levels and therefore warrant remedial action. For ground water,
Maximum Contaminant Levels (MCLs) and non-zero Maximum
Contaminant Level Goals (MCLGs) are often used as remediation
goals. At this Site, however, since there are multiple
contaminants, the cumulative carcinogenic and non-carcinogenic
future use risks associated with the MCLs and non-zero MCLGs for
the contaminants of concern exceed both 1x10-4, for carcinogenic
14
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Dover Gas Uaht SUDElrfund Site Record d Decision
risks, and 1.0, for ,non-carcinogenic risks. Therefore, at
Site EPA does not consider MCLs and non-zero MCLGs to be
protective of human health when there is a possibility of
residential consumption. Under such circumstances risk- or
health-based levels are used as remediation goals.
this
The remediation goals for the Site are as follows:
1. To restore ground water at the Site (which includes all
areas impacted by Site-related contaminants except the NAPL area)
to health-based levels (i.e., to a level where the cumulative
carcinogenic risk is 5.6x10-67 and the Hazard Index does not
exceed 1.0) through active remediation. If each of the
contaminants of concern listed below were present at a particular.
location, the individual health-based clean-up levels for each of
the compounds would be as follows:s
a. benzene 0.04 ppb
b. toluene 76 ppb
c. ethylbenzene 136 ppb
d. . xylenes 10 ppb
e. styrene 100 ppb
f. trichloroethene 0.17 ppb
g. tetrachloroethene 0.12 ppb
h. 1,1-dichloroethene 0.05 ppb
i. 1,2-dichloroethene 6 ppb
j. 1,1-dichloroethane 83. ppb
k. 1, 1, 1-trichloroethane 131 ppb
1. vinyl chloride 0.04 ppb
7In the Proposed Plan, the cumulative carcin~genic risk
remaining once the ground-water clean-up criteria were met was
4.0x10-6. . The change was caused by the addition of three
contaminants of concern (t.-v.). These contaminants where not
detected in the ground water until the Phase III study in the
summer of 1993. The data used to determine the original set of
contaminants of concern was presented in the RI report which was
.submitted in May 1993.
SAt some well locations; either some contaminants of concern
may not be present (especially the chlorinated organics) or there
may be other contaminants that are not listed (other PAHs from
coal tar or carbon disulfide which was found in soils within the
Columbia aquifer but has not yet been detected in the ground
water). At the. end of the remedial action, the cumulative risk
at each monitoring location should not exceed 5.6~10-6 (for.
carcinogenic risks) or 1.0 (for non-carcinogenic risks) for those
contaminants present at that location using a lifetime.
residential ground-water exposure scenario. .
15
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m.
n.
o.
acenaphthene
anthracene
fluoranthene
fluorene
naphthalene
pyrene
manganese
benzo(a) anthracene
benzo(k)fluoranthene
benzo (a) pyrene
Dover Gas Liaht Superfund Site Record of Decision
223 ppb
10950 ppb
149 ppb
1102, ppb
149 ppb
112 ppb
179 ppb
0.01 ppb
0.1 ppb
0.016 ppb
2. Tq prevent exposure to contaminated ground water until
the above clean-up criteria are achieved.
3. To prevent any NAPL from providing a continuing source
of contamination to non-NAPL areas of the ground water.
p.
q.
r.
s.
t.
u.
v.
4.
To remove mobile NAPLs from the ground water.
5. To prevent migration of unacceptable levels of
contamination to the Frederica aquifer.
. 6. To return the soil at tqe former coal gas plant to a
condition where (1) it can either be used consistently with its
"Institutional & Office" zoning designation .with no oth~r
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 (see Figure 4 for the area where the soil clean-up
criteria apply). Each soil alternative identifies the specific
contaminant clean-up criteria that apply to that alternative.
SUMMARY OF REMEDIAL ALTERNATIVES
The following alternatives for addressing the risks at the
site were described in detail in the Feasibility study and/or the
Administrative Record. The next section, "Evaluation of Remedial
Alternatives," will discuss the effectiveness of each of the
alternatives relative to the nine criteria established in Section
300.430(e) (9) (iii) of the NCP (See Table 4), the Site remedial
action objectives, and to each other. The alternatives have been
separated into those that address the ground water and those that
address the former plant soils. EPA's selected remedy for the
site will contain one alternative for each area.
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Dover Gas Uaht Superfund Site Record of Decision
Ground Water
Alternative GW~1
The first alternative is the "no action" alternative. Under
this alternative, the Site ground water would remain as it is.
The identification and evaluation of this alternative is required
under Section300.430(e) (6) of the NCP in order to establish a
baseline for'comparison to the other alternatives. There is no
cost associated with this alternative.
Alternative GW-2
This alternative 'involves using a pump-and-treat system to
remediate the ground water in the shortest time practicable. The
,estimated area requiring ground water remediation is shown in
Figure 1. The ground-water recovery system would be designed in
such a way that the recovery wells would have overlapping zones
of influence throughout the plume area. This would require the
installation of approximately 80 recovery wells (see Figures).
Care would be taken in determining the screen placement of the
wells to maximize the recovery of any NAPLs. Additional wells
may be required just to address NAPLs. The presence of NAPLs in
ground water makes remediation of ground water in the immediate
vicinity of the NAPL difficult. Therefore, this alternative'
would include a provision for invoking the "technical"
impracticability" ARAR waiver in the future for the portions of
the ground water plume containing NAPLs if attainment of MCLs is
determined by EPA to be technically impracticable from an
engineering perspective.
The recovered groundwater would either be (1) treated and
then discharged to the st. Jones River or to a pUblicly owned
treatment works (POTW) or (2) discharged directly to a POTW. The-
actual treatment method would be determined by EPA during the
remedial design. Factors affecting this determination include
the availability of an acceptable POTW; capacity requirements of
the POTW, whether or not the POTW could handle the contamination
and any pre-treatment requirements of the POTW. If on-site
treatment with discharge to the river is necessary, the levels of
contamination in the effluent stream would comply with the
substantive requirements qf the National Pollutant Discharge
Elimination System (NPDES) program. The treatment system may
include, but not be limited to, such unit processes as: air
stripping, biological treatment, carbon adsorption, metals
precipitation, and phase separators to remove NAPLs. Emissions
from any of the unit processes would be captured using secondary
controls such as carbon adsorption (unless the emissions posed no
threat to human health or the environment). Any necessary on- '
site ground-water treatment system would be located at the
17
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Dover Gas Liaht Superfund Site Record of Decision
location of the former coal
treatment system would have
Historical Preservation Act
S 470.
gas plant. Construction of any
meet the requirements of the National
of 1966 (NHPA), as amended 16 U.S.C.
Institutional controls are already in place which prevent
private drinking water wells from being installed in Dover. Some
of the controls m~y have to be modified to highlight that in the
NAPL area, the ground water is not potable. The cost for this
alternative would include $2,176,000 of capital costs and
operations and maintenance costs of $144,000 per year (for 30
years) for a present worth cost of $4,000,000. .
Alternative GW-3
This alternative also involves using a pump-and-treat system
to remediate the ground water. The estimated area requiring
ground water remediation is shown in Figure 1. This alternative
involves splitting the plume into two areas based on the
magnitude of contamination (see Figure 6). A line of recovery
wells would be installed at the downgradient edge of each of the
areas. The wells would be located and operated in such a way as
to prevent contaminants from each particular area from bypassing
the wells at the edge of that area. Care would betaken in
determining the screen placement of the wells to maximize the
recovery of any NAPLs. The line of wells in the middle of the
plume may require wells screened at several depths in the same
location to address NAPLs. As described in Alternative GW-2, the
"technical impracticability" ARAR waiver would be invoked for the
NAPL area in the future if attainment of MCLs is determined by
EPA to be technically impracticable from an engineering
perspective. Treatment of the recovered ground water would be
handled as described in Alternative GW-2.
This system would require approximately 20 wells.
Institutional controls are already in place which' prevent private
drinking water wells from being installed in Dover. Some of the
controls may have to modified to highlight that in the NAPL area,
. the ground water is not potable. The cost for this alternative
would include $544,000 of capital costs and operations and
maintenance costs of $54,000 per year (for 30 years) for a
present worth cost of $1,200,000.
Alternative GW-4
This alternative also involves using a pump-and-treat system
to remediate the ground water. The estimated area requiring
ground water remediation is shown in Figure 1. As with
Alternative GW-3, this alternative involves splitting the plume
into two areas based on the magnitude of contamination {see
18
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Dover Gas Liaht Superfund Site Record Or Decision
Figure 7). A line of recovery wells would be installed at the.
downgradient edge of the complete plume. This line of wells
would be located and operated in such a way as to prevent
contaminants in the Site plume from bypassing the wells. In the
area of greatest contamination (defined by the area of potential
NAPLs), several lines of recovery wells (as opposed to just one
line for this area in Alternative GW-3) would be installed to
recover the NAPLs to the maximum extent practicable (limitations
being the general difficulty of recovering NAPLs and the ability
to properly locate the wells in an urban .setting). As described
in Alternative GW-2, the "technical impracticability" ARAR waiver
would be invoked in the future for the NAPL area if attainment of
MCLs is determined by EPA to be technically impracticable from an
engineering perspective. Treatment of the recovered ground water
would be handled as described in Alternative GW-2.
The description and placement of the treatment system is the
.same as in Alternative GW-2. This system would require
approximately 35 wells. Institutional controls are already in
place which prevent private drinking water wells from being
installed in Dover. Some of the controls may have to be modified
to highlight that ground water in the NAPL area is not potable.
The cost for this alternative would include $952,000 of capital
costs and operations and maintenance costs of $76,500 per year
(for 30 years) for a present worth cost of $1,900,000. .
Alternative GW-S
This alternative involves using a combination of a pump-and-
treat system and natural attenuation to address the ground-water
contamination. The estimated area requiring ground-water
remediation is shown in Figure 1. As with Alternative GW-3, this
alternative involves splitting the plume into two areas based on
the magnitude of contamination (i.e., the presence or absence of .
NAPLs, see Figure 8).. A line of recovery wells would be
installed at the downgradient edge of the NAPL area to prevent
continued migration of contamination from the NAPL area to the
area of dissolved contamination. other wells (a combination of .
horizontal and vertical) would be installed inside the NAPL area
to withdraw any mobile free-phase product to the maximum extent
practicable (limitations being the general difficulty of
recovering NAPLs and the ability to properly locate the wells in
an urban setting). As described in Alternative GW-2, the.
"technical impracticability" ARAR waiver would be invoked in the
future for the NAPL area if attainment of MCLs is determined by
EPA to be technically impracticable from an engineering .
perspective. Treatment of the recovered ground water would be
handled as described in Alternative GW-2.. .
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Dover Gas Light Superfund Site Record of Decision
. For the portion of the plume containing only dissolved
contamination, natural attenuation would be used to return the
ground water to its beneficial use. No drinking water wells
would be allowed until the contaminant levels reached levels
considered safe to drink (the levels listed in the "Remediation
Goals" section). contaminant migration would be monitored. If
the contaminants were determined by EPA to be threatening the
river, a line of recovery wells would be installed along the
st. Jones River to prevent the plume from adversely impacting the
river. The cost for this alternative would include $1,827,000 of
capital costs and operations and maintenance costs of $70,000
year (for 30 years) fora present worth cost of $2,700,000.
Former Coal Gas Plant soils
Alternative S-1
The first alternative is the "no action" alternative. Under
this alternative, the site soils would remain as they are. The
identification and evaluation of this alternative is required
under Section 300.430(e) (6) of theNCP in order to establish a
baseline for comparison to the other alternatives. There is no
cost associated with this alternative.
Alternative 8-2
This alternative involves excavating soil that exceeds the
soil clean-up goals listed below at the location of the former
coal gas plant (see Figure 4). These criteria have been
developed with the goal being to allow any future use that
complies with the current "Institutional & Office" zoning
designation. .These clean-up levels result in a 2.1x10-6 residual
carcinogenic risk and a residual Hazard Index of 1.0 at the site
and are protective of the ground water:
a. benzene 3 ppm
b. toluene 3200 ppm
c. ethylbenzene 1560 ppm
d. xylenes 32000 ppm
e. styrene 3200 ppm
f. benzo(a) anthracene 0.33 ppm
g. benzo(b)fluoranthene 0.33 ppm
h. benzo(k)fluoranthene 1.24 ppm
i. benzo (a) pyrene 0.023 ppm
j. benzo(g,h,i)perylene 1.57 ppm
k. indeno(1,2,3-c,d)pyrene 0.33 ppm
1. naphthalene 12 ppm
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Dover Gas Uaht Superfund Site Record of Decision
Any debris that could be cleaned would be separated from the
rest of the excavated material and cleaned at the site and
disposed of on-site. All other material that fails the clean-up
criteria (including debris, soil, and coal tar sludge) would be
treated off-site and disposed of off-site. The estimated depth
of excavation would be the top of the water table in former
locations of coal gas plant equipment although the exact depth
would be determined by the clean-up criteria (excavation would
not extend below the water table).
Potential treatment technologies for cleanable debris
include sandblasting, steam cleaning, and solvent cleaning. All
other contaminated material would be disposed of in one of
several ways. Some or all ~ay be incinerated off-site, either in
a resource recovery kiln such .as a cement manufacturer where it
would become part of the product or in a hazardous waste.
incinerator. Some of the excavated soil that contains low levels
of contaminants may be landfilled, subject to EPA approval.
Clean fill would be placed in the area of excavation to return
the area to its original elevation. Crushed stone would be
placed in the sections used for parking and grass would be
planted in the other areas.
Prior to any excavation, a data recovery survey would be
performed in order to satisfy the requirements of the National
Historic Preservation Act. This survey would likely include
trenches to examine and recover information about cultural
resources that may be buried at the Site. The construction
activities associated with this alternative are expected to take
six months to complete once the remedial design is finished. The
total capital cost of this alternative is estimated to be
$4,800,000.9 There are no operation and maintenance costs
associated with this alternative, so the present worth cost of
this alternative is also $4,800,000.
Alternative 8-3
This alternative is the same as Alternative S-2 except that
the goal is to return the former coal gas plant to a condition
were 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). The clean-up criteria developed to meet this goal are
depth-dependent. For the surficial soils (defined as the top two
9The cost estimate in the Proposed Plan for this alternative
was $3,700,000. The new cost estimate is based on a revised
estimate of the amount of soil that would be excavated in this
alternative. .
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DoVer Gas Liaht Superfund Site Record of Decision
feet), criteria were set to protect the museum worker over a
career of exposure and are listed below:
a. benzene 28 ppm
b. toluene 56000 ppm
c. ethylbenzene 28000 .ppm
d. styrene 56000 ppm
e. benzo(a) anthracene 1.1 ppm
f. benzo(b)fluoranthene 1.1 ppm
g. benzo(k)fluoranthene 11 ppm
h. benzo (a) pyrene 0.11 ppm
i. benzo(g,h,i)perylene 5 ppm
j. indeno(l, 2, 3-.c,d) pyrene 1.1 ppm
k. naphthalene 11200 ppm
The residual risk associated with
for an exposure scenario assuming
museum is 1x10-6 for carcinogenic
carcinogenic risks.
the above contaminant levels
a 25-year career working at the
risks and 1.0 for non-
.For the subsurface soils (defined as below two feet)
criteria were set to protect the construction worker during a
building project and are listed below:
.a. benzene 1750 ppm'
b. toluene 28000 ppm
c. ethylbenzene 14000 ppm
d. styrene 28000 ppm
e. benzo(a) anthracene 70 ppm
f. benzo(b)fluoranthene 70 ppm
g. benzo(k)fluoranthene 695 ppm
h. benzo(a)pyrene 7 ppm
i. benzo(g,h,i)perylene 315 ppm
j. indeno(1,2,3-c,d)pyrene 70 ppm
k.. naphthalene 5600 ppm
The residual risk associated with the above contaminant levels
for a two-year construction project exposure scenario is 1x10-5
for carcinogenic risks and 1.0 for non-carcinogenic risks. These
soil clean-up levels are also protective of ground water. The
criteria would apply from the two-foot depth to the clay lens
identified during the remedial investigation that is located at
various depths ranging from 14 to 18 feet. 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 capital cost of this alternative is estimated to
be'$3,300,000. There are no operations and maintenance costs
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Dover Gas Uaht Superfund Site Record of Decision
associated with this alternative, so the present worth cost of
this alternative is also $3,300,000.
SUMMARY OF THE COMPARATIVE ANALYSIS OF ALTERNATIVES
The above alternatives were evaluated in detail to determine
which would be the most effective in achieving the goals. of
CERCLA, and in particular, aChieving the remedial action
objectives for~ the site. EPA uses nine criteria to evaluate
alternatives. These criteria are summarized in Table 4. The
first two criteria (overall protection of human health and the.
environment, compliance with ARARs) are threshold criteria. The
selected remedy 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 effectivenessi
implementabilitYi and cost) are the primary balancing criteria.
The remaining two/criteria (state and community acceptance) are
referred to as modifying ,criteria.
Overall Protection of Human Health and the Environment
For the ground water, the "no action" alternative does not
meet this threshold criteria since, if no remedial action is
taken, a person consuming water from a Columbia aquifer well in
the future would be exposed to unacceptable levels of
contamination. Since the "no action" alternative for the ground
water does not meet this threshold criteria, it will not be
considered any further.,
Alternatives GW-2, GW-3, GW-4, and GW-5 all meet this
threshold criteria. In Alternatives GW-2, GW-3, and GW-4, the
recovery systems in the dissolved portion of the plume would be
operated until the contaminant levels are reduced to levels
considered safe to consume (i.e., until the clean-up goals have
been aChieved). In Alternative GW-5, the contamination in the
dissolved portion of the plume would be allowed to attenuate
naturally to the clean-up levels. In each of the alternatives,
the portion of the recovery system in the NAPL area would be
operated in such a way as to prevent continued migration of
contamination from this area. Limits would be set for the air
and water emissions from any treatment system such that the
emissions do not pose a threat to human health or the
environment. Existing institutional controls would prevent any
exposure to the contaminated ground water while it is being
remediated. A ground-water management zone would be set up by
the state to ensure the NAPL area is never used for drinking
water. Alternatives GW-2, GW-3, and GW-4 would protect the
environment by preventing the eventual discharge of the
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Dover Gas Liaht Superfund Site Record of Decision
contaminated ground water into the st. Jones River where it could
pose a threat to aquatic receptors, as well as the public.
Alternative GW-5 would protect the environment by providing for
the possible installation of recovery wells near the st. Jones
River should contaminated ground water pose a threat to the
river.
For the soil, the "no action" alternative does not meet this
threshold criteria since, if no remedial action is taken, the
contaminated soils will (1) continue to leach contaminants to the
ground water and (2) pose an unacceptable threat to future
construction workers and building occupants. Since the "no
action" alternative for soils does not meet this threshold
criteria, it will not be considered any further. Alternatives
8-2 and 8-3 meet this threshold criteria. Through the
. combination of excavation, debris washing, backfilling with clean
fill, and off-site disposal, the soils at the former coal gas
plant location would no longer pose a threat to human health or
the environment. The area would be safe for building
construction and occupancy and would no longer adversely
contribute to ground-water contamination. since Alternative S-2
allows for unlimited. types of building occupancy, it is more
protective of human health than Alternative 8-3. Under
Alternative 8-3, the land use would be restricted to use for the
museum expansion and a parking lot or similar use. Off-site
treatment of the highly contaminated soil and debris by
incineration would permanently destroy the contaminants so they
would never pose a threat again.. Landfi11ing of the soil with
low levels of contamination would prevent exposure to the soil.
compliance with ARARs
Alternatives GW-2, GW-3, GW-4, and GW-5 each meet this
threshold criteria. However, there is the possibility that the
ground water ARARs (MCLs and non-zero MCLGs) may not be met in
the NAPL area. If EPA determines that attainment of MCLs and.
non-zero MCLGs is technically impracticable from an engineering
perspective, then EPA would invoke the "technical
impracticabi1ity~ ARAR waiver. The clean-up criteria for the
dissolved portion of the plume are at or below any MCLs or non-
zero MCLGs for the contaminants of concern. The treatment plant
would be operated in accordance with ARARs addressing air
emissions~ RCRA waste generation and storage, and discharge of
the treated ground water to the st. Jones River or a POTW. The
design of the treatment plant and the installation of wells would
also take into consideration any affected cultural resources as
required by the National Historic Preservation Act, as amended
(NHPA) . .
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Dover Gas Uaht SUDerfund Site Record of Decision
Far the sail, Alternatives S-2 and S-3 meet this threshald
criteria. The majar ARARs assaciated with these alternatives are
the NHPA, RCRA, and Delaware's Hazardaus Substance Cleanup Act
(HSCA). Many af the requirements af the NHPA were met during the
RIfFS thraugh cultural resaurce surveys. As part af each af .
these alternatives, a data recavery aperatian wauld be perf armed
at the beginning af the excavatian to. gather archaealagical
infarmatian. Same af the .sail may be RCRA-hazardaus waste due to.
leachability af benzene. If sa, an-site treatment by
stabilizatian wauld be necessary to. render the waste nan-
hazardaus depending.af the final dispasal site. If any af the
waste is cansidered a RCRA-hazardaus waste, all an-site
treatment, starage, and handling practices wauld be dane in .
accardance with RCRA. Same stabilizatian might also. be required
in Alternative S-3 because af the patential high water cantent af
same af the sail. The main requirement af HSCA as it relates to. .
this Site is that the clean-up criteria must be equal to. ar belaw
the criteria pravided by DNREC far campliance with HSCA. DNREC
has stated that the sail criteria in Alternative S-3 (and
therefare Alternative S-2 as well) meet HSCA requirements.
Long-Term Effectiveness and Permanence
Overall far the graund water, Alternatives GW-2~ GW-4, and
GW-S have the greatest degree af lang-term effectiveness and
permanence because they each call far aggressive measures t~ .
remave free-phase praduct fram the NAPL area which pases a lang-
term threat to. the rest af the Calumbia and the Frederica .
aquifers (Alternative GW-3 anly calls far cantainment af the NAPL
area). In each af the alternatives far the dissalved partian af
the plume, the Site-related cantaminants wauld no. langer pase a
threat to. human health and the enviranment ance the clean-up
criteria are achieved. Each alternative wauld likely always
require same hydraulic cantrals at the end af the NAPL area to.
prevent the spread af cantaminatian. Lacal laws and DNREC's well
permitting pragram will prevent drinking water wells frambeing
installed in areas af cantaminated graund water. The residual
risk ance the clean-up criteria are met wauld be S.6xlO-6 far
carcinagenic risks and 1.0 far nan-carcinagenic risks.' .
. Far the sail, Alternatives S-2 and S-3 rank well in terms af
lang-term effectiveness and permanence. Alternative S-2 wauld
return the praperty to. unrestricted "Institutianal & Office".use
(the land's current zaning designatian). Since the clean-up
requirements far an area zaned "Insti tutianal & Off ice" (1. e. ,
cauld be used far a schaal) are the same. as an area zaned
"Residential," there is no. need to. prevent future use as
residential praperty althaugh this is highly unlikely since,
amang ather reasans, the State is cansidering plans to. expand the
museum. The residual risk ance the clean-up criteria are met
25
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. DOver Gas UQht SUPerfund Site Record of Decision
would be 2.~x~0-6 for carcinogenic risks and 1.0 for non-
carcinogenic.risks for Alternative S-2 (assuming a residentiai
exposure scenario).
Although not providing for unrestricted land use,
Alternative S-3 would allow the land to be used as currently
planned (museum expansion and/or a parking lot). Although
allowable under the zoning designation, the chances that a school
would be built at this location are very remote meaning that.
Alternative .S-3 still provides a good degree of long-term
effectiveness for protection of human health. The residual risk
once the clean-up criteria under Alternative S-3 are met would be
1x10-6 for carcinogenic risks and 1.0 for non-carcinogenic risk
(assuming the museum worker scenario).
In each alternative institutional controls would be
necessary to prevent subsurface contamination from being brought
to and remaining on the surface after a construction project.
This is especially true for Alternative S-3, where the soil below
two feet can not remain on the surface after a construction
project.
Reduction of Toxicity, MObility, or Volume Through Treatment
For the ground water, Alternatives GW-2, GW-3, GW-4, and
GW-S each offer a significant reduction of toxicity, mobility and
volume through treatment, but the degree of reduction varies.
Alternatives GW-2, GW-4, and GW-S provide the greatest reduction
because they remove any mobile NAPLs which represent the greatest
volume of contaminant, the highest level of contamination (i.e.,
the most toxic), and the part of the contamination most likely to
migrate significantly into the Frederica aquifer. In Alternative
GW-3, dense NAPLs could migrate downward and threaten the
Frederica aquifer since this alternative only requires horizontal.
containment of the NAPLarea. The use .of emission controls (if
such equipment is necessary to protect human health and the
environment) and NAPL separation equipment would allow the
. capture and permanent destruction or containment of the
contaminants.
For the soil, both Alternatives 5-2 and S-3 offer a large
reduction of toxicity, mobility, and volume through treatment.
By removing the contaminated soil from the site, the mobility of
the contaminants would be greatly reduced. This is a significant
step in helping remediate the ground water since it will
eliminate one major source of contamination. Overall,
Alternative S-3 provides a greater reduction because, although
the clean-up criteria are higher, the depth of excavation may be
greater (to a clay lens in the upper portion of the Columbia
aquifer) potentially allowing a removal of a much larger mass of
26
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Dover Gas Uaht Superfund Site Record of Decision
contaminants. The toxicity 'and the volume of contaminated
material would be greatly reduced in both alternatives through
the use of off-site incineration. Incineration is an effective
technology for destroying the type of contaminants found at the
site. If a cement kiln is used to incinerate the waste, the soil
would be incorporated into the final product so that there would
not be a final' waste stream requiring disposal.
Short-Term Effectiveness
For the ground water, Alternative GW~5 ranks the best in
term~ of short-term impacts because it is the only alternative
that would not require recovery wells to be installed along
Federal street which is a major street in Dover. Construction
along Federal street would cause major disruptions to traffic and
businesses and would have to be scheduled around several parades
that are yearly events in Dover., Alternative GW-2 ranks the
worst because it would require the greatest number of recovery
wells to be installed. The greater the number of wells that are
drilled, the more significant the impact would be to the local
community since this is a~ urban area~ Also, due to the
historical significance of the area, the more wells required, the
greater the possibility of disturbing cultural resources.
In terms of the time frame -necessary to reach the
remediation goals, Alternative GW-2 would be the fastest and
Alternatives GW-3, GW-4, and GW-S would be the slowest. Although
Alternatives GW-3 and GW-4 would require active pumping of the'
dissolved portion of the plume, compared to natural attenuation
for Alternative GW-S, they may not remediate the ground water
much faster than Alternative GW-S because the withdrawal rate
would be approximately equal to the regional flow rate. Due to
the fact that the Columbia aquifer underneat~ this area of Dover
will probably never be used for drinking water purposes anyway,
the difference in the time-frames necessary to meet the ground-
water clean-up goals is not a significant factor.. .
In each of the alternatives, the local community would be
. protected during the remedial action by properly blocking off
streets and sidewalks during well installation and by the use of
emission controls during the operation of the ground-water
treatment equipment (if such equipment is necessary to protect
human health and the environment). .
For the soil, Alternatives S-2 and S-3 would have moderate
short-term impacts. The possibility exists for the release of
volatile organic compounds during the excavation. Measures would
be taken to ensure the protection of the workers and the local
community. A health and safety plan for the workers would be
Written prior to any excavation to evaluate the type of personal
27
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I
DOver Gas Light Superfund Site Record of Decision
protective equipment that will be required to perform the
excavation. Air monitoring and emergency contingency plaris are
examples of the types of measures that could be used to protect
the local community. The parking lot will be closed during the
excavation. Engineering controls might be necessary to protect
the museum and cemetery during excavation.
ImplemeD~abili~y
. ,
Each of the ground water alternatives is implementable since
the necessary equipment and contractors are readily available.
Alternative GW-5 is by far the easiest to implement because it
~ould not involve installation of wells along Federal street.
Wells along Federal street would require the most coordination
with the City of Dover and the state. Alternative GW-3 is the
next easiest to implement, then Alternative GW-4, and then
Alternative GW-2 with the determining factor being. the number of
wells required. However, each alternative would require
extensive planning because of the construction in an urban
environment. Impacts to businesses, traffic, utility locations,
property access, and cultural resource concerns are examples of
the things that will increase the difficulty in implementing any
of the ground. water alternatives. Due to the urban setting, it
is questionable if Alternative GW-2 is even implementable because
building locations may prevent the proper spacing of wells to get
complete coverage of the plume. The location of utilities, and
cultural resources may also limit the placement of wells.
For the soil, both Alternatives S-2 and S-3 are
implementable. Alternative S-3 would be the easiest to implement
because of the smaller volume of soil to be excavated. The
reduced volume would make it easier to .conduct excavations since
the area to be excavated is surrounded by streets, a cemetery,
and the museum. Precautions can be taken to ensure the safety of
workers and the local community in either case. Excavation and
archaeological services are obtainable. Facilities exist for the
treatment of the excavated material.
Cos~
, For the ground water, the present worth costs for
A).ternatives GW-2, GW-3, GW-4, and GW-5 are $4,000,000,
$1,200,000, $1,900,000, and $2,700,000, respectively. The
present worth cost for each of these alternatives include
significant operational and maintenance costs due to the length
of pumping time required. It should be noted that although the
cost estimate for Alternative GW-5 is higher than that for
Alternative GW-4, it involves less work than Alternative GW-4.
Both involve NAPLrecovery, but Alternative GW-4 includes wells
along Federal street that are not part of Alternative GW-5.
28
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Dover Gas U"ht Superfund Site Record of Decision
Alternative GW-5 was developed in response to public comments,
and therefore the cost estimate was not performed at the same
time as the others. Alternative GW-5 contains a more reliable
cost estimate for the recovery of the NAPLs.
For,the soil, the cost of excavation and disposal under
Alternative S-2 is $4,800,000, and the cost under Alternative S-3
is $3,300,000.
state Acceptance
The State's preferred alternatives are Alternatives S-3 'and
GW-5. For the Site soils, the State believes that the proposed
clean-up levels are consistent with the foreseeable use of the
Site and are protective of individuals most exposed to the Site.
For the ground water, Alternative GW-5 is preferred to the other
four alternatives as best balancing the environmental benefits of
improving the ground water and the environmental risks involved
in wide-scale disruption of human activities, traffic, utilities,
and cultural resources. Alternative GW-5 is protective of human
health and is thought to be as protective of the st. Jones River
as are the other alternatives. The State and community are
concerned that the design of the treatment plant be in keeping
with the historical and aesthetic nature of the neighborhood.
community Acceptance
Overall, since the development of Alternatives GW-5 and S-3
were based significantly upon the comments received during the
extended public comment period, EPA believes that the selection
. of these two alternatives as the overall selected remedy is
supported by the community.
SELECTED REMEDY
Based on an evaluation of the alternatives using the nine
criteria identified above, EPA has selected a combination of
Alternative GW-5 for the ground water and Alternative S-3 for the
soil as the remedy at this site. The "no action" alternative for
either media does not protect human health and the environment
which is one of the threshold criteria and, therefore, can not be
selected. .
For the ground water, Alternative GW-5 provides for overall
protection of human health because it prevents human exposure to .
unacceptable levels of contamination through a combination of
remediation and institutional controls. It provides for overall
protection of the environment by preventing the ground water
29
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Dover Gas Uaht Superfund Site Record of Decision
cont~mination from the Site from ever causing an adverse impact
to the river.
Alternative GW-5 complies with ARARs with the possible
exception of the ground water ARARs (MCLs and non-zero MCLGs).
As noted previously, if it is determined by EPA, that the ground
water ARARs can not be achieved in the NAPL area, EPA will invoke
the "technical impracticability" waiver by issuing an Explanation
of Significant Differences (ESD). The clean-up criteria for the
dissolved portion of the plume are at or below any MCLs or non-
zero MCLGs for the contaminants of concern. The treatment plant
would be operated in accordance with ARARs addressing air
emissions, RCRA waste generation and storage, and NPDES
requirements for the discharge of the treated ground water to the
st. Jones River or a POTW. The design of the treatment plant
would also take into consideration any affected cultural
resources as required by the National Historic Preservation Act,
. as amended.
Alternative GW-5 has' the greatest degree of long-term
effectiveness and permanence.because.it calls for aggressive
measures to remove free-phase product from the NAPL area which
poses a long-term threat to the rest of the Columbia and the
Frederica aquifers. Alternative GW-5 ranks among the highest in
terms of reduction of toxicity, mobility, and volume through.
treatment because it calls for the removal of any NAPLs which
represent the greatest'volume of contaminant, the highest level
of contamination (i.e., the most toxic), and the part of the
contamination mQst likely to migrate significantly into the
Frederica aquifer.
'"
Alternative GW-5 ranks the best in terms of short-term
impacts and implementability because it is the only alternative
that would not require recovery wells to be installed along
Federal Street which is a major street in Dover. The total
present worth of Alternative GW-5 is $2,700,000, and it ranks
third in terms of cost (however, the actual cost differences
between Alternatives GW-2, GW-3, and GW-5 are likely smaller than
previously discussed because of hidden costs in Alternatives GW-2
and GW-3 likely associated with installation of wells along
Federal Street). The State favors the selection of Alternative
GW-5. Although Alternative GW-5 was not in the Proposed Plan and
therefore has not been commented on by the public, it was
developed in response to comments received from the public and is
therefore judged to be the most favorable. in terms of community
acceptance. One major advantage Alternative GW-5 has for the
local community is that it would not require wells along Federal
Street and offers the greatest opportunity not to require a
permanent treatment plant that would occupy land that could be
available for other purposes. Therefore, EPA has determined that
30
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Do~er Gas L.iQht Superfund Site Record of Decision
it is the best alternative for addressing the ground-water
contamination at the Dover Gas Light Superfund Site.
For the soil, Alternative S-3 provides for overall
protection of human health and the environment by reducing s01l
contamination to levels considered safe for the expected land use
and by removing a major source of. continued ground-water
contamination. Alternative S-3 also complies with ARARs.
Alternative S-3 ranks best in terms of reduction of toxicity,
mobility, or volume through treatment, implementability, and cost
and is comparable to Alternative S-2 in terms of short- and long-
term effectiveness. Alternative S-3 has the support of the State
because the soil clean-up criteri~ are based on the most
realistic future land use. Although not in the Proposed Plan,
Alternative S-3 is judged to be supported by the community
because of its lower cost and its smaller potential for impacts
to the mU$eum and the cemetery during construction.
In summary, EPA's selected remedy for the Dover Gas Light
Superfund Site addresses the former coal gas plant soils and the
ground water and involves installing one line of ground-water
recovery wells at the downgradient edge of the NAPL contamination
and other recovery wells within the NAPL area to remove mobile
NAPLs, pumping and treating the ground-water; allowing the.
portion of the ground-water plume that only contains dissolved
contamination to naturally attenuate 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.
Recovery of cultural resource information buried at the former
coal gas plant likely involving excavation of several trenches
would take place prior to complete excavation. The total present
worth cost of EPA's selected remedy is $6,OOO,OOO~
SELECTED REMEDY:
PERFORMANCE STANDARDS
1.
GROUND WATER
1.1.
NAPL Area
1.1.1. A line' of ground-water recovery wells shall be
installed at the downgradient.edge of the area of the plume
containing NAPLs. These we~ls shall be installed and operated in
such a way as to prevent any passage of contamination (either
dissolved or free phase) from the NAPL area. This may require
wells screened at several depths.
1.1.2. These wells shall continue to operate until any
ground water that would migrate from the NAPL area once the wells
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Dever Gas UQht Superfund Site Record of Decision
were turned off has contaminant levels below the ground-water
clean-up criteria as described in Performance Standard 1.3.1.
1.1.3. Between the line of wells called for in Performance
Standard 1.1.1 and the location of the former coal gas plant,
wells shall be installed to remove any NAPL (dense or light) to
the maximum extent practicable given the hydrogeology of the
Columbia aquifer and accessibility to the aquifer. Both
horizontal and vertical wells shall be considered in the remedial
design. No innovative technologies sh~ll be required.
1.1.4. The remedial design shall include an investigation
to further define the extent of any NAPLs in order for the
recovery system to be designed to remove mobile NAPLs to the
maximum extent practicable.
1.1.5. All extracted ground water shall be treated and
discharged to the st. Jones River (or if determined by EPA during
the remedial design to be acceptable, the treated ground water
may be discharged to a publicly owned treatment works (POTW).
This treatment shall include removing all contaminants (metals
and organics, including NAPLs) necessary to meet all discharge
requirements (especially compliance with the substantive
requirements of a National Pollution Discharge Elimination System
[NPDES] permit if discharging to the st. Jones River). If an air
stripper or other vented system is used to treat the ground
water, secondary controls will be necessary in order to comply
with Federal and state air ARARs (see Table 5) if the emissions
exceed the specified amounts in these ARARs. Secondary controls
will also be install,ed if necessary to ensure protectiveness of
human health and the environment (for protection of human health,
secondary emission controls shall be installed if the emissions
from the air stripper cause a greater than 1x10-6excess cancer
risk). It is anticipated that the treatment sludges wil~ be
hazardous waste. Disposal of any treatment sludges or other
wastes including any recovered NAPLs shall be in accordance with
appropriate Federal and state regulations.
1.1.6. The wells described in Performance Standard 1.1.3
shall operate until all recoverable NAPL has been removed from
the Columbia aquifer. The remedial design ,shall include an
operating plan, to be approved by EPA, for the NAPL recovery
wells that discusses such things as the mode of operation (such
as pulsed pumping), monitoring frequency, and methods for
determining the extent of NAPL recovery.
1.2
Area'of Dissolved contamination
1.2.1. The ground-water plume downgradient or side-gradient
of the line of recovery wells described in Performance Standard
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Dover Gas Light Superfund Site Record of Decision
1.1.1 that only contains dissolved contamination shall be allowed
to attenuate naturally to the clean-up criteria described in
Performance Standard 1.3.1.
1.2.2. The remedial design shall include the development of
a ground-water monitoring plan, to be approved by EPA, which
shall describe the sampling of monitoring wells (and installation
if current well locations are not adequate) to monitor the extent
of contamination and the rate of attenuation. The plume shall be
considered clean when twelve consecutive quarters of sampling
results are at or below the criteria listed in Performance
Standard 1.3.1.
1.2.3. The remedial design shall include the development of
ground-water criteria which protect ,human and environmental
receptors in the St. Jones River from exposure to contaminants in
ground water discharging to the river. If the plume does not
attenuate to these levels prior to reaching the river,10 recovery
wells shall be installed near the river to prevent discharge of
ground water containing contamination above these criteria into
the river.11 These well(s) shall operate until the ground-water
near the river is below the criteria to be developed per this
Performance Standard. Any recovered ground water shall be
treated as discussed in Performance Standard 1.1.5.
1.3. Ground-water Clean-up Criteria
1.3.1. Below are the ground-water clean-up criteria for the
Dover Gas Light Superfund Site. These criteria apply to the
complete Site except the NAPL area. The criteria are:
a. benzene 0.04 ppb
b. toluene 76 ppb
c. ethy Ibenzene 136 ppb
d. xylenes 10 ppb
e. styrene 100 ppb
f. trichloroethene 0.17 ppb
10Note that these criteria only need to be developed for
contaminants related to the former coal gas plant and not for any
chlorinated organic contaminants.
11Only contamination from the Dover Gas Light Superfund Site
ground-water plume (currently estimated to extend from the former
coal gas plant to Federal Street) could trigger the criteria to
be developed in this Performance Standard. Similar contamination
from sources that EPA determines are not part of this plume would
not trigger the installation of recovery wells at the river under
this ROD.
33
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2.
SOIL
2.1
g.
h.
tetrachloroethene
1,1-dichloroethene
1,2-dichloroethene
1,1-dichloroethane
1,1,1-trichloroethane
vinyl chloride
acenaphthene
anthracene
fluoranthene
fluorene
naphthalene
pyrene
manganese
benzo(a) anthracene
benzo(k)fluoranthene
benzo(a)pyrene
Dover Gas Licht Superfund Site Record d Decision
0.12
0.05
6
83
131
0.04
223
10950
149
1102
149
112
179
0.01
0.1
0.016
ppb
ppb
ppb
ppb
ppb
ppb"
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
ppb
i.
j.
k.
1.
m.
n.
o.
p.
q.
'r.
s.
t.
u.
v.
soil Excavation
2.1.1. All soil in the area shown in Figure 4 that contains
contaminant levels above those listed in Performance standard 2.4
shall be excavated.
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. '
2.1.5. A statistically significant number of confirmatory
soil samples shall be collected to indicate that the soil'
remaining in the bottom (unless the excavation has already
extended to the clay lens located at a depth of 14 to 20 feet)
and sides of the excavation is below the contaminant levels in
Performance standard 2.4.
2.1.6. Any trees or scrubs that are removed or destroyed as
a result of the excavation shall be replaced with a similar type.
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Dover Gas Light Superfund Site Record of Decision
2.1.7. The area that is currently used as a parking lot
shall be returned to use as a parking lot. Gravel shall be
placed on the top of any backfilled areas of the original parking
lot. Areas of grass that were destroyed by the remedial action
shall be resodded.
2.2. Soil Handling and Disposal
2.2.1. Any soil that is excavated but has contaminant
levels below the clean-up criteria listed in Performance Standard
2.4 can be used as backfill material. However, any soil used to
backfill the top two feet must meet the criteria listed in
Performance Standard 2.4.2.
2.2.2. Any excavated soil that can be used as backfill may
be stockpiled at or near the Site.
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
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 landfill shall be determined during remedial
design 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 Superfund Site.
Residue or waste from any debris cleaning operation shall be
disposed of off-site in accordance'with all appropriate Federal
and State regulations.
2.3. 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.
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Dover Gas Liaht SuPerfund Site Record of Decision
2.4.
Soil Clean-up Criteria
2.4.1. Below are 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 1750 ppm
b. toluene 28000 ppm
c. ethylbenzene 14000 ppm
d. styrene 28000 ppm
e. benzo(a) anthracene 70 ppm
f. benzo(b)fluoranthene 70 ppm
g. benzo(k)fluoranthene 695 ppm
h. benzo(a)pyrene 7 ppm
i. benzo(g,h,i)perylene 315 ppm
j. indeno(1,2,3-c,d)pyrene 70 ppm
k. naphthalene 5600 ppm
2.4.2. Below are the soil clean-up criteria that apply to
the soil from the ground surface to a depth of two feet below
ground surface:
a. benzene 28 ppm
b. toluene 56000 ppm
c. . ethylbenzene 28000 ppm
d. styrene 56000 ppm
e. benzo(a) anthracene 1.1 . ppm
f. benzo(b)fluoranthene 1.1 ppm
g. benzo(k)fluoranthene 11 ppm
h. benzo(a)pyrene 0.11 ppm
i. benzo(g,h,i)perylene 5 ppm
j. indeno(1,2,3-c,d)pyrene 1.1 ppm
k. naphthalene 11200 ppm
2.5. Institutional Controls
2.5.1. A ground-water management zone shall be established
that encompasses both the Columbia and the Frederica aquifer in
any area of the Site that has ground water contaminant levels
above those listed in Performance Standard 1.3.1 plus an adequate
safety zone.
2.5.2. No industrial, agricultural, public drinking water
supply or other wells shall be installed in the Frederica aquifer
in a location such that it may increase the migration of Site.
contamination from the Columbia aquifer.
36
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Dover Gas Light Superfund Site Record of Decision
2.5.3. The deed(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
of releases of hazardous substances have affected the respective
parcels. Notice shall also be placed on the deed(s) 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 unexcavated, yet contaminated, subsurface soil does
not become surface soil.
3. OTHER MISCELLANEOUS PERFORMANCE STANDARDS
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.
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.
37
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Dever Gas Liaht Superfund Site Record of Decision
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 5,
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.
Particulate Air Emissions
'3.3.1. All remedial work shall be done in such a manner as
to minimize transport of airborne particulate emissions. .
3.3.2. As part of the remedial action health and safety
plan, levels of particulate cons1dered to pose an unacceptable
health risk shall be developed along with monitoring requirements
to measure particulate 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
particulate counts are high enough that EPA concludes that
~nacceptable health risks are posed to people on-site or off-
site, appropriate measures shall be taken to reduce the .
particulate count to safe levels off-site, and either to reduce
the particulate 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.
~s
3.5.1. The selected remedy shall attain, at a minimum, all
chemical, location, and action specific ARARs listed in Table 5
unless a statutory waiver is invoked by EPA.
38
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Dover Gas Light Superfund Site Record of Decision
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. S 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 (ARARs) environmental
standards established under Federal and state environmental laws
unless a statutory waiver is invoked. The selected remedy also
must 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 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:
1. Excavating and removing contaminated soils that pose a
threat to construction workers and possibly museum workers once a
, construction project was completed. ..
2. Returning a portion of the Columbia aquifer to a quality
where it no longer poses a threat to human health. ..
3. Removing highly concentrated levels of contamination
from the ground water to significantly reduce the possibility of
the Frederica aquifer becoming contaminated and thereby unusable
as a drinking water source. .
4. Preventing any drinking water wells from being installed
in areas that have not attained the ground-water clean-up
criteria. ' .
The selected remedy will protect the environm~nt by:
,1. Preventing levels of contaminants from the former coal
gas plant that would pose threat to aquatic life from' entering
the st. Jones River.
2. By remediating the ground water (as described above), a.
natural resource.
39
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Dover Gas Llaht Superfund Site Record of Decision
COMPLIANCE WITH APPLICABLE OR RELEVANT AND APPROPRIATE
REOUIREMENTS
The selected remedy, a combination of Alternative GW-5 and
Alternative S-3, shall attain all action, location, and chemical
specific applicable or relevant and appropriate requirements for
the Site which are listed in Table 5 unless waived by EPA. Also
included in the table are criteria, advisories, or guidance to be
considered (TBCs) for the ~mplementation of this remedy.
Several of the ARARs in Table 5 merit further discussion.
First, for the NAPL area, the selected remedy will attain ground
water ARARs (MCLs or non-zero MCLGs) or EPA will invoke the
"technical impracticability" ARAR waiver if EPA determines from
data collected. during the remediation that it is technically
impracticable to meet these requirements.
Second, the substantive requirements of the National
Historic Preservation Act, as amended, shall be met during the
'remedial action through the consideration of how the selected
remedy adversely affects cultural resources that are included or
eligible for inclusion on the National Register of Historic
Places. The soil excavation, well drilling, 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
Of the alternatives that offer adequate protection of human
health and the environment, the selected remedy is the among the
least costly. It also meets all other requirements. of CERCLA and
affords overall effectiveness proportionate to the cost. For the
soil, cost was. a major factor in selecting the remedy.
UTILIZATION OF PERMANENT SOLUTIONS AND ALTERNATIVE TREATMENT
TECHNOLOGIES TO THE MAXIMUM EXTENT PRACTICABLE
Of those alternatives that are protective of human health
and the environment, EPA has determined that the selected remedy
provides the best tradeoff 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.
40
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Dover Gas tight Superfund Site Record of Decision
From the results of the RI/FS, 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 acts 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. The NAPLs are being removed from the
ground water with the extracted ground water undergoing
treatment.
DOCUMENTATION OF SIGNIFICANT CHANGES
Section 117(b) of CERCLA, 42 U.S.C. § 9617(b), requires an
explanation of any significant changes from the preferred
alternative originally presented in the Proposed Plan. The
selected remedy described in this ROD contains a number of
significant-changes from EPA's preferred alternative in the
Proposed Plan. The changes were made in response to comments on
the Proposed Plan and consultations with the State of Delaware.
The major changes are described below:
1. In response to public comments expressing concern about
the fact that EPA's proposed remedy would not meet the goal of
returning the area of NAPLs to drinking water quality, EPA has
added the potential for the "technical impracticability" ARAR
waiver to be invoked (for the NAPL area only) if it becomes
apparent that the pump-and-treat systems described in each of the
ground-water alternatives cannot attain ARARs in the NAPL area.
2. In response to public comments, the selected remedy
includes natural attenuation of the dissolved portion of the
ground-water plume and aggressively attacking the free-phase
product layers in the NAPL area. This prevents wells from being
installed along Federal Street, offers greater protection for the
Frederica aquifer, offers the greatest potential for not having a
permanent treatment plant, and uses the wells that are to be
installed to remove the greatest mass of contaminants.
3. In response to concerns about the soil clean-up criteria
in the Proposed Plan being based on a residential exposure
scenario (since the area is zoned such that a school could be
built at the location of the former coal gas plant), EPA has
modified the criteria. The soil clean-up criteria in the
selected remedy are based on a combination of exposure to soils
during a construction project and long-term exposure while
working at the museum. Institutional controls regulating the
41
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Dover GelS Liaht Superfund Site Record of Decision
land use have also been added to the selected remedy to prevent
use of the land in ways for which the criteria would not be
protective.
4. The soil clean-up criteria have been modified to
to soil down to a clay lens approximately four feet below
water table rather than just to the water table. 'This is
remove NAPL material and protect the ground water.
apply
the
to help
5. The carcinogenic and non-carcinogenic risk values for
the lawn watering and truck washing scenarios have been lowered
due to an error in the numbers reported in the Proposed Plan.
This change did not affect the remedial action objectives or the
selected remedy.
42
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TABLE 1
EXPOSURE ASSUMPTIONS FOR RISK ASSESSMENT
POTENTIAL RECEPTORS
Adult Resident
Drinking ground water
Showering with ground water
Wading in the Si Jones River*
Eating fish from the St Jones
Lawn watering*
Child Resident
Drinking ground water
Bathing with ground water*
Wading in the St Jones River*
Eating fish from the St Jones
Lawn watering*
Washing a truck*
Adult Museum Visitor
Child Museum Visitor
Museum Worker: Normal daily
activity
Museum Worker: Tree planting .
Construction worker: Project at
coal gas location
Construction worker: Nearby
project
Utility repairman
Exposure
Time
(hours/day)
N/A
0.34
2
N/A
0.2
N/A
0.34
2
N/A
0.2
1
2
2
8
8
8
8
8
Exposure
Frequency
(days/year)
350
350
24
350
20
350,
350
24
350
20
25
1
1
250
1
250
250
250
Exposure
Duration
. (years)
24
24
24
24
24
6
6
6
6
6
25
5
5
25
25
2
2
2
Inhalation Rate
(cubic
meters/hour)
N/A
0.83
N/A
N/A
0.83
N/A
N/A
N/A
N/A
0.625
0.83
0.83
0.625
0.83
0.83
0.83
N/A
N/A
Ingestion Rate
(milligrams of
soil/day unless
noted otherwise)
2 liter/day
N/A
N/A
54 grams of
fish/day
N/A
1 liter/day
N/A
N/A
35 grams of
fish/day
N/A
N/A
100
200
100
100
100
100
50
*The risk assessment included dermal exposure as well.
-------
TABLE 2
NON-CARCINOGENIC RISK SUMMARY
HAZARD INDEX FOR HAZARD INDEX FOR TOTAL HAZARD INDEX
POTENTIAL RECEPTORS BTEX. PAHs, METALS CHLORINATED VOCs FOR ALL CONTAMINANTS
(Site-tel8led (Non-Site-tel8led
contaminants) contaminants)
Adult Resident
Drinking ground water 23 71. 94.
Showering with ground water 127 0.55 127.
Wading In the St. Jones River 0.0012 0.019 0.02
Eating fish from the St. Jones 0.15 0.44 0.59
Lawn watering 0.57 0.94 1.5
TOTAL 151 73. 224
Child Resident I
Drinking.ground water 54 165 219
BathIng with ground water 66 . 107 173
.
Wading In the St. Jones River 0.0011 0.016 0.017
Eating fish from the St. Jones 0.45 1.3 1.8
l.awtI watering 0.44 4.4 4.8
TOTAL ' 121 278 399
Washing a truck-TOTAL 1.6 0.94 2.5
Adult Museum VISitor-TOTAL 0.04 0.0 0.04
Child Museum VISitor-TOTAL 0.13 0.0 0.13
Museum Worker
Normal daily ectivity 0.18 0.0 0.18
Tree pI8nIIng 0.0062 0.0 0.0062
TOTAL 0.18 0.0 0.18
Construction worker
Project at coal gas location 7.8 0.0 7.8
Nearby project 0.0 0.0 0.0
TOTAL 7.8 0.0 7.8
Utility repairman-TOTAL 0.0 0.0 0.0
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TABLE 3
CARCINOGENIC RISK SUMMARY
POTENTIAL RECEPTORS
Adult Resident
Drinking ground water
Showering with ground water
Wading in the St Jones River
Eating fish from the St Jones
Lawn watering
TOTAL
Child Resident
Drinking ground water
Bathing with ground water
Wading in the St Jones River
Eating fish from the St Jones
Lawn watering
TOTAL
Washing a truck-TOTAL
Adult Museum Visitor-TOTAL
Child Museum Vfertor-TOTAL
Museum Worker
Normal daily activity
Tree planting
TOTAL
Construction worker
Project at coal gas location
Nearby project
TOTAL
Uility repairman-TOTAL
RISKS FOR BTEX.
PAHs, METALS (Site-
related contaminants)
9.2X105
1.7x10-4
22x108
6.8x10-6
3.0x10-7
2.7x10-4
5.4x105
8.5x10-6
4.8x10-9 '
5.2x106
3.6x10-7
6.8x1O5
9.5x105
5.6x10-8
4.5x107
2.1x106
6.4x107
Z7X1O6
9.1x104
Z5X1O6
9.1x104
1.3x106
RISKS FOR CHLORINATED
VOCs (Non-Site-related
contaminants)
2.8x102
a 2x1 02
3.6x1O6
8.1x105
1.6x104
5.0x102
1.6x102
5.2x103
7.9x1 07
6.1x105
2.2x104
2.2x1 02
4.0X1O2
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
0.0
TOTAL CARCINOGENIC
RISKS FOR ALL
CONTAMINANTS
28x102
22x102
3.6x106
8.8x105
1.8x104
5.0x102
1.6x102
5.2x103
7.9x107
6.6x105
2.2x104
22x102
4.0x102
5.6x108
4.5x107
21x106
6.4x107
27x106
9.1x104
27x106
9.1x10-4
1.3x106
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. TABLE 4
EPA CRITERIA FOR EVALUATING ALTERNATIVES
Threshold Criteria
. Overall Protection of Human Health and the Environment:
Describes how the alternative, as a whol~, achieves and maintains
protection of human health and th~ environment, and how risks
posed through each pathway are eliminated, reduced, or controlled
through treatment, engineering controls, or institutional
controls.
. Compliance with ARARs: Addresses whether a remedy will meet
all of the applicable or relevant and appropriate' requirements
(ARARs) of Federal and state environmental laws and/or justifies'
invoking a waiver.
primarv Balancinq criteria
. Long-Term Effectiveness and Permanence: Considers the ability
of the remedy 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 anticipated performance of the treatment
technologies that may be employed in a remedy.
. Short-Term Effectiveness: Examines the effectiveness of
alternatives in protecting human health and the environment
during the construction and implementation of the remedy, until
the clean-up levels are achieved. .
. Implementability: Evaluates the technical and administrative
feasibility of alternatives and the availability of required
materials and services.
. Cost: Considers the capital and operation and maintenance
(O&M) costs of the alternatives.
Modifvinq criteria
. State Acceptance: Indicates whether the State agency, based on
its r.eview of the Proposed Plan, concurs with, opposes, or has no
comment regarding the preferred alternative.
. Community Acceptance: The community's general response to the
alternatives will be assessed in the Record of Decision following
a review of the public comments received on the Administrative
Record and the Proposed Plan.
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TABLE 5
APPLICABLE
OR RELEVANT AND APPROPRIATE REQUIREMENTS
AND TO BE CONSIDERED MATERIAL (TBCs)
DOVER GAS LIGHT SITE.
(ARARs)
ARAR ApplicabUity to
ARARor TBC Legal Citation Class Requirement Synopsis Seleeted Remedy
I. CHEMICAL SPECIFIC
1. Safe Drinking Water Act 42 U.s;C. ~ 300f et ~.
a. Maximum Contaminant Level 40 C.F.R. ~ 141.50-51 Relevant Non-enforceable health goals for public water supplies. The The Site-specific clean-up criteria are at or below non-
Goids (MCLGs) and NCP requires that. non-zero MCLGs shall be attained by zero MCLGs. The portion of the plume containing
Appropriate remedial actions for ground water that is a current or only dissolved concentrations of contaminants of
potential source of drinking water, where the MCLGs are concern must attain, through natural attenuation, the
relevant and appropriate under the cirCumstances of the clean-up criteria (and therefore comply with this.
release. ARAR) prior to any use of the water for drinking
water purposes.
This ARAR mayor may not be attained in the portion
of the plume containing NAPL.. If EPA detennines
that attainment of non-zero MCLGs is technically
impracticable from an engineering perspective, EPA
will invoke the "technical impracticability" ARAR
waiver.
b. Maximum Contaminant Levels 40 C.F.R. ~ 141.61-62 Relevant Enforceable standards for public drinking water supply The Site-specific clean-up criteria are at or below
(MCLs) and systems (with at least fifteen service connections or used by MCLs. The portion of ~he plume containing only
Appropriate at least 25 persons). The NCP requires that MCLs, for those dissolved concentrations of contaminants of concern
contaminants whose MCLG is zero, shall be attained by must attain, through natural attenuation, the clean-up
. remedial actions for ground water that is a current or criteria (and therefore comply with this ARAR) prior
potential source of drinking water, where the MCLs are to any use of the water for drinking water purposes.
relevant and appropriate under the circumstances of the
release. This ARAR mayor may not be attained in the portion
of the plume containing NAPLs. If EPA detennines
that attainment of MCL. is technically impracticable
from an engineering perspective, EPA will invoke the
"technical impracticability" ARAR waiver.
-------
ARAR Applicability to
ARAR or THC Legal Citation Class Requirement Synopsis Selected Remedy
2. Health Effects Assessment No Legal Citation To be Non-enforceable toxicity data for specific chemicals for use in Much of this information was used to developed the
Considered public health asse$sments. Also "to be considered" are soil and ground-water clean-up criteria.
Carcinogenic Potency Factors and Reference Doses provided
in the EPA Region 3's Risk-Based Concentration Table.
3. Delaware Comprehensive No Legal Citation To Be The reports ~ere adopted as policy by the DNREC To be considered for ground-water monitoring.
Water Resources Management Considered Secretary. Among these reports is the Groundwater Quality
Commiuee Reports, December Management Report, July 1983, which provided Delaware
13, 1983 with a number of tools for dealing with ground-water
contamination.
4. Delaware Surface Water Delaware Surface Water Applicable Criteria are provided to maintain surface water for streams, Any surface water discharge must not cause
Quality Standards as amended, Quality Standards as lakes, rivers, and standing water in wetlands of satisfactory exceedances of these criteria, if more stringent than
Feb. 26, 1993 amended, Feb. 26, 1993 quality consistent with public health and recreational federal water quality criteria, in the St. Jones River.
Sections 3, 4, 5, 6, 8, 9, purposes, the propagation and protection of fish and aquatic
10,11.1,11.2,11.3,11.4, life, and other beneficial uses of water.
11.6,12
Relevant Any standards more stringent than federal water
and quality standards must be used to develop the trigger
Appropriate criteria for installing pumping wells at the St. Jones
River in the event that the plume has not auenuated
pri~r to reaching the river.
II. LOCATION SPECIFIC
1. Coastal Zone Management Act 15 C.F.R. ~ 930.30, Applicable Requires that Federal agencies conducting or supporting Any remedial actions affecting the St. Jones River are
of 1972; Coastal Zone Act 930.37(a), 93039(b-c) activities directly affecting the coastal zone, conduct or required to be consistent, to the maximum extent
Reauthorization Amendments support those activities in a manner that is consistent with practicable, with Delaware's coastal zone management
of199O the approved State coastal zone management program. (See program. Consistency must be considered if treated
Delaware's Comprehensive Update and Routine Program ground water is to be discharged into the 51. Jones
Implementation, March 1993) River, if pumping is required along the river in the
future if natural auenuation does not work, or if
alternative clean-up levels are set for the Columbia
aquifer in order to protect the river.
2
-------
ARAR AppUcabillty to
ARAR or TOC Lelal Citation Class Requlnmen( Synopsis Selected Remedy
2. National Historic Preservation 36 C.F.R. ~ 8OO.4(b-(:), Applicable Requires remedial action to take into account effects on CUltural resource information recovery step to take
Act of 1966, as amended 8OO.4(e), 8OO.5(e), 800.9 properties included on or eligible for the National Register place at the beginning of the soil excavation to gather
of Historic Places. further information to determine the eligibility of the
former coal gas plant location for the National Register
of Historic Places, and, if eligible, this step will provide
the information necessary to mitigate any adverse effect
caused by the excavation.
Also, design of the ground water treatment plant will
have to take into account effects on the historical
setting of the area. Installation of wells will have to
take into account potential effects to cultural resources.
Only substantive requirements must be met.
3. Ground Water Protection No Legal Citation To be Identifies ground water quality to be achieved during The classification of the aquifers at this Site as Class
Strategy of 1984 Considered remedial actions based on aquifer characteristics and use. liB means that EPA's goal is to return the aquifer(s)
EP A 440/6-84-002 to its beneficial use (a drinkable condition) where
practicable. EPA has determined it is practicable to
return the Columbia aquifer to its beneficial use except
in the NAPL area.
III. ACTION SPECIFIC
A. Miscellaneous
1. Delaware Regulations Delaware Regulations Relevant Establishes clean-up criteria for hazardous waste sites. Only Applies to the determination of soil clean-up criteria at
Governing Hazardous Governing Hazardous and criteria considered relevant and appropriate are for ground the location of the former coal gas plant. .
Substance Cleanup, 1193 Substance Cleanup, 1/93 Appropria~e water and soil (htO.s and Hazard Index of 1 using exposure
section 9 assumptions approved by DNREC; or natural background if
higher).
B. Water
1. Clean Water Act 40 C.F.R. ~ 122.41(E), Applicable Enforceable standards for all discharges to waters of the Discharge limits shall be met for all on-site discharges
(CWA); National 122.44, 122.45, 125.61-63, United States. from the ground water treatment facility. qnly
Pollutant Discharse 125.73 substantive requirements shall be met since the
Elimination System . treatment facility will be an on-site facility.
Requirements
2. General Pretreatment 40 C.F.R. ~ 403.5, Applicable Standards for discharge to POlW. Applicable should the extracted ground water or
Regulations 403 .6( c-e) treated ground water be discharged to a POTW.
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ARAR AppncablUty to
ARAR or TOC Legal Citation Class Requirement Synopsis Selected Remedy
3. State of Delaware State of Delaware Applicable Contain requirements governing the location, design, Installation of any monitoring and recovery wells and
Regulations Governing Regulations Governing installation, use, disinfection, modification, repair, and the abandonment of wells shall meet all substantive
the Construction of the Construction of abandonment of all wells and associated pumping equipment. requirements.
Water Wells, Water Wells,
January 20,1987 January 20, 1987
Sections 3, 4, 5, 6, 7, 8, 9,
10
4. Delaware River Basin DRBC Ground Water Applicable Regulate restoration, enhancement, and preservation of Applicable if remedial action involves discharge of
Commission (DRBC) Protected Area waters in the Delaware River basin. In particular, require >50,000 gallons/day average over any month or a
Water Quality Regulation, No.4, 6(f), certain recovery well design, alternate water supply if withdrawal of ground water of 100,000 gallons/day or
9, 10; Water Code of the recovery wells interfere with any domestic or other existing more average over any month.
Basin, Sections 2.20.4, wells, require recovery system not to cause adverse impacts
2.50.2 to the environment.
5. Delaware Regulations Delaware Regulations Applicable Contain information pertaining to water allocation permits May be applicable for the ground-water recovery
Governing the Governing the Allocation and criteria for their approval. system. Only substantive requirements shall be met
Allocation of Water of Water March 1,1987 since the system will be on-site.
March I, 1987 . Sections 1,3,5.05
6. State of Delaware No Legal Citation To Be Policy for ground-water management. To be considered in establishing the ground-water
Groundwater Considered management zone.
Management Plan
November I, 1987 .
7. Delaware Regulations Delaware Regulations Applicable Contain water quality regulations for discharges into surface Applicable for discharge of treated ground water into
Governing Control of Governing Control of and ground water. surface water.
Water Pollution, Water Pollution,
amended 6(l3/83 amended 6(l3/83
Sections 7, 8, 9, to, 11,
12, and 13 /
C.Air
1. Control of Air No Legal Citation To be Policy to guide the selection of controls for air strippers at To be considered in determining if air emission~
Emissions from Air Considered ground-water sites according to the air quality status of the controls are necessary for an air stripper because Kent
Strippers at Superfund site's location (i.e., ozone attainment or non-attainment County is an ozone non-attainment area. Sources most
Ground Water area). in need of controls are those with emissions rates in
Sites, June 15, 1989 excess of 3 IbsJhour or 15 IbsJday or a potential rate of
EPA OSWER Directive 10 tons/year of total VOCs.
9355.0-28
4
-------
ARAR AppUcabWty to
ARAR or TBC upl Citation Class ' Requirement Synopsis Selected Remedy
.2. Delaware Regulations. Delaware Regulations Applicable Sets forth the requirement that a penn it is necessary to If emissions exceed 25 Ibs/day then the substantive
Governing the Control Governing the Control operate an air stripper if emissions will exceed 25 Ibs/day. requirements of the regulation must be met. Pennit
of Air Pollution of Air Pollution Section 2 describes general conditions. Section 19 deals with procedural requirements are not ARARs. In addition,
Regulations odor. Section 24 deals with volatile organic compounds. the emissions from the air stripper must meet the
Numbers 2, 19, and 24 Ambient Air Quality Standards set forth in Regulation
3 of 7 Delaware Code, Chapter 60, Section 6003.
D. Sediments/Solids
1. Delaware Sediment and Delaware Sediment and Applicable Establishes a statewide sediment and stonnwater A stonnwater and sediment management plan
Stormwater Regulations Stonnwater Regulations management program. consistent with Delaware requirements must be
January 23, 1991 January 23, 1991 developed and approved by EPA before construction
Sections 3, 6, 9, 10, II, disturbing over 5,000 square feet of land can begin.
and 15
E. Waste Handling and Disposal
1. Standards Applicable Delaware Regulations Applicable Establish.es standards for generators of hazardous wastes Applicable during soil excavation and to operator(s) of
to Generators of Governing Hazardous including waste determination and accumulation times. the wastewater treatment plant if the wastes generated
Hazardous Waste Waste, M 262.1O(b), are RCRA-hazardous wastes.
262.11,262.34,262.41
2. Standards for Owners and Delaware Regulations Applicable Regulations for owners and operators of TSDFs which define Applies to on-site recovery and treatment systems
Operators of Hazardous Waste Governing Hazardous acceptable management of hazardous wastes. which handle hazardous waste including ground-water
Treatment, Storage, and Waste, M 264.13-18, treatment, soil excavation, and debris cleaning.
Disposal Facilities (TSDF) 26430-37,26450-56
3. RCRA Requirements Delaware Regulations Applicable Requirements for storage of hazardous waste in storage Applicable for temporary storage containers and on-site
for Use and Management of Governing Hazardous containers. treatment systems.
Containers' Waste, M 264.170-177
4. RCRA Requirements Delaware Regulations Applicable Requirements for storage or treatment of hazardous waste in Applicable for on-site treatment systems and temporary
for Tanks Systems Governing Hazardous tank systems. storage tanks containing hazardous wastes.
Waste, M 264.191-199
5. RCRA Requirements EPA Regulations, Applicable Requirements for storage or treatment of hazardous waste in Applicable for on-site treatment systems and temporary
for Tanks Systems 40 C.F.R. M 264.190- tank systems. storage tanks containing hazardous wastes.
196,264.198-199
5
-------
ARAR AppUcabUity to
ARAR or THC Lep) Citation Clall Requirement 8)'110,.11 Selected Remedy
6. RCRA Requirements for Delaware Regulations Applicable Requirements for storage or treatment of hazardous waste in Applicable for ~m-site storage amI/or treatment of
Waste Piles Governing Hazardous . waste piles. excavated soil.
Waste, K 264.251,
264.254,264.256-257,
264.258(a)
7. RCRA Requirements for EPA Regulations, Applicable Requirements for storage or treatment of hazardous waste in Applicable for on-site storage and/or treatment of
Waste Piles 40 C.F.R. K 264.251-254 waste piles. excavated soil.
8. Identification and Delaware Regulations Applicable Identifies solid wastes which are regulated as hazardous Use to determine which materials to be disposed of are
listing of Hazardous Governing Hazardous wastes. hazardous wastes.
Wastes Wastes, K 261.20-24,
264.31,261.33
6
-------
FIGURE 1
Dover Gas Light Superfund Site Map
, \ lY\~\:~~:C:-' ,~~
- _. - '- " " ",\ ~ ,,)) en v- f-.-.-- State .
Gas Pllnt '" ~""'~ ~ ., St. ~ Compl~X
T\ ~' '" ':':':-.a..... " ~ AjIpmfmoIlIlmIls of )
,,..... 1 \;R, ~ „,{ ~....'~,,~ . O. Th ~\ \ ~~
00~ ~ ~"I" ~~~~~~~ ., ~,~ ,,~,~ ~~ II .
. ~ ---....J 'V.~ ~~ ~ ~ ~~,~ ~~ ~ ~
~[Z . ~~'-'" ~, ~ ~ ['-" ~~ .sf
~ , ~ .'- -- ~ ~-,...
~ . ;S"tf\e.~~ ....... ~ . . I
m ~E I Former (1\
~ -- ~ Drv Cleaner ~
Light sne ground water plume ~ TAR BRANCH ~ .... -- -- --
requiring remediation. (Extent of ~ 1A -- ... -- ....
coal tar contamination defines the ~ ~.
Superfund Sne area.) -e.
tt\
\ ~ s~
\ ' \ \ J ~ I I NOT lO SCALE ' I (.
)
-------
FIGURE 2
Dover Gas Light Superfund Site
Former Coal Gas Plant: Selected'Soil Sample Results
8.17
Depth = 14-16 ft.
:m:://f):::::t\\f_:?
ElhytleIlZlllll 17
Tala! Xylenes '0
:$~~:::::@:ttt_/:
NaplllIIIIInI . 88
2-MlltIIy"'lpIIIaIIne .
PhelIIIIItv8ne ~
8.2
Depth = 8-10 ft.
:~::::::::::::::/\(/:::~:(
Benzene 2, 100
TaIuInI 1,800
EIhyIIInz-. 120
&yr.. 820
Tala! Xytenes 870
:~V~f):::::::::::.:t
Naphtlllllnl 13,000
2-M8thyNpIhal8ne 3,800
Ac8napdIIn8 1,400
RIIOI8II8 870
Phenan1hnme 2,800
AnIhrac:IIIe 700
RuaranIhene 960
Pyr8ne 1,100
BenzD(a)anlhrlc8ne 540
ChryMne 540
8.13
Depth = 2-4 ft.
:.IN«:$.:r:::::::\:~t
Naphthalene 450
2-MIIIhytIaplllaIene 340
Ac8napIhyIen8 150
F1ucnne . 140
Phenanthnlne. 280
An~ 88
RucnnIhene 120
Pyr8ne 150
Benza(a)an1hracene 54
Chl)'S8ll8 <48
Benzo(a)pynlne 39
NORTH STREET
z
m
:e
en
-4
:JJ
m
m
-4
DELAWARE
STATE
MUSEUM
BANK LANE
r- - -.., Pre-Existing
- - - J ,Significant Features
NOT TO SCAlE
8-3
Depth = 8-12ft.
tm::@:::r::::::::f:::iI'H!j1lj}:
Benz8nI 11.0
TaIu8ne 1.5
~ 3.3
Tata! Xy18n8 3.8
t~.:~':it':::::;:r:tj"::::
NIpItIIIIene 2,800
~ 870
AcIn8pIIyIInI «10
FIuar88 340
Ph8IIIn1IIIIne 1.100
AntInc8ne 3,000
FIuaranIIene 380
PyI88 320
B-4
Depth =8-10ft.
:W(:Q:::::t:::::::::::/::::::://:ijJijjj:\
BenzIne 811
TaIu8ne 130
8h)tIet1Zll8 W
SIyIn 48
TCItII Xyllnel 150
::'_:;;;:8#:: \'I:}
2-MIIhytIIpIhaI 1,100
Acwpthylene 550 .
FIuar88 380
Ph8IIIn1IIIIne 810
AntInc8ne 240
FIuaranIIene 330
PyI88 500
-------
P1A
me:nH H
BhylJenzene
XylllI88
.......
MW.15A1B
?V~,:::t':/(:::::,::,:::::,:::,,:, :,:::,::,::':::::{,:fii1:
Benzene ' He.SoI
Ethybmene 48.0
Xylall88 , 120.0
na 21.0
:~~~i: ,H':,r
Acwphthylene 51
FIuonIne 20
Nlphlllalene 320
2.Mlllllyllllphlhalenl 140
J. AAnxlnme Value
MW-4A
:~~~l::\":'::::)~r
Toluene 4,300
ElhylJenzene 880
XyIIl'III 3,300
TelrllCllloroelhene 48C)J
na 3,300
::~~!:\: :r:!ftl
Acwphthytene 440.0
AnIIIrlC8l1e 83.0
Banzo(a)lI1thnane ~:~
llIWo(a)pyllne 21.0.1
~ 0210.0
Ruo/llllhene 82.0
Nlphlllalene 440.0
2.Mlllllyllllphlhalene 1.200.0
Phenll1thrana 320.0
:;C::'furan 1~:g,.
CaIbazoIa e.eJ
J . Approximate Value,
FIGURE 3
Dover Gas Light Superfund Site Map
Selected Ground Water Samples
':Pfi:'
870
3,100
Approxlmalt Rmi:ts 01 Dover Gas
UgIC Site 111'0l11li WIler pUna
IIquirilg remediallon.IExtent 01
coal tar contamination defines !hi
Superlll1d Site .IIL)
~ MW-6A
\,,~~;(:,:::,t{)?:t:)::::t~
Toluene 1roJ
Elhyllenzene 200J
Xylall88 220J
o t,2-DlcllloroeIhene 8SO
TelrlChloroelhana 1,500
Trlchloroelhene
MW-6A1/2
:::E~:::}':::r:I':If:rff:::rl1
Toluene, 3,100'
~'ne 1,800
XylBlI88 3,100
TelrllClllorotthInI 48,000
TrIc:hIara8th8na 140J
1100
a£:illm%0;~
Ruo,,", 48.0
Ruo/lllthene '. 4,2J
Nlphlllalene t.900.0
~~l1Iphihalene 580.0
=~hfl!ll8 ~:~J
Dibenr.ofuran UJ
Phenol 40.0
4-Meth~noIo 4.eJ
2,4-Dlniithnnnol UJ
J . Approximate Value
NOT 10 SCALE
MW-6C.o
,~~;f::::::::::::::f~)
. frederica Aquffer
. ".: . "::::.:.:.;.:.:.:.;.:.:.;.:.:.
::: .......~. .: ,".,". ,,::;:;::::::::;:;::::::-:::::
'Menaphthene 0
Acenaphlhylene
AnthflC8l1e
BenZ~~anthlllClll'le
Benz. ne 0
Benz J::/Illthene
gnysene
Ruorene
Ruo/lllthen,
Naphthalene
2-Methylnaphthalene
Phenanthrene
pyrene
Dibenr.ofuran
J. rox
MW-8A
:::I!!!!I::::=:'::::::=mf::':'::
MW.12B
Wi)(1i::{:i???:?:?:t:??:\fiM.:,
H1,2'~na 18.7
TlllrllCllloloelhene m.o
TrIchIoroethena 28.e
MW-12A
:rr~:!::::t::::,(~J
TIIIrIcIIIotoItna 4,700.0
Trtc:hIonIeIhena ' 81.1
MW.12C.
'::;:::::)::::::::)):::::1.&1"
1,2-DIcI1Ioroeth8na U
. FredeIIca Aquffer
J . ApproxIIlllt8 Value
-------
FIGURE 4
Dover Gas Light Supe,rfund Site.
Former Coal Gas Plant: Area of Potential" Soil Remediation
NORTH STREET
z
om
:E
~
:c
m
m
-t
DELAWARE
STATE
MUSEUM
BANK LANE
r - - -I Pre-Existing
~ - - _I Significant Features
NOT TO SCAlE
-------
FIGURE 5
Dover Gas Light Superfund Site.
Alternative GW-2 Well LOCations
Approximate limits of Dover Gas
Light Site ground water plume
requiring remediation. (Extent of
coal tar contamination defines the
Superfund Site area.)
ELM TERRACE \
-.------ ..
---------
o Approximate Well locations '
(Circle = Area of 1 weill Total = 80 wells)
. NOTTO SCAlE
-------
FIGURE 6 .
Dover Gas Light Superfund Site
Alternative GW-3 Well Locations
Approximate limhs of Dover Gas
Light She ground water plume
requiring remediation. (Extent of
coal tar contamination defines the
Superfund She area.)
ELM TERRACE \
----
--...
---
o Approximate Well Locations
(Circle = Area of 1 welV Total = 20 wells)
. NOTTO SCALE
-------
FIGURE 7 .
Dover Gas Light Superfund Site.
Alternative GW.4 Well Locations
Approximate limits of Dover Gas
Light Site groun~ ~ater plu":,e
requiring remediation. (Extent of .
ooal tar contamination defines the .
Superfund Site area.)
------ '
-----
-....
o Approximate Well Locations
(Circle = Area 01 1 weill Tolal = 35 wells)
'NOT TO SCAlE
-------
FIGURE 8
Dover Gas Light Superfund Site
Alternative GW-5 WeULocations
~
Approximate limits of Dover Gas
Light S~e ground water plume
requiring remediation. (Extent of
coal tar contamination defines the
Supe$nd Site area.)
--- .
...--- .
.... -- ....
o Approximate Well Locations
NoT TO SCAlE
-------
. Responsiveness Summary
Dover Gas Light Superfund Site
Dover, Kent. County, Delaware
The Responsiveness Summary for the Dover Gas Light Superfund
Site is divided into the following sections:
SECTION I
~e~i~
This section summarizes recent actions at the Site and
the pUblic's response to the clean-up alternatives
listed in the Proposed Remedial Action Plan (Proposed
Plan). The Proposed Plan outlined various clean-up
alternatives available to address Site contamination
and highlighted EPA's preferred alternative.
SECTION II
Background on Community Involvement
This section reviews the history of community
involvement and interest in the Dover Gas Light
Superfund Site.
SECTION III
Summary of Major Comments and Questions Received
During the Public Comment Period and EPA's
Responses
This section documents comments and questions raised
during the comment period regarding the Site and EPA's
responses to them. .
I.
Overview
In July 1990, Chesapeake Utilities Corporation signed a
Consent Order with EPA and the. Delaware Department of Natural
Resources and Environmental Control (DNREC) to conduct a Remedial
Investigation and Feasibility Study (RI/FS) at the Dover Gas
Light Site. Upon completion of the RIfFS by Chesapeake, EPA.
reviewed the reports ~nd subsequently released the Proposed Plan
on February 2, 1994. The Proposed Plan addressed contaminated
Site soils and ground water. EPA held a public meeting on
Thursday, February 17, 1994, to discuss the Proposed Plan and to
present its preferred alternative to the community. At this
meeting, community members had an opportunity to ask questions
and make comments regarding the results of the RI, the FS, and
the clean-up alternatives listed in the Proposed Plan.
The 30-day public comment period for the Site originally ran
from February 2, 1994, to March 4, 1994. However, due to a
request for an extension, EPA extended the comment period by an
additional 30 days. The comment period ended on April 3, 1994.
1
-------
DOver Gas Light Superfund Site ROD: Responsive Summary
A summary of the comments and questions received during the
public comment period, along with EPA's responses are listed in
Section III of this document.
:n: .
Background on community Involvement
Community interest in the Dover Gas Light Superfund site has
been moderate and has come primarily from local businesses and
citizens who use the Site as a parking lot. EPA held a meeting
in December 1990 to inform local community members of upcoming
site activities. Although attendance at this meeting was low,
local citizens are generally aware of the contamination and
believe that the problem needs to be remedied without major
disruptions to the area.
In May 1992, EPA conducted community interviews with local
residents, officials, and business owners to determine public
awareness of and concerns about the Dover Gas Light Site. EPA
used these community interviews to develop a Community Relations
Plan. The Community Relations Plan addresses community concerns
about the Site and guides two-way communication between EPA and
the community. Many community members expressed concerns about
the impact of Site contamination on the community. More
specifically, citizens were mainly concerned about future work in
the Site area and disruptions in traffic flow, parking
availability, and historic preservation.
. .
III. Summary of Major Comments and Questions Received During the
Public Comment Period and EPA Responses
The responses to the comments received during the public
comment period are divided into two categories: those received
at the public meeting and those submitted in writing. Since
Chesapeake submitted extensive written comments that included its
comments at the public meeting, only responses to the written
comments are presented.
Comments Received at the Public Heeting
1. A question was asked regarding EPA's projected schedule
for implementing its preferred clean-up alternative.
EPA's RESPONSE: Shortly after the Record of Decision (ROD)
is issued, EPA will invite offers from the potentially
responsible parties (PRPs) attempting to implement the ROD, or
will decide to conduct a Fund-financed remedy. Once this process
is complete, the remedial design will probably take several years
and the construction of the remedy about one year.
2
-------
Dowr Gas Light S~rfimd Sitt ROD: Ruponsive Summary
2. A question was asked regarding how long EPA plans to
con~inue pumping and treating the ground water.
EPA's RESPONSE: The wells at the downgradient end of the
non-aqueous phase liquid (NAPL) area will probably operate at
least 30 years and longer to contain migration of heavily
contaminated ground water. The wells within'theNAPL area will
only operate as long as they recover free-phase contamination.
This should be less than ten years. .
3.
ground.
A question was asked if any wells would be visible above
EPA's RESPONSE: Manhole covers for the monitoring and
recovery wells installed in public areas may only be visible
sticking up several inches, if at all.
4. A citizen was concerned that if EPA chose Alternative
GW-2 increasing the number of recovery wells installed in the
plume area, it would affect his property because a number of them
would end up in his back yard.
EPA's RESPONSE: EPA did not chose Alternative GW-2 as its
selected remedy, which included approximately 80 wells.
5. A question was asked if dense non-aqueous phase liquids
(DNAPLs) can harm vegetation.
EPA's RESPONSE: At this Site, NAPLs (dense or light) are
not likely to harm vegetation because of the depth of the water
table.
6. A question was asked if someone can install a drinking
water well after the proposed 30 years of pumping and treating
the contaminated ground water.
EPA's RESPONSE: Once the clean-up levels are attained, EPA
would consider the water safe to drink. Whether a drinking water
well could be installed would depend on what institutional
controls (which currently prohibit drinking water wells from
being installed in the Columbia aquifer at the Site) are in place
at the time the clean-up levels are attained, which may take
longer than 30 years.
7. A question was asked as to whether EPA is applying
drinking.water standards for the ground-water clean-up levels.
EPA's RESPONSE: Due to the high number of contaminants
present in the ground water and their potential cumulative
adverse impact on human health, the use of drinking water
3
-------
DOVtr Gas light Superfund Sitl! ROD: Ruponsiw SlUtImtJTy
standards as clean-up criteria would not be protective of human
health. Therefore, ground-water clean-up criteria have been
developed which are lower than EPA's drinking water standards.
These criteria apply to the portion of the ground-water plume
containing dissolved contamination only. EPA has determined that
in the portion of the plume containing NAPLs, it is technically
impracticable to achieve the clean-up criteria. The remedy for
the NAPL area may achieve drinking water standards although the
goal is only containment and removal of mobile NAPLs.
8. A question was asked whether EPA had explored a passive
recovery method as an option to clean up the site. A comment was
also made that a passive recovery clean-up method would be
cheaper than EPA's preferred alternative.
.EPA's RESPONSE: The type of passive system discussed at the
public meeting (one which would eliminate the need for pumping
wells at the end of the NAPL area) would require a 40 to 50 foot
deep trench across several city blocks which is impractical.
However, the NAPL recovery wells (those installed to remove NAPLs
as opposed to just preventing their migration) may include the
use of passive recovery wells or trenches. The remedial design
will determine the exact type of well. Costs will be considered
during the remedial design. .
9. A question was asked about how institutional controls
factor into the future exposure scenario of the risk assessment
since the City of Dover does not allow anyone to install drinking
water wells within the city limits.
EPA's RESPONSE: Even though the city of Dover does not
presently allow installation of drinking water wells in the area
of the Site, EPA considers the aquifer to be a Class IIB aquifer
meaning that it is a potential future source of drinking water.
As a result, EPA's goal as described in the National oil and
Hazardous Substances Pollution contingency Plan (NCP) is to
restore the ground water to its beneficial use where practicable.
Therefore, a future exposure scenario involving use of the ground
water was included in the risk assessment.
10. A question was asked about where the ground water would
be discharged from the treatment system and if EPA had explored
the possibility of using the existing waste water treatment
system operated by Kent County. A question was also asked as to
whet~er or not treated ground water discharged to the st. Jones
River would cause any pollution problems.
EPA's RESPONSE: The ROD calls for ground water to be
treated and discharged to the st. Jones River. Contaminant
levels would be reduced such that the effluent would not cause
4
-------
DOVtT Gas light .rfund Sit~ ROD: Responsive Summmy
pollution problems in the st. Jones River. However, the ROD does
allow for discharge to a publicly-owned treatment works (POTW) if
the proper requirements can be met. Kent County's POTW is
currently operating over capacity.
11. A question was asked whether EPA considered remedies
other than a pump-and-treat system.
EPA's RESPONSE: The feasibility study discussed a number of
technologies to address the ground water including
bioremediation, in-situ aeration, and installation of permeable
treatment b.eds in the aquifer. The characteristics of the
Columbia aquifer at the site and the urban environment were major
reasons why most of these alternatives where not evaluated in-
depth.
12. A question was asked whether EPA will allow enough
flexibility in the Record of Decision for Chesapeake to meet
EPA's goals with a more cost-efficient clean-up method. A
question was also asked, that because of the minimal movement of
the plume and the potential financial impact on the community,
whether or not EPA would consider not implementing the remedy for
a period of time to allow for the development of new
technologies.
EPA's RESPONSE: EPA has selected natural attenuation and
ground-water pump-and~treat to address the contamination. Next
to natural attenuation, pump-and-treat is one of the simplest and
least expensive treatment options available for the ground water
(especially if some passive wells can be incorporated into the
remedial design). The ROD does allow flexibility in the types of
wells used for recovery of the free product in the NAPL area, .
however, the ROD cannot be as flexible as Chesapeake ,has
requested since the purpose of the ROD is to select a remedY'1 not.
prolong the feasibility study. Cost was considered in the
evaluation of the selected remedy. Delaying implementation of
the remedy will only allow the area of contamination to expand
and increase the cost of the remedy.
13. A question was asked that if the clean-up levels for
the ground water were changed; would the cost of the remedy
change as welL
EPA's RESPONSE: Clean-up levels are chosen that protect
human health and the environment. Then costs are considered when
evaluating remedial alternatives. For this Site, the ground-
water clean-up criteria have little to do with the overall cost
of the selected remedy. The criteria do affect the length of
time for natural attenuation to reach the remedial objectives
which does affect how long the plume will have to be monitored.
5
-------
DOVtr Gas Light SII/„rjund Sit~ ROD: RLsponsiVt Summary
The criteria do not affect the costs at all in the NAPL area
since the goal is not to attain the criteria in this area, but to
contain the contamination and remove any mobile free product.
14. A comment was made concerning the impact to the
Delaware state Museum including delays in expansion while the
Museum is awaiting the Site to be cleaned up. The on-going loss
of the land causes a significant "cultural cost."
EPA's RESPONSE: EPA's plan is to remediate the Site in an
expeditious manner to allow the museum to go ahead with its
.expansion plans.
Comments Submitted in Writing
1. Chesapeake commented that it agreed with EPA's
statements that the Site does not pose any risk and that the only
"unacceptable" risks are not.. based on current or planned uses of
the soils or ground water. "As a result, the remediation can
proceed on a reasonable pace, allowing EPA, DNREC and the
responsible parties .to develop the most effective approach from
both a technical and economic approach." .
EPA's RESPONSE: The Proposed Plan stated that the Site
poses no current risk. The Site does pose a potential .future
risk to human health for planned uses of the land. For example,
building constructors would be exposed to unacceptable levels of
contamination during a museum expansion, which is an expected.
activity that is currently being delayed due to the presence of
contaminated soil.
2. Chesapeake and others commented that EPA's proposed
remedy would not achieve the proposed ground-water clean-up
criteria or restore the ground water to a condition where it can
be used as a water supply.
EPA's RESPONSE: EPA believes that in the NAPL area, the
pump-and-treat system can not meet the ground-water clean-up
criteria. As a result, in the selected remedy the goal for the
NAPL area is no longer to return the ground water to its
beneficial use but to remove mobile NAPL and to contain the
contamination. Since the goal has changed, the clean-up criteria
do not apply to the NAPL area. There is also a question as to
whether MCLs or non-zero MCLGs (which are applicable or relevant
and appropriate requirements [ARARs) can be attained. The
ground-water ARARs are much higher than the clean-up criteria at
this site due to the high number of contaminants of concern. The
selected remedy includes a provision for invoking the "technical
impracticability" ARAR waiver if EPA determines that the ARARs
6
-------
DiMr Gas light Superfund Site ROD: ResponsiVt! SummtJry
'can not be attained in the NAPL area. Since the goals of removal
of mobile NAPL and containment are independent of whether or not
the ARARs are attained~ granting a waiver at this time would have
no impact on the scope of the remedy. A waiver will only be
granted in the future if it is determined by EPA that the
selected remedy can not attain the ground water ARARs in the NAPL
area. EPA expects that natural attenuation will allow the
portion of the plume containing only dissolved contamination to
attain the clean-up criteria.
3. Chesapeake commented the proposed soil clean-up criteria
were "both excessive and technically not achievable."
EPA's RESPONSE: EPA does not believe that the proposed soil
clean-up criteria were either "excessive or technically riot
achievable. II However, in light of further discussions with DNREC
regarding ,the planned use of the location of the former coal gas
plant, the selected remedy ,contains new soil clean-up criteria
which were developed assuming that the museum expansion would
occur rather than the construction of a school. As a result, the
soil clean-up criteria in the ROD are significantly higher than
, those originally proposed by EPA in the Proposed Plan.
4. Chesapeake commented that: 1) EPA's proposed remedy for
the ground water would not be effective because of the presence
of DNAPLs (including tetrachloroethene [PCE]), 2) the clean-up
criteria were so low as to be analytically unverifiable, and
3) EPA's proposed location of wells does not maximize capture of
the S~te contaminants. '
EPA's RESPONSE: EPA agrees that the placement of the wells
at the end of the NAPL area did not maximize the removal of'the
Site contaminants. " The purpose of those wells was to prevent
contamination from the NAPL area, including PCE, from migrating
to the area only containing dissolved contamination. The clean-
up criteria would never be met in the dissolved area if the
complete NAPL area was not contained. Although these wells are
in the same location in the selected remedy, additional wells
have been included to aggressively remove NAPL material
upgradient of these wells. By addressing the dissolved area
through natural attenuation and aggressively attacking the NAPL
area, the greatest amount of contaminant will be removed and the
threat to the Frederica aquifer caused by the DNAPL will be
significantly reduced. The clean-up criteria are analytically
achievable using EPA Method 524.2 with the cryogenic trapping
option and a narrow bore capillary column for the volatile
organic compounds and EPA Method 550 (a high-performance liquid
chromatography method) for the semi-volatile organic compounds.
7
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DflVer Gas light SU[Mrfund Site ROD: RuponsiVt! Summary
. 5. Chesapeake commented that the remedial activities for
Operable Units I and II must be sequenced to ensure that
interference is minimized.
EPA's RESPONSE: There would not'have been any interference
between the remedial activities for Operable Units I and II.
Operable unit I included all of the ground water and the soil at
the former coal gas plant. Operable Unit II included just the
soil at the former dry cleaner at 411 South Governor's Avenue.
However, with EPA'smodified goal for the NAPL area that does not.
include restoring the ground water to its beneficial use,' there
is not a need to remediate the dry cleaner soils as part of this
Superfund site. Therefore, Operable Unit II has been eliminated
from the Site management strategy. As noted in the Proposed
Plan, DNREC is planning to address contaminated soils at the
location of the former dry cleaning establishment using authority
under the State's Hazardous Substance Cleanup Act (HSCA). .
6. Chesapeake commented that the ROD should not select
excavation and incineration for the contaminated soils from the
former coal gas plant but should be flexible enough to allow the
optimum technology to be chosen during the remedial design.
Another commenter stated that the ROD should be flexible enough
to allow for future technology advances that might benefit the
Site. .
EPA's RESPONSE: The purpose of the. feasibility study was to
evaluate different technologies to address the Site. The purpose
of the ROD, not the remedial design, is to select a remedy from
those evaluated during the feasibility study. However, the ROD
has been written with a significant amount of flexibility. The
excavated soil must be treated using thermal destruction, but.
this could range from incineration at a hazardous waste treatment
facility to treatment in a resource recove~y kiln. Soil with
very low levels of contamination may potentially be landfilled.
The ROD also allows on-site treatment of debris with the treated
debris being backfilled on-site. If new technologies become
available that may be applicable to the Site, EPA may, in its
discretion, review those at that time.
7. Chesapeake commented that contamination east of Federal
street from other sources must be remediated along with the Dover
Gas 'Light ground water contamination or the efforts at Dover Gas
Light would be wasted since the Columbia aquifer would still be
contaminated.
EPA's RESPONSE: Under this ROD, EPA only has authority to
address the Superfund Site. Much of the contamination east of
Federal Street is likely from leaking underground storage tanks
east of Federal Street and from the former dry cleaning
8
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D~T Gas Light Superfimd Siu ROD: &sponsive Summary
establishment at 411 South Governor's Avenue. DNREC's
Underground Storage Tank (UST) Program has addressed, and will
undoubtedly continue to address, leaking underground storage
tanks. DNREC's Superfund Program is negotiating with the owner
of the former dry cleaner to address contamination from this
site. By using natural attenuation to address the Dover Gas
Light ground-water contamination, the clean-up time frame is
expected to be lengthy. This will give time for the other
contaminants to attenuate as well. Through the continued efforts
of EPA and DNREC, the overall ground-water quality will improve.
It should also be noted that contaminant sources east of Federal
Street do not contribute to contamination at the Superfund Site
which is defined to be only where contaminants from the former
coal gas plant have come to exist.
8. Several commenters pointed out that page 2 of the
Proposed Plan incorrectly stated that the only coal gas plant
building remaining after the demolition was called a "brick
garage" when it was actually the original retort building.
EPA's RESPONSE:
the ROD.
EPA agrees and has made the correction in
9. Chesapeake
across North Street
chlorinated organic
northern portion of
commented that the Capitol Cleaners location
from the Site is a significant source of
contamination in the ground water in the
the Site.
EPA'S RESPONSE: Most of the northern plume of chlorinated
organics is not part of the Superfund Site including the Capitol
Cleaners location across North Street. DNREC is currently
negotiating with Capitol to study this location. .
10. Chesapeake commented that the geology underneath the
Site includes the Piney Point aquifer which is also used as a
drinking water aquifer for the City of Dover.
EPA's RESPONSE: EPA agrees and has included this
informa~ion in the ROD. .
11. Chesapeake commented that EPA failed to recognize that
the former dry cleaning establishment. at 411 South Governor's
Avenue was a source of BTEX and PAH contamination and that areas
east of MW-6 are more heavily impacted by the dry cleaner than
the coal gas plant.
EPA's RESPONSE:
DNREC during the UST
that the dry cleaner
However, EPA has not
EPA acknowledges that the data collected by
investigation at the dry cleaner indicates
was a source of BTEX and PAH contamination.
determined to what extent the BTEX and PAH
9
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Dover Gas Light SlI{„rjund Site ROD: Ruponsive Summary
contamination east of MW-6 comes from the dry cleaner. In fact,
the soil contamination deep in the Columbia aquifer at MW-6 is
undoubtedly from the coal gas plant. Also, see response to
Comment #26.
12. Chesapeake commented that the Proposed Plan should
reflect the fact that the State of Delaware is a potentially
responsible party (PRP). Chesapeake also commented that Capitol
Cleaners should be named a PRP because the cleanup of the Dover
Gas Light Site will involve cleaning up contamination from a
former Capitol Cleaner plant.
EPA'sRESPONSE: EPA acknowledges that the State of Delaware
is a PRP. EPA is currently conducting a PRP search which at this
time is not complete. Once the PRP search is complete EPA will
determine if there are apy other PRPs at this site and, if any
are found, will then invite them to participate in the cleanup
during the special notice period. . .
13. Chesapeake commented-the "EPA acknowledges that the
ground-water remedy is largely driven by the significant risks
generated by hypothetical contact with chlorinated compounds."
EPA's RESPONSE: EPA only acknowledged that the chlorinated
organic contamination contributed greatly to the overall risk
associated with exposure to the ground water. Remediation at
this Site was triggered by exceedances of 1x10-4 for carcinogenic
risks or 1.0 for non-carcinogenic risks for the coal gas plant-
related contaminants. Once remediation has been triggered,
however, all contaminants must be remediated.
14. Chesapeake commented that any risks related to
contamination in the st. Jones River should be associated
sources of contamination near the river and not the Dover
Light site and that it is highly unlikely that coal gas
contamination will ever reach ' the st. Jones River.
with
Gas
EPA's RESPONSE: The Dover Gas Light plume may in the future
discharge into the st. Jones River (as indicated by the ground-
water model in the remedial investigation submitted by
Chesapeake). Therefore it is appropriate for the baseline risk
assessment to examine the potential risks associated with
contaminants in. the st. Jones River.
risk
soil
both
15. Chesapeake commented that it did not believe that the
assessment for a construction worker exposed to contaminated
underestimated the risk because a worker will be exposed to
contaminated and uncontaminated soil. .
10
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DOIIeI Gas light Superfund Site ROD: RDponsive Summary
EPA's RESPONSE: EPA has reviewed the soil sampling data
collected from borings at the former coal gas plant.. The samples
were collected from areas of substantial visual contamination.
As a result, EPA no longer believes that the r~sks for the
construction worker listed in Tables 1 and 2 underestimate the
risks associated to exposure with subsurface soil. However, EPA
continues to believe that the risk assessment underestimates the
risk for future building occupants (likely museum workers and
visitors) because a construction project could cause contaminated
subsurface soil to become surface soil. The ROD has been changed
to reflect the above discussion.
16. Chesapeake provided comments on Capitol Cleaner's draft
work plan for the study of the former dry cleaning establishment
at 411 South Governor's Avenue.
EPA's RESPONSE: This ROD addr~sses the Dover Gas Light
Superfund Site only, and therefore, it is not appropriate to
discuss Capitol's work plan since the former dry cleaning
establishment is not part of the Superfund Site.
17. Chesapeake commented that ground-water clean-up levels
should not be set for the chlorinated compounds as long as
Capitol Cleaners is not held liable for the cleanup.
EPA's RESPONSE: The ground water can not be restored to its
beneficial use without all of the contaminants being remediated
including the chlorinated organics. Therefore, there must be
clean-up levels for the chlorinated organics. . As discussed
previously, EPA has not completed its PRP search.
18. Chesapeake commented that the ROD should allow the
flexibility of discharging any recovered ground water .to a
publicly-owned treatment works (POTW).
EPA's RESPONSE: EPA agrees and has added to the ROD the
flexibility of using a POTW. To use a POTW, all pre-treatment
requirements would have to be met, and EPA's approval obtained.
19. Chesapeake commented that all three proposed treatment
plant locations present difficulties including the potential
distance from the wells to the treatment plant, access
restrictions, and the impacts to future development.
EPA's RESPONSE: The ROD calls for the treatment plant, if
necessary, to be installed at the location of the former coal gas
plant. Without the wells along Federal Street, the wells are all
in the same general area. The estimated size of the treatment
plant (50 ft. X 100 ft.) would still allow expansion of the
museum and some parking. There would be some loss of parking.
11
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Dover Gas Light Superfund Sili! ROD: ResponsiW! Summary
with the revised remedial action objectives being recovery of
pumpable NAPLs and containment of contamination for the NAPL area
and the use of natural attenuation for the rest of the plume, the
overall amount of recovered ground water in the selected remedy
has been significantly reduced compared to the amount in EPA's
preferred alternative in the Proposed Plan. Even if a treatment
plant is necessary at the beginning of the remediation, it may
not be necessary in the future once only the" containment wells
are required which would further reduce the quantity of recovered
ground water which would increase the pos~ibility of using the
POTW~
20. Chesapeake commented that the costs associated with the
ground-water alternatives were low because operations and.
maintenance (O&M) costs were estimated for only 30 years and
because the wells were being installed in an urban area.
EPA's RESPONSE: EPA acknowledges that there will likely be
an O&M period longer than 30 years but O&M costs are by practice
estimated for a 30-year period. The cost estimate relied
substantially on information in the feasibility study submitted
by Chesapeake which included wells installed in an urban area.
21. Chesapeake expressed concern about the possibility of
soil above the proposed clean-up criteria being underneath the
cemetery and the streets.
EPA's RESPONSE: The soil clean-up criteria in the selected
remedy are significantly higher than those in the Proposed Plan,
and after reviewing the soil boring data, EPA does not expect
soil beyond the limits in Figure 4 to contain contamination above
the criteria except at the water table. At this time EPA does
not expect any excavation beyond the limits in Figure 4.
22. Chesapeake commented that none of the ground-water
alternatives in the Proposed Plan meets the "test for long-term
effectiveness and permanency" (one of the five balancing
criteria, see Table 4) because the clean-up criteria will never
. be achieved. .
EPA's RESPONSE: The "long-term effectiveness and
permanency" criterium is not a pass/fail criterium. Long~term
effectiveness and permanency are viewed along a continuum with
alternatives offering different degrees of either long-term
effectiveness or permanency. The clean-up criteria will be
achieved in the dissolved portion of the plume.
23. Chesapeake commented that the ground-water alternatives
in the Proposed Plan do not meet the reduction of toxicity,
mobility, or volume criteria through treatment because other
12
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Dover Gas Light Superfimd Site ROD: Responsive Summary
sources of contamination may prevent cleanup of the Site and
because Chesapeake questioned the effectiveness of the pump-and-
treat technology.
EPA's RESPONSE: EPA believes each of the ground water
alternatives offers significant reduction of toxicity, mobility,
or volume through treatment. Any contamination that is removed
from the system reduces the mobility and toxicity of the plume.
The alternatives that aggressively attack the NAPLs offer
significant reduction of mobility and toxicity. Each of the
alternatives provided for complete remediation of the dissolved
portion of the plume including contaminants from sources other
than the coal gas plant. Therefore, each alternative offered a
significant reduction in volume.
24. Chesapeake commented that each of the ground-water
alternatives would create significant short-term impacts to the
community.
EPA's RESPONSE: EPA agrees, and in response to comments on
the Proposed Plan, EPA has selected a new alternative which does
not include the wells along Federal Street that are called for in
the other alternatives. Although the selected remedy will impact
the community, the impacts will be significantly less than those
associated with EPA's preferred alternative in the Proposed Plan.
25. Chesapeake commented that excavating the soil may have
significant short-term impacts including the closure of the
Johnson Museum and the Federal Building.
EPA's RESPONSE: Any remediation of the soil, whether on-
site or off-site, will involve short-term impacts including
temporary disruption to area parking and the operation of the
museum. Excavation and removal should involve the shortest
construction time, thereby minimizing short-term impacts.
26. One commenter stated that it did not know of any data
that indicated that underground storage tanks containing
chlorinated solvents were present at the former dry cleaning site
at 411 South Governor's Avenue. The commenter also stated that
EPA's claim that underground storage tanks at this same location
contributed to the BTEX and PAH contamination is unsubstantiated.
EPA's RESPONSE: Data collected as part of a tank removal
and reported in a WIK Associates report dated 5/6/92 indicated
that both chlorinated solvents, BTEX, and PAHs leaked from
underground storage tanks at the location of the former dry
cleaner. Samples from the bottom of several tank pits contained
tetrachloroethene, trichloroethene, xylenes, and/or benzene.
13
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D~r Gas light S~rftmd Sitt! ROD: Ruponsiw Summary
Although not analyzed for, naphthalene is a typical constituent
of gasoline and would likely be found in the soil as well.
27. One commenter stated that there were no risks driving
the remediation of the dissolved ground-water contamination
because current institutional controls would prevent any
exposure.
EPA's RESPONSE: Consistent with the requirements of the
NCP, EPA performs a baseline risk assessment that examines
current and poten~ial future risks without taking into account
current or future institutional controls. As a result, the
Columbia aquifer was assumed to be a future source of drinking
water.
28. One commenter stated that one of the problems with
remediating areas containing DNAPLs is the difficulty associated
with locating all of the reservoirs of DNAPL and that further
studies should be done to define the extent and existence of
DNAPLs. .
EPA's RESPONSE: EPA agrees and has included in the selected
remedy a study to further define the NAPL area so that recovery
and containment wells can be properly placed. '
29. One commenter expressed concern about EPA's proposal of
only excavating contaminated soil down to the top of the water
table which would leave significant soil contamination that would
continue to contaminate the ground water.
EPA's RESPONSE: EPA agrees that the soil borings at the
location of the former coal gas plant showed significant soil
contamination just below the water table and that this
contamination would present a significant continuing source of
ground-water contamination if it remains in place. As a result,
the soil clean-up criteria in the selected remedy apply down to a
clay lens that is approximately five feet 'below the water table
and upon which NAPL material exists.
30. One commenter stated that installation of wells and
construction of a ground-water treatment plant must be done in
compliance with the National Historic Preservation Act (NHPA).
The commenter also stated that EPA must enter into a Memorandum
of Agreement (MOA) with Delaware's State Historic Preservation
Office and the Advisory Council on Historic Preservation
regarding how EPA will mitigate adverse impacts to cultural
resources.
EPA's RESPONSE: EPA agrees that well installation and
construction of a treatment plant may adversely impact cultural
14
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Dover Gas Light S~rfund Site ROD: Ruponsive Summary
resources and intends to comply with 'the NHPA. However, since
this work will take place on the Superfund site, EPA only has to
comply with the substantive requirements of the NHPA and not the
administrative requirements, and therefore a MOA is not
mandatory.
31. One commenter expressed concern about wells being
installed just east of state Street and concern about potential
impacts to plant life, especially several old trees.
EPA's RESPONSE: At this time EPA has no plans to install
recovery wells just east of State Street. If further evaluation
of the NAPL area indicates that NAPLs have spread that far, wells
would be necessary. However, steps would be taken to minimize
any impact to local grounds. .
32. Several commenters questioned whether the risks posed
'by the ground-water contamination warranted an extensive recovery
system given the impacts to downtown and historic areas, and the
potential impact on local property owners (i.e., the perception
of the public as being associated with a Superfund site and
decreased value of their'properties).
EPA's RESPONSE: EPA has determined that given the aquifer
characteristics, the low probability that the ground water will
be used, the lack of any current risks, and the high level of
impacts to the City of Dover if wells were installed a.long
Federal Street, natural attenuation is a better remedy ,for the
dissolved portion of the ground-water contamination. If the
plume does not attenuate sufficiently before it migrates to the
st. Jones River, recovery wells will be installed near the river
which will have only minor impacts to the local community.
, ,
33. The State of Delaware's Public Service Commission
commented that it was concerned that any remedial action be cost
effective and that expenses incurred by a utility that were
incurred "through waste, abuse of discretion, or. bad faith, are
not to be included in the calculation of just and reasonable
utility rates." (Public Service Commission, 3/4/94)
EPA's RESPONSE: EPA is required by CERCLA to select
remedies that are cost effective. Before a remedy can be
evaluated for cost effectiveness, it must be able to protect
human health and the environment from current and potential
future threats from exposure to contamination. The selected
remedy outlined in this ROD is necessary to protect human health
and the environment. EPA has also determined that the selected
remedy is cost effective. Therefore, costs incurred during the
implementation of this ROD would be spent in the best interest of
the public and the environment. EPA has responded to concerns'
15
-------
~r Gas Light S~rfund Site ROD: Respons;ve Summary
raised during the public comment period about costs. The clean-
up criteria for the soil at the former coal gas plant have been
. raised which will sUbstantially reduce the amount of soil to be
excavated and disposed of and the recovery wells originally
proposed to be installed along Federal street have not been
included in the selected remedy at a substantial cost savings.
16
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Attachment A
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:)FFICE OF T~E
"'RECTOR
STATE OF DELAWARE
DEPARTMENT O~ NATURAL RESOURCES By-:::::--:::,
5: :::'-JVIPONMENTA:" CONTROL
DIVISION OF AIR Be WASTE MANAGEMENT
89 K,\:cS H'C\.rNAY
:>~, Sox 1401
~OVE!<, ~E:'':''NA1'!E 19903
TEI..EPHONE: (302) 739.4764
August 2. 1994
Mr. Thomas C. Voltaggio. Director
Hazardous Waste Management Division (3HWOO)
US. EP A Region III
841 Chestnut' Building
Philadelphia. PA 19107
Dover Gas Light Superfund Site
Dear Mr. VoltaggiQ:
RE:
On behalf of the State of Delaware. I am pleased to express concurrence with the
EPA's Record of Decision (draft July, 1994) for the above referenced site. I appreciate
EPA's consideration of the' state's comments on the ROD.
Sincerely, ~ ,.
~.~
Nicholas A. . asquale
Director
:'IIAD:dmg
SFJ94037
cc:
Abe Ferdas. Superfund Branch Chief
Randy StUrgeon. Remedial Project Manager
'. Ii
Z'daUl4're'4 ~ ~ ~ tUe tpJ«I
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