U. S. EPA Superfund Program
Proposed Plan for Record of Decision Amendment
Delaware Sand & Gravel Landfill Superfund Site
New Castle, Delaware
EPA ANNOUNCES PROPOSED PLAN
The United States Environmental Protection
Agency (EPA) is issuing this Proposed Remedial
Action Plan (Proposed Plan) to propose changes to
the cleanup plan for the Delaware Sand & Gravel
Landfill (DS&G) Superfund Site (the Site) and to
solicit public comment on those proposed changes.
The Proposed Plan would modify the remedy
selected in the April 22, 1988 Record of Decision
(ROD), the September 30, 1993 Amendment to the
ROD (ROD Amendment) and the July 2003
Explanation of Significant Differences (ESD), to
address contamination remaining at the Drum
Disposal Area (DDA) and within the Upper
Potomac Aquifer and to prevent potential future
exposure to Site contaminants capable of migrating into indoor air.
The Site is located in New Castle, New Castle County, Delaware and consists of an
approximately 27-acre property which was a sand and gravel quarry before it was
operated as a permitted landfill from 1968 until 1976. The location of the Site and the
Site layout are shown in Figures 1 and 2, respectively.
EPA is the lead agency for the Site under the National Oil and Hazardous Substances
Pollution Contingency Plan (NCP), 40 C.F. R. Part 300, promulgated pursuant to the
Comprehensive Environmental Response, Compensation, and Liability Act of 1980, as
amended (CERCLA), 42 U.S.C. §§ 9601 to 9675, and the Delaware Department of
Natural Resources and Environment Control (DNREC) is the support agency.
EPA is proposing hydraulic containment of source material at the DDA, installation and
operation of groundwater extraction wells in the Upper Potomac Aquifer to restore
groundwater quality, discharge of extracted groundwater to the Wilmington wastewater
treatment plant, extraction and treatment of groundwater using existing and, if necessary,
additional treatment systems at Artesian Water Company's Llangollen well field and
institutional controls to prevent potential future exposure to contaminants capable of
migrating into indoor air. These proposed modifications, which are explained in detail
later in this document, have an estimated present worth cost of $42.3 million. EPA is not
September 2016
Dales lo Remember
September 7. 2016 lo
October 7. 2016
Public Comment Period oil
l-P.Vs Proposed Plan
Public Meeting
September 21. 2016
7:00 to 8:30 pm
William Penn I liuli School
713 I-. IJasin Road
New Castle. 1)1: N72<)
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proposing to modify any other components of the remedy selected in the 1988 ROD,
1993 ROD Amendment and 2003 ESD.
EPA and DNREC encourage the public to review and comment on this proposal.
Included in this Proposed Plan is information summarized from the Supplemental Site
Characterization Report - Revision 2 (Golder Associates, February 2016) and the Final
Feasibility Study - Revision 1 (Golder Associates, May 2016) (Feasibility Study). These
documents and additional information are contained in the Administrative Record for the
Site. The Administrative Record for the Site can be accessed at www.epa.gov/arweb, or
at the following locations:
DNREC
391 Lukens Drive
Newcastle, DE21921
Hours: Call (302) 395-2600
EPA Administrative Records Room
Administrative Coordinator
1650 Arch Street
Philadelphia, PA 19103
Phone: (215) 814-3157
Hours: Monday- Friday 8:30 am to 4:30 pm
EPA will select the final remedy modifications for the Site only after the public comment
period has ended and the comments received have been reviewed and considered.
Comments should be submitted in writing or emailed to EPA's Remedial Project
Manager or Community Involvement Coordinator:
Debra Rossi (3HS23)
Remedial Project Manager
Environmental Protection Agency Region III
1650 Arch Street
Philadelphia, PA 19103
(215)814-3228
Rossi ,Debra@epa. gov
Larry Johnson (3HS52)
Community Involvement Coordinator
Environmental Protection Agency Region III
1650 Arch Street
Philadelphia, PA 19103
(215)814-3239
Johnson.Larry-C@epa.gov
The Proposed Plan includes the following sections:
I. Site Background - Describes the Site setting and operating history and the
history of response actions;
II. Site Characteristics - Summarizes the results of recent supplemental Site
characterization activities and the nature and extent of contamination at the Site;
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III. Reason for the Proposed Change - Explains why additional response actions
are needed;
IV. Scope and Role of the Proposed Response Actions - Describes how the
proposed response actions fits into the overall Site strategy;
V. Summary of Site Risks - Identifies contaminated media which present
unacceptable risks for current or future Site use and identifies current chemicals
of concern in groundwater;
VI. Remedial Action Objectives - Describes what the proposed Site cleanup is
expected to accomplish;
VII. Summary of Remedial Alternatives - Describes the previously selected remedy
for groundwater and the DDA and EPA's proposed changes to the cleanup plan;
VIII. Evaluation of Alternatives - Evaluates the previously selected remedy for
groundwater and the DDA and EPA's proposed changes to the cleanup plan based
on nine criteria;
IX. Preferred Alternative - Describes EPA's preferred remedial alternative and
affirms that it is expected to fulfill statutory and regulatory requirements; and
X. Community Participation - Provides information on how the public can provide
input to the remedy selection process.
I. SITE BACKGROUND
Site Location and Description
The Site is located in the City of New Castle, New Castle County, Delaware. The Site
property is located along Grantham Lane, east of U.S. Highway 13 (Dupont Highway)
and west of Delaware Route 9 (River Road) (see Figure 1). It consists of approximately
27 acres in an area of residential and light-industrial land use and is bounded to the north
and northeast by the Norfolk Southern Railroad tracks and to the west by Army Creek
which discharges into the Delaware River less than one mile east of the Site. The Army
Creek Landfill Superfund Site (Army Creek Landfill) is located immediately west of the
Site on the opposite bank of Army Creek.
The Site property is a former sand and gravel quarry that was later operated as a
permitted landfill from 1968 until 1976. It includes four waste disposal areas (see Figure
2). Three of these - the Grantham South Area, the Drum Disposal Area (DDA) and the
Inert Area - were unlined gravel pits into which waste materials, including hazardous
substances, were deposited. The fourth area, known as the Ridge Area, was used for
temporary storage of chemical waste and was impacted by the spillage of hazardous
substances. Approximately 550,000 cubic yards of industrial and municipal wastes and
construction rubble were disposed of at the Site, including approximately 15,000 drums
containing liquids and sludge from chemical production, manufacturing and petroleum
refining processes.
In addition to the Site property, the Site includes areas to the south and southwest where
hazardous substances have been transported in groundwater.
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Hydrogeolgic Setting
Geologic formations present beneath the Site include the Columbia Formation and the
Potomac Formation. The Columbia Formation consists of sands with beds of clay and
silt. It ranges in thickness from about 10 feet to over 100 feet and represents the surficial
water table aquifer in the area of the Site. The underlying Potomac Formation is a several
hundred foot thick sand deposit divided by silty clays and clays into the Upper, Middle
and Lower Potomac Aquifers. Site investigations have focused on the Columbia Aquifer
and the Upper Potomac Aquifer, which are both Class II aquifers. These two formations
are separated by the Upper Potomac Confining Unit (UPCU), which is comprised of clay
or silty clay. However, areas, referred to as "zero-clay" areas in Site documents, have
been identified where the clay has been breached or eroded away and the Columbia
Aquifer is separated from the Upper Potomac Aquifer sand unit only by a layer of sandy
clay, silt and silty sand referred to in Site documents as the Upper Potomac Confining
Unit Transition Zone (UPCUTZ). Regionally, the natural groundwater flow direction in
the Upper Potomac Aquifer is to the east and southeast, toward the Delaware River. Near
the Site, groundwater in the Upper Potomac Aquifer flows south, toward the Artesian
Water Company's (Artesian's) public water supply wells at the Llangollen well field,
shown in Figure 1.
History of Contamination and Past and On-going Response Actions
Local officials first discovered groundwater degradation in the Upper Potomac Aquifer in
1971 when landfill leachate constituents were detected in a residential well near the
Army Creek Landfill. In 1973, New Castle County installed groundwater recovery wells
in the Upper Potomac Aquifer between the Army Creek Landfill and Artesian's
Llangollen well field to intercept and contain the contaminant plume emanating from the
Army Creek Landfill. Subsequently, the County modified its groundwater recovery well
network, moving pumping locations closer to the Army Creek Landfill to improve system
performance.
In 1975, the State of Delaware (State) installed several monitoring wells at the Site and
initiated enforcement action against the Delaware Sand & Gravel Company, owner and
operator of DS&G, for violations of the State solid waste permit. In 1976, the State
Attorney General's office ordered DS&G closed.
In 1980, the State reduced and capped the permitted groundwater withdrawal rate from
Artesian's Llangollen well field and Artesian extended public water supply lines to
residences along Grantham Lane and the Llangollen Estates subdivision south of the Site.
EPA placed the Site on the National Priorities List (NPL) on September 8, 1983. In
1984, EPA and DNREC performed an emergency removal of more than 1,600 drums
from the surface of the DDA and Ridge Area. DNREC conducted a remedial
investigation and feasibility study at the Site from 1984 to 1987. In April 1988, EPA
issued a Record of Decision (ROD) selecting on-site incineration of contaminated soil
and waste materials at the DDA and the Ridge Area, construction of a Resource
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Conservation and Recovery Act (RCRA) Subtitle C (composite barrier) cap over the
Grantham South Area, installation of a RCRA Subtitle D (single barrier) cap over the
Inert Area, and collection and treatment of contaminated groundwater with discharge of
treated water to Army Creek.
From 1989 to 1991, the United States Army Corps of Engineers (USACE), on behalf of
EPA, constructed the landfill cap over the Grantham South Area. The State of Delaware
assumed responsibility for monitoring and maintenance of the Grantham South Area in
October 1992.
In 1991, 18 potentially responsible parties (PRPs) entered into a Consent Decree under
Sections 106 and 107 of CERCLA with EPA concerning the adjacent Army Creek
Landfill Superfund site (1991 Consent Decree). Under the 1991 Consent Decree, landfill
owner and operator, New Castle County, agreed to install and operate a groundwater
treatment plant and continue to operate groundwater recovery wells to 1) control the
migration of contaminants released from the Army Creek Landfill and DS&G Sites into
the Upper Potomac Aquifer and 2) restore groundwater quality downgradient of the
Army Creek Landfill property boundary to primary drinking water standards.
Between 1991 and 1993, USACE conducted pre-design investigations at the Site which
showed that contamination at the DDA was more widespread and heterogeneous than
previously recognized. In 1992, EPA determined that buried drums at the DDA posed an
imminent threat and entered into an Administrative Order on Consent (AOC) under
Section 106 of CERCLA with 22 PRPs who agreed to design and construct a subsurface
slurry wall around the DDA as an interim removal action.
Based on the results of the pre-design investigations performed by USACE, EPA
reassessed the remedy selected in the 1988 ROD and issued a ROD Amendment in
September 1993. The ROD Amendment upgraded the selected cover system for the Inert
Area to a RCRA Subtitle C cap and changed the selected remedy for contaminated soil at
the DDA and the Ridge Area from excavation and on-site incineration to enclosure
within a slurry wall containment system, including a RCRA Subtitle C cap, with in-situ
treatment by soil vapor extraction and bioventing.
In 1994, the PRPs installed a three-foot-thick soil-bentonite slurry wall, keyed into the
underlying UPCU, around a three-acre area encompassing the DDA and the surrounding
soils affected by historical releases from the DDA. EPA accepted the PRPs' certification
of completion of slurry wall construction in February 1995.
In June 1995, 31 PRPs, referred to as the DS&G Remedial Trust, entered into a Consent
Decree under Sections 106, 107 and 113 of CERCLA with EPA, agreeing to implement
the modified response actions selected in the 1993 ROD Amendment and to monitor and
maintain the Grantham South Area (1995 Consent Decree).
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From 1996 to 1997, the DS&G Remedial Trust constructed a RCRA Subtitle C landfill
cap over the Inert Area. EPA accepted the Remedial Action Report documenting
completion of cap construction in September 1997.
From 1995 to 1997 the DS&G Remedial Trust completed remedial action and
construction activities at the DDA and the Ridge Area. Approximately 5,000 tons of
PCB-contaminated soil, drum carcasses, contaminated solids, asbestos containing
materials and hazardous liquids were excavated or removed and transported to permitted
facilities for disposal. The remainder of the soil excavated from the Ridge Area and the
DDA was combined with woodchips, sand and di-ammonium phosphate to encourage
bioremediation of the soil contaminants and placed in a bio-cell within the slurry wall
surrounding the former DDA. A dewatering system and a bioventing system were
installed to enable circulation of oxygen-enriched air throughout the contaminated soil
within the slurry wall, and a temporary cap1 was constructed over the bioremediation area
(BRA). The DS&G Remedial Trust began operating the dewatering and bioventing
systems at the BRA in 1997.2 In 1998, the DS&G Remedial Trust's consultant noted that
upward seepage from the Potomac Aquifer into the Columbia Aquifer due to artesian
pressure would likely preclude the complete dewatering of the soil at the BRA.
In 1999, bis(2-chloroethyl)ether (BCEE), a Site-related contaminant of concern, was
detected in groundwater at the Llangollen well field. In 2000, Delaware's Department of
Health and Social Services proposed an interim health advisory level for BCEE (0.096
micrograms per liter [|ig/L]) and Artesian installed a granular activated carbon system to
remove BCEE from groundwater pumped from the Llangollen well field prior to its
distribution to customers.
EPA issued an Explanation of Significant Differences (ESD) in July 2003 to clarify and
modify the institutional controls selected for the Site. The Agency issued Unilateral
Administrative Orders (UAOs) under Section 106 of CERCLA to the three separate
owners of the Site property in 2004, 2006 and 2008, respectively, requiring the relevant
Respondents to provide Site access and implement institutional controls establishing land
and groundwater use restrictions. Respondents to the 2006 and 2008 UAOs have
complied with the terms of their respective UAO. EPA is working to secure full
compliance from the former operator of DS&G with the requirements of the 2004 UAO.
In May 2004, the dewatering of the BRA was suspended with EPA approval in order to
allow water levels within the slurry wall to rise during the course of a six-month pilot
study proposed by the DS&G Remedial Trust. The primary purpose of the "slurry-wall
flood test" (SWFT) was to evaluate the impacts, following several years of bioventing, of
1 EPA approved the DS&G Remedial Trust's proposal to employ a temporary cap during
bioventing and defer installation of the RCRA Subtitle C cap until the completion of
bioventing. The temporary cap consists of geosynthetic clay liner covered with 15 inches
of soil.
2 A determination was made, based on pre-design studies, not to perform soil vapor
extraction and to proceed directly to bioventing at the DDA/BRA.
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the remaining soil contamination on shallow groundwater at the BRA. Groundwater
monitoring performed during the SWFT suggested that the soil contamination remaining
at the BRA was continuing to impact shallow groundwater.
In July 2004, EPA approved New Castle County's related pilot study proposal to suspend
operation of the Army Creek Landfill groundwater recovery and treatment system for a
one-year period and refocus groundwater recovery efforts in the area immediately
downgradient of the former DDA where the highest BCEE concentrations had been
observed. One objective of the pilot study was to determine whether rebounding
groundwater elevations in the Upper Potomac Aquifer and the Columbia Aquifer would
cause new releases of hazardous substances to groundwater or Army Creek.3 An
additional objective was to evaluate focused source control measures as an alternative to
the high-volume groundwater extraction required to maintain a groundwater divide
between the Superfund sites and the Llangollen well field. New Castle County shut
down the Army Creek Landfill groundwater recovery wells in October 2004 and began
pumping groundwater from extraction well PW-1 to capture releases from the DDA and
discharging the groundwater to the County's wastewater treatment plant in a cost-sharing
agreement with the DS&G Remedial Trust.
During the SWFT and the New Castle County pilot study, groundwater elevations were
monitored in the Columbia and Upper Potomac Aquifers in the vicinity of the
DDA/BRA. Based on the observed hydraulic connection between the Upper Potomac
Aquifer and the Columbia Aquifer, which prevented dewatering of the soil within the
slurry wall and resulted in ongoing releases of dissolved-phase contaminants from the
DD A/BRA into the Upper Potomac Aquifer, EPA concluded that the remedial action at
the DDA was not performing as intended. EPA's Third Five-Year Review Report for the
Site, issued in 2005, recommended that the DS&G Remedial Trust reassess the response
actions at the DD A/BRA.
In June 2006, DNREC established a groundwater management zone in the vicinity of the
Site which places restrictions and conditions on the installation of new public or domestic
water supply wells to prevent potential exposure to contaminated groundwater.
EPA approved several extensions of the New Castle County pilot study and the SWFT
through early May 2009. Groundwater monitoring during this period showed that
primary drinking water standards had been met at the Army Creek Landfill property
boundary and that the BCEE groundwater plume originated at the DDA and not the Army
Creek Landfill. On May 4, 2009, EPA notified New Castle County that renewed
operation of the Army Creek Landfill groundwater collection and treatment system
would not be required, consistent with the terms of the 1991 Consent Decree for the
Army Creek Landfill site. In order to capture BCEE and other contaminants released
from the DDA into the Upper Potomac Aquifer, the County continued to operate
3 Based on the results of extensive groundwater and stream monitoring, the suspension of
pumping at the Army Creek Landfill well field did not result in new releases of
contamination from the Army Creek Landfill waste management area.
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extraction well PW-1 until October 15, 2012, when the DS&G Remedial Trust assumed
shared responsibility for its operation with EPA funding pursuant to a Disbursement
Agreement between EPA and the DS&G Remedial Trust and New Castle County. Under
the terms of the Disbursement Agreement, EPA reimburses the DS&G Remedial Trust
and the County for costs incurred in operating PW-1 with funds from site-specific special
accounts for both the Army Creek Landfill and the Site.
In 2008, EPA requested that the DS&G Remedial Trust implement additional response
actions at the DDA to provide hydraulic containment of the source area. In May 2009,
the DS&G Remedial Trust began operating a low flow groundwater extraction system
(LFExS) within the slurry wall to mitigate the release of contaminants from the DDA into
the Upper Potomac Aquifer. Groundwater from the system is discharged to the County's
wastewater treatment plant in Wilmington, Delaware. Because the LFExS utilizes
components of the BRA bioventing system, it was necessary to terminate bioventing
operations in order to implement this interim source control measure. Vertical head
differences observed between the Columbia Aquifer and the Upper Potomac Aquifer in
the vicinity of the DDA indicate that the LFExS has generally induced an upward
gradient across the most impacted portions of the slurry-wall containment area since
October 2012, mitigating the release of contaminated groundwater from the DDA into the
Upper Potomac Aquifer.
In April 2010, EPA notified the DS&G Remedial Trust of the need to perform additional
site characterization and a feasibility study to evaluate additional response actions for the
DDA source area and the impacted Upper Potomac Aquifer, including the Llangollen
well field.
II. SITE CHARACTERISTICS
Supplemental Site Characterization and Feasibility Study
Additional site characterization was performed in accordance with Golder Associates'
October 2011 Feasibility Study Work Plan - Revision 2. The following activities were
performed from 2011 through 2013:
• Soil borings were advanced at five locations within the slurry-wall containment
system and soil samples were collected and analyzed for volatile organic
compounds (VOCs) and semi-volatile organic compounds (SVOCs). Soil
samples were also collected and visually inspected to evaluate the micro-
stratigraphy of the UPCU beneath the DDA.
• A new monitoring well was installed in the Columbia Aquifer between the
northern section of the slurry wall and the railroad track. A soil sample collected
from the well borehole was analyzed for VOCs and SVOCs.
• 25 new monitoring wells were installed in the Upper Potomac Aquifer at and
downgradient of the DDA. Borings were advanced using rotosonic drilling with
vertical aquifer profiling to assist in the selection of screened intervals. Soil
samples were collected from the UPCUTZ and analyzed for VOCs and SVOCs to
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evaluate the potential for contaminants to leach into the upper sand and the
potential presence of non-aqueous phase liquid (NAPL). Well screens were set
across the UPCUTZ (11 wells) and the upper (11 wells) and lower (3 wells) sand
units of the Upper Potomac Aquifer.
• Groundwater samples were collected from new and previously existing
monitoring wells and analyzed for VOCs, SVOCs and metals.
• Aquifer testing was performed to determine aquifer hydraulic properties.
The results and findings of the field activities and data evaluations are described in detail
in the Supplemental Site Characterization Report - Revision 2 and are summarized
below:
• Contaminants, including benzene, ethylbenzene, xylenes and BCEE, are present
in both saturated and unsaturated soil within the slurry-wall containment area.4
The maximum concentrations of these contaminants detected in soil samples
collected in 2011 are 1,100 micrograms per kilogram (|ig/kg), 12,000 |ig/kg,
59,000 |ig/kg and 330 |ig/kg, respectively. Benzene, ethylbenzene and xylenes
were also found in the soil sample collected between the slurry wall and the
railroad track, but the concentrations were one to two orders of magnitude lower
than the concentrations within the slurry wall containment system.
• Contaminants, including benzene, ethylbenzene, xylenes and BCEE,
are present in soil in the UPCUTZ but at concentrations that are lower than those
detected in soil at the DDA. The maximum concentrations of these contaminants
detected in soil samples collected in 2012 and 2013 are 1,000 ng/kg, 120 ng/kg,
400 |ig/kg and 12 ng/kg, respectively. 1,4-dioxane is also present in soil in the
UPCUTZ (up to 390 |ig/kg).
• Contaminants have migrated from the Columbia Aquifer at the DDA through
transmissive zones and gaps in the UPCU into the underlying UPCUTZ. Back
diffusion of contaminants from the finer-grained layers in the UPCUTZ into the
coarser-grained layers of the UPCUTZ and the Upper Potomac Aquifer upper
sand represents a continuing source of groundwater impacts.
• A plume of groundwater contaminants extends from the DDA through the Upper
Potomac Aquifer to the Llangollen well field, nearly one mile downgradient. The
primary organic contaminants of concern (COC) are BCEE and 1,4-dioxane5
which are both probable human carcinogens. The highest BCEE concentrations
are found in the UPCUTZ immediately downgradient of the DDA (up to 690
|ig/L) and in the upper sand of the Upper Potomac Aquifer (180 |ig/L at
monitoring well P-6). The highest 1,4-dioxane concentrations are also found in
4 Analytical results for 1,4-dioxane in soil samples collected within the slurry-wall
containment area are not available because 1,4-dioxane was not included on the target
analyte list when the samples were collected. The presence of 1,4-dioxane in
groundwater within the containment area suggests that 1,4-dioxane is also present in the
soil.
5 In 2014, Artesian installed an ultraviolet/hydrogen peroxide treatment system to remove
1,4-dioxane from groundwater pumped from the Llangollen well field.
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the UPCUTZ immediately downgradient of the DDA (up to 2,800 |ig/L) and in
the upper sand (390 |ig/L at monitoring well P-6). The highest concentrations of
BCEE and 1,4-dioxane detected in the lower sand of the Upper Potomac Aquifer
are 36 |ig/L and 150 |ig/L, respectively, at monitoring well UPA-03D. BCEE and
1,4-dioxane concentrations in groundwater in the Upper Potomac Aquifer in 2013
are depicted in Figures 3 and 4, respectively.
• Manganese concentrations in the downgradient portion of the plume (monitoring
wells UPA-02D and MW-26N) have been generally increasing since 2011.
• Concentrations of certain contaminants (e.g., ethylbenzene, 1,2,4-
trimethylbenzene and xylenes) in soil and/or groundwater suggest the potential
presence of residual NAPL in the Columbia Aquifer at the DDA. In addition,
xylene concentrations in groundwater suggest the potential for residual NAPL in
the UPCUTZ in the immediate vicinity of the DDA.
Vapor Intrusion Investigation
Certain chemicals that are released into the subsurface may form hazardous vapors.
Those vapors can be transported through unsaturated soils and eventually enter buildings
through cracks or other conduits in basement floors, walls or foundations. This
phenomenon is known as vapor intrusion. In 2006, the DS&G Remedial Trust concluded
that vapor intrusion did not present unacceptable risks to residents or workers in
buildings near the Site based on VOC and SVOC concentrations in soil gas samples
collected adjacent to the buildings.6
In April and June 2013, the DS&G Remedial Trust collected indoor and outdoor ambient
air samples at an office building adjacent to the Site when the low levels of methane
detected in the building's basement during quarterly monitoring of the Inert Area
exceeded the threshold for additional monitoring established by EPA. The samples were
submitted to a laboratory for analysis of VOCs. The following VOCs were detected at
concentrations above EPA's industrial screening levels in one or both indoor air samples
which were collected from the basement of the office building: benzene, 1,4-
dichlorobenzene, ethylbenzene, trichloroethene, 1,1,2,2-tetrachloroethane, 1,2,4-
trimethylbenzene, 1,2-dibromoethane, 1,2,3-trichloropropane and xylenes. 1,4-
dichlorobenzene was also found in the outdoor air sample at a concentration above the
screening level. It was not determined whether the VOCs detected in the indoor air
samples were caused by landfill gas migration from the Inert Area into the basement of
the building, other potential sources within or near the building, or a combination of the
two.
In November 2014, the DS&G Remedial Trust voluntarily installed and began operating
a sub-slab depressurization system (SSDS) in the office building and the adjoining
automotive repair shop to mitigate the potential for migration of vapors, including
methane, into the building. Confirmatory indoor air samples and an ambient air sample
6 Indoor air concentrations were estimated with Version 3.1 of the Johnson and Ettinger
model vapor intrusion model.
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were collected in December 2014, 30 days following installation of the SSDS. The
indoor air samples were collected from both the unfinished basement and the first floor of
the office building, as well as the office space in the repair garage.
EPA reviewed the confirmatory sample analytical results and found that the VOCs
detected in the indoor air while the system was in operation were within EPA's
acceptable risk range. Based on EPA's evaluation of the performance testing results, the
SSDS is operating as designed and is inducing vacuum conditions beneath the slab to
mitigate the potential for sub-slab vapors to enter the building.
The DS&G Remedial Trust is sampling indoor air at the office building and adjoining
repair shop every five years during the heating season in accordance with the operation
and maintenance (O&M) plan for the Inert Area.
Additional Groundwater Monitoring Performed by EPA
In October 2013 and April 2015, EPA obtained groundwater samples from selected Site
monitoring wells and analyzed the samples for perfluorooctanoic acid (PFOA),
perfluorooctane sulfonate (PFOS) and other perfluoroalkyl substances (PFAS). PFOA
was detected in these samples at concentrations up to an estimated 273 nanograms per
liter (ng/L). PFOS was detected at concentrations up to an estimated 26.8 ng/L. The
DS&G Remedial Trust will begin monitoring groundwater for PFAS in October 2016.
EPA will oversee the monitoring and conduct or oversee a risk analysis to determine if
these contaminants need to be addressed by the response actions at the Site in the future.
III. REASON FOR THE PROPOSED CHANGE
Since EPA selected and the DS&G Remedial Trust and New Castle County implemented
response actions at the Site, additional site characterization has provided the following
new information:
• Transmissive zones and gaps in the UPCU beneath the slurry-wall containment
area have prevented dewatering of the soil at the DDA/BRA, impeding
bioremediation in the saturated zone, and allowed the release of contaminants
from the DDA into the Upper Potomac Aquifer.
• The release of dissolved-phase contaminants from the slurry-wall containment
area into the Upper Potomac Aquifer can be effectively reduced through carefully
monitored and maintained hydraulic control measures.
• The UPCUTZ is a key hydrostratigraphic unit beneath the Site. Releases from
the DDA have impacted this unit which, because of its hydraulic properties, has
become a persistent secondary source of contamination to the Upper Potomac
Aquifer sand units.
• 1,4-dioxane is a groundwater contaminant at the Site; both BCEE and 1,4-
dioxane have migrated in groundwater to the Llangollen well field.
• Documented landfill gas migration up to 110 feet beyond the perimeter of the
Inert Area and along the perimeter of the Grantham South Area represents a
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pathway for potential exposure to Site-related contaminants in indoor air in the
event of future construction near the landfills. The locations of the Inert Area
and the Grantham South Area are shown in Figure 2.
Source control measures selected in the 1993 ROD Amendment and implemented at the
DDA have not prevented contaminant migration into the Upper Potomac Aquifer. In
addition, the contaminated UPCUTZ is a recently identified secondary source of impacts
to groundwater in the Upper Potomac Aquifer sand units which was not addressed by
previous response actions. The New Castle County recovery well network was not
designed or intended to address contaminants in the UPCUTZ and the long-term impacts
of that contamination on the Upper Potomac Aquifer sand units. Based on new
information about the nature and extent of contamination, and fate and transport
mechanisms at the Site, additional response actions are required in order to protect human
health and the environment.
IV. SCOPE AND ROLE OF THE PROPOSED RESPONSE ACTIONS
Previously implemented response actions addressing groundwater and the DDA have not
performed as expected. EPA proposes to modify the remedy selected for groundwater in
the 1988 ROD and the remedy selected for the DDA in the 1993 ROD Amendment, and
to add requirements to protect against potential future vapor intrusion due to migration of
landfill gas. EPA expects the proposed modifications to be the final action for the Site.
EPA's proposed modification would restore contaminated groundwater in the Upper
Potomac Aquifer to beneficial use within a reasonable time frame, prevent exposure to
Site contaminants in drinking water, effectively mitigate the release of contaminants from
the DDA into the Upper Potomac Aquifer, prevent exposure to contaminated soil at the
DDA and eliminate potential future exposure to Site-related contaminants in indoor air.
V. SUMMARY OF SITE RISKS
The 1988 ROD identified unacceptable risks associated with potential future exposure to
contaminated groundwater (due to the presence of benzene, BCEE, chlorobenzene, 1,2-
dichloroethane, ethylbenzene, methylene chloride, toluene, xylenes, phenol, styrene,
methyl ethyl ketone and methyl isobutyl ketone) and direct contact with surface soil (due
to the presence of antimony, arsenic, barium, copper, lead and polychlorinated biphenyls)
at the Ridge Area. Surface soil at the Inert Area, Grantham South Area and DDA, and
Site surface water, sediment and ambient air were found not to present unacceptable risks
to human health or the environment. Risks associated with potential exposure to
subsurface soil were not discussed in the 1988 ROD.
The 1993 ROD Amendment identified contaminated soil at the DDA and the Ridge Area
as sources of groundwater contamination that would present unacceptable risks to any
exposed individuals, and established risk-based soil cleanup standards for groundwater
protection for each of these areas.
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As discussed in Section VI of this Proposed Plan, the currently enforceable groundwater
remediation standards for the Upper Potomac Aquifer are National Primary Drinking
Water Regulations, known as maximum contaminant levels (MCLs) established under
the Safe Drinking Water Act, 42 U.S.C. Section 300g-l, for certain contaminants in
public water systems. In support of the Feasibility Study, Site-specific risk-based
preliminary remediation goals (PRGs) were developed for groundwater in the Upper
Potomac Aquifer. Site-specific groundwater chemicals of concern (COCs) were
identified, and the PRGs developed, based on a risk evaluation of the concentrations of
chemicals of potential concern (COPCs) in groundwater samples collected between April
2012 and April 2014 from monitoring wells in the core of the Upper Potomac Aquifer
groundwater contaminant plume. Consistent with EPA risk assessment guidance, COPCs
were not considered significant contributors to risk and were not identified as COCs if
their individual carcinogenic risk contribution was less than one in a million (1 x 10"6)
and their non-carcinogenic Hazard Quotient (HQ) was less than 0.1 for a target organ
with a Hazard Index (HI) greater than 1.0. In addition, certain COPCs were not retained
as COCs based on their low frequency of detection, consistent with EPA guidance. PRGs
for the identified COCs were selected to achieve a cumulative cancer risk of one in
10,000 (1 x 10"4) and/or a target-organ specific HI of less than 1.0 when considering all
COCs, and to comply with MCLs.
The list of COCs and PRGs for groundwater in the Upper Potomac Aquifer is presented
in Table 1.
Table 1
Chemical of Concern
Selected PRG (jug/L)
Selection Criterion
1,2,4-Trimethylbenzene
11
Target HQ of 0.75
1,2-Dichloroethane
None
*
1,3,5-Trimethylbenzene
None
*
1,4-Dichlorobenzene
None
*
1,4-Dioxane
7.8
Target Risk of 1.0 x 10"5
Arsenic
0.6
Target HQ of 0.1
Benzene
5.0
MCL
Bis(2-chloroethyl)ether
0.14
Target Risk of 1.0 x 10"5
Chlorobenzene
None
*
Chloroform
None
*
Cobalt
6.0
Target HQ of 1.0
Ethylbenzene
15
Target Risk of 1.0 x 10"5
Iron
13,939
Target HQ of 1.0
Manganese
190
Target HQ of 0.44
Naphthalene
None
*
Xylenes (total)
92
Target HQ of 0.44
* PRGs were not developed
pose an unacceptable risk; he
these COCs were taken into
to ensure cumulative risk wil
"or groundwater COCs that are present at levels that do not
)wever, cancer risk and/or non-cancer HQs associated with
account when developing PRGs for the remaining COCs
1 be below EPA's risk criteria.
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The methodology for identifying COCs and deriving the PRGs is more fully described in
Golder Associates' Technical Memorandum, Development of Site-Specific Preliminary
Remediation Goals - Revision 2 (December 2014).
Vapor Intrusion Risk Assessment
As discussed in Section II of this Proposed Plan, VOCs were detected in outdoor and
indoor air samples collected at a business adjacent to the Site in April and June 2013.
EPA performed conservative calculations of potential health risks using the test results
for the air samples collected in June 2013. The estimated risks for exposure to outdoor
air did not exceed EPA's criteria for acceptable risk. However, the estimated risks for
exposure to indoor air exceeded EPA's risk criteria as summarized below:7
• Estimated risks for office building basement indoor air:
> Carcinogenic risk of 2.0 x 10"4
> Non-carcinogenic HI of 4.8
The estimated human health risk is attributable primarily to 1,2-dibromomethane, 1,2,3-
trichloropropane and 1,2,4-trimethylbenzene. 1,2,4-trimethylbenzene is a COC in
groundwater at the Site. However, the source of the VOCs detected in the 2013 indoor
air samples was not confirmed.
Risk Assessment Summary
The Site presents unacceptable risks to human health and additional response actions are
necessary to reduce the risks to levels that are within or below EPA's acceptable risk
range. EPA has determined that implementation of the proposed modifications to EPA's
selected remedy identified in this Proposed Plan are necessary to protect human health
and the environment from actual or threatened releases of hazardous substances.
VI. REMEDIAL ACTION OBJECTIVES
Remedial Action Objectives for Groundwater
The 1988 ROD does not explicitly state a Remedial Action Objective (RAO) for
groundwater impacted by releases from the Site. However, it states that the selected
remedy includes continued operation of the New Castle County groundwater recovery
wells until "the groundwater at the site boundary has consistently met the acceptable
water exposure levels" which are given in Table 7 of the 1988 ROD.
7 These risk estimates were based on the assumption that office workers are exposed to
levels found in the basement air sample 8 hours a day for 250 days a year, over 25 years.
However, the basement is used for storage and the office workers occupy the ground
floor of the building where lower concentrations of Site-related VOCs would be expected
to be found.
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As discussed in Section I of this Proposed Plan, New Castle County, upon entering into
the 1991 Consent Decree for the Army Creek Landfill Site, agreed to operate
groundwater recovery wells in the Upper Potomac Aquifer to attain primary drinking
water standards beyond the Army Creek Landfill property boundary. The discrepancy
between the groundwater cleanup levels given in the 1991 Consent Decree for the Army
Creek Landfill and those in the 1988 ROD for this Site is discussed in EPA's September
2015 Five-Year Review Report for Delaware Sand & Gravel Landfill Superfund Site
which is part of the Administrative Record for the Site. An additional inconsistency
involves the area of attainment: the 1991 Consent Decree for the Army Creek Landfill
specifies that groundwater cleanup levels are to be met beyond the Army Creek Landfill
property boundary while the 1988 ROD for this Site states that the groundwater cleanup
levels are to be met beyond the DS&G Site property boundary.
Remedial Action Objectives for the DDA
The 1993 ROD Amendment identified the following RAOs for the DDA:
• Prevent direct contact with contaminated soil;
• Protect groundwater from hazardous substances leaching from contaminated soil;
• Reduce the soil contaminant concentrations to levels that would not cause
groundwater contaminant concentrations in the Upper Potomac Aquifer to:
> present an exposed individual with a cumulative excess lifetime cancer risk
above "the 10"6 risk range"; or
> cause adverse health effects in an exposed individual (i.e., result in a Hazard
Index (HI) greater than or equal to 1.0).
Modified Remedial Action Objectives
Since implementation of the selected remedial actions, MCLs have been attained at the
Army Creek Landfill property boundary and the temporary cap and fencing at the DDA
have prevented direct contact with contaminated soil. However, the existing remedies
have not achieved the remainder of the RAOs. Furthermore, the RAOs do not address
contamination in the UPCUTZ which represents a secondary source of long-term impacts
to the Upper Potomac Aquifer sands. Nor do the RAOs address COCs in groundwater at
the Llangollen well field or the potential for exposure to Site-related contaminants in
indoor air due to potential vapor intrusion. In addition, the RAOs do not address all of
the groundwater COCs listed in Table 1 of this Proposed Plan. Therefore, the following
modified RAOs were developed:
• Prevent direct contact with contaminated soil enclosed within the slurry wall at the
DDA.
• Prevent migration of contaminants from the DDA that would cause contaminant
concentrations in the groundwater of the Upper Potomac Aquifer or the Columbia
Aquifer to exceed the Site-specific PRGs within the area of attainment (as defined
below).
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• Prevent direct contact with groundwater containing contaminants from the DS&G
Site at levels that exceed the Site-specific PRGs.
• Restore groundwater within the area of attainment (throughout the contaminant
plume, at and beyond the boundary of the Waste Management Area8) to its beneficial
use in a reasonable time frame. The Waste Management Area and the area of
attainment are shown in Figure 5.
• Prevent contaminant migration from subsurface vapor intrusion into indoor air that
would result in unacceptable levels of risk, i.e., prevent exposures that would present
a cumulative excess lifetime cancer risk greater than one in one million (1 x 10"6) or
result in a HI greater than 1.0.
VII. SUMMARY OF REMEDIAL ALTERNATIVES
This section summarizes the portion of the remedy selected in the 1988 ROD, as
amended by the 1993 ROD Amendment and 2003 ESD, that pertains to contaminated
groundwater in the Upper Potomac Aquifer and contaminated soil at the DDA and Ridge
Area (Previously Selected Remedy), and EPA's proposed changes (Preferred Alternative)
for meeting the revised RAOs presented in Section VI of this Proposed Plan. The
Preferred Alternative is one of six remedial alternatives (including No Action) evaluated
in the Feasibility Study and briefly described below. The Preferred Alternative, which is
described below in greater detail, will address 1) contaminated groundwater in the Upper
Potomac Aquifer, including groundwater in the UPCUTZ and groundwater pumped from
Artesian's Llangollen well field, 2) contaminated soil and groundwater within the slurry
wall surrounding the former DDA and 3) potential vapor intrusion at new construction
adjacent to the Inert Area and the Grantham South Area.
Previously Selected Remedy:
The Previously Selected Remedy includes those components of the remedies selected in
the 1988 ROD, 1993 ROD Amendment and the 2003 ESD which address waste and
contaminated soil at the DDA and the Ridge Area and contaminated groundwater in the
Upper Potomac Aquifer. It does not include the response actions that address waste and
contaminated soil at the Grantham South Area and the Inert Area. The Previously
Selected Remedy includes the following components:
• Construction of a slurry wall, keyed into the underlying natural clay layer,9 around
the DDA and the surrounding contaminated soil and groundwater in the Columbia
Aquifer;
• Installation and operation of a groundwater extraction system to dewater the soil
contained within the slurry-wall enclosure;
8 The DS&G Site includes three areas where wastes are being managed on-site (DDA,
Inert Area and Grantham South Area) and one former waste storage area (Ridge Area) in
close proximity. These areas and the small parcels which connect them constitute the
Waste Management Area at the Site.
9A hanging slurry wall was constructed above the zero-clay area northwest of the DDA.
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
• Excavation and offsite treatment or disposal of buried drums, waste and highly
contaminated soil at the DDA and the Ridge Area;
• Transfer of the remaining contaminated soil excavated from the Ridge Area to the
slurry-wall containment area;
• Treatment of the soil within the containment area using soil vapor extraction and
bioventing;
• Construction of a composite barrier (RCRA Subtitle C) cap over the slurry-wall
containment area;
• Installation of perimeter fencing around the containment area;
• Installation of a soil cover over the Ridge Area;
• Continued operation of the Army Creek Landfill groundwater recovery wells until
cleanup levels are met at the DS&G Site property boundary;
• On-site treatment of groundwater and discharge of treated groundwater to Army
Creek;
• Institutional controls to prevent future use of the Site property which could
compromise the effectiveness of the selected remedy and the installation of drinking
water wells on the Site property.
Estimated Capital Cost: $29,241,300 10
Estimated Annual O&M Cost: $380,500 10
Estimated Present Worth Cost: $33,540,100 10
All elements of the Previously Selected Remedy have been implemented with the
exception of soil vapor extraction, the installation of a RCRA Subtitle C cap at the DDA
and the Site property owner's recording of a notice of institutional controls and access
requirements in the land records.
Remedial Alternatives Evaluated in the 2016 Feasibility Study:
Alternative A - No Action
Existing institutional controls would remain in place, there would be no collection and
treatment of groundwater and the temporary cap at the DDA would not be upgraded or
maintained.
Alternative B - DDA Containment and Groundwater Extraction from Upper Potomac
Aquifer with Direct Discharge to Publicly Owned Treatment Works (POTW)
Alternative B represents a limited-action alternative which includes continuation of
interim response actions (operation of the LFExS within the slurry-wall containment
system and operation of groundwater extraction well PW-1 with discharge to the POTW),
construction of a composite barrier cap over the slurry-wall containment area, treatment
10 These figures are the sum of the estimated costs in the 1993 ROD Amendment for
remediation of the DDA and Ridge Area and the estimated costs in the 1988 ROD for
Upper Potomac Aquifer groundwater recovery and treatment. No adjustment was made
to account for the time value of money and these costs are not directly comparable with
the estimated costs for the Preferred Alternative.
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
at the Llangollen well field and institutional controls to prevent potential future exposure
to contaminants capable of migrating into indoor air.
Alternative C - DDA Enhanced Containment and Groundwater Extraction from
UPCUTZ and Upper Potomac Aquifer with Direct Discharge to POTW
Alternative C would provide reliable containment of contaminants at the DDA with an
enhanced LFExS (eLFExS) and construction of a composite barrier cap over the slurry-
wall containment area. It includes continued groundwater extraction and the installation
of additional groundwater extraction wells in the Upper Potomac Aquifer, including the
UPCUTZ, with discharge of extracted groundwater to the POTW. Alternative C would
also include treatment at the Llangollen well field and institutional controls to prevent
potential future exposure to Site contaminants capable of migrating into indoor air.
Alternative D - DDA Soil Flushing and Groundwater Extraction from UPCUTZ and
Upper Potomac Aquifer with Direct Discharge to POTW
Alternative D includes the same components as Alternative C plus treatment of
contaminated soil at the DDA using soil flushing.
Alternative E - DDA Targeted In-situ Chemical Oxidation (ISCO) and Groundwater
Extraction from UPCUTZ and Upper Potomac Aquifer with Direct Discharge to
POTW
Alternative E includes the same components as Alternative C plus treatment of
contaminated soil in targeted areas of the DDA using ISCO.
Alternative F - DDA Excavation and ISCO and Groundwater Extraction from
UPCUTZ and Upper Potomac Aquifer with Direct Discharge to POTW
Alternative F includes the same components as Alternative C plus excavation and
disposal, in an on-site lined landfill, of unsaturated soil at the DDA and treatment of
saturated soil at the DDA using ISCO.
EPA prefers Alternative C to the other alternatives evaluated in the Feasibility Study.
Alternative C would achieve all of the revised RAOs, address the secondary source of
contamination in the UPCUTZ and remediate groundwater throughout the area of
attainment within a reasonable time frame. The operating history of the LFExS indicates
that the remaining contamination at the DDA can be reliably contained by operation of
the eLFExS and placement of a permanent cap included in Alternative C. Alternative A
would not be protective of human health and the environment. Alternative B would not
address contamination in the UPCUTZ or remediate groundwater throughout the area of
attainment within a reasonable time frame. Alternatives D through F, like Alternative C,
would achieve all of the revised RAOs, address contamination in the UPCUTZ and
remediate groundwater within a reasonable time frame. Each of these alternatives
includes additional treatment of the remaining soil contamination at the DDA, entailing
implementation uncertainties and additional costs. However, Alternatives D through F
would not accelerate the groundwater restoration time frame because significant
contaminant mass exists outside the DDA in the fine-grained materials of the UPCUTZ.
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Delaware Sand & Gravel Landfill Superfund Site
Preferred Alternative (Alternative C in the Feasibility Study):
The Preferred Alternative would provide reliable containment of contamination
remaining at the DDA through enhancements to the LFExS which is currently operating
within the slurry wall and installation of a composite barrier cap. This alternative would
also include the installation and operation of groundwater recovery wells in the Upper
Potomac Aquifer, including the UPCUTZ, and extraction and ex-situ treatment of Upper
Potomac Aquifer groundwater utilizing existing and potentially additional treatment
systems at the Llangollen well field in order to restore groundwater to its beneficial use.
In addition, this alternative would employ institutional controls to prevent potential future
exposure to Site-related contaminants in indoor air at levels that would present
unacceptable risks.
The Preferred Alternative addresses the three remediation targets enumerated below and
includes the following remedial components:
1. PDA/Columbia Aquifer soil and groundwater
• Existing slurry-wall system;11
• Enhanced LFExS (eLFExS) pumping at an estimated 25 gallons per minute (gpm)12
and equipped with a backup generator and instrumentation and telemetry for real-time
containment monitoring to maintain inward and upward hydraulic gradients;
• A robust groundwater monitoring program to ensure that the eLFExS is operating as
designed;
• A composite barrier cap to minimize infiltration of precipitation through
contaminated soil contained within the slurry wall surrounding the former DDA.
• Institutional controls to prevent direct contact with contaminated soil, the installation
of drinking water wells on the Site property and other future uses of the property
which could compromise the effectiveness of the remedy.
2. Upper Potomac Aquifer
• Installation and operation of extraction wells in areas determined to optimize capture
and remove contaminant mass from the more highly-impacted areas of the Upper
Potomac Aquifer, including the UPCUTZ. The anticipated locations of the proposed
new extraction wells are shown in Figures 6 and 7. The actual configuration of the
groundwater recovery well network and groundwater extraction rates would be
determined by EPA, in consultation with DNREC, during the remedial design.
• Discharge of groundwater pumped from the DS&G Site extraction wells to the
Wilmington wastewater treatment plant.
11 Costs associated with the slurry wall are not included in the cost estimate for the
Preferred Alternative.
12 The LFExS currently operates at a rate of 8 to 10 gpm.
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• Continued groundwater extraction at Artesian's Llangollen well field with treatment
utilizing existing systems for BCEE and 1,4-dioxane and, if necessary, additional
treatment systems targeting other COCs, such as manganese.
• A robust program to monitor performance of the groundwater extractions wells,
confirm they are preventing migration of the groundwater contaminant plume and
evaluate progress toward the attainment of long-term groundwater remediation goals.
• Institutional controls to prevent future use of the Site property which could
compromise the effectiveness of the remedy and to prevent the installation of
drinking water wells on the Site property.13
3. Potential vapor intrusion
Due to the migration of landfill gas beyond the perimeters of the Grantham South Area
and the Inert Area and the potential for vapor intrusion into nearby buildings (existing
and/or future construction), the Preferred Alternative includes use restrictions to prevent
potential future exposure to Site contaminants capable of migrating into indoor air. The
use restrictions would be implemented through an enforceable institutional control such
as a judicial consent decree, administrative order, or an environmental covenant pursuant
to the Delaware Uniform Environmental Covenants Act (7 Delaware Code, Chapter 79,
§§ 7907-7920) and would ensure that all new habitable buildings constructed on or
adjacent to the Site in areas potentially impacted by landfill gas have, at a minimum, a
foundation vapor barrier and subsurface piping for a SSDS. The institutional controls
would require testing of indoor air in any buildings subject to the controls prior to
occupancy and, should indoor air concentrations equal or exceed EPA risk-based criteria,
activation and operation of a SSDS until such time that EPA determined that landfill gas
migration no longer posed a vapor intrusion risk. The areas subject to these use
restrictions would be determined prior to the remedial design.
Estimated Capital Cost: $14,700,000
Estimated Annual O&M Cost: $2,200,000
Estimated Present Worth Cost: $42,300,000
Common Elements
The Previously Selected Remedy and EPA's Preferred Alternative share several common
elements, including the slurry wall which was installed in 1994, a composite barrier cap
and institutional controls restricting land and groundwater use.
13 Additional groundwater use restrictions have been in effect in the area surrounding the
Site since June 2006, when DNREC established a groundwater management zone (GMZ)
encompassing several hazardous waste disposal facilities near the Site. The GMZ places
restrictions on the installation of new water supply wells throughout the known extent of
the Upper Potomac Aquifer contaminant plume.
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Delaware Sand & Gravel Landfill Superfund Site
VIII. EVALUATION OF ALTERNATIVES
Nine criteria are used to evaluate the different remedial alternatives individually and
against each other in order to select a remedy. This section of the Proposed Plan profiles
the relative performance of the Previously Selected Remedy and the Preferred Alternative
against the nine criteria, noting how it compares to the other option under consideration.
The nine criteria are discussed below. Additional detailed analysis of the Preferred
Alternative may be found in the Feasibility Study in the Administrative Record for the
Site.
l-^aliialion Criteria lor Superl'mul Remedial Ahcrn;ili\cs
1. Overall Protection of Human Health and the Environment determines whether an
alternative eliminates, reduces, or controls threats to public health and the environment through
institutional controls, engineering controls or treatment.
2. Compliance with ARARs (applicable or relevant and appropriate requirements) evaluates
whether an alternative meets federal and state environmental statutes, regulations and other
requirements that pertain to a site, or whether a waiver is justified.
3. Long-term Effectiveness and Permanence considers the ability of an alternative to
maintain protection of human health and the environment over time and takes into account the
adequacy and reliability of containment systems and institutional controls needed to manage the
risk posed by treatment residuals and untreated waste.
4. Reduction of Toxicity, Mobility, or Volume of Contaminants through Treatment
evaluates an alternative's use of treatment technologies that permanently and significantly
reduce the toxicity, mobility or volume of hazardous substances at a site.
5. Short-term Effectiveness considers the length of time needed to implement an alternative
and the risks an alternative poses to workers, residents and the environment during
implementation.
6. Implementability considers the technical and administrative feasibility of implementing the
alternative, including factors such as the availability of materials and services.
7. Cost includes estimated capital and annual operations and maintenance costs, as well as
present worth cost. Present worth cost is the total cost of an alternative over time in today's
dollar value. Cost estimates are expected to be accurate within a range of +50 to -30 percent.
8. State/ Support Agency Acceptance considers whether the state agrees with EPA's analyses
and recommendations as described in the remedial investigation and feasibility study reports
and the Proposed Plan.
9. Community Acceptance considers whether the local community agrees with EPA's
analyses and preferred alternative. Comments received on the Proposed Plan are an important
indicator of community acceptance.
Detailed Analysis of Proposed Remedial Alternatives
1. Overall Protection of Human Health and the Environment
DDA/Columbia Aquifer Soil and Groundwater
The Previously Selected Remedy includes institutional controls (groundwater and land
use restrictions), land use controls (fencing, locked gates) and engineering controls (the
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Delaware Sand & Gravel Landfill Superfund Site
temporary cap over the DDA) which prevent direct contact with contaminated soil and
groundwater. If installation of a RCRA Subtitle C cap were completed in accordance
with the 1993 ROD Amendment, the Previously Selected Remedy would also minimize
infiltration and leaching of soil contaminants into groundwater in the Columbia Aquifer
and prevent potential exposure of ecological receptors to contaminated soil. However,
because transmissive zones and gaps occur in the UPCU beneath the slurry-wall
containment area, the Previously Selected Remedy has not prevented contaminant
releases from the DDA to groundwater in the Upper Potomac Aquifer.
Existing institutional and land use controls and the temporary cap at the DDA prevent
direct contact with contaminated soil and groundwater. The Preferred Alternative
includes additional engineering controls (a composite barrier landfill cap over the DDA
and an eLFExS) which would further protect human health and the environment.
Operation of the eLFExS would provide hydraulic control of the groundwater within the
slurry-wall containment area, effectively eliminating future releases from the DDA to
groundwater in the Upper Potomac Aquifer. Installation and maintenance of a composite
barrier cap would continue to eliminate risk associated with direct contact with DDA
soils, and would also minimize infiltration that results in leaching of contaminants to
groundwater in the Columbia Aquifer and prevent potential exposure of ecological
receptors to contaminated subsurface soil.
Upper Potomac Aquifer
The Previously Selected Remedy called for continued operation of the Army Creek
Landfill groundwater recovery wells to attain "acceptable water exposure levels" beyond
the DS&G Site boundary. That remedial component does not provide long term
protection of human health and the environment for the following reasons: it does not
address 1,4-dioxane and other groundwater COCs; it does not address contamination in
the UPCUTZ; it does not restore groundwater throughout the area of attainment to its
beneficial use; and it does not include treatment to address Site-related COCs in
groundwater at the Llangollen well field.
EPA expects that the Preferred Alternative would restore groundwater in the Upper
Potomac Aquifer to its beneficial use within a reasonable time frame. Site-related COCs
would be reduced to acceptable risk-based concentrations within the area of attainment
through the installation and operation of groundwater extraction wells in areas
determined to optimize capture and continued groundwater extraction at the Llangollen
well field. Groundwater treatment currently provided by Artesian at the Llangollen well
field and existing groundwater use restrictions prevent exposure to contaminated
groundwater. The Preferred Alternative includes treatment of groundwater pumped from
the Llangollen well field to remove Site-related COCs prior to distribution to customers;
this treatment would become a part of the selected remedy.
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Potential Vapor Intrusion Mitigation
The DS&G Remedial Trust is voluntarily operating a SSDS at an office building adjacent
to the Site and will continue to monitor indoor air at the building in accordance with the
O&M plan for the Inert Area. However, the Previously Selected Remedy does not
address potential vapor intrusion and would not prevent potential future exposure to Site
contaminants in indoor air.
The Preferred Alternative would prevent potential future exposure to Site contaminants in
the indoor air of any new habitable buildings constructed on or adjacent to the Site in
areas potentially impacted by landfill gas.
2. Compliance with ARARs
DDA/Columbia Aquifer Soil and Groundwater
During implementation of the Previously Selected Remedy, the on-site storage of
hazardous waste and soil containing hazardous waste excavated at the DDA and the
Ridge Area complied with federal and State regulations for owners and operators of
facilities that treat or store hazardous waste. Drum contents, highly contaminated soil
and groundwater extracted from the Columbia Aquifer within the slurry wall were
evaluated in accordance with federal and State regulations for identification of hazardous
waste; materials determined to be hazardous waste were handled in accordance with
federal and State regulations governing generators and transporters of hazardous waste.
The 1993 ROD Amendment identifies State regulations governing air emissions
[Delaware Regulations Governing the Control of Air Pollution (Section 6003)] and
federal regulations governing emissions from process vents (40 C.F.R. §§ 264.1031-
.1034) as ARARs. However, there was no discharge from process vents during operation
of the bioventing system and, therefore, air emission controls were not implemented.
The Preferred Alternative would comply with State standards for owners and operators of
hazardous waste landfills and federal and State standards governing discharges to
publicly owned treatment works (POTWs) which accept and treat sewage and industrial
wastewater. In particular, the design, construction and O&M of the composite barrier cap
to be installed at the DDA would meet State requirements for closure and post-closure
care of hazardous waste landfills [7 DE Admin. Code 1302 Regulations Governing
Hazardous Waste, §§ 264.310(a) and (b)(1), (5) and (6)] and for monitoring and
inspection during the installation of the cover system [7 DE Admin. Code 1302
Regulations Governing Hazardous Waste, §§ 264.303(a)], Groundwater extracted from
the Columbia Aquifer and discharged to the Wilmington wastewater treatment plant
would comply with effluent limitations established by New Castle County and the City of
Wilmington to meet the requirements of Delaware's National Pollutant Discharge
Elimination System Program (7 DE Admin. Code 7201 Regulations Governing the
Control of Water Pollution, Section 6.0) and would meet any pretreatment standards
established by New Castle County and the City of Wilmington in accordance with the
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NPDES General Pretreatment Regulations for Existing and New Sources of Pollution (40
CFR § 403).
Upper Potomac Aquifer
The 1988 ROD identifies MCLs as ARARs for groundwater remediation and states that
the Previously Selected Remedy "would assist in meeting MCLs at or near the site
boundary" within 10 years. However, benzene concentrations within the area of
attainment in the Upper Potomac Aquifer continue to exceed the MCL. In addition, the
Previously Selected Remedy may not have been compliant with all ARARs for the
protection of surface water. While the Army Creek Landfill groundwater recovery wells
were operating, the treatment plant reduced iron concentrations in the extracted
groundwater to levels that met the established discharge limit for iron; however,
estimated levels of BCEE in the treatment plant effluent exceeded the State water quality
standard for the protection of human health (based on fish consumption) on several
occasions. However, the Previously Selected Remedy did not include treatment to
remove BCEE from extracted groundwater prior to its discharge to Army Creek.
The MCLs and non-zero maximum contaminant level goals (MCLGs) for public drinking
water supplies established under the Safe Drinking Water Act are considered to be
relevant and appropriate standards for groundwater remediation under the Superfund
program. The Preferred Alternative would achieve MCLs and non-zero MCLGs for
groundwater contaminants within the area of attainment over time. Groundwater
extracted from the Upper Potomac Aquifer and discharged to the Wilmington wastewater
treatment plant would comply with effluent limitations established by New Castle County
and the City of Wilmington to meet the requirements of Delaware's National Pollutant
Discharge Elimination System Program (7 DE Admin. Code 7201 Regulations
Governing the Control of Water Pollution, Section 6.0) and would meet any pretreatment
standards established by New Castle County and the City of Wilmington in accordance
with the NPDES General Pretreatment Regulations for Existing and New Sources of
Pollution (40 CFR 403). Any pretreatment of groundwater discharged to the POTW, and
treatment to remove COCs from groundwater extracted from the Llangollen well field,
may result in the generation of hazardous waste. Generated hazardous waste would be
managed in accordance with Delaware's standards applicable to generators of hazardous
waste, including storage and manifesting of hazardous waste (7 DE Admin. Code 1302,
§§262.10-.42).
Potential Vapor Intrusion Mitigation
The Previously Selected Remedy did not address potential vapor intrusion. Therefore,
the 1988 ROD and the 1993 ROD Amendment identified no ARARs for vapor intrusion
mitigation.
The Preferred Alternative includes institutional controls to prevent potential future
exposure to Site contaminants capable of migrating into indoor air. If the institutional
controls include an environmental covenant, it would be implemented in accordance with
24
AR310593
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
the Delaware Uniform Environmental Covenants Act (7 Delaware Code, Chapter 79, §§
7907-7920).
3. Long Term Effectiveness and Permanence
The Previously Selected Remedy has not satisfied the criterion of long-term effectiveness
and permanence. Engineering controls selected in the 1993 ROD Amendment and
implemented at the DDA have not prevented the migration of contaminants from the
DDA into the Upper Potomac Aquifer and groundwater extraction from the Upper
Potomac Aquifer utilizing the Army Creek Landfill recovery wells has not reduced the
magnitude of residual risk from potential exposure to contaminated groundwater to
acceptable levels. These failures are primarily attributable to unknown conditions in the
subsurface at the time of remedy selection. In particular, unidentified gaps and
transmissive zones in the UPCU beneath the DDA prevented adequate containment and
treatment of contaminants at the DDA/BRA and the previously selected groundwater
response action was not designed or intended to address a persistent secondary source of
contamination in the UPCUTZ.
The Preferred Alternative would use containment (a cap and the existing slurry wall) and
hydraulic control (eLFExS with instrumentation and telemetry for real-time monitoring)
to prevent exposure to contaminated soil and minimize the migration of contaminants
from soil and groundwater within the Columbia Aquifer at the DDA into the Upper
Potomac Aquifer. A properly installed and maintained cap and slurry wall and carefully
monitored and maintained eLFExS would provide adequate long-term containment of
contaminated soil and groundwater at the DDA. However, permanent land use
restrictions and perpetual maintenance activities would be required to ensure the long
term effectiveness and permanence of the containment system.
The Preferred Alternative would reduce the risks that would result from the use of
groundwater located within the area of attainment, including groundwater extracted from
the Llangollen well field, to acceptable levels through the extraction and treatment of
groundwater. The installation and operation of groundwater extraction wells in the
UPCUTZ would also mitigate the migration of contaminants from the UPCUTZ into the
upper and lower sand units of the Upper Potomac Aquifer. Upon attainment of the
groundwater cleanup levels throughout the area of attainment, the scope of the current
restrictions on groundwater use could be reevaluated. However, restrictions on the use of
groundwater beneath the Waste Management Area would be needed for the foreseeable
future to prevent unacceptable future exposure risks. It is anticipated that continued
operation of groundwater extraction wells would be required for some time after the
groundwater cleanup levels were met in order to prevent contaminants beneath the Waste
Management Area from migrating to downgradient areas of the Upper Potomac Aquifer.
Migration of landfill gas from the Inert Area and the Grantham South Area may present a
source of unacceptable indoor air quality should new habitable buildings be constructed
adjacent to the landfills. The Preferred Alternative includes institutional controls to
reduce any such risks to acceptable levels.
25
AR310594
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
The long-term effectiveness and permanence of the Preferred Alternative would be
dependent upon the adequacy of the operation, maintenance and monitoring of the
response actions and the implementation of institutional controls. Because wastes would
be left in place, reassessment of the effectiveness of the Preferred Alternative would be
necessary at five-year intervals as required by CERCLA § 121(c).
4. Reduction of Toxicity, Mobility, or Volume through Treatment
The Previously Selected Remedy provided treatment to reduce the toxicity of
contaminants at the DDA and treatment of extracted groundwater to remove iron and
reduce the aquatic toxicity of effluent discharged to Army Creek. However, groundwater
was not treated to remove organic COCs before it was discharged to Army Creek. In
addition, the Previously Selected Remedy did not include treatment of groundwater
extracted from the Llangollen well field.
Bioventing implemented at the DDA as a component of the Previously Selected Remedy
has already produced significant and permanent reductions in the concentrations of
hazardous substances at the DDA. The Preferred Alternative includes operation of an
eLFExS to provide hydraulic control at the DDA, with discharge of the extracted
groundwater to the POTW for treatment.14 The Preferred Alternative also includes
extraction of contaminated groundwater from the Upper Potomac Aquifer, with discharge
of the extracted groundwater to the POTW or treatment of extracted groundwater at the
Llangollen well field, which would reduce the toxicity of contaminants and the volume of
contaminated groundwater at the Site.
5. Short-term Effectiveness
The Previously Selected Remedy employed fencing, a temporary cap at the DDA and
institutional controls to prevent unacceptable risks from potential exposure to
contaminated soil and groundwater on the Site property. However, it does not include
treatment of groundwater extracted from the Llangollen well field to reduce the
concentrations of COCs to acceptable risk- and health-based standards or address
potential future exposure to contaminants in indoor air and, therefore, does not
adequately address short-term risks.
Artesian's treatment of groundwater at the Llangollen well field, previously implemented
institutional controls, and perimeter fencing and a temporary cap at the DDA are
currently preventing unacceptable exposure risks. Short-term risks associated with the
implementation of the Preferred Alternative would be minimal because of the limited
scope of excavation activities. The installation of a composite barrier cap over the DDA
would provide an immediate reduction in the migration of contaminants from unsaturated
soil at the DDA into groundwater. The Preferred Alternative includes the treatment of
14 It is expected that permanent reductions in the toxicity of some COCs would occur
during secondary (biological) treatment at the POTW.
26
AR310595
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
groundwater extracted at the Llangollen well field and would reduce the concentrations
of COCs to acceptable risk- and health-based levels. Groundwater cleanup standards
would ultimately be met throughout the area of attainment in the Upper Potomac Aquifer
and institutional controls are in place and will prevent exposure to contaminated
groundwater until the RAOs are met. Institutional controls would prevent potential
exposure to Site contaminants in indoor air that could result from the migration of landfill
gas.
6. Implementability
The Previously Selected Remedy has been implemented with the exception of soil vapor
extraction and the installation of a composite barrier cap. However, that remedy did not
perform as designed. Subsurface conditions prevented dewatering of the soil at the
DDA/BRA, impeding bioremediation in the saturated zone, and allowed the continued
release of dissolved-phase contaminants from the DD A/BRA into the Upper Potomac
Aquifer. Groundwater response actions did not address contamination in the UPCUTZ or
restore groundwater quality in the Upper Potomac Aquifer downgradient of the Site
property boundary.
The Preferred Alternative would use technology, equipment and materials that are readily
available and generally proven. Pre-design investigations would be required prior to the
installation of groundwater extraction wells and the installation of extraction wells would
be phased in order to optimize the design and performance of the groundwater collection
system. Treatment systems to remove COCs from groundwater extracted at the
Llangollen well field are already in place and operating effectively. Mechanisms exist
within the State and County governments to institute and enforce land use restrictions to
prevent potential exposure to Site contaminants in indoor air.
7. Cost
The estimated present worth cost of the Previously Selected Remedy, $29,241,300, is the
sum of the estimated costs in the 1993 ROD Amendment for remediation of the DDA and
Ridge Area and the estimated costs in the 1988 ROD for Upper Potomac Aquifer
groundwater recovery and treatment. No adjustment was made to account for the time
value of money and these costs are not directly comparable with the estimated costs for
the Preferred Alternative. The Previously Selected Remedy has been implemented with
the exception of soil vapor extraction and installation of a composite barrier cap at the
DDA. The actual costs for implementation are not readily available to EPA since the
DS&G Remedial Trust implemented the remedies and are not obligated to provide cost
information to EPA.
The estimated present worth cost of the Preferred Alternative is $42,300,000. This 30-
year present worth estimate was calculated using a seven percent discount rate.
27
AR310596
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
8. State Acceptance
EPA will evaluate State acceptance of the Preferred Alternative after the public comment
period ends. State comments and EPA's response to any such comments will be
available in the Responsiveness Summary of the ROD Amendment.
9. Community Acceptance
EPA will evaluate community acceptance of the Preferred Alternative after the public
comment period ends. Community comments and EPA's response to any such comments
will be available in the Responsiveness Summary of the ROD Amendment.
IX. PREFERRED ALTERNATIVE
EPA's Preferred Alternative would add the following new components to the remedy
selected in the 1988 ROD, as amended by the 1993 ROD Amendment and the 2003 ESD
(Current Remedy):
• Treatment to remove COCs at Artesian's Llangollen well field; and
• Institutional controls to prevent potential future exposure to Site contaminants in
indoor air.
EPA's Preferred Alternative would modify the Current Remedy as summarized in the
following table:
(iinenl Remedy
Proposed Remedy
• Treatment of contaminated soil at
the Ridge Area and DDA using
bioventing within the slurry-wall
containment area;
• Extraction of groundwater from
the Upper Potomac Aquifer using
the Army Creek Landfill recovery
wells in order to meet cleanup
levels beyond the Site property
boundary;
• Treatment and discharge of
recovered groundwater to Army
Creek.
• Hydraulic control of contaminated
groundwater within the slurry-wall
containment area using an
eLFExS;
• Installation of new groundwater
extraction wells in the Upper
Potomac Aquifer, including the
UPCUTZ;
• Extraction of groundwater from
the Upper Potomac Aquifer,
including the UPCUTZ, in order to
meet new risk- and health-based
groundwater remediation
standards throughout the area of
attainment;
• Discharge of recovered
groundwater to the POTW.
28
AR310597
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
EPA is not proposing to modify any other components of the Current Remedy.
The Preferred Alternative consists of the following new (N), modified (M) or existing (E)
components:
• Slurry-wall system (E);
• Hydraulic control of contaminated groundwater within the slurry-wall system using
an eLFExS (M);
• A composite barrier cap to minimize infiltration of precipitation through
contaminated soil contained within the slurry wall surrounding the former DDA (E);
• Installation and operation of extraction wells in areas determined to optimize capture
and remove contaminant mass from the more highly-impacted areas of the Upper
Potomac Aquifer, including the UPCUTZ (M);
• Discharge of groundwater pumped from the DS&G Site extraction wells to the
Wilmington wastewater treatment plant (M);
• Continued groundwater extraction at Artesian's Llangollen well field with treatment
utilizing existing systems for BCEE and 1,4-dioxane and, if necessary, additional
treatment systems targeting other COCs (N);
• A robust groundwater monitoring program to ensure that the remedial action is
meeting the short-term goal of plume containment and will meet the long-term goal
of aquifer restoration within a reasonable time frame (N);
• Institutional controls to prevent direct contact with contaminated soil, the installation
of drinking water wells on the Site property and other future uses of the Site property
which could compromise the effectiveness of the Selected Remedy (E); and
• Institutional controls to prevent potential future exposure to Site contaminants in
indoor air (N).
Statutory Determination
Based on the information currently available, EPA has determined that the Preferred
Alternative would be protective of human health and the environment, would comply
with ARARs, would be cost effective, and would utilize permanent solutions and
treatment technologies to the maximum extent practicable. Previously implemented
response actions at the DDA included treatment as a principal element. The final remedy
selected by EPA may differ from the Preferred Alternative described in this Proposed
Plan based on public comments or new information. Because wastes would be left in
place, reassessment of the effectiveness of the Preferred Alternative would be performed
at five-year intervals as required by CERCLA § 121(c).
X. COMMUNITY PARTICIPATION
EPA relies on public input so that the remedy selected for each Superfund site meets the
needs and concerns of the local community.
Public Comment Period - To ensure that the community's concerns are being addressed,
a public comment period will open September 7, 2016 and close October 7, 2016.
29
AR310598
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
During this time, the public is encouraged to submit to EPA any comments on the
Proposed Plan.
Public Meeting - A public meeting will be held to discuss the Proposed Plan on
September 21, 2016 from 7:00 p.m. to 8:30 p.m. The public meeting will be held at
William Penn High School on 713 E. Basin Road in New Castle, Delaware.
It is important to note that although EPA has proposed a Preferred Alternative, EPA has
not yet selected the final remedy for the Site. All relevant comments received will be
considered and addressed by EPA before the final remedy is selected for the Site.
Detailed information on the material discussed herein may be found in the Administrative
Record for the Site, which includes the Supplemental Site Characterization Report -
Revision 2, the technical memorandum on Development of Site-Specific Preliminary
Remediation Goals - Revision 2, the Final Feasibility Study - Revision 1 and other
information used by EPA in the decision making process. EPA encourages the public to
review the Administrative Record in order to gain a more comprehensive understanding
of the Site and the Superfund activities that have taken place there. Copies of the
Administrative Record are available for review at www.epa.gov/arweb. or at the
following locations:
DNREC EPA Administrative Records Room
391 Lukens Drive Administrative Coordinator
New Castle, DE 21921 1650 Arch Street
Hours: Call (302) 395-2600 Philadelphia, PA 19103
Phone: (215) 814-3157
Hours: Monday- Friday 8:30 am to 4:30 pm,
by appointment only
Written comments, questions about the Proposed Plan or public meeting, and requests for
information can be sent to either representative below:
Debra Rossi (3HS23)
Remedial Project Manager
Environmental Protection Agency Region III
1650 Arch Street
Philadelphia, PA 19103
(215)814-3228
Rossi ,Debra@epa. gov
-or-
30
AR310599
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Proposed Plan
Delaware Sand & Gravel Landfill Superfund Site
Larry Johnson (3HS52)
Community Involvement Coordinator
Environmental Protection Agency Region III
1650 Arch Street
Philadelphia, PA 19103
(215)814-3239
Johnson.Larry-C@epa.gov
Following the conclusion of the public comment period on this Proposed Plan, EPA will
prepare a Responsiveness Summary. The Responsiveness Summary will summarize and
respond to comments on EPA's Preferred Alternative. EPA will then prepare a formal
decision document, the Record of Decision (ROD) Amendment, which summarizes the
decision process and the remedy modification for the Site. The ROD Amendment will
include the Responsiveness Summary. Copies of the ROD Amendment will be available
for public review in the designated repositories, described above.
31
AR310600
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Path: V:\0Q1 GIS Projects\GIS DS&G\Reports\2013\SSC Report Figs\FIGURE 1.2.mxd
REFERENCES
Base Imagery taken from United States Department of Agriculture
(USDA) National Agriculture Imagery Program (NAIP), 2008.
Spatial Reference:
NAD 1983 HARN StatePlane Delaware FIPS 0700
350
700
1,400
S Feet
1 inch = 700 feet
Q
C
73
m
ro
GENERAL SITE LAYOUT
Delaware Sand and Gravel
Superfund Site
New Castle, Delaware
, Golder
Associates
Manchester, New Hampshire
AR310602
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Path: V:\001 GIS Projects\GIS DS&G\Reports\2013\ST_C\0136052C003_BCEE.mxd
LEGEND
~ Well screened in UPCU Transition Zone included in the current monitoring program
Well screened in UPA Upper Sand included in the current monitoring program
Well screened in UPA Upper Sand not included in the current monitoring program
Well screened in UPA Lower Sand included in the current monitoring program
Well screened in UPA Lower Sand not included in the current monitoring program
Well screened across UPA Upper Sand and Lower Sand included in the current monitoring program
Well screened across UPA Upper Sand and Lower Sand not included in the current monitoring program
O Well screened in Columbia Aquifer included in the current monitoring program
O Well screened in Columbia Aquifer not included in the current monitoring program
BCEE Isoconcentration Contour (Inferred)
14 - BCEE Concentrations (ug/L)
BCEE = BIS(2-CHLOROETHYL)ETHER
ug/L = Micrograms per Liter
REFERENCE
Base data from New Castle County Delaware, Department of Land Use,
"eParcel View Map" web site GIS data download. Data acquired 01/18/2012.
1,200
I Feet
CD
C
rn
CO
BCEE
UPA DOWNGRADIENT OF
WELL PW-1(U)
MARCH - APRIL 2013
Delaware Sand and Gravel
Superfund Site
New Castle, Delaware
r Golder
Associates
Manchester, New Hampshire
AR310603
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Path: V:\001 GIS Projects\GIS DS&G\Reports\2013\ST_C\0136052C004 MDioxane.mxd
LEGEND
it Well screened in UPCU Transition Zone included in the current monitoring program
Well screened in UPA Upper Sand included in the current monitoring program
Well screened in UPA Upper Sand not included in the current monitoring program
Well screened in UPA Lower Sand included in the current monitoring program
Well screened in UPA Lower Sand not included in the current monitoring program
Well screened across UPA Upper Sand and Lower Sand included in the current monitoring program
Well screened across UPA Upper Sand and Lower Sand not included in the current monitoring program
O Well screened in Columbia Aquifer included in the current monitoring program
O Well screened in Columbia Aquifer not included in the current monitoring program
1,4-Dioxane Isoconcentration Contour (Inferred)
14 -1, 4-Dioxane Concentrations (ug/L)
* Indicated data provided by Artesian Water Company
ug/L = Micrograms per Liter
REFERENCE
Base data from New Castle County Delaware, Department of Land Use,
"eParcel View Map" web site GIS data download. Data acquired 01/18/2012.
1,200
I Feet
71
m
<
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GIS
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m
cn
33
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1,4-DIOXANE
UPA DOWNGRADIENT OF
WELL PW-1(U)
MARCH - APRIL 2013
Delaware Sand and Gravel
Superfund Site
New Castle, Delaware
r Golder
Associates
Manchester, New Hampshire
AR310604
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Path: V:\001 GIS Projects\2001\013-6052_DSG\GIS DS&G\Reports\2016\ST_K Final FS\MXD\0136052K003_03.mxd | Modified By: CSCHAEFER
PZ-4-INTR
5# ± N
MHW-1D
MHW-1S Rfelsf-
X >
MHW-1M T/JS
MHW-1D
=W| W "S
MHW-1M
DDA-05
Disposal
Area
Army Creek Landfill
Grantham
South
< "AWC-J1
%AWC-MW1
~:~AWC-MW_5_:
. AWC-MW4jj[
ALDWYN dr
LEGEND
Well screened in UPCU Transition Zone included in DS&G's approved 2011 monitoring program
Well screened in UPA Upper Sand included in DS&G's approved 2011 monitoring program
Well screened in UPA Upper Sand not included in DS&G's approved 2011 monitoring program
Well screened in UPA Lower Sand included in DS&G's approved 2011 monitoring program
Well screened in UPA Lower Sand not included in DS&G's approved 2011 monitoring program
Well screened across UPA Upper Sand and Lower Sand included in DS&G's approved 2011 monitoring program
Well screened across UPA Upper Sand and Lower Sand not included in DS&G's approved 2011 monitoring program
O Well screened in Columbia Aquifer included in DS&G's approved 2011 monitoring program
{J Well screened in Columbia Aquifer not included in DS&G's approved 2011 monitoring program
. H t Preliminary Area of Attainment - The source of contaminated groundwater
w detected in well BW-2 remains under evaluation
\//A Waste Management Area
REFERENCE
Base data from New Castle County Delaware, Department of Land Use, o 300 eoo 1,200
"eParcel View Map" web site GIS data download. Data acquired 01/18/2012. Feet
1 inch = 600 feet
Q
C
m
cn
° WASTE MANAGEMENT AREA AND
s PRELIMINARY AREA OF ATTAINMENT
Delaware Sand arid Gravel
Superfund Site
New Castle, Delaware
r Golder
Associates
Manchester, New Hampshire
AR310605
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C19D
DGC-2S
DDA-05
a
FENCELINE
CENTERLINE OF SLURRY WALL AROUND
DRUM DISPOSAL AREA
RAILROAD
DDA LOW-FLOW EXTRACTION SYSTEM
(LFExS) WELL
MONITORING WELL SCREENED IN
UPPER POTOMAC AQUIFER
UPPER POTOMAC CONFINING UNIT
TRANSITION ZONE (UPCUTZ)
MONITORING WELLS
POTENTIAL UPCUTZ EXTRACTION
WELLS
POTENTIAL UPA EXTRACTION WELLS
NOTES
1. LOCATIONS OF WELLS AND BORINGS ARE APPROXIMATE
REFERENCE
1. BASE MAP TAKEN FROM DIGITAL U.S.6.S. 7.5 MINUTE QUADRANGLES OF WILMINGTON
SOUTH, DELAWARE/NEW JERSEY (DATED 1984). DELAWARE CITY, DELAWARE (DATED 1984),
NEWARK EAST, DELAWARE (DATED 1904) AND SAINT GEORGES, DELAWARE (DATED 1904).
REVISION DESCRIPTION
DES CADD CHK RVW
DELAWARE SAND AND GRAVEL
SUPERFUND SITE
NEWCASTLE, DELAWARE
POTENTIAL EXTRACTION WELL LOCATIONS IN THE
UPCUTZ AND UPA UPPER SAND UPGRADIENT OF
WELL PW-1(U)
r 4 Golder
Associates
PROJECT No.
FILE No. 0136052AH003_Fig4
FIGURE 6
AR310606
-------
LEGEND
LocationsAII
Type_, DownGrad
Well screened in UPCU Transition Zone included in DS&G's approved 2011 monitoring program
Well screened in UPAUpper Sand included in DS&G's approved 2011 monitoring program
Well screened in UPAUpper Sand not included in DS&G's approved 2011 monitoring program
Well screened in UPA Lower Sand included in DS&G's approved 2011 monitoring program
Well screened in UPA Lower Sand not included in DS&G's approved 2011 monitoring program
Well screened across UPAUpper Sand and Lower Sand included in DS&G's approved 2011 monitoring program
V\fell screened across UPAUpper Sand and Lower Sand not included in DS&G's approved 2011 monitoring program
O Well screened in Columbia Aquifer included in DS&G's approved 2011 monitoring program
O Well screened in Columbia Aquifer not included in DS&G's approved 2011 monitoring program
1,200
iFeet
Potential Off-Site Extraction Well
REFERENCE
Pump Station / Discharge Location
Base data from New Castle County Delaware, Department of Land Use,
"eParcel View Map" web site GIS data download. Data acquired 01/18/2012.
CD
C
73
m
¦>1
POTENTIAL EXTRACTION WELL LOCATIONS
IN THE UPA DOWNGRADIENT OF WELL PW-1(U)
PROJECT
Delaware Sand and Gravel
Superfund Site
New Castle, Delaware
Golder
Associates
Manchester, New Hampshire
AR310607
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