, United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROD/R03-86/032
September! 986
Superfund
Record of Decision
Army Creek Landfill, DE
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TECHNICAL REPORT DATA
iPteait read Instructions on the reverse before completing)
1. REPORT NO.
EPA/ROD/R03-86/032
3. RECIPIENT^ ACCESSION NO
4. TITLE AND SUBTITLE
SUPERFUND RECORD OF DECISION
Army Creek Landfill, DE
s. REPORT DATE
^September 30. 1 QSfi
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
I. PERFORMING ORGANIZATION REPORT NO
9. PERFORMING ORGANIZATION NAME AND ADDRESS
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
12. SPONSORING AGENCY NAME AND ADDRESS
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
13. TYPE OF REPORT AND PERIOD COV6BEO
Pi na 1 POD Borvirh
14. SPONSORING AGENCY CODE
800/00
IS. SUPPLEMENTARY NOTES
16. ABSTRACT
The Army Creek Landfill (ACL), formerly"known as the Llangollen Landfill, is located
approximately two miles southwest of New Castle, Delaware, and is adjacent to the
Delaware Sand and Gravel Landfill Superfund site. ACL, a former sand and gravel quarry
is owned by New Castle County. The County operated this 44-acre landfill, which
accepted municipal wastes, from 1960 until its closure in 1968 when it was filled to
capacity. An estimated 1.9 million cubic yards of refuse were landfilled at the site,
30 percent of which (or approximately 600,000 cubic yards) now lies below the seasonal
high water table. In late 1971, water in a residential well downgradient of the site
developed quality problems. Results from a subsequent investigation showed that
leachate, most likely originating from the Army Creek and Delaware Sand and Gravel
Landfills, was contaminating local aquifers. This lead to the installation of a ground
water recovery system designed to maintain a ground water divide between the landfills
and the Artesian Water Company Wellfield located downgradient of the landfills. The
primary contaminants of concern include: VOCs, inorganics, heavy metals, benzene, and
chromium.
The selected remedial action for this site will be implemented in a two-phased
approach. Phase 1: Install a RCRA type cap to minimize infiltration of rainwater.
Capping of the landfill will include site clearing, regrading of the existing cover
(See attached sheet)
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATi Field/Croup
Superfund Record of Decision
Army Creek Landfill, DE
Contaminated Media: soil, sediments, sw, gw
Key contaminants: VOCs, inorganics, heavy
metals, chromium
18. DISTRIBUTION STATEMENT
19. SECURI
CLASS i This Report/
None
21. NO. Of
AGES
20. SECURITY CLASS I Tint page i
22. PRICE
If* f»tm 2220-1 (*•». 4-77) PMCVIOUS COITION i* OBSOLCTC
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EPA/ROD/R03-86/032
Army Creek Landfill, DE
16. ABSTRACT (continued)
surface, adding soil backfill to achieve grades, installing the cap with gas
vents, and construction of drainage ditches to direct run-off away from the
landfill; continue operation of the downgradient recovery well network;
evaluate the capping system and the downgradient pumping network for five
years after the cap is installed. This evaluation will include, but not be
limited to, monitoring water levels, pumping rates and water quality. Phase
2: After the five year evaluation period, a determination will be made on
whether to install upgradient controls to intercept lateral ground water
inflow on the northwestern boundary of the landfill; continue monitoring the
water levels, pumping rates and water quality as in Phase 1; O&M will
include as a minimum, regular inspections and, as necessary, repairs to the
RCRA cap. The ground water recovery system will be monitored to assure that
it is capturing the contaminated plume. The estimated capital cost for this
two-phased remedial action is $12,030,000, or $12,340,000 with upgradient
controls. O&M costs are estimated at $306,000, or $388,000 with upgradient
controls.
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RECORD OF DECISION
REMEDIAL ALTERNATIVE SELECTION
Site: Army Creek Landfill Site, New Castle County, Delaware
Data Reviewed
The underlying technical information, unless otherwised specified, used
for analysis of the cost-effectiveness and feasibility of remedial alternatives
is included in the following documents and project correspondence. I have been
briefed by my staff of their contents, and they form the principal basis for my
decision of the appropriate extent of remedial action.
Feasibility Study for the Army Creek Landfill, New Castle County, Delaware,
(Roy F. Weston, Inc., July 1986)
Endangennent Assessment, Army Creek Landfill (Richard L. Zambito, U.S.
E.P.A. Region III, July 1984)
Hydrogeochemical Studies at a Landfill in Delaware (Mary Jo Baedecker
and Michael A. Apgar, 1984, Studies in Geophysics, Groundwater Contamination,
National Academy Press)
- Recommendations by the Delaware Department of Natural Resources and
Environmental Control
Staff summaries and recommendations
Description of Selected Remedy
0 An initial operable unit for source controls to be implemented in a
two-phased approach.
Phase 1
0 Install a RCRA type cap to minimize infiltration of rainwater. Capping
of the landfill will include site clearing, regrading of the existing cover
surface, adding soil backfill to achieve grades, Installing the cap with gas
vents, and construction of drainage ditches to direct run-off away from the
landfill.
0 Continue operation of the downgradient recovery well network.
0 Evaluate the capping system and the downgradient pumping network for
five years after the cap is Installed to assess effectiveness of the system
during operation. This evaluation will include, but not be limited to, monitoring
water levels, pumping rates and water quality.
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Phase 2
0 After the five year evaluation period, a determination will be made on
whether to install upgradient controls to intercept lateral groundwater inflow
on the northwestern boundary of the landfill.
0 Continue monitoring the water levels, pumping rates and water quality as
in Phase 1.
0 Operation and maintenance (0 & M) will include as a minimum, regular
inspections and, as necessary, repairs to the RCRA cap. The groundwater recovery
system will be monitored to assure that it is capturing the contaminated plume.
Selection of a treatment alternative for the groundwater recovery
well discharges has not been made at this time and will be the subject of a
second operable unit decision document in the. future. A groundwater treatment
remedy has not been selected, because the final NFDES permit has not been
issued. In addition, the Remedial Investigation/Feasibility Study (RI/FS) at
the Delaware Sand & Gravel Superfund site adjacent to Army Creek Landfill, has
not been completed. It is our intention to combine the remedial actions for
these two sites wherever cost-effective.
Also being deferred at this time is a decision on appropriate remedial measures
for sediments in Army Pond. This decision will be made at the same time as
groundwater treatment is considered and after further analysis is accomplished
regarding the actual impacts on Army Pond.
Declarations
Consistent with the Comprehensive Environmental Response and Compensation and
Liability Act of 1980 (CERCLA) (42 U.S.C. § 9601-9657) and the National Contingency
Plan (40 CFR Part 300), I have determined that the remedial action described
above, together with proper operation and maintenance constitutes a cost-effective
remedy which mitigates and minimizes damage to public health, welfare, and the
environment. The remedial action provides for capping the site, continuing
operation of existing downgradient groundwater recovery wells, and the installation
of upgradient groundwater controls in the future as necessary and, therefore,
minimizes the threat of further contamination of the environment. The remedial
action does not affect or violate any areas. A portion of the remedy may
encroach slightly into the floodplain at the south end of the site. If during
detailed design, survey work establishes this, special measures will be taken
to minimize the encroachment and to protect the remedy. The State of Delaware
has been consulted and agrees with the approved remedy. In addition, the
action will require future operation and maintenance activities to ensure the
continued effectiveness of the remedies. These activities will be considered
part of the approved action and eligible for Trust Fund monies for a period of
six months following completion for construction.
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I have determined that the action being taken is appropriate when balanced
against the availability of Trust Fund monies for use at other sites.
'JAMES M'. flEIF
REGIONAL ADMINISTRATOR
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SUMMARY OF REMEDIAL ALTERNATIVE SELECTION
A. SITE LOCATION AND DESCRIPTION
The Army Creek Landfill formerly known as the Llangollen Landfill, is
located approximately two miles southwest of the city of New Castle, Delaware
(Figure 1). The landfill is bordered to the north and west by tracks of the
Penn Central Railroad and on the south and east by Army Creek. The highways
adjacent to the Landfill are Routes 13 and 40 to the west and Route 9 to the
east.
Llangollen Estates, a residential development is located 1/4 mile southwest
of the site. The former Amoco Chemical Plant, closed in 1980 due to fire, is
located 1/4 mile east of the site. Delaware Sand and Gravel, another landfill
which has been placed on the Superfund National Priorities List, is adjacent to
Army Creek Landfill and separated from it only by Army Creek, a tributary of
the Delaware River.
The Army Creek Landfill, a former sand and gravel quarry is owned by New
Castle County. The County operated this 44 acre landfill which accepted municipal
wastes from 1960 until its closure in 1968. During that time, an estimated
1.9 million cubic yards of refuse were landfilled at the site, 30 percent of
which (or approximately 600,000 cubic yards) now lies below the seasonal high
water table.
In late 1971, water in a residential well southwest of the landfill developed
quality problems, such as a distinctly disagreeable odor and permanent staining of
porcelain fixtures. New Castle County and its consultant, Roy F. Weston,
Inc., of West Chester, Pennsylvania, began a multi-year field investigation to
assess the problem. Results from that investigation showed that leachate most
likely originating from the Army Creek and Delaware Sand and Gravel Landfills,
was contaminating local aquifers.
Weston's remedial investigation lead to the installation of a groundwater
recovery system designed to maintain a groundwater divide between the landfills
and the Artesian Water Company Wellfield located downgradient of the landfills.
Contaminated groundwater pumped from the recovery well system was discharged to
Army Creek.
In August 1984, EPA entered into a Consent Order with New Castle County to
perform a Feasibility Study (FS) at the site.
B. SITE GEOLOGY
The Army Creek Landfill is located within the Atlantic Coastal Plain
physiographic province. The coastal plain is composed of a wedge-shaped body
consisting of gravels, sands, silts and clays.
The site is underlain by two water-bearing formations, the Columbia and
the Potomac. The Columbia, the upper-most aquifer beneath the landfill, is of
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Pleistocene Age and is from 10 to 60 feet thick at the site. This formation,
which dips to the southeast, consists of medium to coarse grained sands, gravels,
silts and clays which were deposited in shallow lens-shaped channels (Figure
2). The silt and clay units of the Columbia are discontinuous and do not form
confining units.
The Potomac Formation of Cretaceous Age underlies the Columbia Formation
and is generally separated from it by a confining clay layer at the site. The
Potomac Formation dips to the southeast, is up to 600 feet thick and consists
of silts and clays interbedded with sands and some gravel. The formation is
divided into upper and lower units which are separated by a thick confining
clay unit. The upper Potomac Formation silts and clays are discontinuous and
non-uniform; in some places, the sands of the Columbia and Potomac are in
contact.
C. Site Hydrogeology
Hydrologically, the Potomac upper clay functions as a confining zone for
the underlying aquifer which is known as the upper Potomac Hydrologic zone.
The direction of flow in the Potomac aquifer has been altered significantly
over the past several decades due to withdrawal of water for industrial and
domestic uses. The elevation of the potentiometric surface in the 1950fs,
before significant development of the aquifer, was about 6 meters below sea
level and flow direction was toward Delaware Bay to the southeast. In the
1960's, after wellfields were developed in the Potomac Formation for public
water supplies and industrial use, the direction of flow remained to the south
and east.
Artesian Water Company, a private water company servicing 5,000 customers
in this area, completed its first well at the nearby Llangollen Wellfield in
1952. By 1961, shortly after the Army Creek Landfill opened, there were four
operating wells withdrawing water from the Llangollen Wellfield at an annual
average rate of about 1.42 mgd (million gallons per day). In early 1966,
Artesian completed a new well and had increased its average purnpage to
approximately 1.62 mgd. In 1969, a sixth well was added and the annual average
pumpage from the Llangollen Wellfield Increased to about 1.74(mgd).
In late 1971 and early 1972, five more wells were added to Llangollen Wellfield.
By late 1971, Artesian had increased its pumpage to an annual average of 2.60
mgd. Since then, Artesian Water Company has had to decrease pumpage to 2 mgd
in order to slow down the migration of the contaminants and to avoid contributing
to the problems of salt water intrusion that had become common in the area.
There has been considerable litigation between Artesian Water Company and New
Castle County, over groundwater use. The precise amount of water which Artesian
had withdrawn in the past, or is presently entitled to withdraw Is unclear.
Amoco Chemical Company initiated groundwater withdrawal from the Potomac
aquifer in 1961 for use In their plant operations. Pumpage by Amoco was
discontinued in 1980 when the plant closed due to fire.
It has been estimated that pumpage from the upper Potomac aquifer had
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increased more than seven fold from 1952 to 1972 as a result of groundwater
withdrawals from Artesian's Llangollen Wellfield and the Amoco Chemical Company
plant wells. During this period, it has been reported that the increased pumpage
caused the static water level in Artesian's Llangollen wells to decline up to
65 feet. This decrease in water level resulted in a steepening of the hydrologic
gradient in the upper Potomac aquifer which accelerated the migration of
pollutants from Army Creek and Delaware Sand and Gravel Landfills toward the
Artesian and Amoco production wells.
In late 1971, when one of the residential wells in the vicinity of the Army
Creek Landfill, became contaminated with iron and other chemicals, New Castle
County determined that the leachate generated by the landfill was contaminating
the groundwater in the area. The leachate is produced by water entering the
landfill in two ways:
1. Through direct precipitation on, and infiltration through, the landfill
surface.
2. As groundwater moves laterally into the saturated lower portion of
the landfill.
Analysis of water inflow to the landfill is accomplished by dividing the
landfill into two sections (Figure 3). Section 1, the western section (estimated
area = 760,000 square feet), receives both surface water and groundwater inflow,
and generally has a continuous clay floor of relatively low permeability. As
a result, there exists a relatively thick zone of saturation in this portion
of the landfill.
Section 2, the older, eastern section of the landfill (estimated area =
1,350,000 square feet), receives water primarily by infiltration of direct
precipitation. In the vicinity of Section 2, the contact between the Columbia
and the upper aquifer of the Potomac Formation is often a quite permeable
zone. Here the Potomac clay deposits are relatively thin, sandy, or are absent.
Consequently, water in the Columbia sands moves downward to the Potomac aquifer
rather than laterally through the landfill. In addition, the Columbia sands
have been excavated northeast and south of the landfill. Therefore, elevations
at these points and in the marsh to the east are lower than those of the landfill
surface and, in places, lower than much of the Army Creek Landfill floor.
The surface of the landfill is pocketed with depressions resulting from
the differential subsidence of the refuse. These depressions, coupled with the
remaining flat surface of the landfill prevent stormwater from running off the
landfill. The cover is generally silty, sandy and quite permeable. However,
deposits of clay have accreted in the depressions so that stormwater forms
ponds in the depressions. These ponds contribute to the slow infiltration of
water into the landfill. Because of these surface conditions, it is estimated
that at least 50 percent of the precipitation which falls directly onto the
landfill surface infiltrates through the landfill cover and percolates through
the refuse.
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D. • SITE HISTORY
The Army Creek Landfill occupies an area that was formerly utilized as a
sand and gravel pit. The gravel pit in which Army Creek Landfill was constructed,
was excavated until a hard zone was encountered. This zone marks the base of the
Columbia Formation and the top of the underlying clay.
In 1960, the landfill began operation as a municipal refuse landfill. The
landfill was operated by New Castle County continuously until 1968 when it was
filled to capacity. Refuse placement, compaction and covering operations at the
Army Creek Landfill were carried out by the operators of the gravel pit under
contract to New Castle County. Refuse burial began at the eastern end of the
pit and generally continued toward the pit entrance on the west. The refuse
was generally not well compacted and not regularly covered. The cover material
used was obtained from the pit and includes residential sands, tailing piles
and siltation basin deposits. As the operation progressed, cover material and
landfill space became depleted. This encouraged deeper excavation which may
have removed much of the clay layer which separated the Columbia from the
Potomac formations. This in turn, could have created direct access routes for
leachate to the Potomac from the Columbia. Direct access routes may also have
occurred naturally due to the non-continuous geometry of the Potomac clay.
Improper covering, along with non-consistent compaction and decomposition
of the waste materials, may have contributed to the differential settling of
the waste material which has occurred since the landfill was closed.
In 1970, the landfill was covered with sandy material and the property was
purchased by the County for use as a park. In late 1971, water in a residential
well downgradient of the Army Creek Landfill Site developed severe quality
problems. Evidence of these problems was the odor of the water and staining
of the porcelain fixtures in the residence. In June 1972, New Castle County
commenced a groundwater monitoring program which began with a well installation
and sampling program. Monitoring by various agencies including EPA, United States
Geological Survey, (USGS) New Castle County and the Delaware Department of
Natural Resources and Environmental Control (DNREC) as well as the University
of Illinois has continued up to the present. Monitoring has resulted in the
identification of groundwater contaminants indicative of hazardous waste disposal
as well as typical municipal refuse. It was also determined that the plume of
these contaminants was moving towards the receptors located downgradient of the
landfill. After considering alternative water supplies for the affected residents,
New Castle County paid for an extension of Artesian's Water supply lines to
the first contaminated residence and other homes along Grantham Lane. There
was also a settlement with the homeowners to offset the monthly services costs.
In 1973, recovery wells RW-1, RW-2, RW-3, RW-4, RW-5, RW-6,27,28,29,
31 and 53 were installed in the upper Potomac Aquifer by Roy F. Weston under
the direction of New Castle County (Figure 4). The purpose of the recovery
wells was to intercept and contain the contaminant plume. The pumping of
these wells created a groundwater divide between the Army Creek Landfill and
the Artesian Water Company's Llangollen Wellfield. Beginning in 1977, the
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recovery wells showed a pattern of stability in water quality.
In November 1977, New Castle County conducted a technical Round
Table Conference in order to obtain input and opinions from nationally and
internationally recognized authorities regarding the remediation of the
contaminated groundwater in the vicinity of the landfill. As a result of the
Technical Round Table Conference, a modified recovery system was installed in
1980, which included placement of new recovery wells closer to the landfill in
order to pump more concentrated groundwater and therefore less clean water.
The present recovery well system utilizes Wells 27, 28, 29, 31, RW-1, RW-9,
RW-10, RW-11, RW-12, RW-13, and RW-14.
US EPA has been involved at the site since 1974, when EPA representatives
sampled the recovery wells for the first time. Since then, EPA has sampled the
wells in 1977, 1978 and 1981 for priority pollutants. Based on the sampling
analysis from the recovery and monitoring wells, the Army Creek Landfill site
was proposed for the National Priorities List (NPL) in October of 1981 and was
finalized on the list in September of 1983 due to extensive groundwater
contamination.
In August 1984, EPA entered into a Consent Agreement and Order with New
Castle County to perform a Feasibility Study at the site. New Castle County
submitted the final draft of the study in July 1986.
E. CURRENT SITE STATUS
Groundwater
Since early 1972, intensive field studies have been conducted by the
County, through its consultant Roy F. Weston, Inc., to evaluate the nature and
the extent of the problem and to define and implement necessary controls to
mitigate the groundwater contamination. These efforts included the installation
and operation of the recovery wells in 1973, and monitoring and sampling of
the recovery and monitoring wells.
The analytical results from the various sampling efforts have demonstrated
that the following organic constituents are present in the groundwater: benzene,
1,2,dichloropropane, methylene chloride, 2,4,-dinitrotoluene, n-nitrosodimethy-
lamine, 2,4,6-trichlorophenol, bis(2chloroethyl)ether and chlorodibromomethane.
These contaminants have been detected in concentrations above levels set in
drinking water standards (Table 1).
Inorganic contaminants were also found in water collected from monitoring
and recovery wells. The contaminants include, beryllium, cadmium, chromium,
lead, mercury, nickel, iron and manganese in concentrations above the levels
set in drinking water standards (Tables 2,3,4).
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Surface Water
In 1981, the EPA field investigation team sampled Army Creek for priority
pollutants. The data indicated the presence of organic and inorganic contaminants
in the waters of Army Creek. Organics detected included phenol, bis(2-
ethylhexyl)phthalate, butyl benzylphthalate and di-n-butylphthalate (Table 5).
Inorganics detected were aluminum, barium, cobalt, copper, iron, manganese,
zinc, boron, calcium, magnesium and sodium (Table 6).
Additional water quality sampling for priority pollutant compounds was
conducted by Weston for New Castle County in 1983 in connection with their
NPDES permit application . Samples were analyzed by the New Castle
County Laboratory. No volatile or extractable organic compounds were detected.
The base/neutral organic compounds detected were bis(Z-ethylhexyl) phthalate
and di-n-butyl phthalate (Table 7). Upstream concentrations of both compounds
were greater than downstream concentrations. All values were well below
their respective ambient water quality criteria. Total metals were also analyzed
in 1983. Of the metals analyzed from the water samples, cadmium, lead, mercury,
nickel, and iron were found at higher concentrations upstream than downstream.
Copper, silver, chromium, zinc, and manganese were found downstream at higher
concentrations than upstream. Cadmium and mercury were the only parameters
exceeding water quality criteria upstream and downstream of the pond (Table 8).
The State of Delaware, in connection with the remedial investigation at
Delaware Sand and Gravel, conducted surface water sampling along Army Creek.
No priority pollutants were found to exceed any water quality criteria.
Sediments
DNREC conducted sediment analysis in connection with the remedial
investigation at Delaware Sand and Gravel (Table 9). Eight locations were
sampled: six along Army Creek and Pond; one in a gravel pit pond as background
and one at an intermittent stream east of Delaware Sand and Gravel. A comparison
of this data with the clean stream sediments indicates that the Army Creek
sample concentrations are considerably higher than those of the clean streams.
Utilizing Station 7, the gravel pit pond for comparison and as a local background
source, it is evident that samples taken from Army Creek and Pond have higher
concentrations of all the metals detected. The iron and manganese concentrations
in particular show an increasing trend in the downstream direction. Other
metal concentrations peak at the pond entrance, therefore, sediments have
also been effected by the recovery well discharges.
Bioassays
Also in September 1973, a series of surface water and biotic surveys for
Army Creek and Pond was initiated, to evaluate the affects of the recovery
well discharges on the surface water system. Furthermore, in the past 13 years
of discharges, Roy F. Weston, EPA and the State have taken numerous surface
and sediment samples to determine if high levels of contaminants exist in the
Army Creek and Pond and if so, what the affects of the contaminants have been.
Overall, the results of the bioassays indicated that Army Creek and Pond were
affected by the recovery well discharges, although the impacts were not readily
discernible.
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In March 1986, U.S. EPA and Western conducted split sampling for bioassay
and macrobenthos evaluations. Also well discharges were collected and composited
on a weighted basis from the existing recovery wells for use in the bioassays.
Macrobenthos sampling results by the EPA and Weston were basically in .
agreement and concluded that the the low diversity of the pollution tolerant
benthic species at all stations indicate degraded water quality within the
watershed. The difference in diversity and composition of pollution tolerant
species indicates that the macroinvertebrate community downstream of the pond
is in better condition than the upstream station.
The bioassays were conducted using fathead minnows and Ceriodaphnia dubia.
It was determined by EPA that recovery wells 9,28,29 and 31 exhibited chronic
toxicity, while recovery wells 10,11,12,13,14 and 27 exhibited no chronic toxicity.
DNREC is currently drafting a National Pollution Discharge Elimination
System (NPDES) permit for the discharge of water from the County recovery
wells to Army Creek. At this point it seems likely that only water in the
recovery wells exhibiting chronic toxicity (wells 9,28,29,31) will be required
to be treated prior to discharge into Army Pond. Water from the wells which
exhibit no chronic toxicity (wells 10,11,12,13,14,27) would be permitted
to freely discharge into the pond.
A treatment alternative will not be chosen, at this time, because the
final NPDES permit and its associated discharge limits has not been issued.
In addition, the Delaware Sand and Gravel RI/FS has not been completed, therefore,
we can not determine Delaware Sand and Gravel's contribution to the degradation
of the groundwater, or the Army Creek and Pond at this time. It is our intention
to combine the ultimate groundwater remedial actions at these two sites wherever
possible. Also being deferred at this time is a decision on appropriate remedial
measures for the sediments in Army Pond. Further analyses of the impacts on
Army Pond is required to clarify what measures if any, are required.
This Record of Decision specifically deals with the selection of the source
control alternative to prevent the generation of the leachate that contaminates
the local groundwater. We are deferring our decision on groundwater treatment
alternatives until the RI/FS at Delaware Sand and Gravel is complete and the
NPDES permit is issued.
Environmental Assessment
The remedial investigations performed at the Army Creek Landfill Site
revealed extensive groundwater contamination resulting from the generation of
the leachate at the landfill. The groundwater and the surface water are
contaminated with organic and inorganic priority pollutants, many of which
exceed Water Quality Criteria for human health and aquatic life (Tables 1-4).
The major public health concern at the site is the contamination of the
upper Potomac and Columbia aquifers. The major user of groundwater in the area
is the Artesian Water Company, located near Llangollen Estates.
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In 1973, New Castle County installed its groundwater recovery system to
prevent the migration of contaminated plume towards Artesian's Wellfield. Due to
the success of the groundwater recovery system operated by the County, along with
the reduction in pumpage by Artesian Water Company, the contaminants emanating
from Army Creek Landfill are not currently threatening drinking water supplies.
Army Creek and Army Creek Pond receive surface water runoff and recovery well
discharges from the groundwater recovery system. However, Army Creek and Pond
is restricted for public use, prior to its discharge to the Delaware River, one
mile downstream. The effect of the creek on the Delaware river is expected to
minimize due to dilution.
Surface water bioassays have indicated that the surface water system has
been effected by the recovery well discharges, although the severity of the
impacts on the aquatic life is not readily discernible,
ALTERNATIVE EVALUATION
The major objective for the remedial action to be taken at the Army Creek
Landfill Site is to minimize further groundwater contamination by reducing the
leachate generated by the landfill. The requirements of CERCLA Section 104, of
CERCLA 420 U.S.C. § 9604, EPA's mandate to protect the public health and welfare
and the environment, determine the goals and levels of response for the site.
In an effort to determine remedial alternatives for the subject site,
feasible technologies were identified for consideration in a general response
action table. Available technologies were then screened to eliminate all but
the most definitive and feasible alternatives. This screening included: technical
(site conditions or waste characteristics), environmental and public health,
institutional, performance and cost criteria.
The technologies that have passed the technology screening process were
examined further to identify remedial alternatives. Remedial alternatives
were developed using best engineering judgment to select a technology or
group of technologies that best addresses the problems existing at the site to
protect public health, welfare and the environment. In an effort to provide a
degree of flexibility in the final selection of a remedial action, alternatives
covering a range of remedial action categories have been developed. These
categories are described below:
1. No action: No-action alternatives could include monitoring activities.
2. Alternatives that meet the CERCLA goals of preventing or minimizing
present or future migration of hazardous substances and protecting human health
and the environment, but which do not attain all of the applicable or relevant
standards. (This category may Include an alternative that closely approaches
but does not meet, the level of protection by the applicable or relevant
standards.)
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3. Alternatives that meet CERCLA goals and attain all applicable or
relevant Federal public health and environmental standards, guidance, and
advisories.
A. Alternatives that exceed all applicable or relevant Federal public
health and environmental standards, guidance, and advisories.
5. Alternatives specifying offsite storage, destruction, treatment, or
secure disposal of hazardous substances at a facility approved under the Resource
Conservation and Recovery Act (RCRA). Such a facility must also be in compliance
with all other applicable Environmental Protection Agency (EPA) standards.
The broad evaluation criteria selected were: technical feasibility,
public health, environmental, institutional evaluation, and cost effectiveness.
Within those criteria the following factors were considered.
- Technical Feasibility
"Performance
oImplementab ili ty
"Reliability
- Public Health Evaluation
"Reduction of Health Impacts
- Environmental Evaluation
"Reduction of environmental impacts
"Protection of Natural Resources
- Institutional Evaluation
"Legal requirements, institutional requirements
"Community Impacts
- Cost Effectiveness
"Capital Costs
"Operation and Maintenance Costs
"Present Worth Values
"Sensitivity Analysis
ANALYSIS OF REMEDIAL ALTERNATIVES
Alternate Technologies
Alternate technologies to recycle, destroy or treat the wastes were screened
for use at this site. These technologies included incineration of the waste,
recirculation and/or treatment of the leachate, and block displacement which
consists of sealing the sides and/or bottom of the landfill by grout injection
technique.
These technologies were not chosen for several reasons. The discontinuous
nature of the subsurface soil conditions argued against the technical feasibility
of grouting the sides or bottom.
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Direct leachate recirculation or treatment was evaluated on a pilot scale
in the landfill but clogging of the wells and low permeability of the refuse in
some areas prevented further consideration. Only incineration technology was
retained for further evaluation.
Note: Capital, Operation and Maintenance, and Present Worth Costs for all
alternatives are found in Table 10.
Alternative No. 1 - No Action with Monitoring
The purpose of presenting a No Action Alternative is to provide a basis
for comparison of existing conditions with the other proposed remedial
alternatives. Under the No Action Alternative, no additional remedial activities
would be taken and any current activities would be terminated at the Army Creek
Landfill site. This would mean that the present hydrologic divide between the
groundwater contaminant plume and the Artesian Water Company Wells, maintained
by the recovery well system, would be eliminated.
This alternative includes a long-term monitoring program to provide
information concerning contaminant presence and concentration. Groundwater
monitoring would be performed between the landfill and the Artesian Water Company
wells, and within the wellfield.
The primary public health concern of the No Action Alternative is the
possible health risk resulting from the potential contamination of the downgradient
production wells in the Artesian Water Company wellfield. Current production
from these wells is approximately 2 million gallons a day (mgd), supplying the
equivalent of 5,000 residences with drinking water. The effected population
could increase, should the Artesian Llangollen Wellfield be shut down and the
contaminants be drawn towards other wellfields in the area, including Artesian's
Village, and Fairwinds wellfields located downgradient.
Of main concern is the attenuation of organic compounds found at concentrations
exceeding drinking water criteria in nine of the twelve recovery wells. Table 1
lists the organic compounds found in the recovery wells, the maximum concentrations
encountered, and the drinking water criteria. Under No Action, the contaminants
would most likely be attenuated by dilution, dispersion and absorption prior to
reaching a drinking water source. However, it is not known at what concentration
these organics will persist in the groundwater. Therefore, a potential for
human exposure by ingestion of organic compounds in concentrations above the
drinking water criteria is associated with this alternative. This alternative
would not provide protection to public health or the environment and contamination
of groundwater through leaching of the contaminants would be expected to continue.
Common to All Other Alternatives
All of the source control alternatives discussed below would include a
rigorous, initial sampling and analysis program. Both monitoring and recovery
wells would be sampled for Hazardous Substance List (HSL) compounds in order to
more precisely define the contaminants and their concentrations.
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All of the source control alternatives include downgradient recovery wells
to control the migration of the contaminant plume. A treatment alternative
for the recovery well discharges can not be addressed at this time. The
State of Delaware is in the process of issuing an NPDES permit that would
identify the safe and appropriate levels for contaminants at the point of
discharge into the Army Creek and Pond. Based on those limits, the treatment
alternative will be determined at a later date.
A definite time period for phasing out the downgradient recovery well
system cannot be established at this time for the following reasons:
0 Groundwater quality for organics at the site can not be precisely defined
with existing data.
0 The total impact of the Delaware Sand and Gravel Landfill on the groundwater
is not known at this time.
0 The remedial actions to be taken at the Delaware Sand and Gravel Landfill
are not known. These actions may affect the quality of groundwater at
the Army Creek site.
The following methodology will be considered for phasing out the recovery
well system:
The recovery well system will be evaluated in terms of both the flow system
and water quality for a period of five years after the cap is installed or
after the waste is excavated. If primary drinking water criteria levels are
not met within this evaluation period, alternate concentration levels (ACL)
will be considered. The ACLs will be based on an evaluation to define if
sufficient attenuation will be achieved downgradient of the Army Creek Landfill,
so that drinking water criteria levels will be met at any potential receptors.
These ACLs will be applied at the recovery wells or the property boundary.
When the ACLs are met, the recovery well system could be phased out.
Alternatives that include a cap may encroach on the 100 year floodplain at
the south end of the site. The floodplain extends to approximately the ten
foot contour. During design, detailed surveys and design evaluation will
determine if any portion of the cap must extend to this area. Suitable measures
including gabions or rip-rap may be used to protect the cap and minimize
encroachment in the floodplain.
Alternative No. 2 - Downgradient Pumping
Alternative No. 2 consists of a series of downgradient pumping wells to
recover contaminated groundwater and control its migration. In 1972, when it
was discovered that leachate had entered the underlying confined aquifer in
the Potomac Formation and had contaminated a nearby domestic well, Weston
was retained by New Castle County to investigate the extent of the problem and
propose potential solutions. Preliminary hydrogeologic investigations conducted
by Weston indicated that the leachate had contaminated a substantial volume of
the upper Potomac aquifer and that contaminated groundwater was moving in the
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direction of the Artesian Water Company's Llangollen Wellfield in response to
both the natural groundwater gradient and the pumping effects of the Artesian
wellfield. The nearest Artesian Water Company well was located about 1,600
feet from the edge of the contaminant plume.
Based on preliminary hydrogeologic investigations, a contaminant recovery
and monitoring program was designed and implemented in 1973 as an initial step
towards an eventual solution to the problem. The recovery program was designed to
achieve the following objectives:
0 To control the migration of contaminants towards Artesian Water Company's
wells and to contain them in an area closer to the landfill.
0 To create a groundwater divide between the Artesian wellfield and the
contaminated zone such that the groundwater flow in the contaminated
zone could be reversed and the contaminated groundwater between the
recovery wells and wellfield would move toward the Army Creek Landfill.
0 To recover contaminated water and restore the aquifer water quality.
0 To monitor the water quality and water levels in the area and evaluate
the effectiveness of the recovery program.
0 To develop feasible leachate treatment and disposal methods until some
type of permanent solution to the problem was determined.
As a result, a large number of observation and recovery wells was
constructed. While the observation wells were constructed in both the shallow
Columbia sediments and the underlying Potomac aquifer, the recovery wells were
constructed only in the contaminated zone of the upper Potomac aquifer, which
is the aquifer source used by Artesian.
The initial recovery well system consisted of eleven recovery wells RW-1,
2,3,4,5,6 and wells 27,28,29,31 and 53 (Figure 3). In 1977, the data collected
during the initial operation from 1973 to 1977 was evaluated. The following
conclusions were made at that time based on the evaluation:
0 The recovery wells have been successful in containment of the contaminated
groundwater plume within the groundwater flow south of the Army Creek
Landfill.
0 A groundwater divide has been developed between the Artesian Water Company's
wellfield and the contaminated zone of groundwater. The groundwater flow
in the contaminated zone between the landfill and the Artesian wellfields
has been reversed towards the recovery wells and the Army Creek Landfill.
0 Recovery wells RW-1, RW-3, RW-4, and RW-5 continued to "pull back"
the contaminants to as far as their present locations; these recovery
wells could be phased out of the system in stages by reducing their
pumping rates.
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0 It would be necessary to monitor the water quality in the vicinity of
recovery wells RW-1, RW-3, RW-4 and RW-5 more frequently than usual
when their pumping rates have been reduced. This would assure early
detection of any deterioration in water quality caused by reduced pumping
rates.
0 It appears that most of the inorganic contaminants are discharged into the
upper Potomac aquifer in an area of the landfill north of recovery
wells 27, 28 and 29 and in the southwest corner of the landfill.
0 The total pumping rate of the recovery wells was approximately 1.5 million
gallons per day, which is about 7.5 times more than the average daily rate
of potential leachate production. Leachate would be recovered more
efficiently if the wells were located within and closer to the landfill.
0 Incrustation has caused a significant problem requiring frequent
rehabilitation of the recovery wells. To control the incrustation problem,
the pumping rates of the existing recovery wells should be further
reduced by about 50 percent.
0 When RW-1, RW-3, RW-4 and RW-5 have been phased out of the recovery
program, more recharge will be available for Artesian Water Company's wells,
It was therefore recommended that new wells RW-10, RW-11, RW-12, RW-13 and
RW-14 be installed closer to the landfill such that leachate and contaminated
groundwater could be recovered more efficiently. This was also recommended by
the Round Table Conference in 1977.
In May 1982, the effectiveness of the modified downgradient pumping system
was evaluated through a series of pump tests performed on the new recovery
wells, RW-10, RW-11, RW-12, RW-13 and RW-14. The conclusions and recommendations
generated as a result of the pump tests resulted in the phasing out of recovery
wells RW-2, RW-3, RW-4, RW-5 and RW-6. The current downgradient pumping system
includes RW-14, RW-13, RW-12,31,29,28,27, RW-1, RW-11, RW10, and RW-9 (Figure 3).
The current system has maintained the groundwater divide necessary to intercept
contaminated groundwater.
The clogging of well screens and discharge lines by iron precipitate is a
continuous problem that is addressed through a regular program of well
rehabilitation and pump repair. During the period of June 1982 through April
1983, at least one well was off-line for maintenance, repair or rehabilitation
during any given month, with the exception of June 1982. Since the phasing
out of wells with the porest performance, a biannual maintenance program has
been established to treat and rehabilitate the twelve operating wells.
Maintenance and replacement of parts have been performed as part of the
maintenance program.
Since the recovery well system is already in place and operative, there is
no implementation time necessary for this alternative.
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Sampling and testing performed at the Artesian Water Company's wellfield
and concentration gradient maps of the area have indicated that the downgradient
pumping system along with controlled withdrawal by Artesian has been effective
in containing the contaminated groundwater plume through the creation of a
hydrologic divide between the landfill and the Artesian Water Company's wellfield.
Alternative 2 has therefore been proven to have contained contaminated ground-
water. By controlling the contaminated groundwater the pumping system has
prevented the possible abandonment of the upper Potomac aquifer as a source of
water supply in the production wellfields near the landfill and reduced the
public health risk that could have resulted if the contaminated groundwater
plume was not controlled.
Alternative 2 does not, however, address the source of leachate entering
the Potomac aquifer or the pathways through which water enters the landfill
resulting in leachate production. Precipitation infiltrating through the
landfill surface and groundwater infiltration through the northwest side of
the landfill from the Columbia aquifer will continue under this alternative.
Therefore, leachate migration into the Columbia and upper Potomac aquifer will
continue should Alternative 2 be implemented.
This alternative does not attain all applicable and relevant public health
and environmental standards as defined by CERCLA and RCRA.
Alternative No. 3 - Downgradient Pumping and Landfill Capping
Alternative 3 consists of the downgradient pumping program evaluated under
Alternative 2, and includes capping the landfill with a multi-layered cap.
The multi-layer cap system represents a recently developed .cover technology
that is gaining widespread use as an infiltration control strategy for waste
containment or in-place closure. The multi-layer cap system performs the
basic functions of minimizing infiltration into the waste site; directing and
transmitting percolation and gas migration away from the site; and providing a
final cover for the site and growth medium for vegetation. A typical multi-
layer cap system, as shown on Figure 5, consists of the following three layers:
a) Uppersoil layer. A top soil and native soil layer, typically placed to
a depth of about 12-24 inches. This layer serves to support vegetation,
provide a cover for the drain layer, and divert surface runoff.
b) Middle drain layer. A graded layer of porous flow zone material (e.g.,
sand, gravel, geogrid) to act as a drainage medium. This layer is
typically placed to a depth of about 18 inches.
c) Cap layer. A compacted layer of fine-grained soils of low permeability
designed to divert infiltration that has percolated through the upper
soil layer. This cap layer is typically placed to depths of about 18-
24 inches.
The successful multi-layer cap system incorporates the use of low permeability
materials to provide a surface seal over the contaminated area. A zone of high
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permeability materials, such as graded gravel, aggregate, and drainage geotextiles,
is typically placed over a cap layer to enhance lateral movement of water that
percolates through the upper soil layer. The upper soil layer provides the followii
(a) A soil cover to promote runoff.
(b) A protective cover for the drain layer.
(c) A medium for growth of vegetative cover.
The vegetation not only stabilizes the cover system from possible damage
due to water or wind erosion, but also contributes to moisture loss through
evapotranspiration.
Several major advantages of the multi-layer cover system as compared to a
standard native soil cover include the following:
(a) A protective soil layer is placed over the cap layer; the cap is not
directly exposed to excessive damage due to weathering, cracking or
root penetration.
(b) A drain layer serves to divert additional percolating water so it
does not eventually migrate into the underlying waste material.
(c) Possible slumping of the topsoil and upper soil layers is minimized.
Calculations using hydrologic simulation modeling show that the multi-
layered cover system can divert greater than 90 percent of the precipitation
falling on the site. Since the cover is constructed of natural materials, it is
expected to remain effective over the 30-year evaluation period.
Final design studies will be used to determine the material types and
specifications for the number of layers and thickness of the final cap system.
Any system installed will comply with the RCRA cap requirements.
Alternative 3 provides the same health benefits as Alternative 2 by
containing the contaminant plume through the creation of a hydrologic divide
between the landfill and the Artesian Water Company's wellfield by downgradient
pumping. The recovery pumping program in place at the Army Creek Landfill has
proven to have contained contaminated groundwater close to the landfill. By
controlling the contaminant plume, the pumping system has prevented the possible
abandonment of the upper Potomac aquifer as a source of water supply in the
production wellfields near the landfill.
This alternative attains all applicable and relevant public health and
environmental standards as defined by CERCLA and RCRA.
Alternative No. 4 - Downgradient Pumping, Landfill Capping, and
Upgradient Controls
A. Non-phased Approach - The non-phased approach to Alternative 4 would include
the continuation of the downgradient pumping program and the simultaneous
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construction of the final cap system and the upgradient groundwater controls
(Figure 6). This approach to Alternative 4 provides additional immediate
measures to further mitigate the environmental impacts of the landfill as
compared to Alternative 3. The upgradient controls would intercept and
significantly reduce the groundwater entering the landfill along the north-
western side, thus reducing the potential volume of leachate produced.
The flow of groundwater into the landfill along the northwestern side has
been estimated at 25,000 gpd as compared to 4,000 gpd of precipitation
infiltration.
B. Phased Approach - The phased approach to Alternative 4 involves two phases.
Phase 1 would include installation of the final cap system with continuation
of the downgradient pumping system. The effect on the groundwater quality
as a result of capping the landfill would then be monitored and assessed
prior to initiating Phase 2 upgradient controls. It is possible that
although a significantly greater volume of groundwater passes through the
site than does precipitation, the refuse that comes in contact with the
groundwater has already had much of the contamination leached after almost
seventeen years in a saturated state. Monitoring has also shown that the
groundwater table elevations have dropped over the past twelve years due
to the additional pumping, resulting in a lesser quantity of refuse that
is saturated. Precipitation, on the other hand, percolates through the
entire refuse stratum, allowing for more contact with a greater volume of
landfill material. Following an evaluation period of 5 years after the
cap is installed, the need for upgradient groundwater controls to reduce
leachate production would be determined. This determination would be based
on the evaluation of the monitoring well water levels, pumping rates and
water quality.
Both the phased and non-phased approaches include surface management measures
and gas venting as part of the construction of the cap system.
The technical evaluation of the downgradient pumping program has been
performed under Alternative 2, and the evaluation of the multi-layer cap system
under Alternative 3. Final design analysis will be used to determine the
material types and specifications for the number of layers and thickness of the
final cap system. The analysis for this alternative will therefore concentrate
on evaluating the upgradient controls. An upgradient pumping network is used here
for evaluation purposes only. The final upgradient control (pumping or trench)
would be determined during the design phase. It is anticipated that less pumping,
both in quantity and duration, by the downgradient recovery well system would be
required as a result of capping the landfill. Upgradient controls should
further hasten groundwater cleansing, reducing the time the downgradient system
has to be operated.
The arrangement and number of recovery wells necessary to prevent the
lateral inflow of groundwater into the Army Creek Landfill would be contingent
upon several of the following factors; the volume of inflowing water, the
depth to which the water table must be lowered, and the ability of the Columbia
aquifer to transmit water.
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To intercept the inflowing groundwater and lower the water table within the
landfill, Weston determined that five recovery wells, spaced at 320-foot intervals,
would be needed. The wells could be located directly south of the railroad
tracks along the northwestern boundary of the landfill (Figure 3). To ensure
maximum drainage from the Columbia aquifer, the depth of the wells should
extend to the base of the aquifer (25 to 30 feet).
An evaluation of various pumping rates estimated that a discharge rate of 20
gpm per well would provide maximum drainage of the Columbia aquifer without
exceeding the critical well drawdown limits. The pumping rate of 20 gallons per
minute(gpm) at each of the five wells would remove approximately 144,000 gpd
of groundwater, creating a hydrologic drain for the groundwater enroute to the
landfill. The drawdown influence from the pumping wells would lower the water
table within the refuse. Upgradient pumping would essentially dewater a major
portion of the refuse, leaving only a fraction of the total waste volume saturated
near the base of the Columbia Formation.
The water level in Army Creek could potentially impact the dewatering
influences of the upgradient wells. If the cumulative drawdowns from the five
recovery wells lowers the water table below the water level of Army Creek, then
surface water flow into the Columbia aquifer could be induced. This would
eventually create a steady-state condition between the water levels in the
wells and the stage of the stream. At this time, the variation in the elevation
of the surface water in Army Creek is unknown, and the effect of the stream on
the maximum water table drawdowns cannot be determined.
Alternative 4 provides the same health benefits as Alternatives 2 and 3 by
containing the contaminant plume through the creation of a hydrologic divide
between the landfill and the Artesian Water Company's wellfield'-by downgradient
pumping. Alternative 4 provides further measures to mitigate the environmental
impacts remaining after the implementation of the downgradient pumping and
landfill capping included in Alternative 3. Under the non-phased approach to
Alternative 4, upgradient controls will be installed at the same time the
landfill is capped. Both pathways of infiltration into the landfill would,
therefore, immediately be addressed. Potential leachate production should be
significantly reduced as a result of these actions. It is therefore anticipated
that groundwater cleansing would be further hastened under Alternative 4.
The phased approach would allow for a period of monitoring and assessment
of the effectiveness of capping the landfill on groundwater quality. Following
an evaluation period of 5 years after the cap is installed, the need for additional
measures to reduce leachate production would be determined. This decision
would be based on an evaluation of water levels and water quality at the Army
Creek Landfill.
This alternative attains all applicable and relevant public health and
environmental standards as defined by CERCLA and RCRA.
Alternative 5 - Downgradient Pumping, Partial Removal and Landfill Capping
Alternative 5 consists of the downgradient recovery well system also included
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in Alternatives 3 and 4, the excavation of the landfill refuse in the western
section, and movement of the excavated refuse on the eastern section. The-
eastern section would then be graded and capped with a multi-layered cap system,
and the western section backfilled with clean fill material, graded to drain
surface run-off and vegetated. Erosion and run-off controls would be established
in excavated and fill areas. The saturated refuse in the western section would
require "dewatering" or draining as it is excavated and would be mixed with
dryer refuse to be placed and compacted on the eastern section of the landfill.
A combination of draining/pumping of free liquids from the saturated refuse
and upgradient controls would be required for the dewatering process. Figure 7
provides a graphical presentation of Alternative 5.
This alternative will remove one of the sources of contamination of the
Columbia aquifer and subsequently the upper Potomac aquifer by the excavation
of the western section of the landfill. Field information suggests that
groundwater is infiltrating the refuse laterally in this section of the landfill.
This alternative also addresses the precipitation infiltration through the
removal and redeposition of refuse to the eastern section of the landfill which
would then be capped with a multi-layered cap system. The multi-layered cap system
was evaluated in Alternative 3. Alternative 5 would be effective in addressing
the pathways of infiltration and reducing the potential volume of leachate
produced from an estimated 29,000 gpd (25,000 gpd groundwater infiltration
plus 4,000 gal/day of precipitation infiltration) to an estimated 200 gpd
(precipitation infiltration through multi-layered cap system). Source removal
would provide an effective long-term solution to groundwater contamination at the
site. The useful life of the multi-layered cap system would depend on the
establishment of a maintenance program that would maintain a proper vegetated
cover and integrity of the cap. A properly constructed and maintained cap
should last through the 30-year evaluation period.
Once the vegetation on the multi-layered cap system is established it would
require routine regular maintenance. The entire vegetated area should be mowed
once or twice a year to minimize the potential for growth of deep-rooted
vegetation. The surface cap on the eastern section should be periodically
inspected to assure continued integrity of the capping system. Cracking,
erosion damage, and differential settlement damage would require repairs.
Two of the major concerns resulting from the excavation of the western
section of the existing landfill include the following:
0 Dewatering of the western section would be required before the saturated
refuse is excavated from below the water table. Upgradient controls
similar to the system outlined under Alternative 4 can be used to lower
the water table below the refuse. Complete dewatering may Include the
construction of drains and sump controls, but it is anticipated that
most of the free liquid would be removed by the upgradient controls. The
discharge from the upgradient controls could possibly require treatment.
Since the duration of pumping (if used) will be short-term (time required
to excavate the western section), the most cost effective treatment
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option could possibly be discharge to the local waste treatment facility
(Wilmington Waste Water Treatment Plant).
0 A potential slope stability problem could result between the eastern
section and the western section as excavation of the western section
resulted in deep cuts into landfill refuse. The excavation should proceed
in an "area" type manner to minimize deep cuts and possible stability
problems. Final side shapes after backfilling in the eastern section
should be limited to a maximum ratio of 3 horizontal to 1 vertical
(3:1) to ensure slope stability.
Excavation of the saturated refuse would be accomplished using either backhoes
or draglines working from the top of the working face. If a pocket of non-
refuse or potentially hazardous wastes has been identified, special excavation
and handling procedures would be initiated.
All of the refuse, with the possible exception of waste requiring special
handling, would be loaded onto dump trucks. These vehicles could then haul the
refuse on a temporary access road along the north side of the landfill running
parallel to the existing railroad. Free liquid from the transportation of the
refuse w.ould therefore be contained within the existing landfill area. Extensive
odor control would be necessary within and around the perimeter of the excavation
site for the dump trucks.
After the western section had been completely excavated and backfilled
with a clean soil fill, the eastern section would be prepared for the final
capping. The cap would be placed over the intermediate soil cover and utilize
a multi-layer design. The multi-layer cap system would significantly reduce
precipitation infiltration. Erosion and sedimentation controls would be initiated
until a proper vegetated cover is established. Gas venting and surface management
measures will be installed during the construction of the cap system.
While Alternative No. 5 represents a potential safety risk to the construction
workers, due to the unknown types of wastes and conditions which would be
encountered during excavation, proper safety protocol would reduce the risk.
Alternative 5 provides the same health benefits as Alternatives 2, 3, and 4
by containing the contaminant plume through the creation of a hydrologic divide
between the landfill and the Artesian Water Company's wellfield by the existing
downgradient pumping program. Alternative 5 provides basically the same
environmental benefits as Alternative 4 but addresses the groundwater infiltration
condition in the western portion of the landfill by eliminating the source of
leachate generation through total removal of the refuse in the western section.
Groundwater cleansing would be hastened by the elimination of the source of
contamination. Capping the eastern section with a multi-layer cap would signifi-
cantly reduce precipitation infiltration which would further hasten groundwater
'cleansing.
During excavation, odor and vector problems would likely occur in addition
to the need to handle draining water from saturated refuse. Leachate pumped
during dewatering operations before the saturated refuse is excavated would need
to be collected and treated.
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This alternative attains all applicable and relevant public health and
environmental standards as defined by CERCLA and RCRA.
Alternative 6 - On-site Incineration and Downgradient Pumping
This alternative consists of the construction of an incinerator and power
generator facility adjacent to the subject site, excavating and incinerating
the waste, and backfilling the ash residue on-site. In order for this alternative
to be feasible, the excavated landfill wastes at the site would need to
be mixed with raw-solid waste from nearby communities or other fuel to produce
a combustible mixture. Otherwise, the fuel requirements for burning the wet
waste would be very excessive. Excavation of the saturated material would
require dewatering. This could be achieved by upgradient pumping or pumping
directly from the excavated area. The discharge from the dewatering operation
could require treatment.
This alternative would include continued downgradient pumping to assure that
contaminated groundwater did not reach the Artesian Water Company's wellfield.
A long-term groundwater monitoring program would determine when the downgradient
recovery system could phased out after the landfill had been removed and
incinerated.
Alternative 6 would provides basically the same public health and environmental
benefits as Alternatives 4 and 5 through downgradient pumping and removal of
the source by excavation and incineration. Dry refuse or other fuel would need
to be transported to the site and mixed with the saturated waste to make it
burnable. Air pollution control devices required under RCRA would reduce the
release of contaminants into the air. Incinerator ash and residue would be
backfilled on-site only in areas above the groundwater table and eventually
capped. Dust, odor and drainage of liquids from the saturated waste are problems
associated with the excavation of landfill refuse. Other environmental and
health concerns would be associated with the transport of dry refuse to the
Army Creek Landfill site. These concerns include noise and dust from
transportation and vector problems. Measures such as vector control and site
access routing, would be initiated to mitigate these problems. Construction
activities during excavation could affect wetlands habitats through noise,
surface water diversion practices and dust. Drainage could also have an effect,
if not controlled.
. On-site incineration would be required to meet the technical requirements
of RCRA. In addition to RCRA requirements, the remedy would need to comply
with other applicable State and Federal requirements but would not need a
permit. A monitoring program would also be a mandatory part of the incineration
process. Significant public opposition could be expected to this alternative.
This alternative attains and/or exceeds applicable and relevant public
health and environmental standards as defined by CERCLA and RCRA.
Alternative 7 - Off-site Disposal by Landfilling at an Approved Site and
Downgradient Pumping
This alternative consists of completely removing the landfilled waste by
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standard excavation methods and disposing of the waste in an approved off-site
facility. Upgradient pumping has also been included for the anticipated dewatering
of the saturated material in the bottom of the western part of the landfill
prior to excavation. The landfill area would be backfilled, following complete
excavation of the waste material. This alternative would eliminate a source
of leachate generation (refuse) and thus eliminate the addition of contaminants
to the groundwater.
This alternative includes a downgradient pumping program. Monitoring of
the recovery system will determine when the system can be phased out after
complete removal of the landfilled wastes.
Alternative 7 would provide basically the same public health and environmental
benefits as Alternatives 4, 5, and 6 through downgradient pumping and the
complete removal of the source of contamination by excavation and disposal in
an approved off-site landfill facility. These actions would prevent direct
human exposure and accelerate groundwater cleansing as do Alternatives 4, 5,
and 6. Dust, odor, and noise problems would arise from the excavation and
hauling actions contained in this alternative. The off-site facility would need
to be a RCRA permitted landfill to assure that potential environmental impacts
at the new site are minimized.
Commercial disposal facilities must meet stringent analytical, RCRA, and
State permitting and compliance standards. Using off-site facilities also
would require that the Department of Transportation requirements are met. Opposition
could occur from the State receiving this large quantity of waste (approximately
2,000,000 cubic yards). Off-site facilities could also be reluctant to accept
this large quantity of waste.
This alternative attains and/or exceeds all applicable and relevant public
health and environmental standards as defined by CERCLA and RCRA.
RECOMMENDED ACTION (Table 10)
Section 300.68 (j) of the National Contingency Plan (NCP) states that the
appropriate extent of remedy shall be determined by the lead agency's selection
of the remedial alternative which the agency determines is cost-effective (i.e.,
the lowest cost alternative that is technologically feasible and reliable) and
which effectively mitigates and minimizes damage to, and provides adequate
, protection of public health, welfare, or the environment. Based on our evaluation
of the cost effectiveness of each of the proposed alternatives, of the comments
received from the public, and information received from the Delaware Department
of Natural Resources and Environmental Control, we recommend that the phased
approach Alternative 4B be implemented at the Army Creek Landfill Site.
This alternative Includes downgradient pumping with monitoring, landfill
capping and possibly upgradient controls. This alternative will reduce the
public health risk by possibly containing the contaminant plume through the
downgradient recovery system. This alternative will also control precipitation
infiltration through the landfill surface with a multi-layered cap. Groundwater
infiltration through the northwest side of the landfill from the Columbia
-------
-22-
aquifer will be controlled by upgradient measures; If necessary. Leachate
migration into the Columbia and upper Potomac aquifers will be reduced. The
upgradient controls (pumping or an interception trench) may be installed following
an evaluation period of up to 5 years after the cap is installed. This decision
would be based on an evaluation of water levels and water quality at the Army
Creek Landfill. An additional component of this alternative is a well monitoring
program.
At this time, the selection of a groundwater treatment alternative has not
been made and will be the subject of a future decision document. In particular
this decision has been delayed because the final NPDES permit has not been
issued and the Delaware Sand and Gravel RI/FS has not been completed. It is
EPA's intention to combine the remedial actions at both sites where possible
and cost-effective. Also being deferred at this time is a decision on appropriate
remedial measures for sediments in Army Pond, that decision will be made at the
same time as groundwater treatment is considered and after further analysis is
accomplished regarding the actual impacts on Army Pond.
Operation and Maintenance
At least, quarterly inspection and maintenance will be required during the
operation of the downgradient and upgradient controls. Wells will be inspected
and maintained to insure their continual functioning.
Maintenance of the multi-layered cap will be required to ensure that the
cap is functioning properly in preventing the infiltration of stormwater into
the landfill. Vegetation loss, erosion, cracking or other cap disturbances will
be corrected.
•
Consistency with Other Environmental Laws
Alternatives were examined in light of relevant Federal, state and local
environmental program requirements and in light of all RCRA and CERCLA require-
ments for the closure of hazardous waste landfills and for disposal of excavated
contaminants in offsite hazardous waste facilities, including landfills and
incinerators.
The recommended action meets all applicable and relevant public health and
standards as defined by RCRA and CERCLA.
Evaluation of Alternatives Not Selected (Table 11)
The No-Action Alternative No. 1 with monitoring was not selected since it
would not control the source of contamination and would allow further degradation
of groundwater. Implementation of the No-Action alternative would mean that
the present hydrologic divide between the Army Creek Landfill site and Artesian
Water Company's production wells would no longer exist. Therefore, a potential
for human exposure by ingestion of organic and inorganic compounds in concentrations
above the drinking water criteria would exist. This alternative does not
provide protection to public health and the environment.
-------
-23-
Alternative No. 2 involves downgradient pumping with monitoring. Although
this alternative would reduce the public health risk by containing the contaminant
plume through pumping, it would not, however, address the source of leachate
entering the Potomac aquifer or the pathways in which water enters the landfill
resulting in leachate production. Precipitation infiltration though the landfill
surface and groundwater infiltration through the northwest side of the landfill
from the Columbia aquifer would continue under this alternative. Therefore,
leachate migration into the Columbia and upper Potomac aquifers would continue
for Alternative No. 2.
Alternative No. 3 would involve downgradient pumping with monitoring and
landfill capping. Although this alternative would reduce the public health
risk by containing the contaminant plume through pumping and control precipitation
infiltration through the landfill surface, it would not address groundwater
infiltration through the northwest side of the landfill from the Columbia
aquifer. Therefore, leachate migration into the Columbia and upper Potomac
aquifers would continue for Alternative No. 3.
Alternative No. 5 would involve excavation of the landfill refuse in the
western section, and disposal of the refuse on the eastern section, downgradient
pumping with monitoring and capping. Alternative No. 5 would address the
groundwater infiltration condition in the western portion by eliminating the
source of leachate generation through total removal of the refuse in the western
section of the landfill. This alternative was rejected because it provides
the same benefits as Alternative No. 4, but costs twice as much ($37,930,000
vs. $15,290,000), and would be more difficult to implement.
Alternative 6 would involve on-site incineration and downgradient pumping.
This alternative would provide basically the same public health and environmental
benefits as Alternative 4 through downgradient pumping and removal of the
source by excavations and incineration. This alternative was rejected because
it would provides the same benefits as Alternative No. 4, but would cost 7
times ($108 million vs. $15,290,000) as much and would be more difficult to
implement.
Alternative 7 would involve the complete removal of the landfill and down-
gradient pumping and monitoring. This alternative would provide basically the
same public health and environmental benefits as Alternative 4 through down-
gradient pumping and removal of the source. This alternative was rejected,
because it would provides the same benefits as Alternative 4, but costs 15
times as much ($243,000,000 vs. $15,290,000) and would be more difficult to
implement.
-------
w^EWER
WILMINGTON
ARMYCBEEK
ARMY
ILLANGOLLEN
LANDFILL
DELAWARE
SAND
LANDFILL
CO CHEMICAL CORP.
POLYMER PLANT
ARTESIAN WATER CO.
WELL FIELD
\S£ MAP IS A PORTION OF THE U.SOS. WUIM8TCN SOUTH, DeL.-N.J-
AOfUMQL£(7.9 MMUTE SEKBL, IM7) CONTOUR INTERVAL • 10'
LOCATION OF ARMY CREEK LANDRLL
NEW CASTLE COUNTY. DELAWARE
SCALE'- l"s20OO'
FIGURE 1
WMf K
:=»A7X3S)
-------
i
I
s!
a
<
M
i
LIQUID WASTE DISPOSAL PIT
4O
20
-20
•40
•60
-60
-100
120
--I40
DELAWARE
SAND 8 GRAVEL '
APPROXIMATE
WATER TABLE
IN 1981
LEGEND
SAND WITH CLAY
-I-Jij CLAY WITH SAND
LANDFILL
SOURCE: C K. LEE , JUNE,1982
HYDRQGEQLOGIC SECTION A-A
ARMY CREEK LANDFILL
NEW CASTLE COUNTY. PEL
HORIZONTAI SCALE |"»50O'
NOT TO 1CAL SCALE
. 31
JPORAIOv
-------
DELAWARE SAND ft GRAVEL
LANDFILL
A
AMOCO CHEM COR*
VMER PLANT
ARTESIAN WATER CO
WELL FIELD
o
c
LEGEND
INDICATES LOCATION OF
RECOVERY WELL
•indicates groundwater
flow direction
ARMY CREEK LANDFILL- SITE SKETCH
NEW CASTLE COUNTY. DELAWARE
SCALE = I " = 1000'
i i •
, u-
NMS
CCDRF I : AFOM
-------
o
c
3>
m
LEGEND
• b INDICATES LOCATION OF
RECOVERY WELL
O 54 - INDICATES LOCATION OF
POTOMAC WELLS (DEEP)
• BI&- INDICATES LOCATION OF
COLOMBIA WELLS
(SHALLO^t
ARTESIAN WATER CO
WELL FIELD
ARMY CREEK LANDFILL - NEW CASTLE COUNTY, DELAWARE
LOCATION OF MONITORING. PRODUCTION AND RECOVERY WELLS
SCALE: |"= lOOO'
IMUS
COFFORATION
-------
Vegetated Layer
Horizontal Drain Layer
Low Permeability Soil
Barrier Layer
Regraded Surface
To Treatment/
Discharge
Mul'ilayer
Cap
System
Existing
Cover Surface
Upgradient
Interceptor
Well
Soil Fill
(Local Granular Soils)
1
C
9
PI
N-S CROSS SECTION: ALTERNATIVE 4
-------
f
A Well Point System
to Oewater the Saturated
Refuse Before Reburlal
Will Be Required-
Discharge to Treatment
Final Cover/Cap System
Reburial of
Removed Refuse
<; \ \ ^
Refuse to be
Removed; Area to be
Backfilled with
Clean Soil Fill
Existing Refuse
•n
O
c
a
m
W-E CR' SECTION: ALTERNATIVE 5
-------
t *4 t 1 if m.
UUJ^O/J\t
TABLE 1
jrfJVJ
ORGANIC COMPOUNDS IN RECOVERY WELLS
EXCEEDING DRINKING WATER CRITERIA*
Well
RW-1
RW-10
• RW-11
RW-12
RW-13
RW-1 4
28
29
31
Parameter
Benzene
1 , 2-dichloropropane
Methylene Chloride
2 , 4-dini trotol uene
N-nitrosodimethylamine
1,2-dichloroethane
Benzene
Benzene
1 , 2-dichloropropane
Methylene Chloride
2 , 4y 6-trichlorophenol
BisrX 2-chloroethyl ) ether
1 , 2-dichloropropane
Methylene Chloride
Bix ( 2-chloroethyl ) ether
Benzene
4
Bis ( 2-chloroethyl ) ether
2 , 4-dini trotol uene
Benzene
Benzene
Benzene
Methylene Chloride
Chlorodibromomethane
2 , 4-dini trotol uene
Max . Cone .
(ug/1)
12.0
40.6
32.0
44.0
<10.0
. , 51 . 0
<10.0
10.3
25.1
21.2
3.0
<10.0
26.8
21.3
46.0
37.0
<10.0
38.0
40.0
45.0
150.0
16.3
19.2
116.0
Criteria
Tug/17
5-°b
O.*19c
O.lld ,
o.ogi4a
5.0a
5.0a
5-°b
6.0b .
0.19°
1.8®
0.03d
O.*19c
0.03d
5.0a
0.03d
O.lld
5.0a
5.0a
5.0%
°-19c
0.19?
O.lld
* - All laboratories (1983-1985)
a * Proposed Primary MCL (EPA, 13 November 1985)
b * Proposed RMCL (EPA, 13 November 1985)
c » Water Quality Criteria for Human Health (Fish and Drinking
Water); concentration of total halomethanes (CWA)
d * Water Quality Criteria for Human Health - Fish and Drinking
Water (CWA)
e Water Quality Criteria for Human Health - Adjusted for
Drinking Water (CWA)
-------
TABLE 2
Amy Ci.;.:k l
N>.w 1'o.itlo, ftel »
(lio.nl Viil.si- Quality
Ttit.il Cuioiiitrdt iuii
(mj/1.1
Antiiamy
Ar-tsnic
BoryllliM
Ocfei'lU i|lfl
a-n.ni .». "
C.,-,-0,-
l«,.l
H.,-.:u,V
Nickul
&*mi.M
Silver
•Mulliuui
Zinc
Irjo
HMW.-.H
i*j| 1 54
Uib|.i Jiuro: of dirouiiun; IMu. leached Uiromlura fc.» inlyu
j > Hdtjr Quality Criteria for Ilinin Ibilth - Flili aiiJ Drinking Htbjr ICHA)
b - Int.tr i« Prl-tai/ MCL (Gl'A, 11 NcwutoUir 19651
c - Mitir Quality Criteria for llmnin llotllli - Adjiuldi for Drinklntj WUler Only (CVM)
ii » Witu Quality Criteria - Onjaml^ptIc - Fiat) and Drinking H»t>r (CMA)
.; -> Sj.-onJary K.'l.
f - Proi>Mu<) lt«:
-------
TABLE 3
AKMY (XKfcX IANDFII.I.
tftW OSn.E, CKIAWAIIE
H&1WUIY VKIJ, INGHOANIi: VftTtM QUN.m 198)*
TuLal Con-
cent ration
Joy/1)
Antimony
Ar^aic
Bury 1.1 ium
CaJiiii am
Cliromi un
Cqver
U*«l
Hjrcury
Nickel
Selenium
Siluur
'Hull ium
Zinc
Iron
MU>Jdlk2!U
RW-1
<0.00i
0.0092
* » Aj|»rent Tliredliold Ll»lt Values (CVft)
-------
TABLE
Ntw CiMLle, Dcl.iw-i
Giointl Water Qtiili
Fl'A Si|>l.inli:r 1S84 S^
(n»j/l 1
AMI iin*i/
A.^.i.:
Dii/lliim
Guliiii mi
a,,,,.,,.,
On.;r
, t
M-^-ury' '
Nicki-l
S.J..T,i,«,
Silver
flulliim
Zinc
Wv'll 54
vO.OIIi
.-yoi«l UK; Uil.liny ti«u
Miter
,i •> TijKioity «.i|if for |jriAujtlon of
l> " Pruiur/ Driiikii«| Water Suinkirri
c " Scuufclary Drinklixj Wjler Startlarii
•I = W,iL«r Quality Criteria for Iliinm Ikiilth - AdjiHtui for Drinking Water Only (CMAI
.; = State of Dbl.iuar.i Water Quality Criteria Per Disdianjes (CWA)
f - Wii..-r Qiirility Criteria, Oiijaiioleptic - Fish and Drinking Writer (CWAI
•I - Hr.,.>;ol IMiJ. IEfH, I) Novomlx-r I98S)
> = A(|kir.:iil HiTi-'iliolH Limit Values) IOIA)
-------
Army Creek Landfill
New Castle, Delaware
Army Creek and Pond Water Quality
EPA/FIT Sampling 9-11 November 1981
Organic Concentrations
(discharge)
W (nr. RW-4)
(discharge)
V (nr. Amoco)
Station
I (Rt. 13)
II (RR tracks)
II [ (nr. RW-9)
00
«»
01 J3
8 • A
ff "
ND ND
* ND
* ND
Fluoranthene
ND
*
*
Bis (2-ethylh
Phthalate
*
*
*
Di-n-butyl
Phthalate
*
*
*
Benzo (a)
anthracene
ND
*
*
Oirysene .
ND
*
*
Anthracene
ND
*
*
Phenanthrene
ND
*
*
ND
ND
350.
ND
ND
c $ -
5 2 S 2
« £| 25 *»
es «8 rs fi
N
ND
a a i
ND
Nl.)
ND ND ND ND
ND ND ND ND
ND
ND
ND
ND = Not Detected
*
Indicates chemical present in sample
-------
TABLE 6
Ibtal Coiic.
AI unii inim
Chn»nl ilia
Btrftim
ftiryll hm
C»lmiiun
lRt.ll>
0. fill
w Cwrte, Oel.irfir.;
Amy Cr.s* an.) Pciul Wat.jr Qitillty
lnor.|diiii: Gix.vnl rit Icm i (inj/1 I
H'./Flf S.»n>lln<| 9-11 Ncv.:inh:r 1901
Station III
•«'•'
0.76
Till
Sllu.-r
.n.oio
3rablu «uumln| a hardneaa
»> 100. nij/l.-ifi Cali). ICMtl
I) = Crit^rLi for Fre.iliwi(.;r Aifntlo l.lf-
o - Aoit> IVixluliy Criteria for FrealiwaL-r Aquatic Life (CUM
• ' A|l»r.-iit ThroJliold Limit Valued (CVA)
-------
TABLE 7
Army Creek Landfill
New Castle, Delaware
Army Creek Water Quality
Base/Neutral Organic Compounds (ug/1)
Location
Upstream
Downstream
Surface Water or
Criteria
Date
Sept. 1983
Sept. 1983
Bis(2-ethylhexyl)
Phthalate
13.2
NF
3.0
a*
Di-n-butyl
Phthalate
83.6
40.1
3.0a
* Analyzed by New Castle County Laboratory
NF = Not Found
a = Criteria for Freshwater Aquatic Life for Phthalate Esters (CWA)
* = Apparent Threshold Limit Values (CWA)
-------
TABLE 8
Army Creek Landfill
No* Castle, Delaware
Army Creek Mater Quality
Total Inorganic Caieeiitrat ions (aij/ll
Location
Data
i
!
s s
v
S
I I
§
U|tiii.iiin
<0.010 <0.002 <0.0005 0.0016 O.OIS 0.0064 0.0127 0.0005 0.110 <0.050 <0.0005 <0.002 0.040 2.7« U.luil
l*wn ;i , .uin Sq»t. 198) :
Cri tc-r i.i
0.005Jb* 0.000025°
O.I7C 0.000017° 1.8°
0.7«,
!>/ NvM CaMtle Cm ml .y l^lmalory
* A|4*ir..:iit 'IM.;ilK)lil Limit Val i»j:i OJWA)
** ciii'niii IMI |iiuUibly li_j>,ii^' frtin could inui by
It*)
. In |olyn>jl liiin.: unit. liners.
H ' vc Qitility enter 1.1 for Iliiiun llmlili - riali >u>.t DiuikiiKj Mater ('
b lui id for FreHliwater Atjikitio Life ((VIA)
c .teria fur Fresliwtei A>]ivitic Life - ti>lal r..i:uy<;r,ihli.-
-------
TABLE 9
Amy Creok landfill
New Castle, Delaware
Amy Creek and Pond Sod intent Quality
Ibtal Inorganic Concentrations ((fib)
DNRBC Sailing and Analysis
IW.^1
Co>c.;ntratlon
I run
Haivjai>es.j
i.luoini im
Silvur
Zinc
l«Md
C»)ini mn '
Hii'.;iiry
Arsi.-nic
Selenium
Station 1
21,902,000.
167,000.
18,490.
<10,000.
87,270.
21,400.
<10,000.
<500.
<3000.
<500.
Station 2
9,505,000
190,000.
10,210.
<10,000.
90,920.
142,000.
< 10, 000.
<500.
<3000.
<500.
Station 3
44,010,000.
274,000.
25,540.
<10,000.
274,000.
175,000.
<10,000.
<500.
9260.
710.
Station 4
18,530,000.
398,000.
<10,000.
<10,000.
70,750.
25.410.
< 10, 000.
<500.
<3000.
<500.
Station 5 '
45,175,000.
845,000.
14,920.
<10,000.
143,000.
70,630.
<10,000.
<500.
5470.
<500.
Station 6
27,962,000.
1,320,000.
14,930.
<10,000.
240,000.
56", 750.
<10,000.
630.
13,540.
<500.
Station 7
2,867,000.
24,260.
<10,000.
<10,000.
22,240
10,110.
•*-» -«.
SLit.o,, 4 = Aniy Cr.**. Paid Efflua.t
SLit on 5 -An* Cr*A. l.,d.,r Rdilr,Md Bri.lju
SUtion 6 - Aniy Cr«..-k, Tidal Gat,» East of RouL- Q
Sl.,tio,, 7 ^ GrJW,J Pit i-md
Stal:i.jn 8 - Intermittent Stream Elm of IK 4 c,
-------
Precipitation
Diagrammatic water budget
Vegetative
cover
Geotextile
JL.Drain
Evaootransoiration
Final grade
Percolation
through soil
Percolation through
cap(
-------
Remedial Method
1. No action - monitoring
2. Downgradient pumping
t. Downgradient pumping
and landfill capping
4. Downgradient pumping
landfill capping and
upgradient pumping
5. Partial removal and
on-site disposal,
capping and downgradient
pumping
'h. On-site incineration
and downgradient pumping
7. Off-site disposal at
an approved landfill and
downgradient pumping
Total Capital
TABLE 10
REMEDIAL METHOD COST ESTIMATES - Array Creek Landfill
Total Monitoring/Maintenance Cost
Cost
$250,000
$120,000
Annual
$113,000
$272,000
Present Worth
$1,065,000
$2,565,000
(1)
$12,030,000
$307,000
Non-phased $12,340,000 $393,000
Phased $12,030,0007
$310,000(2) $306,000/$87,000<3)
$35,500,000
$113,500,000
$296,000<4)
$272,006
$2,895,000
$3,705,000
$3,140,000
$2,430,000
$2,565,000
Total Present Worth
Cost
$1,315,000
$2,685,000
$14,925,000
$16,045,000
$15,290,000
$37,930,000
$108,250,000(5)
$239,900,000
$272,000
2,565,000
$243,000,000
(1) Assumes present worth values based on a discount rate of 10% over 30 years.
(2) Assumes construction of upgradient pumping in 10 years @$310,000.
(3) Assumes operation of upgradient pumping in 10 years (?$87,000/yr.
(4) Anticipated annual coat for 15 years after which annual cost is reduced to $96,000.
(5) This'cost estimate is a result of subtracting the revenue figures from the total cost of the project.
-------
TABLE 11
9JMURY EVAI1IATICN OF RUttDIAI. ALTIUN Al.TERNATIVES
AI.'ltKNATlVE
OKT ($1,0001
PRESENT
wtwni
TEUMICAl. CONCERNS
HIUI.IC IKAL'ni AM)
ENVIROHO/TAl. CONCERNS
IHPIiMtNrABII.ITY-SAFETYl
OOMNITY
RESPONSE CCNCERNS
COMB/IS
1. Nu-Aot ion
o Monitoring Oily
'I. nuwngradient Puqplntj
o Hen I tor ing
o Discharge to Appro-
prlate Treatment
i. IXMntjradiunt pumping
o Monitoring
o Discharge to Appro-
(iriate Treabnunt
landfill Cajiplng
o Site Hograding and
Surface Mate' Diver-
sions
1,115 Without hydruloglc controls,
the contaminate plunu will
migrate further downgradient,
resulting In potential human
exposure by ingest Ion of or-
ganic constituents above the
tO~6 Health Risk Criteria.
The continued production of
leachate, would not be con-
trolled continuing tapact
on Coludfcla and Potomac
aguifer.
2,685 Roluces public health risk
by containing the contami-
nant plume by leans of a
nydrologlc divide.
lias prevented possible aban-
donment of Potomac aquifer as
source of teter supply. Ihe
quantity of leachate generated
from precipitation and ground
water Infiltration through
the landfill will not be re-
duced - Impact on environment
will continue.
14,925 Public hualth risk reduced by
containing the contaminant
plume by 'means of a hydrologlc
divide.
Infiltration of precipitation
through the landfill will be
reduced over 96% by capping
the landfill. Ruluclng lea-
diate production should hasten
Downgradient recovery
system has to data a
history of effectiveness.
Water quality of down-
gradient water production
supply wells has been
iralntalned.
System requires periodic
rehabilitation and
maintenance.
Rtqrading and backfilling
of the existing cover is
required bo establish a
site contour pattern to
promote run-off away from
landfill. Degrading to
flatten out existing
slopes to assure slope
stability nay be required.
Publicly Unacceptable
Does not follow projxjsod
guidelines of the EPA
Ground water Protection
Strategy. (CBRICA)
Dues not attain
aj>(>l (cable public
health and environ-
mental standards.
Ihe discharge of recov
ered/treated ground water
mat be per formed within
necessary permitting/
approval process. NPTJGS
permit required If treat-
ed discharge Is to Army
Creek.
The discharge of recov-
ered/treated ground water
must be performed within
necessary permitting/
approval process. NPUES
permit required If treat-
ed discharge is to Army
Creek.
Does not attain
applicable environ-
mental standards -
present cover over
landfill does not
meet RCRA guidelines.
Tills alternative at-
tains applicable and
. 'lei»nt pibllc health
and environmental
standards.
-------
TABLE 11
(ooiitinitud)
i$i.aiu)
PldiSEMP
AI.'ltHNATIVt:
J. (continual)
u Gas VaiLing
Phased A(i>roach
Phase I
Duwnjradlent Pumping
o Monitoring
o Discharge to Ap-
proriate Treat-
ment
landfill Capping
o Site ftugradlo} t
Surface Hater
Diversions
o Gas Vaiting
Phasa 2 ,
llpjradlent Contculs
o Monitoring
o Discharge to.Ap-
propriate Treat-
ment
15,290
HIUI.IC IKAI/m AM)
CONCEHNS
groinl water cleansing but at
an unknown rate. Infiltration
Into landfill of ground tetter
from Columbia aquifer along
northwestern aide will con-
tinue. Contamination of both
Columbia and Potomac aquifer
continue.
(PEHrYVMANCX-MJI.IAHII.m
RUQIMKK-
MKWIS COMWITY
HESPOISE CCMCERNS
Side slopes in the floud
plain mist be protected
with rip rap cover.
cowans
Public health risk reduced by
containing tlie contaminant
pi IKB by iruans of a hydrologlc
divide create by downgradlent
pinplng.
Infiltration of precipitation
through landfill reduced over
96% by capping the landfill.
Present cover provides only
12% reduction In Infiltration.
llpgradlent pwplng network
will significantly reduce the
ground water entering landfill
along northwestern side, re-
diuing further leachate produc-
tion.
After initiating upijradlent
pio|>ing (Phase 21 short-term
effect la oootlnuoJ 100 of a
writer resource, llpji'ad-
ient |UD|>ing will hasten ground
vnler cleansing long-term effect
.s less (jniplng of downgradient
ni'tuork.
Same as I) t In additloni
Itie efficiency of the up-
gradlent pinplng wall
scheme Is largely depen-
dent on the amount of re-
charge through the land-
fill and the water level
elevations In Army Creek.
As with the downgradlent
system, the upgradlent will
require periodic rehabil-
itation (initially) and
maintenance.
Hiere are RCRA design
standards for surface
capping. Proposed cap
will meet SCRA guidelines.
Public concerns about new
activity at the landfill
site must be addressed.
All state erosion, sedi-
ment, and dust control
ordinances would apply
during construction and
until a vegetated cover
Is established.
Sane as 13 t In addition,
wall Installation permits
for the new upgradlent
walls have to be obtained
from the State of
Delaware.
Under the phased ap-
proach the effect nu
the ground water
quality as a result
of capping the land-
fill will be ronllor.il
and assessed prior to
Initiating iipgiadlent
pinplng.
Ittia alternative
attains applicable and
relevant public
and environmental
standards.
naul tor evaluation
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TABLE 11
ALTERNATIVE
4. axitlnuul
5. Partial Hunwal and
Disposal On-Site
o RajraJInj, Back-
filling, Surface
Water Diversions
(•amtftll Capping
o Gas Vaiting
UtMivjradlent Pumping
o Monitoring
o Discharge to Appro-
priate Treatment
OUT ($1,000)
PKESBrr HJBLIC IKAI.ni AND
WORTH UIV1RCNHENTAL CONCERNS
(continued)
TEUMICAL OONCIiKNS
IMPUMEMrABILITY-SAFBTYl
REQUIRE-
MENTS COMNITY
RESPONSE CONCERNS
16,045
17,930
6. On-Slte Incineration
o Conpl.ile Romval
o fXwalerlng of Refuse
by llpjradlent Punning
Ouwryjradlent Pumping
o Monitoring
o Discharge to An>ro-
priate
108,000
Sane aa I4a
Public Health Risk reduced by
containing contaminant plume.
Addresses environmental Im-
pact caused by ground %ater
infiltration by eliminating
tJie source of leachate gen-
eration and has additional
benefit of not removing ad-
ditional water fro* local
source as In Mternatlve 4.
Capping of eastern section
after renewal and disposal of
western section will signifi-
cantly reduced precipitation
Infiltration. Source removal
and capping of landfill will
hasten a ground water cleans-
ing reducing long-term pxuiplng.
During excavation dust t odor
problems will occur as well
as the draining of free water
fron saturated refuse.
Sane public health and envir-
onmental benefits aa Alter-
natives 4 and S. Air pollu-
tion control devices required
under RCRA will reduce the re-
.lease of contaminants Into
the air.
Incinerator ash and residue
backfilled on-slte In areas
above ground water table.
Sane as |4a
Sane as 14
Refuse In western part
below Uie water table
will have to be dewatered
by upgradlent punplng.
Recovered water will
require treatment.
Free liquid drainage and
dust can be control led
using standard construc-
tion approaches but odor
will be aore difficult.
A potential slope stability
problem my result along
the exposed cut section be-
tween the eastern and west-
ern section as excavation
results In deep cuts Into
refuse.
Speclal/haxardous wastes en-
oountered will require
special handling and tran-
sport.
Sane as I) In addition,
odor would bo a signi-
ficant concern to the
local public. Increased
noise is also a concern
during excavation and
disposal operations.
Suitability of Potanac
For AitI on to support In-
cinerator foundations.
Raw refuse fru» of f-site
will be transported to the
site and mixed with the
saturated waste to crake
it burnable.
Compliance with Dataware
Solid Waste Authority's
master plans.
On-Slte Incineration re-
gulated under RCRA. A
Hazardous Waste Manage-
ment Facility Permit Is
requital.
Public qnmsitlijo can lie
antlcl|>ateJ.
COMENTS
Under the non-pliaauil
ajiproach all ranslial
action will be Initi-
ated simultaneously.
This alternative
attains applicable
and relevant public
health and environ-
mental stanrbrrls.
This alternative wis
screened out because
its cost Ts~of an
order of magnltmlu
greater than Alter-
natives 4 anil S whii:li
offer similar (iibllc
health and environ-
mental bunufits.
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TABLE 11
lountlnikjd)
AJ.TCHNATIVE
6. ouotinuul
uub-r ($1,0001
PHESFNT
MOOTI
7. Off-Site Disposal by
Landfill Ing at A(v>rovud
Site
o Caaplete Ranuval of
landfill
o Dtvaterlng of Sat-
urated Refuse by
Upgradient Puling
DtMijradlent Funding
o Monitoring
o Discharge to Appro-
priate Treatment
241,000
HIULIC ItAI.III AND
CUMUEHMS
•MUMICAI. ONJKKNS
(PaiFOOIANCE-ICI.IABII.ITY
IMHimrrABII.ITY-SAFCTYl
GTMUMI'l-Y
concerns
ctmons
llust, odor, and drainage of
free liquids fro* the saturated
waste are problems associated
with the excavation of landfill
refuse.
Otlter environmental and health
concerns are with transport of
raw refuse to tin Army Creek
Site Including noise, dust and
(received vector problems.
Sama public health and envir-
onmental benefits as Alter-
natives 4, 5, and 6. Dust,
odor, drainage of free water
fro* the saturated refuse,
and noise problems will arise
fro* the excavation and haul-
Ing operations.
Availability of HCRA
approved sites.
National Amlilent Air Quality
Standards (NAAQS) apply -
will require Clean Air Act
(CAA) permits.
Transportation of hazard- Sane as 16.
ous waste to an off-site
disposal facility requires
RCRA TSW permits.
M>llc opposition to this
alternative resulted In
the cancellation of an
earlier plan for a dis-
posal site adjacent bo
Army Creek site.
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RESPONSIVENESS SUMMARY
ARMY CREEK LANDFILL SITE
NEW CASTLE COUNTY, DELAWARE
SEPTEMBER 1986
This coranunity relations responsiveness summary is divided into the
following sections:
Section I:
Section II:
Section III:
Section IV:
Overview - A discussion of the EPA's preferred remedial
action alternative.
Background of Coninunity Involvement and Concerns - A
brief. history of the community's interest in and in-
volvement with the Army Creek Landfill Site, including
a discussion of concerns raised by community members
and officials during ranedial planning activities.
Summary of Public Comments Received During the Public
Comment Period and Agency Responses - A summary of
comments categorized by topic and followed by EPA
responses.
Remaining Concerns - A description of remaining community
concerns that should be considered as the EPA and the
State of Delaware Department of Natural Resources and
Environmental Control (DNREC) conduct the remedial
design and ranedial action at the Army Creek site.
In addition to sections I through IV, a list of EPA community relations
activities conducted at the Army Creek site is included as Attachment A
of this responsiveness summary.
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- 2 -
I. Overview
The Remedial Investigation (RI) Report and the Feasibility Study (FS)
Report were released to the public for review and comment on August
21, 1986. This marked the opening of the comment period, which
extended until September 22, 1986. Djring the comment period, the
EPA recommended a preferred remedial alternative from among the seven
alternatives presented in the FS report.
After careful review of and consideration of all alternatives
developed in the FS, the EPA and DNREC recommended the phased approach
described in Alternative 4. This alternative includes the following
components:
0 Regrade the landfill surface to assure a finished compacted
surface and install a capping system to minimize infiltration
of rainwater.
0 Continue the operation of the downgradient recovery well
network.
0 Evaluate the capping systan and the downgradient pumping
network for five years after the cap is installed to assess
systom effectiveness during operation. This evaluation
would include, but not be limited to, monitoring water levels,
pimping rates and water quality.
0 After the evaluation period, if conditions necessitate, install
upgradient controls to intercept lateral groundwater inflow on
the northwestern boundary of the landfill.
0 Continue monitoring of water levels, pumping rates and water
quality.
II. Background of Community Involvement and Concerns
The Army Creek Landfill Site is located 2 miles southwest of New
Castle, Delaware. The site is located on the northwest bank of Army
Creek, which discharges into the Delaware River within 1 mile of the
site. A residential development of more than 200 hones, Llangollen
Estates is the nearest and most directly affected community. Just
beyond this residential area lies the Artesian Water Company's well
field, which supplies water to approximately 5,000 people.
The site was originally used as a sand and gravel pit. The New Castle
County purchased the property in 1960 for use as a municipal landfill.
Waste was deposited from 6 to 35 feet deep over an area covering 44
acres.
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- 3 -
The residents of Llangollen Estates expressed their concern over the
landfill as early as 1960, when plans for the municipal .landfill were
announced. The Llangollen Estates Civic Association filed an un-
successful legal action to prevent the landfill from opening.
Throughout the active life of the landfill, residents of Llangollen
Estates cortplained of rodent and odor problems. The number of
complaints decreased substantially after the landfill was closed and
covered with sand and soil.
In 1971, one Llangollen Estates resident complained that the water in
her home had an odor and stained her porcelain fixtures. The water
was analyzed and found to be contaminated, as was water from several
other private wells. Presently, most Llangollen Estates residents are
receiving municipal water supplied by the Artesian Water Company. .
Residents of Llangollen Estates have followed closely the activities
of all government agencies involved with the Army Creek Landfill.
However, communication between government agencies and citizens during
the time between signing of the FS Consent Order with New Castle County
and release of the FS document was limited. This lack of communication
was a major concern voiced by citizens during the comment period.
III. Summary of Public Comments Received During the Public Comment Period
and Agency Responses
Technical Questions/Concerns Regarding Remedial Alternatives
1. A resident asked for an explanation of upgradient controls.
EPA Response - The installation of upgradient controls is an
option to be considered after the five-year evaluation period.
The capping system and the downgradient punping network will be
evaluated for five years after the cap is installed to assess
the system's effectiveness. If necessary/ upgradient controls
such as recovery wells upgradient of the landfill or trenching
around the landfill would be installed to prevent lateral flow
through the fill material.
2. One ccmraentor asked what was being done at present to control
the contamination into Army Creek.
EPA Response - Contaminated groundwater punped from the recovery
well system at the Army Creek Landfill is discharged into Army
Creek. Presently, DNREC is drafting an NPDES permit which will
establish safe and appropriate levels for contaminants now being
discharged into Army Creek.
3. One commentor questioned if the quality of the recovery well water
would improve upon completion of the remedial action and if so,
would it be plausible to pump this water into the Wilmington Waste
Water Treatment Plant instead of into Army Creek.
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- 4 -
EPA Response - Once the landfill is capped, the quality of ground water
should improve. Pumping into the Wilmington Waste Water Treatment Plant
is an option that will be addressed at a later date.
4. A resident asked how much water was presently being pumped into
Army Creek.
EPA Response - Approximately two million gallons per day.
5. Another resident asked how close the contaminants are to the well
field.
EPA Response - The contaminant plume extends to approximately 1500 feet
away from the Artesian well field.
6. Several ccmmentors questioned the timetable for the remedial action.
EPA Response - Negotiations with responsible parties generally are
limited to 90 days. It is anticipated that the Record of Decision
(ROD) will be finalized by September 30, 1986. The actual design
phase of the project could take up to one year to complete. After
the design phase, the remedial action will be implemented. Once
the action is completed and the cap is in place, the site will be
monitored for five years to determine if the levels of contamination
decrease. An evaluation will then be made regarding the need for
upgradient controls.
7. One resident questioned what factors the Feasibility Study (FS)
took into consideration.
EPA Response - The Feasibility Study considers not only what
contaminants are in the landfill, but the pathways by which
exposure can occur to both humans and the environment.
The purpose of the FS is to evaluate various alternatives to
remediate the source and the contaminated groundwater.
Public Health/Environmental Concerns
1. A resident asked if anyone could say with reasonable assurance
that there will not be a lateral flow of contamination into
the landfill.
EPA Response - EPA will evaluate the effects of any lateral flow
upon completion of the cap. If the effects are significant,
upgradient controls will be installed.
Public Participation Process
1. Several residents expressed their concern over the lack of
information and opportunities for public participation at the
Army Creek site.
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- 5 -
EPA Response - EPA representatives offered to rrvake themselves
available for small group meetings to discuss the FS in detail.
EPA also stated that there will be many more opportunities in
the future for residents to be involved with the decisions made
at the site.
2. Several commentors requested additional time to review the FS and
the preferred alternative. Several residents said they were
outraged at being given only 21 days to comment on a study that
took 2 years to prepare.
EPA Response - A decision to extend the public conment period
could not be made at the meeting, but would be taken into consid-
eration with tlte other comments received, both written and oral.
(The comment period subsequently was extended from September 15
to September 22 as a result of this request.) EPA explained that
citizens would have input for the duration of the project, and
that this Record of Decision could not address recovery well
discharge.
3. Some residents indicated that EPA should begin the cleanup as
soon as possible, and that additional delays should be avoided.
EPA Response - None.
4. A representative of the Llangollen Civic Association asked if
EPA would meet with knowledgeable ccnununity members once they
had a chance to review the FS.
EPA Response - Agreed.
Cost/Funding Issues *
1. A commentor questioned what the cost of the remedial action would
be.
EPA Response - The present worth cost of the remedial alternative
over the next 30 years approximately is $15 million, this includes
capital costs.
2. One resident asked how much New Castle County had spent to date
on the Array Creek Landfill. .
EPA Response - New Castle County has spent $3.85 million to date
on the Feasibility Study and the installation, operation, and
maintenance of the recovery wells.
3. The Artesian Water Company claims that its pumping capacity has
been reduced due to groundwater contamination. The company
believes it should be compensated for this loss as part of this
CERCLA action.
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- 6 -
EPA Response - This question has been discussed at length by.EPA,
the Artesian Water Company ("Artesian") and New Castle County
before and during generation of the Feasibility Study. It is
Artesian's position that it has been forced to draw less water
from its wellfield because of the contamination leaching from
Ar-ny Creek and operation of the recovery well system. Artesian
regards the reduction in capacity as a response cost under CERCLA.
New Castle County is of the view that, if Artesian has lost any
capacity frccn the wellfield, it is for reasons other than
pollution from the landfill. The County has argued that Artesian
has never been entitled to draw more water than it presently takes
from the wellfield, by virtue of state authorization and salt
water intrusion. Artesian has sued New Castle County, and some
other parties over this question, and no final resolution of that
case has been reached.
Both Artesian and the County vigorously presented their
respective positions to EPA during preparation of the Feasibility
Study. The regional staff consulted with headquarters about this
issue, and the final result was a memorandum from Gene A. Lucero,
Director, Office of Waste Programs Enforcement, to Steve Wassersug,
Director, Hazardous Waste Management Division, Region III. In
short, the position of EPA is that replacement of aquifer capacity
is not a goal for this CERCLA cleanup. The wellfield currently in
use is being protected by the existing recovery well system, and
other remedial measures recommended for this site should prevent
future contanination of the aquifer related to contamination frcm
the landfill.
-------
Attachment A
Community telations Activities Conducted at the
Army Creek Landfill Superfund Site.
0 August 3, 1984 - EPA announced signing of a Consent Order with
New Castle County to perform a Feasibility Study for the Army
Creek Landfill.
0 November, 1984 - EPA completed a community relations plan.
0 August 18-20, 1986 - EPA contacted local officials and citizens
regarding release of the FS and set up information centers in
the community.
0 August 21, 1986 - The FS was sent to 4 information centers, and
a press release announcing completion of the FS was distributed.
0 September 10, 1986 - A public meeting was held to discuss the
findings and recommendations of the FS.
8 September 15, 1986 - The comment period was extended until
September 22, 1986.
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