United States
(Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROD/R03-90/091
June 1990
Superfund
Record of Decision;
Army Creek Landfill, DE
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50272.101
REPORT DOCUMENTATION 11. REPOATNO. 12.
. PAGE . EPA/ROD/R03-90/091"
4. Title and Subtitle - -
TJPERFUND RECORD OF DECISION
my Creek Landfill, 'DE
u8cond Remedial Action - Final
7. Aulhor(8'
,3. Reelpl""'" Acc:e88ion No.
5. Report D8te
06/29/90
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.. PwfonnIng Orpnlzatlon ~ No.
8. Pltrfonnlng Org8lniZllllon ...... MIl Add-
10. ProJactIT 88klWork UnIt No.
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11. Contr8C1(C) or Gr-
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EPA/ROD/R03-90/091
Army Creek Landfill, DE
Second Remedial Action- Final
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Abstract (Continued)
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This ROD, the second of two operable units,.. addresses the need to treat the recovered
ground w~ter prior to onsite discharge into Army Creek/Pond. The primary contaminant of
concern with respect to the impact of discharge to surface water is iron.
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The selected remedi~i action for this .site. includes g~ound water pumping &Sing the
recovery well network and treatment using a modified conventional precipitation water
treatment plant which involves aeration, precipitation, sedimentation, and filtration
followed by onsite discharge of the effluent to Army Creek/Pond; sampling and disposal
of sludge generated during the treatment process; and monitoring of the sediment,
recovered ground water, surface water, and wetlands. The estimated present worth cost
for this remedial action is $4,900,000 which includes an annual O&M cost of $294,000.
PERFORMANCE STANDARDS OR GOALS: The recovered ground water will meet State water
quality criteria prior to onsite discharge into Army Creek/Pond. Chemical-specific
goals include iron 1,000 ug/l.
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RECORD OY,DECISION
ARMY CREEK LAND~ILL
OPERABLE UNIT '2
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DECLARATION
site Name and Location
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Army Creek Landfill site
Operable Unit #2
New Castle, Delaware
statement of Basis and Puroose
This decision document presents the selected remedial action
for the Army Creek Landfill site in New Castle, Delaware, which
was chosen in accordance with the requirements of the Comprehen-
sive Environmental Response, Compensation, and Liability Act of
1980 (CERCLA), as amended by the Superfund Amendments and
Reauthorization Act of 1986 (SARA), and, to the extent
practicable, the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP). This decision document explains the
factual and legal basis for selecting the remedy for this site.
The Delaware Department of Natural Resources and
Environmental Control has not concurred with the selected remedy.
The information supporting this remedial action decision is
contained in the administrative record for this site.
Assessment of the Site
Actual or threatened releases of hazardous substances from
this site, if not addressed by implementing the response action
selected in this Record of Decision (ROD), may present an
imminent and substantial endangerment to public health, welfare,
or the environment.
Descriotion of tbe Selected Remedy
This operable unit is the second of two operable units for
the site. The Record of Decision for the first operable unit
selected a remedial alternative for source control including the
installation of a mUlti-layered landfill cap and the operation of
a, recovery well network downgradient from the site to prevent
contaminated groundwater from migrating to potable water supply
wells. This second operable unit addresses the need to treat the
recovery well discharges prior to discharging to Army Creek/Pond.
The selected remedy will reduce the concentration of iron in the
extracted groundwater to a level that is protective of the
designated uses of Army Creek. A monitoring plan will be
implemented to ensure continued compliance with all applicable
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standards. Together, the impl~mentation of the overall remedial
action strategy sel'ected in the first operable unit ROD and..the
second ope~8ble. unit ROD will provide. a quality of water tn.Army
Creek/Pond that is protective of human health and the ..
environment. Hazardous substances will remain on site, therefore
long-term management will be required.'
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The primary component .~f the selec~ed remedy is the con-
structioh arid operation of a water treatment facility that is
capable of reducing the concentration of iron in groundwater
recovered by the recovery well network prior to surface
discharge, amounting to about 1.4 million gallons/day. This
remedial action will require long-term management to assure
compliance.
Declaration of statutory Determinations
The selected remedy is protective of human health and the
environment, complies with Federal and state requirements that
are legally applicable or relevant and appropriate to the
remedial action, and is cost-effective. This remedy utilizes
permanent solutions and alternative treatment (or resource
recovery) technologies to the maximum extent practicable, and it
satisfies the statutory preference for remedies that employ
treatments that reduce toxicity, mobility, or volume as their
principal element.
Because this remedy will result. in hazardous substances
remaining on site above health-based levels, a review will be
conducted within five years after commencement of remedial action
to ensure that the remedy continues to provide adequate protec-
tion of human health and the environment.
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~~ks~
?1kegional Administrator
Region III
b/;1." ho
Date
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RECORD OF DECISION . :-
REMEDIAL ALTERNATIVE SELECTION
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ARMY CREEK LANDFILL SITE
OPERABLE UNIT '2
NEW CASTLE, DELAWARE
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DECISION SUMMARY
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I.
SITE LOCATION AND DESCRIPTION
The Army Creek Landfill is located approxi~ately two miles
southwest of the city of New Castle, Delaware (Figure 1). The
landfil~. is ..bordered.to the: north and west by Conrail tracks and
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
(Figure 2).
on
Llangollen Estates, a residential development, is located 1/4
mile southwest 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 approximately
44-acre landfill which accepted municipal and industrial 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 dis-
agreeable odor and permanent staining of porcelain fixtures. New
Castle County began a mUlti-year field investigation to assess the
problem. Results from that investigation showed that leachate
originating from the Army Creek and Delaware Sand and Gravel
Landfills was contaminating local aquifers.
The County's remedial investigation led 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 is currently
discharged to Army Creek. Army Pond, oriented parallel to the
southern site boundary, is ellipsoid in shape and approximately
2,000 feet long, 175 feet wide, and 1 foot deep. Storm water
runoff fro. the site, as well as flows from the recovery wells, are
collected in this pond. Upstream of the pond, Army Creek is a low-
vplume seasonal stream largely dependent on storm runoff which
empties into the pond. Downstream of the pond the Creek is
enlarged by the flow from the recovery wells, which averages 1.4
million gallons per day. Although the recovery well discharges
represent up to 90 percent of the volume of Army Creek, historical
aerial photos document that Army Creek/Pond was nearly the same
size in the late 1950s. There are high quality wetlands associated
with the Army Creek which are utilized by migratory birds.
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ARMY ~ LAN)FIJ. SITE LOCATION
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ARMY CREEK ACTIVE RECOVERY WElLS
FIGURE 2
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Af8I'( .CMIk
.1 RECOVERY WEU.FIElD
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. Army Creek and its vicinitY"supports a diverse flora and.
fauna.Fi~e species of specia~ concern have been found in Army
Creek or"withi.n the vicinity of the site. These are the gur"':
marigold, smallmouth bass, striped bass, white..crappies and yell~w
bullheads. The bur-marigold is not found on the Army Creek Site,
but rather at the mouth of Army Creek along the Delaware River.
Because of the distance involved, it is not likely this species
would be impacted by the Army Creek Site or its remediation. The
four fish species listed abOve could potentially be impacted by the
Army Creek Site. Although'these species have been found in Army
Creek, they do not appear to be common species in the Creek. White
crappies and smallmouth bass were found two times out of six
sampling events between 1975 and 1983, while yellow bullhead and
striped bass were found only once.
8it8 Geoloqy
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 Pleistocene Age and is from 10 to 60
feet thick at the site. This formation, which dips to the south-
east, consists of medium to coarse grained sands, gravels, silts
and clays which were deposited in shallow lens-shaped channels.
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
nonuniform: in some places, the sands of the Columbia and Potomac
are in contact.
8i~8 Hydrog801ogy
Hydrologically, the Potomac upper clay functions as a confin-
ing zone ~or the underlying aqui~er which is known as the upper
~otomac 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 19505,
before significant devel~pment of the aquifer, was about 19 feet
below sea level and flow direction was toward Delaware Bay to the
southeast. In the 1960s, 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.
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The surface of. the landfill is pocketed with depressions
resul ting from .the differential subsidence of the refuse. .. These
depressions., c'oupled with the remaining flat s~.rface of tW4!"
landfill, retards stormwater fr9m running off the landfill. The
cover is generally silty, sandy and quite permeable. However,
deposits of clay have accreted in the depression$ so that storm-
water forms ponds in the depressions. These ponds contribute to
the slow. infiltration ,of wa,ter. into the '.landfill. Because of these
current' surface conditions, 'it is estimated that at least~o . ..
percent of the precipitation which falls directly onto the 'landfill
surface infiltrates through the landfill cover and percolates
through the refuse.
II.
SITB HISTORY AND BNFORCEMENT ACTIVITIES
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 continu-
ously until 1968 when it was filled to capacity. Refuse place-
ment, 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 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 land-
fill 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 from the Columbia to the
Potomac. Direct access routes may also have occurred naturally due
to the noncontinuous geometry of the Potomac clay.
In late 1971, water in a residential well downgradient of the
Army Creek Landfill Site developed severe quality problems. 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, New Castle County and
the Delaware Department of Natural Resources and Environmental
Control (DHREC) 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 toward 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.
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In 1973, .recovery wells were installed in the upper Potomac
Aquifer by_.New - Castle. County,. '.. The purpose of the recovery ,wells
was to intercept and contain the cont.aminant plume. The p'umping of
these wells created a groundwater divide between the Army.Creek .'
Landfill and the Artesian Water Company's Llangollen Wellfield.
" A modified recovery system was installed in 1980, which
included placement of new recovery wells closer to the landfill in
order tt1 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 and RW-13 (Figure 2).
Based on the sampling analysis from the recovery and moni-
toring 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.
The Army Creek Record of Decision (ROD) for the first oper-
able unit, issued on September 30, 1986, selected a remedial
alternative for source control but deferred selection of
appropriate remedial measures for sediments in Army Pond and a
treatment for the groundwater recovery well discharges to a second
operable unit decision document. The first operable unit ROD
selected a two-phased approach:
Phase I
1.
2.
3.
installation of a mUlti-layer landfill cap
continued operation of the downgradient recovery well network
evaluation of the-remedial action for five years after the cap
is installed to assess the effectiveness of the system during
operation.
Phase II
1.
based on the five-year evaluation, a determination will be
made on whether to install upgradient controls
continue evalua~ion of the effectiveness of the system
opera~ion and main~enance
2.
3.
The extensive studies tha~ have been conducted at the site
have iden~ified contamination in both the groundwater and surface
water. The remedial action strategy selected in the first oper-
able unit, described above, addresses the groundwater contami-
nation and the landfill leachate currently seeping into the surface
water (Army Creek/pond).
In August 1986, EPA issued Notice
Potentially Responsible Parties (PRPs)
implement the remedial ac~ion s~rateqy
operable uni~ Record of Decision. The
Letters to the identified
inviting them to design and
selected in the first
PRPs failed to achieve
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settlement with the EPA. EPA completed the remedial design of a
mUlti-layer landfill cap in~uqust 1989.
In °February 1989, EPA issued Special Notiqe Letters ~oo. the '.
identified PRPs inviting them to conduct the focused Remedial
Investigation and Feasibility Study with respect to the surface
water (Army Creek/Pond) and seciments adjacent .~o the landfill.
The noticed PRPs declined to perform the study. In February 1990,
EPA cOJr\pleted the second operable unit RI/FS. ~o'
III.
SCOPE AND ROLE OP OPERABLE UNIT
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This is the second and final planned operable unit for the
site. The first operable unit provided for the installation of a
hydraulic barrier (cap) over the landfill to prevent vertical
infiltration through the wastes and for the continued operation of
the downgradient recovery well network to prevent the migration of
contaminated groundwater to public supply wells. The recovery well
system is currently operating and the remedial design of the
landfill cap has recently been completed. Actual cap construction
is planned to begin before December 1990. This second operable
unit addresses the need to treat the recovery well discharges,
which, as determined in the Remedial Investigation, do not present
an unacceptable threat to human health but are potentially harmful
to the environment. Sediment sampling revealed contaminant levels
which were within a range expected to be found in a wetland
environment and are therefore not an environmental concern.
The contaminated medium to be addressed in the second operable
unit is the surface water of Army Creek/Pond in general and the
recovery wello discharge in particular.
IV.
HIGHLIGHTS OP COMMUHITY PARTICIPATION
The RI/FS Report and the Proposed Plan for the second operable
unit of the Army Creek site were released to the public for comment
on March 18, 1990. These two documents were made available to the
public in both the administ+ative record and an information
repository maintained at the EPA Docket Room in Region 3 and at
DNREC's New Castle office. The notice of availability for these
two documents was published in the Wilmington News Journal on March
18, 1990. A public comment period on the documents was held from
March 18, 1990, to May 2, 1990. In addition, public meetings were
held on March 26 and April 21, 1990. At these meetings, repre-
sentatives from EPA and DNREC answered questions about problems at
the site and the remedial alternatives under consideration. A
response to the comments received during this period is included in
the Responsiveness summary, which is part of this ROD.
v.
SIT. CHARACTERISTICS
As documented in the first operable unit ROD, the groundwater
beneath and downgradient from the site is contaminated by both
organic and inorganic pollutants at levels exceeding the drinking
water standards. Drinking water standards are the applicable
standards for groundwater because it is withdrawn and used as a
potable water supply. The first operable unit ROD selected the
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continued operation of the existing recovery well network to
prevent the horizontal migration'~f the contaminants to any potable
water supp~y well head. ~~
The grou~dwater recovered by the recovery.,well network ' is
currently being discharged to the Army Creek/Pond surface water. A
determination on the level of treatment required for this recovered
groundwater prior to surface discharge is the primary objective of
this decision docume~t. D~inking water, standards are not appli-
cable to' the' Army Creek/Pond surface water because the cfeek water
is not classified as a potable water source.EPA and DNREC have
established relevant water quality standards pursuant to Sections
304(a) and 303 of the Clean Water Act, respectively, in order to
protect the designated uses of Army Creek/Pond. The designated
uses for Army Creek/Pond include the following: secondary contact
recreation; fish, aquatic life and wildlife. The fresh water
segments are also designated for agricultural water supply uses.
Surface Water
Two studies have compared the stream biota of Army Creek from
locations above and below the landfill, beyond the pond outlet.
The study conducted in 1985 by the State of Delaware found species
richness at stations above and below the landfill to be similar.
Both stations exhibited high densities of macro invertebrates but
relatively low species diversity. Of the species present,
facultative and pollution-tolerant organisms predominated. The
authors suggested these communities were indicative of moderate
inorganic enrichment. The second biomonitoring study was conducted
in 1986 by EPA. This study had three study sites, one upstream
from the landfill, the second in the Army Creek Pond, and the third
downstream of Army Creek Landfill. Results of this study were
similar to those found in the 1985 state of Delaware study. The
EPA study did find that the downstream benthic community had more
taxa and fewer organisms per taxa as well as more groups intolerant
of water pollution, indicating a slight improvement in water
quality over upstream stations. The pond station exhibited very
low species richness and 95 percent of the groups found io the pond
were pollution tolerant. This indicates poor water quality in the
pond. In summary, Army Creek both above and below the landfill
appears to be nutrient enriched. Although chronic toxic effects
due to landfill effluent may be present, the effects cannot be
distinguished from the stream biotic communities due to the
confounding effects of the stream enrichment. The improvement in
the benthic macro invertebrate community below the pond outfall does
suggest that the pond may be operating in a limited capacity as a
filter or aeration system, improving the water quality of the
outflow water.
Based on questions raised by the State regarding the repre-
sentativeness of the results cited in the Remedial Investigation
and Proposed Plan (taken from a report on chemical analyses of fish
samples collected in 1983) a new sampling event was conducted. In
May 1990, separate bioassays were performed on composite fish
fillet samples of five common carp and six american eel collected
by DNREC. Results showed some inorganic contamination by zinc in
both the carp (11.2 ug/g) and the eel (14.9 ug/g). No additional
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inorga~ic c~nsti~uents were iden~ified. organic analyses of the
composl.te fl.sh fl.l.lets have nO,t yet been completed. The fish in
the study ~ere.collected below the landfill at the edge of ' the Army
Creek Sitei .. .; ..
In August 1988, the EPA field inv~stigation team sampled Army
C~eek for priority pollutants. The data indic~ted the presence of
organic and inorganic contaminants in the waters of Army Creek
(Table .1). . Organicscdetec~ed included:,. bis (2-chloroethxl) ether,
1,2-dicnloroethane, ahd phenol. Inorganics detected in two or more
sampling locations included: cadmium, chromium, iron, mercury~ and
zinc. The organic contaminants were well below the Delaware Sur-
face Water Quality Standards (DSWQS) which are known to be
protective of the aquatic environment. The concentration of bis-
(2-chloroethyl)ether may exceed the numeric DSWQS for protection of
human health via fish consumption (identified concentrations are
below detection limits). The concentrations of cadmium, iron,
mercury and zinc were found to exceed the Delaware Surface Water
Quality Standards for chronic toxicity (Table 4). The analysis for
chromium did not differentiate between valences; however, the rela-
tive toxicity of hexavalent chromium is greater than trivalent
chromium. If the majority of the total chromium reported is in the
hexavalent form, the level does exceed the criterion.
Groundwater aecovery .ell Discharge
There are currently ten recovery wells pumping groundwater and
discharging to Army Creek/Pond. New Castle County has arranged to
direct the water pumped from one of the ten wells (RWj9) to the
wilmington POTW. The sampling of the remaining nine recovery well
discharges was carried out on July 6, 1989. The recovery wells
sampled, referred to by the well number assigned to them by New
Castle County upon installation, were numbered 1, 10, 11, 12, 13,
27, 28, 29, and 31 (Figure 2).
To determine the combined effect of these discharges on Army
creek/Pond, the flow weighted average concentrations of the
compounds found in the recovery well discharges were calculated.
Although many organic (Table 2) and inorganic (Table 3) contami-
nants were detected in the discharges, only iron definitively
exceeds the numeric surface water quality criteria. The flow
weighted average concentration of bis(2-chloroethyl)ether in the
discharges may contribute to an "in stream" concentration that may
exceed the numeric criterion established to protect human health
from the fiah consumption exposure route. The current data is
insufficient to make a definitive determination. The numeric and
narrative criteria documented in the Delaware Surface Water Quality
standards as amended on February 2, 1990 (Table 4) are the
standards relevant to surface water bodies.
Surface water quality criteria are constituent concentrations,
levels or narrative statements that represent a quality of water
that supports a particular designated use. As such, they apply "in
stream." In determining maximum allowable discharge concen-
trations, the allowable dilution in the receiving stream is
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SWlUliary
Table 1
of Analytical Re~~lts for Surface
. - Army Creek Landfill
Hew Castle, Delaware
Water Sampling
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organic. contaminants
No. of Range of *Average:-' Instrument Method
Positive . Concen- Concentra- Detection Detec-
. . Detec- ' trations tion Limi ~:.
tion
Chemical tions/ (ug/ L) (ug/L)" (ug/L)'. Limit
No of (ug/L)
Samples
Bis(2-Chloroethyl)- ***
ether 3/8 3.6-7.5 3.4 3.6 10.0
1,2-Dichloroethane 2/8 2-5 1.6 2.0 5.0
Phenol 8/8 92-213 157 50 50.0
Inorqanic Contaminants
No. of *Range of **Average Instrument Method
Chemical Positive Concen- Concentra- Detection Detec-
Detec- trations tion Limit tion
tions/ (ug/L) (ug/L) (ug/L) Limit
No. of (ug/I
Samples
Cadmium 5/8 34-38 25 10.0 10.0
Chromium (Total) 7/8 57-150 84 50.0 50.0
Iron 7/8 980-2,860 1,549 500 500
Mercury 2/8 0.2 0.13 0.2 0.2
Nickel 1/8 150 62 100 100
Thallium 1/8 610 295 500 500
Zinc 8/8 25-640 167 10.0 10.0
*
Concentrations in lab analyses labelled as estimated, "J", were
assumed to equal listed concentrations.
.Values of 1/2 of the Instrument Detection limits were used for
the values of the nondetected results in calculation of averages.
**
***
Each detection identified below the method detection limit;
therefore, concentrations given are approximate values.
Surface water was analyzed for TAL and TCL; only positive
detections reported in summary table.
Botes
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Summary
. Table ~
ot AD41ytical Results tor Recovery
'. Army. Creek Landtill
New Castle, Delaware
Well Discharqe
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Organic contaminants
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No. of *Range of ** Flow Instrument Method
Positive Concen- weighted DetectIon Detec-
Chemical Detect- trations Average Cone. Limit tion
tions (ug/L) (ug/L) (ug/L) Limit
No. of (ug/L)
Samples
Benzene 4/9 14-18 8.0 5 5
Bis(2-Chloroethyl)- 7/9 5-21 11.0 5 10
ether
Bis(2-ethylhexyl)- 1/9 3 1.8 3 10
phthalate
Chlorobenzene 3/9 3-18 4.0 3 5
Chloroform 1/9 6 2.8 5 5
~!4-Dichloroben- 1/9 6 3.6 6 10
zene
1,2-Dichloroethane 2/9 22-50 8.4 5 5
Ethylbenzene 2/9 4 2.6 4 5
Tetrachloroethene 1/9 2 1.1 2 5
Toluene 1/9 19 4.2 5 5
Trichloroethene 1/9 2 1.1 2 5
Total Xylenes 2/9 7-10 4.4 5 5
* (1)
Where duplicate samples were taken, the higher concentration was
used.
(2)
Concentration in lab analyses labelled as estimated, "J", were
assumed to equal the listed concentration.
Values of 1/2 of the Instruction Detection limits were used for
the values of the nondetected results in calculation of averages.
**
'ote'
Discharges were analyzed for Target Compound List (TCL): only
positive detections reported on summary table.
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Table 3
Summary of.ADa1ytical.Result_;ror Recovery Well Discharge "
. . Army Creek Landfill
New castle, Delaware
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Total Inorganic contaminants
....'
."
.. '. No. of *Range of " **Flow InstJtument
Positive Concen- Weighted Detection.
Chemical Detections/ trations Average Limit
No. of (ug/L) Cone. (ug/L)
Samples (ug/L)
Aluminum 1/9 132.0 29.6 12.0
Arsenic 1/9 2.7 1.0 1.8
Barium 9/9 74.5-377.0 184 1.2
Calcium 9/9 8,760-18,800 11,470 17.1
Cobalt 3/9 22.7-36.9 11.8 2.7
Iron 9/9 488-34,300 12,400 8.6
Magnesium 9/9 3,630-13,600 6,670 24.3
Manganese 9/9 249-2,710 945 1.5
Potassium 9/9 1,940-17,000 6,770 407.8
Selenium 2/9 1.4-1.5 0.8 1.4
Sodium 9/9 9,690-80,600 26,840 21.8
*
Concentrations in lab analyses labelled as estimated, "J", were assumed
to equal listed concentrations.
Values of 1/2 of the Instrument detection limits were used for the
values of the nondetected results in calculation of averages.
**
Note,
Discharges were analyzed for Total AnalYte List (TAL): only
positive detections reported in Summary Table.
12
-------
Table 4
"
Chemicals Found to Bxceed Delaware Sarrace water Quality Standards
as Amended on February 2, 1990 (DSWQS) in the Aray Creek/pond
Delaware Surface Water Delaware Surface
. Range of .. Average Quality criterion Water Quality cri-
Concentra- Concentra- terion for Protec-
Chemical tions tion Human Health/Fish consumption tion of Fr)!shwater
(ug/L) (ug/L) (ug/L) Aquatic life
Acute . Chronic
Toxicity Toxicity'
From Recovery Well Discharge
Iron 488-34,300 12,400 NA NA 1,000
Bis(2Chlo-
roethyl) ND-2l 11 1.77 NA NA
Ether - .
1
,
.
Concentrations in lab analyses labelled as estimated, "J", were assumed to equal listed
concentrations.
..
Values of 1/2 of the Instrument detection limits were used for the values of the
nondetected results in calculation of averages. Average concentration in-,Recovery well
discharge is flow weighted.
NO
Not Detected
NA
Not Available
, -
\
,
, "
Recovery well discharges and surface water were analyzed for Total Analyte List and Target
Compound List. only constituents which may exceed or may contribute to an excursion of the
DSWQS are identified. .
Note:
..~..
. .
..
13
-------
Concentrations in lab analyses labelled as estimated, "J", were assumed to equa~..listed
concentrations. .
'Values of 1/2 of the Instrument detection limits were used for the values of the nondetected
results in calculation of averages. Average concentration in Recovery well discharge is flow
,>weighted.
~ardness dependent criterion (100 mg/L used)
. Not Detected ...
Not Available . .. .'
Recovery well discharges and surface water was analyzed for Total Analyte List and Target
Compound List. Only constituents which may exceed or may contribute to an excursion of' the
DSWQS are identified. .
Table 4 (continued)
"
Delaware Surface Water Delaware Surface
. Range of .. Average Quality criterion Water Quality Cri-
Concentra- Concentra- terion for Protec-
Chemical tions tion Human Health/Fish Consumption tion of Freshwater
(ug/L) (ug/L) (ug/L) Aquatic life
Acute Chronic
Toxicity Toxicity
Pro. Surface Water
cadmium 34-38 25 NA 3.9 (a) 1.1 (a)
Chromium 57-150 84 840,000 (trivalent) 1,737 (a) 207 (a)
(Total)
4,200 (hexavalent) 16 (hex) ~1 (hex)
Iron 980-2,860 1,549 NA NA .1, 000
Mercury ND-0.2 0.13 7.1 2.4 0.012
Zinc 25-640 167 NA 117 (a) 106 (a)
Bis(2Chlo- .
roethyl) ND-7.5 3.4 1.77 NA NA
Ether
.
..
(a)
ND
NA
Note:
J
.
-------
. considered. In the case of Army Creek, the upstream portion is
considered an intermittent stream largely dependent on surface water
run-off for flow. In accordance~with DSWQS, the critical flows to be
used in defin~ng ~vailable dilution are: the 50th percentile"or median
flow; the flOw of thirty-day duration with a rec~rrence interVal of' 5
years (30Q5); the flow of seven-day duration with a recurrence interval
of ten years (7Q10); or the flow of one-day duration with a recurrence
inte.rval of ten years (1Q10), depending on the app.1icable criterion
(human carcinogen, systemic toxicant, chronic toxicity or acute
toxicity)!. "" "" ~-&."
Sediments
In August 1988, the EPA field investigation team sampled sediments
in Army Creek/Pond. The data indicated the presence of both organic
" and inorganic contaminants in the creek/pond sediments. Twenty organic
chemicals were found in the sediment (Table 5) while only three were
found in the surface water. The only organic chemical found in both
surface water and sediment. was phenol. Many of the chemicals found
exclusively in the sediment samples have very high organic carbon
partition coefficients, which indicates a propensity for soil and
sediment adsorption. The metals found in the sediment samples include
arsenic, chromium, copper, iron, lead, mercury, nickel, and zinc
(Table 5).
Phenol was not detected in the recovery well discharge sampling
performed for this RI/FS, but it had been detected in earlier sampling
at concentrations far below the surface water concentrations shown in
Table 1. Evidently, the source of phenol is either contaminated
leachate from the landfill', or contaminated runoff from off site.
Regardless of the source of phenol, its concentration in the surface
water does not represent a hazard to human health or aquatic life.
Levels of metals observed in Army Pond and Army Creek sediments
were compared to concentrations of metals occurring naturally in U.s.
soils, shown in Table 6, as compiled by Brown and Associates (1983).
All metals except iron were determined to fall within the ranges cited
by this source. Although Brown and Associates did not include iron in
their publication, the extremely high levels of iron measured in the
creek/pond sediment is clearly an artifact from the introduction of
high concentrations ot dissolved iron in the' recovery well discharges.
The Army Creek/Pond bottom's orange appearance is due to the high
levels of iron which have naturally precipitated out of the water
column.
When c08paring sediment and surface water chemical concentrations
in the Army Pond versus those in Army Creek downstream of the pond the
concentration. are generally ot the same order of magnitude, with
slightly lower values in the downstream locations. This illustrates
the limited natural cleansing effect occurring in the creek/pond itself
(volatilization/biodegradation of organics and precipitation/adsorption
of inorganics).
, First Operable unit Remedial Investigation identified the
presence ot phenol contamination in some of the monitoring wells
constructed through the Army Creek landfill.
15
-------
VI.
SUMMARY OP SITB RISK~
A primary component of the second operable unit remedial
investigation. is .the 'public heaith and environmental risk assessment.
This assessment.qefines the potential and actual risks to human' he91th
and the environment resulting from the presence of hazardous substance~
in the Army Creek/Pond surface water and sediments. The potential risk
presented by the recovery well discharges alone was also evaluated.
'."
To determine ~het~er t~e~e is an act~al exposure or a potential
for exposu~e at th~s s~te w~th respect to surface water, tnemost
likely pathways of contaminant release and transport, and the human and
environmental activity patterns in the area were considered. A
complete exposure pathway has three components:
1.
a source of chemicals that can be released into the
environment
a route of contamination transported through soil, sediment,
air or water
an exposure or contact point for humans or the environment
(plants and animals)
2.
3.
Potential sources of contamination are summarized as follows:
1.
2.
3.
recovery well water discharge
creek and pond surface water
creek and pond sediments
air in the area of the creek and pond
fish caught for human consumption
4.
s.
Although many chemicals were detected during-the sampling
activities, only a few of the chemicals pose a risk to human health.
The identified indicator chemicals in the A~~ Creek/Pond surface
water included: (1)(Z)(])bis(2-Chloroethyl) ether, ()( 1,2-dichloroethane,
(1)cadmium, (1)chromium, (1 >mercury , (1)nickel and (1)zinc. The human health
risk assessment was calculated using the maximum concentration
identified in the' surface water.
The identified indicator chemicals in the ArmX Creek/Pond
sediments included: ()benzo(a)pyrene, (1)arsenic, )chromium, (1)lead,
(1)mercury, (1)nickel and (1)zinc. The human health risk was calculated
using the maximum concentration identified in the sediments.
The identified indicatoE chemicals in the recovery well discharges
included: (1)(2)( )benzene, (1)( )(3)bis(2-chloroethyl) ether,
(1)(2)(])1,2-dichloroethane, (1)arsenic, (1)nickel and (1)zinc. The human
health risk was calculated using the flow-weighted average concentra-
tion identified assuming a single discharge point.
( 1) Potential contaminant of concern with respect to inadver-
tent ingestion route inha-
(2) Potential contaminant of concern with respect to the
lation route
(3) Potential contaminant of concern with respect to the dermal
contact route
16
-------
Table 5
SWlURary.of. ADalytical Results for Previous Sediment s~Plinq
'",' Army creek Landfill
New Castle, Delaware
'.
orqanic contaminants
.. - -No. of.: * Range o'f ** Average Ine-trument
Positive Concentra- Concentra- Dete.ctiol1
Detec- tions tion Limit
Chemical tions/ (mg/L) (mg/L) (mg/L)
No. of
Samples
Acenaphthene 1/8 0.165 0.092 0.165
Acetone 8/8 0.025-0.719 0.254 0.010
Anthracene 2/8 0.180-0.339 0.132 0.180
Benzo(a)Anthracene 3/8 0.258-1.25 0.344 0.258
Benzo(a) Pyrene 4/8 0.239-1.07 0.316 0.239
Benzo(b) Fluoranthene 4/8 0.203-1.33 0.382 0.203
Benzo(g,h,i)Perylene 3/8 0.165-0.715 0.202 0.165
Benzo(k) Fluoranthene 2/8 0.446-0.786 0.278 0.330
2-Butanone 5/8 0.004-0.029 0.009 0.004
Chrysene 4/8 0.274-1.58 0.453 0.274
Di-n-Butylphthalate 7/8 0.236-1.08 0.489 0.330
Fluoranthene 4/8 0.331-1.62 0.556 0.330
Fluorene 1/8 0.161 0.090 0.161
Indeno(1,2,3-cd) 3/8 0.182-0.808 0.229 0.182
Pyrene
4-Methylphenol 1/8 0.139 0.079 0.139
Phenanthrene 3/8 0.402-1.71 0.478 0.330
Phenol 2/8 1.20-1.80 0.693 0.848
Pyrene 4/8 0.302-3.20 0.714 0.302
Toluene 2/8 0.009-0.033 0.007 .005
Total Xylenes 1/8 21 0.005 .005
17
-------
Table 5 (Continued)
. .
Inorganic 'coatam~nant8
'.
No. of *Range of . **Average Instrument
Detections/ Concentra- Concentra- Detection
Chemical No. of tions tion.;. Limit
Samples (mg/L) (mg/L) (mg/L)
. . -. , ...~. '.
Arsenic 7/8 1.1-6 2.91 0.95
Chromium 6/8 8.3-45 19.4 5.0
Copper 6/8 11.3-43.9 21.3 5.0
Iron 8/8 1,830-68,800 22,205 50.0
Lead 7/8 6-97.8 49.6 0.49
Mercury 8/8 0.0459-0.119 0.071 0.01
Nickel 5/8 9.9-26.4 13.5 9.9
Zinc 8/8 16.4-273 106.7 10.0
".
*
Concentrations in lab analyses labelled as estimated, "J",
were assumed to equal listed concentrations.
**
Values of 1/2 of the instrument detection limits were used for
the values of the nondetected results in calculation of
averages.
!)~-te:
Sediments were analyzed for both the Target Analyte List and the
Target Compound List: only positive detections reported in
summary table.
18
-------
Table 6
" Range$ '~nd Averages ot
Xeta1s in Uncontaminated 80i1
'.
Army Creek Landti11
New Castle, Delaware
'.
. ....
','
Range of Average
Chemical Concentrations Concentrations Comments
(mg/kg) (mg/kg)
Arsenic 1-50 ---- Usually 10 ppm or less
Chromium 1-1000 100
Copper 2-100 30
Iron ---- ---- No information given
Lead 10-200 10
Mercury 0.01-0.3 0.03
Nickel 5-500 100
~inc 10-300 50
No information given in Brown and Associates (1983).
19
-------
The .identified inorganic indicator chemical, in fish tissue was
zinc, organic analyses is forthcoming. Bis(2-chloroethyl)ether was
identified as a potential indioator chemical based on its presence in
Army Creek ~nd" its accepted tdoconcentration factor. "
'. .
Potentially exposed human and environmental' receptors (plants and
animals) are as follows:
"
. ~.-
1.
2.
persons trespassing on the site
.:pers.ons residing or-;~orking downwind (to the north) of the
site
aquatic biota in Army Creek/Pond
terrestrial flora and fauna living on site or seasonally
using the site
3.
4.
Monitoring activities have shown that the Artesian Water Company
production wells, used for potable water supply in the area, have not
been adversely affected by site-related contamination. The continued
operation of the recovery well network will prevent them from
becoming contaminated in the future.
Identified potential human exposure routes included:
1.
inadvertent ingestion of groundwater recovery well discharges
(e.g., being splashed in the face), and surface water (e.g.,
falling into the pond)
inhalation of volatile organic compounds from groundwater
recovery well discharges and surface water (e.g., while
playing in or near the pond)
dermal absorption of contaminants from inadvertent exposure,
to recovered groundwater (e.g., being splashed by discharge)
or surface water (e.g., falling into the pond)
fish consumption by recreational anglers
2.
3.
4.
To calculate the risk to public health, certain exposure
estimates were made based on human activity patterns.
- The ingestion rate of both surface water and recovery well
discharges was set at 0.1 liter/day for a 70-kg adult and a 30-
kg child. The absorption fraction was specified as 100 percent
of all contaminants.
- The inhalation rate was set at 1 m3/day for both a 70-kg adult
and a 30-kg child. The absorption fraction was specified as
100 percent of all air contaminants.
- The sediment ingestion rate was set at 50 mg/day for a 70-kg
adult and a 30-kg child.
- The dermal absorption exposure estimates were based on surface
areas of 8,750 cm2'and 19,400 cm2 for 100 percent body exposure
for a child and adult, respectively.
Common to all evaluated scenarios, the exposure frequencies were
six exposures in 30 years for adults and one exposure per year for
six years for a child. Carcinogenic risk was based on an exposure
duration of 30 years. Carcinogenic risk for a child was based on an
exposure duration of six years. A lifetime was considered to be 70
years.
20
-------
The exposure estimate for ingestion of contaminated fish was set
at 5.2 g/day which is the averCise "consumption rate of freshwater fish
by recreational anglers in Delaware. This exposure assessment
assumes tha~ 100 percent of the freshwater fish consumed by. the
"
receptor are taken from Army Creek/Pond. It is""unlikely that a
higher consumption rate will "be ""realized based on the size of the
cr~ek and research conducted by the Delaware Division of Fish and
Wildlife indicating "extremely low catches" in Army Creek.
Toxici ty' 'Assessment S1Damary <:
... :.'
Cancer potency factors (CPFs) have been developed by EPA's
Carcinogenic Assessment Group for estimating excess lifetime cancer
risks associated with exposure to potentially carcinogenic chemicals
(Table 7). CPFs, which are expressed in units of {mg/kg-day)"', are
multiplied by the estimated intake of a potential carcinogen, in
mg/kg-day, to provide an upper-bound estimate of the excess lifetime
cancer risk associated with exposure at the intake level. The term
"upper bound" reflects the conservative estimate of the risks
calculated from the CPF. Use of this approach makes underestimation
of the actual cancer risk highly unlikely. Cancer potency factors
are derived from the results of human epidemiological studies or
chronic animal bioassays to which animal-to-human extrapolation and
uncertainty factors have been applied.
Reference doses (RfDs) have been developed by EPA for indicating
the potential for adverse health effects from exposure to chemicals
exhibiting noncarcinogenic effects (Table 7). RfDs, which are
expressed in units of mg/kg-day, are estimates of lifetime daily
exposure levels for humans, including sensitive individuals.
Estimated intakes of chemicals from environmental media (e.g., the
amount of a chemical ingested from contaminated water) can be
compared to the RfD. RfDs are derived from human epidemiological
studies or animal studies to which uncertainty factors have been
applied (e.g., to account for the use of animal data to predict
effects on humans). These uncertainty factors help ensure that the
RfDs will not underestimate the potential for adverse noncarcinogenic
effects to occur.
Risk Charac~.ri.a~ioD 8U88ary
Excess lifetime cancer risks are determined by multiplying the
intake level with the cancer potency factor. These risks are
probabilities that are qenerally expressed in scientific notation
(e.g., lxlO.' or lE-6). An excess lifetime cancer risk of lXlO.'
indicates that, as a plausible upper bound, an individual has a one
in one million chance of developinq cancer as a result of site-
related exposure to a carcinogen over a 70-year lifetime under the
specific exposure conditions at a site. The summary of total
potential carcinogenic risks (Table 8) shows that none of the
exposure scenarios at this site, with respect to surface water and
sediments, present an unacceptable risk to human health.
-------
I ~~.
Table 7
DoS8-RespoJ1S8 Parameters -- for Indicator Chemicals
Army Creek Landfill
New cas~le, Delaware
"
0.
. .'..
. . , .ti...."."..
Carcinogenic
Potency "
Chronic Factor
Reference
Dose 1 ** EPA Weight
mg/kg/day mg/kg/day of Evidence
Oral I*Inhl orall*Inhl Carcinogenic
Chemical Classification
Inorqanics
Arsenic 0.001 50 A (I,O)
Cac:lmium 0.0005 6.1 Bl (I)
(water)
0.001
(food)
Chromium A (I)
(Trivalent or total) 1.0
(III)
Iron
Lead 1.4E-3 4.3E-4 B2 (I,O)
Mercury 3E-4 B2 (I,O)
Nickel 0.02 0.84 A (I)
(Dust)
Zinc 0.2 -
22
-------
Table 7 continued
- ..
" .. "
..
Carcinogenic
Potency
Chronic Factor '..
Reference
. . .. DOSe.. "1 ** EPA Weight
mg/kg/day mg/kg/day of Evidence
Chemical I*Inhl I*Inhl carcinogenic
Oral Oral Classification
, . orqanics
Benzene 0.029 0.029 A (I,O)
Benzo(a)pyrene B2 (I,O)
Bis(2-chloroethyl) ether 1.1 1.1 B2 (I,O)
1,2-Dichloroethane 0.091 0.091 B2 (I,O)
*
Inhalation
*
A
- Known human carcinogen
B1 - Probable human carcinogen.
in humans.
Limited evidence of carcino-genicity
B2 - Probable human carcinogen. Sufficient evidence of car-
inogenicity in animals with inadequate evidence in humans.
I
- Inhalation.
o
- Oral
23
-------
Ta))le 8
summay of Total. Potentia~Carcinoqenic Risks
..
.. ..
Age Group Exposed
Children Adults
.'Media Scenario 6-11 "yrs 70-yr life span
Groundwater Recovery Ina"dvertent Ingestion" 5. j"X10E-9
1.2x10E-8
Well Discharges
Inhalation of organics 7.2x10E-7 3.1x10E-7
leaving groundwater
Dermal absorption 9.7x10E-7 9.2x10E-7
Sediment * Inadvertent ingestion 4.1x10E-9 1.7x10E-9
Surface Water * Inadvertent ingestion 6.5x10E-9 2.9x10E-9
Inhalation of organics 1.8x10E-7 7.6x10E-9
leaving surface water
Dermal absorption 6.0x10E-8 5.7x10E-7
Fish ** Ingestion NC 7.7x10E-7
*
Sediment and surface water risks were calculated using the highest
pollutant concentrations detected during sampling.
Estimated using calculated average pollutant concentration during
sampling, accepted bioconcentration factor and 5.2 g/day consumption
rate.
**
HC
These values could not be calculated due to a lack of sufficient
information regarding fresh fish consumption for children 6-11 years
old.
24
-------
The potential for health ef~ects resulting from exposure to
noncarcinogenic compounds is e$t{mated by comparing an estimated
daili dose.to ~n aciceptable level. If the ratio exceeds 1.0,. there
is a potential. health risk associated with exposure to that.. '.
particular chemical. The ratios can be added for exposures to
multiple contaminants. The sum, known as a Hazard Index, is not a
m~thematical prediction of the severity of toxi9 effects, but
rather a numerical indicator of the transition 'from acceptable to
unaccep~abl~. levels. ". Table.:- 9 presents ~ summary of the ~.qtal
potential Hazard Indices for the exposure scenarios previously
discussed. Since none of the total Hazard Indices exceeds'1.0,
there is no cause of concern for noncarcinogenic hazard to human
health at the Army Creek site.
Environmental Risks
EPA conducted a survey of the aquatic life present in Army
Pond which identified a very low number of species in the pond. In
addition, 95 percent of those species found in the pond were
pollution tolerant organisms, indicating poor water quality.
Numeric surface water quality criteria have been developed by EPA
and DNREC [promulgated Delaware Surface Water Quality Standards
(DSWQS)] and are of primary utility in assessing acute and chronic
toxicity effects in aquatic organisms. Contaminant-specific
maximum levels have been established in addition to the narrative
criteria for the protection of freshwater aquatic life. The
following contaminants were found to exceed the numeric criteria
for freshwater aquatic life set by DNREC in the surface water:
cadmium, chromium, iron, mercury, and zinc (Table 4). There are
three potential sources of surface water contamination:
1.
2.
3.
recovered groundwater discharged to the surface water
leachate seeps from the Army Creek Landfill
offsite/onsite surface runoff
The average value for contaminants identified in the recovered
groundwater discharges was computed. The only contaminant found to
exceed the numeric DSWQS for protection of freshwater aquatic life
in the discharge is iron (Table 4). This indicates that the source
of cadmium, chromium, mercury and zinc is either the leachate seeps
or surface runoff from the. drainage area.
The installation of the hydraulic barrier (cap) in accordance
with the first Record of Decision will reduce the leaching of
contaminanta from the landfill and modify the flow of runoff in the
area of the landfill surface (first operable unit). If the
recovered groundwater is treated to reduce the concentration of
iron (remedial objective of second operable unit) prior to being
discharged to Army Creek/Pond, the numeric DSWQS known to be
protective of the aquatic environment should be achieved.
Actual or threatened releases of hazardous substances from
this site, if not addressed by implementing the response action
selected in this ROD, may present an imminent and substantial
endangerment to the environment.
25
-------
Table 9
"
summary of Total Potential ,Non-Carcinoqenic Hazard Indices
'.
Age Group Exposed
Chil~r.en Adults
Media Scenario 6-11 yrs 70-yr life span
,'. .' "
Groundwater Recovery Inadvertent ingestion .000015 .0000013
Well Discharges
Sediment * Inadvertent ingestion .00036 .000031
Surface Water * Inadvertent ingestion .0008 .00069
Fish Ingestion HC .0048
*
Sediment and surface water risks were calculated using the highest
pollutant concentrations detected during sampling.
HC
These values could not be calculated due to a lack of sufficient
information regarding average fresh fish consumption for children 6-11
years old.
If the Hazard Index exceeds 1.0, there is a potential health hazard
associated with exposure to the medium.
26
-------
VII. DESCRIPTION OF ALTERNATIVES
The Remedial Investigation '~ound that neither the surface water
nor the re<;oyery, "Well discharges present an unacceptable risk~' t.o
human health' or wel fare; however, the most recent sampl ing results"
indicate that the discharges may'be contributing to an excursion of
, the DSWQS numeric criterion for bis(2-chloroethyl)ether established
for 'protection of human health via the fish consumption exposure
route. The available data is insufficient to determine if the
reportedl-evels are represent'ative of the" character of the ..'recovered
groundwater or an anomaly; hence, chemical-specific treatment will
not yet be proposed. The remedial objective of operable unit two is
to ensure that the recovery well discharges do not exceed the
applicable requirements set forth in the DSWQS that are protective of
, the designated uses of Army Creek/Pond. Based on historical and
. recent analyses, the level of iron in the discharges definitively
contribute to an "in stream" concentration that exceeds the numeric
criterion known to be protective of the aquatic environment. A
reduction of iron prior to surface water discharge is therefore
required.
Four remedial alternatives (including No Action) were developed
as possible response actions for providing a level of water quality
in the recovery well discharges that is protective of the aquatic
environment. Each alternative includes a chemical and biological
monitoring plan. In the event that further monitoring finds the
discharges to be exceeding the numeric or narrative criteria'listed
in the DSWQS, a compliance program will be developed and implemented
(excepting No Action).
The [recovered] groundwater monitoring plan described in the
Proposed Plan was incorrectly identified as being undertaken in
compliance with RCRA Subpart F, 40 C.F.R. 264.100. Reference to the
statute has been deleted from this document.
Alternative '1:
No Action - Xonitorinq Only
Capital Cost:
Annual Operation
Present Worth:
Months to implement:
.
o
.
and Manintenance (O&M) Costs: 0
.
o
o.
The first operable unit Record of Decision requires that
groundwater be extracted from the aquifer adjacent to the site.
Groundwater is currently recovered from the local aquifer by a series
of wells which comprise a recovery well network. Under the No Action
scenario this recovered qroundwater would continue to be discharged
into Army Creek/Pond untreated. The calculated average concentration
of iron beinq discharqed from the recovery well network is in the
range of 6,000 to 12,000 uq/L. This is well above the Delaware
Surface Water Quality standard of 1,000 ug/L considered to be
protective of the aquatic environment.
This alternative also includes lonq-term monitoring of the
surface water, sediments and recovered qroundwater quality to qauge
the effectiveness of the remedy, and a wetland monitorinq and
evaluation plan consistent with the Record of Decision issued for the
27
-------
adjacent Delaware Sand & Gravel Site. Chemical and biological
monitoring of treated groundwater effluent will be conducted
consistent with NPDESrequirements (to ensure that cri~eria and
standards pu~suant to S.ection .'304 (a) of the Clean Water Act..a"re being
attained). At least two surface water .and sedim~nt samplin~ .events
in Army Creek/Pond will be required to assess habitat quality: at
five years after completion of. the landfill cap (consistent with OUl
ROD~ and at one year after pumping and treatment.~as ceased. The
surface water and sediment sampling will include chemistry analyses
and toxicity testing (using cpronic surface water and sediment
bioassays.) .
Army Creek Landfill has affected the habitat (surface water and
sediment) quality and the hydrology of Army Creek/Pond and its
associated wetlands. The Army Creek watershed, previous to the
," existence of Army Creek Landfill, supported valuable wetland habitat.
The wetland areas will be monitored to ensure that comparable habitat
values will be maintained.
Alternative '2:
Conventional Water Treatment
Capital Cost:
Annual O&M Cost:
Present Worth:
Months to implement:
.
$1,874,250
.
260,860
.
3,900,000
.
14
This alternative involves the construction and operation of a
conventional precipitation water. treatment plant. The water
extracted by the recovery well network would be passed through a
combination of unit processes including aeration (cascade aeration),
precipitation (pH adjustment and polYmer addition), and filtration
(sand filtration) before being discharged to Army Creek/Pond.
Support processes include sludge thickening and dewatering. Sludge
generated by the treatment process will be sampled and disposed of
appropriately.
This plant is anticipated to reduce the iron concentration in
the recovered groundwater from the current range of 6,000 to 12,000
ug/L to less than 5,000 ug/L, but not to the 1,000 ug/L target level.
The treatment plant will reduce the volume of iron in the recovered
groundwater discharge by reducing the concentration. The mobility
and potential toxicity to aquatic life associated with iron in the
recovered groundwater would be reduced slightly.
This alternative also includes long-term monitoring of the
surface water, sediments and recovered groundwater quality to gauge
the effectiveness of the remedy, and a wetland monitoring and
evaluation plan consistent with the Record of Decision issued for the
adjacent Delaware Sand' Gravel Site. Chemical and biological
monitoring of treated groundwater effluent will be conducted
consistent with NPDES requirements (to ensure that criteria and
standards pursuant to Section 304(a) of the Clean Water Act are being
attained). At least two surface water and sediment sampling events
in Army Creek/Pond will be required to assess habitat quality: at
five years after completion of the landfill cap (consistent with OUI
* All cost and implementation times are estimated.
28
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. ROD) and at one year after pumping and treatment ..has ceased. The
surface water and sediment sampling will include chemistry analyses
and toxicity testing ,(using chronic surface water and sediment
bioassays)... .' -.
.
'.
Army Creek Landfill has affected the habitat (surface water and
sediment) quality and the hydrology of Army Creek/Pond and its
associated wetlands. The Army Creek watershed, previous to the
existence of Army Creek Landfill, supported valuable wetland habitat.
The wetlapd areas will'be mon-itored to ensure that compara~le habitat
values will be maintained. '. ~
The Army Pond habitat will be managed during groundwater
treatment and for a period of five(S) years after cessation of
groundwater treatment to ensure the dominance of species beneficial
: to fish and wildlife, and to control less desirable reed grasses
(Phragmites spp.). Monitoring of plant species composition and
implementation of a management plan will be reviewed by the
appropriate state and federal natural resource managers.
Alternative '3:
Capital Cost:
Annual O&M Cost:
Present Worth:
Months to implement:
Modified Conventional Water Treatment
*
$2,710,000
*
294,000
*
4,900,000
*
14
In order to ensure achieving the 1,000 ug/L iron surface water
standard in the recovered groundwater prior to discharging to Army
Pond, modifications to the Conventional Water Treatment (Alternative
2) can be incorporated. This "modified" conventional treatment plant
is Alternative 3. Preliminary engineering evaluations indicate that
these modifications should satisfy the objectives; however, other
modifications to the conventional precipitation water treatment plant
might be equally effective and therefore acceptable.
This alternative involves the construction and operation of a
"modified" conventional precipitation water treatment plant. The
water extracted by the recovery well network would be passed through
a combination of unit processes including an influent flow
equalization chamber, aeration (cascade aeration with a blower),
precipitation (pH adjustment and polYmer addition), sedimentation
(settling and thickening chamber), and granular media filtration
before being discharged to Army Creek/Pond. Support processes
include sludg8 thickening and dewatering. Sludge generated by the
treatment process will be sampled and disposed of appropriately.
By meeting the contaminant-specific ARAR (iron DSWQS numeric
criterion of 1,000 ug/L), the effluent from the treatment plant
should be protective of the aquatic environment. The treatment plant
would reduce the volume of iron being discharged into Army Creek/Pond
and the mobility would also be reduced. The potential toxicity to
aquatic life associated with iron in the recovered groundwater would
be eliminated. The facility should be designed in such a manner that
* All cost and implementation times are estimated.
29
I
.-
-------
This alternative also includes long-term monitoring of the
. surface water, sediments and recovered groundwater quality to gauge
subsequent modifications may be i~corporated in the event that the
characterist~cs ~f the irifluent" (recovered groundwater) chang~~ .
the effectiveness of the remedy, and a wetland mo~itoring an~"
evaluation plan consistent with t~e Record of Decision issued for the
adjacent Delaware Sand & Gravel Site. Chemical and biological
moni~oring of treated groundwater effluent will b,.conducted
consistent with NPDES requirements (to ensure that criteria and
standards.pursuant to Section~'04(a) of the Clean Water Act~are being
attained).' At least two surface water and sediment sampling.~vents
in Army Creek/Pond will be required to assess habitat quality: at
five years after completion of the landfill cap (consistent with OUl
ROD) and at one year after pumping and treatment has ceased. The
surface water and sediment sampling will include chemistry analyses
" and toxicity testing (using chronic surface water and sediment
bioassays).
Army Creek Landfill has affected the habitat (surface water and
sediment) quality and the hydrology of Army Creek/Pond and its
associated wetlands. The Army Creek watershed, previous to the
existence of Army Creek Landfill, supported valuable wetland habitat.
The wetland areas will be monitored to ensure that comparable habitat
values will be maintained.
The Army Pond habitat will be managed during groundwater
treatment and for a period of five (5) years after cessation of
groundwater treatment to ensure the dominance of species beneficial
to fish and wildlife, and to control less desirable reed grasses
(Phraqmites spp.). Monitoring of plant species composition and
implementation of a management plan will be reviewed by the
appropriate state and federal natural resource managers.
Alternative '4:
Bnbance4 Conventional Treatment Plant
Capital Cost:
Annual O&M Cost:
Present Worth:
Months to implemen~:
.
$3,344,000
.
351,000
.
6,000,000
.
14
The "Enhanced" conventional water treatment plant employs even
further modification to the Conventional Water Treatment plant
(Alternative 2). Preliminary engineering evaluations indicate that
the Enhanced Conventional Water Treatment plant would achieve iron
concentrationa far below the remedial action objective of 1,000 ug/L
known to be protective of the aquatic environment.
This alternative involves the construction and operation of an
"enhanced" conventional precipitation water treatment plant. The
water extracted by the re~overy well network would be passed through
a combination of unit processes including an influent flow
equalization chamber, aeration (high velocity-nozzle aerator),
precipitation (pH adjustment and polYmer addition), sedimentation
(settling and thickening chamber), granular media filtration and a
* All cost and implementation times are estimated.
30
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catalytic/ion exchange polisher (using "green sahd" zeolite) before
being discharged to Army Creek. Support processes include sludge
thickening and dewatering. Sludge generated by the treatment. process
would be sampled.' and disposed of appropriately. . . .
'.
By meeting the contaminant-specific ARAR (iron DSWQS numeric
criterion of 1,000 ug/L), the discharge from the treatment plant
should be protective of the aquatic environment. ':'The treatment plant
would reduce the volume of ir~n being discharged into Army Pond and
the mobility would also' be reduced. The potential toxicity'to .
aquatic life associated with iron in the recovered groundwater would
be eliminated.
This alternative also includes long-term monitoring of the
surface water, sediments and recovered groundwater quality to gauge
the effectiveness of the remedy, and a wetland monitoring and
evaluation plan consistent with the Record of Decision issued for the
adjacent Delaware Sand & Gravel site. Chemical and biological
monitoring of treated groundwater effluent will be conducted
consistent with NPDES requirements (to ensure that criteria and
standards pursuant to Section 304(a) of the Clean Water Act are being
attained). At least two surface water and sediment sampling events
in Army Creek/Pond will be required to assess habitat quality: at
five years after completion of the landfill cap (consistent with OUl
ROD) and at one year after pumping and treatment has ceased. The
surface water and sediment sampling will include chemistry analyses
and toxicity testing (using chronic surface water and sediment
bioassays).
Army Creek Landfill has affected the habitat (surface water and'
sediment) quality and the hydrology of Army Creek/Pond and its
associated wetlands. The Army Creek watershed, previous to the
existence of Army Creek Landfill, supported valuable wetland habitat.
The wetland areas will be monitored to ensure that comparable habitat
values will be maintained.
The Army Pond habitat will be managed during groundwater
treatment and for a period of five (5) years after cessation of
groundwater treatment to ensure the dominance of species beneficial
to fish and wildlife, and to control less desirable reed grasses
(Phraqmites spp.). Monitoring of plant species composition and
implementation of a management plan will be reviewed by the
appropriate state and federal natural resource managers. .
VZZZ. 8UIIIIARY 01' !'JIB COKPARA'1'ZVB AlmLYSZS 01' AL'1'BIUfA'1'ZVBS
. The following nine criteria were used in the evaluation of the
remedial action alternatives for Operable unit II at the Army Creek
Site:
Threshold criteria
1)
overall protection of human
health and the environment; and
2)
Compliance with applicable or
relevant and appropriate
requirements.
31
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Primary Balancing criteria
. .
Modifying Criteria
. .
3)
4)
5)
6)
...
7)
8)
9)
Long-term e'ffecti veness and
permanence~
Reduction of toxicity,~~obility,
or volume through treatment~ "
Short-term effectiveness;
, "
Implementability; and
, ,
. ~. ".
Cost.
State/support agency acceptance;
and
Community acceptance.
A brief description of each of these criteria is provided in
Table 10.
Overall Protection of Human Health and the Bnvironment
Alternatives 13 and 14 will achieve the remedial objectives for
this second operable unit. Each of these alternatives provide for
the extracted groundwater to be passed through a water treatment
facility which will reduce the iron concentration to 1,000 ug/L (or
less in the case of Alternative 14), which is known to be protective
of the aquatic environment.
The Conventional Water Treatment (Alternative 12) facility would
reduce the iron concentration in the recovered groundwater from the
current range of 6,000 to 12,000 ug/L to less than 5,000 ug/L, but
not to 1,000 ug/L, which is the level known to be protective of the
aquatic environment.
I "
Compliance with ARAR8
Alternatives '3 and '4 will meet the contaminant-specific ARAR
for surface water discharge to Army Creek/Pond by achieving a maximum
iron concentration equal to or less than the criterion that has been
established by DNREC pursuant to Section 303 of the Clean Water Act.
Surface water quality criteria are "in stream" maximum concentrations
that are used by the NPDES program to determine maximum allowable
concentration. in surface water discharges. In accordance with the
Delaware surface water quality standards, when calculating the
maximum allowable discharge concentration for the protection of
aquatic life (chronic toxicity), the effect of dilution is based on
the lowest flow over a seven-day period with a recurrence interval of
ten years. Since the upstream portion of Army Creek is considered to
be an intermittent stream, little dilution effect can be calculated:
therefore, the concentration of iron in the effluent must come close
to meeting the maximum allowable "in stream" standards. In the event
that activities undertaken in accordance with the monitoring plan
confirm that the level of bis(2-chloroethyl)ether is contributing to
the excursion of the applicable criterion or find that the
characteristics of the recovered groundwater change so that the
applicable surface water standards are not being met, a compliance
32
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""
TABLE 10
NINE EVALUATION CRITERIA
'.
'.
1.
Overall Protection of Human 'Health and the Environment addresses
whether or not a remedy provides adequate protection and
""describes how risks posed through each pathw~y are eliminated,
redu?~d C?r control~ed th~ough treatm~nt or engineerin<1.'~
ComDliance with ARARs: Whether or not a remedy will meet all
Applicable or Relevant and Appropriate Requirements (ARARs) of
Federal and state Environmental Statutes and/or provides grounds
for invoking a waiver. Whether or not the remedy complies with
advisories, criteria and guidance that EPA and DNREC have agreed
to follow.
2.
3.
Lonq-Term Effectiveness and Permanence refers to the ability of
a remedy to maintain reliable protection of human health and the
environment over time once cleanup goals have been met.
4.
Reduction of Toxicitv. Mobilitv or Volume is the anticipated
performance of the treatment technologies a remedy may employ.
Short-term Effectiveness addresses the period of time needed to
achieve the protection, and any adverse impacts on human health
and the environment that may be posed during the construction
and implementation period until cleanup goals are achieved.
5.
6.
Imclementabilitv is the technical and administrative feasibility
of a remedy, including the availability of materials and
services needed to implement a particular option.
7.
Cost includes estimated capital, operation and maintenance, and
net present worth costs.
State AcceDtance indicates whether, based on its review of the
RI/FS and Proposed Plan, the State concurs with, opposes, or has
no comment on the identified preferred alternative.
8.
9.
Community Accectance indicates whether, based on its review of
the RI/FS and Proposed Plan, the community concurs with,
opposes, or has no comment on the previously identified
preferred alternative. Community comments and the Agency's
response. have been included in the Responsiveness Summary.
33
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plan will be developed and implemented. Action-specific ARARs such.
as OSHA health and safety requirements, must be met at the tre~tment
facility and will be" further ~valuated during remedial design
activities.:- -' '.
.. "
Alternative #2 will reduce the iron
recovered groundwater to less than 5,000
a"mbient water quality criterion of 1,000
protective of the aquatic environment.
concentration in the
ug/L but will not attain the
ug/L wh~ch is known to be
.. . "" ..&a"'
Alternatives #2, #3 and #4 will meet the location-spec~ficARARS
for protection and management of floodplains and wetlands pursuant to
Federal Executive Orders 11988 and 11990 and State Executive Order
56. Long-term monitoring and wetland evaluation and management will
meet the requirement to minimize the loss or degradation of wetlands,
to restore and rehabilitate the wetland habitat: and to preserve the
natural and beneficial values within the floodplain.
Long-Term Bffectiveness
The long-term effectiveness of both alternatives #3 and #4 is
anticipated to be good. The effectiveness will be maintained as long
as the treatment plant constructed is operated and the landfill cap
continues to function as a hydraulic barrier. The treatment of the
recovered groundwater will be required until the recovery well
network can be shut down or the extracted groundwater meets a level
of water quality that is protective of the designated uses of Army
Creek/Pond prior to treatment.
Alternative '2 will only attain marginal effectiveness by
reducing iron concentrations to less than 5,000 ug/L. The marginal
effectiveness attained will be maintained as long as the treatment
plant constructed is operated and the landfill cap continues to
function as a hydraulic barrier.
R.duction of Tozicity, Mobility aDd Volua.
Alternatives '2, '3 and '4 use treatment to reduce the toxicity,
mobility and volume of iron in the recovered groundwater. Both
Alternatives '3 and '4 are equivalent in their reduction of the
potential toxicity to aquatic life associated with iron in the
recovered groundwater. Alternative'2 will reduce toxicity by
reducing the concentration of iron, however, not by enough to
eliminate the potentially toxic effect. Alternatives '4, '3, and '2,
listed in order of effectiveness, each reduce the volume and mobility
of iron rel.a.ad to the environment by reducing the concentration in
the recovered groundwater prior to discharging to Army creek/Pond.
Sbort-T.ra .ffeetiv.D...
Alternatives '3 and '4 would be expected to yield good short-
term effectiveness with respect to the potential for chronic toxicity
due to high levels of iron in the aquatic environment. Both the
"Modified" and "Enhanced" water treatment facilities would achieve
compliance with the surface water quality criterion (1,000 ug/L)
prior to discharge to Army Creek/pond within approximately two weeks
34
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of plant start-up. However,
expected to be only moderate
overall st~ategy also relies
from the installation of the
acre landfill.
the overall impact of this reduction is
dur~ng the short-term because the
on the positive effect to be r~alized
hydraulic barrier (cap) over the 44- --
" Alternative #2 would be anticipated to yield:-moderate-to-low
effectiveness with respect to, the potential chronic toxicity to the
aquatic environment presented:by iron. E~en after the facility'
achieved its performance standard, the effluent would not achieve
levels known to be protective of the environment.
Implementability
Alternatives #2, #3 and #4 are equally implementable. The
installation and operation of the water treatment facilities could be
accomplished easily. The basic components conceptually included in
all these alternatives are. readily available and regularly installed
by construction contractors. The operability of each of these
alternatives is well understood and routinely carried out. The long-
term monitoring plan included in each of the alternatives is also
easily implemented.
Cost
CERCLA requires selection of a cost-effective remedy (not merely
the lowest cost) that protects human health and the environment and
meets other requirements of the statute. Project cost includes all
construction and operation and maintenance costs incurred over the
life of the project. An analysis of the present worth value of these
costs has been completed for each alternative described in this
Record of Decision, and is summarized in Table 11. Capital costs
include those expenditures necessary to implement a remedial action.
Annual operating costs are included in the present worth cost. The
relative cost, in order of most to least is Alternative #4, #3, #2,
and then #1.
Community Acceptance
The Proposed Plan was released to solicit public comment
regarding the proposed remedial alternatives on March 18, 1990. At
that time a 31 day comment period was opened. A public meeting on
the Proposed Plan was held March 26, 1990, in New Castle, Delaware.
Pursuant to the request of a citizen the public comment period was
extended to May 2, 1990. Comments at the public meeting and during
the. comment period are referenced in the Responsiveness Summary
included in this Record of Decision.
state Acceptance
The State of Delaware has not concurred with this selected
Remedial Action.
35
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IX. THE SELECTED -REMEDY
Alternative '3: "Xodified Conventional. Treatment - 1,000 U9!.L. iron
performance 8tandard.
Capital Cost: $2,710,000
'. Annual Operation & Maintenance Costs:
Present Worth: $4,900,000
$294 ~:OOO
. .
'.
"""""
Based upon consideration of the requirements of CERCLA,. the
detailed evaluation of the alternatives, and public comments, both
EPA and the State of Delaware have determined that Alternative #3 is
the most appropriate remedy for operable Unit II of the Army Creek
site.
" .
The objective of this alternative is to reduce the concentration
of iron in the recovered groundwater to 1,000 ug/L prior to
discharging to Army Creek/Pond. The overall goal of the remedial
activities being taken with respect to the surface water at Army
Creek is to attain the Delaware Surface Water Quality Standards
established pursuant to Section 303 of the Clean Water Act. In the
event that activities undertaken in accordance with the monitoring
plan confirm that the level of bis(2-chloroethyl)ether is
contributing to the excursion of the applicable criterion or find
that the characteristics of the recovered groundwater change so that
the applicable surface water standards are not being met, a
compliance plan will be developed and implemented. The combined
strategy of providing treatment to the recovered groundwater prior to
discharge and installing a landfill cap over Army Creek Landfill to
reduce leachate seepage into Army Creek (in accordance with ROD I) is
expected to achieve an "in stream" water quality that supports the
designated uses and is protective of the aquatic environment.
This alternative a1so includes long-term monitoring of the
treatment plant influent, effluent and Army Creek/Pond surface water
and sediment qua~ity to gauge effectiveness of the selected remedy,
and a wetland monitoring and evaluation plan. The Army Pond habitat
will be managed during groundwater treatment and for a period of five
(5) years after cessation of groundwater treatment to ensure the
dominance of species beneficial to fish and wildlife, and to control
less desirable reed grasses (Phraqmites spp.).
A more detailed description of the selected remedy is provided
in Section VXI. The facility should be designed in such a manner
that subsequent modifications may be incorporated in the event that
the characteristics of the influent (recovered groundwater)- change.
It should be recognized that minor changes to the selected
alternative may be made during design as long as the performance
standard is achieved. These changes in general will reflect the
usual modification resulting from the engineering process.
z. STATUTORY DBTBRMIHATIORS
EPA's primary responsibility at Superfund sites is to undertake
remedial actions that are protective of human health and the
environment. In addition, Section 121 of CERCLA, as amended,
36
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establishes several other statutory requirements "and preferences.
These specify that when completEl.t tbe selected remedial action for
this site must c~mplY with applicable or relevant and appropriate
environmental- standards established under Federal and State .~.' .
environmental laws unless a statutory waiver is qranted. The'
selected remedy also must be cost~effective and utilize treatment
technologies or resource recovery technologies to the maximum extent
practicable. Finally, the statute includes a preference for remedies
that permanently and siqnificantly reduce"the volume, toxic.ity or
mobilityol ha'zardous wastes. '. The following sections discl:1sS how the
selected remedy for this site meets these statutory requirements~
Protection of Human Health and the Environment
The selected remedy protects the environment by providing onsite
treatment of recovered groundwater prior to discharging to Army
Creek/Pond. The combined remedial strategy of capping the landfill
(in accordance with ROD 1), which will reduce landfill leachate
seeping directly into Army Creek/Pond, and operating a treatment
facility to reduce the concentration of iron in the recovered
groundwater prior to discharging will achieve a level of water
quality that is protective of the environment.
The baseline human health risk assessment determined that there
is no unacceptable risk to human health or welfare with respect to
the surface water or sediments at the site. The exposure levels are
well within the 10'4 to 10'7 range within which EPA manages potential
carcinogenic risk and the Hazard Indices for non-carcinogens are much
less than one. The remedy selected in the first Record of Decision
will mitigate the risk presented to human health via groundwater
ingestion.
Attainment of Applicable or Relevant and Appropriate Requirements
The selected remedy will attain all applicable or relevant and
appropriate requirements for the site surface water and associated
wetlands, the contaminants in the surface water, and the actions that
will be implemented. The ARARs are presented below.
Action-specific ARAR8
Water Air Resources Act
(7 Delaware Code Chapter 60, 1983)
The following state requlations are promulgated pursuant to section
6010 of Chapter 60:
rDelawareJ Surface Water Qualitv Standards
sections that clearly apply:
(1990)
* In accordance with CERCLA Section 121(e) no permit shall be
required for actions conducted entirely onsite but substantive
requirements must be met.
37
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Reaulations Governinq the Land- Treatment of Wastes (1988)
section,4.1(a)(i.ii),: Sur~a:ce waters must be free.from 'any
pollutants .which may interfere with attainment and maintenance
of desiqnated uses. ..
section 9.2: General provisions prohibitinq acute
..toxicity to aquatic life, adverse effects on:human
inqe~~ion of contaminate~ aquatic or~anisms.
or chronic
health from
...,;~ .
Section 9.3: Iron requirement of 1,000 uq/L for protection.of
aquatic life aqainst chronic toxicity.
rState) Regulations Governinq Control of Water Pollution (1983)
Section 3.01: Discharge of any pollutant from point source to
surface water requires permit.*
Treatment plant sludqe is subject to requirements of Part
III(S) Section 301 pertaininq to transportation, and treatment
disposal.
Reaulations Governinq Solid Waste (1988)
(Section 6 pertains to industrial landfills)
Section 6.D.3.f: Residuals from on-site leachate treatment
system must be sampled and analyzed for hazardous waste
characteristics per Delaware Hazardous Waste requlations.
Section 6.K.1.a:
post-closure care for 30 years.
Section 6.K.1.e: action necessary to mitiqate threat to human
health or the environment if evidence of contaminant release.
Erosion & Sedimentation Control (7 Delaware Code Chapter 40)
Erosion & Sedimentation Control Requlations (1989)
General state criteria:E&S plan must be developed and followed
durinq construction of the water treatment plant to prevent
increased sedimentation or accelerated erosion into Army Creek.
Clean Water Act (33 U.S.C. I 1251 ~ ~.)
Pursuant to Section 402 of the Clean Water Act, 33 U.S.C. I 1342,
any discharqe of pollutants from a point source to waters of the
United State requires a National Pollutant Discharqe Elimination
System (NPDES) permit. The NPDES permit must contain conditions
that are protective of human health and the aquatic life.
* In accordance with CERCLA Section 121(e) no permit shall be
required for actions conducted entirely onsite but substantive
requirements must be met.
38
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contaminant-sDeci~ic ARARs
, '-"
Hazardous Waste ~anaaement Act- (7 Delaware Code ChaDter 63)
Reaulations Governina Hazar~ous Waste (1988)
Section 262.11: Hazardous waste determination must be made on
" sludge generated by treatment of discharges .',"
. ,
. ,
Clean Wate'r Act (33 u.S'.C.~ i251 et ~)'.
Pursuant to section 303 of the Clean Water Act, 33 U.S.C. ~
1313, the state of Delaware has coupled federal Ambient Water
Quality Criteria [established under section 304(a)] with
designated uses (described in Section 101) to determine Delaware
Surface Water Quality Standards (DSWQS). The recovered
groundwater must receive treatment to reduce the concentration
of chemical constituents to a level that will not exceed DSWQS
that support or are protective of Army Creek's designated uses.
.i....".,..
other criteria. advisories or auidance to be
considered for
this remedial action (TBC's)
State Executive Order 56 on Freshwater Wetlands (1988)
(Including Governor's Roundtable Report on Freshwater Wetlands,
1989)
General policy to minimize the adverse effects to freshwater
wetlands resulting from the construction and operation of the
treatment plant, including the resultant discharges.
Federal Executive Order 11988. FloodDlain Manaaement. 40 C.F.R. Part
6. ADDendix A
Action must avoid adverse effects, minimize potential harm,
restore and preserve natural beneficial value.
Federal Executive Order 11990. Protection of Wetlands. 40 C.F.R. Part
6. ~DDendix A
Action must minimize destruction, loss, or degradation of
wetlands and preserve and enhance the natural and beneficial
values of wetlands. The wetlands management plan will act to
preserve the natural and beneficial valves of the wetlands to
- the wildlife be ensuring that the perimeter of the Army
Creek/Pond is recolonized by indigenous species after the
recovery wells are phased-out or shut down.
Co.t-Bffectiv.n...
EPA and the State believe the selected remedy is cost-effective
in mitigating the risk posed by the surface water adjacent to the
landfill. The selected alternative includes the least costly remedy
which will effectively achieve our remedial objective for this second
operable unit.
39
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utilisation of Permanent Solutions Employing Alternative Technologies
to the Maximum Eztent J»racticable --
The sel~cted remedy is the most appropriate solution fo~:this
operable unit and represents the maximum extent to which permanent"
solutions and treatment can be practicably utilized. Both
alternatives #3 and #4 meet the threshold criteria of being
protective and achieving ARARs and are equal in e£fectiveness with
respect to long-term effectiveness and permanence; reduction in
toxicity,". mobility and..volume::through treatment; short-term:...
effectiveness and implementability. Since alternative #3 and
alternative #4 are equally effective and alternative #3 is less
costly than alternative #4, alternative #3 was selected on the basis
of being more cost-effective. The proposed selection of alternative
#3 was well received by the State and community.
Preference for Treatment
This preference is satisfied since treatment is the principal
element of the chosen alternative.
40
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. .
".
" 'RESPONS IVENESS SUMMARY
FOR THE
PROPOSED REMEDIAL ACTION, OPERABLE
AT THE
ARMY CREEK LANDFILL SITE
NEW CASTLE COUNTY, DELAWARE
June 1990
. '.,.
UNIT 2
....:::
-------
"
". .
I.
II.
--
" ,
" ,
RESPONSIVENESS SUMMARY
FOR THE
PROPOSED REMEDIAL AC:-::U, ":!,=~"-=:'E UNIT 2
AT ':'Hi::
ARMY CREEK LANDFILL SUPERFUND SITE
NEW CASTLE COUNTY, D~LAWARE
"',
TABLE OF CONTENTS
SECTION
Introduction.
. . . .
. . .
. . . . . .
. . .
Public Meeting Comments.
. . . .
. . . .
. . .
A.
Comments on the Operable Unit 1
ROD, Signed September 1986. .
. . . . .
B.
The Proposed Remedy for Operable
Unit 2. . . . . . . . . . . . .
. . . .
C.
Remedial Action for Operable Unit 1 . . .
D.
Site History and Current Status.
. . . .
E. .
General Comments. .
. . . .
. . . . .
III. Written Comments. . .
........
. . . . 13
1
ii
'.
"
. "
~
1
2
2
2
6
8
. . 11
-------
. : RESPONSIVENESS SUMMARY
FOR THE PROPOSED REMED IAL ACTION, OPERABLE UNIT "2"'
A~ THE ARMY CREE~ LANDFILL SUPERfUND S:72
NEW CASTLE COUNTY, DELAWARE
. :'.'
. .
...~ .
1.
INTRODUCTION
."
In accordance with the U.S. Environmental Protection Agency's
(EPA) community relations policy and guidance, the EPA Region III
office held a public comment period from March 19, 1990, through
May 2, 1990, to obtain comments on the Proposed Remedial Action
Plan (PRAP) for Operable Unit 2 at the Army Creek Landfill
Superfund site in New Castle County, Delaware. Operable Unit 2
encompasses the contaminated groundwater recovered through the
existing groundwater recovery wells and discharged untreated into
Army Creek. On March 26, 1990, EPA and the Delaware Department of
Natural Resources and Environmental Control (DNREC) held a public
meeting to obtain public comments on the proposed remedy.
Approximately 80 community residents and interested persons
attended the meeting. Copies of the PRAP were distributed at the
meeting and were placed in the information repositories for the
site.
In response to requests from the public, EPA and DNREC held a
follow-up public meeting on Saturday, April 21, 1990, and extended
the public comment period for two weeks. Approximately 22
individuals attended this meeting.
All public comments received during those meeting and in
writing are documented and summarized in this Responsiveness
Summary. Section II presents a summary of questions and comments
expressed by the public at the March 26 and April 21 public
meetings. Section III then contains a summary of written comments
received during the comment period. All questions and comments are
grouped into general categories, according to subject matter. Each
question or comment is followed by EPA's response.
1
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II.
"
PUBLIC MEETTNG COMMFNTS
"
..
Th~5 S~=~~=~ =~ntains'quest~=~s and comments presented at the
March 26, 1990, p~blic meeting. It also summarizes comments and
questions posed at a followup meeting with loca~ reside~ts held on
April 21, 1990, in the Delaware Department of Natural Resources and
Environmental Control offi~es at 715 Grantham Lane in NeWCastle,
Delaware. Comments contained in this section' are grouped '.according
to subject discussed.
A.
Comments on the Operable Unit
September 1986
Signed
."
1 .
2 .
1 ROD,
A commenter asked whether EPA had considered
excavation as an alternative tor the site, and it
not, why not.
EPA Response: Excavation of the landfill was evaluated
and screened out in the first Operable Unit Feasibility
Study for the site, completed in 1986. Capping was
selected as the most appropriate source control remedy in
the first Record of Decision for the site, and based on
that decision, the multi-layered cap has been designed
and is ready to be constructed.
Another attendee stated that ezcavation would not
seem to be a viable alternative because o~ the
possibility that it would release contamination.
EPA Response: There are many good reasons why excavation
was not selected as the best remedial alternative for the
first Operable Unit. The details are contained in the
July 1986 Feasibility Study.
B.
The Proposed aemedy for Operable Unit
2
1 .
2 .
Several co_enter. a.ked vhether the propo.ed
treatment sy.tem va. experi.ental and hov EPA
could en.ure that it vill not cause ~uture
environmental problems.
EPA Response: There are many treatment facilities
currently operating at other locations that effectively
employ the same basic technologies contained in this
conceptual system. This remedial alternative contains no
new, unproven technologies.
A .eeting attendee asked vhy UA is pumping the
groundwater "hen the problem seems to be "i th
sur~ace vater contamination.
EPA Response: The primary health risk originally
identified at the Army Creek site was presented by
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" .
3 .
'"
, '
, groundwater conta'minat ion, To prevent the cont,aminated
g~oundwater from migrating to the Artesian wat~r'
Company's public,: -.;~; :".J' ',:-: ~ ~heads which a=':' hydraulically
downgradient fro~ ~he landfill, a series of strategically
located recovery wells was installed., This remedial
action has proven to be effective; however, the second
,pperable,unit aq~ressed the potentially adver~e effects
that are presented to the environment by discha~ging the
recovered groundwater to Army Creek Pond, '
Several commenters asked how
determine' whether the remedy
is working.
long it will take to
chosen for the .ite
EPA Response: The improvement of surface water quality
at Army Creek is dependent on two separate but related
actions: treatment of the recovered groundwater prior to
surface water discharge, and installation of the landfill
cap to reduce leachate seepage to Army Creek Pond. Cap
construction is expected to last 24 to 36 months.
Construction of the treatment plant is expected to take
approximately 14 months. The effectiveness of the
remedial action will be monitored continuously. Five
years after the landfill cap is installed, the necessity
for further remedial action (see ROD I, Phase II) will be
determined.
4 .
A commenter a.ked for an
technological differences
treatment (Alternative 3)
(Alternative 4).
explanation of the
between modified
and enhanced treatment
EPA Response: It should be noted that the details of the
process are conceptual and may be modified during the
remedial design activities as long as effectiveness is
met. The primary difference between the two alternatives
is the expected performance. As part of its initial
process, the conceptual enhanced treatment employs a
high-velocity aerator to oxygenate the water and increase
the potential for organic compounds to volatilize. The
final step in enhanced treatment uses "green sand," or
zealite sand, which is a more effective filter than
regular sand and captures iron as part of an ion exchange
process. Therefore, the enhanced treatment uses a more
effective aerator and a more effective filter than
modified treatment.
5 .
One meetin9 attendee a.keel whether there wa. any
way that the co_unity could reque.t SPA to .elect
enhanced treatment over modified treatment.
EPA Response: EPA will take all comments made during the
public comment period into consideration in reaching a
final decision. Every significant question that is
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6 .
. .
7.
8 . .
'. .
- :- bz::~ught up at the meeting .or received in writil!.g.. w'ill be
. responded to in the Responsiveness .summary which will"be
included in the Record of Decision. ?~b:ic =:~ments
definitely influence the Agency's d~~~sion.
. ..'
A commenter asked whether EPA had not in tact
...lreadychosezi"~ the remedy' it preferred t~r the
site, and whether the public comment period "as
meaningtul. This commenter stated that he
believed that the proposed remedy was currently
being bid, and that there "as a Consent Decr.e
between the State and the County to implement the
recommended alternative.
EPA Response: No, EPA has not selected a final remedial
action to address the recovered groundwater at the site
(prior to issuance of the Record of Decision). New
Castle County did enter into and is out of compliance
with a Consent Decree with the State wherein the County
agreed to construct, by June 1990, a treatment facility
capable of achieving an iron concentration of less than
5,000 migrograms/liter (similar to the performance
standards of Alternative 2). If New Castle County
modified the design of the treatment facility to conform
to the performance standards identified as the preferred
alternative in the Proposed Plan, it was on their own
initiative with no pre-decisional EPA approval.
Several commenters asked questions about the
proposed treatment plant, including whether its
capacity will be able to accommodate additional
wells, and whether it would produce any odors or
entail storage lagoons.
EPA Response: The plant will be designed to treat the
high range of the current flow load, approximately 1.9
million gallons daily, with enough contingency capacity
to handle additional wells, if necessary. EPA does not
expect that the treatment plant will emit any unusual
odors. With air dispersion, any extremely low-level
organics that may be released will be dispelled. There
will be no storage lagoons.
Several commenter. a.ked whether the treatment
plant would produce any .ludge and how that
material would be diapo.ed.
EPA Response: The process by which iron is precipitated
out of the groundwater will produce a sludge-like
material. This will be treated by being filtered and
compressed to eliminate the water. EPA will determine
the appropriate method to dispose of this material after
testing it to determine its composition, and will dispos~
of it in compliance with Federal and State guidelines.
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-,
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~- Alt"hough t'races of organic substances may remain-' i.n this
"f'ilter-cake,-" EPA expects that the.. major comp6"nent would
::': ::\etals.
9 .
A commenter asked whether the treatment
not eventually become obsolete.'
plant will
"
.4."'.'"
, .
EPA Response: There are two potential scenariQ~ that
could render the treatment plant obsolete: 1) The source
control remedy is effective and it is determined that the
Artesian Water Company's public supply wells would not be
adversely affected if the recovery wells were shut down,
or 2) The extracted groundwater meets a level of water
quality that is protective of the designated uses of Army
Creek/Pond prior to treatment.
10.
One commenter asked where the qroundwater
treatment plant would be located.
EPA Response: The present, proposed location for the
treatment plant is on land owned or controlled by New
Castle County.
11 .
One meetinq attandee asked how lonq it will take
to operate the treatment system before the levels
of contamination in Army Creek are low enough to
support aquatic life. Another asked whether the
system will operate for 15 years, as it appears in
the Proposed Plan.
EPA Response: The 15-year figure used in the Proposed
Plan was selected as a basis for cost comparison of all
alternatives. The optimal amount of time for system
operation will be determined after the cap is installed
and data become available to evaluate the effectiveness
of the source control remedy. This will be determined
approximately 5 years after the cap is installed.
12.
One attendee stated that it appeared that BPI. and
DNRJ:C were reco_endinq an alternative to reduce
risks to aquatic life rather than human health.
She stated that it wa. hard to believe that the
contaminants found posed a IlU.nute threat to human
health, and asked whether I:PA was protecting fish
and wildlife instead of human health.
EPA Response: The reason it may 'appear that EPA is
emphasizing protection of the aquatic environment rather
than human health as part of Operable Unit 2 is that
Operable Unit 1 addressed risks to human health. The
Agency has done extensive testing to determine whether
the surface water at the site poses any risk to humans
and found that there was no risk under existing
conditions. Therefore, EPA next examined whether the
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C.
. .
13.
14.
~~
, surface water at the site, posed a risk to the ..' .
environment. When EPA selected a strategy of capping'th~
landfill, t~~ 3~~~~~;~ was .specifical:y designed to
prevent contCll!\inated groundwater from reaching the
Artesian Water Company's wells to prbtect human health.
The first actioD that was t~ken -- installing the
"interceptor wells ~- was to ~rotect human heiith.
Several commenters askec! whether natural
attenuation woulc! be sufficient to cleanse the
water without operating the treatment system. One
askec! whether EPA hac! consic!erec! installing the
cap on the site anc! then conc!ucting tests to see
if levels of contaminants coming out of the
lanc!fill hac! been rec!ucec! sufficiently to
eliminate the neec! for the treatment plant.
EPA Response:
.
If the water is not treated prior to discharge to
the surface water it will not meet the standards
established by DNREC to protect the designated uses
of Army Creek.
.
The selected alternative includes continuous
monitoring of the recovered groundwater quality. I
the extracted groundwater meets a level of water
quality that is protective of the designated uses of
Army Creek prior to treatment, the facility will be
shut down.
A meeting attenc!ee askec! whether the Artesian
Water Company's wells would be.. threatened if the
recovery well. cea.ed to operate.
EPA Response: Under current conditions, EPA believes
that if the water recovery wells were turned off, the
Artesian Water Company's water supply wells may be
threatened by continued groundwater emanating from both
the Army Creek and Delaware Sand & Gravel Landfills. EPA
will take a conservative approach to protect human health
by implementing source control measures and then, if
appropriate, phasing out the wells.
aemedial Action for Operable Unit
1 .
1
One meetine; co_enter stated' that the
wa. not aw&re what the first phaae of
planned at the site was and that they
told what it entailed.
co_unity
the action
had not been
EPA Response: In accordance with EPA policy, a public
meeting was held prior to the issuance of the Record of
Decision for the first Operable Unit at the site. The
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2.
3 .
:- addoresses .of attendees at the first meeting wer.eoo used to
send out copies of the Proposed Plap for Opera~le Uni~ 2.
A meeting attendee asked wb.c.t.her the
already capped. .,"
site has been
..
..EPA Response: N,o.. The desi-gn has been compl~ted and EPA
expects to begin the remedial action by the end,of the
calendar year 1990.
Several eommenters
cap design.
asked for an
of the
explanation
EPA Response: First, a grade will be established. Next,
the area will be covered with a one-foot layer of a fine,
clay-like soil that meets an established specification.
This material will be compacted so that water will not be
able to pass through it at more than lxlO-S centimeters/
second. This will be covered by a synthetic liner at
least 40 millimeters thick, whose composition is yet to
be determined but which must meet strict performance
standards established by EPA for such factors as puncture
resistance and flexibility. This layer will be covered
by a one-foot thick layer of sand, and finally by two
feet of soil. Therefore, when rain hits the top of the
landfill, it will pass through the top fill and the sand,
stop at the liner which is a hydraulic barrier, travel.
along the barrier, and ultimately discharge as clean
runoff into Army Pond. There also will be vents in the
cap to allow the controlled release of methane gases
which is commonly generated by degradation in landfills.
4 .
Several cOllUDenters asked who pays
the remedial action.
for the cost of
5 .
EPA Response: More than 30 potentially responsible
parties (PRPs) have been notified of their potential
liability. EPA may attempt to reach a negotiated
settlement with one or more of these PRPs. If settlement
is not achieved, EPA will sue one or more PRP(s) to
recover all past and prospective costs to implement the
remedy.
On. co_enter asked how much soil would be
required to conatruct a 60-acre cap and what
source would be.
its
EPA Response: The cap may require up
of soil. EPA has identified suitable
locally. The specific source will be
the project bid process.
to 8,000 truckloads
borrow areas
determined after
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D.
6.. '. On. c:ommenter asked whether the cap will ~pe 'able
. " to stop leaching of the landfill materials into'
the groundw~ter."
. .
EPA Response: EPA believes installing the 60-acre cap
will, in time, ~ignificantly reduce leaching of
'contaminants into the groundwater. The landf!ll cap will
prevent vertical infiltration of precipitation;" however,
some wastes were landfilled below the seasonal high-water
table. On the western end, the leaching of contaminants
as a result of precipitation will be prevented, but some
leaching is likely to continue due to horizontal
migration of groundwater. The first Operable Unit ROD
includes the continued monitoring of the groundwater. If
it is determined that capping the site is not sufficient,
upgradient controls will be implemented.
7 .
One commenter informed EPA that he remembered a
storm sewer that was buried on the site.
EPA Response: An old, abandoned sewer does run through
the eastern end of the site. A provision for "plugging"
the sewer has been included in the remedial design.
Site
History
anc! Current
Status
1 .
Several commenters asked questions about the
substances that were detected in the site
groundwater and surface water. One attendee
what substances were found and another asked
whether they could pose a danger to humans.
Several asked for a list of these substances.
asked
EPA Response: The first Record of Decision for the site,
dated September 1986, identifies the contaminants that
exceed the primary and secondary drinking water standards
at the site. These substances were detected in one or
more recovery wells adjacent to the site. The organic
substances that were found to exceed primary or secondary
drinking water standards include:
.
Benzene,
1,2-Dichloropropane,
Methylene chloride,
2,4-Dinitrotoluene,
N-Nitrodimethylamine,
2,4,6-Trichlorophenol,
Bis(2-chloroethyl)ether, and
Tetrachlorodibromomethane.
.
.
.
.
.
.
.
The inorganic substances that exceed primary or secondary
. drinking water standards include:
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2 .
3 .
4 .
. Beryl1ium, '.
. Cadmium,
. r'"'--T': .,.....
- ._- ...'a..~ -'~~ ..
. !..:::'Gd,
. Mercury,
. ~~.
. Nickle,
. Iron., and..:: -10:'. '.'
. Manganese.
Under current conditions, these substances do not pose a
threat to human health.
One commenter asked vhether all iron detected in
samplinq could be cominq from the landfill and
whether there are other measurable sources of
iron. .
EPA Response: Iron is a naturally occurring metal
throughout Delaware. The concentration of iron in the
groundwater directly beneath and downgradient of Army
Creek Landfill is exceptionally high. The elevated
levels may be due to iron-laden wastes disposed of in the
landfill or they may be the result of the leachate
leaching iron from the naturally occurring soils.
However, the source of the iron is immaterial. The
presence of iron in the groundwater does not present a
hazard to human health. The levels do not exceed the
secondary drinking water standards. To prevent these
compounds from migrating to the public supply wells, the
recovery well network was installed. The aquatic species
generally are not as sensitive as humans to organic
compounds; however, they are more sensitive to metals
(iron). Therefore, because the groundwater is being
pumped to prevent the contamination of the public supply
wells, the level of iron in the recovered groundwater
must be reduced to levels that are protective of the
aquatic environment prior to surface water discharge,
regardless of the source of the iron.
One co_enter asked vhy the County has been usinq
interceptor vel18 to pump cont&Jldnated qround.ater
a. a temporary measure without cappinq the site.
EPA Response: The County, acted promptly to install the
wells, taking immediate action to mitigate the situation.
When contamination was detected at the edge of Llangollen
Estates, the County acted immediately. EPA commends them
for taking action and installing the recovery wells,
which occurred before EPA's Superfund program was
established.
One co_enter a.ked why, if the heavy ..tal. find
their "ay into the l.achate that qeta into the
pond, the substanc.. are not found in the
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:- gr~undwater
. the pumps.
that
is
affecting
the
discha~;qe"
from
. .
EPA Response: Some of thE metals a=~ getting into the
groundwater. A certain percentage cf the concamination
goes int~ the aquifer and is carried through the
'groundwater to {he .recovery 'wells, where it is'''.captured
and discharged into Army Creek. Another portion of'.
substances is discharged from the side of the landfill
directly into the pond. EPA expected to find elevated
levels of metals, including chromium. A number of
theories may explain this fact. Chromium is not a very
mobile contaminant, so that it may take longer to be
detected in the recovery wells. Also, chromium tends to
absorb to soil particles, such as in the sediment. Each
contaminant has a different mobility. Some contaminants
do not move through the aquifer very well, and tend to
stay at the bottom of the pond and not go further.
5 .
asked whether
be effective.
recovery
the
An attendee
continue to
wells
would
EPA Response: Yes, the effectiveness of the wells is
continuously monitored. Other than recovery wells, there
are many monitoring and piezometer wells strategically
located throughout the area. These wells are used to
examine the water table level. Each recovery well
creates a spherical "cone of depression" due to the
withdrawal of groundwater. By monitoring daily discharge
volumes and evaluating the piezomatic map (three-
dimensional groundwater elevation), the operator can
determine wether or not the recovery well is functioning
effectively. When the recovery well's effectiveness
decreases, it is rehabilitated. All wells at the site
are rehabilitated approximately twice a year, during
which the well is shut down and its screens are cleaned.
Thereafter, it is put back on line fully effective. New
Castle County will continue to pay for the operation and
maintenance of the wells.
6 .
Several co..en~ers asked whether
the site could affect aDY public
contamination
supply well. .
at
EPA Response: The continued monitoring undertaken in the
area has consistently shown the recovery well network to
be effectively creating a groundwater divide between the
landfill and. Artesian's wells.
7 .
Several co_enters sta~ed that there had been
several public meetings about the site in the past
and numerous studies continuing for .everal year. .
They a.ked why it has taken so long ~o begin
remedial action.
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E.
..
- : EPA Response: EPA cannot take action at a hazardous
- waste site until it has completed a thorough s~udy of ,the
site a~ct knows what contaminants ar~ present A:: =~:~
must be gathered. and factored into a careful ~nd informed
decision. The Agency has recently c9mpleted the remedial
design of the landfill cap and is prepared to begin
..construction. ., i'
8 .
One commenter asked how much money
at the site without accomplishing
there.
has be.n spent
remedial actions
EPA Response: Although the actual remedial action has
not been implemented at the site, the studies were
necessary to determine the nature and extent of
contamination at the site and which technologies will
best remediate the site contamination. To date,
approximately $1.2 million have been expended for legal,
technical, and civil investigative tasks associated with
the site, all of which EPA expects to recover from the
(potentially) responsible parties. Technical tasks
completed include: Site Inspection and Preliminary
Assessment; oversight of the first Operable Unit
Feasibility Study; the first Operable Unit Remedial
Design; and the second Operable Unit Remedial
Investigation and Feasibility Study.
General
Comments
1 .
Several meeting attendee. asked what role DNREC
has in the remedial activities at the site.
2 .
EPA Response: The Army Creek site is a Federal-lead
project. However, DNREC reviews and comments on all
documents and is involved in determining technical
details of the project. EPA has been working closely
with the State throughout the process and consults DNREC
prior to making any final decisions.
Several commenters asked what will happen to the
pond after the 9roundwater recovery wells are shut
down.
EPA Response: The volume of the pond will likely
decrease to its original size during the 1960s, before
the installation of the recovery wells. The alteration
of the hydrology may adversely affect the associated
vegetation; hence, a provision for management of the area
has been included in the selected remedy. The Agency's
intention is not to artificially maintain the wetlands,
but to ensure that comparable habitat values are
maintained.
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3. : O~.e commenter asked whether EPA anticipa1;.:8.'
. encountering any surprise contaminants at the
c:~~~~~ s:.~:-.
'.
A -,:t-
. .
EPA Response: The groundwater has been monitored
extensively for. nearly 20 years. It is unlikely that new
.contamin~nts w~rl be discov~~ed. ~.
4 .
One commenter asked from which aquifer the
recovery wells are drawinq water.
EPA Response: The recovery wells are drawing water from
the Upper Potomac aquifer, which is the middle aquifer in
the area.
5 .
Several commenters asked
residents in Llangollen
water.
from what source
Estates receive their
EPA Response: Llangollen Estates residents get their
water from the Artesian Water Company, except for a few
homes that have private wells. Artesian has wells in a
variety of locations in New Castle County, including
those near the Army Creek site.
6 .
A commenter asked when the Army Creek site had
been added to the National Priori ties List.
EPA Response: The site was on the original list
published in September 1983.
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III.
1.
2.
3.
4.
5~
..
....
WRIT'f'Btf.CoMKEtfTS
'.
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".
Nev ~as~l. coun~y a~a~ed ~ha~ ~here ia DO basis for a second
operable uni~ Record of Decision. When ~~. firs~ operable
uni~ vaa issued ~here vas no discussion of embarkinq on .
s..cond..Operabl..:oni~ 8Dcompassinq 9roundva~er ~rea~m.nt. .
EPA Response: The declaration section of the
unit Record of Decision, siqned September 30,
"Selection of a treatment alternative for the
recovery well discharqes has not been made at
will be the subject of a second operable unit
document in the future."
. .
first operable
1986, states,
qroundwater
this time and
decision
Nev Cas~le county .~ated ~hat ~here vas no sUbs~antive basis
for BPA re-openinq ~he 198. [firs~ operable uni~] ROD.
The first operable unit ROD was not re-
EPA Response:
opened.
.ev Ca.~le county state4 ~ha~ BPA shou14 have se~ the iron
compliance level at 5,000 uq/L 4ue to techDoloqy-base4
limits.
EPA Response: The Delaware Surface Water Quality Standards
establish that 1,000 uq/L of iron is protective of Army
Creek's desiqnated uses. Treatment technoloqy capable of
achievinq the required concentration of iron is readily
available. A waiver of the ARAR based on technological
limits is unjustified.
.ew .Castl. county .tate4 that the ARAR .election proce.. is
faulty. .0 .eDtioD i. .a4e iD the ~ocu.e4 RI/~8 ot the
Clean water aot revulation. that esclu4e manaade
imPOundmeDt. like aray PoD4 tro. the 4etiDitions ot "vaters
ot the unite4 State.."
EPA Response: Thi. exclusion applies only to manmade bodies
of water which neither were oriqinally created in waters of
the United State. nor resulted from the impoundment of
watera of the United States.
.ew C..tle County .tate4 that the ~ocu.e4 ax/~8 4i4 not
a..e.. whether a treataent tacility capable ot treating the
cODceDtratioD of iroD iD the recovered groun4water to 5,000
uq/L wou14 M a4equate.
That scenario was evaluated as Alternative
EPA Response:
'2.
.ew Ca.tle county .tate4 that the county it.elf 4i4 Dot
operate the lan4fill 4uriDg the relevant perio4..
-------
7.
8.
9.
10.
11.
EPA.Response: The County operated the facility through" a .
contractual relationship with Landfill, Inc.
New ~..tle county .tated that it is unclear which components
comprise the "systu" to be evaluated in accordance with
operable unit one Phaa. II.
. " 0. . .
~. .
EPA Response:
network.
The landfill cap and the recovery well
New castle county stated that it i. una.are of any surface
leachate seep..
EPA Response:
landfill.
They are at the southwestern edge of the
Ne. castle county stated that enqineers retained by the
County believe that the performance standard included in
Alternative '3 may be achieved more efficiently usinq
different unit processes than those described.
EPA Response: Modifications resulting from the engineerinq
process may be made durinq design as lonq as the performance
standard is achieved.
New castle county .tated that it i. their belief that the
.etland monitorinq and habitat manaqement plan, referenced
in the proposed Plan, i. liaited to a two-year evaluation of
pond and creek water level. and veqetation, a. well a.
possible re-.eedinq with indiqenous species should
Phraqmites dominate.
EPA Response: The County is correct, with one minor
modification. In the event that re-seedinq is required
within the first two years followinq recovery well shut
down, an additional three years of manaqement will be
necessary to ensure the success of the management
activities.
A co..enter wrote tbat he .upport. tbe preferred alternative
but i. ooaoeraed tbat Don-volatile orqanic. may r..ain in
the efflaeat aDd .u9ge.ted tbat a carboD f.lter be added to
the tzea~eDt prooe...
EPA Re.pon.e: Ba.ed on the sampling event conducted during
the Focused RIfFS, iron is the only constituent clearly
exceeding the applicable numeric water quality criteria.
The monitoring plan associated with the selected alternative
will qenerate a .olid water quality data base. If the
recovered groundwater is found to have a persistent organic
substance at a level that is not protective of the
desiqnated u.e. of Army Creek, a compliance proqraa will be
developed and implemented. All option. available to meet
the objective would be evaluated.
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. ,
"
12.
ODe. commeJiter . asked what precautioDs vould be takeD ~o' .
assure that all pollutaDts are removed to detectioD t.vels "
or below. '.
EPA Response: The presence of a pollutan~.,.above its
technological detection limit does not necessarily pose a
risk to human health qr the environment. The AgencM. will
take actions to protect the designated uses of Army ~~eek~
A commented asked what EPA vas proposing to do &bout
sediment and surtace vaters.
13.
EPA Response: Although the sediments are degraded, the risk
assessment found the sediments to pose no unacceptable risk.
The installation of the landfill cap and treatment of the
recovered groundwater prior to discharge is expected to have
a positive effect on both the sediment and surface water
quality. In time, the remedial activities undertaken with
respect to both operable units is expected to achieve a
water quality that is protective of Army Creek's designated
uses.
14.
A commenter stated that he thought that the 5.2 g/day
treshwater tish consumption rate used in the risk assessment
vas low. .
15.
EPA Response: Studies conducted by DNREC have documented
that the average consumption rate of freshwater fish by
recreational anglers in Delaware is 5.2 g/day. The exposure
assessment assumes that the average fisherman catches 100'
of the fish he consumes in Army Creek. Compared to other
fishable freshwater waterways in the state, Army Creek is
very small, has limited access, and, according to the
"Stream and Inland Bays Fish Survey" (Delaware Division of
Fish and Wildlife, 1989), Army Creek ranked 13th out of 14
with respect to number ot fish caught in non-tidal streams.
Using a higher consumption rate for this site specific study
would be unrealistic.
On co..enter .tated hi. concern that chemical compounds aore
tozic than iron aay be di.charged into the stre.. in the
tutur..
EPA R..ponse: Groundwater investigations have documented
the pre.ence of various chemical constituents upgradient of
the recovery well network that are not currently of concern
in the context of this remedial action. Given this fact,
the characteristics of the recovered groundwater have the
potential to change. The Preferred Alternative identified
in the Proposed Plan included a (recovered] groundwater
monitoring plan. The Selected Remedy goes one step further
to clarity that a compliance plan will be developed and
implemented should the monitoring reveal a persistent change
in the character of the recovered groundwater such that the
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di&qh~g~ -is no longer "protective of the designated ~ses of
Army Creek. The applicable requirements .with respect to
water quality which must be achieved prior to surface water
discharge are contained in the Delaware Surface Water
Quality Standards as amended on February 2", 1990 (referred
to as Delaware Ambient Water Quality Criteria in the
Pr.oposed Plan)." . ""'.
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