United States Office of
Environmental Protection Emergency and
Agency Remedial Response
EPA/ROD/R03-91/122
August 1991
&EPA Superfund
Record of Decision
NCR, Millsboro, DE
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50272-101
REPORT DOCUMENTATION i. REPORT NO. 2.
PAGE EPA/ROD/R03-91/122
4. TrtesndSubfflle
SUPERFUND RECORD OF DECISION
NCR, Millsboro, DE
" First Remedial Action - Final
7. AuOior(a)
*
0. Pa forming OrgamfaaUon Name and Address
12. Sponsoring Organization Name and Address
U.S. Environmental Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
3. Recipient Accession No.
S. Report Date
08/12/91
6. '
8. Perfoitnlng Organization Rept No.
10. Pro|ecVTask/Work UnH No.
11. Contract(C) or Grant
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EPA/ROD/R03-91/122
NCR, Millsboro, DE
First Remedial Action - Final
Abstract (Continued)
1981, NCR excavated and disposed of offsite approximately 315 cubic yards of lagoon
sludge and other wastes during RCRA closure of the facility. In 1988, NCR installed a
ground water recovery well and air stripper to prevent continuing migration of a TCE
ground water plume. This Record of Decision (ROD) addresses a final remedy for ground
water contamination. The primary contaminants of concern affecting the ground water
are VOCs, mainly TCE and PCE; other organics; metals including and chromium and lead
and oils.
The selected remedial action for this site includes pumping and treatment of
contaminated ground water using air stripping, followed by carbon adsorption, and
coagulation and filtration, if necessary, to remove chromium; controlling air emissions
from the ground water treatment system, if necessary; discharging the treated water
onsite to surface water and/or through ground water infiltration galleries; conducting
a well survey to identify all wells located within a one-mile radius of the site;
conducting sediment, ground water, and surface water monitoring; and implementing
institutional controls including ground water use and deed restrictions. The estimated
present worth cost for this remedial action is $4,749,000, which includes an annual O&M
cost of $859,000.
PERFORMANCE STANDARDS OR GOALS: Chemical-specific ground water clean-up goals are
based on SDWA MCLs and non-zero MCLGs, and include TCE 5 ug/1 (MCL)' and chromium
100 ug/1 (MCL). Discharge limitations are SDWA MCLs and non-zero MCLGs, SDWA
Underground Injection Control limits; CWA-NPDES; CWA-AWQC and State requirements.
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DECLARATION
FOR THE
RECORD OF DECISION
Site Name and Cbcation
NCR Corporation (Millsboro Plant)
Millsboro, Sussex County, Delaware
Statement of Basis and Purpose
This decision document presents the U.S. Environmental
Protection Agency's (EPA's) selected remedial action for the NCR
Corporation (Millsboro Plant) site (site or NCR Millsboro site)
located in Millsboro, Sussex County, Delaware, which was chosen
in accordance with the requirements of the Comprehensive
Environmental Response, Compensation, and Liability Act (CERCLA)
of 1980, as amended by the Superfund Amendments and
Reauthorization Act (SARA) of 1986 and, to the extent
practicable, the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), 40 C.F.R. Part 300. This decision
document explains the factual and legal basis for selecting the.
remedy for this site. The information supporting this remedial
action decision is contained in the Administrative Record file
for this site.
The State of Delaware concurs with the selected remedy.
Assessment of the Site
Pursuant to duly delegated authority, I hereby determine, in
accordance with Section 106 of CERCLA, 42 U.S.C. Section 9606,
that actual or threatened releases of hazardous substances from
this site as discussed under the Summary of Site Risks Section of
this document, 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.
DESCRIPTION 07 THE REMEDY
This Record of Decision addresses the ground water
contamination in the aquifers underlying the site.
The remedy for this site was selected after careful
evaluation of the overall conditions at the site. The ground
water at the site is highly contaminated with volatile organic
compounds (VOCs), primarily trichloroethylene, and to a lesser
extent chromium. The contaminated ground water continues to
migrate and poses a potential threat to human health and
potential drinking water sources if not addressed by this
remedial action.
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The selected remedy calls for treatment of vocs and also
includes a contingency for providing treatment for chromium in
ground water. Including chromium treatment as a contingency is
based on the limited number of veils (2) onsite which have
chromium concentrations above the Maximum Contaminant Level
(MCL). These wells are believed to^be within the cone of
influence of the present ground water recovery well which pumps
ground water to an air stripper which has been in operation since
July 1988. Analysis of the air stripper effluent has
consistently shown chromium concentrations below MCLs. Further
studies will be performed during the predesign phase to determine
if the chromium treatment will be necessary.
The major components of the selected remedy are:
• Extraction of contaminated ground water using
additional recovery wells until clean up levels are
achieved
• Treatment of VOC contamination in ground water using an
air stripper followed by carbon adsorption of the air
stripper effluent until the cleanup levels (MCLs and
non-zero MCLGs) are achieved
• A provision for chromium treatment using coagulation
and filtration, if determined necessary by EPA to
achieve effluent limitations
• A provision for air emissions controls, if determined
necessary by EPA, during predesign studies
• A combined discharge to surface water and/or onsite
ground water infiltration galleries
• Conducting a well survey to determine the location of
all weJJs within a one mile radius of the site, in
order to update the previous well survey
• Continued quarterly monitoring of ground water until
the clean up levels (MCLs and non-zero MCLGs) are
achieved
• Instituting an annual monitoring program for surface
water and sediments of Iron Branch until the clean up
levels (MCLs and non-zero MCLGs) are achieved
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• Institutional controls restricting ground water use
until clean up levels (MCLs and non-zero MCLGs) are
achieved throughout the entire ground water plume by
establishing and enforcing a state ground water
management zone and property deed restrictions
regarding the installation of wells in the ground water
management'zone.
STATUTORY DETERMINATIONS
s
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 technologies to the
maximum extent practicable and satisfies the statutory preference
for remedies that employ treatment that reduces toxicity,
mobility, or volume as a principal element. Although EPA
believes that the selected remedy will achieve the clean up
levels, it may become apparent during implementation or operation
of the ground water treatment system that contaminant levels are
remaining constant at levels higher than the clean up levels. A
reevaluation of the system performance standards and/or the
remedy may be necessary. Therefore, a review will be conducted
within five years after commencement of remedial action in
accordance with Section 121(c) of CERCLA, 42 U.S.C. $ 9621(c), to
ensure that the remedy continues to provide adequate protection
to human health and the environment.
Edwin B. Erickson Date
Regional Administrator
U.S. Environmental Protection Agency
Region III
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DECISION SUMMARY
NCR BITB
1.0 8ZTB LOCATION AND DESCRIPTION
*
The NCR Millsboro Superfund site is located approximately 0.25
mile southeast of the intersection of Routes 113 and 24 in the
town of Millsboro in Sussex County, Delaware (Figure l). The
site includes the former NCR Corporation property of
approximately 58 acres.
A small stream, Iron Branch borders the site to the north and
northeast. The former NCR Corporation property is bounded to the
east by Conrail railroad tracks, beyond this is an 80-acre parcel
of agricultural land which is also part of the site. Mitchell
Street forms the western boundary and to the south and southeast
are a few residential structures, a mobile home dealership, and
another small stream, Wharton's Branch.
Iron Branch and Wharton's Branch join approximately 1,500 feet
east of the property and flow into the Indian River estuary
approximately 4,500 feet east of the site. Between Iron Branch
and the Indian River, northeast of the site, is a small
residential community known as Riverview. Approximately 500 feet
west of the community is the Millsboro Elementary School.
The predominant surface water features in the vicinity of the NCR
Millsboro site are: (1) Iron Branch, (2) Wharton's Branch and (3)
the Indian River.
Approximately eight residences lie within one block of the site
to the west. These residences, however, are not along the
principal contaminant migration routes from the site. In
addition, approximately 16 residences are located about 1,700
feet north of the site boundary. These too are not located along
principal contaminant migration routes. The residences to the
east-northeast are located in the Riverview community,
approximately 4,000 feet from the building on the site (Figure
2). This neighborhood is of primary concern because it lies along
the predominant contaminant migration route from the site. The
Riverview community is comprised of 46 single-family homes on
approximately 40 lota. Assuming an average occupancy of 3.2
persons per dwelling, the population of the community is
approximately 147 persons..
Geology* Regionally, Delaware is divided into two
physiographic provinces, the Piedmont Province in the northern
part of the state and the Coastal Plain Province throughout the
remaining part. The NCR Millsboro site lies within the southern
portion of Delaware and is within the Coastal Plain Province.
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POOR QUALITY
x ORIGINAL
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M"P of Study Area
Si* Location
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The Columbia Group (Pleistocene Age) overlies older sediments
throughout the Coastal Plain of Delaware. This group is
continental in origin and consists primarily of tan, buff, brown,
or yellow fine to coarse sand and gravel with some silt-clay
lenses. Below..the-Pleistocene or Pliocene sediments is the
Miocene sediments. This series includes sand and gray silty clay
with abundant shell material.
However, in the area of the NCR Millsboro site, the Miocene sands.
directly underlie the Pleistocene sands, making stratigraphic
differentiation difficult. The Columbia Group comprises a major
unconfined aquifer beneath the site. The thickness of the so
called Columbia aquifer is difficult to define because, in
southern Delaware, the sands of the Columbia Group are
hydraulically interconnected with the underlying Miocene sands.
At the site, the bottom of the aquifer is estimated to be about
75-100 feet below ground surface. Contamination above drinking
water standards in the aquifer occurs primarily within the upper
40 feet of the saturated zone.
Soil*i The soil at the NCR Millsboro site is the Evesboro
series consisting of loamy substratum having 0-2% slopes. The
Evesboro series has low to very low moisture capacity. It has
rapid infiltration capacity, thus allowing for low water erosion
damage.
Hydrologyi The Columbia Group forms a major unconfined
aquifer throughout central and southern Delaware and is the main
source of water for domestic, municipal, industrial, and
irrigation purposes. The saturated thickness can range from 25 to
180 feet. Depth to water is usually shallow (less than 25 feet
below ground level). The water table fluctuates with the amount
of precipitation, the effects of the growing versus the non-
growing season, and with withdrawal rates. Proa about mid-October
to early April (the .non-growing season), ground water is
recharged by precipitation after the summer soil-moisture deficit
has been'overcome. When evapotranspiration is occurring (in
areas of a shallow water table) and there is, generally, little
recharge owing to the deficit of soil moisture, water levels
decline. Ground water from the Columbia aquifer discharges to the
small streams draining the Delaware Coastal Plain.
Figures have been published for the regional hydraulic
characteristics of the aquifer, including transmissivity,
hydraulic conductivity, and storage coefficient*. Those figures
were based on pumping teats and reconnaissance methods. The
average transmissivity of the Columbia deposits is about 7,000
sq. ft. per day in central and southern Delaware. Using an
average saturated thickness of 75 feet for these areas, the
average hydraulic conductivity is about 90 feet per day. The
average value of the storage coefficient is 0.14 with a range
from 0.05 to 0.20.
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Subsurface features* There are several underground storage tanks
present at the site, as well as concrete lagoons (basins) which
extend -below the ground surface. These features are discussed in
detail under Section,2.0.
2.0 SITB HISTORY AND ENTORCEMBNT ACTIVITIES
Before 1965, tlie site consisted of undeveloped woodlands and
separate parcels of the site were privately owned by Ayres White
Enterprises, Inc. and the Nillsboro Industrial Development
Corporation. In 1965, Dennis Mitchell Industries (DMI) acquired
the former NCR property and began development that same year.
DMI conducted manufacturing operations on the site until 1966.
The precise nature of the industrial operation is not known;
however, former DMI employees have stated that DMI manufactured
shopping carts, children's car seats, and strollers. DMI's
industrial activities included plating, and generating and
storing waste water sludges in an onsite lagoon.
National Cash Register Company purchased the plant and property
in 1967, and used it to manufacture mechanical cash registers
from 1967 to 1975, and electronic terminal equipment from 1975 to
1980. The National Cash Register Company changed its corporate
name to NCR Corporation (NCR Corp.) in 1974. The activities
conducted from 1967 to 1975 included plating, enameling, heat
treatment, soldering, parts and screw manufacture, and parts
assembly. Before assembly, a chrome finish was applied to parts
exposed in the final product. The chromium plating, heat
treating, enameling, and associated degreasing operations used by
NCR Corp. were the primary sources of hazardous wastes generated
by the facility.
The facility had a vapor degreasing unit contained in a concrete
sump within the plant building which was approximately seven feet
deep by three feet wide by eight feet long. TCE was stored in an
above ground tank outside the plant building and piped into the
building for use in the degreasing process. In the vapor
degreasing process, TCE was heated in a tank, and parts were
placed above the tank, causing the TCE vapor to condense on the
colder part surfaces. The cutting oil and TCE mixture was removed
from the degreasing unit and disposed of along with other waste
cutting oil by a local disposal firm. The degreasing unit was
sold after plating activities were shut down, and the sump was
cleaned, filled in, and covered with concrete in 1976. These
sumps were cleaned out about 10 times a year and approximately
2,000 gallons of waste oil were generated each year. It is
believed that the ground water contamination at the site is due
to spills during the delivery of TCE and from its use during
plant operations.
8
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In addition to plating wastes and decreasing solvents, the
facility produced a variety of waste materials in the form of
oils, greases, and paint wastes. Some of the wastes were drummed
and stored onsite and were routinely picked up and disposed of by
licensed waste haulers.
NCR Corporation used sulfur dioxide gas to reduce hexavalent
chromium from its plating operation. Soluble chromium sulfate was
then treated with caustic material to form insoluble chromium
hydroxide, which was discharged to the waste treatment basins.
The addition of caustic material also served to adjust the pH of
the solution to acceptable ranges. After treatment, wastes were
directed to the onsite lagoons by gravity. Two lagoons were used
for sedimentation and clarification before discharge to Iron
Branch. A third lagoon was used for discharging cooling water.
These lagoons were each approximately 50 feet in length by 25
feet across and 4 feet deep. Each basin had a capacity of
approximately 30,000 gallons (Figure 3).
In 1974, NCR Corporation applied for and received a National
Pollutant Discharge Elimination System (NPOES) permit from the
Department of Natural Resources and Environmental Control (DNREC)
to discharge supernatant from the plating process and the cooling
water to the Iron Branch. The permit stipulated a maximum
discharge rate of 100,000 gallons per day with maximum daily
concentrations of total chromium and hexavalent chromium in the
effluent of 0.6 and 0.06 mg/1, respectively. When the property
was sold in 1981, materials in the lagoons (basins), including
liquids, were removed from the site under manifest by a waste
disposal firm in accordance with Resource Conservation and
Recovery Act (RCRA) regulations.
NCR Corporation disposed of waste sludge on its property in a pit
located along the eastern property boundary (Figure 3). The
waste sludges disposed of in the now closed pit were known to
contain chromium as well as other chemicals associated with
plating processes. These waste sludges were sampled during the
RCRA closure and were found to contain chromium. For a period of
time, NCR Corp. disposed of its waste sludges in the concrete
lagoons. Sludges were removed from the NCR Corp.'s concrete
lagoons Infrequently (every two to three years) and were picked
up and transported offsite for disposal. These sludges and other
wastes, approximately 315 cu yds, were excavated and disposed of
offsite under manifest during the RCRA closure of the facility in
September 1981.
Investigations were conducted in 1981 and 1982 by NCR Corp. under
the direction of DNREC to characterize chromium contamination in
soils and ground water. No other metals or compounds were
detected in soil or ground water samples at levels of concern. In
May 1983, DNREC requested NCR Corporation to investigate into the
potential presence of volatile organic compounds (VOC's). When
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FILL AREA I INDICATED ON
PREVIOUS SURVEY!
0 100
I I I
SCALt •
T W. = TEST WEU
MITCHELL STREET
ZD S
00
oca:
8°
a.
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the presence of TCE in ground water was established, additional
studies were conducted-to characterize the contaminant plume and
to attempt to locate the source of the contamination. In addition
to TCE, l,i-dichloroethane(DCA), trans-1,2- dichloroethylene,
chloroform, 1,2-dichloroethane, 1,1,1-trichloroethane (TCA),
carbon tetrachloride, 1,1,2-trichloromethane,
1,1,2,2-tetrachloroethane, and tetrachloroethylene (PCE) were
detected in ground water samples.
In 1985, additional backhoe excavations were conducted in the
area at the northeast corner of the building. This area had the
highest concentrations of TCE in ground water (Figure 4).
However, despite extensive examination, no nonaqueous-phase TCE
was discovered, and no source was established. A thorough
examination of the location of all the potential sources of
hazardous materials was conducted. This examination of potential
sources included four existing underground storage tanks which
were part of the NCR property and are still present at the site.
* Underground Cutting Oil Tank - Two tanks were used to hold
waste cutting oil. Each tank had a capacity of 2000 gallons.
These tanks were emptied in 1981 and are not in use;
* Underground Fuel Oil Tank - This tank was used to store
No.2 fuel oil which was used to fire the facility boiler. NCR
reported that this tank was once accidentally filled with TCE. A
residue of oil and waste remains. This residue was sampled in
1985 and found to contain low concentrations of TCE and
Tetrachloroethylene (PCE);
* Underground Gasoline Tank - This tank was used at a pumping
station for plant vehicles. This tank is still present, but is
not in use.
The existing underground storage tanks did not appear to be the
source of the ground water contamination at the site. These
tanks were used to store petroleum products which are classified
as hazardous substances under the newly promulgated Interim
Regulations Governing Hazardous Substance cleanup in the State of
Delaware. EPA does not have reason to believe that these tanks
are contributing to the current reason for taking remedial
action. However, DNREC has indicated the existence of these
tanks is a violation of Delaware regulations governing
Underground Storage Tank Systems (7 Delaware C. Ch. 60), since
they have been empty and not in use for over a year.
Under the provisions of CERCLA, the site was placed on the
National Priorities List (NPL) in July, 1987, with a Hazard
Ranking Score of 38.21. The regulations enacted pursuant to
11
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EXTENT OF TCE CONTAMINATION
GROUNOWATER
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CERCLA require that a Remedial Investigation/Feasibility Study
(RI/FS> and a baseline Risk Assessment be conducted at each NPL
site. The purpose, of- the RI is to characterize conditions at the
site. The subsequent FS then develops, screens, and analyzes a
series of remedial alternatives for addressing contamination at
the site.
In March 1988, 'NCR Corp. entered into a Consent Order, to which
EPA was not a party, with the DNREC to conduct a Remedial
Investigation/Feasibility Study (RI/FS) and to implement Initial
Response Measures (IRM) at the site. The objective of the IRM
was to prevent continuing migration of a plume of TCE in the
ground water. NCR Corp. installed a ground water recovery well
and an air stripper in June and July 1988 as an IRM. The recovery
well and the air stripper are still in operation. The RI/FS was
initiated in 1988 and completed in 1991.
3.0 HIGHLIGHTS OT COMKDHZTT PARTICIPATION
In accordance with Sections 113 and 117 of CERCLA, 42 U.S.C. SS
9613 and 9617, the • RI/FS Report and the Proposed Plan along with
the remainder of the Administrative Record file for the NCR
Millsboro site were released to the public for comment for a 30
day period beginning on May 24, 1991 and ending on June 25, 1991.
These two documents were made available to the public in the
Administrative Record file, copies of which are maintained at the
EPA Docket Room in Region Ill's Philadelphia office; the DNREC
office in New Castle, DE; and at the Town Office Building in
Millsboro Township. The notice of availability for these two
documents was published in the Delaware State News and The News
Journal on May 24, 1991. In addition, a public meeting was held
on June 20, 1991. At this meeting, representatives from the EPA
and DNREC answered questions about conditions 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. This decision
document presents the selected remedial action for the NCR
Corporation (Millsboro Plant) site in Millsboro, Delaware, chosen
in accordance with CERCLA as amended by SARA and to the extent
practicable, the National Oil and Hazardous Substances Pollution
Contingency Plan (NCP). The decision for this site is based on
the administrative record file placed in the above mentioned
locations.
4.0 8COPB AMD HOL1 OF REMEDIAL ACTIOV
The Record of Decision (ROD) addresses the ground water
contamination in the aquifers underlying the site. The remedial
action objectives are to prevent exposure to the contaminated
ground water at the site, to restore the ground water to its
beneficial use, and to ensure protectiveness of human health and
13
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the environment from the discharge of ground water into the Iron
Branch. There is no principal threat at this site. Groundvater
contamination is not considered to be a principal threat;
however, it is an expectation that ground water will be
remediated to* its beneficial use, which at this site includes its
use as a source of potable water..
5.0 SUMMARY OF SITB CHARACTERISTICS
NCR Corp. conducted the Remedial Investigation/Feasibility study
(RI/FS) and Risk Assessment (RA) for the site. The RI
characterized the nature and extent of the contamination present
at the site; the RA evaluated the risk to public health and the
environment by both current and future exposure to site
contaminants.
The RI included ground water, soil, surface water and sediment
sampling. The RI revealed levels of TCE and chromium in the
ground water at the site above the maximum contaminant levels
(MCLs). The MCL for TCE is 5 parts per billion (ppb), and the MCL
for chromium is 100 ppb. The following levels, indicated in
parenthesis, represent maximum levels of contaminant detected
during the RI/FS and quarterly monitoring. The highest levels of
TCE (490,000 ppb) were detected in wells behind the northeast
corner of the plant building. This area is considered to be the
source area. Levels of TCE (3,000 ppb) were also detected in
wells located east of the site in the parcel of agricultural land
and just west of the Iron Branch stream. Levels of TCE above MCLs
have not been detected in residential wells east of the Iron
Branch. Levels of chromium in ground water (533 ppb) were limited
to the vicinity of the former plating sludge disposal area.
Levels of TCE (63,000 ppb) and chromium (205,000 ppb) were
detected in subsurface soils northeast of the former NCR
processing plant.
Sampling of the Iron Branch stream conducted during the RI
revealed the following maximum levels of contaminants in surface
water: TCE (70 ppb); acetone (20 ppb); total chromium (< 5.0
ppb); hexavalent chromium (57 ppb); and in sediments : TCE (7
ppb); total chromium (37,000 ppb); hexavalent chromium (15,000
ppb); lead (20,000 ppb); and zinc (50,000 ppb).
The extent of TCB contamination in the upper portion of the
aquifer was delineated based on the distribution of TCE detected
in the onsite monitoring wells. The plume extends downgradient
from the primary source area adjacent to the building, entering
Iron Branch along an approximately 900 - 1,000 foot segment
(Figure 4). Except for monitoring well 11B, the "B" and "C" wells
contained concentrations less than 5.0 ug/1 TCE. The maximum
concentration of TCE in monitoring well 11B was 34.0 ug/1. The
14
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• - «• -
Existing Air Stripper,
Recovery Well and
LOCATIONS
oo
CCCC
8°
o.
figure 5
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"B" and "C" wells are screened at deeper intervals below the
surf ace" than "A" wells (See Figure 5 for well location). [Thus
the majority of TCE contamination is still found in the water
table from the surface downward to the top of the "Bn well
screens (approximately 50 feet below grade or 35 feet of
saturated thickness).] As calculated in the RI, the estimated
volume of the aquifer contaminated with TCE at levels ranging
from 25 to 290,000 ug/L is approximately 8,977,500 cubic feet.
The RI found that the primary source of TCE contamination at the
site was introduced into the environment either by surface spills
or by leaks into subsurface soil in or around the vicinity of the
building and the above ground TCE tank. TCE is a probable human
carcinogen. Chromium was introduced into the environment as a
combination of trivalent and hexavalent states either onto the
soil surface or into subsurface soil in the vicinity of the now
excavated pit into which plating tank sludge was placed.
Chromium is considered to be a human carcinogen by the inhalation
route .
Although there are discontinuities in the concentration profile
of TCE in ground water, the overall observations indicate an
elongated plume extending to Iron Branch. There is no evidence
of downward migration of a dense nonagueous phase liquid (ONAPL) .
The ground water plume is indicative of dissolved transport
rather than a DNAPL.
6.0 SUMMARY OF 8ZTB RISKS
I. Exosure Assessmen
The purpose of the Risk Assessment performed for the NCR
Mil labor o site was to assess the potential human health risks
that may result from exposure to releases at the site in the
absence of remediation.
In order to estimate the human health risk from the
contaminants of concern, an exposure pathway analysis was
performed. An exposure pathway has four necessary elements: 1)
a source and mechanism of chemical release; 2) an environmental
transport medium; 3) a human or environmental exposure point,
and; 4) a feasible human or environmental exposure route at the
point of exposure. The potential for establishing a complete
exposure pathway for the following media was evaluated for the
NCR Millsboro site: ground water, soil, surface water and
sediment of Iron Branch, and air.
The exposure assessment for the evaluation of potential
risks to the environment differs from the human health risk
approach and will be addressed separately in section 6.0 III B.
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A. Contaminants of Concern and the Associated Media:
Indicator chemicals (i.e., chemicals observed at the site
which are most, likely- to pose a threat to public health and the
environment), and the media they apply to for the NCR Millsboro
site are summarized below:
surface water;
trihalomethanes (chloroform, bromodichloromethane,
bromoform, and dibromochloromethane).
trans-l,2-DCE
trichloroethylene (TCE)
stream sediments:
TCE
chromium
soils:
TCE
chromium
around water:
trans-l,2-dichloroethylene (trans-2,l-DCE)
chloroform
tetrachloroethylene (PCE)
TCE
chromium
air;
volatile organic compounds (VOCs) primarily TCE
B. Exposure Pathways:
Exposure pathways were evaluated for two scenarios, current
and future use. The current-use scenario considered the existing
land-us* patterns of the area and evaluated the completeness of
potential exposure pathways based on the current land use
information. For the future use scenario, the exposure pathways
were altered to reflect the effects of possible future land use
patterns.
Tables 1 and 2 summarize the current-use and future-use
pathways, respectively.
17
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Table
Evaluation of Exposure Pathway - Current Use
Media Potential
Source
Surface Water9 Yea
Aquatic Ufe8 Yea
Sedlmenta* Yea
Soil (Sub- Yea
aurface)
Ground water Yea
Transport Media/ Exposure Point/
Releaae Mechanism fjxpoaure Population
Ground Water Dlacharge
to Surface Water
Direct Contact
RlnACCiiiniilAtliMi tiff
Contaminants
In Fish Tissue
Ground Water Dlacharge
to Iron Branch/
Direct Contact
Direct Contact
Ground Water
No
.
Yea
No
No
No
Potential
Exposure floute
y
NA
Ingestlon
of Contaminated
fish tissue
NA
NA
NA
i
t
Pathway
Complete
No
1
1
Yea
No
*
No
No
flow/Direct Contact
O • ' Ground water dlacharge to Iron Branch
OO
18
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Table
Evaluation of Exposure Pathway - Future-Use
Media
Surface Water
Aquatic Life
Sediment
Soil
(Subsurface)
Ground Water
Potential
Source
Ye*
Yes
Yes
Yea
Yea
Tranapoift'aJedla/
Release Mechanism
Groundwater Discharge
to Iron Branch
Plo^ccunitjlrtiofi of
Contaminants In Fish Tissue
Ground Water Discharge to
Iron Branch
Direct Contact
Ground Water Flow
Exposure Point/
Exposure Population
No
Onslte/Humans
No
Onstto/Humans
Humana
Potential
Exposure Route
NA
Ingestlon
NA
Ingestlon/Dermal
Absorption
Ingestlon/lnhalatlon
i
! Pathway
Complete
No
i
Yes
No
*
Yes
Yes
-------
For the current-use scenario the ingestion of fish from Iron
Branch vas the only exposure pathway determined to be a complete
pathway. Complete pathways under the future-use scenario were
ingestion of .ground -water and inhalation of vapors from the use
of contaminated ground water; ingestion of fish from Iron
Branch; and direct contact with contaminated soil.
Since the baseline risk assessment is performed to simulate risks
if no remediation were to occur. Evaluation of the air pathway
was considered incomplete since in the absence of the air
stripper/ which is one component of the IPX, release of
contaminants of concern in ground water to air would be
negligible and not considered a significant pathway. However, in
evaluating the air stripper as a possible means of remediation,
it has been indicated that emissions to air as a result of air
stripping could pose a potential threat for human health and the
environment. Aa a result, further modeling to evaluate the
potential risk due to long term exposure to contaminants of
concern through air emission will be performed during remedial
design.
C. Exposure Point Concentration and Potentially Exposed
Populations :
For each complete exposure scenario quantitative estimates
of chemical intakes by theoretically exposed individuals are
estimated for each chemical of concern. Factors that are
considered in estimating exposures include chemical
concentrations in the environmental media of concern (e.g. soil
and water); characteristics of the population potentially
affected by exposure (e.g. age, body weight); the percentage of a
chemical absorbed into the body by a particular exposure route
(e.g. dermal absorption, inhalation); and exposure conditions
such as the frequency and duration of exposure. The exposure
estimates for the NCR Millsboro site were developed on the basis
of available environmental data and conservative exposure
assumptions to represent reasonable upperbound exposure
conditions. This approach makes it unlikely that actual
exposures would exceed the estimated exposures.
The following section summarizes the assumptions used to
estimate potential exposure point concentrations and chronic
daily intake (GDI) values for the chemicals of concern for each
exposure pathway under the current-use and future-use scenarios.
1. Ingestion of Fish from Iron Branch:
The concentration of contaminants in fish tissue was
estimated by multiplying published bioconcentration factors by
the maximum concentration of each chemical of concern in surface
water. Maximum concentrations in surface water were used to
screen the upper bound risk for this pathway.
20
-------
Future surface water concentrations in the vicinity of the
NCR Millsboro site are unlikely to significantly exceed the
recently measured concentrations; therefore, the current and
future-use exposure point concentrations used in the risk
assessment are the same.
*
Under this exposure scenario it was also assumed that an
exposed adult catches and eats 6.5 grams of fish each day for a
lifetime of 70 years. Table 3 presents the upperbound (worst
case) estimates for Chronic Daily Intakes (CDI) for each of the
contaminants of concern, in addition to the maximum surface water
concentrations and fish bioconcentration factors used to
calculate the GDIs.
2. Direct Contact with Soils:
For purposes of the risk assessment it is assumed that
future development of the NCR Millsboro site for commercial or
residential use could result in onsite construction on, or
residents occupying, the property.
Soil contamination at the site is localized and was detected
only in subsurface soils. Therefore only positive sample results
were used to calculate the arithmetic mean concentration to be
used as the exposure point concentration. Since areas of
localized contamination were used to characterize conditions at
the entire site it is unlikely that health risks will be
underestimated for this exposure pathway.
The primary routes of exposure associated with direct
contact are incidental ingestion of small quantities of soils by
casual hand to mouth activity and dermal absorption of
contaminants in soil.
Under the residential scenario, residents may be exposed to
contaminated soils through yard work, play, and gardening.
Because an exposure duration of 70 years is assumed, intake
estimates for the hypothetical resident are based on 6 years of
exposure at an ingestion rate of 200 mg/day for exposure duration
of 200 days per year (for children age 6 and less) and 64 years
of exposure at 100 mg/day for an exposure frequency of 100 days
per year (for persons older than 6 years of age).
The worker exposure to site contaminants assumes an exposure
duration of 30 years at an ingestion rate of 100 mg/day for an
exposure frequency of 260 days per year.
The chronic daily intake (CDI) values for residents and
workers exposed to chemicals by incidental ingestion of soil are
shown in Table 4.
21
-------
Table
Chronic Dally
Maximum watar BCP* T«* u
eane fm~/i\ ,7 * . IntaJea
"B im*Ml »I/HgI . /a?/Vg^Bv
t-l,2-0ichloroathylana 4.00E-03 , «
*-o 5.94E-07
Tot.! tnh.io-.th.n.. a.401.OJ 3 7j f 36£_o7
Triehl""tllyl"* 7-««-o3 ,o.. ,.,„_„
ch,..luB(VI) ,.„„,,. u ^^
a/ BCP • fi«h bioconctntration factor, I/kg. Th« BCP for total
trihalom«than«a i« baaad oa chloroform.
22 POOR QUALITY
ORIGINAL
-------
Table 4
Chronic Daily Intake of Contaminant* of Concern
by Incidental Ingeation of Soil - Future Uaa Scenario
C«rcioo(«nio Effects
Tricbloroethylene
Arithaetic
Mean Soil
Concentration
0.006
Beaidential Scenario
Child Adult Total
Intake Intake Intake
fyg/fcg/d^y)
-------
For the dermal absorption route TCE is the only contaminant
of concern since dermal absorption of inorganics is assumed to be
negligible.
For the residential exposure it is assumed that the total
exposed body surface area is 2,810'sq. cm and the exposure
frequency is 200 days per year ( for a child up to age 6 years)
and 1,980 sq. cm. for a frequency of 100 days per year (for ages
older than 6 years) for a period of 64 years.
The potential absorbed doses of TCE incurred by residents
and workers by the dermal absorption route of exposure are
presented in Table 5. Table 6 presents total intake by direct
contact with contaminated soil, considering both incidental
ingestion and dermal absorption routes of exposure.
Additional soil sampling was performed as a result of soil
gas analysis revealing levels of concern of VOCs. The results of
this investigation were fully documented in the Supplemental Soil
Investigation Report which is an appendix to the RI report in the
Administrative Record File. The supplemental investigation
occurred after preparation of the risk assessment and revealed
TCE (63 mg/kg) and total chromium (205 mg/kg) values greater than
those previously detected and used in the risk assessment.
Therefore, an additional future residential exposure was
calculated using these maximum contaminant values. Only
calculations based on the residential use scenario were performed
since it is a more conservative estimate of the potential risks
than the worker use scenario. The same assumptions previously
stated were also applied to estimating the risks due to direct
contact with soils at this level of contamination (Table 7).
3. Use of Ground Water as a Potable Water Supply:
There are-~®xisting ground water wells used for domestic
water supply in the vicinity of the NCR Millsboro site. These
wells are located downgradient of the facility on the east side
of Iron Branch. Shallow ground water generally discharges to
Iron Branch. Iron Branch appears to be acting as a hydraulic
barrier since levels of contaminants above MCLs have not been
detected in these domestic wells, therefore the ground water
pathway is not considered a complete pathway under the current-
use scenario. However, it is plausible that in the future wells
could be constructed on site or nearby off site. The future-use
scenario considered the possible future ingestion of, and
inhalation of, VOCs from contaminated ground water.
Exposure estimates for pathways related to ground water use
were based on concentration ranges. The upper and lower bound
concentrations of the range are represented by the arithmetic and
geometric means, respectively. Both means were developed using
monitoring data for shallow onsite wells and well points only,
24
POOR QUALITY
ORIGINAL
-------
08
QO
Chronic Daily Intake of Contaminant* of Concarn
bjr Daraal Absorption - Putura Uaa Bcanario
TricBioroatkyUM
Arittaatic
"aaidantUl Scanario
,
3.61-08 3.18-08 6.
7B-08
3.7B-08
25
-------
Careiaoganic Sffecta
Tricfcloroetnyleoe
Noncarcinogenic Iffecta
Table 6
Total Chronic Daily Int.k. oy Dlr.et Cont.et ¥Ub §Qll
future !!•• Scenario (BC
laaldantial !)•• Scenario
Daraal Total
S.tl-09 3.7B-08 4.3B-08
Worker Bxpoaure
i
Incidental Derawl total
Tocai cnroaiiw
Cbroaiua) VI
3.41-05
3.6B-04
HA 3.6B-05
MA 3.6B-06
5. IE-06
5 IB-07
2.6E-09 3.7B-08 4.0B-08
MA S.IE-06
MA 5.IB-07
MA - not applicable
O _
33 3D
O
-------
Tall* 7
Total
3.7E-4S
3.IB-4M
2.3E-OS
3.2E-44
6.0E-OS
7.0E-04
I.4B-03 I.OE-OS I.5E-4U
CMCOT
NA
NA
S.OE-4B
I.IE-02
I.IE-02
HUM* ,
NA
NA
NA 3E-OI
7E-OI
NA
•/ Th*
MTahtel
Ontawara N>«io«il Phority LiM •*••
CJ1
s§
27
-------
which consistently had higher levels of contamination than the
intermediate and deep wells. Wells for which contamination was
not detectable were included in the calculation of means by
assuming that "a given compound was present at a concentration of
one-half the analytical detection limit.
The highest concentrations of ground water contaminants
appear to be localized in a few wells near the northeast corner
of the plant bhilding. Maximum detected ground water
concentrations were not used as the upper bound exposure level
because such an approach would significantly overstate potential
exposures. Furthermore, it is likely the taste and odor
associated with organic contamination in these wells would make
the water unpalatable. Instead arithmetic and geometric
concentrations were used in the calculation of risk. Use of the
arithmetic mean provides a more conservative or protective risk
assessment. Pursuant to EPA guidance (Risk Assessment Guidance
for Superfund Vol. 1 Dec. 1989), the arithmetic mean
concentrations shall be used or considered for this risk
assessment.
The chronic daily intake values of the contaminants of
concern through ingestion of contaminated ground water were based
on the assumption that a 70-kg person would ingest 2 liters of
water per day (365 days a year) for a duration of 70 years. The
estimated chronic daily intakes by ingestion of drinking water
are presented in Table 8.
The primary additional route of exposure to ground water
involved inhalation of chemicals volatilized to household air
during showering, laundering, cooking, dishwashing, and other
similar activities.
The Risk Assessment performed for the site incorporated a
mathematical model developed by Symms (1986) to estimate VOC
exposures from daily showering with contaminated household water.
The model estimates dose by inhalation during showering as well
as from inhalation of bathroom air following shower use. The
model conservatively assumes that all VOCs in water are released
into the air and that the duration of a shower is 20 minutes.
Total water us* during the shower is assumed to be 200 liters, an
upper bound volume estimate. The standard breathing rate for an
adult as 20 cubic meter per day JS.83 cu m per hour). A shower
stall is assumed to have an air volume of 3 cu m. The model
conservatively assumes that the total amount of VOCs in 200
liters of water fills the shower space. It is also assumed that
an adult will spend an additional 10 minutes in an unventilated
10 cu m bathroom inhaling vapors generated from shower use.
A retention factor is included in the calculation to derive
the absorbed VOC dose. Symms reports a maximum retention factor
28
-------
Table 8
t-1.2-Dicbloro.tbjrl.n*
Cblorofora
T.tr.cbloro.tbyl.n.
Trichloro.cbyl.n.
Cbroaiiw VI
Total cbroaiiw
Upper Bound Conc.ntr.tlon
Arlth. M.n
CflnCi tm*/\\
^^^^^^"^•^•^^•^^•^•^
1. 148-01
1.218-01
2.978-01
4.628*01
6.408-02
6.008-02
Int.k.
fM|/k|/4«y)
3.30E-03
3.508-03
8. 508-03
1.328*00
1.808-03
1.708-03
Lower Bound Conc.ntr.tion
C.o«. B..n
g"Tti (•>/!)
9. 108-03
3.60B-03
S.20B-03
2.488-01
4.488-02
1.958-02
Int.k. ,
f*n»* /•** /A^u*\ '
iBMBl/BlBt/ilMlf 1
^•^^^•^•^^^^^•^•^•.^•^
2.60E-04
1 . 10B-04 '
1 . 408-04
7. IOB-03
1.308-03
%
5. 708-04
go
oo
29
-------
of 0.77 (77%) for chloroform and 0.75 (75%) for TCE. Because
retention factors are not reported for each of the compounds
detected in groundvater in the NCR Millsboro site, a retention
factor of l.CL-(100%)--vas conservatively assumed.
The estimated range of chronic daily intake values for the
inhalation route of exposure is presented in Table 9.
II. Toxicity Assessment Smfljiflrv
The toxicity evaluation of the indicator chemicals selected
for the NCR Millsboro site was conducted to identify relevant
carcinogenic potency or slope factors and/or chronic reference
doses against which exposure point or daily intakes could be
compared in the risk characterization of the site. Indicator
compounds are those which are the most toxic, prevalent,
persistent, mobile, and which contribute the major potential
risks at the site. Only one noncarcinogenic indicator chemical
was identified for the site (chromium via the ingestion route)
potentially carcinogenic indicator compounds; selected for this
site are chromium (inhalation route) tetrachloroethylene,
trichloroethylene, and trihalomethanes (chloroform).
Cancer slope or potency factors have been developed by EPA's
Carcinogenic Assessment Group for estimating excess lifetime
cancer risks associated with exposure to potentially carcinogenic
chemicals. Cancer slope factors, which are expressed in units of
(mg of contaminant/kg of body weight-day)"1, 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 that intake level. The term
"upper bound" reflects the conservative estimate of the risks
calculated from the cancer slope factor. Use of this approach
makes underestimation of the actual cancer risk highly unlikely.
Cancer slope 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. A summary of toxicological information for the
indicator chemicals are shown in Table 10.
Reference doses (RfDs) have been developed by EPA for
indicating the potential for adverse health effects from exposure
to chemicals exhibiting noncarcinogenic effects. RfDs, which are
expressed in units of mg of contaminant/kg-day of body weight,
are estimates of lifetime daily exposure levels for humans,
including sensitive individuals, that are likely to be without an
appreciable risk of adverse health effects. Estimated intakes of
chemicals from environmental media (e.g. the amount of a chemical
ingested from contaminated drinking water) can be compared to the
RfO. RfDs are derived from human epidemiological studies or
animal studies to which uncertainty factors have been applied
30
-------
T«bU 9.-
Chronic tally Znt.k. CC8I) by Znh.l«tion of voc.
- --in Groundvtt.r Ourinf Showtring
Upp.r Bound Conc,ntr«ion law-r Bound Conc.ntr.cion
t-1,2-Dichloro«cnyltn«
Chlorofor*
T«cr«ebloro«chyl«n«
Trichlpro«chyl«n«
Arith. Men
eane (mt /\ >
1.14E-01
1.212-01
2.97E-01
4.62E*01
Zneaka
C»^/k|/H«»>
1.941-02
2.062-02
3.032-02
7.83*00
GMOB. Bfl^n
can* '"If i'1 1
9. 10E-03
3.60E-03
3.20E-03
2.48E-01
Znt«k«
(mt/^ffH^]
1.33E-03
6. 12E-04
8.84E-04
4.22E-02
31
POOR QUALITY
ORIGINAL
-------
Table 10
Health-Baaed Criteria for Contaminants of Concern
Chamioal
Ingestion Exposure
Reference Doae Cancer Slope Factor
Inhalation Bxpoaura
Rafaranoa Doaa Canoar Slop* Factor*
fm/kdal f'1
Chromium (III) 1.0
Chromium (VI) 5.0 x 10
t-l,2-Dlchloroethylene 2.0 x 10
Tetrachloroethylene 1.0 X 10
Trlchloroethylene
Trihalomethanea0 1.0 x 10*
-2
5.1 x 10
-3
5.1 x 10'
1.7 x 10'
6.1 x 10'
|B2|
|B2|
4.
3.
1.
8.
1
3
3
1
x
X
X
X
10
10
10
10
i
1
-3
:l'
|A|
|B2|
IB2)
c
a/ Lattara in brackata indicata EPA*a weight of evidence for carclnoganiclty classification.
b/ Valuaa raportad ara for chlorofor*.
c/ The carclnoganic alopa factor and welght-of-evidence for tetrachloroethylene and trichloroethylene
are being reevaluated by BPA. Quantitative eatlaatea of carclnogenicity have been removed fron
IRIS until the reevaluatlona are coaipleted. Valuea presented in this table were reported in the
HBAST.
Sources: Health Effects Assessment Susmary Tables (HEAST; EPA 1909) Integrated Risk Information
System (IRIS; BPA 1990)
•o
08
DO 33
OO
32
-------
(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.
III. Risk Characterization ••gmmnarv
A. Human Health Risks
For potential carcinogens, risks are estimated as
probabilities. Excess lifetime cancer risks are determined by
multiplying the intake level with the cancer potency factor.
These risks are probabilities that are generally expressed in
scientific notation (e.g. IxlO"6 or 1E-06). An excess lifetime
cancer risk of 1E-06 indicates that, as a plausible upper bound,
an individual has a one chance in one million of developing
cancer as a result of site-related exposure to a carcinogen over
a 70-year lifetime under the specific exposure conditions at a
site.
For assessing the overall potential for noncarcinogenic
effects posed by indicator compounds, the Hazard Index (HI)
method is used. Potential concern for noncarcinogenic effects of
a single medium is expressed as the hazard quotient (HQ) (or the
ratio of the estimated intake derived from the contaminant
concentration in a given medium to the contaminant's reference
dose). By adding the HQs for all contaminants within a medium or
across all media to which a given population may reasonably be
exposed, the Hazard Index (HI) can by generated. The HI provides
a useful reference point for gauging the potential significance
of multiple contaminant exposures within a single medium or
across media.
When reviewing the quantitative information presented in
this section, the following threshold levels should be used. For
the carcinogenic risks, remedial action is generally warranted at
a site when the risk exceeds 1E-04. For noncarcinogenic effects,
a hazard index above a value of 1.0 indicates the potential for
an adverse health effect. Thus, determining the need for
remedial action.
The following is a summary of the potential carcinogenic and
noncarcinogenic effects to human health posed by each exposure
pathway assessed in the risk assessment. Tables 11 and 12
represent the estimated upperbound cancer risks and
noncarcinogenic health risks assessed for each complete exposure
pathway including; ingestion of fish, direct contact with soil,
and use of ground water as a potable supply.
33
-------
Receptor
Population
Currant Land Use
Resident
Future Land Use
Resident
Exposure
Pathway
Table 11
carcinogenic Risk Summary
Chemicals of
Concern
Cancer Risk
Fish
Consuaption
Total trdhalomethanes
Trichloroethylene
Total Pathway Risk
5E-09
1E-06
1E-06
Ground water
ingestion
Chloroform
Tetrachloroethylene
Trichloroethylene
Total Pathway Risk
Inhalation of Chloroform
vapors during Tetrachloroethylene
showering Trichloroethylene
Arithmetic Means
2E-05
4E-04
2E-02
2E-02
2E-03
1E-04
1E-01
Fish
Consumption
Incidental
ingestion of
soils
Total Pathway Risk 1E-01
Total trihalomethanas
Trichloroethylene
Total Pathway Risk 1E-06
Trichloroethylene
Dermal
absorption
Trichloroethylene
Total Upper Bound Risk for Resident, Future Us«
oncentration
5E-09
1E-06
3E-10*
7E-07
3E-09*
8E-06*
18-01*
Incidental Trichloroethylene
ition of
iagosl
•oil
worker
Trichloroethylene
absorption
Total Upper Bound Risk for Worker, Future Use
1E-10*
2E-09*
12-09*
• calculation* based on sits soil concentrations detected during the
supplemental Soils Investigation.
* Calculations based on sits soil concentrations detected prior to the
soil. lm*.ti,.tion.
34
ORIGINAL
-------
Table 12
Honcareinogenic Health Hasard fluaaary
Receptor
population
current Land Uee
Reeideat
Exposure
Pathway
Fish
Consuaption
Future Land Use
Resident
Ground water
ingestion
Fish
Consumption
Incidental
ingestion of
soil
Chemicals of
Concern
Health Hazard
Index
Maximum Concentrations
t-l,2-dichloroethylene 3E-05
Total trihalomethanas 8E-05
Chromium VI 2E-02
Total Pathway Index 2E-02
t-1,2-dichloroethylene
chloroform
Tetrachloroethylene
Chroaiua VI
Total chroaium
Total Pathway Index
t-1,2-dichloroethylene
Total trihaloaethanes
Chroaiua VI
Total Pathway Index
Total Chroaiua
Chroaiua VI
Ar4thaetic Mean
2E-01
4E-01
9E-01
4E-01
2E-03
2E-00
Maximum Concentrations
3E-05
8E-05
2E-02
Total Pathway Index
Total Upper Bound Index for Resident, Future Use
Worker
•Incidental
ingestion of
soil
Total Chroaiua
Chroaiua VZ
* Total Upper Bound Index for worker, Future use
2E-02
8-E-05*
2E-03
2E-03
2E-00
IE-OS
3E-04
32-04
3E-01»
* Calculations based on site soil concentrations detected prior to the
Supplemental Soils Investigation.
• Calculations based on site soil concentration detected during the
Suppleaental Soils Investigation.
POOR QUALITY
35 ORIGINAL
-------
1. Ingestion of Fish from Iron Branch:
Total carffinog.enip risk for the fish consumption pathway is
estimated to be 1E-06, which is within the EPA target risk range
remediation goals. The overall hazard index for this pathway is
significantly less that 1.0 (2E-02 or 0.02), indicating a low
potential for noncarcinogenic health effects resulting from fish
consumption.
The risk analysis for this pathway indicates that adverse
public health effects are not likely, even under the upper bound
assumptions associated with the fish ingestion pathway. The
assessment assumes that levels of site-related contaminants in
Iron Branch will not appreciably increase in the future. This
assumption is reasonable based on the current understanding of
site conditions and the observed levels of ground water
contamination upgradient of the stream. Therefore the current
and future risk values are the same.
2. Direct Contact with Soil:
Potential health risks associated with soil exposure were
evaluated in the risk assessment under future use scenarios for
both onsite workers and residents potentially occupying the
property. In addition, as a result of the supplemental soils
investigation, TCE and chromium were detected in soils at levels
that exceeded those previously used in the risk assessment
calculations. Therefore, additional risk calculations were
performed to evaluate the potential human exposure to
contaminants using the future residential soil exposure scenario.
The upper bound carcinogenic risks associated with ingestion
of soil were estimated to be about 10~10 for both workers and
residents determined by using soil concentration found during the
RI. The noncarcinogenic hazard indices for the soil ingestion
route of exposure are well below 1.0, indicating a low potential
for adverse health effects. The potential cancer risks for
exposure by dermal absorption to TCE in soil are about 10"9 for
both workers and residents. Although chromium was detected in
the soil, dermal absorption of inorganics is considered
negligible, and therefore not included in the analysis for this
exposure route. In addition, it was not possible to evaluate
potential noncarcinogenic hazards associated with TCE exposure by
dermal contact because a reference dose for TCE has not been
developed by EPA.
Because exposures to site contaminants by incidental
ingestion and dermal absorption would both result from direct
contact with soil, the potential risks associated with these
routes of exposure are considered additive. The combined upper
bound cancer risk estimate (10~9) does not however, exceed the
target risk range for remediation.
36
-------
The risk assessment conducted using the higher
concentrations of TCE and chromium detected during the
Supplemental Soils Investigation, which is an addendum to the RI
report, indicates that exposure to chromium is unlikely to pose
significant risk to public health (hazard index -0.3)
(Table 7 and 12). Exposure to TCfi was associated with upper
bound excess cancer risks of 1E-07 for the ingestion route and
8E-06 for the dermal route of exposure, since it provides a more
conservative estimate, only the future residential exposure
scenario was performed using the maximum concentrations found in
the subsurface soils during the Supplemental Soils Investigation
(Table 7).
3. Use of Ground Water as a Potable Supply:
The estimated hazard indices and cancer risks associated
with the use of ground water were derived from both ingestion of
ground water as well as inhalation of vapors from ground water.
The potential carcinogenic risk associated with ingestion of
contaminated ground water is 1E-02. This value exceeds the upper
bound of EPA'a target risk range (1E-04). The total hazard index
for the ingestion route is 2.0, which also exceeds the target
action level of 1.0.
The potential upper bound carcinogenic risks associated with
inhalation of contaminated vapors from ground water is 1E-01.
Noncarcinogenic risks were not evaluated for this route because
inhalation reference doses are not currently available for the
contaminants of concern.
B. Environmental Risks
One approach for assessing environmental risks is to expose
test populations of sensitive indicator organisms to the
environmental media of concern and observe the effects of this
exposure on the organisms. Aquatic life toxicity testing and
bioassays are particularly useful for evaluating sediment because
there are currently no EPA criteria for this medium. This
approach was used at the NCR Millsboro site. ' Stream sediment
quality for Iron Branch was evaluated in a series of elution
bioassays. Acute bioassays and chronic reproductive bioassay
results indicated that stream sediment samples were not toxic to
freshwater or marine species. However, the Remedial
Investigation indicated that shallow ground water generally
discharges to Iron Branch; therefore, continued monitoring of
surface water and sediments of Iron Branch is warranted until the
discharged ground water no longer poses a potential threat to the
Iron Branch environment.
Furthermore, the Iron Branch converges with the Wharton
Branch and flows into the Indian River downstream of the NCR
Millsboro,site. During an ecological investigation at the Indian
37
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River Power Plant, located approximately 2 miles downstream of
the site on the Indian River, an endangered species, the piping
plover, was observed. Continued monitoring of the Iron Branch
must be conducted in 'order to ensure that actions taken at the
NCR Millsboro site do not threaten the existence of this
endangered species or its critical habitat.
IV. Significant Sources of Uncertainty
___ .^__
Discussion of general limitations inherent in the risk
assessment process as well as the uncertainty related to some of
the major assumptions made in this assessment are summarized
below. Several sources of uncertainty have been identified:
1. Environmental sampling and analysis:
Uncertainties in environmental sampling and analysis can
arise from the errors inherent in these processes, from a failure
to take an adequate number of samples to arrive at sufficient
areal resolution, from inadequate areal placement of sampling
points, from mistakes made by the samplers, or from the
heterogeneity of the material being sampled. Much of the field
work conducted at the NCR Millsboro site was intended to
characterize areas of known contamination. Thus, average
concentrations for chemical residuals in environmental media may
be more representative of localized hot spots (i. e areas where
elevated concentrations are located) than of the site as a whole.
2. Exposure parameter estimation:
There are inherent uncertainties in determining the exposure
parameters that are combined with toxicological information to
assess risk. For example, there are a number of uncertainties
regarding assumptions in estimating the likelihood that an
individual would come into contact with chemical contaminants
originating at the site, the concentration of contaminants in the
environmental media of concern, and the period of time over which
such exposures would occur. For example, it is unlikely that
individuals will consume fish caught in Iron Branch or consume
drinking water from the site for an entire lifetime, as is
estimated in the risk assessment. Although the assumptions made
are reasonable, they are not based on direct observations of the
behavior of specific individuals or populations, and exposure is
expected to vary widely among individuals.
3. Toxicological data:
There are major uncertainties in extrapolating both from
animals to humans and from high to low doses. There are
important differences among species in uptake, metabolism, and
organ distribution of carcinogens, as well as species and strain
differences in target site susceptibility. Human populations are
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variable with respect to genetic constitution, diet, occupational
and home environment, activity patterns, and other cultural
factors.
Cancer slope or potency factors used in this assessment are
upper bound estimates of risk. Actual risks are not likely to be
higher than these estimates but could be considerably lover.
This is an important factor contributing to the conservative
nature of the risk assessment procedures. In addition, the
inhalation cancer slope or potency for chromium is based on
epidemiologic studies of individuals exposed in occupational
settings. Data are not currently available to determine if these
slope or potency factors provide reasonable estimates of cancer
risks associated with exposure under conditions considered in
this risk assessment.
4. Combined errors associated with the preceding factors:
Uncertainties from different sources may also be propagated
into larger uncertainties as a result of being combined in the
risk assessment. For example, if the chronic daily intake for a
contaminant measured in the environment is compared to a
reference dose to determine potential health hazard, the
uncertainties in the concentration measurement, exposure
assumptions, and toxicology will all be included in the result.
To ensure that human health is adequately protected, risk
assessors commonly incorporate conservative (unlikely to
underestimate risk) approaches and uncertainty factors in risk
assessments. Therefore, the actual risk posed by a site is
unlikely to be larger but may be significantly lover than that
predicted in the assessment.
V. Conclusion of Summary of Site Risks
As a result of the risk assessment prepared for the NCR
Millsboro site it was determined that an unacceptable risk is
presented from exposure to contaminated ground vater. The
carcinogenic risk under the future-use scenario exceeded the
upper bound limit of EPA's target risk range due to the potential
for ingestion of, and inhalation of vapors from ground vater
contaminated with volatile organic compounds. The hazard index
under the future-use scenario also exceeds 1.0, thus supporting
the conclusion that unacceptable health risks may be posed by
exposure to contaminated ground vater from this site.
In addition, it has been determined that a long term
exposure evaluation must be performed during the remedial design
phase to evaluate the potential risks to human health from air
emissions resulting from the operation of the air stripper. Air
emissions controls may be required in order to ensure that the
39
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VOC emissions from the air stripper stack will not exceed a 1E-06
(1.0 x 10~6) carcinogenic risk exposure to human health.
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 public health, welfare, or the environment.
7.0 DESCRIPTION OT ALTERNATIVES
The National Oil and Hazardous Substances Pollution
Contingency Plan (NCP), EPA's regulations governing the Superfund
Program, requires that the alternative chosen to clean up a
hazardous waste site meet several criteria. The alternative must
protect human health and the environment, be cost effective, and
meet the requirements of environmental regulations. Permanent
solutions to contamination problems should be developed wherever
possible. The solutions should reduce the volume, toxicity, or
mobility of the contaminants. Emphasis is also placed on
treating the wastes at the site, whenever this is possible, and
on applying innovative technologies to clean up the contaminants.
The FS evaluated a variety of technologies to see if they
were appropriate for addressing the contamination at this Site.
The technologies determined to be most appropriate were developed
into remedial alternatives. These alternatives are presented and
discussed below. All costs and implementation timeframes
provided for the alternatives below are estimates. However, the
cost summaries provided below do not include estimates for the
cost of performing surface water and sediment monitoring (common
to all alternatives); or estimates for the cost of providing air
emission controls and air monitoring (common to alternative GW-2
and GW-4). In addition, these summaries do not include costs
associated with predesign studies, or for costs associated with
updating the current well survey information.
COMMOH ELEMENTS* All of the alternatives being considered
include common components. The no action (GW-l) and limited
action (GW-1A) alternatives differ only in that GW-1A restricts
the use of ground water through the use of institutional
controls. Common components of alternatives GW-l and GW-lA are
as follow*:
o Increasing public awareness through public meetings,
presentations in local schools, press releases, posting
signs
o Conducting a well survey to identify the location of
all wells within a one-mile radius of the site in
order to update the previous survey performed
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o Continuing a quarterly ground water monitoring program
o Instituting,an annual surface water and sediment
monitoring program
Aside from the no action and limited action alternatives,
the three treatment alternatives presented vary only in the type
of treatment used to remove contaminants from the ground water.
Common components of the three treatment alternatives (GW-2, GW-3
and GW-4) are as follows:
o Extraction of ground water through the use of recovery
wells until clean up levels are achieved
o Treatment of the VOCs in ground water (method of VOC
treatment varies)
o A contingent provision for treatment of chromium in
ground water using a coagulation and filtration
treatment system, if determined necessary by EPA
to meet effluent limitations.
o A combined discharge of treated ground water to surface
water and/or onsite infiltration galleries
o Restriction of ground water use until clean up levels
are achieved
o Conducting a well survey to identify the location of
all wells within a one-mile radius of the site
o Continuing a quarterly ground water monitoring program
o Instituting an annual surface water and sediment
monitoring program
Chromium treatment is provided as a contingency based on the
limited number of wells onsite which have chromium concentrations
above the MCLs. These wells are believed to be within the cone
of influence of the present ground water recovery well which has
been in operation since July 1988. Analysis of the air stripper
effluent has consistently found chromium concentrations at or
below the MCLs. A study will be performed during the predesign
phase to determine if the chromium treatment is necessary in
order to meet the effluent discharge limitations.
Several remedial technologies were identified and are
presented as alternatives that address ground water contamination
at the NCR Millsboro site. Five alternatives were evaluated to
deal with the risks posed by current and/or future ground water
contamination. The remedial objectives are to address the source
41
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of ground water contamination onsite and to contain the migrating
ground water plume.
The following is'a brief summary of each of the alternatives
evaluated for the NCR Millsboro site:
Alternative OW-li Mo Action
Capital Cost: 0
Annual Operation and Maintenance (O&M) Costs: $144,000
Present Worth: $622,000
The NCP requires that the "no action" alternative be
evaluated at every site to establish a baseline for comparison
with the other alternatives. This alternative consists of the
following activities that can be used to address ground water
contamination when no remedial measures are implemented:
o Increasing public awareness through public meetings,
presentations in local schools, press releases, posting
signs
o Conducting a well survey to identify the location of
all wells within a one-mile radius of the site to
update the previous survey performed
o Continuing the quarterly ground water monitoring
program
o Instituting an annual surface water and sediment
monitoring program.
Capital costs for quarterly monitoring would not be incurred
since a quarterly monitoring program is already in existence and
monitoring wells have already been installed. The time required
to implement this remedy from the onset of the remedial action
phase would be approximately two weeks.
Alternative OW-lAt United Action
Capital Cost: $76,000
Annual Operation and Maintenance (O&M) Costs: $144,000
Present Worth Costs: $697,000.
This alternative varies slightly from the no action
alternative in that it provides for a certain level of protection
by restricting ground water use by using institutional controls,
such as establishing and enforcing a state ground water
management zone and implementing deed restrictions regarding the
installation of wells within this ground water management zone.
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This alternative consists of the following activities:
o. Increasing public awareness through public meetings,
presentations in local schools, press releases and
posting sighs
o Conducting a well survey to identify the location of
all wells within a one mile radius of the site, to
update the previous well survey performed.
o Restricting the use of contaminated ground water for
potable uses by establishing and enforcing a state
ground water management zone and implementing deed
restrictions regarding the installation of wells within
this ground water management zone
o Continuing a quarterly ground water monitoring program
o Instituting an annual surface water and sediment
monitoring program
Since the major elements for the above alternative, namely
drilling services, sampling equipment, and laboratory services
are readily available, this alternative should be easily
implementable.
Alternative QW»2t FUBPin
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clean up levels (MCLs and non-zero MCLGs) are achieved
o Continuing the quarterly ground water monitoring
program until the clean up levels (MCLs and non-zero
MCLGs) are achieved
o Instituting an annual surface water and sediment
monitoring program until the clean up levels (MCLs and
non-fcero MCLGs) are achieved
Alternative GW-2 would utilize the air stripper presently in
operation at the site to treat VOCs in ground water. Air
stripping is a process in which VOCs are removed from an aqueous
waste stream by passing air through the water. Air stripping is
usually accomplished using a packed column equipped with an air
blower. In a packed column, the water stream flows down through
the packing, while the air flows upward and is exhausted out the
top. The packing breaks up the water stream allowing flowing air
to mix with it and remove or strip off the VOCs. The use of the
air stripper would result in the release of VOCs, including TCE,
to ambient air through the stripper stack.
DNREC has performed a separate evaluation of the potential
risks due to emission from the currently operative air stripper
unit. In order to present a conservative or worst case value
DNREC used the highest level of TCE found in the ground water to
date as the concentration being treated by the air stripper unit.
This value was incorporated into a long term exposure evaluation
model in the risk calculation. The potential carcinogenic risk
through this route of exposure is 10"4. A long term exposure
evaluation will be performed during the remedial design phase to
evaluate the potential risk to human health from the air
emissions.
Presently it is unknown whether possible future emissions of
VOCs from the untreated air released from the air stripper stack
will exceed federal and state requirements for air emissions.
The site is located in an area which is presently classified as
an ozone attainment area. If it is determined that these
emissions do exceed either federal or state criteria or if the
classification of the area changes to an ozone non-attainment
area then appropriate air emission control equipment shall be
provided. In addition, air emissions controls will be provided
if it is determined that emissions from the air stripper stack
could result in an exposure to human health in excess of the
lower end of the EPA carcinogenic risk range of 1E-06
(1.0 x 10"6). The costs for such air emission controls are not
included in the estimated cost presented for this alternative and
for alternative GW-4 because such estimates will depend on
information gathered during the predesign and remedial design
phases.
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All the treatment .alternatives that are being discussed (GW-
2, GW-3, and Glf-4) include a contingency for treating chromium if
it is necessary to meet effluent limitations as determined by
EPA. The treatment of ground water to remove the levels of
chromium in order to meet discharge limitations would be done
using the reduction, coagulation, and filtration processes.
Reduction, coagulation and filtration are commonly used
processes for the removal of chromium from wastewater.
Hexavalent chromium is reduced to the less toxic trivalent
chromium using sulfur dioxide and ferrous sulfate. The trivalent
chromium is then precipitated from the aqueous phase using lime
treatment to create insoluble hydroxides which would be removed
by coagulation and aqueous filtration.
Coagulation involves a series of chemical and mechanical
operations. These operations customarily comprise two distinct
phases: mixing, wherein the dissolved coagulant is rapidly
dispersed throughout the water being treated, usually by violent
agitation; and flocculation, involving agitation of the water at
lower velocities for a longer period, during which small
particles grow and agglomerate into well-defined floes of
sufficient size to settle readily.
Filtration is an operation that separates suspended matter
from water by passing it through a porous material. These media
allow water to pass though, but particles are caught when they
collide with the filter media. Common filtration media include
sand, anthracites, diatomaceous earth, or finely woven fabric.
The filters must be backwashed periodically to remove the solids.
The solids which are removed from the filters must then be
disposed of properly according to the requirements of the
Resource Conservation and Recovery Act (RCRA). A pilot study
would be necessary to provide additional information on design,
construction, and operation and maintenance considerations prior
to implementation.
A phased approach is planned for implementation of this
alternative as veil as alternatives GW-3 and GW-4. The first
phase would entail the start of remediation where the highest
levels of VOCs (primarily TCE) have been detected near the former
process plant building and would concentrate on the area within
the former NCR property boundaries west of the Conrail tracks
(Figure 4). This alternative would provide for the installation
of additional recovery wells, at least one of which would be
located in the area of highest contamination or the source area
near the building. The exact number of additional extraction
wells will be determined in consultation with, and as approved
by, EPA during the predesign phase. Additional monitoring wells,
the number 'and location of which shall be approved by EPA, shall
be installed east of the Conrail tracks downgradient of the
source area to further evaluate the necessity for additional
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recovery wells-and/or- expansion of the pump and treat system, if
determined.necessary by EPA, as a result of information gathered
during the first phase of the work,- additional recovery wells
and/or an air stripper unit may be required to be installed for
remediation of the plume downgradient of the source area near the
building. In this respect the remedial action addresses the
contamination in the entire ground water plume. However, by
using a phased approach the ongoing evaluation of the
effectiveness of the remedial action shall provide information
which will then be used to determine the need for additional
monitoring and/or recovery wells. The treated ground water from
the first phase of remediation would be discharged to the surface
water of Iron Branch in compliance with the National Pollutant
Discharge Elimination System (NPDES) requirements of the Clean
Water Act (CWA); or to a ground water infiltration gallery
meeting the regulatory requirements of the Safe Drinking Water
Act (SDWA) Underground Injection Control (40 C.F.R. Parts 144,
145, 146, and 147). The ground water infiltration gallery would
attempt to use the treated water to recharge the aquifer and
flush the contaminated ground water towards the recovery wells to
hasten remediation. If an additional air stripper is required to
treat the ground water plume east of the Conrail tracks, the
treated ground water from this downgradient area would likely be
discharged to the surface water of Iron Branch. However, the
details of the discharge to surface water and/or the infiltration
gallery will be determined during the remedial predesign studies
and approved by EPA. This same phased approach would be used for
all the treatment alternatives; however, each would vary in the
type of treatment provided for VOCs. Treatment would continue
until the contaminants in the ground water are at or below the
MCLs or non-zero maximum contaminant level goals (MCLGs) as
determined by EPA.
A quarterly ground water monitoring program would remain in
effect during this remedial action to monitor both onsite and
offsite wells.
An annual surface water and sediment monitoring program
would also b« put into effect during this remedial action to
monitor Iron Branch.
The use of ground water would be restricted through
institutional controls as described in alternative GW-1A, until
the cleanup levels (MCLs and non-zero MCLGs) are achieved.
The recovery wells can be easily constructed onsite. In
addition, the air stripper needed for this alternative has
already been constructed as part of the interim response measure.
If another air stripper is necessary it would require
approximately six months to construct it. The reduction,
coagulation and filtration treatment unit for the chromium
contingency would take approximately six months to construct.
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Infiltration galleries are commonplace, simple in design, and
easy to construct.- This technology is reliable for handling the
discharge.of treated ground water. The additional recovery wells,
infiltration gallery, and surface water discharge piping would
require approximately six months to design and construct.
Filtration Contingency. Infiltration and/or ffflffflce Water
Discharge
Capital Cost: $1,188,000
Annual O&M Cost: $1,170,000
Present Worth Cost: $6,255,000
This alternative is similar to Alternative GW-2, except that
the treatment for VOCs would be provided by liquid phase carbon
adsorption. Carbon adsorption is used to treat single-phase,
aqueous organic waste materials with high molecular weights, high
boiling points and unsaturated chlorinated hydrocarbons such as
trichloroethylene, the principal contaminant at the site.
The chemistry of carbon is such that most organic compounds
will readily attach themselves to carbon atoms. Carbon used for
adsorption is usually treated to produce a product with a large
surface-to-volume ratio, thereby exposing a maximum number of
carbon atoms as active adsorption sites. Adsorption occurs when
an organic molecule is brought into contact with the surface of
the activated carbon and is held there by physical or chemical
forces.
Carbon adsorption is frequently accomplished using a fixed
bed or countercurrent moving beds. In a fixed bed carbon column,
the waste stream enters near the top of the column through an
influent distributor. The waste stream flows downward through the
carbon bed and exits through an underdrain system. When the head
loss becomes excessive from accumulated suspended solids, the
column is taken off-line and backwashed. The effluent from the
backwashing systea is recirculated through the system. Spent
activated carbon can be regenerated either thermally or by voc
extraction, VOCs are generally reclaimed.
Factors that influence the effectiveness of carbon
adsorption are the adsorptivity and solubility of the material;
the Ph and temperature of the waste stream; the nature of the
specific contaminant; and the raw materials and process used to
activate the carbon. In this alternative the contaminated ground
water from the proposed extraction wells would be piped to a
series of activated carbon units. TCE and other VOCs would be
adsorbed to the carbon. When monitoring indicated breakthrough of
contaminants in the first carbon adsorption unit, (i.e the carbon
material had exhausted its capacity to adsorb VOCs, and VOCs in
ground water were no longer being removed), the ground water
47
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would be redirected to a second unit and the carbon from the
first unit would be replaced and regenerated. Unlike Alternative
GW-2, there would not be any air emissions from the activated
carbon units on site.
Alternative GW-3 is readily implemented using existing
technologies. It would require approximately six to eight months
to implement this alternative following the completion of
remedial design.
This alternative also includes a contingency for providing
treatment for chromium removal by reduction, coagulation, and
infiltration as described in Alternative GW-2, if determined
necessary by EPA during the predesign phase in order to meet
effluent discharge limitations.
As described in GW-1A and GW-2, continued quarterly ground
water monitoring and initiation of annual monitoring of the
surface water and sediment of Iron Branch as well as restriction
of ground water use through institutional controls are all
components of GW-3 also.
This alternative shall proceed in a phased approach as
outlined in alternative GW-2; however, the treatment process for
removal of VOCs would be carbon adsorption. An additional carbon
adsorption unit may be required, as a result of the ongoing
evaluation of the effectiveness of the treatment to address the
contaminant plume downgradient of the source area. The cost
estimates reflect the installation of this additional carbon
adsorption unit as well as the installation of additional ground
water monitoring wells as determined necessary by EPA as a result
of the evaluation performed as part of the first phase of the
remedy.
Coagulation and Tiltration* Infiltration, and/ay p\|pface Water
Discharge
Capital Costs: $1,031,000
Annual O&M Cost: $ 859,000
Present Worth Cost: $4,749,000
In this alternative, treatment of VOC contamination shall be
provided by an air stripper followed by carbon adsorption of the
air stripper effluent.
In an attempt to reduce the levels of TCB in ground water
quickly, new recovery wells shall be installed in the area with
the highest levels of contamination. This could result in air
stripper influent concentrations which would exceed the design
capacity for the air stripper and, therefore, the air stripper
effluent may require additional treatment prior to discharge.
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This alternative provides for the use of the present air
stripper in association with a mobile carbon adsorption unit.
This mobile unit is not expected to be used throughout the life
of the remedial action but would Jae used during the initial
stages of remediation until the levels of vocs in the air
stripper effluent reach acceptable levels (MCLs and non-zero
MCLGs). In addition to providing treatment for the ground water
itself, air emissions from the air stripper will be regulated in
accordance with the State of Delaware Regulations Governing the
Control of Air Pollution and the U.S. EPA's policy on Control of
Air Emission From Superfund Air Strippers at Superfund Ground
Water Sites (OSWER Directive 9355.0-28, June 1989) and be
protective of human health and the environment.
As with alternative GW-2, this alternative will also result
in VOC emissions from the air stripper stack. The costs
summarized above do not reflect the costs for the additional
controls for these emissions nor the associated annual O&M costs.
If it is determined by EPA, that these emissions exceed either
the federal or state criteria, or will result in an exceedence of
a 1E-06 carcinogenic risk to human health, then appropriate air
emission control equipment shall be provided. Alternative GW-4
will also include a contingency for treating chromium if
necessary in order to meet the effluent limitations, as
determined by EPA, by using reduction, coagulation and filtration
as described under alternative GW-2.
A phased approach is also planned for the implementation of
this alternative. This phased approach has already been
described under alternative GW-2. Air stripping with the option
to use the mobile carbon adsorption unit will be initiated in the
most highly contaminated area near the building first;
concurrently additional monitoring wells will be installed
downgradient of this source area. These wells will be used to
evaluate the efficiency of the ongoing remediation as well as the
necessity for additional recovery wells and/or treatment units.
The treated ground water from the initial phase of remediation
would be discharged to surface water of Iron Branch in compliance
with the CWA NPDES program or to a ground water infiltration
gallery located onsite in accordance with the SDWA Underground
Injection Control program. Again, as described under alternative
GW-2 the treated ground water from the second phase of
remediation, if new air stripping units were to be installed,
would mainly be discharged to the surface water of Iron Branch.
The details regarding the discharge of extracted and treated
ground water would be approved by EPA during the predesign phase.
The cost estimates reflect the installation of an additional air
stripper and carbon adsorption unit and installation of
additional ground water wells which may be determined necessary
by EPA as a result of the evaluation performed as part of the
first phase of the remedy.
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This treatment- would continue until the contaminants in the
ground water are at or below the MCL or non-zero MCLG
requirements.
A well survey shall be conducted to determine the location
of all wells within a one mile radius of the site, in order to
update the previous well survey, and facilitate the ground water
monitoring program.
As in alternatives GW-lA, GW-2 and GW-3, a quarterly ground
water monitoring program would remain in effect during this
remedial action to monitor both onsite and offsite wells and an
annual surface water and sediment monitoring program would also
be initiated and performed throughout the remedial action to
monitor discharges to Iron Branch.
The use of ground water would be restricted through
institutional controls, as described in alternative GW-lA, until
the remediation clean up requirements as determined by EPA are
reached.
The technologies included in alternative GW-4 can be readily
implemented, as discussed in the analysis of alternatives GW-2
and GW-3. The time required to add the carbon adsorption system
to the existing treatment train would be approximately four weeks
following the completion of remedial design. The time to install
additional recovery wells and an infiltration gallery would be
six months. If an additional air stripper unit is necessary it
is estimated that 6 months would be required for the installation
following remedial design.
8.0 SUMMARY O> COMPARATIVE ANALYSIS!
The five remedial action alternatives described above were
compared against the nine evaluation criteria as set forth in the
NCP, 40 C.F.R. S 300.430(e) (9). These nine evaluation criteria
can be categorized into three groups: threshold criteria,
primary balancing criteria, and modifying criteria. The criteria
associated with each category are as follows:
A
Overall protection of human health and the environment
Compliance with applicable or relevant and appropriate
requirements (ARARS)
PRIMAR ^TCING CRITERIA
Long-term effectiveness
Reduction of toxicity, mobility, or volume through treatment
Short-term effectiveness
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Implementability -
Cost -
MODIFYING CRITERIA
Community acceptance
Support agency acceptance
These evaluation criteria relate directly to requirements in
Section 121 of CERCLA, 42 U.S.C. S 9621, which determine the
overall feasibility and acceptability of the remedy. Threshold
criteria must be satisfied in order for a remedy to be eligible
for selection. Primary balancing criteria are used to weigh
major trade-offs between remedies. Support agency and community
acceptance are modifying criteria formally taken into account
after public comment is received on the Proposed Plan.
The following discussion summarizes the evaluation of the
five remedial alternatives developed for the NCR Millsboro site
against the nine evaluation criteria.
A primary requirement of CERCLA is that the selected
remedial action be protective of human health and the
environment. A remedy is protective if it reduces current and
potential risks to acceptable levels under the established risk
range posed by each exposure pathway at the site.
Alternative GW-l (No Action) and Alternative GW-1A (Limited
Action) would not meet the site remediation goals, and do not
provide direct protection of human health and the environment.
Alternative GW-1A (Limited Action) would provide some level of
protection by using institutional controls to limit ground water
use. Although these alternatives (GW-l and GW-lA) would provide
information on chemical and physical fat* and transport of
contaminants by continued monitoring of the ground water, they
would do nothing to reduce contamination levels, which currently
exceed MCLs. These alternatives would allow for the further
migration of contamination, and would allow additional human
exposure. Since GW-l and GW-lA are not protective of human
health and the environment they will no longer be considered
viable options in the remainder of this section.
Although alternatives GW-2 (Air Stripping), GW-3 (Carbon
Adsorption), and GW-4 (Air Stripping and Mobile Carbon
Adsorption) would decrease the further offsite migration of
contaminated ground water by actively pumping the ground water
towards the recovery wells, manage the onsite contaminant plume,
and clean the ground water to site remediation standards, GW-4
provides the best overall protection of human health and the
environment. GW-4 provides for a mobile carbon adsorption unit
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to further reduce the VOC concentration in the ground water to
levels below which the presently designed air stripper alone
might not accomplish'.
Alternatives GW-2 and GW-4, however, treat VOC contamination
by using an air stripper which results in the generation and
release of VOCs emissions from the air stack. As previously
stated, the need for air emission controls shall be determined
during predesign. Controls shall be added to the air stripper as
necessary to ensure protection of human health and the
environment, and to meet all state and federal requirements
regarding air emissions.
Compliance with ARARs
Alternatives GW-3 (Carbon Adsorption) and GW-4 (Air
Stripping and Mobile Carbon Adsorption) would meet their
respective applicable or relevant and appropriate requirements
(ARARs) of federal and state environmental laws. They would
comply with state and federal requirements associated with ground
water monitoring (RCRA 40 C.F.R. 264.90-264.101), drinking water
standards (Safe Drinking Water Act MCLs- 40 C.F.R. 141.11-141.16
and MCLG 40 C.F.R. 141.50-141.$!, 50 FR 469-36) and State of
Delaware well construction requirements (7 Delaware Code Ch. 60).
These alternatives would also comply with state and federal
requirements pertaining to point source discharges to surface
water including effluent limitations (Clean Water Act 40 C.F.R.
Part 122), state water quality standards and federal ambient
water quality criteria.
Alternatives GW-3 and GW-4 would also comply with state and
federal requirements for underground injection control of treated
ground water [Safe Drinking Water Act (SDWA) as it applies to the
infiltration gallery: 40 C.F.R. Parts 144, 145, 146 and 147]. It
is unknown whether GW-2 (Air Stripper alone) would meet the
requirements for underground injection control. These levels are
usually set at MCLs. GW-2 may not meet this requirement due to
the possibility of high VOC concentrations in the air stripper
influent during the start-up or initial phase of remedial action.
Alternative* GW-2 and GW-4 would result in VOC emissions to
ambient air. A long tern exposure evaluation will be performed
during the remedial design to evaluate the potential risk to
human health and the environment from the air stripper emissions
and may require additional air emission controls to meet the
state and federal guidelines [Clean Air Act (CAA) National
Ambient Air Quality Standards 40 C.F.R. Part 50; CAA National
Emissions Standards for Hazardous Air Pollution, 40 C.F.R. Part
61; the RCRA Air Emission Standards 40 C.F.R. 264.1030 and
264.1050; the EPA policy for Control of Air Emissions from
Superfund Air Strippers at Superfund Ground Water Sites (OSWER
Directive 93.55.0-28 June 1989) and State of Delaware Regulations
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Governing the Control of Air Pollution] concerning air emissions
from air strippers. In addition, air emissions controls will be
required- in order to ensure the air emissions do not exceed a IE-
06 (l.OxlO"6) carcinogenic risk exposure or a Hazard Index of
greater than 1.0 for protection of human health.
Treatment residues generated as a result of providing
treatment under any of the three treatment alternatives would be
handled in accordance with the disposal requirements of RCRA (40
C.F.R. Part 261, Subpart C, including land disposal restrictions
contained in 40 C.F.R. Part 268).
Long-term effectiveness and permanence!
Alternatives GW-2 (Air Stripping), GW-3 (Carbon Adsorption),
and GW-4 (Air Stripping and Mobile Carbon Adsorption) would
equally reduce the mass of TCE in the aquifer. Each of these
three alternatives includes similar processes for pumping and
disposal of treated ground water and therefore provide the same
level of long-term effectiveness.
The coagulation and filtration treatment (common to GW-2,
GW-3 and GW-4), if necessary as determined by EPA, is a reliable
method for chromium removal. It is very possible that the use of
the coagulation and filtration option would not be required due
to the relatively low levels of chromium found in ground water to
date.
Alternatives GW-2 (Air Stripping), GW-3 (Carbon Adsorption),
and GW-4 (Air Stripping and Carbon Adsorption) would all reduce
the extent to_which the contaminants could migrate by actively
containing the*plume by pumping and then treating the
contaminated ground water. These alternatives also increase the
mobility, within the site boundaries, of the contaminants by
drawing toward the recovery wells.
Alternatives GW-2, GW-3, and GW-4 all work to reduce the
toxicity of the ground water by actively treating the ground
water and reducing the levels of contaminants in the treated
effluent.
Alternatives GW-2, GW-3, and GW-4 all actively remove VOCs
from ground water. However, GW-2 (Air Stripping) and GW-4 (Air
Stripping and Carbon Adsorption) reduce the volume or mass of
VOCs in ground water but allow for the contaminants to be
transferred to the ambient air. Controls for reducing the level
of air emissions to the atmosphere will be implemented if
necessary as determined by EPA. Alternative GW-3 (Carbon
Adsorption) and the additional use of carbon adsorption for the
portion of treated effluent from GW-4 (Air Stripping and Carbon
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Adsorption) nay ultimately destroy the VOCa through the
regeneration of activated carbon; however, the overall reduction
of contaminants depends on the mechanism chosen for regeneration
of the activated carbon. Contaminants may also be released to
the air during regeneration of activated carbon processes; these
releases, if any, would occur offsite.
The use of coagulation and filtration for chromium treatment
will reduce the levels of toxicity and mobility of chromium by
actively removing chromium from the ground water. The volume of
chromium would be reduced in the ground water; however, use of
this treatment system would produce a contaminated sludge which
would have to be disposed of as a hazardous waste.
Short-term Effectiveness
Implementation of any of the treatment alternatives would
result in a slight potential for exposure during installation of
wells and the infiltration gallery. Exposure to workers and
nearby residents through direct contact with and inhalation of
vapors from the contaminated ground water could also occur. In
addition, workers would be exposed to normal construction
hazards. These risks would be similar for alternatives GW-2,
GW-3, and GW-4. However, these risks could be mitigated by
following health and safety practices and standard construction
safety practices.
Alternatives GW-2, GW-3, and GW-4 allow for the potential
exposure to workers from sampling of monitoring wells; however,
this shall also be mitigated by following standard health and
safety protocols.
Implementabilitv
Alternatives GW-2 (Air Stripping) and GW-4 (Air Stripping
and Mobile Carbon Adsorption) could be easily implemented as an
air stripper unit and a recovery well are already in operation at
the site.
Alternatives GW-3 (Carbon Adsorption) and GW-4 (Air
Stripping and Mobile Carbon Adsorption) require the use of
activated carbon units; however, in GW-3 the carbon adsorption
unit will be. constructed and installed onsite; carbon adsorption
units are commercially available. Alternative GW-3 would require
the replacement of activated carbon approximately 15 times per
year and therefore requires a higher degree of maintenance than
GW-4. The carbon adsorption process employed under alternative
GW-4 would not likely be needed for the entire life of treatment
because it will be used as a polishing step after removal of VOCs
by air stripping. In addition, operation of the air stripper
does not require fulltime field presence, as would the carbon
adsorption in GW-3.
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Alternatives GW-2 (Air Stripping) , GW-3 (Carbon Adsorption)
and GW-4 (Air Stripping and Mobile Carbon Adsorption) all require
the installation of an infiltration gallery which would involve
standard construction practices.
The coagulation and filtration contingency treatment common
to alternatives GW-2, GW-3, and GW-4 would employ standard
processes used in the treatment of water and waste water. A
pilot study would be necessary to provide additional information
on design, construction and operation and maintenance
considerations prior to implementation. The onsite presence of a
trained operator would likely be required to implement this
contingency.
Cost
The present worth of GW-l (No Action) and GW-lA (Limited
Action) is $622,000 and $697,000 respectively, neither of these
alternatives employ any treatment activities. The present worth
of GW-2 (Air Stripping) is $4,256,000 including chromium
treatment contingency. The present worth of GW-3 (Carbon
Adsorption) is $6,255,000 including chromium treatment
contingency. The present worth cost of GW-4 (Air Stripping and
Mobile Carbon Adsorption) is $4,749,000 including chromium
treatment contingency. Therefore, GW-l has the lowest present
worth, followed by GW-lA, GW-2, GW-4 and GW-3.
Support Agency Acceptance
The State of Delaware acting as the support agency during
the issuance of the ROD concurs on the selected remedy, as
described in Section 9.0 of this ROD.
Acceptance
Comments received during the public comment period
concerning the various alternatives are summarized in the
Responsiveness Summary which is part of this ROD.
Q _ A
Based on the findings in the RI/PS and the nine criteria listed
above, the EPA has selected alternative GW-4 Pumping, Air
Stripping and Carbon Absorption, Coagulation and Filtration,
Infiltration and/or Surface Water Discharge as the selected
remedy for this site. This remedy consists of the following
major components:
• Extraction of contaminated ground water using.
additional recovery wells until clean up levels are
achieved
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• Treatment of- VOC contamination in ground water using an
air stripper followed by carbon adsorption of the air
stripper effluent until clean up levels (MCLs and non-
zero MCLGs) are achieved'
• A provision for chromium treatment using coagulation
and filtration, if determined necessary by EPA to
achieve effluent limitations
• A provision for air emission controls, if determined
necessary by EPA during predesign studies
• A combined discharge to surface water and/or onsite
ground water infiltration galleries
• Conducting a well survey to determine the location of
all wells within a one mile radius of the site, in
order to update the previous well survey
• Continuing quarterly monitoring of ground water until
the clean up levels (MCLs and non-zero MCLGs) are
achieved
• Instituting an annual monitoring program for surface
water and sediments of Iron Branch until the clean up
levels (MCLs and non-zero MCLGs) are achieved
• Institutional controls restricting ground water use
until clean up levels (MCLs and non-zero MCLGs) are
achieved throughout the entire ground water plume, by
establishing and enforcing a state ground water
management zone and property deed restrictions
regarding the installation of wells in the ground water
management zone
The selected remedy shall achieve the cleanup levels or
remedial action objectives by actively pumping and treating the
contaminated ground water. The selected remedy shall restrict
the use of the contaminated ground water as a drinking water
source until the cleanup levels (MCLs and non-zero MCLGs) are
met. The performance standards for the site are to achieve
levels no greater than the maximum contaminant levels (MCLs) and
non-zero maximum contaminant level goals (MCLGs). The point of
compliance shall be all points throughout the area of the ground
water contaminant plume.
The selected remedy includes provisions to treat the
effluent from the air stripper using carbon adsorption, if it is
determined necessary by EPA, to ensure compliance with effluent
limitations, ARARs and clean up levels. The mobile carbon
adsorption unit specified under the selected remedy shall
provide an additional polishing step to reduce VOC levels after
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air stripping to ensure compliance with ARARs; also, the mobile
unit can- also be removed when it is no longer needed.
The selected remedy shall, if determined necessary by EPA, also
provide for the addition of air emission controls in order to
meet the state and federal emissions requirements and to ensure
that emissions will not result in carcinogenic risk exposure of
greater than l.OE-06 or a hazard index greater than 1.0.
It is estimated that approximately 8,977,500 cubic feet of
aquifer contaminated with VOCs shall need to be remediated. The
FS provided an estimate of five years for this volume of
contaminated ground water to pass through the pump and treat
system. Therefore the costs presented in the FS and in this ROD
are based on five years for implementation of this remedy.
However, the time required to achieve the remedial action
objectives cannot be determined.
A phased approach is planned for the implementation of the
remedial action. The first phase would entail the start of
remediation where the highest levels of VOCs (primarily TCE) have
been detected (See Figure 4) near the former process plant
building. Concurrently, additional monitoring wells shall be
installed downgradient of the source area to further evaluate the
need for additional recovery wells and/or expansion of the pump
and treat system which shall be determined by EPA. In this
respect, the remedial action addresses the contamination in the
entire ground water plume. However by using the phased approach
treatment of ground water from additional onsite recovery wells
can begin quickly, while further predesign studies are conducted
to determine the optimum location for additional extraction wells
which might be needed to contain the entire plume. Once these
predesign studies are conducted, the additional extraction wells
and/or treatment facilities shall be designed and built. It is
possible that the results of these predesign studies shall
require the construction of an additional air stripper, or the
expansion of the existing air stripper and associated
treatment/discharge facilities.
The selected remedy includes a contingency for treating
chromium if necessary as determined by EPA to meet effluent
limitations. The, treatment of ground water to remove the levels
of chromium above the MCL shall be accomplished by using the
reduction, coagulation and filtration processes. The
determination to use this treatment option will be decided during
predesign studies in consultation with and as determined by EPA.
This remedial action shall restore ground water to its
beneficial use, which at this site, includes its use as a
potential drinking water source. Based on information obtained
during the remedial investigation and on a careful analysis of
all remedial alternatives, EPA believes that the selected remedy
will achieve the performance standards. It may become apparent,
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during implementation or operation of the ground water extraction
system and its*modifications, that contaminant levels have ceased
to decline.and are remaining constant at levels higher than the
remediation level goal over some portion of the contaminant
plume. In such a case, the system performance standards and/or
the remedy may be reevaluated by EPA.
The selected remedy shall include ground water extraction
and treatment for a minimum period of five years, throughout
which the system's performance shall be carefully monitored and
analyzed on a quarterly basis, and adjusted as warranted by the
performance data collected during the operation. The time to
achieve performance standards can not as yet be determined, but
the cost for the alternatives were calculated for five years.
Modifications, approved by EPA, to achieve performance
standards may include any or all of the following:
a) at individual wells where cleanup levels have been
attained, pumping may be discontinued;
b) alternating pumping at wells to eliminate stagnation
points;
c) pulse pumping to allow aquifer equilibration and to
allow adsorbed contaminants to partition into ground water; and
d) installation of additional extraction wells or treatment
units to facilitate or accelerate cleanup of the contaminant
plume.
According to the EPA's Evaluation of Ground Water Extraction
Remedies (EPA/540/2-89/054), studies have found that it takes
about seven yearns to achieve a steady state, but once a steady
state is achieved (i.e. the levels of contaminants in the ground
.water remain constant over a period of time), the ground water
will be monitored for an additional year and a half to ensure
that a steady state does exist and is not influenced by seasonal
differences. If the steady state does not meet the cleanup
levels established in this ROD, other alternatives will be
evaluated. If the other alternatives are not practicable or will
not be able to meet the established cleanup levels, then the
performance standards will need to be reevaluated.
As previously stated in this document, the cost summaries
are based on five years of remediation attributed to the
estimated time for the contaminated plume to pass through the
pump and treat system. The costs associated with this selected
remedy are outlined as follows: capital costs of $1,031,000;
annual operation and maintenance (O&M) costs of $859,000 and
present worth costs of $4,749,000. These estimates do not
include the costs for air emissions controls, if they are deemed
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necessary, nor do they include the cost associated with annual
monitoring of the surface water and sediment of iron Branch.
The above estimates do include the costs associated with
treatment of chromium in ground water, if it is determined
necessary by EPA during the predesign study. It should be
recognized that minor changes to the selected remedy may be made
by EPA.
s
10.0 STATUTORY DETBRMIMATIOM
EPA's primary responsibility at Superfund sites is to
undertake remedial actions to protect human health and the
environment. In addition, Section 121 of CERCLA, 42 U.S.C.
S9621, establishes several other statutory requirements and
preferences. These requirements specify that when complete, the
selected remedial action for each site must comply with
applicable or relevant and appropriate (ARARs) environmental
standards established under federal and state environmental laws
unless a statutory waiver is invoked. The selected remedy also
must be cost-effective and utilize treatment technologies or
resource recovery technologies to the maximum extent practicable.
Finally, the statute includes a preference for remedies that
permanently and significantly reduce the volume, toxicity or
mobility of hazardous wastes. The following sections discuss how
the selected remedy for this Site meets these statutory
requirements.
Protection of HTOUP Health and the Bnviropm^n^T 1
The selected remedy protects human health and the
environment by preventing further migration of the contaminated
ground water from the NCR Millsboro site, managing the
contaminant plume and cleaning the ground water to site
remediation, standards. The ongoing onsite and offsite ground
water monitoring program shall provide information on chemical
and physical fate and transport of contaminants. The selected
remedy shall strip the ground water to remove the VOCs. There
would be transfer of VOCs including TCE to the ambient air
through the stripper stack. However, air emission controls shall
be implemented as determined necessary by EPA. The treated
ground water shall either be discharged into the surface waters
of Iron Branch or to an infiltration gallery as determined during
the predesign study. The infiltration gallery shall use the
treated water to recharge the aquifer and flush the contaminated
ground water towards the recovery wells. The treatment or remedy
shall be implemented until the contaminants in the ground water
are at or below the MCLs or non-zero MCLGs, and is protective of
human health and the environment.
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Compliance with Applicable or Relevant and Appropriate
Requirements!
The selected remedy shall attain all action, location and
chemical specific applicable or relevant and appropriate
requirements for the site. The major federal and state ARARs
pertaining to the selected remedy are summarized below.
Action-Specific ARAB'S
I) Water
Clean Water Act's (33 U.S.C. Section 1251) (CWA) National
Pollutant Discharge Elimination System Requirements (enforceable
for all discharges into surface water; 40 C.F.R. Part 122).
Discharge standards are established to regulate the discharge
into navigable waters in order to restore and maintain the
chemical, physical, and biological integrity of the water.
Discharge limitations will be established prior to the start of
remedial actions and the discharge will be monitored to ensure
compliance with the limitations.
Delaware water quality standards (Stream Quality Standard
Section 10). Standards are established in order to regulate the
discharge into waters of the State in order to maintain the
integrity of the water. Discharge limitations for volatile
organic compounds and chromium will be established during the
design phase prior to start of remedial action and discharge will
be monitored to ensure compliance with the limitations.
Delaware Environmental Protection (Title 7, Delaware code,
Chapter 60, Section 6010 - Regulations Governing the Construction
of Water Wells. All wells will be installed and maintained
according to state procedures for permitting, construction, and
abandonment.
II) Air
Delaware Regulations Governing the Control of Air Pollution
(7 Delaware Code, Chapter 60, Section 6003) Regulation 2, Section
2.4, sets forth the requirement that a permit is necessary to
operate an air •tripper if emissions will exceed 2.5 Ibs./day.
If it is determined during the design phase that the air stripper
may exceed the 2.5 Ibs./day emission rate then the substantive
requirements of the regulation shall be met. In addition, the
emissions from the air stripper must meet the Ambient Air Quality
Standards set forth in Regulation 3 of 7 Delaware Code, Chapter
60, Section 6003.
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National Ambient-Air Quality Standards of the Clean Air Act
42 U.S.C. Section 7401 (40 C.F.R. Part 50). Provides air quality
standards for particulate matter and lead. Requirements shall be
adhered to during excavation of soils.
Ill) Hazardous Waste
The Solid Waste Disposal Act, commonly referred to as
the Resource Conservation and Recovery Act of 1976 as amended by
the Hazardous and Solid Waste Amendments of 1984 (RCRA). EPA
will determine whether the wastes generated from the mobile
carbon adsorption unit and/or the waste sludges generated from
the coagulation and filtration process for chromium treatment at
the site constitute "hazardous waste* as that term is used in 40
C.F.R. Part 261. If the wastes generated from the carbon
adsorption process and/or the coagulation and filtration process
are determined to be hazardous wastes, the requirements for land
disposal restrictions, process vent emissions, equipment leak
standards, surface impoundments, generating and transporting
waste under subtitle C of RCRA, as set forth below, shall be
complied with.
- standards Applicable to Generators of Hazardous Waste (40
C.F.R. Part 262)(7 Delaware Code, Chapter 63, Part 262.2).
Establishes standards for generators of hazardous wastes
including waste determination manifests, and pre-transport
requirements. This standard will pertain to wastes generated as
a result of chromium treatment and volatile organic contaminant
treatment.
- Standards Applicable to Transporters of Hazardous Waste
(40 C.F.R. Part 263)(7 Delaware Code, Chapter 63, Part 263).
Sets forth regulations for off-site transporters of hazardous
waste in the handling, transportation, and management of the
waste. This regulation will apply to any company contracted to
transport hazardous material from the site.
- Standards Applicable for Owners and Operators of Hazardous
Waste, Treatment, Storage, and Disposal Facilities (TSDF) (40
C.F.R. Part 264)(7 Delaware Code, Chapter 63, Part 264). Sets
forth regulations for owners of facilities for the treatment,
storage, and disposal of hazardous waste. This will apply to any
of the owners and operators of treatment, storage, or disposal
facilities where wastes generated at the site may be taken to.
-Process Vent Emissions (40 C.F.R. SS 264.1030-1033,
265.1032-1033) Process waste standards apply to waste management
units at CERCLA sites that include specific equipment that manage
hazardous waste with annual average total organics concentrations
of > lOppm by weight. This will apply to the use of the air
stripper. The total organic emissions must be reduced below 1.4
kg/h and 2.8 Mg/yr or installation of a control device that
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achieves 95% oyerall.reduction at the point of release will be
required. .
-Equipment Leak Standards (40 C.F.R. SS 264.1050-62,
265.1050-62) These standards apply to emissions from specified
sources at CERCLA sites where the equipment contains or contacts
hazardous waste with annual average total organics concentration
of > 10% by weight. This will apply to the operation of the air
stripping unit. All leaks must be located and repaired, and
control equipment and monitoring devices must be installed to
meet the design and operating requirements for closed vent
systems.
-Corrective Action program requirements in 40 C.F.R. Subpart
F Section 264.90-264.101 that address ground water monitoring
during remedial action where the disposal of RCRA hazardous
wastes occurs at an existing area of contamination. Monitoring
of ground water will occur in order to ensure that the clean up
levels (MCLs) are achieved.
- Surface impoundments (40 C.F.R. 264.220-264.249 Subpart
K)(7 Delaware Code, Chapter 63, Part 264). The use of existing
surface impoundments at a CERCLA site may require specific
retrofitting requirements, or a waiver or exemption must be
obtained from EPA if RCRA hazardous waste will be disposed of in
the units. The use of the existing concrete basins (lagoons) at
the site for temporary storage of the recovered ground water
during remedial action will meet these requirements, prior to use
of the existing basins (lagoons).
- Land Disposal Restrictions (40 C.F.R. Part 268.1-268.50).
Establishes that movement of excavated materials containing
hazardous waste to new locations and placement in or on land
would trigger land disposal restrictions. If soil and sediment
are moved during remedial action and are determined to be RCRA
wastes, the excavated material shall be properly disposed of or
treated as required by the regulations.
IV) OSHA
Occupational Safety and Health Administration (OSHA)
requirements for workers at remedial action sites (29 C.F.R. Part
1910.120). The regulation specifies the type of safety equipment
and procedures to be followed during site remediation. All
appropriate safety equipment will be onsite and appropriate
procedures will be followed during treatment activities.
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Clinical specific ARAB*
I) Water ---._-
Safe Drinking water Act (SDWA) as amended in 1986 (42 U.s.c.
S300(f)). Maximum Contaminant Levels (MCLs) and non-zero Maximum
Contaminant Levels Goals (MCLGs) contained in 40 C.F.R. Part 141
and 143. Provides standards for 30 toxic compounds/ including 14
compounds adopted as RCRA MCLs, for public drinking systems. The
MCLGs are non-enforceable health goals and are set at levels that
would result in no known or anticipated adverse health effects
with an adequate margin of safety. The MCL and non-zero MCLGs
are used to determine the levels to which ground water should be
remediated. During the predesign study EPA will determine which
MCLs and non-zero MCLGs for volatile organic compounds and
chromium must be met.
SDWA Underground Injection Control Program (UIC) (40 C.F.R.
Parts 144, 145, 146, 147). The UIC program regulates underground
injections into five designated classes of wells. The
construction, operation, or maintenance of an injection well must
not result in the contamination of an underground source of
drinking water at levels that violate MCLs or otherwise adversely
affect the health of persons. The discharge from the
infiltration gallery will meet the substantive requirements of
the UIC program which will be determined in coordination with the
state and federal UIC programs.
Delaware Regulations Governing Underground Injection control
(7 Delaware Code Ch. 60) shall be complied with as they relate to
the infiltration gallery.
Clean Water Act (33 U.S.C. S 1251) Federal Ambient Water
Quality Criteria (AWQC) (40 C.F.R. Part 122) Contaminant levels
regulated by AWQC are provided to protect human health from
exposure to unsafe drinking water, from consuming aquatic
organisms (primarily fish), and from fish consumption alone. The
promulgated values shall be compared to maximum contaminant
levels to determine volatile organic compounds (VOC) and chromium
treatment requirements prior to discharge into surface water.
Delaware Surface Water Quality Standards of February, 1990
(Section 9.3(a)(i) and 9.3(b)(i). Quality criteria are provided
to maintain surface water of satisfactory quality consistent with
public health and recreational purposes, the propagation and
protection of fish and aquatic life, and other beneficial uses of
water. The promulgated values for the volatile organic compounds
and chromium will be compared to determine treatment requirements
prior to discharge to surface water.
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II) Air '_..._-
Clean" Air Act (42 U.S.C. § 7401) - National Ambient Air
Quality Standards (40 C.F.R. Part 50). standards have been
established for several compounds. The promulgated values for
each compound specified during the predesign study would be
compared to maximum contaminant levels and the discharge to
ambient air would not exceed these promulgated values.
s
Location specifio ARARs
I) Water/Wetlands
Procedures for Implementing the Requirements of the Council
on Environmental Quality on the National Environmental Policy Act
(40 C.F.R. Part 6 Appendix A), EPA's policy for carrying out the
provisions of Executive Order 11990 (Protection of Wetlands). No
activity that adversely affects a wetland shall be permitted if a
practicable alternative that has less effect is available. If
there is no other practical alternative, impacts must be
mitigated. Impacts on wetlands have been considered during the
Feasibility Study and will continue to be evaluated during pre-
design and the design phases.
Delaware Wetlands Act of 1973 (Title 7, Chapter 66 Section
6607), revised June 29, 1984. This Act requires activities that
may adversely affect wetlands in Delaware to be permitted.
Permits must be approved by the county or municipality having
jurisdiction. The effects on local wetlands will continue to be
evaluated during the pre-design phase of remediation.
To Be Considered
I) Water
Ground Water Protection Strategy of 1984 (EPA 440/6-84-002).
Identifies ground water quality to be achieved during remedial
actions based on aquifer characteristics and use. The EPA
aquifer classification will be taken into consideration during
design and implementation of the treatment remedy.
EPA Policy for Ground Water Remediation at Superfund Sites
(Directive No. 9355.4-03). This policy recommends approaches to
ground water remediation using a pump and treat system. This
policy will be considered during the ongoing evaluation of the
remedial action.
II) Air
EPA Policy for Control of Air Emissions from Superfund Air
Strippers at Superfund Sites (Directive No. 9355.0-28). This
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policy establishes guidance on the control of air emissions from
air strippers used at Superfund sites for ground water treatment
and establishes procedures for implementation. This guidance
will be considered during design and implementation of the
treatment remedy.
Ill) Ecological
U.S. Endangered Species Act of 1973. Actions taken at the
NCR Millsboro site must not threaten endangered or threatened
species or its critical habitat (50 C.F.R. Section 402.01)
Cost .- Effectiveness
The estimated present worth cost for the selected remedy is
$4,749,000. The remedy is cost-effective in mitigating the risks
posed by the contaminants associated with the site, and meets all
other requirements of CERCLA. The selected remedy shall achieve
the remedial action objectives by actively pumping and treating
the contaminated ground water and.restricting use of the
contaminated ground water as a potable water source until
remedial action objectives are met. The selected remedy includes
provisions to provide a higher level of treatment for VOCs, if it
is deemed necessary by EPA, to ensure compliance with ARARs and
remediation goals.
utilisation of Permanent solutions and Alternative Treatment
Technologies to the Maximum Extent Practicable.
The selected remedy for the NCR Millsboro site utilizes
permanent solutions and treatment technologies to the maximum
extent practicable while providing the best balance among the
other evaluation criteria.
Preference for Treatment as a Principal Element
The selected remedy uses treatment to address the threats
posed by contaminants in the ground water at the site. This
preference is satisfied since treatment of VOCs in ground water
and the contingency for treatment of chromium in ground water are
the principal elements of the selected remedy.
Explanation of Significant Changes from the Proposed Plan
The Proposed Plan identifying EPA's and DNREC's preferred
alternative was released for public comment on May 24, 1991.
DNREC was the lead agency until the end of the public comment
period at which time EPA became the lead agency for issuing the
ROD and for future response actions. The Proposed Plan described
the alternatives studied in detail in the Feasibility Study. EPA
has reviewed all written and verbal comments submitted during the
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comment period and at the public meeting. No significant changes
to the remedy identified in the Proposed Plan were necessary as a
result of comments received during the public comment period.
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APPENDIX A
Responsiveness- Summary for the NCR Corporation (Millsboro Plant)
Superfund - Sit*
*
A public comment period was held from May 24, 1991 through
June 25, 1991 to receive comments from the public on the Remedial
Investigation and Feasibility Study Reports, the Proposed Plan
including EPA's and DNREC's preferred remedial alternative for
the NCR Corporation (Millsboro Plant) site (NCR Millsboro site or
site), and the remainder of the Administrative Record file.
A public meeting was held for the NCR Millsboro Site on June
20, 1991 at 7:00 pm at the Town Office Building at 322 Lincoln
Highway and Mitchell street in Millsboro, Delaware. The public
meeting was attended by DNREC and EPA staff, Potentially
Responsible Parties (PRPs) representatives, local officials, area
residents and property owners. The public meeting was preceded
by a briefing for public officials held at 3:00 pm at the same
location. The briefing was attended by DNREC and EPA staff, and
local public officials and representatives. The purpose of the
public meeting was to present and discuss the findings of the
RI/FS and to apprise meeting participants of EPA's and DNREC's
preferred remedial alternative for the NCR Millsboro site. The
meeting provided the opportunity for the public to ask questions
and express their opinions and concerns.
All verbal comments received during the public meeting and
those received in writing during the public comment period are
documented and summarized in this Responsiveness Summary. The
questions and comments are grouped into general categories
according to subject matter. Each question or comment is
followed by EPA's and DNREC's response.
I. Remedial Investigation and Interla Remedial Measure
A. around water
1. On* of the PRPs inquired if EPA and DNREC were aware of
the fact that trichloroethylene (TCE) was detected in a well
located on the agricultural land east of the Conrail tracks at
the site, and asked whether the remedial action proposed
addressed this contamination.
Response;
EPA and DNREC are aware of the TCE levels detected in well
24 located on the agricultural property adjacent to the former
NCR Corporation property and which is part of the NCR Millsboro
site. Levels of TCE above the maximum contaminant level (MCL)
have been detected during the RI/FS in this well. The objective
of the preferred remedial action alternative is to restore the
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ground water to its. beneficial use and to meet MCLs and non-zero
MCLGs throughout the entire ground water plume. The remedial
action as outlined in the Record of Decision will address this
contamination.
2. A local resident asked if there was any uptake of
contaminated ground water by crops on the agricultural land.
Response;
DNREC and EPA responded that to the best of their knowledge,
the contaminated ground water is not being used for irrigational
purposes on this property. In addition, the ground water level
in this area is located 10-20 feet below the surface and would
not be available for uptake by the root system of the crops or in
contact with the crops. DNREC stated that investigations
performed, not in conjunction with the NCR Millsboro site,
indicate that TCE has not been found in the plant material when
water contaminated with TCE was used for irrigation of crops.
However, these studies do indicate that TCE has been found in the
surface soil when water contaminated with TCE was used for
irrigation.
3. A local property owner inquired if the residents of the
Riveryiew residential community were in danger as a result of the
ground water contamination at the site.
Response:
A monitoring program (residential and monitoring wells) is
and shall continue to be in effect until the remedial action
goals are achieved. Monitoring data collected to date have not
detected contaminants above MCLs in the wells located in the
Riverview Community. Results of the Remedial Investigation
indicate that the ground water at the site generally discharges
to Iron Branch which acts as a hydraulic barrier between the
contaminant plume and the area of the aquifer used by the
residents of the- Riverview community as a source of potable
water. The residential and monitoring wells will continue to be
sampled, and if a problem occurs the community would be notified
and appropriate action would be taken at that time.
4. A local elected official asked for assurance that the
community, apart from those who use public water sources, will be
protected froa the ground water contamination posed by the NCR
Corporation (Millsboro Plant) site.
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Response:
The remedy selected is protective of human health and the
environment. As mentioned above, the quarterly ground water
monitoring program shall remain in effect until the remedial
action objectives (compliance with MCLs and non-zero MCLGs) have
been reached. If a problem or contamination is detected, the
community will be informed and appropriate action shall be taken
at that time. ^In addition, institutional controls outlined in
the Record of Decision shall be enforced to restrict the use of
contaminated ground water.
B. Surface Water
5. Several questions were asked by a local resident
pertaining to the extent of surface water contamination in Iron
Branch and surface water in the vicinity of the NCR Corporation
(Millsboro Plant) site.
Response;
The Remedial Investigation indicated that the contaminated
ground water generally discharges to Iron Branch. Iron Branch is
located north and northeast of the former NCR Corporation
property, and Whartons Branch is located south and southeast of
the site. Iron Branch and Whartons Branch converge northeast of
the former NCR Corp. property and flow northeast to the Indian
River. The details of the surface water and sediment sampling of
Iron Branch and Whartons Branch can be found in the Remedial
Investigation Report (pp. 4-36 through 4-60) and in the stream
Sediment Quality Investigation Report (August 1988) and
Supplemental Sediment Quality Investigation Report (December
1989) located in the Administrative Record file for the site.
Levels of TCB have been detected, during the Remedial
Investigation, in the surface water of Iron Branch; however, not
above the ambient water quality criteria. In general, the
sampling data indicated that levels of TCE decrease downstream as
the surface water flows toward* Indian River. At the Public
Meeting, DNRBC emphasized that TCE in the surface water is
generally released to the air very rapidly.
Levels; of hexavalent chromium have been detected above EPA's
and Delaware's Hater Quality Criteria for Protection of Aquatic
Life, but these values are questionable due to the fact that
total chromium values from these surface water samplings were
less than those of the hexavalent chromium values. Total
chromium analytical values are generally higher than the
hexavalent chromium values since the total chromium analytical
test also detects hexavalent chromium and the values for
hexavalent chromium would be incorporated into the concentration
value reported for total chromium. The hexavalent chromium
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values which were higher than the total chromium concentrations
may be due to -interferences by other constituents in the sample
which were-interpreted as hexavalent chromium as a result of the
analytical method used.
The results of sediment sampling indicate that chromium
(hexavalent and total) concentrations do not constitute a toxic
problem to the biological life associated with this site based on
statistical analysis of the levels of chromium detected in the
stream during the Remedial Investigation.
The last sampling event of Iron Branch occurred in 1989,
during the Remedial Investigation. Since the discharge of
contaminated ground water to Iron Branch is ongoing, EPA and
DNREC emphasized that annual monitoring of the surface water and
sediments of Iron Branch shall be performed as a part of the
selected remedy in order to ensure that the remedy is protective
of human health and the environment.
6. A PRP questioned the necessity for continued monitoring
of Iron Branch.
Response:
EPA and DNREC agreed that the results of the Remedial
Investigation indicate that contaminants in the ground water
migrating from the site do not currently present a toxicity
problem; however, contaminated ground water continues to
discharge to Iron Branch. Therefore, monitoring shall be
performed to ensure that the remedy is protective of human health
and the environment*
c. interim Remedial Measure
7. A commenter asked if there has been a significant
decrease in the level of TCE since the air stripper and recovery
well have been in operation.
Responsei
Review by EPA and DNREC of the data from the quarterly
ground water monitoring and ground water sampling performed since
the air stripper has been in operation indicate a reduction from
approximately 310,000 parts per billion (ppb) in 1988 to
approximately 160,000 ppb in 1990 in well point six (WP-6).
Thus, it appears that the recovery well which is in place has had
a positive effect on reducing the levels of TCE in the ground
water.
8. One local resident inquired if the present air stripper
and recovery well are controlling the plume migration.
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Response!
Quarterly evaluation reports of the effectiveness of the
recovery well and air stripper unit, prepared as part of the
Remedial/Investigation indicate that the majority of the plume
source is being contained by the pumping and extraction of ground
water through the recovery well. Ground water generally
discharges to the Iron Branch; quarterly sampling of monitoring
and domestic wells indicates that the plume has not migrated to
the Riverview Community downgradient of the site. The quarterly
ground water monitoring program shall continue to evaluate the
effectiveness of the present air stripping process.
D. Air Emissions
9. A local resident requested a) information on air
monitoring data collected to date, and; b) information on how the
EPA and DNREC would determine if air emission controls were
necessary for the air stripper unit(s).
Response;
a) Limited air monitoring data is available from the
Remedial Investigation. This data is presented in Section 5.5 of
the Remedial Investigation report which is available in the
Administrative Record file located at the repositories. Air
monitoring data has not been collected directly from the
emissions from the air stripper; however, an estimate of air
emissions has been calculated by evaluating the air stripper
influent and effluent data in association with the air stripper
efficiency (Gaussian dispersion equation) to determine the
estimated rate of volatile organic compound emissions. These
calculated values indicate that the present operating air
stripper is in compliance with the nonpromulgated requirements of
the DNREC air permit program which states that the emission
source must not result in the exceedence of 1% of the American
Conference of Governmental Industrial Hygienists (ACGIH)
threshold limit value (TLV) for TCE (50ppm) at the property line
or must not result in an exceedence of O.Sppm. EPA shall require
additional air modeling in order to ensure that the air emissions
from the air stripper are protective of human health.
b) EPA shall require a long term exposure evaluation in
order to estimate the potential carcinogenic and non-carcinogenic
risks posed by air emission from the operation of the air
stripper. Risk calculations shall be performed during predesign
studies to ensure that emission controls shall be designed and
constructed, if necessary. Air emission controls shall be
required if the risk calculations indicate a potential
carcinogenic risk of greater than 1E-06 (lxlO~6) and/or a hazard
index greater than 1.0, which represents the lower end of the EPA
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risk rang* identified in the National Oil and Hazardous
Substances Pollution Contingency Plan (NCP). EPA asserts that by
limiting the emissions to a 1E-06 carcinogenic risk and/ or a
hazard index of 1.0, the selected remedy is protective of human
health. The exposure model used to evaluate these risks shall to
the extent possible consider air emissions contributed by nearby
surrounding sources in order to calculate the total exposure
risks to the public.
B. Underground storage Tanks (U8T)
10. The PRPs asked several questions regarding the existence
of underground storage tanks (USTs) at the site, and if they will
be addressed as part of this remedial action.
Response:
There is no evidence indicating that the existing USTs are a
source of the contamination addressed by the selected remedial
action. Therefore, the UST requirements are not considered
applicable or relevant and appropriate requirements (ARARs) to
the selected remedy. However, DNREC has determined that the
tanks are currently in violation of the Delaware Regulations
Governing Underground Storage Tank Systems and must be addressed
accordingly. Therefore the issue of the USTs will be initially
deferred to Delaware's UST Program and dealt with according to
their regulations and will not be addressed in this Record of
Decision.
F. Risk Assessment
11. A PRP stated that the risk assessment for the site does
not address the risks associated with children swimming in Iron
Branch.
Responses
The risk assessment performed for the NCR Corporation
(Millsboro Plant) site did consider swimming in Iron Branch a
potential exposure route. However, it was excluded from further
consideration based on the following: (1) The segment of Iron
Branch in the vicinity of the site has not been known to be used
for recreational swimming or fishing; (2) it is located in a
swampy area not readily accessible; (3) the shallow and brackish
water, is not an attractive swimming habitat. Therefore, the
frequency and duration of exposure to surface water by direct
contact was considered negligible and not addressed further in
the risk assessment (Refer to P. 7-31 of the Remedial
Investigation Report).
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II. Preferred Remedial Action Alternative
A. Air Emissions
12. A local resident and one of the PRPs stated that they
prefer alternative GW-3 which would utilize a liquid phase carbon
adsorption treatment unit for treatment of volatile organic
compounds (VOCs), and would not require a discharge to ambient
air. A PRP was concerned that the preferred alternative may
result in air emissions which exceed a 1.0 x 10"4 (1E-04) risk
exposure to humans especially those nearby workers and residents.
Response;
EPA continues to believe and DNREC agrees, that the
selection of alternative GW-4 (Air Stripping with carbon
adsorption) as opposed to alternative GW-3 (Carbon Adsorption) is
the best alternative for the site based on the findings of the
RI/FS and evaluation against the nine criteria listed in the NCP.
Alternatives GW-3 and GW-4 basically meet all the requirements of
the evaluation criteria, as described in the Record of Decision
(ROD). However, as stated in the Record of Decision alternative
GW-4 (air stripping and mobile carbon adsorption) is preferred
for the following reasons:
• It is readily implemented as one stripper is already in
place and operational at the site
• Use of the air stripper at the site, has
already proven to be successful in reducing the levels
of VOCs in the ground water
• It is nor* cost effective than alternative GW-3
Alternative GW-3 requires the replacement of activated
carbon approximately 15 times per year, and therefore requires a
high level of maintenance. The saturated activated carbon must
be regenerated and may generate hazardous waste that must be
disposed of in accordance with the Resource Conservation and
Recovery Act (RCRA) requirements. Alternative GW-4 also requires
the use of activated carbon, but much less carbon will be
required sine* it will only be used as a secondary treatment step
in alternative GW-4.
EPA would not select an alternative which was not protective of
human health and the environment. The selected remedy (GW-4)
requires that emission control units be constructed if they are
determined- to be necessary by EPA during predesign studies. Air
emissions from the air stripper(s) will meet all the state and
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federal emissions requirements in addition to not exceeding a 1E-
06 (l.OxlO"6) carcinogenic risk value or a hazard index greater
than l.a in order to be protective of human health and the
environment. A long term exposure'model will be utilized during
the predesign study in order to evaluate the potential exposure
to human health from the air stripper treatment unit(s).
13. A PRP argued that the assumption that high levels of
TCE in the airsstripper influent will be sustained may be an
unnecessarily conservative approach to use during air modeling to
determine if air emission controls are necessary. The PRP does
not believe it is appropriate to use the highest concentration of
TCE detected in ground water to date in the calculations to
determine the risk associated with air emissions. This approach
had been used by DNREC to perform an initial screening to
estimate the potential exposure due to operation of the air
stripper.
Response:
EPA and DNREC stated on several occasions, as documented in
the Administrative Record file for the site, .that a long term
exposure model is necessary to evaluate the potential exposure to
humans due to air emissions from the air stripping unit(s). EPA
and DNREC have agreed to utilize this model in order to gather
more information during predesign studies so that the model is
more representative of the actual exposure scenario. The exact
components of the model shall be determined in the predesign
phase. EPA, acting pursuant to the NCP, will use the lower end
of the risk range (i.e., 10~6) as the "point of departure", in
making a decision on the requirement for air emission controls
for protection of human health .
B. Clean up levels
14. A PRP expressed concern that the clean up levels or
standards were not adequately defined in the Proposed Remedial
Action Plan.
The clean up levels are clearly defined in the Record of
Decision for the site. The clean up levels for the VOCs and
chromium in the ground water plume are defined as maximum
contaminant levels (MCLs) and non-zero maximum contaminant level
goals (MCLGs), to be achieved throughout the ground water plume.
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c. Infiltration Gallery
15. A PRP stated that it was unclear in the Proposed
Remedial Action Plan that the reason that Alternative GW-2 may
not comply with the applicable or relevant and appropriate
requirements (ARARS) is due to the possible noncompliance with
the underground injection control program requirements as they
relate to the infiltration gallery.
Response!
It is clearly indicated in the Record of Decision that the
reason EPA does not know whether the alternative GW-2 would
comply with ARARS is due to the underground injection control
program. The treated ground water will be discharged to surface
water and ground water. The ground water discharge will be
through the use of infiltration galleries to help facilitate the
flow of contaminated ground water towards the recovery wells.
EPA believes that as a result of the high levels of volatile
organic compounds in the air stripper influent during the initial
start-up of the air stripper system the treated ground water
discharged from the air stripper may not meet the levels
established by the underground injection control program for such
discharges.
D. Phased Approach to Remedial Design/Remedial Action
16. One of the PRPs stated that the ROD should indicate the
flexibility and ongoing evaluation of the remedial action to
allow for modifications to the remedy to achieve clean up levels
in accordance~t*ith the NCP, and that the Proposed Remedial Action
Plan did not adequately define the scope of this ongoing
evaluation and remediation.
Response;
EPA has further defined the phased approach to be used
during remediation of the site in the Record of Decision (ROD).
This phased approach has been summarized in section 7.0 under
alternative GW-2 and section 9.0 of the ROD.
B. costs
17. A PRP commented that the Proposed Remedial Action Plan
does not clearly define the elements of cost for each alternative
nor all the activities to be initiated at the site.
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Response;
Both the Proposed Remedial Action Plan and the ROD present
the estimated costs for each alternative. The estimated costs
presented in the documents reflect the cost associated with
remediation of contaminants throughout the ground water plume.
The estimates include the cost associated with the phased
approach for remediation by including cost estimates for
additional monitoring wells for the area of plume downgradient of
the source area and the costs associated with constructing and
implementing additional treatment units to address this
downgradient contamination. The cost estimates presented are
based on a five year period for implementation of the remedial
action. However, EPA cannot accurately predict how long
remediation will take. The cost estimates do not reflect the
cost associated with annual monitoring of surface water and
sediment. Also not reflected in the estimated costs, are the
design, construction, and annual operation and maintenance costs
for air emission controls, if they are determined necessary
during the predesign study.
Further details on the costs can be found in Section 4.0 of
the Feasibility study (FS) and the FS addendum in the
Administrative Record file.
18. A local resident asked who will fund this clean up
action and if NCR Corporation would still remain liable for the
clean up or remediation.
Response;
NCR Corporation explained that they had made a commitment
several years ago to do whatever was required to clean up the
site, and indicated that NCR Corporation and DNREC currently have
a consent order which includes remediation of the site. EPA was
not a party to that Consent Order and EPA explained that after
the ROD issuance, Special Notice letters are issued to PRPs for a
site, granting them the opportunity to perform the Remedial
Design/Remedial Action (RD/RA). If EPA and the PRPs do not reach
a settlement, EPA considers its other options, including
enforcement or performing the clean up using Superfund monies.
Also see answer to number 20 below. EPA is investigating other
PRPs and will continue their efforts to identify other PRPs under
CERCLA who night also be liable for performing and financing the
Remedial Design/Remedial Action.
r. institutional controls
19. A PRP asked if the institutional controls referenced in
the Proposed Remedial Action Plan referred to placing
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restrictions on ground water as a drinking source or if some
other type of Institutional controls were included.
Response;
Institutional controls will encompass the restriction of
ground water use not only for drinking but for agricultural and
commercial use also. A ground water management zone (GMZ) will
be established at the state level within the area of the site and
the adjacent potentially effected areas. The GMZ will restrict
the installation of wells within this designated area. Property
deed restrictions would also be established in order to ensure a
means by which to enforce the restriction of well installation
within the GMZ.
a. Schedule for Implementation and Remediation
20. Several local residents asked when the remedial action
would start and how long it would take to achieve the clean up
levels.
Response!
EPA explained that a Record of Decision (ROD) for the site
would follow after the close of the public comment period. EPA
shall issue Special Notice Letters to the currently known
Potentially Responsible Parties. The Special Notice Letters
trigger a sixty (60) day moratorium period on response activities
at the site. Section 122(e) of CERCLA, 42 U.S.C. S 9622(e).
During the sixty-day moratorium the PRPs are invited to
participate in formal negotiations for a settlement to conduct or
finance the response activities required at the site. The sixty-
day negotiation period will be extended for an additional sixty
days if the PRPs provide a good faith offer. If the PRPs and EPA
reach a settlement it must be embodied in a Consent Decree. If
negotiations fail, EPA will determine whether to issue a
Unilateral Order against the PRPs or to conduct the RD/RA and
afterward* seek cost recovery of monies spent. Once an agreement
or decision has been reached regarding the terms under which the
RD/RA will be conducted a predesign study work plan and
subsequent design work plans and design documents would be
submitted to EPA. These documents must be developed, reviewed,
revised if necessary, and approved by EPA prior to submittal of
the final remedial action work plan. The final remedial action
work plan must be approved prior to any construction onsite. EPA
estimates it may take 18-20 months before construction would
begin. It is presently unknown how long remediation to clean up
levels will take; however, the air stripper and recovery well
which are presently operating will continue to operate during the
entire period during which remedial design is underway. The
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quarterly ground water monitoring program presently in operation
shall continue-to be-in effect.
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5ENT BY: DIM Of Oir/uasts M9mt9: a- 1-91 9:44OM ; 13023234561-» 21539'?~i=a;» 3
STATC OF DELAWARE
OtPARTMtNT OF NATURAL RESOURCES
ft ENVIRONMENTAL CONTROL
8* Kmct H>C»W»T
»o sex i4ot
^ OOVM. OILAWA4C 1 0*03 TKLdWOMft (308) 73C . 44OS
9(C»CTAftV r*«.
12 July 1991
Mr. Edwia B. Brlckaon
IU|ien«l Ateiniitrator
U.S. I.?. A l«gl
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