United States
Environmental Protection
Agency
Office of
Emergency and
Remedial Response
EPA/ROO/R09-90/048
September 1630
&EPA
Superfund
Record of Decision
Stringfellow, CA
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50272 101
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REPORT DOCUMENTA T10N I I. REPORT NO. I ~ ~ ~8 Ac--'«In No.
PAGE EPA/ROD/R09-90/048
... TIlle end ..... I. ....... D*
SUPERFUND RECORD OF DECISION 09/30/90
Stringfellow, CA ..
Fourth Remedial Action
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The Stringfellow site is an inactive hazardous waste disposal facility in Riverside
County, California, approximately 50 miles east of Los Angeles. The site is divided
into four zones: the onsite/upper mid-canyon area, which includes a l7-acre, inactive
industrial. disposal area in the southern portion of the Jurupa Mountains (Zone 1); the
mid-canyon area (Zone 2); the lower canyon area (Zone 3); and the community of Glen Avon
(Zone 4). From 1956 to 1972, approximately 34 million gallons of industrial waste from
metal finishing, electroplating, and DDT production were dispos~d of in unlined
evaporation ponds located throughout Zone 1. Some of the wastes from these ponds
migrated into the ground water system and were transported 2 miles downgradient (under
Zones 2 and 3) to form a ground water plume beneath the Glen Avon community (Zone 4) .
Between 1975 and 1980, the State removed approximately 6.5 million gallons of
unspecified liquid waste and DDT-contaminated material from the site. In 1980, EPA
removed approximately 10 million gallons of contaminated water, reinforced containment
barriers, and improved a truck loading area. Further removal actions included
installing french drain system fences; removal of all remaining surface liquids;
partially neutralizing and capping the wastes; installing a gravel drain network,
(See Attached Page)
17. Doc\Im8nI An8IpIa L De8crIpt-
Record of Decisio~ - Stringfellow, CA
Fourth Remedial Action
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Key Contaminants: VO(:s (TCE)
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EPA/ROD/R09-90/048
Stringfellow, CA
Fourth Remedial Action
Abstract (continued)
monitoring wells, and surface channels: and constructing a surface barrier and leachate
collection system downgradient from the original evaporation ponds. In 1983, the first
Record of Decision (ROD) provided an interim remedial measure and addressed additional
fencing of the site and implemented erosion control and offsite disposal of the extracted
leachate. In 1984, a second ROD addressed construction of an onsite pretreatment plant
for contaminated ground water, and the third ROD in 1987, specified installation of a
ground water extraction system in the lower canyon area (Zone 3), as well as surface
channels to direct surface water runoff. This fourth ROD addresses the contaminated
ground water in Zone 1 (an interim measure) and in Zone 4, and proposes treatability
studies to remediate the source material in Zone 1. A future ROD will specify the source
treatment methods as well as a remedy for any remaining ground water contamination in
Zone 1. The primary contaminants of concern affecting the ground water include VOCs such
as TCE.
The selected remedial action for this site includes dewatering the bedrock in the
original disposal area (Zone 1), followed by ground water treatment at the existing
pretreatment plant, and offsite discharge to a publicly owned treatment works (POTW)
facility: ground water pumping and treatment using air stripping or granular activated
carbon, and reverse osmosis in Zone 4, followed by onsite reinjection or disposal in an
industrial sewer; conducting field tests on reinjection of treated ground water into
Zones 2 and 3: and performing treatability tests on soil vapor extraction at Zone 1. The
estimated present worth cost of this remedial action is $115,000,000, which includes
unspecified O&M costs.
PERFORMANCE STANDARDS OR GOALS: No remediation goals have been determined in this ROD
for Zone 1 ground water contamination, because this is an interim measure.
Chemical-specific goals for ground water in Zone 4 include TCE 5.0 ug/l (SDWA MCLs).
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RECORD OF DECISION DECLARATION
SITE NAME AND LOCATION
Stringfellow Hazardous Waste Site
Riverside County, California
STATEMENT OF BASIS AND PURPOSE
This decision document for the Stringfellow site in
Riverside County, California selects certain interim remedial
actions, which have been chosen in accordance with the
Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA), 42 U.S.C. §§ 9601 e£. sea.. as amended by the
Superfund Amendments and Reauthorization Act of 1986 (SARA), and
the National Contingency Plan, 40 C.F.R. Part 300. The decisions
in this ROD are based upon the contents of the administrative
record for the Stringfellow site.
The State of California, while given the opportunity to
concur upon the remedy selected in this Record of Decision,
remains silent.
ASSESSMENT OF THE SITE
Actual or threatened releases of hazardous substances from
this site, if not addressed by implementing the response actions
selected in this ROD, may present an imminent and substantial
endangerment to public health, welfare and the environment.
DESCRIPTION OF THE REMEDY
This is the fourth interim action ROD for the site. The
first ROD involved initial abatement activities including
fencing, erosion control, interim source control, and off-site
hauling and disposal of contaminated liquids. The second ROD
involved construction of an on-site pretreatment plant to treat
contaminated groundwater. The third ROD involved installation of
a groundwater barrier system in the lower canyon and installation
of peripheral surface channels to direct upgradient surface water
runoff. This fourth interim action ROD addresses the groundwater
pathway in Zone 1 (the original disposal area) and Zone 4 (the
Community) by selecting actions that mitigate further degradation
of groundwater at the disposal source and downgradient. The
major components of the selected remedies include:
— Dewatering of the original disposal area, Zone i; using a
system of extraction wells, followed by treatment of the
extracted water at the existing mid-canyon pretreatment
plant and disposal to a POTW for further treatment; and
— Installation of a groundwater extraction system in the
community to extract and treat contaminated groundwater that
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has migrated downgradient to Zone 4, followed by reinjectio^
of the treated water.
In addition, a field test of soil-vapor extraction will be
performed to determine the technology's implementability,
effectiveness, and costs for removal of volatile organic
compounds (VOCs) from Zone 1 soils. Field studies on reinjection
of treated groundwater into Zone 2 and 3 also will be pursued.
STATUTORY DETERMINATIONS
The selected remedy is protective of human health and the
environment, complies with federal or state requirements that are
legally applicable or relevant and appropriate to the remedial
action, and is cost effective. This remedy utilizes permanent
solutions and 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.
LO
DANIEL wv MCGOVERN A^ Date
Regional Administrator
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1990 RECORD OF DECISION
DECISION SUMMARY
STRINGFELLOW HAZARDOUS WASTE SITE
SITE LOCATION AND DESCRIPTION
The Stringfellow Hazardous Waste Site (also referred to as
"site," "Stringfellow," or "Stringfellow site") is located in
Riverside County, California, approximately 50 miles east of Los
Angeles (Figure l). The original disposal area is located at the
head of Pyrite Canyon in the southern portion of the Jurupa Moun-
tains. The plume of contaminated groundwater, extending ap-
proximately 2 miles south of U.S. Highway 60 into the community
of Glen Avon, is located within the Glen Avon Basin aquifer,
which in the past served as a source of drinking and agricultural
water. At present, the Glen Avon Basin aquifer does not serve as
a primary source of drinking water for local residents.
The remedial actions selected in this Record of Decision
(ROD) address the pathway of primary concern to public health,
exposure to contaminated groundwater. These measures offer an
opportunity to reduce site-related risk and prevent further
degradation of downgradient groundwater.
For purposes of organizing remedial investigation/feasiblity
study (RI/FS) information, the site, including its contaminated
plume of groundwater, has been divided into four geographic zones
(Figure 2).
The term "on-site" used to describe Zone l is in reference
to the zone as the orginal disposal area, and not to the defini-
tion of "on-site" in the National Contingency Plan (NCP). The
MCP defines on-site as the "areal extent of contamination and all
suitable areas in very close proximity to the contamination
necessary for implementation of the response action." 40 C.F.R.
section 300.5; 55 Fed. Reg. 8817 (3/8/90). Using the NCP defini-
tion, the entire plume of contamination, and therefore all zones,
is considered "on-site." Pursuant to CERCLA section I21(e), no
federal, state or local permit is required for any remedial ac-
tion conducted entirely on-site as long as the actions are taken
within the zone and the substantive portions or the ARAR are ad-
dressed.
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Zone l: Qn-site/Upper Mid-Canvon Area
Zone l includes the original 17-acre disposal area in the
northern part of Pyrite Canyon, southward to approximately 600
feet below the subsurface barrier. There is no residential or
commercial population in this zone. Zone 1 groundwater is con-
taminated with a large number of organic and inorganic con-
taminants, including heavy metals.
Zone 2; Mid-Canvon Area
Zone 2 encompasses the portion of Pyrite Canyon that extends
from the southern edge of Zone l to the existing mid-canyon ex-
traction wells. Zone 2 has no residential population and limited
commercial use as a rock quarry. Zone 2 groundwater is
moderately to heavily contaminated. The contaminants of concern
are primarily soluble, volatile organics, and soluble inorganics.
Moving southward through Zone 2, the groundwater contains rapidly
decreasing to neglible amounts of heavy metals.
Zone 3: Lower Canvon Area
Zone 3 extends from the mid-canyon extraction wells down to
the lower canyon extraction system, north of U.S. Highway 60.
There are no private residences in Zone 3, although two active T
businesses are located within the zone. Zone 3 groundwater is
low to moderately contaminated. The contaminants of concern are
soluble, volatile organics, and soluble inorganics.
Zone 4; Community of Glen Avon Area
Zone 4 includes the area south of Highway 60 to the leading
edge of the plume of site-related contaminated groundwater, ap-
proximately 12,000 feet from Zone 1. The affected area is popu-
lated with a number of private residences. The contaminants of
concern in the groundwater in this zone are relatively low levels
of a small number of soluble, volatile organics, and soluble in-
organics. At present, the Glen Avon Basin aquifer (within which
the Stringfellow plume lies) does not serve as a primary source
of drinking water for local residents.
SITE HISTORY AND ENFORCEMENT ACTIVITIES
The site was operated by the Stringfellow Quarry company
from August 21, 1956, to November 19, 1972, as a state authorized
hazardous waste disposal facility. Approximately 34 million gal-
lons of industrial wastes (primarily from metal finishing,
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electroplating and DDT production) were placed in unlined
evaporation ponds located throughout the 17-acre disposal area.
Some of these wastes migrated downward, entered the groundwater,
and moved various distances downgradient. The site was volun-
tarily closed in 1972.
Removal Activities
In 1975, after declaring the site a public nuisance, the
California Regional Water Quality Control Board (RWQCB) began
studies to evaluate alternatives for abatement of the risks posed
by the site. Between 1975 and 1980, the RWQCB developed reports,
conducted a controlled release of contaminants to Pyrite Creek
after heavy rains, and removed approximately 6.5 million gallons
of liquid wastes and DDT contaminated material.
In 1980, federal involvement was initiated at Stringfellow
after an inspection by the U.S. Environmental Protection Agency
(EPA) and the U.S. Coast Guard (USCG). The EPA Regional Response
Team (RRT) and the USCG Strike Team, using EPA funds, assisted
the RWQCB in mitigating the threat of a catastrophic discharge of
contaminated water. This response resulted in the removal of ap-
proximately 10 million gallons of contaminated water, reinforce-
ment of containment barriers, and improvements to the truck load-
ing area. Other activities completed by the RRT and USCG after
1980 include installation of a french drain, spring box, sumps,
and fencing, and improvements to surface drainage.
In 1980, the RWQCB adopted an Interim Abatement Program
(IAP) to further address the site. The IAP was designed to con-
tain the wastes and minimize the risk of further contaminant
migration. The program included the removal of all surface li-
quids; partial neutralization and capping of the wastes; instal-
lation of a gravel drain network, interceptor wells, monitoring
veils, and surface channels; and construction of a clay core sub-
surface barrier and leachate collection system downgradient of
the original evaporation ponds.
In 1981, the California Department of Health Services (DHS)
became the lead state agency for Stringfellow-related cleanup,
although the RWQCB continued its involvement at the site.
The Stringfellow site was placed on the Environmental Protection
Agency's (EPA) National Priorities List in 1983.
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Interim Remedial Measures
On July 22, 1983, EPA signed its first Record of Decision
(ROD) selecting certain interim remedial measures (IRM) and al-
lowing the state to be reimbursed for the earlier abatement ac-
tions taken by the RWQCB. Among other actions, the IRM included
additional fencing of the site, erosion control, and hauling and
off-site disposal of extracted leachate. The IRM were undertaken
primarily by DHS using EPA funding under a cooperative agreement.
DBS began receiving such funding in 1983.
Fast-Track Remedial Investigation/Feasibility Study
EPA conducted a fast-track remedial
investigation/feasibility study (RI/FS) between September 1983
and May 1984. Based primarily upon the fast-track RI/FS, a
second ROD was issued by EPA on July 18, 1984. The ROD selected,
as an interim measure, the construction and operation and main-
tenance of a mid-canyon extraction well system and pretreatment
plant to remove and treat contaminated groundwater.
The pretreatment system consists of lime precipitation for
metals removal, followed by granular activated carbon treatment
for removal of the organic contaminants. Under a discharge per-
mit from the Santa Ana Watershed Project Authority (SAWPA), the
treated effluent is currently trucked to a local industrial sewer
line, the Santa Ana Regional Interceptor (SARI). The effluent
then receives additional treatment at a publicly-owned treatment
works (POTW) in Orange County. Sludge generated from the
pretreatment process is dewatered and taken to an EPA-approved
land disposal facility.
Although DHS holds the discharge permit from SAWPA, EPA has
entered into an interagency agreement with the U.S. Army Corps of
Engineers (the Corps) for field oversight of the pretreatment
plant. The Corps, in turn, uses a contractor to operate and
maintain the pretreatment plant.
The pretreatment plant's influent, treatment process, and
effluent are monitored extensively to ensure quality performance.
Since start-up operations, the plant has consistently met the
stringent requirements of SAWPA's discharge permit. As of Decem-
ber, 1989, over 30 million gallons of contaminated groundwater
have been treated at the plant, and approximately 15,000 pounds
of metals and 135,000 pounds of organics have been removed.
Pretreatment plant operations are ongoing.
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Full-Scale Remedial Investigation/Feasibility Study (RI/FS)
With funding provided by EPA under the cooperative agree-
ment, DHS procured a contractor to conduct a full-scale RI/FS for
the Stringfellow site. The RI/FS was initiated in 1984 to
characterize the site and to identify and evaluate alternatives
for final site cleanup. The FS assessed 86 potentially ap-
plicable technologies. Certain of these technologies have been
combined into five remedial alternatives (RAs). Detailed evalua-
tion of the five alternatives was performed, as were a number of
treatability studies. Although a majority of the work on the
RI/FS has been completed, work is still ongoing, including addi-
tional soil treatability studies (see "Highlights of Community
Participation").
The draft RI report was released to the public in June,
1987, followed by the draft FS report in June 1988. Public meet-
ings on the draft FS report were held in September 1988.
Alternate Water Supply
Analysis of water samples taken during site investigations
detected radiation. In response, DHS sampled private drinking
water supply wells in the site area. Although the elevated
levels of radioactivity were later determined to be naturally oc-
curing and not related to the contamination at the site, in the
summer of 1984, in response primarily to continued concern with
drinking water quality, DHS initiated an interim program to
provide bottled water to nearly 400 Glen Avon residences.
Bottled water was supplied to give anyone in identified areas of
elevated groundwater radioactivity an alternate supply of domes-
tic water, and to eliminate any domestic dependence on
groundwater near the potential influence of contamination from
the Stringfellow site. In October 1985, California Senate Bill
1063 provided State funds to hook up residences, which had been
receiving State supplied bottled water, to the Jurupa Community
Services District. The connections began in June 1986, and were
completed in 1989.
Earlv Implementation Actions
Based upon the ongoing remedial alternative (RA) evaluation
in the full-scale RI/FS, additional interim remedial activities
were selected in a third ROD issued by EPA on June 24, 1987.
These additional actions included: l) the installation of a
•groundwater extraction system in the lower canyon area (Zone 3)
with treatment of the extracted groundwater at the existing
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pretreatment plant; 2) the installation of surface channels
around the north end of the original disposal area in Zone l; 3)
the southward extension of the existing eastern and western sur-
face channels; and 4) the reconstruction of the Pyrite Creek
channel.
Using cooperative agreement funding, DHS procured contrac-
tors to design these actions, and to construct the surface chan-
nels around the north end of the orginal disposal area and the
southward extension of the existing surface channels. DHS' con-
tractors completed the design in 1988 and the construction of the
channels in 1990. A number of potentially responsible parties
(PRPs), through an Administrative Order on Consent (AOC), in-
stalled the extraction system and reconstructed the Pyrite Creek
channel (see "Federal Enforcement," below).
Federal Enforcement
In August and October 1982, EPA issued to over 200 poten-
tially responsible parties (PRPs), General Notice and Demand let-
ters, combined with information requests, under sections 104 and
113 of the federal Comprehensive Environmental Response, Compen-
sation, and Liability Act (CERCLA). The governments' negotiators
held an initial meeting with the PRPs in November 1982, follower'
by a number of settlement meetings. An acceptable settlement
agreement was not reached.
On April 21, 1983, the United States and the State of
California filed a civil suit in the United States District Court
for the Central District of California (U.S. v. J.B. Stringfel-
low. Jr.. et. al.. Civil Number 83-2501 JMI (C.D. Cal.)).
Eighteen generators, four transporters, and nine owner/operators
were named as defendants in the lawsuit. On June 4, 1987, the
District Court granted the government's motion for partial sum-
mary judgment against fifteen of the defendants on the issue of
liability under section 107 of CERCLA. A sixteenth defendant
recently has been added to the judgment. A case management order
divides the litigation into three phases: 1) liability, 2)
0remedy/damages, and 3) cost allocation. Litigation is ongoing.
To facilitate legal discussions with the governments, fol-
lowing suit initiation, the defendants formed a steering com-
mittee. A technical subcommittee was also formed and meets with
EPA and DHS technical staff approximately once every quarter to
exchange technical information. The community's technical ad-
visor is invited to these meetings. Local and other state
government representatives are also invited depending on the
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agenda covered by the technical discussions.
In Ma'y 1988, sixteen of the defendants agreed, in an Ad-
ministrative Order on Consent (AOC), to construct certain of the
interim actions that were selected in the third ROD issued by EPA
on June 24, 1987. The AOC did not include the design and opera-
tion and maintenance of the groundwater extraction system, the
installation of the northern channels or the southward extension
of the existing channels. Rather, using cooperative agreement
funding, DHS' contractors completed the design and constructed
the channels. Operation and maintenance of the pretreatment
plant resides with EPA.
Proposed Remediation Plans
Community Groundwater Proposed Plan
In June 1988, EPA and DHS released a Proposed Plan to ad-
dress site-related groundwater contamination in the community of
Glen Avon (Community Groundwater Proposed Plan). The Plan
proposed to extract, treat (through air stripping and reverse
osmosis), and reinject the treated groundwater. The public had
an opportunity to comment on the Community Groundwater Proposed
Plan from June to November 1988. Two public meetings addressing
the Plan were held in September 1988.
Overall Proposed Plan
At one of the public meetings in September 1988, Riverside
Representative George Brown held an open congressional hearing on
the Stringfellow site. At the hearing, the Agencies' agreed to
conduct additional soil treatability studies before maJcing a
decision on the final remedy for Zone 1. Testimony by members of
the community and the U.S. Office of Technology Assessment
reflected the belief that certain soil treatment technologies
should be further evaluated because of possible technical
developments since the issuance of the draft FS report.
In response to the hearing and to public input, EPA and DHS
developed a new remedial alternative, RA6. consequently in
February 1989, the Agencies released for public comment a second
plan (Overall Proposed Plan) proposing to implement RA6. EPA and
DHS also released a fact sheet in April 1989 reflecting recalcu-
lated estimated groundwater flow in the community area (Zone 4).
The April fact sheet described the revised estimated cost com-
parisons and cleanup times for the Community Groundwater Proposed
Plan, and for the RAs considered in the draft FS report.
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The., proposed remedy, RA6 , of the Overall Proposed Plan in-
cluded, for Zones 2-4, the long-term continuation of
downgradient plume management activities. For Zone 1, the Plan
proposed to dewater the area, use soil-gas extraction
(hereinafter referred to as "soil-vapor extraction," or "SVE")
for removal of volatile organic compounds (VOCs) if tests proved
favorable, complete additional soil treatability studies, and in
stall an improved cap.
HIGHLIGHTS OF COMMUNITY PARTICIPATION
The community of Glen Avon has been kept actively informed
of the cleanup progress and actions taken at the Stringfellow
site. One of the primary means of keeping the public informed
has been through the DHS publication of the "Stringfellow
Update." Updates have been published approximately every other
month since late 1984, and are mailed to. over 3,000 Glen Avon
residents and interested parties. The Community Groundwater
Proposed Plan was released through the June/July 1988
"Stringfellow Update," and the Overall Proposed Plan through the
February/March 1989 "Stringfellow Update."
C Comment Periods
EPA and DHS sought public comment on the draft RI/FS repor,.
and on the two proposed plans. The comment period for the draft
RI report began in June etnd ended in October 1987. The public
had an opportunity to comment on the draft FS report and Com-
munity Groundwater Proposed Plan from June through November 1988
The comment periods for the Overall Proposed Plan and the April
fact sheet began in March 1989, and April 1989, respectively.
The comment period for both documents closed in June 1989.
c Meetings
Public meetings and workshops have been held in and near
Glen Avon to present cleanup information and to receive input
from the public. Public meetings on the draft FS report and Com-
munity Groundwater Proposed Plan were held in Riverside and
Orange Counties in September 1988. A public meeting on the Over-
all Proposed Plan was held in Riverside County in March 1989.
In addition to public meetings, the Stringfellow Advisory
Committee (SAC) --- an amalgum of community, government, and
private interests --- meets once a month to discuss cleanup
progress at the site, and the remedial activities being pursued
by EPA and DHS. The SAC is comprised of a community leader,
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elected representatives, local officials, and EPA and DHS staff
and management. SAC meetings are open to the public.
community Input: ROD
Public comment, in various forums, indicated the community's
strong belief that the final remedial decision for Zone 1 should
be deferred until after the completion of additional soil
treatability studies. Nevertheless, pending the studies, the
community supported the issuance of a separate ROD to address
the cleanup of the groundwater underlying the Glen Avon area
(Zone 4), and the dewatering and soil-vapor extraction actions in
Zone l .
The Agencies agreed with the suggestions provided by the
community, and have adopted its strategy as reflected in this ROD
(see "Scope and Role of Response Actions of This ROD"). The
final remedial decisions on the long-term plume management, and
the final response actions for Zone 1, will be addressed in a
subsequent ROD, following completion of the RI/FS, including the
additional soil treatability studies.
Community Input; Significant/Episodic Storm and Seismic Events
In response to community concerns regarding flooding and
possible exposure to contaminants via the surface water pathway,
EPA and DHS are evaluating the potential effect
significant/episodic storm or seismic events may have on the
site's engineered structures and downgradient community. After a
conceptual plan for the analysis was presented to the public for
comment in March 1990, the Agencies' proposed a detailed analyti-
cal approach and again sought public comment. EPA and DHS will
share their written analyses for discussion with the SAC.
Communit Input: Additional Soil Treat ii.v Studies
Following the Agencies' agreement ~o conduct additional soil
treatability studies for Zone 1, EPA and DHS prepared discussion
papers on the purpose and objectives of the studies. EPA's Of-
fice of Research and Development (ORD) is providing technical ex-
pertise and analysis to assist the. Agencies in determining the
implementability , costs, long-term and short-term effectiveness,
and reduction in contaminant toxicity, mobility, and volume (TMV)
of the soil technologies being considered. The information
gained from these treatability studies, along with the alterna-
tives currently in the draft FS report, will be evaluated by EPA
and DHS (using the nine superfund criteria described under
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"Summary of Comparative Analysis") in making the final remedial
decision for the Zone 1 area. The treatability studies process
is currently under discussion between EPA, DHS, and the com-
munity.
Information Repositories
Documents issued for public comment, such as the draft RI/FS
reports, proposed plans, and other information relevant to the
Stringfellow site remediation and decision-making process are
routinely transmitted to and made available for inspection at a
number of information repositories located in Riverside and
Orange Counties. The Administrative Record for this ROD will be
located at EPA's offices in San Francisco, DHS' offices in
Sacramento, and the Glen Avon Branch Library.
Responsiveness Summary
During public comment periods and associated public meet-
ings, residents, elected officials, community organizations, the
community technical advisor, and the PRPs submitted comments on
the draft RI report, draft FS report, and two proposed plans.
The attached responsiveness summary responds to those comments
relevant to the remedial decisions selected in this ROD.
SCOPE AND ROLE OF RESPONSE ACTIONS IN THIS ROD
The primary pathway of concern for the response actions
selected in this ROD is groundwater. As described in the Com-
munity Groundwater Proposed Plan, the ROD incorporates the deci-
sion to remediate the site-related contaminated plume of
groundwater in the community area (Zone 4). In addition, the ROD
selects two source control measures for Zone 1 identified in the
Overall Proposed Plan: l) dewatering, and 2) field testing of
soil-vapor extraction (SVE). These interim response actions are
limited in scope, and after the RI/FS and additional soil
treatability studies are completed, will be followed by selection
of the final site remedy. Accordingly, while the Agencies have
identified certain contaminant-specific remediation goals in this
ROD, cleanup levels for the site as a whole cannot be finalized
until the long-term plume management of the zones is decided.
The response actions selected for Zone 4 in this ROD are, there-
fore, interim decisions, although the Agencies do not envision
any additional selection of cleanup technologies for this zone.
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SUMMARY OF SITE CHARACTERISTICS
This section summarizes information in the draft RI report
that is relevant to the remedial actions considered in this ROD.
During operation of the Stringfellow site, liquid wastes
were placed in unlined ponds located throughout the 17-acre dis-
posal area. Some of the wastes migrated downward, entered the
groundwater, mixed with clean groundwater, and moved various dis-
tances dovmgradient, depending upon the chemical and physical in-
teractions with the geologic units.
Groundwater contamination extends from Zone 1 into the com-
munity of Glen Avon, Zone 4, as shown in Figure 3. The leading
edge of the contaminant plume is defined by the presence of
trichloroethylene (TCE) in groundwater, and is approximately
11,000 to 12,000 feet south-southwest of Zone l at the intersec-
tion of Agate Street and Jurupa Road in Glen Avon. The plume
width in the Glen Avon area is up to 900 feet.
Zone l
The soil/fill material in Zone 1 is contaminated with a
variety of chemicals, including chlorinated solvents, pesticides,
PCBs, heavy metals, acidic materials, and volatile and semi-
volatile organic pollutants. The predominant organic contaminant
identified in Zone 1 soils is para-chlorobenzene sulfonic acid
(p-CBSA), a by-product of DDT manufacturing. Volatile organics
(e.g., TCE and chloroform) constitute less than l percent of the
soil contaminant mass. Metals such as nickel, chromium, and cad-
mium are present. Sulfates are also found in high concentra-
tions.
The inorganic and organic contaminants which have migrated
from the soils into the groundwater in this zone, and which con-
stitute the greatest percentage of the contamination, are the
sulfates and p-CBSA, respectively. Eased on available informa-
tion and studies, p-CBSA is not considered to be toxic to human
health. Sulfates can be harmful in high concentrations. Metals,
such as cadmium, chromium, and nickel, and VOCs, such as
chlorobenzene, chloroform, and trichloroethylene are also found
in the Zone l groundwater. The VOCs constitute less than 1 per-
cent of the dissolved organic carbon in the groundwater, but many
individual components exceed federal/state drinking water levels.
Mean concentrations of at least eight inorganic constituents and
nine organic constituents exceed federal maximum contaminant
levels (MCLs), secondary maximum contaminant levels (SMCLs),
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maximum contaminant level goals (MCLGs), or adjusted ambient
water quality criteria (AWQC): cadmium, chromium, copper,
fluoride, iron, manganese, nitrate, zinc, chlorobenzene,
chloroform, l ,2-dichlorobenzene, l,4-dichlorobenzene, 1,2-
dichloroethylene, l,1,2,2-trichloroethane, tetrachloroethylene,
trichloroethylene, and xylene.
Groundwater contamination is prevalent in all three
groundwater strata (alluvium, decomposed granite, and bedrock) in
Zone 1.
Zone 4
The draft RI report found that in Zone 4, the only site-
related organic groundwater contaminant that exceeds federal max-
imum contaminant levels (MCLs) for drinking water is TCE. The
federal MCL is 5 ug/1. TCE, as measured in 1985 and 1986 and
reported in the draft RI report, reached as high as 436 ug/1 in
this zone. At the plume's leading edge (Agate and Jurupa
Streets) TCE was detected at less than the MCL.
Chloroform is also found in excess of health-based levels.
In the absence of a federal MCL specific to chloroform, the
Agencies are looking to the concentration, 6.0 ug/1, associated
with an excess cancer risk of 10~6 as the level that is protec-
tive of human health. This concentration coincides with the
State of California's Action Level. Chloroform concentrations as
measured in 1985 and 1986 and reported in the draft RI report,
reached as high as 32 ug/1 in the Zone 4 plume.
Other dissolved organic contaminants measured above back-
ground in Zone 4 include chlorobenzene, l,2-dichlorobenzene, and
p-CBSA. With respect to the first two contaminants, the levels
found in the groundwater are lower than proposed federal MCLs
(the proposed MCL for chlorobenzene is .1 mg/1 and for 1,2
dichlorobenze is .6 mg/1). There are no standards or guidelines
for p-CBSA, but as discussed earlier, p-C3SA has not been deter-
mined to be toxic to human health.
With respect to inorganic compounds, the findings of the RI
indicate that there is no heavy metal contamination in Zone 4
groundwater. As pH increases, heavy metals in the groundwater
precipitate from solution or react with aquifer materials ap-
proximately 1,000 feet downgradient of the subsurface barrier in
Zone 1. The inorganic contaminants found in the downgradient
zones are sulfates and nitrates. Within the plume of con-
taminated groundwater, concentrations of these contaminants are
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as much as 4 to 5 times higher than within the surrounding
aquifer. Plume concentrations of nitrates and sulfates exceed
the federal MCL and proposed MCL, respectively, with respect to
nitrates, currently available data indicate that anthropogenic
background levels in the community area also are elevated and
exceed the federal MCL.
The contaminants in Zone 4 are predominantly confined to the
alluvium (uppermost) groundwater stratum. Groundwater contamina-
tion underlying the community can be described three dimen-
sionally as a relatively narrow plume, increasing from ap-
proximately 300 to as much as 900 feet wide, and extending to as
deep as 100 feet below the surface. TCE contamination has
migrated 11,000 to 12,000 feet southwest of Zone 1, and is
migrating at an approximate effective rate of 250 feet per year
(assuming that groundwater and its dissolved TCE are moving at
the same rate).
Zone 4 is highly populated, and contains private residences
with operable water wells. Few private wells have been found to
be contaminated, and none are presently used for drinking water.
SUMMARY OF SITE RISKS
The baseline risk assessment conducted as part of the RI ex-
amined human ingestion of contaminated groundwater and surface
water, ingestion of contaminated soil, and inhalation of airborne
contaminated soil particles and volatile compounds. Because this
ROD focuses on remedial actions affecting the groundwater path-
way, the risk assessment findings 'for this pathway alone are sum-
marized.
Groundwater Pathway
The findings of the RI risk assessment indicate that the ex-
posure pathway of primary concern is the potential human exposure
to contaminated groundwater. As discussed earlier, the
groundwater beneath Zone 1 is contaminated with a large number of
soluble organic and inorganic contaminants, including heavy met-
als. Moving southward along the plume to Zone 2, the groundwater
is moderately to heavily contaminated with soluble, volatile or-
ganics and soluble inorganics. In this zone, the heavy metals
begin to rapidly decrease and become neglible before entering
Zone 3. The Zone 3 groundwater is minimally to moderately con-
taminated with soluble, volatile organics, principally TCE and
chloroform, and soluble, inorganics, principally nitrates and
sulfates. At the downgradient end of the plume in Zone 4, the
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concentrations of the carcinogenic compounds (principally TCE and
chloroform), and of the inorganic compounds (principally nitrates
and sulfates) have significantly decreased from Zone 1.
Contaminants of Concern
TCE and chloroform were selected as the basis for the public
health evaluation of the groundwater exposure pathway because
they are the only carcinogenic chemicals found above federal MCLs
or health-based levels in the community plume, and thus presented
the greatest human exposure risk.
Exposure Assessment
The Stringfellow plume of contaminated groundwater lies
within the Glen Avon Basin aquifer. The aquifer is not currently
used as a drinking water supply for local residents. However, it
is considered to a be a potential source of drinking water and is
located within a groundwater subbasin (Chino III) with Class I
characteristics.
Toxicity Assessment and Health Effects
TCE has a relatively low acute toxicity, but exposure to
high doses can cause central nervous system depression, long-ter^
neurological effects, dermatitis, and peripheral neuropathy. TCE
is a probable human carcinogen and a proven animal carcinogen.
Chloroform can cause nausea, dizziness, and acute central nervous
system depression, as well as chronic liver and kidney damage.
This substance has been listed as a probable human carcinogen by
EPA.
Cancer potency factors have been developed by EPA's Car-
cinogenic Assessment Group for estimating the excess lifetime
cancer risks associated with exposure to potentially carcinogenic
chemicals. The cancer potency factor, expressed in units of
(mg/kg/day) , is multiplied by the average intake of a potential
carcinogen to provide an estimate of the upper bound lifetime ex-
cess cancer risk associated with exposure at that intake level.
The term "upper bound" reflects the conservative nature of the
risks calculated from the cancer potency factor, which are un-
likely to underestimate the actual cancer risk. The cancer
potency factors are derived from the results of human
epidemiological studies or chronic animal bioassays to which un-
certainty factors have been added. The cancer potency factor for
TCE is l.l x 10~2 (mg/kg/day) . The cancer potency factor for
chloroform is 8.1 x 10~z (mg/kg/day) .
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The toxicity of nitrate in humans is due to the body's
reduction of nitrate to nitrite. This reaction takes place in
saliva of humans at all ages and in the gastrointestinal tract of
infants during the first three months of life. The toxicity of
nitrite is demonstrated by vasodilatory/cardiovascular effects at
high dose levels and methemoglobinemia at lower dose levels.
Methemoglobinemia is an effect in which hemoglobin is oxidized to
methemoglobin resulting in asphyxia. Infants up to 3 months of
age are the most susceptible subpopulation with regard to
nitrate. 50 Fed. Reg. 46973 (November 13, 1985).
There is no evidence of adverse chronic health effects in
animals or humans from exposure to sulfate in drinking water, 50
Fed. Reg. 46979 (November 13, 1985). The only adverse effects
noted from exposure to high levels of sulfate are diarrhea and
dehydration. Infants appear to be more sensitive to sulfate than
adults. There are limited data on the acute effects of sulfate.
Information compiled from questionnaires indicated that at con-
centrations of sulfate above 1,000 mg/1, the majority of respon-
dents noted a laxative effect. Animal studies suggest that sul-
fate is not mutagenic, carcinogenic or teratogenic in mammals.
55 Fed. Reg. 30382 (July 25, 1990).
Risk Characterization
The risk characterization quantifies potential risks to
human health in the event that the contaminated plume of
groundwater is used as a residential source of drinking water.
The site-specific risk values are estimated by incorporating in-
formation from the exposure assessment and the toxicity assess-
ment for the identified contaminants of concern. Excess lifetime
cancer risks are determined by multiplying the intake or exposure
level by the cancer potency factor.
Although no one is currently using the contaminated plume of
groundwater as a domestic water supply, ingestion of the
groundwater currently underlying the community zone 'Zone 4) is
associated with an excess cancer risk of approximately 10" .
This risk increases by two orders of magnitude to approximately
10 moving upgradient from Zone 4 to Zone 1.
The exposure assumptions of the risk assessment that an
individual weighing 70 kilograms will drink 2 liters of water per
day for 70 years were used to calculate the risks associated
with use of this water in the community by current and future
residents. In addition, the risk calculation incorporated a
range of concentrations representing the maximum and minimum
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measured levels for TCE and chloroform.
Another indication of risks associated with human use of the
contaminated plume of groundwater is comparison to health-based
ARARs, such as MCLs, MCL goals, and State action levels. Plume
concentrations are greater than ARARs for TCE, chloroform,
nitrates, and sulfates.
Zone 1 Risk Reduction
The principal threat from Zone 1 derives from the presence
of a large mass of water-soluble contaminants that can migrate
and contaminate downgradient groundwater. Water-soluble con-
taminants above health-based levels which have migrated the far-
thest are the volatile organic compounds (VOCs), principally TCE
and chloroform, and two inorganic compounds, nitrates and sul-
fates. Although VOCs represent less than one per cent of the
mass of contaminants present in Zone 1, they are significant be-
cause of their relative mobililty, and because they are the major
toxic organic contaminants found in the downgradient groundwater
plume.
Zone 4 Risk Reduction
Response action in the community area is necessary to reduc
the human health risk from contaminants in the plume of
groundwater to levels that are protective of human health.
Response action is also expected to prevent the further migration
of the contaminated groundwater plume. Without remediation, con-
tinued plume migration could further contaminate the Glen Avon
aquifer, as well as parts of the larger Chino III subbasin. Ad-
ditional risks exist from exposure to contaminated groundwater
through ingestion and, to a lesser extent, through dermal contact
and inhalation of volatilized chemicals.
DESCRIPTION OF ALTERNATIVES
The following sections discuss the alternatives considered
for response actions in Zones 1 and 4. The description of the
alternatives, as well as the summaries of the comparative
•analysis, reflect the interim and limited nature of the Agencies'
response action decisions in this ROD.
Zone l
Dewatering
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Active dewatering of the Zone 1 area is expected to reduce
the threat of further contamination of groundwater, and to remove
substantial amounts of VOCs and other water-soluble, mobile con-
taminants currently in the groundwater. Lowering the water table
in Zone 1 is also expected to reduce the long-term health risks
by decreasing the volume and mobility of VOCs and other soluble
contaminants. Dewatering will serve to prepare the subsurface
for soil-vapor extraction (SVE) and/or other treatment tech-
nologies that may, as a result of currently ongoing treatability
studies, be selected in the final ROD.
Dewatering: No Action Alternative
The "no action" alternative involves no further effort to
control the source or the migration of site-related groundwater
contamination underlying Zone 1. Inaction with respect to Zone 1
groundwater will lengthen the time to achieve cleanup in all
downgradient zones.
Dewatering: Gallery Drainage Tunnel (Adit) System
As described in the draft FS report, one way to dewater Zone
1 is through a gallery drainage tunnel, or adit. The oval-shaped
tunnel would be routed around Zone 1 and be constructed in com-
petent bedrock. The gallery would include two sets of drain
holes drilled laterally, one set to drain contaminated
groundwater from beneath the site, and one set to redirect uncon-
taminated groundwater away from the site. The drained water
would be piped to the existing mid-canyon pretreatment plant for
removal of metals and organic compounds. The treated effluent
would then be transported to the Santa Ana Regional Interceptor
(SARI) where it would be piped to a POTW for further treatment.
Using the gallery system, initial dewatering to bedrock is
anticipated to take one year, and to remove over 50% of the
soluble organics and inorganics estimated to be present in the
Zone 1 groundwater. Depending upon "he Agencies' final remedial
decision for Zone 1, maintaining the lowered water table level
could be required in perpetuity. The estimated costs from Appen-
dix A to the draft FS report, are presented, below.
Capital cost: S 27,000,000
Operations/Maintenance (first year): 500,000
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Dewaterir. Surface Extraction Wells
Anot: ^r way to dewater Zone 1 is through a series of
groundwater extraction wells. Depending upon the cumulative ex-
traction rates of these wells and drawdown characteristics, wells
would iteratively be added to the dewatering matrix. Installa-
tion, followed by a review of effectiveness, would guide the
location and placement of subsequent wells. Based upon the es-
timates of well yields and spacings required by the rock struc-
ture and the continuity of the fracture system, the draft FS
report conceptualized a total of 18 to 36 wells. The actual num-
ber of wells, however, may not be confirmed until most or all of
the wells have been installed and the system has been tested.
The extracted groundwater would be treated at the existing mid-
canyon pretreatment plant, transported to the SARI line, and, ul-
timately, to a POTW for further treatment.
As with the gallery system, initial dewatering to bedrock is
anticipated to take one year, and to remove over 50% of the
soluble organics and inorganics estimated to be present in the
Zone 1 groundwater. Depending on the outcome of the Agencies'
final remedial decision for Zone 1, maintaining the lowered water
table level could be required in perpetuity. The revised es-
timated costs, including costs associated with maintaining the
dewatering system in perpetuity, are presented, below.
Capital cost: S 4,000,000
Present Worth (7% discount rate): 47,000,000
Zone 4
Cleanup of the site-related contaminated groundwater in the
community area (Zone 4) is a component of all remedial alterna-
tives (RAs) evaluated in the FS report, except for the "no ac-
tion" alternative.
Zone 4 Groundwater Cleanup: Mo action
This alternative involves no further action to clean up the
site-related contaminated groundwater in the community area, or
to prevent the further migration of the contaminant plume.
Zone 4 Groundwater Cleanup: Extraction, No Treatment, Disposal
to SARI
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This alternative involves extracting contaminated water from
wells placed in the Zone 4 plume. As the contaminated water is
extracted, uncontaminated groundwater from the surrounding
aquifer will naturally flush the plume clean over time.
The extracted groundwater would be discharged to the SARI in-
dustrial sewer line via an anticipated 15-mile pipeline, extend-
ing from Zone 4 to the sewer drop point. The chemical quality of
the extracted water would be expected to be within the present
quality limits of the industrial sewer discharge permit for the
mid-canyon pretreatment plant, and therefore should not require
further treatment. If the extracted water exceeds the water
quality limits of the discharge permit, or if discharge to the
industrial sewer is not permitted without treating the VOCs, the
VOCs would be removed prior to disposal. For purposes of es-
timating costs, air stripping was assumed to be the treatment
technology for removing VOCs.
Currently, under the SAWPA permit a maximum volume of
187,000 gallons per day can be discharged to the SARI line. The
discharge permit would likely have to be modified to allow for
the much larger volume expected to be generated by implementing
this alternative.
Based upon a revised flow rate of 160 gpm, this alternative
is estimated to reduce TCE to the federal MCL of 5 ug/1 in ap-
proximately 75 years. The estimated costs are shown, below.
Capital costs
(pipeline extension, no treatment): S 11,000,000
Present Worth (7% discount rate): 48,000,000
Capital costs
(pipeline extension, air stripping): S 12,000,000
Present Worth (7% discount rate): 52,000,000
Zone 4 Groundwater Cleanup: Extraction, Treatment, Reinjection
As with the previous alternative, this alternative involves
extracting contaminated groundwater along the Zone 4 plume. Un-
like the previous alternative, this alternative involves replace-
ment of the extracted and treated groundwater by reinjection
along the periphery of the contaminant plume. The extraction and
reinjection wells would be located and operated in a way to keep
the existing contaminated groundwater plume hydraulically con-
tained. A closed system would be sought in which contaminated
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groundwater flow is from less contaminated toward more con-
taminated groundwater.
Pending confirmation by design studies, this alternative is
envisioned to involve the following processes:
o Extraction of contaminated groundwater.
o Treatment to remove volatile organic contaminants (air
stripping).
o Treatment to remove inorganic contaminants prior to
reinjection (reverse osmosis (RO)).
o Reinjection of treated water along the periphery of the
plume.
o Disposal of RO concentrate to the SARI line.
Reinjection of the treated water is expected to hasten clean
up of the Zone 4 plume by a factor of three. The SAWPA permit
may need to be modified to allow for an increased volume that
could be generated by implementing this alternative. Based on g
revised flow rate of 430 gpm, the estimated costs of this alter
native are provided, below.
Capital costs
(air stripping, RO, pipeline extension): S 19,000,000
Present Worth (7% discount rate): S 68,000,000
DESCRIPTION OF ALTERNATIVES:
COMPLIANCE WITH OTHER LAWS AND ARARs
Under Section 121(d) of the Comprehensive Environmental
Response, Compensation, and Liability Act (CERCLA), as amended,
42 U.S.C. section 121(d), remedial actions must attain a degree
of cleanup that assures protection of human health and the en-
vironment. Additionally, remedial actions that leave any hazard-
ous substance, pollutant, or contaminant on-site must meet a
cleanup level or standard of control that at least attains
federal and more stringent state standards, requirements,
criteria, or limitations that are "applicable or relevant and ap-
propriate" under the circumstances of the release. These re-
quirements, known as "ARARs", may be waived in certain instances.
CERCLA section I21(d)(4). TO be considered as ARAR, a require-
ment must be promulgated, 40 C.F.R.section 300.400(g)(4) ; be sub-
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stantive rather than administrative, 55 Fed. Reg. 8756-57 (March
8, 1990); and be a requirement of an "environmental" law as
provided in CERCLA section 121(d)(2)(A)(i).
"Applicable" or "relevant and appropriate" requirements are
defined fully in the revised National Contingency Plan (NCP), 55
Fed. Reg. 8666-8865 (March 8, 1990), 40 C.F.R. Part 300. In sum,
"applicable" requirements are those standards, criteria, or
limitations promulgated under federal or state environmental law
that specifically address a hazardous substance, pollutant, con-
taminant, remedial action, location, or other circumstance at a
CERCLA site. Where a promulgated standard, criteria, or limita-
tion is not directly applicable, it may be "relevant and ap-
propriate" if, in the exercise of the Agencies' discretion, it
addresses problems or situations sufficiently similar to those
encountered to be well-suited to the particular site.
ARARs may be (a) "chemical-specific," which are generally
health- or risk-based numerical values or methodologies that set
limits upon concentrations of specific contaminants in the en-
vironment; (b) "location-specific," which are generally restric-
tions upon certain types of activities because of existing site
characteristics (e.g. wetland, floodplain, historic site); or (c)
"action-specific" , which are technology or activity based
restrictions triggered by the type of remedial action under con-
sideration. In addition to ARARs, EPA or the State may, as ap-
propriate, identify other advisories, criteria, or guidance,
whether or not promulgated, to be considered for a particular
site. While not mandatory, the Agencies may identify and rely
upon TBCs, as they are known, to assist in determining what
cleanup level is protective or to otherwise assist the design of
Superfund remedies.
The response actions considered and selected in this ROD are
interim measures designed to mitigate site-related risks to human
health and the environment and prevent further groundwater
degradation. Accordingly, the ARARs discussion below focuses
primarily upon compliance with those ARARs and environmental re-
quirements specific to the interim actions selected. At the time
the Agencies finalize remedial action decisions for the site,
compliance with ARARs and final selection of cleanup levels will
be fully addressed.
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Zone 1: Compliance With Other Laws and ARARs
ARARs
For the action of dewatering, the federal Clean Water Act's
pretreatment standards, authorized under section 307(b), 33
U.S.C. section 1317(b), and 40 C.F.R. Part 403; and the National
Pollutant Discharge Elimination System (NPDES) standards, under
section 311, 33 U.S.C. section 1317, are applicable to the off-
site discharge of treated water to the SARI sewer line. Those
standards applicable are currently set forth in the SAWPA permit
governing effluent discharges from the existing mid-canyon
pretreatment plant. Disposal of the extracted water from the
dewatering system will be in compliance with the existing permit
standards and any relevant modifications. There are no
location-specific applicable or relevant and appropriate require-
ments pertinent to the interim actions considered for zone l be-
cause it is not within 200 feet of a fault nor within a 100-year
floodplain.
Recently EPA promulgated land disposal restrictions, includ-
ing treatment standards for the Third Third scheduled wastes un-
der the Resource Conservation and Recovery Act, 42 U.S.C. sectic
6924 (m) and 40 C.F.R. Part 148 (55 Fed. Reg. 22520-720 (June 1,
1990)). The Agencies are currently evaluating these standards
and are aware that they may be applicable to the disposal of the
treatment sludge at the pretreatment plant. While compliance
with the Third Third, if necessary, may increase the costs of
disposal associated with the dewatering alternative, the
Agencies' preliminary analysis indicates there will be no effect
upon the decision to dewater Zone 1.
Identification and selection of final cleanup levels for
the chemical contaminants in the soil and groundwater in Zone 1
will be made at the time final remedial actions are selected for
the Zone. Dewatering Zone 1 neither precludes achieving, nor is
inconsistent with meeting, any chemical-specific cleanup levels
that may be chosen for site-related contaminants in Zone 1.
Zone 4: Compliance With Other Laws and ARARs
ARARS
No location-specific ARARs have been identified for the ac-
tion alternatives considered for Zone 4 groundwater cleanup.
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For the first alternative (extraction, no treatment, dis-
posal to the SARI), the Clean Water Act pretreatment and NPDES
standards, as discussed above under the dewatering alternative,
are applicable to the disposal of the extracted water to the
SARI. These standards, as currently set forth in the existing
SAWPA permit, are likely to require modification because of the
expected increase in discharge volume associated with this alter-
native. This alternative, if implemented, will comply with ap-
plicable permit standards, including any necessary modifications.
For the second alternative (extraction, treatment,
reinjection), the Agencies have identified potential ARARs for
both treatment and reinjection. With respect to air stripping,
the extracted water win be treated at the mid-canyon pretreat-
ment plant to meet the federal drinking water MCL for TCE (5.0
ug/l) and the 10~6 risk level for chloroform (6.0 ug/1). In ad-
dition, the South Coast Air Quality Management District's
(SCAQMD) Regulation XIII, federally enforceable under the Clean
Air Act section 110, 42 U.S.C. section 7410, is applicable to
emissions of VOCs from new sources. The SCAQMD recently promul-
gated a more stringent version of Regulation XIII that is ap-
plicable. Regulation XIII requires best available control tech-
nology (BACT) when incremental emissions of various air pol-
lutants, including volatile organic compounds, exceed a certain
threshold.
An additional guideline to be considered (TBC) for air is
the SCAQMD's Rule 1167. Because a recent court ruling stayed en-
forcement of the Rule, it is not considered ARAR. Nevertheless,
the purpose of the Rule is to control emissions of VOCs as
precursors to ozone formation in the South Coast Basin, where the
Stringfellow site lies. The Rule requires that all air stripping
facilities treating contaminated groundwater that emit more than
one pound per day of total VOC emissions install controls capable
of reducing air emissions by 90 percent. Consideration of Rule
1167 in addition to the SCAQMD's Regulation XIII VOC emissions
standards is warranted by, and consistent with, EPA OSWER Direc-
tive 9355.0-28, "Control of Air Emissions From Superfund Air
Stripers at Superfund Groundwater Sites." In nonattainment areas
like the South Coast Air Basin, which is acknowledged to have the
worst ambient air quality in the nation, the Directive seeks to
incorporate the use of controls for air strippers, consequently,
the air stripping treatment system will employ activated carbon
adsorption at the air-stripper off-gas to meet ARARS and control
VOC air emissions.
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For the action of reinjection, the Underground Injection
Control (UIC) program with respect to Class V Wells, pursuant to
the Safe Drinking Water Act and 40 C.F.R. Part 144, Subpart B,
and the California Regional Water Quality control Board's "Water
Quality Control Plan, Santa Ana River Basin" (Basin Plan) provide
the interim action ARARs for TCE, nitrates, and sulfates. The
UIC program requires that reinjection into Class V Wells, such as
those at the site, may not cause a violation of an existing
drinking water standard (MCL) under the SDWA, in this case 5 ug/1
for TCE and 10 mg/1 as N for nitrates. With respect to nitrates,
the California Basin Plan's water quality objective of 11 mg/1 as
N is the State standard directly applicable to the reinjection of
nitrates. Nitrate concentrations in the receiving formation are
believed to exceed the drinking water standard, and thus reinjec-
tion of treated water should not cause a violation of the SDWA
requirements under the UIC program. Nevertheless, the UIC stan-
dards are relevant to potential underground sources of drinking
water and appropriate action ARARs under the circumstances where
the effectiveness of the technology considered for removal of
nitrates is anticipated to produce injectate that meets or ex-
ceeds either the UIC level of 10 mg/1, or the applicable Basin
Plan objective of 11 mg/1. Consequently, both TCE and nitrates
will be reinjected at the UIC program levels (5 ug/1 and 10 mg/1
as N, respectively).
In the absence of a federal standard for sulfates the
California Basin Plan's water quality objective of 110 mg/l is
directly applicable to the action of reinjection. Treated water
from the Zone 4 extraction system will be reinjected at the Basin
Plan objective.
Remediation Goals
The Zone 4 response action decisions made in this ROD are
considered interim for the reasons noted below. Nevertheless,
the Agencies do not expect to select further Zone 4 response ac-
tions beyond those chosen in this ROD. The Agencies are, there-
fore, identifying remediation goals for the contaminants found in
the Zone 4 groundwater. The remediation goals, although being
set here for Zone 4 plume cleanup, will not be finalized until
the decision for long-term management of the contaminated
groundwater in all downgradient zones is made.
Identification of remediation goals in this ROD for the com-
munity area (Zone 4) is based upon CERCLA's objective of restor-
ing and protecting usable groundwater to the extent possible.
The Stringfellow plume is located within the Chino III subbasin,
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which is a Class I aquifer having the potential for, and desig-
nated use as, a potential source of drinking water. Under these
circumstances, the NCP indicates that the Agencies should look to
the maximum contaminant levels (MCLs) and maximum contaminant
level goals (MCLGs) under the Safe Drinking Water Act (SDWA), 42
U.S.C. section 300f, as potential cleanup levels. While these
standards are not directly applicable because the community resi-
dents are not currently relying upon the groundwater as a drink-
ing water source, they are relevant and appropriate health-based
standards. In the absence of a federal standard, the Agencies
looked to more stringent state standards or, if unavailable, a
concentration based upon a 10~6 carcinogenic risk level.
The only site related organic contaminants in Zone 4 that
were found in excess of health-based levels are TCE and
chloroform. For TCE, the federal MCL and state promulgated stan-
dard are the same, at 5.0 ug/1. Although the MCLG for TCE is
zero, EPA has determined that a zero-based MCLG is not ap-
propriate as a remediation goal. Therefore, the Agencies have
identified the remediation goal for TCE in Zone 4 as 5.0 ug/1.
While there is neither an MCL nor an MCLG specific to
chloroform, there is a federal MCL of 100 ug/1 for total
trihalomethanes, which includes chloroform. The standard,
however, is based on an analysis evaluating the health benefits
of chlorinating public drinking water supplies against the
detrimental effects of the production of trihalomethanes as a
result of chlorinating those supplies. The Agencies, therefore,
determined that the MCL for trihalomethane is not an ARAR for a
nonchlorinated source such as the Stringfellow contaminant plume.
Since no other ARAR was available, the concentration, 6.0 ug/1,
associated with an excess cancer risk of 10 6 was identified as
the cleanup goal for chloroform. This concentration coincides
with the State of California Action Level. In identifying the
goal, the Agencies have concluded that a chloroform concentration
in the plume of 6.0 ug/1 is appropriate for the circumstances of
the Stringfellow site, and will be protective of numan health.
Based on available data, the Agencies believe that the
remediation goals for TCE and chloroform can be achieved. The
Agencies do recognize, however, that recent studies by EPA sug-
gest that groundwater extraction and treatment are not, in all
cases, completely successful in reducing contaminants to health-
based levels. If it becomes apparent during operation of the
system, that contaminant levels have ceased to decline or are
declining at a much slower rate than anticipated, and are remain-
ing at levels higher than the remediation goal, such goal and/or
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the selected remedy may be reevaluated at the discretion of the
Agencies.
Both nitrates and sulfates are present in the Zone 4 con-
taminant plume. The federal MCL (10 mg/1 as N) for nitrates has
been identified as a potentially "relevant and appropriate" Zone
4 remediation goal. In the course of reviewing and evaluating
the public comments on the Community Groundwater Proposed Plan
and draft FS report, the Agencies have determined that setting
such a cleanup goal presents a problem. While existing data in-
dicate that nitrate levels within the plume exceed the federal
MCL, the data also suggest that, in many locations, the back-
ground concentration of nitrates also exceed this standard. The
situation raises questions as to the technical practicability of
achieving a cleanup goal which is lower than background condi-
tions. Based upon present knowledge, the Agencies are consider-
ing invoking an ARAR waiver to allow the remediation goal for
nitrates to be set at background concentrations rather than at
the federal MCL. Because the issue has not been the subject of
focused discussion and public comment, the Agencies will defer
finalizing the remediation goal for nitrates until after an op-
portunity for public input.
With respect to sulfates, the EPA has recently issued a
proposed rule under SDWA which now identifies sulfate drinking
water concentrations that pose a threat to human health. Prior
to this proposal, sulfate concentrations were set as a non-
enforceable secondary MCL for the aesthetic value of drinking
water. The proposed rule is a potential ARAR, which will be con-
sidered in setting the final remediation goal for sulfates in the
contaminant plume.
SUMMARY OF COMPARATIVE ANALYSIS
As noted previously, the remedial actions described in this
ROD are interim measures. Accordingly, the comparative analysis
between the interim measures considered here is limited to ensur-
ing that the chosen alternatives are consistent with any poten-
tial final remedy and the Superfund criteria relevant to the in-
terim measure being considered. The draft FS report provides ad-
ditional detailed analysis of remedial alternatives. To
facilitate the interim analysis here, the nine criteria are iden-
tified, below.
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Nine Superfund Criteria
1. Overall protection of human health and the environment.
2. Compliance with ARARs.
3. Long-term effectiveness.
4. Reduction of toxicity, mobility, and volume (TMV).
5. Short-term effectiveness.
6. Implementability.
7. COSt.
8. State acceptance.
9. Community acceptance.
Zone l
Dewatering: No Action
The "no action" alternative fails to meet criteria 1, 2, 3,
4, 5, 8, or 9. This alternative can be implemented, by inaction,
at no cost.
Dewatering: Gallery versus Surface Extraction Wells
Both alternatives would meet ARARs, and the relevant techni-
cal criteria reduction of TMV, short-term effectiveness, long-
term effectiveness, and implementability. While the standards in
the SAWPA permit must be met for dewatering, such standards are
being consistently met by treatment of extracted water at the
mid-canyon pretreatment plant. Continued compliance should not
be affected by dewatering. Both alternatives would result in the
removal of a significant volume of the soluble, mobile con-
taminants from the plume, including those of primary concern,
VOCs. Dewatering will physically isolate remaining contaminants
by eliminating the potential for groundwater transport. The ex-
tracted water would be treated at the existing pretreatment plant
to remove metals and organics. Both dewatering alternatives can
be implemented. Any necessary precautions to ensure short-term
protectiveness would be taken during construction and implementa-
tion.
The capital costs associated with the gallery system are
higher than those for the surface extraction wells. The com-
munity and State of California favor selection of dewatering
through use of surface extraction wells.
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Zone 4
Community Groundwater Cleanup: No Action
The "no action" alternative fails to meet Superfund criteria
l, 2, 3, 4, 5, 8, or 9. This alternative can be implemented, by
inaction, at no cost.
Community Groundwater Cleanup: 1. Extraction, No Treatment,
Disposal to SARI
2. Extraction, Treatment,
Reinjection
Both alternatives meet the first six superfund criteria.
Through continous extraction and treatment of contaminated
groundwater from Zone 4, reductions in contaminant concentrations
to the cleanup levels identified by the Agencies will be suffi-
ciently protective of human health and the environment. Im-
plementation c^each alternative will meet action-specific ARARs
and TBCs regarolng use of air strippers. Contaminant volumes un-
der either alternative will decrease without further degrading
the surrounding aquifer.
Contaminant removal combined with treatment will provide
long-term effectiveness and ensure short-term protection from aa
adverse impacts on human health and the environment during con-
struction and implementation. Consideration of implementability
and cost shift the balance in favor of the second alternative.
If a major modification of the SAWPA permit is not granted to in-
crease allowable discharge of treated water, it may not be pos-
sible to implement the first alternative. With respect to costs,
the first alternative appears to be less costly. If modeling in-
dications of cleanup time are correct, the first alternative
could take three times as long as the second alternative to
achieve the remediation goals identified for Zone 4. Selection
of the second alternative is favored by the State and the com-
munity.
THE SELECTED REMEDY
Zone 1
As an interim response action in Zone l, the Agencies have
selected dewatering using a matrix of surface extraction wells
that would be iteratively installed throughout the Zone 1 area.
Initial dewatering to bedrock is anticipated to take one
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year, and to remove over 50% of the soluble organics and inor-
ganics estimated to be present in the Zone 1 groundwater.
Depending on the outcome of the Agencies' final remedial decision
for Zone 1, maintaining the lowered water table level could be
required in perpetuity.
At this time, there are no remediation goals being set
through this ROD for Zone 1. Implementation of this alternative
would include compliance with all identified ARARs.
Zone 4
The Agencies also have selected as an interim response
measure cleanup of the community groundwater through extraction,
treatment, and reinjection.
Under the selected alternative, a number of wells would be
installed along the center line of the plume south of U.S. Highway
60 to extract contaminated groundwater. Additonal wells in-
stalled at the sides of the plume would reinject treated water to
accelerate plume cleanup. An estimated extraction rate between
200 and 600 gallons per minute is expected. This rate and the
feasibility of reinjection will be confirmed by field studies
prior to final design and implementation.
If reinjection is feasible, the extracted water would be
temporarily stored and piped to an air stripping unit, where TCE
and chloroform in the water would be removed to meet concentra-
tions of 5.0 ug/l and 6.0 ug/1, respectively. The treated water
would then be put through reverse osmosis to reduce the nitrates
and sulfates to acceptable levels (10 mg/1 as N and 110 mg/1,
respectively) prior to being reinjected.
The decision whether to use air stripping, as opposed to
granular activated carbon, to remove VOCs is considered a design
decision that will be confirmed through design studies.
Similarly, use of reverse osmosis as opposed to another technol-
ogy is subject to design studies. In lieu of reverse osmosis,
the Agencies are also considering an offset through use of a
Chino III subbasin desalter to remove nitrates and sulfates.
If reinjection is not feasible, the Agencies may pursue
disposing of the extracted water (after treatment to reduce VOCs,
and nitrates and sulfates, if necessary) through a sanitary or
industrial sewer.
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Field Tests and studies
Soil-Vapor Extraction in Zone. 1
This ROD includes a commitment to conduct a field test of
soil-vapor extraction (SVE). Full-scale implementation of the
technology will be pursued if the following conditions are met:
1) the results of the field test indicate that the technology can
be successfully implemented at the site in a cost-effective man-
ner; and 2) implementation of the technology win not be incon-
sistent with nor preclude the final response action taken in Zone
1. These determinations cannot be made at this time, but will be
made by the Agencies during the development and implementation of
the field test, and upon completion of the additional soil
treatability studies. The decision whether to implement a full-
scale SVE system will be documented at a later date.
If successful, soil-vapor extraction could further reduce
the future migration of VOCs into the groundwater by removing
them from the unsaturated soil above the water table. Such
removal is anticipated to reduce the long-term health risks by
decreasing the volume of VOCs in the soil, and thus the future
volume of VOCs that could potentially migrate into the
groundwater and be transported towards the downgradient com-
munity. SVE is anticipated to reduce the short-term health risk
from emissions of VOCs during implementation of ex-situ soil
treatment technologies, if chosen as part of the final remedy,
and to hasten the remediation of Zone 1. Although VOCs represent
less than one per cent of the mass of contaminants present in
Zone 1, they are significant contaminants because of their rela-
tive mobililty and toxicity, and because they are the major or-
ganic contaminants found in the downgradient groundwater plume.
In-situ SVE involves a patented process whereby a vaccuum is
placed upon wells in the ground above the lowered water table,
forcing air to flow through the pore spaces of unsaturated con-
taminated soil. The above-ground support equipment vould include
blowers, water/gas separators, and vapor-phase activated carbon
adsorption equipment. The extracted air would contain both
volatile organics and moisture (water vapor), so a water/gas
separator would be required to separate the moisture from the
air. The small volume of water separated out of the water/gas
separator would be conveyed to the. existing mid-canyon pretreat-
ment-plant. The volatile .contaminants in the vapor phase would
be adsorbed onto the activated carbon, which would be
regenerated. - "~ .5==* »--•-•-• : -
- 30 r
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The costs of a full-scale SVE system based on revised FS es-
timates are presented, below.
Capital costs: S 15,000,000
Present Worth (7% discount rate): 24,000,000
In pursuing a field test of SVE, ARARs will be met. For the
SVE field test, the existing SAWPA permit, embodying the ap-
plicable standards under the Clean Water Act's federal pretreat-
ment regulations, 40 C.F.R. Part 403, and its NPDES requirements,
33 U.S.C. section 1311, govern the off-site discharge of treated
water to the SARI. The manifest requirements under the Resource
Conservation and Recovery Act, 40 C.F.R. Part 262, are applicable
to the off-site disposal of spent carbon to an approved regenera-
tion facility. Finally, the VOC emissions standards under
Regulation XIII, as federally enforceable under the Clean Air
Act, and as enforceable by the State of California under it
revised regulation, are applicable to the SVE field tests.
Regulation XIII requires best available control technology
(BACT) when incremental emissions of various air pollutants, in-
cluding volatile organic compounds, exceed a certain threshold.
Rule 1167 of the SCAQMD and EPA's OSWER Directive 9355.0-28
relating to the control of air emissions at Superfund groundwater
sites will be considered to the extent they are suitable to VOC
air emissions from the SVE process.
Reinjection of Treated Groundwater in Zones 2 and 3
Also included in this ROD is a commitment to conduct field
studies on the reinjection of treated groundwater into Zones 2
and 3. The type of information expected to be gained from such
studies include estimated costs, implementability, long-term ef-
fectiveness, short-term effectiveness, and reduction in con-
taminant toxicity, mobility, and volume (TMV). This information,
along with information on community and state acceptance, protec-
tion of public health and the environment, and compliance with
ARARs will be used by the Agencies in determining whether to
implement reinjection in Zones 2 and 3. The decision to imple-
ment a reinjection system will be documented at a later date.
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STATUTORY DETERMINATIONS
Zone I
Dewatering
Dewatering of Zone 1 is an interim measure that offers an
opportunity to reduce risk and prevent further degradation of
dovmgradient groundwater. It does not preclude nor is it incon-
sistent with potential future remedial actions. During initial
dewatering, all action-specific ARARs will be met. No location-
specific ARARs have been identified. Remediation goals for Zone
l are not being addressed by this ROD.
The dewatering process includes treatment at the existing
pretreatment plant of the water-soluble contaminants in Zone l,
such as VOCs, other organics, and metals. Dewatering will reduce
the risk of human exposure to contaminated groundwater in Zone 1
by extracting and treating most of the contaminated groundwater
beneath the zone. Minimizing contact between the source con-
taminants and uncontaminated groundwater infiltrating into the
area will greatly reduce the quantity of contaminants that could
migrate downgradient from Zone 1. This is an important aspect r*
any final remedial decision for the site.
During construction and implementation of the dewatering
system, there may be short-term potential for minimal increase of
VOC air emissions from well vents, relief valves in force mains,
or interim storage tank vents. Based on an analysis of potential
air contamination health risks associated with the implementation
duration, the excess lifetime carcinogenic risk from inhalation
exposure in the community is approximately 2 x 10 8, and in
Pyrite Canyon approximately 2 x 10~ . These are within the al-
lowable range for excess cancer risk.
Dewatering using surface extraction wells is cost effective
in that it provides substantive reduction in the volume and sub-
sequent mobility of the soluble, mobile contaminants in Zone l at
a cost reasonable to the level of protectiveness. The draft FS
report estimates that over 50% of the aqueous-phase contaminant
mass in Zone 1 will be removed during the initial period of
dewatering.
There does not appear to be any threat to natural resources
or any impact on the 100-year floodplain that would result from
dewatering. According to a map included in the Riverside County
Comprehensive General Plan, there are no unique plant communities
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in the Glen Avon area. Nor are there endangered, rare, or
threatened animal species near the Stringfellow site. Although
several birds, mammals, reptiles, and amphibians have been seen
in the vicinity of Pyrite Canyon, no significant, rare or unique
permanent habitat in the vicinity of Highway 60 has been ob-
served.
Zone 4
Community Groundwater Cleanup
During system operation, action-specific ARARs and TBCs will
be met. There are no forseen unacceptable short-term risks or
cross-media impacts that could be caused by its implementation.
The selected remedy is not estimated to be the least expen-
sive alternative for cleaning up the community groundwater, but
in light of the confidence levels associated with the cost es-
timates, the actual costs may not be significantly different than
the alternative which involved extraction, no treatment, and dis-
posal to the SARI. Because the Agencies anticipate the selected
alternative will hasten the cleanup of Zone 4, the Agencies have
determined that the selected response action is the more cost-
effective of the alternatives considered.
The selected remedy will reduce the toxicity, mobility, and
volume of Stringfellow-related contaminants in the affected com-
munity south of Highway 60. The remedy is the most appropriate
solution as it also represents the maximum extent to which per-
manent solutions and treatment can be practically utilized in a
cost-effective manner.
Under CERCLA's amended provisions, the statutory preference
for treatment is satisfied by the selected remedy. The ap-
proaches taken for sidestream and residual management, to be con-
firmed by design studies prior to final design and implementa-
tion, will comply with all requirements.
During construction and implementation of the system, there
may be short-term potential for minimal increase of VOC emissions
into the air from well vents, relief valves in force mains, or
interim storage tank vents. Based on an analysis of potential
air contamination health risks associated with the implementation
duration, the excess lifetime carcinogenic risk from inhalation
exposure in the community is approximately 2 x 10", and in
Pyrite Canyon approximately 2 x 10". These are within the ac-
ceptable range for excess cancer risk.
- 33 -
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According to a map included in the Riverside county Com-
prehensive General Plan, there are no unique plant communities in
the Glen Avon area. Nor are there endangered, rare, or
threatened animal species near the Stringfellow site. Although
several birds, mammals, reptiles, and amphibians have been seen
in the vicinity of Pyrite Canyon, no significant, rare or unique
permanent habitat in the vicinity of Highway 60 has been ob-
served.
All of the actions in this ROD are supported by the State
and the community.
CHANGES FROM AND
CLARIFICATIONS TO THE PROPOSED PLANS
None of the changes and clarifications discussed below war-
rant public notice and comment, nor affect the remedies selected.
In response to comments on the draft FS report and the Com-
munity Groundwater Proposed Plan, estimated extraction rates in
Zone 4 were recalculated and now appear to be significantly lower
than previously believed. The lowered extraction rates affected
the estimated cleanup times and costs for the alternatives beim
considered, and thus were recalculated. The revised estimates
are reflected in the April 1989, "Stringfellow Update" newsletter
and reference documents. Predicting the groundwater cleanup time
is difficult and existing methods are inexact. Actual extraction
rate and yield need to be confirmed through further collection
and evaluation of field data.
The new estimated times for cleanup of the Zone 4 con-
taminant plume presented in this ROD are two to three times
longer than those reflected in the Proposed Plan. However, the
recalculations still show that the alternative chosen is an-
ticipated to hasten cleanup in Zone 4. With respect to estimated
costs, the new figures indicate that the alternative chosen is
more costly. Cost figures were calculated using both 7 percent
and 10 percent discount rates.
The Community Groundwater Proposed Plan did not mention the
necessary first phase of the remedial design, which will involve
collection and evaluation of field data in the contaminant plume.
This task will enatole a more accurate design of the remedial sys-
tem. Installing prototype extraction wells in selected areas of
the community plume, and performing short-term and long-term
pumping tests, will provide valuable information on aquifer
- 34 -
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characteristics and water quantity and quality to be extracted
and treated. Based on this information, it may become necessary
to maJce changes to the treatment and disposal process currently
envisioned. The modifications will be made during detailed
remedial design, and if warranted, will be documented at a later
date.
The Community Groundwater Proposed Plan assumed that no
treatment would be needed for the extracted water to be dis-
charged to an industrial sewer, such as the SARI. This was based
on the assumption that the chemical quality of the extracted
water would be within the present quality limits of the SAWPA
discharge permit. In case the extracted water is found to exceed
the discharge permit water quality limit, or if discharge to the
industrial sewer is not permitted without reducing VOC concentra-
tions in the extracted water, the water would be treated for VOC
removal prior to discharge. Thus the alternative with disposal
to the SARI line has been evaluated in two different ways: (1)
without using air stripping (no treatment), and (2) using air
stripping before discharge to an industrial sewer. For both
these subalternatives, cleanup time is still estimated to be ap-
proximately three times longer than the alternative selected.
Therefore, addition of this subalternative did not alter the
selection of the remedy.
The Community Groundwater Proposed Plan indicated that the
State Action Level for chloroform (4.3 ug/1) would be set as the
remediation goal. As discussed in this ROD, the remediation goal
for chloroform has been identified as 6.0 ug/1. The concentra-
tion coincides with the new state Action Level, as well as EPA's
10~6 carcinogenic risk level.
With respect to nitrates and sulfates, the Community
Groundwater Proposed Plan implied a number of things which subse-
quently have been clarified through this ROD. First, the
response action in Zone 4 is on-site. Therefore, a permit from
the Regional Water Quality Control Board is not required, al-
though the substantive portions of the Basin Plan applicable to
the response action win need to be met. Secondly, the Proposed
Plan indicated that the cleanup (remediation) goal for nitrates
vould be the federal MCL. As discussed earlier, the Agencies are
considering setting the goal at background by invoking a waiver
based on the technical impractacability of meeting a cleanup
standard which is lower than anthropogenic background conditions
which currently are believed to exceed the federal MCL. Thirdly,
with respect to sulfates, the Proposed Plan implied that the
remediation goal would be set at the water quality objective
- 35 -
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specified in the RWQCB's Basin Plan. Rather, in setting the
remediation goal, the Agencies will consider the proposed EPA MCL
for sulfates. If the rule is promulgated, the MCL will become
ARAR.
The Overall Proposed Plan stated that soil-vapor extraction
(SVE) would be implemented if a field test proved favorable. The
ROD offers further explanation by clarifying that the Agencies
are committed to full-scale implementation of SVE if the field
test indicates that SVE could be successfully used at the site in
a cost-effective manner, and that implementation of SVE would not
preclude nor be inconsistent with the final remedial decision for
Zone l. These determinations cannot be made at this time, but
win be made by the Agencies during the development and implemen-
tation of the test and upon completion of the additional soil
treataJbility studies. The decision whether to implement SVE will
documented at a later date.
The Overall Proposed Plan also implied that a ROD covering
RA6 in its entirety would be issued by the Agencies. In response
to community comment, and through issuance of this ROD, the
Agencies have agreed to first pursue the dewatering and SVE
aspects of RA6, and to combine these with the decision to
remediate the groundwater plume in the community area. Long-te^
continuation of downgradient plume management activities will bt
addressed in the final ROD.
- 36 -
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GLEN STRINGFELLOW
AVON *SITE
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Figure 1
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