PB96-963116
EPA/ESD/R10-96/149
December 1996
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Western Processing Co., Inc.,
Kent, WA
12/11/1995
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
REGION 10
1200 Sixth Avenue
Seattle, Washington 98101
December 11, 1995
EXPLANATION OF SIGNIFICANT DIFFERENCES
WESTERN PROCESSING SUPERFUND SITE
INTRODUCTION
Site Name And Location;
Western Processing
Kent, Washington
Lead And Support Agencies:
U.S. Environmental Protection Agency (EPA)
Washington Department of Ecology
Statutes That Require Explanation Of Significant Differences
(ESP):
Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA), Section 117(c) and National Oil and Hazardous
Substances Pollution Contingency Plan (NCP) ,
Section 300.435(c)(2)(i)
Technical Impracticability (TI) Waiver Petition And Alternative
Remedy;
On September 12, 1995, the Western Processing Trust Fund
(Trust), on behalf of the consenting defendants, submitted a
Petition to the U.S. Environmental Protection Agency (EPA) and
the Washington Department of Ecology (Ecology) for a waiver of
certain performance standards and the opportunity to shift the
focus of the ongoing remediation from groundwater restoration to
containment. Specifically, the Trust requested a TI waiver for
certain performance standards because the standards could not be
achieved in a reasonable time frame and at a reasonable cost. In
addition to the waiver request, the Trust proposed to modify the
remediation strategy.
Upon review of the Petition and our analysis of the Consent
Decree and the applicable statutes, we have determined that the
modifications to the remedy should be processed as an Explanation
of Significant Differences (BSD). We have also determined that
implementation of the alternative remedy does not require setting
or waiving any additional performance standards at this time.
' Printed on Recycled Paper
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Application of the waiver provision in Section 121 of the
Comprehensive Environmental Response, Compensation, and Liability
Act (CERCLA) as amended by SARA, necessarily assumes that
applicable or relevant and appropriate requirements (ARAR's) were
identified before the final remedy was selected. Since the
Western Processing superfund site has a pre-SARA Record of
Decision, there are no statutorily required ARAR's to waive.
On November 22, 1995, Ecology and EPA conceptually approved
the Alternative Remedy presented in the Petition. The
Alternative Remedy is fundamentally consistent with the Record of
Decision and should significantly reduce remediation costs while
still protecting human health and the environment.
Need For An ESP;
The new Alternative Remedy relies heavily upon several
measures that were already selected in the Amended ROD including
institutional controls, pumping and treating groundwater, a RCRA
consistent CAP over the site, trans plume control, and long term
monitoring.
The reason for this BSD is to address the hot spot
remediation, slurry wall, and the change from mass removal
pumping to containment pumping. The 1986 Amended ROD did mention
that new remedies may be considered and addressed in additional
ROD amendments, however EPA has now determined that an BSD is
more appropriate for this type of action.
It should be noted that the site has been remediated
consistent with the amended ROD and the Consent Decree for the
past several years and that a significant amount of contamination
has been removed as documented in the Trust's Petition. With the
implementation of the alternative remedy, the remedial action
will continue to be protective of human health and the
environment and consistent with the NCP.
Administrative Record;
This BSD" will become part of the Administrative Record for
the Western Processing Superfund site, which is available to the
public at the following location:
U.S. Environmental Protection Agency
1200 Sixth Avenue
Seattle, Washington 98101
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SITE BACKGROUND
From 1961 to 1983, approximately 300 businesses transported
industrial wastes to the Western Processing Company, where they
were stored, reclaimed, or buried. Spills and the improper
storage or disposition of reclamation by-products caused heavy
contamination of the site soils, the shallow groundwater beneath
the site, and the adjacent Mill Creek. Investigations identified
more than 90 of EPA's priority pollutants at the site, most in
the categories of volatile and semivolatile organic compounds and
heavy metals.
The Western Processing site cleanup began with an EPA
emergency removal of large quantities of the most hazardous
substances in the spring and fall of 1983. The state of
Washington also implemented storm water control measures.
Immediately after these actions, a court order closed the Western
Processing facility. Phase I of the two-part remediation, the
surface cleanup conducted by PRPs under a Consent Decree, began
in 1984 with the removal of all surface materials and buildings
and continued in 1986 with on-site treatment and off-site
incineration of approximately 6,000 gallons of dioxin-
contaminated oily liquid.
EPA signed the ROD in 1985 and signed an amended ROD in 1986
to account for a newly discovered off-property contamination
plume. Phase II of the remediation, the subsurface cleanup, also
conducted by the PRPs under a consent decree, began in 1986 and
included 1) extensive soil and waste sampling, 2) excavation and
off-site disposal of approximately 25,000 cubic yards of highly
contaminated subsurface wastes; 3) installation of infiltration
trenches, extraction and monitoring wells, and a slurry wall; and
4) construction of an air stripping system and a metals treatment
plant. The treatment plant began continuously operating at 100
gallons per minute (gpm) in October 1988 and increased to
approximately 200 gpm in November 1989. The consent decree
requires operation for at least 5 to 7 years and until cleanup
standards are met, followed by monitoring for approximately 30
years.
In April .1990 the cleanup achieved interim goals for Mill
Creek. EPA issued an Interim Close Out Report for the site in
December 1991. In 1992, EPA reached cost recovery settlements
with three PRPs. During the summer of 1993 the PRPs excavated
contaminated soil and sediment from Mill Creek and the East
Drain. . .
In late 1993 several new extraction wells were installed to
improve the removal rate efficiency. An infiltration enhancement
program was also initiated. Also, the PRPs submitted a petition
to cease operation of the groundwater extraction and treatment
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system. EPA and the Washington Department of Ecology provided
extensive comments and determined that the request was premature.
In 1994 the PRPs began to conduct bioremediation and soil
fixation tests to determine the feasibility of implementing these
supplemental controls on a few hot spot areas. Additional work
was done in Mill Creek including the placement of pea gravel in
certain reaches. A shallow well extraction system was •>
constructed along the East Drain to control potential releases of
contaminants to the drain.
In 1995 the PRPs finished the bioremediation and soil
fixation tests. Additionally, they examined the effects of
rebound to determine what will happen to the remaining
contamination when they turn off the extraction system. The PRPs
are continuing to monitor on and off-site contamination.
REMEDY SELECTED IN THE ROD
EPA signed the original ROD in September 1985. The ROD was
then amended in September 1986 to account for a newly discovered
off-site contamination plume commonly referred to as the trans
plume.
The remedy selected in the amended ROD consisted of the
following major elements:
1. Conduct extensive soil and. waste sampling.
2. Excavation and off-site disposal of highly contaminated
subsurface wastes.
3. Excavate or cover all remaining contaminated soils
outside the Western Processing property that are above
background.
4. Construct and operate, for a minimum of 5 to 7 years, a
groundwater extraction system for the shallow zone.
5. Construct and operate a groundwater extraction arid
treatment system for the trans plume in the deep zone.
6. Construct, operate, and maintain a groundwater
treatment plant.
7. Construct, operate and maintain a stormwater control
system.
8. Excavate contaminated Mill Creek and East Drain
sediments which may have been affected by Western
Processing.
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9. Extensive monitoring of Mill Creek, the East brain,
groundwater, and the groundwater extraction system
performance.
10. Construct and maintain a RCRA consistent cap over
Area I after the pumping is completed.
11. Long-term surface water and groundwater monitoring for
approximately 30 years after the cap is placed.
12. Perform conditionally required actions if the
performance standards are not achieved, or if it
appears that more than 20 years of groundwater
extraction will be necessary.
13. Apply institutional controls such as deed restrictions
as needed to limit groundwater extraction in the
general vicinity of the site and maintain the integrity
of the cap and slurry wall.
All of the major elements were implemented except for items
10 through 13 which are future action events. These future
action items are included in the Alternative Remedy.
ALTERNATIVE REMEDY
The new Alternative Remedy outlined in the Trust's Petition
includes the following elements:
1. Apply institutional controls for purposes of protecting
the cap and slurry wall and limiting groundwater usage
on site and in the immediate area.
2. Containment pumping and treatment of extracted
groundwater from inside the slurry wall. The current
extraction rates will be significantly reduced.
3. Containment pumping and treatment of extracted
groundwater from the trans plume area.
4. Construction of a RCRA consistent cap over the site
after the existing extraction and treatment systems are
removed.
5. Long-term surface water and groundwater monitoring for
30 years after the cap is constructed unless the time
frame is modified. There will be five year reviews to
assess the effectiveness of the remediation and the
continued need for monitoring.
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6. Retain the current slurry wall and construct a cut-off
wall parallel to South 196th Street.
t,
7. Hot spot remediation of targeted areas using
bioremediation, thermal desorption, and stabilization
techniques.
8. Site maintenance for 30 years after the cap is
constructed unless the time frame is modified.
9. Development of a contingency plan for mitigating
potential releases from the site if containment pumping
is not effective.
SIGNIFICANT DIFFERENCES IN THE ALTERNATIVE REMEDY
The Alternative Remedy is fundamentally consistent with the
selected remedy contained in the amended ROD. The new remedy's
control measures are basically the same as those contained in the
amended ROD including enforcement of institutional controls,
continued pumping and treating of groundwater, construction of a
RCRA consistent cap and long term monitoring. Significant
differences between the new and old remedy, or changes in
operating philosophy, are addressed below.
Existing Slurry Wall And New Cutoff Wall
Thfe original slurry wall was installed by the Trust in 1988
as a field modification to the remedial action. The slurry wall
is a 4,400-ft long vertical barrier that is 40 to 50 feet deep,
and 30 inches thick. Although the slurry wall was not
specifically included in the selected remedy contained in the
amended ROD, this remedial option was considered and evaluated in
the Feasibility Study and again in the original ROD.
The slurry wall provides horizontal flow control in the
upper aquifer. By blocking contaminated water from leaving the
site, the pumping and cleanup efficiency is improved. The wall
also provides extra protection for Mill Greek and East Drain.
The Alternative Remedy retains the current slurry wall
intact and includes the construction of a supplemental cutoff
wall immediately south of the S. 196th Street right-of-way. This
will continue to help protect Mill Creek and East Drain from the
remaining site contamination and reduce the amount of groundwater
pumping necessary to maintain containment.
With the cutoff wall, the area north of South 196th Street
called Cell 7, will be segregated from the remaining hot spot
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areas of contamination. Because of the cutoff wall and low
levels of contamination now found in Cell 7, a RCRA type of cap
will not be necessary for this area.
Hot Spot Remediation
The Mill Creek standards defined in the Consent Decree have
been attained and the cis 1,2-dichloroethene (cis) standard
nearly attained in the trans plume area. However, higher levels
of contamination called "hot spots" remain in certain locations
primarily inside the slurry wall. The ROD states that if the
performance standards are not achieved, or if it appears that
more than 20 years of groundwater extraction will be necessary,
then conditionally required actions should be implemented.
Figures 4-20 through 4-24 of the Petition identify hotspot areas
where this may occur.
* Bioremediation of VOC Contamination
The Alternative Remedy requires the use of in-situ
bioremediation for remediating three hot spot areas in the
shallow aquifer identified in Figures 4-22 and 4-24. The
bioremediation will be conducted by applying a sodium
acetate nutrient to the VOC contaminated areas. Field tests
have demonstrated that the bioremediation will break the
trichloroethylene (TCE) down to cis 1,2 dichloroethene which
in turn will biodegrade to vinyl chloride.
Test results suggest that the vinyl chloride would then
~ biodegrade to harmless ethene. Even if the biodegradation
to ethene doesn't occur immediately, there will be a
reduction in the total VOC mass and any remaining
contamination would still be captured inside the slurry
wall. .
* Thermal Desorption and Stabilization of Treated Soils
One shallow area in the center of the site that
contains both heavy metals and VOC's will be excavated
(approximately 5,000 cubic yards). Most likely a portable
thermal desorption treatment unit will be brought onto the
site and the excavated material will be processed to remove
the VOC's. The treated material will then be.stabilized, to
reduce the mobility of the heavy metals, and placed back in
the excavated hole. The thermal desorption process would
not be necessary if an effective means to stabilize both the
VOC's and metals can be .found. Since the pre-SARA ROD
effectively precluded ARAR's when it was signed, the new
Land Disposal Regulations would not apply.
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CHANGE FROM MASS REMOVAL PUMPING TO CONTAINMENT PUMPING
The Trust requested that the present mass removal extraction
pumping be changed to containment pumping. Although this
represents a major change in the operation of the pump and treat
system at Western Processing, it remains.fundamentally consistent
with the amended ROD.
Containment pumping within the slurry wall will be conducted
with a new extraction and treatment system that is significantly
smaller than the existing system. The new wells will be
constructed with an individual adjustable positive displacement
pump similar to the existing U-wells rather than the current
vacuum extraction system. Treatment of VOC's will be by air
stripping and vapor phase carbon adsorption. Treatment for heavy
metals is not expected to be necessary because of the location of
the wells, but will be conducted as necessary to meet the
appropriate discharge limits. Treated groundwater will be
discharged to either Mill Creek or the publicly owned treatment
works (POTW).
Vinyl Chloride And Future Additional Cleanup Standards
In subparagraphs XIX.D.4 through XIX.D.6 of the Consent
Decree, the Governments reserve the right to require the
consenting defendants to remedy or abate conditions when
previously unknown or undetected conditions arise or additional
information on health effects becomes available that indicates
the presence of "an imminent and substantial endangerment to the
public health or welfare or the environment."
Vinyl chloride in the trans wells could present such an
endangerment. The risk analysis shows that vinyl chloride is the
most hazardous substance at the site. While cis 1,2
dichloroethene concentrations have been decreasing in the trans
plume area, vinyl chloride concentrations are generally
increasing or staying level.
While EPA and Ecology are not setting vinyl chloride
standards at this time, we will revisit the need to set standards
during future five year reviews, or sooner if necessary. It is
likely that containment pumping in the trans plume area will be
required for the next several years even if the cis 1,2
dichloroethene performance standards are attained. Additional
containment pumping is necessary to ensure that the Zone B
aquifer is not further degraded by releases of vinyl chloride
into the surrounding area.
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SUPPORT AGENCY COMMENTS
Consistent with EPA guidance, the Washington State
Department of Ecology reviewed this ESD and had no suggested
changes to the text. Ecology supports this action and the
implementation of the described Alternative Remedy.
AFFIRMATION OF STATUTORY DETERMINATIONS
Considering the new information developed during the
remedial action and the resulting changes made to the selected
remedy, EPA and Ecology believe that the Alternative Remedy
remains protective of human health and the environment. The
Amended Remedy utilizes permanent solutions to the maximum extent
practicable for this site and is cost-effective. It complies
with the NCP and other federal and state requirements that were
identified as applicable, relevant or to be considered for this
remedial action at the time the original ROD Amendment was
signed.
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PUBLIC PARTICIPATION ACTIVITIES
This BSD and supporting information will become a part of
the Administrative Record for the site. For additional
information regarding this BSD, please contact the Superfund Site
Manager for the Western Processing site:
Loren McPhillips
1200 Sixth Avenue, HW-113
Seattle, Washington 98101
(206) 553-4903
joren McPhillips, Superfund Site Manager
Date
Approved by:
Michael" F. Gearheatd
Associate Director
Environmental Cleanup Office
Date
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