PB95-963115
EPA/ESD/R09-91/126
February 1995
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Koppers Co., Inc.
Oroville, CA
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KOPPERS SUPERFUND SITE
OROVILLE, CALIFORNIA
EXPLANATION OF SIGNIFICANT DIFFERENCES
U.S. Environmental Prote~ti~n Agency
Region IX - S~n Francisco, California
January 199].
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EXPLANATION OF SIGNIFICANT DIFFERENCES
Koppers Superfund site
Oroville, California
. January 1991
I.
Introduction
The purpose of this document is to explain the significant
differences between the Record of Decision (ROD) signed by the
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U. S. Environmental Protection Agency (EPA) in September 1989 and \
reissued on April 4, 1990, and the remedy that will be imple-
mented at the Koppers Superfund Site.
Under Section 117 of the
Comprehensive Environmental Response, Compensation and Liability
Act of 1980, as amended by. the Superfund Amendment .and
Reauthorization Act of 1986 (CERCLA), 42 U.S.C. ~ 9617, EPA is
required to publish an Explanation of Significant Differences
(ESD) whenever a significant change is made to a remedi~laction .
plan.
. . .. .
This document provides a brief background on the Koppers
Site, describes the changes to the ROD that EPA .is now making and
explains the ways in which these changes affect implementation of
the remedy originally sele.cted by EPA.
Based on a review of the technical data in the administra-
tive record, EPA is changing 'the ROD to provide for separate
cleanup standards for subsurface soil at the Site.
This change
is necessary to ensure that the cleanup standards for such soil
will address protection of groundwater.
EPA is also clarifying the use of institutional controls as
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part of the selected remedy.
The ROD refers to institutional ac-
tions that will be implemented for all alternatives, but provides
no further discussion of such actions.
EPA is now clarifying the
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intent of that reference and the appropriate scope of institu-
tional controls.
EPA is issuing this ESD rather than amending the ROD because
the changes and clarifications do not result in a fundamental
change to the overall remedy selected in the ROD.
II.
Backqround
A.- site name and location
The Koppers Superfund Site1 comprises an operating, 200-acre
wood-treating plant located in Butte County, California, just
south of the city limits of Oroville, and an area primarily south
of the plant defined by a plume of contaminated groundwater
originating beneath the plant.
The plant itself lies in the
. floodplain .about. 3000 feet east of. the Feather River, on the
fringe of an area where gold mining dredge operations occurred in
the early 1900s.
At the time the Remedial Investigation of the
Site began, the plant was owned and operated by Koppers Company,
Inc. (Koppers).
In 1988, BNS Acquisitions, Inc. (BNS), acquired
Koppers and subsequently sold the Tar and Wood Products section,.
including the Oroville plant, to Koppers Industries, Inc.
(KII),
which is the current owner and operator.
However, BNS retained
liability for CERCLA matters at the Site.
In January 1989, BNS
merged into Koppers Company, Inc., and the name was changed to
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1. For purposes of this ESD, the term "Site" means both the
property on which the wood treating plant is located and the
areal extent of contamination originating from the property. In
the ROD, the term "site" refers only to the property on which the
plant is located.
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Beazer Materials and Services, Inc.
~n April 1990, the name of
Beazer Materials and Services, Inc., was changed to Beazer East,
Inc. (Beazer).
B.
Identification of Lead and ~upport Agencies
Since mid-1985, EPA has been the lead agency at the Koppers
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Site.
The California Department of Health Services (DHS) and the
California Regional Water Quality Control Board - Central Valley
Region (RWQCB) are the support agencies for the Koppers Site.
c.
Circumstances
As part of its .Remedial Investigation (RI) work, Koppers
developed a computer model to estimate the migration of con-
taminated groundwater 'from the plant.
.EPAexpected that this
model would also provide information about the movement of con-
tamin~nts from soils into the groundwater.
That information
, would have assisted EPA in establishing cleanup objectives for
subsurface soils based on protection of ground~ater.
However,
the modeling work was not completed in time .for incorporation
into the Endangerment Assessment and thus into the Feasibility
Study (FS).
As a result, EPA established a single set of soil
cleanup objectives based primarily on the risk of direct contact
with contaminated soil.
EPA has re-examined the basis for setting the existing soil
cleanup objectives.
With the exception of the objective for
pentachlorophenol (PCP), these soil cleanup objectives are based
on the health risk of direct exposure (either via ingestion, der-
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mal contact or inhalation of dust) to contaminated soil.
EPA has
concluded that for deeper subsurface soils, the direct exposure
scenario is not appropriate.
However, because the contaminants
in these deeper soils leach into groundwater, there is an ex-
posure pathway through .groundwater use (for example, when such
water is used as a domestic water supply).
Thus, EPA intends to .
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establish cleanup standards for subsurface soils based on protec-
tion of groundwa~er.
EPA has also decided to clarify the ROD's requirements
regarding institutional controls.
This ESD does not change the ROD's cleanup objectives or
selected technologies for the treatment and cleanup of con-
taminated groundwater.
D.
statement Regarding the Administrative Record
rhis ESD will become part of the Administrative Record file
located at:
u.s. Environmenta~ Protection
Superfund Records Center (9th
75 Hawthorne Street
San Francisco, CA 94105
~gency, Region IX
Floor)
Meriam Library
California State University, Chico
Chico, CA 95929
E.
Site History
sin~e 1955, Koppers and subsequently KII have operated
several wood treating.processes at the plant.
Chemical preserva-
tives, including PCP, creosote, and chromated copper arsenate
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solution, have been applied in pressurized treatment vessels.
Waste~aters from the creosote and PCP processes were discharged
directly to unlined ponds near the western plant boundary.
There
have been two explosions of the PCP treatment process (1963 and
1987), the latter of which was. followed by an EPA-directed
cleanup of fire debris and removal and stabilization of surface
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soils.
In 1971, PCP was detected in ground~ater beneath the plant.
In 1972, this contamination was found in residential wells south-
west of the plant.
In 1973, the RWQCB issued an order to Kop-
pers, which led to cleanup activities and process changes.
That
order was rescinded in 1974.
In 1981, the RWQCB and the DHS
directed investigations of contamination at the plant.
The RWQCB
issued t~o orders in 1982 for the cleanup, of contaminated soils
and groundwater.
In September 1983, EPA proposed the Site for inclusion on
the National Priorities List (NPL). EPA placed the Site on the
NPL on September 21, 1984 (49 Fed. Reg. 37070).
The RI report ~as completed in August 1988, and an FS report
~as completed in, May 1989.' An operable unit ROD for' soil and
ground~ater cleanup was signed in September 1989 and reissued on
April 4, 1990.
F.
Nature and Extent of Contamination
Chemical preservatives including PCP, creosote and chromated
copper arsenate have been applied at the plant to wood in pres-
surized treatment vessels.
Wood treatment solutions dripped to
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the ground as the treated wood was handled. Wastewaters from
creosote and PCP wood treating processes were discharged directly
to unlined ponds near the western boundary of the plant. The
creosote wastes included polynuclear aromatic hydrocarbons, a
group of compounds found in cr~osote.
From 1963 to 1973, Koppers
used a caustic solution to rinse excess PCP from treated wood
poles placed over unlined soil.
. The contaminants found at the Site to dat~ include, but are
.not limited to, pentachlorophenol ~ isopropyl ether,' arsenic,
polychlorinated dibenzodioxins/dibenzofurans (PCDDs/PCDFs),
polynuclear aromatic hydrocarbons (PARs), and chromium.
Wood treating operations and wastewater handling at the
plant have contaminatad Sit~ soils.
Contaminated soil has become
airborrie due to vehicular traffic and wind erosion.
Water pass-
ing over contaminated soils has affected or contaminated surface
waters and sediments at the plant, and soil contaminants have
leached into groundwater beneath the plant.
Contaminated
groundwater has, in turn, migrated beyond the plant property and
now extends in a plume approximately two miles gouth of the
plant.
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In 1986, Koppers began providing.an alternative water
supply to residents whose wells were affected by the plume of
contaminated groundwater.
G.
Description of the ROD
The Operable Unit ROD for soil and groundwater remedies was
signed in September 1~89 and reissued on April 4, 1990.
The ROD
selected a variety of remedial actions for soil ~nd groundwater
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units.
Of the four soil units identified, three (51, 52, 54)
were based on the primary contaminant(s) present in each.
The
fourth soil unit (53) consists of the current process area.
The
affected groundwater was divided into two units (on-plant and
off-plant) because of the variation in the contaminants.
The
,
size and nature of these soil and groundwater units are described \\
on page 31 of the ROD.
The selected remedies are summarized
below:
o Groundwater extraction, treatment (with activated carbon),
and reinjection systems to reduce contamination in
groundwater via two distinct systems - one at the plant and
one located above the plume which extends approximately two
miles south of the plant.
The existing alternative water
supply will be continued until remedial objectives for the
aquifer are attained.
o 50il remed~es consisting of:
i) In-situ biodegradation of soil contaminants (primarily
PCP) in Unit 51;
ii) Excavation, treatment by soil washing to re~ove con-
taminants (primarily' PAHs), and on-plant disposal of
soil in Unit 52;
iii) Construction of a cap over Unit 53, and, as necessary,
construction of additional extraction wells immediately
downgradient of Unit 53 to contain contaminated
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groundwater migrating from this area.
As part of the
selected re~edy for this unit, the contaminated soil
beneath the process area, when accessible, shall be
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addressed in a manner consistent with soils in other
soil units; and
iv) Excavation, treatment by chemical fixation to immobi-
lize contaminants (primarily arsenic and chromium), and
on-plant disposal of ' soil in Unit 54.
'The ROD established numerical remedial objectives for all
5ite contaminants of concern that are required to be met through
cleanup.
The remedial objectives for soil and groundwater are
summarized in Table 10-1 (page 62) of the ROD.
The remedial ob-
jectives for soil were derived as follows:
Basis
Heal th Risk'
. Exposure
Scenario
Exposure to
surface soils
(future residents)
Contaminant
PAHs
. . PCDD/PCDFs
Arsenic
Remedial
Obiective+'
0.19 ppm
30 ppt .
Background*
Inhalation of
airborne dust
Chromium
Background-
ARA.'q ( TTLC )
n/a
PCP
17 ppm
+ppm = parts per million
ppt = parts per trillion
*Risk-based remedial objectives are below estimated background
concentrations.
These objectives would have to be attained in all contaminated
soils, which are estimated to range in maximum depth from 5 feet
(in Unit 54) to 25 feet (in Unit 52).
As illustrated in the
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table above, these remedial objectives are, for the most part,
based on achieving a 10-6 cancer risk for direct exposure (via
ingestion, dermal contact or inhalation) to contaminated soils.
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The ROD also noted that institutional actions, such as site
access and groundwater use restrictions, would be implemented for
all alternatives.
III.
Description of Siqnifican~ Differences
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This ESD modifies certain portions of EPA's ROD issued on
April 4, 1990.
To the extent that this ESD differs from the ROD,
the ESD ~upersedes the ROD.
As explained in greater detail
below, this ESD addresses the following issues:
1. The existing remedial objectives for soil remain in ef-
fect for surface soils down to a depth of five feet.
2. EPA will "establish cleanup standards for" subsurface
soil to provide for protection of groundwater.
3. Institutional actions will be included as interim
measures as part of the remedies for soil and
groundwater.
A. Remedial Objectives for Surface 80i1
The existing remedial objectives for soil are based on the
health risks from direct exposure to such soils, either through
ingestion, dermal contact or inhalation of dust.
The depth of
cleanup should be adequate to assure that future residential
development and use of the plant property will not expose resi-
dents to soil exceeding the "direct exposure" cleanup objectives.
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EPA has determined that the appropriate depth in this case is
five feet.
The existing remedial objectives, defined in Table
10-1 of .the ROD and also .in Table 2-3 of the FS, remain in effect
for surface soils (that is, all soil up to five feet below ground
surface).
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The selection of five feet as the lower limit of "surface"
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soils is based upon consideration of the possible depth of soil
excavation that. might occur if the Site is developed for residen-
tial use.
Excavations considered included those that would occur
during development (for example, foundations, utilities, and/or
septic systems) as well as those which could occur after initial
development (for example, landscaping, additions and improvements
to dwellings, or utility repair/modification).
'~PA'contacted local govern~ental agencies regarding building
codes and construction practices common to residential develop-
ment in the Oroville area.
Discussions with these local agencies
established that routine excavations are in most cases-limited to
five feet or less in depth.
The Butte County Public Works
Department indicated that excavations for found~tions for conven-
tional two-story houses in the area are typically eighteen inches
deep.
Basements are rarely found in new houses constructed in'
the area.
Utility lines on residential lots (gas, electric and.
water) are buried one to two feet below the surface.
Sewer con-
nections from houses to street mains are laid at a slope of 1/4.
inch per foot of pipe (that is, approximately one foot deep for
every fifty feet of pipe).
Butte County Environmental Health
Department indicated that septic system leach lines are buried
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two feet underground, while septic tanks require excavation of
five to six feet.
Discussions with area builders indicate that
post-construction excavations generally range from three to five
feet for such items as lawn and garden irrigation systems, fence
posts and large plantings.
EPA has concluded that the revision in the depth to which
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surface soil remedial objectives ~hall apply does not result in
any change to the selected remedial technologies for surface
,soils.
B. Cleanup standards for Subsurface Soil
For contaminants in subsurface soils, defined herein as
soils five feet or more below the surface, the exposure pathway
been contaminated by leachate from the soils.
is not direct contact but exposure through groundwater that has.
Contaminated sub-
surface soils must be controlled as a source of groundwater con-
tamination.
Rather than rely on a single set of remedial objectives to
provide for both protection from exposure to contaminated soil
'. and protection, of groundwater quality, EPA will establish a
separate set of cleanup standards for subsurface soil to provide
for protection of groundwater.
In the Endangerment Assessment (EA), risks posed by con-
taminated groundwater were calculated assuming that existing
average and maximum contaminant'concentrations would remain con-
stant over the period pf exposure (see EA Section 5.4).
As noted
in the EA, such risks "may be underestimated if leaching from
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Site soils leads to increased downgradient concentrations."
The
FS also acknowledged that contaminated soil is a potential source
of continuing groundwater degradation and.that those remedial al-
ternatives which involve removal of either contaminants or con-
taminated soil would aid the groundwater clean-up process.
While,
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soil cleanup based on the existing "direct exposure" scenario
would reduce the potential of contaminated soils to serve as a
continuing source 'of groundwater .contamination, it is more ap-
'propriate to establish specific standards for long-term protec-
tion of groundwater.
The extent to which a contaminant will leach from soils
into
groundwater is a function of numerous Site-specific factors.
As
part of'its RIfFS work, Koppers performed some computer modeling
stu,dies regarding leaching and degradation of 'contaminants.
However, this information is not sufficient to determine the ap-
proprjate cleanup standards (based on source control) for con-
taminants in subsurface soils.
During remedial design, additional data will be collected to
evaluate the leachability and degradation of. soil contaminants
under conditions that exist at the Site.
Data collected will
cover the variation in both soil and contaminant types present
among the soil units.
Such data will then be used to evaluate
the "source potential" of the contaminated soil and the resulting
impacts on groundwater quality.
EPA will then select, through a
future ESD or ROD amendment, cleanup standards for subsurface
soil that, when achie~ed, will protect groundwater.
Among the
factors that will be considered is whether these soil cleanup
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standards will extend the time frame identified in the ROD for
achieving groundwater remedial objectives.
After selection of
.cleanup standards for subsurface soils, EPA will reexamine the
technologies selected in the ROD for cleaning subsurface soils to
determine.if they are still appropriate.
c. Institutional Actions
The FS makes several references to institutional actions
that are part of the various alternatives for soil and
groundwater remedial action.
.Section 4.15 of the FS reaffirms
that such actions are common to all alternatives.
That section
discusses the possible institutional actions, including
groundwater monitoring, Site access restrictions and restrictions
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on the use of properties' on the Site,. including the Xoppers
plant.
Access restriction to the plant property currently consists
of signs and security patrols.
The property is staffed 24
hours/day.
EPA may evaluate Site access to determine whether ad-
ditional measures such as fencing, electronic monitoring or post~
ing of guards may be warranted to reduce the possibility of unin-
tentional contact with contaminated areas of the Site during
design and implementation of remedial actions.
Deed restrictions shall be imposed on future residential use
of the plant property as an interim measure until such ~ime as.
EPA determines that the Site is clean enough to remove those
restrictions.
Despit~ current zoning restrictions and the
presence of the KII plant, residential development could occur.
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Zoning restrictions are not permanent, and KII could sell the
property to residential developers.
The plant is. near other
residential property and is otherwise suited for residential use.
Substantial time will be required to complete remedial actions
for the Site, and the deed rest~ictions are therefore appropriate
interim measures.
IV. Support Aqency Comments
The State of California concurs with the changes to the ROD
proposed by EPA.
V. Affirmation of the statutory Determinations
Considering the changes that have been made to the selected
remedy by this ESD, EPA believes that the remedy remains protec-
tive of human hEalth and the environment, complies with all
ARARsJ uses permanent solutions and alternative technology to the
maximum extent practicable, and is cost-effective.
In addition,
the remedy satisfies the statutory preference for treatment as a
principal element and for use of permanent solutions and innova-
tive technologies to the maximum extent practicable for this .Site
(See Section 121 of CERCLA, 42 U.S.C. S 9621).
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