PB95-963122
EPA/ESD/R09-94/128
March 1995
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Selma Pressure Treating
Company, Selma, CA
10/26/1993
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SFUND RECORDS eTR
1047-00485
.SELMA PRESSURE TREATING COMPANY SUPERFUND SITE
Final
EXPLANATION OF SIGNIFICANT DIFFERENCES
From the 1988 Record of Decision
I.
Introduction
On September 24, 1988, the united States Environmental
Protection Agency (EPA) signed a Record of Decision (ROD) for the
final remedial actions at the Selma Pressure Treating Company
Superfund site, located in Selma, California. The EPA is the lead
agency for the investigation and clean up of the site; the primary
state agency is the California Environmental Protection Agency,
Department of Toxic Substances Control.
Since 1988, the EPA has been conducting treatability studies,
collecting: additional field data, and preparing design plans and
specifications for construction of the remedy. In the course of
conducting these additional studies and preparing detailed designs,
the EPA in consultation with other regulatory agencies has modified
certain aspects of the remedial actions and clean up levels. The
purpose of this document is to explain the significant differences
that. have come about since the ROD was written in 1988. These
differences, though significant, are not a fund~mental alteration
of the remedy described in the ROD.
. Under section 117 of the Comprehensive Environmental Response,
compensation, and Liability Act of 1980, as amended (CERCLA), 42
U.S.C. S9617, and pursuant to 40 C.F.R. section 300.435(c) (2) (i)
(55 Fed.Reg. 8666, 8852 (March 8, 1990», EPA is required to
publish an Explanation of Significant Differences (ESD) whenever a
significant (but not fundamental) change is made to a final
remedial action plan as described in a ROD.
This document provides a brief background of the Selma site,
a summary of the remedy selected in the ROD, a description of the
changes to the ROD that EPA is now making (including how the
changes affect the remedy originally selected by the EPA in the
1988 ROD), and an explanation of why the EPA is making these
changes to the ROD. .
The EPA is issuing this ESD to clarify certain aspects of the
clean up standards for the site, to explain changes in certain
remedial action details described in the ROD, and to document.
compliance wi th Land Disposal Restrictions under the Resource
Conservation and Recovery Act through a Treatability Variance.
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This ESD:
(A) changes the term "clean up goal" to "clean up standard"
wherever it is used in the ROD;
(B) revises the clean up standard for arsenic in surface
soils from 50 mg/kg to 25 mg/kg, a more stringent standard;
(C) sets a clean up standard for pentachlorophenol in ground
water at 1 ppb to comply with a new, more stringent drinking water
Maximum Contaminant Level (MCL) and sets a clean up standard for
pentachlorophenol in soil at 17 ppm; ,
(D) identifies additional areas of soil contamination that
require excavation and treatment, and revises the total volume and
on site disposal location;
(E) modifies the implementation of the ground water extrac-
tion and reinjection system to reflect a more phased, ,observational
approach for the siting and design of the wells, with an initial
phase consisting of 4 extraction and 6 reinjection wells; and
(F) documents compliance with RCRA Land Disposal Restrictions
through a Treatability Variance for the contaminated soil.
As re'quired by 40 C.F.R. section 300.825(a) (2), the ESD will
become part of the Administrative Record file for the Selma site.
This file is available for pUblic review during normal business
hours in the EPA Region 9 Superfund Record Center, 75 Hawthorne
Street, San Francisco, California, 94105.
II.
Summary of site History. Contamination Problems. and Selected
Remedy
site History
The Selma site is located in Fresno County, California, about
15 miles south of Fresno and adjacent to the southern city limits
of Selma. The site comprises approximately 18 acres, including a
4 acre wood treatment facility and 14 acres of adjacent vineyards
that were used for site drainage. Zoned for heavy industrial use,
the site is located in a transit~on zone between agricultural,
residential, and industrial areas. There are 12 residences and
businesses within 1/4 mile of the site.
The company that originally operated at the site, Selma
Pressure Treating Company, ceased operation and filed for
bankruptcy in 1981. There is another wood treating company, Selma
Treating Company, currently leasing the land and operating on the
site.
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The wood preserving process originally employed at the site
involved dipP1ng wood into a mixture of pentachlorophenol and oil,
and then drying the wood in open racks to let the excess liquid
drip off. A new facility was constructed in 1965, and the company
converted to a pressure treating process which consisted of
conditioning the wood and impregnating' it with chemical
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preservati ves. Kno~ chemical preservatives used at the si te
include Fluor-chromium-arsenate-phenol, chromated copper arsenate,
pentachlorophenol, copper-8-quinolinolate, LST concentrate, and
Woodtox 140 RTU..
Prior to 1982, discharge practices included: (1) runoff into
drainage and percolation ditches, (2) drainage into dry wells, (3)
spillage onto open ground, (4) placement into an unlined pond and
a sludge pit, and (5) discharges to the adjacent vineyards.
Contamination Problems
Efforts by regulatory agencies to get the company to comply
wi th clean up orders were unsuccessful and the company went
bankrupt in 1981. EPA placed the site on the National Priorities
List of hazardous waste sites in 1983.
A Remedial Investigation/Feasibility study was conducted by
the EPA to characterize the areas of contamination and develop
clean up alternatives for the site. The investigations revealed
several areas of soil contamination and a plume of contaminated
ground water eminating from the site. Elevated levels of the heavy
metals arsenic, chromium and copper were found in both surface.and
subsurface soils. Soil analyses also showed elevated levels of the
organic compounds pentachlorophenol (PCP) and dioxin/furan. While
there were several contaminants at elevated levels in the soil,
chromium was the only contaminant found to be significantly
. elevated in the ground water.
Additional soil and groundwater studies were conducted after
the ROD was signed to provide more detailed characterization for
the design of the remedial actions. The supplemental investigation
of the soils provided a more accurate delineation of the areas of
contamination and identified additional areas needing remediation.
The supplemental ground water investigations provided a more
accurate picture of the extent. of contamination and the pumping
characteristics of the aquifer, and revealed that the ground water
table had dropped to below the elevations where the highest levels
of chromium had been found' during the original investigation.
Sampling and analysis of the ground water utilizing more sensitive
protocols also revealed that PCP may be present in levels exceeding
a new, more stringent drinking water MCL of 1ppb, promulgated
after the ROD was prepared (the previously proposed MCL for PCP had
been 37 ppb).
Remedy Selected in the 1988 ROD
The remedy selected in the original Record of Decision is
composed of two components, one for contaminated soils and one for
contaminated ground water. The soil remediation component consists
of excavating the contaminated soil, treating it on site with a
fixative agent, and then backfilling and compacting the fixed
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material on site. fixed areas of soil were then to be covered with
a RCRA cap. For remediation of the contaminated ground water, the
ROD calls for extraction and treatment of it in an on site facility
utilizing a conventional precipitation, coagulation, and floc-
culation process, with either reinjection or off site disposal of
the treated effluent, and disposal of sludge at an approved off
site landfill. Institutional controls were also required to
prevent future activities or developments on the site that could
impact the integrity and maintenance of capped materials or create
opportunities for increased exposures such as those that would
occur in a residential area.
The ROD defined clean up goals for the soil and ground water
components in terms of organic and heavy metal contaminants that,
according to the risk assessment, would act as indicator
contaminants and drive the clean up. For soils the two driving
organic and heavy metal contaminants were found to be dioxin/furan, ,
with a clean up goal of 1 ppb by TCDD equivalents, and arsenic with
a clean up goal of 50 ppm. For ground water the ROD set a single
clean up goal of 50 ppb for total chromium, which was the MCL at
the time. '
criteria were also established for treatment of the excavated
soil prior to redisposal. Treated soil was required to meet RCRA
requirements. The maximum concentration of arsenic and chromium in
treated soil, using EP toxic;:ity te;:;ting, was 5 mg/l under 40 C.F.R.
Part 261.24, and 37 ppm for pcp using a total waste analysis under
40C.F.R. Part 268.
III. DescriDtion of the Siqnificant Differences and the Basis for
Those Differences
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This ESD clarifies and modifies several portions of EPA's 1988
ROD for the Selma site. To the extent that this ESD differs from
the ROD, the ESD supersedes the ROD.
The fundamental nature of the remedial actions for the Selma
site have not changed; contaminated soils are still to be
excavated, treated with a fixative agent, disposed of on site, and
capped in accordance with RCRA standards. Ground water is still to
be extracted, treated using conventional precipitation to remove
chromium contamination, and reinjected into the aquifer.
Certain aspects of the remedy have been modified as a result
of 1) additional data gathered subsequent to the ROD; 2) changes in
Federal and State promulgated standards for contaminants found at
the site; 3) reconsideration'during the design phase of certain
aspects of technical and material handling; and 4) clarification of
the applicability of RCRA Land Disposal Restrictions for soil and
debris. The significant changes from the ROD, and the rationale
for those changes, are as follows.
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A.
Cle~n up Standards
This ESD uses the term "clean up standard" rather than "clean
up goal". This ESD changes the term "clean up goal" to "clean up
standard" wherever it occurs in the 1988 ROD.
B.
Clean up Standard for Arsenic in Surface Soils
The clean up standard for arsenic in surface soils identified
in the ROD, 50 ppm, was selected to be protective of all direct.
contact exposure scenarios except on site residential development.
The ROD further required implementation of institutional controls
to prevent future on site residential development.
Upon subsequent consultation with the California Environmental
Protection Agency and review of other RODs from throughout the U.s.
that have subsequently set arsenic clean up standards for direct
contact exposure scenarios, EPA has determined that a lower clean
up standard for arsenic is appropriate, and would not rely on
institutional controls to assure adequate health protection.
Therefore,' a new clean up standard of 25 ppm has been established
for arsenic in surface soils at the Selma site. All surface soils
(down to a: depth of five feet) containing arsenic in excess of 25
ppm shall be excavated, treated, and disposed of beneath a RCRA
cap.
C.
Clean up Standard for Pentachlorophenol in Ground Water
The 1988 ROD did not identify a specific clean up standard for
PCP in ground water, since it had not been detected in ground water
at levels any where near the MCL proposed at the time the ROD was
signed, 200 ppb. Subsequent revisions to the drinking water MCLs
have resulted in the PCP level being lowered to 1 ppb. PCP has
been detected in ground water on or near the site in levels
elevated above 1 ppb. Therefore, this ESD establishes a clean up
standard of 1 ppb for PCP in ground water at the Selma site, and
requires that the treated effluent from the ground water treatment
plant meet the same standard before it is reinjected or otherwise
discharged.
The new, stricter MCL for PCP came about due to new evidence
on the potential carcinogenicity of the compound. Based on this
information, EPA and California DTSC re-evaluated the need for a
soil clean up standard for PCP; based on our risk analyses, a new
soil clean up standard of 17 ppm has been selected to assure that
direct human exposures to soil at the site do not exceed the
acceptable risk range prescribed in the NCP, and to assure that
residual levels remaining at the site do not have the potential to
cause ground water contamination.
It should be noted that the federal MCL for chromium was
changed in July 1992, from 50 ppb to 100 ppb. Since the California
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state MCL has not been relaxed, we have retained the same clean up
standard for chromium in ground water that was selected in the ROD,
50 ppb. Should the state MCL be revised to match the federal MCL,
the clean up standard for chromium in ground water at the Selma
site will also be adjusted to 100 ppb.
D.
Additional Areas of Soil contamination to be Excavated
The 1988 ROD identified four areas where contaminated soil
exceeded clean up standards and required clean up. At the time of
the ROD, the total volume of soils requiring remediation was
estimated at 16,100 cubic yards, and the treated soils were to be
backfilled into the areas from which they were excavated.
Subsequent soil investigations provided more precise volume
estimates and identified additional areas where contaminated soil
"exceeds clean up standards and requires excavation and treatment.
The revised list of areas requiring excavation are identified in
Table A. The new estimate for the total volume of contaminated
soil to be excavated is now 11,500 cy. Also, rather than returning
treated soils to the areas where they were excavated, all treated
soils will now be consolidated into a single" unit on the site,
under a single RCRA cap.
Changes in the Design of the Ground Water Extraction,
Treatment, and Disposal System
The ROD described the ground water remediation both in concept
(i~e. extraction of ground water exceeding MCLs, treatment, and
disposal either by reinjection or off site discharge), and in
detail (construction of 25 extraction wells, 50 feet deep, pumped
at a cumulative total of 1,040 gallons per minute). Although the
concept remains the same (with the addition of the 1 ppb clean up
standard for PCP identified in paragraph C above), the design of
the extraction and treatment system has been modified. Rather than
installing 25 wells, the ground water extraction system will be
developed in phases, with the first phase consisting of 4 wells,
screened at a depth of 70 feet. The treatment plant will be
constructed to an effective design capacity of 250 gpm, and will be
expandable. Treated effluent will be discharged back into the
aquifer through 8 injection wells. Based on information gathered
from the operation of this initial phase of ground water
extraction, treatment, and reinjection, additional wells will be
installed and/or additional treatment plant capacity will be
constructed, as appropriate. "
E.
F.
Documentation of Compliance with
Restrictions through a Treatability
Contaminated soil
Land Disposal
Variance for
As described in the original Record of" Decision, RCRA Land
Disposal Restrictions (40 C.F.R. Part 268) are applicable to the
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Area
TABLE A
CONTAMINATED
SOILS EXCAVATION***
Location
A
West half of South Percolation
Length Width Depth Soils Vo'l.ume
(feet)' "(feet) (feet) (cubic yards)
,/ 335 f~ 14 ft 10 ft 1740 cy
135 ft 14 ft 10 ft I 700 cy
122 ft 70 ft *10 ft I 3160 cy
235 ft 14 ft I 25 ft 3050 cy
1185 ft 114 ft 10 ft 960 cy
! N/A I ,..;: (25 ft): , 5 ft 360 cy
1141 ft 114 ft 1 f~ 7S cy I
I I I
HI ! N/A "1:(25 ft)' 15ft 1455 cy
H2 I N/ A "r.(25 ":t) 2 15ft '/.
H3 . N / A I"r. (25 ft)' 110 ft
r** 11,500 cy
i
i TOTAL
.
B
East half ,of South Percolation
C
'Unlined Waste Disposal Pond
D
West half
Ditcl1
I ,East half
i Ditch
,of North Percolation
E
of North Percolation
F'
G
Wood Treatment Area
I Cal Trans Ditch
I Southeast Disposal Area
H
.
"'*
"'**
Ave:age Depth
Circular Surface Area
Does not include "Possible Contaminated
~~ also be excavated.
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Soils", which, as shown in the Plans,
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remedial actions for contaminated soil at the Selma site. However,
the ROD did not appropriately identify the means by which the
remedial actions will comply with the LDRs. The ROD inaccurately
stated that the contaminated soil is considered to be a K001 listed
waste under 40 C.F.R. Part 261.32. K001 is a class of listed
wastes under RCRA consisting of sludges and tank bottoms from
treatment processes for wood preservative wastes. The soil at the
Selma site became contaminated from dripping, spillage, and the
direct discharge of spent wood treating solutions onto the
property. The levels of contamination exceed the threshold. for
RCRA characteristic wastes. Therefore, the Selma soil is a
characteristic, rather than a listed RCRA waste.
Because the contaminated soil at the Selma site is a
character istic RCRA waste, treatment must comply with Land Disposal
Restrictions. Often, Superfund wastes differ significantly from
the waste used to set the LDR treatment standard (LDR treatment
standards are generally based on treating less complex matrices of
industrial process wastes, rather than contaminated soil and
debris). Since treatment standards have not yet been promulgated
for soil and debris, there is a presumption that Superfund response
actions involving the placement of soil and debris will utilize a
Treatability Variance to comply with the LDRs.
The selected remedy for contaminated soils at the Selma site
will comply with the LDRs through a Treatability Variance under 40
C.F.R. Part 268.44. 'TQ.is Variance will result in the use of a
fixation/solidification technology to attain the Agency's interim
treatment level range for the contaminated soil at the site. The
treatment level range established through a Treatability Variance
for each constituent as determined by the indicated analyses are:
Pentachlorophenol
Chromium
Arsenic
90 - 99% reduction (TWA)
95 - 99.9% reduction (TCLP)
90 - 99.9% reduction (TCLP)
Based
soil from
operation
standards.
on treatability studies conducted on the contaminated
the Selma site, it is' anticipated that full scale
of the selected technology will comply with these
IV.
SUDDort Aqencv Comments
The California Environmental Protection Agency, Department of
Toxic Substances Control was provided an opportunity to comment on
this draft ESD before it was sent out for public review. Based on
comments recei ved from DTSC, EPA added language in the ESD
pertaining to the soil clean up standard of 17 ppm for
pentachlorophenol. .
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V.
Affirmation of the statutory Determinations
considering the new information that has been developed and
the changes that have been made to the selected remedy, the EPA
believes that the remedy remains protective of human health and the
environment, complies with federal and state requirements that were
identified in the ROD and in this ESD as applicable or relevant and
appropriate to this remedial action at the time this ESD was
signed, and is cost-effective. In addition, the revised remedy
utilizes permanent solutions and al ternati ve treatment technologies
to the maximum extent practicable for this site.
VI.
Public ParticiDation
A pUblic notice fact sheet describing this Explanation of
Significant Differences was distributed to people on EPA's mailing
list of interested community members for the Selma site in May
1992. A public notice was also placed in the Fresno Bee newspaper
on May 8, 1992. The fact sheet summarized the changes proposed in
the draft ESD, identified the repository in Selma where the entire
text of the draft ESD could be reviewed, and provided a period for
public comments from May 8 to June 8, 1992. (A public comment
period was included for this ESD because EPA invoked a RCRA
treatability variance.) EPA received no public comments on the
draft ESD. Therefore,' the changes identified in this ESD are
identical to the changes identified in the version made available
to the public in May 1992.
~w~
John C. Wise
Deputy Regional Administrator
10. 2(, ..£:1:3 .
Date
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