PB95-963127
EPA/ESD/R08-95/100
March 1995
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Chemical Sales Superfund
Site (O.U. 2), Denver, CO
11/29/1994
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EXPLANATION OF SIGNIFICANT DIFFERENCE (ESD)
Chemical Sales Company Superfund Site
Operable Unit 2
OVERVIEW .
The pmpose of this document is to expJain the significant differences between the remedy chosen
in the U.S. Environmental Protection Agency (EPA) Record of Decision (ROD), signed June
27, 1991, and the remedy which will be implemented at the Chemical Sales Company (CSC)
Superfund Site (Site), Operable Unit 2 (Om), located in Commerce, ColOI3.do. EPA is in the
role of lead agency while the Colorado Department of Public Health and Environment (CDPHE)
is in the role of support agency. .
This ESD provides a brief background on the Site, describes the original remedy selected in the
ROD, and explains the ways in which the modified remedy differs from the original. It a1so
provides a snmm~ry of the support agency's comments on the changes to the remedy, discusses
the modified remedy's compliance with a111egal requirements, and provides details with respect
to obtaining more information or submitting comments oonceming the modified remedy.
This document is prepared in fu1fillment of EP A's public participation responsibilities under
Section 117( c) of the Comprehensive Environmental Response, Compensation, and Liability Act
of 1980 (CERCLA), as amended by the Superfund Amendments and Reauthor.i.mion Act of
1986 (SARA) and Section 3oo.435(c)(2)(i) of the National Contingency Plan (NCP). Itpresents
only a summary of the changes to the remedy and a synopsis of information on the Site. It will
become part of the Administrative Record File (NCP 300.825(a)(2», which is available for
public review at the following location:
Environmental Protection Agency
999 18th Street, suite 500 .
Denver, CO 80202
8th Floor, North Tower .
Hours: Monday -Friday, 8:00 a.m. - 4:30 p.m.
(303) 294-7691
SITE HISTORY AND BACKGROUND
The Chemical Sales Company Superfund Site om is located in south Adams County and
includes and addresses ground water contam1n~t1on north of Sand Creek. It is approximately
bounded by Holly Street to the west; Sand Creek to the south; Quebec to the east; and 88th.
Avenue East, to the north. Please see the attached map.
. .
In 1981, EPA conducted a random national survey of drinking water .systems. During this
survey, several organic chemicals were detected in SACWSD alluvial municipal water supply
wells, and additional sampling confirmed these results. In December, 1986, an RIfFS was
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STAPLETON
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o 8.680 17.360
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CHEMICAL SALES COMPANY. OU2
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. completed, which indicated widespread contamin:.rion by chlorinated volatile organic compounds .
in ground water along the eastern portion of "Off-Post Rocky Mountain Arsenal (RMA) OUl"
(Off-Post RMA OUl). The selected remedy was a pennanent water treatment system for
SACWSD water. The Klein Water Treatment Facility (KWTF) was constmcted and began
operating in October, 1989, and approximately 400 residents within the CSC om site were
connected to SACWSD. .
In April, 1986, a soil gas smvey, and elevated trichloroethylene (TeE) values were discovered
in the northem portion of the CSC property in OUI. In August, 1986, EPA installed monitoring
wells in the area where TCE was observed, which were sampled in late August and early
September, 1986. The results of these studies indicated the release of hazMdous substances into
ground water from the CSC property. EP A then proposed the CSC site for the National
Priorities List (NPL) in June, 1988. This listing was fin~1i7.ed in August 1990.
om remedial design activities at the Site began in February, 1992. In the course of conducting
these activities, EPA has obtained new information which has resulted in the need for this ESD.
SUMMARY OF THE 1991.RECORD OF DECISION
The objective of the remedy selected in the ROD is to prevent migration of conrnmin::.tP.rl ground
water in om and to restore chemical concentrations in ground water in om and to acceptable
levels for indoor use (Le., drinking and showering) based on federal and State drinking water
standards. The action described addresses ground water only.
The major components of the selected remedy include:
...
Extraction of conrnmin:.ted ground water within the PCB plume;
...
Treatment of the ground water by air stripping technology;
Re-injection of the treated ground water by injection wells;
...
....
. Monitoring of ground water;
...
Continued capture and treatment of PCB and TCB - cont:.min:.te(f ground water by the
existing Klein Water Treatment Plant; and
...
V olunta.ry abandonment of bedrock wells.
DESCRIPTION OF SIGNIFICANT DIFFERENCE
As stated above, the original remedy called for the pumping of two plumes of conrnmin=tte(l
ground water. The PCB plume, originating near 56th and Quebec, was going to require active
treatment by air stripping, and reinjection. of the treated water into the aquifer. In light of new
information, EP A and CDPHE are proposing to alleviate this component of the remedy dUe to
dispersion of the bigh concentIations of PCB that the system was envisioned to treat.
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Thus, the first three above buIleted components of the remedy will be e1imin:tted. The residual
plume (TeE) will continue to be captured by the SACWSD system. A ground water monitoring
system will be installed and a monitoring program implemented by CDPHE. The pmpose of
. this monitoring system will be to provide information that can be used to evaluate the
effectiveness of the remedial action.
The sampling information used to determine that the PCB pump-and-treat system is no longer
necessary is located in the Chemical Sales om Remedial Design Report. This report can be
reviewed at the EP A Superfund Records Center, located at the address listed above.
SUPPORT AGENCY COMMENTS
. .
The Colorado Department of Public Health and Environment (CDPHE) concurs with this
document. CDPHE also stated that if the contamination should present a threat to either human
health or the environment in the future, based upon the monitoring mentioned.in this document,
action will be taken by the agencies. to address the threat.
STATUTORY DETERM1NATIONS
Considering the new information that has been developed and the changes which have been made
to the selected remedy, EP A and the State believe that the remedy remains protective of human
health and the environment, complies with federal and state requirements that are applicable or
relevant and appropriate to this remedial action, and is cost-effective. In addition, the revised
. remedy utilizes permaneJ;1t solutions and alternative treatment technologies to the maximum .
extent practicable for this Site. .
PUBLIC PARTICIPATION ACTIVITIES .
ThisESD will become part of the Administrative Record File pursuant to Section 300.825(a)(2)
of the NCP. The Administrative Record File is available for public review at the following
location:
EPA Superfund Records Center
999 18th Street, Suite 800
Denver, Colorado 80202
(303) 294-7691
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ADMINISTRATIVE RECORD
EXPLANATION OP SIGNIFICANT DIFFERENCES
RECORD OF DECISION (ROD) - OPERABLE UNIT II
CHEMICAL SALES COMPANY SUPERFUND SITE
DECLARATION
Considering the new information that has been developed and
the changes that have been made to the remedy selected in the
June 1991 ROD, EPA has determined that the remedy remains
protective of human health and the environment, complies with
Federal and State requirements that are applicable or relevant or
appropriate to this remedial action and is cost-effective. In
addition, the revised remedy utilized permanent solutions and
alternative treatment technologies to the extent practicable.
^
Robert L. Dupreyv?
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