PB97-963154
EPA/541/R-97/172
January 1998
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
City Disposal Corp. Landfill
Dunn, WI
6/11/1997
floor
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EXPLANATION OF SIGNIFICANT DIFFERENCES
FOR THE
CITY DISPOSAL CORPORATION LANDFILL
DUNN, WISCONSIN
The purpose of this document is to explain and justify changes to a portion of the remedy at the
City Disposal Corporation Landfill (CDCL) Superfund site In brief, the changes involve
temporary extraction and treatment of contaminated groundwater at the site According to this
solution, contaminated groundwater will be extracted on-site and transported for off-site
treatment and disposal The extracted groundwater may be treated at a nearby publicly owned
treatment works (POTW) or possibly another nearby Superfund site, the Hagen Farm site For
further details concerning the nature of these changes, please refer to Section IV herein,
concerning the "Description of the Significant Differences and the Basis for the Differences "
I. Introduction
The CDCL site is located on approximately 38 acres of land in section 30, township 6 North,
range 10 East in Dane County, Wisconsin. The landfill was opened in the mid 1960s, and closed
in 1977 Household wastes, industrial wastes, general construction wastes, and debris were
disposed at the site Industrial wastes included, but were not limited to, discarded solvents from
plastics manufacture, paint wastes, oily residues, etc Total volume of wastes disposed are
approximately 700,000 cubic yards. Of the twelve cells which existed at the site for waste
disposal, it is believed that Cells 6 and 12 received largely industrial wastes
The site was placed on the National Priorities list in 1984 In 1987 and 1988, various persons
entered into an agreement with the United States Environmental Protection Agency (U.S. EPA)
for conduct of a Remedial Investigation and Feasibility Study (RI/FS) This effort was completed
in 1992, and the RI/FS and a proposed plan for remedial action was placed before the public.
Leading groundwater contaminants associated with the site were found to include tetrahydrofuran
(THF), 2-butanone, acetone, carbon tetrachloride, trichloroethene (TCE), and toluene.
The lead agency for the remedial action at this site is the US. EPA The State of Wisconsin's
Department of Natural Resources (WDNR) is the support agency for the conduct of remedial
activities at the CDCL site under the authority of the Comprehensive Environmental Response,
Compensation and Liability Act (CERCLA), 1980 PL 96-510, 42 U.S.C. 9600, et seq..
commonly known as Superfund In September 1992 the US EPA issued a Record of Decision
(ROD) which outlined the remedy selection process and the selected remediation for this site
This document provides a discussion of significant changes to the manner in which the selected
remedy will be carried out
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II. Requirements to Address Significant Changes
As the lead agency, the U S EPA may determine that a significant change to the selected remedy.
as described in the ROD, is necessary after the ROD is signed Section 11 7 © of CERCLA
requires that after adoption of a remedial action plan, as described in a ROD
•• (1) if any remedial action is taken,
»• (2) if any enforcement action under Section 106 is taken, or
•• (3) if any settlement or consent decrees under Section 106 or Section 122 is entered into,
and if such action, settlement, or decree differs in any significant respects from the final
plan, the lead agency shall publish an Explanation of Significant Differences (ESD) and the
reasons such changes were made (42 US C 9617(c))
The US EPA, in consultation with the WDNR, has determined that significant changes should be
made to the manner in which the remedial action plan, as described in the ROD, is carried out
These necessary changes are discussed further in Section IV
The ESD will be available for review in the administrative record established for the CDCL site
This record is located in both the seventh-floor Records Center at US EPA offices at 77 West
Jackson Boulevard, Chicago, Illinois and at the information repository available locally for this
site at the Dunn Town Hall, which is located at 4155 County Trunk Highway B, McFarland,
Wisconsin Opportunity for review is available during normal business hours US EPA
Remedial Project Manager Russell Hart, (312) 886-4844, or WDNR Project Manager, Mike
Schmoller, (608) 275-3303, may also be contacted
III. Background
A. Site History
In September 1992, US EPA signed a Record of Decision (ROD) calling for placement of a
nonhazardous waste cover over the majority orthe site, placement of a hazardous waste cover
over Cells 6 and 12, landfill gas venting and treatment and groundwater extraction and treatment,
along with appropriate monitoring
In March 1993, US EPA issued a Unilateral Administrative Order (UAO) which called for the
private conduct of necessary remedial design and remedial act'on (RD/RA) to bring about
execution of the ROD The UAO was issued to a potentially responsible party, Waste
Management of Wisconsin, Inc., associated with the site
Conduct of the remedial work at the CDCL site has proceeded in two distinct phases Source
control elements of the remedy have been given first priority, such that design activity performed
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in 1994 emphasized appropriate site cover and gas venting It was reasoned that a reduction in
infiltration of precipitation through the waste mass would help in simplifying groundwater control
efforts Hence, following remedial design approval by the agencies, installation of the landfill gas
collection system and clay cap was performed from June through October 1995 Work on the
collection system involved the excavation of trenches followed by the installation of piping The
cap included a 2-foot thick clay cap over the entire landfill, a 40-mil high density polyethylene
geomembrane cap and geonet/geotextile composite drainage layer over Cells 6 and 12, and an 18-
inch cover soil and 6-inch topsoil layer over the entire landfill An on-site clay deposit was
investigated and found to be suitable for cap construction, thereby removing a concern expressed
by WDNR and the public about the potential difficulty of bringing in truckloads of clay from an
outside source.
Once this work was complete, attention shifted to groundwater control elements of the remedy
In late 1995-early 1996, a pump test was convicted at the site to assist in providing an estimate of
extraction rates necessary to capture the plume of groundwater contaminants Treatability tests
were conducted using site water samples to help determine the most efficient and cost-effective
means of removing groundwater contaminants
B. Summary of Site Contamination Regarding Groundwater
For conceptual purposes, the site has been divided into six area zones so as to characterize
groundwater contamination. Area zones I, IV, and VI are located east of Badfish Creek,
southeast of the landfill, and southwest of the landfill, respectively. Organic chemical compounds
have been found to be either at nondetectable levels or otherwise are at negligible levels in
groundwater associated with these areas. Area VI is considered an upgradient zone
Areas II and V are located north and east of Cell 12, respectively, while Area III is north of Cell
6 Sampling of groundwater wells in Area III resulted in findings of THF and TCE at levels of 12
and 8 ug/1, respectively. TCE was found at a level of 11 ug/1 in Area V. Area II revealed sharply
higher findings. At a depth of 58 feet, 2-butanone was detected at a concentration of
approximately 520,000 ug/1, THF at a level oc 170,000 ug/1, and toluene was 2000 ug/1 At the
greater depth of 78 feet, concentrations of these contaminants dropped significantly 2-butanone
was 240 ug/1, THF at 2,100 ug/l, and toluene was at 43 ug/l
C. ROD Provisions
The original ROD was signed for the site on September 28, 1992 The ROD addressed the
collection and treatment of contaminated groundwater However, the US. EPA and WDNR
have since determined that there is a need to make changes in the execution of the remedy with
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regard to contaminated groundwater management These changes are discussed in the following
section
IV. Description of the Significant Differences and the Basis for the Differences
A. Description
As described in the ROD, CDCL groundwater management was to have entailed on-site treatment
of collected groundwater and discharge to nearby Badfish Creek in accordance with appropriate
effluent limitations Commencement of remedial action for groundwater management at CDCL
was not contemplated until all pertinent design steps involving groundwater were complete
However, US EPA and WDNR believe that there is significant advantage to be realized by early
commencement of remedial action for groundwater management at CDCL This would likely
involve temporary shipment of collected groundwater from CDCL to another compatible facility,
and a combined discharge from the other facility Badfish Creek would not be the expected
receiving water for the discharge A series of events leads to this conclusion
B. Basis
As noted in Section III A of this document, treatability tests have been performed in an effort to
determine the most efficient and cost-effective means of removing groundwater contaminants
The Groundwater Treatability Study Report which summarized these efforts gave equal weight to
two leading approaches to possible permanent groundwater treatment at CDCL These
approaches consisted of either biological treatment as might be carried out in a sequencing batch
reactor, or a combination of UV-oxidation supplemented by air stripping The report
recommended further pilot work, but noted that the ultimate decision could be aided if steady-
state extraction conditions could be realized at the CDCL site
Both WDNR and US. EPA strongly advocate that any necessary further field study to refine
these treatment techniques not be performed as a " ;tand alone" item Rather, we believe that
commencing interim aclio.i as soon as possible to extract the contaminated groundwater and
provide temporary off-site treatment would help bring about - if not steady-state conditions - then
at least more predictable contaminant concentrations which may help in determining the long-term
means of groundwater treatment at CDCL
On December 3, 1996, U.S. EPA and Waste Management of Wisconsin, Inc. representatives
appeared at a meeting of the Dunkirk Township board to discuss one possible means of
performing interim action, which would be to utilize the nearby Hagen Farm groundwater
treatment facility for receipt of groundwater originating from CDCL CDCL and Hagen Farm
groundwater and means of treatment now employed at Hagen Farm are compatible In US
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EPA's view, the leading concerns raised at that time were the indeterminate length of time for
groundwater hauling to be conducted, and the possibility of numerous daily trips between the
sites
In February 1997, WDNR and US EPA received a modified plan concerning execution of the
interim action This plan was distributed to representatives of both Dunn and Dunkirk
Townships The time frame for conduct of the action had been considerably shortened, so as not
to exceed six months Also, the number of truck trips from CDCL to the as yet unnamed
receiving destination had been reduced considerably. Under most circumstances, water would not
be hauled more than five days per week, and usually only once daily On Mondays or following
holidays, 2-3 trips to the receiving destination may be necessary to work off volume
accumulated The appropriate de?fination might be any facility capable of providing adequate
treatment of the CDCL water such that satisfactory effluent results are achieved
In Wisconsin, major elements of the National Pollutant Discharge Elimination System (NPDES)
and Resource Conservation and Recovery Act (RCRA) have been delegated to the State Hence,
the primary regulating body over such matters as appropriate hauling manifests, any necessary
waste permits, appropriate degree of treatment prior to discharge, etc , would be handled by the
WDNR Local ordinances concerning compatibility and lack of interference with publicly owned
treatment works (POTW) would also require attainment, as appropriate. The interim receiving
facility could then be any facility which satisfactorily meets permit requirements and effluent
limitations in accordance with appropriate waste management steps In the case of a POTW,
provided that Waste Management of Wisconsin, Inc. made ample demonstration to the POTW
that the water would not interfere or pass through the POTW without sufficient treatment, and
that the WDNR was satisfied the receiving POTW had an acceptable compliance history, the
transaction should be able to occur.
WDNR and US. EPA expect that the interim action could be conducted from roughly the June-
December 1997 time period. At the end of that time, monitoring results would be compiled, and
a commitment made to a permanent treatment concept to be conducted at CDCL During 1998,
it would be expected that all groundwater treatment design would be completed, and a permanent
groundwater treatment facility established at the CDCL site
Three extraction wells would serve the CDCL site for this interim period Usage would be made
of the well from which samples were obtained for treatability study. This well is located in the
highly contaminated Area II zone noted earlier in this document. Another extraction well has
been installed elsewhere within Area II, approximately 100 feet from the first extraction well. A
third extraction well has been installed in Area III The CDCL extraction wells were installed
near the end of 1996 Commencement of shipments of CDCL water could begin by June 1997,
pending adequate demonstration of effluent attainment, no-interference, and waste management
issues
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Both WDNR and US EPA see considerable potential advantage to be gained through this
interim action Actual groundwater remedial action could commence at CDCL perhaps a year
ahead of what would be possible otherwise, plus the insight gained in noting contaminant levels
encountered during this time would provide valuable information in selecting the appropriate
permanent treatment mechanism
V. Affirmation of the Statutory Determination
The US EPA and the WDNR believe that the remedy proposed in this ESD remains protective
of human health and the environment, and complies with state and federal requirements that are
legally applicable or relevant and appropriate to this remedial action The proposed remedy is
also more cost effective than the remedy currently in the ROD In addition, this revised remedy
approach continues to utilize permanent solutions ar"1 treatment technologies to the maximum
extent practicable for this site
VI. Support Agency Comments
The WDNTl, as the support agency, has had an opportunity to comment on this ESD WDNR
agrees with the modification to remedial action as described in this ESD
VII. Public Participation Activities
The ESD will be added to the administrative record for the CDCL site. US. EPA has developed
several Fact Sheets since the ROD was executed to inform interested parties as to CDCL site
progress. U.S EPA has provided both Dunn and Dunkirk Townships, in which are located the
CDCL and Hagen Farm sites, respectively, a copy of the interim remedial action plan
William E. Muno, Director/ Date
Superfund Division
US Environmental Protection Agency
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