PB97-963153
EPA/541/R-97/171
January 1998
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Moss-American (Kerr-McGee Oil Co.)
Milwaukee, WI
4/29/1997
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EXPLANATION OF SIGNIFICANT DIFFERENCES
FOR THE
MOSS-AMERICAN SUPERFUND SITE
MILWAUKEE, WISCONSIN
The purpose of this document is to explain and justify changes to the conduct of a portion of the
remedy for the Moss-American Superfiind site. In brief, the changes involve the manner in which
contaminated groundwater at the site is collected and treated, and the estimate of time for which
collection and treatment may be required. For further details on the nature of the changes, please
refer to Section IV herein, concerning the "Description of the Significant Differences and the
Basis for the Differences."
I. Introduction
The eighty-eight acre Moss-American site includes the former location of the Moss-American
creosoteing facility, several miles of the Little Menomonee River - a portion of which flows
through the eastern half of the former wood preservation facility - and adjacent flood plain soils.
The site is located in the northwestern section of the City of Milwaukee, County of Milwaukee,
State of Wisconsin, at the southeast corner of the intersection of Brown Deer and Granville
Roads, at 8716 Granville Road. Approximately 65 acres of the site are undeveloped Milwaukee
County park land. Approximately 23 acres are owned by the Union Pacific (formerly the Chicago
and Northwestern) Railroad, and used as an automobile and light truck transport,
loading/unloading, and storage area.
The Statement of Work (SOW) for the Remedial Design and Remedial Action (RD/RA) work
plan developed for the Moss-American site identifies polycyclic aromatic hydrocarbons (PAHs)
derived from creosote as being the major contaminants of concern at the site. Contamination was
found in the soils at the former wood preserving facility, in the groundwater associated with the
site, and in sediments of the Little Menomonee River at and below the former wood preserving
facility.
The lead agency for the remedial action at this site is the United States Environmental Protection
Agency (U.S. EPA). The State of Wisconsin's Department of Natural Resources (WDNR) is the
support agency for the conduct of remedial activities at the Moss-American 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 Superfiind. In
September 1990 the U.S. EPA, with the concurrence of WDNR, 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. Requirement 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 117 (c) 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 U.S.C. 9617(c))
The U.S. EPA, in consultation with the WDNR, has det3rmined 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 become part of the administrative record file. This record is located in both the
seventh-floor Records Center at U.S. EPA offices at 77 West Jackson Boulevard, Chicago,
Illinois and at the information repository and administrative record available locally for this site at
the Mill Road Library, which is located at 6431 North 76th Street, Milwaukee, Wisconsin.
Opportunity for review is available during normal business hours.
IIL Background
A. Site History
In 1921, the T. J. Moss Tie Company established a wood preserving facility west of the Little
Menomonee River. The plant preserved railroad ties, poles, and fence posts with creosote, a
mixture of numerous chemical compounds, derived from coal tar. While No. 6 fuel oil was also
used, no evidence of pentachlorophenol usage was noted at the Moss-American site. Operations
at a creosote plant might involve storage facilities for both creosote and fuels, a boiler used to
make steam to heat the creosote and aid in application to the wood through usage of heat and
pressure, incoming timbers unloading/storage, transportation of timbers to the creosote
application facility by rail car, and subsequent storage in a drying area. After these processes
were complete, the treated timbers could be shipped to customers. Potential for release of
materials exists throughout the storage, application, and drying processes.
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Kerr-McGee Chemical Corporation (KMCC) purchased the facility in 1963 and changed the
facility's name to Moss-American. The name was changed again in 1974 to Kerr-McGee
Chemical Corporation - Forest Products Division.
For a time, the facility discharged wastes to settling ponds that ultimately discharged to the Little
Menomonee River. These discharges ceased when the plant diverted its process water discharge
to the Milwaukee sanitary sewerage system. Production at the facility ceased in 1976.
KMCC cleaned out eight former settling ponds and dredged about 1700 feet of river to remove
creosote-contaminated soil and sediment.
In 1983, the facility was placed on the National Priorities List (NPL) pursuant to Section 105 of
CERCLA. Following discussions with potentially responsible parties concerning performance of
a Remedial Investigation/Feasibility Study (RI/FS), U.S. EPA determined in 1987 that it would
conduct such study.
Following development of the 1990 ROD, U.S. EPA again entered into discussions with
potentially responsible parties. On December 30, 1991, the United States lodged a consent decree
with the Federal District Court in Milwaukee. This agreement calls for implementation of the
remedy as set fortl. in the ROD by the KMCC. The decree was entered by the Court in March
1996. KMCC had previously moved on with the accomplishment of certain tasks called for in the
SOW and made a part of the decree. One such task involved verifying the presence and extent of
free-product residues of creosote associated with soils just above the groundwater table, or as
"pools" collecting at the soil/groundwater interface.
B. Summary of Site Contamination Regarding Groundwater
Indications of groundwater contamination were greatest at monitoring wells 4S and 8S as
collected during the course of the RI Well 4S is located near the former wood treating plant's
processing and drip tracks. Well 8S is several hundred feet to the east of well 4S and is near the
Little Menomonee River. Contaminants at well 4S found in the greatest concentrations were
naphthalene at 5500 ug/1, phenanthrene at 2000 ug/1, and acenaphthene at 1400 ug/1. Free
product was observed at well 8S. Relatively small concentrations of xylene and ethyl benzene,
about 45 and 27 ug/1, respectively, were also detected at monitoring well 4S. These compounds
are sometimes referred to as the BTEX class of compounds.
In 1994, pre-design monitoring efforts conducted at the site attempted to deal with the questions
of whether there was significant groundwater contamination on the east side of the Little
Menomonee River, as well as degree of interconnection between shallow aquifers on the east and
west sides of the Little Menomonee River. Findings indicated that although there is a connection
between aquifers on either side of the river, there was negligible groundwater contamination to
the east of the river. Hence, groundwater remediation efforts will focus on the west side of the
river. Pre-design monitoring efforts, conducted in June and September of 1994, indicated that the
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two most contaminated wells were monitoring wells 4S and 7S. Well 7S is located slightly south
of the railroad tracks and west of the Little Menomonee River near the northern edge of the site.
Naphthalene was the leading contaminant in both wells, occurring at a level of 1100 ug/1 in well
4S and 3000 ug/1 in well 7S.
C. ROD Provisions
The Record of Decision (ROD) for the site was signed on September 27, 1990. The ROD
addressed the collection and treatment of contaminated groundwater, excavation and treatment by
soil washing/bioslurry techniques of more highly contaminated soils and sediments, consolidation
of the treatment residuals with and containment of other contaminated soils, and the creation of a
new river channel with subsequent filling in of the existing channel. The ROD envisioned some
flexibility in groundwater treatment by providing the option of using granular activated carbon or
a comparable method demonstrated in the predesigu phase to remove semi-volatiles in the
description of the design of the treatment system at page 16. However, it is specified that
contaminated groundwater would be collected by a series of supplemental drains, leading into an
interceptor drain, and that a vertical barrier would be placed along the east wall of the main drain
trench to prevent discharge to and recharge from the river (pp. 16 and 39) and did not provide an
alternative to oil water separation for removing nonaqueous phase liquids (p .16).
Since signing the ROD, the U.S. EPA and the WDNR have determined that there is a need to
make changes in the execution or conduct of the remedy with regard to groundwater. 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, site groundwater problems were to be addressed by installing a system
of drains on the west side of the Little Menomonee River, and having these drains lead to a
collection sump. A vertical barrier was to be placed to the east of the main collection system so
as to preclude discharge of contaminated materials into the river as well as prevent river recharges
from reaching the collection system. The ROD also envisioned usage of an extraction system to
aid in groundwater collection, as evidenced by language on page 37 of the ROD.
Collection/treatment of free-product which may have moved with the groundwater was to be
provided by usage of an oil-water separator. It should be noted that the original ROD did not
emphasize means of optimizing free-product recovery. Once sufficient quantity was collected,
such free-product material was to undergo incineration. Granular activated carbon was to be used
to remove other organic contaminants.
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The alternative selected in the ROD also envisioned addressing risks posed by soil contamination
through a combination of treatment and containment of residuals derived therefrom plus lesser
contaminated soils Containment was to have consisted of a relatively permeable soil cap.
A perceived advantage of the combination of soils treatment plus usage of a relatively permeable
cover was that a flushing action would be promoted through the remaining soil mass, such that
contaminants would be flushed into and removed from the site groundwater within a relatively
short time - on the order of 10 years. Alternatives that featured only containment, or treatment
followed by soils containment using an impermeable type cover were estimated to require at least
an order of magnitude longer in order to restore the contaminated aquifer at the site.
Both the ROD and the RD/RA SOW made allowance for modification of groundwater treatment
system with a demonstrated alternative (ROD at p. 16, SOW at p. 5). The SOW echoed the
flexibility of the ROD and provided the added opportunity to demonstrate during the predesign
that an alternative collection and treatment system will be equally as effective and reliable (SOW
at p. 5).
What the ROD did not appear to contemplate was the added challenge posed to groundwater
management through the presence of significant, extractable deposits of free-product creosote.
The means of groundwater collection and treatment on which design now focuses is a method
known as the funnel and gate system. Basically, a funnel and gate system would redirect
groundwater flow through usage of sheet piling driven into a silty clay till confining soil layer
underneath the contaminated aquifer. Sections of piling would be interconnected and sealed.
Flow would be directed to open parts of the funnels, called "gates", where in place degradation of
organic contaminants would occur Treatment would be accomplished by introducing air and
nutrients within the gates Air and nutrients are expected to facilitate the growth of indigenous
bacteria in the treatment zones. The bacteria would degrade the organic contaminants, facilitating
their removal from the groundwater flowing through the gates.
B. Basis
In 1994, technical consultants working on behalf of the KMCC conducted predesign field work
which noted the presence of extractable quantities of free product creosote on a portion of the site
some 9-10' below the ground's surface KMCC is a signatory party to the RD/RA Consent
Decree, along with U.S. EPA and WDNR
Based on the predesign results, U.S. EPA issued correspondence to Kerr-McGee requesting that
initial priority be given in removing the free product and to begin the overall design for the
groundwater collection/treatment portions of the cleanup project. At this point, removing the free
product consists of installation of several extraction wells, conductivity probes to distinguish
between creosote materials and groundwater, and storage vessels for creosote materials and
predominantly water waste During the 1995-1996 operating seasons, approximately 3100
gallons of free product creosote was collected and removed from the site. Subsequent attention
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may be given to consideration of steps to supplement or enhance free-product collection. U.S.
EPA notes that free product creosote constitutes a subset of a class of contaminants known as
"dense nonaqueous phase liquids," or DNAPLs.
Compared to the means of groundwater management as originally described in the ROD, the
funnel and gate system may offer certain advantages. While exhibiting certain heterogeneity, soils
at the Moss-American site generally tend to be relatively fine-grained. This condition tends to
lead to relatively slow groundwater movement; hence there would appear to be opportunity for
adequate time for contaminant treatment as water is directed through a given gate. Design
information indicates that once optimum nutrient/air dosages are established, that groundwater
contaminants such as those that occur at the Moss-American site may undergo effective aerobic
degradatioa
Basically, a funnel and gate system would redirect groundwater flow through usage of sheet piling
driven into a silty clay till confining soil layer underneath the contaminated aquifer. Sections of
piling would be interconnected and sealed. Engineered soil media (gates) would be introduced so
as to preferentially direct groundwater flow. Treatment would be accomplished by introducing air
and nutrients in-situ in the zones of preferential groundwater flow so as to bring about the
biological reduction of BTEX and PAH compounds in the groundwater.
Design envisions two parallel lines of funnel and gate systems eventually in operation. The
western most line would be placed near the boundary line between Railroad and County property
Another line would run roughly parallel to the Little Menomonee River, just west of the river. An
effective monitoring scheme consisting of several groundwater wells is an essential part of the
system as well.
Design information available to U.S. EPA and WDNR recommends that a pilot-scale system be
constructed at the site prior to full-scale implementation, consistent with predesign tasks 19 and
20 of the SOW, so as to evaluate the short-term performance of the treatment system and to
provide for improvements as may be necessary in full-scale application. U.S. EPA and WDNR
believe opportunity for such demonstration is appropriate. Should unforeseen difficulties arise in
such maiiers as adequate capture of contaminated groundwater or sufficient removal efficiency in
dealing with site groundwater contaminants, U.S. EPA and WDNR would seek other approaches
to groundwater management.
During the course of the pilot work, the funnel and gate system would attempt to develop those
conditions of oxygen and nutrient addition necessary to bring about optimum performance. One
gate would be operated as a "control" gate to serve as a baseline comparison to the active
treatment gates. No oxygen enhancement nor nutrient addition would occur at the control gate.
A second gate would be subdivided into two smaller "active" gates where varying dosages of
oxygen and nutrients would occur for comparison and system optimization.
Velocity of groundwater flow through the gates should be low enough so as to allow for
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sufficient treatment. In order to help prevent free-product migration into the treatment gates, it is
proposed to install engineered sumps on the upgradient side of the gate. An extraction system
similar in concept to the currently operating free-product removal system could be activated and
operated so as to remove and manage any residual free-product thus collected.
Performance monitoring of the pilot system would be necessary to evaluate the effectiveness of
the treatment gates in bringing about biodegradation of groundwater contaminants, and in
ensuring that the system properly bounds the groundwater contaminant plume and directs it
toward the treatment gates. A system of upgradient, in-gate, side gradient and downgradient
monitoring wells is envisioned for such purposes. Parameters to undergo periodic evaluation
would include, but not necessarily be limited to, such constituents as oxygen-demanding
substances, BTEX compounds, and PAHs.
As noted elsewhere in this document, effective DNAPLs management, in terms of efficient
recovery, is now seen as an important element of overall groundwater management.
KMCC has proposed to conduct the pilot-scale evaluation of the system for 18-24 months. (This
time estimate is based on the relatively low hydraulic conductivity of the site soils and
groundwater flow velocity.) U.S. EPA and WDNR believe this may be an excessively long
period of time for fhis type of work, and will work with KMCC to complete the evaluation in a
shorter time frame, if possible.
The ROD contains a remedial goal of preventing contaminated groundwater from migrating from
the site into the Little Menomonee River. Currently available information, including predesign
investigation efforts to define the extent of contamination, on the site conditions appears to show
evidence of contaminated groundwater and possibly DNAPLs migrating into the Little
Menomonee River. The most recently available groundwater data for the site is a November
1996 sampling event. This data indicates that in some monitoring wells the contaminant levels
exceed groundwater standards for the site (ARARs). The agencies must be assured that during
the course of funnel and gate groundwater treatment no discharge to the Little Menomonee River
that exceeds groundwater standards or contains DNAPLs. Qualitative observation during the
1994 pre-design work noted the presence of a sheen on the river which may be attributable to the
movement of DNAPL into the river. Since that time, a free-product collection system has been
installed. However, the operation of this system is on a seasonal basis. While some free-product
extraction wells showed evidence of diminishing product layer thickness as 1996 progressed -
notably wells PW-1 and PW-3 - this trend was not uniform. There has been no consistent,
ongoing groundwater monitoring effort at the site to determine with certainty if contaminated
groundwater and/or DNAPLs are entering the river. Hence, there appears to be the need to
conduct further groundwater monitoring to confirm if this is occurring. To resolve this matter,
KMCC will be asked to conduct a further investigation of groundwater conditions, with the
installation of additional monitoring wells and a geoprobe (temporary probe monitoring wells)
investigation, existing nested/clustered monitoring well review and additional groundwater
monitoring. The purpose of this investigation would be to shed more light on DNAPL presence
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at depth, and to determine if DNAPL and/or contaminated groundwater are entering the river.
The exact scope of the investigation would be worked out in advance with appropriate U.S. EPA
and WDNR hydrogeology specialists. This groundwater investigation will be conducted as soon
as possible. The agencies will require that, if necessary, based on the results of the additional
groundwater investigation, the pilot groundwater action be designed so as to prevent such
migration, if it is confirmed to exist. This containment effort, if required, would begin at the time
the pilot scale evaluation begins, and would continue during the evaluation. It may be necessary
to continue to design and operate such a containment system as part of the full scale groundwater
remediation system.
One possible way to augment and supplement funnel and gate treatment would be to install a
system of sumps at certain points if the area of the groundwater/DNAPLs problem is relatively
small. If the problem is broader, then another possible design to contain the contaminated
groundwater and DNAPL is to construct the funnel parallel to the Little Menomonee River and
cover (or "plug") the gates so the funnel acts as a containment wall. Hydraulic controls, likely in
the form of groundwater trenches, would be installed on the upgradient side of the wall.
Contaminated groundwater and free product from this collection system would be managed
appropriately, either through treatment and discharge to the sanitary sewer or to the River after
appropriate discharge standards are met, or by hauling the liquid wastes to an approved hazardous
waste management treatment, storage or disposal facility.
Design information indicates that capital construction cost for the funnel and gate system
described above is nearly identical to those for the more conventional groundwater treatment
approach discussed in the ROD. However, operation and maintenance costs for the funnel and
gate approach appear to offer a considerable cost advantage in comparison to the conventional
approach. Since the presence of a larger quantity of free product creosote than anticipated by the
ROD may complicate groundwater management on at least a portion of the site, and offer the
potential for a considerably longer period of time in which groundwater collection and treatment
must occur, differentials in operation and maintenance costs take on increasing importance.
U.S. EPA does not propose to modify overall groundwater management goals for the site at this
time. U.S. EPA continues to believe that attainment of applicable or relevant and appropriate
regulations (ARARs) regarding groundwater Quality are important for the Moss-American site.
Information is needed to show whether this revised approach will achieve groundwater
restoration goals in a suitable timeframe. Therefore, one of the goals of the pilot-scale work is to
show if the revised approach will meet state and federal groundwater ARARs. Should the pilot
work show that the approach will not achieve those standards, a revised approach will be
developed that will meet such standards.
U.S. EPA believes that adoption of the funnel and gate means of groundwater collection and
treatment merits serious consideration and opportunity for demonstration of usage on a full-scale
application based on the expected reduced operating costs of this system, and the potential need
to require operation of this system on at least a portion of the site for a longer period of time than
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originally predicted by the ROD, due to the presence of a relatively large amount of free-product
creosote.
DNAPLS pose a particular challenge to groundwater management in that they are not dissolved
within groundwater, may act as continuing sources of groundwater contamination, and may have
movement patterns different from the overall aquifer DNAPLs may migrate into less-accessible
regions of the aquifer, or may tend to adhere to certain soils, and only slowly desorb into
groundwater so as to allow capture. It is expected that the proposed funnel and gate system, with
proper design elements, in conjunction with the current or expanded free product recovery
system, will contain and remove the DNAPL at the site. It is expected that the design will assure
that the DNAPL will not enter the treatment gates, which would likely cause problems with their
operation.
V. Affirmation of the Statutory Determir -»v:on
Considering the new information that has been developed and the change which may be required
in the execution of the selected remedy, the U.S. EPA and the WDNR believe that this change is
protective of human health and the environment, complies with state and federal requirements that
are legally applicable or relevant and appropriate to this remedial action and is more cost
effective. In addition, this revised remedy approach continues to utilize permanent solutions and
treatment technologies to the maximum extent practicable for this site.
VI. Support Agency Comments
The WDNR, as the support agency, has had an opportunity to comment on this ESD. WDNR
comments have been addressed and WDNR concurs 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 Moss-American site. U.S. EPA and
WDNR will prepare a Fact Sheet type summary of this ESD for distribution to those persons
already on the Moss-American site mailing list, and other interested parties. The Fact Sheet will
note that if members of the public would like to discuss Moss-American site issues pertaining to
this ESD at greater length, they should contact the staff members noted in that document. U.S.
EPA and WDNR will monitor the results of funnel and gate system pilot-scale work, and will
provide interested persons with a summary of such findings before making recommendations as to
full-scale utilization of the funnel and gate groundwater management approach for the Moss-
American site.
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William E Muno, Directo/ Date
Superfund Division '
U.S. Environmental Protection Agency
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