PB97-963150
EPA/541/R-97/168
January 1998
EPA Superfund
Explanation of Significant Difference
for the Record of Decision:
Powell Road Landfill
Dayton, OH
1/23/1997
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UNITED STATES i:\VIRi >NMENTA1. PROTECTION AGENCY
RIXilON V
Date: M 2 31981
Subject: Request for Concurrence cm the Explanation of Significant Differences,
Powell Road LfrndiyfOstTc. I luher I lights. Ohio
From: Wendy Cart
Remedial Response Branch'
Sandra Otaka, Chief
Multi-Media Branch 2, Section 3
Office of Regional Counsel
To: William E. Muno, Director \j\)
Superfund Division
This memorandum conveys our recommendation that you concur with the attached Explanation
of Significant Differences ("ESD") for the Powell Road Landfill site, which is located in Huber
Heights, Montgomery County, Ohio. The ESD modifies the remedy selected in the September
30, 1993, Record of Decision by postponing design and implementation of groundwater systems
until other components are completed, and evaluation of continued groundwater monitoring data
is completed. Design and implementation revisions or lack thereof for the groundwater system
will then be examined and a compliant remedy will be applied.
The ESD was prepared in accordance with the Comprehensive Environmental Response,
Compensation, and Liability Act. 42 U.S.C. Section 9601 et seg., as amended by the Superfund
Amendments and Reauthorization Act of 1 9X6. Public Law 99-499; to the extent practicable, the
National Contingency Plan, 40 CFR Part 300: and Agency policy. We have reviewed the
attached document and have concluded that the ESD is both legally and technically sufficient.
As such, we believe that implementation of this remedial measure is a proper exercise of your
delegated authority. Your signature (below) wi'l indicate your concurrence.
Please feel free to contact either of us should you have any questions.
William E. Myno, Director
Superfund Division
Disapprove: _ Date:
William E. Muno, Director
Superfund Division
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EXPLANATION OF SIGNIFICANT DIFFERENCES
POWELL ROAD LANDFILL
HUBER HEIGHT, OHIO
I Introduction
The Powell Road Landfill site (the "Site"1) is located in Huber Heights, Ohio, a suburb in the northern
Dayton metropolitan area of Montgomery County, Ohio. The site is located at 4060 Powell Road,
Huber Heights, Ohio and encompasses approximately 70 acres. It is bordered to the north by Powell
Road and residential housing, to the east by an intermittent stream, to the west by wooded areas and
to the south by wooded areas and the Great Miami River. The actual area for waste disposal covers
approximately 36 acres, rising 30 to 40 feet above the surrounding terrain. The nearest residents are
about 200 feet north of the landfill on Powell Road. A residential area known as Eldorado Plat is
immediately south of the Great Miami River to the south of the landfill. The site is located on till,
lacustrine deposits, bedrock and the outwash (t "posits that constitute the Great Miami River buried
valley aquifer, which is a designated sole-source aquifer under U.S. EPA's Safe Drinking Water Act
The US. Environmental Protection Agency ("U.S. EPA") and the Ohio Environmental Protection
Agency ("Ohio EPA") are the lead and support agencies, respectively, for conducting the remedial
action at the Site under the authority of the Comprehensive Environmental Response, Compensation,
and Liability Act ("CERCLA") of 1980, as amended by the 1986 Superfund Amendments and
Reauthorization Act ("SARA"), 42 U.S.C. Section 9601, et seq. U.S. EPA issued a Record of
Decision ("ROD") on September 30, 1993, which outlined the remedy selection process and the
selected clean-up action for the Site. The selected remedial action addresses the sources of the
contamination by containment of the landfill and contaminated soils and treatment of leachate and
ground water. The major components of the selected remedial action are:
institutional controls
improved landfill cap with liner
excavation of contaminated soils
consolidation of contaminated soils under landfill cap
ground water monitoring
flood protection
storm water controls
active landfill gas collection with flare
leachate extraction
on-site leachate treatment
extraction of ground water from the shallow aquifer adjacent to the landfill
on-site ground water treatment
discharge of treated ground water and leachate to river.
n'The term "Site", as used herein, refers to the location where the treatment, storage,
disposal or other placement of hazardous substances was conducted at the Powell Road Landfill,
or otherwise came to be located as a result of disposal operations at the Powell Road Landfill.
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Ohio EPA concurred with the selected remedy in the ROD.
Pursuant to Section 117(c) of CERCLA, 42 U.S.C. §9617(c) and 40 CFR 300.435 (c), U.S. EPA
offers herein an explanation of the significant differences ("ESD") from the ROD remedy that will
now be incorporated into the final remedial action.
II Summary of Proposed and Accepted Significant Differences from the ROD Remedy
As a result of ground water quality data gathered throughout the remedial investigation and during
the pre-design field investigations, the potentially responsible parties ("PRPs") proposed
discontinuing the ground water extraction and treatment portions of the remedial design and remedial
action. Upon careful review of the supporting documentation on which the proposal was based, U. S.
EPA and Ohio EPA (the Agencies) have determined that discontinuing these portions of the selected
remedy is not appropriate. However, for reasons explained below, the Agencies have also determined
that allowing the ground-water portions of the remedy to be designed and implemented after the
remaining remedial components are in place ''chasing) is protective of human health and the
environment and an acceptable change to the selected remedy.
Section 117(c) of CERCLA, as amended by SARA, states that:
[a]fter adoption of a final remedial action plan-
(1) if any remedial action is taken,
(2) if any enforcement action under section 106 is taken, or
(3) if any settlement or consent decree 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 President or the State shall publish an explanation of the significant differences and the
reasons such changes were made.
Under the National Contingency Plan ("NCP"), 40 CFR Part 300, promulgated pursuant to Section
105 of CERCLA, and U.S. EPA guidance, a significant difference is an incremental change to a
component of the remedy that does not fundamentally alter the overall remedial approach A
fundamental change, on the other hand, is one that actually changes the basic feature or overall
approach of the remedy to be implemented at a site, (e.g., if a remedy was changed from a
containment remedy to incineration) and requires a 30-day public comment period.
This Explanation of Significant Differences (ESD) is necessary to document that U.S. EPA and Ohio
EPA have decided to modify the remedy selected in the September 1993 ROD. The Agencies believe
that the overall protectiveness of human health and the environment provided by the selected remedy
will not be compromised by this modification.
This document shall become part of the permanent administrative record file for the Site, which is
available for viewing at the Dayton & Montgomery County Public Library, Huber Heights Branch,
Huber Heights, Ohio, and at US. EPA regional offices in Chicago, Illinois, during normal business
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hours The site file is also available for public Viewing at Ohio EPA's southwest district office in
Dayton, Ohio The Administrative Record Update is attached as Appendix 1 for a record overview
III. Summary oFSite History. Enforcement Activities. Site Contamination, and Selected Remedy
A. Site History
The Site is a former gravel pit which was converted to a landfill in 1959 and operated until 1984
under several different owners. The current owner is SCA Services of Ohio, a subsidiary of Waste
Management of North America, Inc. Commercial, industrial, and non-hazardous domestic wastes
were disposed of in the landfill. Degradation of these wastes resulted in a release of hazardous
substances. It is also believed that improper disposal of certain types of industrial waste have
occurred at the landfill, including ink waste, paint sludge, strontium chromate and benzidine. The
landfill ceased operation in 1984 and was capped and seeded in 1985.
The Site was proposed for listing on the National Priorities List ("NPL") on September 8, 1983, and
was listed on the NPL on September 21, 1984.
In December, 1984, after identifying contamination in the ground water in the area of the Site, the
Ohio EPA requested U.S. EPA's support to determine if an imminent and substantial endangerment
to human health or the environment existed. U.S. EPA's Technical Assistance Team ("TAT")
sampled 46 private lesidential wells. Sampling results identified low levels of VOCs in 6 residential
wells After reviewing these sampling results, U.S. EPA determined that an imminent and substantial
risk to human health and the environment was not present at that time, and emergency actions were
not required at that time. However, the U.S. EPA recommended that several activities be conducted
in the area, which included conducting a detailed Remedial Investigation of the Powell Road Landfill
B Enforcement Activities
In April, 1986, negotiations began for a 106 Administrative Order on Consent ("AOC") under which
Potentially Responsible Parties (PRPs) would perform the Remedial Investigation/Feasibility Study
("RI/FS") at the Site. These negotiations terminated in May, 1986, and U.S EPA began performance
oftheRI/FSattheSite.
During June of 1987, one PRP, SCA Services of Ohio, Incorporated, contacted U.S. EPA and
expressed interest in taking over performance of the RI/FS. On November 12, 1987, an AOC was
entered into between the U.S. EPA, the Ohio EPA, and SCA Services of Ohio, Incorporated ("SCA")
(currently a subsidiary of Waste Management of North America, Inc.). This AOC requires SCA to
conduct an RI/FS and to pay all past cost associated with the Site The final RI report was approved
in March of 1992 and the FS was approved in March of 1993.
Initial PRP search activities at this Site identified seven (7) PRPs. General Notices of Potential
Liability and CERCLA Section 104(e) Information Requests were issued to all seven (7) PRPs on
December 2, 1985 Since 1985, U.S EPA has issued approximately 400 Information Request and
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follow-up Information Requests General Notice letters were sent to thirty-seven (37) PRPs in May,
1993. U. S. EPA and Ohio EPA entered negotiations with an expanded PRP group to perform the
remedial design work as detailed in the ROD. In June, 1994, a three-party order became effective
for the Site requiring the PRPs to design all phases of the cleanup. The PRP group has been
satisfactorily conducting the remedial design ("RD"). Additional future Information Requests and
follow-up Information Requests will be issued as appropriate.
C. Site Contamination
The RI determined the nature and extent of on-site and off-site contamination, and estimated the risks
posed by the Site to human health and the environment. The RI Report, finalized in February, 1992,
identified the following contamination:
On-Site (contamination associated with the Site)
Landfill gases consisting of methane with detectable concentrations of volatile organic
compounds (VOCs).
Leachate (landfill liquids) consisting of VOCs, semivolatile organic compounds and
inorganic compounds
Surface and near-surface soils containing semivolatile organics, pesticides and
polychlorinated biphenyls (PCBs)
Shallow and primary aquifers adjacent to the landfill containing VOCs.
Primary aquifer south of the river (Eldorado Plat area) containing VOCs.
Off-Site (contamination not associated with the Site)
Primary aquifer south of the river (Needmore Road area) containing VOCs. A
connection between the Site and contamination found in this area could not be
confirmed and is therefore not addressed by the final remedial action.
Additional sampling of soils, leachate, and ground ^ ater was conducted during the pre-design field
investigation. The water-quality data from 1983 through 1995 indicates that ground-water quality
has improved or remained consistent and has not degraded since 1988 In addition, the contaminant
concentrations in the ground water in the vicinity of the Site are at very low levels.
D Description of the Selected Remedy as Set Forth in the ROD
The remedial action will be a final site-wide remedy. The selected remedial action addresses the
sources of the contamination by containment of the landfill and contaminated soils as well as
treatment of leachate and ground water. The major components of the selected remedial action for
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the Powell Road Landfill are:
Institutional controls, including site security, deed restrictions and access controls
Flood protection, including but not limited to seeding and mulching unvegetated
areas, maintaining temporary control measures, and protecting existing vegetation.
Storm water controls including berms, discharge ditches, etc. to dissipate the energy
of the storm water flow and reduce erosion potential.
Excavation of contaminated soils and consolidation of soils under the improved
landfill cap.
An improved landfill cap consisting of a low permeability layer, a drainage layer, a
geotextile layer, and a vegetative soil layer.
A leachate extraction2 and collection system consisting of a series of vertical
extraction wells installed in the landfilled waste designed to extract leachate in order
to prevent its migration out of the landfilled waste.
A ground-water extraction system to capture contaminated ground water from the
shallow aquifer adjacent to the landfill.
On-site treatment systems to treat extracted leachate and ground water.
Active landfill gas collection to and treatment with a flare.
Discharge of treated ground water and leachate to river in accordance with an
NPDES permit.
Monitoring systems for ground water, air, points of compliance, and the extraction/
treatment/discharge systems, in order to determine the effectiveness of the remedial
actions.
The selected remedial action will address the principal threats posed by the Site. The ROD contains
a number of remedial components which are unaffected by this ESD and are not discussed in this
ESD
IV Summary of Significant Differences
The ROD remedy, as described above, is mainly a containment remedy which relies on a physical
component (cap) as the primary barrier to contaminant movement. The leachate extraction system
serves as a supplement. The changes to the ROD described herein provides for a containment
remedy; however, the use of the groundwater extraction and treatment system may be de-emphasized
and a need to evaluate its enhancement to the remedy is appropriate.
As a result of discussions involving the Agencies and PRPs, the following significant changes are
being proposed by the PRPs:
2This extraction system will be installed inside the containment system. The leachate
extraction wells will be pumped as required. The leachate extracted water will be treated before
discharge.
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Cl) Postponement of the design and implementation of a shallow groundwater extraction and
treatment system until all other related components of the remedy are completed;
(2) Revisions for the design and implementation of the shalloxv groundwater extraction and
treatment system will be examined and evaluated after continued monitoring of groundwater
and calculating groundwater travel time, by the Agencies, and
(3) Thereafter, one of the following will be applied to the remedy:
• Continue the design and implementation of the extraction and treatment system;
• Continue monitoring the groundwater;
• Request a formal investigation and report on groundwater conditions; or
• Amend the ROD to delete the groundwater portion of the remedy.
V. Explanation of Significant Differences
U.S EPA and Ohio EPA have determined that a significant change will be made to the Site remedial
action plan. The significant change to the remedy is:
(1) A postponement of the design and implementation of the shallow ground water extraction and
treatment system until completion of design and implementation of all other selected remedy
components. Once the remaining components of the selected remedial action are designed,
constructed and operational, the Agencies shall require the PRPs do a study to calculate
ground-water travel time from the northern edge of the landfill to the monitoring wells
immediately south of the landfill. At the end of the study to calculate ground-water travel
time, plus an agreed upon amount of time for error, the Agencies will evaluate whether
ground-water contaminant levels are increasing, remaining the same, or continuing to decline,
and whether ground-water cleanup levels have been achieved. Based on these results the
Agencies may decide to take one of the following courses of action:
resume the design and implementation of the extraction and treatment system, or
continue monitoring the implemented portions of the remedy and ground-water
quality; or
request an investigation of and report on groundwater conditions, or
amend the ROD to delete the grounJwater portion of the remedy.
The Agencies have determined that this change is not considered to be a fundamental change and that
no public comment period is warranted; however, a public meeting will be held to discuss the
significant changes set out herein The date and location of the public meeting will be announced by
advertisement in a local newspaper of general circulation.
The basis for this significant change primarily rests on water-quality data. Secondary factors include
design considerations and historic performance of similar sites.
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Water quality data from 1983 through 1995 demonstrate that ground-water quality has improved or
remained consistent and has not degraded since 1988 Total VOC concentrations in on-site shallow
ground water have decreased and trends are either level or concentrations are very low or non-
detectable. VOCs in the primary aquifer on-site have only been consistently detected at one location
and the concentration has declined between 1988 and 1995. No trends indicative of rising VOC
concentrations appear in the data. Additional data gathered by the City of Dayton have not identified
a plume from the site in the primary aquifer south of the Great Miami River. Inorganic analyses
demonstrate that analyte trends are level or decreasing and are generally within background water
qualny ranges.
With regard to design considerations, the implementation of a ground-water pump and treat system
at this time may only show decreases in contaminant concentrations due to dilution caused by
pumping large quantities of ground water. In addition, while there appears to be a hydraulic
connection between landfill leachate and the aquifer, there is no indication of significant releases or
slugs of leachate. Any future leakage may be reduced by implementing the additional source control
measures required by the ROD, including tht :-nproved cap and leachate extraction system. Thus,
it is expected that the already low contaminant concentrations may decrease even further after
implementation of the other remedial components. Furthermore, it has been demonstrated at sites
similar to Powell Road Landfill that ground-water extraction and treatment systems are not effective
in removing low VOC concentrations, or making the aquifer pristine (Evaluation of Ground-Water
Extraction Remedies: Phase II, Vol. 1 and 2, February, 1992).
VI. Support Agency Comments
The Ohio EPA is in agreement with the modifications and approach3 made by the U.S. EPA to the
September 1993 Powell Road Landfill ROD, as expressed in this ESD
VII Affirmation of Statutory Determination
U.S. EPA has determined that the selected remedy, with the changes described above, will be
protective of human health and the environment, will comply with federal and State requirements that
are applicable or relevant and appropriate to this remedial action, and will be cost-effective. In
addition, the revised remedy utilizes permanent solutions and alternative treatment technologies to
the maximum extent practicable for this Site. Upon careful scrutiny of the suggested changes and the
information submitted to support such changes, U.S. EPA, therefore, has changed the remedy set out
in the ROD in the manner described above.
J40 C.F.R. 300.435(c); "Interim Final Guidance on Preparing Superfund Decision
Documents," (OSWER Directive 9355.3-02), June 1989, U.S. EPA Office of Emergency and
Remedial Response, at pp. 8-10 to 8-16.
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