PB96-963127
EPA/AMD/R01-96/12S
April 1997
EPA Superfund
Record of Decision Amendment:
Coakley Landfill Site,
North Hampton, NH
5/17/1996
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DECLARATION FOR THE
EXPLANATION OF SIGNIFICANT DIFFERENCES
COAKLEY LANDFILL STJPERFUND SITE
SITE NAME AND LOCATION
Coakley Landfill Superfund Site
North Hampton and Greenland, New Hampshire
STATEMENT OF PURPOSE
This decision document sets forth the basis'for the determination
to issue the attached Explanation of Significant Differences
(BSD) for the Coakley Landfill Superfund Site in North Hampton
and Greenland, New Hampshire.
SXATuTORVPAS IS FOR ISSUANCg j)F TEE ESP
Under Section 117(c) of the Comprehensive Environmental Response,
Compensation, and Liability Act (CERCLA), 42 U.S.C. § 9617{c), if
the U.S. Environmental Protection Agency (EPA) determines that
the remedial action being undertaken at a site differs
significantly from the Record of Decision (ROD) for that site,
EPA shall publish an explanation of the significant differences
between the remedial action being undertaken and the remedial
action set forth in the ROD and the reasons such changes are
being made. Section 300.435(c) of the National Contingency Plan
(NCP), 40 C.F.R. § 300.435{c), and EPA guidance (Office of Solid
Waste and Emergency Response [OSWER] Directive 9355.3-02),
indicate that an BSD, rather .than a Record of Decision (ROD)
amendment, is appropriate where the changes being made to the
remedy are significant but do not fundamentally alter the overall
remedy with respect to scope, performance, or cost. Because the
adjustments to the ROD provided in the ESD are significant but do
not fundamentally alter the overall remedy for the Site with
respect to scope, performance, or cost, this ESD is properly
being issued.
In accordance with Section 300.435(c) of the NCP, this ESD and
supporting documentation will become part of the Administrative
Record which is available for public review at both the EPA
Region I Records Center in Boston, Massachusetts and the North
Hampton Public Library in North Hampton, New Hampshire.
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OVERVIEW OF Tp^ BSD
Based on data generated during extensive pre-design studies and
other new information developed after the ROD was issued, the
landfill gas management component of the selected remedy
described in the ROD issued June 20, 1990, has been modified.
The ROD required collection and treatment of landfill gases
generated below the cap by means of an active interior gas
collection system The collected gases would be treated on-site
by a thermal destruction process. Evaluations using data not
available when the ROD was issued indicated that rates of gas
generation and levels of hazardous substances in the landfill gas
would be lower than those assumed and used for the preparation of
the ROD. Therefore, after consultation with NHDES, EPA has
concluded that a passive landfill gas collection and venting
system will prevent off-site, sub-surface migration of landfill
gases and be protective of human health and the environment,
while saving significant costs.
DECLARATION
For the foregoing reasons, by my signature below, I approve the
issuance of an Explanation of Significant Differences for the
Coakley Landfill Superfund Site in North Hampton and Greenland,
New Hampshire, and the changes stated therein.
7 19% (Taafr
Linda M. Murphy, Direfctor
Office of Site Remediation and
Restoration
U.S. E.P.A., Region I
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EXPLANATION OF SIGNIFICANT DIFFERENCES
COAKLEY LANDFILL SUPERFUND SITE
NORTH HAMPTON AND GREENLAND, NEW HAMPSHIRE
I. INTRODUCTION
A. Site Name and Location
Site Name: Coakley Landfill Superfund Site
Site Location: Towns of North Hampton and Greenland,
Rockingham County, New Hampshire
B. Lead and Support Agencies
Lead Agency: United States Environmental Protection
Agency
Support Agency: New Hampshire Department of
Environmental Services
C. Legal Authority
Under Section 117(c) of the Comprehensive Environmental Response,
Compensat-ion, and Liability Act (CERCLA) , 42 U.S.C. § 9617(c),
Section 300.435(c) of the National Contingency Plan (NCP), 40
C.F.R. § 300.435{c), and U.S. Environmental Protection Ageny
(EPA) guidance {Office of Solid Waste and Emergency Response
[OSWER] Directive 9355.3-02), if EPA determines that differences
in the remedial action significantly change but do not
fundamentally alter the remedy selected in the Record of Decision
(ROD) with respect to scope, performance, or cost, EPA shall
publish an explanation of the significant differences between the
remedial action being undertaken and the remedial action set
forth in the ROD and the reasons such changes are being made.
D. Summary of Circumstances Necessitating this Explanation
of Significant Differences
The volume of the gas generated within the landfill and the
constituents contained in that gas were evaluated during the Pre-
Design Investigation conducted by the Coakley Landfill Group
under EPA and NHDES oversight in accordance with the Consent
Decree Scope of Work for the Site. The evaluation took into
account standards which must be achieved (Applicable or Relevant
and Appropriate Federal and State environmental laws and
regulations [ARARs] ) and public health risks. This evaluation
used data which were not available when the ROD for the source
control remedy was written.
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EXPLANATION OF SIGNIFICANT DIFFERENCES
COAICLSY LANDFILL SUPKRFUND SITS
Hay. 1996 ' Page 2
S. Availability of Documents
This Explanation of Significant Differences (BSD) and supporting
documentation shall become part of the Administrative Record for
the Site. The BSD, supporting documentation for the BSD, and the
Administrative Record are available to the public at the
following locations and may be reviewed at the times listed:
U.S. Environmental Protection Agency
Records Center
90 Canal Street
Boston, MA 02114
(617) 573-5729
Weekdays from 10:00 a.m. to 1:00 p.m.,
and from 2:00 p.m. to 5:00 p.m.
North Hampton Public Library
235 Atlantic Avenue
North Hampton, NH 03878
(603) 692-4587
Monday through Thursday from 10:00 a.m. to 8:00 p.m. and
Friday from 10:00 a.m. to 5:00 p.m.
II. SUMMARY OF SITE HISTORY, CONTAMINATION PROBLEMS, AND
SELECTED REMEDY
A. Site History and Contamination Problems
The Coakley Landfill Superfund Site (the Site) includes
approximately 92 acres located within the Towns of Greenland and
North Hampton, Rockingham County, New Hampshire (See Site Map
below). The actual landfill covers approximately 27 acres of
this property. The Site is located about 400 to 800 feet west of
Lafayette Road (U.S.Route l), directly south of Breakfast Hill
Road, and about 2.5 miles northeast of the center of the Town of
North Hampton. A more complete description of the Site can be
found in the Remedial Investigation Report, Chapter 2, Pages 2-1
to 2-6.
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EXPLANATION OF SIGNIFICANT DIFFERENCES
COAKLBY LANDFILL SDPBRFOND SITE
M*y, 1996
P*?e 3
COAKLEY LANDFILL
SITEMAP
Landfill operations began in 1972, with the southern portion of
the Site used for refuse from the New Hampshire municipalities of
Portsmouth, North Hampton, Newington, and New. Castle, along with
Pease Air Force Base. Concurrent with landfill operations, rock
quarrying was conducted at the Site from approximately 1973
through 1977. Much of the refuse disposed of at Coakley Landfill
was placed in open (some liquid-filled) trenches created by rock
quarrying and sand and gravel mining.
From 1972 until July 1982, the Site accepted municipal waste. In
1982, the City of Portsmouth began operating a refuse-to-energy
plant on leased property at Pease Air Force Base. From July 1982
through July 1985, Pease Air Force Base and the municipalities of
Rye, North Hampton, Portsmouth, New Castle, Newington and Derry,
among others, began transporting their, refuse to this plant for
incineration. The Coakley Landfill generally accepted only
incinerator residue from the new plant after July, 1982. In
March 1983, the New Hampshire Bureau of Solid Waste Management
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BXPLANATION OP SIGWXFICANT DIFPBRKNCBS
COAKLBY LANDFILL SUPKRFOND SITS
»«y, 1996 Page 4
ordered the landfill closed to all waste disposal except burnt
residue from the incinerator. In July, 1985, the landfill was
closed to all disposal activities.
In 1979, the New Hampshire Waste Management Division received a
complaint concerning leachate breakouts in the area. A
subsequent investigation by the Bureau of Solid Waste Management
resulted in the discovery of allegedly empty drums with markings
indicative of cyanide waste.
A second complaint was received in early 1983 by the New
Hampshire Water Supply and Pollution Control Commission (WSPCC)
regarding the water quality from a domestic drinking water well.
Testing revealed the presence of five different Volatile Organic
Compounds (VOCs).
A subsequent confirmatory sampling beyond these initial wells
detected VOC contamination to the south, southeast,and northeast
of the Coakley Landfill. As a result, the Town of North Hampton
extended public water to Lafayette Terrace in 1983 and to Birch
and North Roads in 1986. Prior to this time, commercial and
residential water supply came from private wells.
Also in 1983, the Rye Water District completed a water main
extension along Washington Road to the corner of Lafayette Road
and. along Dow Lane. . This extension brought the public water
supply into the area due east and southeast of the Rye Landfill.
In December 1983, the Coakley Landfill was proposed for listing
on the National Priority List (NPL), and in 1986 it was listed
and ranked as No. 689.
A cooperative agreement was signed with the State of New
Hampshire on August 12, 1985 to conduct a Remedial
Investigation/Feasibility Study (RI/FS). The contractor, Roy F.
Weston, Inc., completed the RI and the FS which were released for
public comment on October 31, 1988, and March 2, 1990,
respectively. The Proposed Plan containing EPA's preferred
alternative was released with the FS. On June 28, 1990, EPA
issued a Record of Decision (ROD) for the source control operable
unit of the Coakley Landfill Superfund Site (Site). On
March 2, 1991, EPA issued an BSD concerning modifications to the
source control remedy related to landfill cap construction and
emissions from air strippers used to treat the groundwater.
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EXPLANATION OP SIGNIFICANT DIFFERENCES
COAKLBY LANDFILL SUPERFUND SITS
Hay, 1996 Page S
B. Summary of the Selected Remedy
The selected source control remedy is the first operable unit of
a two operable unit approach to the remediation of the Site. It
provides for the remediation of the source at the Coakley Site
including the contaminated groundwater beneath and in the
vicinity of the landfill (i.e., source control). The second
operable unit addressed groundwater contamination which has
migrated from the landfill, beyond the property boundary (i.e.
management of migration) through natural attenuation of the
contaminated groundwater along with institutional controls to
prevent exposure to the contamination. This BSD affects only the
source control remedy.
The source control remedy involves consolidating sediments and
solid waste followed by capping the landfill and extracting and
treating on-site groundwater and landfill gases. The major
components of the remedy are:
l. Consolidating sediment in the wetlands
2. Consolidating solid waste;
3. Capping the landfill;
4. Fencing the landfill;
5. Collecting and treating landfill gases;
6. Extracting and treating groundwater;
7. Long-term environmental monitoring; and
8. Institutional controls where possible.
III. DESCRIPTION OF SIGNIFICANT DIFFERENCES
Since the signing of the ROD, an extensive Pre-Design
Investigation was conducted by the Coakley Landfill Group, with
EPA and NHDES oversight, pursuant to the Consent Decree Scope of
Work. This investigation indicated that modifications to the
landfill gas management component of the selected remedy could
achieve significant cost savings while remaining protective of
public health and the environment.
The ROD required collection and treatment of landfill gases
generated below the cap by means of an active interior gas
collection/recovery system. The collected gases would be treated
on-site by a thermal destruction process. Through the use of
mathematical models based upon sampling done at the landfill
during the Pre-Design Investigation, gas generation rates were
able to be more accurately predicted and their impacts evaluated.
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EXPLANATION OF SIOTTFICAHT DIFPBRKNCK3
COAKLBT LANDFILL SUPBHTOND SITB
May, 1996 Page 6
In addition, the predicted ambient air concentrations of
hazardous constituents in the gas were evaluated and compared to
ARARs and health risk levels. Based on these evaluations, rates
of gas generation and levels of hazardous substances in the
landfill gas were found to be lower than those assumed and used
for the preparation of the ROD. Furthermore, a review of
landfills recently closed in the State indicates that passive gas
collection and venting has been effective in preventing off-site
migration of landfill gas beneath impermeable covers. The design
of the system at the Coakley Landfill is conservative based on a
review of selected landfills having similar characteristics. The
thickness of the gas collection layer (12 inches), the number of
vents per acre (2.5), and the number of annual air samples (25),
exceed requirements at the other sites.
In addition, the passive gas management system will result in a
capital cost savings of $346,500 and a present worth cost savings
for operations and maintenance over a 30 year period of $320,400.
Therefore, after consultation with NHDES, EPA has concluded that
a passive landfill gas collection and venting system will prevent
off-site, sub-surface migration of landfill gases, while saving
significant costs. In addition, this system will meet all
standards for ambient air quality.
The proposed modification embodied in this BSD will protect human
health and the environment, will comply with, all applicable or
relevant and appropriate Federal and State requirements, and will
provide for a long-term and permanent remedy for the Site to a
similar degree as the remedy outlined in the ROD as modified by
the first BSD, and will pose the same short-term, construction-
related risks as the remedy contained in the ROD, as modified in
the first BSD. In addition, the proposed modification to the
remedy will reduce construction costs, as well as, operation and
maintenance costs.
IV. SUPPORT AGENCY COMMENTS
The State of New Hampshire has participated with EPA in reviewing
the modifications to the design which are described herein and
concurs with the approach adopted by EPA.
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EXPLANATION OP SIGNIFICANT DIFFERENCES
COAKLHY LANDFILL SUPSRFUND SITE
May, 1996 P«g« 7
V. STATUTORY DETERMINATION
Considering the above outlined adjustment to the selected remedy
set forth in the ROD, as modified in the first ESD, EPA believes
that the remedy remains protective of human health and the
environment, complies with all Federal and State requirements
that are applicable or relevant and appropriate to this remedial
action, and is cost-effective.
VI. PUBLIC INFORMATION
This BSD and the Administrative Record are available for public
review at the locations and times listed in Section I.', above.
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