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New Hampshire Department of Environmental Services

Site Summaries

Coakley Landfill Site
North Hampton
Contact: Drew Hoffman (603) 271-6778

The Coakley Landfill Superfund site is located in the towns of North Hampton and Greenland and abuts the town of Rye to the east. Situated on the southernmost portion of a 92-acre parcel, the landfill received municipal and industrial wastes from 1972 to 1982. From 1982 to 1985, when land-filling activities terminated, the site received incinerator residue from the Portsmouth Refuse-to-Energy Facility at Pease Air Force Base.
In 1983, the State received a complaint from residents, living near the southeastern corner of the landfill, about the quality of water coming from their water supply wells. Water samples were taken and the results of the chemical analyses reported the presence of volatile organic compounds (VOCs) in several residential wells. Water lines from three local utility companies were promptly extended into the area and, by the end of 1983, most of the homes and businesses east of the site were connected to public water supplies.

The site was listed on the National Priorities List in December of 1983. The subsequent remedial investigation and feasibility study (RI/FS) was completed in 1989. The findings of the RI/FS identified the landfill as the source of contamination in local surface waters, groundwater and, to an unknown extent, in wetlands to the west.

The first Record of Decision (ROD) for the site, signed in June of 1990, required constructing a landfill cap and treating contaminated groundwater. It separated response actions to be taken in the immediate vicinity of the landfill (i.e., source control) from those taken to address contamination outside the landfill footprint (i.e., management of migration).

Operable Unit 1 (OU-1) is a source control action intended to minimize further degradation of the environment by isolating the contaminant sources. The ROD for OU-1 includes consolidating sediments on the landfill, consolidating refuse material within the landfill footprint, constructing a multi-layered landfill cap over the landfill, treating groundwater and landfill gases, and long-term monitoring. Pre-design studies began in the summer of 1992. Construction of the landfill cap began in the fall of 1996 and was completed in August 1998.
Due to limited information concerning off-site contamination of wetlands, a second operable unit (OU-2) required further evaluation of site conditions in order to determine the most appropriate response action. A second ROD for the site to address management of migration was issued in September 1994. The ROD for OU-2 calls for groundwater monitoring over the next thirty years while contamination naturally attenuates and the elimination of potential threats posed by the future ingestion of contaminated groundwater by implementing institutional controls restricting the use of the groundwater.

Following completion of the landfill cap, the plume of VOC-contaminated groundwater stopped expanding and began attenuating.  Therefore, EPA issued an Explanation of Significant Differences on September 29, 1999, that removed the requirement to treat groundwater directly beneath the landfill.  However, a newly identified contaminant of concern, 1,4-dioxane, was also identified to be migrating from the landfill to the north and west. 

The Second Five-Year Review was finalized in September 2006 by EPA. A site-wide protectiveness determination could not be made in this review due to sporadic violations of off-site methane gas levels. Follow-up actions included continued quarterly monitoring of compliance boundary gas probes and installation of gas alarm systems in adjacent buildings/homes that may be at risk. Since 2006, methane levels have decreased significantly with no exceedance of regulatory standards in any probe since 2011. Regular monitoring of the gas probes is on-going.

The September 2011 Five-Year Review concluded that the remedy remained protective of human health and the environment in the short-term.  Long-term protectiveness has also been achieved at OU-1 based on continued maintenance of the landfill cap, long-term monitoring, and use restrictions being in-place. Long-term protectiveness will also be achieved at OU-2 when interim groundwater cleanup levels for all contaminants of concern are met and restrictions on the use of groundwater within OU-2 can be removed. Monitoring of the site will continue until cleanup levels for the contaminants of concern are met.  The next Five Year-Review is scheduled for September 2016.

Recent exceedances of drinking water standards for several contaminants (i.e., arsenic, manganese and 1,4-dioxane) at the northwest corner of the existing groundwater management zone prompted the agencies to request the responsible parties to conduct additional sampling of residential wells beyond the area of concern. While no private wells sampled exceeded the current drinking water standard for 1,4-dioxane, expanded residential sampling in the area north of the site will be incorporated into the regular sampling program.  In addition, the groundwater management zone (GMZ) was expanded recently to include additional properties to the north/northwest of the site.  Given the absence of public water to the north of the site, future development in this area that utilizes bedrock groundwater for public use is of concern to DES and EPA and will be closely monitored. 

NH Department of Environmental Services | 29 Hazen Drive | PO Box 95 | Concord, NH 03302-0095
(603) 271-3503 | TDD Access: Relay NH 1-800-735-2964 | Hours: M-F, 8am-4pm

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