The Kearsarge Metallurgical Corporation Site (Site) is located on the bank of Pequawket Pond in Conway Village, New Hampshire. Between 1964 and 1982, KMC manufactured stainless steel metal castings. Investigations by NHDES revealed that for many years waste materials generated during the casting process had been improperly stored and disposed on-site.
In 1982, approximately 54,000 pounds of corrosive solids, 17,800 gallons of acids and 600 gallons of flammable liquids, including industrial solvents, were removed from the Site by the PRPs. Monitoring wells were installed, and the sampling results confirmed the presence of volatile organic compounds (VOCs) in the groundwater.
In September 1984, the Site was added to the National Priorities List. The remedial investigation and feasibility study was completed in June 1990. EPA issued a Record of Decision (ROD) in September 1990 that defined two cleanup remedies: (1) removal of the “waste pile” and, (2) construction and operation of a groundwater extraction and treatment system.
In 1992, 13,621 tons of casting sand and soil were excavated and disposed at an off-site landfill. Approximately 30 to 40 cubic yards of contaminated soil was excavated from the former septic tank and leach field system and transported to a licensed hazardous waste disposal facility.
The design and construction of the groundwater extraction and treatment system was completed in 1994. In the fall of 1994, NHDES awarded a contract for the operation and maintenance of the groundwater treatment plant. The treatment plant has a capacity of up to 60,000 gallons of water per day.
In the summers of 1998 and 2003, EPA conducted five-year reviews of the Site and, in both cases, determined that the remedial action remained protective of human health and the environment.
In the fall of 2000, the treatment plant operations were modified by installing an extraction trench in the “culvert area” to enhance the groundwater extraction and reduce the cleanup time for achieving cleanup standards in groundwater. The new trench approximately doubled the rate of groundwater extraction in the “culvert area”. NHDES and its contractor agreed to temporarily pulse pump from the Hobbs Street wells to facilitate the removal of contaminants contained in the unsaturated drawdown zone of the extraction wells. After four months of pulse pumping, the sampling data did not show elevated levels of contaminants, therefore, suggesting the absence of remnant contaminants in the drawdown zone of these wells. As a result, pumping of the Hobbs Street wells was returned to normal continuous operation until February 2004, when the acquisition of sufficient analytical data supported shutting down the Hobbs Street wells.
In 2002, NHDES’ contractor completed a site characterization and cleanup assessment at the site in order to optimize the cleanup action and reduce the time necessary to operate the treatment facility. Discovered during this assessment was a previously undetected area of soil contamination that exceeded the soil leaching standard of the Department’s Risk Characterization and Management Policy.
Left in place, the contaminated soil would continue to impact groundwater and lengthen the time required to achieve cleanup goals by approximately 48 years. As a result, EPA and NHDES concluded that it would be most cost effective for the contaminated soil to be excavated and disposed in an off-site permitted landfill facility where the soil would not pose a risk to the groundwater. This source removal action began in October 2003 and was completed in January 2004 removing approximately 5,670 tons of chlorinated solvent-impacted soil.
Evaluation of the effectiveness of the source removal action to reduce groundwater contaminants in the culvert area has been on-going since completion of the source removal action. Site-wide groundwater data collected through September 2009 showed only one monitoring well that intermittently exceeded the cleanup standard for 1,1,1-trichloroethane (TCA, 200 parts per billion), historically the primary contaminant of concern at the site. Beginning in March 2004, samples collected from the extraction began a steep downward trend, no longer exceeding the cleanup standard for TCA, and approached non-detection (2 parts per billion) in 2005.
In December, 2005, the decision was made by the Department, with EPA concurrence, to discontinue extraction and treatment of the groundwater. The decision to shut down the system was supported by sampling data showing that the extracted water met cleanup standards. The mass of volatile organic compounds (VOCs) that was being removed, relative to the volume of water being extracted, was low.
Following the shutdown of the groundwater treatment plant in December 2005, contamination levels in groundwater rebounded and the plume of contamination expanded within the boundaries of the Site. However, in 2008 the groundwater plume began to contract as the rebound affect diminished. It is anticipated that the plume will continue to contract and eventually achieve cleanup standards.
EPA’s 2008 Third Five Year Review for the Site deferred a protectiveness statement until further information is obtained. Additional informational needs included: (1) evaluation of options to implement site institutional controls (ICs) to establish protective mechanisms that will ensure that the public is not exposed to site contaminants via consumption of groundwater or direct exposure to residual contamination in site soils; (2) an evaluation of monitored natural attenuation as a remedy; (3) EPA decision document to allow for a remedy change from active pumping and treatment of groundwater to monitored natural attenuation; and (4) evaluation of the potential for site-related contaminants to migrate into existing site buildings via vapor migration.
The properties constituting the site have been abandoned. Given the difficulty of establishing ICs on abandoned properties, the New Hampshire Department of Justice obtained an order from the New Hampshire Superior Court that provides for the implementation of activity and use restrictions on the abandoned properties. The activity and use restrictions include limitations on groundwater use and soil excavation and prohibit the use of the properties as a residence, school or nursery. The Court Order to implement these restrictions was recorded at the Carroll County Registry of Deeds on March 19, 2010.
Consideration of monitored natural attenuation as an alternate remedy will be evaluated in a focused feasibility study that will be prepared in 2010. The focused feasibility study, if sufficiently justifying a remedy change to natural attenuation, will support EPA’s preparation of a decision document for that remedy change. A public meeting and comment period will be provided should a remedy change be implemented.
Finally, an evaluation of the potential for site-related contamination to migrate into buildings via vapor migration was presented in a letter report dated April 14, 2009, prepared by Weston Solutions Inc., a state contractor. The findings conclude that the groundwater plume at the KMC Site does not pose a risk of vapor intrusion into any buildings on or near the Site.