The Kearsarge Metallurgical Corporation site is located on the northern bank of Pequawket Pond in Conway Village, New Hampshire. Between 1964 and 1982, KMC manufactured stainless steel metal castings. Investigations by DES 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, DES 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". DES and its contractor agreed to temporarily pulse pump from the Hobbs Street wells to facilitate the removal of residual 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, DES's 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 concentrated 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 DES concluded that it would be most cost effective for the contaminated soil to be excavated and disposed in an off-site permitted landfill 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 well began a steep downward trend, no longer exceeding the cleanup standard for TCA, and approached non-detection (2 parts per billion) for all volatile organic compounds (VOCs) in 2005.
In December, 2005, the decision was made by DES, 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 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. Since 2008, the plume has remained relatively stable with variability in contaminant levels based on groundwater table fluctuations.
EPA's 2008 Third Five Year Review for the site deferred a protectiveness statement until further information was obtained. Additional informational needs included: (1) evaluation of the potential for site-related contaminants to migrate into existing site buildings via vapor migration; (2) evaluation of options to implement site institutional controls 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; (3) an evaluation of monitored natural attenuation as a remedy; and (4) EPA decision document to allow for a remedy change from active pumping and treatment of groundwater to monitored natural attenuation.
An evaluation of the potential for site-related contamination to migrate into buildings via vapor migration was presented in a 2009 letter report with findings concluding that the groundwater plume at the KMC site does not pose a risk of vapor intrusion into any buildings on or near the site.
The properties constituting the site have been abandoned by previous owners. Given the difficulty of establishing institutional controls 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 restriction prohibits (1) the extraction of groundwater for purposes other than carrying out the remedy as specified in the administrative record for the site; (2) any activity, including soil excavation and groundwater extraction, interfering with the remedy established in the administrative record for the site; and (3) use of property soils for the production of food for human consumption. The Court Order and the Activity & Use Restrictions were recorded at the Carroll County Registry of Deeds on March 19, 2010 and August 30, 2011, respectively.
Monitored natural attenuation (MNA) as an alternate remedy was evaluated in a January 2012 Focused Feasibility Study (FFS) which provided the basis for a May 8, 2012 Proposed Plan that selected MNA as the preferred remedy to be adopted. Following a 30 day public comment period, the Proposed Plan was made final in a September 2012 Amended Record of Decision (AROD). All of these documents can be found on the EPA's web site.
Once the groundwater extraction and treatment remedy were changed to MNA, the treatment plant contents and building were no longer needed for remedy implementation. In a March 23, 2012 letter, EPA concurred with the Department's approach to allow transfer of the treatment plant building, remaining contents (excepting equipment identified for reuse by EPA or the State), and property to the Town of Conway upon their taking of the two parcels constituting the Site through a tax deed. The Town of Conway Board of Selectmen voted to take the property at their August 21, 2012 meeting.