The New Hampshire Plating Company site is located in the town of Merrimack on Wright Avenue, off the Daniel Webster Highway. The 13.1-acre property is in a light industrial and commercial area. The Merrimack River is located 600 feet east of the site. Horseshoe Pond lies 900 feet to the south. The site consisted of a former electroplating operations building, a paved parking lot, a 6,000-gallon underground storage tank and a wastewater lagoon system.
Between 1962 and 1985, large volumes of electroplating wastes were discharged into a system of four unlined lagoons. Cyanide wastes, metal plating sludge, acids, and solvents were routinely discharged to the lagoon system. The lagoon system was in what were once natural wetlands that appeared to have been altered by the disposal practices of the New Hampshire Plating Company (NHPC). The interior of the NHPC operations building was contaminated with high levels of heavy metals. NHPC operations ceased in 1985.
Interim remedial activities were conducted at the site in June 1987. The activities included: the treatment of the lagoon system with lime and sodium hypochlorite solution; the removal of debris, drums, and plating tank liquids from the property; and some cleaning of the former manufacturing building.
Between May 1990 and November 1991, EPA conducted emergency removal actions at the site that included: fixation for 4,500 cubic yards of contaminated soil and 1,110 cubic yards of sludge; removal of 800 gallons of #2 fuel oil from the underground storage tank under the NHPC facility building; consolidation and capping of the highly contaminated soil in Lagoon 1; covering the remaining lagoons and holding cell with 12-18 inches of clean soil; and seeding the clean soil. The site was listed on the National Priorities List (NPL) in October 1992.
A Non Time-Critical Removal Action (NTCRA) was completed in late 1994. The NTRCA consisted primarily of the demolition and disposal of the building structure (including asbestos containing material) and disposal of visibly contaminated soils from beneath the building.
Based on information contained in the Remedial Investigation/Feasibility Study (RI/FS) documents, EPA and DES selected a Proposed Plan to cleanup contaminated media at the site. EPA issued a Record-of-Decision (ROD) in October 1998 that called for in-situ chemical fixation of contaminated soil and establishment of a Groundwater Management Zone to allow for monitored natural attenuation of contaminants in groundwater.
The restoration or creation of on-site wetlands to compensate for impacted wetlands was considered impractical due to cost and limited space. To meet the requirements of wetland mitigation, EPA and DES jointly agreed to purchase and preserve an ecologically rare and significant wetland in the adjacent town of Litchfield. The wetland, known as Grassy Pond, was purchased by DES in May 1998 under an agreement with EPA. The purchase represented a unique opportunity to use Superfund wetlands mitigation funds to acquire a critically important wetlands area and the surrounding upland, and permanently protect it. DES, the town of Litchfield’s Conservation Commission, and The Nature Conservancy finalized a Natural Areas Protection Agreement in December 2000.
The agreement required the parties to produce a property management plan for Grassy Pond, which was completed late 2002. EPA and DES also provided funds in the fall of 2002 for the purchase of additional wetlands in the town of Merrimack as part of the site wetland mitigation effort.
The town of Merrimack was awarded a Superfund Redevelopment Pilot Program grant in 2001 to enhance its role in planning the reuse of the site by providing funding and other assistance to evaluate reuse options. The town developed a draft Reuse Plan to help identify the town’s desire for reuse of the site after EPA and DES completed the anticipated cleanup. The plan identified a number of potential redevelopment options and recommended that recreational fields be proposed for reuse of the site.
In August 2004, EPA secured the funding for the final cleanup work required at the site. In November 2004, EPA and DES prepared the site for remedial construction activities, including well and piezometer decommissioning services. A total of 47 monitoring wells and 21 piezometers were decommissioned, so that the property could be accessed by construction equipment. EPA contractors excavated and treated approximately 95,000 tons of contaminated soil from areas of the site. The excavated soil was treated with a process known as “chemical fixation” that binds metal contaminants preventing them from being available to migrate and contaminate the underlying groundwater. The treated soil was then backfilled into the excavation areas and graded with the rest of the property. A permeable cap was constructed over the treated soils. Remedial construction activities were completed in late fall 2006.
In early 2007, a network of groundwater wells was installed so that EPA and DES can monitor contaminant level over time following completion of the source control remedy. The monitoring will determine the concentrations of volatile organic compounds (VOCs), 1, 4-dioxane, metals, and cyanide potentially present in the shallow overburden aquifer, deep overburden aquifer, and bedrock aquifer underlying the site.
The site’s first Five-Year Review Report was completed in December 2009. Recommendations included institutional controls for both the NHPC property and groundwater. Evaluate groundwater monitoring data to assess the potential for vapor intrusion at abutting properties. Monitor metals in the pore water and sediments in the transition zones between groundwater and surface water to evaluate potential ecological risk.
Periodic monitoring of the ground water and surface water continues under DES supervision.