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.
In 1987, the lagoon system was stabilized, contaminated debris on the site was removed, and the NHPC building was given a superficial cleaning under the supervision of the New Hampshire Department of Environmental Services (DES). In 1990, approximately 13,600 tons of contaminated sludge and soil at the property were stabilized on-site by the Environmental Protection Agency (EPA); 5,600 tons of contaminated sludge and soil was consolidated under an impermeable cap in a former lagoon area; and an additional 5,000 tons of soil were disposed off-site.
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.
Full-scale remedial construction activities began in the Summer of 2005 which included the excavation of all remaining contaminated soils and sludge from the site, treatment of contaminated soils through chemical fixation, backfilling treated soils on-site, regrading excavated areas, and the construction of a two-foot soil cover system over the backfilled treated soils. These activities were completed in December 2006.
The site's first Five-Year Review Report was completed in December 2009. In 2012, EPA completed a vapor intrusion assessment of nearby occupied structures and determined they were not at risk from the vapor intrusion pathway. Additional investigations in bedrock were conducted in 2012 to address certain data gaps identified in the first Five-Year Review Report and assess arsenic levels in bedrock south of Horseshoe Pond.
DES continues to conduct periodic monitoring of volatile organic compounds, 1, 4-dioxane, metals, and cyanide in the shallow overburden aquifer, deep overburden aquifer, bedrock aquifer and surface water.