The former Mohawk Tannery site, also called Granite State Leathers, encompasses approximately 30 acres on the Nashua River in Nashua. The tannery operation occupied about 15 of the 30 acres and produced tanned hides for leather between 1924 and 1984. It has been inactive since then, and the adjacent residential community has expanded in the vicinity of the site.
While in operation, the tannery generated both alkaline and acid waste streams from its hide preparation and the tanning processes. Little is known about the tannery waste treatment and management practices prior to the 1960s. From the 1960s until the completion of an on-site treatment facility in 1981, the acid waste stream passed through a series of five settling basins and was then discharged to the Nashua River via an open channel. The alkaline waste stream was conveyed to a screen building for removal of solids, and then to two impoundment lagoons, located within the river’s 100-year floodplain, for long-term sedimentation. After settling, the liquid fraction of the alkaline waste stream was discharged directly to the Nashua River, and sludge was periodically dredged from the lagoons and disposed of on-site in several unlined landfills.
The estimated 60,000 cubic yards of sludge that remain in the lagoons and unlined landfills are a continuing potential threat to groundwater and the Nashua River. None of the disposal areas were designed, constructed, or maintained in accordance modern standards, and there are concerns about migration of dissolved contaminants and the possibility of a catastrophic washout during a flood. The site was proposed for the National Priorities List (NPL) on the basis of these past disposal practices. The site has not been added to the NPL.
US Environmental Protection Agency completed a time-critical removal of 55 drums of hazardous materials and asbestos-containing material from the former tannery building in January 2001. An engineering evaluation/cost analysis (EE/CA) was completed in July 2002, and a remedial investigation was completed in June 2005. These studies provided a basis for the development and evaluation of potential cleanup options.
The New Hampshire Department of Environmental Services, the EPA, and the city of Nashua continue to review options for this site. During 2009 the EPA conducted pilot tests to determine whether the site can be stabilized in place using a solidification stabilization process. Such an approach would be less expansive than excavating and hauling the material to a suitable disposal site, while still allowing the site to be suitable for some types of reuse. The results of the study were mostly positive.