The Mohawk Tannery operated in Nashua, New Hampshire from 1924 to 1984, leaving behind lagoons, pits, and drainage basins filled with tannery waste. EPA proposed the site for the National Priorities List in May 2000. Cleanup is now underway, though the site has not yet reached remedy selection, construction completion, or final deletion from the list.
The site is contaminated with heavy metals including chromium, zinc, arsenic, antimony, cadmium, and manganese, along with dioxins, pentachlorophenol, benzo(a)pyrene, semi-volatile organic compounds, and asbestos. These contaminants sit in open lagoons and surface soils, with the highest concentrations in the northern parcel near the Nashua River. Two large disposal areas border the river directly, one of them inside the 100-year flood plain. Groundwater in the southern parcel exceeds safe levels for residential use. About 5,025 people rely on groundwater wells within 4 miles of the site, and fishing takes place downstream on both the Nashua and Merrimack Rivers.
Risk assessments from 2002, 2005, and 2013 found that the northern parcel sludge areas pose the greatest risks to human health. Cancer risks are driven mainly by dioxins, pentachlorophenol, arsenic, and benzo(a)pyrene. Non-cancer hazards come primarily from arsenic, antimony, cadmium, manganese, and 4-methylphenol. The contaminated soils and groundwater also pose risks to wildlife and ecological receptors. Human exposure control and groundwater migration control cannot be determined due to insufficient data.
EPA performed an initial removal action from September 2000 to January 2001, clearing asbestos-containing material and contaminated drums. In 2019, EPA approved a non-time-critical removal action calling for excavation, consolidation, and impermeable capping of contaminated sludge and soils. EPA reached a cost-sharing agreement with developer Blaylock Holdings LLC in December 2020, later modified in May 2025. Cleanup began on December 10, 2025, under Blaylock's direction with oversight from EPA and the New Hampshire Department of Environmental Services. The work will consolidate roughly 68,150 cubic yards of contaminated sludge, build a vertical containment barrier around former lagoons, and install an impermeable cap designed to withstand a 500-year flood event. Flood storage loss will be addressed through mitigation structures. The project is expected to last 24 to 36 months, after which Blaylock plans to redevelop the property into residential units.
Community members can follow cleanup progress at www.thorndikedevelopment.com/mohawktannery. EPA holds public informational meetings throughout construction. Site documents, including fact sheets, news releases, and administrative records, are available at the Nashua Public Library (2 Court Street, Nashua, NH, 603-594-3412) and at the EPA Region 1 Records and Information Center in Boston (5 Post Office Square, Suite 100, 617-918-1440). For printed updates or to join the mailing list, contact the EPA's Community Involvement Coordinator.
