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The Nyanza Chemical Waste Dump site is a 35-acre area next to an active industrial complex in Ashland, Massachusetts. From 1917 to 1978, facilities produced textile dyes, intermediates and other products on site. Nyanza Inc. operated on site from 1965 until 1978. Large volumes of industrial wastewater containing high levels of acids and numerous organic and inorganic chemicals, including mercury, were generated by these facilities, leading to soil and groundwater contamination. Over 45,000 tons of chemical sludges generated by Nyanza's wastewater treatment processes, along with spent solvents and other chemical wastes, were buried on site. The area that contained the largest amount of buried waste and exposed sludge is referred to as the Hill section. The current owner leases the old plant grounds to various businesses.

The site was added to EPA's National Priority List on December 30, 1982.

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What Has Been Done to Clean Up the Site?

The site is being addressed through federal and state actions.

The site is being addressed in five stages: initial actions and four long-term remedial phases focused on source control and cleanup of the soil, off-site groundwater, wetlands and the Sudbury River.

Source Control: EPA's source control remedy included excavating all outlying sludge deposits and contaminated soils and sediments associated with these deposits; consolidating this material with the on-site Hill sludge deposits; capping the Hill section to prevent water from entering it and spreading contaminants; putting in a groundwater and surface water diversion system on the upgradient side of the Hill area; backfilling excavated areas to original grade; fencing the site; establishing a vegetative cover in the wetland areas; and expanding groundwater monitoring. Cleanup actions took place between 1990 and 1992.

Off-Site Groundwater: EPA selected an interim remedy to clean up off-site groundwater contamination in 1991. The selected remedy was to pump and treat the contaminated groundwater from the most contaminated portions of the plume for five years. However, due to the discovery of additional contamination, EPA reevaluated the remedy. After additional data collection and risk assessment, with added emphasis on potential indoor air contamination, EPA updated the remedy in 2006. It includes the extraction of dense non-aqueous phase liquid (DNAPL) from the groundwater plume as well as the installation of vapor mitigation systems in homes overlying the contaminated plume. Forty systems were installed in 2007. The Massachusetts Department of Environmental Protection (MassDEP) inspects these systems annually. EPA also conducted subsurface investigations to locate pockets of recoverable DNAPL. Wellhead treatment systems will recover the DNAPL.

Wetlands: The remedy for contaminated sediment and surface water of the adjacent eastern wetlands and drainageways between the site and the Sudbury River included excavation of the contaminated material and its placement in the on-site landfill. Over 45,000 cubic yards of mercury-contaminated sediments were excavated from four areas (Eastern Wetland, Trolley Brook, Outfall Creek, Lower Raceway) and disposed of in the on-site landfill. EPA completed all cleanup activities between 1999 and 2001.

Sudbury River: The remedy relies on monitoring, institutional controls such as continued posting of warning signs, and the addition of a thin-layer sand cap over the most highly contaminated sediments.

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What Is the Current Site Status?

MassDEP is currently responsible for site operation and maintenance activities. The excavation of contaminated soil and capping of the Hill area of the site have reduced the potential of exposure to hazardous substances by controlling contaminant migration and isolating wastes. Wetland excavations and restoration have eliminated the ongoing mercury contamination source to the Sudbury River. In 2007, EPA reposted the river with signs warning against the consumption of contaminated fish. The warning signs are inspected annually. These actions have made the site safer during cleanup.

Operation and maintenance activities and monitoring are ongoing.

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