The Nyanza Chemical Waste Dump is located on Megunko Road in Ashland, Massachusetts. The site was formerly the location of the Nyanza Chemical Company which operated a dye manufacturing facility at the property from 1965 to 1978. The Nyanza Company was one of the first and largest dye manufacturers in the United States. More than 100 different chemicals including volatile organic compounds (VOCs), semi-volatile organic compounds (SVOCs), dye manufacturing compounds, and metals have been detected on the approximately 35-acre site. In the past, liquid wastes have been discharged from the Nyanza site into the environment in several ways including into an underground vault, unlined lagoons, and nearby brooks and wetlands.

The Nyanza site is located in the central section of Ashland in a largely residential area. Chemical sludges generated by the dye manufacturing process were disposed of on an area of high ground referred to as, "Megunko Hill". Sludges containing large quantities of heavy metals (such as cadmium, chromium, lead, and mercury), aromatic amines (such as benzidine and 1-naphthylamine), and VOCs (such as 1,4-dichlorobenzene, trichloroethylene, and vinyl chloride) spilled and washed down the side of Megunko Hill to the wetlands below. Heavy metal sludges and organic solvents were disposed of in the lower industrial area in active lagoons or the underground vault. As a result, the groundwater beneath the site is highly contaminated with VOCs, SVOCs and metals. Anecdotal reports from the Ashland community provide evidence that children playing in the Megunko Hill area would often return home with blistered hands and discolored clothing.

In 1982, the U.S. Environmental Protection Agency placed the Nyanza site on the National Priority List. The Massachusetts Department of Environmental Protection (MDEP) restricted site access in 1982 by installing a partial fence. However, portions of the site were accessible to the public until the fence line was expanded in 1985.

In 1986, the Massachusetts Department of Public Health issued a fish advisory for the Sudbury River in Ashland to its confluence with the Assabet River in Concord, Massachusetts. The fish advisory warns residents to not eat any fish from the Sudbury River between Ashland and Concord due to mercury contamination.

This information is provided by the Community Assessment Program within the Department of Public Health.