The Dow Chemical Company began operations in 1897. The facility covers approximately 1,900 acres. It abuts the Tittabawassee River, with the majority of the plant located on the east side of the river and south of the city of Midland. Past waste disposal practices, fugitive emissions, and incineration at Dow have resulted in on and off-site contamination. Off-site contamination extends over 50 miles downstream of the Dow Midland facility through the Tittabawassee and Saginaw Rivers and into Saginaw Bay.
Dioxins (including furans) are the primary contaminants found off-site, although other contaminants have been identified as well. Dioxins are a group of chemicals that persist in the environment and build up in the food chain. The toxicity of individual dioxins is assessed and combined to determine the "toxic equivalence concentration," or TEQ, of the mixture. The Agency for Toxic Substances and Disease Registry Web site has a description of dioxin and its associated risk factors.
At various times during operation, the Midland Plant produced over 1,000 different organic and inorganic chemicals. Dioxins and furans were byproducts formed during the manufacture of chlorine-based products, including chlorophenolic compounds manufactured at the plant since the 1930s. Elevated dioxin levels in and along the Tittabawassee River appear to be primarily attributable to liquid wastes that were discharged in the past directly into the river from the Dow Midland facility. Over time, changes in waste management practices included installation and operation of a wastewater treatment plant. Changes in the wastewater treatment plant and subsequent incorporation of pollution controls have reduced or eliminated releases from the Midland Plant to the river. The Tittabawassee River may also be subject to flooding and stream bank erosion, particularly during high-energy stream flow events. As a result, dioxin contamination has spread to other locations within the flood plain of the Tittabawassee River, as well as to downstream locations.
The highest dioxin concentrations detected to date are 110,000 parts per trillion TEQ in the Tittabawassee River and 1,600,000 parts per trillion TEQ in the Saginaw River. These high levels led to Dow's cleanup of four hot spots in 2007, with EPA oversight. Fish and invertebrates within the Tittabawassee and Saginaw Rivers are contaminated. The Michigan Department of Community Health has issued fish and game consumption advisories.
In July 2008 an agreement was reached with Dow Chemical to clean up dioxin contamination in the Riverside Boulevard neighborhood.