Buying on Ann Arbor's west side or in Scio Township? Know about the groundwater plume

If you’re house-hunting on the west side of Ann Arbor or in Scio Township, here’s a local issue worth understanding: a plume of a chemical called 1,4-dioxane in the groundwater. It came from the old Gelman Sciences factory on Wagner Road, which used the solvent from the 1960s into the 1980s. The contamination was found in 1986 and has slowly spread underground ever since, beneath roughly three square miles of western Ann Arbor and parts of Scio and Ann Arbor townships. The chemical dissolves completely in water and is considered a likely cause of cancer, so it’s treated seriously. Here’s the practical picture for a buyer. Most Ann Arbor homes are on city water, which comes mainly from the Huron River and is tested regularly — and the city watches the plume closely, since the main worry is whether dioxane could one day reach the river near the city’s water intake. Within the contaminated area, the state has drawn a “Prohibition Zone” where groundwater can’t be used for drinking; many affected homes there have been connected to city water instead. The cleanup has been under court supervision since 1992 and has long been criticized as too slow — and in March 2026 the site was added to the federal Superfund list, which brings more money and authority to finish the job. The bottom line: for any home in this area, find out whether it’s on city water or a private well, whether it sits in the Prohibition Zone, and look it up on the state’s online dioxane map. Recent state testing of nearby wells has come back below the drinking-water limit, but it’s a real, ongoing situation worth asking about.