Gelman Sciences dioxane plume now a federal Superfund site

August 31, 2026Clayey High Lime Till Plains

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A solvent plume that has been moving through the ground west of Ann Arbor since the 1960s is now a federal Superfund site.¹ EPA added Gelman Sciences to the National Priorities List on March 13 of this year, with a Hazard Ranking System score of 50; the threshold for listing is 28.5.¹ The record names a single contaminant of concern: 1,4-dioxane, the solvent the plant used in making medical filters and disposed of on site, largely by spraying wastewater onto the ground.²

The chemistry is what made this a decades-long problem rather than a spill. 1,4-dioxane mixes with water completely, barely clings to soil particles, and resists the soil bacteria that break down most industrial solvents.³ So it does not sit where it was put. In this till-plain landscape, clay-rich glacial deposits threaded with buried sand and gravel, the plume has followed those permeable lenses for miles, closing a city water supply well and spreading under residential neighborhoods along the way.

The record names the Huron River as the surface water that receives this groundwater.² Ann Arbor's drinking water intake is on that river, at Barton Pond.⁴

Being listed is a beginning, not a remedy. The site carries no cleanup milestones yet, which is exactly what a five-month-old listing looks like: no remedial investigation completed, no cleanup plan selected, nothing built. What the listing does is move oversight of a contamination case that has been managed under a 1985 state consent judgment into the federal Superfund process, with the funding and enforcement authority that carries.

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