EPA Settlement Orders Gelman to Contain 1,4-Dioxane Plume in Ann Arbor

A 3-to-4-square-mile plume of 1,4-dioxane-contaminated groundwater will face new containment, monitoring and study obligations under an administrative settlement the U.S. Environmental Protection Agency announced Friday with Gelman Sciences LLC.

The agreement targets the so-called Gelman plume, a contaminated groundwater body sitting just west of the Huron River in and around Ann Arbor, Michigan. According to the EPA, the plume "has migrated into aquifers that supply drinking water."

The stakes are concrete. Barton Pond, the source of 85% of Ann Arbor's drinking water, sits downstream on the Huron River, and regulators and local advocates have watched the plume's slow eastward spread for decades.

What does the settlement require?

Under the agreement, Gelman must take five actions:

• Slow the plume's spread toward the Huron River by increasing groundwater extraction and treatment on the plume's eastern edge
• Increase monitoring to better define that eastern edge
• Excavate contaminated soil at a portion of the former Gelman facility
• Conduct a feasibility study assessing the extent of contamination and potential remediation options
• Fund an independent expert to explain technical site conditions and possible actions to the community

The EPA announced the deal as an administrative settlement agreement — a binding set of company obligations rather than a suggestion, and the first major federal enforcement product since the site's listing in March on the Superfund National Priorities List.

That listing paved the way for expanded EPA oversight, including this agreement. It layers onto an older state framework: a 1992 court-supervised consent judgement between Gelman and Michigan that required the company to manage the spread of 1,4-dioxane on the site without assuming liability for the contamination. Local advocates have long argued that judgement falls short.

What is the contamination?

The plume stems from contaminated wastewater Gelman dumped at its medical filter manufacturing facility beginning in the late 1960s. The contamination was discovered in 1986 — nearly 20 years after the dumping started — and has continued spreading since.

The chemical at issue, 1,4-dioxane, is classified by the EPA as "likely to be carcinogenic to humans." Specific human health impacts remain poorly understood, but animal studies show the chemical can cause liver and kidney damage.

The result is a decades-old, still-moving contamination front that now intersects drinking water aquifers.

What do advocates say?

Rebecca Esselman, executive director of the Huron River Watershed Council, said she was encouraged by the federal settlement, though she had not yet reviewed all details of the 100-page agreement.

"What we know about groundwater contaminations like this is there's no cleaning it up 100%," Esselman said. "And that is a legacy that we'll have to live with in perpetuity in the Huron River."

She set a high bar for what should follow. The plume needs "an aggressive cleanup," Esselman said. "And residents and local governments have waited too long and the risks are too high for anything shy of that."

What happens next?

The near-term markers are mechanical: expanded extraction and treatment on the plume's eastern edge, denser monitoring to map that boundary, soil excavation at the former facility, and a feasibility study that will define the scale of any full remediation.

The feasibility study is the decision point. Its findings will determine whether the cleanup matches the aggressive standard advocates demand or repeats what they see as the failures of the 1992 consent judgement — and the Superfund listing gives the EPA the leverage to enforce whatever comes out of it.