ANN ARBOR, MI – City officials are inviting residents to a public meeting to learn about options for better tracking a plume of toxic chemical pollution spreading through the area’s groundwater.

The city has been working with consultant Tetra Tech in recent months to study locations for installing more monitoring wells between the Gelman dioxane plume’s northern edge and Barton Pond, the city’s main drinking water source on the Huron River.

Environmental activists have complained for years there aren’t enough monitoring wells to know exactly where the plume is moving and some are worried finger-like extensions may be passing between monitoring wells and advancing toward the river undetected.

An informational meeting is scheduled for 7-9 p.m. Oct. 28 inside the council chambers at city hall, 301 E. Huron St.

It’s expected to include a presentation of the work performed by Tetra Tech and a discussion of the consultant’s recommendations, as well as time for questions from residents. The meeting also will be televised by CTN and available to watch online.

The city’s study of monitoring well locations involves six phases of work and is being done to ensure protection of the city’s water supply.

The first phase in July and August included reviewing existing contamination data, including well logs and dioxane test results from the Michigan Department of Environment, Great Lakes, and Energy, Washtenaw County Health Department, Coalition for Action on Remediation of Dioxane and polluter Gelman Sciences.

The second phase in August and September included generating a three-dimensional model to understand contaminant-migration paths and identify gaps where more monitoring wells are needed.

The third phase in September involved getting feedback from Central Michigan University Professor Larry Lemke, who has spent years studying the plume, and incorporating his input.

The fourth phase was to involve collecting water samples from several existing monitoring wells along the plume’s northern edge and testing for dioxane using a method with a lower detection limit than what’s currently used. Due to inability to get Gelman to agree to it, that was not completed, according to the city.

While the data would have been valuable, the city is proceeding with developing recommendations without it, officials said.

The fifth phase now involves presenting well location recommendations to the public and getting feedback.

The final results and recommendations are expected to be presented to City Council by year’s end, and the city’s staff intends to engage various stakeholders, including state and county officials.

It’s yet to be decided how to fund the additional monitoring wells. The city, county, state and other local entities are still involved in litigation against Gelman Sciences, which discharged large quantities of dioxane into the environment between the 1960s and 1980s.

With limited pump-and-treat remediation by the polluter over the years, dioxane has spread for miles through the area’s groundwater and is infiltrating the Allen Creek drain pipes at West Park that flush out to the Huron River. With dioxane in shallow groundwater, some worry it could seep into home basements and pose vapor-intrusion risks.

The city’s biggest fear is that high concentrations of dioxane could reach Barton Pond. The city discovered trace amounts of dioxane in the city’s treated drinking water from the pond earlier this year.

The plume also is a threat to private drinking water wells in surrounding township areas, and some wells have had to be shut down because of the contamination.

Dioxane is classified by the Environmental Protection Agency as likely to be carcinogenic to humans by all routes of exposure. It also can cause kidney and liver damage, and respiratory problems.

Just a few parts per billion in drinking water, with long-term exposure, poses a 1 in 100,000 cancer risk, according to the EPA.

The state initially sued Gelman in 1988, leading to a Washtenaw County Circuit Court consent judgment in 1992 that has been amended multiple times, most recently in 2011. That essentially governs the plume and allows it to spread through the city at high concentrations to the Huron River downstream of Barton Pond.

Local officials came together last month to discuss next steps in the legal case against Gelman Sciences, deciding to continue efforts to negotiate with the polluter and then reconvene Dec. 12. They’re also considering seeking a federal Superfund cleanup.

Gelman Sciences was acquired in 1997 by Pall Corp., which was acquired in 2015 by Danaher Corp., a multibillion-dollar corporation that some local officials and residents argue has the financial resources to do a better cleanup.