1,4-Dioxane

The drinking water for the City of Ann Arbor comes from the Huron River and groundwater wells that are monitored regularly before and after treatment to ensure water remains safe from 1,4-dioxane and other contaminants. The results of the city’s water testing are posted as frequently as available (typically monthly).

On March 12, 2026, the Enviromental Protection Agency (EPA) added the Gelman Sciences site to the Superfund National Priorities List (NPL), a list of the nation's most contaminated sites. This means that regulatory oversight will shift from the Michigan Department of Environment, Great Lakes, and Energy (EGLE) to the EPA. The city will be meeting with its state, local, and now federal partners in the coming weeks and months to discuss immediate steps in the transition.

Once a site is designated as superfund, the EPA conducts further studies to determine the nature and extent of the contamination and help identify feasible treatment options. A cleanup plan is then selected and documented in a record of decision. The timeline for design and cleanup work at an NPL site is highly variable and can take from a few years to several decades. However, at any time the EPA may use Superfund removal enforcement authority to quickly address imminent and substantial endangerment to public health or the environment.

EGLE asked EPA to add the site to the NPL in 2021. Following years of site assessments, EPA proposed to add site to the NPL in March 2024. EPA held a 60-day public comment period that garnered 151 public comments. Responses to the comments, which were primarily in support of the listing, are included in the final rule which is published on EPA’s website. The city provided the following comments supporting NPL listing:

City of Ann Arbor Public Comment in Support of Gelman NPL Listing (PDF).

Gelman Sciences Inc. (later acquired by Pall Corporation and now part of Danaher), used dioxane in its medical filter manufacturing processes at its Wagner Road facility from the mid-1960s to the mid-1980s. During this period, wastewater containing dioxane was disposed of onsite. In the mid-1980s, dioxane contamination was detected offsite in nearby surface and ground water.

A plume is a volume of contaminated groundwater that extends outward from a source. The 1,4-dioxane plume originating from the Wagner facility is moving through ground water, with local geology dictating its direction and speed. The plume area includes parts of Scio Township and western Ann Arbor. Currently, more than 250 monitoring wells are in place to track water levels and 1,4-dioxane concentrations.

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View the Gelman Site of 1,4-Dioxane Contamination Web Map for more details.

Dioxane is a human made compound that mixes easily in water. It is used in industry as a solvent to manufacture other chemicals and is a by-product in many items, including paint strippers, dyes, greases, antifreeze, and aircraft deicing fluids. It also is found in other chemicals that are used to manufacture cosmetics, detergents, deodorants, and shampoos.

The International Agency for Research on Cancer has determined that 1,4-dioxane is 'possibly carcinogenic' to humans because it is a known carcinogen in animals. The United States Environmental Protection Agency (EPA) states that it is likely to be carcinogenic to humans by all routes of exposure. The EPA recently conducted a risk evaluation for dioxane under the Toxic Substances Control Act.

On March 12, 2026 the Gelman site was added to the Superfund National Priorities List. While this means that regulatory oversight will shift from the Michigan Department of Environment, Great Lakes, and Energy (EGLE) to the EPA, the timeline for the management transition will not be instantaneous. Both agencies have the most up-to-date information on their respective websites regarding the management transition:

*While cleanup requirements may change due to the March 12, 2026 addition of the Gelman site to the Superfund National Priorities List, near-term clean-up response will continue to be managed by EGLE and the requirements of the Fourth Amended Consent Judgement.

In 1992, the Washtenaw County Circuit Court entered a Consent Judgment regarding Gelman's dioxane contamination. The Consent Judgment and its amendments dictate Gelman’s obligations to investigate, clean up, contain, and monitor the contaminated groundwater under the direction of EGLE. ​Four amendments to the original Consent Judgment have been entered by the Court, the most recent being entered in 2023:

The Fourth Amendment to the Judgement, among other requirements, reduced the drinking water criteria from 85 to 7.2 parts per billion (ppb) and the groundwater to surface water interface (GSI) criteria from 2,800 to 280 ppb, consistent with current State of Michigan cleanup criteria.

*While cleanup requirements may change due to the March 12, 2026 addition of the Gelman site to the Superfund National Priorities List, near-term clean-up response will continue to be managed by EGLE and the requirements of the Fourth Amended Consent Judgement.

In 2005, following a State vs. Gelman lawsuit, the Court established a Prohibition Zone (PZ) as an Institutional Control. An Institutional Control is a set of restrictions on the activities at a contaminated area, which are often prescribed in legal documents, that help minimize the potential for human exposure. An Institutional Control may be used alone, or in conjunction with cleanup activities that remove or treat contamination. The PZ has been expanded since 2005.

The PZ allows dioxane to remain and migrate in groundwater within the zone, at concentrations above the groundwater residential drinking water cleanup criterion, rather than be cleaned up. The “prohibition" part of the PZ title refers to a prohibition against installing, maintaining, or operating wells for drinking water or irrigation purposes on land within those boundaries. The entire land area in the scope of the PZ is within the boundaries of the City of Ann Arbor. The city independently requires all properties within city limits—regardless of where they are relative to the PZ—to connect to the city's municipal water supply system rather than obtain water from wells. The location of the PZ can be viewed on the EGLE's Contamination Web Map​​​.

Gelman operates a pump-and-treat system, part of which is within the PZ, where wells pump contaminated water out of the ground, treat it, and discharge the treated water into surface water. Treatment activities are dictated by the Consent Judgement, while the discharge to surface water is regulated by a National Pollutant Discharge Elimination System (NPDES) permit issued by EGLE. Both the Consent Judgement activities and the NPDES permit are currently managed by EGLE.

The plume is monitored by Gelman and EGLE through a network of over 250 monitoring wells across the city and Scio Township. The locations of wells and frequency of sampling are dictated by the Consent Judgement (Gelman also has installed some wells under a settlement agreement with the city entered in 2006). Results are reported to EGLE and a selection of impacted stakeholders. In addition to the monitoring wells, EGLE contracts with the Washtenaw County Health Department to conduct residential well monitoring along the northern edge of the PZ. Up-to-date monitoring and residential well sampling data can be found on EGLE's Contamination Web Map.​

While the city has taken on several roles over the decades, the priority has always been to safeguard the health of its residents. The city has worked collaboratively with Gelman, EGLE, Washtenaw County Health Department, Ann Arbor and Scio Townships, and watershed groups on various initiatives to best address the contamination. While the city is not involved in active litigation, it has pursued litigation in the past when appropriate: 

  • In 2004 and 2005, the city filed actions in state and federal courts against Gelman regarding dioxane released and migrating from Gelman's property.
  • In 2006, the city and Gelman entered into a Settlement Agreement in which Gelman agreed to compensate the city, monitor water quality, among other activities. 
  • In 2023, the city filed a lawsuit against Gelman to enforce its rights under the 2006 Settlement Agreement.
  • In a separate legal action in 2016, the city intervened in the State’s lawsuit against Gelman to address the changes in dioxane cleanup criteria. After several years of litigation, the Fourth Amended and Restated Consent Judgment was finalized despite lingering objections from the city and others. While the city is no longer active in litigation regarding the Consent Judgement, it continues to advocate for appropriate response measures.

The city's current area of focus is the protection of its drinking water intake in Barton Pond on the Huron River, where 85% of the city's water is sourced. The city continues to work with Gelman, EGLE, and other stakeholders to advocate for appropriate monitoring mechanisms that can provide sufficient planning time should the plume move closer to the Huron River. The city implemented a sentinel well monitoring program in 2020 at its own expense to monitor the plume at the northern edge of the PZ. A sentinel well monitors a location in an uncontaminated area, between a known area of contamination and a drinking water supply. Routine monitoring of the sentinel well may provide advance warning of contamination migration toward the drinking water supply, allowing time for the city to plan a response.

The city will continue to update this website with the most recent information, which will also be included in a quarterly Gelman Update newsletter that includes agency updates and treatment information:

EGLE contracts with the Washtenaw County Health Department to conduct residential well testing on an annual basis. If dioxane levels are confirmed to be above health-based limits, EGLE will initiate plans to connect the home to municipal water. These results are eventually incorporated into EGLE’s database, linked above. A Drinking Water Well Sampling Map of the most recent results can be found on the County’s website:

The city installed a sentinel well in 2020 along the northern border of the PZ, from which quarterly groundwater samples are tested for dioxane. The city aims to incorporate this data into the EGLE database. The final sentinel well report and informational meeting recording can be found below: 

The city conducted wet basement testing for dioxane in 2020 to determine whether dioxane was present in flood water in areas that met specific criteria. No dioxane was found. Additional information can be found below: 

Aside from EGLE and EPA, several local agencies are also engaged in the Gelman cleanup, and provide dioxane-specific information on their respective websites: 

Please contact Erin Donnelly, Environmental Services Manager, for additional information EDonnelly@a2gov.org.