Well Water and PFAS Groundwater Contamination in Washington County, Minnesota

Where the contamination came from, and how big it is

Beginning in the 1940s and continuing into the 1970s, the 3M Company disposed of PFAS-containing waste at several East Metro sites: 3M's own disposal sites in Oakdale, Woodbury, and Cottage Grove, and the former Washington County Landfill in Lake Elmo. Those chemicals -- per- and polyfluoroalkyl substances, persistent compounds that don't break down naturally in the environment -- leached into groundwater over decades, and a county drainage project built in 1987 appears to have accelerated their underground spread. Minnesota regulators have identified a resulting plume covering more than 150 square miles, affecting the drinking water supplies of over 140,000 Minnesotans across the East Metro, and MPCA's own monitoring shows the plume is still moving, generally toward the St. Croix River.

The $850 million settlement and what it actually pays for

In 2010, Minnesota's Attorney General sued 3M over the contamination's damage to drinking water and natural resources in the southeast Twin Cities metro. That litigation ended in a 2018 settlement of $850 million, which now funds the state's East Metro response: free sampling of eligible private wells, installation and maintenance of point-of-entry treatment systems for contaminated private wells (at no cost to the homeowner), connection of some affected properties to municipal water, and permanent sealing of wells too contaminated or unnecessary to keep in service. As one concrete example, roughly 200 homes in Lake Elmo's Tablyn Park and Lake Elmo Heights neighborhoods have been connected to the municipal water system, and roughly 200 PFAS-impacted private wells have been permanently sealed by licensed contractors as part of the response.

Separately, the state has committed a further $700 million toward a comprehensive drinking-water plan for 14 East Metro communities (including Cottage Grove, Lake Elmo, and Maplewood, among others), covering six new or expanded water treatment plants, treatment for 33 municipal wells, connecting 296 homes to municipal water, and providing home water filtration systems to private-well homeowners who remain on private water. And in 2026, MPCA released results of a seven-year feasibility study recommending large-scale regional remediation -- a series of wells around the East Metro to pump and treat contaminated groundwater directly, aimed at protecting both current and future drinking water supplies for an area serving roughly 174,000 people.

How to check a specific well or parcel

MPCA maintains an interactive map for the East Metro well-sampling program that lets you locate a specific address and see whether it falls within the priority sampling area (marked by a dashed boundary on the map). If a property sits inside that area and has an untested private well, you can submit a Groundwater Sampling Request through MPCA at no cost. MPCA states it will contact you within about 30 business days to schedule sampling, with results and any recommended next steps (which can include free point-of-entry treatment or, in some cases, connection to municipal water or well sealing) delivered within roughly 8 to 12 weeks. Washington County's own Contamination Areas and Water Tests pages are a useful starting point for orienting yourself before going to MPCA's map and request form directly.

A separate, statewide disclosure requirement that applies here

Independent of the PFAS-specific programs above, Minnesota Statutes section 103I.235/103I.236 requires that before a seller signs an agreement to sell or transfer real property not served by a municipal water system, the seller must disclose in writing to the buyer whether the property is located within a "Special Well and Boring Construction Area" (SWBCA) -- a state mechanism for controlling well construction, repair, and permanent sealing in areas where groundwater contamination has occurred or may occur. This disclosure obligation exists statewide, but it is directly relevant to a private-well purchase anywhere in Washington County's PFAS-affected communities, and worth confirming as part of any purchase agreement regardless of whether the specific parcel has already been tested.

It's not only PFAS: nitrate contamination in Cottage Grove and Denmark Township

Separately from the 3M PFAS plume, available reporting identifies nitrate groundwater contamination concentrated specifically in Cottage Grove and Denmark Township, attributed to a combination of land use practices and locally sensitive geologic conditions rather than to legacy industrial waste disposal. We could not independently verify this against a primary Minnesota Department of Health or MPCA nitrate dataset and flag it here as a lead to check directly rather than a fully confirmed finding -- but it is one more reason that any land purchase relying on a private well in this county deserves a direct water-quality check rather than an assumption either way.

What this means for your purchase

If a target parcel is in or near Oakdale, Woodbury, Cottage Grove, or Lake Elmo and will rely on a private well, check MPCA's East Metro well-sampling map for that address before you're under contract, not after. If the property already has a private well, ask the seller directly for its testing history and any PFAS or nitrate results, and get the Special Well and Boring Construction Area disclosure in writing as part of your purchase agreement. If the well has already been tested and treated or the property has been connected to municipal water under the settlement programs, get documentation of that too -- it materially affects both water quality and, potentially, future maintenance obligations or municipal water fees.