Well Water in Washington County, Missouri: the Old Lead Belt Legacy

Why this county specifically: three centuries of lead mining

Washington County is one of the oldest continuously worked mining districts in North America -- lead extraction here dates to French colonial settlement in the early 1700s, well before Missouri statehood, and mining, milling, and smelting continued across the district for roughly three centuries. That history left elevated concentrations of lead, arsenic, barium, and cadmium in soil, sediment, surface water, and groundwater across a wide area of the county, not confined to the old mine shafts and mill sites themselves. As has happened in other Missouri lead-mining counties, some residents also unknowingly used lead-contaminated mine gravel ('chat') as fill dirt, driveway material, and even playground surfacing over the decades, spreading contamination beyond the immediate mining footprint.

EPA organizes its response as the Washington County Lead District (WCLD), comprising four separate Superfund sites on the National Priorities List: Furnace Creek, Old Mines, Potosi, and Richwoods. The Potosi, Old Mines, and Richwoods sites were added to the NPL in March 2008, with Furnace Creek investigated under a related but separate track. The Old Mines site alone covers roughly 90 square miles in the northeastern part of the county -- a reminder that "the Lead District" is not a single small industrial site but a substantial share of the county's land area.

The well-testing numbers, and what the interim remedy actually does

The single most important number for a land buyer here: since 2006, more than 4,800 private domestic wells have been tested across the district, and roughly one in seven has come back contaminated with lead and/or other heavy metals. That is a large, systematically collected sample, not an anecdotal concern, and it reflects an active, ongoing EPA program rather than a closed historical episode. As of spring 2025, soil excavation was actively underway at both the Old Mines and Potosi sites under a private remediation contractor, with cleanup work consisting of excavating contaminated soil and gravel, replacing it with clean fill, and restoring vegetation.

For wells that test positive, EPA's 2022 Interim Record of Decision established point-of-use (POU) water treatment systems as the interim remedy -- essentially a certified filtration system installed at the point where water is used, removing lead and other targeted contaminants before they reach a tap. At the Old Mines site alone, roughly 181 private wells qualified for a POU unit. This is explicitly an interim measure: EPA continues a remedial investigation and feasibility study aimed at identifying a final remedy for the contaminated aquifer itself, meaning the POU approach addresses exposure at individual properties without yet resolving the underlying groundwater contamination. Testing and remediation of qualifying wells (and yards) is provided at no cost to the property owner under the program.

What to actually check before relying on a well here

1. Ask directly whether the well on a specific parcel has ever been tested through the Washington County Lead District program, and if so, request the test results and any POU system installation history -- a documented clean test, or a properly maintained POU system, is meaningfully different from an untested well of unknown status.
2. Check the parcel's location against the four Superfund site boundaries (Furnace Creek, Old Mines, Potosi, Richwoods) through EPA's Washington County Lead District site profiles -- proximity to a site boundary is the first screening question, though contamination from historic gravel reuse is not always confined neatly within mapped lines.
3. If the well hasn't been tested, or you're planning to drill a new one, arrange independent water testing for lead and the other WCLD-associated metals (arsenic, barium, cadmium) as part of your due diligence, in addition to any standard water-quality testing you'd do for a rural property.
4. If a POU treatment system is already installed, ask who is responsible for its ongoing maintenance and filter replacement after the property changes hands, and whether that responsibility is documented anywhere (a service agreement, an EPA program record, or seller disclosure).
5. Remember that a property outside the four mapped NPL boundaries is not automatically free of legacy mining impacts, given the historic use of mine gravel as general fill and driveway material across the county -- a reasonable independent water test is worthwhile even for land that reads as outside the formally designated sites.