The Southwest Jefferson County Mining site covers Jefferson County, Missouri, where lead mining dating back to the early 1700s left behind widespread contamination. The EPA added the site to the National Priorities List (NPL) in September 2009. The NPL is the federal government's roster of the most serious hazardous waste sites in the country. The site is divided into eight operable units, each targeting a specific geographic area or type of contamination.
The main contaminants are arsenic, barium, cadmium, chromium, and lead. These have been found in residential soils, sediment, surface water, and groundwater. Lead is the primary health concern. It is toxic to humans and animals, and the biggest risk comes from children and others accidentally swallowing contaminated soil. The EPA has determined that human exposure is not currently under control, meaning unsafe levels remain and people could reasonably come into contact with them. Contaminated groundwater is also still moving and has not been stabilized.
Cleanup work started in 2004 and remedial action began formally in September 2013. As of December 2024, the EPA had sampled more than 7,121 residential properties and cleaned up over 1,773 of them. Two smaller residential areas linked to contaminated soil from trucking and farming finished cleanup in September 2016, covering 241 properties combined. In January 2024, the EPA updated its lead guidance to address soils above 200 parts per million (ppm). Over 1,300 private wells have been sampled, and more than 130 exceed the lead action level of 15 parts per billion (ppb). The EPA is providing point-of-use water treatment filters to residents with affected wells. Health advisory signs are posted along the Big River, where elevated lead levels were found in sediment. Four operable units covering mine waste piles, rail lines, the Valles Mines area, and unconsolidated mine waste do not yet have cleanup decision documents in place. A Five-Year Review completed in June 2025 found the site remedy is progressing. Full construction completion and deletion from the NPL have not yet occurred.
Residents can get free yard and well testing by contacting the EPA. The current remediation contractor, EA Engineering Science and Technology Inc., began excavation work in 2023 and may contact residents by phone, door knock, or mail to arrange access. Community members can also access free, independent technical help through the Technical Assistance Services for Communities (TASC) program, which provides scientists and engineers to help residents understand the cleanup process. The EPA's Community Involvement Coordinator, Shaylee Borcsani, can be reached by phone or email for questions, testing requests, or general information.
