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The Washington County Lead District Site consists of high concentrations of lead contamination from nearly 285 years of mining activities. The primary problem areas at this Site which require action are lead contaminated soils in yards and lead contaminated drinking water.
The Site is located in a heavily mined region of eastern Missouri known as the Washington County Lead District. The Potosi Area Site primarily includes residential areas within and around the towns of Potosi, Mineral Point, and Cadet and is only a portion of the larger Washington County Lead Mining District.
Although lead was known to be in Southeast Missouri as early as the 1600s, serious mining did not begin until around 1720 when Phillipe Francois Renault established Mine La Motte in present day Madison County, Missouri (part of the Madison County Mines NPL Site). By 1725, Old Mines and Mine Renault were opened in present day Washington County. The smelted lead was molded (lead pigs) and transported to Ste. Genevieve, Missouri on the Mississippi River where it was shipped to France via New Orleans. Lead mining in Southeast Missouri has been continuous until the present day where lead is still mined in the Viburnum Trend which includes part of Washington County (Doe Run’s Viburnum Mine 29).
In Washington County, Mine Au Breton (current day Potosi) was established in the late 1700s and eventually was taken over by Moses F. Austin (father of Stephen F. Austin of Texas fame) whose mining and reverberatory furnace smelting techniques significantly increased lead production which at that time was shipped to Spain. During the years of 1798 to 1804, Mine Au Breton produced more lead than all of the other Upper Louisiana mines combined. The Missouri Department of Natural Resources has identified over 1000 lead and barite mining, milling and smelter sites in Washington County through historic information.
Toward the end of the American Civil War, lead deposits in Washington County ran low and the industry declined. It was soon replaced by the surface mining of Barite (Barium Sulfate) which was used in rubber, paint, soap, drilling fluids and medical products. Many lead mines were “overmined” for the barite which was also associated with Galena (lead Sulfide). The Barite was separated from the clay initially by hand washing and then by mechanical Barite washing plants which were introduced into the area in the 1920s. In 1941, Missouri accounted for 40% of United States Barite production.
Barite Mines in the Potosi area include the following:
Hornsey Brothers Boars Head Lodge Mine
Hornsey Brothers Cadet Mine
Hornsey Brothers Gun Club Mine
Milchem Settle Mine
Milchem Keyes Branch Mine
Dresser Minerals Potosi Mine
Dempsey Mine
Pfizer Mineral Point Mine
Imco Apex Mine
NL Baroid Fountain Farm Mine
NL Baroid Cadet Mine
In June 2005, the Missouri Department of Natural Resources (MDNR) began an integrated assessment which included soil and groundwater sampling in the Potosi area. During this sampling event, MDNR sampled the soil at 359 residences located on or near mining or mine waste disposal areas. Based on this data, approximately 65% of these residential properties had soils which exceeded 400 milligrams per kilogram (mg/kg) and roughly 18% had soils which exceeded 1,200 parts per million (ppm) for lead. The MDNR also sampled approximately 172 private drinking water wells in the Potosi area in June 2005. Of these 172 wells sampled, 36 exceeded 15 parts per billion (ppb) for lead, and one well exceeded 5 ppb cadmium, which are the current Maximum Contaminant Levels for lead and cadmium in drinking water.
In October 2005, EPA began sampling in the Potosi Area to support the removal action. EPA sampled 534 residential properties with the following results:
Properties with lead levels less than 400 ppm: 331
Properties with lead levels 400 to 1199 ppm: 150
Properties with lead levels greater than 1200 ppm: 52
Properties with drip zone only greater than 400 ppm: 1
Properties where drinking water exceeded the removal action levels: 55
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