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 that 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 was eventually 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 in which, at that time, was shipped to Spain. From 1798-1804, Mine Au Breton produced more lead than all of the other Upper Louisiana mines combined. The Missouri Department of Natural Resources (MDNR) 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) that was used in rubber, paint, soap, drilling fluids, and medical products. Many lead mines were over mined 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 that were introduced into the area in the 1920s. In 1941, Missouri accounted for 40 percent 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, MDNR began an integrated assessment that 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 that exceeded 400 milligrams per kilogram (mg/kg) and roughly 18% had soils that 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 wells 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
Site-specific contractor crews (Prudent Technologies) began yard excavations under contract no. EP-S7-08-03, option-year II, on April 6, 2009. A total of 29 residential yards were cleaned up under this contract-option year. Due to heavy rains throughout April and May, completion of excavation and backfill activities were significantly delayed. Final excavation work was completed during the week of June 29, 2009.
The START contractor continued to sample residences as requests for sampling were received. The START contractor also continued to provide removal support for residential yard excavation.
To date, the cleanup contractors have removed the following estimated amounts of contaminated materials from high child-use areas and residential properties:
ERRS Contractor: 111,432 cubic yards
Site Specific Contractor: 64,012 cubic yards
Activities conducted to date are:
Properties Screened: 1,685
Number with lead (Pb) greater than 1199 ppm:: 210
Number of properties excavated by ERRS: 91
Number of properties excavated by Prudent:114
Number of drinking water wells sampled:769
Number of wells exceeding RAL (15 ppb): 177
Number of homes with bottled water provided: 169
The ERRS contractor is continuing to provide bottled water to affected residents. In addition, the EPA Superfund Division has begun a pilot study on point-of-use water filters. It is expected that filters will replace bottled water as a temporary drinking water alternative under the removal program.
The site-specific contractor has completed 29 properties under this contract option and a total of 114 properties under the overall Potosi contract. The status of future remedial activities will be determined by the Superfund Remedial Program Manager.
The removal program will continue to provide alternative drinking water to affected homes as needed.
Prudent Technologies will remain on the site until October 2009 for maintenance of grass and additional landscaping and restoration activities. This assistance is being conducted in accordance with the 90-day guarantee established in Modification 011 of this contract.
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