The Southwest Jefferson County Lead District Site OU00/OU1 consists of high concentrations of lead contamination from mining. The ore would normally be hauled from the mines to the concentrators (also known as the "mills") where it was formed into lead concentrate. Lead concentrate at the Site was/is derived from the physical concentration of lead sulfide ore and is typically 70 to 80 percent - 700,000 to 800,000 parts per million (ppm) lead sulfide.
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The primary problem areas at this Site that requires action are lead-contaminated soils in yards and drinking water wells contaminated with metals.
Jefferson County is located in southeastern Missouri and bordered on the north by St. Louis County and the Meramec River; on the east by the Mississippi River; on the south by St. Genevieve and St. Francis Counties; and on the west by Washington and Franklin Counties. The county encompasses 664 square miles. According to the 2000 Census, the population of Jefferson County is 198,099. The county seat is located in Hillsboro, Missouri. Jefferson County organized in 1818, and named in honor of former President Thomas Jefferson.
Mining activities in Jefferson County began in the early 1800s, in southern Jefferson County, where the Cambrian dolomite source rock is concentrated along the Big River and other major streams. The first production operation was a lead shot tower erected in 1809, in the southern part of Herculaneum. Two mines were in operation as early as 1818, (1) the Gray's mine located on the Big River and (2) the McKane’s Mine located on the Dry Creek. Many other mines opened in the 1830s and 1840s, for the production of lead, zinc and barium (tiff). By 1855, three smelters were operating in Jefferson County, including the Valles Mines, the Mammoth Mines and the Sandy Mines. Historical records indicate that over three million pounds of lead shipped out of Jefferson County annually during this time period, making it one of the leading lead producers.
The Inventory of Mines Occurrences and Prospects database lists 253 historical sites associated with mining and production operations in Jefferson County. Of the 253 mining sites, 202 were for lead or lead and other commodities, particularly zinc and tiff. Most of the remaining sites were exclusively tiff mines. Past mining operators in Jefferson County included the St. Joe Lead Company (now the Doe Run), the Valles Mining Company, the Big River Lead Company, Del Stocking, the Magnolia Mining & Milling Company, the Sandy Mining Company, the National Lead Company, the Bennett Lead & Zinc Company, the Walther Mining Company, Ed Dixon, the Big River Lead Mine, the M. Development Company and Iva Schmitz-Rome & John. Of these operators, the Doe Run is the only mining operator currently listed in Jefferson County. Their predecessor, the St. Joe Lead Company, opened the Doe Run’s smelter in 1892. In 2003, the Doe Run smelter was producing over 100,000 tons of lead a year. The Valles Mining Company is also still in existence, but no longer mines for lead. According to historical records from approximately 1824 through the 1930s, the company operated the lead mining and smelting operation at the Valles Mines. The ruins of several ore-milling structures, a former smelter, chat piles and mill wastes are still present in the vicinity of the Valles Mines.
In September 2006, the U.S. Environmental Protection Agency began an integrated site assessment, which included soil and groundwater sampling in the area. During the sampling events, the EPA sampled the soil at 353 residences located on or near mining or mine waste disposal areas. Based on this data, approximately 22 percent (55) of these residential properties had soils which exceeded 400 ppm, and roughly 6 percent (22) had soils which exceeded 1,200 ppm for lead. Beginning in September 2006, the EPA also sampled approximately 304 private drinking water wells in Jefferson County. Of the 304 wells sampled, 36 (12 percent) were found with lead levels greater than 15 parts per billion (ppb), and two with cadmium levels greater than 5 ppb. Of those wells with lead greater than 15 ppb, 16 (5 percent) had lead levels greater than 30 ppb.
The primary contaminant of concern at this Site is lead and lead compounds. The EPA has documented a total of lead concentrations in soil in residential yards at levels exceeding 1,200 ppm. Drinking water samples collected by the EPA indicate a significant release of heavy metal contaminants, particularly lead, into the groundwater.
Lead, lead compounds, arsenic and cadmium are hazardous substances (as defined by section 101(14) of the Comprehensive Environmental Response, Compensation, and Liability Act of 1980, and is listed at 40 Code of Federal Regulations § 302.4, and have been detected in the ground water, soils, and mining wastes at the site).