Missouri has a long and extensive history of lead (Pb), Zinc (Zn), and other metals mining. Since the 1720’s, over 6,000 individual explorations or mines have been registered within 51 of the 115 Missouri counties, with known production occurring in 39 counties. The Southeast Missouri Lead Mining District (SEMOLMD) is a combination of the “Old Lead Belt” and the Viburnum Trend. The Old Lead Belt is generally considered to comprise parts of seven counties including Crawford, Franklin, Iron, Jefferson, Madison, St. Francois, Ste. Genevieve, and Washington counties. The Viburnum Trend or New Lead Belt was identified in 1955 and ore production was initiated by the early 1960’s. The Viburnum Trend comprises parts of six Missouri counties including Crawford, Dent, Iron, Reynolds, Shannon and Washington counties and production of Pb, Zn, copper and silver continues there today. According to the U.S. Geological Survey (USGS) the Viburnum Trend and Old Lead Belt ranked #1 and #2, respectively for lead production within the United States and the Viburnum Trend ranked #10 for zinc production.
Mining and milling in Missouri in the early days consisted of hand dug surface pits. The ore was separated from the host or waste rock by hand-sorting and passing through course screens or jigs (sometimes called grizzlies). Lead was generally smelted on-site or close to the mine using crude hearths that burned wood. Mining techniques became more sophisticated with the introduction of the diamond-tipped drill in the 1860s, and mines generally became deeper and larger. Ore was separated from the host or waste rock by larger-scale milling techniques. Hearths were replaced by coal burning furnaces and eventually modern-day smelters. Milling consisted of separating coarse material from the ore with screens and jigs, which produced chat, and then through a gravity-separation aqueous process, which produced finer grained tailings. Tailings were typically deposited in an impoundment formed behind coarser grained chat, which served as a dam or berm. The mill wastes (chat and tailings) were often deposited on the ground near the mines with little control or regard to erosion. Indeed, mine wastes were known to be flushed down stream as a means of disposal. Most of the modern mining production in St. Francois and Madison Counties and the Viburnum Trend was from deep underground mines.
At this time, SEMOLMD contains three NPL sites: the Big River Mine Tailings Site (aka St. Francois County Mine Site or SFCMS), the Southwest Jefferson County Mining Site, and the Madison County Mine Site (MCMS). The Big River and Madison County sites contain several mine and mill sites across the counties with large mill tailings impoundments and chat piles covering thousands of acres of land. Both sites also have streams that contain many miles of heavy-metal contaminated sediment, including the Big River for the St. Francois County and Jefferson County site and the Little St. Francois River for the Madison County site. The trustees estimate that the Big River has over 90 miles of contaminated sediment from the St.Francois, Jefferson and Washington County sites. The Madison County Mine Tailings site contributes contaminated sediment to the Little St. Francois River.
Supporting habitats and food chains for federally listed species and migratory birds are contaminated with concentrations of hazardous substances that exceed exposure thresholds known to cause adverse effects. In total, it is estimated that releases from these mining sites have contaminated over 100 miles of stream sediment with Pb, Cd, Ba, Ni, Cu, and/or Zn. Over 3,500 acres of land are contaminated or covered with mine/mill waste in St. Francois and Madison Counties. It is estimated that 25,000 acres in the Viburnum Trend are contaminated by hazardous substances. The trustees are assessing impacts to natural resources, including the federally endangered pink mucket, scaleshell, spectaclecase, and sheepnose mussels, and migratory birds due to contaminated habitat and possible direct toxicity. The FWS has particular concern over endangered freshwater mussels. The Meramec River (below the Big River) supports some of the largest remaining populations of the federally endangered pink mucket, (Lampsilis orbiculata), scaleshell (Leptodea leptodon), sheepnose (Plethobasus cyphyus), and spectaclecase (Cumberlandia monodonta).