The Site exists within an area of approximately 436 square miles and includes all of St. Francois County with the exception of the former Mine La Motte tract that extends into St. Francois County’s southern border just north of the community of Mine La Motte, Missouri. St. Francois County is the location of a former mining region known as the "Old Lead Belt". The area is still referred to as the “Mineral Area”.  The population center of the area is located approximately 70 miles south of St. Louis.  Six large areas of mine waste covering an area of approximately 110 square miles are present within the Site.  The areas included are the Bonne Terre Mine Tailings Site, the Leadwood Mine Tailings Site, the Elvins Mine Tailings Site, the Federal Mine Tailings Site, the Desloge Mine Tailings Site, the National Mine Tailings Site, and the Doe Run Mine Tailings Site.  Migration of lead-contaminated mine waste from these large tailings piles through human and environmental mechanisms has occurred.  This response is not limited to these mine waste areas.

1.1.2.2 Description of Threat

The primary contaminant of concern at the Site is lead and lead compounds.  Lead and lead compounds are hazardous substances as defined by Section 101(14) of CERCLA, listed at 40 CFR  § 302.4, and have been detected in the soils at the Site.  EPA has documented total lead concentrations in soil at the Site at levels exceeding the residential soil screening level of 400 mg/kg.  Lead is classified by EPA as a probable human carcinogen and is a cumulative toxicant.  A significant amount of lead that enters the body is stored in the bone for many years and can cause irreversible health effects.

EPA initiated a limited Removal Site Evaluation (RSE) at the Site on October 4, 2010, to assess a limited number of residential properties around the Columbia Lead Mine Sub-Site, as well as school and child day care facilities located across the “Area of Contamination” established in the 2004 Administrative Order on Consent between EPA and the Doe Run Company. 

Field screening results of composite samples collected from areas of exposed soil documented that a release of a hazardous substance (lead) occurred at the Site.  The initial investigation focused areas where children play.  Lead was identified by field portable X-Ray Fluorescent (XRF) Spectroscopy at elevated levels, based on the residential screening level of 400 mg/kg lead, in 11 of 11 school properties, 16 of 17 child day care facilities, and 19 of 19 residential properties. 

Previous assessments by the Potentially Responsible Party (PRP) also identified properties with elevated lead concentrations that have not been remediated to date.  Approximately 34 residential properties have previously been identified with lead concentrations exceeding 1,200 mg/kg.  Approximately 729 residential properties are known to exist at the Site with lead concentrations in the 400 to 1,199 mg/kg range.

The greatest areas of concern at the Site that require removal action are the exposed lead-contaminated soils in areas where children 84 months of age or less or other sensitive populations could be exposed.