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fi Environmental Protection Agency <br />What is a mine backfill well? <br />What types of fluids are injected <br />into mine backfill wells? <br />Do injectate constituents exceed <br />drinking water standards at the <br />point of injection? <br />What are the characteristics of <br />the injection zone of a mine <br />backfill well? <br />Are there any contamination <br />incidents associated with mine <br />backfill wells? <br />Are mine backfill wells <br />vulnerable to spills or illicit <br />discharges? <br />How many mine backfill wells <br />exist in the United States? <br />Where are mine backfill wells <br />located within the United <br />States? <br />How are mine backfill wells <br />regulated in states with the <br />largest number of this type of <br />well? <br />Where can I obtain additional <br />information on mine backfill <br />wells? <br />CLASS V UIC STUDY FACT SHEET <br />MINE BACKFILL WELLS <br />Office of <br />Ground Water and <br />Drinking Water <br />Mine backfill wells are used in many mining regions throughout the country to inject a mixture of <br />water and sand, mill tailings, or other materials into mined out portions of underground mines. <br />These wells can serve a variety of purposes, including subsidence prevention, filling dangerous <br />mine openings, disposing of wastes from mine operations, and fire control. <br />The physical characteristics and chemical composition of materials injected into backfill wells <br />vary widely depending on the source of the backfill material, the method of injection, and any <br />additives (e.g., cement) that may be included. In general, the materials include slurries of sand, <br />gravel, cement, mill tailings or refuse, fly ash, or other solids. <br />Available data from leaching tests (e.g., USEPA Method 1311- -TCLP) of backfill materials <br />indicate that concentrations of antimony, arsenic, barium, beryllium, boron, cadmium, chromium, <br />lead, mercury, molybdenum, nickel, selenium, thallium, sulfate, and zinc frequently exceed <br />primary drinking water standards and health advisory levels. Levels of aluminum, copper, iron, <br />manganese, total dissolved solids, sulfate, and pH frequently exceed secondary drinking water <br />standards. <br />Mine backfill wells inject into mined out portions of underground mines. The environmental <br />settings in which the mines are located and injection occurs are diverse. <br />No incidents of contamination of an underground source of drinking water have been identified <br />that are directly attributable to injection into mine backfill wells. Although ground water <br />contamination is not uncommon at mining sites, it is generally difficult to identify the specific <br />causes. The chance that backfill injection will contribute to ground water contamination is highly <br />dependent on site conditions, including mine mineralogy, site hydrogeology, backfill <br />characteristics, and injection practices. <br />The vulnerability of mine backfill wells to receiving spills or illicit discharges depends on site - <br />specific conditions and practices. For example, if coal ash is hauled to a mine site, slurried with <br />water, and then injected, the likelihood of contamination of the injected material resulting from a <br />spill or illicit discharge is relatively low. On the other hand, if mill tailings are collected in a <br />tailings pond along with site runoff and other facility wastes prior to injection, then the likelihood <br />of contamination of the backfill material by spills would be higher. <br />There are approximately 5,000 documented mine backfill wells and more than 7,800 wells <br />estimated to exist in the United States. <br />Mine backfill wells are known to exist in 17 states. However, more than 90 percent of the <br />documented wells reported are in four states: WV (401), OH (3,570), ND (200), and ID (575). <br />Permit by rule: ID, KS, TX, IL, and ND (sometimes general or individual permits are required) <br />General permit: WY <br />Individual or area permit: WV, OH, IN, PA <br />For general information, contact the Safe Drinking Water Hotline, toll -free 800 - 426 -4791. The <br />Safe Drinking Water Hotline is open Monday through Friday, excluding federal holidays, from <br />9:00 a.m. to 5:30 p.m. Eastern Standard Time. For technical inquiries, contact Amber Moreen, <br />Underground Injection Control Program, Office of Ground Water and Drinking Water (mail code <br />4606), EPA, 401 M Street, SW, Washington, D.C., 20460. Phone: 202 - 260 -4891. E -mail: <br />moreen.amber @epa.gov. The complete Class V UIC Study (EPA /816 -R -99 -014, September <br />1999), which includes a volume addressing mine backfill wells (Volume 10), can be found at <br />http://www.epa.gov/OGWDWAlickl5study.litml. <br />