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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.
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