Under the Mining Law of 1872 (30 U.S.C. 22 et seq. ), United States citizens and businesses may freely prospect for hard rock minerals—such as gold, silver, lead, and copper—on most federal lands not specifically closed to mining. Although all mining claims must be filed with the Bureau of Land Management (BLM), each agency is responsible for the surface management of mining activities that take place on lands it manages. When mining operators or other responsible parties have previously failed to reclaim areas where mining operations have taken place on federal lands and are currently economically unable to do so, the burden of cleaning up these properties may fall upon the taxpayers. Regulations promulgated by BLM and the Forest Service in 1980 and 1974, respectively, require that once mining activities are completed, the mine operators must reclaim all areas disturbed by their operations as soon as possible. Furthermore, according to the Department of the Interior and the Forest Service, even before these regulations were promulgated, the operators were responsible for cleaning up their sites under state laws requiring the reclamation of such sites and under laws prohibiting the creation of nuisances. Mining operations that were ongoing when BLM’s and the Forest Service’s regulations were promulgated were allowed to continue, but they had to be brought into compliance with each agency’s surface management regulations. According to Department of the Interior and Forest Service officials, the Comprehensive Environmental Response, Compensation, and Liability Act (42 U.S.C. 9601 et seq.) imposes liability on mining operators for cleaning up abandoned mining operations that release hazardous substances on federal lands. National Park Service and Fish and Wildlife Service (FWS) lands have generally been withdrawn from mineral exploration. However, there are abandoned hard rock mine sites on these lands. Some are sites that preexisted the establishment or expansion of a park or wildlife refuge, and some are sites whose operators had valid existing rights when the lands were withdrawn from mining but have not reclaimed the sites. In addition to the land-managing agencies, two other agencies within the Department of the Interior—the Bureau of Mines and U.S. Geological Survey (USGS)—have addressed the issue of abandoned hard rock mines. The Bureau of Mines is concerned with mineral production and environmental remediation technologies. USGS assesses mineral resources and mining-related environmental problems. Attempts to determine how many hard rock mines lie abandoned nationwide have not resulted in a definitive inventory of these mines on federal lands. The four major land-managing agencies are in various stages of inventorying the abandoned mines on the lands they manage. Other organizations, such as the Bureau of Mines and the Mineral Policy Center,have also attempted to estimate the number of sites. However, because these sites are defined and counted differently, the individual results cannot be meaningfully combined or compared. BLM, which began an inventory in 1994, has made no overall estimate of the number of abandoned mine sites. BLM’s Nevada and Utah state offices are piloting the agency’s inventory approach, and several other state offices, including Colorado and Montana, have also begun field inventories, with the following results: The Nevada state office estimates 400,000 mine openings, structures, and other individual components of mining operations statewide, regardless of who owns the land. As the inventory progresses, it will differentiate between federal and other lands. The Utah state office is working with the state of Utah to inventory sites. On the basis of information from the state of Utah’s Abandoned Mine Reclamation Program and some fieldwork, the estimated number of sites in Utah is 17,000 to 20,000 on public and private lands. The Colorado state office, which expects to complete its portion of the inventory in 1996, is identifying a smaller number of sites on federal lands than it expected. While officials initially expected to find as many as 15,000 sites on federal lands in Colorado, field staff have found that few of the mines are actually located on BLM-managed lands. The Montana state office, working in cooperation with the Montana Bureau of Mines and Geology, has identified about 1,000 sites on BLM-managed lands in that state. The National Park Service, in an effort begun in 1984, has counted the number of abandoned hard rock mines in almost all of its units—99 percent, according to officials—except for some in Alaska and the 3.1 million acres over which it acquired jurisdiction as a result of the California Desert Protection Act of 1994 (P.L. 103-433). The agency has tallied 2,500 sites, but the field personnel responsible for the inventory defined sites in different ways. Although the National Park Service defines a “site” as a “particular operation . . . or area where mining occurred, which may . . . multiple ‘openings,’ i.e., shafts, adits, inclines, pits, prospects, etc.,” the agency’s units defined sites in different ways, according to officials. For example, one unit defined a site as a grouping of mining-related features; others designated individual features, such as a single mine opening, as one site. According to FWS, the agency’s wildlife refuges contain approximately 240 abandoned hard rock mine sites. FWS obtained this information on the number of sites by reviewing its mining files and requesting confirmation from its field offices. FWS does not consider abandoned hard rock mines a major problem on its refuges. According to the Forest Service, there are about 25,000 sites within National Forest boundaries. The Forest Service identified these sites using aerial photography and fieldwork, and the data were compiled by the U.S. Department of Agriculture’s Office of the Inspector General through a questionnaire. The Forest Service is attempting to more precisely screen the sites in individual forests and expects to complete this effort in 1997. The Bureau of Mines and USGS have estimated the total number of abandoned hard rock mines on federal lands. However, these estimates cannot be meaningfully compared with any of the other estimates because they vary in scope and in the types of data used for the estimates. The Bureau of Mines estimates that there are 15,300 sites on the lands managed by the agencies within the Department of the Interior and 12,500 sites on the lands managed by the Forest Service. These estimates are based on information in the Minerals Availability System/Minerals Industry Location System, a computerized database containing information about the location of and past activities at over 200,000 mineral deposits. However, these data were collected for purposes other than inventorying abandoned mines, and although they identify areas where mining occurred, they do not account for all mine sites and features. As a result, according to a National Park Service report and BLM officials, these data require further confirmation to ensure their accuracy. Although USGS has not independently inventoried abandoned mine sites, it compiled data from the land-managing agencies in response to a congressional request for information about sites containing hazardous materials on the lands managed by the Department of the Interior. Using the assumption that all abandoned hard rock mines are potentially contaminated, USGS estimated that, as of July 1994, there were approximately 88,000 sites on the lands managed by agencies within the Department of the Interior. USGS obtained these data from the agencies, with the exception of BLM. For the lands managed by that agency, USGS made estimates from data included in a 1991 report by the Western Governors’ Association entitled Inactive and Abandoned Noncoal Mines—A Scoping Study. The 1991 report of the Western Governors’ Association reported data obtained from 33 states on abandoned and inactive hard rock mines. However, the report cautioned that “The findings presented are not comparable among states because of variability in the definitions . . . used by states, and variability in the type and quality of data available to states. Neither the number of sites, nor the cost of remediation, reported by individual states can be totalled to present a consistent national total.” The Western Governors’ Association, in an effort funded by the Bureau of Mines, is working with state and federal agencies and private organizations to recommend consistent terminology and guidelines that would aid in future inventories. In a June 1993 report, the Mineral Policy Center estimated that there were about 560,000 mine sites on public and private lands. This estimate was also based upon data reported by the Western Governors’ Association, supplemented with interviews and documents from state officials and discussions with private contractors and consultants. The problems posed by abandoned hard rock mines can generally be classified as physical safety hazards or environmental degradation. Physical safety hazards, which can lead to human injury or death, may include concealed shafts or pits, unsafe structures, and explosives. Conditions causing environmental degradation may include drainage of toxic or acidic water, which could result in soil and groundwater contamination or biological impacts. However, because not all of the agencies have completed their inventories, they have not conducted the necessary fieldwork to identify how many mine sites with problems of each type are on the lands they manage. Furthermore, the factors the agencies use to classify their inventories are not consistent from agency to agency. According to BLM’s guidance on the inventory, as sites are identified they should be placed in categories according to the presence or potential for safety or environmental hazards, as well as reclamation needs. BLM also has a basic ranking system, but the agency has not yet compared the rankings across state or field offices. BLM’s inventory in Nevada found extensive safety hazards and confirmed that most of the chemically hazardous sites are already known. The current focus of BLM’s Montana state office is on approximately 100 sites that are affecting water quality. The National Park Service classifies sites according to the type and degree of hazard they present. Each site that will require reclamation is ranked on the basis of its (1) degree of hazard, (2) degree of impact on the environment, and (3) accessibility.