Acid Mine Drainage:
Innovative Treatment Technologies
Mining practices, present and past, cause environmental problems that can damage ecosystems and human health. Mining disturbs geologic formations that took millions of years to form; likewise, related natural systems and processes are disturbed, e.g. hydrology. Once disruption has taken place a variety of problems may arise, from physical hazards to pollution of water and soil.The most severe and widespread
environmental problems almost always have to do with water, indeed all of the treatment technologies that will be discussed in this paper are designed for water or the prevention of water contact with solids.
There has been a lot of effort to quantify the universe of abandoned mines, the results vary. Some of the problem lies in definition. While some agencies define a site as a particular opening; others define a site as all of the openings at a particular location as one mine site. The Bureau of Land Management claims that estimates from Federal land management agencies, state and privately owned lands have ranged from about 80,000 to hundreds of thousands of small to medium-sized sites (U.S. Dept. of the Interior, 2003b). The Office of Surface Mining describes the problem in terms of money, “of the $8.2 billion of high priority [physical hazards] coal related AML problems in the AML inventory, $6.6 billion, 80%, have yet to be reclaimed; furthermore, “almost ninety percent of the $2.0 billion of coal related environmental problems in the AML inventory are not reclaimed. And this represents only a small part of the total problem as no systematic effort has been made to inventory these problems” (U.S. Dept. of the Interior, 2002a). To give one last perspective, the Mineral Policy Center, a non-profit organization, claims that there are 557,000 abandoned mines - mostly in the western United States (2003). Although it is difficult to say exactly how many sites exist, the number of abandoned mine sites in the US is enormous.
For roughly 25 years there have been efforts to address the dangers created by the past 250 - 300 years of large-scale mining in this country. The Surface Mining Coal and Reclamation Act (SMCRA), passed in 1977, requires a tax on coal production to be set aside in a fund for remediation efforts at abandoned coal mines. However, many abandoned mines are hard rock mines and are typically not eligible for SMCRA funding, though there are some exceptions. Other sources of funding may come from CWA grants, CERCLA grants or State funding. While there has been significant progress, there are still many sites without adequate funding. For example, California has no abandoned coal mines, therefore ineligible for SMCRA funding. A multi-stakeholder task force in California identified lack of funding as a key impediment to cleanup of abandoned mines in the state (see Appendix A). Some states have started to lobby for funding, for example, Colorado House Representative Mark Udall is seeking legislation that would create a fund for hard rock sites similar to that created by SMCRA.
Many states and agencies have only recently finished inventorying the number of sites and begun to evaluate sites to determine priorities for cleanup. States and other agencies that are doing remediation under SMCRA must address Priority 1 & 2 problems - those dealing with physical dangers - before they are able to use funding to address Priority 3 problems - environmental problems and/or high priority non-coal sites. The priority number system was defined by the U.S. Department of the Interior.
Due to limited resources, especially in the case of hard rock mines, innovative technologies can offer a plausible solution to the environmental threats created by abandoned mines. Traditional water treatments are modeled after wastewater treatment plants, which are machine intensive, chemical dependant, and require continuous operations and maintenance (O & M) staff. Traditional solid mine waste remediation tactics involve covering of piles and water diversion tactics which do not treat wastes but rather mitigate their impacts. The innovative technologies that will be discussed in this paper are largely passive treatment systems. Passive treatment systems are described as having little O & M costs, require little chemical application, and few if any mechanical devices (Hedin et al., 1994). Passive treatment systems can be a good solution for small drainage sites that might otherwise have few treatment options.
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