Extent of Problem
Abandoned mine lands (AMLs) present serious threats to human health and the environment. Addressing AML impacts is becoming increasingly important due to increased exposure to people and risks of accidents, injuries, and tort claims. There are estimates of as many as 500,000 abandoned mines in our nation.
Increased population growth is also reflected in higher demand for outdoor recreation on public lands. Recreation areas, national by-ways, and campground facilities on public lands can be located in proximity to AML sites. Use of Off-Highway Vehicles often transpires at AML sites amid risks of dangerous shafts, and exposure to contaminants in the soil, water and air. Recreational fishing can place anglers in proximity of AML sites, and is impacted by decreased fish population among polluted waters stemming from AML sites, and available fish may pose significant uptake of contaminants when consumed.
Uranium mines pose the added threat of radiation exposure to the list of health concerns. The mining of uranium ores by underground and surface methods produces large and small amounts of bulk waste material. These materials contain naturally occurring radioactive components and become exposed to the environment through mining activities. Because the waste rock and soil have little or no practical use, they are generally stored on land near the mine site. Continued exposure to these materials can cause severe health problems.
Typical kinds of environmental problems stemming from AML sites include: contaminated/acidic surface and ground water; and stockpiled waste rock and mill tailing piles.
Sedimentation and Sediment Contamination
Surface runoff can carry AML-originated silt and debris down-stream, eventually leading to stream clogging. Sedimentation results in the blockage of the stream and can cause flooding of roads and/or residences and pose a danger to the public. Sedimentation may also cause adverse impacts on fish.
Highly acidic water rich in metals, or, AMD, is a serious problem at many abandoned mines. Abandoned mines can produce AMD for more than 100 years and, consequently, pose significant risks to surface water and ground water. AMD can lower the pH of surrounding surface water, making it corrosive and unable to support many forms of aquatic life and vegetation. Humans may also be affected by consuming water and fish tissue with a metal content.
Air pollution occurs at mining sites during excavation and transportation. Blowing dust from AML sites is a common concern, as many mines are in arid western states. Some sources of dust may be from road traffic in the mine pit and surrounding areas, rock crushers located in pits and in mills, and tailings ponds. The toxicity of the dust depends on the proximity of environmental receptors and the type of ore being mined. High levels of arsenic, lead, and radionuclides tend to pose the greatest risk.
Threatened & Endangered Species
Threatened and endangered species may reside in or around AML affected lands and waters. This is especially true for bat species. Adits, entrances to mines, often provide bat habitat. In many instances, the bats are displaced from their preferred roosting sites by encroaching human development and wanton destruction. Although mines are human-made habitats, as we disturb, alter, or destroy natural habitats for bats, human-made habitats become critical in the conservation of bat species.
Bats are the major biological controllers of nighttime flying insects and play an important ecosystem role. Insects controlled by bats include many agricultural and forest pest insects. For example, a single little brown bat can catch 600 mosquitoes in just one hour. In the southwest United States, many desert plant species are dependent on pollination by bats.
Bat grates and cupolas are cost effective closure methods that protect and promote bat habitat by allowing bats to pass in and out of a mine while blocking human entry. BLM installs bat grates/cupolas when mine openings are determined to be beneficial as habitat for bats.