Environmental Impact of The Coal Industry - Water Management

Water Management

Open-pit mining requires large amounts of water for coal preparation plants and dust suppression. To meet this requirement mines acquire (and remove) surface or groundwater supplies from nearby agricultural or domestic users, which reduces the productivity of these operations or halts them. These water resources (once separated from their original environment) are rarely returned after mining, creating a permanent degradation in agricultural productivity. Underground mining has a similar (but lesser) effect, due to a lower need for dust-suppression water; however, it still requires sufficient water for coal-washing.

Groundwater supplies may be adversely affected by surface mining. These impacts include drainage of usable water from shallow aquifers; lowering of water levels in adjacent areas and changes in flow direction within aquifers; contamination of usable aquifers below mining operations due to infiltration (percolation) of poor-quality mine water; and increased infiltration of precipitation on spoil piles. Where coal (or carbonaceous shale) is present, increased infiltration may result in:

• Increased runoff of poor-quality water and erosion from spoil piles
• Recharge of poor-quality water to shallow groundwater aquifers
• Poor-quality water flow to nearby streams

This may contaminate both groundwater and nearby streams for long periods. Deterioration of stream quality results from acid mine drainage, toxic trace elements, high content of dissolved solids in mine drainage water, and increased sediment loads discharged to streams.

When coal surfaces are exposed, pyrite comes in contact with water and air and forms sulfuric acid. As water drains from the mine, the acid moves into the waterways; as long as rain falls on the mine tailings the sulfuric-acid production continues, whether the mine is still operating or not. This process is known as acid rock drainage or acid mine drainage. If the coal is strip mined, the entire exposed seam leaches sulfuric acid; this leaves the subsoil infertile on the surface and begins to pollute streams.

Also waste piles and coal storage piles can yield sediment to streams. Leached water from these piles can be acid and contain toxic trace elements. Surface waters may be rendered unfit for agriculture, human consumption, bathing, or other household uses. Lakes formed in abandoned surface-mining operations are more likely to be acid if there is coal or carbonaceous shale present in spoil piles, especially if these materials are near the surface and contain pyrites. Sulfuric acid is formed when minerals containing sulphide are oxidised through air contact; this causes acid rain. Leftover chemical deposits from explosives are toxic and increase the salt content of mine water, contaminating it.

By the late 1930s, it was estimated that American coal mines produced about 2.3 million tons of sulfuric acid annually. In the Ohio River basin, 1,200 operating coal mines drained an estimated annual 1.4 million tonnes of sulfuric acid into the drainage basin during the 1960s; thousands of abandoned coal mines leached acid as well. In Pennsylvania alone, mine drainage had blighted 2,000 stream miles by 1967.

To mitigate these problems, water is monitored at coal mines. The five principal technologies used to control water flow at mine sites are:

• Diversion systems
• Containment ponds
• Groundwater pumping systems
• Subsurface drainage systems
• Subsurface barriers

In the case of acid mine drainage, contaminated water is generally pumped to a treatment facility which neutralizes its contaminants.