Why is it dangerous for rainwater to flow through piles of waste coal?

Answer 1

Abandoned Mine Lands (AML) are those lands, contaminated or scarred by PAST mining activity including: extraction, or processing of coal, ores and minerals. Sixty percent of these abandoned mines in the USA can be found in just three states: Kentucky, Pennsylvania, and, West Virginia.

Coal refuse piles represent a significant subset of AML sites. These sites present both some unique problems and opportunities. The piles are typically barren and highly erosive.The bituminous piles in particular can leach highly concentrated substances with acidity values in the thousands of mg/L, and which can include, in addition to typical parameters, elevated levels of some trace metals such as arsenic, lead, copper, and chromium. The cost of reclaiming these piles using conventional techniques is high, and the extremely poor water quality is often beyond the reach of current passive treatment technology.


Hundreds of millions of tons of coal mining refuse have long imposed an environmental burden on the land. Pennsylvania's Bureau of Abandoned Mine Reclamation estimates the cost to eliminate these abandoned mine problems and complete the cleanup of AML sites in Pennsylvania alone to be approximately $14.6 billion and take nearly 500 years.

AMD (Abandoned Mine Drainage or Acid Mine Drainage) is water contaminated when pyrite (an iron sulfide found in coal refuse piles) is exposed and reacts with air and water to form sulfuric acid and dissolved iron. Some or all of this iron can precipitate to form the red, orange, or yellow sediments in the bottom of streams containing mine drainage. The acid runoff further dissolves heavy metals such as copper, lead, and mercury into ground or surface water. About half of the coal-mine discharges in Pennsylvania are acidic, with a pH greater than 5. There are a number of major environmental problems caused by AMD. It disrupts growth and reproduction of aquatic plants and animals, diminishes valued recreational fish species, degrades outdoor recreation and tourism, contaminates surface and groundwater drinking supplies, and causes acid corrosion of infrastructure like waste-water pipes.

It is estimated that the acid leached from abandoned coal mines and coal refuse piles contributed to the degradation of more than 3,000 miles of streams and associated ground waters. In Pennsylvania it is the most extensive water pollution problem affecting four of its major river basins. Because coal mine drainage can contain toxic concentrations of acid, metals, and sediment, many of the mining impacted streams are lacking aquatic life. Consequently, states lose millions of dollars annually that could be generated if sport fishing were restored in the affected streams. The estimated taxpayer cost for restoring the damaged watersheds is many billions of dollars. Pennsylvania taxpayers have to date, invested millions of dollars to construct acid mine drainage treatment plants to treat AMD discharges.

Answer 2

Rainwater flowing through piles of waste coal can pick up harmful pollutants such as heavy metals and contaminants present in the coal. This can result in the runoff becoming acidic and polluting nearby water sources, leading to water contamination and harming aquatic life. Additionally, the leaching of these pollutants into the environment can have long-term ecological impacts.