Coal and Water Pollution

Coal is more often associated with billowing smokestacks than it is with water. But virtually every stage of coal’s lifecycle—from mining to processing to burning—can impact local water supplies, sometimes with devastating effect.

Coal mining

Mining operations can negatively impact water supplies, often with long-lasting effects. The fundamental issue involves contamination of nearby rivers, lakes, and aquifers by what comes out of a coal mine—usually highly acidic water containing heavy metals like arsenic, copper, and lead. The process is known as acid mine drainage. It happens when certain substances (typically iron sulfide, FeS2, or fool’s gold) is oxidized after being exposed to air and water. Runoff can change the pH of nearby streams to the same level as vinegar.

Another form of coal mining, conducted mostly in Central Appalachia, is called mountain top removal, a highly destructive process of flattening entire mountains to uncover thin coal seams that are not accessible by traditional underground methods. After clearcutting forests and removing vegetation, explosives are used to blast away the tops of mountains, sometimes destroying as much as 600 feet or more of elevation. The resulting debris is typically dumped into the valleys below.

To date, the practice has buried more than 2,000 miles of headwater streams and polluted many more.

Finally, after coal is mined, it is typically washed with water and chemicals to remove impurities before it’s burned. The resulting coal slurry must then be stored, often with coal ash (see below) or in improvised ponds that can leak, spill, or fail. In 2000, the bottom of a Kentucky coal slurry impoundment gave way, contaminating more than a hundred miles of rivers and streams with more than 300,000,000 gallons of thick black sludge—30 times larger than the Exxon-Valdez oil spill.

Coal ash

When coal is burned it leaves behind a grey powder-like substance known as coal ash. Although the exact chemical composition depends on the type of coal burned, all coal ash contains concentrated amounts of toxic elements, including arsenic, lead, and mercury.

More than 100 million tons of coal ash and other waste products are produced by coal-fired power plants in the United States every year (see a map here). About a third of that waste is reused in some way (often in concrete); the rest is stored in landfills, abandoned mines, and hazardous, highly toxic ponds.

• Most coal ash is stored in unlined ponds or pits. Over time, heavy metals in the ash can escape into nearby waterways and contaminate drinking water.
• Exposure to coal ash is linked with a heightened risk for cancer as well as heart damage, reproductive problems, neurological disorders, and other serious health conditions.

In 2014, 39,000 tons of coal ash spilled into the Dan River in North Carolina. Six years earlier, more than 5 million cubic yards of coal ash spilled into Tennessee’s Emory River—one of the country’s largest environmental disasters ever.

Water use

All coal plants rely on water. They function by heating water to create steam, which then turns turbines, generating electricity.

But the water must come from somewhere—typically a nearby river or lake.

• “Once-through” coal plants pump the water directly from a water source, heat it up, then discharge it back. The waste water is typically hotter (by up to 20-25° F) than the water that receives it, creating "thermal pollution" that can decrease fertility and increase heart rates in fish. A typical once-through system withdraws and discharges between 70 and 180 billion gallons of water per year.
• “Wet-recirculating” plants avoid this problem by cooling and reusing water. However, these systems lose water during the cooling process, meaning they consume relatively more water per year—upwards of 1.7 to 4 billions of gallons per year.

These and other energy-water collisions may worsen as the climate heats up. For example: droughts can restrict the amount of water available to coal plants, forcing them to shut down. And hot weather can make water supplies too warm for cooling, forcing power plants to reduce their electricity production when it’s needed most (hot days are also peak electricity usage days).

The Union of Concerned Scientists has spent decades advocating for clean energy technologies. You can read more about cleaner, reliable alternatives to coal—like wind and solar—here >