EMCBC Mining and the Environment Primer: Acid Mine Drainage

Jamie Kneen Communications and Outreach Coordinator responsible for: strategic research, social media, and public engagement; our Africa program, environmental assessment, and uranium mining.

Industry, labour, government, and environmentalists agree on one issue: that Acid Mine Drainage (AMD) is the number one environmental problem facing the mining industry. Acid Mine Drainage:

  • devastates fish and aquatic habitat,
  • is virtually impossible to reverse with existing technology, and
  • once started, costs millions of dollars annually to treat and can continue for centuries.

AMD occurs when sulphide-bearing minerals in rock are exposed to air and water, changing the sulphide sulphur to sulphuric acid. This acid can dissolve heavy metals found in waste rock and tailings such as lead, zinc, copper, arsenic, selenium, mercury, and cadmium, into ground and surface water. Certain bacteria, naturally present, can significantly increase the rate of this reaction. AMD and heavy metals pollution can poison ground and drinking water. AMD can destroy aquatic life and habitat. Ore bodies commonly mined that pose AMD risk in BC are: gold, silver, copper, iron, zinc, lead (or multi-metal combinations), and coal.

Acid drainage can and does occur naturally at specific sites. It happens when sulphide minerals are exposed to weathering and react with water and oxygen to produce sulphuric acid, which is carried away in runoff. This process is called acid rock drainage (ARD). In mining, however, the scale and impact of the acid generation (here usually called acid mine drainage) can be pushed far beyond natural limits.

Acid generation results from exposure to air and water. This means that the more surface area of rock exposed, the greater the amount of acid. During the mining process, hundreds, sometimes thousands of tons of rock are dug up and crushed each day. The acid then leaches through the ground and releases heavy metals such as lead, zinc, copper, arsenic, selenium, mercury and cadmium.

The Equity Silver mine near Houston, shown here, will require treatment for AMD for at least the next 500 years. On Vancouver Island, the Mt. Washington mine operated for only three years. However, it has left a deadly legacy of acid and heavy metals that has virtually eliminated what was a $2 million annual fishery on the Tsolum River.

Acid mine drainage can develop at several points throughout the mining process: in underground workings, open pit mine faces, waste rock dumps, tailings deposits, and ore stockpiles. Acid generation can last for decades, centuries, or longer, and its impacts can travel many miles downstream. Roman mine sites in Great Britain continue to generate acid drainage 2,000 years after mining ceased.

As concerned individuals committed to the protection and respect of our natural world, we can:

  • identify operating or abandoned mine sites in our regions,
  • learn about how mine sites are being monitored, what permits have been issued, and how citizens are involved in decision making.
  • get more information about AMD and other mining issues across BC and in our community, and
  • insist that prevention of AMD is the only acceptable and responsible strategy.

For a detailed examination of AMD, see our report on Acid Mine Drainage and water issues.