EPA says it isn't monitoring an estimated 161,000 abandoned mines

The agency has said it doesn't monitor hundreds of thousands of abandoned mines, or know which one could be the source of the next big toxic spill

The Environmental Protection Agency (EPA) has said it has no system for monitoring hundreds of thousands of abandoned mines that pock the American landscape, or knowing which one could be the source of the next big toxic spill.

"EPA does not maintain records of the number of mines or tailings dams in the US," a spokesman for the federal agency told the Guardian. In the western US, the EPA estimates there may be 161,000 abandoned "hard rock" mines, where metals such as gold, silver and copper were once dug. But the nationwide threat left by these bygone miners remains largely unknown and unwatched.