Mixing oxygen, water, and iron pyrite in old abandoned mines produces a toxin called acid mine drainage, one of the most serious and long-lasting effects of previously unregulated coal mining in Pennsylvania and West Virginia. Friendship Hill is among 145 National Park Service units affected by abandoned mines and one of 60 with serious water pollution. Through a partnership with the U.S. Geological Survey, the National Park Service is actively treating the acid mine drainage polluting Ice Pond Run with new techniques being researched.