An estimated 500,000 orphan mines exist in the United States, most of which are former hardrock mines located in the West. Thousands of watersheds and stream miles are impacted by drainage and runoff from these mines, one of the largest sources of water pollution in the region.

At many orphan mine sites and processing areas, disturbed rock and waste piles contain high levels of sulfides and heavy metals. These piles, when exposed to air and water, undergo physical and chemical reactions that create acid drainage. As this drainage runs through mineral-rich rock, it often picks up other metals - such as arsenic, cadmium, lead, mercury and zinc - in solution or in suspension as sediment. When this runoff enters local streams and rivers, it can severely degrade water quality, damage or destroy insect, plant and animal life.

In many cases, the parties responsible for the pollution from orphan mine sites no longer exist or are not financially viable. Yet, a variety of interests, including nonprofit organizations and state and local governments - are eager to voluntarily clean up these abandoned sites even though they are not responsible for the pollution. Many potential Good Samaritans have expressed concerns that they may be held liable under the Clean Water Act and CERCLA. This obstacle has prevented many cleanup projects from moving forward.