Underground injection wells, where water and/or other substances are injected into the Earth, are used for a wide variety of purposes. The U.S. Environmental Protection Agency (EPA) regulates around 850,000 underground injection wells through its Underground Injection Control program under the Safe Drinking Water Act. The EPA defines six classes of wells based on their use^[1]:

The Environmental Protection Agency (EPA) provides a range of resources which address the health effects of contaminants in drinking water. Their Drinking Water Contaminants page provides a useful background on the sources and effects of drinking water contaminants for the following contaminant types:

Water flowing through active or abandoned mine sites can become polluted by the material being mined^[1]. By far the most common mine drainage problem is that of acid mine drainage (AMD). Sulfuric acid is produced when water interacts with sulfur-bearing materials in the presence of oxygen and common bacteria^[1].