English: Acid mine drainage flowing away from collapsed entrance to the Davis Mine pyrite mine near Rowe, Massachusetts, USA. The mine was active from 1882 to 1911, after which the mine filled with water and began generating acidic drainage (Becerra et al., 2009). Near the mine entrance, drainage pH is near 2, and outside of the waste rock area, pH ranges from about 4.5 to 6 (Becerra et al., 2009).