Numerical Indices of the Severity of Acidic Mine Drainage: Broadening the Applicability of the Gray Acid Mine Drainage Index

The Gray acid mine drainage index (AMDI) was developed to detect, quantify, and categorise mine water and to monitor recovery of contaminated sites. A modified index (MAMDI) is proposed, incorporating the concentration of the dissolved metals that are present (at significant levels) and analysed at a site, and adjusting the weighting to reflect, in part, the maximum contaminant levels permitted by the U.S. EPA and WHO. In 98% of 206 analytical results applied to MAMDI, one or more of the four metals (Al, Zn, Cu, or Cd) used in AMDI were replaced by Mn, Ni, As, Pb, Tl, CN, and Be, while 63% had two or more replaced. A scatter diagram shows that in general, MAMDI is lower than AMDI when the total score is less than 50 and greater when the score is more than 50.