Covering Pre-existing, Acid-producing Fills with Alkaline Sandstone to Control Acid Mine Drainage

Abstract

In Boone County, West Virginia, small valley fills composed of overburden from the Number 5 Block coal seam were constructed during previous mining operations before overburden analysis was required to predict acid-producing potential. Using the modified acid–base accounting procedure, we found that these fills contain acid-producing materials, and in fact, they do produce acidic drainage. Black Castle Mining Company began operating in the area during the late 1980s and, in the process of removing coal from deeper in the geologic column, encountered alkaline sandstone, which they used to construct valley fills around and below the pre-existing fills that were discharging acidic drainage. Water quality from existing fills had pH from 3.5 to 4.5, and acidities up to 200 mg/L as CaCO3. After covering the existing fills with alkaline sandstone, drainage water had a pH of >6.2 and contained net alkalinity. This has eliminated the need for chemical treatment of acid mine drainage from the pre-existing, pre-law valley fills.