EVALUATION OF A COMPOSITE SOIL COVER TO CONTROL ACID WASTE ROCK PILE DRAINAGE

Acid mine drainage (AMD) research under the MEND program has been ongo ing since 1988 at the Heath Steele Mines waste rock piles including su lphide material, outside Newcastle, NE. In 1989 approximately 10,000 m t of waste rock was placed on a pre pared sand base with an underlying impermeable membrane. The waste rock pile was heavily instrumented So r measuring oxygen concentrations and temperatures. In September 1991, a composite soil cover designed for the Heath Steele climatic conditi ons, using local soils, was placed over the pile, creating a totally e nclosed system. Moisture content and oxygen probes were installed with in the composite soil cover to monitor changes within the soils over t ime, while two large-size lysimeters were installed below the cover to monitor the hydraulic conductivity of the cover. The waste rock site has been monitored on a monthly basis since installation of the cover, for performance of both cover and waste rock. The monitoring shows ve ry clearly that the placement of the composite soil cover has had a ma jor impact on the generation of AMD. Major reductions in temperature a nd oxygen concentrations within the waste rock pile indicate that the cover has significantly inhibited the oxidation reaction that generate s the AMD. Performance data have shown that the cover has maintained i ts integrity under the climatic conditions of the area.