Evapotranspiration cover performance in a high desert environment, north waste rock disposal facility, Rain Mine, USA

摘要

Newmont Mining Corporation conducted a performance audit of an evapotranspiration (ET) cover constructed in 2002 at an acid generating waste rock disposal facility located at 2,000 m elevation. Based on technology available at that time, the monolithic ET cover design included approximately 0.9 m of local alluvium with native sagebrush steppe vegetation. The site receives an average of 540 mm of precipitation annually, 84% of which falls during October to April. The cover did not significantly reduce infiltration into the waste rock, as measured by a seepage collection system constructed beneath the waste rock facility. Average annual seepage following reclamation has ranged from 38,000 to 193,000 cu. m, or 13 to 44 % of annual precipitation for the 76 ha facility. Peak monthly average rates during the spring have been as much as 10 litres per second (Us). Seepage chemistry is poor, with pH typically below 3, total dissolved solids concentration ranging from 5 to 30 g/L, and elevated metals concentrations.