Sand-sized limestone treatment of streams impacted by acid mine drainage

Direct single point, instream applications of limestone sand were made in t wo streams severely acidified by acid mine drainage. After high flows distr ibuted the sand downstream, dissolution of the limestone significantly redu ced the acid loads in both streams. Data from the treated stream sections a nd laboratory experiments showed that the efficiency of treatment was more dependent on limestone particle size than CaCO3 content. Results from the s tream treated with a narrow range of limestone sand-sized particles showed a high utilization efficiency with nearly complete dissolution of the limes tone. The data indicated that monthly addition of limestone sand may be suf ficient for complete treatment of the streams studied. An analysis of such a treatment scheme indicated it to be highly cost efficient when compared t o other active and passive treatment systems.