Submitted to: Mining History Association Meeting
Publication Type: Proceedings
Publication Acceptance Date: 5/1/2001
Publication Date: 6/25/2001
Citation: Interpretive Summary: This paper summarizes a pilot-scale test of in site remediation of mine wastes using biosolids plus limestone, a method developed by USDA and cooperators, and tested at several locations before this larger scale test near Leadville, CO. Mine wastes had been dispersed along the Arkansas River below Leadville, CO, and had become barren due to oxidation of metal sulfides. Using locally available materials, a test was established. After one year, measures of the effectiveness of the remediation were undertaken in the laboratory and field. The untreated mine waste was very highly metal contaminated, and very acidic; ryegrass was killed by Zn phytotoxicity during germination, but on the treated tailings, the ryegrass grew well. Earthworm toxicity testing showed that earthworms died on the untreated tailings, but survived and grew on the treated tailings. Soil microbial testing showed that populations remained low but still much improved on the treated tailings. The test of the effectiveness of the biosolids plus limestone remediation method was applied to a 4.5 ha previously barren site. Effective vegetative cover was established. Forages growing on the site would be safe for consumption by wildlife and livestock. Concern remained about possible risk to earthworm consuming small mammals, but it was not possible to test for this risk in the present test. Thus further studies are needed to support full application of the new green remediation technology.
Technical Abstract: The US-EPA has been evaluating emerging cost-effective green engineering solutions, such as the U.S. Department of Agriculture (USDA) developed applications of biosolids plus limestone equivalent to large area metals mining sites. A site in Leadville, CO, was characterized by discrete 0.5-1.0 ha parcels of fluvial mine tailings deposits along the embankment of the Upper Arkansas River. The contaminants of concern in the tailings were zinc, lead, cadmium, copper and manganese, with zinc concentrations from 50,000 to 100,000 mg/kg dry soil. A 4.5 ha pilot demonstration project mixed 224 t/ha biosolids with 224 t/ha limestone, and incorporated the remedial mix using heavy equipment. After one year, the Environmental Response Team evaluated changes in the physical, chemical, biological and toxicological characteristics of the soil through metals analysis, agronomic assessment, assessment of soil microbial community structure and function, and rye grass and earthworm toxicity testing. The results showed that the effectiveness of biosolids application for remediating large area base metals mining sites in not perfect, but is an encouragingly positive and cost-effective remedial alternative for future large area mining-related Superfund Sites. More care is required in selecting alternative low cost liming agents so that they have small particle size and rapid reaction rates needed to achieve rapid revegetation.