Demonstration of subaqueous disposal of mill wastes, Jasper County, MO

The Jasper County Superfund Site in Jasper County, Missouri contains more than 5 000 000 cubic yards of mill waste from the historic lead and zinc mines of the Tri-State Mining District. Remediation alternatives evaluated in a Feasibility Study (NewFields 2003) include conventional soil caps, engineered repositories, and in-place revegetation with topsoil and municipal biosolids. One alternative is to use the mill wastes as fill in mine subsidence pits, the surface depressions resulting from collapse of underground mine workings. Regulatory concerns that subaqueous disposal would negatively impact water quality in the shallow aquifer led to placement of 58 000 cubic yards of zinc mill tailings as unsegregated fill in a flooded one-acre subsidence pit. The tailings contain about 2 percent zinc and lesser amounts of lead, cadmium, and iron. Monitoring in nearby wells and ponds did not detect any significant changes in water chemistry. Permeability and gradient information from the field test was used to calculate zinc loading to the shallow aquifer.