Heavy Metals in Subsurface Waters of Reclaimed Frac Sand Mine Soils.

Silica sand mining for frac sand production has increased substantially in the United States over the last five years. Since only a certain size range of sand is desirable for hydraulic fracturing of shale oil and gas formations, the processing of sand generates large volumes of unwanted material, which consists mostly of silt and clay (commonly referred to as fines or muds). These materials are typically incorporated with overburden and used to fill in the mined area during reclamation. A 3-acre reclamation site was established at an active frac sand mine in Chippewa County, Wisconsin to evaluate the effects of using the fines as a soil amendment during reclamation. Fine may improve site reclamation since frac sand mines are typically located where native soils are shallow and sandy, making vegetation establishment challenging due to limited soil moisture and nutrient retention capacity. However, one potential concern is that the fines may be a source of heavy metals. Plots were established using a randomized complete block design in a split-plot arrangement with application of waste fines as the main treatment. Fines were applied below the subsoil and topsoil at approximately 30 cm. Subsurface water quality was monitored using suction cup lysimeters installed at 30 cm at 5 locations within each plot. Leachate samples were collected bimonthly during the growing season and analyzed for heavy metals using ICP-MS.