Evaluating the Risk of Nitrogen Losses in Reclaimed Soils Due to Polyacrylamide Use in Frac Sand Mining.

Hydraulic fracturing currently plays a major role in United States energy production. In order to retrieve oil and gas from shale bedrock, large amounts of sand are required. Once mined, sandstone is crushed, mixed with water, and sieved to isolate desirable fraction sizes. Polyacrylamide (a nitrogen polymer) is used to help settle the undesirable silt and clay particles out of the water so the water can be reused. Traditionally, the silt and clay are put back in the ground as overburden but recently have been used to augment soils during reclamation. A long-term field study is being conducted in Chippewa County, Wisconsin to evaluate the effects of using waste fines as a soil amendment during reclamation. A 3-acre reclamation site was established at an active mine in 2015 to quantify subsurface water chemistry. Plots were established using a randomized complete block design in a split-plot arrangement with application of waste fines as the main treatment. Waste fines were applied as a 30 cm layer, on average 32 cm below the subsoil and topsoil. Subsurface water quality was monitored using suction cup lysimeters installed at 30 cm depth at 5 locations within each plot. Leachate samples were collected bimonthly during the growing season and analyzed for ammonium and nitrate using a LACHAT analyzer. The results from our last two field seasons will be presented.