Integration of Surface Water Management with Mitigation of Groundwater Impacts at a Proposed Phosphate Mine Overburden Facility

Environmental impact evaluation of proposed phosphate mine overburden fills at the J.R. Simplot Smoky Canyon Mine, in Southeastern Idaho indicated that leaching of the overburden by infiltrating precipitation could potentially contaminate local groundwater with selenium. The Idaho Department of Environmental Quality (IDEQ) required that groundwater impacts be reasonably localized to the immediate mine vicinity. A number of best management practices (BMPs) were incorporated into the design of the overburden fills to reduce potential surface water and groundwater impacts, but groundwater quality impacts were still predicted to extend off site in the long term (100 years). A number of alternatives were then evaluated to reduce the infiltration of precipitation into the overburden through use of low permeability covers. These were rejected for cost and engineering feasibility reasons. Use of modified infiltration trench technology for stormwater management at the periphery of the proposed overburden fills was then evaluated for recharge of runoff into the local groundwater. Both the State and the EPA already approve this technology as a stormwater management BMP. Groundwater impact modeling showed that incorporation of runoff recharge areas into the margins of the overburden fills would be effective in containing the area of groundwater impacts to the immediate mine vicinity. This design was eventually approved by the IDEQ, EPA, and the Federal land management agencies and has potential applicability in similar hydrogeologic situations at other mining operations.

Buck, B.W., and B. Winegar, 2003. Joint Conference - Billings Land Reclamation Symposium and American Society of Mining and Reclamation, June 3-6, Billings, Montana.