EVALUATING REMEDIATION ALTERNATIVES FOR MINE DRAINAGE, LITTLE COTTONWOOD CREEK, UTAH

Descriptive studies have documented mine-drainage problems at countless locations worldwide. The vast occurrence of mine drainage presents a staggering challenge for remediation. A reactive solute transport model is a tool that can move beyond descriptive study and help to evaluate options for remediation in a way that maximizes improvements to streams and minimizes cost of remediation and could save valuable resources and time. As an example, the model was calibrated from two detailed mass-loading studies in Little Cottonwood Creek (LCC), Utah, to evaluate remediation options. Metal loading to LCC is dominated by discharge from two mine drainage tunnels. Discharge from the upstream tunnel (CCR) has been treated by a pilot fen to reduce metal loading to LCC. Discharge from the downstream tunnel (WDT) can be controlled because of a bulkhead that creates a mine pool. The first mass-loading study quantified the effects of fen treatment on CCR discharge and minimal discharge from the WDT tunnel, and the second study quantified loading with no fen treatment of CCR discharge and maximum discharge from the WDT tunnel. Simulations of remedial options for three compliance locations suggest that although regulation of discharge from the WDT results in lower Cu and Zn concentrations, some treatment of the CCR inflow by the fen would be required to meet applicable water-quality standards. Simulation results also suggest that water-quality standards at the upstream and downstream compliance locations may be met by using different combinations of fen treatment and WDT regulation, but that complete compliance in the middle compliance location would require the highest level of fen treatment and the greatest regulation of WDT discharge. Reactive transport modeling is a useful tool for the evaluation of remedial alternatives in natural systems, where complex interaction between multiple hydrologic and geochemical processes determine metal fate.