Simulation of An Alluvial Aquifer and Its Interaction with a River to Evaluate Remedial Alternatives at a Mine Site

A numerical groundwater flow and solute transport model was developed for the Red River alluvial aquifer and debris flows at the mouths of side drainages along the Chevron Mining Inc. mine near Questa, New Mexico. Simulated groundwater inflows from tributary drainages were estimated using a watershed yield approach.  Watershed yield approximates recharge to groundwater assuming there is no runoff. Yield estimates were used in a sulfate loading analysis from contributing watersheds, some of which contain waste rock piles at the mine that are underlain by naturally-occurring hydrothermal scars. The model simulated the interaction between the alluvial aquifer and the Red River, which was an important aspect in evaluating possible remedial alternatives. The model was calibrated to alluvial and colluvial water levels and sulfate loading from groundwater, and also to sulfate loads removed from existing groundwater withdrawal wells and spring collection systems downgradient of the waste rock piles. The calibrated model was used as a predictive tool to evaluate various groundwater extraction remedial alternatives to capture constituent loads from the mine site, reduce concentrations in the alluvial aquifer, and reduce loading of the Red River.