MODELING METALS TRANSPORT IN COPPER MINING TERRAIN

An HSPF model was developed to simulate the transport of dissolved copper and zinc in a southeast Arizona watershed impacted by mining and other land disturbances. HSPF allowed explicit modeling of numerous stormwater diversions and other hydrologic complexities. Copper and zinc loads were simulated in an empirical fashion, largely by assigning observed concentrations to runoff and interflow from nine different land types including disturbed areas and stockpiles. It was necessary to model large internal loads from suspended/bed sediment to calibrate the HSPF model.Model scenarios included the simulation of several different remedial scenarios as well as a “pre-mining” scenario intended to predict the lowest achievable copper and zinc concentrations. Results demonstrated that remedial scenarios can significantly reduce copper and zinc concentrations in the stream, but that it unlikely that current water quality standards could be met even if the watershed was undisturbed.