Quantification of mine-drainage inflows to Little Cottonwood Creek, Utah, using a tracer-injection and synoptic-sampling study

Historic mining in Little Cottonwood Canyon in Utah has left behind many mi ne drainage tunnels that discharge water to Little Cottonwood Creek. To qua ntify the major sources of mine drainage to the stream, synoptic sampling w as conducted during a tracer injection under low flow conditions (September 1998). There were distinct increases in discharge downstream from mine dra inage and major tributary inflows that represented the total surface and su bsurface contributions. The chemistry of stream water determined from synop tic sampling was controlled by the weathering of carbonate rocks and mine d rainage inflows. Buffering by carbonate rocks maintained a high pH througho ut the study reach. Most of the metal loading was from four surface-water i nflows and three subsurface inflows. The main subsurface inflow was from a mine pool in the Wasatch Tunnel. Natural attenuation of all the metals resu lted in the formation of colloidal solids, sorption of some metals, and acc umulation onto the streambed. The deposition on the streambed could contrib ute to chronic toxicity for aquatic organisms. Information from the study w ill help to make decisions about environmental restoration.