Hydrology of the Prospector Square area, Summit County, Utah

The Silver Creek tailings site is in Prospector Square, a commercial development and residential community in Summit County, Utah. This study assessed the presence of metals and the movement of groundwater in the unconsolidated valley-fill and consolidated-rock aquifers underlying the tailings. The unconsolidated valley fill is a poorly sorted mixture of clay, silt, sand, and gravel, with intermittent layers of clay. The hydraulic conductivity, estimated on the basis of slug tests, ranged from 1 to 14 ft/day. An aquifer-interference test indicated that water in the valley fill underlying the tailings site did not move toward the pumped municipal well completed in the consolidated-rock aquifer. Concentrations of dissolved and suspended cadmium, manganese, and zinc were greater than background in surface water only during low-flow conditions. Concentrations of suspended iron and lead were greater than background concentrations upstream from the tailings site, but concentrations decreased progressively downstream and during later sampling rounds. Concentrations of dissolved cadmium, managanese, and zinc were greater than background concentrations in water from six wells and one drain. Dissolved arsenic and lead were detected in water from a well downgradient from Prospector Square, but were not detected in water from any of the other wells. Concentrations of all selected metals detected in stream-sediment samples, were detected in similar concentrations in tailings samples. Concentrations of metals in surface and groundwater could increase if the pH of the water decreases substantially from the present (1988) values of about 7 (neutral). (USGS)