CONCEPTUALIZING, CHARACTERIZING, AND MODELING THE IMPACTED UPPER SILVER CREEK HYDROLOGIC SYSTEM, UTAH, ON THE WATERSHED SCALE: AN INTEGRATED, INTERDISCIPLINARY, HIERARCHICAL APPROACH

The Upper Silver Creek Watershed includes the town of Park City, Utah, and the surrounding area, including two ski resorts. The area, which lies within the headwaters of the Weber River, was the site of the 2002 Winter Olympics. The watershed is a former silver mining area with a legacy of heavy-metal contamination in waters and soils related to nearly 1,200 miles of mine tunnels, tailings dumps, and waste rock piles. Currently, six active CERCLIS sites are in the watershed, one site is proposed for the National Priorities List, and Silver Creek is listed on the state’s 303(d) list for zinc and cadmium and is targeted for TMDL (total maximum daily load) development. Our objective is to use existing data to develop a watershed-based, hierarchical analysis and an integrated conceptual model, focused on groundwater, to aid in characterization of contaminant migration pathways from overlapping sources in the watershed.

We characterized the complex, multiscale hydrogeology of the Upper Silver Creek Watershed area by using hierarchical systems analysis of multidisciplinary data. Existing data sources were used to quantify climate, vegetation, surface water, topography, anthropogenic activities, soils, geomorphology, geology, and geochemistry. The hydrogeologic units were delineated spatially from a 3-D geologic model of the area. Significant permeable layers or major conduits for groundwater flow were identified, and hydrogeologic properties of these units were estimated by using available data. The hydrogeologic framework was then displayed as a solid block model to visualize and analyze the watershed system. Both surface water and groundwater subsystems were characterized. Significant groundwater flow, discharge, and recharge areas — and the relationship of these areas to the surrounding terrain and areas of environmental impact — were assessed and interrelated, and a potentiometric surface involving the critical sites was interpreted. The results, which show how each contaminant site is related to the watershed-scale hydrologic system, enable area stakeholders to reassess each site with respect to the whole hydrologic system. The analysis will allow a comprehensive, complex mathematical model to be constructed for future management and decision making.