USE OF A THREE-DIMENSIONAL HYDRODYNAMIC MODEL TO SUPPORT AND REVISE MANAGEMENT DECISIONS REGARDING SELENIUM INPUTS TO THE GREAT SALT LAKE ECOSYSTEM

A tissue-based selenium (Se) standard was recently adopted by the State of Utah for the open waters of Great Salt Lake (GSL). Localized Se concentrations in the south shore area of the lake have been under continued scrutiny by concerned citizen groups, as well as State and Federal regulators, because of current and planned Se inputs to this part of the ecosystem. Based on studies conducted by the State of Utah and the U.S. Geological Survey during 2006-08, the south shore of GSL consistently receives some of the most elevated concentrations of Se relative to other inflow areas to the lake. These Se inputs are from natural inflows (Lee Creek and Goggin Drain) and from anthropogenic inflows associated with discharge from the Kennecott Utah Copper Corporation (KUCC) smelter tailings (up to 54 ug/L). Additional Se input to the south shore area includes a planned waste stream from the Jordan Valley Water Conservancy District (JVWCD) groundwater treatment plant. To date (2014), no information exists on how Se concentrations vary in the south shore areas of GSL as a function of varying lake levels, salinities, input sources/concentrations, surface currents, and wind speed and direction. During 2011, a rhodamine WT dye tracer was injected near the mouth of Lee Creek and the movement of this freshwater plume in the hypersaline water of GSL was mapped using an autonomous underwater vehicle and a manned boat, equipped with calibrated flurometers. Incorporating these field data into a 3-D model provides insight into possible discharge management scenarios to minimize the impacts of Se inputs to sensitive lake habitats. Generalized Environmental Modeling System for Surface waters (GEMSS) 3-D model simulations indicate that a strategically positioned 1,200-m long, rock-filled boardwalk may deflect freshwater inflow and the associated Se plumes away from shoreline waterfowl habitats, while also providing tourist access to offshore areas of GSL. Ongoing model calibration approaches will be presented along with additional 3-D modeling results that will include the simulation of JVWCD Se input.