PARENT SESSION
PM13 - Selenium: Sources, Pathways, Receptors
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P331) Selenium inputs and outputs at Stewart Lake Waterfowl Management Area during the annual flood of 2001.

Rowland, Ryan^*,1, Naftz, David¹, ¹ U.S. Geological Survey, Salt Lake City, Utah, USA

ABSTRACT- Extensive studies of Stewart Lake conducted from 1986 to 1990 detected elevated selenium concentrations in water and bottom sediment that resulted in poor nesting success by waterfowl and elevated selenium accumulation by fish. In an effort to lower the concentration of selenium in the bottom sediment, Stewart Lake has been flooded with water diverted from the Green River and subsequently drained on an annual basis since 1997. To compute the net mass of selenium removed from Stewart Lake during the annual flood of 2001, the U.S. Geological Survey did a fine-scale temporal measurement of the selenium load into and out of Stewart Lake. Additional selenium loads from uncontrolled seepage along the north end of Stewart Lake also were quantified. The total volume of water that entered Stewart Lake was 2.53 x 10⁶ cubic meters (2.44 x 10⁶ cubic meters from the Green River and 8.51 x 10⁴ cubic meters from seepage along the north end of Stewart Lake). The total mass of selenium that entered Stewart Lake during the flood was 3.5 kilograms (2.7 kilograms from the Green River and 0.8 kilograms from seepage along the north end of Stewart Lake). The total volume of water that exited Stewart Lake at the outlet was 2.53 x 10⁶ cubic meters, and the mass of selenium that exited Stewart Lake at the outlet was 10.3 kilograms. The net mass of selenium that exited Stewart Lake at the outlet was 6.8 kilograms. Assuming the excess selenium originated from the bottom sediment, the annual flood removed 0.4 percent of the estimated 1,665 kilograms of selenium that exists in the top 15 centimeters of bottom sediment at Stewart Lake. The relatively small net mass of selenium removed from Stewart Lake during the flood and drain cycle of 2001 illustrates that this is not a successful bottom-sediment remediation strategy. Based on these results, alternative remediation strategies are being considered including sediment removal and additional seepage diversion from Stewart Lake.

Key words: selenium, remediation, bottom sediment, wetland