USGS Publications Warehouse

Abstract

Physical and chemical data were collected in May and August, 1995, from an irrigated area of the Wind River Federal Irrigation Project, Wind River Indian Reservation, Wyoming. Surface-water samples were collected from irrigation drains, ponds and streams in the Sharp Nose Draw and Mill Creek drainage areas, and from the Little Wind River. These samples were analyzed for selenium and mercury, as well as other selected inorganic constituents. Of the 13 samples collected in May, 6 had selenium concentrations greater than the U.S. Environmental Protection Agency's (USEPA) chronic aquatic-life criterion of 5 mg/L (micrograms per liter) and one exceeded the aquatic-life acute criteria of 20 mg/L. Samples with selenium concentrations exceeding aquatic criteria were collected from Sharp Nose Draw and the Mill Creek drainage areas. Selenium concentrations in all 12 samples collected in August were less than the laboratory minimum reporting level of 5 mg/L. The large selenium concentrations were associated with large dissolved solids concentrations that occur prior to the irrigation season when accumulated salts are flushed to drainages through ground water and natural precipitation. Mercury concentrations were less than the laboratory minimum reporting level of 0.1 mg/L for all samples except one collected in May that had a concentration of 0.3 mg/L. This concentration was larger than the aquatic-life chronic criterion of 0.012 mg/L established by the USEPA, but less than the aquatic-life acute criterion of 2.4 mg/L for mercury established by the USEPA.