Characterization of Selenium Sources in the Lower Gunnison River Basin

Science Center Objects

High concentrations of dissolved selenium have been detected in the lower Gunnison River basin including the Uncompahgre River basin. Butler and others (1991 and 1996) identified the highest concentrations of selenium in surface waters in areas that are irrigated on soils derived from Mancos Shale. In July 1997, the Colorado Water Quality Control Commission amended the classifications and numeric Standards for the Gunnison River Basin.

These amendments included new standards for dissolved selenium and the adoption of temporary modifications to selenium standards in three river segments and for one lake in the lower Gunnison River basin.

These sites are now included on the State of Colorado 303(d) list of impaired waters. The Gunnison Basin Selenium Task Force (STF) was formed to address the issue of exceedence of instream selenium standards in the basin. In addition, the Department of Interior National Irrigation Water Quality Program (NIWQP) is investigating the feasibility of remediating selenium sources in the lower Gunnison River basin.

OBJECTIVES:

Data characterizing selenium concentrations for streams tributary to the North Fork of the Gunnison River and the Gunnison River from the confluence of the North Fork of the Gunnison River near Grand Junction, Colorado. Tributaries basins on the east side of the Uncompahgre Valley.

  1. Characterize dissolved selenium loads at the outflow of about 15 to 20 selected tributaries, the North Fork of the Gunnison River, and the Gunnison River. Streamflow, dissolved selenium concentrations, and field measurements of pH, specific conductance, and water temperature will be collected and analyzed.
  2. Characterize selenium sources, with spatially intensive synoptic sampling on the east side of the Uncompahgre Valley. This characterization will be done in Loutzenhizer Arroyo, the unnamed tributary drainage southwest of Loutzenhizer Arroyo, and Cedar Creek.
  3. Characterize the spatial distribution of selenium in soils by coordinating tracer investigations with soil surveys being done in the study basins. This comprehensive data set that couples selenium sources with occurrence of selenium in the streams.
  4. To develop cumulative loading curves for dissolved selenium for each tracer investigation.