History of Selenium Problems in the Uncompahgre and Gunnison River Basins
Mancos Shale (adobe hills) near Montrose, CO
BACKGROUND
In 1983, incidences of mortality, deformities, and decreased reproduction in fish and aquatic birds were first discovered by the U.S. Fish and Wildlife Service at the Kesterson Wildlife Refuge in the western San Joaquin Valley, California, where irrigation drainage waters with high concentrations of selenium were collected. Due to concerns that problems with selenium toxicity may not be confined to the Kesterson Refuge, in 1985, the U.S. Department of the Interior began a program to study the effects of irrigation drainage on the water quality of the Western United States.
Subsequent investigations by the National Irrigation Water Quality Program (NIWQP) and the United States Geological Survey (USGS) in 1987-88 indicated that irrigation drainage from the Uncompahgre Project along the Western Slope of Colorado, a Bureau of Reclamation (BOR) irrigation project, might be a primary source of selenium, dissolved solids and other constituents to the Gunnison and Uncompahgre rivers, and Sweitzer Lake. Additional studies conducted by in 1991-93, found that about 64 percent of water samples collected from the lower Gunnison River and about 50 percent of samples from the Colorado River near the Colorado-Utah line exceeded the U.S. Environmental Protection Agency (EPA) selenium criterion of 5 m g/L (micro grams per liter) for protection of aquatic life.
Based on these results it appears that drainage from the Uncompahgre Project and the Grand Valley may account for as much as 75% of the selenium load to the Colorado River near the Colorado-Utah line. The primary source areas for selenium were determined to be the eastern side of the Uncompahgre Valley, and the western one-half of the Grand Valley, where extensive irrigation is located on Mancos Shales (see map).
SELENIUM STANDARDS ARE AMENDED & THE TMDL PROCESS BEGINS
On July 14, 1997, the Colorado Water Quality Control Commission amended the Classifications and Numeric Standards for the Gunnison and Lower Dolores River Basins (Regulation No. 35). These amendments included the adoption of new standards for selenium and the adoption of temporary modifications for selenium standards in four segments of the basin. These segments are now included in the Colorado 303D list of "impaired waters" (see map of targeted segments). Section 303D of the Clean Water Act requires States to identify waters that do not or are not expected to meet applicable water quality standards with technology-based controls alone.
Once listed, the State is required to prioritize these waters, analyze the causes of the water quality problem, and allocate the responsibility for controlling the problem. All stream segments listed on the 303D list are then subject to analysis called the Total Maximum Daily Load (TMDL) process. The TMDL is an estimate of the greatest amount of a specific pollutant, in this case selenium, that a given waterbody or stream segment can receive without violating water quality standards.
As part of the TMDL process, the State must quantify the pollution sources and determine allowable loads to both point and non-point pollution sources. A point source is defined a pollution coming from a single identifiable source, such as effluent from a sewage treatment pipe. Non-point source pollution is pollution discharged over a large land area, not from one specific location. This may include drainage from irrigated areas or suburban lawns, as well as stormwater runoff, and soil erosion. In the case of non-point sources, voluntary controls or locally enacted controls are necessary to implement the TMDLs.
This is where the Gunnsion Basin Selenium Task Force comes in. We are a group of private, local, state and federal agencies committed to finding ways to reduce selenium and aid in the development TMDLs, while preserving the viability and lifestyle of the Lower Gunnison Valley.