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. . . C> .h Ul CJ1 area upstream from Laguna Dam. and (3) prepare a USGS Water-Resources Investigations Report that documents the data collected. interpretation of those data, and the method proposed for the Yuma area and prepare a USGS Fact Sheet on the Yuma method. The study began in July 1997. Field Screening of Water, Bottom Sediment, and Biota Associated with Irrigation Drainage in the Yuma Project Area, Arizona In response to concerns expressed by the U.S. Congress, the U.S. Department of Interior began a program in late 1985 to identify the nature and extent of irrigation-induced water-quality problems that might exist in western states. Water, bottom sediment, and biota were sampled during 1986-87 in the lower Colorado River valley north of Yuma. With the exception of selenium, no inorganic constituents exceeded any existing standards, criteria, or guidelines for the protection of fish and wildlife resources. During the last several years there has been increasing concern about the quality of irrigation drainage waters in the Yuma Valley, Arizona. and its potential to cause harmful effects onhuman health, fish, and wildlife. In 1995, theV.S. Geological Survey collected and analyzed surface water and bottom sediment and the U.S. Fish and Wildlife Service collected and analyzed biota from 9 sites in a Department of Interior sponsored irrigation project, the Yuma project area. Measurements of water and air temperature, specific conductance, pH, and alkalinity in water were made on site. Water samples were analyzed for concentrations of major ions, nitrite plus nitrate, and selected trace metals. Bottom sediment and biota were analyzed for selected trace metals and pesticides. Analyses for the water, bottom-sediment, and biota samples are available. A report is pending publication in 1998. Field screening of water quality, bottom sediment, and biota associated with irrigation drainage in the Yuma Valley, Arizona, 1995: U.S. Geological Survey Water-Resources Investigation Report by Saeid Tadayon, Kirke King, Brenda Andrewes, and William Roberts. Colorado Irrigation Drainage Study of the Lower Gunnison and Grand Valley Area A reconnaissance investigation of the Uncompahgre Project was done in 1987-88 and a report published in 1991. That study focused on selenium problems at Sweitzer Lake. The reconnaissance investigation also collected selenium and other trace-element data and salinity data for the Uncompahgre and Gunnison Rivers. The results of the reconnaissance study indicated that the Uncompahgre Project was a significant source of selenium. A detailed study was done in 1991-93 to determine source areas of selenium and geochemical processes affecting selenium concentrations in water and to determine if selenium was adversely affecting fish and migratory birds. The Grand Valley was a known source of salinity, and was suspected that it may be a significant selenium source; therefore, the Grand Valley was included in the detailed study. Various surface-and ground-water, mineralogic, geologic, and biological data were collected for the detailed study, and the data were published in 1994. An interperative report for the detailed study was published in late 1996. 7 , ~ ~