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IRRIGAnON DRAINAGE TOXICITY STUDIES " N ..... Williams, and Gila Rivers; and (4) the U.S. Fish -..1 and Wildlife Service manages the Havasu, W Cibola, and Imperial National Wildlife Refuges for migratory and endangered wildlife habitat, wann water fish habitat, and public use recreation. Agricultural practices in this area are dominated by production of cotton, produce, and alfalfa, which are subject to frequent chemical treatments. All of the refuges are located near intensively farmed agricultural areas and are inOuenced chemically by irrigation return flows. The purpose of the initial study was to determine, from existing data and reconnaissance field sampling, whether irrigation drainage waters have caused or have the potential to cause harmful effecu on human health, fish and wildlife, or other water uses. The field screening determined whether corrective action is needed and laid the groundwork for more detailed investigations, if needed, to determine the extent. magnitude, and causes of the irrigation drainage quality problem. Water, bottom material, and plant and animal tissues were collected and ana lyzed for trace elements and organic contaminants to determine existing or potential toxic effects on humans, fish, and wildlife. Contaminants of particular concern were selenium, thallium, toxaphene, and DOT and iu derivatives. All samples were collected using approved collection techniques. Water, bottom material, plant and animal tissue samples, and field observations were collected at 11 sites along the Lower Colorado River from Davis Dam to below Laguna Dam. A concerted effort was made to distribute sampling sites upstream and downstream from irrigation districts and national 'ft'ildlife refuges. Sampling was accomplished at a time when irrigation returns were likely to ha\'e a high percentage of flow that had passed through the soil horizons. Because irrigated agriculture is a 12-month-per-year activity in the Lower Colorado River valley and the Colorado River is so highly regulated, the spring season was considered the best time to sample at maximum impact. This sampling schedule allowed for optimum information at a minimum cost for the reconnaissance study. The reconnaissance phase of the study was completed and a report published entitled "Reconnaissance Investigation of Water Quality, Bottom Sediment, and Biota Associated \\,ith Irrigation Drainage in the Lower Colorado River Valley, Arizona, California, and Nevada, 1986.87.- See U.S. Geological Survey Water Resources Investigations Report 88-4022. In the Lower Colorado River valley area, with the exception of selenium and DOE sampling locations were found to be relatively free of high concentrations of selected toxic inorganic and synthetic organic trace constituents that could be a threat to humans, fish, and wildlife. A detailed study has not yet been initiated. Middle Gunnison River Study Acid mine drainage and numerous mine tailings occur along Red Creek near Ouray, Colorado. High concentrations of selenium and several trace elements have been found in the Gunnison River. These contaminants are now being retained in Ridgway Reservoir, Dalla8 Creek Project, recently constructed by the Reclamation. The fate of the inflowing heavy metals is being studied by the Bureau of Reclamation and the State of Colorado. At the present time, fish in Ridgway Reservoir have been detennined safe for human consumption. Additional studies and possibly corrective actions will be considered in the next few years. At the present time, these studies are being considered by the Gunnison Task Group but are not officially part of the study. The reconnaissance study for the Middle Gunnison River began in 1989. The final report on this study should be published in 1991. A detailed study of an expanded area in the Gunnison River drainage involving several adjacent Reclamation sponsored irrigation projects should begin in 1991 or 1992. High selenium and heavy metal concentrations have been found in fish and waterfowl tissue samples at various locations along the Gunnison River. High selenium concentrations continue to exist at Switzer Lake, but the impacts to fish do not