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III-1 ...... (Cl Ut U) PART III. COLORADO RIVER VATER QUALITY ASSESSMENT An important objective of this report is to assess the suitability of Colorado River water for various beneficial uses. Salinity is the major threat to the Colorado River and is covered in detail in other parts of this report. This portion of the report covers other areas of concerns that the Department of the Interior is investigating. Two areas of concern include potential toxicity from irrigation return flows and the productivity of the fisheries in the Colorado River Basin rivers and reservoirs. A. Irrigation Drainage Toxicity Studies During the last several years, there has been increasing concern about the quality of irrigation drainage, surface and subsurface water draining irrigated land, and its potential effects on human health, fish, and wildlife. Large concentrations of selenium have been detected in subsurface drainage from irrigated land in the western part of the San Joaquin Valley, .California. In 1983, incidences of mortality, birth defects, and reproductive failures in waterfowl were discovered by the U.S. Fish and Wildlife Service at the Kesterson National Wildlife Refuge in the western San Joaquin Valley, where drainage water was impounded. In addition, potentially toxic trace elements and pesticide residues have been detected in irrigation drainages of other Western States. Because of concerns expressed by the U.S. Congress, the Department of the Interior (Interior) initiated a program in late 1985 to identify the nature and extent of water quality problems induced by irrigation drainage that might exist in the western States. In October 1985, an interagency group, the "Task Group on Irrigation Drainage", was formed ,,,thin the Interior. The Task Group subsequently prepared a comprehensive plan for reviewing irrigation drainage concerns for which Interior has responsibility. Initially, the Task Group identified 19 locations in 13 states that warranted reconnaissance investigations. These locations relate to 3 specific areas of Interior responsibilities: irrigation or drainage facilities constructed or managed by Interior, national wildlife refuges that receive irrigation drainage, and other migratory bird or endangered species management areas that receive water from Interior funded projects. Nine of the 19 locations were selected for initiation of reconnaissance investigations in 1986. Two of these 19 locations were within the Colorado River Basin. Each reconnaissance investigation was conducted by an interagency field team composed of a scientist from the U. S. Geological Survey as a team leader, with additional Geological Survey, U.S. Fish and Wildlife Service, and U.S. Bureau of Reclamation scientists representing several different disciplines. The investigations were directed toward determining whether irrigation drainage has caused or has the potential to cause significant harmful effects on human health, fish, wildlife, or other beneficial uses.