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\ Chapter 3 Colorado River Water 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 concern that the Department of the Interior (Interior) is investigating. Two areas of concern include potential toxicity from irrigations return flows and the productivity of the fisheries in the Colorado River Basin rivers and reservoirs. IRRIGATION DRAINAGE TOXICITY STUDIES \ \ \ \ Concern about the quality of irrigation drainage, surface and subsurface water draining from irrigated land, and its potential effects on human health, fish, and wildlife resulted in formation of the Department of Interior Irrigation Drainage Water Quality Task Group (Task Group). Large concentrations of selenium have been observed 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 (FWS) at the Kesterson National Wildlife Refuge in the ,western San Joaquin Valley, where drainage , water was impounded. In addition, potentially \ tl~xic trace elements and pesticide residues have been detected in irrigation drainages of other Western States. The Task Group initiated a program in late 1985 to identify the nature and extent of water quality problems induced by irrigation drainage. 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. The scope of the investigation includes the following four areas: .' project irrigation or drainage facilities constructed or managed by Interior; · national wildlife refuges managed by Interior; · other migratory bird/endangered species management areas that receive water from Interior-funded projects; and · human health. The program evolved into a multi phase process. The five phases are (1) site identification, (2) reconnaissance investigations, (3) detailed studies, (4) planning, and (5) remediation. Nine of the 19 initially identified locations were selected for reconnaissance investigations in 1986. Two of these 19 locations were within the Colorado River Basin, including the middle Green River and Lower Colorado River. Additional reconnaissance studies in the Colorado River Basin initiated since then include Pine River (1988), Middle Gunnison (1989), Dolores (1990), and Navajo (Upper San Juan River; 1990). Each reconnaissance investigation was conducted by interagency teams composed of scientists from the U.S. Geological Survey (USGS) (team leader), FWS, and Bureau of Reclamation (Reclamation). 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 the beneficial use of water.