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III PURPOSE AND NEED FOR THIS ACTION The Colorado River system naturally carries a large load of salts (dissolved solids) and suspended sediment. Streamflow depletions resulting from trans- basin diversions, and for irrigation, municipal and industrial uses signifi- cantly reduce the supply of water available for dilution of salt loads in the lower river system. In recent years salinity concentrations in the Colorado River have adversely affected downstream irrigated crop production and other uses of the water. The problem is especially severe for water delivered to California, Arizona and Mexico. Recognition of the water quality problem in the region has caused a number of studies to be made since about 1960. 7he Colorado River Basin Water Quality Control Project was established in 1960 by the Division of Water Supply and Pollution Control, U.S. Public Health Service. Studies by the Environmental Protection Agency (1971) produced a series of reports on "The Mineral Quality Problem in the Colorado River Basin." Salinity in the river also is documented by the Bureau of Reclamation (l'971 and 1974) Status Reports; Colorado River Water Quality Improvement Program Biannual Progress Reports "Quality of Water, Colorado River Basinj" and U.S. Geological Survey Professional Paper 441, "Water Resources of the Upper Colorado River Basin - Technical Report" by Irons and others (1965). Section 201(c) of the Colorado Basin Salinity Control Act (Public Law 93-320) directs the Secretary of the Interior, the Administrator of the Environment~l Protection Agency, and the Secretary of Agriculture to cooperate and coordinate their activities effectively to carry out objectives of Title II of P.L. 93-320 as the basin states continue developing their compact apportioned water. In addition, the Lower Gunnison Basin Unit in Colorado and the Uintah Basin Unit in Utah are two of twelve irrigation source control units listed in Section 203 of P.L. 93-320 for the expeditious completion of a planning report as a means to implement the salinity control policy adopted for the Colorado River. The USDA studies carried out under Public Law 93-320 were done using funds available under Section 6 of Public Law 83-566, the Watershed Protection and Flood Prevention Act. In the course of these studies the SCS cooperated with the USBR in the development of the Final Environmental Statement for the Colorado River Water Quality Improvement Program (May 19, 1977). The Pl:'ogram EIS covers alternative methods for salinity control as well as the overall impacts of structural measures and onfarm management measures.. These discussions will not be repeated in this supplement. Additional information is now available from SCS environmental evaluations of USDA federally assisted nonproject actions already underway. This information indicates that implementation of various onfarm irrigation water management measures in the Lower Gunnison and Uintah Basin Units could cause significant adverse local or cumulative impacts on the environment. Therefore, the Soil Conservation Service has prepared this supple- ment to the Colorado River Water Quality Improvement Program Final Environmental Statement to more specifically reflect these local 'and cumulative impacts, and to display alternative solutions. Section 303 of the Clean Water Act requires adoption of water quality- standards applicable to interstate waters. The Act's objective is "to restore and maintain the chemical, physical, and biological integrity".of the Nation's waters" (Section 101), and the Administrator of EPA is required, in cooperation with other Federal, State and local agencies, "to develop comprehensive programs for preventing, III-1 I I I I I I I I I I I I I