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~i!~1~:) SUMMARY Introduction The Uinta Basin Unit of the Colorado River W8ter Quality Improvement Program (CRWQIP) would concrete line 55.5 mile8 of agricultural water conveyance systems in the Green River Basin of northeastern Utah. The lining, to be constructed on canals and laterals in the unit area, would reduce the area's present salt contribution of about 450,000 ton8 annu- ally by a range of 21,000 to 30,000 tons per yearl/ at an average cost effectiveness of $88 per ton of salt removed. Planning studies on the Uinta Basin Unit were conducted in accord- ance with the Colorado River Ba8in Salinity Control Act of June 24, 1974 (Public Law 93-320), and the Federal Water Pollution Control Act Amend- ments of October 1972 (Public Law 92-500), as amended by the Clean Water Act of 1977 (Public Law 95-217). Public Law 98-569 of October 30, 1984, amended the S81inity Control Act. The Salinity Control Act originally authorized the unit for 8tudy as part of a b88inwide progr8m of works for the enhancement and protection of the quality of water aV8ilable in the Colorado River. The Uinta B8sin Unit studies included the determination of salt- loading mech8nisms, development of altern8tive8 for reducing the salt contribution, identification of potential beneficial uses of saline water, evaluation of alternatives, and selection of a recommended plan. Bureau of Reclamation (Reclamation) studies and field investig8tions indicate that two mechanisms are associated with salt loading in the Uinta Basin. The principal contributing mechanism is the dis801ution of salt8 from the soil and subsurface materials by subsurface water, much of which i8 from conveyance system seepage and deep-percolating irriga- tion water. The lesser contributing mechanism is the displacement of saline ground water. Reclamation studie8 for the unit have concentrated on reducing 8alt loading by improving conveyance system efficiency, more particularly by canal and lateral lining to reduce seepage. The Soil Conservation Service (SCS) is implementing a program for reducing salt loading by improving on-farm irrigation efficiency. Problems and Needs At its headwsters in the mountains of north-central Colorado, the Colorado River has a salinity concentration of 50 milligrams per liter (mg/L). The concentration progressively increases downstream as a result of water diversions and salt contributions from a v8riety of sources. In 1983, the hi8torical average salinity concentration at 1/ Because of the uncertaint ies in some variab les used in the hydrosalinity analysis, reason8ble ranges for these variables were defined. This resulted in a range for the 8alt load reduction. 5-1 \ .'" ~ <,'. ~\ tjl,.}l0JO