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34 "') Q) ~ -.J ..UINTA BASIN UNIT, UTAH 1979 USDA Plan, Salinity Control Report 1982 Environmental Impact Statement 1991 Uinta Basin Expansion Plan/EIS 1994 Monitoring and Evaluation Report 1- '1-9'1 December 1993 The uinta Basin unit is located in northeastern Utah in Dushesne and Unitah Counties, The area treated lies within the Ashley Creek, Brush Creek, and Duchesne River watersheds, which flow into the Green River, The Uintah basin is underlain by four massive shale formations, the Duchense River, Uinta, Mancos, and Mesa Verde. They provide an infinite source of salt, which can be weathered by deep percolating irrigation water, Based on USGS gage data the salt load to the Green River from the Duchense River averages 380,000 tons per year in 442,000 acre feet of water; in addition, Brush, Ashley, and several other creeks put an additional 100,000 tons of salt per year directly into the Green River. The salt pickup from irrigation based on USGS inflow and outflow evaluations of gaging stations on the system is 240,000 tons of salt per year or 1.2 tons per irrigated acre. The flow of the Duchesne River and tributaries are at the vagaries of the weather and suffer feast and famine. The basin has high spring runoff followed by water shortages in the summer. The last seven years have been characterized by drought, and some of the districts started to run out of water July 1, The Uintah basin is quite diverse, as well as large; There are several hundred miles of streams and irrigation canals delivering water to about 205,000 acres of irrigated land. The variations include: high mountain meadows to hot dry desert; eight soil associations formed by different climate and parent material; four different geologic formations, which means different salt loadings; and 200 independently operated ditch companies with different mean seasonal and annual water shortages. Therefore, the determinations of salt loading requires an analysis by hydrologic subareas to incorporate significant variations, During 1976 and 1977 62 drains in the Uintah basin were monitored for flow and salinity concentration by SCS, During the 1970's USBR monitored drains and canals throughout the basin, See table C-1 from the USDA report for a sample of the drains monitored. Monitored data by USGS, SCS, and USBR was used to determine the salinity concentration of irrigation water applied and drainage return flow. The difference is the salt pickup from the underlying saline aquifer,