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<br /> <br />SUMMARY <br /> <br />The Big Sandy River Unit of the Colorado River Basin Salinity <br />Control Program is predominately an agricultural area containing about <br />1,227,500 acres. This area, consisting of portions of three counties, <br />Fremont, Sublette, and Sweetwater, is primarily utilized by livestock, <br />both cattle and sheep. Located within the approximate center of the <br />area is the Eden Valley Irrigation Project, the subject of this <br />salinity control study by the U.S. Department of Agriculture (USDA). <br /> <br />Irrigation was introduced in the valley in 1886, when settlers were <br />issued permits to divert water from the Big Sandy River. Due to project <br />actions beginning with the Eden Irrigation and Land Company in the early <br />1900's, the Rock Springs Land and Water Company and the Wyoming Land and <br />Water Company in the 1930's, and the existing Eden Valley Irrigation and <br />Drainage District, there has been an increase of irrigated land in Eden <br />Valley to the present 15,700 acres. During 1962-1973, the Eden Valley <br />irrigation project served an average of 84 farms, averaging 173 acres <br />per farm. Total farm population is 279 people; 79 of the 84 operators <br />currently are part-time farmers. <br /> <br />Mineral resources in the upper Green River Basin and the emphasis <br />that is being placed on those resources have produced an intensification <br />of mineral investigations in the Big Sandy River Unit Study Area. These <br />investigations have included seismographic studies using the drilling <br />and explosive charge technique. There are no mines in the Study Area at <br />the present time. <br /> <br />Under the Colorado River Basin Salinity Control Act (Public Law <br />93-320), USDA's Soil Conservation Service (SCS) had the responsibility <br />for studying the effects of on-farm irrigation improvements to reduce <br />salinity loadings to the Colorado River. Under the same authority, <br />Interior's Water and Power Resources Service (WPRS), formerly the Bureau <br />of Reclamation, is currently studying off-farm conveyance and storage <br />system improvements and their effects on salinity contributions to the <br />Colorado River. <br /> <br />In carrying out this study, basic data was gathered from the WPRS, <br />United States Geological Survey, Bureau of Land Management, Wyoming <br />State Engineer's Office, Water Resources Research Institute of Wyoming, <br />and the Eden Valley Irrigation and Drainage District. SCS conducted <br />special surveys and investigations to obtain other necessary data for <br />this study. These included discussions with farmers to inventory pre- <br />sent irrigation practices, stream and drainage flow measurements, and <br />compiling data on the soils and geology of Eden Valley. <br /> <br />o Using this basic data and a data base period of 1960 through 1977, <br />lt was determined that the Big Sandy River contributed about 149,200 <br />tons of salt annually into the Green River and the Colorado River system. <br />Most of the salt is leached from the underlying Bridger and Green River <br />marine shale formations, and carried to the Big Sandy River by under- <br />9ro~nd aquifers. Excessive irrigation on highly permeable soils and <br />lrrlgation delivery system seepage provide water for deep percolation to <br /> <br />S-l <br /> <br />..'(4'1 <br />G.Jl'l'.j <br />