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CHAPTER I INTRODUCTION ~:'<"t.::J The climate of the area is cold and dry in the winter with minimum tem- peratures often as low as -40oF. The summers are dry and mild with maximum temperatures only occasionally getting above 90oF. The unit area is sparsely populated and predominantly agricultural. Of the l,227,520 acres in the Big Sandy River Basin, l7,000 acres are presently under irrigation. The remaining lands are used primarily for grazing cattle and sheep. Most of the area is public land administered by the Bureau of Land Management. A small part is under Water and Power withdrawal for the Eden Project and the remainder is privately owned. Previous Investigations The Big Sandy River area was included as part of a water quality study of the entire Colorado River System by the Federal Water Pollution Control Admin- istration between 1963 and 1970. The results of this study were published in 1971 by the Environmental Protection Agency under the title of Mineral Quality Problems in the Colorado River Basin. The U.S. Geological Survey (USGS) has installed seven gaging stations on the Big Sandy River and tributaries for stream discharge and water quality determination. Some records extend as far back as 1910. Two of the stations have been discontinued; one in 1971 and one in 1973. Water and Power has been collecting water samples at established stations along the Big Sandy River and tributaries for quality determination since 1954. In 1973 an atmospheric freezing experiment was conducted in cooperation with the University of Wyoming. The purpose was to determine the feasibility of separating fresh water from the saline water by atmospheric freezing. The results of the experiment are contained in the report, Atmospheric Freezing pilot Test of Salt Removal From Big Sandy River - CRWQIP - University of Wyoming, Laramie, Wyoming - July 1974. Subsequent to the passage of the Colorado River Basin Salinity Control Act, Public Law 93-320, in 1974, Water and Power has been investigating salin- ity mechanisms producing the saline ground water. About lOO small diameter observation wells have been dri lled throughout the area along with three large diameter test wells. Seventy-two of the wells have been test pumped to determine aquifer parameters such as, transmissivity, permeability, yield, storage coefficiency, and quality of water. Saline springs and seeps amounting to 25 to 30 cfs discharge into the river along a l5-mile reach. The quality of the saline water varies from 3,000 to 5,500 mg/L and is primarily a sodium sulfate type water. From analysis of the data gathered, a salt loading mechanism has been identified. The major source of contribution is the Green River Formation shale layer under the upper sand and soil layers. Since the soil is sandy with a low water holding capacity, excess water is supplied to the Eden Valley irrigated lands. This water filters down through the sand layer and enters 5 0 J II ','[) ,-.-'0, '~1J/