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The recommended plan consists of collecting both surface and ~ subsurface salt water at Dotsero, and transporting the salt water in a gravity 00 flow pressure line to Glenwood Springs where additional surface and subsurface ~ salt water would be collected and added to the Dotsero salt water. The water t'J would then be piped through a gravity pressure line to evaporation ponds at the Colorado-Utah border. The current plan is not as cost effective as other units being implemented and, under Colorado water law, evaporation is not considered a beneficial use of water. A planning report concluding the study was completed in February 1986. Other alternatives are being considered which involve a beneficial use of the saline water. 6. Grand Valley Unit (Reclamation and USDA) The Grand valley Unit is located in western Mesa County in west-central Colorado. For the most part, the unit area includes the entire irrigated portion of the Grand Valley consisting of about 71,000 acres and involving about 200 miles of canals and about 500 miles of laterals. The Grand Valley is estimated to contribute an average of about 580,000 tons of salt annually to the Colorado River. Most of these salts are leached from the soil and the underlying Mancos Formation by ground water that receives its recharge from canal, lateral, and on-farm seepage. The Mancos Formation is a thick sequence of gray fossil shale varying locally from 4,000 to 5,000 feet thick. Salts present in the shale are mostly calcium sulfate with smaller amounts of sodium chloride, sodium sulfate, and magnesium sulfate. Calcium sulfate (gypsum) is commonly found in crystal form in open joints and fractures of the shale. Below the soil, the weathered zone of Mancos shale transmits water along open joints, fractures, and bedding planes. Percolating water from irrigation and conveyance system seepage dissolves salts from the weathered 3hale zone. Development of the Grand valley Unit was planned in stages. Stage One, encompassing about 10 percent of the unit area, consisted of concrete lining 6.8 miles of canal, consolidating 34 miles of open laterals into 29 miles of pipe laterals, and installing an automated moss and debris removal structure. This work was completed in April 1983. To test the effects of Stage One improvements on ground water flows and quality, a hydrologically isolated basin, the Reed wash study area, was instrumented to monitor surface and ground water inflow and outflows. The canal and lateral salt loading reduction in Stage One was determined to be 21,900 tons. Detailed information on surface and ground water inflows and outflows to selected basins within the unit were collected and used to develop water and salt budgets. In addition, an intensive drilling and aquifer testing program was conducted in both the areas underlaid by cobble deposits and in the weathered Mancos Shale areas. The purpose of this program was to determine aquifer characteristics, such as hydraulic conductivity, as well as to identify quality and direction of ground water flow. VII-16 ...