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30 w ~ CO ..0:.. Concurrent to the construction of the surface facilities and after completion of the injection well, contracts were initiated with the Department of Ene~gy and the U.S. Geological Survey to analyze the injection brine and resident formation brine in the well. The studies are to determine if the brines are chemically compatible and what steps might be taken to control compatibility problems. The preliminary results of the studies indicate the potential for compatibility problems. Alternatives solutions are being investigated to insure the longevity of the injection well. Grand Valley Unit (Reclamation and USDA). The Grand Valley Unit in western Mesa County in west-central Colorado includes about 71,000 acres and involves about 200 miles of canals and 500 miles of laterals. Grand Valley contributes an estimated 580,000 tons of salt annually to the Colorado River. Most of the salts are leached from the soil and underlying Mancos Formation by ground water that receives its recharge from canal, lateral, and onfarm seepage. The Mancos Formation is a thick sequence of gray marine 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 chlo+ide, sodium sulfate, and magnesium sulfate. Calcium sulfate (gypsum), is commonly found in crystal form in open joints and fractures in the upper portion of the shale. Below the soil derived from the shale, the weathered zone of Mancos shale transmits water along open joints, fractures, and bedding planes. Percolating water from irrig~tjon and conveyance system seepage dissolves salts from the weathered shale zone. The excess percolating water and seepage contribute to saline ground water flows that return to the river. Development of the Grand Valley Unit, by Reclamation, was planned in stages. Stage One, encompassing about 10 percent of the uni t area, consisted of concrete lining 6.8 miles of canal, consolidating 34 miles of open laterals int:' ~9 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 sub-basin, the Reed Wash stUdy area, was instrumented to monitor surface and ground water inflow and outflow. Salt loading reduction in Stage One from the canal and lateral improvements was determined to be 21,900 tons per year. Detailed information on surface and ground water inflow and outflow to 'other selected sllb-basins wi thin the unit were collected and used to develop water and sal tbudgets. In addition, an intensive drilling and aquifer testing program was conducted in both the areas underlain by coh71e deposits and in the weathered Mancos shale. The purpose of this program was to determine aquifer