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<br />this contribution by 180,000 tons per year resulting in a reduction of the <br />salinity concentration at Imperial Dam of about 18 mg/L. <br /> <br />In 1978, a definite plan report and an environmental impact statement were <br />prepared, which presented a recommended plan. The plan involved pumping <br />brine from wells paralleling the Dolores River adjacent to brine inflow <br />areas and disposing of the brine in a large evaporation pond in Dry Creek <br />Basin. The plan also provided for removal of toxic and corrosive hydrogen <br />sulfide gas associated with the brine for surface disposal. <br /> <br />Before installing permanent facilities, a brine inflow control verification <br />program was initiated. A series of 18 production wells and 100 monitoring <br />wells were installed, along with a temporary holding pond and 3 miles of <br />pipeline. Initially, a pumping rate of 5 ft3/s was anticipated for <br />controlling brine inflow, but test pumping has shown that a reduced rate of <br />2 ft3/s is satisfactory. The reduced rate changed the criteria for <br />evaluating the br.ne disposal methods, making a deep well injection option <br />more attractive than pond evaporation. <br /> <br />The brine disposal plan using deep well injection has been evaluated and is <br />technically, environmentally, and economically acceptable. Accordingly, <br />the new plan consists of disposing of the brine in a permeable, isolated, <br />limestone formation deep under Paradox Valley. The project as planned is <br />acceptable to the local public and will cause no significant environmental <br />impact. The project should be in operation by 1988. <br /> <br />Grand Valley Unit, Colorado <br /> <br />The Grand Valley Unit is designed to reduce salt contributions to the <br />Co 1 orado Ri ver by decreasi ng deep percol at i on resulting from conveyance <br />system seepage and irrigation. Reclamation estimates that the unit's <br />combi ned USDA-Rec 1 amat ion efforts woul d reduce the salt load enteri ng the <br />Colorado River in Grand Valley by about 410,000 tons annually, resulting in <br />a reduction of salinity concentration at Imperial Dam of 41 mg/L. The <br />reduction would be accomplished by a cooperative program conducted by <br />Reclamation and the SCS (Soil Conservation Service), an agency of the USDA <br />(U.S. Department of Agriculture). <br /> <br />The unit is being developed in stages to allow construction in the portions <br />of the valley where plans and designs are complete while investigations <br />continue on the rest of the unit. Results from Stage One are being evalu- <br />ated before proceed i ng with construct i on of the rest of the uni t. Moni- <br />toring thus far has shown an initial annual reduction of 9,000 tons as a <br />result of USDA and Reclamation efforts in the Stage One area. <br /> <br />Stage One development involved concrete lining and rehabilitation of struc- <br />tures along a 6.8-mile section of the Government High1ine Canal in the <br />western end of Grand Valley. Stage One construction is basically complete. <br />Thirteen laterals that now serve the area are being consolidated into 11 <br />and placed in pipe sections. The lateral construction was about 70 percent <br />complete at the end of August. <br /> <br />xiv <br />