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<br />J <br /> <br />Federal regulations provide for temporary increases above the 1972 <br />levels if control measures are included in the plan. Should water <br />development projects be completed Defore control measures are identified <br />or brought on line, temporary increases above the criteria could result <br />and these increases will be in conformance with the regulation. With <br />completion of control projects, those now in the plan or those to be <br />added subsequently, salinity would return to or below the criteria <br />level. <br /> <br />PROBLEMS IN THE GRAND VALLEY <br /> <br />Analysis of water qual ity data by the U. S. Geological Survey (USGS) <br />indicate that the Grand Valley contributes about 600,000 to 700,000 tons <br />of salt annually to the Colorado River. Most of these salts are thought <br />to be leached .'rom the soil and underlying t1ancos Shale and carried into <br />the river by deep percolation from irrigation and seepage from water <br />delivery and tai1water collection systems, <br /> <br />Both natural runoff and irrigation contribute to the problem, either by <br />salt concentration or by salt loading. Salt .concentration is caused by <br />removal of water from the river system through consumptive use by <br />irrigated crops and phreatophytes. As water is consumed through evapo- <br />ration and transpiration, its mineral constituents remain in the ground <br />water. Salt loading occurs as ground water dissolves subsurface minerals <br />while flowing back to the Colorado River. Although both processes are <br />at work in the Grand Valley, salt loading is the major cause of the <br />salinity increase. <br /> <br />Gr~und water return flows from the irrigated area to the Colorado River <br />contain as much salt now as they did at the inception of irrigation and <br />it is assumed this will continue because excess water dissolves salt <br />from the Mancos Shale formation. Two conditions substantiate this <br />conclusion: (1) water quality information on the artesian ground water <br />aquifer collected at several well sites by the U. S. Department of <br />Agriculture in 1915; Agricultural Research Service-Soil Conservation <br />Service Project in 1951, and Agricultural Research Service in 1973, to <br />1975, indicate no change in water qual ity of the aquifer. Hydrostatic <br />pressures toward the Colorado River rule out the river as a source of <br />water to the aquifer; (2) diversions to the irrigated area since instal- <br />lation of Government High! ine Canal in 1917 are essentially unchanged. <br />Situations indicate that salt loading by subsurface return flows to the <br />Colorado River from irrigated areas have been relatively constant over <br />this 60-year period. <br /> <br />Erosion from the upland watershed also contributes sediment and salt to <br />the Colorado River. Sheet, rill, gully and streambank erosion results <br />in 2.9 million tons of sediment with about 80,000 tons of salt being <br />added to river annually. <br /> <br />\~11 <br /> <br />7 <br />