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<br />18 <br /> <br /> <br />~ <br />~ <br />~ <br />~ <br /> <br />small increases in average mineral concentrations, particularly <br /> <br />toward the end of the period, caused by construction of reservoirs, <br /> <br />increased irrigation, and out-of-basin diversions. The research <br /> <br />also found that most of the mineral burden of the Colorado River, <br /> <br />like most of its flow, originates in the Upper Basin. The largest <br /> <br />individual increment to the mineral burden of the Colorado River <br /> <br />below the compact point and above Imperial Dam was found to be the <br /> <br />Blue Springs located near the mouth of the Little Colorado River. <br /> <br />The report further shows that a principal increase in salinity in <br /> <br />the lower reach is derived from irrigated land in the Parker and <br /> <br />Palo Verde valleys. The increasing out-of-basin diversions are <br /> <br />also reported as contributing to the rising salinity concentration <br /> <br />levels. <br /> <br />The Mirieral Quality Problem in the Colorado River Basin (EPA) <br /> <br />In 1971, the EPA released its report entitled "The Mineral Quality <br /> <br />Problem in the Colorado River Basin." In this report, salinity and <br /> <br />streamflow data for the 1942-1961 period of record were used as a <br /> <br />basis for estimating average salinity concentrations under various <br /> <br />conditions of water development and use. Under these conditions, <br /> <br />concentrations at Hoover Dam were estimated to average about 700 and <br /> <br />760 mg/l in 1960 and 1970, and 880 and 990 mg/l in 1980 and 2010, <br /> <br />respectively. At Imperial Dam, the report estimates 760 and 870 mg/l <br />