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<br />. <br /> <br />. <br /> <br />. <br /> <br />o <br />A <br />l\:.. <br />o <br /> <br />CHAPTER II <br /> <br />NEED FOR ACTION <br /> <br />Colorado River Basin Salinity <br /> <br />~alt pickup from the Big Sandy River Basin and other areas has <br /> <br />rellul~ed in a deterioration of the quality of water in the Colorado <br /> <br />River as flows have been developed for beneficial use. The river and <br /> <br />its tributaries at the headwaters in the mountains of Colorado, Wyoming, <br /> <br />and Utah have a salinity of about 50 mg/L. The concentration increases <br /> <br />downstream as a result of water diversions and salt contributions from a <br /> <br />variety of sources and in 1979 averaged sbout 810 mg/L at Imperial Dam, <br /> <br />the last major diversion point on the river in the United States. <br /> <br />Unless control measures are undertaken, the concentrations are expected <br /> <br />to increase as the Basin States continue to develop their compact- <br /> <br />apportioned water. <br /> <br />Water of 1,000 mg/L or less is generally considered to be sat is- <br /> <br />factory for irrigating most crops, although concentrations of 500 mg/L <br /> <br />csn have detrimental effects on salt-sensitive crops. On land with good <br /> <br />drainage, wster exceeding 1,000 mg/L can be used for crops with high <br /> <br />aalt tolerances. The EPA recommends that public drinking water contain <br /> <br />less than 500 mg/L. <br /> <br />The salinity of the river results from two general causes--salt <br /> <br />loading and salt concentration. Salt loading is the addition of salt to <br /> <br />23 <br />