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<br />W <br />...:E <br />o <br />1:0 <br /> <br />4 <br /> <br />Should these increases in salin~ty levels occur, the agricul- <br />ture in the Imperial, Coachella, Gila and Yuma Valleys would be <br /> <br />further threatened. Also, a poorer water quality would be diverted <br /> <br />to the Metropolitan Water District of Southern California and the <br /> <br />Las Vegas Valley Water District, causing further economic losses to <br /> <br />the very large block of domestic water users in California and Nevada. <br /> <br />Upon completion of the Central Arizona Project, water users in the <br /> <br />Phoenix and Tucson areas would be similarly affected. <br /> <br />The enactment of the Federal Water POllution Control Act <br /> <br />Amendments of 1972 (Public Law 92-60Q) and the conclusion of negotia- <br /> <br />tions with Mexico regarding the control of salinity in waters delivered <br /> <br />to Mexico have greatly increased the needs for salinity investigations <br /> <br />in this river basin, <br /> <br />Various studies have been accomplished by different government <br /> <br />agencies on the salinity problem in the Colorado River Basin. Be- <br /> <br />cause of non-uniformity in assumptions, data sets, and procedures, <br /> <br />the findings of these studies differ. However, the conclusions <br /> <br />derived are generally s~milar. The major conclusions (U.S. Bureau <br /> <br /> <br />of Reclamation, 1974) are that the largest portion of the mineral <br /> <br />burden was found to originate in the.upper basin, that natural sources <br /> <br />were ,thought to be the major contributors to the salt loading, that <br /> <br />salinity was projected to continually increase in the lower reaches <br /> <br />unless control programs are implemented, and that the impact of the <br /> <br />increasing salinity levels was found. to be primarily economic. <br /> <br />In order to evaluate the salinity problem, it is essential to <br /> <br />identify the point and diffuse sources of salinity (Fig, 1.2) and to <br />