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"'..' >t~'" ~ ~. PROGRAM OBJECTIVE The Paradox Valley Unit is a part of the Bureau of ReclamationB Colorado River Water Quality Improvement Program, which is a comprehensive 10-year effort to control salinity levels in the lower main stem of the river. The river, draining an area of 242,000 square miles in the southwestern United States and 2,000 square miles in Mexico, is the most highly regulated in the nation and provides water supplies to millions of people in seven states. Historically characterized by high concentration of dissolved solids, the river has been progressively increasing in salinity as larger portions of the flow have been diverted for use and will .continue to do so as the upper basin states develop their allocated water supplies. The phenomenon is particularly noticeable in the lower basin. The average salinity at Imperial Dam is presently about 850 milligrams perli ter (mg/l) and could reach a value of from l,160 mg/l to ;,340 m~il by the year 2000.1/ .. Deteriorating water quality poses definite economic problems for the 10 million water users in the lower reaches of the river system. Recent Bureau of Reclamation studies have indicated average annual losses of about $230,000 for each increase of one mg/l at Imperial Dam. The total .- damages attributable to salinity in the Low~r Colorado River Basin amounted to approximately $53 million in 1973 and are expected to reach about $124 million annually by the year 2000 if corrective measures are not imple- mented. This not only affects the southwestern United States, but has also become an important factor in our international relations with the United Mexican States, which are guaranteed an annual supply of 1,500,000 acre-feet of Colorado River water by a 1944 treaty. The objective of the Bureau's program is to eliminate slightly over 1.5 million tons of salt per year from the river, which will reduce the anticipated salinity at Imperial Dam by about 150 mg/l. The control ()l"f 583 measures will ultimately be designed to maintain the salt concentrations at or below their present levels in the lower basin. This will allow the continuation of present beneficial uses which would otherwise be threat- ened with serious economic damage. The implementation of the Paradox Valley Unit would reduce the annual salt inflow by an average of 180,000 tons and 1/ Department of the Interior, Bureau of Reclamation, Colorado River Water ...... _L___ T"I____.. rT~.....~,~.,...,r 107L.) PAUP TT_n.