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. PART V COLORADO RIVER WATER QUALITY ASSESSMENT and have The upper Coachella Valley area is experiencIng its ground ...:aeers are being overdrafted. Depths to fallen ove. 75 feet. rapid growth. ground water .... e.Jl ~. C"." The Ocotillo-Coyote Wells area is 30 miles west of the city of El Centro in Imperial County. The qual icy of ground water in the area has been suitable for dcrnestic use. but there is concern nolo, that over- pumpage for commercial transport could create a saline intrusion. The Regional Board and others have petitioned Federal agencies to seek corrections through Mexican officials of the problems on the New River. Through strong insistence, there has been some recent improvement in the New River's water quality at the border crossing. Fa 11 o.....ing discussions between the United States and Mexican Presidents, additions .....ere made to the United Stat~s-Mexican Water Treaty that call for prompt corrections to the remaining .....aste problems. The city of !'1exicali brought its waste treatment systems back into operation. Earl ier engineering salinity can be held at present this would he quite expensive. invest igat ions sho..... that levels, but the physical the 'NOrks Sa I ton Sea to achieve . Southern California is almost entirely dependent upon imported .....ater, .....ith the Colorado supply being one of the three important sources. The dollar cost to California of increased salinity has been documented else\ooohere. Examples of uses \o.ohich are affected and some of the results of increased salinity folIo...... Agriculture in the Coachella, Imperial, Palo Verde, and Bard Valleys is very important to the National market because of the winter gro.....ing season. The heavily urbanized areas along the coast rely upon the Colorado for municipal supplies. Present Colorado River sal inity levels are marginally suitable for the key beneficial uses. The water can be softened (for domestic use) by additional treatment, hut that process aggravates the salt balance problems in the long run. Blending with other imported supplies of lower sal inity is practiced, but increased demand on those other supplies for additional blending to offset Colorado salinity increases 'NOuld have serious adverse effects. . Most of the sal inity in the Colorado derives from sources upstream from California, but there are local contributions in the Palo Verde Region. The Colorado River Basin Salinity Control Forum has developed a plan for sal inity control of the Colorado River. The Cal i- fornia Regional ~'ater Quality Control Board (Region 7), which borders the river, closely monitors any developments ...ohich might impose addi- tional salt loads on the river. Workinf! .....ith the Palo Verde Irrigation District, the Colorado River Board of California, and the tlSGS, the Ref!ional Board has investi~ated possible sources of nonpoint salt load- ings in the area. 20