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- < lSi.l WATER QUALITY The dissolved mineral concentration (salinity) in the Lo~er Colora~o River Basin is naturally high, It IS further II?-creased by a significant degree by the act.lOns of m.an through(I) salt loading-the pickup of mIn- eral salt, largely by ir~igation return flows, and (2) salt concentratIng-the loss of water from the system through evaporation, tran- spiration, and out-of-basin export. Under present conditions, the salinity at Parker Dam where Colorado River water is divert- ed by the Metropolitan Water District large- ly for urban use on the southern California Coastal Plain, averages around 740 parts per million of total dissolved solids (ppm). Downstream at Imperial Dam, where diver- sions are made for the major California agri- cultural water users in Imperial, Coachella, and Yuma Valleys, salinity currently aver- ages about 865 ppm. There are still a number of upstream water development projects which are not yet fully developed, and other projects are under con- struction or in the planning stages, all of which will, when in full operation, contrib- ute to substantial increases in salinity of the water used by California. If no salinity con- trol measures are undertaken, the Colorado River Board estimates that, by the turn of the century, the average salinity will be approxi- mately 1100 ppm at Parker Dam and 1300 ppm at Imperial Dam. It is estimated that these increases in salinity would cost the California water users alone approximately $40 million per year by the year 2000. There would also be damages to water users in other states and in Mexico. The Colorado River Board's August 1970 report, "Need for Controlling Salinity of the Colorado River," outlines the problem and has served to stimulate interest by other . states and the federal government to develop programs to control the river's salinity. 24 Environmental Protection Agency Report on Colorado River Salinity In April 1971, the Environmental Protec- tion Agency (EPA) issued its draft ~eport entitled, "Mineral Q!Jality Problem m the Colorado River Basin." The long-awaited re- port had been in preparati~n for many ye~rs by the Colorado River BaSIn Water Q!Jahty Control Project of EP A and its predecessor agencies. This Project was th~ res.ul.t of rec- ommendations made at the first Jomt Fed- eral-State "Conference in the Matter of Pol- lution of the Interstate Waters of the Colorado River and Its Tributaries," held in January 1960. The Conference was author- ized by Section 8 of the Federal Water Pollu- tion Control Act and was called at the re- quest of the Colorado River Basi~ St~tes to consider all types of water pollutIOn In the Colorado RiYllr-Basin. Conferees include one representative from the water pollution con- trol agencies of each of the seve~ colorado River Basin States and representatives of the EP A,. The California State Water Resources Control Board assigned one of its Board members or staff to serve as California's con- feree. The EPA's draft report contained the fol- lowing recommendations: "I. A broad policy objective be adopted for the entire Colorado River System which would result In sa- linity concentrations being maintained at or be- low levels presently found in the lower Colorado River. 2. Criteria for salinity concentrations be adopted by appropriate Colorado River Basin states in accord- ance with the Federal Water PollutIOn Control Act as amended. As a minimum, these criteria sho~ld require that for any giv~n month th7 aver' age concentrations of !otal dIssolved sohds be maintained below 800 mllhgrams per hter (mg/ 1) at Hoover Dam and 1,000 mg/I at Imperial Dam. J. A State-Federal task group be established immedi- ately to develop additional salinitr control cr,lterla at key points throughout the baSin whIch will ac- complish the objective of Recommendation No.1. ., \i " '; .1 I, I I I , , (