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. ''::; ,~ ~ o..J QUALITY OF WATER COLORADO RIVER BASL\' PR(X;RESS REPORT o smr-lARY . This report presents the various important water quality aspects of the Colorado River. Although several ;.ater quality parameters are dis- cussed. the major part of the report is allotted to salinity (total dis- solved solids) because it is presently the most serious quality problem on the river system. The historical, present modified, and future salinity conditions of '..Ater of the Colorado River down to Imperial Dam are presented in this report. The historical is represented by a tabulation of the re- corded or estimated past condition at 17 quality of \.ete. stations for the 1941-72 period. The present modified condition includes adjustments of the historic condition bas...>d on the assumption that developments completed durin~ the 1941-72 period were in operation for the full period. The future is depicted by condition of 1980, 1990 and year 2000 and is an estimated projection after the presently authorized developments, projects proposed for authorization and other future anticipated projects are placed in oper- ation. Under historic conditions the average concentration of dissolved solids of the Colorado River at Lees Ferry W3.S about 0.76 ton per acre-foot, below Hoover Dam about 0.94 ton per acre-foot, am at Imperial Dam about 1.04 tons per acre-foot for the 1941-72 period. Under present modified conditions (that is assuming the projects that started operating sometime during the 1941-72 period were in operation through- out the entire period) the concentrations would have been about 0.83; 1.02, and 1.15 tons per acre-foot, respectively, at the three stations. It has been assumed for purposes of this study that the average rate ~lf pickup of dissolved solids from ne\tl' irrigated lands \"QuId be in the range of zero to 2 tons per acre. The effect of salt contributed from new lards is thus evaluated by computations of salinity concentrations using zero tons per acre pickup and 2 tons per acre pickup. It W3.S also assumed no additional pickup of dissolved solids ~)Uld occur for lards already under irrigation. Under future flow depletions projected for 1980, 1990 and 2000 con- ditions, assuming negligible salinity control measures, and using the assumed zero to 2 tons per acre pickup on the ne\o: irrigated lands, the concentrations are estimated as follows: .