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C..> w 1-' o QUALITY OF WATER COLORADO RIVER Bl\.SIN PROGRESS REPORT . SUMMARy This report gives the :past, the present modified, and the expected quality of water of the Colorado River down to Imperial Dam. The :past is represented by a tabulation of the determined or estimated historic condition at seventeen quality of water stations for the 1941-64 period. The present modified condition includes adjustments of the historic con- dition based on the assumption that new developments begun during the 1941~64 period were in operation for the full period. The expected qual- ity condition is an estimate of the quality situation after the presently authorized developments and some projects proposed for authorization are placed in operation. The effects of authorized developments are presented in five different increments. Studies of chemical trends indicate that under historic conditions the average concentration of dissolved solids of the Colorado River at Lees Ferry had about 0.74 ton per acre-foot, below Hoover Dam about 0.93 ton per acre-foot, and at Imperial Dam about L 01 tons per acre- foot for the 1941-61 period. Under present modified conditions, that is assuming that the recently constructed projects were in operation for the entire period, the concen- trations would have been about 0.79, 0.98, and 1.10 tons per acre-foot, respectively, at the three stations. It has been assumed for purposes of this study that the rate of pickup of dissolved solids from new irrigated lands woUld vary from zero to two tons per acre. Under the expected condition, with all authorized projects and proj- ects proposed for authorization in operation and with an assumed piCkup of two tons per acre on the new irrigated lands, the concentrations are estimated to be 1.02 tons per acre-foot at Lees Ferry, 1.30 tons per acre-foot below Hoover Dam, and 1.56 tons per acre-foot at Imperial Dam. The depletions used in this report for the projects, both author- ized and proposed for authorization together with present developments and other proposals, are estimated to be the ultimate depletions for the developments listed. other developments, as yet not identifiable, are expected to occur and will reduce the quantities of water shown for the various stations and cause slightly greater concentrations than indi- cated in this report.