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. '\ . . o 00 ~ ~ QUALITY OF WATER COLORADO RIVER BASIN PROGRESS REPORT SUMMARY This report prepared and updated every two years presents the various important water quality aspects of the Colorado River. Although several water quality parameters are discussed, the major part of the report is allotted to salinity (total dissolved solids) because it is presently the most serious quality problem on the river system. The historical, present modified, and future salinity conditions of water of the Colorado River down to Imperial Dam are presented in this report. The historical is represented by a tabulation of the recorded or esti- mated past condition at 20 quality of water stations for the 1941-76 period. Although various other studies have used different periods of records such as the 1906 to present, this report has used the 1941-76 period because most salinity records in the basin do not extend back beyond about 1941. The present (1976) modified condition includes adjustments to the historic condition based on the assumption that all developments existing in 1976 were in operation for the full 1941-76 period. Estimated future conditions are shown for the years 1980, 1990, and 2000, They are estimated projections, including past projects, presently authorized developments, projects proposed for authorization, and other future anticipated projects. Under historic conditions the average concentration of dissolved solids of the Colorado River at Lees Ferry was about 558 mg/l, below Hoover Dam about 692 mg/l, and at Imperial Dam about 768 mg/I for the 1941-76 period. Under present modified conditions (that is 1941-76 historical flows modified to reflect present depletions), the concentrations would have been about 602, 738, and 839 mg/l, respectively, at the three stations, The projection of future water quality conditions was based on 1941-76 averages rather than a year-by-year study. The Colorado River Simulation model was not used because the data base was not completed in time. The Colorado River Storage Project model was also considered, but it does not show quality conditions at any of the selected stations above Lees Ferry. The CRSM and CRSP models are further discussed in Part X. There are some limitations in using a model based on averages since upper and lower limits are not defined and the actual conditions for several years in the future may not truly be represented. 1