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. PART 11/ CAUSES OF SALiNITY J. Municipal and Industrial Sources of Salinity ,-. oJ' o ~ Salt loads contributed to the Colorado River systpm by munlCi- pal and industrial sources are generally minor, total iog about percent of the basin salt load. Future increases in salt loads from these sources are expected to be smal t relative to the total basin salt burden and will have only a minor effect on salinity levels. .... Most municipal and industrial ....astes are relatively low in total salt load in comparison ....ith natural and agricultural sources, and complete elimination of such waste discharges ....ould have little effect on salinity concentrations in the main riv~r system. Since these wastes are point sources of salinity, control could be achieved if salinity levels in the waste beinK discharged (i.e., industrial brines) warrant such control. The energy shortage has caused an Increase of inter<"st for construction of large energy producing industries within the Colorado River Basin. With emphasis placo'!d on improving the water quality in the basin, these industries have been under pressure by State and Federal agencies to prevent the return of salts to the river by consuming all water diverted for use. . Development of oil and gas, oil shale, and mineral resources in the basin also has the potential to increase salt loading. !1any saline ground water aquifers are static (very little .....Her movement) until they are disturbed by drilling or mining activities. An example of Where this has happened is the Meeker Dome Salinity Control Unit described in Part VIII Which came about as the result of deep ground water, high in di.s- solved salts, flowing back to the surface through abandoned oil wells. B. Increased Concentration from Water Depletions Addition of salts to the river system is not the only cause of increased sal inity concentrat ions. The dt>plet ion of water of better quality than in downstream reaches produces a concentrating effect on the waters of the downstream reaches. This concentrating effect occurs to a greater degree when the diverted salts return to the river than when they are depleted along with the water. 1. In-basin Depletons . Consumptive use of water for irrigation within the basin is responsible for the largest depletions while municipal and industrial us~s account for a lesser depl~tion. Evaporation from r~serVOlr and stream surfaces also produces large depletions. Phreatophytes cause significant water losses by evapotranspiration, especially in the Lower Basin below Hoover Dam. In most cas~s where in-basin deplet ions occur, the diverted salts return to the river system, adding significantly to the increase in concentration. Only in the case of large industri~s such as steam powerplants are the salts depleted along with the water. 12