| OCR Text |
Show Department of Interior1s Progress Report No. 22 on quality of water, Reclamation attempts to modify historical flow by taking into account subsequent developments along the river which affect present water quality conditions. On either basis, the Unit would add to the increasing salinity problem of the lower Colorado River. It is assumed that the present average salinity condition of 7^- 5 mg/ l below Hoover Dam would remain without Unit development. However, it is likely that without the Unit the Ute Indian Tribe would develop water to serve about 29,000 acres of Tribal lands. This would increase the dissolved solids below Hoover Dam by about the same amount projected under Bonneville Unit development. Recently the Environmental Protection Agency estimated-*--^ an annual cost of $ Ul, U00 per mg/ l increase to water users below Hoover Dam for increases in total dissolved solids. Using this estimated cost, the annual economic impact attributable to the Bonneville Unit would range from $ laU, 000 to $ 580,000 for salinity increases of 10 mg/ l and Ik mg/ l, respectively. The damages below Hoover Dam that would result from increase in salinity would occur to irrigation, municipal, industrial, and domestic uses. Crops grown in the Lower Colorado River Basin differ in sensitivity to a salt concentration in the soil root zone, with some crops tolerating significantly higher concentrations than others. Although many factors besides salinity concentrations affect the growth of crops ( drainability, weather patterns, method and efficiency of irrigation, etc.), higher concentrated water has a definite adverse effect on some crops. Also, in areas where salt may accumulate, costly drains will be needed to leach the salts from the soil. Municipal, industrial, and domestic uses of high saline waters result in higher pretreatment costs for industrial uses, costs of water softeners or additional soaps and detergents, and costs of corrosion of pipes and other water- related facilities. The desirable characteristics of the water for domestic drinking purposes may also be reduced because of higher salt concentrations. The Bureau of Reclamation estimated an increase in salt concentration of the water below Hoover Dam of about 10 mg/ l as a result of the Bonneville Unit. This results from a depletion of 166,000 acre- feet of water and a net reduction in salt load of 27,000 tons, which is transported out of the basin. It should be recognized that any project depleting water of better quality than at a point downstream will cause an increase in concentration at the point downstream even though no additional salt is picked up by the project or, as in some cases such as the Bonneville Unit, where the salt load is actually reduced by 399 |
