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<br />PROBLEMS AND NEEDS <br /> <br />Salinity <br /> <br />The Colorado River, at its headwaters in the mountains of north-central <br />Colorado, has a salinity (dissolved mineral concentration) of only <br />about 50 mg/L. The salinity progressively increases downstream as a <br />result of water diversions and salt contributions from a variety of <br />sources. In 1979, the salinity concentration averaged about 810 mg/L at <br />Imperial Dam, the last major diversion point on the Colorado River in the <br />United States. Without control measures, the concentration is projected <br />in increase, possibly reaching a level of 1,140 mg/L at Imperial Dam, by <br />the year 2000. <br /> <br />The high salt load of 10 million tons of salt annually in the Lower Colorado <br />River Basin adversely affect more than 10 million people and 1 million <br />acres of irrigated farmland in the United States. Basinwide, municipal and <br />industrial water users and irrigators experience estimated direct and indirect <br />annual economic losses of $450,000 (January 1980 prices) for each increase of <br />1 mg/L in salinity at Imperial Dam. Users below PVID area experience losses <br />of about $135,000 for each increase of 1 mg/L in salinity at Imperial Dam. <br /> <br />The losses associated with municipal and industrial use occur primarily from <br />increased water treatment costs, accelerated pipe corrosion and appliance <br />wear, increased soap and detergent needs, and decreased water palatability. <br />The Public Health Service recommends drinking water contain no more than <br />500 mg/L of TDS (total dissolved solids). For irrigators, the higher concen- <br />trations cause decreased crop yields, altered crop patterns, increased <br />leaching and drainage requirements, and increased management costs. Agricul- <br />tural losses (either through lower yields or increased production/management <br />costs) begin when salinity levels of applied irrigation water reach <br />700 to 850 mg/L, depending upon soil conditions and type of crop grown. <br /> <br />Salt loading occurs as a result of weathering and dissolution of the soluble <br />salts in soil and substrata. In addition, salt concentration occurs because <br />of the consumptive use, such as agricultural or industrial applications of <br />the water in the basin. Generally, the application of irrigation water <br />results in increased salt concentrations because of both loading and consump- <br />tive use. The salt load fluctuates annually with the overall basin water <br />supply. Without management, as the states continue to develop their compact- <br />apportioned waters, the river's salinity at Imperial Dam is projected to <br />increase. <br /> <br />As the following graph 1/ indicates, since 1940 the general trend of salinity <br />at Imperial Dam has been upward, although since 1970 the salinity concentra- <br />tions have decreased. This recent downward trend is believed to be a result <br />of the construction of Colorado River Storage Project reservoirs such as Glen <br />Canyon Dam. It is theorized that these reservoirs, while filling, are retaining <br />a portion of the salts that would otherwise be flowing down to Imperial Dam <br /> <br />1/ Graph is based upon studies done for Quality of Water - Colorado <br />~asin, Progress Report No, 10, January 1981, U,S. Department of the <br />Figures from which the graph were taken are from tables D and E. <br /> <br />River <br />Interior. <br /> <br />(02932 <br /> <br />6 <br />