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<br />~ <br />o <br />A <br />-.I <br /> <br />in the Colorado River. Studies conducted on a variety of <br />irrigation waters by the FAO [27J show that sulfate has no <br />appreciable effect on agricultural uses. In fact, gypsum is <br />often applied to agricultural soils to maintain calcium at <br />levels sufficient to avoid permeability or toxicity problems <br />that develop where irrigation waters are high in sodium <br />[27J. Sulfate also appears to have little effect on munici- <br />pal uses, even though concentrations in the Lower Colorado <br />River Basin are slightly higher than the first tier drinking <br />water standards of 250 mg/l. <br />There are no drinking water standards on calcium and <br />carbonate, but it is well known that these are the principal <br />hardness agents responsible for severe scaling problems in <br />municipal water systems of Colorado River water users. <br />Kleinman and Brown [6J estimated that $240,500 in economic <br />'dam",ges were incurred per mg/l TDS by municipal users in the <br />LO\'1"r Colorado River Basin. These estimates would probably <br />be "onsiderably higher if they were expressed per mg/l cal- <br />cillIn carbonate. Lake Powell and Lake Mead collectively re- <br />moved an average of 38 mg/l of calcium carbonate per year <br />over the 1970-79 period. This has greatly reduced the eco- <br />nomic damages to municipal water systems. Moreover, rates of <br />calcite precipitation in the impoundments would be even <br />higher were it not for polyphenol inhibition. Similarly, <br />calcite precipitation in Lake Mead would probably increase <br />significantly if phytoplankton productivity could be <br />restored to pre-Lake Powell levels. <br />, Sodium and chloride are the only, other ions that make <br />up a significant fraction of the TDS in the Colorado River. <br />Dissolution of halite and evaporation in the impoundments <br />caused a slight increase in concentrations of these ions. <br />Sodium, via the effect it has on sodium adsorption ratios, <br />is especially harmful to agricultural crops [27J. Based on <br />the FAO recommended guidelines, sodium adsorption ratios are <br />approaching levels at Parker and Imperial Dams that could <br />present a problem for agricultural users (Paulson unpubl. <br />data). This may warrant some form of control in the future, <br />which could probably best be achieved by controlling point <br />source sodium and chloride inputs, rather than TDS. <br />Based on information presented by USDI [4J, and USGS <br />data collected in rivers near salinity control projects, it <br />appears that the Las Vegas Wash and Grand Valley sources are <br />primarily sulfate salts. Implementation of these projects <br />would decrease TDS by 4 mg/l and 43 mg/l, respectively, but <br />this would probably have little effect on beneficial uses <br />because the salts are primarily sulfate. However, the salts <br />originating from the Paradox Valley area appear to be com- <br />prised primarily of sodium and chloride. Similarly, Glen- <br />wood and Dotsero Springs in Colorado, which are being con- <br />sidered for salinity control, are comprised primarily of <br /> <br />15 <br />