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<br />Diversions from the Upper Colorado River Basin into surrounding <br />basins occur at or near ~he headwaters where the river's water has <br />a very low salt content. This removal of high quality water, <br />even though some salt is also removed from the ,Basin, results in <br />a salt concentrating effect downstream. <br />Most industrial plants in the last few years, particularly large <br />coal-fired thermal electric generating plants, have been designed <br />to eliminate the return of cooling tower blowdown water to the <br />Colorado River. As water is circulated through the cooling towers, <br />a part of it evaporates and the dissolved solids in the remainin-g <br />water become more and more concentrated. As cooling water must <br />be maintained at or below specific levels of salinity, a portion <br />of the c::mcentrated water is removed or "blown down" and replaced <br />.rith fresh water. When this blowdoWn is not returned to the river <br />system, tr.e salt load in the water diverted is removed from the <br />river. Even though these no-return uses remove salt from the river, <br />the river's concentration of dissolved 'solids usually increases <br />below the point of use because of the reduced flow resulting from <br />the beneficial use. The effects on river salinity of a r.o-return <br />consumptive use are similar to those of an out-of-basin export. <br />Historically, salt loads cO:1tributedby municipal and industrial , <br />sources have been minor, totaling about 1 percent of the Basin salt <br />load for the period 1942-61. With the exception of concentrated <br />returns from the Las Vegas, Nevada, area most municipal and <br />industrial wastes in the Basin are relatively low in total salt load. <br /> <br />" <br /> <br />-16- . <br />