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<br />. ,-,.- -"'> <br />1 j~:_, <br /> <br />. <br /> <br />. <br /> <br />Present Sources of Salinity <br />In its natural state, it is estimated that the Colorado River's <br /> <br />dissolved mineral load averaged about 5.1 million mns per year at a <br />concentration of about 250 parts of dissolved salts per million parts <br />of water (ppm) at Lees Ferry, Arizona, which is located just a few <br />miles downstream of Glen Canyon Dam. About 80 percent of the natu- <br />rally occurring salts come from oiffuse sources and about 20 percent <br />are from natural point sources, such as mineral springs and exposed <br /> <br />[ormations of highly soluble minerals. There is little that can be <br /> <br /> <br />~one to control salts that are derived from diffuse sources, but <br /> <br />there is a gre~t interest in the natural point sources as many of <br /> <br />them are susceptible of control. <br /> <br />When pioneerinc farmers moved into the Colorado River Basin, <br /> <br />their activities had the net effect of increasing the salinity of <br /> <br /> <br />the Colorado River. The main use of the river water was and still <br /> <br />is for irrigation, which increases the salinity in two ways. First, <br /> <br />some of the water is consumptively used or is lost through evaporation <br /> <br />so that the amount returned to the river is less than the amount di- <br /> <br />verted. About two million acre-feet are consumed annually in this <br /> <br />manner; thus, the salts in the river w&ter are concentrated in a <br /> <br />smaller volume of water. Secondly, the water that does return to the <br />river not only returns the salts contained in the water that was <br />diverted but picks up additional salts from the soils to which it is <br />a?plied ann from the underlying formations. <br />Studies have been made that indicate 3.5 million tons of salts <br /> <br />are added annually to the Colorado River Ly return flows from irrigat2' <br /> <br />-3- <br />