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<br />. <br /> <br />. <br /> <br />History of Salinity in the Colorado River <br /> <br />Even if man had never settled the Colorado River Basin, <br />the Colorado River would have had a higher level of salinity <br />than most any other river in the United States. The river <br />basin encompasses some 242,000 square miles in the United <br />States: A great deal of this land, some 70%, is federally. <br />owned or controlled either as national forests, parks, monu- <br />ments or Indian reservations or as publically owned land. <br />It was. in part due to this ownership of land that Congress <br />undertook the financial responsibility through the Colorado <br />River Salinity Control Act of 1974 to initiate the 16 pro- <br />posed salinity control projects. <br /> <br />Salinity in the Colorado River Basin is the result <br />of two basic processes: one, salt loading, increasing the <br />total salt burden carried by the river: two, salt concen- <br />trating, concentrating the salt burden in a lesser volume <br />of water due to a reduced water supply. Both processes <br />may result from both natural and man-made conditions. <br /> <br />Salt loading occurs naturally from surface and ground <br />water runoffs as well as from mineral springs. Man-made <br />salt loading results from irrigation return flow and in- <br />dustrial or municipal discharges. Salt concentration is <br />a natural result of stream or reservoir evaporation and <br />consumption by phreatophytes and other riparian vegetation. <br />Man- caused salt concentration results from consumptive <br />use or diversion of water from the stream. <br /> <br />Of the man-made increases in salinity, irrigation is <br />the major source. It contributes to both salt loading and <br />salt concentration. According to the 1975 Forum Report <br />(CWQCC "Appendix CO) agriculture accounts for 37% of the <br />total basin salt concentration (page 13, Table 1). Diver- <br />sions from the Upper Colorado River Basin at or near the <br />headwaters where the river's water has a very low salt <br />content into surrounding basins, along with industrial and <br />municipal consumptive in basin use, account for a relatively <br />minor 4% of man-made concentrations. <br /> <br />The EPA has estimated in its 1971 report "The Mineral <br />Quality Problem in the Colorado River Basin" that almost <br />two-thirds of the average annual salt load and one half <br />the concentration at Hoover Dam f9r the period 1942 through <br />1961 was caused by natural sources. Almost the same results <br />were shown in the report for the 1963 through 1966 period. <br />Table 1 of this initial report is attached to the written <br />comments presented to you as Exhibit 1. <br /> <br />~~ <br /> <br />-2- <br />