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CHAPTER I PURPOSE AND NEED <br />without water quality improvement projects are expected to follow an • <br />overall rising trend as depletions continue to increase. <br />In response to the Federal Water Pollution Control Act and its <br />amendments (Public Law 92-500, October 1972), the seven Colorado River <br />Basin States adopted and the Environmental Protection Agency approved <br />numeric criteria for three points on the Lower Colorado River as shown <br />in Table 2. <br />Table 2 <br />Numeric criteria for salinity <br />on the Lower Colorado River <br />Annual <br />flow-weighted <br />concentration <br />Station (mg/L) <br />Below Hoover Dam 723 <br />Below Parker Dam 747 <br />At Imperial Dam 879 <br />The goal of the salinity control program is to maintain concentra- <br />tions at or below these criteria. Depletions within the Colorado River <br />Basin are projected to increase from 9.6 million acre-feet per year in <br />1983 to 12.6 million acre-feet by 2010. With full development of the <br />compact-apportioned waters, depletions could increase to 15 million acre- • <br />feet annually. Unless control measures are implemented to prevent the <br />salinity increase, concentrations at Imperial Dam are estimated to in- <br />crease from the 1983 measured, average level of 710 mg/L to an average <br />of 1,012 mg/L by 2010. <br />Based on studies conducted by Reclamation and the SCS, full imple- <br />mentation of all authorized salinity control measures (Reclamation and <br />SCS measures authorized for construction) could maintain the salinity <br />criteria at Imperial Dam until about 2005.1/ By 2010, the salinity <br />levels are expected to reach 904 mg/L and will continue to increase with <br />further development. During some years, the concentrations would exceed <br />those predicted levels. Table 3 shows expected salinity levels in 2010 <br />with and without additional salinity control measures. <br />Table 3 <br />Mean annual salinity at Imperial Dam <br />(mg/L) <br />1983 2010 <br />Without additional salinity 710 1,012 <br />control measures <br />With full implementation of <br />salinity control measures 1/710 904 <br />Standard at Imperial Dam 879 879 <br />1/ Flow-weighted mean for the calendar year <br />1983. <br />1/ U.S. Department of the Interior. January 1985. Quality of <br />Water, Colorado River Basin, Progress Report No. 12. <br />10 <br />