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. Cl Cl W ,.jd . . CHAPTER 3 - NUMERIC CRITERIA FOR SALINITY Overview As discussed earlier in this report, the EP A promulgated a regulation which set forth a basinwide salinity control policy for the Colorado River Basin, This policy required that the flow- weighted average annual salinity in the lower mainstem of the Colorado River be maintained at or below the 1972 levels, The Basin states, acting through the Forum, addressed this requirement in its first Review entitled Water Quality Standards for Salinity Includinl? Numeric Criteria and Plan ofImplementation for Salinity Control- Colorado River System dated June 1975, In the 1975 Review, the Forum proposed three stations as appropriate points in the lower mainstem of the Colorado River at which to measure the flow-weighted average arumal salinity, These stations are located at the following points: (1) below Hoover Dam; (2) below Parker Dam; and (3) at Imperial Dam. In 1972, the flow-weighted average annual salinity for these stations were determined by Reclamation from daily flow and salinity data collected by USGS and Reclamation and became the numeric criteria, The criteria for each of those stations is as follows: Below Hoover Dam Below Parker Dam At Imperial Dam 723 rugIL 747 mgIL 879 mgIL There is no inference that 1972 was chosen as the basis for establishing the numeric criteria because that year represented a typical or average year, The basis for selecting these stations is their proximity to key diversion facilities on the lower Colorado River. The State of Nevada diverts Colorado River mainstem water from Lake Mead for use in the Las Vegas area, and its return flows move into the Lake and are part of the water supply available below Hoover Dam, The Metropolitan Water District of Southern California and the Central Arizona Project divert water from Lake Havasu, impounded behind Parker Dam, for many millions of water users in southern California and central Arizona, The large agricultural areas in the Imperial and Coachella Valleys in California and the Yuma area in Arizona and California are served by diversions made at Imperial Dam, The criteria were established to protect infrastructure and crop production rather than human health or fish and wildlife values, The salinity concentrations that are anticipated in the future, even without salinity control efforts, have not been shown to have adverse effects on human health or wildlife, Thus, the Colorado River Salinity Control Program is different from most other water quality standards compliance programs. 3-1