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~ ~ ~ ~ CHAPTER III. WATER QUALITY STANDARDS FOR SALINITY Criteria The Forum developed and agreed upon basinwide water quality standards for salinity, including numeric criteria and a plan of implementation for salinity control in 1975 (1975 Forum report). In order to provide for sound water quality objectives, based on a basinwide approach, numeric criteria were established at three key stations (below Hoover, below Parker, and at Imperial Dams). The key stations were selected due,to their proximity to major diversions in the Lower Basin. The State of Nevada diverts Colorado River main stem water from Lake Mead for municipal and industrial uses in the Las Vegas area. The Metropolitan Water District of Southern Caljfornia ahtl the Central Arizona Project divert water from Lake Havasu for all uses. The large agricultural areas in the Imperial and Coachella Valleys in California and the Yuma area in Arizona and California are served by diversions at Imperial Dam. The flow-weighted average annual salinity for the year 1972, as determined by the Bureau of Reclamation from daily flow and salinity data collected by the U.S. Geological Survey and the Bureau of Reclamation, were selected as the numeric criteria. They are as follows~/: Below Hoover Dam Below Parker Dam Imperial Dam 723 mg/l 747 mg/l 879 mg/l Each of the Basin states adopted the 1975 Forum report as ' its standards for salinity. The state-adopted water quality standards were subsequently approved by EPA. In response to Section 303(c) of the Clean Water Act, the Forum in 1978, 1981, and 1984 reviewed the standards. After each review, the Forum determined that the 1975 criteria were still appropriate. The Forum also reviewed and modified the plan of implementation in 1978, 1981, and again in 1984. Appropriate documents were adopted by the states. ~ Again, in 1987, the Forum, in response to Section 303(c), reviewed the criteria and determined that the 1975 criteria are still appropriate. II The weighted average annual salinity at the three locations in the lower mainstem of the Colorado River where numerical criteria have been established was and continues to be computed by the Bureau of Reclamation utilizing salinity data determined by the "calculation method" (sum of constituents). The calculation method is described in the latest edition of the U.S. Geological Survey Techniques of Water Resources Investigations - "Methods for Determination of Inorganic Substances in Water and Fluvial Sediments." -19-