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:. . . , , The report prepared by EPA on the mineral quality problem in the Colorado aiver Basin provided the basis for development of salinity standards in 1975. This report included three alternatives for salinity control in the river: 1) augmentation of basin water supply 1 2) reduction of salt loads1 3) limitation of further depletion of basin water supply. The report concluded that a basin-wide salt load reduction program appeared to be the most feasible of the three salinity controls. In essence this alternative included impoundment and evaporation of saline water from point sources, diversion of runoff in streams around areas of high salt pickup, improvement of irrigation and drainage practices, improvement of irrigation conveyance facilities, desalinization of saline discharges from natural and man- made sources, and desalinization of water supplies at points of use with appropriate disposaL of waste. brine. The report estimated that if fully implemented the program would reduce average salinity concentrations at Hoover Dam by about 150 mg/l in 1980 and 275 mg/l in 2010. In 1975 the seven state Colorado River Basin Salinity Control Forum prepared a report which included numeric criteria and a plan of implementation and recommended that each state adopt the report as its salinity standards. Each of the Colorado River Basin states adopted the recom- mended standards which were approved by EPA in November, 1976. Pursuant to the mandate of the Clean Water Act of 1977 that water. quality standards be reviewed every three years, the Forum in 1978 began the process of revising the salinity standards. As part of that process the Forum has conducted a series of salt routing studies to provide estimates of future salinity levels at selected points in the basin under different assumptions as to both the available water supply and future water use. A detailed discussion of this Forum study is included in the 1979 third annual progress report, Water Quality Standards for Salinity, Colorado River System, prepared by the Colorado River Basin Salinity Control Forum. The cover page of that report is attached hereto as Exhibit 2, a full copy has been introduced into the administrative record of this proceeding by the state. The progress report concludes at page 24 that, "Salinity levels since 1972 have been declining. A part of the decrease is now considered to be due in part to an apparent change in the flow vs. salt load relationship which occurred in the period after 1968 with the filling and operation of the major reservoirs of the upper basin... It appears that a significant reduction in salt load has occurred in this Colorado River above Cisco, Utah beginning in about 1969. Analysis of the data for the river reach Lees Ferry to Grand Canyon also indicates a reduction in salt load beginning about 1955 and again after the close of-.Glen Canyon Dam." -3-