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r --'.,-'. - ,,,.;-",,' ','L :..' DEVELOPING SALINITY CONTROL TARGETS Compliance with the Salinity Standards The water quality (salinity) standards for the Basin have been established at three locations in the Lower Colorado River Basin where water quality affects end users of the water. The standards call for maintenance offlow- weighted average annual salinity concentrations (numeric criteria) in the lower mainstem of the Colorado River and a Plan of Implementation for future controls. The water quality standards are based on the Water Quality Standards for Salinity, Including Numeric Criteria and Plan of Implementation for Salinity Control, Colorado River System, prepared by the Colorado River Basin Salinity Control Forum (Forum), June 1975. This document was submitted by each of the Basin States and approved by the Environmental Protection Agency. In SU=ary, the report states: The numeric criteria for the Colorado River System are to be established at levels corresponding to the flow-weighted average annual concentrations in the lower mainstem during calendar year 1972. The flow-weighted average annual salinity for the year 1972 was used. These values were determined by the Bureau of Reclamation from daily flow and salinity data collected by the U.S. Geological Survey and the Bureau of Reclamation. Based on this analysis, the numeric criteria are 723 milligrams per liter (mg/L) below Hoover Dam, 747 mg/L below Parker Dam, and 879 mg/L at Imperial Dam. . It should be recognized that the river system is subject to highly variable annual flow. The frequency, duration, and availability of carryover storage greatly affect the salinity of the lower mainstem; and, therefore, it is probable that salinity levels will exceed the numeric criteria in some years and be well below the criteria in others. However, under the above assumptions, the average salinity will be maintained at or below 1972 levels. ~;; 1~~ .~. :'( If.~ ! J'~ f~ ~ "':; ~~i~ Periodic increases above the criteria as a result of reservoir conditions or periods of below normal long-time average annual river flow also will be in conformance with the regulation. With satisfactory reservoir conditions and when river flows return to the long-time average annual flow or above, concentrations are expected to be at or below the criteria level. ':,,:-, ;'. :.', ,.:,; ~~:- . .'.-. The Federal regulations provide for temporary increases above the 1972 levels if control measures are included in the plan. Should water development projects that deplete fresh water inflows or add to saline I: ,,: 0002.7 20