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2 by the states as individual numeric criteria and plan ~or salinity N ~ control within those states. Subsequently, each of the seven Basin ~ VJ States adopted the numeric criteria and the plan of implementation, which were approved by EPA. Section 303 of the Clean Water Act of 1977, requires that water quality standards be reviewed at least once every 3 years. The report being considered today was prepared under that provision of the Act. #2 The Colorado River Basin covers some 242,000 square miles of watershed. The Basin is divided at Lee Ferry, separating the Upper Basin from the Lower Basin. The major points of concern for which numeric criteria have been set are at Hoover, Parker, and Imperial Dams. #3 The river has had a history of generally increasing salinity since continuous recor~s were kept sometime in the early 1940's. It can be seen that this trend is almost a continuous increase until 1970. At that point salinity levels off and a slight d~cline is experienced since 1972. However, it now appears that downward trend has ceased. at least at Hoover and Parker Dams. #4 This slide presents an indication of the change in salinity at the three stations between 1972 through 19$0. The 1972 levels are the adopted numeric criteria at the three stations. It should be noted that currently salinity is running below the numeric criteria at all three stations. 1/5 A large part of the salt load of the Colorado River comes from natural} diffuse and point sources. In fact that amounts to about 62 percent, while irrigated agriculture represents 33 percent, .~ ..- -, ,Jl.:__./-' ." ..;,; ..i.:' ~__~_-;:; - .', _ _ _ _ '. __t~_,_--,;] .ili" 1;",""h~>,-;~~jsiiii