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0022tf8 Salinity of the Lower Colorado River /41 complex was then intended to. treat 129 million gallons of drainage water per day (145.000 acre-feet per year) using ad- vanced technology. making it the largest desalting plant in the world. It would produce 43,000 acre. feet of brine as a waste product from the plant that would be bypassed to the Santa Clara slough and would not be a part of treaty deliveries to Mexico. Congress also authorized the extensions of the Wellton- Mohawk bypass drain to the Santa Clara slough and other auxiliary works. A Flew concrete-lined canal was authorized in place of the forty-nine mile earthen Coachella Canal of the Boulder Canyon Project so that the water saved would x:eplace waters that might have to be released from storage to meet de- livery requirements to Mexico under the agreement. 10 This was consistent with the provisions of Public Law 93-320 that re- placement of the water wasted by the desalting plant and water bypassed to the Santa Clara slough are to be national obliga- tions. except in years when there is water llowing in the Col- orado River in excess of the amount necessary to supply uses in the United States plus the guaranteed delivery of 1.5 million acre-feet to Mexico, the excess to be determined by the U.S. Sec- tion of the International Boundary and Water Commission. Further, Congress authorized construction of well fields capa- ble of pumping 160,000 acre-feet of water per year along the Arizona-Sonora border for use in the United States. 11 Congress authorized appropriation of $121,500.000 for the construction of the works required for the desalting com- plex, and $34,000,000 for the works and lands needed for the protective well fields.12 In 1980, Congress authOriZed a major increase in appropriations to cover increased costs of the de- salting plant, to pay for mitigation measures and to allow modiflcations in design.13 The Domestic Sallnlty Control Program By 1970, pressures increased within the United States to curb rising salinity levels in the Colorado River upstream of Imperial Dam. Salinity was expected to continue increasing with upper basin water development. Lower basin states water users would be adversely affected by heightened salinity, and renewed problems with Mexico might follow. The federalgov- ernment, through the Environmental Protecllon Agency (EPA) , pressed for numerical limitations on the salinity at state boundaries that might inhibit upper basin development. To avoid this problem, the Department of the Interior explored salinity control measures that would enable development to continue without further impairing salinity upstream of Imperial Dam.