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12 ~ C) o ~..... CoO en The differential of 115 ppm ~ 30 ppm TOS specified in Minute No. 242 CO can be achieved in two ways. The first is to exclude all Wellton- Mohawk drainage from the waters delivered to Mexico and to replace them with waters from above Imperial Dam. The other is to treat the drainage waters so they will have the same salinity as waters from above Imperial Dam. To exclude the drainage from the waters delivered to Mexico as a part of the Treaty deliveries, it would be necessary to eliminate irrigation operations in the Well ton-Mohawk Division of the Gila Project or to bypass all its drainage waters around Mexico's point of diversion. To shut down the Wellton-Mohawk Division of the .Gila Project is not considered economically or politically viable. To bypass all of the Well ton-Mohawk drainage waters would entail the loss of from 175,000 to 220,000 acre-feet annually from the Colorado River system, a prospect wholly unacceptable to the Colorado River Basin states. Therefore, the method most acceptable to United States interests is to modify the Well ton-Mohawk drainage waters so that they will have the same salinity as waters from abofe Imperial Dam. This is the purpose of the Colorado River International Salinity Control Project, involving the improvement of irrigation efficiency, regulating flood flows, construction of a desalting complex and the replacement of the first 49 miles of the Coachella Canal, presently unlined, to substitute for the waters bypassed. Replacing the unlined canal will save about 132,000 acre-feet of water per year which will be available for substitution until required by California users. To reduce the quantity of water requiring treatment by the desalting complex, the Well ton-Mohawk drainage flows will be reduced by improving on-farm irrigation efficiencies and by reducing the project acreage from the authorized 75,000 acres to 65,000 acres. These steps are estimated to reduce the drainage flows from 220,000 to 175,000 acre-feet per year by the time the desalting plant begins operation. A further undertaking is the regulation of Gila River floodwaters that infiltrate the Well ton-Mohawk aquifer and necessitates ground water pumping which may overtax the existing drain conveyance facilities. To lessen this prospect, operation procedures would be developed to limit flood releases from Painted Rock Reservoir, a Corps of Engineers facility on the Gila River with a capacity of 2.5 MAF. The Salinity Control Act provides for acquisition of an interest in reservoir lands to allow for temporary storage behind Painted Rock Dam of flood waters. Beginning at the origin of the Well ton-Mohawk drainage flows, the desalting complex will operate as follows: The drainage flows from