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TITLE I PROGRAM 49 California. This could happen by the end of the 1990 calendar year. Protective and Regulatory Pumping (Reclamation> In December 1972, Mexico began pumping ground water from a well field near San Luis, Arizona, and located immediately south of the International Boundary separating Arizona and Sonora, Mexico. Studies indicated that the pumping draws water stored in the ground-water reservoir underlying the Yuma area in the United States and in time would affect the surface drain flows historically delivered to Mexico as part of United States' obligation under the 1944 Water Treaty. These flows had been about 125,000 acre-feet of drain flow and 15,000 acre-feet of canal wasteway flow annually. More recent annual flows total only about 105,000 acre-feet at the Southerly International Boundary and will gradually be reduced to about the 15,000 acre-feet of canal wasteway flow due to the combined ground-water pumping in Mexico and the United States. Public Law 93-320 authorizes the Secretary to construct, operate, and maintain a well field for ground-water pumping in a 5-mile zone adjacent to the International Boundary near San Luis, Arizona. The well field, known as the Protective and Regulatory Pumping Unit, will ultimately have the capacity to produce up to 160,000 acre- feet per year. Water produced from the well field is (1) delivered to Mexico for credit against the Treaty obligation and (2) used in the United States. The law also authorized the Secretary to acquire approximately 23,500 acres of private, State, and State leased lands within the 5-mile zone near the boundary. The purpose of this land acquisition is to limit agricultural development within the zone, thereby limiting ground water pumping to the 160,000 acre-feet per year as required by Minute No. 242. About 10,000 acres of Bureau of Reclamation (Reclamation) withdrawn land are used to assist in this control. Ultimate production in the 5-mile zone will be 160,000 acre-feet per year; of that, the amount to be delivered to Mexico is expected to be 125,000 acre-feet per year. This quantity, along with 15,000 acre-feet of wasteway flows, will furnish the necessary 140,OOO-acre-foot delivery at the Southerly International Boundary. The balance of the water available from the well field could be sold to other users in the area. Contracts have been completed for construction of the first 21 wells, a conveyance channel, appurtenances, and an operation and maintenance road. Future construction to complete the 30 to 40 well system depends on need. Yuma Desalting Plant (Reclamation> The Yuma Desalting Plant is being built on a 60-acre tract ofland 6 miles west of Yuma, Arizona. The purpose of the plant is to upgrade the quality of drainage water from the Wellton-Mohawk Irrigation and Drainage District (WMIDD) so that it can be returned to the Colorado River and credited toward treaty deliveries to Mexico. The operational design parameters set up for the plant determined that a membrane desalting process was technically feasible and is economically suitable for the Yuma Desalting Plant operation. The factors included in this formula are the volume of water delivered to Mexico; the salinity differential required by Minute No. 242; the salinity of the Colorado River at Imperial Dam; the volume of drain water treated; the salinity of the drain water; a number of other factors related to the diffuse return flows below Imperial Dam; and plant operational factors. A study done in 1978 by the Advisory Committee on Irrig{ltion Efficiency, WMIDD, recommended expansion of onfarm measures which were expected to result in an irrigation drain flow of about 108,000 acre-feet per year. In addition, the Colorado River Salinity Control Forum has established a salinity standard at Imperial Dam of879 milligrams per liter (mg;IL). Using the salt balance formula and assuming an irrigation drain flow of 108,000 acre-feet and salinity of the Colorado River water at Imperial D8lIl of 838 mg;IL, a plant size of 73 million gallons per