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t.~ Q ~ 0) Colorado River Basin Salinity Control Project Protective and Regulatory Pumping Unit, Title I Division Arizona: Yuma County Lower Colorado Region Bureau of Reclamation The Protective and Regulatory Pumping Unit is one of three components authorized under Title I of the Colorado River Basin Salinity Control Aclo The other two components are the Desalting Complex Unit and the Coachella Canal Unit, which are cO\:erecl in separate brochures. The Protective and Regulatory Pumping Unit is located within a 5~mile~wide strip of land along the United States/Mexico horder in southwestern Arizona. The strip of land extends about 13 miles eastward from the vicinity of San Luis., Arizona. The objectives of the unit are to manage and conserve the United Stales ground-water resources for the benefit of the United States, and to provide obligated water deliveries to Mexico The unit has been de\'eloped by constructing a well field and delivery system, called the 242 Well Field and Lateral, to intercept part of the ground.water underflow that is moving southward into Mexico from Yuma Mesa in the United States. Prior to enactment of Public Law 93.320 (which autho- rized the unit) and Minute 242 (which effect, pump- ing limitations), this ground.water underflow was be- ing increased by withdrawls of ground water in Mexico from the San Luis Mesa Well Field immediately ,outh of the Southerly International Boundary, the boundary between Arizona and Mexico near San Luis, Arizona, and Sonora, Mexico. The development of the unit in the United States will reduce the amount of ground-water underflow to Mexico. The ground water recovered by the unit is collected in a conveyance system (the 242 Lateral) and is delivered to Mexico by the United States a a portion of the treaty obligations of Colorado River water. Major features of the unit consist of the field of 35 wells, the 242 Lateral and other connecting laterals, a 34.5-kilovolt transmission line, and attendant facilities. D~_;__ D_..'_:__ ?/O-f PLAN There are no natural or constructed surface drains to carry irrigation drainage water from Yuma Mesa. Some of the Colorado River water used for irrigating the mesa's agricultural lands infiltrates into the underlying aquifers in the United States and flows south into Mexico. Since much of this water is being lost to Mexico without being credited as treaty deliveries from the United States, interception and pumping of the ground. water underflow, by the 242 Well Field will permit the recovery of part of this valuable water resource. As this water is credited through surface deliveries to Mexico, an equal amount of water can be retained in storage upstream for beneficial use in the United States. In accordance with the agreement of Minute No. 242, each country is limited to pumping no more than 160,000 acre-feet of ground water per year within its 5.mile zone. In Mexico, ground water is pumped by the 63 well, of the San Lui, Mesa Well Field, The water i, then collected in a canal and conveyed to agricultural land" In the United States, the unit well field is planned with a maximum total pumping capacity of 125,000 acre.feet of ground water per year. This, coupled with about 15,000 acre-feet per year of drainage return flow, will permit the United States to deliver about 140,000 acre-feel of water per year into the Mexican canal system near lhe Southerly International Boundary. This is in combination with 1.36 million acre-feet per year of drainage and regulatory flows of water delivered to Mexico upstream at the Northerly International Boun. dary. The legislation also provides that private water users within the 5.mile zone may also use an additional 35,000 acre-feet of water per year, part of which may be supplied by 10 additional wells which could bring the total to a possible 45 wells. These additional well, may be required primarily for peaking capacit~ that is. at any given moment the short-term demand may exceed the capacity of 35 wells.