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I I I I I I I I I I I I I I I I I I I Executive Summary Purpose The purpose of this report is to evaluate the merits of operating the Yuma Desalting Plant (Desalting Plant), examine alternatives, and make a recommendation as to the Preferred Plan of Action for the remainder of the interim period. The Desalting Plant (See location map), the Bypass Drain to the Santa Clara Slough, and the concrete lining of the Coachella Canal are integral features of the works authorized by the Colorado River Basin Salinity Control Act of 1974 (Public Law 93-320) (1974 Act). Operation of the Desalting Plant will allow poor quality drainage water from the Wellton-Mohawk Irrigation and Drainage District (WMIDD) to be conserved, returned to the Colorado River, and used to meet the United States commitments to the 1944 Water Treaty (1944 Treaty) with Mexico for the delivery of water to Mexico. Currently, the drainage water is not returned to the river but discharged to the Santa Clara Slough via the Bypass Drain as a temporary means of reducing salinity levels in the river to meet the Colorado River salinity obligation to Mexico under Minute No. 242 of the International Boundary and Water Commission (Minute No. 242). The United States has temporary use of about 132,000 acre- feet (af) per year of conserved water supplies, developed by lining the Coachella Canal, to offset the impact on reservoir storage of providing additional releases, in lieu of using WMIDD drainage return flow, to meet the 1944 Treaty with Mexico. This temporary supply of conserved water was originally intended to be used during an interim period while the Desalting Plant was under construction and while Colorado River water use in the Lower Colorado River Basin (Lower Basin) continued to be less than apportioned supplies. Construction of the Desalting Plant is now complete; however, water use in the Lower Basin continues to be less than the apportioned supply, and the interim period is expected to extend for at least a few more years and possibly longer. Following a review of the history and a description of the works authorized by the Act's Title I program, the report presents five basic alternatives and several variations of these alternatives. Within the alternatives section, the legal, institutional, and technical issues of each alternative are developed and discussed. Measures that were considered, but eliminated, are also presented. Title I Objectives The objective of Title I is to allow the United States to comply with its obligations under Minute No. 242, considered an extension of the 1944 Treaty, to address salinity without depriving the Colorado River Basin States (Basin States) of any of their apportioned water supply.