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CHAPTER I Authorization The Grand Valley Unit was authorized for construction by the Colo- rado River Basin Salinity Control Act of June 24, 1974 (Public Law 93-320), as part of a basinwide program for enhancing and protecting the quality of water available in the Colorado River for use in the United States and the Republic of Mexico. Title I of the act, which was di- rected toward controlling the salinity of river water below Imperial Dam for use in the United States and Mexico, authorized the construction of a desalting complex and other measures to ensure acceptable salinity levels. Title II of the act provided for programs to control the salinity of the Colorado River upstream from Imperial Dam. Title II also author- ized the construction of four salinity control units including the Grand Valley Unit. Public Law 98-569, enacted in October 1984, amended Title II provisions and provided for using pipe laterals, replacing incidental fish and wildlife values foregone, and reimbursing non-Federal entities for operation and maintenance costs that exceed those that would have been incurred in the thorough and timely operation and maintenance of the system without unit development. Background To accomplish salt reduction, a two-segment program is being con- • ducted by the Bureau of Reclamation and the U.S. Department of Agricul- ture, Soil Conservation Service (SCS). Reclamation and SCS activities are being closely coordinated. The segment for improving the water sys- tems is being directed by Reclamation, while the on-farm improvement segment, consisting of upgrading farm irrigation systems and improving irrigation management, is being conducted by the SCS, whose program will be discussed subsequently in this chapter. The Grand Valley Unit was planned in stages so that construction could begin in a portion of the valley where plans and designs were com- plete and where monitoring could be conducted to assess salinity control effectiveness and environmental impacts. Stage One, encompassing about 10 percent of the unit area and completed in April 1983, consisted of concrete lining 6.8 miles of canal, consolidating 34.2 miles of open laterals into 29.7 miles of pipe, and installing an automated moss and debris removal structure. The Stage One area is designated by the cross- hatching on the Frontispiece Map. The Stage Two area involves the re- mainder of the valley outside of Stage One except specified areas as discussed in Chapter 'III. Planning investigations for Stage Two began in November 1981. An FEIS, containing preliminary environmental information and cumu- lative impacts for the original units in Title II of the Salinity Control Act (including the Grand Valley Unit), was filed in May 1977 (Reclamation and SCS 1977). In June 1978, a Negative Determination of Environmental Impact was prepared on Stage One development (Reclamation 1978). This PURPOSE AND NEED 2