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• CHAPTER I PURPOSE AND NEED This Final Environmental Impact Statement (FEIS) for the Grand Val- ley Unit of the Colorado River Basin Salinity Control Project is prepared in compliance with the National Environmental Policy Act (NEPA) of 1969 (Public Law 91-190) and under current guidelines established by the Council on Environmental Quality, the U.S. Department of the Interior, and the Bureau of Reclamation (Reclamation). The purpose of the state- ment is to evaluate environmental impacts that could occur with the con- struction of either of the two viable plans for Stage Two of the Grand Valley Unit. The statement is also intended to serve environmental re- view requirements in compliance with Executive Orders 11980, Floodplain Management, and 11990, Protection of Wetlands. Location The Grand Valley Unit is located along the Colorado River in western Mesa County in west-central Colorado. For the most part, the unit area includes the irrigated portion of the Grand Valley consisting of approxi- • mately 70,000 acres of land irrigated by both Federal and private sys- tems, as shown on the Frontispiece Map. The city of Grand Junction, located at the confluence of the Colorado and Gunnison Rivers in the central part of the valley, is the largest Colorado community west of the Continental Divide and serves as the business and economic center of western Colorado. Other communities in the valley are Palisade and Clifton to the east of Grand Junction and Fruita, Loma, and Mack to the west. Purpose of the Unit The overall purpose of the Grand Valley Unit is to decrease salt loading to the Colorado River. The salt loading from the unit area is estimated at 580,000 tons annually, which represents 7.0 percent of the average annual salt loading at Imperial Dam, the last major diversion point of the Colorado River in the United States. The origin of the salt is the Mancos Formation, which underlies the Grand Valley and con- sists of a sequence of thick beds of marine shale containing salt. At the land surface, the Mancos Formation exhibits a thin, weathered, and fractured zone characterized by open joints and bedding planes which often contain gypsum and other minerals. This zone acts as an aquifer which allows water from conveyance system seepage and irrigation deep percolation to dissolve salts from the shale and to convey them to natu- ral drainages and the Colorado River. I ~