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. , "o::l" -' o o (,.-;; o A. DESCRIPTION OF THE PROPOSAL 1. Introduction The Grand Valley Unit was authorized by the Colorado River Basin Salinity Control Act (P.L. 93-320). The act included a total of four construction units in the Colorado River Basin and authorized investiga- tions on several other units. A cumulative environmental impact state- ment was prepared on the entire Colorado River Water Quality Improvement Program (FES 77-15) and included impac'ts of the Grand Valley Unit in relation to the other units. An Environmental Assessment on the Grand Valley Unit was published in December 1977 and distributed to concerned agencies and organizations. Comments received were overwhelmingly in support of the project, but there were two major areas of concern: adequacy of wildlife measures and the effectiveness of canal lining in salinity control. The current Bureau of Reclamation wildlife plan takes into consideration the concerns of both the Fish and Wildlife Service and the Colorado Division of Wildlife by inclusion of a wildlife moni- toring program and wildlife habitat acquisition consistent with these agencies' estimates of impacts and needs. Current construction plans call for the development of Stage One, an area about 10 percent of the unit, which will be constructed and mon- itored to provide background information for evaluating implemented pro- cedures. As suggested by the Environmental Protection Agency, the resulting data will be used in planning the remainder of the unit and similar salinity control projects. This negative determination addresses only the impacts of Stage One construction. Further development of the Grand Valley Unit is dependent on data received from'the monitoring programs and on conclusions drawn from observations to be made in the Stage One area. Impacts of the remainder of the unit will be addressed in the Draft and Final Environ- mental Statements to be prepared and filed with the Environmental Pro- tection Agency before initiation of further construction. 2. Overall Project Plan The Grand Valley Uuit would be designed to reduce the salt loading into the Colorado River from the Grand Valley by about 410,000 tons annually by decreasing the amount of water moving through saline snb- strata and subsequent salt pickup. -The reduction would result in a decrease in salinity of approximately 43 mg/L at Imperial Dam, which is the last historic measuring station before the river enters Mexico and is situated near Yuma, Ariz. The reduction would be accomplished by a three-part program planned and implemented by the Bureau of Reclamation of the U.S. Department of the Interior and the Soil Conservation Service of the U.S. Department of Agriculture. A-l