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Sl.M1lIRY vegas wash (Wash) is the prilllary drainage channel for the Las Vegas "alley, in Clark County, Nevada. It conveys discharge fran sewage ;'ttreatnent facilities, mban nmoff, secondary recharge fran lawn and golf . course watering and ground-water seepage to Las Vegas Bay, an ann of Lake ~d, on the Colorado River. The Bureau of Reclamation (Reclamation) began studying the Wash in 1978 as part of a basin-wiele effort to control salinity in the Colorado River. Feclamation focused on identifying major sources of salt loading to the wash, and developing a cost-effective salinity control strategy acceptable to local entities and interests. Four salinity control strategies were identified: ground-water collection; ground-water prevention; ground-water flow reduction; and no action. These strategies were not developed simultaneously, but evolved one at a time. During this process scme strategies were detennined to be nonfeasible and were eliminated. The ground-water collection strategy would collect saline water for disposal in evaporation ponds or treat it by reverse osmosis desalinization. It was detennined to be not cost effective for salinity control. The ground-water prevention strategy would prevent surface flows fran caning into contact with native salt deposits. This strategy includes the Pittman Bypass Pipeline, built in 1985, which keeps relatively fresh cooling water fran local industries, foonerly discharged to an unlined ditch, fran seeping through native salt deposits, picking up salt, and conveying it to the Wash. The second feature of the strategy, the Bypass Channel, which was not constructed, would have raooved sewage treatIIent plant effluent fran the Wash flood plain for a distance of 4.5 miles. In theory, the Bypass Channel would have prevented surface water fran recharging the underflow of the Wash and leaching salt fran the Wash alluvium. This feature met with resistance fran local entities that were concemed that the effluent would no longer benefit fran a natural nutrient raooval process. Consensus has not been reached on the effectiveness of natural nutrient raooval by wetlands vegetation. The Bypass Channel would also raoove water necessary for SUfPOrting a wetlands habitat. The ground-water flow reduction strategy provided for reducing the flow of ground water through the use of a detention basin system. The system would have been catprised of a series of dikes constructed to cx:eate basins to detain surface water flowing through the Wash. A test basin (D14) was constructed to detennine if ground water entering and lOOITing through a basin toward the main channel would stratify, with denser, more saline water remaining at greater depths. A ccrrputer simulation model indicated that this strategy would not perfOJ:Il\ as hypothesized. i