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1} .'. , . (1) 00 (\1 N V Q April 20, 1984 LAS VEGAS WASH UNIT CRBSCP, NEVADA PLANNING PROGRESS An October 1982 Status Report recommended a salinity control strategy for Las Vegas Wash (Wash) based on preventing waste-water seepage from recharging the ground water. Recent studies indicate that salt loading is induced by the disposal of waste water into unlined wasteways or basins, and the seepage leaches salt from the underlying evaporite deposits. Reclamation has begun a verification program in the Pittman area which would monitor the ground-water response to the elimination of waste-water seepage from unlined ditches. Installation of a 3.5-mile Pittman Bypass Pipeline began in March 1984 and should be completed in November 1984. The residual 9round-water flow should be diminished but may be more saline. To demonstrate the feasibility of establishing and maintaining native vegetation with available ground water, a vegetation test site is being planned. An effort is being made to coordinate planning of further salinity control action with plans of county and municipal governments. Several local entities have expressed opposition against a Bypass Channel proposed in the 1982 Status Report. The primary issues appear to be: (1) the possible impacts the Bypass Channel would have on the existing and proposed wetlands environment in the Wash, and (2) the possible increased sewage treatment costs resulting from reduction of treatment capability of the Wash. Other issues relate to water rights and Colorado River return flow credit. In response to local issues and recent changes in the location of salt pickup by the surface stream flow, another salinity control strategy has been identified which involves the detention of ground-water in subsurface basins. Each basin would be fonned by a peripheral trench excavated to bedrock and filled with a high density, viscous, fluid (slurry). Soil, cement, and other additives may be used to make the slurry become a relatively impermeable wall. Development of this ground-water flow reduction strategy began in November 1983, with discussions of the concept with state and local government agencies and adVisory groups. Local response has been relatively positive, primarily because sewage treatment plant effluent would not be diverted from the Wash flood plain. Reclamation is currently considering a proposed verification program which would monitor ground-water and vegetation response to ground-water detention basins. The salinity control effectiveness and environmental impacts demonstrated by the Ground-Water Flow Reduction and the Pittman Verification Programs would provide essential supporting information for any further plan development for the Las Vegas Wash Unit.