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<br />Alternatives developed within the La Verkin Springs Unit 1981 <br />~.. Concluding Report were reanalyzed along with new alternatives developed during <br />00 this study. The reanalysis was based on geologic data from 1983 field studies <br />~ and updated and refined hydrologic data and feasibility grade designs prepared <br />~' during the previous study. <br /> <br />A preliminary findings report recommending the study be discontinued <br />because of poor cost effectiveness was submitted to the Office of the <br />COmrrUssioner in January 1984. The Salinity Control forum and the Office of <br />the Commissioner have concurred with the recommendation. The preliminary <br />findings report recommending discontinuance of the study was released in <br />August 1984. <br /> <br />8. Las Vegas wash Unit (Reclamation) <br /> <br />Las Vegas Wash (Wash) is a natural drainage channel providing the <br />only surface water outlet for the entire 2,193 square miles of Las Vegas <br />Valley. A drainage area of 1,586 square miles directly contributes to the <br />wash which conveys storm runoff and wastewater to Las Vegas Bay, an arm of <br />Lake Mead. Located in Clark County in southern Nevada, the Las Vegas Valley <br />contains the largest population center in the State. Three cities (North Las <br />Vegas, Las vegas, and Henderson) and other communities are drained by <br />tributaries to the wash. Studies evaluating salinity contributed by the Wash <br />are concerned mainly with the lO-mile reach upstream of Las Vegas Bay. The <br />Wash flood plain and adjacent area support about 1,500 acres of halophyte, <br />hydrophyte, and phreatophyte vegetation. <br /> <br />Before water development in the valley, the wash was a generally <br />barren and sandy channel which contained discharge only during brief periods <br />of major storm runoff. The growth of the communities in the valley <br />contributed increasing amounts of wastewater discharge to the Wash until the <br />flow became perennial. Return flows to the wash are from sewage treatment <br />plant effluent, industrial cooling water, urban irrigation, and agricultural <br />drainage. This wastewater carries a solute load of 150,000 tons per year; <br />however, the wastewater leaches an additional 80,000 tons per year of salt as <br />it flows into the Wash. About 63 percent of the salt pickup is calcium <br />sulfate and 26 percent is sodium chloride. <br /> <br />Past investigations associated with plan development have been <br />described in previous progress reports. Construction of an interception <br />facility to collect saline ground water was begun in 1977 but delayed in 1978 <br />to allow time to reevaluate changing ground water conditions. <br /> <br />One alternative salinity control strategy would be to prevent <br />seepage of wastewater and minor storm runoff by placing it in a bypass channel <br />running parallel to the wash for about 4 miles, circumventing salt deposits in <br />the wash alluvium. The bypass channel has been viewed by some local entities <br />as being in conflict with nutrient control and wildlife habitat improvement <br />objectives. A consensus of local support for the bypass channel does not <br />appear obtainable while wastewater treatment issues remain unresolved. <br /> <br />The seepage prevention strategy for salinity control is being studied by <br />the Pittman Verification Program. once-through cooling water discharged by <br />industries near pittman has been diverted form unlined ditches to a 3.5 mile <br />pipeline. Piezometers in the Pittman area are being used to monitor ground <br />water levels and quality. The curtailment of seepage from the unlined ditches <br /> <br />VlI-18 <br /> <br />.... <br />