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<br />I <br /> <br />Colorado River Basin Salinity Control Program <br /> <br />Las Vegas Wash Unit <br /> <br />t,~ <br /><.>-' <br />,,) <br />,<-'. <br /> <br />The Las Vegas \\-.'ash is a natura] dramage channel providing {he only surface water outler for the <br />entIre 2.193 square miles of Las Vegas Valley. The Las Vegas Wash Unit con....eys storm runoff <br />and wastewater from Las Vegas Valley to Las Vegas Bay. an arm of Lake ~1ead. Located in <br />Clark County in southern ~e\'ada, the Las Vegas Valley contains the largest population center in <br />the Stale. Studies evaluating salmity contributed by the Las Vegas Wash are concerned mainly <br />with the IO-mile reach upSITeam of Las Vegas Bay. <br /> <br />Bdore urban water development in (he valley. the Las Vegas V..rash was a generally barren. sandy <br />channel which contained discharge only durmg brief periods of major stonn runoff. Gro.....th of <br />communities in the valley contributed increasing amounts of .....astewater discharge [Q the Las Vegas <br />Wash until the flo..... became perennial. Return flows 10 the Las Vegas \\.'ash include sewage <br />treatment planl effluent, industrial cooling water. and urban Irrlgation. Solute load (tons) of this <br />\l,a~tewaler has been increasing as discharge continues to mcrease. <br /> <br />Construction of an interception facility to collect saline groundwaler was begun in 1977, but <br />delayed in 1978 to allo..... lime 10 re-evaluate changing groundwater condilions. Several salinity <br />control strategies were addressed dunng the re-evalualion period. One strategy would ha.....e <br />prevented seepage of wastewater and minor Sloml runoff by placing it in a bypass channel running <br />parallel to the Las Vegas Wash for about .; mIles. circumventing salt deposits in the Las Vegas <br />Wa<;h alluvium. The bypass channel .....as viewed by some local enmies as being in contlict .....ith <br />nutrient control and wildlife habitat improvement objectives. and a consensus of local support was <br />not otllained. <br /> <br />In order 10 test the salinity removal effecliveness of separating .....astewater discharge from highly <br />saline SOlIs. a pipeline was constructed to divert industrial rerum tlow from an open. unlined ditch <br />1010 a pipeline appro."(imately .; miles long. Called the Pittman Bypass Pipeline. this facility has <br />reduced ground\l,ater now and consequent pickup of salts leached from the soil. resulting in an <br />eqimated decline in salt loadmg [0 the Colorado River of 3.800 tons per year. <br /> <br />Another strategy for salinity comrol Reclamalion srudied was reducing groundwater tlow by <br />constructing detemion di!.:es across the Las Vegas Wash. The hypothesis was that groundwater <br />delamed behind the di!.:es .....ould malify, with relalively high quality waler collecting at the top. <br />ThiS higher qualit)" .....ater would then spill 10 the Las Vegas Wash channel. Howe\'er. Simulation of <br />the concept by USGS using computer models indicated that stratIfication would nOI occur. and the <br />groundwaler detention strategy would nOl be effective in reducing salinity in the Las Vegas Wash. <br /> <br />Rec1anlJlion has discontinued efforts for developing and implementing further salt.reduction <br />mategies for the Las Vegas Wash UOlt. A strategy is apparently nOI available that is cost effective. <br />technically feaSIble. and publicl)' acceptable al thiS lime. A final report was published In <br />September 1989. Quarterly water quality monitoring is continuing. Salinity levels appear to be <br />increasing in the Wash <br /> <br />49 <br /> <br />- <br />