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. . '.. ':_.: :;,'. ,",.:,. .,':~~: :-,t: '-. :'.' :~',~t:.- :><'.,'--"':~-. :~.~~ ~~ '-:..;.' -:.':- ;-' ". ...-..,..~. - I~. . ;:-; ~:,:::.... -.~,:-:-::'''':.'~~--I'' . - . of salt. Reclamation has evaluated several alternatives but has not yet found a feasible method of sal inity control. ~ c..... o 07 Alternatives developed within the La Verkin Springs Unit 1981 Concluding Repon were re-analyzed along with new alternatives. The re-analysis was based on geologic data from 1983 field studies, updated and refined hydrologic data, and feasibility grade designs prepared during the previous study. A preliminary findings repon was prepared in 1984 and recommended the study be discontinued because of poor cost effectiveness. Las Vegas Wash Las Vegas Wash is a natural drainage channel providing the only surface water outlet for the entire 2,193 square miles of Las Vegas Valley. The Las Vegas Wasb conveys storm runoff and wastewater from Las Vegas Valley to Las Vegas Bay, an arm of Lake Mead. Located in Clark: County in southern Nevada, the Las Vegas Valley contains the largest population center in the State. Studies evaluating salinity contributed by the Las Vegas Wash are concerned mainly with the IO-mile reach upstream of Las Vegas Bay. Before urban water development in the valley, the Las Vegas Wash was a generally barren, sandy channel which contained discharge only during brief periods of major storm runoff. Growth of communities in the valley contributed increasing amounts of wastewater discharge to the Las Vegas Wash until the flow became perennial. Return flows to the Las Vegas Wash include sewage treatment plant effluent, industrial cooling water, and urban irrigation. Solute load (tons) of this wastewater has been increasing as discharge continues to increase. However, salinity concentrations have been declining due tathese increased flows. \ f. ~; ::~ Construction of an interception facility to collect saline ground water was begun in 1977 but delayed in 1978 to allow time to re-evaluate changing ground-water conditions. Several salinity control strategies were addressed during the re-evaluation period. One strategy would have prevented seepage of wastewater and minor storm runoff by placing it in a bypass cbannel running parallel to the Las Vegas Wasb for about 4 miles, circumventing salt deposits in the Las Vegas Wasb alluvium. The bypass channel was viewed by some local entities as being in conflict with nutrient control and wildlife habitat improvement objectives, and a consensus of local support was not obtained. ~. <. :{. ..J ~;~ .l:~i ::~~.. fBf.1 ~~{? '''-'' ~ ' :.~ .....~ In order to test t\1e salinity removal effectiveness of separating wastewater discharge from highly saline soils, a pipeline was constructed to divert industrial return flow from an open, unlined ditch into a.pipeline approximately 4 miles long. Called the Pittman Bypass Pipeline, this facility has reduced ground-water flow and consequent pickup of salts leached from the soil, resulting in an estimated decline in salt loading to the Colorado River of 3,800 tons per year. '.r.-:;;: ~j,f t;f~~ ~;~ ~it~ '::'~:"/ :~!i~ .~r~~i Another strategy for salinity control Reclamation studied was reducing ground-water flow by constructing detilntion dikes across the Las Vegas Wash. The bypothesis was that ground water detained behind the dikes would stratify, with relatively high quality water collecting at the top. This higber quality water would then spill to the Las Vegas Wash channel. However, simulation of the concept by the U.S. Geological Survey using computer models indicated that stratification would not occur, and the ground-water detention strategy would not be effective in reducing salinity in the Las Vegas Wash. ,..':.: ::t/~ 29 a~~\ 'r~.:c :;~::~;: '..' ;.:~ .",'.1' ..:"::~~.: .' '.J.-- ,.,"::: ':'.'-: ',';." .', :".~.:. >/\ "," .<';>