Full Description

The Las Vegas Wash (Wash) is the sole drainage from the Las Vegas Valley watershed(~1,600 square miles) that discharges to Lake Mead. Flows to the Wash include highly-treatedwastewater from three wastewater treatment facilities in the valley, urban runoff, shallowgroundwater, and stormwater. Increased population and urbanization in the valley over the lastthree decades has resulted in increased flows to the Wash that caused significant erosion andwetland loss. Since 1998, a Comprehensive Adaptive Management Plan (CAMP) has beendeveloped and implemented to control erosion, to improve water quality, and to enhance theecosystem in the Wash. Constructing erosion control structures along the Wash has created morewetland acreage in the Wash, which offers many positive environmental benefits. However,increased areas of wetlands have also caused some concern over the bioaccumulation of severaltrace metals and metalloids. Due to its tendency to bioaccumulate in aquatic ecosystems,selenium (Se) has regularly been monitored in the water of the Las Vegas Wash and thetributaries and seeps into the Wash. This monitoring program has established a baseline dataset ofSe concentrations in the Wash and its tributaries.Water samples have been collected monthly from eight locations in the mainstream Washchannel and quarterly from eight locations in the tributaries. All samples were collected andpreserved using ultra-clean sampling and preservation techniques. To ensure proper QA/QC andbecause of the low detection limits, water samples were analyzed by three different laboratoriesfor verification. Selenium data continues to be fairly consistent for each sample location andamong the different laboratories. In general, the tributaries with shallow groundwater inputs orlong flow paths have elevated total selenium concentrations, ranging from 10 to 25 ppb, whereassamples from the mainstream Wash sites are relatively low in total selenium ( 5 ppb) due to thedilution provided by inflows of wastewater treatment plant effluent. Additional data collectionhas allowed for the identification of zones of elevated Se concentrations in the tributaries and forthe Se mass balance calculations within the system. Includes 13 references, tables, figures.

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Edition: Vol. - No. Published: 01/11/2004 Number of Pages: 13File Size: 1 file , 1.2 MB