Measurements of Stream Discharge and Analysis of Surface Water/Groundwater Interactions in Las Vegas Wash, Las Vegas, NV

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The Black Mountain Industrial (BMI) complex, in Henderson, Nevada, has been the site of industrial chemical production since 1942. Perchlorate contaminants, from activities at BMI, have moved through the groundwater system and have been discovered in the Las Vegas Wash, prompting water resource investigations and groundwater treatment by the Nevada Division of Environmental Protection (NDEP). The USGS Nevada Water Science Center is assisting NDEP's efforts by providing additional surface-water discharge data that are evaluated to better understand the spatial extent, timing, and hydraulics controlling groundwater/surface-water interactions along the Las Vegas Wash. 

On-site clean-up and groundwater contamination instigations have been ongoing at the BMI complex since 1998. In 2012, a summary analysis of perchlorate concentrations in the groundwater identified perchlorate plumes with concentrations ranging from more than 1,000 mg/L at the BMI complex, in the shallow groundwater, to less than 1 mg/L at Las Vegas Wash. Currently, NDEP conducts water-quality analyses, groundwater monitoring, and groundwater flow-system evaluation to understand the occurrence and movement of perchlorate in the hydrologic system around Las Vegas Wash. Additionally, NDEP manages remediation facilities that remove perchlorate from the groundwater flow system up-gradient of the Las Vegas Wash at the BMI complex.

The USGS NVWSC, in cooperation with NDEP, is quantifying stream discharge and evaluating surface-water/groundwater interactions that affect perchlorate concentrations within the study area. Activities associated with this effort include:

1) Installation and operation of three new surface-water gaging stations along Las Vegas Wash. The gages are run in conjunction with existing sites and will be operated for 5 years. New Stations include:

2) Four, day-long, synoptic discharge measurement collection activities over a two-year period; two during the winter period (December 2016, and December 2017) of low evapotranspiration, and two during the summer period (June 2017 and June 2018) of high evapotranspiration.

  • These single day events occur throughout an 8-hour period at sites of interest between continuous gaging stations, with discharge measurements collected each hour.

The objective of these activities is to assist Nevada Division of Environmental Protection perchlorate monitoring, assessment, and remediation efforts in the Las Vegas Wash by providing additional stream discharge data and analysis of surface water/groundwater interactions. Additional data is needed to determine the occurrence and loading of perchlorate in the main channel, and to better understand the spatial extent, timing, and hydraulics controlling groundwater/surface-water interactions along the Las Vegas Wash. Data from this study will be analyzed for trends, seasonal variation, base-flow analysis at select locations along the Las Vegas Wash.  

 

USGS surface-water gaging stations, seepage study collection locations, and weir structures along Las Vegas Wash, Las Vegas, Nev
USGS surface-water gaging stations, seepage study collection locations, and weir structures along Las Vegas Wash, Las Vegas, Nev.  (Public domain.)