In 2003, chlorinated volatile organic compounds (CVOCs) associated with dry cleaning operations were discovered in the groundwater beneath a former dry cleaning facility in Las Vegas, NV. Broadbent was contracted to conduct on- and off-site characterization activities. Broadbent prepared and implemented a detailed Site Characterization Work Plan (Work Plan) which included design, construction oversight, development, and soil and groundwater sample collection from seven groundwater monitor wells. Groundwater sample laboratory analytical results indicated the on- and off-site presence of dissolved tetrachloroethylene (PCE), trichloroethylene (TCE), dichloroethylene (DCE) and vinyl chloride (VC) constituent concentrations in groundwater in excess of their respective Maximum Contaminant Levels (MCLs). Broadbent prepared and implemented a subsequent Work Plan to monitor groundwater beneath the site and to conduct VC remediation activities via an enhanced in-situ bioremediation process (EISB).
The EISB approach included installation of three additional wells to be utilized for monitoring and as iSOC® (in-situ Submerged Oxygen Curtain) remediation wells, and installation of iSOC® components into four existing wells associated with the facility. The iSOC® system is designed to inject oxygen at a low flow rate into groundwater thereby increasing the dissolved oxygen concentration in proximity to each well point.
The additional dissolved oxygen enhances the indigenous aerobic bacteria population, thereby increasing the rate of VC bio-attenuation in this area. The EISB system was initiated in 2005 and operated for three years, and was effective in removing the off-site plume component and reducing overall concentrations on-site. Since the post remediation contaminate plume had been reduced to a limited area beneath the property, the Nevada Division of Environmental Protection (NDEP) approved a request to shut off the EISB system and move into monitored natural attenuation (MNA). MNA activities include semi-annual low-flow sample collection and reporting. The contaminant plume has remained stable since MNA activities were initiated.