In 1994, two releases of petroleum hydrocarbons were discovered in the underground storage tank (UST) system at a major rental car facility at McCarran International Airport in Las Vegas, Nevada. Since 1995, Broadbent has performed investigation and remediation of soil and groundwater at the facility and properties downgradient of the facility that have been impacted by the release. Two additional facilities upgradient of the rental car facility have also had confirmed releases and have been identified as additional contributors to the impacted groundwater found in the vicinity of the rental car facility. The axis of the commingled shallow (20 to 25 feet below ground surface) dissolved methyl tertiary-butyl ether (MTBE) groundwater plume associated with these releases historically extended over 5,000 feet and was once the largest MTBE plume in Nevada.
Remedial activities associated with the shallow groundwater MTBE plume reduced the shallow groundwater MTBE plume to three small plumes associated with each source area and one detached downgradient plume. Previous calculations of remediation system effectiveness have demonstrated a reduction of the MTBE contaminant weight by as much as 30% per year.
In 2007, the rental car facilities at McCarran International Airport were closed and moved to an off- site location. At that time, the UST systems were decommissioned and removed from the rental car facility. During removal, two new releases of petroleum hydrocarbons were identified, resulting in the performance of substantial soil excavation activities. Soil samples collected from 35 feet below ground surface showed that the vertical extent of impacted soil was never reached during excavation. Consequently, monitoring wells were installed to deeper groundwater zones which were found to be heavily impacted by dissolved MTBE. Additional characterization identified vertical hydraulic gradients and more transmissive lithology at an intermediate groundwater zone which over time had created a vertically-stratified MTBE plume with the highest concentrations located in a 10-foot thick zone approximately 42 to 52 feet below ground surface.
In 2011, Broadbent conducted a nine-month pilot test utilizing hybrid ozone/hydrogen peroxide injection technology designed to target the vertically-stratified MTBE plume in the intermediate groundwater zone. Concentrations of dissolved MTBE in the vertically-stratified MTBE plume were reduced by >95% within the injection zone. Due to the success of the pilot test, Broadbent is moving forward with a full-scale installation of this remedial technology with operations anticipated to commence in the fourth quarter of 2012.