Geosyntec was contracted for the redevelopment of a former defense manufacturing facility into a Home Depot store and garden center by means of remediation of legacy contamination (vadose zone and shallow groundwater), and to attain regulatory closure.
Geosyntec's Scope of Services
Home Depot USA, Inc. retained Geosyntec in 2000 to design and operate a remedy to address the vadose zone and shallow groundwater contamination at a former defense manufacturing facility in Burbank within Southern California's San Fernando Valley. The remedy addressed hexavalent chromium, other heavy metals, polychlorinated biphenyls (PCBs) and petroleum hydrocarbons in soil via excavation of 13,600 yd3 of impacted soil. Volatile organic compounds (VOCs) in soil and groundwater were targeted for removal via soil vapor extraction (SVE) and a dual phase extraction (DPE) dewatering system supported by a 2,600-ft long slurry wall around the site. Geosyntec led the agency negotiations (2001-present), supported the project's Environmental Impact Report (2001-2004) and managed the construction (2004-2005). Home Depot then built the store, which opened in early 2006.
From 2006-2010, Geosyntec operated and optimized the SVE and DPE systems to maximize mass removal of VOCs. This included pulsed operations, varied venting strategies and rebound testing. A key factor included coordinating operations with Home Depot's 24-hour store operations to limit disruptions to customers and employees, and prioritize safety. More than 3,600 pounds of VOCs were removed, and 99 percent reduction in VOCs was observed. After successful rebound testing, the agency approved decommissioning of the SVE/DPE systems and agreed that the VOC remedy was complete.
An increased regulatory focus in the San Fernando Valley on hexavalent chromium (Cr6+) over the past several years led to the need for a remedy to decrease Cr6+ concentrations in the shallow groundwater. Geosyntec designed and implemented an in situ chemical reduction (ISCR) remedy for Cr6+ by injecting 880,000 gallons of calcium polysulfide solution into the soil and groundwater (188 locations total) in 2014. The ISCR was successful in reducing concentrations of Cr6+ from as high as 6,100 µg/L to <5 µg/L in groundwater.
To demonstrate the project's success, Geosyntec updated the human health risk assessment; collected confirmation samples in soil, vapor and groundwater; and conducted modeling to demonstrate a very low risk that residual VOCs and hexavalent chromium could migrate to the underlying regional drinking water aquifer. On this basis, the Regional Water Quality Control Board, Los Angeles Region (RWQCB) in January 2016 granted full site closure.
The remedy has removed more than 12 million gallons of impacted water and over 3,600 lbs. of VOCs; substantial additional reduction of the Cr6+ mass was successfully completed with ISCR. Full site closure was achieved. Regulators and other stakeholders have praised this work on behalf of the client and the environment."Your team has run an exemplary program with utmost technical competence, honest endeavor, and goodwill," said Alex Lapostol, contractor to U.S. EPA.