Formatted Title
Combined Remedy for Rapid Redevelopment of Multi-Acre TCE and 1,4-Dioxane Plumes
Background/Objectives
Historic manufacturing resulted in multiple releases of volatile organic compounds (VOCs) at a 23-acre property. Operations ceased in the 1980s, and the former building was demolished. The property remained vacant for nearly 40 years with redevelopment inhibited by the subsurface contamination. Groundwater in overburden and bedrock are impacted with trichloroethene (TCE); cis-1,2-dichloroethene, vinyl chloride, 1,1-dichloroethene; 1,1- dichloroethane; and 1,1,1-trichloroethane, and 1,4-dioxane. Increased demand for warehousing renewed interest in construction and remediation. A network of monitoring wells was used to determine the extents of VOCs in overburden and bedrock groundwater in seven identified treatment areas. A desire to begin construction as soon as possible after property transfer necessitated a rapid remediation strategy. The remediation objectives were to effectively reduce contaminant concentrations in groundwater with a single injection mobilization and to progress the site into the state monitored natural attenuation (MNA) program. A higher degree of remediation focus was placed within the footprint of the future building where access would not be available post-construction.
Approach/Activities
A combined remedy approach was developed with in situ chemical oxidation (ISCO) selected for two overburden and two bedrock groundwater treatment areas with chlorinated VOCs and 1,4-dioxane exceeding remediation target concentrations. Enhanced in situ dechlorination (EISD) was chosen for two overburden and one bedrock groundwater treatment areas where only chlorinated VOCs exceed remediation target concentrations. The footprint of the seven groundwater remediation areas ranged from 15,000 to 126,000 square feet. Reviewing treatment area size and contaminant concentrations, the remediation approach incorporated source area injection grids and a series of permeable reactive barriers (PRBs). The ISCO treatment combined modified Fenton’s reagent (catalyzed hydrogen peroxide with chelated iron and oxidant stabilizer) and activated sodium persulfate to enhance desorption of contaminant from soils and provide a persistent oxidant. The EISD treatment included emulsified vegetable oil (EVO) as electron donor, zero valent iron (ZVI), and bioaugmentation; different EVO and ZVI specifications were applied to each of the three EISD areas based on injection orientation, geology, and contaminant concentrations.
Results/Lessons Learned
To meet the desired construction schedule, the injections were performed using two injection crews over a six-month period into more than 600 injection points, including 47 bedrock injection wells, with more than 770,000 gallons of remediation solutions. Injection activities were performed in parallel with earth moving and ground improvement activities, which required additional coordination of remediation activities. Areas with the highest 1,4-dioxane concentrations that were within the future building footprint received two injection events within the six-month mobilization. One year following the completion of the injection event, VOC and 1,4-dioxane concentrations were significantly reduced within all seven groundwater treatment areas and construction was well underway.