Formatted Title
Four Configurations of Subgrade Biogeochemical Reactors at a Facility as a Replacement for Long-Term Hydraulic Containment
Background/Objectives
In situ subgrade biogeochemical reactors (SBGRs) are a unique technology that can be creatively implemented in various configurations for the treatment of contaminant source areas and/or groundwater plumes. SBGRs can utilize both passive groundwater flow and/or recirculation of groundwater for the treatment of contaminants. Additionally, SBGRs are typically constructed using locally sourced, non-refined or “waste” products, making it a green and sustainable remediation (GSR) technology. Because of the effectiveness, flexibility, and sustainable nature of the technology, SBGRs were implemented with four separate configurations at a chemical manufacturing facility in the southeast United States (site) for the treatment of a unique mixture of chlorinated and brominated volatile organic compounds in groundwater. This presentation will provide an overview of the four different applications of the SBGR technology at the site, including differences in layouts, construction methods, results, and lessons learned from each application.
Approach/Activities
Prior to full-scale implementation of the SBGR technology at the site, a drum-scale test was performed using site groundwater to optimize the treatment media for site-specific constituents of concern (COCs). The most promising treatment media was then field-tested in situ as a pilot passive reactive barrier (PRB), and results were compared to an adjacent air sparging barrier. Based on the results of the pilot test, the SBGR technology proved to be more effective. As such, four separate SBGR applications have been implemented at the site in various configurations including 1) a PRB to treat groundwater under natural flow conditions along the property boundary; 2) a series of PRBs across a groundwater plume to treat groundwater under natural flow conditions, supplemented by groundwater recirculation; 3) an in-ground, lined modular reactor with two BGR treatment cells operating in parallel, followed by aeration treatment cells (ATCs); and 4) groundwater extraction and treatment through ex situ SBGR treatment drums with reinjection into upgradient areas of a plume previously amended with EVO substrate.
Results/Lessons Learned
Performance results from the first 1 to 2 years of monitoring at each system will be presented, along with lessons learned during implementation/operation. Results for the first 6 months of operation of the PRB indicate over 90% reduction of COCs as groundwater flows through the barrier. The series of PRBs across the groundwater plume, supplemented by recirculation, has been in operation for approximately 6 months and a total of 150,000 gallons of water has been treated. The in-ground, lined modular reactor has been in operation for approximately 1 year, and effluent COC concentrations have been reduced by over 99% as compared to influent concentrations. The ex situ SBGR drum treatment system is scheduled for start up in October 2023 and results will be included in this presentation.
Lessons learned will focus on challenges encountered during installation and operation. Challenges during implementation included material availability and the use of a one pass trencher to place treatment media. Operational lessons learned include check valve and flow meter troubleshooting during system start up, infiltration of impacted groundwater into a lined system, and simplification of system operation using real-time transducers.