Subgrade Biogeochemical Reactors: Design and Performance of Multiple Configurations

Subgrade biogeochemical reactors (SBGRs) are a unique green and sustainable remediation (GSR) technology for treatment of contaminant source areas and groundwater plume hot spots. SBGRs have been configured for multiple in situ treatment methods, including: enhanced reductive dechlorination (ERD), sulfate-enhanced degradation, and aerobic degradation. SBGRs have been used to effectively treat chlorinated volatile organic compounds (CVOCs) and/or fuel related contaminants in soil and groundwater, and treatment of other contaminants continues to be evaluated.

This technology is used to address persistent source area contamination at a lower cost and in a sustainable manner. SBGRs consist of the following common elements: 1) excavation of contaminated source area soils, 2) backfill of the excavation with gravel and SBGR amendments tailored to the contaminant(s) of concern, and 3) installation of a solar- or wind-powered pumping system to recirculate groundwater through the SBGR for treatment. Use of locally sourced farm and tree byproducts, reclaimed construction materials, along with off-grid groundwater pumping, creates a low-cost, low‑maintenance, and sustainable remediation solution.

SBGRs have been constructed in multiple configurations, including designs capable of meeting limited access restrictions at heavily industrialized sites or at sites with land surface disturbance restrictions due to sensitive species and wetland habitat issues. The SBGR treatment media has also been selected for multiple contaminants based on site-specific conditions. For ERD approaches at CVOC sites, SBGR treatment media have contained various types of organic mulch, new or recycled vegetable oil, iron pyrite, or magnetite sands. For fuel-related sites, SBGR treatment media have included recycled gypsum products for sulfate-enhanced degradation, or oxygen-enhancing amendments for aerobic degradation. This presentation will summarize the advantages and limitations of the SBGR technology. We will discuss performance results from several SBGRs, which are achieving 95-99% total molar reduction of contaminants and rapidly cleaning up contaminant source areas.