Bio-enhanced Soil Bentonite Slurry Trench Cutoff Walls

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Soil-bentonite (SB) slurry trench cutoff walls have been employed for over fifty years as vertical barriers to control the migration of contaminants in the subsurface. The low hydraulic conductivity of the SB backfill reduces advective contaminant transport such that diffusive contaminant transport regulates contaminant migration. To date, SB research has examined factors influencing hydraulic conductivity and enhancements (such as zeolites and organophilic clays) that provide additional sorption of inorganic constituents. This paper demonstrates the viability of a microbially enhanced SB wall that would serve as both a low-hydraulic conductivity barrier to contaminant transport and a biologically active treatment zone for the biodegradation of organic contaminants. Microbial activity acts to improve SB performance by both lowering the hydraulic conductivity by bioclogging and by biologically treating contaminants as they migrate through the wall. Unlike permeable reactive barriers, a bioenhanced SB wall retards contaminant transport, thereby increasing the residence time needed for the biodegradation of contaminants. Data presented herein include evidence of anaerobic microbial communities surviving and thriving in SB backfill through enhancements such as provision of electron donors and acceptors as well as specialized contaminant degrading bacterial populations. The bioenhanced microbial community native to SB backfill demonstrated a statistically significant reduction in the concentrations of trichloroethylene compared to control samples that had not been biologically enhanced. Test results include those from both batch and column tests. This research demonstrates the viability of a microbially enhanced SB slurry trench cutoff wall and identifies further research needed to progress to field trial evaluation.

2025 International Conference on Bio-mediated and Bio-inspired Geotechnics (ICBBG2025)

General session: Bio-mediated methods for infrastructure construction