Biofilm Barrier Formation and Per- Sistence in Variable Saturated Zones

A novel strategy for containment of contaminated groundwater consists of a biologically produced extracellular polysaccharide (EPS) barrier, i.e. biobarrier, within a subsurface formation. To bring this technology closer to field scale, a PVC column (12 inch [30.5 cm] diameter x 48 inches [121.9 cm] high) was constructed to examine the effects of thick biofilms in porous media under radial flow conditions. Bacteria (Pseudomonas fluorescens, a facultative anaerobe capable of denitrification) and nutrients were injected down a center injection well and allowed to flow radially outward through a sand-gravel mixture to the edge of the column. The bacteria were allowed to grow on the surface of the porous medium and produce thick biofilms that reduced the hydraulic conductivity of the soil. Nitrate was added as the electron acceptor to the column to facilitate denitrification during anaerobic growth. Bacterial growth created a reactive biobarrier that not only reduced the hydraulic conductivity of the soil, but also completely utilized nitrate and dissolved oxygen within 24 hours, creating anaerobic conditions throughout the column. Introduction of bacteria and nutrients above the static water level generated a biobarrier in the vadose zone. Creation of an elevated biobarrier in the field offers the potential for hydraulic containment of a dissolved contaminant plume.