Frozen soil subsurface barriers: formation and ice erosion

Before and during soil remediation, frozen soil barriers are used to provide containment of liquid contaminants so as to prevent their migration to adjacent areas. Questions concerning formation of frozen gravelly sand barriers in the vadose zone and barrier resistance to ice erosion by liquid contaminants provided the impetus for this study. Bench-scale barriers with full and partial ice saturation were studied. For comparison, one barrier was formed in gravelly sand using water injection via a bentonite-water slurry. The bentonite increased the slurry viscosity, thereby providing a water retention period suitable for freezing. Liquid contaminants included a sodium nitrate solution (freezing point of −5°C) and an antifreeze solution (freezing point of −33°C). Results showed that ice erosion in the bench-scale barriers occurred when the contaminant freezing point depression was lower than the temperature of the frozen soil. When liquid contaminants entered the voids of partially ice saturated frozen soil, the rate of ice erosion was significantly increased. Full ice saturation and barrier temperatures below the freezing point depression of the contaminant are needed to minimize ice erosion.