Reduction of Residual Dense Non-Aqueous Phase Liquids (DNAPL) in Groundwater Using Natural Freezing of Soils in Cold Regions in Combination with Microbial Polymer Gels

Abstract

DNAPL contamination and remediation is one of the major environmental concernstoday. Current remediation techniques are ill equipped to deal with DNAPL remediation. Duringremediation, due to the heterogeneities of the aquifers, the mass of the contaminants in therelatively high permeability zones are removed but the mass in the relatively low permeability zones remain as residuals and thus serve as a source of continuous contamination. This is amajor contributing factor for the failure of remediation technologies. In a literature review madeby University of Michigan, there has never been a single documented clean up of a DNAPLcontaminated site.<br><br>Reducing the temperature of soil formations can modify aquifer flow paths. The naturalfreezing of soils in winter may be used effectively to modify the flow paths. In summerpermeability modification can be accomplished by emplacement of microbial polymer gels. Weare investigating a novel method where a combination of natural freezing in winter and amicrobial polymer are used to reduce the mass of residual DNAPL from contaminated soils.This remediation method supplements the shortcomings of conventional remediationtechniques.<br><br>We have conducted a series of lab scale experiments to investigate the efficiency of naturalfreezing and microbial polymer for permeability modification. At temperatures below 4C, thepermeability of layered soil drops drastically suggesting that the relatively high permeabilityzones are blocked due to the formation of pore ice but the flow still takes place in the lowpermeability zones. Freezing has an important impact on contaminant removal and our resultssuggest that bulk removal of contaminant increases with decrease in temperature. Attemperatures above 4C, permeability modification can still be achieved by injecting a microbialpolymer gel like curdlan. The objective of this paper is to provide results of our investigationutilizing natural freezing for permeability modification and the resulting reduction in the volumeof residual DNAPL.