Numerical and Experimental Investigation of Active and Passive Spreading for Groundwater Remediation

During in situ remediation of contaminated groundwater, a chemical or biological amendment is introduced into a contaminant plume to react with and degrade the contaminant. Since the degradation reactions only occur where the amendment and the contaminant are sufficiently close, the success of in situ remediation is controlled by the degree to which the amendment spreads into the contaminant plume. Spreading is defined as the reconfiguration of the plume geometry, which occurs as a result of spatially and temporally varying flow fields. Spreading can occur passively due to spatially varying velocity caused by aquifer heterogeneity. Spreading can also occur actively by inducing spatially and temporally varying flow fields through injections and extractions of clean water in wells surrounding the contaminated site. We used coupled numerical investigations and laboratory experiments to explore the effects of active spreading and passive spreading on contaminant degradation. We report here on the effects of passive spreading on contaminant degradation. We analyze the features of the flow field and plume geometry that encourage spreading contaminant degradation, so that the results from the numerical investigation and experiments can be used to design active spreading pumping sequences for other aquifers with other heterogeneity patterns.