Developing injection / extraction schemes to enhance mixing in groundwater for improved in-situ remediation

Creating favorable mixing conditions in aquifers has the potential to improve the efficiency of in-situ remediation of groundwater. In current practice of in-situ remediation, the treatment solution, containing chemical or biological amendments, is either drawn through the aquifer using a downgradient extraction well or left to travel with ambient groundwater flow. Neither of these scenarios provides opportunity to enlarge the interfacial area between the treatment solution and the contaminated groundwater where degradation reactions occur. We hypothesize that by sequentially injecting or extracting clean water at multiple wells in the aquifer, the interface between the treatment solution and the contaminated groundwater can be stretched and folded to create unique geometries that provide additional surface area for reaction, thereby accelerating the treatment process. This strategy of injection and extraction is expected to be feasible for practical application since pumping rates and duration are limited as compared to other injection / extraction approaches, for example the pulsed dipole approach investigated by others. Dispersion during the sequential injection / extraction is examined using random-walk numerical simulations to compare the degree of spreading caused by this transient injection / extraction with the degree of spreading caused by the dispersion alone. Finally, the simulations are evaluated to quantify the degree to which reaction rates are enhanced through the injection / extraction scheme.