Groundwater Mixing Using Pulsed Dipole Injection/Extraction Wells

Mixing is notoriously difficult in groundwater aquifers, because the Reynolds number is very small. This can limit site remediation, and inducing mixing within the groundwater aquifer could speed the chemical processes or otherwise reduce the amount of time needed to meet site remediation goals. A recent analytical model suggests that mixing in groundwater aquifers may be achieved through pulsed dipole injection and extraction from groundwater wells. Building on past work, this study uses MODFLOW, a finite-difference groundwater flow model code developed by the U.S. Geological Survey, to simulate the flow of groundwater and the movement of particles within a two-dimensional confined aquifer. The analysis shows the effects of pulsing the wells, modifying the frequency of pulsing, and changing the lag time between pulses. Mixing within the groundwater aquifer is shown graphically through the pathlines of the particles and quantified using Lyapunov exponents to determine if the flow is chaotic based on the positions and paths of particles within the aquifer. The model indicates that the pulsed dipole injection/extraction leads to increased mixing within the aquifer.