Axisymmetric simulation of aquifer storage and recovery with SEAWAT and the Sea Water Intrusion (SWI) Package for MODFLOW

SEAWAT and the Sea Water Intrusion (SWI) Package for MODFLOW were used to simulate hypothetical aquifer storage and recovery (ASR) scenarios under constantand variable-density conditions. To test the codes, both models were used to represent two-dimensional axisymmetric groundwater flow near an ASR well. The models were “tricked” into representing axisymmetric flow by multiplying the input values for horizontal and vertical hydraulic conductivity, specific storage, and porosity by 2πr, where r is the radial distance from the well to the cell center. Additionally, the logarithmic transmissivity weighting option was used, instead of the harmonic weighting option, to ensure that the calculated horizontal conductances were consistent with axisymmetric flow. Results from constant-density simulations were in good agreement with the Theis solution and the equation for an expanding cylinder. For variable-density conditions, SEAWAT and SWI results also were similar, provided that a large vertical hydraulic conductivity value was used for the SEAWAT simulation. Results from a sensitivity analysis with SEAWAT indicated that recovery efficiency is highly dependent on vertical grid resolution, vertical hydraulic conductivity, native aquifer salinity, storage time, and hydrodynamic dispersion.