Optimized well positioning for down-gradient capture of infiltrated water
Summary
The recovery of single-well aquifer storage and recovery (ASR) systems is negatively impacted by
background flow. Here, the benefits and risks of using a down-gradient abstraction well in an aquifer
storage transfer and recovery (ASTR) system were studied. A one-layered model was constructed using
MODFLOW 6, to evaluate the effect of ambient flow, dispersion, injection volume and uncertainties in
magnitude and angle of the flow velocity on the RE and optimized down-gradient well position.
Numerical modelling showed that the numerical optimized well distance closely relates to the analytical
calculated displacement distance for longitudinal dispersivities ≤ 0.5 m. At these dispersivities, ASTR
systems at optimized well distances, with ambient flow > 0 m/y result in higher RE’s compared to ASR
systems up to 60% of the total injected water volume. Smaller injection volumes with smaller resulting
hydraulic radii showed high sensitivity to edge effects decreasing both the optimized well distance and
corresponding optimized RE. Uncertainties in angle and magnitude of the groundwater flow decrease
the effectivity of the optimized well positioning and with that also the RE drops. ASTR systems are
potentially powerful systems to increase RE in regions with ambient flow. Their success is, however,
highly dependent on the accurate determination of subsurface parameters, such as direction and
magnitude of ambient flow