Optimized well positioning for down-gradient capture of infiltrated water

Abstract

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