Comparison of simulated recharge from drywells and infiltration basins: a modeling study

Authors: SASIDHARAN, SALINI - University Of California; Bradford, Scott; SIMUNEK, JIRI - University Of California; KRAEMER, STEPHEN - Environmental Protection Agency (EPA)

Submitted to: Journal of Hydrology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/28/2020
Publication Date: 11/4/2020
Citation: Sasidharan, S., Bradford, S.A., Simunek, J., Kraemer, S.R. 2020. Comparison of simulated recharge from drywells and infiltration basins: a modeling study. Journal of Hydrology. 594. Article 125720. https://doi.org/10.1016/j.jhydrol.2020.125720.
DOI: https://doi.org/10.1016/j.jhydrol.2020.125720

Interpretive Summary: Infiltration basins and drywells are commonly used to capture stormwater and recharge groundwater, but their performance has not been previously compared. A computer model was employed to simulate the behavior of both recharge approaches. Results demonstrate that five drywells can replace a 70 m diameter infiltration basin to achieve significantly higher infiltration and recharge over 20 years of operation. In addition, a drywell can facilitate rapid infiltration and recharge, and minimize contaminant leaching from shallow clay layers by releasing water below them. These results will be of interest to scientists, engineers, water managers, and government regulators concerned with sustainable groundwater management.

Technical Abstract: Drywells (DWs) and infiltration basins (IBs) are widely used as managed aquifer recharge (MAR) devices to capture stormwater runoff and recharge groundwater. However, no published research has compared the performance of these two engineered systems under shared conditions. Numerical experiments were conducted on an idealized 2D-axisymmetric domain using the HYDRUS (2D/3D) software to systematically study the performance of a circular IB design (diameter and area) and partially penetrating DW (38 m length with water table > 60 m). The effects of subsurface heterogeneity on infiltration, recharge, and storage from the DW and IB under constant head conditions were investigated. The mean cumulative infiltration (µI) and recharge (µR) volumes increased, and the arrival time of recharge decreased with the IB area. Values of µI were higher for a 70 m diameter IB than an DW, whereas the value of µR was higher for a DW after 1-year of a constant head simulation under selected subsurface heterogeneity conditions. A comparison between mean µI, µR, and mean vadose zone storage (µS) values for all DW and IB stochastic simulations (70 for each MAR scenario) under steady-state conditions demonstrated that five DWs can replace a 70 m diameter IB to achieve significantly higher infiltration and recharge over 20 years of operation. Additional numerical experiments were conducted to study the influence of a shallow clay layer by considering an IB, DW, and a DW integrated into an IB. The presence of such a low permeable layer delayed groundwater recharge from an IB. In contrast, a DW can penetrate tight clay layers and release water below them and facilitate rapid infiltration and recharge. The potential benefits of a DW compared to an IB include a smaller footprint, the potential for pre-treatments to remove contaminants, less evaporation, less mobilization of in-situ contaminants, and potentially lower maintenance costs. Besides, this study demonstrates that combining both IB and DW helps to get the best out of both MAR techniques.