Laboratory Study of Low-Flow Rates on Clogging Processes for Application to Small-Diameter Injection Wells

A new concept in aquifer storage and recovery (ASR) aims to lower costs by using gravity-induced infiltration and small diameter wells installed with direct-push technology. Such systems will have significantly lower injection rates than traditional ASR. Clogging is a major concern for ASR systems; however, previous investigations of injection well clogging assumed a high injection rate. To address this bias, this study investigates the potential for clogging in low-flow (<0.38 m³/min) ASR injection wells. The effects of low-flow rate injection on hydraulic conductivity and geochemistry were examined using laboratory columns packed with sand and gravel taken from an experimental low-flow ASR site. Changes in hydraulic conductivity and geochemistry were monitored over 17 days using two types of source water (treated surface water and native groundwater) at three different flow rates (Darcy velocities 1 m/d, 3 m/d, 5 m/d). The hydraulic conductivity of the lowest flow rate columns decreased below initial levels by at least one order of magnitude during the experiment. Observations of biofilm in effluent tubing suggest bacterial clogging reduced the hydraulic conductivity in medium and low flow treated surface water columns, but bacterial abundance was not quantified in this study. Clay dispersion was estimated to be an important process, partially reversing the bacterial clogging. Further understanding of clogging factors at low flow rates will aid in the selection of the most beneficial clogging prediction tests and pretreatment and redevelopment methods for low-flow ASR systems.