Investigating contaminant leakage in sawtooth-configured non-pumping reactive wells: A sandbox test approach

Abstract

Non-pumping reactive wells (NPRWs) are passive remediation technologies for contaminated groundwater that use various configurations of wells filled with reactive materials. This study evaluated the performance of sawtooth array NPRWs, which is a configuration that considers minimum well spacing for ground stability, and investigated contaminant leakage through them. A sandbox was constructed to observe point-by-point differences in cadmium (Cd) concentrations through the NPRWs. Groundwater flow and solute transport were simulated numerically to determine contaminant leakage and decontamination performance. Finally, the performance of the saw tooth-configured NPRWs was evaluated considering removal efficiency and longevity. The sandbox test results showed that the Cd concentrations exhibited very similar upgradient trends. Significant downgradient decontamination of Cd by the reactive materials was confirmed. Specifically, the Cd concentrations exhibited highly dispersed or wide spatial variations at each point, indicating contaminant leakage. The Langmuir sorption model, which uses the concept of maximum sorption capacity, was the most suitable for explaining the occurrence of contaminant leakage. The removal efficiency decreased over time because of the leakage of pollutants and the longevity was determined to be 890 h. The investigation of contaminant leakage provides a method for quantitatively assessing the performance of NPRWs facility and can be valuable in the design phase for optimizing NPRWs configurations, including suggesting safety factors to prevent leaks.