Pumping Induced Hydraulic Gradient Driven Tracer Migration through Defects: Implications for Rapid Detection of Leakage in Vertical Flexible Barrier

Abstract

Vertical flexible barriers (VFBs) are widely used for contaminant source separation and risk control. Inherent or externally caused damage to a VFB can affect its effectiveness in pollution containment and control, but its effective detection is a major challenge due to its concealed nature. This paper presents a combined pumping and tracer approach to detect defects in VFBs. A high-performance model is used to model the detection process revealing the migration and distribution behavior of the tracer in the triple media system of wellbore–aquifer–VFB to better understand the effectiveness of the method and its performance indicators, including response time, detectable depth, and defect size, and to optimize its application. Simulation results show that the tracer quickly moves through the defect to the monitoring well, and temporal tracer concentration reveals details of the breach in the wall. Sensitivity analysis reveals influential factors, including defect size, depth, and tracer concentration. Results indicate that the size and depth of defects will affect the penetration and response time. Breakthrough is less clear, and response time is longer if defects are small and deep. However, a higher tracer injection concentration can shorten the response time and increase tracer concentration in the monitoring well. Therefore, it is necessary to design the tracer dosing concentration according to the site conditions. For the Yancheng site, tracer concentration was increased from 1000 ppb to 2660 ppb to ensure the detection of leakage points at 4 m or deeper.