ELECTRICAL AND WELL MONITORING OF CHLORIDE TRACER IN A KARST SINKHOLE IN THE ARBUCKLE-SIMPSON AQUIFER

As part of increased water management, there is a desire to implement artificial recharge in a rural portion of the Arbuckle-Simpson Aquifer (ASA). Research presented here is part of a larger research effort at the City of Ada Managed Aquifer Recharge Research (CAMARR) Site in the ASA. In October 2023, a chloride tracer test was conducted in a large karst sinkhole. Approximately 19,000 liters of aquifer water was mixed with sodium chloride to a target concentration of 250 mg/L. The tracer was released over a period of 40 minutes via hose from a mixing tank into the sinkhole. Wells in the vicinity were sampled for chloride, temperature and EC changes every 8 hours. Two Transient Electrical Resistivity Imaging (TERI) lines were established so that data could be collected on either side of the sinkhole orthogonal to a fault to monitor the chloride tracer moving in the subsurface. A resistivity dataset was collected on each line every 6-8 hours for approximately three days. Preliminary results show that a tracer of this concentration was not detected in the well samples. The TERI data indicated that the majority of the tracer was left in the vadose zone and would not be detectable using the well data alone. The results indicate that recharge may spend more time in the vadose zone allowing for equilibrium with aquifer conditions and time for decay processes to occur before entering the phreatic zone.