Application of Geophysical Logging Techniques for Multi-Channel Well Design and Installation in a Karst Aquifer

HydroPhysical^TM logging, along with optical and acoustic televiewer logging, was applied in five open bedrock boreholes at the Volunteer Army Ammunition Plant (VOAAP) in Chattanooga, Tennessee to identify water-bearing fractures and conduits. Data obtained from the HydroPhysical^TM (HpL) and geophysical logging was evaluated in real time in the field so that Solinist Continuous Multi-channel Tubing "CMT" wells with multiple sampling chambers could be properly constructed. The fracture zones were identified to evaluate the distribution of explosive contaminants in the karst aquifer wherein primary flow paths are through solution-enlarged fractures and bedding planes. The CMT wells are designed to provide vertical head distribution within fracture zones and vertical contaminant profiles in support of the groundwater corrective measures study (CMS) and long term monitoring points. The HpL logging techniques identified water-bearing fracture zones in each borehole under ambient and stressed conditions with flow rates ranging from 0.007 to 18.5 gpm. The number of water-bearing fracture zones identified ranged from one to eight per borehole. Additionally, optical or acoustic televiewer data was acquired for greater depth resolution of fractures and fracture orientation information. Based on the HydroPhysical^TM data, CMT wells were installed in each borehole with multiple fracture zones with the well screens targeting specific water-bearing fractures. The depths of the screened intervals for the multi-chamber wells ranged from 43 to 145 feet bgs. Contaminant profiles generated from the multi-chamber wells showed concentrations of explosives varied widely among fractures within each well. The HpL and geophysical logging accurately defined preferential flow zones at lower cost and requiring less time than traditional techniques. Once logged, data were evaluated in the field, which allowed the CMT wells to be designed, constructed, and installed by the geologist with minimal delays.