TRANSIENT ELECTRICAL RESISTIVITY IMAGING OF A TRACER TEST, TAHLEQUAH, OK

An experimental research site in Tahlequah, Oklahoma was used to conduct groundwater tracing experiments during Fall 2007. The aquifer is composed primarily of cobbles and coarse sands deposited by the Baron Fork Creek. Electrical resistivity imaging was utilized to monitor changes in the subsurface over time as a Rhodamine WT/ potassium phosphate tracer was injected into a constant-head trench at the surface. An Advanced Geosciences, Inc. SuperSting R8 was used to produce 2D resistivity datasets as a series of data points were collected along an electrode line. Two approximately orthogonal lines were used to collect the data. The electrode lines consisted of 28 electrodes with approximately 1.5 meter spacing. A background dataset was collected to determine the resistive properties of the site prior to the tracer experiment. Subsequently, water was injected into the trench to obtain a constant head on the injection trench. Electrical resistivity images were collected as groundwater achieved steady state and the tracer was then introduced to the system. After the experiment was complete, the images were used to generate a resistivity model of tracer movement through the subsurface. The resistivity data depicts tracer migration along preferential flow paths within the fluvial sediment.