Mapping of joint orientation using Ground Penetrating Radar, Electrical Conductivity and Azimuthal Resistivity.

We are mapping contaminate flow pathways with the use of Ground Penetrating Radar (GPR), Electrical Azimuthal Resistivity (EAR) and Electrical Conductivity (EC) methods in the Beech Creek Limestone at the Crane Naval Base, central Indiana. The burning of ammunition in the past has led to the contamination of the Beech Creek aquifer a highly fractured and karstified limestone. Multiple springs (A, A¢ and C) are being studied with geophysical methods in order to further understand the complex fractured hydrologic system. Six survey sites were used for data collection. Two control sites were used because of direct access to caves that allowed us to measure joint orientations. One site within the larger area was used for the collection of the EAR data. Grid systems were used to collect all of the GPR and EC data and a 360-degree array was used for the EAR data collection. These methods were used to locate and map the joint orientations within the watershed. The strike and dip data shows joint orientations that are different from one ridge to the other. The West Ridge shows a combination of North/South and East /West joint orientations and the East Ridge shows a distinct East/West joint orientation. One control site shows a crisscross pattern of joints. Preliminary results from the geophysical methods show joint orientations, which are similar to the collected field strike and dip measurements. The original EC and two-dimensional GPR results show these patterns the best. GPR data collected at the Ammunition Burning Grounds show directions that are similar to previous determined joint orientation. It also identifies various Karst features within the survey area. EAR data at the Ammunition Burning Ground, suggests that previous assumed joint orientation were correct. Additional GPR coverage will allow the use of three-dimensional models and more conductivity data will provide further constraint on the joint orientations.