HR: 0800h
AN: H41F-0481    [Abstracts]
TI: GPR Response to the Introduction of LNAPL in the Vadose Zone
AU: * Pyke, K A
EM: pyke.10@osu.edu
AF: The Ohio State University, 275 Menenhall Laboratory 125 S Oval Mall, Columbus, OH 43210 United States
AU: Daniels, J J
EM: jeff@geology.ohio-state.edu
AF: The Ohio State University, 275 Menenhall Laboratory 125 S Oval Mall, Columbus, OH 43210 United States
AU: Eyuboglu, S A
EM: eyuboglu.1@geology.ohio-state.edu
AF: The Ohio State University, 275 Menenhall Laboratory 125 S Oval Mall, Columbus, OH 43210 United States
AB: Ground penetrating radar data was collected during a physical model experiment that utilized a polyethylene tank and a non-reactive sand matrix to simulate the introduction of distant point source LNAPL contamination in the vadose zone under fluctuating water table conditions. The experiment was conducted in a step wise fashion and various conditions (unsaturated, saturated, residual saturation) were characterized with GPR measurements. As a result of this approach, a more quantitative comparison was possible for each step and results were compared with mass balance information. Results of the study indicate that under saturated conditions the main reflector of GPR energy is indicative of the capillary fringe and not the actual water table. Well readings and mass balance of water input into the system confirm this interpretation. The introduction of LNAPL at the base of the tank during the experiment yielded a complex GPR signal from the gasoline table, and the amplitude of this reflector decayed as stabilization was achieved. In addition, there was an initial decrease in the amplitude of the reflection from the bottom of the tank when gasoline was pumped into the system; however, this amplitude increased with time as a result of the redistribution of fluids in the subsurface. The reflection coefficient between gasoline saturated sand and the polyethylene tank is approximately 30% lower than that observed for the water saturated sand and polyethylene tank, indicating that the amplitude variation is directly related to the distribution of fluids at depth. After gasoline was pumped into the tank and stabilization was achieved, the experiment included increasing the height of the gasoline table through the addition of water. Again, an initial increase in amplitude for the fluid table reflector was observed that decays with time to background noise level. Interpretation of the radar measurements after pumping ceased indicated a redistribution of fluids at depth creating a gradational boundary that decreased the electrical property contrast. This behavior has been observed in the field and has been interpreted as a muted signal related to the presence of LNAPL. This experiment has helped to define a more quantitative approach to LNAPL detection and estimating the volume of product from GPR measurements.
DE: 1835 Hydrogeophysics
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: Fall Meeting 2005