Site Studies Of Ground Penetrating Radar For Monitoring Petroleum Product Contaminants

Ground penetrating radar (GPR) provides a possible means of mapping<br>hydrocarbons in the vadose zone. Results of controlled surveys in a sand test pit<br>at The Ohio State University demonstrate conclusively that there is a clear high<br>amplitude GPR anomaly over plastic containers containing diesel fuel and<br>containers containing the host sand material saturated with diesel fuel.<br>Results of surveys at a site in Northern Indiana show a correlation between the<br>decrease of the GPR signal amplitude in the vicinity of the gasoline concentration<br>and the presence of gasoline. A decreased amplitude of the GPR signal is<br>present in the capillary fringe region above the water table at this site, suggesting<br>that vapor-phase hydrocarbons may affect the propagation of the<br>electromagnetic wave. Possible explanations for the observed high amplitude<br>reflections over the confined hydrocarbons in the test pit and the low amplitudes<br>in the field include: 1) the hydrocarbon product may be contained in small<br>dispersed concentrations in the vadose zone, or 2) the hydrocarbon product may<br>have a high loss tangent. Small dispersed concentrations of hydrocarbon<br>product above the water table cotild cause reflecting and diffracting boundaries,<br>resulting in many small isolated anomalies on a GPR record. A high loss tangent<br>for the hydrocarbon product could help to explain both the observed decrease in<br>amplitude for the electromagnetic wave propagating through the capillary fringe,<br>and the high amplitude reflections from the saturated hydrocarbons.