Experiments on the Detection of Organic Contaminants in the Vadose Zone

Abstract

The subject of detecting non-aqueous organic contaminants using ground penetrating radar (GPR) has garnered widespread research interest in the last decade. Daniels and others (1995) reported that at some field sites a distinctive GPR response can be observed over volatile organic contaminant plumes. The use of three dimensional (3-D) GPR data imaging techniques and a consideration of contaminant vapor effects can provide another avenue for identifying and mapping areas of organic contamination. This combined exploration approach is being pursued in response to greater awareness of contaminant behavior in the vadose zone and the advent of more powerful GPR data visualization computer software. In this study, the effects of shallow organic contamination on the GPR response were examined at two petroleum hydrocarbon spill sites and in controlled tank model studies. The results show that the detection of organic contaminants using GPR can be made in certain hydrogeologic environmental conditions. Detection potential is improved by arid conditions, including seasons when the rainfall amount is low. Arid conditions can be temporarily simulated at sites where a blacktop cap or a surface layer of frozen ground is present over the hydrocarbon. Conditions that improve the general penetration capability of GPR (e.g., homogeneous, low-permittivity soil conditions) also improve the detectability of hydrocarbons.