Detecting subsurface contamination using ground penetrating radar and amplitude variation with offset analysis

Characterization of contamination in the subsurface is expensive, difficult, and often unreliable. Characterizing Dense Non-Aqueous Phase Liquid (DNAPL) contamination is especially difficult. Geophysical methods, including ground penetrating radar (GPR), are well-suited to measurement of NAPL contamination, as they offer the potential to detect isolated contaminant distributions that borehole monitoring or other methods may miss. We measure the Amplitude Variation with Offset (AVO) response of radar energy to a chlorinated solvent (3M Novec HFE-7200) in a laboratory experiment through controlled injections of the 7200 fluid into a saturated sand/clay system. We demonstrate well defined AVO anomalies associated with the simulate DNAPL spill. The experiment shows that AVO anomalies can be induced when the contaminant layer is as thin as 1/30 the wavelength of the signal at the dominant frequency.