Using ground penetrating radar in the investigation of LNAPL contamination within a controlled environment

Electrical resistivity, electromagnetic induction and ground-penetrating radar are state-of-the-art geophysical methods that can be effectively used for the detection of underground contamination of soils and aquifers. After a thorough understanding of their operation principles, data acquisition procedures and processing, and a literature review that considers their usability for the detection of light non-aqueous phase liquids (LNAPL) in particular, a laboratory test was set in order to assess a controlled fuel oil spill and injection with GPR. The test experiment evaluated the performance of a 2.0 GHz frequency GPR device in the characterisation of a shallow sand tank setup. The test was divided into different situations involving acquisitions for two different levels of water saturation, and two acquisitions after the addition of fuel oil to one of the sides of the tank for comparison purposes. The profile images obtained showed a travel time delay associated with increasing water content and a high amplitude anomaly in the contaminated zone of the tank for the contaminated scenario, with an increasing amplitude proportional to the volume of free-phase fuel oil injected. The high frequency of the antenna provided an outstanding resolution for the radargrams, and the wave velocity and relative dielectric permittivity of the materials were estimated from their reflection profiles.