Groundwater is an important source of fresh water and, consequently, its quality should be properly monitored. Different contaminants can be identified with different types of equipment and/or measurement procedures. Fuel oil contamination forms a "floating" layer over the water table, which has different electrical properties, therefore electromagnetic techniques can be used to image such contaminants. This paper presents a scale-laboratory test where a 2.0 GHz ground penetrating radar (GPR) is used to assess a controlled-fuel oil injection in a shallow sand tank setup. The test examined several scenarios involving different levels of water saturation and fuel oil contamination. The increase of water content produces a reduction of EM wave propagation velocity, moving some fixed/reference targets to higher reflection times. We use simplified relations to obtain approximated dielectric permittivity values, where the inverted results are consistent with those available in the literature for similar scenarios. Rather than suggesting a true quantitative procedure, these observations could be exploited in a qualitative long-term monitoring strategy in common field situations where a contaminant enters a soil matrix and moves through its pore spaces. Finally, the integration of GPR measurements with other monitoring techniques could increase the reliability of the interpretation and the sensitivity to the contaminant concentration
