Lab-scale Tests in the Detection of a Multi-phase DNAPL

In order to improve the understanding of the sensitivity of geophysical investigation to different phases of contaminant, GPR, electric resistivity and TDR measurements performed to detect and monitor DNAPLs spilled in a saturated media are analyzed. The experiment was performed in a Plexiglas cell filled with saturated grain glasses, simulating a permeable sand media, and hydrofluoroether (HFE-7100) simulating the contaminant. The results showed that GPR is more sensitive to the separate phase of contaminant because the dissolved phase does not significantly influence the electric permittivity. These results were confirmed by TDR measurement. On the contrary the electric resistive measurements resulted sensitive to all phases of contaminant (gaseous, separate and dissolved). The water flow and the variation of the water table contribute to the dissolution and migration of the DNAPL, even if the lab experiment showed that it cannot be easily removed within a saturated medium because its separate phase remains trapped within the pores and, very slowly, it moves downwards, also in the presence of a water flow.