LNAPL trapping observed by Laser-Induced Fluorescence (LIF) technique

Abstract

Contaminated site conceptual models are, in general, the first significant result of environmental management. However, it is necessary to understand the complexity of the contaminated compartments to adopt the best remediation alternative of a contaminated site. Subsurface spatial distribution of light non-aqueous phase liquid (LNAPL) usually with high spatial variability and, consequently complex, must be well known. Furthermore, the seasonal water-level fluctuation induces LNAPL trapping and detrapping phenomena and delimits a vertical redistribution zone (smear zone) of contamination, increasing the subsurface complexity. Aiming to solve data gaps left by conventional technique of investigation the laser-induced fluorescence (LIF) technique was used to evaluate the trapping phenomenon in a kerosene-type jet fuel contaminated site situated in the interior of the State of São Paulo. The results of fluorescence tests and water-level measurements in local aquifer show trapped LNAPL in the saturated zone with well-marked boundaries that define the smear zone. Qualitative analysis shows contamination similarity in most of investigated points, with low-intensity fluorescence signal at the shortest response wavelengths, compatible with light hydrocarbons depletion by natural attenuation.