Use of Laser Induced Fluorescence to Detect DNAPL and Fluorophore Mixtures In-Situ

We present results from laboratory investigations on the fluorescence of Dense NonAqueous Phase Liquids (DNAPL) and fluorophore mixtures, characterized using a Luminescence Spectrometer. Fluorophores such as aromatic compounds (e.g. benzene, toluene, ethylbenzene and xylenes, as well as other constituents of petroleum fuels, oils, lubricants and greases) are present as co-contaminants in many DNAPL spills. Concentration as low as 5% of fluorophore in the DNAPL solvent are easily detectable. Using the difference in characteristic fluorescence wavelengths for the various fluorophores, we are able to distinguish between naturally occurring fluorophores in the DNAPL solvent and introduced fluorophores. Field investigations using a Laser Induced Fluorescence (LIF) probe at several sites corroborate our laboratory results. Results to date indicate that the LIF probe will be applicable only for a qualitative assessment of DNAPL saturation, but may be useful in combination with other probes in the cone penetrometer for DNAPL source delineation.