Use of LIF for real-time in-situ mixed NAPL source zone detection

he site characterization and analysis cone penetrometer system (SCAPS), equ ipped with realtime fluorophore detection capabilities, was used to delinea te subsurface contaminant releases in an area where plating shop waste was temporarily stored. Records indicated that various nonaqueous phase liquids (NAPLs) were released at the site. The investigators advanced the SCAPS la ser-induced fluorescence (LIF) sensor to depths beneath the water table of the principal water-bearing zone. The water table was located approximately 6 feet (1.8 m) below ground surface (bgs) across the site. Fluorescence, a ttributed to fuel compounds commingled with chlorinated solvents, was obser ved at depths ranging from 4.0 to 11.5 feet (1.2 to 3.5 m) bgs. Fluorescenc e, attributed to naturally occurring organic materials (by process of elimi nation and spectral characteristics) commingled with chlorinated solvent co nstituents, was observed at depths ranging from approximately 13 to 40 feet (4.0 to 12.2 m) bgs. Fluorescence responses from compounds confirmed to be commingled with chlorinated solvents indicates that the SCAPS fluorophore detection system is capable of indirectly delineating vadose zone and subaq ueous chlorinated solvents and other dense nonaqueous phase liquids (DNAPLs ) at contaminant release sites. This confirmation effort represents the fir st documented account of the successful. application of LIF to identify a m ixed DNAPL/LNAPL source zone.