Laser-induced Fluorescence Frozen Core Analysis to Improve NAPL Conceptual Site Models
Laser-induced Fluorescence Frozen Core Analysis to Improve
NAPL Conceptual Site Models
Jeff Gentry and Mike Niemet (CH2M)
Randy St. Germain (Dakota Technologies)
Jeff Gentry is a Senior Principal Engineer with 30 years of experience in the evaluation, design, and construction of NAPL-related remedies in sediment and in upland sites. Jeff provides technical direction on a large number of projects dealing with NAPL-impacted sediment for private and government clients and has implemented NAPL management technologies including permeable barrier walls, capping, and other methods. His projects range from large Superfund sites to individual commercial waterfront properties. He leads the development of NAPL migration laboratory methods with CH2M’s Applied Sciences Laboratory and works closely with university researchers to bring the latest innovative methods to field applications.
Laser-induced fluorescence (LIF) is a technique that can detect non-aqueous phase liquids (NAPLs) such as petroleum fuels/oils, coal tars, and creosotes. Direct push logging of the NAPL’s inherent fluorescence with depth provides rapid and cost-effective delineation of NAPL. Conducting a multitude of LIF logs at NAPL sites allows a detailed NAPL conceptual site model. For Manufacture Gas Plant sites, TarGOST (Tar-specific green optical sensing tool) has become the de facto standard for in situ delineation of MGP NAPL impact (EPRI 2014, Generic Work Plan to Assess DNAPL Mobility at MGP sites). Typically the results of LIF borings are collected and a fraction of the locations will use a second boring near the LIF boring to “align” the LIF readout with other data such as the pore fluid saturation or NAPL mobility. However, because of the heterogeneous distribution of NAPL (especially DNAPL) over a small scale, this approach has uncertainty in aligning data from two borings. Dakota Technologies and CH2M have teamed to develop a laser-induced fluorescence frozen core analysis (LIFFCA) technique that allows for direct comparison of LIF response to non-aqueous phase liquid (NAPL) saturation on frozen sample segments cut from intact cores. LIFFCA allows for direct comparison of LIF response to geotechnical and chemical properties of the exact same intact core segment. Because LIF is a non-destructive method, the frozen sample segments can shipped to Dakota for LIFFCA. The core segments can be subjected to LIFFCA and the exact same core segments can then later be returned for geotechnical and/or chemical testing.