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LIF Introduction Print E-mail
ImageFluorescence is a property of some compounds where absorbed light stimulates the release of photons (light) of a longer wavelength. Fluorescence, a property of many aromatic hydrocarbons, can be used to detect small amounts of substance in/on a much larger matrix. Here we will discuss the use of Laser Induced Fluorescence (LIF) for purposes of site investigation.

The fluorescence of PAHs has both a spectral and temporal component. Real-world environmental samples typically contain at least several (if not dozens) of different PAHs along with other fluorophores, and the PAH fluorescence spectra overlap to form broad and fairly featureless spectral and temporal emission (compared to pure PAH spectra). If we were to record the temporal decay waveforms across the entire spectrum we would record what is called a wavelength-time matrix (WTM) that would describe the fluorescence emission completely. Dakota's LIF systems monitor four unique bands of this emission in real-time.

lif-common fuels
WTM's of common fuels

How It Works

The system developed by Dakota sends excitation light through fiber optic cable strung within rods. The light exits through a window in the side of the probe. As the probe is advanced the soil is exposed to the excitation light. If fluorescent compounds exist (i.e. contaminants) light is emitted. The "signal" light is transmitted through a fiber, back up hole to be analyzed. Responses are indicated in real-time on a graph of signal vs. depth. The graph can also display color logs and waveforms to aid in identification of the contaminant present.

Benefits of LIF

  • Production rate - 200 to 400 ft. per day depending on soil conditions and grouting methods.
  • No samples - LIF collects and displays data in real time. Therefore no samples are collected.
  • Decontamination - With a special rod wiper and no sampling equipment, decontamination is virtually eliminated.
  • Quick results - Results can be printed out before the rods can be extracted from the ground. Providing real-time decision making and results in a true seek-and-find style of site characterization.

lif-screening concept
LIF screening concept

Publications

"In situ Characterization of NAPL with TarGOST® at MGP Sites" (external link, valid 2006-07): R. St. Germain, S. Adamek and T. Rudolph,  Land Contamination & Reclamation, 14(2), 573-578(6) (2006)

"Case study: confirmation of TarGOST laser-induced fluorescence DNAPL delineation with soil boring data" (external link, valid 2006-07): M. B. Okin, S. M. Carroll, W. R. Fisher, and R. W. St. Germain,  Land Contamination & Reclamation, 14(2), 573-578(6) (2006)

"Demonstration of a Method for the Direct Determination of PAHs in Submerged Sediments" (external link, valid 2006-07): T. Grundl, J. Aldstadt, J. Harb, R. St. Germain, and R. Scheweitzer,  Environ. Sci. Technol., 14(2), 37(6), 1189-1197 (2003)

"An  In-Situ Laser-Induced Fluorescence System for Polycylic Aromatic Hydrocarbon-Contaminated Sediment" (external link, valid 2006-07): J. Aldstadt, R. St. Germain, T. Grundl, and R. Scheweitzer, United States Environmental Protection Agency, Great Lakes National Program Office (2002)

"Chemometric treatment of multimode laser-induced fluorescence (LIF) data of fuel-spiked soils" (external link, valid 2006-07): M. H. Van Benthem, B. C. Mitchell, G. D. Gillispie, and R. W. St. Germain,  Advanced Technologies for Environmental Monitoring and Remediation, Tuan Vo-Dinh, Editor, Proc. SPIE, 2835, 167-179 (1996)

 
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