U.S. EPA Contaminated Site Cleanup Information (CLU-IN)

U.S. Environmental Protection Agency
U.S. EPA Technology Innovation and Field Services Division

Dense Nonaqueous Phase Liquids (DNAPLs)

Detection and Site Characterization

Multi-Component Waste

Induced Fluorescence

The following discussion is taken from Site Characterization Technologies for DNAPL Investigations, EPA 542-R-04-017Adobe PDF Logo.

Induced fluorescence techniques that measure the fluorescent response of a chemical to ultraviolet (UV) light provide a qualitative indication of the presence of contamination in the subsurface. The most likely chemical contaminants to be measured with the equipment commercially available are those containing two or more aromatic rings. The commercially available equipment can be categorized into two design classes based on the method used to generate the UV light used to induce fluorescence: lasers and mercury vapor lamps.

The laser-induced fluorescence (LIF) probe is a sensor that was developed for deployment on a cone penetrometer test (CPT) rig for depth-discrete detection of contaminants that fluoresce. It can, however, be adapted to most direct push rigs. LIF can provide only a qualitative indication of the relative presence of fluorescing chemicals, primarily of polycyclic aromatic hydrocarbons (PAHs). Calcite and several other minerals also fluoresce, so background levels should always be checked to ensure proper readings. Most DNAPL compounds (excluding coal tars and creosotes) do not fluoresce at standard excitation wavelengths; however, LIF may be used to investigate them if there is evidence that they have been mixed with compounds, such as fuels, that do fluoresce. In these cases, fluorescence is used to infer the presence of DNAPLs.

The developer of the LIF equipment has modified the light frequency used by the Rapid Optical Screening Tool (ROST™) to make it more specific to coal tars and heavy oils. The Tar-Specific Green Optical Screening Tool (TarGOST®) tool has been tested by the Edison Power Research Institute and has received favorable comment. More information on ROST™ and TarGOST® is provided below.

Courtesy Vertek Manuafacturing a Division of ARA
Courtesy Vertek Manuafacturing a Division of ARA

The mercury-lamp-induced fluorescence instrument, sometimes referred to as a fuel fluorescence detector (FFD), has been replaced by the developer with a UV light emitting diode (UV-LED). The UV-LED is very similar to LIF except that it uses a UV-LED as its light source. The system uses a metal housing with a sapphire optical window that is mounted above the cone and sleeve strain gauges of a CPT rig. Within this housing are an LED and two photomultipliers. The LED emits a 254-nm UV light through the sapphire window as it is advanced at 2 cm/sec. This light is both absorbed and reflected back through the window. The light absorbed by the MAHs and PAHs is re-emitted at a lower energy by these hydrocarbons. The re-emitted light falls on the two photomultipliers, which turn its intensity into an electrical current that is logged at the surface as output in millivolts versus depth. The higher the current, the more contaminated the subsurface.

Courtesy: Vertek a Division of ARA
Courtesy: Vertek a
Division of ARA

The photomultipliers are set to collect two different ranges of fluorescence emissions. One is sensitive to 280-450 nm wavelengths, and the other is sensitive to 475+ nm wavelengths. By collecting these energy ranges, a comparison can be made between intensities that potentially will allow differentiation between lighter and heavier fuels.

While the UV-LED technology can be used for creosote sites, which frequently contain substantial amounts of naphthalene and anthracene, instruments using UV-LED light sources generally are not recommended for coal tar and heavy oil sites.

For Further Information

Adobe PDF LogoAn In Situ Laser-Induced Fluorescence System for Polycylic Aromatic Hydrocarbon-Contaminated Sediments
J. Aldstadt, R. St. Germain, T. Grundl, and R. Schweitzer.
U.S. EPA, Great Lakes National Program Office, 54 pp, 2002

This report discusses the deployment of a LIF instrument aboard a ship for the purpose of testing sediments for the presence of PAHs.

Adobe PDF LogoDNAPL Source Evaluation at a Portion of the Cabot Carbon/Koppers Superfund Site
J.W. Mercer, J.P. Toth, J.R. Erickson, M. Slenska, and M. Brourman.
Proceedings of the First International Conference on DNAPL Characterization and Remediation, September 25-28, 2006, Pittsburgh, PA.

This case history describes an investigation at a site in Florida where creosote was used for wood treating. The investigation made use of a LIF instrument and direct push soil coring. The LIF instrument produced some false positives that the authors attribute to the presence of calcite.

Adobe PDF LogoHart Creosoting Company, Jasper Texas: EPA Superfund Record of Decision
U.S. EPA Region 6, EPA/ROD/R2006060001481, 123 pp, 2006

This document contains a detailed description of the investigation process at the Hart Creosoting Company in which LIF instrumentation played a prominent role.

Adobe PDF LogoIn-Situ LIF System for PAH Contaminated Sediments
R. St. Germain.
Detailed Investigation of the Minnesota Slip, Featuring Laser Induced Fluorescence: Appendix B. Minnesota Pollution Control Agency, MPCA Technical Document tdr-g1-01, 18 pp, 2002

This report provides a detailed technical description of the ROST™ system and its application to PAH (tar-related) contaminated sediments in the St Louis River at the United States Steel Duluth Works site.

Laser-Induced Fluorescence
U.S. EPA, Hazardous Waste Clean-Up Information website.

This EPA-sponsored page contains a full discussion of the LIF technology.

Adobe PDF LogoMcCormick and Baxter Superfund Site Case Study, Stockton, California
U.S. EPA, Office of Solid Waste and Emergency Response, Technology Innovation Office, 104 pp.

This cost and performance report describes a dynamic field investigation in which CPT/LIF was used to characterize creosote DNAPL at a former wood treating site.

Adobe PDF LogoReal-Time In Situ Detection of Organic Contaminants by Laser-Induced Fluorescence System
J. Solc, J.A. Sorensen, and D.J. Stepan.
DE-FC26-98FT40320-04, 45 pp, 1999

Laser-induced fluorescence imaging (LIFI) is an optical technique in which the fluorescence of compounds irradiated by a laser is measured. The system uses a pulsed excimer laser with a light wavelength of 308 nanometers. LIFI, which can be used to detect either subsurface petroleum hydrocarbons or uranium, provides a method to rapidly survey a site. It can be used to identify contaminant "hot spots," assist in waste cleanup activities, and monitor remedial progress, but it is not sufficiently developed to permit accurate contaminant quantitation. Various versions of LIFI systems have been tested, including hand-held, airborne, and direct push technology systems. The LIF sensor discussed in this report was deployed in a percussion soil probing device.

More Information Within DNAPLS Section of Contaminant Focus on This Topic
Tar-Specific Green Optical Screening Tool (TarGOST®)

The coal tar and heavy oil response to conventional LIF instruments is typically weak. TarGOST® has been developed specifically for these types of contaminants.

Adobe PDF LogoThe Rapid Optical Screening Tool (ROST™) Laser-Induced Fluorescence (LIF) System for Screening of Petroleum Hydrocarbons in Subsurface Soils: Environmental Technology Verification Report
G. Bujewski and B. Rutherford.
U.S. EPA, Environmental Technology Verification Program, 86 pp, 1997

ROST™ detects the presence and quantitates the amount of aromatic petroleum hydrocarbons in the subsurface by the laser-induced fluorescence. The ROST™ is a tunable dye laser-induced fluorescence system designed as a field screening tool for detecting petroleum hydrocarbons in the subsurface. The ROST™ LIF system uses a pulsed laser coupled with an optical detector to make fluorescence measurements via optical fibers. The measurement is made through a sapphire window on a probe that is pushed into the ground with a truck-mounted cone penetrometer. The ROST™ approach permits temporary or permanent installation of the LIF equipment on a CPT truck or other direct push vehicle, although a dedicated ROST™ unit could be installed permanently in a CPT. The CPT LIF system uses a steel probe containing the LIF sapphire optical window as well as the cone and sleeve strain gauges. The excitation and emission optical fibers are isolated from the soil system by a 6.35-mm diameter sapphire window located 60 cm from the probe tip and mounted flush with the outside of the probe. The ROST™ LIF system uses 600-µm diameter fibers that are up to 100 m in length. The ROST™ LIF primary laser uses a neodymium-doped yttrium aluminum garnet pump (Nd:YAG) laser that produces 532-nm light at 50 Hertz (Hz) with a pulse energy of 50 mJ. The light from the primary laser pumps a rhodamine 6G dye laser whose output is then frequency-doubled to produce UV light. The laser system used in the ROST™ is capable of generating wavelengths of light ranging from about 280 nm to about 300 nm, depending on the dye being used. The wavelength of light produced by the ROST™ LIF laser is tunable within this range. The laser system is coupled to a silica-clad UV/visible light-transmitting optical fiber. This fiber and the collection fiber are integrated with the geotechnical probe and umbilical of a standard truck-mounted CPT system.

Adobe PDF LogoThe Site Characterization and Analysis Penetrometer System (SCAPS) Laser-Induced Fluorescence (LIF) Sensor and Support System: Environmental Technology Verification Report
G. Bujewski and B. Rutherford.
U.S. EPA, Environmental Technology Verification Program, 96 pp, 1997

The CPT LIF systems use a steel probe containing the LIF sapphire optical window and cone and sleeve strain gauges. The excitation and emission optical fibers are isolated from the soil system by a 6.35-mm diameter sapphire window located 60 cm from the probe tip and mounted flush with the outside of the probe. The SCAPS LIF fibers are 500 µm in diameter and up to 100 m in length. The SCAPS LIF pulsed laser fiber optic-based system uses 337-nm UV light from a pulsed nitrogen laser with a 0.8-ns pulse width and a pulse energy of 1.4 mJ. The nitrogen laser is coupled to a silica-clad UV/visible light transmitting optical fiber. This fiber and the collection fiber are integrated with the geotechnical probe and umbilical of a standard truck-mounted CPT system. The SCAPS LIF system uses a pulsed laser fiberoptic-based sensor. As the pulse from the laser is launched into the excitation fiber, a photodiode is triggered that generates a synchronization pulse, which is fed into a pulse delay generator. The pulse from this apparatus is used to gate a photodiode array (PDA) detector. Fluorescence stimulated in the in situ soil "sample" by the laser is collected by the emission fiber and returned to a spectrograph, where it is dispersed spectrally on the PDA. This arrangement allows rapid acquisition of spectral data. Readout of a fluorescence emission spectrum performed by an EG&G PARC Model 1460 optical multichannel analyzer requires approximately 16 ms. For a laser firing at a rate of 20 Hz, an entire fluorescence emission spectrum measurement, composed of the average of responses from 20 laser firings, can be collected in approximately 1 second. Under normal operating conditions, fluorescence emission spectra are collected once per second as the penetrometer probe is pushed into the ground at a rate of approximately 1 m/min. This yields a measurement with a vertical spatial resolution of approximately 0.2 feet. A host computer equipped with custom software controls the fiber optic fluorometer sensor system and stores fluorescence emission spectra and conventional CPT sleeve friction and tip resistance data. The host computer is also used to generate real-time depth plots of fluorescent intensity at the spectral peak, wavelength of spectral peak, sleeve friction and tip resistance, and soil type characteristics as interpreted from the strain gauge data. The fluorescent intensity in the spectral window is plotted as a function of depth in real time as the probe is pushed into the soil. The entire fluorescent emission spectrum is stored on a fixed hard disk to facilitate post-processing of the data.

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