The Fugro Geoscience, Inc., (Fugro) Rapid Optical Screening Tool (ROST) is a tunable dye laser system used with a cone penetrometer. The technology provides subsurface information such as detection of aromatic hydrocarbon contaminants in soils.
The ROST consists of a cone penetrometer (CPT) probe connected to a laser-induced fluorescence (LIF) sensor. A complete system consists of a truck, hydraulic rams and controllers, and the probe itself. The weight of the truck provides a static reaction force, typically 25 tons, to advance the CPT probe. The CPT probe, which is mounted on the end of the series of push rods, contains sensors that continuously log tip pressure and sleeve friction. The data from these sensors are used to map subsurface stratigraphy. Conductivity or pore pressure sensors can be pushed into the ground.
The ROST system can be deployed with any conventional CPT system and advanced along with other types of sensors. The CPT probe contains a sapphire window that is mounted flush with the outside of the stainless- steel probe above the cone penetrometer tip. Light from an excitation laser passes through the sapphire window and is directed onto the soil as the CPT probe is advanced. The aromatic contaminants in the soil are fluoresced, and fiber optics return this information to the surface.
The main ROST system components are as follows:
The ROST system can be operated in both dynamic (push) and static modes. In the dynamic mode, the CPT probe equipped with the LIF sensor is advanced into the soil. In this mode, which Fugro refers to as fluorescence versus depth, the excitation laser wavelength and fluorescence emission monitoring wavelength are held constant. The fluorescence emission intensity is plotted as a function of depth below ground surface. The excitation wavelength is tunable across a range of wavelengths (266 nanometers [nm] to 310 nm) in order to capture contaminants such as benzene, toluene, ethylbenzene, xylene, naphthalene, and heavier polynuclear aromatic hydrocarbons (PAH). The emission monochromator is set at a wavelength to capture the peak intensity of the contaminants being investigated.
Once areas of significant contamination have been identified in the dynamic mode, the ROST system can be operated in the static mode to identify fuel types. In this mode, the CPT probe is held at a fixed depth. The fluorescence technician, who is observing the fluorescence signal, can signal the hydraulic operator to halt the push so that this "fingerprinting" information can be obtained. The ROST system also can operate in the static mode when additional push rods are added to the string.
The Fugro ROST system is designed to qualitatively and semi-quantitatively identify classes of petroleum, PAH, and volatile organic compound contamination in subsurface soil samples.
The ROST system was demonstrated in EPA Region 7, at sites in Iowa, Kansas, and Nebraska. The sampling and field analysis was conducted during September 1994. The Innovative Technology Evaluation Report (EPA/540/R-95/519) is available from EPA.
ROST's performance was verified by the Consortium for Site Characterization Technology (CSCT) at sites in California and New Mexico. CSCT is a partnership program involving EPA, the Department of Defense, and the Department of Energy. The CSCT field evaluations were conducted in May and November 1995 and the final report from the evaluation is available from EPA or Fugro.
Since the SITE and CSCT evaluations, multi-wavelength monitoring and continuous product differentiation features have been added to the system. These features are designed to further enhance ROST's detection and source identification capabilities.
EPA PROJECT MANAGER:
Eric Koglin
U.S. EPA
National Exposure Research Laboratory
Characterization Research Division
P.O. Box 93478
Las Vegas, NV 89193-3478
702-798-2432
Fax: 702-798-2261
TECHNOLOGY DEVELOPER CONTACTS:
Andrew Taer
Fugro Geosciences, Inc.
6105 Rookin
Houston, TX 77074
1-800-75FUGRO
Fax: 713-778-5501