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U.S. EPA Technology Innovation and Field Services Division

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Cone Penetrometer Mounted Sensors

From Tech Trends August 1995

CONE PENETROMETER MOUNTED SENSORS

By Lary Jack, EPA National Exposure Research Laboratory, Las Vegas

In August 1994, the EPA Superfund Innovative Technology Evaluation (SITE) Program completed a field demonstration of cone penetrometer-mounted chemical sensors. Two of the technologies evaluated were: (1) the Rapid Optical Screening Tool (ROST) marketed by Loral Corporation; and (2) the Site Characterization and Analysis Penetrometer System (SCAPS) Laser Induced Fluorescence (LIF) developed by the Army, Navy and Air Force. These technologies were designed to detect fluorescing compounds such as petroleum wastes and coal tars with rapid sampling and real-time, relatively low cost analysis of the physical and chemical characteristics of subsurface soil. The inherent advantages of such cone penetrometer sensor systems are the high rate of penetration (speed) and the low level of waste generation. Of particular note, is that much of the data is acquired without stoppage and plotted on continuous logs as the data is obtained.

The SITE demonstration took place at three sites within EPA Region 7, which were selected because of their varying concentrations of wastes (coal tar and petroleum fuels) and their ranges in soil textures. Both technologies are attachments designed to fit a standard cone penetrometer (CP) rig which simultaneously provides a continuous log of subsurface materials. Two fiber optic cables run from the sensor up through the center of the penetrometer rods along with the wires coming from the load cells in the CP. One fiber optic transmits laser induced, monochromatic light from the truck down to the sensor where it passes through a sapphire window on the side of the tool. Since the cone is pushing its way into the earth, the window is in direct contact with the soil; and, the light passes through the window into the soil. The light energy excites hydrocarbon compounds and causes them to fluoresce, with the resultant energy passing up to the second fiber optic cable to an analyzer in the truck. This produces a log of the contamination while the signal from the standard CP head produces (after translation by software) a similar continuous soil classification log.

The SITE demonstration evaluated the effectiveness of these sensor systems in sampling and analyzing the physical and chemical characteristics of each waste site's subsurface soils, by comparing each technology's results to the results obtained using conventional reference methods. The demonstration found that the SCAPS and ROST technologies produced screening level data for the contamination while the standard CP produced screening level soil classifications. Specifically the qualitative assessment showed that the stratigraphic and the chemical cross sections of the SCAPS and ROST, and associated CP sensors, were comparable to the reference methods in their ability to map subsurface contaminant plumes at petroleum fuel and coal tar contamination sites. In most cases, a consistent relationship between the fluorescence data and the reference method data was identified. Increases in contaminant concentrations were generally followed by increases in measured fluorescence. Data from both technologies identified similar zones of subsurface petroleum and coal tar contamination at each of the three demonstration sites relative to the reference methods. Both technologies produced continuous profiles, while the reference methods took only a few selective samples targeting boundaries and zones of contamination. For the SITE demonstration, both technologies could produce relatively continuous data on petroleum or coal tar contaminant distribution over a 30-foot depth in approximately 1.5 hours. (The use of these sensors is restricted to the maximum push depth of the cone penetrometer truck. This depth can be as much as 300 feet, or in the case of the demonstration, 30 to 70 feet.)

Based on the SITE demonstration, these technologies produce screening level data. A powerful aspect of both technologies is that they can be advanced with a standard cone penetrometer to provide continuous descriptions of the subsurface soil concurrently with the chemical data. The combination of chemical and physical sensors allows investigation and remediation decisions to be made more efficiently onsite and will reduce the number of samples that need to be submitted for costly confirmatory analyses. The added benefit of these sensors functioning without requiring physical sampling allows them to produce data in subsurface environments that restrict conventional sampling.

The ROST technology is currently available as a service from the developer. The technology is designed to be operated by trained technicians. The SCAPS technology is designed to be operated by trained technicians from the Army Environmental Center, Army Corps of Engineers, Navy, Air Force and the Waterways Experiment Section. The SCAPS technology is not currently available for use by private citizens or corporations, although it is available to State and Federal agencies. The target contaminants are primarily polyaromatic hydrocarbons; and, most often, this technology is applied at petroleum fuel release sites.

For more information, call Lary Jack at EPA's National Exposure Research Laboratory at 702-798-2373. Innovative Technology Evaluation Reports on ROST and SCAPS, as well as the other cone penetrometer systems evaluated in the SITE demonstration should be available by November 1995.


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