Fiber-Optic/Cone Penetrometer System for Subsurface Heavy Metal Detection
This effort will develop a fiber-optic, laser-induced breakdown spectroscopy (LIBS) sensor and cone penetrometer system for subsurface detection and analysis of heavy metals. A rugged, small-sized, multianalyte sensor system will aid in characterizing and remediating contaminated land sites by reducing costs and analysis time. The project consists of a six-month base phase, which if successful may be followed by an 18-month option. The base phase will involve the design, construction, and evaluation of fiber-optic probes and simulated penetrometer configurations to prove feasibility of the concept for analysis of soil samples. Probes will be evaluated for their ability to perform quantitative analysis of Cr and Pb (or other DOE-specified elements). The option would consist of fabricating an integrated, rugged LIBS/penetrometer system to be tested in the laboratory and a DOE field site.
Progress
The mechanical testing of the penetrometer probe housings was completed. Three primary issues were evaluated:
For the first test, the penetrometer housing with the sacrificial tip was pushed onto a heavy steel plate. This test was conducted only for the sacrificial sleeve configuration because we were concerned about deformation of the tip during refusal. Applied Research Associates performed the test and concluded that the sacrificial tips could support the 22 tons of down force (maximum for the truck) without deformity. In addition to the steel plate test, the tip was pushed into the ground until refusal without damage to the machined parts.
For the second test, the probe housings were deployed into several different types of soils and retracted. Both the sacrificial tip and sleeve designs were deployed as required to access the soil for analysis.
For the third test, a small camera was installed in the sacrificial tip housing to produce videotape of the location and characteristics of the soil as the housing is retracted. As the housing was retracted, the video clearly showed the sacrificial tip being left behind and it showed that the soil stayed primarily at the position of the outer surface of the upper portion of the cone. In other words, the video showed that the soil did not "collapse" back into the hole as the penetrometer was retracted. This is important for proper functioning of the focussing optics to produce an adequate spark.
The containers for shipping and deployment of the system were received, and fabrication began. Details of how to specifically mount electrical and optical feedthroughs are being worked on and should be completed by late April.
SEA, with help from Energy and Environmental Research Center (EERC) personnel, worked on finalizing the electrical connection plan between all of the components, specifically the timing of the laser and detection scheme and the RS232 instrumentation control. The end result of this analysis was to use as much off-the-shelf software as possible to minimize time spent writing application-specific software that is inflexible for the developed system. A dedicated software package will not be selected until all of the requirements are determined during field work. Additions and modifications will be made to the detector software to run other instruments. This will continue for several months. This month, a potentially improved method was developed to deliver the laser down the penetrometer to the sensing location. The method is rugged and may produce a better spark analysis than is achieved using optical fibers. This new method uses novel waveguides to deliver the laser, and there is practically no chance of damage from high-power radiation, which is a concern when using optical fibers. For the near future, both methods will be tested; then we will determine which will be more applicable to the present application.
The EERC effort is continuing, and they received return information from the questionnaire they distributed to various heavy metal contaminated sites in Montana.
They are evaluating which sites may be attractive for the laser-induced breakdown spectroscopy system being developed. SEA also supplied the EERC with sample data to start investigating data analysis techniques.
PI: Stephen Saggese, Science and Engineering Associates,
FETC COR: Karen Cohen, (412) 892-6667
February 1997 Report
April 1997 Report
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