Novel Optical Detection Schemes for In-Situ Mapping of Volatile Organochlorides in The Vadose Zone [report]

S. Michael Angel
2004 unpublished
The long-term objective of this research is to develop a system for measuring and identifying a wide range of volatile organic hydrocarbons, including organochlorides, at ppb levels in-situ in the subsurface ("at-depth") using a fiber-optic REMPI probe. (In this renewal proposal we would also like to expand the range of analytes to include contaminated soil and certain metal pollutants such as Hg and Pb). And, to do this in a ruggedized system that is compatible with existing fiber-optic
more » ... , Raman and fluorescence probes and image guides. The specific focus of much of the proposed work is to identify and optimize those experimental parameters which effect the in-situ determination of organic molecules using resonance-enhanced multi-photon ionization (REMPI). To accomplish this goal we will systematically investigate the dependence of REMPI on laser wavelength, power and other experimental parameters for a variety of high-priority groundwater and vadose zone contaminants to determine optimal measurement conditions. Emphasis will be placed on visible or fiber-optic compatible wavelengths of excitation so that the high transmission of fiberoptics can be fully utilized. A fiber-optic REMPI system is being designed that is suitable for integration into an existing cone penetrometer system being delivered by LLNL. Fiber-optic probe designs that we tested in the first studies will be refined by LLNL. Probe performance will be predicted using previously developed optical techniques 42,43 and also using electrostatic field models. The specific studies that will be performed are described in the following sections. This work is novel in several ways: • visible or fiber-optic compatible wavelengths of excitation will be the focus of much of the work; • the research team is highly multidisciplinary with groups from both academic and DOE labs PI: S. Michael Angel PROJECT NARRATIVE DOE/Office of Science Notice 03-02 Renewal Proposal 13 groups will be working on the same topics but in this project we combine fundamental research (at USC) with technology development (at LLNL). The highly multidisciplinary nature of this research team will improve our chances of successfully completing the project with the generation of technology that can be used by DOE in support of subsurface remediation efforts. Research Changes in Renewal Application The original long-term goals of this research project have not changed. Several tasks have been refined and/or extended based on knowledge gained as a result of our prior research. Prior research accomplishments are described in detail in the Prior Results Section. Research tasks that are still needed to move towards our long-term goals are described in detail in the Research Plan Section. Briefly, most of our original tasks were completed or significant progress was made. However, we underestimated the amount of effort that would be required to make detailed REMPI measurements of chlorinated compounds and interferences using both UV and visible wavelength lasers, to purchase and install the necessary laser systems, and to teach new graduate students to use them effectively. However, this has been a tremendous learning experience for the students and they are now generating high quality REMPI data. We would like to complete the detailed studies of mixtures and interferent compounds that were outlined previously. Also, we would like to expand our studies t o include the measurement of VOC, and Hg and Pb contaminants in soils. We did not forsee the possibility of such measurements in our original proposal but now realize it is a natural extension of our vapor-phase work. In preliminary experiments, described below, we have found that contaminated soil samples can be measured using REMPI following laser desorption by the same laser pulse that is used to make the REMPI measurement. This capability should greatly extend the range of contaminants that can be measured by REMPI to include soils contaminated with VOCs, and also nonvolatile substances like larger organic compounds and even heavy metals. We are also expanding the data analysis section to include multivariate analysis, PLS and simplex optimization as an efficient method for determining the optimal laser wavelengths for REMPI measurements of samples containing mixtures of contaminants. For this purpose we will bring in an expert in the area of multivariate analysis, Professor Steve Morgan, for one year. Preliminary analysis of samples containing 3 and 4-component mixtures of BTEX compounds was successful. We will purchase a low-cost, ruggedized OPO laser system (~$20K) to evaluate new REMPI sensors using soil columns that were designed as part of the original proposed work. This will also be useful to gain experience for future field trials. Field trials are not included in the proposed budget for this fundamental research proposal. However, considerable interest has been shown by those involved in the planning of integrated field demos in our REMPI sensor. We expect to pursue funding in the very near future to participate in a field demonstration, and we feel the REMPI sensor could be field tested almost immediately for selcted contaminants. As a result of our collaboration with LLNL we have found that electrostatic field modeling can be very useful in the design of our REMPI sensors. Thus, LLNL will bring in an expert in this area to help with sensor optimization. LLNL will also construct third generation sensors and deliver a cone penetrometer system and detailed plans to USC in preparation for future field trials. Estimate of Anticipated Unexpended Funds: $0.00 SIGNIFICANCE OF PROJECT TO THE EM MISSION Contributions to The DOE Missions: A stated mission of the DOE is to develop new types of sensors for rapid detection of chemical contaminants in the subsurface including those associated with TRU and mixed wastes with PI: S. Michael Angel PROJECT NARRATIVE DOE/Office of Science Notice 03-02 Renewal Proposal
doi:10.2172/823367 fatcat:74oiycexqffyplz7hh5zmqpcbu