Evaluation of Subsurface Oxygen Sensors for Remediation Monitoring


  • Dong X. Li,

    1. Dong X. Li (Unocal, Environmental Technology Group, 376 S. Valencia Ave., Brea, CA 92621) is a research engineer and has been a member of Unocal's Environmental Technology Group since 1991. Currently he is involved in several bioventing field studies using innovative sensor technology. He has worked on vapor biofiltration and soil bioventing for petroleum hydrocarbon removal in the past two years. He also worked on air emission control issues, including hydrogen sulfide abatement in the refinery processes and pilot plant study on Unocal's Selectox process. Dong received a B.S. from Cal Poly University, Pomona, and an M.S. and a Ph.D. from Washington State University, all in chemical engineering.
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  • Paul D. Lundegard

    1. Paul D. Lundegard (Unocal, Environmental Technology Group, 376 S. Valencia Ave., Brea, CA 92621) received a B.S. in geology from the College of William and Mary, an M.S. in geology from the University of Cincinnati, and a Ph.D. in geology from the University of Texas at Austin. He is a California registered geologist and has worked at the Unocal Fred L. Hartley Research Center since 1985. His research on air sparing behavior involves high-level field investigations coupled with numerical simulation.
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Continuous remediation monitoring using sensors is potentially a more effective and inexpensive alternative to current methods of sample collection and analysis. Gaseous components of a system are the most mobile and easiest to monitor. Continuous monitoring of soil gases such as oxygen, carbon dioxide, and contaminant vapors can provide important quantitative information regarding the progress of bioremediation efforts and the area of influence of air sparging or soil venting. Laboratory and field tests of a commercially available oxygen sensor show that the subsurface oxygen sensor provides rapid and accurate data on vapor phase oxygen concentrations. The sensor is well suited for monitoring gas flow and oxygen consumption in the vadose zone during air sparging and bioventing. The sensor performs well in permeable, unsaturated soil environments and recovers completely after being submerged during temporary saturated conditions. Calibrations of the in situ oxygen sensors were found to be stable after one year of continuous subsurface operation. However, application of the sensor in saturated soil conditions is limited. The three major advantages of this sensor for in situ monitoring arc as follows: (1) it allows data acquisition at any specified time interval; (2) it provides potentially more accurate data by minimizing disturbance of subsurface conditions; and (3) it minimizes the cost of field and laboratory procedures involved in sample retrieval and analysis.