Monitoring Air Sparging Using Resistivity Tomography |
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| Authors: | Susan Schima Douglas J LaBrecque Paul D Lundegard |
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| Institution: | Susan Schitna;is a geophysicist at SteamTech Environmental Services (4520 California Ave., Ste. 210, Bakers field, CA 93309;(805) 322–6478) where she uses electrical resistance tomography for monitoring environmental remediations and other geotechnical applications. She received a B.S. in geophysics from the New Mexico Institute of Mining and Technology in 1991 and an M.S. in geological and geophysical engineering from the University of Arizona in 1994. She is a member of SEG, AGU, AWG, and EEGS. Dr. Douglas J. LaBrecque;received a B.S. in geology from New Mexico State University and an M.S. and Ph.D. in geophysics from the University of Utah in 1982 and 1989, respectively. He is presently an assistant professor of geophysical engineering at the University of Arizona in Tucson, Arizona (The University of Arizona, Department of Mining and Geological Engineering, Bldg. #12, Tucson, AZ 85721). Prior to that he was a professor of geophysics at the University of Missouri-Rolla, and a scientist for Lockheed. His research includes electrical tomography as applied to environmental monitoring and mining exploration. He is a member of SEG, AGU, and EEGS. Dr. Paul D. Lundegard;(Fred L. Hartley Research Center, 376 S. Valencia Ave., Brea, CA 92621) is a research associate working for UNOCAL's Environmental Technology Group. He 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 a member of the American Petroleum Institute Soil and Ground Water Technical Task Force. His research on air sparging behavior involves high-level field investigations coupled with numerical multiphase simulation. |
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| Abstract: | Air sparging is a relatively new technique for the remediation of ground water contaminated with petroleum hydrocarbons. In this technique, air is injected below the water table, beneath the contaminated soil. Remediation occurs by a combination of contaminant partitioning into the vapor phase and enhanced biodegradation. The air is usually removed by vacuum extraction in the vadose zone.
The efficiency of remediation from air sparging is a function of the air flow pattern, although the distribution of the injected air is still poorly understood. Cross-borehole resistivity surveys were performed at a former service station in Florence, Oregon, to address this unknown. The resistivity measurements were made using six wells, one of which was the sparge well. Data were collected over a two-week period during and after several air injections, or sparge events. Resistivity images were calculated between wells using an algorithm that assumes axially symmetric structures. The movement of the injected air through time was defined by regions of large increases in resistivity, greater than 100 percent from the background. During early sparge times, air moved outward and upward from the injection point as it ascended to the unsaturated zone. At later sparge times, the air flow reached a somewhat stable cone-shaped pattern radiating out and up from the injection point. Two days after sparging was discontinued, a residue of entrained air remained in the saturated zone, as indicated by a zone of 60 to 80 percent water saturation. |
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