Technology Status Report: In Situ Flushing - CLU-IN

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In Situ Flushing Project Summaries GWRTAC Case Study Database In two experiments, distinct DNAPL banks were formed. For these experiments, the bank numbers were 0.96 and 1.05. Upon contact with the surfactant solution, PCE was immediately mobilized downward, forming a pool at the bottom of the cell. The surfactant solution flowed preferentially along the top of the micro-cell as the mobilized PCE migrated downward, leaving a less permeable region at the bottom of the cell. Because the PCE pool was less viscous than the aqueous phase, the pool moved faster than the aqueous phase and began climbing up the surfactant front. As the PCE climbed up the surfactant front, a bank of PCE formed at this front, i.e., a DNAPL bank formed. Figure 2 is a representative set of images taken from a surfactant experiment with "DNAPL bank formation." Figure 2. Distinct DNAPL bank formation (Refer to internet source to view) In four experiments, less distinct DNAPL banks were formed. PCE was mobilized upon contact with the surfactant front, forming a DNAPL pool at the surfactant/clean water front. As the surfactant mobilized DNAPL, some of the DNAPL moved ahead of the surfactant front, where the interfacial tension increased, retrapping the DNAPL until the front reached it once again. This process resulted in the formation of a DNAPL bank at the leading edge of the surfactant front. This process has been reported elsewhere, by Constantinides and Payatakes (5) and Pennell et al. (6). As shown in the series of images in Figure 3 below, these banks were not as distinct as the banks formed in the two experiments depicted in Figure 2. Figure 3. Diffuse DNAPL bank formation (Refer to internet source to view) In the experiments depicted in Figures 2 and 3, PCE was mobilized in the directions of flow, not in the direction of gravity (as in the downward mobilization experiments depicted in Figure 1). This behavior was expected because of the dominant viscous forces (compared to the buoyancy forces) and because the displaced fluid was less viscous than the flushing fluid. At bank numbers less than 0.8 and greater than 2, the macroscopic flow behavior (i.e., whether downward mobilization or DNAPL bank formation occurs) is easily explained by examination of the relative magnitude and direction of the viscous and buoyancy forces. However, the data suggest that a DNAPL bank may or may not form around a bank number of 1. This is a critical region, where the DNAPL must "climb" up the surfactant/clean water front to form a bank. If the surfactant solution lowers the IFT sufficiently on the upgradient side of the front, then the DNAPL moves down this front and a DNAPL bank does not form. At bank numbers of 2 and greater, though, the force acting on the DNAPL in the direction of flow is sufficiently large that a DNAPL bank always forms. Because the bank number relies on general physical and chemical properties, it should be applicable to flushing of any homogeneous porous media. Further testing is required to verify this hypothesis. References 1. Patrick, R., Ford, E., and Quarles, J., Groundwater Contamination in the United States, Second Edition, University of Pennsylvania Press, 1987. 2. Mackay, D. M. and Cherry, J. A., Groundwater contamination: pump-and-treat remediation, Environmental Science and Technology, 23(6), 630-636, 1989. Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 158 of 164 Copyright GWRTAC 1998 Revision 1 Tuesday, November 17, 1998
In Situ Flushing Project Summaries GWRTAC Case Study Database 3. Pankow, J. F. and Cherry, J. A., Dense Chlorinated Solvents and other DNAPLs in Groundwater, Waterloo Press, Portland, 1996. 4. Hawthorne, R. G., Two-phase flow in two-dimensional systems— effects of rate, viscosity, and density on fluid displacement in porous media, Petroleum Transactions AIME, 219, 81-87, 1960. 5. Constantinides, G. N. and Payatakes, A. C., A theoretical model of collision and coalescence of ganglia in porous media, Journal of Colloid and Interface Science, 141(2), 486-504, 1991. 6. Pennell, K. D., Pope, G. A., and Abriola, L. M., Influence of viscous and buoyancy forces on the mobilization of residual tetrachloroethylene during surfactant flushing, Environmental Science and Technology, 30(4), 1328-1335, 1996. Report(s)/Publication(s) (Additional Information Sources): Hall, Joy L., and Cass T. Miller, 1998: "Bank Formation During Surfactant Flushing of Porous Media", ESENotes, Spring 1998, Vol. 33, Issue 1, University of North Carolina, Chapel Hill, NC, available at http://www.sph.unc.edu/envr/esenotes/spring98/hall.htm. Hall, Joy L., Paul T. Imhoff, Clinton S. Wilson, and Cass T. Miller, 1997: "Surfactant-Enhanced Mobilization of Dense Nonaqueous Phase Liquids in Groundwater Remediation", Center for Multiphase Research News Reprint, Vol. 3, No. 1, Fall/Winter 1997, Department of Environmental Sciences and Engineering, School of Public Health, University of North Carolina at Chapel Hill, available at http://cmr.sph.unc.edu/CMR/home.html. Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 159 of 164 Copyright GWRTAC 1998 Revision 1 Tuesday, November 17, 1998
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Technology Status Report Technology
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ABSTRACT This technology status rep
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LIST OF TABLES Table Title Page 1 I
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1.0 INTRODUCTION / PURPOSE OF STATU
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a laboratory-scale project. As illu
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3.1 Flushing Solutions 3.0 ANALYSIS
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(approximately eight) full-scale pr
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Table 1. In Situ Flushing - Summary
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Table 3 In Situ Flushing - Geology
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Table 4 In Situ Flushing - Recovere
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Full-Scale/Commercial 26% Figure 2.
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Site Remediation 25% Figure 4. In S
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NAPL Removal 34% Figure 6. In Situ
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Figure 8. In Situ Flushing - Distri
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Number of Projects 35 30 25 20 15 1
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Number of Case Studies 45 40 35 30
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25 ft and 50 ft and 10 ft and 100 f
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Unconfined Aquifer 65% Figure 16. I
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In Situ Flushing Project Summaries
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Technology Status Report: In Situ Flushing - CLU-IN

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