Technology Status Report: In Situ Flushing - CLU-IN

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In Situ Flushing Project Summaries GWRTAC Case Study Database GWRTAC ID: FLSH0079 Project Name: University of North Carolina - Bank Formation in Surfactant R City: Chapel Hill State/Province: NC Primary GWRTAC Personal Communication Source (Name/Organization): Project Summary: Joy Hall Black & Veatch Report(s)/Publication(s) (GWRTAC Source): 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. At the University of North Carolina at Chapel Hill, reseachers associated with the Center for Multiphase Research (CMR) have conducted laboratory experiments to quantify the dynamics of surfactant enhanced mobilization of DNAPL, including factors leading to bank formation. The following two articles are available on the internet, and the 1998 article is printed below. 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. Hall and Miller 1998 Reprinted below with written permission from author Joy Hall: Bank Formation During Surfactant Flushing of Porous Media Joy L. Hall and Cass T. Miller As surface sources of drinking water are less able to meet growing demands, the dependence on groundwater has continued to increase in the United States and all over the world. Groundwater is the primary source of drinking water for over 50% of Americans, with over 75% of American cities relying on groundwater for at least part of their drinking water supplies (1). The most common types of groundwater pollutants are organic compounds that are highly immiscible in water (2), often Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 156 of 164 Copyright GWRTAC 1998 Revision 1 Tuesday, November 17, 1998
In Situ Flushing Project Summaries GWRTAC Case Study Database referred to as nonaqueous phase liquids. Denser-than-water nonaqueous phase liquids (DNAPLs) frequently enter the subsurface as a separate phase and migrate downward due to gravity. After the bulk of the DNAPL migrates through the aquifer, discrete "blobs" or ganglia of DNAPL are entrapped, held in the pore spaces by capillary forces. Under low flow conditions typical in aquifers, these blobs of residual DNAPL are immobile and dissolve very slowly, thereby creating long-term sources of contamination (3). Surfactants can be used to dramatically reduce remediation times via increased solubilization through micellar partitioning, increased mobilization through reductions in interfacial tension, or a combination of both. Mobilization has a greater potential to increase remediation efficiency over solubilization alone, but, if uncontrolled, the mobilized DNAPL may sink deeper into the aquifer where it is more difficult to remediate and may contaminate previously pristine portions of the aquifer. Particular mobilization regimes are more easily controlled and thus preferred during surfactant flushing. Bank formation, the creation of a continuous phase of DNAPL at the surfactant front, can lead to increased efficiency in DNAPL removal and may be used to control migration of mobilized DNAPL (4, 5). The purpose of this investigation was to examine the mobilization of residual DNAPL in wellcharacterized, two-dimensional homogeneous porous media during surfactant flushing to 1) determine the critical conditions that lead to different mobilization regimes, 2) quantify the factors leading to DNAPL bank formation, and 3) examine the use of a dimensionless grouping for predicting DNAPL bank formation as a function of viscous and buoyancy forces. For all experiments, a 1:1 mixture of two food-grade, anionic surfactants, sodium diamyl sulfosuccinate (Aerosol AY) and sodium dioctyl sulfosuccinate (Aerosol OT) were selected for the surfactant flushing solution. Tetrachloroethylene, a representative groundwater pollutant, was selected as the DNAPL. Experiments were conducted in two well-characterized cells packed with glass beads. Explanations of the mobilization regimes are given using a dimensionless grouping of system parameters defined as the bank number. The bank number was defined as the total force acting on a DNAPL ganglion in the flow direction divided by the force acting on the same ganglion in a direction perpendicular to the flow. A bank number of 1 indicates a balance in viscous and buoyancy forces. Different bank numbers were achieved by varying the angle of the cell (i.e., the angle of flow) and the surfactant injection rate. For each experiment, an aqueous solution of 1% Aerosol AY/OT was injected into the cell. Upon contact with the surfactant solution, the vast majority of the PCE was immediately mobilized as a separate phase for all experiments. In five experiments, PCE was immediately mobilized downward upon contact with the surfactant solution, forming a PCE pool at the bottom of the cell. This mobilization regime was termed "downward mobilization." As the experiments progressed, the pool grew, moved through the cell, and finally exited the cell. Bank numbers for these experiments ranged from 0.41 to 1.34. Nearly complete downward mobilization in these experiments was expected due to the dominating effect of the gravitational force on the mobilized DNAPL ganglia. Figure 1 is a representative set of images taken at three separate times during a surfactant experiment where downward mobilization was observed, resulting in the formation of a DNAPL pool. Figure 1. Downward mobilization with DNAPL pool formation (Refer to internet source to view) Ground-Water Remediation Technologies Analysis Center Operated by Concurrent Technologies Corporation Appendix - Page 157 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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