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Effect of Porous Media and Fluid Properties on Dense Non-Aqueous Phase Liquid Migration and Dilution Mass Flux

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EFFECT OF POROUS MEDIA AND FLUID PROPERTIES ON DENSE NONAQUEOUS PHASE LIQUID MIGRATION AND DILUTION MASS FLUX By CHRISTIAN T. TOTTEN A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLOR IDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2005

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Copyright 2005 by Christian T. Totten

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iii ACKNOWLEDGMENTS During my time at the University of Florid a, I have received a great deal of help from many people. I would like to thank all of those who gave me assistance, exchanged ideas, or simply listened. My primary thanks go to my advisory committee chairperson, Dr. Michael Annable. His guidance, patience and open door policy have truly made this a great and enjoyable learning experience. I also would like to thank Dr. Joseph Delfino as my cochair for all his guidance and for encouraging me to attend the University of Florida. I also thank my other committee members, Dr. James Jawitz and Dr. Kirk Hatfield, for their teaching and support. I would like to thank Dr. Matt Booth and Dr. Jaehyun C ho for all their help and advice in the lab. Without them, I am not sure if I would be able to find the lab to this date! Fortunately, having a chairperson and cochai r has given me the opportunity to meet and work with students from two research group s. I have met great people and learned as much from them than I have in more formal settings. I thank all of them for their support, advice, knowledge and the o ccasional game of Literati. I must thank the United States Air Force and the Biomedical Sciences Corps for giving me this opportunity by sponsoring me in this endeavor. Special thanks go to Mr. Nelson Gibbs, who supported my application in th e first place. Without his support, this would not have happened. Also, I thank th e Strategic Environmental Research and

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iv Development Program, Department of Defense, who in part funded this research (CU1295: Impacts of DNAPL Source Zone Tr eatment: Experimental and Modeling Assessment of Benefits of Partial Source Removal). Lastly, I must thank my wife, Yvonne, and children, Alec and Simone, for their support and willingness to follow me to wherever the Air Force decides to send us. They have been great in letting me pursue my goa ls and doing whatever it takes to get there.

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v TABLE OF CONTENTS page ACKNOWLEDGMENTS.................................................................................................iii LIST OF TABLES...........................................................................................................viii LIST OF FIGURES...........................................................................................................ix ABSTRACT.....................................................................................................................xi ii CHAPTER 1 INTRODUCTION........................................................................................................1 Background...................................................................................................................1 Geometry and Orientation to Flow........................................................................6 Pooled DNAPL......................................................................................................7 Residual DNAPL...................................................................................................8 Migration process...........................................................................................9 Entrapment process......................................................................................10 Relating Media Property Ch aracteristics to the Contaminant Mass Flux...........12 Binary model................................................................................................12 Fractional mass flux versus fractiona l mass loading and total mass flux....12 Study Objectives.........................................................................................................15 General Methodology.................................................................................................16 Dissertation Organization...........................................................................................19 2 WETTABILITY STUDIES........................................................................................20 Introduction.................................................................................................................20 Theoretical Background..............................................................................................22 Study Objective..........................................................................................................28 Methods and Materials...............................................................................................28 Water/Air Entry Pressure Measurements............................................................28 Oil Entry Pressure Measurements.......................................................................32 Results and Discussion...............................................................................................33 Conclusions.................................................................................................................34 3 INVESTIGATION OF THE RE LATIONSHIP BETWEEN MEDIA PROPERTIES (GRAIN SIZE AND W ETTABILITY) AND MASS FLUX............36

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vi Introduction.................................................................................................................36 Theoretical Background..............................................................................................36 Grain Size............................................................................................................37 Wettability...........................................................................................................39 Study Objective..........................................................................................................42 Materials and Methods...............................................................................................42 General Experimental Procedure.........................................................................42 Hydrophilic Sand Packing Procedure..................................................................42 Hydrophobic Sand Packing Procedure................................................................44 PCE Introduction and Sampling..........................................................................45 Hydraulic Controls..............................................................................................46 Octadecyl Trichlorosilane Treat ment and Retardation Factor............................46 Results and Discussion...............................................................................................47 Grain Size Comparison Re sults and Discussion.................................................50 Wettability Results and Discussion.....................................................................57 Flow By-passing and Rate Limited Mass Transfer.............................................63 Conclusions.................................................................................................................67 4 INVESTIGATION OF THE RE LATIONSHIP BETWEEN FLUID PROPERTIES (INTERFACIAL TENSION AND DENSITY DIFFERENTIAL) AND MASS FLUX....................................................................................................69 Introduction.................................................................................................................69 Theoretical Background..............................................................................................69 Entrapment and Migration...................................................................................69 Interfacial Tension...............................................................................................70 Density.................................................................................................................72 Study Objectives.........................................................................................................72 Materials and Methods...............................................................................................73 General Experimental..........................................................................................73 Density Modification...........................................................................................73 Interfacial Tension Modification.........................................................................74 Results and Discussion...............................................................................................76 IFT Modification Results and Discussion...........................................................76 Density Modification Re sults and Discussion.....................................................79 Flow By-Passing and Mass Tr ansfer Rate Limitation.........................................85 Conclusions.................................................................................................................86 5 INVESTIGATION OF CONTAMINANT MASS FLUX HYSTERESIS................87 Introduction.................................................................................................................87 Theoretical Background..............................................................................................88 Study Objective..........................................................................................................90 Materials and Methods...............................................................................................90 Results and Discussion...............................................................................................91 Conclusions.................................................................................................................93

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vii 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS..............................94 Summary.....................................................................................................................94 Conclusions.................................................................................................................95 Recommendations.......................................................................................................96 APPENDIX A AIR, WATER, AND OIL ENTRY PRESSURE BREAKTHROUGH GRAPHS FOR HYDROPHOBIC MIXTURES.........................................................................97 B TWO-DIMENSIONAL FLOW CHAM BER DISTRIBUTION CONTOURS FOR GRAIN SIZE AND WETTABILI TY EXPERIMENTS..........................................106 C TWO-DIMENSIONAL FLOW CHAM BER DISTRIBUTION CONTOURS FOR INTERFACIAL TENSION AND DENSIT Y MODIFICATION EXPERIMENTS115 LIST OF REFERENCES.................................................................................................120 BIOGRAPHICAL SKETCH...........................................................................................127

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viii LIST OF TABLES Table page 2.1 Calculated contact angles.........................................................................................34 3.1 Calculated bond, capillary and total tra pping numbers ...........................................38 3.2 Media properties.......................................................................................................44 3.3 Correlation analysis using box 28 40/60 (0.32) sand sieve value.........................57 3.4 Correlation analysis using box 22 40/60 (0.32) sand sieve value.........................57 3.5 Force balance data....................................................................................................63 3.6 Theoretical force balance results..............................................................................63 4.1 Density sieve size experiments................................................................................73 4.2 Decane/PCE densities and respective mole and volume fractions...........................74 4.3 Interfacial values tested and respective Span 80 percentage....................................76 4.4 Calculated bond, capillary and to tal trapping number for each IFT........................78 B.1 Injection amount and associated sketch number....................................................106

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ix LIST OF FIGURES Figure page 1.1 Source zone and associated flux across a control plane.............................................4 1.2 Hypothetical source zones of equal ma ss and their relative mass flux values...........5 1.3 Hypothetical flux values per unit mass/volume of contaminant................................6 1.4 Hypothetical source zones of equal mass and their relative values......................13 1.5 Example value curves...........................................................................................14 1.6 Experimental Design................................................................................................17 1.7 Two-dimensional flow chamber design...................................................................18 2.1 Contact angle through aqueous phase of a DNAPL.................................................23 2.2 Example capillary pressure curves illustrating paramenters used............................26 2.3 Water entry pressure/Air entry pressure column design..........................................29 2.4 Volume change as a function of wate r entry head for 50% OTS treated sand.........30 2.5 Volume change as a function of air entry head for 50% OTS treated sand.............31 2.6 Oil entry pressure in the pres ence of water column set-up......................................32 2.7 Water (air), air (water), and o il (water) Entry Pressure Values...............................35 3.1 Schematic diagram of pressures/ forces action on a NAPL globule.........................37 3.2 Schematic diagram of pressures/ forces action on a NAPL globule ........................41 3.3 Two dimensional chamber set-up............................................................................43 3.4 100% OTS treated 30/40 (0.48) sieve sand at 2.5 ml of PCE..................................48 3.5 100% OTS treated 30/40 (0.48) sand contaminant volume versus flux...................48 3.6 Untreated 30/40 (0.48) sieve sand at 4.5 ml PCE content........................................49

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x 3.7 Untreated 30/40 (0.48) sand contaminant volume versus flux.................................49 3.8 30/40 (0.48) sand pooling experiment......................................................................51 3.9 30/40 (0.48) sand experiment PCE distribution.......................................................51 3.10 Volume versus percent ma ss flux grain size comparisons.......................................52 3.11 20/30 (0.68) and 50/70 (0.23) duplicate experiment................................................54 3.12 30/40 (0.48) sieve sa nd curve fit example...............................................................54 3.13 Curve fit comparisons (grain size)...........................................................................55 3.14 versus grain size diameter.....................................................................................56 3.15 30/40 (0.48) Sand 25% OTS mix trace....................................................................58 3.16 30/40 (0.48) Sand 100% hydrophobic mix trace......................................................58 3.17 Volume versus percent mass flux hydrophobic comparisons..................................60 3.18 75% and 100% OTS treated data curve fit examples...............................................62 3.19 Curve fit comparisons (wettability)..........................................................................62 3.20 Example sketch superimposed over 0.5 cm grid......................................................65 3.21 20/30 curve comparison...........................................................................................66 3.22 Hydrophobic sand curve comparisons.....................................................................66 4.1 Span 80 percentage and resultan t interfacial tension Semi-Log..............................75 4.2 Maximum PCE concentration as function of percent surfactant (Span 80).............75 4.3 3 dynes/cm interfacial tension distribution..............................................................77 4.4 47 dynes/cm interfacial tension distribution............................................................77 4.5 Interfacial tension comparisons................................................................................78 4.6 Interfacial tension curve fit......................................................................................79 4.7 Untreated PCE distribution......................................................................................80 4.8 1.1 density distribution.............................................................................................80 4.9 Density comparisons................................................................................................82

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xi 4.10 Density curve fit.......................................................................................................83 4.11 1.4 density distribution.............................................................................................84 4.12 Curve comparisons for 1.1 density PCE in 30/40 sand............................................84 4.13 Curve comparisons for 1.4 density PCE in 30/40 sand............................................85 5.1 Reversible flux loading and dissolution processes...................................................89 5.2 Hysteretic flux loading and dissolution processes...................................................89 5.3 TCE mass increase/dissol ution experiment one.......................................................92 5.4 Breakthrough curve..................................................................................................92 5.5 TCE mass increase/dissol ution experiment two ......................................................93 A.1 Untreated sand air entry pr essure (water saturated).................................................97 A.2 25% Octadecyltrichlorosila ne (OTS) treated air entry pr essure (water saturated)..98 A.3 40% OTS treated air entry pressure (water saturated).............................................98 A.4 50% OTS treated air entry pressure (water saturated).............................................99 A.5 60% OTS treated air entry pressure (water saturated).............................................99 A.6 75% OTS treated air entry pressure (water saturated)...........................................100 A.7 100% OTS treated air entry pressure (water saturated).........................................100 A.8 100% OTS treated water entr y pressure (air saturated).........................................101 A.9 75% OTS treated water entr y pressure (air saturated)...........................................101 A.10 60% OTS treated water entr y pressure (air saturated)...........................................102 A.11 50% OTS treated water entr y pressure (air saturated)...........................................102 A.12 40% OTS treated water entr y pressure (air saturated)...........................................103 A.13 Untreated oil entry pressure (water saturated).......................................................103 A.14 25% OTS treated oil entry pressure (water saturated)...........................................104 A.15 50% OTS treated oil entry pressure (water saturated)...........................................104 A.16 75% OTS treated oil entry pressure (water saturated)...........................................105

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xii B.1 20-30 Sieve trace experiment 1..............................................................................106 B.2 20-30 Sieve trace experiment 2..............................................................................107 B.3 30-40 Sieve pooled PCE trace................................................................................107 B.4 30/40 Sieve trace....................................................................................................108 B.5 40-50 Sieve trace....................................................................................................108 B.6 40-60 Sieve trace experiment 1..............................................................................109 B.7 40-60 Sieve trace experiment 2..............................................................................109 B.8 50-70 Sieve trace experiment 1..............................................................................110 B.9 50-70 Sieve trace experiment 2..............................................................................110 B.10 30/40 Sand 25% OTS mix trace (denatured alcohol (DA))...................................111 B.11 30/40 Sand 50% hydrophobic mix trace (reagent alcohol (RA))...........................111 B.12 30/40 Sand 50% hydrophobic mix trace (DA).......................................................112 B.13 30/40 Sand 75% hydrophobic mix trace (RA).......................................................112 B.14 30/40 Sand 75% hydrophobic mix trace (DA).......................................................113 B.15 30/40 Sand 90% hydrophobic mix trace (DA).......................................................113 B.16 30/40 Sand 100% hydrophobic mix trace (RA).....................................................114 B.17 30/40 Sand 100% hydrophobic mix trace (DA).....................................................114 C.1 Untreated (47 dynes/cm) PCE................................................................................115 C.2 0.025% (13 dynes/cm) Span 80 treated PCE.........................................................116 C.3 0.05% (3 dynes/cm) Span 80 treated PCE.............................................................116 C.4 1.4 Density PCE in 30/40 sieve sand.....................................................................117 C.5 1.1 Density PCE in 30/40 sieve sand.....................................................................117 C.6 1.0 Density in 30/40 sieve sand..............................................................................118 C.7 Untreated 40/50 sieve sand....................................................................................118 C.8 1.1 Density PCE in 40/50 sieve sand.....................................................................119

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Abstract of Dissertation Pres ented to the Graduate School of the University of Florida in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy EFFECT OF POROUS MEDIA AND FLUID PROPERTIES ON DENSE NONAQUEOUS PHASE LIQUID MIGRAT ION AND DILUTION MASS FLUX By Christian T. Totten August 2005 Chair: Michael D. Annable Cochair: Joeseph J. Delfino Major Department: Environmental Engineering Sciences The influence of porous media and flui d properties on Non Aqueous Phase Liquid (NAPL) residual geometry and associated contaminant mass flux characteristics was investigated. Contaminant mass flux is a func tion of the source zone cross sectional area exposed to groundwater flow. Porous medi a and fluid properties affect source zone morphology leading to cross sectional area de velopment. Media grain size and NAPL wettability were varied for relative comp arisons. Fluid properties including density differential and interfacial tension between NAPL and water were varied for relative comparisons. The percent mass flux of perchloroethylene was measured and the relationship between mass flux and mass loading was developed for different systems. Results indicated wettability conditions of the media as well as density differential between fluids had the greatest influence on contaminant flux values from the NAPL source zone. The results showed that as density differential decreased and the media xiii

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became more hydrophobic, the relationship between relative mass flux and percent mass value changed from a non-linear to a linear relationship. Va rying grain size had little effect on the magnitude of ma ss flux values but showed correlation with the mass flux and mass load relationship. The results indica ted that interfacial te nsion between fluids had minimal effect on mass flux values and a consistent logarithmic relationship between mass flux and mass load was observed. Dissolution experiments using trichloroeth ylene were completed to determine the relationship between flux values produced during mass loading and flux values produced during mass reduction. The flux development during loading appears to be hysteretic with flux development during ma ss reduction of dissolution. xiv

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CHAPTER 1 INTRODUCTION Background Non-aqueous phase liquids (NAPLs) are ch emicals that have limited solubility in water. That is, they exist as a separate phase from water. There are two broad categories of NAPLs. NAPLs that are less dense th an water are called light non-aqueous phase liquids (LNAPLs), and those that are denser than water are called dense non-aqueous phase liquids (DNAPLs). Their densities rela tive to water cause each type of NAPL to behave differently when released into an aqui fer. LNAPLs will float to the top of the water table. This characteristic allows eas ier remediation relative to its DNAPL cousin, which tends to sink. A DNAPL will sink through an aquifer until it reaches an impermeable layer where it will collect and reside as a pooled separate phase. They are commonly referred to as sinkers and toxic blobs (Gordon, 1996). If fractures or breaks exist in the impermeable layer, the DNAPL could migr ate deeper making access for remediation more difficult. Most DNAPLs undergo only limited degradation in the subsurface and can persist for many years while slowly re leasing, through dissolution, soluble organic constituents into the grou ndwater (Newell and Ross, 1992) Their persistence in groundwater, combined with their low solubility, poses great challenges for DNAPL remediation. Chlorinated solvents are chemicals used for their dissolving capabilities. Perchloroethylene (PCE) and trichloroethyl ene (TCE) are two of the most commonly 1

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2 manufactured and used chlorinated solvents. DNAPLs such as perchloroethylene are one of the most common groundwater contaminants found because of their extensive use as industrial degreasers as well as a variety of ot her uses. They are of concern because of the health hazards posed to humans (Envir onmental Protection Agency [EPA], 2003a&b; Office of Pollution Prevention and Toxics [OPPT], 1994). Many are also dangerous because of the chemical byproducts produ ced during degradation. For example, trichloroethylene (TCE), used as an industria l degreaser, may degrade into vinyl chloride which is a known carcinogen (EPA, 2003c; NJDHSS, 2002). Perchloroethylene is a colorless organic liquid with a mild chloroform -like odor and has an absolute solubility in water of 150 mg/l (25 oC) and a density of 1.626 g/cm3 (20 oC) (Verschueren, 1983) and has a Henrys constant of 0.0153 atm-m3/mol. Trichloroethylene is a colorless or blue organic liquid and also has a chloroform -like odor similar to that of PCE. Trichloroethylene has an aque ous solubility of 1100 mg/l (25 oC) and a density of 1.46 g/cm3 (20 oC) (Verschueren, 1983) and has a Henrys constant of 0.0103 atm-m3/mol. Although DNAPLs have been used for seve ral decades, only r ecently have they gained attention for causing significant envi ronmental and human health problems. As recently as 1993, the EPA reported that over 60% of sites with organic contamination are likely caused by DNAPLs and that 70% of all superfund sites with groundwater contamination have NAPLs present (Gordon, 1996). For example, the EPA has determined that more than 1 million pounds of PCE were released to land and water between 1987 and 1993 (EPA, 2003a). Consider ing that production and usage of PCE predates this time period, one could assume that more PCE was released before, as well

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3 as since this time period. These assumptions make it apparent that DNAPLs such as PCE are suspected to contaminate a large number of sites. Because of their apparent ubiquity and pers istence in the environment and risk to human health, management of DNAPL contamination in groundw ater sources is critical for providing the public with safe, reliable s ources of drinking wate r. An understanding of how DNAPLs behave in groundwater systems is critical to both management and remediation of DNAPL sources. Many studies have been completed to demonstrate that source zone remediation techni ques can remove a large port ion of the contaminant mass present (Brooks et al. 2002; Falta et al., 1997; Fiorenza 2000;F ountain et al., 1995; Fountain et al., 1996; Jawitz et al., 1998b; Jawitz et al., 2000; Lo we et al., 1999; Martel et al., 1998; Meinardus et al., 2002; Rao et al., 1997). Additionally, a common performance metric for source zone removal has been total mass fraction or volume fraction of contaminant removed (Fiorenza, 2000; Jawitz et al., 1998b; Jawitz et al., 2000; Lowe et al., 1999; Martel et al., 1998; McCray and Brusseau, 1998; Me inardus et al., 2002; Rao et al., 1997). This performance metric may only provide partial assessment of remediation effectiveness. Contaminant flux [M]/[L2][T] is a metric that is becoming more widely used to characterize contaminant source zone s (Figure 1.1) (Einarson and Mackay, 2001). The relationship between mass flux and the mass of contaminant is no t clear (Parker and Park, 2004; Rao and Jawitz, 2003). It is assu med that source longevity is more directly related to mass and volume values; however flux is more a function of how the mass/volume is distributed. How the mass/volume of the DNAPL is distri buted is considered the source zone geometry. How the source zone geometry is oriented with respect to the flow field

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4 creates a transverse area of exposure. Cont aminant flux is a functi on of this transverse area of the source zone exposed to flow. contaminant Flux (J) Control plane SOURCE ZONE contaminant Flux (J) Control plane SOURCE ZONE Figure 1.1. Source zone and associat ed flux across a control plane Figure 1.2 displays hypothetical source zone s of similar mass but oriented very differently with respect to the flow field. The distributions shown on the top of Figure 1.2 display a source zone profile with resultant fluxes annotated with J1 and J2. Each contour represents a discrete and equal mass loading event. The initial loading represented by the inner contour event produces geometries of equal area and hence will produce similar flux values. However, each subsequent loading event would result in each source zone producing diffe rent flux values with J2 ultimately being greater than J1. The lower distributions shown in Figure 1.2 pr ovide a planar view with resultant fluxes annotated with J3 and J4. Again, each contour represents a discrete and equal mass loading event. The initial geometry repr esented by the inner c ontour hypothetically provides the same transverse area, although th ey are dissimilar in shape, resulting in similar flux values. However, each subsequent loading event shows the transverse areas with respect to flow increase more for the geometry represented by J4 than J3. This results in J4 being ultimately greater than J3. This is an example of how similar mass introduction can result in vastly different tr ansverse areas. The resulting dissolution mass

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5 flux values per loading event may look like th ose displayed in Figure 1.3. This exposed transverse area is determined by the orientati on of the source zone to the aqueous flow field. Figure 1.2. Hypothetical source zo nes of equal mass and their relative mass flux values J1 J2 J2>J x y z z x y z J3 J4 J4>J

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6 Figure 1.3. Hypothetical flux values pe r unit mass/volume of contaminant Geometry and Orientation to Flow Here, geometry refers to the shap e of the entire NAPL source zone and orientation is how the sour ce zone is placed with resp ect to the groundwater flow direction. To better characterize orientat ion and geometry, NAPL source zones are divided into two sections that will contribute to mass transfer from the non-aqueous to the aqueous phase. The first section is the resi dual DNAPL suspended in the soil matrix by capillary forces and the s econd is the pooled section wh ere DNAPL collects on top of a less permeable or impermeable layer (Sal e and McWhorter, 2001). This separation identifies the potential difference in DNAPL saturation percentages between each section as well as the potential differe nce in exposed contaminant surface to cross sectional flow. Illangasekare et al. (1995) demonstrated that in general, DNAPL saturation of the contaminant suspended as residual increases as a function of dept h until pooling above a less permeable layer. Hofstee et al. (1998) demonstrated that PCE in a two-dimensional 0 0.05 0.1 0.15 0.2 0.25 0.3 0.001.002.003.004.005.006.00PCE (ml)J/Jmax (C/Cmax) J4J1 or J3 J2

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7 heterogeneous porous medium consisted of water-entrapped PCE and PCE existing as a continuous pool on top of the coarse-fine sand interface. Pooling will continue until the oil entry pressure is reached to allow the DNAPL to displace the water in the finer lower permeability sand (Corey, 2003). Sale and McWhorter (2001) stated that mass transfer occurs primarily at the leading edges of contaminant subzones or ge ometrically separated sources of NAPL and that mass transfer through the remainder of the source will be inhibited by upstream interferences. Additionally, if local equili brium is assumed, the part of the NAPL source providing the largest leading e dge with respect to aqueous flow would be the largest contributor to contaminant ma ss flux. It may be that th e residual NAPL provides the larger leading edge exposure when compared to the pooled portion, and is thus the likely larger contributor to contaminant flux. Pooled DNAPL Pooled DNAPL is that portion of the cont aminant mass that collects on top of an impermeable or low permeability layer in an aquifer (Pankow and Cherry, 1996; Sale and McWhorter, 2001). The pooled portion of a contaminant source will typically have a larger NAPL saturation compared to the por tion of DNAPL trapped as residual. The pooled portion typically w ill spread out horizontally along the boundary of the impermeable or low permeable layer. The pool ing and horizontal spr eading create a thin geometry and an orientation resulting in sm all leading edge exposure with respect to groundwater flow. Because of the larger vol ume compared to the trapped residual and the small mass transfer area, pooled sources ar e likely to produce low flux but persist for long periods of time (Johnson and Pankow, 1992).

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8 Residual DNAPL Extensive work has been focused on studies of media and fluid property interaction and their effect on DNAPL mobilization, pooling and entrapment (Abrams, 1975; Bradford and Leij, 1995; Hofstee et al., 1998; Illangaskare et al., 1995; Mayer and Miller, 1990; Moore and Slobod, 1956; Morrow et al., 1 988; Ng et al., 1978; Patel and Greaves, 1987; Pennell et al., 1996; Ryan and Dhir, 1993) Capillary forces and their ratio to viscous and buoyancy forces play a signifi cant role in DNAPL behavior in the subsurface (Dawson and Roberts, 1997). Granular porous media are typi cally water wet and because of this quality, water will be drawn in to the media by capillary forces. In a water wet environment, the capillary forces can be orders of magnitude larger than viscous forces, resulting in capillarity being the domin ant force. Capillary forces will draw water into smaller pores, leaving oil in the larger po re spaces. The residual oil exists as isolated globules in the larger pore spaces (Moore a nd Slobad, 1956). The shapes of these isolated globules depend on soil homogeneity /heterogeneity which dictates the pore body to pore neck ratio or aspect ratio. Homoge neous packs of uniformly sized media have a low aspect ratio wherein NAPL blobs are spherically shaped, single pore bodies. Heterogeneous packs have a high aspect ratio and are irregularly shaped and can be connected by multiple pores (Chatzis et al., 1983; Cho, 2001; Morrow and Heller, 1985). Residual DNAPL is important because of its ability to produce relatively high contaminant fluxes for a given mass when compared to pooled sources. The contaminant fluxes are a function of residual geometry and orientation to flow. Geometry and orientation of residual DNAPL are determined by migration and entrapment processes.

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9 Migration process The residual NAPL can take on a variety of geometries and orient ations to flow as it migrates through the porous media. It can move vertically or horizontally through the saturated zone. The vertical and lateral migration of DNAPL is of more interest because it is usually oriented 90o to water flow, providing the le ading edges and largest area for contaminant flux production. Vertical m ovement of DNAPLs is described by the following equation (Fetter, 1999): ) ( cos 2w o p tg r r Ho (1-1) where Ho is the critical height or head required to displace water in a pore, is the interfacial tension between liquids, is wetting angle, rt pore is throat radius, rp is pore radius, g is acceleration due to gravity, w is water density and o is DNAPL density. The properties related to media characteristics are rp, rt and The pore throat and pore radii are approximated as functions of medi a diameter (d) as follows (Fetter, 1999): rp = 0.212d (1-2a) rt = 0.077d (1-2b) Horizontal movement of DN APL in the saturated zone becomes important if the pressure gradient causing horizontal moveme nt can overcome gravitation influences. Horizontal flow is given as follows (Fetter, 1999): ) / 1 / 1 ( 2p t or r L dx dP (1-3) where Lo is the length of the continuous DNAP L phase in the direction of flow. In general, DNAPLs can migrate two ways. The first is a finger type geometry that will trickle down through the porous me dia as a thin line producing discontinuous

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10 blobs retained as residual. Contaminant fingering occurs when a uniformly infiltrating front is split into stringers due to inst ability from pore scale permeability variations (Fetter, 1999). Various studies have been conducted to gain a better understanding of fingering causes and behavior (Brewster et al., 1995; Held and Illangasekare, 1995-a; Held and Illangasekare, 1995-b; Hofstee et al., 1998; Illangase kare et al., 1995; Peters and Flock, 1981; Wang and Feyen, 1998). Th e second migration pathway involves a more uniform geometry where the NAPL is in itially distributed in to the pores producing a uniform advancing front and di stribution of trapped NAPL. Th is might be the result of more rapid infiltration or displacement by a viscous NAPL. This type of displacement may be more likley in oil-wet media. Each of these geometries provides large differences in interfacial and overall c ontact area between the aque ous and non-aqueous phases. Entrapment process As mentioned above, NAPL entrapment is di rectly related to capillary forces and their ratio to viscous and buoyancy (gravitati onal) forces. The Capillary Number is defined as the ratio of viscous to capillary forces and the Bond Number is the ratio of buoyancy forces to capillary forces (Perry and Chilton, 1973). Capillary Number os v NC ow w w ca (1-4) Bond Number cos ) / (ow Bon k N (1-5) where vw [L/T] is the pore velocity, w [FT/L2]is the water viscosity, ow [F/L] is the interfacial tension between NAPL and water, [M/L3] is the density difference between immiscible fluids, k [L2] is intrinsic permeability and n [L3L-3] is porosity of the porous medium. Pennell et al. (1996) combined th e Capillary and Bond numbers into a Total

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11 Trapping Number (NT) used to develop PCE desatura tion curves in a one-dimensional chamber. The NT was developed to combine viscous a nd buoyancy forces with capillary forces into a single, comprehensive value. The NT combines force relationships into a single equation and numerical value to al low for simple mobility and saturation characterization. It is important to note that the mobility referred to in relation to trapping number is the ability to mobilize en trapped residual DNAPL and not migration. The NT identifies those media and fluid propert ies important to entrapped NAPL residual and entrapped residual mobility. The NT for a vertical flow system is as follows: NT = |NCa + NBo| (1-6) In the horizontal flow case, it is calculated as follows: Bo 2 Ca 2 TN N N (1-7) Theoretically, changing any of the elements in the Capillary or Bond number could change the overall NT, possibly resulting in different entrapment characteristics for a given NAPL. Pennell et al. (1996) perfor med surfactant flooding where PCE-water interfacial tension was reduced. The result was increased mobility and reduced saturation of entrapped PCE. Additionally, different co mbinations of element values will result in the same Capillary and Bond Number and hence, the same overall NT value. The elements of The Capillary and Bond numbers related to media properties are intrinsic permeability, wettability, and poros ity. For homogenous media of equal size spheres, porosity is a fairly consistent characteristic. However, intrinsic permeability and wettability can be varied greatly by grain size diameter changes and contact angle modification respectively.

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12 Relating Media Property Characterist ics to the Contaminant Mass Flux Binary model The dissolution mass flux generated by a pa rticular source zone as a function of geometry and orientation can be described us ing a Binary Model (Jawitz et al., 2003). The model treats the multidimensional flow fiel d as a collection of non-interacting stream tubes with each tube being either contaminat ed or clean. The collection of stream-tubes would be the entire domain such as an aquifer. The fraction (f) of the stream-tubes contaminated would be the source zo ne and the remaining fraction (1-f) would be the clean portion of the domain. The contaminated fraction (f ) is directly related to source zone geometry and orientation to flow. In general, media and fl uid properties dictate migration and entrapment processes. If medi a or fluid modifications affect source zone geometry, contaminant mass flux values could be affected as a result of changing f values. Fractional mass flux versus fraction al mass loading and total mass flux The hypothetical dissolution mass flux and mass loading relationships displayed in Figure 1.3 provide absolute flux and mass valu es for a given system and how they relate to each other. Another interes ting characteristic of these curv es is their shape. The shape of the curve gives insight into how flux values are achieved during the mass loading process. The shape of these curves could be fit using the following simple empirical model: Y = X where Y represents fractional source strength, X is fractional mass increase and is system efficiency. This is similar to the model approach proposed by Rao et al. (2001) for mass depletion, flux reduction relationships. This model is a retrospective look at the

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13 flux and mass relationships of a given system because they are normalized to each systems maximum mass and flux values. This allows curve shape non-linearity comparison from one system to another. Fi gure 1.4 displays hypot hetical source zones of similar mass or volume and their related values. Figure 1.5 disp lays the range of curves that could be encountered for any given system with determining the shape of the curve. Figure 1.4. Hypothetical source zo nes of equal mass and their relative values x y z z x y z 12 3 4 2> 1 4> 3

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14 Figure 1.5. Example value curves A linear relationship or value of approximately one (1 .0) would indicate a one-toone relationship between fractional mass increas e and fractional flux increase. As the value decreases below 1.0, the curves become logarithmic, indicating higher relative flux increase per fractional mass at lower frac tional mass values. As the fractional mass continues to increase, the increase in fractional flux slows. The lower the value, the more pronounced this loading behavior becomes. The opposite occurs for values greater than one and the curves become expo nential in shape, requiring greater mass to generate most of its fractional flux. It wo uld occur in a system where flux production is delayed during mass loading. One such syst em would be a heterogeneous system where the DNAPL source would gather on a low permeability lens until breakthrough or Example Curves0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 00.10.20.30.40.50.60.70.80.91Fractional mass/volume increasefractional flux increase < 1 > 1 = 1

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15 spilling occurred producing a larger residual cr oss section to produce higher flux values. It could be argued that is an all inclusive value captu ring a wide range of media and fluid characteristics that aff ect dissolution efficiency. Study Objectives Based on the background provided above, the following objectives of this research were to: 1. Determine the relationship between hydrophobic media content and water, air and oil entry pressure and related contact angle values. Water wet, oil wet, and intermediate wet systems were investigated to determine water entry pressure, air entry pressure, and oil entry pressure trends. 2. Determine the relationship between porous media properties and contaminant mass flux. Two media properties, grain size and wettability, were studied to determine their influence on geometry an d contaminant mass flux properties in a two dimensional flow chamber. A reduction in grain size may affect migration and entrapment characteristics and ultimately DNAP L geometry. DNAPL distributions in an oil wet media may influence geometry of a source zone, possibly affecting contaminant mass flux properties. Absolute mass and flux value relationships as well as values were determined for these media systems. 3. Determine the relationship between fluid properties contaminant and mass flux. DNAPL migration in saturated porous medi a is influenced in part by the density differential between the aqueous and non-aq ueous phase. Changing this differential while keeping other characteristics constant could change DNAPL mi gration. This study assessed the influence of reducing the density differential between immiscible fluids and

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16 the effect that differential reduction has on DNAPL migration and associated contaminant mass flux properties. Interfacial tension is an important physical property that can influence migration of DNAPLs such as PCE. Lowering interfacial tension of PCE may increase migration, thereby influencing source zone geometry, and ultimately contaminant mass flux properties. Absolute mass and fl ux value relationships as well as values were determined for these fluid systems. 4. Determine the mass loading and dissolution behavior of TCE. Contaminant mass flux curves generated through mass loadin g were compared to those resulting from mass reduction. This provided insight into the relationship between mass loading and mass dissolution processes. General Methodology The following general overall design was implemented as part of the experimental portion of this research. Various parameters were held constant while a single parameter was varied. The following general set up was used for each experiment. A series of experiments was conducted in a two-dimens ional simulated aquifer experiments in systems as shown in Figure 1.6. The design shown in Figure 1.6 is just an example to show that one characteristic can be varied wh ile others are held constant and is not an indication of the exact variations of this research. The two dime nsional flow chamber employed was similar in design to those used by Jawitz et al. (1998a ) and Conrad et al. (2002), and reviewed by Chev alier and Petersen (1999).

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17 Figure 1.6. Experimental Design The chamber design is shown in Figure 1. 7. The simulated wells on each end of the column had slots at intervals of 4 slots pe r cm and served as the influent and effluent wells. Injection of PCE took pl ace in the center of the chamber as shown in Figure 1.7. PCE injection was made through the wall of the column using a needle securely fixed with epoxy into the glass wall. PCE was in jected through the needle using a gas tight syringe placed on a syringe pump.

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18 Figure 1.7. Two-dimensional flow chamber design The two dimensional flow chamber was p acked uniformly with the appropriate medium for the specific object ive. The top of the medium was covered with Bentonite clay to maintain media pressure saturation and minimize volatile losses. NAPL was injected into the side of the column at a specified rate using the syringe pump. The PCE volume was injected in a stepwise fashion at a particular volume per injection up to a predetermined total volume. All measurements were conducted under steady-state, saturated flow conditions. Effluent samples were collected after the system achieved steady state mass flux. The number of pore vol umes required to achieve mass flux steady state was experimentally derived. An Oil-Re d-O dye tracer was added to the PCE to aid

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19 in visual observation of the PCE in the 2-D co lumn (Jeong et al., 2002). Flow rates were controlled to maintain a constant mass transfer rate from one experiment to another and to aid in comparisons of the va rious experimental results. Samples collected throughout the experime nt were analyzed using a Perkin Elmer AutoSystem XL Gas Chromatograph (GC) with a Flame Ionization Detector (FID). The FID was appropriate because it met the sensi tivity requirements of the expected sample concentrations and its low selectivity was no t impaired by the relatively clean samples (PCE being the only contaminant). Each sa mple was analyzed for PCE concentration which was used to calculate PCE percent mass flux. Dissertation Organization Each of the following chapters, 2-5, is writt en as a stand alone paper. Each chapter contains an Introduction, Methods and Materials, Results and Discussion, and Conclusion. Chapter 2 includes results of the wettability properties study. Chapter 3 discusses results of the media properties study. Chapter 4 presents the results of the fluid properties study. Chapter 5 presents th e TCE mass loading and dissolution study. Chapter 6 is a summary of this research a nd presents major conclusions of the overall effort and identifies recommendations for future research.

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20 CHAPTER 2 WETTABILITY STUDIES Introduction Wettability is the relative affinity of the so lid media for fluids such as air, water or organic immiscible liquid (OIL) (Wilson, 1988). The degree of wettability is a function of the solid surface, OIL properties and comp osition of the water. Hydrophilic sands have an affinity for water because of thei r polarity and are considered water wet. Hydrophobic sands have more affinity for oil, or perhaps air, than water because they have a non polar surface and are considered oil wet. Moore and Slobod (1956) divided soil into three categories which include (1) wa ter wet and (2) oil wet soils, and added (3) intermediate wettability soil. The intermediate wettability category has characteristics of both hydrophilic and hydrophobic media. Understanding wettability is of great intere st to both the environmental restoration and oil industries because oil and contaminan t recovery is greatly influenced by this porous media property. Donaldson (1969) re ported that oil recove ry, as a function of water injected, is greater from water wet cores than oil wet cores. He went on to state that some findings indicate that oil recove ry is better in interm ediate wettability soil environments rather than either extreme. According to Wilson (1988), it is typically assumed in reservoir engineering studies that rock is water wet. However, he report ed that Treiber et al. (1972) studied reservoir rocks from 55 oil reservoirs, 15 being water wet, 3 of intermediate wettability and 37 as oil wet. Although these findings are related to oil reservoirs, it is an indication of the

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21 variability in wettability condi tions that are possible. Powe rs et al. (1996) found that a wide range of wetting conditions can be ex pected following spills of complex NAPL mixtures to the subsurface. Silica surfaces are hydrophilic or natu rally polar and can have their wetting characteristics changed in a variety of ways. Silica surfaces such as quartz sand can be altered by organic material becoming deposited on their surface and/or by the adsorption of polar oxygen-, nitrogen-, or sulfu r-containing compounds. These deposition and adsorption processes can occur through phys ical (heat), chemical (adsorption), or biological means (Wilson, 1988). Wilson (1 988) reported that fires convert heavy waxlike substances in the vegetative cover to an organic coating. Th is organic coating can alter the wettability of characteristics of the a ffected soil. Although this is an example of a physical mechanism, it appears that ultimat ely the coating had adsorbed to the surface of the media, altering wettability. Powers and Tamblin (1993) found that polar molecules of high molecular weight or surfactants added to commercial gasoline as deicers, corrosion inhibitors, or carburetor cleaners increased hydrophobicity as they adso rbed to quartz slides This indicates a potential for a wide range of wettability char acteristics at sites where OIL products have been released. The biological mechanisms that affect s ubsurface wettability are poorly understood (Wilson, 1988). However, it is apparent micro-organisms play an important role in affecting subsurface wettability. Wilson (19 88) reported golf course putting greens at various courses around the country face management problems due to soil hydrophobicity. Under these conditions, a layer occur creating high water content and

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22 anaerobic conditions. This favors growth of microorganisms that deposit hydrophobic coatings of organic metal sulfides on soil particles. It is clear that the assumption of wate r wet subsurface media may not always be appropriate. This is an important assumption impacting a wide range of areas from golf course management, oil recovery, and contamin ant remediation. For example, wettability conditions may impact the effectiveness of DNAPL remediation methods if there is an affinity between DNAPL and media surface. It is important to be able to quantify wettability conditions for better management practices. Theoretical Background Measurement of wettability can be ma de qualitatively and quantitatively. Donaldson et al. (1969) listed several method s for qualitatively assessing wettability. They determined that these methods could only classify a system as water wet or oil wet, but lacked the ability to satisfactorily classify intermediate wettability systems. Powers et al. (1996) demonstrated a qu alitative bottle test that was able to visually distinguish between intermediate wetting systems. This method is qualitative because it determines system wettability based on observation of NAPL distribution between solid and aqueous phase and does not provide a quantitative value. This method is useful for relative system comparisons. This appears to be a quick method for determining relative wettability characteristics for a variety of systems and does not suffer from the same limitations of the methods listed by Donalds on et al. (1969). Howe ver, when developing oil recovery and remediation stra tegies, a more quantitative approach may be required. Contact angle is often considered the be st measure for quantifying wettability and is widely used (Bahrani et al., 1973; Br adford and Leij, 1995; Fink, 1970; Moore and Slobod, 1956; Letey et al., 1962; Powers et al., 1996; Watson and Letey, 1970). Powers

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23 et al. (1996) and Bradford and Leij ( 1995) reported that the contact angle ( ) between two fluids and a solid surface is the result of mechanical equilibrium or horizontal force balance among the interfacial energi es as described in Youngs equation so sw = owcos( ) (2-1) where is interfacial energy and solid, organi c, and aqueous phases are represented by superscripts, s, o, and w respectively. Direct measurement of the contact angl e is one method fo r quantifying contact angles. Contact angles can be measured by static or dynamic methods. For static methods, advanced or receded contact angl es are measured, while for dynamic methods, the angles are referred to as advancing or receding. The contact angles are usually measured through the aqueous phase with 0o to 90o being water wet and 90o to 180o being oil wet, and neutral wetting around 90o (Figure 2.1). Figure 2.1. Contact angle thro ugh aqueous phase of a DNAPL Powers et al. (1996) reported that vari ous researchers used different ranges of contact angles to categorize neutral wettability. For exam ple, Powers et al. (1996) reported that Treiber et al. (1972) used 72o-105o and Morrow (1976) used 62o-133o. Slobod and Moore (1956) used adva ncing contact angles of near 30o to describe watersolid surface DNAPL aqueous phase = contact angle through aqueous phase

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24 wet systems and angle greater that 90o to be oil wet with intermediate systems in between. An example of a static method was used by Powers et al. (1996). They exposed a quartz slide surface to a variety of organic phases to achieve a variety of wetting conditions. These slides were then submerge d in groundwater and exposed separately to a variety NAPLs including gasoline, diesel fuel fuel oil, crude oil, creosote, coal tar, toluene, and TCE. The NAPLs formed dr ops on the treated slides. DNAPLs were placed on the top of the slides while LNAP L drops formed under the slides. After equilibration was achieved, a goniometer was us ed to directly measur e the contact angle. Advanced angles were measured on each side of the slide. This method is similar to the sessile drop method used by Fink (1970). In th is method, water is added to a flat level surface being tested until furthe r additions increase the drop di ameter, but not the height. The contact angle is a function of this height and therefore can be calculated. Since the water is being added, the advanced contact a ngle is calculated. These methods work well for quantifying homogeneously coated me dia. However, some media may be a combination of a variety of surf aces, some organic and some not. The contact angle of a porous media can be calculated by measuring infiltration rates (Bahrani et al., 1973; Jamison, 1946; and Letey et al., 1962). Letey et al. (1962) used the following equation to calculate contact angles: L rgh nr Q8 ) cos 2 ( (2-2) where Q is the water entry rate at the soil surf ace, n is porosity, r is the capillary radius, is the density of solution, h is the cap illary length plus depth of solution above capillary, is surface tension of solution, L is capillary length and is viscosity of the

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25 solution. In this equation, r and are unknown so a reference fl uid such as ethanol with a known is used to experimentally measure r to be used for other treatments. Water entry rates were then experimentally measured for various media treatments altering contact angle. With all other data known, contact angle was calculated using the above equation. Similarly, Bahrani et al. (1973) us ed infiltration rates to experimentally derive penetrability coefficients used to calcul ate contact angle. They derived these penetrability coefficients after each of six wetting and drying cycles. They determined that wetting, leaching and drying cycles chan ge contact angles si gnificantly from one cycle to the next. However, they also de termined that changing surface tension of the water and changes in soil porosity show ed no significant impact on wetting. Letey et al. (1962) determined that infiltration rates did not hold true for sand columns and resorted to capil lary rise at equilibrium, pc = pg. They experimentally measured h using sand columns and calcu lated contact angle using the following equation: gr h ) cos( 2 Contact angle can be represented by capilla ry pressure by the following equation: r p p pow w nw c) cos( 2 (2-4) where pc = capillary pressure, pnw = non-wetting fluid pressure, pw = wetting fluid pressure, ow = interfacial tension between oil and wetting phase, = contact angle and r is capillary tube radius. This relationship between capillary pressu re and contact angle can be used to quantify the wetting characte ristics of a two phase system. The United States Bureau of Mines (USBM) (Donaldson et al., 1969; Powers et al., 1996) and the

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26 Amott-Harvey (Powers et al., 1996) methods are commonly used. Each method uses data obtained from comparing imbibition and drainage capillary pressure/saturation curves (Figure 2.2). Figure 2.2. Example capillary pressure curv es illustrating paramenters used for : (a) USBM; (b) Amott-Harvey wettability indices (Powers et al. 1996) The USBM method compares imbibition and drai nage areas to assign a wettability index using the following equation (Powers et al. 1996): Iusbm = log(A1/A2) (2-5) where A1 is the area under the drainage cu rve to the horizontal axis and A2 is the area above the imbibition curve to the horizontal axis (Figure 2.2). The Amott-Harvey method uses different data from capillary pre ssure curves to calculate a wettability index using the following equation (Powers et al. 1996): ) 1 ( ) (w r o r o s w s ahS S S S I (2-6) where Ss w = difference between saturation at Pc = 0 and the residual saturation of the water phase, Ss o= difference between saturation at Pc = 0 and the residual saturation of the oil phase, and Sr o = residual saturation of the oil phase and Sr w = residual saturation of the water phase. None of these methods di rectly calculate the co ntact angle, however

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27 they do give a numerical value for system we ttability that is direct ly related to contact angle. Fink (1970) experimentally measured br eakthrough pressure for water repellent soils to quantify system wetting. This is essentially equivalent to the entry pressure or hd that can be readily identified and quantified on a typical Brooks-Corey capillary pressure curve. Fluid entry pressures can be determined for air in the presence of water or oil, water in the presence of oil or air, and oil in the presence of water or air. An example would be oil penetrating water saturated hydrophilic porous media. Depending on conditions of the system such as type of o il, water composition, and surface type, the oil will require a certain amount of head or entr y pressure to displace the water in the porous media. These entry pressure values are directly related to system wettability. Fink (1970) used the experimentally determined h (entry pressure) value in equation 2-3 to calculate He compared the calculated values from the sessile drop method to the values calculated using the breakthrough pressu re method. He assumed theoretically they would be equal but determined that they were not. However, he noted that they each showed similar trends, and th erefore each could be used to make relative comparisons between wetting systems. There are many methods for quantifying syst em wettability. It appears that most methods cannot be compared to each other di rectly. However trends can be compared from one method to the next as well as wetting systems can be quantified and compared to each other if a consistent met hod of measurement is used.

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28 Study Objective The objective of this study was to conduc t water entry pressure air and oil entry pressure tests for silica sand with various fractio ns of organic (silane) coated media. This was to quantify system wettability for a water wet, oil wet and intermediate wet systems. Methods and Materials Water/Air Entry Pressure Measurements A series of water entry pressure (WEP) and air entry pressure (AEP) tests were completed for sands with octadecyl trichlorosilane (OTS) treatment percentages of 0, 25, 40, 50, 60, 75, and 100%. Organosilanes such as OTS are effective for changing the surface polarity of the media resulting in an oil-wet environment. Hydrophobic sand was created using an OTS treatment method used by Bradford and Leij (1995) and Le Grange (1993) as follows: 475 ml of denatured or reagent alcohol mixed w ith 25 ml of OTS to create a 5% OTS mixture; 575 ml of 30/ 40 Accusand was added to the 5% OTS solution and mixed for 5 hours. At the completion of mixing, the excess so lution was drained off and the sand was rinsed again with denatured or reagent alcohol. The sand was then heat dried for several hours. To create each of the hydrophobic/hydrophilic percent volume combinations listed earlier, the appropriate amount of OTS treated sand was mixed with untreated sand to create the desired OTS/untreated sand perc ent ratio. Denatured alcohol was used for all experiments. Additionally, reagent alcohol treated sand was used for a second 100% OTS experiment. The WEP and AEP for OTS/untreated sand mi xtures listed above were determined using the apparatus shown in Figure 2.3. For the WEP measurements, each mixture listed in above was packed to a depth of 6 cm in the bottom of a long glass column. The column was plugged at the bottom with a rubbe r stopper with a hole in the center. The

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29 stopper had a stainless steel mesh filter pla ced on top to support the sand in the glass tube. The stopper was attached to a burette using a section of tubing. The burette was placed so that the top was level with th e bottom of the sand in the column. Water was placed in the burette to contact the bottom of the soil column. Figure 2.3. Water entry pressure/A ir entry pressure column design The burette was then raised in approximately 0.5 to 2 cm increments increasing the head of water at the bottom of the sand and allowed to stabilize for several minutes. The volume in the burette was recorded for each in crement. The height at which the volume sand burette column vacuum Flask w/ water

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30 of water began to enter the sand column was us ed as the head required for water entry or WEP (See Figure 2.4). 0 0.5 1 1.5 2 2.5 3 3.5 4 01234567Water Height (cm)Volume (ml) Figure 2.4. Volume change as a function of water entry head for 50% OTS treated sand For the AEP tests, approximately 6 cm of sand for 0, 25, 40, 50, 60, 75, and 100% mixtures was placed in the bottom of a long glass column (Figure 2.3). The top of the column was plugged with a stopper attached to a T valve. The T valve was connected to a vacuum source and the side port of an Erle nmeyer flask. The flask was filled with water and sealed at the top with a rubber stopp er. The stopper had a glass straw with one end submerged in the water. The top of th e flask was attached via rubber hose to the stopper at the bottom of the column. This system was closed looped, preventing the water from leaving the flask. The vacuum was turned on for 15 to 20 minutes to de-gas the water in the flask. The tube attached to the side port of the flask was then crimped, allowing the vacuum to draw the water through the top of the flask and into the bottom of

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31 the column. A vacuum was used to facilitate water saturating the OIL and intermediate wet sand mixtures. Water was allowed to enter the column, saturating the sand as the water was drawn up by the vacuum. When the sand was completely saturated with water, the vacuum was shut off and the top of the flask was detached from the hose. This hose was then placed on the bottom of a burette. Water was allowed to exit the bottom of the column filling the burette until the top of the water table in the column was equal to the top of the sand. The height of the burette and volume of water in the burette was adjusted such that with the water table at the top of the sand, the level of the water was at the bottom of the burette. The burette was then lo wered in increments of 0.5 to 1.5 cm. For each height, the volume in the burette was m easured and recorded. The height at which the volume of water began to enter the burette was assumed to be the head required for air entry or AEP (See Figure 2.5). 0 1 2 3 4 5 6 7 8 024681012141618Negative Water Height (cm)Volume (ml) Figure 2.5. Volume change as a function of air entry head for 50% OTS treated sand

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32 Oil Entry Pressure Measurements A series of oil entry pressure (OEP) test s using PCE in the presence of water were completed for sands with OTS treatment percentages of 0, 25, 50, 75 and 90%. The OEP for these OTS/untreated sand mixtures we re determined using the apparatus shown in Figure 2.6. Each mixture listed was wet p acked to an approximate depth of 5 cm in the bottom of a short glass column. The column was plugged at the bottom with a rubber stopper with a hole in the center. The stoppe r had a stainless steel mesh filter placed on top to support the sand in the glass tube. A rubber tube was attached to the stopper at one end and a burette at the other end. There wa s a three way valve in the closed position between the burette and column. The wate r used for wet packing was degassed with helium for approximately 15 minutes prior to pa cking. This is necessary because silane coated sand has an affinity for air in the presence of water. Figure 2.6. Oil entry pressure in the presence of water column set-up Sand mix Burette w/PCE Column w/water Vacuum

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33 Regardless of degassing, air bubbles were sti ll present during the packing process. The column was sealed and a vacuum applied to fu rther remove the air from the system. The column was then reopened and the sand was tamped down into the column to achieve a tight sand packing. A vacuum was applied again followed by compacting of the sand. This process was repeated until all visible air was removed. The burette was placed so that its top was level with the bottom of the sand in the column. Perchloroethylene was placed in the burette and drained through the three way valve to remove any air from the line while maintaining the water level in the column. After the air ha d been drained, the valve was placed as such to allow the PCE and water to contact. The burette was raised such that the PCE contacted the bottom of the soil column. The burette was then raised in approximately 0.5 to 2 cm increments increa sing the head of PCE at the bottom of the sand and allowed to stabilize for several minutes. The volume in the burette was recorded for each increment and the height at which the volume of PCE began to enter the sand column was assumed to be the head re quired for Oil entry or OEP similar to the process for water entry pressure in the presence of air. Results and Discussion The pressure breakthrough curves for each sand mixture are displayed in Appendix A. Calculated contact angle values are show n in Table 2.1. The contact angles were calculated using equation 2-3 (Fink, 1970) and the WEPa AEPw, and OEPa values as height (cm). Water contact angles decrease d as OTS percentage decreased. All contact angles were >90, indicating oil wet system Contact angles for 25% and 0% mixtures were estimated from the projected capillary ri se shown in Figure 2.7. Air contact angles did not vary indicating air is always the non-we tting fluid. Oil contact angles decreased as OTS percentage decreased, indicating the media becoming more water wet. The

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34 WEPa, AEPw and OEP values as a function of hydrophobic media percentage are displayed in Figure 2.7. The WEPa for the hydrophobic sand decreased from a maximum of 9 cm to 5 cm as the hydrophobic percentage decreased. The mixtures exhibited hydrophobic behavior down to 40% OTS (hydrophobic) sand content. Water entry pressure for the 25% OTS sand content could no t be measured because the water rose by capillary action, indicating the switch from hydrophobic to hydrophilic behavior. The air entry pressure with respect to OTS percentage showed a slight decline from 15 cm to 12 cm in AEPw from 0% to 75% OTS percentage re spectively. The 100% OTS sand showed a slight increase back to 13 cm. This is a s light indication that the untreated sand retains the water or requires more pressure to begi n draining water when compared to the OTS treated sand mixtures. Oil entry pressure was affected by the changing hydrophobicity, requiring less entry pressure as hydrophobi city increased. The point at which entry pressure is no longer required and PCE is drawn into the sand by capillary action appears to be between 75% and 90% OTS treated sand content. Table 2.1. Calculated contact angles % OTS Water in air degrees Air in water degrees OIL in water degrees 100 128.5 25.8 90 90.0 75 121.2 33.8 86.1 60 114.5 33.8 50 114.5 25.8 80.3 40 110.2 28.8 25 90.0 25.8 78.3 0 0.0 0.0 66.1 Conclusions The change in percent OTS treated sand influences water entry and oil entry pressure values. The displayed trend shows that as OTS percentage decreases, water

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35 entry pressure values decreased from 15 cm of capillary rise to -9 cm of entry head. As the OTS percentage increased, the oil entry pres sure values decreased from 6 cm of entry head until reaching 90% at which the sand displayed hydrophobic characteristics and drew the PCE into the media by capillary action. The trend related to air entry pressure showed that AEP values were not sensitive to OTS percentage changes. Bradford and Leij (1995) noted that air is always consider ed the non-wetting flui d, therefore, water would be the wetting fluid regardless of soil treatment. This might explain the insensitivity of the AEP values. Figure 2.7. Water (air), ai r (water), and oil (water) En try Pressure Values for each mixture percentage Note data points +/1cm -15 -10 -5 0 5 10 15 20 0102030405060708090100% OTSHeight (cm) Water Entry Pressure Air Entry Pressure Oil Entry Pressure projected

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36 CHAPTER 3 INVESTIGATION OF THE RELATIONS HIP BETWEEN MEDIA PROPERTIES (GRAIN SIZE AND WETTABILITY) AND MASS FLUX Introduction As Dense Non-Aqueous Phase Liquids (DNAP L) migrate in the subsurface, media and fluid properties influence how and wher e they will travel and distribute. DNAPLs, serve as long term contaminant sources slowly dissolving into the aquifer. Typically, the solubilities of NAPLs in water are quite lo w; however, they are usually orders of magnitude higher than applicable drinking wa ter/clean up standards. An understanding of how porous media and fluid properties affect travel and distributi on behavior is needed to develop effective remediation strategies to manage these long term contaminant sources. Media properties such as soil type media heterogeneity or homogeneity, grain size, grain shape, and wettability charac teristics are needed to characterize DNAPL source zones. These properties influence co ntaminant behavior in sub-surface systems. What remains after migration is contaminant re sidual that is suspe nded or trapped in the porous media as residual and/or pooled on an impermeable layer at a low point in the aquifer. The residual and pooled NAPL surfaces provide a contact area based on geometry and orientation for NAPL to transfer to the aqueous phase. Theoretical Background Porous media grain size and contact angle (wettability) are the common components governing NAPL migration and entrapment processes.

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37 Grain Size Grain size is an important parameter that affects the flow, gravitational and capillary pressures acting on a DNAPL globule in the subsurface. Pennell et al. (1996) proposed a pore entrapment model describing the forces acting on a NAPL globule that affect its mobilization after entrapment. A similar model can be used to observe the forces acting on a NAPL globule during migr ation processes. Figure 3.1 displays the forces acting on a NAPL globule in a pore. Sand Sand Sand Sand NAPL y x waterPcPcPcPcPiPiPiPiPg Sand Sand Sand Sand NAPL y x waterPcPcPcPcPiPiPiPiPg Figure 3.1. Schematic diagram of pre ssures/forces action on a NAPL globule Capillary forces are represented by Pc, injection forces Pi and gravitational forces are Pg. The forces identified are similar to those identified by Pennell et al. (1996) shown in equation 3-1 with the excepti on of the injection force. L

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38 water flow + gravity = capillary n ow w w wr Cos l g q k 2 sin b nr r where 1 (3-1) where w is the fluid viscosity, is the density differential, qw is the darcy flux, kw is intrinsic permeability, l is average length of DNAPL globule, is the angle with respect to flow, is the contact angle, rn is neck or throat radius, and rb is blob radius. As grain size changes, intrinsic permeability changes affecting the flow conditions, the potential length of the globule changes aff ecting globule size and we ight, and the throat radius changes affect capill ary pressure. In a system where groundwater flow is perpendicular to gravitational forces, the flow force will be less significant compared to gravitational forces when determining migrati on behavior in the direction of gravity and transverse to the flow field. Additionally, the flow force is a magnitude smaller through a range of sand sizes when compared to the gravity forces (Table 3.1). Table 3.1. Calculated bond, capillary and to tal trapping numbers us ing equations 1-4 and 1-5 Seive K (cm/sec) Ki(cm2) Nbond Ncapillary NT 20/30 0.149 1.35E-06 6.55E -06 1.50E-07 6.55E-06 30/40 0.143 1.29E-06 6.25E -06 1.50E-07 6.25E-06 40/50 0.091 8.31E-07 4.00E -06 1.50E-07 4.01E-06 40/60 0.088 7.97E-07 3.84E -06 1.50E-07 3.84E-06 50/70 0.063 5.72E-07 2.75E -06 1.50E-07 2.76E-06 The injection force or pressure is the pressure imposed on the NAPL by the injection of the NAPL into the system. This pressure is a function of injection rate and fluid viscosity. This is unique to the lab environment since NAPL injection through a syringe is a common method of NAPL introduct ion into two-dimensional columns. As grain size decreases, the Pc increases against the NAPL glob ule, requiring higher entry

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39 pressure to move the globule from one pore to the next. As the Pc increases, the effect Pg has decreases and Pi becomes more significant near the point of injection. This may cause the globule to migrate in all directions rather than be dominated in the direction of gravity. This effect becomes less significan t the further away the NAPL migrates from the injection port. This effect may possibl y cause more spreading of the NAPL as the grain size decreases. Entrapment processes are also affected by grain size. Maintaining all other components of the NT constant, changing the grain si ze diameter will change the Bond Number and the NT. NAPL residual saturation appear s to be sensitive to changing NT (Dawson and Roberts, 1997; Saripalli et al., 1997) and as NT increased, saturation decreased. This is consistent with the findings of Pennell et al. (1996). Wettability Wettability is a property of interest because of its effect on oil (NAPL) recovery. Wettability in porous media is the relative a ffinity of the solid component of the media for fluids such as air, water or oil (Wilson, 1988). Hydrophili c soils have an affinity for water while hydrophobic soils have an affinity for oil. Soils can become oil wet through physical, chemical, or biological mechanisms (Bradford and Leij, 1995; Wilson, 1988). According to Wilson (1988), physical mechanis ms such as heat can aid in depositing organic material on the soil. The chemical mechanism involves adsorption of compounds that change the surface polarity of the media. It has been reported that cationic surfactants and additives in gasoline can cause water-we t material to become oil-wet (Bradford and Leij, 1995; Powers and Tambin, 1995; Powers et al., 1996). Additionally, Powers et al. (1996) found that complex NAPL mixtures can create a wide range of wetting conditions.

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40 Biological mechanisms are the least und erstood and beyond the scope of this study (Wilson, 1988). Wettability is typically measured by the advancing contact angle for water displacing oil (Bahrani et al., 1973; Moore and Slobod, 1956; Powers et al., 1996). The contact angle formed between two fluid phases and a solid surface is a result of equilibrium among interfacial energies be tween interfaces and is defined by Youngs equation as follows (Powers et al., 1996): soswow (3-2) where is the interfacial energy with s, o, and w representing solid, oil, and water, respectively. Strongly water wet systems have contact angles near 30o while oil wet systems are assigned contact angles of greater than 90o. Contact angle is an important physical parameter when considering vertical mo vement of DNAPLs. It is represented as a required parameter in equation 1-1 in chap ter 1. Additionally, it affects the capillary pressure acting on a DNAPL in a pore. Figure 3.2 displays the pressure forces acting on residual DNAPL in a pore. It is similar to Fi gure 3.1, however, the capillary pressure can act against the DNAPL trapping it in the pore or it can act by pulling the DNAPL out of the pore similar to capillary wicking. Th e direction in which cap illary forces act is dependent on the contact angle between the aqueous phase and DNAPL with respect to the media surface. As the contact angle increases and the media becomes oil wet, capillary forces may act in favor of draw ing the DNAPL into the media by capillary wicking. Equation 3-1 shows that contac t angle has a great e ffect on the capillary pressure of the system. Considering only gravitational and capillary pressures, as the capillary pressure grows, gravitation forces become less influential. As the capillary

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41 forces decrease, gravitational forces become more influential until potentially the contact angle exceeds 90o and becomes an oil wet system. Contact angle is also represented in both the Bond and Capillary Numbers in the denominator as Cos As approaches 90o or an oil-wet system, Cos approaches zero increasing both the Bond and Capillary numbers and thus the NT. This may reduce entrapment potential. Sand Sand Sand Sand NAPL y x waterPcPcPcPcPiPiPiPiPg Sand Sand Sand Sand NAPL y x waterPcPcPcPcPiPiPiPiPg Figure 3.2. Schematic diagram of pressu res/forces action on a NAPL globule with variable capillary pressure

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42 Study Objective The objective of this study was to cond uct two types of two dimensional chamber studies designed to investigate soil media m odifications and their effect on contaminant geometry and orientation, and ultimately, contaminant mass flux and system efficiency. A set of experiments was completed varying grain size and generate mass loading versus mass flux curves. Another set was to comp leted changing the media polarity creating an oil-wet environment and generate mass loadi ng versus mass flux curves. Finally, a two dimensional chamber experiment was conducted to quantify a contaminant pools percent contribution to mass flux compared to th e residual mass contribution. Maximum contaminant mass flux values and system efficiency ( ) values were investigated. Materials and Methods General Experimental Procedure A two-dimensional (2-D) chamber as descri bed in Chapter 1 (Figure 3.3) was used for each media study. An experiment was condu cted for each sand size listed in Table 3.2 and for each hydrophobic media percentage as follows: 25%, 50%, 75%, 90%, and 100% hydrophobic sand. A total of 11 combinations were investigated. Each experiment lasted approximately two weeks in length. The ex perimental endpoint was determined when a physical parameter of the chamber was exceeded, e.g. when PCE infiltrated one or both wells. Hydrophilic Sand Packing Procedure Sand was added through the top of the chamber in approximately 5 cm thick intervals. After each interval the sand was mixed with a st ir bar and then the box was vibrated to settle and compact the sand. All packing was done under water wet

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43 conditions to minimize air entrapment. Th is procedure was continued until the chamber was filled with enough sand to cover the well sc reens (approximately 10 cm). A layer of bentonite clay was added on top of the sand to simulate a confined aquifer and eliminate the complexities of a capillary fringe. E nough clay was added to create a wet clay thickness of approximately 2-3 cm. This p acking procedure was followed for each sand size to provide hydraulic and media consiste ncy from experiment to experiment. Figure 3.3. Two dimensional chamber set-up

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44 Table 3.2. Media properties Grain Size Diameter in mm Seive Size min max avg 20/30 0.50 0.85 0.68 30/40 0.33 0.60 0.48 40/50 0.25 0.42 0.35 40/60 0.21 0.42 0.32 50/70 0.15 0.30 0.23 Hydrophobic Sand Packing Procedure Due to the nature of hydrophobic media, a different packing method was required to ensure that a saturated environment was created. The chamber was dry packed with hydrophobic sand in a similar fashion described using 5cm thick layers and stirring. Dry Bentonite clay was added to the top of the sa nd layer and hydrated wi th a water bottle to create a clay seal over the dry hydrophobic sand. Carbon di oxide was introduced into the influent port of the chamber to purge the ch amber of air. Carbon dioxide was selected because of its high solubility in water. Initially the wells and the effluent port were left open to prevent any air from being trapped in the casing portion of the wells. The wells were then sealed and effluent gas was collect ed in a 0.5 L Tevlar bag attached to the effluent port. The bag was filled and evacuat ed to track the number of pore volumes displaced in the chamber by CO2. Approximately 50 pore volumes were displaced. Water was then introduced into the influent a nd effluent ports of the chamber to facilitate saturating the sand from the sides of th e chamber to the center. The trapped CO2 was dissolved into the water. As most of the chamber became sa turated, an area of trapped CO2 was created in the center of the box as th e water front from each side of the chamber moved towards the center. At this point, the effluent port was released from the water source and water was allowed to flow through the chamber. As the water flowed through

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45 the chamber, the remaining trapped CO2 in the center of the box was dissolved into the water creating a water saturated media. PCE Introduction and Sampling HPLC grade PCE (CAS 127-18-4), colored red with Oil-red-O dye (< 1X10-4 M, CAS 1320-06-05) was used for each experiment. The PCE was injected into the center of the rear of the chamber 6.5 cm from the bot tom and approximately 4.0-4.5 cm from the top of the sand layer, except for the pooling experiment. In the pooling experiment, the injection port was 1 cm from the bottom of th e chamber. The PCE was injected through a 20 gauge stainless steel needle glued into the rear of the box. The needle entered the box at a 90o angle to the glass side and protruded 0.7 cm into the box so PCE entered in the center of the width (1.4 cm) of the box. The needle was attached to a 10 ml gastight syringe attached to a syringe pump. A baseline effluent sample was collected prior to PCE injection. PCE was then injected at a rate of 0.1 ml/min for 5 minutes for a total of 0.5 ml injected. A sufficient number of pore volumes (>8) were passed th rough the chamber to allow the injected PCE to reach a quasi steady state dissolution. Samples were collected after injection to determine the breakthrough characteristics. The number of pore volumes at which concentration did not vary was the point at which steady state was assumed to be achieved. An effluent sample was colle cted in a two ml vial to measure PCE concentration. This was used with the m easured flow rate to quantify the mass flux generated from the injection. Another 0.5 ml of PCE was then injected and allowed to reach quasi steady state with a subsequent e ffluent sample collected. Additionally, an outline of the PCE distribution (light red coloration in the sand) was traced on transparency paper attached to the side of th e chamber to maintain a qualitative record of

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46 the PCE geometry and orientation after each inj ection. Reflected light was used to help identify the PCE when producing the outline. Th e outlines only represent one side of the column and distributions across the thickne ss of the box were not observed. This procedure was repeated until a physical para meter of the chamber was exceeded. This was usually after a total of fi ve to five and a half ml of PCE was introduced into the box over period of approximately two weeks. Sa mples collected in the two ml vials were analyzed using a Perkin-Elmer Gas Chromatograph Auto XL with a Flame Ionization Detector. Turbochrome Navigator 4.1 software was used. The method for detection used was as follows: Carrier Pressure 7.0 psig, 35 oC oven hold for six minutes, Temperature ramp from 35 oC to 110 oC at 5 oC/min, Injection Temp 180 oC, Detector Temperature 250 oC. Hydraulic Controls A constant head was maintained at the influent well using a Marriott Bottle controlling the effluent discharge height. Th e head was maintained at approximately two to three cm above the surface of the sand me dia to accommodate the clay layer. The effluent rate was maintained by adjusting the effluent discharge height. The rate was approximately 0.7 ml/min. This produced a specific discharge of 68 cm/day. Based on a porosity of 0.377, this gives a pore velocity of 180 cm/day. Octadecyl Trichlorosilane Trea tment and Retardation Factor Hydrophobic sand was created using an oc tadecyl trichlorosilane (OTS) treatment method (Bradford and Leij, 1995; Le Grange 1993). Organosilanes are effective for changing the surface polarity of the media re sulting in an oil-wet media. Hydrophobic sand was created as needed by the follow ing method: 475 ml of denatured/reagent alcohol mixed with 25 ml of OTS to create a 5% OTS mixture. Accusand (575 ml of

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47 30/40 mesh size) was added to the 5% OTS solution and tumbled for 5 hours. At the completion of mixing, the excess solution was drained off and the sand was rinsed again with denatured/reagent alcohol. The sand was th en dried for 24 hours. To create each of the hydrophobic/hydrophilic percent combinations listed in Table 3.2, the appropriate amount of OTS treated sand was mixed homogene ously with the untreated sand to create the desired percent ratio. As annotated in Ta ble 3.2, denatured alcohol was used for all experiments. Duplicate experiments were run for the 50%, 75%, and 100% mixtures using the reagent alcohol during the mixing procedure. This sand mixture was then tumbled for an hour to create a homogeneous distribution. Bradford et al. (2000) determined the Freundlich distribution coefficient (Kf sw) f and n for PCE in an OTS treated 20/30 (0.68) sieve sand to be 2.01 and 1.06, respectively. This is nearly a linear relationship. Using the following equation: K Rb 1 (3-3) where b is the bulk density (1.55 g/ml), Kf sw is substituted for K and is the volumetric water content (0.3). The retardation fact or was approximately 11. A minimum of 11 pore volumes were used to achieve temporary steady state. Results and Discussion To gain an appreciation for how some of th e distributions and their associated flux values differed, the hydrophobic and hydrophili c system results are shown in Figures 3.4through 3.7. The hydrophobic or 100% OTS tr eated sand distribution is shown in Figure 3.4 with its associated flux curve shown in Figure 3.5. The untreated or hydrophilic system is shown in figures 3.6 and 3.7. It is obvious how much the geometries differ between these systems and how those differences are reflected in their respective flux

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48 curves. The remainder of this section will discuss the grain size experiments and wettability experiments separately. Figure 3.4. 100% OTS treated 30/40 (0 .48) sieve sand at 2.5 ml of PCE 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.001.002.003.004.005.006.00 PCE (ml)C/Cmax (J/Jmax) Figure 3.5. 100% OTS treated 30/40 (0.4 8) sand contaminant volume versus flux

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49 Figure 3.6. Untreated 30/40 (0.48) sieve sand at 4.5 ml PCE content 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.000.501.001.502.002.503.003.504.004.505.00 PCE (ml)C/Cmax (J/Jmax) Figure 3.7. Untreated 30/40 (0.48) sand contaminant volume versus flux

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50 Grain Size Comparison Results and Discussion For each experiment conducted with different size porous media, a trace sketch of the PCE distribution was generated. A tr ace of the distribution was drawn after each injection reached steady state on a single transparency, resulting in a cumulative distribution drawing (Appendix B). Figures 3.8 and 3.9 are examples of these drawings for the 30/40 (0.48) sand and pooling experiment respectively. A qualitative comparison of the final geometry for each sand size was ma de using the drawings in Appendix B. In general, predictability of geometry and PCE behavior based on sieve size was not obvious. Pooling began in each experiment by the second injection or one ml with the exception of the 40/50 (0.35) sieve experime nt, which appeared to have begun after the fourth injection or two ml. Figure 3.10 shows the quantitative comparison of each volume versus percent mass flux curve for each si eve size and the pooling experiment. In this figure, the C/Cmax values were gene rated by dividing calculated flux values generated from measured PCE concentrations and flow rates by a calculated maximum flux value based on equilibrium solubility limit and applied flow. The values can be thought of as scaled concentration of mass fl ux. These values were then graphed against their associated injection volumes. Each of the curves appears to be non-linear in shape with the exception of the pooling curve. Th e logarithmic shape indicates an initial rapid establishment and increase in flux per unit volume of PCE, followed by a plateau. These results show the first several injections are th e largest contributors to flux with the later injections having minimal impact. This is possibly because the first several injections contribute to the residual geometry with the la ter injections contributi ng more to the pool.

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51 Figure 3.8. 30/40 (0.48) sand pooling experiment Figure 3.9. 30/40 (0.48) sa nd experiment PCE distribution

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52 Figure 3.10. Volume versus percen t mass flux grain size comparisons 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.001.002.003.004.005.006.007.00 PCE (ml)C/Cmax(J/Jmax) 20/30 30/40 40/50 40/60 (22) 40/60 (28) 50/70 30/40 Pool

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This is supported by the results of the pooling experiment, which show the pooling contributes significantly less mass flux per unit volume when compared to the combined residual and pooled values. The 20/3 0 (0.68) sieve sand has the lowest C/Cmax value of 0.27 and the 40/50 sieve sand has the highest C/Cmax value of 0.38. Using the binary model, the maximum C/Cmax value is estimated to be 0.60. This is based on the injection point position of 6cm from the bottom of the 10 cm chamber and assumes residual distributed homogeneously (vertical and depth) from injection point to chamber bottom. The values observed during each ex periment are lower because migration did not produce homogeneously distribute d PCE in the vertical plane. There was no clear pattern between sa nd size and flux values, but there was indication that as grain size decreased, flux va lues increase. To confirm this, additional experiments using 20/30 (0.68) and 50/70 (0. 23) sand was performed. The results are shown in Figure 3.11 and confirm that finer sands produce higher flux values relative to the course sands. This is possibly due to more lateral spreading caused by the finer grain size resulting in a larger cross sectional area. Curves were fitted to data using the Y=X model. Figure 3.12 provides an example of collected data and the associated fit curve for the 30/40 sieve sand. Figure 3.13 displays the fitted curves for each gr ain size. These curves were generated from dimensionless/normalized data to facilitate comparison. The data was normalized by using the maximum mass and flux values fo r each respective experiment. These curves display the contaminant mass flux versus loading characteristics for the sands investigated. Sand sieves 20/30 (0.68), 30/40 (0.48) and 40/50 (0.35) each have virtually

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54 the same values and therefore curve shape. This indicates that the vertical migration from injection to injection of the PCE in each of these sands were similar. Figure 3.11. 20/30 (0.68) and 50/70 (0.23) duplicate experiment Figure 3.12. 30/40 (0.48) sieve sand curve fit example 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.000.100.200.300.400.500.600.700.800.901.00 fraction massfraction mass flux Actual curve fit 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 0.001.002.003.004.005.006.00 PCE (ml)C/Cmax(J/Jmax) 20/30 sieve 50/70 sieve 30/40 Pooled 20/30 sieve 50/70 sieve

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55 Figure 3.13. Curve fit comparisons (grain size) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.000.100.200.300.400.500.600.700.800.901.00 Fraction VolumeFraction Mass Flux 20/30 (0.41) 30/40 (0.40) 40/50 (0.42) 40/60 (0.07) 50/70 (0.22) 40/60 (0.24)

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The duplicate experiments for the 40/60 (0.32) sieve sands were performed and identified as boxes 22 and 28. A comparison of these two experiments displays the variability of migration characteristics. This could be due to the wider sieve range relative to the other sands. Figu re 3.14 graphically displays the and grain size relationship with one line representing box 22 data and the other using box 28 data. The 50/70 sieve sand demonstrated the most efficient loading by developing the largest percentage of its flux value at a lower mass percentage. Tables 3.3 and 3.4 display the correlation analysis between each of the sands physical characteristics and its estimated value. Figure 3.14. versus grain size diameter R2 = 0.5562 R2 = 0.3867 0 0.05 0.1 0.15 0.2 0.25 0.3 0.35 0.4 0.45 0.5 00.10.20.30.40.50.60.70.8 diameter (mm) value Box 28 Box 22 Linear (Box 28) Linear (Box 22)

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57 Table 3.3. Correlation analysis us ing box 28 40/60 (0.32) sand sieve value bx28 diameter variancesurface area hydraulic conductivity beta 20/30 0.68 0.27 146 8.98 0.44 30/40 0.48 0.12 275 8.57 0.40 40/50 0.33 0.08 301 5.49 0.42 40/60 0.32 0.13 307 5.27 0.24 50/70 0.23 0.05 423 3.78 0.22 r r2 diameter 0.75 0.55 variance 0.53 surface area -0.77 Hydraulic conductivity 0.78 Table 3.4. Correlation analysis us ing box 22 40/60 (0.32) sand sieve value bx22 diameter variancesurface area hydraulic conductivity beta 20/30 0.68 0.27 146 8.98 0.44 30/40 0.48 0.12 275 8.57 0.40 40/50 0.33 0.08 301 5.49 0.42 40/60 0.32 0.13 307 5.27 0.07 50/70 0.23 0.05 423 3.78 0.22 r r2 diameter 0.62 0.38 variance 0.35 surface area -0.55 hydraulic conductivity 0.65 Wettability Results and Discussion As performed for the grain size compar isons, in each experiment (percent wettability) a trace sketch of the PCE distribution was generated. A trace of the distribution was drawn after each injection reached steady state on a single transparency, resulting in a cumulative dist ribution drawing (Appendix B). Figures 3.15 and 3.16 are examples of these drawings. A qualitative comparison between the geometries for 0%,

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58 25%, 50%, 75%, 90% and 100% media mixt ures was made using the drawings in Appendix B. Figure 3.15. 30/40 (0.48) Sand 25% OTS mix trace Figure 3.16. 30/40 (0.48) Sand 100% hydrophobic mix trace

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59 In general, as the hydrophobicity increa sed, the PCE distributed more uniformly and with increasing connectivity. Because of the water wet media used in the 0% experiment, the PCE was not subject to the globbing observed in the 25%, 50% and 75% mixtures and appears to have been more evenly distributed than the intermediate hydrophobic media. The globbing observed is when the PCE would collect in discrete concentrated sections in the media and did no t have a more uniform distribution. The 0%, 25%, 50% and 75% mixtures displayed a fing ered distribution with the 90% mixture beginning to transition to the more uniform spreading shown in the 100% mixture. Additionally, capillary wicking was primarily observed in 100% mixtures with some minimal wicking occurring in the 90% mixt ure. Apparently, a significant amount of the media (> 90%) must be OTS treated to allow capillary forces to overcome gravitational forces and cause unifor m lateral and vertical spreading. A quantitative comparison was made and shown in Figure 3.17. The flux is presented as C/Cmax or J/Jmax since flow rate (Q) and area is constant is each experiment. In general, the 100% an d 90% mixtures appear produce the higher maximum percent mass flux values when compar ed to the intermediate and 0% mixtures. Comparing these curves to their associated sketch, it appears the ve rtical movement of the PCE above the injection point was the diffe ring factor in flux production. More PCE exposure to the horizontal aqueous flow appear s to have resulted in higher flux values. There appears to be little difference in fl ux values between the 0%, 25%, 50% and 75% mixtures. This might be due to the interm ediate mixtures providing similar overall surface area contact between the PCE and aqueous phase as the 0% sand

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60 Figure 3.17. Volume versus percen t mass flux hydrophobic comparisons 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.001.002.003.004.005.006.00 PCE (ml)C/Cmax(J/Jmax) 100% (RA) 25% (DA) 50% (DA) 75% (DA) 90% (DA) 100% (DA) untreated 50% (RA) 75% (RA)

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The intermediate soils tended to collect the PCE residual in disconnected globs while the 0% appeared to a more evenly distributed fingered residual. Additionally, Moore and Slobad (1956) found that porous media of the intermediate wettability had lower water imbibing tendency than in the st rongly water wet system. They state that imbibition, though still present, is not the do minating displacement process. As a result, the capillary and viscous forces are of equal importance and the water will flow down both sizes of pores at nearly the same velocity. The result is lowered oil saturation at breakthrough compare to either wettability extremes. As examples of the wettability curve fit data, Figure 3.18 displays the 75% and 100% OTS treated sands data and associated fit curves. Figure 3.19 displays the fitted curves for each wettability percentage. Ther e is little difference between the shapes of the curves for 0%-90% hydrophobicity. The 100% RA treated sand and 100% DA treated sand are more linear relative to the other sands and demonstr ated by their higher values. This may be due to capillary forces countering gravitational forces, causing a slower vertical downward migration and th us, a less efficient system. This may be explained by the force balance performed usi ng equation 3-1 and the system data listed in Table 3.5. Flow forces were ignored due to or ientation of flow with respect to gravity. Table 3.6 displays the results of theoreti cal capillary rise, h, and both gravity and capillary pressures acting on the NAPL globule. The force balance indicates that gravity pressures remain constant with changing cont act angle. However, as the contact angle increases and the system becomes oil wet, gravity may become more significant. Additionally, in order to achieve capillary rise, the system must become oil wet as indicated by the 90o contact angle. According to the entry pressure findings in Chapter

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62 two, the system becomes oil wet at approximately 90% OTS treated sand content. This supports why the system must be >90% treate d sand in order to achie ve capillary rise and overcome gravitation forces. Figure 3.18. 75% and 100% OTS treated data curve fit examples Figure 3.19. Curve fit comparisons (wettability) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.000.200.400.600.801.00 Fraction VolumeFraction Mass Flux 75% (0.39) 75% actual 100% actual 100% (0.52) 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.000.100.200.300.400.500.600.700.800.901.00 Fraction VolumeFraction Mass Flux UT-90% (0.39) 100%DA (0.72) 100%RA (0.52)

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63 Table 3.5. Force balance data = 90degrees rp=0.0106cm l= 0.0212cm d= 0.05cm rt=0.00385cm = 0.636792 = 0.65g/ml g=980cm/sec2 oil= 1.65g/ml = 47dynes/cm Table 3.6. Theoretical force balance results Cos( ) h (cm) capillary pressure 0 1.00 -38.3 155E2 10 0.98 37.7 153E2 20 0.94 36.0 146E2 30 0.87 33.2 134E2 40 0.77 29.3 119E2 50 0.64 24.6 9993 60 0.50 19.1 7773 70 0.34 13.1 5317 80 0.17 6.66 2699 82 0.14 5.33 2163 84 0.10 4.01 1625 86 0.07 2.67 1084 88 0.03 1.34 542 90 0.00 0.00 0.00 92 -0.03 -1.34 -542 94 -0.07 -2.67 -1084 96 -0.10 -4.01 -1625 98 -0.14 -5.33 -2163 100 -0.17 -6.66 -2699 110 -0.34 -13.1 -5317 120 -0.50 -19.1 -7773 130 -0.64 -24.6 -9993 140 -0.77 -29.3 -119E2 150 -0.87 -33.1 -134E2 160 -0.94 -36.0 -146E2 170 -0.98 -37.7 -153E2 180 -1.00 -38.3 -155E2 Flow By-passing and Rate Limited Mass Transfer Concentrations of NAPL compounds in groundwater are usually less than their aqueous solubility due to irregular distribut ions, non-uniform flow patterns, dilution and sorption effects, and rate limited mass transfer (Hunt, et al., 1988; So erens et al, 1998).

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64 Powers et al. (1992) performed one-dimensional column experiments to determine the physical characteristics which affect mass transfer rates. These experiments were performed using homogeneously distributed NAPL source zones and determined that grain size, source zone length and Darcy veloc ity impact mass transfer coefficients under one dimensional column conditions. This method may overestimate mass transfer coefficients when applied to heterogeneous ly distributed NAPL source zones such as those created in this research. Soerens et al. (1998) concluded that nonequilibrium or non-ideal dissolution of NAPL can be represented by mass transfer rate limitations, flow by-passing due to media or distribution heterogeneities, or a comb ination of these mechanisms. Experimental curves generated from this research were compared to ideal equilibrium curves and curves developed using mass transfer rate estimations to determine if potential flow by passing, rate limitation or both is occurring. The equilibrium and mass transfer curves were developed for the 20/30 (0.68) sand and 100% hydrophobic sand experiments. Figure 20 shows an example of a sketch superimposed over a 0.5 cm grid. The equilibrium curves were determined by assuming equilibrium dissolution has been reached after each loading event. The equi librium curve was constructed by estimating the percentage of the flow field exposed to PCE after each loading event. This was done by adding the number of verti cal grids containing PCE and di viding it by the total grid height. The mass transfer rate curves were developed by calculating the modified Sherwood number used by Powers et al. (1992). The Modified Sherwood number was then used to estimate the mass tr ansfer rate and finally the C/Cs as a function of length of the PCE per each grid height.

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65 Figure 3.20. Example sketch superimposed over 0.5 cm grid Figures 3.21 and 3.22 display the resulta nt equilibrium and mass transfer rate estimated curves in relation to the expe rimental data generated curves. Figure 3.21 displays the results for the 20/ 30 (0.68) sand and indicates that based on the length of the source zone after each loading event, that equilibrium may not have been achieved. Additionally, the experimental data curve is lower than the mass transfer rate generated curve. This indicates that both flow by-passing and mass tran sfer rate limitation may be occurring. Figure 3.22 shows the results for the 100% hydrophobic sand (30/40) and it indicates that the source zone is sufficient in length throughout th e loading event that equilibrium is achieved. Additionally, the e xperimental data compares relatively well to the equilibrium and mass transf er rate curves, however sti ll indicating some potential bypassing. The hydrophobic data compares more favorably than the 20/30 sand because it 1cm

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66 achieves equilibrium and possibly has less by-passing because of the uniform distribution of the PCE resulting from capillary wicking in the hydrophobic media. 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.001.002.003.004.005.006.00PCE (ml)C/Cmax(J/Jmax) Experimental Equilibrium Non-Equilibrium Figure 3.21. 20/30 curve comparison 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.001.002.003.004.005.006.00 PCE (ml)C/Cmax(J/Jmax) Experimental Equilibrium Non-Equilibrium Figure 3.22. Hydrophobic sand curve comparisons.

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67 Conclusions Grain size did not appear to affect the geometry of the residual and pooled PCE in such a way that was predictable. The grain size appears to affect the percent flux, with the flux increasing as the grain size decreases. It appears the determining factor for mass flux values was the cross sect ional exposure of the PCE to perpendicular aqueous flow. The residual PCE portion was found to contribute the larges t portion of mass flux relative to the pooled section, although the pooled sec tion appears to be wher e the majority of the PCE collected. Assuming local equilibrium assumption, pores with PCE present may likely reach the solubility limit of the PCE, regardless of saturation percentage. Based on this assumption, each experiment should produce similar flux values because the vertical exposure of the PCE to the aqueous flow fo r each experiment was the same, however, the lateral distribution is not the same due to sp reading. As the grain size decreases, more lateral spreading of PCE occu rs, increasing flux. The pool ed experiment supports the hypothesis that the residual mass produces the largest percentage of flux relative to the pooled source flux. The pooled source flux produce 0.05% of C/Cmax with the combined residual and pooled sources produc ing a range from 0.27 to 0.38 C/Cmax. In general, remediating the residual may remove relativ ely small amounts of PCE compared to the possible total mass, but could provide the grea test reduction in fl ux values. However, pooled flux values are still greater than clean-up requirements and will be a persistent flux source. The mass loading/mass flux efficiency or values are somewhat correlated to grain size. The wettability experi ments showed that nearly all (> of the media must be OTS treated top affect residual geometry and percent mass flux values. As the media

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68 approached 100% hydrophobicity, the capi llary forces were able to overcome gravitational forces and spread the PCE abov e the point of injection. Although lower hydrophobic mixture percenta ges may not produce increased mass flux values, because of capillary forces retaining the PCE, removal of PCE from the pore may be difficult because of its affinity for the media surface. he mass loading/mass flux efficiency ) only became affected after a significant portion of the sand was treated (>90%). Otherwise, there is consistency in values for the remaining sands. Flow by-passing and mass transfer rate limitation may be occurring resulting in lower than expected experimental values. Qualitatively, most of the source zones produced are of sufficient length to achieve equilibrium indicating that by-passing is the most likely cause of lowe r than expected values.

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69 CHAPTER 4 INVESTIGATION OF THE RELATIONS HIP BETWEEN FLUID PROPERTIES (INTERFACIAL TENSION AND DENSITY DIFFERENTIAL) AND MASS FLUX Introduction Chlorinated solvents such as perchlor oethylene (PCE) are commonly found at many contaminated sites. They have been popular as industrial degreasers and because of past poor management practices and the th reat they pose to human health, they have become a major concern at many contaminated sites throughout the coun try. It is likely that many chlorinated solvents have been used with a variety of different chemicals during various industrial processes and ac tivities. The chemicals comprising these mixtures could interact creating a single new mixture, causing them to behave in the sub surface in very different ways than as single separate components. Depending on the mole fractions of each component, miscibility and a variety of other conditions, surface and bulk properties for the new mixture ca n be vastly different from its individual separate predecessors (Brusseau, 1993; Seo a nd McCray, 2002). Surface activity such as interfacial tension and bulk pr operties such as density di fferential between aqueous and non-aqueous phases can be affected (B russeau, 1993; Seo and McCray, 2002). Theoretical Background Entrapment and Migration The common fluid to fluid properties re presented in both the entrapment and migration processes are density differential and interfacial tension between aqueous and non-aqueous phases. As previously discu ssed in Chapter 1, contaminant flux is a

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70 function of surface contact area between aq ueous and non-aqueous phases and contact area is a function of geometry and orientatio n to flow of the contaminant source zone. Entrapment and migration were the two pro cesses discussed that influence source zone geometric and orientation development. DNAPL vertical and horizontal migration processes are governed by the following equations: ) ( 2wo p tg r r Cos Ho (4-1) ) / 1 / 1 ( 2p t or r L dx dP (4-2) where Ho is the critical height or head required to displace water in a pore, is the interfacial tension between liquids, is wetting angle, rt pore is throat radius, rp is pore radius, g is acceleration due to gravity, Lo is the length of the continuous DNAPL phase in the direction of flow, rw is water density and ro is DNAPL density. Additionally, using the force balance equation from Chapter 3, it can be seen that changes in density differential affect the gravitational pressure, and changes in the interfacial tension can affect the capillary pressure of the system. These parameters also affect the entrapment process which is described using the Capilla ry and Bond numbers discussed in Chapter one. Interfacial Tension Interfacial tension (IFT) results from the co-existence of immiscible liquids at different pressures and is measured by the for ce that exists in the interface separating the two fluids (Pankow and Cherry, 1996). Th e interfacial tensi on between water and another chemical only exist when the fluids are immiscible. In particular, the surface tension of chlorinated solvent DNAPLs with re spect to water has a significant impact on how chlorinated solvents penetrate the capilla ry fringe and migrate through the saturated

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71 zone. As the chlorinated solvent migrates thro ugh the capillary fringe, it is held up by the capillary retention of water until enough head is built up to overcome retention. The capillary retention is directly proportiona l to the interfacial tension and inversely proportional to radius of curvature (Lowe et al., 1999). As interfacial tension increases and pore size and density decreases, more head is required to produce downward migration. This may result in a lateral move ment of liquid along la yers of finer grain sands. Interfacial tension properties of DNAPLs are important when considering remediation techniques. Surfactants alter interfacial tension between immiscible fluids by altering fluid interfaces. They accomplish this through the nature of their amphiphilic structure. Surfactants are typically mol ecules with a hydrophilic group or head at one end attached to a long hydrophobic hydrocarbon chain or tail. The hydrophilic head will have an affinity for water while the hydrophobic ta il will have an affinity for non-aqueous contaminants or oils. Surfactants are classifi ed by the nature of th eir hydrophilic groups, which are anionic, cationic, and non-ionic. An ionic surfactants give rise to a negatively charged surfactant ion and a positively char ged counter-ion upon disso lution in water. They are sensitive to the presence of salts in solution. Cationic surfactants yield a positively charged surfactant ion and a negatively charged counter-ion upon dissolution in water. Cationic surfactant s are not widely used because of their potential toxicity (Lowe et al., 1999). Nonionic surfactants do not ionize in wa ter and are insensitive to the presence of salts in solution. The amphiphilic structure allows the surf actant to accumulate at the NAPL-water interface. The hydrophilic group resides in the aqueous phase with the hydrophobic tail

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72 residing in the NAPL. Depending on the co ncentration of surfact ant at the interface, NAPL solubility and/or interfacial tension will be modified. The manner in which the surfactant distri butes in a surfactant-water-NAPL system is categorized by three systems. Winsor Type I, II, and III. The Winsor Type I system has micelles of oil droplets in the aqueous phase. Winsor Type II creates reverse micelles with droplets of water in the oil phase. Winsor Type III is a middle phase micro-emulsion with ultra-low interfacial tensions. Density Density plays an important role in DNAPL migration. It is the property which defines a liquid as being dense or light relative to water. If a liquid is determined to be dense, it has a specific gravity greater than one and if it is light, its specific gravity is less than one. In many situations, NAPL density varies from water by 10-50%, with only a 1% difference being needed to influence fl uid movement (Mercer and Cohen, 1990). Because of the density differential, DNAPLs may move down a physical gradient counter to the hydraulic gradient; however, this can be impeded by capillary and/or impermeability resistance. DNAPL spreadin g will occur along pathways of least capillary and permeability re sistance (Mercer and Cohen, 1990). This must be considered when determining the location of DNAPLs in groundwater, because the liquid may not simply sink to the lowest point in an aquifer. Additionally, the unique spreading of DNAPLs must be considered when con ducting co-solvent or surfactant assisted remediation. Study Objectives The objectives of this study was to conduct two dimensional chamber studies designed to investigate fluid, fluid prope rty effects on contaminant geometry and

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73 orientation and ultimately contaminant mass flux and system efficiency as discussed in chapter 3. The first objective was to vary density differential and generate mass loading versus mass flux curves. The second object ive was to change the interfacial tension between the fluids and generate mass lo ading versus mass flux curves. Maximum contaminant mass flux values and system efficiency ( ) values were investigated. Materials and Methods General Experimental A two dimensional chamber as describe d in chapter one was used for each experiment. The hydrophilic packing procedur es and hydrological controls described in chapter three were followed. The PCE mate rial and injection methods described in chapter 3 were used. A total of nine experi ments using 30/40 and 40/50 sieve sand were completed. Density Modification An experiment for each density and sieve size combination listed in Table 4.1 was completed. Table 4.1. Density sieve size experiments PCE Density (g/ml) 1.0 1.1 1.4 1.6 30/40 Sieve x x x x 40/50 Sieve x x To achieve the densities listed in Table 4. 1, the appropriate mole fractions of PCE and decane were mixed together (Table 4.2). Decane was selected because of its density (0.73 g/ml), and its low solubility in wa ter to ensure limited partitioning from the nonaqueous to the aqueous phase.

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74 Table 4.2. Decane/PCE densities and respective mole and volume fractions volume fraction mole fraction PCE Decane PCE Decane 1 0.3 0.7 0.45 0.55 1.1 0.41 0.59 0.57 0.43 1.4 0.75 0.25 0.85 0.15 1.65 1 0 1 0 Additionally is has similar interfacial tension properties (52 dynes/cm) compared to PCE in relation to water. The IFT of 50/50 mole fraction of PCE and Decane mixture was measured using a tensiometer to determined if the resultant mixture had an IFT value in between the IFT values for pure PCE and Decane. The IFT for decane and water was measured to be 43 dynes/cm, PCE and water was 37 dynes/cm, and the mixture resulted in an IFT of 39 dynes/cm. This supports th at Seo and McCray (2002) determined there is a linear relationship between multi-component mole fractions and IFT properties of the mixture. Interfacial Tension Modification Interfacial tension between PCE and water was modified by adding 0.0025%, 0.005%, 0.01%, 0.025%, 0.05% and 0.1% by volume Span 80 to PCE. Span 80 (sorbitan monooleate) was selected because of its lo w hydrophile/lipophile balance (HLB) value of 4.3. A low HLB surfactant was required to limit partitioning of the surfactant into the aqueous phase. The relationship between % surfactant added and interfacial tension between PCE and water is shown in Figur es 4.1. The relation ship between Cmax and percent surfactant is shown in Figure 4.2.

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75 y = 24.991e-44.328xR2 = 0.9808 1 10 100 00.010.020.030.040.050.06 % Span 80 in PCEIFT (dynes/cm) Figure 4.1. Span 80 percentage and re sultant interfacial tension Semi-Log y = 223.32x + 183.7 R2 = 0.32140.00 50.00 100.00 150.00 200.00 250.00 00.020.040.060.080.10.12% Span 80Cmax mg/L Figure 4.2. Maximum PCE concentration as function of percent surfactant (Span 80)

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76 An experiment for each interf acial tension value listed in Table 4.3 was completed. The low IFT of 3 dynes/cm was selected because at greater Span 80 percentages cloudiness occurred. Table 4.3. Interfacial values tested and respective Span 80 percentage Interfacial Tension (dynes/cm) 3* 0.05% Span 80 *not shown on graph estimated based on curve fit equation shown in Figs 4.1 and 4.2 13 0.025% Span 80 47 0% Span 80 Results and Discussion IFT Modification Results and Discussion For each experiment (interfacial tension) a trace sketch of the PCE distribution was generated. A trace of the distribution was dr awn after each injecti on reached steady state on a single transparency, resul ting in a cumulative distributio n drawing (Appendix C). A qualitative comparison using sketches in Appendix C was made between each interfacial tension experiment shows a difference in migra tion characteristics as IFT decreases. As the IFT decreased, the resi dual geometry became more spread out. Figures 4.3 and 4.4 are an example in how th e distribution behavior of PCE changes as the IFT is lowered. This may be from th e lower IFT influencing the migration of the PCE in a horizontal direction in addition to vertical movement. Pooling for each began by the second injection, so the vertical migration was not affected by lowering the IFT, indicating that density differential co ntrolled vertical migration.

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77 Figure 4.3. 3 dynes/cm interfacial tension distribution Figure 4.4. 47 dynes/cm interfacial tension distribution Figure 4.5 displays similar results be tween each IFT experiment. As the IFT decreased, the relative C/Cmax values appear to increase slightly. This may be due to more uniform migration occurring in the thickness of the chamber as the PCE migrates vertically. The maximum values appear to be bounded by injection point location.

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78 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.001.002.003.004.005.006.00PCE (ml)C/Cmax(J/Jmax) Untreated (47 dynes/cm) 13 dynes/cm 3 dynes/cm Figure 4.5. Interfacial tension comparisons Figure 4.6 displays the relative curve fits for each IFT with the associated data. They are essentially the same, indicating regardless of IFT, vertical migration characteristics appear to be the same for each. Ultra low IFTs may be required to affect migration or prevent entrapment. Table 4. 4 tabulates the bond, capillary and total trapping number for each IFT. These values indicate that entrapment will still occur, because Pennell et al. (1996) reports mobilization when NT = 1E-3. However, to achieve these ultra low IFTs, solubility would increa se dramatically (Pennell et al., 1996). Table 4.4. Calculated bond, capillary and total trapping number for each IFT IFT (dynes/cm) NBo NCa NT 47 9.8E-5 2.3E-6 9.8E-5 13 2.3E-5 5.4E-6 2.3E-5 3 6.2E-5 4.9E-6 6.2E-5

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79 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.000.100.200.300.400.500.600.700.800.901.00Fraction VolumeFraction Mass Flux 47 dynes/cm (0.40) 13 dynes/cm (0.41) 3 dynes/cm (0.40) 47 dynes/cm 13 dynes/cm 3 dynes/cm Figure 4.6. Interfacial tension curve fit Density Modification Results and Discussion For each density experiment a trace sketch of the PCE distribution was generated. A trace of the distribution was drawn after each injection reached st eady state on a single transparency, resulting in a cumulativ e distribution drawing (Appendix C). A qualitative comparison between density experiments reveals interesting results using the drawings in Appendix C. As th e density decreased, vertical and lateral migration characteristics changed. Figures 4.7 and 4.8 provide a qua litative comparison between distributions of PCE and PCE treated to achieve 1.1 mg/l ( ).

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80 Figure 4.7 Untreated PCE distribution Figure 4.8. 1.1 density distribution The comparison shows how differently PCE migrates and distributes as is decreased. Vertical migration was slower from injection to injection in the lower density experiments when compared to the untrea ted PCE experiments. In the untreated experiments pooling usually began by the seco nd injection (1.0 ml), indicating complete vertical migration from injection port to chamber bottom. The lower density experiments required as many as nine injections (4.5 ml) to cause full migration from injection port to

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81 bottom and in the case of the 1.0 density PCE, no pooling occurred indicating no full downward migration. The C/Cmax values were similar with the 1.1 in the 30/40 sieve sand showing the largest value followed by th e 1.0 density PCE in the 30/40 sand (Figure 4.9). These results are probably due to th e PCE being able to migrate above and below the injection port, providing a larger cross se ctional area exposure to flow compared to the untreated PCE experiments. Figure 4.10 compares the fitted curves for each density experiment. The lower density experiments displayed a linear mass lo ading/mass flux relationship compared to the untreated experiments which were more non linear. These curves coupled with the traces indicating reduced vertical migration per each injection indicate the curves are a function of density differential. A faster downward migration results in higher flux values at low masses when compared to slower downward migration results. The 1.4 and values were expected to be in between the 1.0, 1.1 and 1.65 density values. However, the 1.4 value was closer to the lower density values. This may be explained by Figure 4.11. The downward mi gration appeared to be delayed by possible layering. This caused the vertical migration to behave similarly to the migrations seen at the lower densities. This resulted in a more linear value.

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82 Figure 4.9 Density comparisons 0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.001.002.003.004.005.006.007.00 PCE (ml)C/Cmax(J/Jmax) 30/40 untreated 30/40 1.1 rho 30/40 1.0 rho 40/50 untreated 40/50 1.1 rho 30/40 1.4 rho

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83 Figure 4.10. Density curve fit 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00 0.000.100.200.300.400.500.600.700.800.901.00 Fraction VolumeFraction Mass Flux 30/40 1.0 (0.91) 30/40 1.1 (0.89) 30/40 1.4 (0.81) 30/40 (0.40) 40/50 1.1 (0.86) 40/50 (0.42)

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84 Figure 4.11. 1.4 density distribution 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 0.001.002.003.004.005.006.00 PCE (ml)C/Cmax(J/Jmax) Experimental Equilibrium Non-Equilibrium Figure 4.12. Curve comparisons for 1.1 density PCE in 30/40 sand

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85 0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.001.002.003.004.005.006.00 PCE (ml)C/Cmax(J/Jmax) Experimental Equilibrium Non-Equilibrium Figure 4.13. Curve comparisons for 1.4 density PCE in 30/40 sand Flow By-Passing and Mass Transfer Rate Limitation Figures 4.12 and 4.13 shows a comparison of mass flux versus mass loading curves based on equilibrium, mass transfer rate, and experimental data. For both the 1.1 and 1.4 density source zones, sufficient contact length is produced during the loading process, indicating that equilibrium is achieved. The lower flux values shown from the experimental data indicate th at flow by-passing is likely occurring and accounts for most of the reduction from expected equilibrium values. This is due to the PCE not being homogeneously distributed across the width of the domain. For both the 1.1 and 1.4 density source zones, sufficient contact length is produced during the loading process, indicating that equilibrium is achieved. The lower flux values shown from the experimental data indicate th at flow by-passing is likely occurring and accounts for most of the reduction from expected equilibrium values. This is due to the PCE not being homogeneously distributed across the width of the domain.

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86 Conclusions Changes in density appear to slightly affect both the C/Cmax and values. Decreasing density slows vertical migration a nd delayed pooling leadi ng to less efficient, more linear mass loading /mass flux behavior and higher values when compared to untreated PCE values. As the density diffe rential decreased, the residual geometry became more uniformly spread out. As density differential decreased, residual geometry more uniformly spread. The interfacial tension for the range cons idered did not affect flux values. It appears that interfacial tensio n must be ultra-low in order for the PCE not to become entrapped (Pennell et al., 1996). The IF Ts tested were not low enough to cause instantaneous mobilization of the PCE, therefor e a residual zone was left after migration resulting in similar flux values compared to the untreated system. Finally, flow by-passing is occurring a nd producing lower than expected flux values when compared to equilibrium conditions.

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87 CHAPTER 5 INVESTIGATION OF CONTAMINANT MASS FLUX HYSTERESIS Introduction Currently, there is little research investig ating the life cycle of a contaminant spill and the manner in which contaminant flux values vary through mass increase and eventual mass reduction and dissolution. Mo st source zone contaminant research has focused on mass fraction or volume fraction removal of contaminant (Rao et al. 1997, Jawitz et al. 1998b, Martel et al. 1998, McCray and Brusseau 1998, Lowe et al. 1999, Fiorenza 2000, Jawitz et al. 2000, Meinar dus et al. 2002). In particular, field investigations are typically limited to this focus because of their retrospective nature. Other research has gone furt her to investigate theoretical models by evaluating the relationship between mass redu ction and contaminant flux reduction (Berglund, 1997; Rao and Jawitz, 2003; Sale and McWhorter 2001) The focus of this research topic is retrospective since it focuses on source z one and flux characteristics after the contaminant has been introduced into a partic ular setting. The ma ss loading process and its contaminant flux behavior in relation to the mass reduction and dissolution process has not been considered. Flux behavior as a function of loading is a more convenient method for associating flux values to known contaminant mass values. If a relationship between flux loading curves and flux reducti on curves can be made, flux loading curves may be a more convenient pred ictor of flux reduction beha vior which pertains to mass reduction.

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88 Theoretical Background Typically, hysteresis in the context of hydrology is associated with soil-water retention curves and the relationship betw een drying and wetting curves. When the drying curve and the wetting curve are not the sa me, there exists hysteresis (Fetter, 1999). This concept may be applied to contaminan t mass-contaminant flux curves associated with Dense Non-Aqueous Phase Liquids (DNAPL). When a spill occurs into the subsurface, it may happen as a chronic event as opposed to one catastrophic, acute event. The chronic spill may occur as a continuous event or a series of spills from the same sour ce into the same location such as an aquifer. Considering the series of spills scenario, after each spill, mass would be added to the source zone. Each addition of contaminan t mass contributes to the development and geometry of the source zone. The source zone is divided into the residual mass which is suspended in the porous media and the pool ed mass which collects on top of a lower permeability layers. As contaminant mass is added, the residual geometry is developed and eventually a pooled portion begins to deve lop. During this loading process, there is an associated mass flux with each contaminan t mass amount added. Local equilibrium is assumed as well as a contaminant that has a su itably low solubility to allow a steady state flux condition to be reached in between c ontaminant mass additions. After the loading process is complete, eventually the source zone mass would begin to decrease through dissolution. The residual mass would be re moved first with the pool source persisting longer. During the dissolution removal proc ess, there will be an associated mass flux with each remaining contaminant mass. The mass loading/flux increase curve can relate to the mass reduction/flux reduction curve in two ways; the process is reve rsible or it is hyster etic. The reversible

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89 process is the dissolution flux curve and it follows the same curve established during the loading process. Figure 5.1 shows some exampl es of reversible curves. In the hysteretic process, the dissolution flux curve does not fo llow the same curve back to the origin as shown in Figure 5.2. Figure 5.1. Reversible flux lo ading and dissolution processes Figure 5.2. Hysteretic flux lo ading and dissolution processes

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90 The physical events associated with the reversible process are those events which occurred last during the loading process an d will occur first during the dissolution process. For example, as a spill occurs, the residual geometry is created and if a lower permeability layer exists below the spill source, pooling will occur on the layer. The associated flux behavior with this loading event would be a rapid establishment of flux followed by a plateau as pooling becomes more prevalent. An example of this is shown as the top curve in Figure 5.1. For the disso lution flux behavior to follow this curve in reverse, the pool would have to be removed first followed by th e residual. If the residual were to be removed first, th e process would than be hyster etic and the dissolution curve would be different than the loading curve (Figur e 5.2). It is important to note that the physical conditions of the media such as hete rogeneities and flow conditions will have an impact in mass loading/mass reduction relationship. Study Objective The objective of this study was to determine the relationship between DNAPL mass flux curves associated with contam inant mass loading and mass flux curves associated with contaminant mass removal. Flux loading curves were compared to flux removal curves to determine if the relationship was hysteretic. Materials and Methods A two dimensional chamber as described in chapter one was used for this experiment. The hydrophilic packing pr ocedures using 30/40 sieve sand and hydrological controls described in chapter th ree were followed. Trichloroethylene (TCE) was the DNAPL used because of its moderate water solubility (1100 mg/L) and concern for its toxicity and ubiquity. This is low enough to allow steady st ate conditions to occur before significant mass has partitioned into the water, while still being high enough to

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91 allow mass to dissolve in a timely fashion. The injection and sampling methods described in chapter three were used. Results and Discussion Two experiments were run to compare the mass loading flux curves to the mass dissolution flux curves. The results of the fi rst experiment are shown in Figure 5.3. A total of 7000 mg of TCE was introduced in increments of 700 mg. Accounting for dissolution of the TCE during th e loading process resulted in approximately 6000 mg of mass present at the point loading was discontinued and dissolution to construct the mass reduction curve began. There were approxi mately three pore volumes in between each injection and sampling event during mass loadin g and mass dissolution. This resulted in the curve shown in Figure 5.3. There appear s to be a rapid decrease in flux within 10 pore volumes of PCE introduction discontinua tion. As discussed in chapter 3, the residual source zone produces the largest pe rcentage of dissolution flux when compared to the pooled source zone. The rapid decrease in flux observed indica tes that the residual was removed rapidly with the pool remainin g and being removed more slowly. This indicates that the mass that is loaded first is removed first or first in is first out. This produces a hysteretic process. A non-hyste retic process would have the pool removed first since it represents the mass last introduced. The second experiment yielded similar result s. During this experiment, 1400 mg of TCE was introduced during two injections of 700 mg each. Two separate injections were done to remain consistent with previously used loading procedures. Reduced mass introduction was done to facilitate timeliness of the experiment. Figure 5.4 displays the breakthrough curve and Figure 5.5 displays the mass reduction, flux reduction curve. Again, there appears to be a rapid decreas e in flux within 10 pore volumes of PCE

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92 introduction discontinuation, indicating the re sidual was removed first and while the pool was removed more slowly, resultin g in a hysteretic process. Figure 5.3. TCE mass increase/dissoluti on experiment one Note the rapid flux decrease following stoppage of mass introduction 0 50 100 150 200 250 300 0510152025 Volume (L)C (mg/L) Figure 5.4. Breakthrough curve 0.00 50.00 100.00 150.00 200.00 250.00 300.00 01000200030004000500060007000 Mass (mg)C (mg/L)

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93 0 50 100 150 200 250 300 02004006008001000120014001600 Mass (mg)C (mg/L) Actual Dissolution Data Predicted Loading Curve Figure 5.5. TCE mass increase/dissoluti on experiment two note the rapid flux decrease following stoppage of mass introduction Conclusions When considering homogenous media systems where pooling of a DNAPL occurs, the relationship between the mass loading flux and the dissolution mass flux appears to be hysteretic. Th is indicates that during the loading process, the residual source zone is constructed followed by the p ool source zone constr uction. However, during the dissolution process, the residual source zone ap pears to be removed more quickly than the pooled source zone resulting in a rapid reduction in fl ux. This results in a hysteretic process. This hysteretic relatio nship could potentially be used for predicting mass dissolution, mass removal behavior using mass loading, mass dissolution information. For a homogeneous media, it appears that the mass that is first introduced and is retained in the residual zone is th e mass that is first removed from the system.

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94 CHAPTER 6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS Summary The overall goal of this research was to study the effect of media and fluid properties on DNAPL migra tion geometry and contaminant mass flux. The major objectives were as follows: (1) Determin e the relationship between hydrophobic media content and water, air and oil entry pressu re and related entry pressure values, (2) Determine the relationship between contam inant mass flux and media properties, (3) Determine the relationship between contaminant mass flux and fluid properties, (4) Determine the mass loading and dissolution behavior of TCE. The findings from the hydrophobic media study indicate that water and oil entry pressure measurements are sensitive to media wettability and can be used as a relative indicator of system wettability. Grain size and wettability proper ties of the media affected flux values and mass loading, flux value relationships. In general, each media size produced a non-linear relationship between mass loading and disso lution flux. As grain size decreased, dissolution flux increased. Nearly oil wet media increased dissolution flux and produced a more linear relationship between mass loadi ng and dissolution flux relative to water wet media. Density differential between the DNAPL and water had no apparent effect on total flux values, however, a near linear relationship between mass loading and dissolution flux was observed as density differe ntial approached zero. Interfacial tension had no apparent effect on flux values for th e range of IFTs considered. The relationship between flux produced during loading events is hysteretic when compared to the flux

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95 reduction mass reduction relationship. Sp ecific conclusions and recommendations are listed below. Conclusions The following conclusions are drawn as they relate to the research performed to meet this studys objectives: As oil wettability of the media decreases water entry pressure decreases and oil entry pressure increases There is no apparent effect of oil wettab ility on air entry pressu re due to air being the non-wetting fluid rega rdless of media type Grain size affects lateral PCE migration, thereby increasing contaminant flux as grain size decreases The residual source zone is the greatest contributor of contaminant flux compared to the pooled source zone Grain size has a 0.75 correlation to values 90% + oil wet sand using octadecyltrichlo ro silane (OTS) coating was required to affect residual geometry and influence contaminant mass flux values 90% + oil wet sand allows capillary forces to overcome differential and gravity effects A reduced linearized relationship between mass fraction loading and flux fraction increase, indicating delayed pooling Interfacial tension (IFT) had no effect on flux values and values for the range of IFT values considered Flux values are lower than expect ed due to potential flow bypassing Sufficient contact length between source z one and aqueous phase is required to reach equilibrium In considering homogeneous systems where pooling of DNAPL occurs, the relationship between mass loading flux va lues and mass dissolution flux values is hysteretic

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96 Recommendations The following recommendations are made to further the extent of knowledge relating to this research: A larger range of grain sizes should be considered to further clarify grain size effects on mass flux and values Silane coatings other than OTS should be studied to further investigate wettability effects on DNAPL migration geometry and contaminant mass flux values Ultra low IFT values should be consid ered to investigate DNAPL entrapment behavior and its effect on contaminant mass flux and values Geometries such as pooled only, residual only, or various pooled and residual combinations in heterogeneous media s hould be investigated to determine if loading/dissolution behavior is revers ible or hysteretic for other system configurations Combinations of variables should be cons idered i.e. low density differential and low interfacial tension, etc. Fluid viscosity modificati on should be considered Contaminant injection rate should be va ried to observe impact on source zone geometry development

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97 APPENDIX A AIR, WATER, AND OIL ENTRY PRES SURE BREAKTHROUGH GRAPHS FOR HYDROPHOBIC MIXTURES 0 0.5 1 1.5 2 2.5 3 3.5 0246810121416 Height (cm)Volume (ml) Figure A.1. Untreated sand air en try pressure (water saturated)

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98 0 0.5 1 1.5 2 2.5 3 02468101214 Height (cm)Volume (ml) Figure A.2. 25% Octadecyltrichlorosilane (OTS) treated air entry pressure (water saturated) 0 0.5 1 1.5 2 2.5 3 3.5 4 02468101214 Height (cm)Volume (ml) Figure A.3. 40% OTS treated air entry pressure (water saturated)

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99 0 1 2 3 4 5 6 7 8 024681012141618 Height (cm)Volume (ml) Figure A.4. 50% OTS treated air entry pressure (water saturated) 0 0.5 1 1.5 2 2.5 3 3.5 4 02468101214 Height (cm)Volume (ml) Figure A.5. 60% OTS treated air entry pressure (water saturated)

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100 0 0.5 1 1.5 2 2.5 3 3.5 024681012 Height (cm)Volume (ml) Figure A.6. 75% OTS treated air entry pressure (water saturated) 0 2 4 6 8 10 12 02468101214 Height (cm)Volume (ml) Figure A.7. 100% OTS treated air entry pressure (water saturated)

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101 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 024681012 Height (cm)Volume (ml) Figure A.8. 100% OTS treated water entry pressure (air saturated) 0 0.5 1 1.5 2 2.5 3 3.5 4 012345678 Height (cm)Volume (ml) Figure A.9. 75% OTS treated water entry pressure (air saturated)

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102 0 0.5 1 1.5 2 2.5 3 01234567 Height (cm)Volume (ml) Figure A.10. 60% OTS treated water entry pressure (air saturated) 0 0.5 1 1.5 2 2.5 3 3.5 4 01234567 Height (cm)Volume (ml) Figure A.11. 50% OTS treated water entry pressure (air saturated)

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103 0 0.5 1 1.5 2 2.5 3 3.5 0123456 Height (cm)Volume (ml) Figure A.12. 40% OTS treated water entry pressure (air saturated) 0 0.5 1 1.5 2 2.5 0246810121416 H (cm)Vol (ml) Figure A.13. Untreated oil entr y pressure (water saturated)

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104 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0123456 H (cm)vol (ml) Figure A.14. 25% OTS treated oil entry pressure (water saturated) 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 0123456 H (cm)Vol (ml) Figure A.15. 50% OTS treated oil entry pressure (water saturated)

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105 0 0.2 0.4 0.6 0.8 1 1.2 00.511.522.533.544.5 H (cm)Vol (ml) Figure A.16. 75% OTS treated oil entry pressure (water saturated)

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106 APPENDIX B TWO-DIMENSIONAL FLOW CHAMBE R DISTRIBUTION CONTOURS FOR GRAIN SIZE AND WETTABI LITY EXPERIMENTS Table B.1. Injection amount and associated sketch number Injection Amount (ml) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 etc Sketch Number 1 2 3 4 5 6 7 8 etc Figure B.1. 20-30 Sieve trace experiment 1 1 c m

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107 Figure B.2. 20-30 Sieve trace experiment 2 Figure B.3. 30-40 Sieve pooled PCE trace 1 c m 1 c m

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108 Figure B.4. 30/40 Sieve trace Figure B.5. 40-50 Sieve trace 1 c m 1 c m

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109 Figure B.6. 40-60 Sieve trace experiment 1 Figure B.7. 40-60 Sieve trace experiment 2 1 c m 1 c m

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110 Figure B.8. 50-70 Sieve trace experiment 1 Figure B.9. 50-70 Sieve trace experiment 2 1 c m 1 c m

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111 Figure B.10. 30/40 Sand 25% OTS mix trace (denatured alcohol (DA)) Figure B.11. 30/40 Sand 50% hydrophob ic mix trace (reagent alcohol (RA)) 1 c m 1 c m

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112 Figure B.12. 30/40 Sand 50% hydrophobic mix trace (DA) Figure B.13. 30/40 Sand 75% hydrophobic mix trace (RA) 1 c m 1 c m

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113 Figure B.14. 30/40 Sand 75% hydrophobic mix trace (DA) Figure B.15. 30/40 Sand 90% hydrophobic mix trace (DA) 1 c m 1 c m

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114 Figure B.16. 30/40 Sand 100% hydrophobic mix trace (RA) Figure B.17. 30/40 Sand 100% hydrophobic mix trace (DA) 1 c m 1 c m

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115 APPENDIX C TWO-DIMENSIONAL FLOW CHAMBE R DISTRIBUTION CONTOURS FOR INTERFACIAL TENSION AND DENSIT Y MODIFICATION EXPERIMENTS Figure C.1. Untreated (47 dynes/cm) PCE 1 c m

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116 Figure C.2. 0.025% (13 dynes/cm) Span 80 treated PCE Figure C.3. 0.05% (3 dynes/cm) Span 80 treated PCE 1 c m 1 c m

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117 Figure C.4. 1.4 Density PCE in 30/40 sieve sand Figure C.5. 1.1 Density PCE in 30/40 sieve sand 1 c m 1 c m

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118 Figure C.6. 1.0 Density in 30/40 sieve sand Figure C.7. Untreated 40/50 sieve sand 1 c m 1 c m

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119 Figure C.8. 1.1 Density PCE in 40/50 sieve sand 1 c m

PAGE 134

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123 Jawitz, J. W., R. K. Sillan, M. D. Annable, P. S. C. Rao, and K. Warner, In Situ Alcohol Flushing of a DNAPL Source Zone at a Dr y Cleaner Site, Environmental Science & Technology 34:3722-3729, 2000. Jawitz, J. W., M.D. Annable, G.G. De mmy, and P.S.C. Rao. Estimating Nonaqueous Phase Liquid Variability using Partiti oning Tracer Higher Temporal Moments, Water Resources Research, 39(7):1192-1209, 2003. Jeong, S., A.L. Wood, and T.R. Ree. Effects of Pure and Dyed PCE on Physical and Interfacial Properties of Remedial Solutions Journal of Hazardous Materials, 95(12):125-135, 11 Nov 2002. Johnson, R.L. and J.F. Pankow, Dissolution of Dense Chlorinated Solvents into Groundwater. 2. Source Functions for Pools of Solvent, Environmental Science Technology, 26:896-901, 1992. Le Grange, J.D. and J.L. Markham. Eff ects of Surface Hydrati on on the Deposition of Silane Monolayers on Silica, Langmuir, 9:1749-1753, 1993. Letey, J., J. Osborn, R.E. and Pelishek. Measur ement of Liquid-Solid Contact Angles in Soil and Sand, Soil Science, 93(3):149-153 Mar, 1962. Lowe, D. F., C. L. Oubre and C. H. Ward. Surfactants and Cosolvents for NAPL Remediation CRC Press, Boca Raton, FL 1999. Martel, R., P.J. Gelinas, and L. Saumure. Aquifer Washing by Mice ller Solutions: 3 Field Test at the Thouin Sand Pit (LAssomp tion, Quebec, Canada). Journal of Contaminant Hydrology, 30:33-48, 1998. Mayer, A. S. and C.T. Miller. The Influence of Porous Medium Characteristics and Measurement Scale on Poor-Scale Distri butions of Residual Nonaqueous-Phase Liquids. Journal of Contaminant Hydrology, 11:189-213, 1992. McCray, J. E. and M. L. Brusseau. Cyclodextrin-Enhanced In-situ flushing of Multiple Component Immiscible Organic Liquid C ontamination at the Field Scale: Mass Removal Effectiveness. Environm ental Science & Technology 32:1285-1293 1998. Meinardus, H. W., V. Dwarakanath, J. Ewing, G. J. Hirasaki, R. E. Jackson, M. Jin, J. S. Ginn, J. T. Londergan, C.A. miller, and G. A. Pope. Performance Assessment of NAPL Remediation in Heterogeneous Alluvium, Journal of Contaminant Hydrology 54:173-193, 2002. Mercer, J. W. and R.M. Cohen. A Review of Immiscible Fluids in the Subsurface: Properties, Models, Characterization a nd Remediation, Journal of Contaminant Hydrology, 6:107-163, 1990.

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124 Miller, C. T., M.M Poirer-McNeill, and A.S. Mayer. Dissolution of Trapped Nonaqueous Phase Liquids: Mass Transfer Characteristics, Water Resources Research, 26(11):2783-2796, Nov, 1990. Moore, T. F. and R.L. Slobod. The Effect of Viscosity and Capillarity on the Displacement of Oil by Water, Producers Monthly, 20-30, Aug, 1956. Morrow, N.R. and J. P. Heller. Fundamentals of Enhanced O il recovery, in Enhanced Oil Recovery, 1: Fundamental and Analyses, Elsevier Publishing Co., New York, 1985. Morrow, N.R., I. Chatzis, and J.J Taber. En trapment and Mobilizati on of Residual Oil in Bead Packs, SPE Reservoir Engineering, 927-934, Aug, 1988. New Jersey Department of Health and Seni or Services [NJDHSS] Hazardous Substance Fact Sheet, Tetrachloroethylene, Mar, 2002. Newell, C. J. and R.R Ross. EPA Publication 9355.4-07FS, Estimating Potential for Occurrence of DNAPL at Superfund Sites, Jan, 1992. Ng, K.M., H.T. Davis, and L.E. Scriven. Visualization of Blob Mechanics in Flow Through Porous Media, Chemical Engineering Science, 33:1009-1017, 1978. Office of Pollution Prevention and Toxics Chem ical Fact Sheet [OPPT], Chemicals in the Environment: Perchloroethylene (C as N. 127-18-4), EPA 749-F-94-020, Aug, 1994. Parker, J.C. and E. Park. Modeling Filed-Scale Dense Nonaqueous Phase Liquid Dissolution Kinetics in Heterogeneous A quifers, Water Resources Research, 40, 2004. Pankow, J. F. and J.A. Cherry. Dense Chlorinated Solvents and other DNAPLs in Groundwater, Waterloo Press, Portland, Oregon (IFT), 1996. Patel, K. and M. Greaves. Role of Capill ary and Viscous Forces in Mobilization of Residual Oil, The Canadian Journal of Chemical Engineering, 65:676-679, Aug, 1987. Pennell, K.D., G.A. Pope, and L.M. Abriola. Influence of Viscous and Bouyancy Forces on the Mobilization of Residual Tetrachlo rethylene During Surfactant Flushing, Environmental Science and Technology, 20:1328-1335, 1996. Perry, P.H. and C.H. Chilton. Chemical Engineers Handbook 5 th Edition McGraw-Hill, 1973. Peters, J.E. and D.L. Flock. The Onset of Instability During Two-Phase Immiscible Displacement in Porous Media, Society of Petroleum Engineers Journal, 249-258, Apr, 1981.

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126 Treiber, L.E., D.L. Archer, and W.W Owens, A Laboratory Evaluation of the Wettability of Fifty Oil Producing Reservoirs, Societ y of Petroleum Engineers Journal, 12:531539, 1972. Verschueren, K. Handbook of Environmental Data on Organic Chemicals, 2 nd edition, Van Nostrand Reinhol d, New York, NY, 1983. Wang, A., J. Feyen, and D.E. Elrick. Predic tion of Fingering in Porous Media, Water Resources Research. 34(9):2183-2190, Sep 1998. Watson, C.L. and J. Letey. Indices for Char acterizing Soil-Water Repellency Based upon Contact Angle-Surface Tension Relationshi ps, Soil Science Society of America Proceedings, 34:841-844, 1970. Wilson, J.L. The Need for Research: Physical Processes Land; The Role of Wetting in Environmental Problems, Presented at Proceedings of the Association of Environmental Engineering Professors, Conference on Fundamental Research Directions in Environmental En gineering, Nov 13-15, Arlington, VA 1988.

PAGE 141

127 BIOGRAPHICAL SKETCH Christian T. Totten was born in New London, CT, on October 28, 1966, the youngest of six children. He graduated from Fitch Senior High School, Groton, CT, in June 1984, and immediately attended Wester n New England College in Springfield, MA. In May 1988, he was awarded a Bachelor of Science degree in mechanical engineering. Following graduation he worked as an engi neer at Portsmouth Naval Shipyard, NH. He remained at the shipyard until September, 1989, when he was commissioned a second lieutenant in the U.S. Air Force as a bioenvironmental engineer. His first duty location was Pope Air Force Base (AFB), Fayetteville, NC, where he held the position of Chief, Bioenvironmental Engineering Services. In May of 1994 he was transferred to WrightPatterson AFB, where he attended the Ai r Force Institute of Technology (AFIT) until December 1995. He received a Master of Science degree in engineering and environmental management and was tran sferred to the Air Force Center for Environmental Excellence (AFCEE) at Brooks AFB, San Antonio, TX. While at the AFCEE, he worked in both the environmen tal restoration and compliance programs until May 1999. Upon acceptance to an Air Force sponsored fellowship at the Pentagon, Chris was transferred to Washington, D.C. He se rved at the Pentagon for three years as a fellow, action officer, and executive officer to the Assistant Secretary of the Air Force. Upon selection for an Air Force-sponsored gr aduate program, Chris transferred to the University of Florida, Gainesville, FL, in August 2002. Chris has a wife, Yvonne, and two children, Alec and Simone.


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Title: Effect of Porous Media and Fluid Properties on Dense Non-Aqueous Phase Liquid Migration and Dilution Mass Flux
Physical Description: Mixed Material
Copyright Date: 2008

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EFFECT OF POROUS MEDIA AND FLUID PROPERTIES ON DENSE NON-
AQUEOUS PHASE LIQUID MIGRATION AND
DILUTION MASS FLUX















By

CHRISTIAN T. TOTTEN


A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL
OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT
OF THE REQUIREMENTS FOR THE DEGREE OF
DOCTOR OF PHILOSOPHY

UNIVERSITY OF FLORIDA


2005

































Copyright 2005

by

Christian T. Totten















ACKNOWLEDGMENTS

During my time at the University of Florida, I have received a great deal of help

from many people. I would like to thank all of those who gave me assistance, exchanged

ideas, or simply listened.

My primary thanks go to my advisory committee chairperson, Dr. Michael

Annable. His guidance, patience and open door policy have truly made this a great and

enjoyable learning experience. I also would like to thank Dr. Joseph Delfino as my co-

chair for all his guidance and for encouraging me to attend the University of Florida. I

also thank my other committee members, Dr. James Jawitz and Dr. Kirk Hatfield, for

their teaching and support.

I would like to thank Dr. Matt Booth and Dr. Jaehyun Cho for all their help and

advice in the lab. Without them, I am not sure if I would be able to find the lab to this

date!

Fortunately, having a chairperson and cochair has given me the opportunity to meet

and work with students from two research groups. I have met great people and learned as

much from them than I have in more formal settings. I thank all of them for their

support, advice, knowledge and the occasional game of Literati.

I must thank the United States Air Force and the Biomedical Sciences Corps for

giving me this opportunity by sponsoring me in this endeavor. Special thanks go to Mr.

Nelson Gibbs, who supported my application in the first place. Without his support, this

would not have happened. Also, I thank the Strategic Environmental Research and









Development Program, Department of Defense, who in part funded this research (CU-

1295: Impacts of DNAPL Source Zone Treatment: Experimental and Modeling

Assessment of Benefits of Partial Source Removal).

Lastly, I must thank my wife, Yvonne, and children, Alec and Simone, for their

support and willingness to follow me to wherever the Air Force decides to send us. They

have been great in letting me pursue my goals and doing whatever it takes to get there.
















TABLE OF CONTENTS

page

A C K N O W L E D G M E N T S ................................................................................................. iii

LIST O F TA B LE S .................. ............. ............................ .............. viii

LIST OF FIGURES ......... ......................... ...... ........ ............ ix

A B S T R A C T .......................................... ..................................................x iii

CHAPTER

1 IN TR OD U CTION ............................................... .. ......................... ..

B background ................................... ......... ........................... ...............
Geom etry and Orientation to Flow .................................... ........................ 6
P ooled D N A P L .................................................................................. .. 7
Residual DN APL .................. ............................ ....... ................ .8
M igration process .................. .......................... ......... ................ .9
Entrapm ent process ................ .............. .............. ... ..... ........ ..............10
Relating Media Property Characteristics to the Contaminant Mass Flux ..........12
B inary m odel ............... ...................... .... ............. ............... 12
Fractional mass flux versus fractional mass loading and total mass flux ....12
Stu dy O bjectiv es ................................................. ................ 15
G general M methodology ................................................ ........ .. ............ 16
D issertation O organization ............................................................. ............... 19

2 W ETTABILITY STUDIES......................................................... ............... 20

Introdu action ...................................... ................................................. 2 0
T heoretical B ackground...................................................................... ..................22
Stu dy O bjectiv e ................................................................2 8
M eth od s an d M materials .................................................................... .....................2 8
W ater/Air Entry Pressure M easurements.................................... .................28
Oil Entry Pressure M easurem ents ............................................ ............... 32
R results and D iscu ssion .............................. ........................ .. ...... .... ...... ...... 33
C o n clu sio n s..................................................... ................ 3 4

3 INVESTIGATION OF THE RELATIONSHIP BETWEEN MEDIA
PROPERTIES (GRAIN SIZE AND WETTABILITY) AND MASS FLUX ............36


v









In tro d u ctio n .......................................................................................3 6
T heoretical B ackground...................................................................... ..................36
G rain S iz e ................................................................3 7
W ettab ility ..................................................................................................... 3 9
Study O objective .............................................. .. .. ........... ..... ...... 42
M materials and M ethods ....................................................................... ..................42
G general Experim ental Procedure..................................... ......... ............... 42
Hydrophilic Sand Packing Procedure............................... ....... ............... 42
Hydrophobic Sand Packing Procedure......................................................44
PCE Introduction and Sam pling................................... .................................... 45
H hydraulic C controls .............. ........ .............................. .............. ..... ........... 46
Octadecyl Trichlorosilane Treatment and Retardation Factor ..........................46
R results and D discussion ............. .............. ... .............................. ......... 47
Grain Size Comparison Results and Discussion ...........................................50
Wettability Results and Discussion..............................................................57
Flow By-passing and Rate Limited Mass Transfer ...........................................63
C o n clu sio n s..................................................... ................ 6 7

4 INVESTIGATION OF THE RELATIONSHIP BETWEEN FLUID
PROPERTIES INTERFACIALL TENSION AND DENSITY DIFFERENTIAL)
A N D M A SS FL U X .......................................................................... ....................69

In tro d u ctio n .......................................................................................6 9
T heoretical B ackground...................................................................... ..................69
Entrapm ent and M igration........................................................ ............... 69
Interfacial T ension ............ .................................................... .... ......... ... 70
D en sity ...................................... ................................................ 7 2
Stu dy O bjectiv es ................................................. ................. 72
M materials and M methods ....................................................................... ..................73
G general Experim ental .............................................. ....... ....................... 73
D ensity M odification......... .................................................. ...... ............. 73
Interfacial Tension M odification..................................... ......... ............... 74
Results and Discussion .................................. ......... ................. 76
IFT Modification Results and Discussion ............... ................................. 76
Density Modification Results and Discussion.........................................79
Flow By-Passing and Mass Transfer Rate Limitation.............................85
C o n clu sio n s..................................................... ................ 8 6

5 INVESTIGATION OF CONTAMINANT MASS FLUX HYSTERESIS ................87

In tro d u ctio n ............. .. .. ................ ................................................................. 8 7
T heoretical B ackground............................................ ....................................... 88
Stu dy O bjectiv e ................................................................90
M materials and M methods ....................................................................... ..................90
R results and D iscu ssion .............................. ........................ .. ...... .... ...... ...... 9 1
C o n clu sio n s..................................................... ............... 9 3









6 SUMMARY, CONCLUSIONS AND RECOMMENDATIONS ...........................94

S u m m a ry ............................................................................................................... 9 4
C o n c lu sio n s........................................................................................................... 9 5
Recommendations........ .......... ......... .................. ........ 96

APPENDIX

A AIR, WATER, AND OIL ENTRY PRESSURE BREAKTHROUGH GRAPHS
FOR HYDROPHOBIC M IXTURES ........................................ ...... ............... 97

B TWO-DIMENSIONAL FLOW CHAMBER DISTRIBUTION CONTOURS FOR
GRAIN SIZE AND WETTABILITY EXPERIMENTS .............. ....................106

C TWO-DIMENSIONAL FLOW CHAMBER DISTRIBUTION CONTOURS FOR
INTERFACIAL TENSION AND DENSITY MODIFICATION EXPERIMENTS 115

L IST O F R E FE R E N C E S ........................................................................ ................... 120

BIOGRAPHICAL SKETCH ............................................................. ............... 127
















LIST OF TABLES


Table page

2.1 Calculated contact angles ........................................................... ............... 34

3.1 Calculated bond, capillary and total trapping numbers .......................................38

3.2 M edia properties......... .................................................................. .......... ....... 44

3.3 Correlation analysis using box 28 40/60 (0.32) sand sieve 3 value.........................57

3.4 Correlation analysis using box 22 40/60 (0.32) sand sieve 3 value.........................57

3.5 Force balance data ................................................... ..... .. ........ .... 63

3.6 Theoretical force balance results.................................... ........................... ......... 63

4.1 D ensity sieve size experim ents ........................................... ......................... 73

4.2 Decane/PCE densities and respective mole and volume fractions.........................74

4.3 Interfacial values tested and respective Span 80 percentage........................ 76

4.4 Calculated bond, capillary and total trapping number for each IFT ......................78

B.1 Injection amount and associated sketch number............................... ...............106
















LIST OF FIGURES


Figure pge

1.1 Source zone and associated flux across a control plane.................... .............4

1.2 Hypothetical source zones of equal mass and their relative mass flux values...........5

1.3 Hypothetical flux values per unit mass/volume of contaminant.............................6

1.4 Hypothetical source zones of equal mass and their relative 3 values .................... 13

1.5 E x am ple P v alu e curv es ........................................... .......................................... 14

1.6 Experim mental D design .......................... ........... .......................... ............... 17

1.7 Two-dimensional flow chamber design ........ ...... ...... ............... .............. 18

2.1 Contact angle through aqueous phase of a DNAPL.....................................23

2.2 Example capillary pressure curves illustrating parameters used............................26

2.3 Water entry pressure/Air entry pressure column design .......................................29

2.4 Volume change as a function of water entry head for 50% OTS treated sand.........30

2.5 Volume change as a function of air entry head for 50% OTS treated sand.............31

2.6 Oil entry pressure in the presence of water column set-up ................................32

2.7 Water (air), air (water), and oil (water) Entry Pressure Values ............................35

3.1 Schematic diagram of pressures/forces action on a NAPL globule......................37

3.2 Schematic diagram of pressures/forces action on a NAPL globule ...................41

3.3 Tw o dim ensional cham ber set-up ................................................. .....................43

3.4 100% OTS treated 30/40 (0.48) sieve sand at 2.5 ml of PCE.............. ...............48

3.5 100% OTS treated 30/40 (0.48) sand contaminant volume versus flux................48

3.6 Untreated 30/40 (0.48) sieve sand at 4.5 ml PCE content.................. .......... 49









3.7 Untreated 30/40 (0.48) sand contaminant volume versus flux..............................49

3.8 30/40 (0.48) sand pooling experim ent.................................. ........................ 51

3.9 30/40 (0.48) sand experiment PCE distribution ..................................................51

3.10 Volume versus percent mass flux grain size comparisons................... ..............52

3.11 20/30 (0.68) and 50/70 (0.23) duplicate experiment............................. .............54

3.12 30/40 (0.48) sieve sand curve fit example.................................... ............... 54

3.13 Curve fit com prisons (grain size) ........................................ ........ ............... 55

3.14 versus grain size diam eter ......... ................. ................................ .. ............. 56

3.15 30/40 (0.48) Sand 25% OTS mix trace ........................................ ............... 58

3.16 30/40 (0.48) Sand 100% hydrophobic mix trace.................... ........................... 58

3.17 Volume versus percent mass flux hydrophobic comparisons ................................60

3.18 75% and 100% OTS treated data curve fit examples......................................62

3.19 Curve fit comparisons (wettability)..................... ..... .......................... 62

3.20 Example sketch superimposed over 0.5 cm grid.................... ........................... 65

3 .2 1 20/30 curve com prison ................................................................ .....................66

3.22 Hydrophobic sand curve comparisons. ........................................ ............... 66

4.1 Span 80 percentage and resultant interfacial tension Semi-Log ...........................75

4.2 Maximum PCE concentration as function of percent surfactant (Span 80).............75

4.3 3 dynes/cm interfacial tension distribution ................................... .................77

4.4 47 dynes/cm interfacial tension distribution ................................. ..................... 77

4.5 Interfacial tension comparisons................................................... .. .................78

4.6 Interfacial tension curve fit ............................................. ............................. 79

4.7 U treated PCE distribution ............................................. ............................. 80

4.8 1.1 density distribution ............ .... .......................................... .. 80

4.9 D density com prisons ...................... ................ ................. ..... ...... 82









4.10 D density curve fit ....................... ....... ........................ ........... 83

4.11 1.4 density distribution ......................................................................... 84

4.12 Curve comparisons for 1.1 density PCE in 30/40 sand ................. ...............84

4.13 Curve comparisons for 1.4 density PCE in 30/40 sand ................. ...............85

5.1 Reversible flux loading and dissolution processes........................................89

5.2 Hysteretic flux loading and dissolution processes .........................................89

5.3 TCE mass increase/dissolution experiment one .................................................92

5.4 Breakthrough curve .................. ...................................... .. ............ 92

5.5 TCE mass increase/dissolution experiment two ............................................... 93

A. 1 Untreated sand air entry pressure (water saturated) ...........................................97

A.2 25% Octadecyltrichlorosilane (OTS) treated air entry pressure (water saturated) ..98

A.3 40% OTS treated air entry pressure (water saturated) ..........................................98

A.4 50% OTS treated air entry pressure (water saturated) ..........................................99

A.5 60% OTS treated air entry pressure (water saturated) ..........................................99

A.6 75% OTS treated air entry pressure (water saturated) .......................................100

A.7 100% OTS treated air entry pressure (water saturated) .............. ... ...............100

A.8 100% OTS treated water entry pressure (air saturated) .............. ... ...............101

A.9 75% OTS treated water entry pressure (air saturated) .......................................101

A. 10 60% OTS treated water entry pressure (air saturated) ..................................102

A. 11 50% OTS treated water entry pressure (air saturated) ........................................102

A. 12 40% OTS treated water entry pressure (air saturated) ........................................103

A. 13 Untreated oil entry pressure (water saturated) ..................................... ........103

A. 14 25% OTS treated oil entry pressure (water saturated) .......................................104

A. 15 50% OTS treated oil entry pressure (water saturated) ...........................104

A.16 75% OTS treated oil entry pressure (water saturated) .......................................105









B .1 20-30 Sieve trace experim ent 1 ........................................ ......................... 106

B .2 20-30 Sieve trace experim ent 2 .................................... ........................... ......... 107

B.3 30-40 Sieve pooled PCE trace .......................... ............... 107

B.4 30/40 Sieve trace ............... ........... .................. ........ ............ 108

B.5 40-50 Sieve trace ........ ......... .......... ............. ............ ......... 108

B .6 40-60 Sieve trace experim ent 1 ........................................ ........................ 109

B .7 40-60 Sieve trace experim ent 2 .................................... ........................... ......... 109

B.8 50-70 Sieve trace experiment 1 ............................... ...............110

B .9 50-70 Sieve trace experim ent 2 ................................. .............. .........................110

B. 10 30/40 Sand 25% OTS mix trace (denatured alcohol (DA)) ..................................111

B.11 30/40 Sand 50% hydrophobic mix trace (reagent alcohol (RA))...........................111

B. 12 30/40 Sand 50% hydrophobic mix trace (DA)...................................................... 112

B. 13 30/40 Sand 75% hydrophobic mix trace (RA)...................................................... 112

B. 14 30/40 Sand 75% hydrophobic mix trace (DA)......................................................113

B. 15 30/40 Sand 90% hydrophobic mix trace (DA)......................................................113

B. 16 30/40 Sand 100% hydrophobic mix trace (RA).....................................................114

B. 17 30/40 Sand 100% hydrophobic mix trace (DA).....................................................114

C. 1 Untreated (47 dynes/cm) PCE ............. ................... ................... 115

C.2 0.025% (13 dynes/cm) Span 80 treated PCE ....... .....................................116

C.3 0.05% (3 dynes/cm) Span 80 treated PCE ............. .................................116

C.4 1.4 Density PCE in 30/40 sieve sand ................ .......... .............................. 117

C.5 1.1 Density PCE in 30/40 sieve sand .................................... 117

C .6 1.0 D ensity in 30/40 sieve sand......................................... .......... ............... 118

C.7 Untreated 40/50 sieve sand .......................... .................. 118

C.8 1.1 Density PCE in 40/50 sieve sand .................................... 119















Abstract of Dissertation Presented to the Graduate School
of the University of Florida in Partial Fulfillment of the
Requirements for the Degree of Doctor of Philosophy

EFFECT OF POROUS MEDIA AND FLUID PROPERTIES ON DENSE NON-
AQUEOUS PHASE LIQUID MIGRATION AND DILUTION MASS FLUX


By

Christian T. Totten

August 2005

Chair: Michael D. Annable
Cochair: Joeseph J. Delfino
Major Department: Environmental Engineering Sciences

The influence of porous media and fluid properties on Non Aqueous Phase Liquid

(NAPL) residual geometry and associated contaminant mass flux characteristics was

investigated. Contaminant mass flux is a function of the source zone cross sectional area

exposed to groundwater flow. Porous media and fluid properties affect source zone

morphology leading to cross sectional area development. Media grain size and NAPL

wettability were varied for relative comparisons. Fluid properties including density

differential and interfacial tension between NAPL and water were varied for relative

comparisons. The percent mass flux of perchloroethylene was measured and the

relationship between mass flux and mass loading was developed for different systems.

Results indicated wettability conditions of the media as well as density differential

between fluids had the greatest influence on contaminant flux values from the NAPL

source zone. The results showed that as density differential decreased and the media









became more hydrophobic, the relationship between relative mass flux and percent mass

value changed from a non-linear to a linear relationship. Varying grain size had little

effect on the magnitude of mass flux values but showed correlation with the mass flux

and mass load relationship. The results indicated that interfacial tension between fluids

had minimal effect on mass flux values and a consistent logarithmic relationship between

mass flux and mass load was observed.

Dissolution experiments using trichloroethylene were completed to determine the

relationship between flux values produced during mass loading and flux values produced

during mass reduction. The flux development during loading appears to be hysteretic

with flux development during mass reduction of dissolution.














CHAPTER 1
INTRODUCTION

Background

Non-aqueous phase liquids (NAPLs) are chemicals that have limited solubility in

water. That is, they exist as a separate phase from water. There are two broad categories

of NAPLs. NAPLs that are less dense than water are called light non-aqueous phase

liquids (LNAPLs), and those that are denser than water are called dense non-aqueous

phase liquids (DNAPLs). Their densities relative to water cause each type of NAPL to

behave differently when released into an aquifer. LNAPLs will "float" to the top of the

water table. This characteristic allows easier remediation relative to its DNAPL cousin,

which tends to sink.

A DNAPL will "sink" through an aquifer until it reaches an impermeable layer

where it will collect and reside as a pooled separate phase. They are commonly referred

to as "sinkers" and "toxic blobs" (Gordon, 1996). If fractures or breaks exist in the

impermeable layer, the DNAPL could migrate deeper making access for remediation

more difficult. Most DNAPLs undergo only limited degradation in the subsurface and

can persist for many years while slowly releasing, through dissolution, soluble organic

constituents into the groundwater (Newell and Ross, 1992). Their persistence in

groundwater, combined with their low solubility, poses great challenges for DNAPL

remediation.

Chlorinated solvents are chemicals used for their dissolving capabilities.

Perchloroethylene (PCE) and trichloroethylene (TCE) are two of the most commonly









manufactured and used chlorinated solvents. DNAPLs such as perchloroethylene are one

of the most common groundwater contaminants found because of their extensive use as

industrial degreasers as well as a variety of other uses. They are of concern because of

the health hazards posed to humans (Environmental Protection Agency [EPA], 2003a&b;

Office of Pollution Prevention and Toxics [OPPT], 1994). Many are also dangerous

because of the chemical byproducts produced during degradation. For example,

trichloroethylene (TCE), used as an industrial degreaser, may degrade into vinyl chloride

which is a known carcinogen (EPA, 2003c; NJDHSS, 2002). Perchloroethylene is a

colorless organic liquid with a mild chloroform-like odor and has an absolute solubility in

water of 150 mg/1 (25 C) and a density of 1.626 g/cm3 (20 C) (Verschueren, 1983) and

has a Henry's constant of 0.0153 atm-m3/mol. Trichloroethylene is a colorless or blue

organic liquid and also has a chloroform-like odor similar to that of PCE.

Trichloroethylene has an aqueous solubility of 1100 mg/1 (25 C) and a density of 1.46

g/cm3 (20 C) (Verschueren, 1983) and has a Henry's constant of 0.0103 atm-m3/mol.

Although DNAPLs have been used for several decades, only recently have they

gained attention for causing significant environmental and human health problems. As

recently as 1993, the EPA reported that over 60% of sites with organic contamination are

likely caused by DNAPLs and that 70% of all superfund sites with groundwater

contamination have NAPLs present (Gordon, 1996). For example, the EPA has

determined that more than 1 million pounds of PCE were released to land and water

between 1987 and 1993 (EPA, 2003a). Considering that production and usage of PCE

predates this time period, one could assume that more PCE was released before, as well









as since this time period. These assumptions make it apparent that DNAPLs such as PCE

are suspected to contaminate a large number of sites.

Because of their apparent ubiquity and persistence in the environment and risk to

human health, management of DNAPL contamination in groundwater sources is critical

for providing the public with safe, reliable sources of drinking water. An understanding

of how DNAPLs behave in groundwater systems is critical to both management and

remediation of DNAPL sources. Many studies have been completed to demonstrate that

source zone remediation techniques can remove a large portion of the contaminant mass

present (Brooks et al. 2002; Falta et al., 1997; Fiorenza 2000;Fountain et al., 1995;

Fountain et al., 1996; Jawitz et al., 1998b; Jawitz et al., 2000; Lowe et al., 1999; Martel et

al., 1998; Meinardus et al., 2002; Rao et al., 1997). Additionally, a common performance

metric for source zone removal has been total mass fraction or volume fraction of

contaminant removed (Fiorenza, 2000; Jawitz et al., 1998b; Jawitz et al., 2000; Lowe et

al., 1999; Martel et al., 1998; McCray and Brusseau, 1998; Meinardus et al., 2002; Rao et

al., 1997). This performance metric may only provide partial assessment of remediation

effectiveness. Contaminant flux [M]/[L2][T] is a metric that is becoming more widely

used to characterize contaminant source zones (Figure 1.1) (Einarson and Mackay, 2001).

The relationship between mass flux and the mass of contaminant is not clear (Parker and

Park, 2004; Rao and Jawitz, 2003). It is assumed that source longevity is more directly

related to mass and volume values; however flux is more a function of how the

mass/volume is distributed.

How the mass/volume of the DNAPL is distributed is considered the source zone

geometry. How the source zone geometry is oriented with respect to the flow field









creates a transverse area of exposure. Contaminant flux is a function of this transverse

area of the source zone exposed to flow.

IF Control plane








SOURCE ZONE

Figure 1.1. Source zone and associated flux across a control plane

Figure 1.2 displays hypothetical source zones of similar mass but oriented very

differently with respect to the flow field. The distributions shown on the top of Figure

1.2 display a source zone profile with resultant fluxes annotated with Ji and J2. Each

contour represents a discrete and equal mass loading event. The initial loading

represented by the inner contour event produces geometries of equal area and hence will

produce similar flux values. However, each subsequent loading event would result in

each source zone producing different flux values with J2 ultimately being greater than J1.

The lower distributions shown in Figure 1.2 provide a planar view with resultant fluxes

annotated with J3 and J4. Again, each contour represents a discrete and equal mass

loading event. The initial geometry represented by the inner contour hypothetically

provides the same transverse area, although they are dissimilar in shape, resulting in

similar flux values. However, each subsequent loading event shows the transverse areas

with respect to flow increase more for the geometry represented by J4 than J3. This

results in J4 being ultimately greater than J3. This is an example of how similar mass

introduction can result in vastly different transverse areas. The resulting dissolution mass






flux values per loading event may look like those displayed in Figure 1.3. This exposed
transverse area is determined by the orientation of the source zone to the aqueous flow
field.
P UM


Z

X


J1


Z -



x



z


J2>J


J3


J4


J4>J
Figure 1.2. Hypothetical source zones of equal mass and their relative mass flux values


No












0.3
J4
0.25
J2
S0.25

0.15
M J, or J3
0.1 -

0.05

0 -
0.00 1.00 2.00 3.00 4.00 5.00 6.00
PCE (ml)


Figure 1.3. Hypothetical flux values per unit mass/volume of contaminant

Geometry and Orientation to Flow

Here, "geometry" refers to the shape of the entire NAPL source zone and

"orientation" is how the source zone is placed with respect to the groundwater flow

direction. To better characterize orientation and geometry, NAPL source zones are

divided into two sections that will contribute to mass transfer from the non-aqueous to the

aqueous phase. The first section is the residual DNAPL suspended in the soil matrix by

capillary forces and the second is the pooled section where DNAPL collects on top of a

less permeable or impermeable layer (Sale and McWhorter, 2001). This separation

identifies the potential difference in DNAPL saturation percentages between each section

as well as the potential difference in exposed contaminant surface to cross sectional flow.

Illangasekare et al. (1995) demonstrated that in general, DNAPL saturation of the

contaminant suspended as residual increases as a function of depth until pooling above a

less permeable layer. Hofstee et al. (1998) demonstrated that PCE in a two-dimensional









heterogeneous porous medium consisted of water-entrapped PCE and PCE existing as a

continuous pool on top of the coarse-fine sand interface. Pooling will continue until the

oil entry pressure is reached to allow the DNAPL to displace the water in the finer lower

permeability sand (Corey, 2003).

Sale and McWhorter (2001) stated that mass transfer occurs primarily at the

leading edges of contaminant subzones or geometrically separated sources of NAPL and

that mass transfer through the remainder of the source will be inhibited by upstream

interference. Additionally, if local equilibrium is assumed, the part of the NAPL source

providing the largest leading edge with respect to aqueous flow would be the largest

contributor to contaminant mass flux. It may be that the residual NAPL provides the

larger leading edge exposure when compared to the pooled portion, and is thus the likely

larger contributor to contaminant flux.

Pooled DNAPL

Pooled DNAPL is that portion of the contaminant mass that collects on top of an

impermeable or low permeability layer in an aquifer (Pankow and Cherry, 1996; Sale and

McWhorter, 2001). The pooled portion of a contaminant source will typically have a

larger NAPL saturation compared to the portion of DNAPL trapped as residual. The

pooled portion typically will spread out horizontally along the boundary of the

impermeable or low permeable layer. The pooling and horizontal spreading create a thin

geometry and an orientation resulting in small leading edge exposure with respect to

groundwater flow. Because of the larger volume compared to the trapped residual and

the small mass transfer area, pooled sources are likely to produce low flux but persist for

long periods of time (Johnson and Pankow, 1992).









Residual DNAPL

Extensive work has been focused on studies of media and fluid property interaction

and their effect on DNAPL mobilization, pooling and entrapment (Abrams, 1975;

Bradford and Leij, 1995; Hofstee et al., 1998; Illangaskare et al., 1995; Mayer and Miller,

1990; Moore and Slobod, 1956; Morrow et al., 1988; Ng et al., 1978; Patel and Greaves,

1987; Pennell et al., 1996; Ryan and Dhir, 1993). Capillary forces and their ratio to

viscous and buoyancy forces play a significant role in DNAPL behavior in the sub-

surface (Dawson and Roberts, 1997). Granular porous media are typically water wet and

because of this quality, water will be drawn into the media by capillary forces. In a water

wet environment, the capillary forces can be orders of magnitude larger than viscous

forces, resulting in capillarity being the dominant force. Capillary forces will draw water

into smaller pores, leaving oil in the larger pore spaces. The residual oil exists as isolated

globules in the larger pore spaces (Moore and Slobad, 1956). The shapes of these

isolated globules depend on soil homogeneity/heterogeneity which dictates the pore body

to pore neck ratio or aspect ratio. Homogeneous packs of uniformly sized media have a

low aspect ratio wherein NAPL blobs are spherically shaped, single pore bodies.

Heterogeneous packs have a high aspect ratio and are irregularly shaped and can be

connected by multiple pores (Chatzis et al., 1983; Cho, 2001; Morrow and Heller, 1985).

Residual DNAPL is important because of its ability to produce relatively high

contaminant fluxes for a given mass when compared to pooled sources. The contaminant

fluxes are a function of residual geometry and orientation to flow. Geometry and

orientation of residual DNAPL are determined by migration and entrapment processes.









Migration process

The residual NAPL can take on a variety of geometries and orientations to flow as

it migrates through the porous media. It can move vertically or horizontally through the

saturated zone. The vertical and lateral migration of DNAPL is of more interest because

it is usually oriented 900 to water flow, providing the leading edges and largest area for

contaminant flux production. Vertical movement of DNAPLs is described by the

following equation (Fetter, 1999):

20 cos O(1/rt 1/rp)
Ho = (1-1)
g(pw po)

where Ho is the critical height or head required to displace water in a pore, ois the

interfacial tension between liquids, Ois wetting angle, rt pore is throat radius, rp is pore

radius, g is acceleration due to gravity, p, is water density and po is DNAPL density.

The properties related to media characteristics are rp, rt and 0. The pore throat and pore

radii are approximated as functions of media diameter (d) as follows (Fetter, 1999):

rp= 0.212d (1-2a)

r= 0.077d (1-2b)

Horizontal movement of DNAPL in the saturated zone becomes important if the

pressure gradient causing horizontal movement can overcome gravitation influences.

Horizontal flow is given as follows (Fetter, 1999):

dP 2 (1-3)
(1-3)
dx Lo(1/rt -1/rp)

where Lo is the length of the continuous DNAPL phase in the direction of flow.

In general, DNAPLs can migrate two ways. The first is a "finger" type geometry

that will trickle down through the porous media as a thin line producing discontinuous









blobs retained as residual. Contaminant fingering occurs when a uniformly infiltrating

front is split into "stringers" due to instability from pore scale permeability variations

(Fetter, 1999). Various studies have been conducted to gain a better understanding of

fingering causes and behavior (Brewster et al., 1995; Held and Illangasekare, 1995-a;

Held and Illangasekare, 1995-b; Hofstee et al., 1998; Illangasekare et al., 1995; Peters

and Flock, 1981; Wang and Feyen, 1998). The second migration pathway involves a

more uniform geometry where the NAPL is initially distributed into the pores producing

a uniform advancing front and distribution of trapped NAPL. This might be the result of

more rapid infiltration or displacement by a viscous NAPL. This type of displacement

may be more likley in oil-wet media. Each of these geometries provides large differences

in interfacial and overall contact area between the aqueous and non-aqueous phases.

Entrapment process

As mentioned above, NAPL entrapment is directly related to capillary forces and

their ratio to viscous and buoyancy (gravitational) forces. The Capillary Number is

defined as the ratio of viscous to capillary forces and the Bond Number is the ratio of

buoyancy forces to capillary forces (Perry and Chilton, 1973).


Capillary Number N a = vw/ (1-4)
YowcosO

Ap(k / n)
Bond Number NBo (1-5)
yow cos

where Vw [L/T] is the pore velocity, jtw [FT/L2]is the water viscosity, Yow [F/L] is the

interfacial tension between NAPL and water, Ap [M/L3] is the density difference between

immiscible fluids, k [L2] is intrinsic permeability and n [L3L-3] is porosity of the porous

medium. Pennell et al. (1996) combined the Capillary and Bond numbers into a Total









Trapping Number (NT) used to develop PCE desaturation curves in a one-dimensional

chamber. The NT was developed to combine viscous and buoyancy forces with capillary

forces into a single, comprehensive value. The NT combines force relationships into a

single equation and numerical value to allow for simple mobility and saturation

characterization. It is important to note that the mobility referred to in relation to

trapping number is the ability to mobilize entrapped residual DNAPL and not migration.

The NT identifies those media and fluid properties important to entrapped NAPL residual

and entrapped residual mobility. The NT for a vertical flow system is as follows:

NT = INca + NBo| (1-6)

In the horizontal flow case, it is calculated as follows:

NT= N a+N Bo (1-7)

Theoretically, changing any of the elements in the Capillary or Bond number could

change the overall NT, possibly resulting in different entrapment characteristics for a

given NAPL. Pennell et al. (1996) performed surfactant flooding where PCE-water

interfacial tension was reduced. The result was increased mobility and reduced saturation

of entrapped PCE. Additionally, different combinations of element values will result in

the same Capillary and Bond Number and hence, the same overall NT value.

The elements of The Capillary and Bond numbers related to media properties are

intrinsic permeability, wettability, and porosity. For homogenous media of equal size

spheres, porosity is a fairly consistent characteristic. However, intrinsic permeability and

wettability can be varied greatly by grain size diameter changes and contact angle

modification respectively.









Relating Media Property Characteristics to the Contaminant Mass Flux

Binary model

The dissolution mass flux generated by a particular source zone as a function of

geometry and orientation can be described using a Binary Model (Jawitz et al., 2003).

The model treats the multidimensional flow field as a collection of non-interacting stream

tubes with each tube being either contaminated or clean. The collection of stream-tubes

would be the entire domain such as an aquifer. The fraction (f) of the stream-tubes

contaminated would be the source zone and the remaining fraction (1-/) would be the

clean portion of the domain. The contaminated fraction (f) is directly related to source

zone geometry and orientation to flow. In general, media and fluid properties dictate

migration and entrapment processes. If media or fluid modifications affect source zone

geometry, contaminant mass flux values could be affected as a result of changing

values.

Fractional mass flux versus fractional mass loading and total mass flux

The hypothetical dissolution mass flux and mass loading relationships displayed in

Figure 1.3 provide absolute flux and mass values for a given system and how they relate

to each other. Another interesting characteristic of these curves is their shape. The shape

of the curve gives insight into how flux values are achieved during the mass loading

process. The shape of these curves could be fit using the following simple empirical

model:

Y = X (1-8)

where Y represents fractional source strength, X is fractional mass increase and 3 is

system efficiency. This is similar to the model approach proposed by Rao et al. (2001)

for mass depletion, flux reduction relationships. This model is a retrospective look at the


















--

499*M


13

flux and mass relationships of a given system because they are normalized to each
system's maximum mass and flux values. This allows curve shape non-linearity
comparison from one system to another. Figure 1.4 displays hypothetical source zones of
similar mass or volume and their related 3 values. Figure 1.5 displays the range of curves
that could be encountered for any given system with 3 determining the shape of the
curve.


p1


Z
X


I~I

x


P2


P4


P3


a


Figure 1.4. Hypothetical source zones of equal mass and their relative 3 values


132


p1


.____


P4>P3











Example p Curves




0.9

0.8

o 0.7 1

o 0.6

S05 P=1

.2 0.4

0.3

0.2
p>1
0.1

0
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1
Fractional mass/volume increase


Figure 1.5. Example 3 value curves

A linear relationship or 3 value of approximately one (1.0) would indicate a one-to-

one relationship between fractional mass increase and fractional flux increase. As the 3

value decreases below 1.0, the curves become logarithmic, indicating higher relative flux

increase per fractional mass at lower fractional mass values. As the fractional mass

continues to increase, the increase in fractional flux slows. The lower the 3 value, the

more pronounced this loading behavior becomes. The opposite occurs for 3 values

greater than one and the curves become exponential in shape, requiring greater mass to

generate most of its fractional flux. It would occur in a system where flux production is

delayed during mass loading. One such system would be a heterogeneous system where

the DNAPL source would gather on a low permeability lens until breakthrough or









spilling occurred producing a larger residual cross section to produce higher flux values.

It could be argued that 3 is an all inclusive value capturing a wide range of media and

fluid characteristics that affect dissolution efficiency.

Study Objectives

Based on the background provided above, the following objectives of this research

were to:

1. Determine the relationship between hydrophobic media content and water, air

and oil entry pressure and related contact angle values. Water wet, oil wet, and

intermediate wet systems were investigated to determine water entry pressure, air entry

pressure, and oil entry pressure trends.

2. Determine the relationship between porous media properties and

contaminant mass flux. Two media properties, grain size and wettability, were studied

to determine their influence on geometry and contaminant mass flux properties in a two

dimensional flow chamber. A reduction in grain size may affect migration and

entrapment characteristics and ultimately DNAPL geometry. DNAPL distributions in an

oil wet media may influence geometry of a source zone, possibly affecting contaminant

mass flux properties. Absolute mass and flux value relationships as well as values were

determined for these media systems.

3. Determine the relationship between fluid properties contaminant and mass

flux. DNAPL migration in saturated porous media is influenced in part by the density

differential between the aqueous and non-aqueous phase. Changing this differential

while keeping other characteristics constant could change DNAPL migration. This study

assessed the influence of reducing the density differential between immiscible fluids and









the effect that differential reduction has on DNAPL migration and associated

contaminant mass flux properties.

Interfacial tension is an important physical property that can influence migration of

DNAPLs such as PCE. Lowering interfacial tension of PCE may increase migration,

thereby influencing source zone geometry, and ultimately contaminant mass flux

properties. Absolute mass and flux value relationships as well as 3 values were

determined for these fluid systems.

4. Determine the mass loading and dissolution behavior of TCE. Contaminant

mass flux curves generated through mass loading were compared to those resulting from

mass reduction. This provided insight into the relationship between mass loading and

mass dissolution processes.

General Methodology

The following general overall design was implemented as part of the experimental

portion of this research. Various parameters were held constant while a single parameter

was varied.

The following general set up was used for each experiment. A series of

experiments was conducted in a two-dimensional simulated aquifer experiments in

systems as shown in Figure 1.6. The design shown in Figure 1.6 is just an example to

show that one characteristic can be varied while others are held constant and is not an

indication of the exact variations of this research. The two dimensional flow chamber

employed was similar in design to those used by Jawitz et al. (1998a) and Conrad et al.

(2002), and reviewed by Chevalier and Petersen (1999).



















grain size






III




grai sie





Irterfacial Tension!
Capmaiy Pressure


Figure 1.6. Experimental Design

The chamber design is shown in Figure 1.7. The "simulated wells" on each end of

the column had slots at intervals of 4 slots per cm and served as the influent and effluent

wells. Injection of PCE took place in the center of the chamber as shown in Figure 1.7.

PCE injection was made through the wall of the column using a needle securely fixed

with epoxy into the glass wall. PCE was injected through the needle using a gas tight

syringe placed on a syringe pump.

























14cm


7/ 1.4cm


- 28.5 cm


Figure 1.7. Two-dimensional flow chamber design

The two dimensional flow chamber was packed uniformly with the appropriate

medium for the specific objective. The top of the medium was covered with Bentonite

clay to maintain media pressure saturation and minimize volatile losses. NAPL was

injected into the side of the column at a specified rate using the syringe pump. The PCE

volume was injected in a stepwise fashion at a particular volume per injection up to a

predetermined total volume. All measurements were conducted under steady-state,

saturated flow conditions. Effluent samples were collected after the system achieved

steady state mass flux. The number of pore volumes required to achieve mass flux steady

state was experimentally derived. An Oil-Red-O dye tracer was added to the PCE to aid









in visual observation of the PCE in the 2-D column (Jeong et al., 2002). Flow rates were

controlled to maintain a constant mass transfer rate from one experiment to another and

to aid in comparisons of the various experimental results.

Samples collected throughout the experiment were analyzed using a Perkin Elmer

AutoSystem XL Gas Chromatograph (GC) with a Flame Ionization Detector (FID). The

FID was appropriate because it met the sensitivity requirements of the expected sample

concentrations and its low selectivity was not impaired by the relatively clean samples

(PCE being the only contaminant). Each sample was analyzed for PCE concentration

which was used to calculate PCE percent mass flux.

Dissertation Organization

Each of the following chapters, 2-5, is written as a stand alone paper. Each chapter

contains an Introduction, Methods and Materials, Results and Discussion, and

Conclusion. Chapter 2 includes results of the wettability properties study. Chapter 3

discusses results of the media properties study. Chapter 4 presents the results of the fluid

properties study. Chapter 5 presents the TCE mass loading and dissolution study.

Chapter 6 is a summary of this research and presents major conclusions of the overall

effort and identifies recommendations for future research.














CHAPTER 2
WETTABILITY STUDIES

Introduction

Wettability is the relative affinity of the solid media for fluids such as air, water or

organic immiscible liquid (OIL) (Wilson, 1988). The degree ofwettability is a function

of the solid surface, OIL properties and composition of the water. Hydrophilic sands

have an affinity for water because of their polarity and are considered water wet.

Hydrophobic sands have more affinity for oil, or perhaps air, than water because they

have a non polar surface and are considered oil wet. Moore and Slobod (1956) divided

soil into three categories which include (1) water wet and (2) oil wet soils, and added (3)

intermediate wettability soil. The intermediate wettability category has characteristics of

both hydrophilic and hydrophobic media.

Understanding wettability is of great interest to both the environmental restoration

and oil industries because oil and contaminant recovery is greatly influenced by this

porous media property. Donaldson (1969) reported that oil recovery, as a function of

water injected, is greater from water wet cores than oil wet cores. He went on to state

that some findings indicate that oil recovery is better in intermediate wettability soil

environments rather than either extreme.

According to Wilson (1988), it is typically assumed in reservoir engineering studies

that rock is water wet. However, he reported that Treiber et al. (1972) studied reservoir

rocks from 55 oil reservoirs, 15 being water wet, 3 of intermediate wettability and 37 as

oil wet. Although these findings are related to oil reservoirs, it is an indication of the









variability in wettability conditions that are possible. Powers et al. (1996) found that a

wide range of wetting conditions can be expected following spills of complex NAPL

mixtures to the subsurface.

Silica surfaces are hydrophilic or naturally polar and can have their wetting

characteristics changed in a variety of ways. Silica surfaces such as quartz sand can be

altered by organic material becoming deposited on their surface and/or by the adsorption

of polar oxygen-, nitrogen-, or sulfur-containing compounds. These deposition and

adsorption processes can occur through physical (heat), chemical (adsorption), or

biological means (Wilson, 1988). Wilson (1988) reported that fires convert heavy wax-

like substances in the vegetative cover to an organic coating. This organic coating can

alter the wettability of characteristics of the affected soil. Although this is an example of

a physical mechanism, it appears that ultimately the coating had adsorbed to the surface

of the media, altering wettability.

Powers and Tamblin (1993) found that polar molecules of high molecular weight or

surfactants added to commercial gasoline as deicers, corrosion inhibitors, or carburetor

cleaners increased hydrophobicity as they adsorbed to quartz slides. This indicates a

potential for a wide range of wettability characteristics at sites where OIL products have

been released.

The biological mechanisms that affect subsurface wettability are poorly understood

(Wilson, 1988). However, it is apparent micro-organisms play an important role in

affecting subsurface wettability. Wilson (1988) reported golf course putting greens at

various courses around the country face management problems due to soil

hydrophobicity. Under these conditions, a layer occur creating high water content and









anaerobic conditions. This favors growth of microorganisms that deposit hydrophobic

coatings of organic metal sulfides on soil particles.

It is clear that the assumption of water wet subsurface media may not always be

appropriate. This is an important assumption impacting a wide range of areas from golf

course management, oil recovery, and contaminant remediation. For example, wettability

conditions may impact the effectiveness of DNAPL remediation methods if there is an

affinity between DNAPL and media surface. It is important to be able to quantify

wettability conditions for better management practices.

Theoretical Background

Measurement of wettability can be made qualitatively and quantitatively.

Donaldson et al. (1969) listed several methods for qualitatively assessing wettability.

They determined that these methods could only classify a system as water wet or oil wet,

but lacked the ability to satisfactorily classify intermediate wettability systems. Powers

et al. (1996) demonstrated a qualitative bottle test that was able to visually distinguish

between intermediate wetting systems. This method is qualitative because it determines

system wettability based on observation of NAPL distribution between solid and aqueous

phase and does not provide a quantitative value. This method is useful for relative

system comparisons. This appears to be a quick method for determining relative

wettability characteristics for a variety of systems and does not suffer from the same

limitations of the methods listed by Donaldson et al. (1969). However, when developing

oil recovery and remediation strategies, a more quantitative approach may be required.

Contact angle is often considered the best measure for quantifying wettability and

is widely used (Bahrani et al., 1973; Bradford and Leij, 1995; Fink, 1970; Moore and

Slobod, 1956; Letey et al., 1962; Powers et al., 1996; Watson and Letey, 1970). Powers









et al. (1996) and Bradford and Leij (1995) reported that the contact angle (0) between

two fluids and a solid surface is the result of mechanical equilibrium or horizontal force

balance among the interfacial energies as described in Young's equation

yso s= yowcos(0) (2-1)

where y is interfacial energy and solid, organic, and aqueous phases are represented by

superscripts, s, o, and w respectively.

Direct measurement of the contact angle is one method for quantifying contact

angles. Contact angles can be measured by static or dynamic methods. For static

methods, advanced or receded contact angles are measured, while for dynamic methods,

the angles are referred to as advancing or receding. The contact angles are usually

measured through the aqueous phase with 0 to 900 being water wet and 900 to 1800 being

oil wet, and neutral wetting around 900 (Figure 2.1).


aqueous phase
0 = contact angle
through aqueous
phase DNAPL



solid surface

Figure 2.1. Contact angle through aqueous phase of a DNAPL

Powers et al. (1996) reported that various researchers used different ranges of

contact angles to categorize neutral wettability. For example, Powers et al. (1996)

reported that Treiber et al. (1972) used 72-1050 and Morrow (1976) used 62-133.

Slobod and Moore (1956) used advancing contact angles of near 300 to describe water-









wet systems and angle greater that 900 to be oil wet with intermediate systems in

between.

An example of a static method was used by Powers et al. (1996). They exposed a

quartz slide surface to a variety of organic phases to achieve a variety of wetting

conditions. These slides were then submerged in groundwater and exposed separately to

a variety NAPLs including gasoline, diesel fuel, fuel oil, crude oil, creosote, coal tar,

toluene, and TCE. The NAPLs formed drops on the treated slides. DNAPLs were

placed on the top of the slides while LNAPL drops formed under the slides. After

equilibration was achieved, a goniometer was used to directly measure the contact angle.

Advanced angles were measured on each side of the slide. This method is similar to the

sessile drop method used by Fink (1970). In this method, water is added to a flat level

surface being tested until further additions increase the drop diameter, but not the height.

The contact angle is a function of this height and therefore can be calculated. Since the

water is being added, the advanced contact angle is calculated. These methods work well

for quantifying homogeneously coated media. However, some media may be a

combination of a variety of surfaces, some organic and some not.

The contact angle of a porous media can be calculated by measuring infiltration

rates (Bahrani et al., 1973; Jamison, 1946; and Letey et al., 1962). Letey et al. (1962)

used the following equation to calculate contact angles:

nr(prgh + 2ycos) (2-2)
8L/

where Q" is the water entry rate at the soil surface, n is porosity, r is the capillary radius,

p is the density of solution, h is the capillary length plus depth of solution above

capillary, y is surface tension of solution, L is capillary length and r is viscosity of the









solution. In this equation, r and 0 are unknown so a reference fluid such as ethanol with a

known 0 is used to experimentally measure r to be used for other treatments. Water entry

rates were then experimentally measured for various media treatments altering contact

angle. With all other data known, contact angle 0 was calculated using the above

equation. Similarly, Bahrani et al. (1973) used infiltration rates to experimentally derive

penetrability coefficients used to calculate contact angle. They derived these

penetrability coefficients after each of six wetting and drying cycles. They determined

that wetting, leaching and drying cycles change contact angles significantly from one

cycle to the next. However, they also determined that changing surface tension of the

water and changes in soil porosity showed no significant impact on wetting.

Letey et al. (1962) determined that infiltration rates did not hold true for sand

columns and resorted to capillary rise at equilibrium, p, = pg. They experimentally

measured h using sand columns and calculated contact angle using the following

equation:


h = 2ycos() (2-3)
pgr

Contact angle can be represented by capillary pressure by the following equation:


Pc = P 2 cos() (2-4)
r

where p, = capillary pressure, pn" = non-wetting fluid pressure, p" = wetting fluid

pressure, yow = interfacial tension between oil and wetting phase, c = contact angle and r

is capillary tube radius. This relationship between capillary pressure and contact angle

can be used to quantify the wetting characteristics of a two phase system. The United

States Bureau of Mines (USBM) (Donaldson et al., 1969; Powers et al., 1996) and the









Amott-Harvey (Powers et al., 1996) methods are commonly used. Each method uses data

obtained from comparing imbibition and drainage capillary pressure/saturation curves

(Figure 2.2).






bS S,
L0 i drabbiion



(a) UISBM (b) Arr,,on 1-. rv "
3 Aqueous Phase Saturation (-)

Figure 2.2. Example capillary pressure curves illustrating parameters used for : (a)
USBM; (b) Amott-Harvey wettability indices (Powers et al. 1996)

The USBM method compares imbibition and drainage areas to assign a wettability index
using the following equation (Powers et al. 1996):
Iusbm = log(Ai/A2) (2-5)

where A1 is the area under the drainage curve to the horizontal axis and A2 is the area

above the imbibition curve to the horizontal axis (Figure 2.2). The Amott-Harvey

method uses different data from capillary pressure curves to calculate a wettability index

using the following equation (Powers et al. 1996):

(lAS aS,)
h = AS(2-6)
S(1- S, Sw")

where ASs = difference between saturation at Pc = 0 and the residual saturation of the

water phase, ASs= difference between saturation at Pc = 0 and the residual saturation of

the oil phase, and Sr= residual saturation of the oil phase and Srw= residual saturation of

the water phase. None of these methods directly calculate the contact angle, however









they do give a numerical value for system wettability that is directly related to contact

angle.

Fink (1970) experimentally measured breakthrough pressure for water repellent

soils to quantify system wetting. This is essentially equivalent to the entry pressure or hd

that can be readily identified and quantified on a typical Brooks-Corey capillary pressure

curve. Fluid entry pressures can be determined for air in the presence of water or oil,

water in the presence of oil or air, and oil in the presence of water or air. An example

would be oil penetrating water saturated hydrophilic porous media. Depending on

conditions of the system such as type of oil, water composition, and surface type, the oil

will require a certain amount of head or entry pressure to displace the water in the porous

media. These entry pressure values are directly related to system wettability. Fink

(1970) used the experimentally determined h (entry pressure) value in equation 2-3 to

calculate 0. He compared the calculated 0 values from the sessile drop method to the 0

values calculated using the breakthrough pressure method. He assumed theoretically they

would be equal but determined that they were not. However, he noted that they each

showed similar trends, and therefore each could be used to make relative comparisons

between wetting systems.

There are many methods for quantifying system wettability. It appears that most

methods cannot be compared to each other directly. However trends can be compared

from one method to the next as well as wetting systems can be quantified and compared

to each other if a consistent method of measurement is used.









Study Objective

The objective of this study was to conduct water entry pressure, air and oil entry

pressure tests for silica sand with various fractions of organic (silane) coated media. This

was to quantify system wettability for a water wet, oil wet and intermediate wet systems.

Methods and Materials

Water/Air Entry Pressure Measurements

A series of water entry pressure (WEP) and air entry pressure (AEP) tests were

completed for sands with octadecyl trichlorosilane (OTS) treatment percentages of 0, 25,

40, 50, 60, 75, and 100%. Organosilanes such as OTS are effective for changing the

surface polarity of the media resulting in an oil-wet environment. Hydrophobic sand was

created using an OTS treatment method used by Bradford and Leij (1995) and Le Grange

(1993) as follows: 475 ml of denatured or reagent alcohol mixed with 25 ml of OTS to

create a 5% OTS mixture; 575 ml of 30/40 Accusand was added to the 5% OTS solution

and mixed for 5 hours. At the completion of mixing, the excess solution was drained off

and the sand was rinsed again with denatured or reagent alcohol. The sand was then heat

dried for several hours. To create each of the hydrophobic/hydrophilic percent volume

combinations listed earlier, the appropriate amount of OTS treated sand was mixed with

untreated sand to create the desired OTS/untreated sand percent ratio. Denatured alcohol

was used for all experiments. Additionally, reagent alcohol treated sand was used for a

second 100% OTS experiment.

The WEP and AEP for OTS/untreated sand mixtures listed above were determined

using the apparatus shown in Figure 2.3. For the WEP measurements, each mixture

listed in above was packed to a depth of 6 cm in the bottom of a long glass column. The

column was plugged at the bottom with a rubber stopper with a hole in the center. The









stopper had a stainless steel mesh filter placed on top to support the sand in the glass

tube. The stopper was attached to a burette using a section of 4" tubing. The burette

was placed so that the top was level with the bottom of the sand in the column. Water

was placed in the burette to contact the bottom of the soil column.


Figure 2.3. Water entry pressure/Air entry pressure column design

The burette was then raised in approximately 0.5 to 2 cm increments increasing the

head of water at the bottom of the sand and allowed to stabilize for several minutes. The

volume in the burette was recorded for each increment. The height at which the volume










of water began to enter the sand column was used as the head required for water entry or

WEP (See Figure 2.4).





35




25




S15
16




05

0
0 1 2 3 4 5 6 7
Water Height (cm)



Figure 2.4. Volume change as a function of water entry head for 50% OTS treated sand

For the AEP tests, approximately 6 cm of sand for 0, 25, 40, 50, 60, 75, and 100%

mixtures was placed in the bottom of a long glass column (Figure 2.3). The top of the

column was plugged with a stopper attached to a T valve. The T valve was connected to

a vacuum source and the side port of an Erlenmeyer flask. The flask was filled with

water and sealed at the top with a rubber stopper. The stopper had a glass straw with one

end submerged in the water. The top of the flask was attached via rubber hose to the

stopper at the bottom of the column. This system was closed looped, preventing the

water from leaving the flask. The vacuum was turned on for 15 to 20 minutes to de-gas

the water in the flask. The tube attached to the side port of the flask was then crimped,

allowing the vacuum to draw the water through the top of the flask and into the bottom of











the column. A vacuum was used to facilitate water saturating the OIL and intermediate


wet sand mixtures. Water was allowed to enter the column, saturating the sand as the


water was drawn up by the vacuum. When the sand was completely saturated with water,


the vacuum was shut off and the top of the flask was detached from the hose. This hose


was then placed on the bottom of a burette. Water was allowed to exit the bottom of the


column filling the burette until the top of the water table in the column was equal to the


top of the sand. The height of the burette and volume of water in the burette was adjusted


such that with the water table at the top of the sand, the level of the water was at the


bottom of the burette. The burette was then lowered in increments of 0.5 to 1.5 cm. For


each height, the volume in the burette was measured and recorded. The height at which


the volume of water began to enter the burette was assumed to be the head required for


air entry or AEP (See Figure 2.5).


8


7


6


5

4i
2


3







0
0 2 4 6 8 10 12 14 16 18
Negative Water Height (cm)

Figure 2.5. Volume change as a function of air entry head for 50% OTS treated sand








Oil Entry Pressure Measurements
A series of oil entry pressure (OEP) tests using PCE in the presence of water were
completed for sands with OTS treatment percentages of 0, 25, 50, 75 and 90%. The
OEP for these OTS/untreated sand mixtures were determined using the apparatus shown
in Figure 2.6. Each mixture listed was wet packed to an approximate depth of 5 cm in the
bottom of a short glass column. The column was plugged at the bottom with a rubber
stopper with a hole in the center. The stopper had a stainless steel mesh filter placed on
top to support the sand in the glass tube. A rubber tube was attached to the stopper at one
end and a burette at the other end. There was a three way valve in the closed position
between the burette and column. The water used for wet packing was degassed with
helium for approximately 15 minutes prior to packing. This is necessary because silane
coated sand has an affinity for air in the presence of water.


Column
w/water


Sand
mix


Vacuum

A


Burette w/PCE



hi


Figure 2.6. Oil entry pressure in the presence of water column set-up









Regardless of degassing, air bubbles were still present during the packing process. The

column was sealed and a vacuum applied to further remove the air from the system. The

column was then reopened and the sand was tamped down into the column to achieve a

tight sand packing. A vacuum was applied again followed by compacting of the sand.

This process was repeated until all visible air was removed. The burette was placed so

that its top was level with the bottom of the sand in the column. Perchloroethylene was

placed in the burette and drained through the three way valve to remove any air from the

line while maintaining the water level in the column. After the air had been drained, the

valve was placed as such to allow the PCE and water to contact. The burette was raised

such that the PCE contacted the bottom of the soil column. The burette was then raised in

approximately 0.5 to 2 cm increments increasing the head of PCE at the bottom of the

sand and allowed to stabilize for several minutes. The volume in the burette was

recorded for each increment and the height at which the volume of PCE began to enter

the sand column was assumed to be the head required for Oil entry or OEP similar to the

process for water entry pressure in the presence of air.

Results and Discussion

The pressure breakthrough curves for each sand mixture are displayed in Appendix

A. Calculated contact angle values are shown in Table 2.1. The contact angles were

calculated using equation 2-3 (Fink, 1970) and the WEPa AEPw, and OEPa values as

height (cm). Water contact angles decreased as OTS percentage decreased. All contact

angles were >90, indicating oil wet system. Contact angles for 25% and 0% mixtures

were estimated from the projected capillary rise shown in Figure 2.7. Air contact angles

did not vary indicating air is always the non-wetting fluid. Oil contact angles decreased

as OTS percentage decreased, indicating the media becoming more water wet. The









WEPa, AEPw and OEP values as a function of hydrophobic media percentage are

displayed in Figure 2.7. The WEPa for the hydrophobic sand decreased from a maximum

of 9 cm to 5 cm as the hydrophobic percentage decreased. The mixtures exhibited

hydrophobic behavior down to 40% OTS (hydrophobic) sand content. Water entry

pressure for the 25% OTS sand content could not be measured because the water rose by

capillary action, indicating the switch from hydrophobic to hydrophilic behavior. The air

entry pressure with respect to OTS percentage showed a slight decline from 15 cm to 12

cm in AEPw from 0% to 75% OTS percentage respectively. The 100% OTS sand showed

a slight increase back to 13 cm. This is a slight indication that the untreated sand retains

the water or requires more pressure to begin draining water when compared to the OTS

treated sand mixtures. Oil entry pressure was affected by the changing hydrophobicity,

requiring less entry pressure as hydrophobicity increased. The point at which entry

pressure is no longer required and PCE is drawn into the sand by capillary action appears

to be between 75% and 90% OTS treated sand content.

Table 2.1. Calculated contact angles
Water Air 0 (in OIL 0 (in
0 (in air) water) water)
% OTS degrees degrees degrees
100 128.5 25.8
90 90.0
75 121.2 33.8 86.1
60 114.5 33.8
50 114.5 25.8 80.3
40 110.2 28.8
25 90.0 25.8 78.3
0 0.0 0.0 66.1


Conclusions

The change in percent OTS treated sand influences water entry and oil entry

pressure values. The displayed trend shows that as OTS percentage decreases, water










entry pressure values decreased from 15 cm of capillary rise to -9 cm of entry head. As

the OTS percentage increased, the oil entry pressure values decreased from 6 cm of entry

head until reaching 90% at which the sand displayed hydrophobic characteristics and

drew the PCE into the media by capillary action. The trend related to air entry pressure

showed that AEP values were not sensitive to OTS percentage changes. Bradford and

Leij (1995) noted that air is always considered the non-wetting fluid, therefore, water

would be the wetting fluid regardless of soil treatment. This might explain the

insensitivity of the AEP values.


% OTS
Water Entry Pressure Air Entry Pressure Oil Entry Pressure 1 projected


Figure 2.7. Water (air), air (water), and oil (water) Entry Pressure Values for each
mixture percentage Note data points +/- 1cm


10 20 40 50 60 70 80 90
10 20 Sd 40 50 60 70 80 90 1K














CHAPTER 3
INVESTIGATION OF THE RELATIONSHIP BETWEEN MEDIA PROPERTIES
(GRAIN SIZE AND WETTABILITY) AND MASS FLUX

Introduction

As Dense Non-Aqueous Phase Liquids (DNAPL) migrate in the subsurface, media

and fluid properties influence how and where they will travel and distribute. DNAPLs,

serve as long term contaminant sources slowly dissolving into the aquifer. Typically, the

solubilities of NAPLs in water are quite low; however, they are usually orders of

magnitude higher than applicable drinking water/clean up standards. An understanding

of how porous media and fluid properties affect travel and distribution behavior is needed

to develop effective remediation strategies to manage these long term contaminant

sources. Media properties such as soil type, media heterogeneity or homogeneity, grain

size, grain shape, and wettability characteristics are needed to characterize DNAPL

source zones. These properties influence contaminant behavior in sub-surface systems.

What remains after migration is contaminant residual that is suspended or trapped in the

porous media as residual and/or pooled on an impermeable layer at a low point in the

aquifer. The residual and pooled NAPL surfaces provide a contact area based on

geometry and orientation for NAPL to transfer to the aqueous phase.

Theoretical Background

Porous media grain size and contact angle (wettability) are the common

components governing NAPL migration and entrapment processes.









Grain Size

Grain size is an important parameter that affects the flow, gravitational and

capillary pressures acting on a DNAPL globule in the subsurface. Pennell et al. (1996)

proposed a pore entrapment model describing the forces acting on a NAPL globule that

affect its mobilization after entrapment. A similar model can be used to observe the

forces acting on a NAPL globule during migration processes. Figure 3.1 displays the

forces acting on a NAPL globule in a pore.


L'x


Sand



P
^^.A
PC __ __ __ __ N


Sand



waerP
water o P


Pg PI PI

Figure 3.1. Schematic diagram of pressures/forces action on a NAPL globule


Capillary forces are represented by Pc, injection forces Pi and gravitational forces

are Pg. The forces identified are similar to those identified by Pennell et al. (1996) shown

in equation 3-1 with the exception of the injection force.









water flow + gravity = capillary

Wp q + ApgAl sin a Cos whereft =1 r" (3-1)
k r rb

where ,tw is the fluid viscosity, Ap is the density differential, qw is the darcy flux,

kw is intrinsic permeability, Al is average length of DNAPL globule, ao is the angle with

respect to flow, 0 is the contact angle, rn is neck or throat radius, and rb is blob radius. As

grain size changes, intrinsic permeability changes affecting the flow conditions, the

potential length of the globule changes affecting globule size and weight, and the throat

radius changes affect capillary pressure. In a system where groundwater flow is

perpendicular to gravitational forces, the flow force will be less significant compared to

gravitational forces when determining migration behavior in the direction of gravity and

transverse to the flow field. Additionally, the flow force is a magnitude smaller through a

range of sand sizes when compared to the gravity forces (Table 3.1).

Table 3.1. Calculated bond, capillary and total trapping numbers using equations 1-4 and
1-5
K
Seive (cm/sec) K,(cm2) Nbond Ncapllary NT
20/30 0.149 1.35E-06 6.55E-06 1.50E-07 6.55E-06
30/40 0.143 1.29E-06 6.25E-06 1.50E-07 6.25E-06
40/50 0.091 8.31E-07 4.00E-06 1.50E-07 4.01E-06
40/60 0.088 7.97E-07 3.84E-06 1.50E-07 3.84E-06
50/70 0.063 5.72E-07 2.75E-06 1.50E-07 2.76E-06


The injection force or pressure is the pressure imposed on the NAPL by the

injection of the NAPL into the system. This pressure is a function of injection rate and

fluid viscosity. This is unique to the lab environment since NAPL injection through a

syringe is a common method of NAPL introduction into two-dimensional columns. As

grain size decreases, the Pc increases against the NAPL globule, requiring higher entry









pressure to move the globule from one pore to the next. As the Pc increases, the effect Pg

has decreases and Pi becomes more significant near the point of injection. This may

cause the globule to migrate in all directions rather than be dominated in the direction of

gravity. This effect becomes less significant the further away the NAPL migrates from

the injection port. This effect may possibly cause more spreading of the NAPL as the

grain size decreases.

Entrapment processes are also affected by grain size. Maintaining all other

components of the NT constant, changing the grain size diameter will change the Bond

Number and the NT. NAPL residual saturation appears to be sensitive to changing NT

(Dawson and Roberts, 1997; Saripalli et al., 1997) and as NT increased, saturation

decreased. This is consistent with the findings of Pennell et al. (1996).

Wettability

Wettability is a property of interest because of its effect on oil (NAPL) recovery.

Wettability in porous media is the relative affinity of the solid component of the media

for fluids such as air, water or oil (Wilson, 1988). Hydrophilic soils have an affinity for

water while hydrophobic soils have an affinity for oil. Soils can become oil wet through

physical, chemical, or biological mechanisms (Bradford and Leij, 1995; Wilson, 1988).

According to Wilson (1988), physical mechanisms such as heat can aid in depositing

organic material on the soil. The chemical mechanism involves adsorption of compounds

that change the surface polarity of the media. It has been reported that cationic surfactants

and additives in gasoline can cause water-wet material to become oil-wet (Bradford and

Leij, 1995; Powers and Tambin, 1995; Powers et al., 1996). Additionally, Powers et al.

(1996) found that complex NAPL mixtures can create a wide range of wetting conditions.









Biological mechanisms are the least understood and beyond the scope of this study

(Wilson, 1988).

Wettability is typically measured by the advancing contact angle for water

displacing oil (Bahrani et al., 1973; Moore and Slobod, 1956; Powers et al., 1996). The

contact angle formed between two fluid phases and a solid surface is a result of

equilibrium among interfacial energies between interfaces and is defined by Young's

equation as follows (Powers et al., 1996):

o sw =yow (3-2)

where y is the interfacial energy with s, o, and w representing solid, oil, and water,

respectively. Strongly water wet systems have contact angles 0 near 300 while oil wet

systems are assigned contact angles of greater than 900. Contact angle is an important

physical parameter when considering vertical movement of DNAPLs. It is represented as

a required parameter in equation 1-1 in chapter 1. Additionally, it affects the capillary

pressure acting on a DNAPL in a pore. Figure 3.2 displays the pressure forces acting on

residual DNAPL in a pore. It is similar to Figure 3.1, however, the capillary pressure can

act against the DNAPL trapping it in the pore or it can act by pulling the DNAPL out of

the pore similar to capillary wickingg". The direction in which capillary forces act is

dependent on the contact angle between the aqueous phase and DNAPL with respect to

the media surface. As the contact angle increases and the media becomes oil wet,

capillary forces may act in favor of drawing the DNAPL into the media by capillary

wickingg". Equation 3-1 shows that contact angle has a great effect on the capillary

pressure of the system. Considering only gravitational and capillary pressures, as the

capillary pressure grows, gravitation forces become less influential. As the capillary






41


forces decrease, gravitational forces become more influential until potentially the contact

angle exceeds 90 and becomes an oil wet system.

Contact angle is also represented in both the Bond and Capillary Numbers in the

denominator as CosO. As 0 approaches 900 or an oil-wet system, CosO approaches zero

increasing both the Bond and Capillary numbers and thus the NT. This may reduce

entrapment potential.


y Pi pc


P X









NAPL
PI


> Pi
- Pc


P, Pi Pc

Figure 3.2. Schematic diagram of pressures/forces action on a NAPL globule with
variable capillary pressure









Study Objective

The objective of this study was to conduct two types of two dimensional chamber

studies designed to investigate soil media modifications and their effect on contaminant

geometry and orientation, and ultimately, contaminant mass flux and system efficiency.

A set of experiments was completed varying grain size and generate mass loading versus

mass flux curves. Another set was to completed changing the media polarity creating an

oil-wet environment and generate mass loading versus mass flux curves. Finally, a two

dimensional chamber experiment was conducted to quantify a contaminant pool's percent

contribution to mass flux compared to the residual mass contribution. Maximum

contaminant mass flux values and system efficiency (3) values were investigated.

Materials and Methods

General Experimental Procedure

A two-dimensional (2-D) chamber as described in Chapter 1 (Figure 3.3) was used

for each media study. An experiment was conducted for each sand size listed in Table

3.2 and for each hydrophobic media percentage as follows: 25%, 50%, 75%, 90%, and

100% hydrophobic sand.

A total of 11 combinations were investigated. Each experiment lasted

approximately two weeks in length. The experimental endpoint was determined when a

physical parameter of the chamber was exceeded, e.g. when PCE infiltrated one or both

wells.

Hydrophilic Sand Packing Procedure

Sand was added through the top of the chamber in approximately 5 cm thick

intervals. After each interval, the sand was mixed with a stir bar and then the box was

vibrated to settle and compact the sand. All packing was done under water wet









conditions to minimize air entrapment. This procedure was continued until the chamber

was filled with enough sand to cover the well screens (approximately 10 cm). A layer of

bentonite clay was added on top of the sand to simulate a confined aquifer and eliminate

the complexities of a capillary fringe. Enough clay was added to create a wet clay

thickness of approximately 2-3 cm. This packing procedure was followed for each sand

size to provide hydraulic and media consistency from experiment to experiment.


Figure 3.3. Two dimensional chamber set-up


influent


] Effklnu t

28un
X wmnSn Pft









Table 3.2. Media properties
Grain Size Diameter in mm
Seive Size min max avg
20/30 0.50 0.85 0.68
30/40 0.33 0.60 0.48
40/50 0.25 0.42 0.35
40/60 0.21 0.42 0.32
50/70 0.15 0.30 0.23

Hydrophobic Sand Packing Procedure

Due to the nature of hydrophobic media, a different packing method was required

to ensure that a saturated environment was created. The chamber was dry packed with

hydrophobic sand in a similar fashion described using 5cm thick layers and stirring. Dry

Bentonite clay was added to the top of the sand layer and hydrated with a water bottle to

create a clay seal over the dry hydrophobic sand. Carbon dioxide was introduced into the

influent port of the chamber to purge the chamber of air. Carbon dioxide was selected

because of its high solubility in water. Initially the wells and the effluent port were left

open to prevent any air from being trapped in the casing portion of the wells. The wells

were then sealed and effluent gas was collected in a 0.5 L Tevlar bag attached to the

effluent port. The bag was filled and evacuated to track the number of pore volumes

displaced in the chamber by CO2. Approximately 50 pore volumes were displaced.

Water was then introduced into the influent and effluent ports of the chamber to facilitate

saturating the sand from the sides of the chamber to the center. The trapped CO2 was

dissolved into the water. As most of the chamber became saturated, an area of trapped

CO2 was created in the center of the box as the water front from each side of the chamber

moved towards the center. At this point, the effluent port was released from the water

source and water was allowed to flow through the chamber. As the water flowed through









the chamber, the remaining trapped CO2 in the center of the box was dissolved into the

water creating a water saturated media.

PCE Introduction and Sampling

HPLC grade PCE (CAS 127-18-4), colored red with Oil-red-O dye (< 1X10-4 M,

CAS 1320-06-05) was used for each experiment. The PCE was injected into the center of

the rear of the chamber 6.5 cm from the bottom and approximately 4.0-4.5 cm from the

top of the sand layer, except for the pooling experiment. In the pooling experiment, the

injection port was 1 cm from the bottom of the chamber. The PCE was injected through

a 20 gauge stainless steel needle glued into the rear of the box. The needle entered the

box at a 900 angle to the glass side and protruded 0.7 cm into the box so PCE entered in

the center of the width (1.4 cm) of the box. The needle was attached to a 10 ml gastight

syringe attached to a syringe pump.

A baseline effluent sample was collected prior to PCE injection. PCE was then

injected at a rate of 0.1 ml/min for 5 minutes for a total of 0.5 ml injected. A sufficient

number of pore volumes (>8) were passed through the chamber to allow the injected PCE

to reach a quasi steady state dissolution. Samples were collected after injection to

determine the breakthrough characteristics. The number of pore volumes at which

concentration did not vary was the point at which steady state was assumed to be

achieved. An effluent sample was collected in a two ml vial to measure PCE

concentration. This was used with the measured flow rate to quantify the mass flux

generated from the injection. Another 0.5 ml of PCE was then injected and allowed to

reach quasi steady state with a subsequent effluent sample collected. Additionally, an

outline of the PCE distribution (light red coloration in the sand) was traced on

transparency paper attached to the side of the chamber to maintain a qualitative record of









the PCE geometry and orientation after each injection. Reflected light was used to help

identify the PCE when producing the outline. The outlines only represent one side of the

column and distributions across the thickness of the box were not observed. This

procedure was repeated until a physical parameter of the chamber was exceeded. This

was usually after a total of five to five and a half ml of PCE was introduced into the box

over period of approximately two weeks. Samples collected in the two ml vials were

analyzed using a Perkin-Elmer Gas Chromatograph Auto XL with a Flame Ionization

Detector. Turbochrome Navigator 4.1 software was used. The method for detection used

was as follows: Carrier Pressure 7.0 psig, 35 C oven hold for six minutes, Temperature

ramp from 35 C to 110 C at 5 oC/min, Injection Temp 180 C, Detector Temperature

250 oC.

Hydraulic Controls

A constant head was maintained at the influent well using a Marriott Bottle

controlling the effluent discharge height. The head was maintained at approximately two

to three cm above the surface of the sand media to accommodate the clay layer. The

effluent rate was maintained by adjusting the effluent discharge height. The rate was

approximately 0.7 ml/min. This produced a specific discharge of 68 cm/day. Based on a

porosity of 0.377, this gives a pore velocity of 180 cm/day.

Octadecyl Trichlorosilane Treatment and Retardation Factor

Hydrophobic sand was created using an octadecyl trichlorosilane (OTS) treatment

method (Bradford and Leij, 1995; Le Grange, 1993). Organosilanes are effective for

changing the surface polarity of the media resulting in an oil-wet media. Hydrophobic

sand was created as needed by the following method: 475 ml of denatured/reagent

alcohol mixed with 25 ml of OTS to create a 5% OTS mixture. Accusand (575 ml of









30/40 mesh size) was added to the 5% OTS solution and tumbled for 5 hours. At the

completion of mixing, the excess solution was drained off and the sand was rinsed again

with denatured/reagent alcohol. The sand was then dried for 24 hours. To create each of

the hydrophobic/hydrophilic percent combinations listed in Table 3.2, the appropriate

amount of OTS treated sand was mixed homogeneously with the untreated sand to create

the desired percent ratio. As annotated in Table 3.2, denatured alcohol was used for all

experiments. Duplicate experiments were run for the 50%, 75%, and 100% mixtures

using the reagent alcohol during the mixing procedure. This sand mixture was then

tumbled for an hour to create a homogeneous distribution.

Bradford et al. (2000) determined the Freundlich distribution coefficient (Kfw) f

and n for PCE in an OTS treated 20/30 (0.68) sieve sand to be 2.01 and 1.06,

respectively. This is nearly a linear relationship. Using the following equation:

PbK
R = 1+b (3-3)
0

where pb is the bulk density (1.55 g/ml), Kf" is substituted for K and 0 is the volumetric

water content (0.3). The retardation factor was approximately 11. A minimum of 11

pore volumes were used to achieve temporary steady state.

Results and Discussion

To gain an appreciation for how some of the distributions and their associated flux

values differed, the hydrophobic and hydrophilic system results are shown in Figures 3.4-

through 3.7. The hydrophobic or 100% OTS treated sand distribution is shown in Figure

3.4 with its associated flux curve shown in Figure 3.5. The untreated or hydrophilic

system is shown in figures 3.6 and 3.7. It is obvious how much the geometries differ

between these systems and how those differences are reflected in their respective flux











curves. The remainder of this section will discuss the grain size experiments and


wettability experiments separately.


Figure 3.4. 100% OTS treated 30/40 (0.48) sieve sand at 2.5 ml of PCE


0 00 1 00 200 300
PCE (ml)


4 00 500 600


Figure 3.5. 100% OTS treated 30/40 (0.48) sand contaminant volume versus flux


73







49





























Figure 3.6. Untreated 30/40 (0.48) sieve sand at 4.5 ml PCE content


000 050 1 00 1 50 200 250 300 350 400 450 500
SPCE (m l)


Figure 3.7. Untreated 30/40 (0.48) sand contaminant volume versus flux









Grain Size Comparison Results and Discussion

For each experiment conducted with different size porous media, a trace sketch of

the PCE distribution was generated. A trace of the distribution was drawn after each

injection reached steady state on a single transparency, resulting in a cumulative

distribution drawing (Appendix B). Figures 3.8 and 3.9 are examples of these drawings

for the 30/40 (0.48) sand and pooling experiment respectively. A qualitative comparison

of the final geometry for each sand size was made using the drawings in Appendix B. In

general, predictability of geometry and PCE behavior based on sieve size was not

obvious. Pooling began in each experiment by the second injection or one ml with the

exception of the 40/50 (0.35) sieve experiment, which appeared to have begun after the

fourth injection or two ml. Figure 3.10 shows the quantitative comparison of each

volume versus percent mass flux curve for each sieve size and the pooling experiment. In

this figure, the C/Cmax values were generated by dividing calculated flux values

generated from measured PCE concentrations and flow rates by a calculated maximum

flux value based on equilibrium solubility limit and applied flow. The values can be

thought of as scaled concentration of mass flux. These values were then graphed against

their associated injection volumes. Each of the curves appears to be non-linear in shape

with the exception of the pooling curve. The logarithmic shape indicates an initial rapid

establishment and increase in flux per unit volume of PCE, followed by a plateau. These

results show the first several injections are the largest contributors to flux with the later

injections having minimal impact. This is possibly because the first several injections

contribute to the residual geometry with the later injections contributing more to the pool.


























3ooe


Figure 3.8. 30/40 (0.48) sand pooling experiment


0.
,







Figure 3.9.30/40 (0.48) sand experiment PCE distribution




Figure 3.9. 30/40 (0.48) sand experiment PCE distribution


















0.45


0.4




0.3 -- ------- ----m-- -30/40
0.4 --------






0.25 -i 40/50

S- 40/60 (22)
0.2 -40/60 (28)

0.15 -- 50/70
o l .."











0.1 ,

0.05 30/40
I I I








0
0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00
PCE (ml)


Figure 3.10. Volume versus percent mass flux grain size comparisons









This is supported by the results of the pooling experiment, which show the pooling

contributes significantly less mass flux per unit volume when compared to the combined

residual and pooled values. The 20/30 (0.68) sieve sand has the lowest C/Cmax value of

0.27 and the 40/50 sieve sand has the highest C/Cmax value of 0.38. Using the binary

model, the maximum C/Cmax value is estimated to be 0.60. This is based on the

injection point position of 6cm from the bottom of the 10 cm chamber and assumes

residual distributed homogeneously (vertical and depth) from injection point to chamber

bottom. The values observed during each experiment are lower because migration did

not produce homogeneously distributed PCE in the vertical plane.

There was no clear pattern between sand size and flux values, but there was

indication that as grain size decreased, flux values increase. To confirm this, additional

experiments using 20/30 (0.68) and 50/70 (0.23) sand was performed. The results are

shown in Figure 3.11 and confirm that finer sands produce higher flux values relative to

the course sands. This is possibly due to more lateral spreading caused by the finer grain

size resulting in a larger cross sectional area.

Curves were fitted to data using the Y=XO model. Figure 3.12 provides an

example of collected data and the associated fit curve for the 30/40 sieve sand. Figure

3.13 displays the fitted curves for each grain size. These curves were generated from

dimensionless/normalized data to facilitate comparison. The data was normalized by

using the maximum mass and flux values for each respective experiment. These curves

display the contaminant mass flux versus loading characteristics for the sands

investigated. Sand sieves 20/30 (0.68), 30/40 (0.48) and 40/50 (0.35) each have virtually









54




the same 3 values and therefore curve shape. This indicates that the vertical migration



from injection to injection of the PCE in each of these sands were similar.


- 20/30 sieve

- --50/70 sieve

--- 30/40 Pooled

- -- 20/30 sieve

--50/70 sieve


300
PCE (ml)


Figure 3.11. 20/30 (0.68) and 50/70 (0.23) duplicate experiment






1 00

090

080

070

0 60
Actual
050
c --curvefit

e 040

030

020

010

0 00
000 010 020 030 040 050 060 070 080 090 1 00
fraction mass


Figure 3.12. 30/40 (0.48) sieve sand curve fit example


600


















1.00


0.90 -------


0.80

/ 20/30
0.70 I- (0.41)
I
S-----30/40
i. 0.60 -- (0.40)
) 40/50
0 0.50 (0.42)
. 40/60
S0.40 (0.07)

L-- 50/70
0.30 (0.22)

---40/60
0.20 4 (0.24)


0.10


0.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Fraction Volume


Figure 3.13. Curve fit comparisons (grain size)












The duplicate experiments for the 40/60 (0.32) sieve sands were performed and


identified as boxes 22 and 28. A comparison of these two experiments displays the


variability of migration characteristics. This could be due to the wider sieve range


relative to the other sands. Figure 3.14 graphically displays the 3 and grain size


relationship with one line representing box 22 data and the other using box 28 data.


The 50/70 sieve sand demonstrated the most efficient loading by developing the


largest percentage of its flux value at a lower mass percentage. Tables 3.3 and 3.4


display the correlation analysis between each of the sand's physical characteristics and its


estimated 3 value.



05

045
R2 = 0 5562
04
o 4 ; -------------------* ^. /---------

S/ R2 = 03867
0 35--

03
0/ # Box 28
SBox 22
S0 25
-Linear (Box 28)
Linear (Box 22)
02

0 15

01

0 05

0
0 01 02 03 04 05 06 07 08
diameter (mm)


Figure 3.14. 3 versus grain size diameter










Table 3.3. Correlation analysis using box 28 40/60 (0.32) sand sieve 3 value
bx28
hydraulic
diameter variance surface area conductivity beta
20/30 0.68 0.27 146 8.98 0.44
30/40 0.48 0.12 275 8.57 0.40
40/50 0.33 0.08 301 5.49 0.42
40/60 0.32 0.13 307 5.27 0.24
50/70 0.23 0.05 423 3.78 0.22

r r2
diameter 0.75 0.55
variance 0.53
surface area -0.77
Hydraulic
conductivity 0.78

Table 3.4. Correlation analysis using box 22 40/60 (0.32) sand sieve 3 value
bx22
hydraulic
diameter variance surface area conductivity beta
20/30 0.68 0.27 146 8.98 0.44
30/40 0.48 0.12 275 8.57 0.40
40/50 0.33 0.08 301 5.49 0.42
40/60 0.32 0.13 307 5.27 0.07
50/70 0.23 0.05 423 3.78 0.22

r r2
diameter 0.62 0.38
variance 0.35
surface area -0.55
hydraulic
conductivity 0.65


Wettability Results and Discussion

As performed for the grain size comparisons, in each experiment (percent

wettability) a trace sketch of the PCE distribution was generated. A trace of the

distribution was drawn after each injection reached steady state on a single transparency,

resulting in a cumulative distribution drawing (Appendix B). Figures 3.15 and 3.16 are

examples of these drawings. A qualitative comparison between the geometries for 0%,









25%, 50%, 75%, 90% and 100% media mixtures was made using the drawings in

Appendix B.


Figure 3.15. 30/40 (0.48) Sand 25% OTS mix trace


Figure 3.16. 30/40 (0.48) Sand 100% hydrophobic mix trace


OLC







3aes to

ftbCb oy


S=_fAL~~


IqO,16 WP









In general, as the hydrophobicity increased, the PCE distributed more uniformly

and with increasing connectivity. Because of the water wet media used in the 0%

experiment, the PCE was not subject to the "globbing" observed in the 25%, 50% and

75% mixtures and appears to have been more evenly distributed than the intermediate

hydrophobic media. The "globbing" observed is when the PCE would collect in discrete

concentrated sections in the media and did not have a more uniform distribution. The 0%,

25%, 50% and 75% mixtures displayed a fingered distribution with the 90% mixture

beginning to transition to the more uniform spreading shown in the 100% mixture.

Additionally, capillary wickingg" was primarily observed in 100% mixtures with some

minimal wickingg" occurring in the 90% mixture. Apparently, a significant amount of

the media (>90%) must be OTS treated to allow capillary forces to overcome

gravitational forces and cause uniform lateral and vertical spreading.

A quantitative comparison was made and shown in Figure 3.17. The flux is

presented as C/Cmax or J/Jmax since flow rate (Q) and area is constant is each

experiment. In general, the 100% and 90% mixtures appear produce the higher

maximum percent mass flux values when compared to the intermediate and 0% mixtures.

Comparing these curves to their associated sketch, it appears the vertical movement of

the PCE above the injection point was the differing factor in flux production. More PCE

exposure to the horizontal aqueous flow appears to have resulted in higher flux values.

There appears to be little difference in flux values between the 0%, 25%, 50% and 75%

mixtures. This might be due to the intermediate mixtures providing similar overall

surface area contact between the PCE and aqueous phase as the 0% sand


















0.90


0.80__ 100% (RA)

0.70- 25% (DA)
0.70 ii mm

-- *-- 50% (DA)
0.60

M -A-75% (DA)
S0.50-
S---- --90% (DA)
E 0.40 _
100% (DA)


-- -untreated

0.20
S / ---50% (RA)

0.10 -^----
0.1 --- 75% (RA)


0.00 -
0.00 1.00 2.00 3.00 4.00 5.00 6.00
PCE (ml)


Figure 3.17. Volume versus percent mass flux hydrophobic comparisons









The intermediate soils tended to collect the PCE residual in disconnected globs

while the 0% appeared to a more evenly distributed fingered residual. Additionally,

Moore and Slobad (1956) found that porous media of the intermediate wettability had

lower water imbibing tendency than in the strongly water wet system. They state that

imbibition, though still present, is not the dominating displacement process. As a result,

the capillary and viscous forces are of equal importance and the water will flow down

both sizes of pores at nearly the same velocity. The result is lowered oil saturation at

breakthrough compare to either wettability extremes.

As examples of the wettability curve fit data, Figure 3.18 displays the 75% and

100% OTS treated sands data and associated fit curves. Figure 3.19 displays the fitted

curves for each wettability percentage. There is little difference between the shapes of

the curves for 0%-90% hydrophobicity. The 100% RA treated sand and 100% DA

treated sand are more linear relative to the other sands and demonstrated by their higher 3

values. This may be due to capillary forces countering gravitational forces, causing a

slower vertical downward migration and thus, a less efficient system. This may be

explained by the force balance performed using equation 3-1 and the system data listed in

Table 3.5. Flow forces were ignored due to orientation of flow with respect to gravity.

Table 3.6 displays the results of theoretical capillary rise, h, and both gravity and

capillary pressures acting on the NAPL globule. The force balance indicates that gravity

pressures remain constant with changing contact angle. However, as the contact angle

increases and the system becomes oil wet, gravity may become more significant.

Additionally, in order to achieve capillary rise, the system must become oil wet as

indicated by the 900 contact angle. According to the entry pressure findings in Chapter








62



two, the system becomes oil wet at approximately 90% OTS treated sand content. This


supports why the system must be >90% treated sand in order to achieve capillary rise and


overcome gravitation forces.

P UM


Figure 3.18. 75% and 100% OTS treated data curve fit examples





1 00

0 90

0 80

0 70

L 060 UT-90% (0 39)
050 n100%DA (072)
.5 o --o-----.-- ---- -----------------T--O----O------





0 00 010 020 030 040 050 060 070 080 090 1 00
c00n RAV(052)
S040-
L-
030

0 20

010

0 00
000 010 020 030 040 050 060 070 080 090 100
Fraction Volume


Figure 3.19. Curve fit comparisons (wettability)


1.00 --

0.90 -

0.80 -


U-
S0.70 -

S0.-60 -
U)
- 0.50 -

I 0.40 -
CU
L 0.30 -

0.20

0.10 /

0.00 1
0.00


0.20 0.40 0.60 0.80 1.00
Fraction Volume










Table 3.5. Force balance data
a= 90 degrees r,= 0.0106 cm Al= 0.0212 cm
d= 0.05 cm rt= 0.00385 cm 3= 0.636792
Ap= 0.65 g/ml g= 980 cm/sec2 Poli= 1.65 g/ml
c7= 47 dynes/cm


Table 3.6. Theoretical force balance results
capillary
0 Cos(0) h (cm) pressure

0 1.00 -38.3 155E2
10 0.98 37.7 153E2
20 0.94 36.0 146E2
30 0.87 33.2 134E2
40 0.77 29.3 119E2
50 0.64 24.6 9993
60 0.50 19.1 7773
70 0.34 13.1 5317
80 0.17 6.66 2699
82 0.14 5.33 2163
84 0.10 4.01 1625
86 0.07 2.67 1084
88 0.03 1.34 542
90 0.00 0.00 0.00
92 -0.03 -1.34 -542
94 -0.07 -2.67 -1084
96 -0.10 -4.01 -1625
98 -0.14 -5.33 -2163
100 -0.17 -6.66 -2699
110 -0.34 -13.1 -5317
120 -0.50 -19.1 -7773
130 -0.64 -24.6 -9993
140 -0.77 -29.3 -119E2
150 -0.87 -33.1 -134E2
160 -0.94 -36.0 -146E2
170 -0.98 -37.7 -153E2
180 -1.00 -38.3 -155E2


Flow By-passing and Rate Limited Mass Transfer

Concentrations of NAPL compounds in groundwater are usually less than their

aqueous solubility due to irregular distributions, non-uniform flow patterns, dilution and

sorption effects, and rate limited mass transfer (Hunt, et al., 1988; Soerens et al, 1998).









Powers et al. (1992) performed one-dimensional column experiments to determine the

physical characteristics which affect mass transfer rates. These experiments were

performed using homogeneously distributed NAPL source zones and determined that

grain size, source zone length and Darcy velocity impact mass transfer coefficients under

one dimensional column conditions. This method may overestimate mass transfer

coefficients when applied to heterogeneously distributed NAPL source zones such as

those created in this research.

Soerens et al. (1998) concluded that non-equilibrium or non-ideal dissolution of

NAPL can be represented by mass transfer rate limitations, flow by-passing due to media

or distribution heterogeneities, or a combination of these mechanisms. Experimental

curves generated from this research were compared to ideal equilibrium curves and

curves developed using mass transfer rate estimations to determine if potential flow by

passing, rate limitation or both is occurring. The equilibrium and mass transfer curves

were developed for the 20/30 (0.68) sand and 100% hydrophobic sand experiments.

Figure 20 shows an example of a sketch superimposed over a 0.5 cm grid. The

equilibrium curves were determined by assuming equilibrium dissolution has been

reached after each loading event. The equilibrium curve was constructed by estimating

the percentage of the flow field exposed to PCE after each loading event. This was done

by adding the number of vertical grids containing PCE and dividing it by the total grid

height. The mass transfer rate curves were developed by calculating the modified

Sherwood number used by Powers et al. (1992). The Modified Sherwood number was

then used to estimate the mass transfer rate and finally the C/Cs as a function of length of

the PCE per each grid height.



































Figure 3.20. Example sketch superimposed over 0.5 cm grid

Figures 3.21 and 3.22 display the resultant equilibrium and mass transfer rate

estimated curves in relation to the experimental data generated curves. Figure 3.21

displays the results for the 20/30 (0.68) sand and indicates that based on the length of the

source zone after each loading event, that equilibrium may not have been achieved.

Additionally, the experimental data curve is lower than the mass transfer rate generated

curve. This indicates that both flow by-passing and mass transfer rate limitation may be

occurring. Figure 3.22 shows the results for the 100% hydrophobic sand (30/40) and it

indicates that the source zone is sufficient in length throughout the loading event that

equilibrium is achieved. Additionally, the experimental data compares relatively well to

the equilibrium and mass transfer rate curves, however still indicating some potential by-

passing. The hydrophobic data compares more favorably than the 20/30 sand because it


1 cm














toogo








66



achieves equilibrium and possibly has less by-passing because of the uniform distribution


of the PCE resulting from capillary wicking in the hydrophobic media.


--- Experimental
-- Equilibrium
Non-Equilibrium


000 100 200 300
PCE (ml)


Figure 3.21. 20/30 curve comparison


400 500 600


0.90

0.80








S0.40 --- ---NnEqu-llbnum


S--- Non-Equllhbnum
0.30


0.20
0.50 -4-Experimental

| --- Equilibnum

U 0.30- Non-Equilibnum


0.20 --

0.10


0.00 F
0.00 1.00 2.00 3.00 4.00 5.00 6.00
PCE (ml)


Figure 3.22. Hydrophobic sand curve comparisons.









Conclusions

Grain size did not appear to affect the geometry of the residual and pooled PCE in

such a way that was predictable. The grain size appears to affect the percent flux, with

the flux increasing as the grain size decreases. It appears the determining factor for mass

flux values was the cross sectional exposure of the PCE to perpendicular aqueous flow.

The residual PCE portion was found to contribute the largest portion of mass flux relative

to the pooled section, although the pooled section appears to be where the majority of the

PCE collected. Assuming local equilibrium assumption, pores with PCE present may

likely reach the solubility limit of the PCE, regardless of saturation percentage. Based on

this assumption, each experiment should produce similar flux values because the vertical

exposure of the PCE to the aqueous flow for each experiment was the same, however, the

lateral distribution is not the same due to spreading. As the grain size decreases, more

lateral spreading of PCE occurs, increasing flux. The pooled experiment supports the

hypothesis that the residual mass produces the largest percentage of flux relative to the

pooled source flux. The pooled source flux produce 0.05% of C/Cmax with the combined

residual and pooled sources producing a range from 0.27 to 0.38 C/Cmax. In general,

remediating the residual may remove relatively small amounts of PCE compared to the

possible total mass, but could provide the greatest reduction in flux values. However,

pooled flux values are still greater than clean-up requirements and will be a persistent

flux source.

The mass loading/mass flux efficiency or 3 values are somewhat correlated to

grain size. The wettability experiments showed that nearly all (>90 %) of the media must

be OTS treated top affect residual geometry and percent mass flux values. As the media









approached 100% hydrophobicity, the capillary forces were able to overcome

gravitational forces and spread the PCE above the point of injection. Although lower

hydrophobic mixture percentages may not produce increased mass flux values, because

of capillary forces retaining the PCE, removal of PCE from the pore may be difficult

because of its affinity for the media surface.

The mass loading/mass flux efficiency (3) only became affected after a significant

portion of the sand was treated (>90%). Otherwise, there is consistency in 3 values for

the remaining sands.

Flow by-passing and mass transfer rate limitation may be occurring resulting in

lower than expected experimental values. Qualitatively, most of the source zones

produced are of sufficient length to achieve equilibrium indicating that by-passing is the

most likely cause of lower than expected values.














CHAPTER 4
INVESTIGATION OF THE RELATIONSHIP BETWEEN FLUID PROPERTIES
INTERFACIALL TENSION AND DENSITY DIFFERENTIAL) AND MASS FLUX

Introduction

Chlorinated solvents such as perchloroethylene (PCE) are commonly found at

many contaminated sites. They have been popular as industrial degreasers and because

of past poor management practices and the threat they pose to human health, they have

become a major concern at many contaminated sites throughout the country. It is likely

that many chlorinated solvents have been used with a variety of different chemicals

during various industrial processes and activities. The chemicals comprising these

mixtures could interact creating a single "new" mixture, causing them to behave in the

sub surface in very different ways than as single separate components. Depending on the

mole fractions of each component, miscibility, and a variety of other conditions, surface

and bulk properties for the "new" mixture can be vastly different from its individual

separate predecessors (Brusseau, 1993; Seo and McCray, 2002). Surface activity such as

interfacial tension and bulk properties such as density differential between aqueous and

non-aqueous phases can be affected (Brusseau, 1993; Seo and McCray, 2002).

Theoretical Background

Entrapment and Migration

The common fluid to fluid properties represented in both the entrapment and

migration processes are density differential and interfacial tension between aqueous and

non-aqueous phases. As previously discussed in Chapter 1, contaminant flux is a









function of surface contact area between aqueous and non-aqueous phases and contact

area is a function of geometry and orientation to flow of the contaminant source zone.

Entrapment and migration were the two processes discussed that influence source zone

geometric and orientation development. DNAPL vertical and horizontal migration

processes are governed by the following equations:

Ho 2oCosO(1/rt -r) (4-1)
g(pw po)
dP 2r
S2cT (4-2)
dx Lo(1/ rt -1/ rp)
where Ho is the critical height or head required to displace water in a pore, y is the

interfacial tension between liquids, 0 is wetting angle, rt pore is throat radius, rp is pore

radius, g is acceleration due to gravity, Lo is the length of the continuous DNAPL phase

in the direction of flow, rw is water density and ro is DNAPL density. Additionally, using

the force balance equation from Chapter 3, it can be seen that changes in density

differential affect the gravitational pressure, and changes in the interfacial tension can

affect the capillary pressure of the system. These parameters also affect the entrapment

process which is described using the Capillary and Bond numbers discussed in Chapter

one.

Interfacial Tension

Interfacial tension (IFT) results from the co-existence of immiscible liquids at

different pressures and is measured by the force that exists in the interface separating the

two fluids (Pankow and Cherry, 1996). The interfacial tension between water and

another chemical only exist when the fluids are immiscible. In particular, the surface

tension of chlorinated solvent DNAPLs with respect to water has a significant impact on

how chlorinated solvents penetrate the capillary fringe and migrate through the saturated









zone. As the chlorinated solvent migrates through the capillary fringe, it is held up by the

capillary retention of water until enough head is built up to overcome retention. The

capillary retention is directly proportional to the interfacial tension and inversely

proportional to radius of curvature (Lowe et al., 1999). As interfacial tension increases

and pore size and density decreases, more head is required to produce downward

migration. This may result in a lateral movement of liquid along layers of finer grain

sands. Interfacial tension properties of DNAPLs are important when considering

remediation techniques.

Surfactants alter interfacial tension between immiscible fluids by altering fluid

interfaces. They accomplish this through the nature of their amphiphilic structure.

Surfactants are typically molecules with a hydrophilic group or head at one end attached

to a long hydrophobic hydrocarbon chain or tail. The hydrophilic head will have an

affinity for water while the hydrophobic tail will have an affinity for non-aqueous

contaminants or oils. Surfactants are classified by the nature of their hydrophilic groups,

which are anionic, cationic, and non-ionic. Anionic surfactants give rise to a negatively

charged surfactant ion and a positively charged counter-ion upon dissolution in water.

They are sensitive to the presence of salts in solution. Cationic surfactants yield a

positively charged surfactant ion and a negatively charged counter-ion upon dissolution

in water. Cationic surfactants are not widely used because of their potential toxicity

(Lowe et al., 1999). Nonionic surfactants do not ionize in water and are insensitive to the

presence of salts in solution.

The amphiphilic structure allows the surfactant to accumulate at the NAPL-water

interface. The hydrophilic group resides in the aqueous phase with the hydrophobic tail









residing in the NAPL. Depending on the concentration of surfactant at the interface,

NAPL solubility and/or interfacial tension will be modified.

The manner in which the surfactant distributes in a surfactant-water-NAPL system

is categorized by three systems. Winsor Type I, II, and III. The Winsor Type I system

has micelles of oil droplets in the aqueous phase. Winsor Type II creates "reverse

micelles" with droplets of water in the oil phase. Winsor Type III is a middle phase

micro-emulsion with ultra-low interfacial tensions.

Density

Density plays an important role in DNAPL migration. It is the property which

defines a liquid as being dense or light relative to water. If a liquid is determined to be

dense, it has a specific gravity greater than one and if it is light, its specific gravity is less

than one. In many situations, NAPL density varies from water by 10-50%, with only a

1% difference being needed to influence fluid movement (Mercer and Cohen, 1990).

Because of the density differential, DNAPLs may move down a physical gradient counter

to the hydraulic gradient; however, this can be impeded by capillary and/or

impermeability resistance. DNAPL spreading will occur along pathways of least

capillary and permeability resistance (Mercer and Cohen, 1990). This must be

considered when determining the location of DNAPLs in groundwater, because the liquid

may not simply sink to the lowest point in an aquifer. Additionally, the unique spreading

of DNAPLs must be considered when conducting co-solvent or surfactant assisted

remediation.

Study Objectives

The objectives of this study was to conduct two dimensional chamber studies

designed to investigate fluid, fluid property effects on contaminant geometry and









orientation and ultimately contaminant mass flux and system efficiency as discussed in

chapter 3. The first objective was to vary density differential and generate mass loading

versus mass flux curves. The second objective was to change the interfacial tension

between the fluids and generate mass loading versus mass flux curves. Maximum

contaminant mass flux values and system efficiency (3) values were investigated.

Materials and Methods

General Experimental

A two dimensional chamber as described in chapter one was used for each

experiment. The hydrophilic packing procedures and hydrological controls described in

chapter three were followed. The PCE material and injection methods described in

chapter 3 were used. A total of nine experiments using 30/40 and 40/50 sieve sand were

completed.

Density Modification

An experiment for each density and sieve size combination listed in Table 4.1 was

completed.

Table 4.1. Density sieve size experiments
PCE Density 1.0 1.1 1.4 1.6
(g/ml)
30/40 Sieve x x x x
40/50 Sieve x x

To achieve the densities listed in Table 4.1, the appropriate mole fractions of PCE

and decane were mixed together (Table 4.2). Decane was selected because of its density

(0.73 g/ml), and its low solubility in water to ensure limited partitioning from the non-

aqueous to the aqueous phase.









Table 4.2. Decane/PCE densities and respective mole and volume fractions

S volume fraction mole fraction
PCE Decane PCE Decane
1 0.3 0.7 0.45 0.55
1.1 0.41 0.59 0.57 0.43
1.4 0.75 0.25 0.85 0.15
1.65 1 0 1 0

Additionally is has similar interfacial tension properties (52 dynes/cm) compared to

PCE in relation to water. The IFT of 50/50 mole fraction of PCE and Decane mixture

was measured using a tensiometer to determined if the resultant mixture had an IFT value

in between the IFT values for pure PCE and Decane. The IFT for decane and water was

measured to be 43 dynes/cm, PCE and water was 37 dynes/cm, and the mixture resulted

in an IFT of 39 dynes/cm. This supports that Seo and McCray (2002) determined there is

a linear relationship between multi-component mole fractions and IFT properties of the

mixture.

Interfacial Tension Modification

Interfacial tension between PCE and water was modified by adding 0.0025%,

0.005%, 0.01%, 0.025%, 0.05% and 0.1% by volume Span 80 to PCE. Span 80 (sorbitan

monooleate) was selected because of its low hydrophile/lipophile balance (HLB) value of

4.3. A low HLB surfactant was required to limit partitioning of the surfactant into the

aqueous phase. The relationship between % surfactant added and interfacial tension

between PCE and water is shown in Figures 4.1. The relation ship between Cmax and

percent surfactant is shown in Figure 4.2.













100











10

y = 24.991 e-44328x
R2 = 0.9808







1
0 0.01 0.02 0.03 0.04 0.05 0.06
% Span 80 in PCE


Figure 4.1.


250.00




200.00


150.00




100.00


Span 80 percentage and resultant interfacial tension Semi-Log


50.00-




0.00-
0 0.02 0.04 0.06 0.08 0.1 0.12
% Span 80

Figure 4.2. Maximum PCE concentration as function of percent surfactant (Span 80)


y = 223.32x + 183.7
R2 = 0.3214



* *










An experiment for each interfacial tension value listed in Table 4.3 was completed.

The low IFT of 3 dynes/cm was selected because at greater Span 80 percentages

cloudiness occurred.

Table 4.3. Interfacial values tested and respective Span 80 percentage

Interfacial Tension 3* 13 47
(dynes/cm) 0.05% Span 80 0.025% Span 80 0% Span 80
*not shown on graph -
estimated based on curve fit
equation shown in Figs 4.1
and 4.2


Results and Discussion

IFT Modification Results and Discussion

For each experiment interfaciall tension) a trace sketch of the PCE distribution was

generated. A trace of the distribution was drawn after each injection reached steady state

on a single transparency, resulting in a cumulative distribution drawing (Appendix C).

A qualitative comparison using sketches in Appendix C was made between each

interfacial tension experiment shows a difference in migration characteristics as IFT

decreases. As the IFT decreased, the residual geometry became more spread out.

Figures 4.3 and 4.4 are an example in how the distribution behavior of PCE changes as

the IFT is lowered. This may be from the lower IFT influencing the migration of the

PCE in a horizontal direction in addition to vertical movement. Pooling for each began

by the second injection, so the vertical migration was not affected by lowering the IFT,

indicating that density differential controlled vertical migration.

























Figure 4.3. 3 dynes/cm interfacial tension distribution


Figure 4.4. 47 dynes/cm interfacial tension distribution

Figure 4.5 displays similar results between each IFT experiment. As the IFT

decreased, the relative C/Cmax values appear to increase slightly. This may be due to

more uniform migration occurring in the thickness of the chamber as the PCE migrates

vertically. The maximum values appear to be bounded by injection point location.























0.25
S0.5 -*- Untreated (47
Sdynes/cm)
J 0.20- ---13 dynes/cm

0.15 -A-3 dynes/cm

0.10

0.05

0.00 I
0.00 1.00 2.00 3.00 4.00 5.00 6.00
PCE (ml)

Figure 4.5. Interfacial tension comparisons

Figure 4.6 displays the relative curve fits for each IFT with the associated data.

They are essentially the same, indicating regardless of IFT, vertical migration

characteristics appear to be the same for each. Ultra low IFTs may be required to affect

migration or prevent entrapment. Table 4.4 tabulates the bond, capillary and total

trapping number for each IFT. These values indicate that entrapment will still occur,

because Pennell et al. (1996) reports mobilization when NT = 1E-3. However, to achieve

these ultra low IFTs, solubility would increase dramatically (Pennell et al., 1996).

Table 4.4. Calculated bond, capillary and total trapping number for each IFT
IFT (dynes/cm) NBo Nca NT
47 9.8E-5 2.3E-6 9.8E-5
13 2.3E-5 5.4E-6 2.3E-5
3 6.2E-5 4.9E-6 6.2E-5







79






1.00

0.90

0.80

0.70
X -A-47 dynes/cm (0 40)
[ 0.60 --13 dynes/cm (0 41)
S) --3 dynes/cm (0 40)
2 0.50 / 47 dynes/cm
.0 A 13 dynes/cm
0.40
S/ 3 dynes/cm

0.30

0.20

0.10

0.00
0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70 0.80 0.90 1.00
Fraction Volume

Figure 4.6. Interfacial tension curve fit

Density Modification Results and Discussion

For each density experiment a trace sketch of the PCE distribution was generated.


A trace of the distribution was drawn after each injection reached steady state on a single


transparency, resulting in a cumulative distribution drawing (Appendix C).


A qualitative comparison between density experiments reveals interesting results


using the drawings in Appendix C. As the density decreased, vertical and lateral


migration characteristics changed. Figures 4.7 and 4.8 provide a qualitative comparison


between distributions of PCE and PCE treated to achieve 1.1 mg/1 (p).

























Figure 4.7 Untreated PCE distribution


L ib"" bA


Figure 4.8. 1.1 density distribution

The comparison shows how differently PCE migrates and distributes as p is

decreased. Vertical migration was slower from injection to injection in the lower density

experiments when compared to the untreated PCE experiments. In the untreated

experiments pooling usually began by the second injection (1.0 ml), indicating complete

vertical migration from injection port to chamber bottom. The lower density experiments

required as many as nine injections (4.5 ml) to cause full migration from injection port to









bottom and in the case of the 1.0 density PCE, no pooling occurred indicating no full

downward migration. The C/Cmax values were similar with the 1.1 p in the 30/40 sieve

sand showing the largest value followed by the 1.0 density PCE in the 30/40 sand (Figure

4.9). These results are probably due to the PCE being able to migrate above and below

the injection port, providing a larger cross sectional area exposure to flow compared to

the untreated PCE experiments.

Figure 4.10 compares the fitted curves for each density experiment. The lower

density experiments displayed a linear mass loading/mass flux relationship compared to

the untreated experiments which were more non linear. These curves coupled with the

traces indicating reduced vertical migration per each injection indicate the curves are a

function of density differential. A faster downward migration results in higher flux

values at low masses when compared to slower downward migration results. The 1.4

p and P values were expected to be in between the 1.0, 1.1 and 1.65 density P values.

However, the 1.4 P value was closer to the lower density P values. This may be

explained by Figure 4.11. The downward migration appeared to be delayed by possible

layering. This caused the vertical migration to behave similarly to the migrations seen at

the lower densities. This resulted in a more linear P value.




















0.50


0.45


0.40


0.35


0.30


0.25


0.20


0.15


0.10


0.05


0.00
0


5.00


6.00


---30/40 untreated

-1-30/40 1.1 rho

--30/40 1.0 rho

- 40/50 untreated

-K-40/50 1.1 rho

--030/40 1.4 rho


7.00


Figure 4.9 Density comparisons


3.00 4.00
PCE (ml)


.00


1.00


2.00


....... ....... .......
.. .. .. .. .. .. .. .. .. .. ...





































xI
2';
X7 1 Z


,;Oop,


Ai


1.00


0.90


0.80


0.70


0.60


0.50


0.40


0.30


0.20


0.10


0.00
0


-- 30/401.0 (0.91)


-- 30/40 1.1 (0.89)


- 30/401.4 (0.81)


x 30/40 (0.40)


-- 40/501.1 (0.86)


- .- -40/50 (0.42)


0.70 0.80 0.90 1.00


Figure 4.10. Density curve fit


0.10 0.20 0.30 0.40 0.50 0.60
Fraction Volume


.00








84






























Figure 4.11. 1.4 density distribution


0.90

0.80

0.70

0.60


0.50
Experimental
0.7 ------------U-- -------



E 0.40 Equilibrium

0.30 Non-Equilibrium
0.30 /

0.20

0.10

0.00
0.00 1.00 2.00 3.00 4.00 5.00 6.00
PCE (ml)

Figure 4.12. Curve comparisons for 1.1 density PCE in 30/40 sand











0.70


0.60 -- Pll


0.50

E 0.40
S- Experimental
x .3 -1--- Equilibnum
S0.30 -f- -- Non-Equilibnum


0.20


0.10 "

0.00 1
0.00 1.00 2.00 3.00 4.00 5.00 6.00
PCE (ml)

Figure 4.13. Curve comparisons for 1.4 density PCE in 30/40 sand

Flow By-Passing and Mass Transfer Rate Limitation

Figures 4.12 and 4.13 shows a comparison of mass flux versus mass loading curves

based on equilibrium, mass transfer rate, and experimental data.

For both the 1.1 and 1.4 density source zones, sufficient contact length is produced

during the loading process, indicating that equilibrium is achieved. The lower flux values

shown from the experimental data indicate that flow by-passing is likely occurring and

accounts for most of the reduction from expected equilibrium values. This is due to the

PCE not being homogeneously distributed across the width of the domain.

For both the 1.1 and 1.4 density source zones, sufficient contact length is produced

during the loading process, indicating that equilibrium is achieved. The lower flux values

shown from the experimental data indicate that flow by-passing is likely occurring and

accounts for most of the reduction from expected equilibrium values. This is due to the

PCE not being homogeneously distributed across the width of the domain.









Conclusions

Changes in density appear to slightly affect both the C/Cmax and 3 values.

Decreasing density slows vertical migration and delayed pooling leading to less efficient,

more linear mass loading /mass flux behavior and higher 3 values when compared to

untreated PCE values. As the density differential decreased, the residual geometry

became more uniformly spread out. As density differential decreased, residual geometry

more uniformly spread.

The interfacial tension for the range considered did not affect flux values. It

appears that interfacial tension must be ultra-low in order for the PCE not to become

entrapped (Pennell et al., 1996). The IFTs tested were not low enough to cause

instantaneous mobilization of the PCE, therefore a residual zone was left after migration

resulting in similar flux values compared to the untreated system.

Finally, flow by-passing is occurring and producing lower than expected flux

values when compared to equilibrium conditions.