Grantee Research Project Results
2000 Progress Report: The Effect of Clay on DNAPL Behavior During Alcohol Flushing
EPA Grant Number: R827120Title: The Effect of Clay on DNAPL Behavior During Alcohol Flushing
Investigators: Hayden, Nancy J.
Institution: University of Vermont
EPA Project Officer: Aja, Hayley
Project Period: December 1, 1998 through November 11, 2001 (Extended to June 21, 2003)
Project Period Covered by this Report: December 1, 1999 through November 11, 2000
Project Amount: $375,240
RFA: Exploratory Research - Environmental Engineering (1998) RFA Text | Recipients Lists
Research Category: Sustainable and Healthy Communities , Land and Waste Management , Safer Chemicals
Objective:
The overall objective of this project is to investigate the effect of clay and clay colloids on the distribution of dense non-aqueous phase liquids (DNAPLs) in porous media and the subsequent effect on DNAPL distribution, mass transfer, and interfacial phenomena during alcohol flushing. An improved understanding of DNAPL behavior is critical for improving restoration attempts using in situ methods such as alcohol flushing. A series of experiments and analyses are being performed at pore and column scales to meet the project objectives. Kaolinite and Ca-montmorillonite clays are being used for the majority of experiments. Isopropyl alcohol (IPA) and tetrachloroethylene (PCE) are being used as the alcohol and DNAPL, respectively.Progress Summary:
Steady progress has been made in the pressure-saturation, mobilization, and permeability studies. Pressure-saturation (Pc-S) experiments were run using columns containing a well-sorted Ottawa white sand (S) and 10 percent mixtures of both Kaolinite and Ca-montmorillonite with the Ottawa sand (10 percent K and 10 percent M, respectively). Most columns were packed to a bulk density of 1.8 g/cm3. The experiments have resulted in five successful drainage curve replicates of 10 percent K, four successful drainage curve replicates of 10 percent M, and four successful drainage curve replicates of S. The drainage curves were reproducible for all three groups of experiments (10 percent K, 10 percent M, and S). Representative drainage curves for sand, 10 percent K and 10 percent M columns are shown in Figure 1, and Table 1 summarizes the key features of these columns.
Figure 1. Typical drainage curves from one set of Pc-S experiments.
Table 1. Drainage Curve Summary.
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(rb ? 1.72 g/cm3) |
(rb ? 1.80 g/cm3) |
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Mobilization experiments were performed on sand, 10 percent K and 10 percent M columns once the pressure-saturation experiments were completed and the PCE was allowed to drain to a residual saturation. Successive increments of IPA were flushed through the column to determine the alcohol concentration at the onset of mobilization. PCE was mobilized with the lowest concentration of IPA in the 10 percent M columns and mobilized at approximately the same concentration of IPA in the sand and 10 percent K columns. This suggests that Ca-montmorillonite may affect DNAPL mobilization through its smaller pores; larger pore-size distribution; interfacial interactions between clay, DNAPL, and pore fluid; or some combined effect of these factors. It should be noted that a statistically significant decrease in PCE/water interfacial tension was measured in solutions containing Ca-montmorillonite during the interfacial tension studies completed in Year 1. It also should be noted that clay colloids in the effluent were observed in many experiments.
Two permeability experiments have been completed on 10 percent M and 10 percent K columns. The permeability was measured in each experiment using a fixed-wall permeameter with successive solutions of 0, 20, 40, 60, 80, and 100 percent IPA (by volume). In the first experiment, a 0.01M CaCl2 buffer solution was mixed with the IPA to make the solutions. The amount of the CaCl2 in the flushing solution decreased as the percent IPA increased. In the second experiment, deionized water was first mixed with the IPA and then CaCl2 was added to maintain a constant ionic concentration in the solution. Control columns for each clay type were run during every experiment to investigate flow induced changes in permeability and measurement variability. The experimental protocol was identical for control and treatment columns with the exception that only the buffer solution was used in the control columns.
There were differences between the results of the 10 percent M decreasing and constant ionic concentration experiments suggesting that the ionic concentration of the pore solution below 0.01 M affects permeability of Ca-montmorillonite containing sediments. There was very little difference in the decreasing and constant ionic concentration experiments in the 10 percent K study suggesting that the ionic concentration of the pore solution below 0.01 M does not affect the permeability of kaolinite-containing sediments. There was a slight decrease in permeability between 0 and 20 percent IPA in both experiments. The permeability was not constant in the control columns. Clay was observed occasionally in the effluent suggesting that the clay in the 10 percent K columns was mobile with the 0.01 M buffer, but was not once IPA entered the pore space.
Future Activities:
The pressure-saturation and permeability studies will be completed in Year 3. Experimental results will be analyzed and synthesized to elucidate the mechanisms affecting clay and DNAPL behavior during alcohol flushing. Additional data will be collected using clay colloid displacement, DNAPL transport, and visualization experiments.Journal Articles:
No journal articles submitted with this report: View all 8 publications for this projectSupplemental Keywords:
groundwater, soil, solvents, NAPL, DNAPL, remediation, environmental chemistry, cleanup., RFA, Scientific Discipline, Air, Toxics, Waste, Remediation, Environmental Chemistry, HAPS, chemical mixtures, Hazardous Waste, Engineering, Hazardous, Electron Microscopy, Engineering, Chemistry, & Physics, hazardous waste treatment, DNAPL, alcohol flushing, infrared spectroscopy sensor, interfacial phenomena, mass transfer, electrophoretic studies, hazardous chemicals, restoration, clayProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.