Grantee Research Project Results
2004 Progress Report: A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
EPA Grant Number: R831276C003Subproject: this is subproject number 003 , established and managed by the Center Director under grant CR831276
(EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
Center: HSRC (2001) - South and Southwest HSRC
Center Director: Reible, Danny D.
Title: A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
Investigators: Bedient, Philip B. , Rixey, William G.
Institution: Rice University
EPA Project Officer: Aja, Hayley
Project Period: December 1, 2003 through November 30, 2004
Project Period Covered by this Report: December 1, 2003 through November 30, 2004
Project Amount: Refer to main center abstract for funding details.
RFA: Gulf Coast Hazardous Substance Research Center (Lamar University) (1996) RFA Text | Recipients Lists
Research Category: Hazardous Waste/Remediation , Targeted Research
Objective:
Methyl tertiary-butyl ether (MTBE) contamination in groundwater and surface water in the United States is widespread and considered a major threat to drinking water resources. The fuel oxygenate is therefore being phased out, and ethanol is the leading oxygenate to replace MTBE. To prevent a repeat of the problems associated with MTBE, the potential impacts to groundwater quality resulting from the inevitable releases of ethanol-blended gasoline must be understood. There have been some prior laboratory studies that have addressed the cosolubilization of benzene by ethanol, including research by Dr. Rixey at the University of Houston (UH). A larger-scale investigation, however, is needed to address more thoroughly the environmental implications associated with the use of ethanol additive fuels. Therefore, the objective of this research project is to simulate spill scenarios in the field with a controlled pilot-scale system. Experiments are being conducted in a well-instrumented, large-scale tank to assess three scenarios: (1) the impact of fuel-grade ethanol into a tank containing no existing contamination; (2) the impact of fuel-grade ethanol onto existing gasoline contamination; and (3) the impact of gasohol.
Progress Summary:
In Year 1, bench-scale laboratory experiments were completed for spill scenario 1 and preliminary results were obtained for spill scenario 2. Large-scale experiments were completed for spill scenario 1. The results for the large-scale experiments are described herein. The results for the laboratory-scale experiments are discussed in the Annual Report for R831276C016.
Two large-scale experiments were completed in fall 2003 and spring 2004 of Year 1 in the Experimental Control Release System (ECRS) tank. This ECRS tank had a width of 7 ft, a depth of 6 ft, and a length of 18 ft. The first set of experiments was with neat (100%) ethanol and the second set was with fuel grade (95% ethanol). A repeat of the fuel grade spill currently is being conducted in a new slightly smaller tank (width = 6 ft, depth = 4 ft, and length = 12 ft) that is more manageable and has been designed to better fit our needs. The results from this second fuel grade test are not yet available but will be reported at a later date.
Large-Scale Neat Ethanol Experiments
Prior to conducting the fuel-grade ethanol (95% ethanol/5% synthetic gasoline) spill experiment 1, a spill of neat (100%) ethanol was conducted. This experiment was preceded by a bromide (Br)-tracer experiment. In this first set of tracer and ethanol spill experiments, 10 gallons of a 5,000 mg/L Br-aqueous solution was spilled into a 7 ft long trench across the entire width of the ECRS tank. The bottom of the trench was approximately 6 inches above the water table. Following infiltration of the Br-solution, samples were taken at various points (300 aqueous and 30 soil samples taken from 33 sampling locations) and breakthrough curves were developed. Following the Br-tracer experiment, 5 gallons of water were introduced followed by 10 gallons of 100 percent ethanol. Samples were taken at various points downstream of the source of injection and breakthrough curves for ethanol were developed. After running the experiment for 7 days the bromide had run through the entire tank and appeared in the outflow. Minimal ethanol, however, was observed in the sampling lines by this point and based on soil samples, the ethanol remained largely in the vadose zone within a few feet of the source of the spill. The system continued to run for more than 1 month and concentrations no higher than 2900 mg/L ethanol were observed in any of the 33 sampling locations.
The results of the neat ethanol experiment indicated significant short-circuiting occurred in our theoretically homogeneous system. In an effort to focus on transport within the saturated zone and skip the uncertainty that arises from the vadose zone addition, for the subsequent fuel-grade ethanol experiment the ethanol was injected directly onto the water table. In addition, sampling lines were moved closer together, to assist in capturing the plume, and the focus of the study area was made smaller to improve mass-balance calculations and sample collection capabilities.
Large-Scale Fuel-Grade Ethanol Experiments
For the fuel-grade ethanol experiment, a 20 gallon Br-solution was first injected followed by a 5 gallon water flush, then 20 gallons of 100 percent ethanol and a final 5 gallon flush. A comparison of the breakthrough curves for Br and ethanol indicated that dissolution into the groundwater improved, but still less than 30 percent of the mass was observed in the first sampling transect 1 ft away. Horizontal movement of the ethanol within the capillary zone in both directions from the source also was observed, traveling almost 2 ft upgradient. Another key observation within the source was a phase separation between the ethanol and the hydrocarbons, as was evident by a color marking on the sand within the source zone trench. The hydrocarbon nonaqueous phase liquid (NAPL) left a red marking from the Sudan red dye at the highest level where the combined ethanol/hydrocarbon mixture resided before complete infiltration into the subsurface. The ethanol left a yellow smear from the fluorescence a few inches just above the red stained region, indicating the presence of no NAPL and that the ethanol moved higher into the capillary zone than the NAPL components.
The hydrocarbon recovery results in the fuel-grade ethanol experiment proceeded as would be predicted based on their respective solubilities. Nearly 100 percent recovery of benzene was observed, followed by 50 percent toluene, 20 percent xylene, 8 percent trimethylbenzene, and octane being at nondetectable levels. The mass fractions were normalized to the Br data because the flow field in the study was unable to be characterized through any other manner. These values were calculated based on the assumption that nearly 100 percent recovery of the conservative Br-tracer was observed and that the ethanol mixture’s constituents transported with the same flow velocity as the bromide.
Br was used as a conservative tracer in both experiments and was added just before the introduction of the ethanol solutions to assist in the hydrogeologic tracking of the contaminants. In the first experiment, the break through curves indicated the presence of extensive heterogeneities and short-circuiting in the upper 2 ft region of the ECRS. Hydraulic conductivities were calculated in the range of 1.295E-02 to 9.711E-03 cm/second, the larger values generally observed through the center. Overall, however, the Br did move at the velocity of the groundwater. In the second experiment, the Br appeared to be trapped with the ethanol hydrocarbon mixture and moved much slower than anticipated, indicating an unusual find to be considered in future experiments.
Future Activities:
We will: (1) perform spill scenario 2, neat ethanol onto an existing trapped gasoline source; (2) perform spill scenario 3, gasohol on existing contamination; (3) conduct tracer studies to characterize the hydraulic properties of the media within the tank prior to performing spill scenarios 2 and 3; (4) for each of the spill experiments, monitor aqueous concentrations for ethanol and various gasoline components of environmental concern (e.g., benzene, toluene, ethylbenzene, xylene, and 1,2,4- trimethylbenzene) in samples from several sampling locations within the tank as well as from the effluent versus time and analyze soil cores to determine the mass that remained in the source region; (5) analyze results from all three spill scenarios to evaluate the cosolvency effects; (6) analyze further soil cores to determine the mass that remained in the source region and that traveled within the capillary zone; and (7) model the tracer test results and head elevations from the large-scale experiments using MODFLOW to understand the flow field dynamics.
Journal Articles:
No journal articles submitted with this report: View all 2 publications for this subprojectSupplemental Keywords:
fuel oxygenates, cosolvency effects, vadose zone transport, near-field scale tank, gasoline contamination, waste, ecological risk assessment, environmental engineering, hazardous waste, advanced treatment technologies, bioremediation, contaminated waste sites, groundwater contamination, petroleum contaminants, hydrocarbon,, RFA, Scientific Discipline, Water, Waste, POLLUTANTS/TOXICS, Contaminated Sediments, Environmental Chemistry, Chemicals, Hazardous Waste, Ecology and Ecosystems, Drinking Water, Environmental Engineering, Hazardous, hazardous waste treatment, NAPL, leaking underground storage tanks, MTBE, contaminated sediment, hazardous waste storage, benzene, contaminated soil, BTEX, gasoline leaks, groundwater remediation, ethanol, contaminated groundwater, other - risk management, drinking water contaminantsRelevant Websites:
http://dept.lamar.edu/gchsrc/ Exit
Progress and Final Reports:
Original AbstractMain Center Abstract and Reports:
CR831276 HSRC (2001) - South and Southwest HSRC Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
R831276C001 DNAPL Source Control by Reductive Dechlorination with Fe(II)
R831276C002 Arsenic Removal and Stabilization with Synthesized Pyrite
R831276C003 A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
R831276C004 Visible-Light-Responsive Titania Modified with Aerogel/Ferroelectric Optical Materials for VOC Oxidation
R831276C005 Development of a Microwave-Induced On-Site Regeneration Technology for Advancing the Control of Mercury and VOC Emissions Employing Activated Carbon
R831276C006 Pollution Prevention through Functionality Tracking and Property Integration
R831276C007 Compact Nephelometer System for On-Line Monitoring of Particulate Matter Emissions
R831276C008 Effect of Pitting Corrosion Promoters on the Treatment of Waters Contaminated with a Nitroaromatic Compounds Using Integrated Reductive/Oxidative Processes
R831276C009 Linear Polymer Chain and Bioengineered Chelators for Metals Remediation
R831276C010 Treatment of Perchlorate Contaminated Water Using a Combined Biotic/Abiotic Process
R831276C011 Rapid Determination of Microbial Pathways for Pollutant Degradation
R831276C012 Simulations of the Emission, Transport, Chemistry and Deposition of Atmospheric Mercury in the Upper Gulf Coast Region
R831276C013 Reduction of Environmental Impact and Improvement of Intrinsic Security in Unsteady-state
R831276C014 Integrated Chemical Complex and Cogeneration Analysis System: Greenhouse Gas Management and Pollution Prevention Solutions
R831276C015 Improved Combustion Catalysts for NOx Emission Reduction
R831276C016 A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
R831276C017 Minimization of Hazardous Ion-Exchange Brine Waste by Biological Treatment of Perchlorate and Nitrate to Allow Brine Recycle
R831276C018 Integrated Chemical Complex and Cogeneration Analysis System: Greenhouse Gas Management and Pollution Prevention Solutions
The 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.
Project Research Results
Main Center: CR831276
64 publications for this center
18 journal articles for this center