Grantee Research Project Results
2004 Progress Report: A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
EPA Grant Number: R831276C016Subproject: this is subproject number 016 , 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: Texas - Indiana Virtual STAR Center
Center Director: Gustafsson , Jan-Ake
Title: A Large-Scale Experimental Investigation of the Impact of Ethanol on Groundwater Contamination
Investigators: Rixey, William G. , Bedient, Philip B.
Institution: University of Houston - University Park , 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 phase 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.
The purpose of this overall joint research is to simulate spill scenarios in the field with large-scale and bench-scale experiments. Three different spill scenarios are being studied. Experiments are being conducted to assess: (1) Spill Scenario 1, the impact of fuel-grade ethanol (95% ethanol) into a tank containing no existing contamination; (2) Spill Scenario 2, the impact of neat ethanol onto existing gasoline contamination; and (3) Spill Scenario 3, the impact of gasoline containing smaller amounts of ethanol (10%, i.e., gasohol).
Both large-scale and bench-scale laboratory experiments are being conducted. Rice University is taking the lead on the large-scale tank tests and corresponding large-scale modeling activities. The University of Houston (UH) is responsible for the bench-scale laboratory tests and corresponding modeling studies. Both institutions are actively involved in the planning, execution, and analysis of the large-scale experiments. UH also is providing analytical support for both the large-scale experiments and the bench-scale studies.
Progress Summary:
In Year 1, bench-scale laboratory experiments were completed for spill scenario 1 and preliminary results were obtained for spill scenario 2. Preliminary large-scale experiments were conducted for spill scenario 1, and additional large-scale experiments for spill scenario 1 followed by experiments for spill scenario 2 are planned for Year 2. The results for the bench-scale laboratory experiments are described below. The results for the large-scale experiments will be reported separately by Rice University (Grant No. R831276C003). UH provided laboratory analytical support for ethanol and benzene, toluene, and xylene (BTX) concentrations in groundwater and soil for these tests as well as participate in the preparation of the pilot spill tank and in the sampling and operation of the tank experiments. Briefly, two large-scale experiments were completed in fall 2003 and spring 2004 of Year 1 in a pilot-scale tank. This tank had a width of 7 ft, a depth of 7 ft, and a length of 20 ft. The first set of experiments was with neat (100%) ethanol and the second set was with fuel-grade (95%) ethanol. A second fuel-grade ethanol experiment is underway.
Bench-Scale Experiments
Water-saturated column experiments were conducted to investigate the impact of ethanol on the concentrations of BTX and other hydrocarbons in groundwater near a source of contamination.
The following two ethanol spill scenarios were studied:
- Spill Scenario 1: Spills of fuel-grade ethanol without existing contamination.
- Spill Scenario 2: Spills of neat ethanol with existing nonaqueous phase liquid (NAPL) contamination.
Seven experiments (including two duplicate experiments) have been completed in Year 1. Three column experiments that simulate scenario 1 (fuel-grade ethanol with no existing NAPL), three column experiments that simulate scenario 2 (neat ethanol onto an existing NAPL source), and an additional experiment conducted with 100 percent ethanol with no existing NAPL.
For the Scenario 1 experiments, the fuel-grade ethanol was created by mixing pure ethanol and the same five-component NAPL mixture at different volume ratios. Two different concentrations of ethanol/NAPL in the fuel-grade ethanol were used: one contained 95 percent ethanol and 5 percent NAPL, and the other contained 97.5 percent ethanol and 2.5 percent NAPL. In both sets of experiments, effluent samples were collected and concentrations of ethanol and each of the NAPL components were measured versus time. For the Scenario 2 experiments, an ethanol-free, five-component NAPL mixture was first packed into a water-saturated column to act as a residually trapped NAPL source, and then a pulse of neat ethanol was introduced into the column to simulate a neat ethanol spill onto residual NAPL, followed by ethanol-free water.
Results and Conclusions from Year 1 Experiments To Date
The bench-scale experiments have demonstrated that the two different spill scenarios can yield different BTX and other hydrocarbon concentrations for the same amount of ethanol and NAPL spilled into the subsurface. For neat ethanol spilled onto existing NAPL (Scenario 2), the maximum BTX and other hydrocarbon concentrations that were observed in the aqueous phase appear to be controlled by equilibrium dissolution from NAPL into the concentrated ethanol pulse. For fuel-grade ethanol spilled without an existing NAPL source (Scenario 1), the maximum BTX and other hydrocarbon concentrations that were observed appear to be determined by the composition of the diluted fuel mixture as long as the solubility limit in the ethanol/water phase was not exceeded.
The conditions studied to date for the fuel-grade ethanol scenario (scenario 1) were selected to simulate large volume spills of 95 percent and 97.5 percent fuel grade ethanol mixtures. These laboratory experiments yielded very high peak effluent ethanol concentrations (600,000 mg/L) and likely represent maximum BTX concentrations that can be expected in groundwater near a source of contamination.
Comparison to Large-Scale Tank Studies
Our bench-scale studies have been designed to complement the larger-scale experiments that are being conducted in the pilot-scale system at Rice University.
The preliminary bench-scale experiments were conducted with pulses of ethanol sufficiently large to generate maximum ethanol concentrations that could be expected in ground water. Our neat ethanol and fuel grade ethanol Year 1 results from the large-scale tests indicated a peak ethanol concentration 25,000 mg/L. This is lower than the maximum concentration for bench-scale experiment 1 (150,000 mg/L). The lower peak ethanol concentrations were a result of a small fraction of the ethanol entering groundwater. Our observations from the large-scale experiments completed to date have suggested some very important additional bench-scale tests that should be conducted to answer questions related to the complex generation of the ethanol/NAPL source. It is becoming clear that understanding the generation of the source is key to understanding groundwater impacts. As a result, two-dimensional (2D) bench-scale tests have been incorporated into our Year 2 and Year 3 plans.
Future Activities:
Activities to be performed by UH are identified below:
- Laboratory column experiments will be conducted at UH to assess the impact of gasohol (Scenario 3) on existing contamination.
- Additional bench scale column experiments for Spill Scenario 1 (fuel grade ethanol) and Scenario 2 (neat ethanol onto existing NAPL contamination) will be conducted with lower volume ethanol pulse injections.
- Bench-scale studies in the 2D bench-scale tank will be conducted to better understand how sources of ethanol and NAPL from injections of fuel-grade ethanol (95% ethanol-5% NAPL) are generated.
- Quantitative analysis of the experimental results. Source dissolution models developed at UH that include the effects of cosolubilization by ethanol will integrated with models developed at Rice University to analyze the tank experiments.
- A final report that will indicate how these results can be used for the management of ethanol impacts.
Publications/Presentations: See the list of publications/presentations included in the 2004 Annual Report for Grant No. R831276C003.
Supplemental Keywords:
fuel oxygenates, cosolvency, 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, monitoring, 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 Texas - Indiana Virtual STAR Center Subprojects under this Center: (EPA does not fund or establish subprojects; EPA awards and manages the overall grant for this center).
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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
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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
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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.