Research Highlights

Measuring Ground Water Contaminants Through Image Analysis Tools

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Ground water that has become contaminated by chemicals that are sparingly soluble in water, such as chlorinated solvents, presents a serious ecological and human health risk. Ground water remediation scientists at EPA’s National Risk Management Research Laboratory (NRMRL) are using absorption and light refraction analysis to determine the saturation distribution of common ground water contaminants in order to facilitate research on the development of effective methods for remediating sites impacted by these chemicals.

Background

EPA ground water research programs help to ensure the safety of U.S. water resources by treatment and removal of hazardous contaminants.

Any liquid contaminant that is denser than water is referred to as a DNAPL (dense nonaqueous phase liquid). Contamination of the subsurface environment by DNAPLs is a serious environmental challenge since these liquids have the potential to migrate downward and accumulate in aquifers. While conventional technologies for DNAPL mitigation, such as excavation or pumping and treating, have demonstrated some success, the search continues for more effective remediation technologies with lower life-cycle costs. Designing effective remediation requires accurate knowledge of the subsurface DNAPL content and its spatial distribution. To this end, numerical models are developed to assist in evaluating and predicting the impact of these contaminants. These numerical models are usually validated against quantitative laboratory experiments. In addition to model validation, high-quality laboratory data also improve our understanding of contaminant behavior in the subsurface environment, which, in turn, helps in designing an effective remediation technology. However, only a limited number of laboratory techniques can be used to accurately measure DNAPL and water content in physical models (flow chambers) and some of them entail risks. For example, techniques to quantify fluid content using X-ray or gamma ray measurements are slow and costly, and present the potential hazards of working with high-energy sources. An alternative technique that has been gaining popularity is the use of light transmission visualization (LTV) to quantify DNAPL saturation.

Risk Management Research

EPA researchers have developed a modified LTV method that takes into account both absorption and refraction light theories to measure DNAPL distribution in two-dimensional laboratory aquifer models. This innovative approach analyzes digital images of the models pixel by pixel to determine DNAPL saturation and its spatial distribution. Using this LTV technique, the saturation of pure (undyed) DNAPL was measured whereas previous approaches required the addition of a dye to the DNAPL. While the addition of dye enhances visualization, it can also alter the chemical and physical properties of the DNAPL. In addition, the NRMRL method has eliminated the need for the tedious process of developing a calibration curve, another drawback of older lab methods.

The EPA approach can provide a more accurate assessment of the behavior of multiphase liquids (in this case, tetrachloroethylene) in porous media. Laboratory investigations by the LTV team are being used to evaluate the relationship between contaminant mass in source zones and the rate of contaminant release from these zones. This relationship is fundamental to the design of effective and cost-efficient remediation strategies at hazardous waste sites. By developing a method that advances the state of the science for understanding and remediating DNAPL source zones, the NRMRL research team has also advanced the EPA mission for protecting human health and the environment.

When Researchers Talk . . .

Sometimes research ideas are generated by friendly exchanges between scientists. That’s what happened when Subhas Sikdar, associate director for science at NRMRL, posed an idea to his colleague Dibaker Bhattacharyya (“DB”), a chemical engineer and faculty member of the University of Kentucky Center of Membrane Sciences. When Sikdar challenged DB to develop a membrane that could capture toxic metals with capacities on the order of one pound of metal captured per pound of absorbent material used—up to a 1000 percent increase in efficiency over existing methods—DB took the idea back to his laboratory. In due time, he more than met the challenge. With subsequent support from EPA, the Department of Defense and industry, he developed membranes that capture toxic metals such as mercury, lead, cadmium, barium and others from contaminated water with very low levels of these pollutants. The research collaboration also addressed the removal of polychlorinated biphenyls (PCBs) from water. Although PCBs were banned in the 1970s, they persist in soils and ground water, creating a health hazard to humans and animals. DB’s research applied catalytic properties to nanotechnology materials, essentially multiplying the surface properties of the membrane, expanding its filtration and holding capabilities and allowing further treatment to render toxics like PCBs harmless. For a complete discussion of this research, go to the University of Kentucky's Odyssey Web site. To learn more about current EPA nanotechnology research, see EPA’s Nanomaterial Research Strategy.

Contact

Jane Ice, NRMRL Office of Public Affairs (513) 569-7311

Hot Off the Presses—NRMRL Publications

Book

Thurston, H. W., M. T. Heberling, and A. Schrecongost. (2009) Environmental Economics for Watershed Restoration. CRC Press - Taylor & Francis Group, LLC, Boca Raton, FL.

Journal Articles

Agarwal, S., S. R. Al-Abed, D. D. Dionysiou, and E. Graybill. (2009) “Reactivity of Substituted Chlorines and Ensuing Dechlorination Pathways of Select PCB Congeners with Pd/Mg Bimetallics.” Environmental Science and Technology. American Chemical Society, Washington, DC, 43(3):915–921.

Beak, D. G. and R. T. Wilkin. (2009) “Performance of a Zerovalent Iron Reactive Barrier for the Treatment of Arsenic in Groundwater: Part 2. Geochemical Modeling and Solid Phase Studies.” Journal of Contaminant Hydrology. Elsevier BV, Amsterdam, Netherlands, 106(1-2):15–28.

Berger, P., R. M. Clark, D. J. Reasoner, E. W. Rice, and J. W. Santo-Domingo. (2009) “Drinking Water.” In: Encyclopedia of Microbiology. 3rd Edition. Elsevier Science, New York, NY, 1:121–137.

Butler, B. A. (2009) “Effect of pH, Ionic Strength, Dissolved Organic Carbon, Time, and Particle Size on Metals Release from Mine Drainage Impacted Streambed Sediments.” Water Research. Elsevier Science Ltd, New York, NY, 43(5):1392–1402.

Dugan, N. R., D. J. Williams, M. Meyer, R. R. Schneider, T. F. Speth, and D. H. Metz. (2009) “The Impact of Temperature on the Performance of Anaerobic Biological Treatment of Perchlorate in Drinking Water.” Water Research. Elsevier Science Ltd, New York, NY, 43(7):1867–1878.

Ludwig, R. D., D. J. Smyth, D. W. Blowes, L. E. Spink, R. T. Wilkin, D. G. Jewett, and C. J. Weisener. (2009) “Treatment of Arsenic, Heavy Metals, and Acidity Using a Mixed ZVI-Compost PRB.” Environmental Science and Technology. American Chemical Society, Washington, DC, 43(6):1970–1976.

Wilkin, R. T., S. D. Acree, R. R. Ross, D. G. Beak, and T. R. Lee. (2009) “Performance of a Zerovalent Iron Reactive Barrier for the Treatment of Arsenic in Groundwater: Part 1. Hydrogeochemical Studies.” Journal of Contaminant Hydrology Elsevier Science Ltd, New York, NY, 106(1-2):1–14.

Huling, S., D. Brown, and R. Luhrs. (2009) “Bioremediation/Natural Attenuation Continues after ISCO Treatment.” In Technology News and Trends, U.S. EPA Office of Superfund Remediation and Technology Innovation, Washington, D.C. (41):7–10.

US EPA (2009) Berghage, R., D. Beattie, A. Jarrett, C. Thurig, F. Razaei, and T. O’Connor. “Green Roofs for Stormwater Runoff Control (PDF).” (81 pp, 2.76 MB) EPA/600/R-09/026.

US EPA (2009) Cumming, L. J., A. S. Chen, and L. Wang. “Arsenic Removal from Drinking Water by Adsorptive Media. U.S. EPA Demonstration Project at Rollinsford, NH, Final Performance Evaluation Report (PDF).” (123 pp, 5.13 MB) EPA/600/R-09/017.

US EPA (2009) Cumming, L. J., A. S. Chen, and L. Wang. “Arsenic and Antimony Removal from Drinking Water by Adsorptive Media - U.S. EPA Demonstration Project at South Truckee Meadows General Improvement District (STMGID), NV, Final Performance Evaluation Report (PDF).” (79 pp, 4.3 MB) EPA/600/R-09/016.

US EPA (2009) “Environmental Technology Verification: Test Report of Mobile Source Emission Control Devices - Johnson Matthey PCRT2 1000, Version 2, Filter + Diesel Oxidation Catalyst (PDF).” (29 pp, 523 KB) EPA/600/R-09/034.

US EPA (2009) Shiao, H. T., A. S. Chen, L. Wang, and W. E. Condit. “Arsenic Removal from Drinking Water by Iron Removal - U.S. EPA Demonstration Project at Big Sauk Lake Mobile Home Park in Sauk Centre, MN. Final Performance Evaluation Report (PDF).” (81 pp, 4 MB) EPA/600/R-09/013.

US EPA (2009) Park, B., M. Mansfield, and N. M. Lewis. “Bioremediation of Pit Lakes - Gilt Edge Mine (PDF).” (74 pp, 2.8 MB) EPA/540/R-09/002.

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