Bioremediation in Fractured Rock: 1. Modeling to Inform Design,Monitoring, and Expectations |
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| Authors: | Claire R Tiedeman Allen M Shapiro Paul A Hsieh Thomas E Imbrigiotta Daniel J Goode Pierre J Lacombe Mary F DeFlaun Scott R Drew Carole D Johnson John H Williams Gary P Curtis |
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| Institution: | 1. U.S. Geological Survey, 12201 Sunrise Valley Drive, Mail Stop 431, Reston, VA 20192;2. U.S. Geological Survey, 345 Middlefield Road, Mail Stop 496, Menlo Park, CA 94025;3. U.S. Geological Survey, 3450 Princeton Pike, Suite 110, Lawrenceville, NJ 08648;4. Geosyntec Consultants, 7 Graphics Drive, Suite 106, Ewing Township, NJ 08628;5. U.S. Geological Survey, 11 Sherman Place, Unit 5015, Storrs, CT 06269;6. U.S. Geological Survey, 425 Jordan Road, Troy, NY 12180 |
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| Abstract: | Field characterization of a trichloroethene (TCE) source area in fractured mudstones produced a detailed understanding of the geology, contaminant distribution in fractures and the rock matrix, and hydraulic and transport properties. Groundwater flow and chemical transport modeling that synthesized the field characterization information proved critical for designing bioremediation of the source area. The planned bioremediation involved injecting emulsified vegetable oil and bacteria to enhance the naturally occurring biodegradation of TCE. The flow and transport modeling showed that injection will spread amendments widely over a zone of lower‐permeability fractures, with long residence times expected because of small velocities after injection and sorption of emulsified vegetable oil onto solids. Amendments transported out of this zone will be diluted by groundwater flux from other areas, limiting bioremediation effectiveness downgradient. At nearby pumping wells, further dilution is expected to make bioremediation effects undetectable in the pumped water. The results emphasize that in fracture‐dominated flow regimes, the extent of injected amendments cannot be conceptualized using simple homogeneous models of groundwater flow commonly adopted to design injections in unconsolidated porous media (e.g., radial diverging or dipole flow regimes). Instead, it is important to synthesize site characterization information using a groundwater flow model that includes discrete features representing high‐ and low‐permeability fractures. This type of model accounts for the highly heterogeneous hydraulic conductivity and groundwater fluxes in fractured‐rock aquifers, and facilitates designing injection strategies that target specific volumes of the aquifer and maximize the distribution of amendments over these volumes. |
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