Stochastic evaluation of subsurface contaminant discharges under physical,chemical, and biological heterogeneities |
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| Authors: | M Mohamed K Hatfield A Hassan H Klammler |
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| Institution: | 1. Civil and Environmental Engineering Department, United Arab Emirates University, P.O. Box 17555, Alain, United Arab Emirates;2. Irrigation and Hydraulics Department, Faculty of Engineering, Cairo University, P.O. Box 12211, Giza 12613, Egypt;3. Civil and Coastal Engineering Department, University of Florida, P.O. Box 116580, Gainesville, FL 32611, USA;4. Department of Environmental Science and Sustainable Development, Federal University of Bahia, Barreiras, Bahia, Brazil |
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| Abstract: | A finite element 2D Monte Carlo approach is used to evaluate the sensitivity of groundwater contaminant discharges to a Damkohler number ω and spatial variability in aquifer hydraulic conductivity, initial microbial biomass concentrations, and electron acceptor/donor concentrations. Bioattenuation is most sensitive to spatial variations in incipient biomass and critical electron donors/acceptors for ω ≥ 1 (i.e., when pore-water residence times are high compared to the time needed for microbial growth or contaminant attenuation). Under these conditions, critical reaction processes can become substrate-limited at multiple locations throughout the aquifer; which in turn increases expected contaminant discharges and their uncertainties at monitored transects. For ω ≤ 0.2, contaminant discharge is not sensitive to incipient biomass variations. Physical heterogeneities expedite plume arrival and delay departure at transects and in turn attenuate peak discharges but do not affect cumulative contaminant discharges. Physical heterogeneities do, however, induce transect mass discharge variances that are bimodal functions of time; the first peak beings consistently higher. A simple stream tube model is invoked to explain the occurrence of peaks in contaminant discharge variance. |
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| Keywords: | Monte Carlo Mass discharge Groundwater Biodegradation |
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