Case Study of Steady Oxygen Concentration Gradients in a Groundwater Plume from a Highway Infiltration Basin |
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Authors: | David W. Ostendorf Chul Park Camelia Rotaru Marina S. Pereira |
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Affiliation: | 1Professor, Dept. of Civil and Environmental Engineering, Univ. of Massachusetts, Amherst, MA 01003 (corresponding author). E-mail: ostendorf@ecs.umass.edu 2Assistant Professor, Dept. of Civil and Environmental Engineering, Univ. of Massachusetts, Amherst, MA 01003. 3Research Assistant, Dept. of Civil and Environmental Engineering, Univ. of Massachusetts, Amherst, MA 01003.
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Abstract: | We measure and model the steady transport of specific conductivity and dissolved oxygen through a groundwater plume from a highway infiltration basin in southeastern Massachusetts. Specific conductivity is treated as a conservative surrogate for runoff contamination, and the data calibrate a 0.27-m vertical dispersivity α of the aquifer and the bottom streamline elevation of the plume, which falls to an 8-m depth below the water table. The dissolved oxygen degrades as a first order reactant in the plume to levels below 1 mg/L, with a decay constant λ of 0.12?day?1. The latter may be attributed in part to the historical use of an alternative de-icing agent calcium magnesium acetate on the highway, since acetate is a readily biodegradable substrate for microorganisms. The calibrated kinetics suggest that plume microbes and geochemistry degrade oxygen over two orders of magnitude faster than their ambient groundwater counterparts, which impose a linear decrease of dissolved oxygen concentration below the plume. Simulations suggest that the anoxic groundwater plume extends 1,600 m downgradient of the infiltration basin, a distance that will shorten by an order of magnitude if salt is used exclusively to de-ice the highway. |
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Keywords: | Groundwater pollution Dissolved oxygen Stormwater management Infiltration Runoff Highways and roads Case studies |
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