Modeling natural attenuation of wastewater-contaminated aquifers over different scales

Rojas Scheffer, Veronica C

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Modeling natural attenuation of wastewater-contaminated aquifers over different scales

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Characterizing the effects of subsurface wastewater effluent discharges remains as a significant challenge impacting both ground-water and surface water resources. Important aspects of this challenge relate to the quantification of the main processes affecting oxygen consumption within a wastewater plume and to the ability of representing these conditions over a range of scales. The goal of this research is to improve our understanding of the relevant processes affecting oxygen consumption and thus, controlling natural attenuation in wastewater contaminated aquifers, and also to characterize and quantify these processes through modeling approaches considering different scales. The analysis included consideration of restoration processes associated with a former sewage disposal discharge in Falmouth, MA. The discharge was removed in 1995, and the site has been experiencing natural restoration since removal. A small-scale natural gradient tracer test, completed 6 years after cessation of sewage disposal, was used in previous research to develop parameters to characterize aerobic respiration and nitrification processes, key oxygen consuming processes for this site. In addition, field monitoring by the United States Geological Survey has provided a series of concentration profiles at different locations along the flowpath associated with the contaminant source. For this research, predictions obtained with the existing model were used in conjunction with these concentration profiles to assess the sensitivity and applicability in the parameters from this small-scale test, as well as their pertinence to the larger scale restoration process. By evaluating the applicability of this model to different scales and the associated variability of key model parameters, the approach provided an improved characterization of the primary processes affecting oxygen consumption.

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