Abstract

Traditional geostatistical approaches for estimating distributions of hydraulic conductivity fail to reflect sharp contrasts that occur at boundaries between different stratigraphic units, thus limiting the accuracy of contaminant-transport models. We present an approach to incorporate a stratigraphic framework into geostatistical simulation at the scale of a plume, to better represent aquifer heterogeneity. The approach was developed and tested at the Schoolcraft Bioremediation Site in southwestern Michigan, where detailed estimates of aquifer properties were needed to accurately simulate multi-component reactive transport and to design an effective bioremediation strategy. The sediments at the site were deposited as glaciofluvial outwash downstream of the Kalamazoo Moraine, and consist mainly of fine to medium sands with interbedded gravels and silts. A series of 18-meter-long continuous cores was collected in the vicinity of the bioremediation-system delivery wells. These cores were assessed for sedimentary facies, grain-size distribution, porosity, and hydraulic conductivity. Sedimentologic measurements from outcrop analogs supplemented the core data from the site. On the basis of the core data, the aquifer was separated into four stratigraphic units, and the measured conductivity values were geostatistically interpolated within each stratigraphic unit. The stratigraphically based estimates of hydraulic conductivity were used as input to a high-resolution, three-dimensional model of groundwater flow and solute transport in the region. The model with stratigraphic interpolation provided better transport predictions for an injected tracer pulse than models that do not incorporate the stratigraphy.

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Biteman, et al (2004)