EXAMINING SCALE DEPENDENCE OF HYDRAULIC CONDUCTIVITY IN GLACIAL SEDIMENTS FOR IMPROVING PREDICTIONS OF CONTAMINANT PLUME RESPONSE TO FLOW SYSTEM TRANSIENTS

Predicting contaminant transport and fate in groundwater requires detailed, three- dimensional assessment of the hydraulic conductivity distribution. Glacial sediments, particularly those associated with an ice marginal environment, are often highly heterogeneous making hydraulic conductivity (K) results very sensitive to the scale of measurement. The objective of this study is to use methods targeting a variety of measurement scales to quantify K variability for ice marginal sediments that has influenced the mass and phase distributions of mixed organic contaminants in the DNAPL and dissolved phases. Numerous sediment samples were collected from five cores as part of a previous study to represent all observed lithofacies. Grain size distributions are being determined for these samples to estimate K at the decimeter scale using established empirical equations. High-resolution Westbay multilevel systems (MLS) with depth-discrete monitoring intervals specifically designed to target each of the observed facies associations were installed at the site as part of several past studies. These MLSs provide an opportunity to assess trends in K with depth at an intermediate scale (2-10 meters). Pneumatic slug tests are being conducted in the MLS monitoring intervals using high-resolution pressure sensors for improved precision and accuracy. In addition, hydraulic head measurements have been collected at least once every 5 minutes for the last two years from 14 monitoring wells completed in the glacial sediments. These data document head perturbations due to precipitation and remediation system pumping and are being used to characterize K at a hectometer scale. Results from each scale of measurement are used to assess the variability in K due to the heterogeneity of the sediments in the context of hydrogeologic and plume variability. Ultimately, K representative of a variety of scales is necessary in order to understand the full range of transport processes relevant at the site including DNAPL migration and accumulations influencing source zone fluxes, plume transport processes, and delivery of amendments under consideration for use in potential active remediation strategies.