The hydrogeologic properties of a drumlin till with relation to contaminant transport
This thesis describes an investigation of the hydraulics of the southwest quadrant of a drumlin in Eastern Massachusetts. A road salt storage facility was located on the site and had contaminated the groundwater. The drumlin was found to consist of a layer of natural fill, a layer of brown till, and a layer of gray till sitting directly on bedrock. Values obtained from laboratory testing were all typical for glacial till.
Groundwater monitoring wells were installed around the site for monthly groundwater quality sampling, measurement of piezometric head, and slug tests. Piezometric head varied periodically with time with variations from a yearly average that decreased with depth. Hydraulic conductivity measured from the slug tests varied almost over five orders of magnitude, with no lateral trend, but a general decreasing trend with depth. Data were analyzed with mathematical equations and a numerical three-dimensional model. Both models yielded results consistent with each other and measured values. Based on the models, bedrock was found to be permeable but incompressible.
Test pits revealed oxidation, root holes, and discontinuities in the brown till. The discontinuities were analyzed using analytical equations, and it was found that these could explain the wide range of hydraulic conductivities in the brown till. The wide range of the hydraulic conductivity in the gray till could be explained by the presence boulders and cobbles in the gray till creating channels for groundwater flow.
Groundwater flow was found to be primarily vertical through the brown till, then radial at the brown gray/till interface because of the lower mean hydraulic conductivity of the gray till. Highest radial flow and chloride flux occurs to the southwest towards a landfill located directly downhill from the salt storage facility, with minimal flow in the other directions. Chloride contamination was shown by the calibrated model to flow primarily by advection, so it follows the same path as the groundwater. Background chloride concentrations in the deep wells in the gray till confirm that the chloride does not enter deep into the gray till.