Interdisciplinary Geophysical Program to Assess 1,4-Dioxane Impacts in Glacial Deposits and Fractured Bedrock
Geophysical methods included: (i) review of historic orthophotos that identified two primary lineaments, one east-west trending (corresponding with groundwater flow direction) and one north-south trending (corresponding with the large wetland feature) that intersect within the study area; (ii) an electrical resistivity survey conducted along multiple survey lines within the study area to identify areas of potential leachate migration, identify potentially steeply dipping fluid-filled fractures in bedrock, and support bedrock surface interpolation; and, (iii) drilling and downhole logging of five bedrock boreholes to identify and characterize potential water bearing fractures for subsequent packer isolation sampling.
The results of the resistivity survey were utilized to refine the locations of the bedrock boreholes prior to drilling. The interpolated depth of the bedrock surface, as identified during the resistivity survey, remained consistent with during drilling observations. Borehole logging data was plotted using a series of vertical profiles and great circle projections and identified primarily east-west and north-south trending planar features consistent with the alignment of previously identified air photo lineaments. Combining the suite of geophysical tools resulted in effective subsurface characterization and minimized “overdrilling” of field explorations to achieve investigation objectives.