GROUND PENETRATING RADAR: A NONINVASIVE, HIGH RESOLUTION METHOD FOR THE DEVELOPMENT OF FACIES MODELS IN ESKERS

Since many sites for groundwater exploration and extraction occur in glacial environments, earth scientists need to know more about their complex subsurface architecture. Such deposits also vary in geotechnical, hydrogeological and geochemical properties, thus lateral mapping of sediments is an important objective. Ground penetrating radar (GPR) can significantly aid in the subsurface investigation of high energy glaciofluvial environments, such as eskers. In this work we examine the use of GPR as an electromagnetic geophysical tool to non-invasively image the sedimentary attributes of glacial depositional environments and their potential relation to local hydrology. At several different locations in North America, we collected high-resolution datasets within glacial deposits using portable, digital GPR systems (pulseEKKO and RAMAC). The first dataset was collected on several eskers along the former glacial margins of SW Alberta. The second dataset from Maine was collected within Caribou Bog which is a large multi-unit peatland surrounded by esker deposit outcrops from the Katahdin system. Previous studies in the area showed the presence of elevated mineral soil surfaces underneath the peat soil interpreted as buried eskers. The use of different antennae frequencies (50, 100 and 200 MHz) provided subsurface stratigraphic information ranging in depth from 7 to 55 m. The profiles were interpreted using radar stratigraphic principles which aided in the mapping radar facies units within the glaciofluvial deposits. Several of the eskers we imaged, for example, are characterized by internal horizontal-to-wavy reflection patterns with numerous reflections dipping in the inferred direction of meltwater flow. Hydrological measurements (consisting of seven monitoring well clusters across the study area) were also collected at Caribou Bog to investigate the contrast between inorganic (esker) and organic (peat) sediments into flow properties. The results showed certain correlation between stronger downward hydraulic gradients and proximity to the esker crests. Our work provides insight into the non-invasive characterization of eskers and their sedimentary attributes. These findings also have implications for aquifer characterization and groundwater flow models in glaciated basins.