The determination of the suitability of ground penetrating radar to map "windows" in the protective clay/silt aquitard of the Fredericton aquifer
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Date
2000
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University of New Brunswick
Abstract
Ground Penetrating Radar (GPR) is a non-invasive geophysical technique that can be
used to determine the subsurface features at a site. This method utilizes changes in material
properties (i.e. conductivity, dielectric constant) to provide a detailed image of the underlying
geology stratigraphy.
The City of Fredericton's main source of potable water is a glaciofluvial sand and
gravel aquifer that is overlain by a lacustrine clay/silt unit of variable thickness and a fluvial
sand and gravel deposit. The sites chosen for this investigation are located near the
Fredericton well field in the Wilmot Park and Smythe Street area of the City's Downtown.
Through previous borehole data (Violette, 1990) available for these locations, the confining
clay/silt layer is known to exhibit breaks or 'windows' that can be potential sources of
recharge or contamination for the aquifer. It would therefore be useful to locate these
'windows' to prevent possible migration of hazardous material into the water supply and to aid
in determining the extent of recharge to the aquifer at these locations.
The method of GPR profiling with 50 and 100 MHz antennas proved to be an effective
means of determining the presence (or lack) of clay/silt due to the high attenuation caused by
this highly conductive lacustrine sediment. The clay/silt layer was interpreted as a strong
reflector that appears to have a gently slope to the South. This was evidenced by the fact that
the reflector varied from - 8 0 to -105 ns in the N-S profiles (9, 11, 12 and 13). The
location of the clay window near Smythe Street and in the Southeast corner of Wilmot Park
have been positioned using the interpreted radar data.