Resistivity imaging through a recharge zone for the Fredericton aquifer

Abstract

The Fredericton aquifer is the primary source of drinking water for the City of Fredericton. It is composed of outwash sands and gravels and confined by a lacustrine clay/silt aquitard. Discontinuities in the clay/silt aquitard, or "windows", are known to occur in at least three locations throughout the aquifer and are areas of aquifer recharge and potential contamination by infiltration of surface water. Ground conductivity(EM31) and resistivity surveys were conducted along the river banks of the Saint John River, Fredericton in the fall of 2001. These surveys were able to identify the location of an aquitard window, believed to be a recharge zone for the Fredericton aquifer, and image the resistivity structure through its profile by numerically inverting the apparent resistivity data collected. The results of the resistivity imaging revealed the presence of two pods of clay/silt, approximately 55 and 75 metres wide, within the recharge zone on the south river bank of the Saint John River. The aquitard window was not found to extend to the north river bank of the river.