Variability Of Electrical Resistivity At The Rice Creek Field Station, Oswego, New York: Implications For The Distribution Of Groundwater

Electrical resistivity measurements were made to determine the variability of surficial<br>deposits, the depth to bedrock and to characterize the distribution of groundwater at the Rice<br>Creek Field Station near Oswego, New York. The field station is underlain by drumlin deposits<br>and ablation till associated with Pleistocene glaciation. These deposits reside on Ordovician<br>quartz sandstone of the Oswego Formation that outcrops within 1500 m of the study site.<br>Locally the Oswego Formation contains subvertical fractures with an average spacing of less than<br>0.5 m. Twenty offset Wenner electrical resistivity surveys were conducted in June and August of<br>1998 along trails and across an open field within the field station grounds. Analysis of<br>pseudosections and simple 1-D modeling and 2-D least squares inversion indicate the following:<br>1) low resistivity zones associated with perched water tables within the chaotic drumlin deposits;<br>2) highly variable and resistive near-surface measurements along Rice Creek indicative of large<br>(>l m diameter) glacial erratics as observed in the creek bed; 3) a transitional zone below -250 ft<br>elevation of subcircular highs separated by relatively low resistivities that continue into the<br>deepest portions of the data, which is coincident with the projected depth to bedrock beneath the<br>field station and is interpreted to be an undersaturated zone within the fractured Oswego<br>Sandstone; and 4) low resistivities below an elevation of - 190 ft are interpreted to be the top of<br>the saturated domain within the fractured bedrock.