THREE DIMENSIONAL ELECTRICAL RESISTIVITY ANALYSIS OF THE RICE CREEK REGION, OSWEGO, NEW YORK

C. New York is underlain by Pleistocene glacial till and is host to a drumlin field that extends from the Tug Hill Plateau to the region west of Rochester. The Rice Creek region is located in Oswego, part of the Rice Creek field station (RCFS-SUNY Oswego), and the location of the field site for this study. Within this region there are several drumlins separated by open valleys with wetlands. The main objective of this investigation was to examine the interaction between groundwater and surface water in this setting using electrical resistivity to develop a three dimensional aquifer model. During the Fall 2007, a series of electrical resistivity surveys were completed over the southern end of the Rice Creek drumlin. The survey design was developed to cover an area about 0.1 sq km within the grounds of the RCFS. To complete this survey, a total of ten roll-along Wenner resistivity lines were conducted, with each ~250-300 m long and spaced ~50 m apart. Two cross surveys were conducted each ~500 m long. Each survey was made up of several sets of data collected using a 24-node (3 m spacing) automated system that allows for data collection to a depth of about 10.5 meters. Pseudosections and inversion models were produced for each line to visualize the electrical "structure" in two dimensions. The overall results were compiled into a three dimensional data set to generate a groundwater model. It is apparent from the pseudosections that material variations must exist that control the distribution of groundwater. There is a crescent shaped moderate- to high- (200-350 ohm-m) resistivity anomaly that occurs at several deep levels in the data (10.5-9.0 m). Although this anomaly appears to fade at shallower levels (7.5-6.0 m), it merges with a high anomaly (350-500 ohm-m) near the surface (4.5-1.5 m). The local drumlins are characterize as unsorted gravel, sand, silt and clay, but there appears to be some systematic variation that influences the distribution of groundwater within this deposit. Possibly, post-depositional reworking of the drumlin materials in the vicinity of Rice Creek, in addition to flood deposition of clay resulted in a local barrier to restrict the movement of groundwater from the drumlin to the local wetland. This hypothesis will be tested with a core to confirm the material content of the various resistivity anomalies and further constrain the three dimensional model.