MAPPING SURFACE- AND GROUNDWATER INTERACTION IN THE WETLAND TO UPLAND TRANSITION WITHIN WITH GLACIAL DEPOSITS USING HIGH-RESOLUTION ELECTRICAL RESISTIVITY TECHNIQUES, OSWEGO COUNTY, NEW YORK

Throughout Oswego Co, NY, various types of Pleistocene glacial till reside on the Paleozoic bedrock. The dominant till includes drumlins that are separated by open flat valleys know locally as the "muck-lands". The "muck-lands" contain organic deposits associated with hardwood wetlands. In 2007, unseasonably dry weather resulted in low water levels within many of these wetlands. These conditions provided an opportunity to examine the interaction between surface and groundwater within and adjacent to these isolated basins, using high-resolution electrical resistivity techniques. A site in the town of New Haven, NY was studied. The study site is where a small wetland (0.4 sq. km) narrows (300 m wide) between a drumlin (west) and outwash gravel (east). The field experiments involved 24-node Wenner arrays using a an automated resistivity meter. A (400 meter) roll-along survey was conducted using 3 m node spacings to produce 7 data levels with a penetration depth of about 10.5 m. Additionally, well data, shallow pits, and cores were used to constrain the geophysical anomalies and to trace them in the subsurface. In effect, a high-resolution resistivity profile coupled with other subsurface data were used to produce a cross section spanning the wetland to examine the controls on surface water distribution and "map" the extension into the subsurface. Pseudosections produced from the resistivity data revealed consistent patterns of high and low anomalies across the site. A high anomaly (300-500 ohm-m) correlates with the drumlin and outwash deposits, and it appears that the drumlin material extends beneath the wetland. A 4 m core from the wetland contained a section of varves that correlates with the high- to low (50-200 ohm-m) transition, and also confirmed the presence of coarse material at ~6 m. The overall pattern of the resitivity data suggests that the varve deposits are draped on the margin of the drumlin at the western side of the basin. However, at the eastern side it appears that the outwash deposits are incised into the varves. With the varves controlling the migration of groundwater, there appears to be little interaction between the surface water in the wetland and the western drumlin, but the outwash deposit to the east may serve as a subsurface pathway that drains the wetland.