MAPPING THE SURFACE WATER - GROUNDWATER INTERACTION IN GLACIAL TILL: ELECTRICAL RESITIVITY IN MY BACKYARD

Using high-resolution electrical resistivity techniques, a variety of unconsolidated to semi-consolidated glacial till were studied to characterize the groundwater to surface water interaction, and develop three dimensional models of aquifers in the till. The field surveys involved 24-node Wenner arrays using a resistivity meter with an automated switching system. Three field locations in different types of glacial till were examined. A grid of survey lines were run for each field location, making sure to anchor each survey to places where surface water meets dry ground. Using the 24-node system and a 3m spacing, seven levels of data were collected to a depth of about 10.5m. Individual surveys span about 65m on the ground, but roll-along surveys produced data sets that span hundreds of meters.

The field locations for this study are in Cayuga and Oswego Co., NY: McIntyre Bluff, Rice Creek Field Station (RCFS), and a location in the town of New Haven. McIntyre Bluff is a place where a drumlin has been sharply eroded along the shore of Lake Ontario. More than 15m of exposure reveals a variety of till ranging in size from clay to erratics. Two long perpendicular surveys were completed across the drumlin, with one ending at the lake shore edge. At the RCFS, a grid of surveys were done on the flank of a drumlin adjacent to a large pond surrounded by wetlands. An abandon quarry exposes pebble to cobble gravel deposits at the New Haven site. A grid of resistivity surveys were conducted with a number of the lines starting and ending at the water edge to local wetlands.

Pseudosections produced from the resistivity data revealed interesting patterns of high and low anomalies for all locations. At all sites, low electrical resistivity anomalies occur immediately adjacent and beneath the wetland areas suggesting the extension of the surface water into the groundwater. The interior of the surveys are very complex. At the New Haven site, it appears that the gravel deposit produced a very high resistivity anomaly with values ranging from 1000-7000 ohm-m. When mapped in 3D, the high anomaly is surrounded aerially and below by a low anomaly that extends to the near-surface approaching the surface water. At McIntyre Bluff and RCFS, the interior anomalies are not so simple, and there appears to be no consistent pattern. This probably reflects a complex distribution of clay to gravel deposits that make up the drumlins.