DEFINING ELECTRICAL RESISTIVITY TOMOGRAPHY (ERT) FACIES FOR GLACIAL DEPOSITS IN CENTRAL NEW YORK

Tracking the interaction between surface and groundwater in glacial sedimentary deposits is generally problematic and to a great extent unpredictable, due to the wide variation in sediment size and distribution, porosity and permeability that is associated with the varied depositional environments. This problem is compounded in regions with little to no exposure of the deposits for direct characterization. Over a period of many field seasons in central NY, numerous ERT surveys were completed over a variety of glacial deposits at several locations per depositional environment. For example, four different locations of glacial outwash deposits were examined, in addition to the tops and flanks of drumlins, and glacial lake deposits. As well, the transitions between these depositional settings were surveyed. The following ERT characteristics were repeatedly documented (ERT Facies): 1) The top of drumlins produced discontinuous low (80-120 ohm-m) ER domains (10 m scale) that are highly irregular in shape; 2) The flank of drumlins produce continuous near-surface low (100-150 ohm-m) ER domains that overlie a chaotic ERT high (500-1000 ohm-m)anomaly pattern; 3) Low (80-120 ohm-m) discontinuous channel-shaped ER anomalies separated by general moderate (150-300 ohm-m) anomaly backgroud, dominate outwash; 4) Within glacial lake varve deposits, consistently the ERT surveys produced laterally continuous very low anomalies (<50 ohm-m) that overlie a continuous moderate (150-300 ohm-m) anomaly. As before, these observations were made at several locations for each depositional setting with generally predictable results. Therefore, in regions with glacial deposits, with few exposures or the lack of borehole data, the application of ERT facies may aid in the identification of general deposit types.