Seasonal Water Table Variations in the Onondaga FM, Western NY

Karst watersheds are vulnerable to surface and groundwater contamination because of complex surface-water/groundwater interactions. The Onondaga Formation is a known karst lithology in New York State that is heavily farmed and is an important aquifer for domestic water supplies. This formation has suffered several incidents of well contamination as a result of the application of fertilizer. Traditionally, the concern is water flowing down from the soil zone which carries with it pollutants derived from the surface. This process is assumed to be controlled by the transmissivity and vertical hydraulic gradient in the soil and bedrock. In parts of the Onondaga FM in western NY however, this process may also be controlled by the position of the seasonal piezometric surface. In this study we test the hypothesis that dynamic water table rises in the early spring are capable of inundating the base of the epikarst zone, where accumulated pollutants may then be washed into open fractures. To test this hypothesis, transducers have been installed in wells and sinkholes and karst-related flooding has been monitored. The results suggest that the water table in the Onondaga FM between Leroy and Caledonia are extremely dynamic, with rises as rapid as 3 meters per day occurring. Total water level range is also large, with some sites having greater than 15 meters of annual variation. The timing of karst-related flooding events in swallets suggest that they are related to this regional, seasonal shift in water table. This study seeks to better understand the dynamics of water table movement in this region in order to map areas that are sensitive to groundwater pollution and to consider the implications in storm water management.