The Importance of Bedrock Hydrogeology in Assessing U.S.-Canada Transboundary Groundwater Resources: The Chateauguay River and Lake Champlain Basins

A basic understanding of underlying hydrogeologic systems is critical to the sound management of groundwater resources across shared boundaries.  In the case of the Chateauguay River Basin, which encompasses a transboundary watershed with roughly half of its surface area located in northern New York State (USA) and half in southern Quebec Province (Canada), the Potsdam Sandstone forms the regional bedrock aquifer that extends across international jurisdictions.  A comprehensive field program was undertaken to characterize the hydrogeologic properties of these fractured rocks and to understand their influence on groundwater movement.  Long-term aquifer tests detected drawdown along bedding in boreholes located more than 1 km apart, and flow zones were identified at the same stratigraphic horizon in two boreholes separated by more than 4 km.  Springs are ubiquitous on both sides of the border and occur where water-bearing fractures intercept terrain topography.  Focused discharges at rates ranging from 1,000 to 5,000 L/min were measured at several springs, thus providing evidence of an aquifer that is supported by a broad, regional collection system.  The compilation of field data indicates that flow is confined to discrete, subhorizontal fracture planes that may extend relatively unimpeded for hundreds of meters to kilometers due to the distinctive properties of Potsdam Sandstone.  These results emphasize the interdependent nature of groundwater resources across this border.

            A newly established project is designed to characterize the hydrologic systems of the contiguous Richelieu and Yamaska River Basins located to the east of the Chateauguay study area.  The Richelieu Basin is the northern extension of the Lake Champlain watershed located in Vermont (USA), and field studies will again examine transboundary groundwater movement as a function of varying bedrock hydrogeology.  The Chateauguay River Basin is an official UNESCO Transboundary Aquifer and efforts are underway to include the Lake Champlain watershed under this designation.