HYDROGEOLOGY OF THE POTSDAM SANDSTONE AQUIFER AND SPRINGS IN THE CHATEAUGAY AREA, NORTHERN NEW YORK

The Potsdam sandstone of Cambrian age forms a transboundary aquifer that extends from northern New York into southern Quebec. The Potsdam sandstone is a gradational sequence of arkose, subarkose, and orthoquartzite that unconformably overlies Precambrian metamorphic bedrock. In the Chateaugay area, thick till overlies the Potsdam sandstone except in the east where the till is discontinuous. A network of Pleistocene ice-marginal channels have been cut into the till, and along the Chateaugay River, a deep bedrock gorge has been carved by post-glacial erosion.

A series of major springs discharge adjacent to tributaries of the Chateaugay River at rates ranging from 300 to 1800 gallons per minute. The springs are used for municipal, bottled-water, and fish-hatchery supply. Wells in the Chateaugay area penetrate subhorizontal bedrock fracture zones with hydraulic heads that generally decrease with depth. Wells that intercept shallow fractures near the top of bedrock display shallow water levels, while wells that intercept deep fractures show deep water levels. Cascading water and downward flow are common in wells that penetrate both shallow and deep fracture zones.

Hydrogeologic investigations near Ellenburg, New York and Covey Hill in southernmost Quebec confirm the presence of areally extensive fracture zones related to bedding in the Potsdam sandstone aquifer. These observations, and those from the Chateaugay area, are consistent with a conceptual model of the Chateaugay springs and bedrock gorge being points of discharge for a gently dipping series of bedding-related fracture zones. The major recharge areas for the springs probably are in the east where till cover is discontinuous. The abandoned ice-marginal channels, where cut to bedrock, may serve as focused points of recharge.

A water-bottling plant to be supplied by pumpage from the Potsdam aquifer is proposed for a site northeast of the Chateaugay area in Franklin, Quebec. Aquifer simulation suggests that more than half of the contributing area for the proposed well site would be on the New York side of the border, and the area would abut the recharge areas conceptualized for the northern Chateaugay springs.