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JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 112, B04403, doi:10.1029/2006JB004485, 2007

Hydrogeologic controls imposed by mechanical stratigraphy in layered rocks of the Châteauguay River Basin, a U.S.-Canada transborder aquifer

Roger Morin

U.S. Geological Survey, Denver, Colorado, USA


Réjean Godin

Centre d'Études sur les Ressources Minérales, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada


Miroslav Nastev

Geological Survey of Canada, Québec, Québec, Canada


Alain Rouleau

Centre d'Études sur les Ressources Minérales, Université du Québec à Chicoutimi, Chicoutimi, Québec, Canada


Abstract

The Châteauguay River Basin delineates a transborder watershed with roughly half of its surface area located in northern New York State and half in southern Québec Province, Canada. As part of a multidisciplinary study designed to characterize the hydrogeologic properties of this basin, geophysical logs were obtained in 12 wells strategically located to penetrate the four major sedimentary rock formations that constitute the regional aquifers. The layered rocks were classified according to their elastic properties into three primary units: soft sandstone, hard sandstone, and dolostone. Downhole measurements were analyzed to identify fracture patterns associated with each unit and to evaluate their role in controlling groundwater flow. Fracture networks are composed of orthogonal sets of laterally extensive, subhorizontal bedding plane partings and bed-delimited, subvertical joints with spacings that are consistent with rock mechanics principles and stress models. The vertical distribution of transmissive zones is confined to a few select bedding plane fractures, with soft sandstone having the fewest (one per 70-m depth) and hard sandstone the most (five per 70-m depth). Bed-normal permeability is examined using a probabilistic model that considers the lengths of flow paths winding along joints and bedding plane fractures. Soft sandstone has the smallest bed-normal permeability primarily because of its wide, geomechanically undersaturated joint spacing. Results indicate that the three formations have similar values of bulk transmissivity, within roughly an order of magnitude, but that each rock unit has its own unique system of groundwater flow paths that constitute that transmissivity.

Received 4 May 2006; accepted 20 November 2006; published 6 April 2007.

Keywords: hydrogeophysics; fractured-rock hydrology; elastic properties.

Index Terms: 1822 Hydrology: Geomechanics; 1829 Hydrology: Groundwater hydrology; 5104 Physical Properties of Rocks: Fracture and flow; 1835 Hydrology: Hydrogeophysics; 1895 Hydrology: Instruments and techniques: monitoring.

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Citation: Morin, R., R. Godin, M. Nastev, and A. Rouleau (2007), Hydrogeologic controls imposed by mechanical stratigraphy in layered rocks of the Châteauguay River Basin, a U.S.-Canada transborder aquifer, J. Geophys. Res., 112, B04403, doi:10.1029/2006JB004485.