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GEOPHYSICAL RESEARCH LETTERS, VOL. 30, NO. 18, 1961, doi:10.1029/2003GL017913, 2003

Hydraulic transience and the role of bedding fractures in a bedrock aquitard, southeastern Wisconsin, USA

Timothy T. Eaton

Wisconsin Geological and Natural History Survey, Madison, Wisconsin, USA


Kenneth R. Bradbury

Wisconsin Geological and Natural History Survey, Madison, Wisconsin, USA


Abstract

Hydraulic heads in a dolomitic shale bedrock aquitard in Wisconsin, USA, are apparently not in equilibrium with drawdown in the underlying aquifer system caused by pumping for municipal supply over the last century. Measurements of head with depth, downhole geophysical logs, and estimates of hydraulic conductivity indicate very low vertical hydraulic diffusivity, and show that high horizontal permeability within the aquitard due to bedding-plane fracture zones can allow lateral groundwater flow. Unlike the hydrogeological conceptual models used in many investigations, flow in aquitards cannot always be inferred to be primarily one-dimensional and vertical. Failure to account for transient conditions and lateral flow in similar settings of intensive groundwater pumping could lead to error in estimates of aquitard leakage and underlying aquifer properties.

Received 6 June 2003; accepted 26 August 2003; published 26 September 2003.

Index Terms: 1829 Hydrology: Groundwater hydrology; 5114 Physical Properties of Rocks: Permeability and porosity; 5104 Physical Properties of Rocks: Fracture and flow; 0915 Exploration Geophysics: Downhole methods; 1884 Hydrology: Water supply.

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Citation: Eaton, T. T., and K. R. Bradbury (2003), Hydraulic transience and the role of bedding fractures in a bedrock aquitard, southeastern Wisconsin, USA, Geophys. Res. Lett., 30(18), 1961, doi:10.1029/2003GL017913.