Predictive Depositional Model for Glacial Aquifers

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In an investigation of the hydrogeology of bedrock valley fills in northeastern Wisconsin, it was determined that the yield and spatial distribution of glacial aquifers are controlled by bedrock topography and glacial geology. Lithologic control for identification and classification of aquifer units was obtained from several hundred drillers' logs calibrated by auger borings and interviews. Transmissivities of drift aquifers calculated from specific capacity tests using Jacob's equation agree well with estimates made from lithologic logs. Seismic refraction and gravity surveys were coupled with well log data to derive a bedrock elevation map. Vertical variability maps calculated from the lithologic logs show that bedrock topography strongly influences the distribution and character of glacial units, and clearly delineate the two glacial aquifer types present, valley and morainal units. Morainal units parallel the Late Wisconsin end moraine trends, while valley units are perpendicular to the moraines. The morainal units are small ice-contact features such as kames, fans, and deltas. The valley units are stream deposits and may have been deposited subglacially. Valley aquifers are the most productive units. Using lithologic and geophysical data, and statistical analysis, a predictive depositional model can be proposed. This conceptual model allows knowledge of bedrock topography to be coupled with glacial geology to predict the spatial distribution of glacial aquifers.

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Groundwater, v. 19, issue 2, p. 133-137