A procedure for delineation of bedrock fracture zones under glacial drift formations in ohio

TLDR: In this article, the authors analyzed the hydraulic conductivity of private single-home water wells in the sandstone formations in Geauga and Portage Counties of Northeastern Ohio and found that the porosity can be either primary or secondary or a combination of the two, referred to as dual porosity.

Abstract: In any aquifer the porosity can be either primary or secondary or a combination of the two, referred to as dual porosity. Primary porosity is the diffused, inter-granular porosity inherent to the rock, generated at the time of lithogenesis. Secondary porosity is the porosity created by post-genetic processes, e.g. fracturing or dissolution of the rock. Rates of groundwater production from bedrock sandstone units are commonly directly related to the presence and extent of secondary porosity. Bedrock fracturing can be product of tectonic stress or, in recently glaciated areas, unloading from the retreat of glaciers. The goals of our study were to test the hypothesis that the values of hydraulic conductivity, computed from the data stored in water well archives for single-home water wells penetrating bedrock sandstone formations may delineate mappable areas of high hydraulic conductivity, thus showing the distribution of fracture zones. We analyzed ninety-one well logs of private single-home water wells drilled through the glacial sediments into the sandstone bedrock formations in Geauga and Portage Counties of Northeastern Ohio. Aquifer thickness in each water well was determined from the lithological profiles, while the specific capacity data from production tests were used to estimate the values of the coefficient of transmissivity for each well. Combination of the two parameters yielded mappable values of hydraulic conductivity. The resulting values of hydraulic conductivity were characterized by a distinctly binary distribution, with low values apparently corresponding to massive un-fractured zones and high values corresponding to fractured zones with dual porosity. Once contoured on a map, these zones appeared clearly, with a transition between the areas of high and low hydraulic conductivity, i.e. high and low potential for groundwater production, respectively.