Analysis of Hydraulic Conductivities in Fractured Rocks Near Oak Ridge, Tennessee

摘要

More than 1,500 observation wells have been drilled near Oak Ridge National Laboratory since 1949, and more than 380 values of hydraulic conductivity have been determined. Groundwater in this area occurs in fractures in the regolith and the underlying bedrock. The hydraulic conductivity data show that water-bearing fractures are very common but that most wells yield less than 1 L/min of water. These data are lognormally distributed, and there are only local similarities in the hydraulic conductivities of nearby wells. Analysis of the data using cumulative probability graphs shows several significant deviations that otherwisse would have been obscure. There is almost no difference between the hydraulic conductivities of regolith wells and bedrock wells, suggesting a similar mode of groundwater occurrence in these materials. There is also little difference between wells in the Conasauga Group and wells in the Chickamauga Group, suggesting that lithologic differences are less important than other factors in determining the spatial frequency and aperture of open fractures in these units. Comparison of hydraulic conductivity values grouped by well depth and by the depth of packer tests in coreholes shows two distinctive populations. The characteristics of the first population can be used to predict groundwater flows and well yields to a depth of about 20 m. The characteristics of the second population can be used to predict flows and yields at deeper levels. 15 refs., 2 figs., 4 tabs. (ERA citation 13:031365)