HYDRAULIC CONDUCTIVITY OF THE HARTSHORNE SANDSTONE IN POPE COUNTY, ARKANSAS

A method was employed to measure regional hydraulic conductivity in the Hartshorne Sandstone, a fractured-rock aquifer, in an area of Pope County, Arkansas. In this method the hydraulic conductivity, K, is calculated from the Darcy’s Law equation, Q=KiA, using values for other parameters of the equation measured in the field. For the calculation, regional groundwater discharge, Q, is obtained by measuring stream discharge at two gauging stations in a local creek, the increase in discharge at the downstream station being attributable to discharge from the groundwater system. The total area of the stream bed between the two stations constitutes the cross sectional area, A, through which groundwater discharges. The head gradient, i, driving the flow is measured from local wells in the water-table aquifer. Application of this method to the vicinity of Galla Creek on Carrion Crow Mountain yielded a value of K ≈ 3 ft/d (0.9 m/d). This value falls near the high end of a range of K values obtained from 12 slug tests performed in wells of the same vicinity. It is likely that the main influence on the regional water budget with regard to groundwater discharge into Galla Creek is the flow through the larger fractures in the system. Because aquifers of the Arkansas River Valley, like the Hartshorne Sandstone, have a highly variable local distribution of fractures, this regional method is a preferable alternative to determination of K from slug tests or other borehole aquifer tests for rocks of the Arkansas River Valley. Determination of hydraulic conductivity by this method should be useful for such applications as estimating hydrologic impact of coal mining.