Flow in a limestone aquifer as determined from water tracing and water levels in wells

Abstract

The Inner Bluegrass Karst Region of central Kentucky, U.S.A., is a fluviokarst underlain by flat-lying slightly argillaceous limestones (Ordovician). Water tracing and field observations have shown the aquifer to be divisible into groundwater basins and intervening interbasin areas. Flow in groundwater basins is in a dendritic system of solution conduits at depths as great as 35 m beneath the surface which often passes beneath surface divides to emerge at low-level springs, in contrast to interbasin areas in which the flow is shallow and generally parallels surface slopes. The availability of relatively dense water-level data in an area in which a number of water traces had been conducted allowed a comparison between the configuration of the potentiometric surface and water tracing data. The potentiometric surface map was generally consistent with the location of groundwater basins and interbasin areas. In addition, water levels near streams were found to be controlled by the stream and a few wells indicated perched aquifers. The potentiometric surface, however, failed to show narrow groundwater basins and did not adequately indicate groundwater flow directions previously established by water tracing. Although well data may furnish valuable supplemental information, it is concluded that water tracing is necessary to determine adequately subsurface flow directions in the region and in similar karst aquifers elsewhere.