The Impact of the Aquifer Framework on Groundwater Flow in the Dakota Aquifer of Kansas: ABSTRACT

Abstract

The movement of water and dissolved solids in the Dakota aquifer is affected by the distribution and degree of interconnection of the discontinuous sandstone aquifers in the formations that constitute the aquifer in Kansas. In Kansas, the Dakota aquifer framework consists of the nonmarine to paralic to marine sequences of interbedded thin sandstones, shales, siltstones, and thick channel sandstones. The spatial arrangement of aquifers and confining beds can be determined from an understanding of the depositional history of unconformity bounded stratigraphic sequences. These formations are divisible into several such sequences. The lower sequence contains the Cheyenne Sandstone and Kiowa Formation. The second sequence contains the lower half of the Dakota Formation with the upper half making up the basal part of the third sequence. Strata deposited in marine environments dominate the sequence to the west, depositionally basinward, and nonmarine and nearshore deposits dominate to the east, depositionally landward. Two hydrostratigraphic units are defined on state-wide gamma-ray log cross sections that are calibrated to cores. The lower unit (Cheyenne Sandstone and Longford Member of the Kiowa Formation) is separated from the upper unit (Dakota Formation) by a thick section of low-hydraulic conductivity marine shale in the Kiowa Formation. This shale decreasesmore » in thickness eastward due to lateral facies changes into Longford Member shoreline deposits and from erosional truncation at the base of the Dakota Formation. In central Kansas, where the shale is not present the two hydrostratigraphic units are amalgamated and hydraulically connected. This is illustrated by means of a vertical cross section showing potentiometric contours and flow directions.« less