Dakota Home Report Archive FY91 Ann Rep

The Dakota Aquifer Program--Annual Report, FY91

by P. Allen Macfarlane, D.O. Whittemore, T. Chu, J.J. Butler Jr., A. Wade, J. Coleman, J.H. Doveton, J. Mitchell, and S. Kay
Kansas Geological Survey, The University of Kansas
Lawrence, Kansas

Kansas Geological Survey
Open-file Report 92-1

Executive Summary

Localized depletion of near-surface sources of water in the Ogallala and alluvial valley aquifers coupled with the need to develop new water supplies in western and central Kansas is focusing the attention of planning and regulatory agencies on the next available source of ground water, the Dakota aquifer. Insufficient information on the quantity and quality of ground waters, effects of withdrawals, and the impact of oil-brine disposal in shallow zones beneath the aquifer has limited the ability of state agencies to evaluate this aquifer as a major water source for the future. Those areas of the Dakota aquifer currently undergoing development are managed with little or no technical guidance for policy decisions.

On the basis of work conducted by the Kansas Geological Survey in FY89, several water quantity and quality problems associated with long-term development were identified. These problem areas relate to (1) water availability, (2) sources of recharge and their effects on water quality in the Dakota aquifer, (3) the impact of withdrawals of water from the Ogallala and Dakota aquifer in southwestern Kansas on future water-supply availability, (4) the effect of shallow disposal of produced oil brines on the Dakota aquifer in central Kansas, (5) the delineation of usable zones in the Dakota aquifer, and (6) the effect of saltwater discharge from the Dakota aquifer on water quality in central Kansas stream-aquifer systems.

For FY90-93 the overall objective of the Dakota aquifer program is to characterize subregionally the water resources potential of areas where the Dakota aquifer is shallowest and is undergoing development in central and southwestern Kansas. This region was subdivided geographically into three separate subareas of investigation. In these subareas the aquifer is used extensively for irrigation, public water supply, and industrial uses. Up-to-date information, although not exhaustive, is available in the three main subareas of investigation to determine how past development has affected this source of water and to project the effects of future management policies.

In FY91 the Kansas Geological Survey undertook a diverse research program in geology, geohydrology, and geochemistry that focused on the three investigation subareas defined in the FY90 Annual Report. An important program emphasis of the FY91-92 Dakota aquifer program is the definition of (1) aquifer units, which allow the movement of ground water and are the primary sources for wells, and (2) aquitards, or aquicludes, which impede the movement of ground water. The classification of the Dakota aquifer framework into aquifer and non-aquifer units is useful for developing an understanding of regional ground-water flow patterns and hydraulic connection between aquifers on a variety of spatial and temporal scales. The ground-water flow pattern is an important constraint on the quantity and quality of ground water available to wells. Research into the details concerning the past geologic processes that produced the arrangement of these units in the Dakota aquifer is being conducted because the major ancient fluvial and deltaic systems controlled the deposition of sandstones, the principal water-producing porous media in the Dakota aquifer. Information on the location of stream valleys and delta systems at the time of deposition is a key element in the prediction of sandstone body trend and distribution and thus, of hydraulic continuity. The results of this work are being fed into other program areas dealing with the development of cross-sectional models of ground-water flow in the Dakota and adjacent aquifers and chemical reaction-mass transport models of the geochemical evolution of water quality. To conduct this research, we have significantly expanded the southwestern and south-central Kansas portions of the geophysical log and geologic data bases to produce the required level of detail.

In the program area that emphasizes geohydrology, the focus was (1) construction of monitoring sites in Lincoln, Cloud, Hodgeman, and Finney counties; (2) completion of hydrologic testing and water sampling at the Lincoln and Cloud County monitoring sites to provide hydrologic properties and water-quality data and a base for long-term observation of water levels; (3) completion of the geohydrology study in Washington, eastern Republic, and northern Cloud counties; and (4) continuation of a study to determine the factors controlling the predevelopment (steady-state) regional flow system in southeastern Colorado and southwestern and central Kansas using cross-sectional models.

The geochemical part of the program focused on (1) collection and analysis of water samples from wells in southwestern and central Kansas for water-quality assessment of Dakota ground waters and entry into the water-quality data base, (2) initiation of work to produce groundwater chemistry atlases, (3) continuation of the water-quality use assessment for water supplies, and (4) continuation of the assessment of coupled geochemical and mass transport models to simulate chemical reactions and transport along flow paths in the Dakota aquifer.

In the area of research support the annual report of the FY90 Dakota Aquifer Program was completed and published as KGS Open-file Report 91-1. The results of the central Kansas test hole drilling program are reported in KGS Open-File Report 91-1A, and the results of a pumping test in Washington County are reported in KGS Open-File Report 91-1B.

In FY92-93 the results of the subarea investigations begun in FY90 will be combined to characterize the Dakota aquifer in central and southwestern Kansas. The objectives of the FY92 Dakota Aquifer Program are (1) to integrate the FY90-91 results of the southwestern, south-central, and north-central subarea investigations with the results of ongoing field studies in shallow areas of the Dakota aquifer within and outside of the subarea investigations and (2) to begin development of steady-state computer simulations of ground-water flow in the Dakota and adjacent aquifer systems in southwestern and central Kansas and southeastern Colorado using a phased approach. Computer models will be used to determine the factors controlling the ground-water flow system, such as the arrangement of aquifer and aquitard units, and the effect of topography, and to estimate the amount of recharge to and discharge from the aquifer (FY92, Phase 1).

Completion of these objectives is required for the development of a three-dimensional model that can be used to simulate temporal changes in ground-water flow resulting from pumping or injection and mass transport. In FY92 the Kansas Geological Survey, in cooperation with the U.S. Geological Survey, will install one monitoring site within the Dakota aquifer in southwestern Kansas and will conduct tests to gain insight into the relationship of the Dakota aquifer to the overlying High Plains and underlying saltwater-bearing aquifers. The objective of the FY93 Dakota Aquifer Program (Phase 2) will be to continue using models of the Dakota aquifer to assess the effects of pumpage or injection on water quality. These models will be used to assess the effect of various water-management scenarios.

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Kansas Geological Survey, Dakota Project
Original report available from the Kansas Geological Survey.
Electronic version placed online Nov. 1998
Scientific comments to P. Allen Macfarlane
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