In order to evaluate the potential for upward migration of these brines, the Kansas Geological Survey conducted a subregional hydrogeologic investigation of the Great Plains and Cedar Hills aquifers to assess the geologic and hydrologic factors affecting containment of the disposed and naturally-occurring brines. Sandstones, shales and mudstones of the Dakota Formation, Kiowa Formation, and Cheyenne Sandstone comprise the framework of the Great Plains aquifer.
Sandstone, siltstone, and shale of the Cedar Hills Formation comprise the framework of the Cedar Hills aquifer. In the eastern half of the area, the Cedar Hills aquifer directly underlies the Great Plains aquifer, but in the western part relatively impermeable Jurassic and Permian strata separate these two aquifer systems. Ground-water flow in the Great Plains aquifer is generally from the deeper part of the Western Kansas basin and southern outcrop areas towards the Smoky Hill and Saline Rivers. Ground-water flow in the Cedar Hills aquifer is subparallel to the flow in the Great Plains aquifer where they are in contact.
Elsewhere in the western part of the area the configuration of the Cedar Hills potentiometric surface has been affected by fluid injection. Total dissolved solids concentrations of ground waters in the Cedar Hills and lower Great Plains aquifers are generally greater than 20,000 mg/l and decrease vertically upward into the upper part of the Great Plains aquifer.
Throughout the central Kansas area, the hydrologic data from the monitoring sites indicates vertically upward movement of fluids from the Cedar Hills and into the Great Plains aquifer. This is supported by the similarity of general water chemistry, Br/Cl versus Cl mixing curves, and the stable isotope data between aquifers. Hydrologic testing suggest that upward movement of brines may be facilitated locally by fractures. These results indicate that shallow underground disposal of oil-field brines should be discontinued in the area of interconnection between the Cedar Hills and Great Plains aquifers.