Abstract

Electromagnetic induction (EM) and natural gamma-ray (GR) borehole logs were used to investigate the intrusion of saltwater into the Great Bend Prairie aquifer of south-central Kansas. The inherent cross correlation between the log types was optimized such that the GR log was used to correct the EM log for the aquifer-clay component of the signal. The corrected logs were then converted into equivalent chloride concentration units and processed by curve-fitting techniques to generate an objective, quantitative set of parameters that characterizes the freshwater-saltwater transition zone in the aquifer. Results of the curve-fit analysis were then used to estimate consistently the interface depth of the 500 mg/L chloride concentration level. Results from three years of observations at monitoring sites provide compelling evidence for a state of dynamic equilibrium between freshwater and saltwater in response to hydrologic stresses including recharge and pumping discharge.