INTEGRATED GEOPHYSICAL METHODS FOR CORRELATING THE UPPER MISSISSIPPI EMBAYMENT AQUIFER SYSTEM HYDROSTRATIGRAPHY: JACKSON PURCHASE, WESTERN KENTUCKY U.S.A

Increased groundwater use for agricultural irrigation in the Jackson Purchase has prompted questions related to groundwater availability and sustainability. A key factor in answering these questions is knowing the extent and thickness of the local aquifers. Ninety-eight natural gamma-ray well logs, as well as 75 resistivity logs have been used to improve the resolution of the upper Claiborne aquifer (UCA) and middle Claiborne confining unit (MCCU) in the southwestern part of the Jackson Purchase. Three east–west-oriented cross sections, 28-55 km in length, show the upper Mississippi embayment aquifer system (MEAS) hydrostratigraphy is not as uniform as previously thought. The thicknesses of the UCA and MCCU range between 12-46 m, and 6-52 m, respectively. The current geophysical log data are insufficient to define the middle Claiborne aquifer. Surface electrical resistivity and seismic lines were acquired and compared with the geophysical logs at well-constrained sites to test their limits for resolving these hydrostratigraphic units. Various arrays for the electrical resistivity tests were considered. The Schlumberger array provided the optimal electrical resolution. Previous research indicates that P-wave seismic reflection data provide low-to-moderate resolution of the interfaces separating the aquifers and confining unit. Additional seismic reflection soundings using S-waves will be tested for improved seismic resolution limits. Aquifer and confining unit surfaces and thicknesses within the MEAS, in Kentucky, need to be better defined in order to more accurately evaluate groundwater availability and aquifer interaction. This will require integrated invasive and non-invasive techniques to provide the needed resolution in a cost-effective manner.