HYDROLOGIC ASSESSMENT OF THE OZARK AQUIFER IN GREENE COUNTY, MO

The hydraulic properties of the Ozark Aquifer and its upper confining unit were measured as part of the site characterization for the Shallow Carbon Sequestration Demonstration Project. The goal was to delineate the cone of depression/capture zone (of any upward leaking CO₂) produced by three onsite production wells above the CO₂ injection zone and to model future changes in this cone due to increased pumpage in nearby municipal wells.

Several regional flow models of the Ozark Aquifer have been published previously, but we are unaware of any supporting field measurements of the relevant hydrologic properties in southwest Missouri. A three month cessation of pumping in two of the three production wells allowed a unique opportunity for such measurements. When water levels reached a quasi-steady state with respect to the remaining well, the Thiem solution gave limiting transmissivity values of 0.015 and 0.042 ft²/sec. Upon restart of one of the idled wells, the transient response in the third well gave transmissivities ranging between 0.017 and 0.025 ft²/sec. with storativity centered around 6 x 10^-4. Analytical models were not particularly sensitive to leakance values of the confining layer (the Northview Formation), but indicate a vertical hydraulic conductivity < 10^-9 ft/sec. When steady-state conditions were reached again for all three wells, flow-net analysis gave a transmissivity of 0.011 ft/sec. Thus, direct field measurements provide a median transmissivity of 0.027 ft²/sec.

Digital model simulations of the steady potentiometric surface closely match measured levels with a calibrated transmissivity of 0.027 ft²/sec and a vertical hydraulic conductivity within the confining unit of 9 x 10^-11 ft/sec. Thus, these calibrated values are very consistent with measured values and the calibrated model should provide reasonable estimates of the future capture zone under various pumping scenarios.

This material is based upon work sponsored by the Department of Energy National Energy Technology Laboratory under Award Number DE-NT0006642 to City Utilities of Springfield, MO.