Evaluation of methods for determination of hydraulic properties in an aquifer-aquitard system hydrologically connected to a river

Field and laboratory methods have been used to determine the hydraulic properties in a multiple-layer aquifer-aquitard system that is hydrologically connected to a river. First, hypothetical pumping tests in aquifer-aquitard systems were performed to evaluate the feasibility of MODFLOW-PEST in determining these parameters. Sensitivity analyses showed that: the horizontal hydraulic conductivity in the aquifer has the highest composite sensitivity; the vertical hydraulic conductivity has higher composite sensitivity than the horizontal hydraulic conductivity in the aquitard; and a partial penetration pumping well in an aquifer layer can improve the quality of the estimated parameters. This inverse approach was then used to analyze a pumping-recovery test conducted near the Platte River in southeastern Nebraska, USA. The hydraulic conductivities and specific yield were calculated for the aquitard and aquifer. The direct-push technique was used to generate sediment columns; permeameter tests on these columns produced the vertical hydraulic conductivities that are compatible with those obtained from the pumping-recovery test. Thus, the combination of the direct-push technique with permeameter tests provides a new method for estimation of vertical hydraulic conductivity. The hydraulic conductivity, determined from grain-size analysis, is smaller than the horizontal one but larger than the vertical one determined by the pumping-recovery test.