Frequency dependent hydraulic properties estimated from oscillatory pumping tests in an unconfined aquifer

Oscillatory pumping tests were conducted at the Boise Hydrogeophysical Research Site. A periodic pressure signal is generated by pumping and injecting water into the aquifer consecutively and the pressure response is recorded at many points around the source. We present and analyze the data from the field test after applying Fourier analysis. We then match the data with a recently derived analytical solution for homogeneous formations to estimate the equivalent aquifer properties: conductivity K, specific storage S_s and specific yield S_y. The estimated values are shown to be in agreement with previous estimates conducted at this site. We observe variations in the estimated parameters with different oscillation periods of pumping. The trend of the parameters with changing period is discussed and compared to predictions by existing theory and laboratory experiments dealing with dynamic effective properties. It is shown that the results are qualitatively consistent with recent works on effective properties of formations of spatially variable properties in oscillatory flow. To grasp the impact of heterogeneity, a simple configuration is proposed, helping explain the observed increase in effective conductivity with decreasing period.