Constant-head test in a leaky aquifer with a finite-thickness skin
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Constant-head test is a commonly used aquifer testing method in groundwater hydrology. A mathematical model for constant-head test in a leaky aquifer with a finite-thickness skin was developed in this study. Three different aquifer-aquitard systems were considered and the Laplace-domain solutions were obtained and then inverted numerically with the Stehfest method to yield the time-domain solutions. The well discharges for different cases were computed and a sensitivity analysis of the well discharge on different parameters was performed. The results indicated that the dimensionless transmissivity of the aquitard had little effect on the well discharge at early times while a larger transmissivity of the aquitard leaded to a larger well discharge at late times. The well discharge for the positive skin was smaller than that without the skin while the well discharge for the negative skin was larger than that without the skin, where positive and negative skins refer to the cases in which the permeability values of the skin zones are less and greater than that of the formation zone, respectively. A thicker skin resulted in a smaller well discharge for the positive skin case but leaded to a larger well discharge for the negative skin case at late times. We also found that the drawdown for the positive skin case was less than that for the negative skin case at the same time, and a positive skin might result in delayed response of the aquifer to pumping. The sensitivity analysis indicated that the well discharge was sensitive to the properties of the skin zone, but not sensitive to the properties of the aquitards for the aquifer-aquitard system presented in this study. 2011 Elsevier B.V.
