Neuman-Witherspoon Solution for Confined Two-Aquifer Systems

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Neuman-Witherspoon Solution for Confined Two-Aquifer Systems with Leakage

Description

A mathematical solution by Neuman-Witherspoon (1969) is useful for determining the hydraulic properties of leaky aquifer systems (transmissivity and storage coefficient of the pumped aquifer; vertical hydraulic conductivity and storage coefficient of aquitard; and transmissivity and storage coefficient of the unpumped aquifer). Analysis involves matching the solution to water-level displacement data collected during a pumping test. Observation wells may be screened in the pumped aquifer, unpumped aquifer or aquitard.

Unlike the Hantush-Jacob (1955) and Hantush (1960) solutions for leaky aquifers, the Neuman-Witherspoon (1969) solution accounts for drawdown in the unpumped aquifer. Neuman and Witherspoon showed that the assumption of no drawdown in the unpumped aquifer (i.e., a constant head boundary condition) can lead to significant errors when estimating the hydraulic properties of the pumped aquifer.

AQTESOLV for Windows provides visual and automatic methods for matching the Neuman-Witherspoon solution to pumping test data. This easy-to-use and intuitive software promotes rapid and accurate determination of aquifer properties.

Assumptions

The following assumptions apply to the use of the Neuman-Witherspoon solution:

	aquifer has infinite areal extent
	aquifer is homogeneous, isotropic and of uniform thickness
	aquifer potentiometric surface is initially horizontal
	pumping well is fully penetrating
	flow to pumping well is horizontal
	aquifer is leaky
	flow is unsteady
	water is released instantaneously from storage with decline of hydraulic head
	diameter of pumping well is very small so that storage in the well can be neglected
	confining bed has infinite areal extent, uniform vertical hydraulic conductivity and storage coefficient, and uniform thickness
	flow in the aquitard is vertical

Solution Options

AQTESOLV for Windows provides the following options for the Neuman-Witherspoon solution:

	variable pumping rates
	multiple pumping wells
	multiple observation wells

References

Neuman, S.P. and P.A. Witherspoon, 1969. Theory of flow in a confined two aquifer system, Water Resources Research, vol. 5, no. 4, pp. 803-816.