This test method is one of several available for determining vertical anisotropy ratio. Among other available methods are Weeks ((5); see Test Method D5473), that relies on distance-drawdown data, and Way and McKee (6), that utilizes time-drawdown data. An important restriction of the Weeks distance-drawdown method is that the observation wells must have identical construction (screened intervals) and two or more of the observation wells must be located at a distance from the pumped well beyond the effects of partial penetration. The procedure described in this test method general distance-drawdown method, in that it works in theory for any observation well configuration incorporating three or more wells, provided some of the wells are within the zone where flow is affected by partial penetration.

Assumptions:

Control well discharges at a constant rate, Q.

Control well is of infinitesimal diameter and partially penetrates the aquifer.

Data are obtained from a number of partially penetrating observation wells, some screened at elevations similar to that in the pumped well and some screened at different elevations.

The aquifer is confined, homogeneous and areally extensive. The aquifer may be anisotropic, and, if so, the directions of maximum and minimum hydraulic conductivity are horizontal and vertical, respectively.

Discharge from the well is derived exclusively from storage in the aquifer.

Calculation Requirements-Application of this method is computationally intensive. The function, f_s, shown in (Eq 4) must be evaluated numerous times using arbitrary input parameters. It is not practical to use existing, somewhat limited, tables of values for f_s and, because this equation is rather formidable, it is not readily tractable by hand. Because of this, it is assumed the practitioner using this test method will have available a computerized procedure for evaluating the function f_s. This can be accomplished using commercially available mathematical software including some spreadsheet applications, or by writing programs in languages such as Fortran or C.