Interpretation of Slug and Packer Tests in Anisotropic Aquifers

Slug and packer tests provide data for determining the local value of hydraulic conductivity in aquifers. However, most techniques commonly used for test interpretation disregard any anisotropy of the tested formation. Using dimensional analysis, an extension of available methods for interpretation of slug and packer tests to anisotropic conditions is developed. The technique is a transformation of the radial dimension via the well radius, and involves dividing the true well radius by the square root of the anisotropy ratio which must be specified a priori. This technique can be applied to formulae, computer programs, graphs, or tabulated data available for confined or unconfined isotropic conditions. It also reduces the number of computer computations. As an example, the technique is used to extend the Bouwer and Rice (1976) method, which was developed for isotropic conditions, to anisotropic conditions. A comparison of the Bouwer and Rice (1976) method corrected for anisotropy, with the Widdowson et al. (1990) method, yields horizontal hydraulic conductivities differing by 8% (in one typical case). Ignoring anisotropy for the same case results in a 44% underestimation of horizontal conductivity.