Kansas Geological Survey
Part of the Well Tests for Site Characterization Project
by Ralf Brauchler, James J. Butler, Jr., M.S. Aufman, S.E. McKay, W. McCall, S. Knobbe, and J.M. Healey
Eos Trans. AGU, 85(47), Fall Meeting Supplement, Abstract H21E-1049, 2004
Slug tests have traditionally been utilized as a means to determine the hydraulic conductivity (K) of an aquifer at a relatively small scale. When performed in a cross-hole mode, however, slug tests can be used to gain considerably more information. Despite the common perception that a slug test only affects a small volume of the aquifer in the vicinity of the test well, response data with a reasonable signal to noise ratio can be collected at distances of over several hundred times the radius of the screen of the test well. Analysis of such data can yield estimates of specific storage and the horizontal and vertical components of K, as well as providing insight into aquifer heterogeneity. Although cross-hole slug tests have been used in some previous studies, the utility of the approach has been limited by the need for relatively closely spaced wells. That limitation, however, can be readily overcome in unconsolidated formations by exploiting the access to the shallow subsurface provided by direct-push (DP) technology. DP technology can be used to install observation points at positions most advantageous for a particular study and then to reposition points between tests. The potential of DP cross-hole slug tests was investigated in a well-characterized sand and gravel aquifer underlying the Kansas River floodplain. An extensive series of slug tests were performed to assess the dependence of test data on the radius and screen length of the test well, and the lateral and vertical position of the observation interval. Using a 0.05-m test well, response data with a reasonable signal to noise ratio were obtained at observation intervals separated from the test well by over 11 m laterally and up to 3 m vertically. The results of these tests indicate that DP cross-hole slug tests could be a valuable tool for a variety of applications ranging from estimation of bulk aquifer properties to monitoring of temporal changes in the hydraulic properties of permeable reactive barriers. This approach is particularly well-suited for providing information about anisotropy in hydraulic conductivity, a quantity that is rarely known but often of considerable practical importance, especially for the design of remediation systems.