19-29 Gw F-j 05

Spatial variations in hydraulic conductivity (K) can have a significant impact on the transport of contaminants in ground water. An understanding of the three-dimensional distribution of K at a site is often necessary for reliable transport predictions and the design of effective remediation strategies. Conventional field methods, however, can rarely provide information on the spatial variations in K at the needed level of detail and accuracy in a cost-effective manner. For example, pumping tests provide a large-scale average of K (Butler and Liu 1993; Meier et al. 1998), while methods based on empirical relationships or laboratory analyses provide estimates with a high degree of uncertainty (Butler and Bahr 1988; Farrar 1996; Lunne et al. 1997). Single-well hydraulic tests (e.g., slug tests, dipole-flow tests) can be an effective means of obtaining high-resolution K data (Yeh et al. 1995; Zlotnik and Zurbuchen 1998), but the cost of well installation is often substantial. As a result, there is rarely sufficient information at a site to assess the influence of spatial variations in K on contaminant transport. Thus, there is a clear need to develop site characterization methods that enable information about the three-dimensional distribution of K to be determined in a timeand cost-efficient manner (National Research Council 1994). The development of one such method is described in this paper. Over the last two decades, direct-push (DP) technology has become a widely used alternative to conventional drilling-based methods for site characterization investigations in unconsolidated formations. This technology involves advancing a small-diameter rod string, with a sensor/tool at its lower end, using hydraulic rams and the weight of a large truck (cone penetrometer technology) or a combination of hydraulic rams and a high-frequency hammer (Geoprobe Systems 1998). DP technology is currently used in environmental investigations for a variety of applications including soil coring, ground water and soil Abstract Spatial variations in hydraulic conductivity (K) can significantly affect the transport of contaminants in ground water. Conventional field methods, however, rarely provide a description of these variations at the level of detail necessary for reliable transport predictions and effective remediation designs. A direct-push (DP) method, hydrostratigraphic profiling, has been developed to characterize the spatial variability of both electrical conductivity (EC) and hydraulic conductivity in unconsolidated formations in a cost-effective manner. This method couples a dual-rod approach for performing slug tests in DP equipment with high-resolution EC logging. The method was evaluated at an extensively studied site in the Kansas River floodplain. A series of profiles was performed on a surface grid, resulting in a detailed depiction of the three-dimensional distribution of EC and K. Good agreement was found between K estimates obtained from this approach and those obtained using other methods. The results of the field evaluation indicate that DP hydrostratigraphic profiling is a promising method for obtaining detailed information about spatial variations in subsurface properties without the need for permanent wells.