Use of CPT and other direct push methods for (hydro-) stratigraphic aquifer characterization - A field study

Every environmental site investigation aims at delineating near-surface (hydro-) stratigraphic units and their characterization. To determine the type and hydraulic properties of sedimentary deposits, direct push (DP) sensor probes and tools are promising methods and are therefore frequently applied to measure high-resolution vertical profiles of soil properties. Given the variety of these tools, the objective of this paper is to compare selected DP tools for the (hydro-) stratigraphic subsurface characterization in a heterogeneous unconsolidated sedimentary aquifer. An overview of current DP applications is given and selected DP tools were tested for reproducibility, as well as their ability to reflect soil variability and to estimate hydraulic conductivity, K. Although resolution differences exist, all of the applied methods captured the main aquifer structure. Correlations of the DP-based K estimates or proxies with DP slug tests (DPST) show that it is possible to describe the aquifer hydraulic structure on less than a metre scale by combining DPST data and continuous DP measurements. Although correlations are site-specific and appropriate DP tools must be chosen, DP is a reliable and efficient alternative for characterizing even strongly heterogeneous sites with complex sedimentary architectures.