Using Direct-Push for characterization of hydraulic conductivity distributions

It is a matter of fact that almost all problems in hydrogeology require the detailed knowledge of the distribution of hydraulic properties in the subsurface. In this context, the parameter distribution of hydraulic conductivity is of special importance as it controls flow and transport in the subsurface. Typically, hydraulic properties are not directly accessible and not very many methods allow resolving their spatial distribution. E.g. it is well known, that pumping tests integrate over a larger aquifer volume where different portions of the aquifer contribute with different weighing. Other methods such as hydraulic tomography allow for a better resolution of the subsurface, however conducting such experiments may become quite cumbersome and inversion algorithms are typically not trivial and might require extensive computational resources. Aiming on the characterization of hydraulic conductivity distributions, an alternative approach for such purposes is the use of Direct-Push technology. With this technology, specialized probes are dynamically or statically pushed into the subsurface allowing the in-situ measurement of parameters (geotechnical, geophysical, hydraulic or geochemical) with a high vertical resolution. Other probes enable the collection of samples from the subsurface. It is widely recognized that the application of this technology allows for a reduction of costs with increased information content. In this presentation an overview of Direct-Push based approaches for the characterization of hydraulic conductivity distributions with a special focus on novel methods is given. This will include - among others - the application of the Direct-Push Injection Logging System (DPIL) and the Hydraulic Profiling Tool (HPT) which allow for a semi-quantitative estimation of hydraulic conductivity distributions. By the combination with other techniques, e.g. such as the Direct-Push based slug tests (DPST), a quantification of profiles of hydraulic conductivity can be realized. In this context, the advantages of a fully automated slug testing device will be presented which permits the performance of fully controllable and reproducible slug tests. Based on field examples, a critical assessment of the advantages, limitations and the potential of the different methods will be given. It will be shown that the different methods have different ranges of applicability and different resolutions. Also, the different support volumes of the different methods may complicate an exact quantification of the hydraulic conductivity profiles.