Rapid field application of hydraulic tomography for resolving aquifer heterogeneity in unconsolidated sediments

A new framework is introduced for hydraulic tomography application and validation in the field. Our motivation is the need for methods that are both efficient and expressive for resolving the spatial distribution of heterogeneous hydraulic properties in aquifers. The presented strategy involves time-efficient field experiments and a computationally efficient inversion scheme. By exploiting the early travel time diagnostics of the hydraulic pressure pulses recorded during tomographic cross-well tests, and new application of attenuation inversion, only short-term pumping tests are required. Many of these can be conducted in one day. The procedure is developed by a numerical experiment with a highly heterogeneous aquifer analogue and then applied to a field case with a shallow, unconsolidated sedimentary aquifer, the Stegemuhle site in Germany. It is demonstrated that the performance of a suite of tomographic short-term pumping tests, data processing and inversion for the reconstruction of heterogeneous diffusivity and specific storage distribution is possible within one day. Additionally, direct-push injection logging is performed at the field site, and the obtained field data is utilized for successful validation of the hydraulic tomograms. We also compare both methods with respect to the necessary requirements, time demand in the field and complexity of interpretation.