A Comparison of Five Different Techniques to Determine Hydraulic Conductivity of a Riparian Soil in North Bavaria, Germany

Soil saturated hydraulic conductivity (Ks) is a predominant input factor when forecasting the vertical transport of contaminants through the soil or when estimating the flood retention capacity of the soil. Displacement of contaminants in the soil over extended periods of time can be attributed mainly to matrix flow, whereas flow through macropores becomes significant under untypically wet conditions, e.g., during spills or rain storms. To obtain matrix conductivities for a soil, the effects of macropores should be excluded. However, the Ks values of a soil profile are unlikely to be reflected solely by pedotransfer tables based on soil texture and bulk density. In this study, we examined five different methods (pedotransfer table, soil core, borehole permeameter, particle-size distribution curve, and instantaneous profile) to determine Ks values for a mercury-contaminated riparian soil for subsequent simulation of long-term mercury displacement toward groundwater. We found that the determined Ks values increased in the following order: borehole permeameter < particle-size distribution curve < pedotransfer table < instantaneous profile < soil core. The instantaneous profile method yielded Ks values of matrix flow, which additionally reflected the structure-related features of Ks values as provided by the soil core method. Despite being labor intensive and requiring expensive field sensors, the instantaneous profile method may provide the best representative in-situ Ks values for the studied site.