A steady-state tracer test with sulfur hexafluoride (SF6) in the UpperMuschelkalk aquifer in Stuttgart

摘要

In the city of Stuttgart, long plumes of volatile chlorinated hydrocarbons (VCHCs) had developed over several aquifers before hydraulic protection and remediation activities were initiated. To analyze the complex flow field and the transport of contaminants in the vicinity of alow-conductivity fault (Schloss-Storung), which is oriented perpendicular to the flow direction within the karst aquifer of the Upper Muschelkalk, asteady-state tracer test was performed using sulfur hexafluoride as atracer gas. Thus, the spreading of aVCHC plume around the fault could be outlined more precisely. The derived travel time of eight months shows that flow occurs predominantly around and partially below the low-conductivity fault, deflecting the VCHC plume. Additionally, spreading of the contaminants is limited by microbial degradation of the VCHCs, starting in the fault zone and continuing further downgradient. Breakthrough curves of the tracer could be reproduced in anumerical model by varying both the porosity of the aquifer-matrix system and the corresponding exchange coefficient.