Unravelling Contaminant Pathways through a Detailed Seismic Investigation, Varberg - Southwest Sweden

Abstract

Summary As demand for underground infrastructure grows worldwide, and in particular in Sweden, concerns on their environmental impact and disturbance in the subsurface increase too. A major issue with underground infrastructure projects can sometimes be connected with their vicinity to potential contaminated sites from industrial works in the past (e.g., over 80,000 are known in Sweden). In such circumstances, any excavation may accelerate mobilization of subsurface contaminants into aquifers and fertile soils. It is therefore important that migration pathways that these contaminants may use are delineated in a great level of details, so the appropriate remediation strategies are applied. To study potential contaminant pathways (bedrock depressions and fractures) in preparation for the construction of a double-track underground train tunnel, we acquired 12 seismic profiles in the city of Varberg, Sweden. The profiles were acquired using a combination of a state-of-the-art seismic MEMs-based landstreamer and wireless seismic recorders. Traveltime tomography results were complemented by more than 20 new boreholes, and together helped to identify contaminant pathways and connect them to a series of observed highly-contaminated zones away from the site. Prior to our seismic survey, these have been sought of having a different origin than from the main contamination site.