Mapping pollution and coastal hydrogeology with helicopterborne transient electromagnetic measurements

Coastal hydrology is becoming the focus of increasing interest for several reasons. Hydrogeological models need good boundary conditions at the coastline, and with the expected sea level rise due to climate changes, it becomes increasingly important to grasp the dynamics of coastal hydrology in order to predict the consequences of sea level rise for nature and society. We present a helicopterborne transient electromagnetic survey from a region at the North Sea coast in western Jutland, Denmark, carried out at a seriously polluted site with the dual purpose of assessing the extent of the pollution and mapping the coastal hydrogeology to provide data for remediation activities. Data are subjected to constrained inversion with one- dimensional multi-layer (smooth) models. The extent of the pollution plume estimated from a conductive anomaly in the survey results is mainly in accordance with results from other investigations, but also points to hitherto unknown directions of seepage. The interleaving of freshwater extending under the offshore shallow sea and saltwater infiltrating under the onshore freshwater aquifer can be clearly discerned and preferential flow channels are revealed.