Mapping pollution and coastal hydrogeology with helicopterborne transient electromagnetic measurements

Abstract

Coastal hydrology is becoming the focus of increasing interest for several reasons. Hydrogeological models need good boundary conditions at the coast line, 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 with the purpose of mapping the coastal hydrogeology at a seriously polluted site to assist in the assessment of the extent of the pollution and to provide data for remediation activities. Data are subjected to constrained inversion with onedimensional multi-layer (smooth) models. The results are presented as model sections and as maps of mean conductivity in elevation intervals. The extent of the pollution plume estimated from the survey results is mainly in accordance with results from other investigations, but also points to hitherto unknown directions of seepage. The interleaving of fresh water extending under the offshore shallow sea and the salt water infiltrating under the onshore fresh water aquifer can be clearly discerned and reveals preferential flow channels.