Geological characterization of contaminated sites near the city of Horsens, Denmark.

Keywords: geological modelling, urban area, contaminant transport
In Denmark, contaminations from industry, farming and households represent a significant threat to groundwater resources since water treatment in Denmark relies solely on two simple steps: 1) oxygenation of the source water and 2) filtration by means of water saturated, rapid biofilters. Consequently, there is a focus on identifying and locating contaminated sites on a national level. Insufficient knowledge about the geology and hydrology at the sites poses a significant challenge for remediation efforts. The lack of information about the subsurface introduces significant uncertainties in projections on the fate of contaminants. Moreover, as cities grew over the years, several contaminations are now located in urban areas where data compilation and remediation efforts are often challenged by logistics.
In this study we carry out a geological characterization of three contaminated sites situated in urban and semi-urban areas around the city of Horsens in corporation with authorities. The existing data from the three field sites include lithological profiles from boreholes. In order to increase the data density, Electrical Resistivity Tomography (ERT), Induced Polarization (IP), and multi-configuration Ground Conductivity Meter (DualEM421) based mapping was carried out at the three field sites. Based on the borehole information and the high-density geophysical data, detailed 3D geological models of the sites were constructed. The 3D geological models serve as a basis for simulating contaminant transport at the field sites. The study demonstrates how detailed information about the geological setting in conjunction with contaminant transport modelling, can minimize the uncertainties of projections on the fate of the contaminant. Based on the work, we were able to pinpoint the best strategies and solutions for future remediation efforts at the three sites.