Mapping threats to the ground water table

Client Profile

The Department of Geosciences and Natural Resource Management (IGN) is a broadly based department at the Faculty of Science at the University of Copenhagen. IGN’s activities include research and development, BSc and MSc courses and adult education/continuity training, servicing the public sector, innovation, monitoring, consultancy and outreach as well as international development and environmental assistance.

Challenge

The site of an old dry cleaner facility was investigated to map the spread of tetrachloroethylene, a highly carcinogenic solvent used in dry cleaning, in Kristianstad, Sweden. The land and the shallow groundwater was already polluted by tetrachloroethylene and other pollutants, and the main concern was that the contaminants may reach the deeper water table, which is also the source of local drinking water. The ground had already been examined using traditional drilling methods, the objective was to further determine the extent of contamination.

Solution

New surveys and resistivity measurements were carried out using an ABEM Terrameter LS from Guideline Geo. From the large amount of data collected, 2D and 3D models were created which have made possible very detailed images of the site and its immediate surroundings. This in turn has provided more accurate data for the positioning of drill holes and a more comprehensive and quantitative basis for action planning.

Results

The extensive and accurate results from the Färgaren 2-D and 3-D models show the possibilities for urban ERT surveying as a non-intrusive, cost- and time-efficient method for subsurface imaging. ERT can be used in combination with traditional sampling methods to provide very extensive and detailed information about underground formations, greatly reduce the number of necessary boreholes, and guide a more effective placement of boreholes. Decontamination was scheduled for 2014 (Engdahl et.al. 2011). The plan was to install sheet piling (retaining wall) and excavate the upper meters of most heavily polluted soil, with a supplementary in situ sanitation of PCE that is already dissolved in the identified groundwater pollution plume.