Application of ERT and IP for localisation of chlorinated hydrocarbons at a former dry-cleaning facility

Sammanfattning: At Hagforstvätten a dry-cleaning facility operated 1970 – 1993 and leached huge amounts of tetrachloroethene (PCE) to soil and groundwater. This study was conducted at the contaminated site and focused on applying the geophysical methods Electrical Resistivity Tomography (ERT) and Induced Polarization (IP) to investigate if it was possible to locate source zone, degradation zones and groundwater plumes of PCE. A background survey including GPR, DUALEM and magnetic gradiometer was conducted to study geological features and man-made structures that could interfere with the ERT and IP measurements. Drillings and chemical samplings were used as a complement to ERT and IP measurements to validate and strengthen the interpretation of resistivity and IP as caused by geological units, PCE or man-made disturbances. Due to the large heterogeneity in the subsurface of Hagforstvätten it is our opinion that it is a challenge to distinguish anomalies in resistivities and chargabilities as caused by pollutants. A promising outcome from the survey was however that a source of PCE located south of the dry-cleaning facility was distinguished as a degradation zone. In the northern part of the area indications of a groundwater plume were detected, however the sparse reference data in the area makes the interpretation more uncertain. Even though the interpretation of the pollutant situation is difficult at the site, ERT and IP have increased the understanding of the complex subsurface. This information is important to understand how PCE can be stored and spread in the area. Based on our results, we believe that ERT and IP are most suitable for monitoring how the high concentrations of PCE at the secondary source changes with time, for example during a future remediation.