Oskarshamn site investigation Vertical electric sounding and inversion of helicopter-borne EM measurements

Electrical soundings have been performed in the Oskarhamn site investigation area. The aim of the project was to gain better knowledge about the resistivity ranges for different soil types that appear in the area. Different clayey soils had overlapping resistivity ranges with a mutual geometric mean of 46 Ωm. The moraine in the area is of high resistivity with a geometric mean for unsaturated parts of 9,940 Ωm and 1,585 Ωm for water-saturated parts. The high resistivity of the moraine is interpreted to be due to the small amounts of fine-grained fractions and the presence of boulders. The new information was compiled into maps of assumed soil cover thickness and resistivity together with other information sources. These maps were then used as constraints in inversion of helicopter-borne electromagnetic data. This resulted in maps of calculated soil cover conductance, thickness and resistivity over the entire area covered by the helicopter-borne measurements.