f Application of geoelectrical methods to the detection of polluted soils at shallow depth

The main reason of investigations was to test geophysical methods (mainly geoelectrical ones) in the degraded area and also to find resistivity anomalies and check usability of resistivity methods in applying to detect sources of soil and water contamination. Borne -Sulinowo area is an old German artillery firing ground that was taken over in 1945 by the Red Army and next it was the main headquater of the soviet troops in Poland. It has been returned to Poland since 1992. Parts of the area are heavy polluted, contaminated and degraded. Damages and pollution of soils, surface, subsurface and groundwaters have occurred there. Borne - Sulinowo firing ground is situated in the area which was in the range of glaciation. Hence it is covered with Quaternary sediments. In majority they are sands. Below the sands there is a complex of boulder clays. In the area of Borne - Sulinowo two water-bearing beds have been discovered. The first one is located at a depth of 3-20 m below theground level. This is an unconfined aquifer. The second one is situated under the clay complex. Therefore pollution could affect only the first aquifer. Oil derivative substances have become the main sources of soils contamination as well as surface and groundwater from the first water level. Degradation of surface and a top layer of soil is the result of construction over 100 different military structures. Some of them have not been accurately recognised yet. The region of „base A” has been selected as an experimental area for testing of some geophysical methods. It is the area of approx. 23 ha and it is located in the close neighbourhood of Pile Lake and Pilawka River. Approximately 1000 gasoline and oil containers were located there and several, actually damaged, military structures partially covered by forest or soil. In the „base A” area shallow geoelectrical measurements were carried out with TERRAMETER SAS 300C equipment and electromagnetic profiling (9,7 kHz) with EM-31 equipment. An electrical resistivity survey was carried out along three selected profiles using symmetrical Wenner’s spacing (AB = 9m). The apparent DC resistivity and apparent EM conductivity maps have been drawn. In all cases anomalies of higher electrical resistivity are well correlated with EM survey. The higher resistivity anomaly is localised in the neighbourhood of existing empty fuel container (Fig.1.). Near-by the container two measurement lines have been situated. A certain number of smaller positive resistivity anomalies in the „base A” have been found. They could be connected with the big number of hidden iron units and existing destroyed bunkers. The complex impedance background is high - about 10.000 Ωm - in the whole investigated area (Fig.1.). Because of the fact that it was a fuel base the high resistivity might be related to the oil derivatives contamination of the whole base area.