Geophysical and Geochemical Methods Used for Safeguarding HSE When Constructing a Major Pipeline in the Baltic Sea

Abstract

Abstract The paper presents a method for identifying chemical and conventional munitions on the seabed. The method has been used on the Nord Stream Pipeline Project, where a combination of geophysical and geochemical investigations was used to identify munitions along the pipeline routes in the Baltic Sea. Traditional marine geophysical survey (comprising measurements with multibeam echosounder, side scan sonar, single magnetometer and seismic equipment) was combined with a newly developed instrument – a gradiometer array - that made it possible to detect ferrous objects on the seabed. The magnetic data was correlated with multibeam and side scan sonar data and this formed the basis of objects that were visually inspected with a ROV (Remotely Operated Vehicle). The underwater footage of the objects made it possible to distinguish munitions from other objects on the seabed and to determine the type of munitions. Geochemical methods were used to identify traces of chemical warfare agents from dumped chemical munitions. Sampling of sediment cores and pore water were conducted along the Nord Stream route near a dumping site in the southern Baltic Sea. Subsequently the samples were analysed in laboratory. The results from the analysis showed that only very few stations had evidence of traces from warfare agents. The results from the geophysical investigations were the identification of a number of sea mines along the pipeline route. These were all cleared before the construction of the Nord Stream pipeline began, in order to safeguard HSE. The applied method, using a combination of geophysical and geochemical surveys, for detection of munitions and chemical warfare agents can be used in other oil and gas projects in areas, were munitions has been dumped.