Overvåkning av PCB-forurensning ved ubåtbunkeren i Laksevåg - 2008

A monitoring program for the period 2006 – 2008 is established to assess suspected leaching of PCB from the submarine pen in Laksevåg, Bergen. This report presents the results from the whole monitoring period. The program is carried out by FFI on assignment from The Norwegian Defence Estates Agency (FB). Preventive measures in the form of removing contaminated mud from a culvert and sand traps in the pen were carried out by FB in 2005. The objective of this study is to monitor the effects of these measures on transport of PCB from the submarine pen to the surrounding harbour basin. The monitoring consisted of three parts. One part focused on measuring the concentration of PCB in water inside the demolished dry dock number 4, while the second part focused on measuring the possible leaching of PCB from this dry dock to the harbour basin. In the third part the concentration of PCB in mud from the cleaned culvert and sand traps was measured in order to detect new influx of PCB. Water from wells inside the demolished dry dock number 4 and from the harbour basin outside this dock were sampled with a high volume water sampler developed by FFI. Leaching of PCB from the dry dock was monitored by introducing a geophysical barrier in the water column outside dry dock number 4. The role of this barrier was to limit diffusion and dilution of any PCB leaching from the dry dock. Water samples from the high volume water sampler and SPMDs were used to measure the concentrations of PCB inside, and outside the geophysical barrier to determine the likelihood of PCB leaching from the submarine pen. In 2006, 2007 and 2008 the measured concentration of PCB in water inside dry dock number 4 was higher compared to the levels in the surrounding harbour basin. It is therefore likely that a source of PCB exists in this dry dock, and that it may represent a possible source of PCB contamination to the surrounding harbour basin. Results show that the concentration of PCB in water is elevated inside the geophysical barrier compared to the surrounding harbour basin. This result indicates transport of PCB from the demolished dry dock number 4 to the harbour basin. However, this transport is very small and almost non-detectable even using a geophysical barrier to limit diffusion and dilution of the contaminants. This small flux of PCB from the dry dock is likely to have no significant effect on the marine environment in the surrounding harbour basin. The concentration of PCB in mud from the culvert and sand traps is still high and has partly increased during the monitoring period. This indicates the presence of active sources of PCB at, or close to the submarine pen in Laksevåg. To prevent these sources from contaminating the marine environment in the harbour basin, it is recommended that the sources of PCB should be identified and, if possible, measures implemented.