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www.sea-technology.com February 2017 / st 23 S eventy-two years after the end of World War II, a large amount of ammunition from the war still dozes in the North and Baltic Seas. For example, toward the end of WWII, a German U-864 subma- rine was sunk by the British submarine Venturer at an outlet of the Bergen Fjord in Norway's waters. The wreck is broken in two major sections, rest- ing at about 150-m depth on a subsea slope. The submarine has had a payload of 67 tons of mer- cury stored in steel containers. These containers are now failing due to corrosion, creating a high risk of severe mercury contamination into the en- vironment. After the wreck was rediscovered in 2003, there was an ongoing discussion on how to remedy the situation. Local citizens started an initiative for the removal of the submarine and its toxic load, con- cerned about the environmental consequences of mercury pollution. Once released into the ocean, the inorganic mercury could become converted to methylmercury by microbes. This form of mercury is even more dangerous than inorganic mercury because if this toxin makes its way into humans, it is transported freely throughout the body, as well as across the blood-brain barrier. It can also be bio- magnified in the aquatic food chain and accumu- late in fish. For this reason, fishing in the area of this wreck was stopped. After extensive evaluation, the Norwegian Coastal Admin- istration (NCA) in Ålesund, Norway, decided, as a first mea- sure, to stabilize the wreckage by counterfilling the subsea valley upon whose slope the wreck is resting to prevent slid- ing of the submarine sections and to cover up and prevent further spreading of the potentially contaminated sediment. A corresponding tender was put out for installing the counterfill. As the rock, gravel and sand dumping was likely to stir up potentially contaminated sediment in the area, exten- sive environmental monitoring accompanying the work was required. Van Oord of Rotterdam, Netherlands, was selected as the general contractor for the counterfill op- eration, subcontracting environmental monitoring activi- ties to the Norwegian Institute for Water Research (NIVA) in Oslo, Norway. develogic of Hamburg, Germany, was selected as supplier for the real-time environmental mon- itoring system. Lead time from ordering the system to de- livery of all components was less than four months. Stabilizing a Toxic WWII Submarine Wreck Monitoring System Detects Possible Mercury Contamination By Markus Motz • Thomas Radtke (Top) Deployment of the SB.600 spar buoy carried out by the vessel Siddis Mariner. (Bottom) Deployment of the CSL.1000 seafloor lander.