Subsea IMR provider, N-Sea, has successfully completed an unexploded ordnance (UXO) survey, ID and disposal campaign for the TenneT project, BorWin3.

Taking place between January and August this year, the work scope involved surveying the seabed to identify and remove undiscovered explosive devices along the cable route of BorWin3.

Transmission system operator, TenneT’s grid connection system connects wind parks in the North Sea with the high-voltage grid onshore. The survey campaign undertaken by N-Sea comprised a geophysical survey (multibeam, Side Scan Sonar (SSS), Sub Bottom Profiler (SBP) and Magnetometry) of 137 targets within the main cable corridor and adjacent anchor corridors, totalling almost 2000km.

N-Sea managed this project from Eemshaven, with a local team managing all near shore and offshore vessels whilst processing all acquired data. Four survey vessels were utilised, including the Noordhoek Pathfinder.

The investigation element of the project resulted in three positively-identified explosives; two sea mines and one grenade. The sea mines were destroyed on site, with N-Sea coordinating the operation under supervision of the German explosive ordnance disposal service. Requiring a more accurate identification, the grenade disposal was carried out on board a separate vessel, through use of a mobile x-ray machine.

N-Sea’s CEO, Gerard Keser, said: “The corridor started in very shallow water mudflats for a 12 nautical mile zone, north of Borkum in Germany, which is a very challenging environment known for its shallow waters, high currents and continuously moving sandbanks.

“Despite the many challenges and intricacies of the campaign, we successfully identified and destroyed three explosive devices and are proud to have been involved in such an important project. We are delighted to have provided an efficient and safe service, with no incidents, which reflected our ability to always provide ‘safe, sound and swift’ solutions.”