There’s no way of ever knowing for sure just how many mines and bombs litter the seas in which we work, but dealing with UXO (unexploded ordnance) to ensure the safety of offshore construction teams is something that can’t be left to guesswork.
Recently two 500lb unexploded wartime bombs were discovered near the site of a wind farm off the coast of Sussex. The devices were found close to one another within the parameters of E.On’s £1.3bn Rampion wind farm.
Of the mines dropped in World War One, it is estimated that the post-war sweeping operations picked up between 30% – 70%, leaving behind a considerable amount. These mines, joined by more left behind during World War Two, are unpredictable. Some were designed to sink to the seabed, others to float. The buoyant ones – naturally – don’t stay where they were dropped. For instance, while the Netherlands remained neutral in WW1, records kept by Dutch authorities reveal that almost 6,500 mines were carried by the tides to their coastal areas. Decades of sea movement means many now lie buried just beneath the seabed.
It’s not just mines to be concerned about. UXO risks also come from unexploded bombs, munitions and torpedoes on board sunk vessels and aircraft.
And as if that weren’t enough, there is the additional problem of dumped munitions – millions of tonnes of them, including ones of a chemical nature. The practice has been going on since 1945 and while there are official dump sites, a common problem was that those tasked with taking the loads to the sites often dumped the cargo along the way, so there’s no way to determine where exactly the munitions are.
With all of these potential UXO issues, the need for an effective and appropriate method to deal with them is clear, particularly with the increase in offshore marine projects including geotechnical investigation, drilling, pipe laying and cable laying and foundation installation. The MD at UK-based UXO management company 6 Alpha Associates, Simon Cooke, told owjonline.com that UXO poses a fourfold risk to delivering marine projects as planned and on time. “First, it can cause property damage through inadvertent detonation, potentially resulting in significant damage to equipment and surrounding project infrastructure. Second, the mismanagement of an UXO survey process – possibly leading to the belated discovery or detonation of munitions onsite – can lead to substantial construction delays, downtime and cost overruns. Third, any uncontrolled explosion poses a direct threat to the safety of personnel working in the immediate environment, including divers and crew working on vessels. Finally project directors and contractors who fail to carry out proper investigations into the threat of UXO on construction sites are accountable by law and could face unlimited fines and severe reputational damage in the eventuality of injury to personnel.”
So what’s to be done? Quite a lot actually – and step up hydrographic surveyors – this is your time to shine! To carry out a thorough assessment of a site operators should be doing an investigation survey, an identification survey, UXO removal and/or construction rerouting. Take Ordtek’s process used recently at the site of a proposed offshore wind farm in the German Bight. A staggering 11,000 air mines had been dropped in this area between 1941 and 1945. The work consisted of high res multi-beam sound echo, sidescan sonar and magnetometer surveys which identified 250 potential UXO items. A ROV was brought in to examine them, and using a TSS (EM) pulse induction system, detected non-ferrous metallic objects. In total seven large UXO items were discovered and six were detonated in situ.
However there are a number of challenges for operators: the aluminium mines used by the Germans in World War Two can’t be detected by traditional technology, and poor visibility and large magnetic fields can act as a cloaking device.
Ordtek is leading the way in pioneering techniques to improve UXO detection – because every advance means operators are less dependent on weather, they can be more productive, sign-offs on UXOs can come faster and areas once deemed impenetrable are accessible. Its principal consultant Lee Gooderam told owjonline.com, “New technology can help pinpoint unexploded mines, bombs and missiles at new offshore energy sites. Cutting-edge equipment using 3D ‘chirps’ sonar, which penetrates the seabed to find buried UXO such as aluminium mines buried up to 7m deep, as well as electromagnetic sensors and other specialised sonar are also being used to spot UXO in challenging conditions and are helping to clear offshore windfarm and cabling sites.”
We hope this has been a bit of a light bulb moment for some of you. There will be significant opportunities in this field for those with in-demand skills such as Oasis Montaj for Geophysicists and QINSy for Online Surveyors. If you haven’t got them but are interested, we’re here to help.