All parties needed to be confident that pUXO risks – to personnel, the environment, infrastructure and equipment – across the site had been identified, addressed and were as low as reasonably practicable (ALARP) before the construction phase started.
A Fugro team of survey experts had already carried out the initial broad geological and geophysical investigations, metocean surveys and laboratory assessments for the site.
A subsequent UXO survey by a third-party supplier had identified multiple pUXO anomalies within the cable route corridor, so Ørsted awarded Fugro a further commission – this time to carry out a localised inspection of pUXO targets.
UXO risk mitigation survey
Localised pUXO inspection campaign
Our 20-strong team of experts conducted the campaign on the CVOW demonstration site, which is located 43 km off the coast of Virginia Beach and includes the export cable route and two turbine locations. The purpose of the campaign was to:
- Inspect and identify surface and subsurface targets specified by Ørsted within the cable route corridor;
- Confirm whether the targets were explosive ordnance (EO);
- Remove any non-EO items that might hinder the project.
Working in challenging conditions
We deployed our ROV from a single third-party vessel, working in water depths that ranged from 7 m nearshore to 35 m at the turbine locations. Working at such shallow water depths in the nearshore areas required careful communication between the vessel master, the ROV pilots and the operation leads. To ensure the safety of crew and equipment throughout the project, we maintained a minimum separation of 50 m between the vessel and the pUXO targets.
Identifying and clearing the specified targets
Underwater visibility on site was mainly very poor, and deteriorated to zero visibility during excavation operations. Aided by an acoustic camera system, we identified all the specified targets as non-EO and used the ROV’s two remote-controlled arms to move them away from the planned cable route. For partially and fully buried targets, we used a dredge pump to clear or excavate them to 1.5 m below the sea floor, ready for inspection by the client’s UXO specialist.
Our operational approach emphasised safety and efficiency. By combining several key tools and sensors, our FCV-3000 150 hp ROV was able to capture multiple data streams used in the pUXO identification process.
To minimise costs, we selected and worked from a single vessel that was small enough for nearshore operations yet large enough to cope with open ocean weather conditions.
- Our global marine UXO expertise, local staff and fit-for-purpose assets enabled the client to reduce the UXO risk to ALARP within the cable route corridor and at the two turbine locations;
- We used our subsea acoustic positioning solution to ensure safe and efficient operations from a single, third-party vessel in shallow and deep water. This prevented the need for the costly mobilisation of a second vessel;
- We worked in partnership with the client and third-party suppliers to deliver the offshore field results within the stipulated 24-hour period. This enabled the remaining development activities to advance as planned