Provision of marine UXO Risk Mitigation at Millwall Docks

On behalf of the Canal and River Trust (CRT), Fellows were contracted by Land & Water Services Ltd to provide UXO risk mitigation services at Millwall Docks on the Isle of Dogs. The client’s scope of works included the placement of heavy mooring blocks with chain attachments to mooring pontoons for houseboats. The UXO risk in this area is significant with several recent finds of German aerial bombs at development sites due to the high bombing density the site underwent during WW2. 

Solution

On review of the client’s scope of works, Fellows recommended a variety of UXO risk mitigation services. These included intrusive survey by Cone Penetration Test (CPT) probing of potential anchor positions in conjunction with a Side Scan Sonar (SSS) survey of the entire dock bottom to identify any items of potential UXO (pUXO) that might be impacted by the anchor blocks or mooring chains. Initially Fellows contracted InSitu Site Investigation Services to conduct the intrusive survey by placing a mini CPT rig onto a workboat in order to probe the seabed locations. Fellows then worked with SAND Geophysics Ltd who conducted the SSS of the dock bottom area from a small vessel. On completion of the surveys, Fellows analysed the results and data from both of these risk mitigation procedures and assessed that one of the 19 targets detected possessed significant UXO like properties (size, shape and structure) and was therefore classified as pUXO and should either be avoided or investigated. 

As avoidance was not an option due to the constrained size of the dock area, Fellows then worked with Interdive Services Ltd who provided a vehicle mounted dive system, thereby saving on the time and expense of using a diving barge or vessel . Once all safety preparations for diving were complete, a Fellows UXO diver investigated and identified the target. 

Outcome 

Although the item was confirmed as non-UXO and was identified as an old fuel tank. Fellows risk mitigation procedures followed the guidance given in CIRIA Report C754 (UXO in the marine environment) and allowed the client to ensure that they could start the planned works in the knowledge that the UXO risk in the dock area had been reduced to ALARP. 

Effective use of the right systems for the environment kept the costs low and the project within the right timescale so the client could start the seabed works as planned. 

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