UXO clearance and disposal operations at Sofia OWF
Enabling construction through accurate target identification.
Industry
Renewables
Company
Sofia Offshore Wind Farm Limited
Location
East Coast of UK
Site
Sofia Offshore Wind Farm, Dogger Bank, Southern North Sea
Date
August 2022
Techniques
High Order / Relocation
Introduction
Once operational, Sofia Offshore Wind Farm, located on Dogger Bank in the Southern North Sea, will be one of the world’s largest offshore wind farms. With a projected 1.4GW of installed capacity and the potential to power 1.2 million average-use, UK homes annually, it represents the largest project in RWE’s offshore wind portfolio. The energy it generates is expected to save the UK more than 2.5 million tonnes of carbon emissions per year* thereby contributing to the UK government’s overall carbon reduction programme.
Before offshore construction could begin at Sofia, it was necessary for the protection of personnel and assets to complete efficient and safe UXO and archaeological investigation and clearance operations. Our technology and personnel were deployed on this project, contracted through a third-party contractor.
Our technology and personnel were chosen for this project because our technical capabilities met all MMO licence requirements and could be delivered at a competitive rate.
The Challenge
The brief was to investigate potential UXO and archaeological targets (pARCh) detected on, and under, the seabed within a specified, shallow-water offshore area of the North Sea.
Targets requiring investigation were located within the:
- Export cable corridor, nearshore including the beach and offshore
- Array cable corridors
- Substation location and jack-up vessel zones
- Foundation / turbine locations and jack-up vessel zones
- Laydown and spare areas
Confirmation was required for both the employer and the installation contractors that all confirmed UXO had been identified and safely and responsibly disposed of so that risk was reduced to as low as reasonably practicable (ALARP), and development of the offshore wind farm could begin.
~600km2
Array area
21 – 37m
Array water depths
Up to 82m
Export cable corridor water depth
Sand
Seabed sediment
Strong
Tidal currents
Challenging
Weather conditions
The Details
The scope of work was divided into two distinct campaigns – Campaign 1 (nearshore including export cable route) to be undertaken in Summer 2021, and Campaign 2 (offshore and array site) in Summer 2022.
Requirements included:
- project management and accountability for all necessary resources e.g. provision of manpower, supervision, tools, tackle, explosives, plant and equipment
- provision of full EOD specialist marine spread
• DPII vessel
• 2 WROVs
• EOD Workshop
• 2 x Explosives storage
• Magazines
• 1 x EOD RhiB
• 1 x Remote Ordnance Lifting System (ROLS)
• Primary energetics and NONEL / remote initiators
- provision of a senior/advanced level EOD qualified UXO Disposal Controller with 10 years (minimum) experience
- ability to use both low and high order methods as required with remote detonation
- use of Industry Best Practice Marine Mammal Acoustic Dispersal System
- support in the recovery, removal and disposal of all UXO-related debris
- data management and detailed reporting
The Solution
Work-class ROV
Our experienced personnel were able to determine target identification with support of work-class ROV (Triton XLX) operations, using real-time, HD and Adaptive Resolution Imaging Sonar cameras.
High order
Confirmed UXO targets were disposed of using the Barracuda High Order method. Necessary mitigation measures including bubble curtains were employed. Resulting fragments were recovered and disposed of responsibly in a licensed waste facility.
ROLS
The Remote Ordnance Lifting System (ROLS) was deployed to relocate 4 items. ROLS is only available through us in UK and Europe.
Grab
Our experienced personnel were able to mark pUXO targets safe, allowing for relocation/recovery by an orange peel seabed boulder clearance grab as appropriate.
The Result
200 pUXO
Offshore Targets
2 cUXO
Offshore Targets
All works were successfully carried out in line with customer expectations, with relevant licences and permits and in accordance with relevant industry regulations and guidelines.
Weather opportunities were optimised and downtime minimised whilst ensuring safety of personnel and equipment.
ALARP certificates were issued in a timely manner to enable construction activities to commence.
“Sofia’s unexploded ordnance and archaeology campaign was safely and successfully completed, clearing the way for the start of offshore construction in 2023.”
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* Statistic taken from the Sofia Wind Farm website https://sofiawindfarm.com/about/ on 23 December 2024 which uses BEIS’s “all fossil fuels” emissions statistic of 446 tonnes of carbon dioxide per GWh of electricity supplied in the Digest of UK Energy Statistics (July 2020).
