Marine Utilities
Sizewell C's three offshore utility lines are under construction
Sizewell C Harbour Authority; project-specific desalination pipe-pull notice
An active harbour notice covers Sizewell C's treated-wastewater outfall and the temporary desalination intake and outfall. The CDO pipe pull was scheduled in April and the two desalination pipe pulls in June. Both operation-specific notices have since closed, while the wider three-line notice remains active.
What changed
The current harbour register keeps Notice 11 active and lists the CDO and desalination pipe-pull notices as inactive. Notice 11 started sequential boring and lining across all three lines. Notice 19 scheduled the CDO pull around 16 April. Notice 24 scheduled the desalination intake and outfall pulls around 3 June using approximately 500-metre floating pipes, NP497, C-Odyssey and supporting vessels. The harbour programme continues through pipe installation and head structures. Planning documents provide assessment-stage head locations, while Sizewell C's water page says the temporary plant will meet most construction demand. Head installation, testing, acceptance and first production water remain unpublished.
Why it matters
This is a working marine package, not a desalination concept on paper. The desalination operation required two approximately 500-metre floating pipes, jack-up barge NP497, C-Odyssey on a four-point mooring, guard vessels and diving. The same offshore corridor also carries the CDO, while permanent cooling-water works remain a different scope.
Decision read
What remains open
The closed pipe-pull notices support the end of those discrete marine operations. They do not prove that the three utility systems are finished. Head placement, as-built surveys, pressure and hydraulic tests, environmental clearance, plant connection and first desalinated water still need their own evidence. Notice 11 remains active, so the project stays in construction.
Next watchpoints
- Status of the active three-line construction notice
- Installation of the two desalination heads and CDO head
- As-built tunnel and pipeline records
- Pressure, integrity and hydraulic tests
- Environmental and discharge compliance
- Temporary desalination plant connection and first water
- Removal of temporary heads after construction use
Knowledge context
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Sources used 9
- Active and inactive Notices to Mariners Sizewell C Harbour Authority, Current register reviewed 20 July 2026
- Notice 11 of 2026: Construction of CDO DESAL Sizewell C Harbour Authority, 12 February 2026
- Notice 19 of 2026: Combined Drainage Outfall pipe pull works Sizewell C Harbour Authority, April 2026
- Notice 24 of 2026: Desalination intake and outfall pipe pull works Sizewell C Harbour Authority, 30 May 2026
- Sizewell C marine works and indicative programme Sizewell C Harbour Authority, Current page reviewed 20 July 2026
- Sizewell C construction water plan Sizewell C Limited, Current page reviewed 20 July 2026
- Fourth Environmental Statement Addendum, Volume 1 Sizewell C Limited via Planning Inspectorate, 2021
- Draft Coastal Processes Monitoring and Mitigation Plan Sizewell C Limited via Planning Inspectorate, 2021
- Sizewell C forms Civil Works Alliance Sizewell C Limited, 30 June 2025
Corrections and methodology
Facts are dated to the source record above. IMWO updates the brief when procurement, award, delivery, or scope evidence materially changes.
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