Watch video: Dredging mud at Hinkley Point C

Key facts

  1. The mud in the Bristol channel has been independently tested by CEFAS in 2009, 2013 and 2017, as commissioned by Natural Resources Wales and EDF Energy

  2. 12 samples were taken in May 2017 by CEFAS, who concluded that the levels of radioactivity in the mud are so low that they equate to ‘not radioactive’ under UK law

  3. The mud poses no threat to human health or the environment

  4. The dredged mud must be kept within the Special Area of Conservation (SAC). Cardiff Grounds is the only suitable site within the SAC that’s large enough to handle the amount of mud we need to move.

Why do we need to dredge?

As part of the construction of Hinkley Point C, we will be dredging mud and sediment from the seabed off the Hinkley Point C site ahead of the drilling of six vertical shafts for the cooling water system. The cooling water system is a significant piece of infrastructure, which involves tunneling more than 3km out into the Bristol Channel.

In order to do this, it is necessary to dredge the immediate area where we will be installing the vertical shafts. This process began in September 2018 and contractors have now completed the licensed work to dredge and deposit mud in the Severn Estuary.  Further dredging will be required as the construction progresses and we will work closely with the appropriate experts to prepare our licence application and will again comply with all requirements. We also fully support all efforts to inform and explain the dredging work to the public.

EDF Energy is one of many companies - over many decades - dredging and depositing sediment in the Bristol Channel for industrial or construction purposes.

The sediment we and others are dredging in the Bristol Channel is typical of the sediment found anywhere in the Bristol Channel, and as such it is no different to the sediment already at the Cardiff Grounds. It is not classed as radioactive under UK law and poses no threat to human health or the environment.

Is the mud and sediment radioactive?

The sediment is typical of sediment found elsewhere in the Bristol Channel, and under UK law it is not radioactive.

Radioactivity occurs naturally, including in foods we eat, and can be artificial/produced by human activities. Any sediment in UK coastal waters will contain naturally occurring levels of radiation, and in areas of industrial activity there may be extremely low levels of artificial radiation present.

In the case of the Bristol Channel, the very low levels of radioactivity identified in the sediment are predominantly naturally occurring (over 80%), with a small amount of artificial radioactivity, which will have originated from legacy discharges from hospitals, medical isotope manufacturing facilities (including those formerly based in Cardiff) and nuclear facilities. Whether the radioactivity is naturally occurring or artificial this has no impact on how it interacts with the human environment.

Who carried out the tests?

The tests were carried out by CEFAS, an executive agency of the UK Government. CEFAS has some of the most advanced radiation testing equipment in the world and also provides services to Natural Resources Wales and the Welsh Government, as well as the Marine Management Organisation.

Why Cardiff Grounds?

Why is Cardiff Grounds being used?

While there are other licensed disposal sites in the Channel, the Cardiff Grounds is the only suitable site large enough to handle the amount of the type of sediment we will dredge, and as the sediment was confirmed to pose no environmental or health risks there is no need to relocate it elsewhere.

Cardiff Grounds has been a licensed disposal site since the 1980s, and takes on average 1,500,000m3 of sediment each year. It is important to emphasise that EDF Energy is not the only company licensed to use the Cardiff Grounds - the site will have received several million cubic metres of dredged sediment from other parts of the Bristol Channel over several decades.

Why don’t you use another location?

The area we are dredging is within a recognised Special Area of Conservation (SAC). Any sediment removed from this area, must be put back into this area in order to maintain the natural balance of sediment in the SAC.

Within this SAC, the Cardiff Grounds are the largest and only suitable grounds to deposit sediment from EDF Energy and other companies conducting dredging in the Channel.

Taking account of the natural and artificial radioactivity together, the dose received would be:


times less than a pilot's annual dose


times less than the average Radon dose in Pembrokeshire


to eating 20 bananas per year

This is an infinitesimally small level of exposure to radiation, far below the threshold requiring a more detailed assessment or even close to approaching a radiation dose that could impact human health or the environment.

The testing process



CEFAS obtained sediment samples at depths up to 4.8m as part of the HPC Planning Application.

Levels of radioactivity in the sediment are found to be so low they equate to ‘not radioactive’ in law. In addition, no artificial radioactivity was observed below 2m.


Natural Resources Wales commissioned an independent analysis by CEFAS to determine the radioactive characteristics of the sediment to assess the licence application. 17 sediment samples were taken in 2013.

Levels of radioactivity in the sediment are found to be so low they equate to ‘not radioactive’ in law.


EDF Energy commissioned CEFAS to undertake an analysis as required, and approved, by NRW to support the Licence. 12 sediment samples were taken in May 2017.

Levels of radioactivity in the sediment are found to be so low they equate to ‘not radioactive’ in law.


How thorough were the tests?

The tests were carried out independently by CEFAS (an executive agency of the UK Government), which carries out work to the highest international standards.

The analysis techniques used detect the presence of alpha-, beta- and gamma-emitting radionuclides (atoms that have excess nuclear energy which makes them unstable), rather than just testing for a few select radionuclides. Simply put, if a radionuclide is present it will be detected by the testing equipment.

Depth of the tests

The sediment has been tested at depth. In 2009 CEFAS obtained sediment samples at depths up to 4.8m to support the HPC Planning Application. No artificial radioactivity was observed below 2m. This is likely because any sediment at a depth of greater than 2m depth will have accumulated hundreds if not thousands of years ago, prior to the start of industrial activity in the area. As a consequence, repeated testing to greater depth is not required.

How does Wales benefit from Hinkley Point C?

As well as being part of the National Grid network that will benefit from the affordable and reliable low carbon electricity produced by Hinkley Point C, Wales is benefiting during its construction.

Apart from local workers at the Somerset site, the largest group of employees come from Wales – over 1,000 Welsh residents have worked on the project so far.

More than 200,000 tonnes of Welsh steel are being supplied to the project and valuable contracts have already been awarded to Welsh companies in areas including steel fabrication, training, engineering, scaffolding, water management, transportation and site services.

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Call us on 0333 009 7070 (24 hour free phone number).

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