Plans to dump hundreds of thousands of tonnes of sediment from Hinkley Point into the Bristol Channel at Portishead face a legal challenge.

Environmental groups represented by Tarian Hafren say the Marine Management Organisation unlawfully varied EDF Energy’s licence to deposit dredged material at the Severn Estuary Marine Protection Area.

The disposal site is close to Portbury Wharf Salt Marsh, a Site of Special Scientific Interest and part of the Severn Estuary Special Protection Area.

Tarian Hafren argues that the MMO did not have the statutory power to change the licence for dredging to include dumping, did not give adequate reasons for doing so, failed to examine the potential impact of the dredging on marine life, and ignored a less harmful method of waste disposal.

High Court judge Beverley Lang ruled that the grounds for a judicial review are arguable and the claim will be heard this spring.

Cian Ciaran for Tarian Hafren said: “The Welsh National Marine Plan accepts no dumping in the Welsh half of the estuary, but the Welsh authorities failed to press MMO to comply on the English side.

“As Geiger Bay, we established at court in 2018 that the Welsh authorities were wrong to license dumping near Cardiff. Let’s now compel the MMO to respect the protected status that’s needed for both fish stocks and wildlife.”

He said a report had shown that alternative on-land cooling systems should be used instead.

EDF Energy secured permission in August to dredge and dump material from Hinkley Point C off Portishead, despite objections from North Somerset Council and Portishead Town Council and their calls for a public inquiry.

Rowan Smith from law firm Leigh Day, which is representing Tarian Hafren, said: “Our client has been clear from the outset that the MMO did not have the legal power to license the dumping of mud from Hinkley Point C in the Severn Estuary in the way that it did.

“The court’s decision vindicates why this case is being brought. Our client’s aims are to uphold the Marine Protection Area’s special conservation status.”

Tarian Hafren has launched a crowd funding campaign to raise £60,000 to cover its legal costs.

An MMO spokesperson said: “The marine licence was varied following a public consultation exercise and based on the best available scientific evidence. As legal proceedings remain ongoing it is not appropriate to comment further at this time.”

Chris Fayers, EDF’s head of environment for the 3.2-gigawatt project said: “Hinkley Point C is one of Britain’s biggest projects in the fight to protect the environment from climate change.

“Mud dredging in the Severn is normal practice and extensive testing by the Government’s marine science agency the Centre for the Environment, Fisheries, and Aquaculture Sciences has shown the mud is safe and poses no risk to the public or the environment.

“An independent report commissioned by the Welsh Government found the mud to be suitable for disposal at sea. We have engaged positively with stakeholders throughout and a public consultation was also carried out.”