Plans for a €500 million facility labelled a “monster sewage plant” by locals in north Dublin have been given the go ahead by An Bord Pleanala.

The controversial Greater Dublin Drainage Project drew objections from almost 14,000 people and was the subject of a four-day oral hearing earlier this year.

Irish Water say the plant at Clonshaugh near Dublin Airport is necessary to cater for future population growth and because the Ringsend plant is operating at over capacity.

Locals have vowed to intensify their campaign against the plant and are prepared to take their fight all the way to the European courts. 

Environmentalists and marine experts have warned that the operation could have catastrophic consequences for Dublin Bay – putting at risk its status as the only UNESCO Biosphere in a capital city globally.

Plans include a 13km underground orbital sewer from Blanchardstown to Clonshaugh that will intercept existing flows to Ringsend, and a new pumping station at Abbotstown.

The permission also allows for a 12km outfall pipeline to bring the treated wastewater out to sea via the Baldoyle Estuary for discharge around 1km north east of Ireland’s Eye.

Irish Water said at an oral hearing that sea conditions there will allow for “optimal dispersal” of the effluent which will have been treated with ultra violet disinfectant.

Sabrina Joyce-Kemper, spokesperson for the ‘Solution not Pollution’ campaign, warned: “This plant will have the capacity to dump 300 million litres of waste water every 24 hours just off Ireland’s Eye.

“We’re ready to initiate a judicial review in the High Court and after reading the Board’s decision feel that they have left themselves open to legal proceedings by failing to appropriately assess the project under the EU Birds and Habitats directives.” 

In its decision, the board said there would be negative temporary effects during construction involving noise, vibration and disturbance which would may have to include the rehousing of some residents.

Other areas affected would include parts of Connolly Hospital and St Francis Hospice but mitigation measures will included a 1km tunnel to accommodate the orbital pipeline through the campus.

And it warned that there would be “slight or short and very localised negative impacts” on marine mammals and birds during construction.

Local residents, farmers, water sport clubs and environmentalists had opposed the plan fearing the effect on the local land and the sea.

Minister for Communications, Climate Action and Environment Richard Bruton made a submission questioning the plan, calling for the “suitability” of the proposal to be “robustly questioned”.

Irish Water hopes to have the facility up and running by 2026.