Proposed dumping of 824,000 tons of Tunnel spoil in Dublin Bay

Jan 14 2013 Posted by Office Administraton

Divers are usually a very quiet lot of people enjoying the peace and calm of the sea both on top of it in our boats and at the bottom enjoying all the creatures who live there.  You generally only see us in the papers when a sea tragedy occurs and we then give freely of their time and energies to help out.  If you are out around Dalkey  Island, the Muglins of Ireland Eye on Wednesday evenings, Saturday and Sunday morning you will see boat loads of divers quietly enjoying their sport.

Every few years the diving water visibility in Dublin bay is destroyed by one or other sort of dumping at sea in the bay.  The reason is usually that the Liffey mouth at the shipping berths needs regular dredging to keep the river open for shipping. The visibility gets so bad a times in the Bay that at the bottom one can bump into your buddy without first seeing them.  Diving in such conditions is dangerous and the dive is usually cut short when the 2 diver loose each other in the water and have to surface.

To see a notice in the Irish Times on December 20th that Dublin City Council was applying to dump spoil for the next 3 years in the Bay was disturbing.  It was even more disturbing to read on the DCC website that they intend to dump 824,000 tons of material there.  We are signatories of the  OSPAR Convention 1998 which allows only inert materials of natural origin  to be dumped at sea, provided there is no reasonable alternative. The spoil from Tunnel boring being a slurry cocktail of chemicals in anything but that.

So what is happening. The Ringsend Sewage Plant is now too small to cope with all Dublin’s toilet and drainage waste.  Should the water off every road, path and roof be diverted elsewhere this would not be the case, but as it is when we have heavy rain the plant is inadequate for the water loads for treatment.  So they are extending the plant and want to build an out fall pipeline under the sea in tunnel going out 9 Kilometres from the Ringsend plant.

The tunnel will be dug by a TBM a Tunnel Boring Machine starting off at Ringsend and going out the 9 Km to sea way down in the rock. What few realise these machines grind the rock rather than break it and the resulting spoil is awet sand, dust paste that leaves the machine on a wet conveyor.  This is what will make up the 824,000 ton they wish to get a licence to dump in the bay. Limestone dust is the main constituent of cement and this cocktail will form a layer on the sea bed killing every life form below. Limestone dust is also soluble in water and will leave Dublin bay looking like it had been dosed with “Milk of Magnesia The experience of the Dublin Port tunnel construction is very important here.  Many dangerous fissure were encountered there that had to be infilled with concrete and the drilled out. More important in the Supporting document for the submission Roadstone were asked if they could use this tunnel spoil for aggregate for concrete, the reply from the report  “From discussions with Roadstone it is considered that recycling for reuse as an aggregate is highly unlikely due to the quality of material and based on experience form the Dublin Port Tunnel and the high dust content of the spoil. 

Also, there are small quantities of pyrites naturally occurring in the excavated limestone spoil which make it less suitable for construction materials. “

The application is suitably vague in detail are the Contract for the tunnel construction is to be design and build, so the design and construction methods are not know at this time , yet they wish to get a licence to dump the spoil, this spoil will varygreatly depending on the tunnelling machine used. Many different chemicals are used both to lubricate the Tunnel cutting heads and to infill fissures in the Limestone, it would be impossible to remove these from the slurry at the back of the Tunnelling machine, they would end up in the bay also.

To cap all this on “ Monday, December 3th – Jimmy Deenihan TD, Minister for Arts, Heritage and the Gaeltacht, has today proposed six new marine sites for designation as Special Areas of Conservation (SACs) to protect marine habitats and species listed on the 1992 EU Habitats Directive.”  One of these areas cover both the sewer outfall area and the dumping of the tunell spoil area “Rockabill to Dalkey Island Reefs and Harbour Porpoise

The marine life in the huge spoil dumping area will be completely destroyed as will all the fish spawning areas adjacent to it.  There is no need to dump this spoil material here.  It could be used for coastal protection down in Wexford or for the building of a new harbour in Balbriggan.  If a few heads were knocked together we could have a win situation here.   It is simply not good enough to plump for the cheapest option.

Peadar Farrell   Diving instructor Curragh Sub Aqua Club