A little piece of Ireland will end up as part of the Dutch road system under plans to clean up the former Dublin Gas Company site off Sir John Rogerson's Quay. The 22-acre site is contaminated with the chemical residues of almost two centuries of gas manufacture and can't be developed until it is cleaned up.

The five section site straddles key locations in the Grand Canal Docks area, with frontage on both the River Liffey and the Grand Canal basin. It was sold to the Dublin Docklands Development Authority last year for a reported £18 million, a knockdown price given its location. The cost of reclaiming the site is estimated to be at least £12 million, and this would have influenced its value.

The current plan calls for several metres of soil and rubble to be removed from large areas of the overall site. Up to 150,000 tonnes of material may have to be dug up and shipped abroad for decontamination treatment, according to the specialist UK company hired to oversee the project.

A British consulting engineering firm, Parkman Ltd, was contracted to prepare an outline plan for site renewal and this was submitted to the Environmental Protection Agency last Wednesday. Now the company has been retained by the docklands authority to prepare the detailed plan and to manage the project on site, according to John Crowther, Parkman's operations director.

The work will not require an environmental impact statement because it is only a site clear up, Mr Crowther said, but it does need a waste disposal licence from the Environment Protection Agency (EPA) because potentially hazardous materials will be dislodged and moved away. The EPA will also have to be satisfied that there will be no contamination of groundwater when the clean-up is under way.

The company has much experience in clearing up former gasworks sites in the UK and has dealt with 150 contaminated sites there. It was also contracted to deal with the Bord Gais Eireann (BGE) site reclamation at Albert Road Cork, now nearing completion.

The project will take between 12 and 18 months to complete, Mr Crowther said, but could be delayed because BGE ais Eireann still has a depot on part of the site and is not ready to move. "We may well have a two-phased operation."

Preliminary inspection and testing has shown that the site holds nothing out of the ordinary, he said. "From the point of view of it having been a gasworks, it is fairly typical. The thing that changes is the ground conditions, the geology."

Cleaning them up can be a "bit of a detective game" because any one location may have residues left behind by different gas production technologies. "The tendency with gasworks is they are not constant, the technology evolved. There are several generations of works there."

THERE will be no on-site treatment of contaminated soils, he said, because of the specialist equipment needed to clean up the soil. "It is not easy to treat. A lot of the material is tar or oil based." Installing the equipment would take too long. "We need to be able to deal with this site in a reasonable period of time. It would have been nice to do it on site but it would have been a very protracted procedure."

The contaminated soil cannot be treated in Ireland. "It is a bit of a frustration that there is no facility in Ireland to treat this," he said. The material excavated from Albert Street was shipped to the Netherlands and soil dug from the Dublin site will also go either to Rotterdam or to facilities in Britain.

Export to Rotterdam means that Irish terra firma will become part of the road system in the Netherlands. The soil and rubble is decontaminated by "thermal desorption", heating which reduces soil and waste to a heavy but safe residue suitable as a construction material.

A range of potentially toxic materials could be be uncovered on site, including complex hydrocarbons and heavy metal pollution, so stringent controls must be applied to prevent contamination leaving the site, he said. "There is quite a sophisticated health and safety aspect" to the project.

The entire 22-acre site will first be ringed with a seven to 10-metre deep underground wall. Large bore holes will be filled with water-impermeable concrete that will isolate the site and keep loosened materials from mixing with groundwater. "We need to be able to control the ground water on the site," Mr Crowther said.

Overbear will then be sorted and tested. "We will be specifying a regime of sampling and testing to decide what has to go away on the ship," he said. Some obviously contaminated material will be shipped immediately but other areas will be tested to see if they are polluted. It was important to avoid sending away more material for treatment than was necessary.

Old buildings and foundations would be crushed and used later as fill. Large areas would have to be excavated up to three metres deep and even deeper where old tanks stood he explained.

INITIAL plans call for the construction of an enclosed, high-rise conveyor belt to carry the excavated material directly to ships berthed at the quayside, a procedure that would control dust transport off site.

A range of dust and pollution monitors will be installed in site, he said, and workers may also have to wear monitors if active in heavily polluted areas.

The plans also cater for smells escaping from the site, Mr Crowther said. "Uncover tarry type materials and they can smell." This becomes a particular problem if there is housing close by, as was the case in Cork. Smells can be reduced by using water misting systems which wash down the volatile substances.

There are no plans to backfill the site and bring it up to its former level, he said. "We envisage that the site will be reduced to near tide level."

The building developments expected to follow reclamation would likely have further excavations for underground car-parks and foundations and this material could be used to backfill the site.