SURVEY work at the Bord Gais former gasworks off Sir John Rogerson's Quay is expected to begin within a week. It is the first stage in a planned environmental clean-up of the valuable 22-acre property.

Bord Gais has appointed UK consulting engineers Parkman Environment, which will carry out a detailed site investigation and prepare a strategy for renewing the site in, association with Michael Punch and Partners and RPS Cairns.

The survey will involve drilling and extensive soil sampling to establish levels of chemical residues and also pinpoint any unidentified underground tanks or burial pits for old equipment, says Ted Stevens, spokesman for Parkman Environment.

The work is scheduled to begin by mid-April. "By the end of May, we will know what we are dealing with on the site," says Mr Stevens. The company will then make recommendations on how the site clean-up should proceed and at what cost.

The company has advised on reclamation works at 120 gas sites in Britain, he says. "The first stage is to examine the site and report on the options. By June, everyone will know what they are dealing with."

The 22 acres are owned by Bord Gais Eireann, but control of the site will fall to the new Docklands Development Authority, due to be established by the end of the month. A master plan for the entire docks area is scheduled for release at about the same time.

Dublin Corporation granted planning permission for the site some time ago, with provision for 1,300 apartments, a hotel, leisure facilities, light industrial units and several office blocks - but any development depends on the successful conclusion of the clean-up - the removal of waste chemicals and pollution left behind by almost 150 years of town gas production.

The eventual financial return to BGE also hinges on this. The site could be worth up to £1 million per acre according to James Meagher of the Sherry FitzGerald estate agency. BGE's nearby 7.5-acre Barrow Street site was sold for an estimated £9 million to £10 million, which gives a potential guideline price of £27 million £30 million.

And the Dublin 2000 consortium, which made an approach to BGE for a joint development several months ago, is understood to have valued the site at £28 million. Dublin 2000 was prepared to pay BGE that amount less the cost of satisfactory reclamation of the site, estimated at up to £20 million.

BGE was "working closely" with the Dublin Docklands Task, Force in relation to the site, according to a statement on Parkman's appointment issued by the gas company.

"We want to secure an early redevelopment of our site as part of the overall regeneration master plan and are currently preparing strategic plans for the relocation of our operations currently located on the site," according to BGE's chief executive, Philip Cronin.

Less clear was the need for the survey work. An extensive assessment of the site was carried out by O'Connor Sutton Cronin, consulting engineers during the planning hearings associated with BGE's development application. Now another group of engineers will examine the same site.

O'Connor Sutton Cronin's work "was a condition of the planning permission we were seeking", according to a BGE spokeswoman. The permission for the site in turn required a more detailed site investigation before building could begin.

Mr Sean O'Laoire of Murray O'Laoire Associates, the architects for the gasworks project, contradicts this. The initial survey "was deemed to be satisfactory to satisfy the demands of the Environmental Impact Assessment of the site", he says. It was one of the first EIAs inquired for an urban project under EU regulations, and there was a framework agreed between ourselves, O'Connor Sutton Cronin and the corporation, which satisfied them that time," says Mr O'Laoire. "It didn't imply a more detailed investigation had to be done."

He suggests, however, the new survey could deliver a greater level of assurance for the development and its future safety. "It does give a firmer basis both on financial and logistical grounds."

The 22 acres will almost certainly have to be viewed as a single block for clean-up purposes, James Meagher believes. Acre by acre reclamation of the site would not be a runner. A sub-division at the periphery of the site could be cleared, but the risk of crossover of contaminants from uncleared "land would always exist.

The clean-up, however, may not be all that bad. There were "fairly mild levels of contamination on most gas board sites" in Britain, according to Mr Stevens of Parkman. And there are "umpteen different ways to deal with it".

The main decision is whether to cap and seal the site or clear it completely. The former involves removing the worst of the contamination and then installing an impermeable membrane to isolate what remains underneath new construction. The latter is more radical and involves the complete removal and disposal of all contaminated soil and a full restoration of the site.

Companies are "increasingly" going for reclamation rather than removal because no one Wants to have to deal with the waste", says Mr Stevens.

Ireland does not have a dump where contaminated soil could be discarded, so removal would be a very expensive option with a site as large as the former gasworks.

Other clean-up techniques can be employed however. A form of "soil washing" was used at a Nottingham site, says Mr Stevens, where soils were cleansed before being put back.

But the question remains: how clean is clean enough? Is there an acceptable level of residue that can be left behind? What might lie underfoot is likely to become an issue for purchasers considering expensive accommodation, no matter how attractive the views over the Liffey and Dublin Bay.