The costs and planning implications of the recent landslide at Killiney which stopped train traffic on the commuter and intercity routes to the southeast have yet to be divulged by Iarnrod Eireann.

A number of possible causes have been put forward for the landslide, from the very heavy rains in the area at the time to building work taking place on many parts of Killiney Hill which may divert natural watercourses.

Iarnrod Eireann has recruited a Dutch firm of engineers to advise the company on the best handling of the situation, including investigating possible causes and remedial works. With heavy earth moving machinery on site for at least a week, not to mention the cost of the closure of the railway, Iarnrod Eireann's expenditure is likely to exceed £1 million.

According to the company, the landslide which disrupted services involved "several hundred tonnes" of earth falling across the railway line. While this was cleared quickly, Iarnrod Eireann engineering staff determined that the slide had resulted in part of the remaining section being destabilised.

The company indicated that the source of the landslide is privately owned land. A spokesman for Iarnrod Eireann, Mr Barry Kenny, indicated that both the landowner and the company had engineers advising them on the remedial work.

A team of 50 personnel were on site, including sub-contractors, working around the clock under arc lights. There were about a half dozen earth moving machines and a number of lorries were employed to deliver small rocks to the site.

Mr Kenny said he was aware that some development work had been taking place on the site prior to the landslide but added "we don't honestly know what effect this had, if any." Mr Kenny pointed to the heavy rainfalls which occurred in November and again in the past week and said that "this may have been the cause".

At the time of the landslide, a spokesman for Dun Laoghaire/Rathdown County Council said the council was treating the matter as primarily an issue involving "a private landowner" although he added that the council would be maintaining a "watching brief" on the remedial works carried out to ensure public safety and guard against any landslide on public open space.

The county council had established that some development work was being carried out on the entrance to the site but the spokesman said it could not say if this had any bearing on the landslide.

PD councillor, Mr Victor Boyhan, tabled a long and detailed question to the council on recent planning permissions, building on the hill and the results of the council's own investigation into the incident. In a short reply, the council replied that while it had commenced proceedings against a landowner for the unauthorised raising of a wall in the area, it was not thought that this had anything to do with the mudslide.