A unique engineering method will be used to repair a major ground water leak, likely caused by a mature cedar tree on Queenstown's Marine Parade, QLDC Engineering engineer Lane Vermaas said.

Recent routine inspections confirmed that the Marine Parade pump station was dealing with lake water, in addition to the town's normal sewerage flow, at the rate of  approximately 6 or 7 litres per second, equating to a flow excess of 600,000 litres a day.

"Fortunately with the successful completion last year of the new additional CBD (Central Business District) sewer pipeline, we have been able to quickly pinpoint the problem," Mr Vermaas said.

"Its likely that the large tree, situated in the Marine Parade historic precinct, has displaced several of the concrete sewer pipes, allowing the water to pour in from the lake ground water," Mr Vermaas said.

The normal emergency work procedure would be to excavate a trench along the broken section and then replace the pipes.

"Due to the nature of the very loose gravel ground conditions and the nearness to the base of this cedar tree, our concern was that the tree could be damaged, so instead we have devised something quite unique" Mr Vermaas said.

Beginning Friday, contractors would instead dig two reasonably large holes, approximately 20 metres each side of the tree and would then cut into the concrete pipe, inserting a polyethylene liner.

"This will allow for some flexible movement unlike the current concrete pipe. An isolating valve will also be installed to allow for future options, should the problem recur," he said.

During the repair, scheduled to take approximately 10 days, the sewage flow from the old main would be re-directed through the new CBD ring main.

"We will of course try to keep the disruption to a minimum and most importantly, the work will be completed before the Winter Festival begins on July 1," Mr Vermaas said.

The contractors on site will be Lakes Contract Services, Just Dig It and Steve Rout Contracting.

ENDS

For further information please contact Lane Vermaas ph 03 441 0499.

By: Tamah