Friday, 18 December 2020
Change in approach required for major Wakatipu wastewater upgrade
Unforeseen ground conditions means drilling no longer possible.
Queenstown Lakes District Council (QLDC) will be changing its approach to completing a major wastewater upgrade underway in the Queenstown Town Centre, due to unforeseen and unusual ground conditions.
QLDC Chief Engineer Ulrich Glasner confirmed that the plan to install 870m of wastewater pipe under the Queenstown Town Centre via a method called horizontal directional drilling is having to change having encountered some unexpected materials.
“While we spent considerable time and effort completing geotech investigations along the pipeline route to determine the suitability of horizontal directional drilling, we hit what is likely to be prehistoric timber 20 metres underground. That’s twice the height of the Naylor Love scaffolding in town at the moment, so it’s a long way down. The material is currently being tested to determine its origins.”
“Due to this, and following further technical assessments it has been agreed that the most appropriate approach is to complete the pipe installation using traditional open cut trenches,” Mr Glasner said.
QLDC General Manager Property and Infrastructure Peter Hansby said that while the outcome isn’t what had been planned for, the possibility that the drilling may not be successful was identified as a risk during the project planning and a ‘Plan B’ has already been designed and consented.
“Horizontal Directional drilling is widely used throughout Aotearoa New Zealand and the rest of the world and we were confident that our early investigations had indicated appropriate conditions. However, with projects such as this there is always a risk that we could encounter challenging ground conditions and it was important that we put the time and effort into planning upfront so that we could quickly change track if required,” Mr Hansby said.
“The new approach results in a number of changes to the project, including a new pipe alignment and timings for construction. It also provides opportunities to integrate with other projects underway or planned such as the town centre street upgrades and upgrades at the Te Kararo Queenstown Gardens.”
Mr Hansby acknowledged that the new approach would cause more disruption than originally planned and that the project team would be putting significant effort into working with affected stakeholders to talk through their concerns and consider mitigation efforts and maintain access.
“We very much have an open door policy and the contractors will be working hard to maintain a close working relationship with those affected throughout the project,” Mr Hansby said.
“The team will be out talking to affected residents and businesses in the lead up to Christmas and the intention is to start further service location works later in January 2021.
In the meantime, construction of a new Pump Station at the Recreation Ground is mostly complete and 900m of new wastewater pipe has been installed along Park Street.
Updated details about the project, including a new pipe alignment map and construction programme can be found at https://www.qldc.govt.nz/your-council/major-projects/recreation-ground-wastewater-pump-station-and-rising-main
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