Poor quality soil and swampy conditions have been blamed for a $500,000 budget blowout for a 3.6km section of the Crown Range Rd upgrade.
Queenstown Lakes District Council roading manager Ian Marshall said the section from Royal Burn to Glencoe contained less than optimum materials, which had been found over a substantial part of the road and in "unexpected locations", resulting in almost $500,000 added to the bill for that section of road reconstruction.
The budget for the section was $3.88 million, but due to the significant amount of unexpected undercutting increasing costs, the final figure was $4.318 million, Mr Marshall said.
The work had already been carried out and had left the road at full strength, which would be "enduring on a stretch of road that has traditionally proved expensive to maintain".
Mr Marshall said he had looked into whether sufficient investigation had been done on the section before the work began but it was possible that would not have uncovered the problems as the poor soil was found in "totally unexpected locations".
"There is always a balance that needs to be struck between the amount of money spent on investigation to help the predictability and the total cost of the job.
"Some investigation can be expensive but give good information about what has to be done.
"Yet, in the end, it merely adds to the cost of the job given that the work identified as the result of the investigation was always going to have been done anyway."
That analogy was particularly relevant when applied to the Royal Burn to Glencoe job, he said.
"More investigation would have shown a greater amount of undercutting would have been required, but the actual conditions unearthed were in totally unexpected areas.
"So, it is likely that even if more investigation was carried out, it would not have been extensive enough to identify the full extent of the problem and then the material still had to be removed."
A meeting had been held with the contractor and the consultant to analyse the total cost of the project and understand the detail of the variations, where "rigorous examination" of the costs was done, he said.
"It must be pointed out that the project team's performance has not been an issue in this project. They have worked actively to find cheaper solutions to problems that have arisen."
The financial impact of the blowout was "minor" with money redirected from an upgrade scheduled for Malaghans Rd.
