Transmission Gully earthworks estimate undershoots by 50%

Greater Wellington Regional Council's environment committee wants an update on the $850 million Transmission Gully project after learning consents for the 27-kilometre four-lane highway underestimated earthworks by 50 percent.

The general manager's report to the committee for today's meeting in Wellington showed an additional 4.1 million cubic metres of earthworks is needed beyond what was already consented in a fast-tracked board of inquiry process. GWRC manager of environmental regulation Al Cross told the committee new consents will be needed on a non-notified basis.

If the extra work had been found to fall outside the original scope and required a notified consent process, Cross said it would've been "pretty hard for the project", given it's working to an April 2020 timeline.

"Because these large projects, particularly under the PPP (public private partnership) framework, go on to consenting at very basic concept at a design level - 10-to-20 percent design detail - the devil really is in the detail," Cross said. "It simply wasn't foreseen by NZTA (New Zealand Transport Agency) at the consenting stage."

Cross said it's "relatively typical" for large NZTA projects to get consent with limited design details, and that smaller programmes are usually much closer to their target.

Project manager Wellington Gateway Partnership has previously indicated it was preparing for a bigger earthworks programme than envisaged in monthly reports to NZTA, released to BusinessDesk under the Official Information Act, showing the construction joint venture between Cimic Group-owned CPB Contractors and HEB Construction.

No estimate was given of projected additional costs, which will be borne by the PPP consortium.

Cross confirmed this was the first time the council's reports had used the figures showing the increased scale of the earthworks programme and that any extra costs will be an issue for the joint venture and Wellington Gateway Partnership. Cross said the joint venture hadn't talked about the extra work "pushing out the timing beyond April 2020."

In January, CPB and HEB tasked their consenting teams to focus on acquiring a single permit that "gives flexibility and a buffer to give certainty and efficiency for earthworks production", and in March and April updates the project manager said the additional stage 2 earthworks strategy may trigger the need for up to 12 revisions of site-specific environmental management plans.

The report shows some consent applications have been granted, some are being processed, and some have yet to be lodged. Cross said the consents will have to consider whether the additional work falls within the scope set by the original board of inquiry process, much of which will be about the volume of sediment discharged into Porirua harbour. The original consent allowed for 3,000 tonnes of sediment to be discharged, but since then geotechnical work had scaled back the likely discharge to just 300 tonnes which gives "a lot more confidence about them able to operate within that consented offering," he said.

The project has adaptive management processes, but Cross said the performance has been mixed and council is working with the joint venture on improving it.

Nigel Corry, general manager of environment management, reminded the committee that the contractual arrangement of the project, whether it falls within budget and is completed by the April 2020 timeframe, isn't an issue for the council, which was a regulator in the process. However, he offered to organise a briefing with the joint venture, which committee chair Sue Kedgley took up.

"It's hard to see how 50 percent extra earthworks would be unforeseen. Thankfully the budget blowout, as I say, will not be something we'll have to confront," Kedgley said. "We've got an action point out of that which is a briefing to follow at our next meeting."

CPB and HEB went on a hiring drive earlier this year in preparation of the extra earthworks needed, and its voluntary staff turnover improved this year, falling to an annual rolling average rate of 17.3 percent in April from 22 percent in October.

The Kaikoura earthquake and downpour in November last year caused major delays on parts of the project, requiring remediation and clean-up work. However, the monthly updates show the project bounced back from that work, completing much of it in December, while some lost time caused by rain in February had been recovered after a steady fine spell. The project passed 1 million cubic metres of bulk earthworks in March and another 301,000 cubic metres was shifted in April despite early rain and public holidays shortening the weeks.

Activity on the project stepped up earlier this year with project man-hours on a 12-month rolling total reaching 1.27 million in April, from about 897,000 in November.

(BusinessDesk)