Safety risks for contractors on the $16.5 million Muldoon's Corner project shut down the scheme for two days this month.
Helen Pinson, New Zealand Transport Agency (NZTA) communications advisor, said that earlier this month contractors working on the project encountered problems with groundwater.
She said a "potential for slippage" was revealed after contractors dug a steep track on the site to serve as a temporary road for the transport of spoil and earth from one part of the site to another.
Department of Labour inspectors went to the site and met the contractors to discuss the dangers, Ms Pilson said.
"The site was temporarily closed to allow geotechnical specialists to provide advice on how to safely manage the issue," she said.
The site was shut down for two days, Ms Pilson said, while the area was assessed and a plan prepared to manage the ground water before "measures were put in place" to ensure adequate drainage and work on the project resumed.
"The safety of workers on our sites is paramount, and the NZTA is committed to completing all of our projects safely and on time."
Construction began on the site in August, she said, more than two years earlier than scheduled and NZTA "are working with the contractor to ensure the closure does not impact on the overall timetable of the project and we are confident this will not be the case".
The project is due to be completed in 23012 and "will improve safety on this difficult section" of SH2, where heavy vehicles travelling in opposite directions are unable to easily pass each other, Mrs Pilson said.