The head of the Ministry for the Environment has been forced to admit he does now know how it will be able to clean up the contaminated Mapua chemical site to a level to meet consent conditions.
Chief executive Paul Reynolds appeared before the Local Government and Environment Select Committee at Parliament on Thursday to defend the ministry's handling of the clean-up of the site near Nelson.
An investigation by the Parliamentary Commissioner for the Environment highlighted mistakes and mismanagement in the project.
The commissioner's report showed dioxins and toxins were released from an exhaust stack for a year without any monitoring.
It also raised concerns about the Environment Ministry's use of copper sulphate as a reagent in the clean-up and then discharging it into the estuary.
When pressed by MPs, Dr Reynolds would not accept that the ministry might have breached its resource consent by discharging the copper in water.
But he admitted he does not know how it will be able to clean up the copper to a level to meet consent conditions.