Despite repeated attempts the Northland Regional Council has still not been able to contact the owner of land where the Marsden pipeline ruptured.
The pipe broke last month, disrupting fuel supplies from the Northland refinery and causing dozens of flights in and out of Auckland Airport to be cancelled - affecting thousands of travellers.
It forced fuel to be trucked into the city, and a month on, the council's investigation has reached an impasse.
The council has been trying to contact the owner of the Ruakaka lifestyle block where the pipeline's owner, Refining NZ, said it was damaged by a digger.
Council regulatory manager Colin Dall said it was investigating the incident as a potential breach of the Resource Management Act (RMA).
It carries a maximum penalty of $300,000 for an individual, and twice that for a company.
Mr Dall said his staff have the landowner's phone number but he was not responding.
"We've certainly contacted him and left a message on his voicemail but it appears he's not picking up at this particular time," he said.
Mr Dall said the council would also be writing to the landowner, but had no powers under the RMA to compel him to talk to investigators.
"We don't have the same powers as the police. We can certainly invite people in to talk to us but we can't compel them to do that," he said.
Neighbours of the pipeline property had confirmed to council investigators that diggers had worked on the site in recent years, Mr Dall said.
The council would now try to confirm that he had not left the country, he said.
"We are not sure if that's something Customs or Immigration could tell us, or if there are privacy issues but it's a question we'll be asking," he said.