Some of Wanganui's largest businesses could be temporarily shut down if the Wanganui District Council receives an expected abatement notice from Horizons Regional Council.
Mayor Annette Main confirmed that she was waiting to receive an abatement notice today relating to the stench which has been wafting over the city from the malfunctioning wastewater treatment plant for the past month.
Six Wanganui businesses - known as wet industries - are implicated in three recent dumps of excess waste, including fat, protein material and sulphides, into the wastewater treatment plant.
These businesses are Tasman Tanning, Open Country Dairy, AFFCO Imlay, Land Meat, Mars, and Cavalier Spinners.
It is not known which business, or businesses, is responsible for the dumps.
Ms Main said the abatement notice would have implications for these businesses.
"If we can't abide by the abatement notice to get rid of the smell, the only thing we can do is go back to the industries and stop them putting their waste into the treatment plant.
"And yes, that could potentially close them down."
Ms Main told the Wanganui Chronicle she wrote to each of the businesses yesterday to tell them the dumping needed to stop, "whether it's by accident or not".
Previously, she said the businesses she had spoken to "had all indicated they did not wish the dumping to happen."
"And since we can't prove which company it was, all we can do is write to every single one of them, remind them of their obligations under their consents, and tell them that the public of Wanganui expects them to be abiding by them."
Ms Main said each of these business had a trade waste discharge consent which was specific to that business. Tasman Tanning has two consents because it operates from two sites.
She said the consents had to be renewed every year.
"When a business signs up to a trade waste discharge consent, it is agreeing that it can operate within that level. So there should be no reason for any of them to breach their consent.
"The consents talk about maximum volumes, what can be in [the waste] - how much suspended solids, what the Ph has to be, how much oil and grease, how much sulphate.
"They're also supposed to have flow meters, although it's my understanding that not all of them do.
"And if a discharge isn't recorded then it's just gone."
Ms Main said the system needed to be changed so that information was provided to the council on "who was dumping what".
She said it was possible Horizons could prosecute the council over the smell, although she thought that was unlikely.
"I am worried about prosecution because that would mean a fine, and a fine would mean money that could better be used to fix the problem at the plant," she said.
Horizons issued the council with a warning notice in December, saying it had breached regional rules relating to discharge to air.
Horizons' general manager of strategy and regulation, Nic Peet, confirmed that Horizons would be taking further action this week.
But he said Horizons supported the council in working to solve its problems with the plant.
"Our role is as the regulator, but we will assist where appropriate," Mr Peet said.