Refining NZ says thick black smoke which issued from its Marsden Point Oil Refinery is allowed under the company's resource consent, but the problem could cost up to $8 million in lost revenue.
The smoke, described by Ruakaka resident Robyn Hembry as "thick, black and stinking", was emitted as part of a series of "flaring" incidents, following a fault with the Refinery's hydrocracker - a hydrogen processing unit which usually produces fuel components.
Ms Hembry said she was "appalled" by the week-long flaring, particularly that which occurred on March 13, when smoke billowed from a refinery chimney for two hours, dispersing towards Ruakaka Village.
"It was black, billowing, thick, toxic smoke. I drove up there and the smell was appalling - you could hardly breathe," Ms Hembry said. "What environmental health effect is it having on the local people? It's unbelievable."
Refining NZ's Greg McNeill said an electrical fault at the hydrocracker had caused it to go into safe shutdown. This meant hydrocarbons normally consumed by unit were instead released into the atmosphere.