Trade waste has been confirmed as the main factor in persistent consent breaches by Rangitikei District Council.

The Rangitikei council is in breach of its consent from Horizons Regional Council to discharge from its wastewater system into the Tutaenui Stream, due to excessive levels of ammonia and discolouration of discharge water. It will be months before the problem is fixed.

It has also been revealed that records of what trade waste has been put through the wastewater treatment system have not been kept for several years, making the environmental impact hard to calculate.

The district council commissioned Opus to look into the effect of leachate from the Bonny Glen dump, and Opus confirmed the leachate was the main contributor to the consent breaches.

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Leachate is put into the system which mixes with the town's wastewater before being discharged.

But the Opus report said leachate tanker logs and leachate strength data from between 2006 and 2013 could not be provided.

Leachate is put into the waste water system about every second day under a "gentleman's agreement" between the council and Bonny Glen operators Midwest Disposals Ltd. There is no signed contract between the two parties.

Some days leachate can contribute almost 70 per cent of the ammoniacal nitrogen levels which regularly exceed consented levels.

In 2010, the council and multinational malting company Malteurop signed a trade waste agreement. Malteurop contributed $500,000 to the upgrade of the wastewater plant and pays $40,000 annually towards operating costs.

The agreement limits the strength and volume of Malteurop's waste but the report again revealed records were not being kept.

"Only one trade waste sample result was available and no flow data. Therefore the actual flows and loads contributed by Malteurop have not been possible to calculate," the report said and it added there was a need to build a further anaerobic pond or pre-treatment facility for the leachate.

Horizons environmental protection officer Robert Rose confirmed the district council had been in breach of its consent, but it appears RDC will not yet face penalties.

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"Horizons has requested RDC to outline what they're going to do to address this issue. We expect a response by the end of January," Mr Rose said.

Rangitikei asset and infrastructure committee chair Dean McManaway said: "It's pretty much telling us what we already know. We've got to deal with it, we cannot let this go on."

The easiest solution would be to not accept the waste, but for the "gentleman's agreement that we do take it". "We're going to have to look at a way to address the ammonia and the colour in the leachate before it goes into our ponds.

"At the end of the day, they are going to have to pay. There's going to be quite a big outlay for them."

Mr McManaway said it was a worry that records of what was being put through the system had not been maintained.

Mayor Andy Watson said the Bonny Glen Leachate was only part of the problem and the effectiveness of the whole wastewater system needed review.