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Christchurch City Council seeks variation to discharge consent

5 August 2005

Christchurch City Council will apply for a variation to its Estuary Resource Consent seeking a level of ammonia discharge that its waste treatment plant can meet.

While the upgraded waste treatment plant has been very successful in reducing the levels of carbon and faecal coliform in the discharge, none of the plant’s four previous upgrades have targeted reducing nutrient levels, including ammonia, City Water and Waste Manager Mark Christison says.

“The council is currently in breach of ammonia mass loadings and will shortly breach both mass loadings and concentration limits under tighter conditions from October this year,” he says.

Ammonia reduction will not be necessary when the new Ocean Outfall is commissioned in 2009 due to the high dilution rates that occur at the outfall diffusers about 3km off shore.

“Short of spending many millions of ratepayers’ money there is little the council can do to reduce ammonia levels, ” Mr Christison says. “In addition, building the required modification would take at least two to three years, by which stage the ocean outfall will be well on track. In the meantime, we need discharge conditions that reflect plant capabilities.”

He says the plant’s wastewater treatment is a carbon removal and not a nitrogen reduction or biological nutrient removal process. The ammonia coming into the plant roughly equals the ammonia discharge in the effluent.

Mr Christison says the council is not looking at discharging effluent with an ammonia concentration any higher than what has historically been discharged into the estuary.  “While we will continue our trials to try to reduce the levels of ammonia being discharged into the estuary, the only option we have available at this stage is to seek a consent variation which recognises the capability of the Christchurch Wastewater Treatment Plant.”

The council informed Environment Canterbury (ECan) and the Discharge Audit Group of the situation earlier this year and has updated interested parties throughout the trial process. The Council will lodge its application with ECan for a variation next month. The consent is likely to be publicly notified, Mr Christison says.

Fish surveys and enhanced ammonia sampling will continue in the estuary to improve the scientific evidence on the effects of the present discharge. The council will also continue evaluating its treatment processes in a bid to improve the discharge quality within the technology limits of the current treatment plant.

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