Waipukerau wastewater plant pond closed

The new anaerobic pond and a stormwater balancing pond were only built at the Waipukurau wastewater treatment plant earlier this year at a cost of $1.6 million. The district council has closed down the anaerobic pond because it is contributing to smells at the plant. Photo / File

After only a few months of operating, the anaerobic pond at the Waipukurau wastewater treatment plant has been shut down, as the plant continues to fail to meet ammonia discharge limits and emit odours that are rankling nearby residents.

The anaerobic pond and a stormwater balancing pond were built by CHB District council for $1.6 million, in part to deal with the ongoing odour problems by reducing the amount of effluent loaded with organic material entering the plant.

But in a situation described by CHB mayor Alex Walker as unacceptable, the council revealed it had been forced to close down the anaerobic pond because it was continuing to add to the smells plaguing residents since last summer.

Chief executive Monique Davidson said the smell from the Waipukurau plant was initially due to high hydrogen sulphide levels coming to the surface of the new stormwater balancing pond from the outflow of the anaerobic pond.

"We applied a top dressing solution of sodium nitrate, and this has been partly effective at reducing the odour. Despite this, some smells are still being emitted from the anaerobic pond, so we have closed it down until a permanent solution is installed."

Ms Davidson said the council had purchased additional aeration units which were due to be installed last week to try and reduce the odours.

"What the additional aeration units won't fix is the ammonium levels, which are higher than the consented allowances. This is a concern to the council," she said.

Ms Davidson confirmed that both the Waipukurau and Waipawa plants, which were upgraded to floating wetland models in 2013, both failed to meet ammonia consent limits.

Originally expected to cost $6 million, by March this year the upgrade costs had reached $8m - $2.8m for Waipawa, and $5.2m at Waipukurau.

Councillor Gerard Minehan, a Mt Herbert Rd resident who lives near the plant, supported a motion by mayor Alex Walker to conduct a review into theviability of both plants and their ability to meet current resource consent requirements.

The motion also said the scope of the report, due by mid-November, needed to include all resource consent requirements for both systems, the capacity of the system to deal with current residential and trade waste demands, as well as future growth projections for the district.

"What we want to know is, that if it [the Waipukurau plant] is a flop, how are we going to rectify it - if we can - because the fixes aren't doing the fixes anymore," Mr Minehan said.

If the review found the plant was not fit for purpose, it would leave council in a tough situation with so much money spent to date, he said.

"But we have to start thinking what our next options are, because it needs to get sorted," said Mr Minehan, who had to turn off his air conditioner at home last summer because of the stench, which he said had been just as bad this winter.

"If it's this bad now, imagine what it's going to be like in summer. It's going to be horrendous."

Chief executive Monique Davidson said council would be "upfront and transparent" about the findings of the November review.

"Council is committed to finding a long-term sustainable solution, not just a band aid. Given the long history associated with this treatment plant we need to ensure that this is dealt with in a way which finds a final resolution."

Asked if council had any legal recourse to recoup costs against WaterClean Technologies, the company that upgraded the plants, she said council and its legal advisors were working through a process with the company around those issues.