Christchurch sewerage system on brink of failure

Last updated 05:00 02/04/2011

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Christchurch's sewerage system is on the verge of collapse, threatening to blanket the city in an "almighty stink" till Christmas.

Christchurch City Council water and waste operations maintenance manager Mike Bourke said staff were working furiously to fix the quake-hit sewerage system, but it remained on a "knife-edge".

He called on Christchurch residents to work harder to conserve water or risk overloading the sewage ponds, leading to a city-wide stench.

"If we overload the ponds it will create an almighty stink. It won't just affect the eastern suburbs, you'll smell it in Hornby."

The choke point was the quake-crippled Bromley wastewater treatment plant, which was processing sewage at only 30 per cent of its normal level.

That had forced the council to release more untreated water into the 230 hectares of oxidation ponds and there was a 50 per cent chance that the oxygen level would drop below functional levels, turning the placid lakes into a vast cesspit.

Once the tipping point was reached it would be difficult to reverse and the smell could linger for months.

"It will take many months to get them operating, probably till Christmas."

The Bromley plant has also been dealing with an influx of debris and sand which has infiltrated the crippled pipe system, putting further pressure on its already-stressed filtering tanks.

Bourke said since February 22, the plant had sucked about 1000 tonnes of sand out of the sewerage network.

The plant itself could take anywhere from six months to two years to fix.

The council was still building a picture of how badly damaged the sewerage system was, but with many pipes too clogged with sand to inspect, this could take up to eight months.

He compared the sewerage network to a tree, with each home a leaf connected to a sewerage branch, which in turn was attached to the main trunk leading down to the treatment plant.

Repairs were starting at the tips of the branches and working back to the main trunk, meaning some repaired pipes would still fail to work until breaks further down the line were discovered, Bourke said.

The council has 92 trucks flushing sand out of pipes and 11 crews putting cameras down mains to survey the damage.

The latest figures show that six per cent, or 96 kilometres, of Christchurch's sewerage mains were not working, with a further 27 per cent, or 474km, working only slowly.

The slow-moving flow of effluent in the pipes was presenting the biggest headache for council, and also potentially health authorities, because they were still leaking millions of litres into backyards, rivers and the sea, he said.

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A quarter of Christchurch's sewage, about 40 million litres a day, was still leaking out of broken pipes.

While this was a massive improvement from 60 million litres a day just two weeks ago, it would still be months rather than weeks before rivers and beaches were found to be safe.

"I'd hope come summer you would be able to surf again."

For residents in eastern Christchurch using chemical toilets, Bourke said the wait for a flushing loo could take anything from a month to a year.

- The Press

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