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Three-and-a-half years after construction started, Watercare’s $230 million wastewater treatment plant at Snells Beach was officially opened on September 15.
The facility is the lynch-pin in a $450 million five-phase programme of new infrastructure being rolled out to improve sewage disposal and cope with growth in the Warkworth and Snells Beach areas.
The other four components are the new pumping station at Lucy Moore Memorial Park in Warkworth, a five-kilometre transfer pipeline from there to Snells, a new outfall pipe that runs out 800-metres beyond Martins Bay, and the much-anticipated growth-servicing pipeline from Warkworth Showgrounds to Lucy Moore, which will be built next year.
The treatment plant alone involved up to 190 people working for more than 500,000 hours and required 30,000 cubic metres of earth to be moved, not to mention 100km of electrical cable, 1.8km of stainless steel pipe and 8000 cubic metres of concrete.
Project manager Casper Kruger said constructing such a big facility had been far from straightforward.
“It’s a very complex piece of kit and there are lot of different disciplines involved,” he said. “It’s a very long and tedious process to get it all done.”
However, he said it was well worth it to provide Mahurangi with a state-of-the-art facility to replace old and dated treatment plants at Warkworth and Snells.
“It’s a complete change in approach. We can do far better quality of wastewater and to a much larger scale, and it’s a lot cleaner.”
Kruger said the scope of the project had been adjusted as work progressed, with some aspects brought forward, as it was easier and safer than trying to add them in the future when the plant was fully operational.
“This includes adding a fourth membrane bioreactor train, for example, and we have extra tanks for future capacity.”
Now the plant is up and running, the old treatment plants will be decommissioned and work will start as soon as possible on the final link in the new infrastructure chain, the Warkworth growth pipeline.
That’s something that can’t come soon enough for oyster farmer Tom Waters, who said the new plant hadn’t stopped yet another overflow into the Mahurangi River during rain last Wednesday
“Until every element of the treatment plant is finished, we’re still going to get sewage overflows until the end of next year, if not further,” he said. “We’ve only had 20mm of rain, but the reality is it hasn’t fixed the problem.”
However, there was some good news last week for Snells Beach residents now construction is finished, Watercare has reopened the walking trail between the bottom of Hamatana Road and Grange Street.
What’s the difference? New vs old …
Screening – New plant: screens everything bigger than 2mm. Old plants: Warkworth had 3mm screens, Snells no screens at all.
Grit removal – New plant: two dedicated tanks and grit washing kit. Old plants: Warkworth, one very small gravel sump; Snells, no grit removal facilities.
Filtration – New plant: very fine membranes that filter all particles larger than 0.02 microns (small enough to capture many viruses). Old plants: no effective filtration.
Ultraviolet disinfection – New plant: much higher standard than old Warkworth plant, due to clarity of membrane-filtered water. Old Snells plant, no UV treatment.
Biological treatment – New plant: activated sludge reactor tanks (‘engine room’ of the plant where bacteria break down solids and remove nitrogen; can handle 4 million litres of sewage a day), with four times the capacity of the oxidation ditch at the old Warkworth plant.
Process water – New plant: effluent clean enough for some of it to be recycled within the plant for sprays, flushing and hoses. Old plants: not possible.
