The next stage in the $13 million upgrade of Whangarei's sewerage system is being planned as the $4.5 million Okara to Kioreroa pipeline and pump upgrade nears completion.
The pipeline and pumps will ensure peak wastewater flows during all but the most extreme storm events will be pumped from the Okara Pumping Station to Kioreroa Road Wastewater Treatment Plant for primary treatment.
During severe storms, more than 90 percent of wastewater received at the Okara pumping station is rainwater that has infiltrated the sewer system.
Council has an ongoing programme to trace infiltration points as one action in a five-pronged strategy to tackle wastewater overflows but it is anticipated that Whangarei's system, like all sewerage systems in the world, will continue to receive stormwater for the foreseeable future.
The first step in tackling Whangarei's wastewater issues is the key action of making sure the high volumes of diluted wastewater are pumped to Kioreroa Road and not spilled direct to the Hatea River and Whangarei Harbour.
Planning is well under way for the next stage, which is the upgrading of the plant to enable treatment of this greater volume of wastewater to higher standards. This will make Whangarei's sewerage system among the highest performing systems in the country.
One of the options considered at this stage includes the installation at the plant of high-rate filters and additional intensive bombardment of wastewater with UV rays to kill bacteria.
Council has also purchased a block of land in Kioreroa Road to extend the capacity to treat storm flows, with decisions yet to be made on whether the site will be used for increased storage or to extend the wetlands, which is the final stage of treatment.
Chief Executive Officer Mark Simpson said acquiring the block of land was a significant step toward Whangarei once again leading the country in the containment and treatment of wastewater.
"It future-proofs our system by allowing us extra options for the later stages in the upgrade of the city's wastewater system.
"We can build storage so we hold the diluted wastewater until it can be released to the treatment plant for normal treatment. This might mean there are odour issues to resolve, but they are not a major problem.
"Alternatively, we can use the land to enlarge the wetlands, which give treated wastewater its final polishing before it is released to Limeburners Creek.
"Each of these approaches is an effective method to cope with storm flows and dramatically reduce the risk of water quality in the harbour being compromised."
Mr Simpson said the options were being evaluated not just in terms of cost, but also in timeliness.
Residents had made it clear they were anxious to see the upgrade completed, so Council was intent on getting the right solutions in place as soon as possible.
Council has also already purchased property in Whareora Road for the establishment of storage facilities there to dramatically reduce the risk of spills from the Hatea pumping station.
How does Whangarei's sewerage system compare?
Auckland: More than 2000 overflows containing untreated wastewater from its network in 2008 alone.
Gisborne: Wastewater subject to primary treatment only is piped to sea only one mile out from the city's swimming beach. Now spending $39 million on a treatment plant.
Wellington: Until recent years, primary treated wastewater was pumped into Cook Strait on the outgoing tide.
North Shore: Has been suffering an average 12 wet weather wastewater overflows a year. Has a $235 million programme to reduce this to two a year by 2021.
Christchurch: An average 8 overflows per year led to an $80 million, 15-year programme to reduce overflows to one every two years.
Hutt City: Spending $21 million to clean up Waiwhetu Stream which receives storm overflows. Just given Wellington Regional Council approval to continue to send overflows to the stream for a further 15 years.
Whangarei: Has over a period of years averaged two wet weather overflows per year, but spending $13 million and aiming to reduce wet weather overflows to one in five years, and treating all storm flows to high standards.