Whangarei District has had no harbour closures due to sewage spills following storms since 2012 and has achieved this result at a total of $24m.
In the past, storm water and groundwater flowed into the District’s sewer system during major rainstorms and a mix of storm water and untreated sewage overflowed into the environment. That is not the case any more.
“In 2008 the community told us loud and clear that that kind of closure was unacceptable and we needed to fix the system," said Council Waste Water Manager Andrew Carvell.
“We asked what the community really wanted – was it to prevent storm water from getting into the waste water system and causing untreated overflows (at a cost of around $200m), or was it being able to rely on a clean harbour and still be able to fish, gather shellfish and swim after storms?
“The people wanted a clean harbour, so we looked at how to achieve that. Rain runs to the lowest point in any system, and ultimately to the sea. We could not realistically keep it out of our sewerage system, but we found we could make sure it was held, treated and controlled, rather than discharged untreated as it had been in the past.
“We sought advice from tangata whenua, the Northland Regional Council, Northport and contracted local engineers and branches of construction firms including United Civil Contractors, Fulton Hogan, Downers and Hydrotech.
“We worked together with a single goal in mind – a clean, safe harbour water, fish and shellfish after storms and we achieved the result we, and the community wanted.
“We looked at ways to prevent the storm water getting into the sewer system and the price to achieve that would have been about $200 Million. Our community could not afford that, so we decided to expand our sewer system and build new facilities to hold it and treat the huge quantities of wastewater going into it. That way we could control the water that discharged into the environment and make sure it was very clean.
“We have also reorganised our network to reduce sewage spills at specific spots. Since this work was done we have had no harbour closures associated with sewer overflows and we have had a steady improvement in customer satisfaction.”
“As a result of our $24m programme of projects the risk to public health from sewer spills in wet weather has largely been addressed with key overflow sites eliminated or the bacterial discharge reduced by more than 99.9%.
“The last major work in the series is the overflow tank at Tarewa Park (Tarewa Tank). It includes a 650m3 storage tank and an ultraviolet disinfection system, to hold and treat the water that comes into the system during big storms.
“Other projects have included pipeline renewals and upgrades and improvements to the sewer treatment and disposal systems.