In a move to safeguard public health, Gisborne District Council is investigating a study to examine viral persistence in shellfish following sewage overflows.
During extreme weather events, treated and untreated wastewater can enter waterways and potentially contaminate shellfish, causing a risk to human health.
At Tuesday’s wastewater management committee (WMC) meeting, members voted to proceed with a sampling programme as required by consent processes, working with Cawthron Institute to submit a revised draft methodology to the WMC for review.
The study is required by Wet Weather and Dry Weather Overflows Consent processes, and the sample collection span must be in a minimum of four locations, spanning rivers and coastal areas.
The council previously consulted with The Cawthron Institute in May 2022 and was given an estimated cost of $140,000 per wet weather event, which would sample at seven specified sites to detect various pathogens.
The council report said Cawthron outlined mussels as the preferred species for sampling and suggested four river spots - Taruheru River at Peel St Bridge, Waimatā River opposite Anzac Park, Turanganui River ( at the railway bridge), and one at the mouth of Tūranganui River.
The other three sites are marine-based, Kaiti Beach, Midway Beach at Stanley Rd, and a control site situated just west of Tuamotu Island, or an alternative control site could be Tuaheni Point, the report said.
Water manager Leo Kelso said an external expert within the relevant field must advise the methodology and the methodology must be in place by the next wet weather overflow event.
Kelso said one part of the study was setting the baseline and then measuring against that baseline after an overflow event.
The team looked at whether there were any pre-existing data within the council that could be used as a baseline and fell within the timing of a wet weather overflow event.
The report said, “Communication with the Ministry of Primary Industries (MPI) shellfish monitoring programme revealed that they conduct biotoxin testing weekly, but not virological or bacteriological assessments.”
Kelso said the recommendation was to go back to the Cawthron Institute and see if they could refine the proposal to bring the costs down to a more acceptable level or present different cost options for consideration.
It was possible to potentially work alongside MPI, he said.
Councillor Tony Robinson said he doubted there would be mussels in some of the suggested test areas.
“Maybe we should find out what shellfish consistently can be found in those spots, and say ‘hey, this is what’s there ... can that work with any methodology?’
“I’m conscious of the cost - $140,000 is not cheap.
“We’ve got to provide data for four sites. They are suggesting data for seven sites . . . that’s almost double.”
He suggested a good idea would be to find out the locations of the MPI test sites.
“If the DrainWise programme is successful we may struggle to get an overflow event,” he said.
Kelso said there were questions from the compliance team about any follow-up testing required within the consent processes.
Councillor Nick Tupara said the methodology should be passed through the tangata whenua reference group.
Kelso said this was possible.
Robinson said given the costs and that there was no assigned budget, it would have to “come out of standard kete and it needs to happen fast”.
“I would be talking to MPI and going back to Crawthron to try to renegotiate that methodology,” he said.
Kelso said the aim would be to have the methodology ready for review for the wastewater management committee’s next meeting.
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