Selwyn residents believe waste from the Pines Treatment Plant is polluting their groundwater. Photo: RNZ
Concerned Selwyn residents say nitrate levels in their drinking water are being pushed up by human effluent spread on fields near their homes.
The residents believe waste from the nearby Pines Treatment Plant is seeping through the rocky soil and polluting their groundwater.
Several years of testing by residents, Lincoln University students and Greenpeace have shown consistently high nitrate levels.
More recently, testing at a number of local wells in May last year showed not just high concentrations of nitrate-nitrogen - in some places over and above the legal maximum allowed in drinking water - but also "a small but significant concentration of fluoride."
Bethels Road resident Brian Patchett said the residents have been informed the fluoride is most probably coming from human waste.
He said nearly 50 of his neighbours had signed a letter to the council they planned to deliver at Wednesday's Selwyn District Council meeting, demanding a sit down with the district council and Environment Canterbury.
They want a detailed outline of how the treatment system works, and how it is anticipated it will cope with the extra sewage as the scheme is expanded to nearby Leeston and Southbridge, as well as test results of the treated effluent.
The residents also want a commitment that no more sewage will be brought in from outside the originally designated area.
But Patchett said what they most wanted to hear was how the two councils planned to improve the quality of their well water.
He acknowledged many people across the region were already dealing with high nitrates from agriculture, but the sewage was compounding the issue, leaving them with a "double dose".
Many residents have installed expensive filters, dug deeper wells - only to find no reduction in nitrate concentration in some cases - and set up water-distilling and rainwater collecting systems, he said, expensive measures to fix a problem not of their making.
The Pines Wastewater Treatment plant was constructed in 2012 originally with an 80 hectare area for treated wastewater to be sprayed on and capacity for a connected population of 6000.
But the town of Rolleston alone now counts on around 30,000 residents, the Selwyn District is the fastest growing in the country.
Modular additions have seen the plant expand to service a population of more than 42,000, and the area irrigated had grown to 245 hectares.
Selwyn District Council modelling suggests that by 2053 the Pines could be serving more than 117,000 people.
Otago University research fellow Marnie Prickett said she was not surprised at the levels of concern among the residents.
"The history of the situation in Canterbury is that the councils - and particularly Environment Canterbury, which is responsible for regulation - has failed again and again to protect people's drinking water, to the point that we now have a quite an extreme situation where 10 percent of water sampled there already breaches our drinking water limits."
"The community has a right to be worried and angry."
She said sewage irrigation could be effective when it was done well, but it depended on the location and vulnerabilities of each site.
While Prickett did not have the full details of the Pines scheme, she said there could be issues given Canterbury's very stony soils.
"Nitrate pollution in particular very easily moves through that soil and down into the groundwater."
Prickett said the residents were caught in a "huge gap" in the way councils treated private bore users, which they said were outside of their ambit.
"I would say that's a really irresponsible position to take because Environment Canterbury is responsible for the quality of groundwater generally speaking.
"It has been responsible for maintaining or improving water bodies since 2014, when that clause came into freshwater policy, and there's been other laws that would have allowed them to protect people's groundwater.
"It's a case of regulatory failure, and they've allowed for people's once potable water now to become undrinkable."
She wanted to see Environment Canterbury treat the situation with more urgency.
"I think ECan needs to have a moment of admitting that they have made some major mistakes around how they've managed people's drinking water - or not managed it in this case.
"They need to do some urgent evaluation of why the rules they have in place aren't working to protect drinking water, and they need to stop giving the public the impression that we just have to wait because things will get better in 20 years - we can see there are decisions being made even now that will contribute to the situation in some places getting worse."
When public necessities like water were not protected, people were left to navigate the cost and risk alone, she said.
Brian Patchett agreed, saying the councils' position they aren't responsible for the safety of private wells made no sense given well owners could not control what councils allowed to go into groundwater, he said.
"It's just so counterintuitive when there's absolutely nothing we can do about it."
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