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Alliance Group last year applied to renew applications to take water for processing purposes from and into the Mataura River.
It also asked to use an existing weir to dam and divert water.
On day two of a three-day hearing, questions from commissioners
raised queries over the completeness of data used in the company’s application evidence.
The Mataura River is classified as degraded, based on E.coli and dissolved inorganic nitrogen levels.
Commissioner Sharon McGarry said there was a gap in upstream sampling of water quality.
She was told that while it was possible to sample, it was a challenging section of river, from a health and safety perspective.
In terms of human health risk, the company’s evidence states there was a significant increase in E.coli downstream of the plant, but it was explained this did not correlate with risk from pathogens.
Alliance witness Dr Chris Dada recommended more pathogen sampling be done by the company to dispel any uncertainty.
A comprehensive monitoring programme had also been recommended.
However, Dr Dada said even in the worst case scenario of low river flow and peak wastewater discharge, treatment of the discharge water under current consents was enough to reduce risk to swimmer health downstream of the plant.
He also endorsed the planned plant upgrades to be made as soon as possible.
These included ultra-violet treatment that would reduce the levels of E.Coli.
Alliance witness Azam Khan said while alternative options to the consent activities were investigated, they were considered less feasible.
"Storage has got its own set of challenges."
However, he said opportunities may arise in the future to discharge on to land with well drained soil.
After all Alliance evidence was heard, there would be one person speaking to their public submission and evidence from Environment Southland.
The hearing will continue today and a decision must be made within 15 working days after the hearing closes, unless further information is requested.
The decision was not expected this year.