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Thursday, 17 April 2025

Latest treated wastewater test results remain well within consent limits

QLDC has today published the latest testing results from Shotover Wastewater Treatment Plant.

QLDC Shotover Wastewater Treatment Plant Mega Menu 500Px X 200Px Mar25

Queenstown Lakes District Council (QLDC) has today published the latest testing results from Shotover Wastewater Treatment Plant and data from multiple water monitoring sites on Shotover and Kawarau rivers, after direct discharge of treated wastewater to Shotover River began on Monday 31 March 2025.

The results for the treated wastewater sampled on Thursday 3 April remain well within consented limits set by regulator Otago Regional Council (ORC):

  • E. coli levels were below 10cfu (colony-forming units) per 100ml (10cfu being the lowest concentration that can be reliably measured)

  • Total suspended solids were 11.7mg per litre

* QLDC’s consent limit for E. coli requires a geomean and a 90th percentile of less than 260cfu/100mL, and for total suspended solids an annual mean and 95th percentile of less than 30mg/L and 50mg/L respectively.

* Percentile means the percentage of results that need to be below the upper test limit (i.e., 90th percentile means 90% of results need to be below the limit, etc).

QLDC Infrastructure Operations Manager Simon Mason said the results continued to reflect a well-performing treatment plant.

“These samples are taken after the last treatment process at the facility where UV disinfection occurs, immediately before the treated wastewater is discharged from the facility,” said Mr Mason.

“Samples from the discharge channel or from within the Shotover and Kawarau rivers are not a reliable indicator of the actual quality of the treated wastewater, as they can be affected by external factors unrelated to the facility itself. However, we are monitoring these locations to ensure we have a full understanding of any potential effects of the discharge on these environments.”

Water samples from sites on Shotover and Kawarau rivers have been tested for E. coli concentrations (along with other parameters) to determine what effect the discharge is having on the receiving environment. Findings include:

  • As of 10 April, E. coli levels were measured at 18.7cfu (colony forming units) per 100ml approximately 50 metres downstream of the discharge channel, well within the nationally accepted safe levels for contact recreation of 260cfu/100ml.

  • In Kawarau River downstream of the confluence with Shotover River and adjacent to Shotover Country, E. coli levels were most recently measured at 39.9cfu/100ml.

Mr Mason confirmed that while testing reflected some initial increase in E. coli levels associated with the start of the discharge, these results had returned to baseline levels quickly.

“It’s likely the discharge of treated wastewater through the channel initially collected organic matter, which has since normalised following the initial flush,” said Mr Mason.

“E. coli within the receiving environment will always fluctuate over time and can be affected by wildlife sources in the catchment, especially after rainfall events that generate run-off.”

A resource consent application has been lodged with the ORC to enable works within the riverbed to be completed to provide for a significant flowing braid in close proximity to the discharge point to improve mixing of the treated wastewater into the river.

ENDS | KUA MUTU.

Media contact: communications@qldc.govt.nz or call 03 441 1802.

FURTHER INFORMATION | Kā pāroko tāpiri:

Compliance sample results (Thursday 3 April): https://www.qldc.govt.nz/media/aunfzd1h/ar-25-nc-010135-02.pdf

River monitoring data as of Thursday 10 April: https://www.qldc.govt.nz/media/fw2nv35s/qldc_shotover-wwtp-monitoring-results_apr25.pdf

Map of river monitoring sites: https://www.qldc.govt.nz/media/fznnva11/qldc_shotover-wwtp-monitoring-map_apr25.pdf

Why we test for E. coli

E. coli is a type of bacteria commonly found in the intestines of warm-blooded animals, including people.

They’re a useful indicator of whether bacteria, viruses, or protozoa (single-celled parasites, like cryptosporidium and giardia) that can make people sick are present in soil and freshwater.

Land Air Water Aotearoa (LAWA) information on recreational water monitoring: https://www.lawa.org.nz/learn/factsheets/can-i-swim-here/coastal-and-freshwater-recreational-monitoring

For a summary of the current situation and a comprehensive list of FAQs visit: www.qldc.govt.nz/shotoverFAQs

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