Queenstown Lakes District Council (QLDC) has today published test results from treated wastewater discharged from its Shotover Wastewater Treatment Plant (WWTP). They are the first test results following the start of direct discharge of treated wastewater into the Shotover River that began on Monday.

The results, which can be found on the QLDC website, were 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); this compares to QLDC’s consent limit which requires a geomean and a 90th percentile* of less than 260cfu/100ml, and the nationally accepted safe levels for contact recreation (also at 260cfu/100ml).
• Total suspended solids were 14mg/l compared to QLDC’s consent which requires an annual mean and 95th percentile* of less than 30mg/l and 50mg/l respectively.

* meaning the percentage of results matching a specific ‘percentile’ that need to be below the upper test limit (i.e. 90th percentile mean 90% of results need to be below the limit, etc).

QLDC Infrastructure Operations Manager Simon Mason said the results reflected a well-operating treatment plant.

“For compliance purposes we test samples taken immediately downstream of the last treatment process within the plant, in this case the UV disinfection step. Any sampling completed further along the water’s journey to the river are not reliable indicators of the actual treatment performance given they can be affected by external factors unrelated to the functioning of the plant. For example, animal faeces such as from birds and dogs are known to cause spikes in E.coli readings.”

“However, in light of the discharge directly to the river, we will now be undertaking monitoring upstream and downstream of the discharge point to ensure we have a full understanding of any effects of the discharge. These results will be shared with ORC as regulator and made publicly available on our website. Typically, these tests are processed in around two weeks by the external lab.”

Mr Mason confirmed that onsite testing of the treated wastewater is historically conducted daily, and that this would continue under the new discharge regime.

“These onsite tests are indicative of operational performance in that they would quickly show if there were any issues with the quality of wastewater at the end of the treatment process. However, we also send samples to an external laboratory for analysis on a weekly basis. Compliance results are shared with ORC (as regulator) on a monthly basis in accordance with the conditions of our existing resource consent,” he said.

Notes:

• For a summary of the current situation and a comprehensive list of FAQs visit: Short term approach for managing wastewater discharge | Queenstown Lakes District Council
• Previous media releases:
  • 30 March 2025; Direct discharge of treated wastewater into Shotover River to commence on Monday morning: https://www.qldc.govt.nz/2025/march/25-03-30-direct-discharge-of-treated-wastewater-into-shotover-river-to-commence-on-monday-morning/
  • 21 March 2025; Update on Shotover Wastewater Treatment Plant: 25 03 21 Update on Shotover Wastewater Treatment Plant | Queenstown Lakes District Council
  • 13 February 2025; No treatment process failure at Shotover Wastewater Treatment Plant: https://www.qldc.govt.nz/2025/february/25-02-13-no-treatment-process-failure-at-shotover-wastewater-treatment-plant/
  • 17 January 2025; Statement on Shotover Wastewater Treatment Plant (WWTP): https://www.qldc.govt.nz/2025/january/25-01-17-statement-on-shotover-wastewater-treatment-plant-wwtp/
  • 19 November 2024; Update on Shotover Waste Water Treatment Plant: https://www.qldc.govt.nz/2024/november/24-11-19-update-on-shotover-waste-water-treatment-plant/
• To watch a recording of the onsite media stand-up on Wednesday 26 March visit: https://youtu.be/IQhwkhFjkjU?si=kpfvRk7ypTSEgaSd

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