How is the quality of the wastewater monitored to assess whether it is compliant with conditions of consent, and what is monitored?
When we monitor the discharge quality, we focus on the impact to the receiving waters of the Kāeo River. We collect samples monthly from two points, about 10 metres upstream and 15 metres downstream of the discharge point. We also do weekly samples at the wastewater treatment site itself.
We measure for several things (analytes), which includes discharge volumes, F-specific bacteriophage, pH, dissolved oxygen, faecal coliform, E.coli and ammoniacal nitrogen. Not everything we measure has a consent limit. Also, the frequency and timing of when we measure these is variable. This is because we are trying to compare the quality of the wastewater before and after treatment at the plant as well as comparing the river water quality upstream and downstream of the discharge. We are revising our approach to monitoring as part of our consent application, with the goal of improving our ability to gather good, comparable data.
The table below shows number of times the consent limit was exceeded on any of these, and what that figure is as a percentage of the total number of measurements taken in the 3-year period ending October 2021.
Analytes | Exceedances | Frequency |
Discharge volume (effluent) | 0 | 0% |
F-Specific bacteriophage[1] (influent & effluent) | 12 | 35% |
pH (downstream) | 6 | 15% |
Dissolved oxygen (upstream & downstream) | 0 | 0% |
Faecal coliform (upstream & downstream) | 1 | 3% |
E.coli (upstream & downstream) | 0 | 0% |
Ammoniacal nitrogen (downstream) | 2 | 5% |