Indicators 2.6.19–2.6.21

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System

Water Type

Feed Dependent

Species

Indicators 2.6.19–2.6.21

by Contact on 8 October 2026

Requirement

The UoC shall conduct monitoring of DO concentration and DO saturation, following the method outlined in Appendix 8 (8.11).

The UoC shall demonstrate that the weekly average of daily DO saturation is ≥65% in freshwater and ≥70% in seawater.3535Waterbodies with salinity levels 30-49 ppt (parts per thousand) shall be considered as seawater for this Indicator.

The UoC shall demonstrate that ≤5% of the weekly averages of daily DO concentrations are <2mg/l. An exception applies if the UoC cannot demonstrate this, in which case the UoC shall: – Demonstrate ≥70% saturation by conducting continuous monitoring using an electronic probe and recorder with a 15-minute sampling frequency for at least one week; or, – Ensure percentage saturation results are consistent with results from an ‘upstream, near-field’ non-impacted reference location, at least 500m upstream of the site.

How Do I Interpret This Requirement?

  • For both diffuse-source and point-source effluent releases, the UoC should monitor and record percent saturation of DO.

  • All measurements should be taken using a calibrated oxygen meter or equivalent method.

  • The percent saturations should then be calculated based on the monitoring data.

  • The analytical methods for DO sampling can be found in Appendix 8 (8.12).

  • Any missed samples or deviations in sampling time should be accompanied by a written justification.

  • The UoC can measure DO concentration and saturation immediately downstream of the last site in a waterbody whilst still following the sampling method in Appendix 8 (8.11).

  • This may reduce sampling costs when there are multiple sites discharging point source effluent releases to a Type B waterbody near each other.

Evidence of Implementation

  • The oxygen meter has been calibrated according to the technical specifications.

  • Records of measurement locations, demonstrating monitoring took place immediately downstream from the outflow point, or in the receiving waterbody downstream from the site for diffuse source releases.

  • Records of daily monitoring of DO concentration and saturation, which result in weekly averages of daily DO saturation.

  • ≤5% of the weekly averages of daily DO concentrations are 2mg/l.

  • Written justifications are maintained for any missed samples or deviations in sampling times.

Auditors Should Confirm

  • The UoC has calibrated the oxygen meter according to the technical specifications.

  • Measurement locations were immediately downstream from the outflow point, or in the receiving waterbody downstream from the site for diffuse source releases.

  • Weekly averages of daily DO saturation are presented by the UoC and that the averages are ≥65% for freshwater and ≥70% for seawater.

  • The UoC has presented evidence that ≤5% of weekly samples fall under 2 mg/L DO.

  • Written justifications are provided for any missed samples or deviations in sampling times.