Page 3898 - Week 11 - Thursday, 24 November 2022

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Molonglo River—sewage

Mr Rattenbury (in reply to a question and a supplementary question by Ms Lawder and Mr Milligan on Tuesday, 18 October 2022):

During recent rain events, the Office of the Environment Protection Authority (EPA) received notifications from Icon Water indicating that, due to significantly increased inflows, the Lower Molonglo Water Quality Control Centre (LMWQCC) released partially treated effluent from the bypass storage dam. These overflows were not treated to a maximum capacity. However, the overflows were partially treated and consistent with the Environment Authorisation (EA) approved Environment Management Plan associated with the LMWQCC.

Routine water quality testing indicated that the LMWQCC remained compliant with the conditions of the relevant EA, as indicated below –

LMWQCC Effluent results

EPA Licence Result Summary August 2022

August 2022 – 100% Compliance

EPA Licence Result Summary September 2022

September 2022 – 100% Compliance

Based off previous sampling and similar events, the EPA considers that the high volume background flows from persistent rain, as well as the partial treatment of the effluent, would have provided significant dilution and therefore mitigated environmental harm.

The EPA understands that the LMWQCC was operating at full capacity during these events and was not aware of any equipment being ‘offline’.

The following table has been supplied by Icon Water as part of their reporting on this event and EPA analysis is provided.

It shows that the treated volumes during the recent peak rain events were about twice the Average Dry Weather Flow (ADWF), at 150 to 198 ML/day compared with a current average of 100ML/day. This suggests an additional 50-98 ML/day associated with the wet weather. The key outlying of peak instantaneous flow is also worth noting, and is likely to have been a key feature driving overflows. The difficulty of emptying ponds between consecutive rain events is also a challenge, not just in the ACT but across much of Australia. The EPA is actively engaging with Icon Water to support efforts to reduce the risk of overflows, noting that such efforts require considerable lead times and financial investments.

(A copy of the attachment is available at the Chamber Support Office.)

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