Licence conditions for pollution studies and reduction program


Licence conditions for pollution studies and reduction programs

Licence number: 2647
Title: Pollution Reduction Program 12 - Wyong South STP Wet Weather Pond Remediation
Start date: 16 Oct 2021
Licence Condition
Background During the significant rainfall events of 2020 and 2021, the Wyong South Wet Weather Storage Pond (WSWWSP) overtopped due to the rate of inflow exceeding the capacity of the plant to store and pump to the outfall. The WSWWSP has no dedicated spillway, and the overtopping events resulted in uncontrolled discharges of treated effluent over the pond wall to downstream waters and subsequently to Ourimbah Creek. At the time of the discharges, the licensee notified the EPA of concerns regarding the structural integrity of the WSWWSP wall and in order to mitigate risk of failure, implemented emergency pumping to Ourimbah Creek to reduce levels in the WSWWSP and subsequently reduce the risk of wall failure. The licensee subsequently engaged an external consultant to investigate structural wall integrity and recommend mitigative actions. During implementation of the actions from that report, the licensee has identified that over the course of the life of the pond, biosolids have accumulated at the base of the WSWWSP which has created a reduction in depth and volume of capacity. The licensee proposes that removal of the accumulated biosolids will significantly increase the storage capacity for WSWWSP during wet weather events. This, combined with ongoing effective pond and reticulation maintenance, will provide increased capacity to manage repeat occurrences of the significant inflows experienced during the 2020 and 2021 rainfall events.  However, even with this increased capacity, modelling by the licensee has suggested other pond modifications may also be necessary. Deliverables The licensee must engage a suitably qualified and experienced person to investigate and provide a report containing a full scope of works and actions recommended to safely maximise storage capacity and safely deal with high volume inflows and outflows at the WSWWSP. The licensee must provide a copy of the report along with a plan of upgrade and remediation works and actions to the EPA's Director - Metropolitan North at by no later than Friday 30 April 2023. All works identified in the report must be completed by no later than 5pm Friday 29 December 2024.