ECOLOGICAL RISK ASSESSMENT OF WASTEWATER DISCHARGES
INFORMING SENSIBLE OUTCOMES
A Laidlaw, J Day, J Mullins
Publication Date (Web): 8 April 2016
North East Water implemented an ecological risk assessment (ERA) program for wastewater treatment plant (WWTP) discharges in 2008. The aim of an ERA is to use science to determine the level of risk that a wastewater discharge may pose to a receiving waterway. This evidence is then used to inform management decisions, such as treatment upgrades or amendments to discharge licences. An ERA was conducted for North East Water’s Beechworth WWTP and is provided here as a case study of a successful ERA.
The Beechworth WWTP discharges treated wastewater to a nearby waterway and has historically breached the discharge licence limits set by the Victorian environmental regulator, the Environment Protection Authority (EPA). The discharge licence for Beechworth WWTP was issued by the EPA in 1975 to the then Beechworth Sewer Authority. The licence limits were arbitrary, unchanged since 1975 and had never matched the actual performance of the WWTP. In 1997, the licence was transferred to the newly formed North East Water.
The Beechworth WWTP is located in a sub-alpine area that experiences cold, wet winters and hot, dry summers. Discharge typically occurs during the cooler months of the year when nitrification in the lagoons is limited. No ammonia-nitrogen is removed when the lagoons reach a temperature of 15°C or less.
North East Water had been in discussions with the EPA for nearly a decade to resolve issues relating to the Beechworth WWTP discharge non-compliance. These conversations were steering towards an expensive mechanical plant solution in the region of $6 million. A major infrastructure upgrade was planned to meet discharge compliance when North East Water was invited by the regulator to participate in a pilot ERA in 2008 under EPA’s Draft Guidelines for Risk Assessment of Wastewater Discharges to Waterways.
The four key stages of EPA’s risk assessment framework.
The EPA’s risk assessment framework consists of four key stages. Catchment stakeholders were included at each stage of the process. Beneficial uses and values were initially identified. These are aspects of the water environment that the community wants to protect and can include not only ecological values, but also social, health, cultural and economic values. Stressors contained in the discharge and their interactions with these values were also identified. Data was collected over a number of years to investigate the value/stressor relationships. This included water quality monitoring, biological assessment and algae monitoring.
The eventual findings of the ERA indicated that the discharge had minimal impact on the values of the receiving waterways. North East Water worked closely with the regulator to utilise the outcomes of the ERA to amend the discharge licence and commit to continual environmental improvement. The outcome has resulted in the WWTP meeting discharge compliance for the first time in 40 years. The ERA process was unprecedented and at times challenging, but demonstrated that an evidence-based approach can achieve an outcome that is agreeable to all parties, including the environment and North East Water’s customers.
North East Water has since completed ERAs for seven other WWTPs that discharge to waterways. Outcomes from these include licence amendments and planned capital upgrades. Additionally, ERAs have also commenced for WWTPs that may discharge during periods of wet weather. The outcomes of these will assist to inform arrangements for emergency discharges or application for discharge licences.
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