At Tonkin + Taylor, we recognise the critical importance of managing water quality and addressing the potential impacts of climate change on On-Site Effluent Treatment (OSET) systems.

Our team undertook a comprehensive assessment for the Bay of Plenty Regional Council to evaluate these impacts, identify failure modes, and develop effective strategies for managing water quality in the face of changing environmental conditions.

The project involved thoroughly analysing the potential climate change impacts on OSET systems. We examined various factors, including the spatial distribution of receiving environments and the likelihood of adverse water quality effects.

By identifying the specific failure modes associated with climate change, valuable insights were gained into the challenges that OSET systems may have faced.

To ensure proactive monitoring and management of water quality, the team developed a robust conceptual groundwater monitoring programme for Bay of Plenty Regional Council to consider when developing new OSET provisions. This programme recommended the ongoing assessment of water quality parameters to help identify any emerging issues or trends. By closely monitoring groundwater quality, there is an ability to implement timely interventions and respond effectively to potential risks.

We also developed a set of trigger and response-based interventions to address water quality concerns associated with OSET systems. These interventions were designed to be proactive and adaptive, enabling timely action when specific triggers or thresholds were met. By implementing these interventions, we were able to identify approaches to mitigate potential risks and maintain optimal water quality standards.

Based on our findings and recommendations, we worked closely with Bay of Plenty Regional Council to recommend updates to the operative OSET Plan and incorporated the latest knowledge and strategies to manage water quality effectively in the context of climate change. By integrating new provisions and measures, we have developed an approach to ensure that OSET systems remain resilient and can deliver high-quality effluent treatment.


  • Climate change impact assessment on OSET systems
  • Conceptual groundwater monitoring programme
  • Trigger and response-based interventions
  • Potential new provisions for OSET plan updates for water quality management


  • Bay of Plenty Regional Council

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