Evaluating Environmental Impacts of Combined Sewer Overflows on the Tamar River

TasWater operates a combined sewerage system that services the greater Launceston area in northern Tasmania. The operation of the system is of interest to the local community and key stakeholders, who are concerned that the performance of the system is having significant impact on the receiving environment.

This paper discusses the development of a long-term strategy based on understanding the frequency, extent and environmental impact of overflows relative to other continual or intermittent discharges. Following initial data gathering and stakeholder engagement, the evaluation criteria established were:

• Responsibility to the community
• Public health
• River health
• Public perception

A long list of upgrade options was assessed at a high level against these criteria; four options were shortlisted. Each option addresses different stakeholder concerns at varying levels;

• Screening of overflows to reduce the visible material discharged.
• Provision of storage within the network to reduce the frequency and volumes of spill.
• Sewer separation to provide a new wastewater system, and converting the current combined network into a stormwater network.
• Conveyance / consolidation solutions to either consolidate existing overflows, or to direct the overflows to less sensitive receiving environments.

Each option has been assessed against the sub-criteria and concept costs were established.