December 2017 Tamar Estuary
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- Treatment option High level description
Tamar Estuary River Health Action Plan 2
to minimise input of faecal matter into tributaries, while improved effluent management practices in dairies and the implementation of riparian zones on grazing properties were also assessed to have good potential for pathogen load reduction. The Macquarie and North Esk catchments are the focus of these actions and build on the significant success NRM North have had in addressing these challenges in the Meander catchment. With respect to the urban catchment actions, the WQIP 2015 had focused on water sensitive urban design (WSUD), but it was found that these actions don’t provide great benefit for cost when looking at pathogen load reduction. Instead action options in the urban area turned to focussing on removing cross connections from separated sewerage and stormwater systems, where recent programs by Launceston City Council had been shown to deliver good reductions in sewage load during overflow events. Three different investment budgets, $2 million, $5 million and $10 million, were considered and a series of actions allocated for each budget amount. The chart below shows the expected reductions in pathogen, nutrient and solids concentrations in the Launceston to Legana zone (Zone 1) at the various investment levels. The far right of the chart includes the benefits possible from a full investment of all the programs initially considered by the Working Group ($117 million). The findings show that there are significant benefits in reducing Zone 1 pathogens that cause a threat to public health (i.e. enterococci) for relatively small investments. It is the Taskforce’s view that a $10 million investment in catchment actions would be preferable and deliver around 80 per cent of what is possible for the full $117 million of initially considered actions. Tamar Estuary River Health Action Plan 3
The Combined System Overflow Working Group leveraged off work already commenced by the Launceston City Council to build a detailed hydraulic model of the combined system. The model allowed a better understanding of how the network functions in various levels of rainfall event and through this greater detail became known about where the majority of overflows from the system occur. The Group then shortlisted a number of possible mitigation treatments (captured in the table below).
7.
Legislation, regulation and policy improvement Changes to the legislative and regulatory environment to incentivise continuous improvement of the combined system 8.
and education Ongoing monitoring of river health to facilitate continuous system improvement, education streams and warnings in the event of an overflow 9.
improvements and system optimisation Review existing operational environment of the combined system to ensure existing infrastructure is operating efficiently and effectively (i.e. Margaret Street Detention Basin and weir levels at CSO locations) 10.
(primarily WSUD treatments) Develop the framework required to transition from "traditional" drainage systems to WSUD drainage systems including detention, wetlands, ponds, bio-filtration systems and infiltration systems to decrease runoff frequency, volume and peak flow. Green infrastructure would also be considered for the immediate mitigation options 11.
Screening, preliminary treatment and/or Installation of screening and chemical treatment facilities at the 3 key CSO locations
Tamar Estuary River Health Action Plan 4
disinfection at CSO locations
12. Offline storage Underground storage tanks located at the key CSO locations 13.
Live storage Storage within the existing system, requiring baffles, weirs, actuators at the 3 key CSO locations
14.
Separation Full separation of the combined system and construction of a separated sewer and stormwater network 15.
sewage catchments Diversion of the West Launceston and South Launceston trunk sewerage mains directly to the Ti Tree Bend STP
16. Diversion of separated stormwater catchments Construction of required stormwater drainage components to enable direct discharge to the Estuary at Margaret Street
17. System upgrade i.e. additional combined rising main to Ti Tree Bend and reconfiguration of network components Increase the pump rate to Ti Tree Bend for the key CSO locations 18.
movement of discharges further downstream. Pump combined discharge further downstream to where the Estuary widens and dilution is increased
A multi-criteria analysis and preliminary examination of these treatments led to a shortlisting of six “hard” infrastructure projects as being the most feasible in terms of their practical delivery and expected return on investment as measured by reduction of sewage loading to the Estuary. These projects were: 1.
The West Launceston Diversion – a diversion of the separated sewerage catchment that currently joins the combined system at the Margaret Street pump station (and therefore which can then be overflowed to the Estuary in higher rainfall events) and instead extend the trunk main directly to Ti Tree Bend sewerage treatment plant; 2.
pumping rates and adding a new combined rising main to Ti Tree Bend to accommodate the increased flows;
3.
An offline storage located at New Margaret Street Pump Station – a project to provide a storage to capture the “first flush” sewage that would otherwise spill straight to the Estuary in higher rainfall events, that can then be bled back into the system and receive treatment at Ti Tree Bend; 4.
5.
The South Launceston Diversion – similar to project 1, this project would see the separated sewerage catchment that joins the combined system at Shields, Tamar and Willis Streets being redirected to a new pump station and sent straight to Ti Tree Bend; and 6.
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