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River Health Action Plan
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The last storage is proposed to be underground in the vicinity of Black Bridge and Boland Street (near to the
Esplanade) and would nominally be 3.0ML. It is estimated to cost $6.7 million ($7.6 million total present cost) and
would reduce sewage load by approximately 9 per cent.
It should be noted that these reductions in load are predicated on the storages being empty before rain events.
The South Launceston Diversion
Under dry weather flow conditions, the sewage flows from the catchments associated with the South Launceston
trunk sewer are directed to Ti Tree Bend STP, however under wet weather conditions, a series of Combined
System Overflow Pump Stations (at Shields, Tamar and Willis Streets) lift sewage contaminated stormwater over
the levee banks into the North Esk River to minimise the risk of flooding to the lower level areas of Launceston.
The intention of this project would be to reduce the sewage component of the discharge to the Estuary from the
pump stations located at Shields Street, Tamar Street and Willis Street by diverting the flow via a new rising main
direct to Ti Tree Bend.
In order to facilitate this mitigation option, a variety of works will be required to upgrade the sewer system
between Hoblers Bridge Road and the Ti Tree Bend STP. In summary, the works required include:
Diversion of the South Launceston trunk sewer to a new pumping facility in the vicinity of Black Bridge and
Boland Street;
Diversion of the Boland Street SPS rising main to the new
pumping facility;
Installation of a new transfer main between the proposed pumping facility and Ti Tree Bend STP; and
Connection works at Ti Tree Bend.
The construction of the rising main to facilitate this diversion will enable the connection of the separated sewer
catchments located in the Inveresk precinct. With significant development imminent due to the relocation of the
University of Tasmania's Launceston campus, the potential to convey sewage flows from the precinct directly to
Ti Tree Bend STP will reduce the sewage loading at Forster Street and therefore; the volume of sewage ultimately
discharged to the Estuary during wet weather flow conditions.
The capital cost of this project is estimated at $18.1 million (total present costs of $22.4 million) and is expected
to result in a reduction in loading to the Estuary of approximately 13 per cent of current load. It should be noted
that the proposed route of construction for the trunk sewer diversion would likely require much upheaval
through Launceston’s eastern suburbs and as such would need careful management. This project is also potentially
part of the LSIP strategy.
Decreased loading in context
To put these loading reductions in some further context, the pump records for the New Margaret Street Pump
Station indicate that a CSO to the Estuary from this location occurred on approximately 50 days during the
period of 1 January 2017 – 10 October 2017. Based on theoretical pump rates, 60 per cent of these overflows
were of magnitude 5ML or less (please note, these overflow volumes do not include volume of discharge from the
Old Margaret Street pump station). With the proposed 4.2ML holding tank and increased pump rate to Ti Tree
Bend, it is likely the frequency of CSO at this location will more than halve.
Tamar Estuary
River Health Action Plan
36
Furthermore, the modelling showed a significant percentage decrease in the sewage loading to the Estuary in the
more frequent events (i.e. rainfall of a level that occurs 12 events per year or more). The reduction of sewage
loading discharged to the Estuary by events of magnitude 12EY or more totalled approximately 85 per cent.
5.7
Regulatory and “Green” Infrastructure Findings
Overflows from Launceston’s combined sewage and stormwater system are not subject to the conditions
contained within the Ti Tree Bend STP’s Environment Protection Notice. The Department of Primary Industries
Parks Water and Environment’s Sewage Pumping Station Environmental Guidelines 1999 recommend that every
effort should be made to minimise the impact of combined overflows, however the guidelines have no legal force.
It would appear that the combined overflows are outside the statutory framework, other than section 23A of the
Environmental Management and Pollution Control Act 1994 where overflows could be called in under the general
environment nuisance provisions.
The working group found that changes to the legislative and regulatory environment could be made to incentivise
works within the combined system to reduce the environmental harm caused by discharges to the Estuary. Given
an appropriate regulatory environment appropriate goals, objectives and strategies could be identified for the
combined system.
In order to decrease contaminants entering Launceston's waterways, a review of legislation, regulations and policy
is recommended. It is best practice throughout the western world to regulate combined system overflows with
conditions such as:
Elimination of CSOs during dry weather.
Pollution prevention programs to reduce containments in CSOs.
Public notification to ensure that the public receives adequate notification of CSO occurrences and impacts,
and the location of CSO outfalls.
Minimise or eliminate solid and floatable materials' discharge to the receiving environment from CSOs.
Improved operation and regular maintenance programs for the sewer system and CSO outfalls.
Maximum use of the collection system for storage.
Maximise flow to treatment plants.
Accurate and timely reporting of all CSO events, including date, time, location, and quality and volume of
the effluent discharged, including discharge from gravity overflows.
Review and modification of pre-treatment requirements to ensure that CSO impacts are minimised.
Ambient monitoring to effectively characterise CSO impacts and the efficacy of CSO controls.
These frameworks need not need to go as far as prescribing the load or concentration of overflows, but instead
ensure that the asset owner or service provider is moving towards best possible practice and optimising the
whole system for the benefit of the Estuary.
Other potential benefits of legislative or regulatory acknowledgement of the combined system is, in the context
of a $400 million plus cost to fully separate the system, is that it legitimises the system’s existence and changes
the conversation from “third world infrastructure” to “permissible infrastructure that exists in other modern
cities throughout the world.