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levels particularly high at St Leonards and the yacht basin. High sediment and pathogen load at the upstream site
at St Leonards is largely catchment driven, with livestock the likely source of most of the pathogens. By day 4,
Enterococci counts at most sites had returned to baseline levels, with the exception of North Esk River at
Inveresk and the yacht basin, and the Tamar Estuary at T2 Kings Bridge. It’s likely that these sites remained
elevated as the pulse of water from the North Esk catchment made its way downstream and into the upper
estuary. By day 5, all sites had returned to baseline (pre-rain) levels.
While only based on one event, this detailed event monitoring data appears to confirm what was previously
thought likely. That is, that a first flush of pathogens occurs in large rainfall events and the Upper Tamar soon
returns to pre rainfall pathogen levels.
Figure 8. Event monitoring data, September 2017
5.5
Peer review
Richard Roll, Environmental Engineer with GHD in Buffalo, New York State, spent a week in Launceston
providing specialist oversight of the treatment options considered. Richard has extensive experience directing
technical services for the City of Niagara Falls which has a combined drainage system and which has completed a
long term control plan to comply with combined system overflow reduction requirements (administered by the
US Environment Protection Agency).
Richard was able to bring a perspective of the regulatory environment in the USA, which provides the principal
driver for overflow reduction and environmental improvement. Specific improvement projects for specific
municipalities are determined by mandated water quality goals for their respective receiving waters. Typically,
municipal programs are composed of mixed measures such as runoff reduction, better collection system
maintenance practices, wet weather storage, conveyance enhancement, and treatment facility capacity
improvements. There are a myriad of combined sewer collection systems in the USA that are being brought into
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water quality compliance without the need for extensive separation programs, and with no plans to separate in
the future.
A frequent control measure in the USA involves constructing a deep tunnel system for active storage of excessive
wet weather flows while also transporting the stored volumes toward treatment facilities. It may also be possible
to reduce the number of outfalls and pumping stations depending upon tunnel routing. Exploring this possibility
with Launceston City Council’s environmental scientists and engineers led to a consensus that local soils,
particularly between the North Esk River and the treatment facility, are problematic and would discourage such a
measure. The scale of such projects also tend to make them rather expensive choices.
After considering Launceston’s service area, sewer collection system, treatment abilities and improvement goals,
Richard expressed his opinion that a well-planned scheme of additional wet weather storage, improved
conveyance to the Ti Tree Bend facility, and vigilant sewer maintenance practices presents a very good approach
to achieving the desired waterway impact(s). Extensive sewer separation, or a constellation of new wet weather
treatment facilities at remote locations, were not expected to be comparably efficacious solutions.
It is the Taskforce’s view that bringing an international perspective to investigations relating to the combined
system was very useful. It should be made clear that combined systems are accepted infrastructure in major cities
around the world. While separation of the two systems would be preferable, most cities have confronted the fact
that this is often extremely expensive, but of equal concern, requires complete upheaval to the foundations of a
city and also requires thousands of household front or back yards to be excavated to ensure pipes leaving those
properties are also separated.
For this reason, regulatory frameworks have often been established to ensure that there are moves to best
practice management and a driver for continual consideration of capital upgrade, noting that the United States is
just one country that has faced this problem and there are other countries, Europe in particular, that would be
worth exploring further.
5.6
Hard Infrastructure Findings
The multi-criteria analysis and preliminary examination 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 were the actions contained at points 6, 9 and 11 in Table 2 and include:
1.
The West Launceston Diversion;
2.
New Combined Rising Main;
3.
The offline storage located at New Margaret Street Pump Station;
4.
The offline storage located at Forster Street Pump Station;
5.
The South Launceston Diversion; and
6.
The offline storage proposed to service the Esplanade.
Each of these proposed projects are examined in detail below, including their expected cost and forecast
reduction in loading in sewage to the Estuary.