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balanced the needs of stakeholders and customers, and that met
environmental, social, and project objectives’.
The key to success in these projects is achieving customer
confidence, and individual customer home plans were created for
every property to ensure that the design could translate to the
customer’s property. This was particularly important to understand
the customer’s needs and preferences in order to mitigate
construction and operational impacts wherever possible.
The Alliance created unique design solutions to suit local conditions.
For the Bargo Buxton Scheme, a design change driven by several
factors, such as cost, community feedback and environmental
impacts, led to the design and installation of a wastewater transfer
main system to achieve a gravity feed over 14 kilometres.
‘The gravity system removed the need for treatment and pumping
stations, saving as much as $10 million in additional infrastructure
and energy costs. The design allowed Sydney Water to remove
the proposed sub-surface irrigation wastewater treatment plants
and meet the requirements of the local communities, who were
opposed to the placement of wastewater treatment plants
throughout the villages,’ says Marrone.
The design significantly reduced the use of electricity to run the
pumping stations and water recycling plants, and it significantly
lowered maintenance requirements. As a preferred construction
option, horizontal directional drilling (HDD) also reduced
environmental and community impacts.
Ashley Jagoe, Manager Major Projects, Sydney Water, says, ‘Given
the relatively small diameter of the wastewater transfer pipeline,
HDD provided a significant cost benefit not only in construction,
but also by eliminating any restoration required between the
launch and receipt points.
‘A total of almost nine kilometres of transfer main installed via
HDD in Bargo/Buxton meant that road restoration, spoil disposal
and vegetation clearing was kept to an absolute minimum. Using
HDD avoided high points along the pipe alignment, minimised
impacts around schools, mine sites and commercial premises, and
protected environmentally sensitive and endangered ecological
communities, along with heritage sites,’ he says.
The design of the Bargo Buxton transfer main pushed the
boundaries of using gravity to move wastewater long distances
An oversized pipe was constructed at the head of the Bargo
Transfer Main that served as in-line storage. This would essentially
allow the gravity system to behave in a similar fashion to a
pressurised wastewater system with pumping stations.
There were challenges in maintaining the hydraulic profile, as the
elevation difference between the villages is around 50 metres,
and the topography along the Buxton alignment included a rise
of about five metres. These factors would have required the
remaining gravity section to be constructed at a much greater
depth to achieve the required performance.
The solution to this challenge was to use an 800-metre inverted
siphon to minimise the transfer main depth at Buxton. It also
included around three kilometres of the upper section of the
Buxton transfer main being built on-grade, until it reached the
operating level in the Bargo in-line storage pipe. Barometric
loops were installed at the start of each transfer main to keep the
reticulation system pressurised.
The inverted siphon designed successfully for Bargo/Buxton as
part of the process to address the topography challenges can now
be used anywhere on the Sydney Water network.
The Priority Sewerage Program is a valuable case study of
successful collaboration between Alliance partners, the community
‘Retrofitting wastewater systems in established communities has
been a key challenge, but effective community consultation and
planning minimised disruption during the construction phase,
resulting in outstanding community satisfaction,’ says Jagoe.
Thousands of customers on Sydney’s fringe now have the benefits of
a new wastewater system, which has provided a significant range of
benefits to individual households and local communities in general.
THE KEY TO SUCCESS
IN THESE PROJECTS IS
HOME PLANS WERE
CREATED FOR EVERY
PROPERTY TO ENSURE
THAT THE DESIGN COULD
TRANSLATE TO THE
THE PRIORITY SEWERAGE
PROGRAM IS A VALUABLE
CASE STUDY OF SUCCESSFUL
THE COMMUNITY AND
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