he Dudley Charlestown system transports wastewater from the Dudley Charlestown catchment to the Burwood Beach Wastewater treatment plant. This trunk main was part of the Hunter Water upgrade management plan for the Dudley Charlestown upgrade project, which involved abandoning the Kahibah 1 wastewater pump station.
Hunter Water awarded Kembla the contract to convert the existing gravity sewer main to a pressure-assisted sewer system.
The location of this sewer presented unique challenges for the Kembla project team due to the carrier locations inside the Glenrock State National Park, which were only accessible by way of a fire trail.
Design concept
Kembla’s preferred design and construction method was to use a pressure grade cured-in-place pipe (CIPP) liner to upgrade the existing wastewater carrier and to seal the existing maintenance holes by installing fabricated fiberglass bends.
The works involved the design and engineering of suitable DN 600 mm fiberglass bends to match the existing conduits change in direction at 17 individual locations, then coupling these prefabricated bends to Kembla’s Enviroliner pressure grade CIPP liner.
There were 34 excavations throughout the Yuelarbah Management Trail from Glenrock State Conservation Area to the Burwood Beach treatment plant.
Enviroliner technology
Kembla’s Enviroliner system is a CIPP method for the renovation of pipelines. The system inverts a resin-impregnated flexible tube into the existing conduit by using either air or hydrostatic pressure. The tube is then cured to a hardened state while held in contact with the conduit.
For this project, the task was to design and install a suitable CIPP liner capable of holding a pressure bar of 7.
Kembla, in co-operation with its liner suppliers, designed a pressure grade CIPP Enviroliner for this purpose, allowing Hunter Water to avoid an expensive dig and relay exercise within the pristine national park.
Environmental and community benefits
With the assistance of its environmental consultants, Kembla worked in close liaison with stakeholders such as the National Parks and Wildlife Service, Hunter Water Australia and Hunter Water Corporation over a period of eight months whilst the upgrade was completed.
Due to the environmental significance of the site, track preparation works were carefully planned and executed to enable vehicle access along the existing Glenrock fire tracks. This included temporary relocation of obstructions such as logs and boulders, trimming, removing and/or tying back of overhanging branches, saplings and weeds.
Four-wheel drives were utilised by the crew for rough terrain and creek crossings. Erosion and sedimentation control measures were implemented during the construction, along with the use of appropriate temporary sediment fencing and sediment control binding.
Kembla takes its responsibilities towards environmental stewardship very seriously so measures to minimise the impact of these works on the creek and trail areas were necessary, the company said.
During the course of the rehabilitation works, Kembla was involved in 14 separate Enviroliner air inversions of various lengths. The longest inversion length was 210 m through four maintenance holes along the Yuelarbah Management trail.
Kembla said that careful consideration was taken regarding site-specific environmental factors such as flora and fauna, the ramification of the flow management layout, all site traffic movements including the new hazard that site civil works presented to track pedestrian users.
Safety
A safety benefit of CIPP is there is no requirement for personnel to be inside the pipe or maintenance hole whilst installation occurs.
Kembla Managing Director Chris Meredith said “This reduces the daily risk and exposure to our staff eliminating the danger of working in a confined space whilst the sewer is isolated.”
Conclusion
The completed work has enabled Hunter Water to abandon the Kahibah 1 wastewater pump station, by upgrading what would have been a redundant gravity sewer, to a pressure assisted sewer system using Trenchless Technology.
“The civil installation by a dig and relay method to install a new pressure main at this location was simply not an option,” Mr Meredith said. “Trenchless Technology was an innovative solution utilising an existing, potentially redundant pipe asset.
“Hunter Water Corporation contractor performance appraisal confirms that Kembla Watertech performed well, demonstrating good technical expertise, along with a very co-operative project management team and is recommended for further work with Hunter Water Corporation,” Mr Meredith said.