Galston and Glenorie Retic Wastewater Scheme

UEA Trenchless has successfully completed the installation of approximately 11.5 kilometres of PE Reticulation pipework by horizontal directional drilling (HDD) for the Glenorie Galston Pressure Sewer Project.

Glenorie and Galston are two un-sewered urban villages, approximately 35 kilometres northwest of Sydney, that have been chosen to receive improved wastewater services as part of the Priority Sewerage Program (PSP) set by the NSW Government. The wastewater service is a pressure sewerage system and will service about 380 properties in Galston and 240 properties in Glenorie. The areas to be serviced by the PSP are referred to as the Glenorie Subsidised Servicing Area (SSA) and Galston SSA. Wastewater from Galston and Glenorie will be transferred to the existing network at Dural, then to West Hornsby Treatment Plant for treatment.

The Glenorie Subsidised Service Area (SSA) Pressure Sewer System (PSS) reticulation receives pumped flows from the properties within the SSA and transfers them to a pump station on Whites Road. The work included installation by HDD of 5,175 metres of pressure reticulation sewers, ranging in size from OD50 to OD110, to service all properties within the Glenorie SSA.

The Galston Subsidised Service Area (SSA) Pressure Sewer System (PSS) reticulation receives pumped flows from the properties within the SSA and transfers them to a new pump station on Mid Dural Road near the fire station.

The work included installation by HDD of approximately 6,175 metres of pressure reticulation sewers, ranging in size from OD50 to OD125, to service all properties within the Galston SSA.

Extensive service locating and vacuum excavation in advance ensured minimum disruption, with the HDD rigs constantly drilling from one site to the next without having to prepare at the start of each run. This pre-work also enabled the ability to redesign if required before crews moved into each area, minimising risk of damaging existing services; only one water service was damaged over the entire project.

The challenges faced with this project were:

  • Changing ground conditions. Within Glenorie, of the 5,175 metres drilled, 3,302 metres were in sandstone and of the 6,175 metres drilled in Galston, 2,186 metres were in sandstone.
  • Aquifers throughout entire region. “An aquifer is a body of saturated rock through which water can easily move. Aquifers must be both permeable and porous and include such rock types as sandstone, conglomerate, fractured limestone and unconsolidated sand and gravel.” When a bore drills through an aquifer, water constantly flows out of the bore hole which creates additional disposable fluids. It also makes restoration difficult as a weak spot is created which becomes water logged.
  • Limited timeframe. This meant that multiple crews performing different tasks on the project had to work in close proximity.

UEA commenced drilling in January 2015 and completed all HDD works by April 2015. A combination of DitchWitch All Terrain rigs were used to successfully install the PE pipes in mixed ground conditions.