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Core Drilling completes Glenbrook STP transfer directional borehole contract

Sydney Water Corporation awarded a contract for the construction of directional boreholes at the Glenbrook Sewer Treatment Plant to Coe Drilling.
As part of Water Plan 21, Sydney Water Corporation (SWC) is proposing to amplify the Penrith Sewage Treatment Plant (STP) to cater for growth in the Penrith sewerage catchment, and to decommission the Glenbrook STP. Sewage from the Glenbrook sewerage system will be transferred to Penrith STP via a new pipeline, which will be constructed in part using Horizontal Directional Drilling (HDD).
In total, three boreholes were constructed as part of the project with the longest and most complex being a 986 m on grade installation beneath Lapstone Hill, which terminated within the live Glenbrook STP.
Project Delivery - Glenbrook STP Crossings
The Glenbrook STP transfer directional borehole construction contract involved the design, construction, installation and commissioning of HDPE transfer pipelines for sewerage from the Glenbrook STP and from Sewerage Pump Station 805 using HDD Technology. The drilling and pipeline installation was part of a challenging and highly complex project. The project team developed and implemented a detailed engineering design and execution methodology to minimise potential drilling and pipeline installation risks.
Geology
The geology to be encountered for the project indicated that the subsurface lithology to the depth of the investigation was relatively consistent, comprising highly abrasive Hawkesbury Sandstone with sub horizontal bedding. The rock was generally quartz rich of medium to high strength with many ironstone cemented bands. Geological features encountered during the drilling operations included a north-south trending fault.
Equipment
The crossings were constructed using three of five Coe Drilling rigs. The CoeDrill 550 and CoeDrill 90 were used, as well as an American Augers DD6. ParaTracker and Magnetic Ranging were used to control the grade of 3.25 per cent on the longest of the boreholes L1, which included a horizontal alignment change of 26 degrees in order to exit the ground within the confined limits of the Glenbrook STP. Borehole size was 813 mm.
L3 was a 315 m long crossing connecting Leonay with Lapstone, and involved complex curve geometry in order to maintain maximum cover and grade beneath the State Rail Sydney-Katoomba railway lines. Borehole size was 813 mm.
L2 connected the downstream end of L3 with SPS 805 and crossed beneath the Great Western Highway. The SPS will later be decommissioned as part of future Sydney Water works. The works also included pipeline testing and grouting of the borehole annulas to prevent long term groundwater changes in the area. Borehole size was 445 mm.

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