Dudley Charlestown Wastewater Project
The Dudley Charlestown Wastewater system transports wastewater from the Dudley Charlestown catchment to the Burwood Beach Treatment Works. The existing system includes the Kahibah pump station which pumps flow over the hills in the Glenrock State Recreation Area and discharges into a gravity carrier which flows to Burwood Beach Treatment Works.
The new sewer will enable the removal of the Kahibah 1 pump station and reduce the wet weather overflow impacts on the environment. The bore was made difficult by the site constraints of the state recreation area, the very limited access to the exit pit and bore line and exacting grade tolerances of -2% with no zero or positive grade allowable. The grade complexity with further compounded by the varying geology comprising of conglomerate sandstone, siltstone, mudstone and a fractured 2.5metre thick un-worked coal seam intersecting the bore path for 65m.
Initial design works started in February 2009 with UEA and Bowdens Group working together to submit design options, a draft proposal and then a final detailed design confirming grade and pipe diameter suitability.
Once the physical constraints of the bore had been agreed, works began helping to secure approval from the National Parks and Wildlife Service to allow for land clearing for the rig setup and excavation of the 4 metre square x 5m deep exit pit. Site preparation works began in early March 2009 with the clearing of bushland to allow UEA’s Vermeer D300x500 drill rig, DFE 700gal/min cleaning system and support equipment. Detailed survey works were undertaken of the bore line to enable accurate tracking of the bore using the Vector Magnetics steering tool. Steering was undertaken using a combination of beacon tracking and Paratrak 2 wire track systems through the dense bushland covering the bore line.
Due to the fractured coal seam and concerns over fluid loss it was decided to back ream the bore straight to size. The use of PDC reamers enabled steady progression through the varying ground conditions with a clear distinction between ground conditions evident especially when pure black coal chips could be seen coming off of the DFE shaker screens.
With the bore hole complete and conditioned pipe installation began. Due to the limited access to the exit pit, close proximity to Flaggy Creek and being within a popular National Park pipe installation needed to be undertaken in a weld and push operation.