McMahon Services was engaged to undertake the 273ha Ash Storage Area Rehabilitation at the decommissioned Augusta Power Stations site.
The first stage of the rehabilitation required covering the Ash Storage Area with a liquid dust suppressing concentrate called Vital Bon-Matt Stonewall. Diluted in water in concentrations of 10%, the Vital Bon-Matt formed a strong, flexible and long acting surface coating, penetrating and binding the surface of ash. The chemical provides an environmentally sound, immobile formula, free of heavy metals, minerals or solvent.
Application was not possible using traditional water trucks as the geotechnical properties of the ash meant such large vehicles would sink due to their high-ground pressure wheels. McMahon Services engaged aviation contractor Aerotech to provide an Air Tractor (AT) 802 single engine fire-bombing aircraft with a pilot to evenly distribute the suppressant across the Ash Storage Area.
Approximately 3,100L of Vital Bon-Matt solution was distributed with each run. The suppressant was dyed with green food colouring providing a clear indication of areas covered. The process enabled 212ha to be covered in what is believed to be a first in Australia.
The second stage required covering the Ash Storage Area with 150mm of material composed of a sand and clay blend sourced from a borrow pit approximately 1km from the site. Several D6 swamped tracked dozers worked together with a D7 dozer concurrently to construct 4.0m wide by 0.5m high embankment fingers into a lattice arrangement across the site, allowing the cover material to be distributed evenly across the Ash Storage Area.
Like the water truck, ground pressures exerted from standard earthmoving dozers and dump trucks were too high to operate outside of the fingers that were constructed across the Ash Storage Area. To mitigate this, McMahon Services purchased a PistenBully 600 snow plough from the German manufacturers and then modified the wide-tracked, low ground-pressure vehicle to evenly spread out the soil clay blend across the site, reaching areas other plant and equipment could not.
Additional low ground pressure, swamp tracked D6 dozers were utilised together with the PistenBully to spread the borrow pit material using GPS inbuilt controls to a uniform depth of 150mm across the Ash Storage Area. By project completion, over 650,000m³ of borrow pit fill material will cover the Ash Storage Area preventing future dust generation and providing a growing medium for vegetation to establish as part of the seeding works.
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