Full Scale Remediation (Excavation)
To remediate the former Macdonaldtown Gasworks site, the contaminated material was being excavated and transported to a licensed facility where it was treated, if required, before being disposed of to a licensed landfill. The full scale excavation process commenced once all of the retaining walls were installed and the environmental control enclosure, emission control system and water treatment plant were commissioned.
The environmental control enclosure covered the middle section of the site where the soil contained high contaminant concentrations at significant depths. The largest retaining walls were built adjacent to this area and have remained in place now that the project is complete. The retaining walls helped maximise the removal of the contaminated material by allowing deep vertical excavations of up to 9 metres without conventionally battering the excavation (meaning without creating an inclined surface).
The excavation area was developed based on data collected over many years of site investigation works. The data from these investigations was used to estimate the locations, concentrations and depths of contamination. The full scale excavation used two 20-tonne excavators that dug in a planned sequence to remove the contaminated soil.
A detailed excavation model was used that considered all relevant site information including the contamination data, geotechnical parameters of the soil, the site’s heritage assets and adjacent structures. The excavation was routinely surveyed which allowed progress to be accurately tracked. This method ensured that the excavation removed the maximum volume of contaminated soil while still remaining within the geotechnical limits.
All excavated surfaces were validated prior to being backfilled with suitable clean material. Validation means that the surfaces met the requirements detailed in the Remedial Strategy and the Auditor-approved Remedial Works and Validation Plan.