Site: Breakfast Creek, South-East Queesland
Scope: Removal of asbestos and hazardous waste via excavation and treatment of hazardous soils, sediment extraction and treatment of contaminated groundwater. Site reinstatement works included backfill and compaction of excavations, landscaping, revegetation and pavement reconstruction, installation of drainage, long term sediment and environmental controls.
Total project: $18 million.
Duration: 22 Months.
Project background: The Brisbane River has historically been regarded as Queensland’s central manufacturing hub due to it’s proximity to major terminals and ports for export of commodities. The contract remediated a major industrial facility used for manufacturing of solvent and dioxin chemicals from the early 1930s to the late 1990s.
The five hectare site remained derelict for some time post operation. Large areas were contaminated with herbicides and pesticides, preservatives, vinyl chloride, trichloroethylene, chlorine gas and plastics. In addition, extensive land reclamation had been undertaken using excavation and demolition materials and factory residues as the infill material. This resulted in the spread of contaminants into the sediments in the bay.
Given that the site was adjacent to residential and ecologically sensitive aquatic environments, the remediation strategy included extensive provisions to minimise community odour impacts and to protect the local environment.
Methodology and scope of works: The excavation of hazardous soils was conducted in a purpose built odour minimising tent structure which was more than one hectare in area and 20 metres in height.
The remediation area comprised 12 independent warehouse storage and manufacturing plants. The removal of friable and bonded asbestos and other hazardous building materials such as lead and PCBs was required prior to demolition of the structures. Following demolition, odorous contaminated soils were excavated and treated, approximately 400,000 cubic metres. Extraction and treatment of 5 million litres of contaminated groundwater and sludges and subsequent backfilling and reinstatement of excavated areas was also undertaken.
The site was remediated to levels suitable for commercial, public open space and residential developments. To meet the environmental and aesthetic concerns raised by the community following the completion of remedial works, civil works including landscaping, drainage, stormwater and sediments controls and installation of security fencing for safety were carried out.
With respect to the remedial methods, a Step-By-Step process was used involving indirectly heated thermal desorption (ITD) and the base-catalysed dechlorination (BCD) to remediate the site contaminants. The ITD process involved applying heat to the outside of a kiln which held the contaminated soil. The contaminants were volatilized from the soil in a controlled way so that other toxic by-products (such as dioxins) were not formed in the process.
Following the initial process, an additional step was required to remove the isolated contaminants. The BCD process was then subjected to the soil which used sodium hydroxide (caustic soda) to strip the chlorine from the contaminants, forming common salt.