The many options considered for remediation of the former Macdonaldtown Gasworks site were compared from a social, environmental and economic perspective. Through a review of the available options and the Environmental Assessment, the most efficient and effective method of remediating the site was determined.
The remediation involved the following main processes:
Excavation and disposal
This process involved the excavation of contaminated soil which had been classified as requiring offsite disposal. The excavated material was trucked to a facility licensed by the Environment Protection Authority (EPA) where it was disposed of.
Excavation, offsite treatment and disposal
This process was reserved for the most contaminated materials on the site, generally the tar-impacted soil and tarry waste, and involved the excavation and trucking of the materials to an EPA-licensed treatment facility where they were subject to a process referred to as ‘cement stabilisation.’ This process involved the addition of cement and water to the contaminated material to immobilise or ‘lock up’ the contaminants. Once the treated material reached the required immobilisation target, it was safely disposed of at an EPA-licensed landfill. This immobilisation process was approved by the EPA.
Excavation and onsite reuse
Some materials on the site were not contaminated or not sufficiently contaminated to require offsite disposal. Where it was appropriate, and in accordance with the plans approved by the EPA-accredited Site Auditor, these materials were reused on the site (generally at depth and with clean imported materials placed on top). Examples of materials which were reused include surface soils with low levels of contamination and demolition wastes such as bricks and concrete that could be crushed.
Impacted soil was excavated to the extent practicable. When there were heritage or geotechnical constraints which prevented excavation from occurring (for example, from beneath the southern gasholder), the remnant material was managed in-situ. This strategy was endorsed by the Site Auditor.
Approximately 37,000 tonnes of contaminated material was removed from the remediation site by road in covered trucks. No contaminated soil was returned to the site after removal, even if it had been treated. The site was reinstated with clean fill and material that met the reuse criteria.
The volume of soil, fill, tarry waste and other material that was excavated was approved by the Site Auditor following an extensive drilling, sampling and testing program.