Offsite Treatment Trials
Determining the most suitable treatment method
During the project planning phase, a targeted investigation was performed to determine remediation excavation areas and to estimate excavation volumes. The investigation also involved removing small samples of contaminated material and treating them at a specially licensed offsite facility using a variety of technologies:
- Bioremediation – the use of naturally occurring organisms to break down contaminants in material into less contaminated or non-toxic substances;
- Stabilisation (also known as immobilisation) – the mixing of additives such as cement to ‘lock up’ contaminants in material; and
- Ex-situ chemical oxidation – the addition of an oxidising agent to contaminated material within an external vessel to mineralise the contaminants.
The trials were necessary to determine the most suitable method for treating the contaminated material. They demonstrated that stabilisation would be the most effective method and would allow the treated material to be disposed of offsite at a licensed landfill.
Optimising the chosen treatment method
Following the selection of stabilisation as the most suitable treatment method it was necessary to carry out further trials to determine:
- The most effective additive(s) for treating the contaminated material; and
- The required dosing rate of additive(s) to ensure that the material could be disposed of offsite.
These trials involved treatment of multiple samples of contaminated material using different combinations and quantities of approved additives under conditions that imitated full scale treatment. The results were analysed in a laboratory and the most effective combination was chosen. In some instances, additional trials were conducted to enhance the strategy.
The results of the stabilisation method trials were presented to the NSW Environmental Protection Agency (EPA). Based on these results, the EPA issued a Specific Immobilisation Approval (SIA). The SIA detailed the conditions under which specific contaminated materials were to be treated. It also detailed the criteria that had to be met to demonstrate successful stabilisation, permitting disposal of the treated material at a licensed landfill.