Remediation of former gasworks sites is complicated by the presence of mixed organic and inorganic contaminants commonly found in the soil and groundwater around the sites. The organic contaminants (e.g. polycyclic aromatic hydrocarbons – PAHs) are usually the driver for the remediation, rather than heavy metals, although both organic and inorganic contaminants need to be considered.
Remediation operations must not result in adverse impacts on the environment or human health. Aspects to be considered include air quality, odours, water quality, noise levels and waste management. All work on-site must take into account the various provisions of planning, environmental and occupational health and safety legislation.
The Guidelines for Consultants Reporting on Contaminated Sites (1997) and Guidelines for the NSW Site Auditor Scheme (1998 or updates) provide guidance on issues relevant to the remediation of contaminated sites, including the development of a remedial action plan and a validation strategy. These publications are available from DEC’s Environment Line.
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The preferred hierarchy of options for site clean up and management as published in the Guidelines for the NSW Site Auditor Scheme (1998 or updates) is:
- on-site treatment of the contamination so that it is destroyed or the associated risk is reduced to an acceptable level.
- off-site treatment of excavated soil so that the contamination is either destroyed or the associated risk is reduced to an acceptable level, after which it is returned to the site.
If neither of these options is practical, consider the following:
- removal of contaminated material to an approved site or facility – refer to Environmental Guidelines: Assessment, Classification and Management of Liquid & Non-Liquid Wastes (1999) – and replacement, where necessary, with validated clean fill,
- consolidation and isolation of the soil on-site by containment with a properly designed barrier (this will require the development and implementation of a site management plan with appropriate approvals from, and possibly regulation by, DEC and/or a relevant planning authority, and may also require ongoing monitoring to ensure the integrity of the barrier/containment cell).
Where the assessment indicates that remediation would have no net environmental benefit – or a net adverse environmental effect – an appropriate management strategy must be implemented to address the contamination.