Project overview
iEnvi was engaged to complete a Targeted Soil Assessment for a coastal site being progressed for low-density residential development. The assessment focused on the footprint of a former shed that had been excluded from an earlier investigation, creating a data gap required by Council prior to development consent.
Issue and regulatory trigger
Anecdotal information and historical site works suggested prior remediation to manage apparent coal tar/creosote contamination associated with oyster rack processing. Council required confirmation that soils beneath the former shed did not pose an unacceptable risk to human health or the environment for the proposed residential land use.
Investigation approach
- Targeted surface and near-surface soil sampling focused on the area beneath and immediately adjacent to the former shed footprint to close the data gap.
- Laboratory analysis included PAH speciation and, where indicated, additional targeted analyses for phenolic compounds to help discriminate coal tar sources from other PAH sources.
- Interpretation considered the range of PAH compounds (isomer patterns) and the context of visual/physical evidence (e.g. surface asphalt fragments) to identify likely sources.
Key findings
- PAHs were detected in surface soils at concentrations that initially triggered a potential coal tar concern based on generic screening.
- Further PAH fingerprinting and analysis for phenolic compounds indicated the PAH profile was not consistent with residual coal tar from treated timber.
- Visual inspection and context supported that the PAHs were most likely attributable to low-level asphalt fragments in surface soils rather than coal tar residues.
Risk assessment and outcome
On the basis of the targeted sampling, analytical fingerprinting and site context, iEnvi concluded that residual coal tar was not detected and that environmental and human health risks were low for the proposed low-density residential use. This assessment closed the data gap required by Council and supported the grant of development consent.
Practical takeaways for developers and certifiers
- Targeted sampling to close a specific data gap can be more cost-effective and faster than a full-scale redevelopment investigation when historical impacts are localized.
- PAH detection alone does not prove coal tar — PAH fingerprinting and additional analytes (for example phenolic compounds) are useful for source discrimination and can materially affect remedial or management needs.
- Documenting the investigative rationale and demonstrating how results relate to the proposed land use are key to satisfying Council and progressing consent.
Next steps and recommendations
- Retain records of sampling locations, laboratory reports and interpretive rationale in the development approval documentation.
- If future earthworks or deeper excavation are proposed, consider verification sampling or a site-specific management plan to manage any deeper or unexpected contamination.
- Engage a contaminated land consultant early where historical industrial or processing activities are known — targeted, analytical approaches can reduce risk, cost and approval timeframes.
Contact iEnvi — for confidential advice about targeted investigations, source discrimination or contamination management, call 13000 43684 or use our contact page.
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