Acid sulphate soils (ASS) are a significant environmental and construction concern across coastal South East Queensland. When ASS is disturbed — through excavation, drainage changes, or development — it can release sulfuric acid, causing severe structural and environmental damage.
Key Triggers for Investigation
Local councils across SEQ (including Brisbane, Gold Coast, and Sunshine Coast) have strict planning schemes regarding ASS. An investigation is generally triggered when development occurs in mapped risk areas (typically below 5m AHD) and involves:
- Excavation: Removing soil, such as for basement car parks, swimming pools, or deep trenching for services.
- Filling: Placing significant amounts of fill on the site, which can displace groundwater and expose underlying ASS.
- Dewatering: Lowering the groundwater table temporarily or permanently during construction.
The Investigation Process
If triggered, a preliminary ASS assessment is required. This involves drilling boreholes, collecting samples at specific depth intervals, and conducting field screening tests. If field tests indicate the presence of ASS, samples are sent to a NATA-accredited laboratory for detailed analysis. Based on these results, an ASS Management Plan may be required to safely neutralise the soil during construction.