Acid Sulfate Soil Investigation and Management Plan, Mornington Peninsula VIC

Project summary

iEnvi was engaged to investigate potential acid sulfate soils (PASS) for an industrial development in Hastings on the Mornington Peninsula, Victoria. The scope included targeted boreholes through likely soil horizons, field screening, laboratory acid–base accounting, mapping of PASS, and preparation and implementation of an Acid Sulfate Soil Management Plan (ASSMP) to manage construction risks.

Why acid sulfate soils matter

Acid sulfate soils form naturally in coastal, estuarine and low-lying environments. If left undisturbed they are usually benign; however, when sulphidic horizons are exposed to oxygen they can produce strong acidity (sulfuric acid) and soluble iron. This can cause:

• soil and surface water acidification and poor water quality,
• mobilisation of metals and other contaminants,
• corrosion and damage to concrete and buried infrastructure,
• ecosystem harm including reduced oxygen and fish kills in extreme cases.

What we did on site

• Installed 24 soil bores and collected nearly 50 soil samples across relevant depths to characterise soil horizons and locate PASS.
• Performed field pHF (field pH) and pHFOX (field peroxide-oxidised pH) tests on all samples prior to dispatch to laboratory. These field tests screen for potential acidity and the effect of oxidation.
• Submitted samples for laboratory SPOCAS testing (Suspension Peroxide Oxidation Combined Acidity and Sulphate) to quantify actual and potential acidity and the soil’s neutralising capacity.
• Mapped the location and extent of PASS across the site and prepared an ASSMP describing on-site management, handling, stockpiling, testing and water quality controls during construction.

Key technical outcomes

• PASS locations were identified and mapped to guide earthworks and excavation controls.
• The ASSMP outlined trigger levels, testing frequencies, handling procedures and water-quality monitoring to avoid offsite impacts and protect infrastructure.
• Construction-phase testing and monitoring were scheduled to verify controls and demonstrate compliance during disturbance of sulphidic soils.

Practical takeaways for developers and project managers

• Early investigation reduces transaction and construction risk: mapping PASS before bulk earthworks avoids unexpected delays, expensive remediation and potential regulatory enforcement.
• Simple field screening (pHF/pHFOX) plus a reliable laboratory method (e.g. SPOCAS) gives a defensible basis for management decisions and disposal/reuse options.
• An ASSMP that ties field triggers to laboratory confirmation and water-quality monitoring both protects the environment and smooths approvals with regulators.
• Proper on-site management often keeps material on-site and reduces transport and disposal costs compared with ad-hoc removal.

Project status and timing

This account records the investigation and management plan developed for the Hastings development (project published in 2019). The ASSMP was implemented during construction as the project progressed; if you require current status for this site, contact iEnvi for a project update.

Need help with acid sulfate soils?

iEnvi provides site assessment, ASSMPs, construction-phase monitoring and regulatory liaison to manage acid sulfate soil risk for developments across coastal Victoria. For a confidential discussion, call 13000 43684 or contact us.