Surfside, Batemans Bay — Acid Sulfate Soil Management Plan for Residential Construction
Confluence Environmental prepared an Acid Sulfate Soil Management Plan (ASSMP) for a proposed residential development on a 580 m² property at Surfside, near Batemans Bay on the NSW South Coast.
The plan supported the development application and established procedures for managing potentially acid-generating soils during footing installation, service trenching and minor earthworks.
About the project
The proposed dwelling required localised excavation for concrete piers, underground services and adjustments to site levels.
The property was mapped as Class 3 acid sulfate soil land within a low-lying coastal setting. Existing geotechnical information identified sandy subsurface soils and shallow groundwater, making the management of excavated material an important construction consideration.
Confluence reviewed the proposed works, available geotechnical information and environmental mapping to develop a management approach suited to the scale of the project.
Project at a glance:
Site area: Approximately 580 m².
Development: New residential dwelling.
Mapped constraint: Class 3 acid sulfate soil land.
Proposed foundations: 450 mm diameter concrete piers.
Deliverable: Site-specific Acid Sulfate Soil Management Plan.
Assessing the construction requirements
Confluence considered the relationship between the proposed excavation works, mapped acid sulfate soil potential and groundwater conditions recorded during the previous geotechnical investigation.
The assessment drew on geological mapping, coastal topography, groundwater records and the available footing recommendations. It identified the potential for excavation to disturb susceptible soil horizons or encounter groundwater if conditions differed from those anticipated.
The presence and severity of acid sulfate soils had not been confirmed through dedicated testing. The plan therefore adopted a precautionary approach, with procedures for managing suspect material and confirming treatment requirements during construction.
Practical procedures for excavation and soil handling
The ASSMP established responsibilities for the construction team and procedures for:
Containing and covering excavated material.
Separating stockpiles from surrounding soils and controlling runoff.
Sampling suspect material to assess acid-generating potential.
Determining treatment requirements from laboratory results.
Applying and documenting lime treatment where required.
Validating treated material before considering reuse or disposal.
The approach was tailored to localised pier excavations and service works, with provision for contained handling of relatively small quantities of spoil.
Planning for groundwater and changing conditions
Although dewatering was not proposed, the plan included contingency procedures should groundwater be encountered during construction.
It also identified circumstances requiring further environmental advice, including deeper excavations, increased spoil volumes, unexpected soil conditions or evidence of acidic drainage.
These provisions gave the construction team a process for responding to changes rather than relying solely on the conditions anticipated during design.
Connecting soil management with disposal requirements
The plan addressed both acid sulfate soil treatment and the separate assessment required for off-site disposal.
It established requirements for treatment records, validation information and waste classification, providing a documented process for determining an appropriate destination for excavated material.
Supporting coastal development
Confluence’s ASSMP translated the mapped acid sulfate soil constraint into site-specific construction procedures, supporting the development application and planning of the proposed works.
The deliverable provided the builder with responsibilities, soil-handling requirements and contingency measures to follow during excavation, while identifying where testing and further advice would be needed.
Planning construction in Batemans Bay, Eurobodalla or elsewhere on the NSW South Coast? Contact Confluence Environmental for acid sulfate soil assessment and management planning.