Acid sulfate soils
What acid sulfate soils are in NSW: classes 1 to 5, how they affect CDC and DA eligibility, and what builders need to check before starting work.
Ask Chalkline about this →Acid sulfate soils are naturally occurring soils and sediments containing iron sulfides (mostly pyrite). When these soils are disturbed or drained and exposed to air, the sulfides oxidise to form sulfuric acid, which can damage concrete footings, steel reinforcement, and stormwater systems, and harm nearby waterways. NSW classifies acid sulfate soils in five risk classes (Class 1 being the highest risk): the class that applies to a lot is shown on the Section 10.7 planning certificate and on council mapping.
For builders and certifiers, the class matters for CDC eligibility and DA conditions. Class 1 and Class 2 acid sulfate soils on a site generally disqualify it from the CDC pathway under the Housing Code and require a DA with specialist geotechnical or environmental assessment and an acid sulfate soils management plan. Classes 3 to 5 carry lower risk and attract less restrictive assessment requirements, though conditions on excavation and drainage may still apply.
Also known as: Acid sulphate soils, ASS.
Category: Approvals, Site assessment.
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Last updated: 2026-05-08. Verified: 2026-05-08.