Two soil problems regularly turn up in NSW development applications: urban salinity across much of Western Sydney, and acid sulfate soils on low-lying land near the coast, estuaries and river floodplains. Salinity is a building durability issue. Salts mobilised by water attack concrete, masonry and steel, and the Guidelines to Accompany the Map of Salinity Potential in Western Sydney identify areas of known, high and moderate salinity potential across Blacktown, Camden, Campbelltown, Fairfield, Liverpool, Penrith and parts of neighbouring councils. Acid sulfate soils are an environmental and structural issue controlled through an acid sulfate soils clause in most coastal and floodplain LEPs. That clause maps land in Classes 1 to 5 and requires consent, and usually an assessment or management plan, for works below set depths or works that lower the water table. For builders, both issues are about getting the soil information early enough to design for it.
Key takeaways
- Urban salinity in Western Sydney affects concrete, masonry and steel, and is mapped in the Department’s map of salinity potential, which is accurate only at 1:100,000 scale and is not a substitute for site investigation.
- Growth area DCPs commonly require a salinity report and salinity management plan for land in mapped salinity and soil aggressivity areas, often with certification at completion.
- Acid sulfate soil clauses in LEPs map land as Class 1 to 5; Class 1 triggers consent for any works, Classes 2 to 4 for works below set depths or that lower the water table, and Class 5 for works within 500 metres of Class 1 to 4 land that lower the water table below 1 metre AHD.
- Where the clause is triggered, councils generally expect a preliminary acid sulfate soil assessment and, if acid sulfate soils are present, a management plan before consent.
- Both issues are cheapest to deal with at design stage: footing and slab specifications, damp-proofing, excavation depth and dewatering decisions all follow from the soil information.
Who this is for: builders and developers working on houses, duplexes and townhouses in the Western Sydney growth areas and older suburbs, and on low-lying land on the Central Coast, Lake Macquarie, the Hawkesbury and Georges River, who need to know when soil reports are required and what they change.
What is urban salinity and where does it occur in Western Sydney?
The Department’s guidelines to the map of salinity potential explain that salinisation occurs when salts stored in the soil profile are mobilised by the movement of water, and evaporation and accumulation raise salt levels to the point that vegetation and building materials such as concrete and steel are affected. The map covers Blacktown, Camden, Campbelltown, Fairfield, the former Holroyd area, Liverpool and Penrith, and parts of Auburn, Bankstown, the Hills, the Hawkesbury, Parramatta and Wollondilly. It uses four categories: areas of known salinity, high salinity potential, moderate salinity potential and very low salinity potential.
The guidelines are clear on limitations: boundaries are valid only at 1:100,000 scale and should not be used at property scale, and the map is not a substitute for on-site investigation. Practically, a lot inside a high potential area may test fine, and a lot outside it may not. Development changes how water moves (irrigation, leaking services, filled ground, removed vegetation), which is why salinity can appear after an estate is built.
When does a council ask for a salinity report?
In the North West and South West growth areas, the Growth Centre precinct DCPs commonly require DAs on land with an identified salinity risk to be accompanied by information showing how design and construction will address salinity. Typical requirements, seen in Blacktown and Camden growth precinct assessments, include a salinity report, a salinity management plan prepared in line with the DCP’s salinity appendix, and certification by a qualified person at completion. Camden DCP 2019 asks that, where a salinity report is prepared, it include a salinity management plan addressing construction requirements in the relevant Australian Standards. Outside the growth areas, councils typically raise salinity through geotechnical reports, engineering specifications and conditions.
| Salinity finding | Typical design and construction response |
|---|---|
| Low or no salinity | Standard slab and footing specification; good site drainage |
| Moderate salinity or aggressive soil | Higher concrete exposure classification and cover, damp-proof courses and membranes, salt-resistant masonry |
| High salinity | Engineered specification, limited deep cut and fill, landscape and irrigation controls, stormwater design that avoids recharge |
The structural engineer sets the actual specification against the relevant Australian Standards. The planning point is to have the salinity information before the engineer designs the slab, not after the council’s RFI.
What are acid sulfate soils and how do the LEP classes work?
Acid sulfate soils are natural sediments containing iron sulfides, common in low-lying coastal, estuarine and floodplain land. Undisturbed and waterlogged, they are harmless. Excavated or drained, they oxidise and produce sulfuric acid, which damages concrete and steel, harms waterways and can mobilise metals. Most coastal and floodplain LEPs include an acid sulfate soils clause (clause 6.1 in Fairfield LEP 2013 and clause 7.1 in Coffs Harbour LEP 2012 are examples) and an acid sulfate soils map. Council guidance from Eurobodalla and Coffs Harbour summarises the classes:
| Class | Works that need consent (typical wording) |
|---|---|
| Class 1 | Any works |
| Class 2 | Works below the natural ground surface, or works likely to lower the water table |
| Class 3 | Works more than 1 metre below the natural ground surface, or likely to lower the water table more than 1 metre below it |
| Class 4 | Works more than 2 metres below the natural ground surface, or likely to lower the water table more than 2 metres below it |
| Class 5 | Works within 500 metres of adjacent Class 1 to 4 land, below 5 metres AHD, likely to lower the water table below 1 metre AHD on that adjacent land |
Where the clause is triggered, the council generally needs to be satisfied, through a preliminary assessment, that acid sulfate soils are not present, or that an acid sulfate soils management plan is in place. Check the wording of your council’s clause; the depths and exceptions vary slightly between LEPs.
The steps we recommend
- At due diligence, check the salinity potential map (Western Sydney) and the LEP acid sulfate soils map, and note the class.
- Read the DCP chapter or growth precinct DCP provisions on salinity, and the LEP acid sulfate soils clause.
- Commission the geotechnical investigation with salinity and aggressivity testing, and acid sulfate soil sampling where the class and proposed works trigger it.
- Design excavation depth, basements, pools and stormwater with the results in mind; avoiding deep excavation on Class 2 or 3 land can remove the trigger altogether.
- Lodge the DA with the salinity report and management plan, or the acid sulfate soils assessment and management plan.
- Carry the management measures into the construction certificate specification and the construction management plan.
- Keep certification at completion where the DCP or consent requires it.
Where builders get caught
On salinity, the common problem is a standard slab specification on a site later found to be saline, leading to a condition requiring redesign before the construction certificate. On acid sulfate soils, it is the pool, the inground rainwater tank or the stormwater detention tank that pushes excavation below the trigger depth on a lot where the house itself would not. Dewatering during construction is the other trigger: pumping out a trench on Class 3 or 4 land can lower the water table enough to engage the clause even if the excavation is shallow.
Definitions
- Urban salinity
- The accumulation of salts in soils and groundwater in urban areas, damaging buildings, roads and vegetation.
- Soil aggressivity
- The tendency of soil and groundwater chemistry (salts, sulfates, acidity) to attack concrete and steel.
- Acid sulfate soils
- Soils containing iron sulfides that produce sulfuric acid when exposed to air by excavation or drainage.
- AHD
- Australian Height Datum, the national reference level for elevations, approximately mean sea level.
- Acid sulfate soils management plan
- A plan setting out how acid sulfate soils will be excavated, treated, stored and monitored to avoid environmental harm.
Frequently asked questions
Do I need a salinity report for a house in Western Sydney?
Often in the growth area precincts, where DCPs require one for land in mapped salinity risk areas. Elsewhere, salinity is usually addressed through the geotechnical report and the engineer’s specification.
How do I find out if my land has acid sulfate soils?
Check the acid sulfate soils map in your council’s LEP, available through the NSW Planning Portal spatial viewer. The class tells you which works need consent. Only sampling confirms whether acid sulfate soils are actually present.
Does a Class 5 acid sulfate soils mapping affect a normal house?
Usually not. Class 5 is triggered by works likely to lower the water table below 1 metre AHD on adjacent Class 1 to 4 land, which ordinary house construction rarely does.
Can salinity be dealt with after the DA?
Sometimes through conditions, but it is cheaper and faster to have the soil information before the slab and footings are designed and before the DA is lodged.
Soil constraints are part of every development due diligence report we prepare in the Western Sydney growth areas and on low-lying coastal land, and the findings are written into the Statement of Environmental Effects. If you are about to design on a site with mapped salinity or acid sulfate soils, request a fee proposal.
Sources and references
- NSW Government, Guidelines to Accompany Map of Salinity Potential in Western Sydney (2002), accessed October 2026
- Eurobodalla Shire Council, Acid sulfate soils, accessed October 2026
- Coffs Harbour City Council, Development on land with acid sulfate soils, accessed October 2026
- NSW Planning Portal, Spatial viewer (LEP acid sulfate soils maps), accessed October 2026
Information disclaimer. This article is general planning information prepared by the URBA Planning Team and is current at the date of publication. It is not planning, legal or financial advice for any specific property. Planning instruments, development control plans, state policies and the National Construction Code are amended regularly and councils interpret them differently; the controls quoted here should be confirmed against the versions in force at the date of lodgement and against the consent authority’s current requirements. Reliance on this article is at the reader’s own risk. URBA Planning, a division of Contrive Consultants Pty Ltd, accepts no liability for loss arising from its use. For advice on a specific site, contact URBA for a fee proposal.