A salinity assessment evaluates the salt content in soil and groundwater to determine their suitability for construction and to recommend protective measures.
High salinity can cause corrosion of buried structures, damage to concrete, and adverse effects on vegetation and pavement performance.
What Is a Salinity Assessment?
Salinity assessment measures the concentration of soluble salts in soil and groundwater. In a construction context, it is primarily concerned with:
- Corrosion risk to buried steel pipes, sheet piles, and reinforcement
- Concrete attack from sulfates and chlorides
- Pavement failure from salt crystallisation beneath seals
- Vegetation impact — landscaping and rehabilitation planning
- Earthworks compatibility — salt-affected fill materials
Australia has widespread salt-affected soils and shallow saline groundwater, particularly in:
| Region | Salinity Issue |
|---|---|
| Murray-Darling Basin | Dryland salinity from rising water tables |
| Southern QLD / Northern NSW | Coastal saline zones, estuarine deposits |
| South-western WA | Extensive dryland salinity (clearing of native vegetation) |
| SA / Vic | Saline groundwater near the Murray River |
| Coastal zones (all states) | Marine salt influence, tidal zones |
Measurement Parameters
| Parameter | Standard | Significance |
|---|---|---|
| Electrical Conductivity (EC) | AS 1289.4.4.1 | Total soluble salt content (1:5 soil:water extract) |
| Chloride (Cl⁻) | AS 1289.4.4.1 | Corrosion risk indicator |
| Sulfate (SO₄²⁻) | AS 1289.4.4.1 | Concrete aggressivity indicator |
| Sodium Adsorption Ratio (SAR) | AS 1289.4.4.1 | Soil dispersivity — earthworks implications |
| pH | AS 1289.4.3.1 | Acid sulfate soil indicator |
Salinity Classification
| EC (1:5) dS/m | Salinity Level | Construction Implications |
|---|---|---|
| < 0.15 | Non-saline | Minimal risk |
| 0.15–0.3 | Slightly saline | Monitor for sensitive uses |
| 0.3–0.6 | Moderately saline | Corrosion risk for buried steel |
| 0.6–1.2 | Saline | Significant corrosion risk, concrete protection needed |
| 1.2–2.4 | Highly saline | Specialist design required |
| > 2.4 | Extremely saline | Not suitable for standard construction without mitigation |
Sampling and Testing
Sample Collection
- Soil samples at depths corresponding to foundation, service, and groundwater levels
- Groundwater samples from boreholes (if water table encountered)
- Samples from multiple locations across the site to assess variability
- Samples sealed in airtight containers to prevent moisture loss
Laboratory Testing
Salinity testing is typically conducted by a NATA-accredited laboratory using:
| Test | Standard | Purpose |
|---|---|---|
| EC (1:5 soil:water extract) | AS 1289.4.4.1 | Measure total soluble salts |
| Soluble chloride content | AS 1289.4.4.1 | Corrosion risk |
| Soluble sulfate content | AS 1289.4.4.1 | Concrete aggressivity |
| pH | AS 1289.4.3.1 | Acid sulfate soil screening |
| SAR | AS 1289.4.4.1 | Soil dispersivity |
Construction Implications
Concrete
High sulfate and chloride content requires:
- Sulfate-resisting cement (Type SR)
- Increased concrete cover to reinforcement
- Reduced water-cement ratio
- Protective coatings or membranes
Buried Steel
Saline soils accelerate corrosion. Mitigation options:
- Epoxy-coated or galvanised steel
- Cathodic protection system
- Increased wall thickness (corrosion allowance)
- Protective wrapping or coatings
Pavements
Salt crystallisation beneath asphalt seals can cause:
- Pavement delamination
- Edge cracking
- Loss of seal integrity
Requires salt-resistant base materials and improved drainage.
Earthworks
Salt-affected soils may be dispersive (prone to erosion and piping):
- Requires stabilisation with lime or gypsum
- May be unsuitable for use as engineered fill
- Requires special compaction and drainage measures
Australian Standards
| Standard | Relevance |
|---|---|
| AS 1289.4.4.1 | Determination of EC, chloride, sulfate and SAR |
| AS 1289.4.3.1 | Determination of pH |
| AS 2159 | Piling — chemical exposure classification |
| AS 3600 | Concrete structures — exposure classes |
| AS 4312 | Corrosion of buried metal structures |
Frequently Asked Questions
Do I need a salinity assessment for my project?
If your site is in a known saline area (coastal zone, Murray Basin, WA wheatbelt) or if adjacent projects have identified saline conditions, a salinity assessment is advisable. Councils may require it for certain developments.
Can salinity be managed on site?
Yes. Common management strategies include:
- Installing drainage to lower the water table
- Using salt-tolerant materials
- Applying protective coatings to buried structures
- Importing low-salinity fill for critical zones
What is the difference between salinity and acid sulfate soils?
Salinity relates to soluble salt content, while acid sulfate soils produce sulfuric acid when exposed to oxygen. Both may occur at the same site but require different management approaches.