Volatile chemical vapours and gases can enter buildings through soil. These vapours and gases come from nearby subsurface soil or groundwater. This is called vapour intrusion.
These vapours and gases can cause fire and explosion. They can also be a risk to the health of people who live or work in the affected buildings.
Vapours can include chemicals found in chlorinated hydrocarbons:
- tetrachlorethene (PCE)
- trichloroethene (TCE).
To learn more about the health effects of PCE, refer to Tetrachlorethene (PCE) from vapour intrusion and your health.
Causes of vapour intrusion
Poor environmental practices and industry activities can cause vapour intrusion. These could be current or historical. For example, vapour intrusion can be caused by:
- leaking pipes
- leaking underground petroleum storage systems
- spills of toxic chemicals
- liquid waste disposal.
Table 2 of Planning Victoria's Planning Practice Note 30: Potentially contaminated land lists activities that can cause vapour intrusion. Refer to the section 'Adjacent contaminating activity'.
Vapour intrusion is more likely when a site is immediately next to the source of contamination. However, it can also happen at sites further away.
Many factors impact whether vapour intrusion can happen, including:
- the amount of nearby land contamination
- how close the contamination is to the soil surface
- the soil structure
- depth to groundwater
- cracks in building foundations or floorboards
- building ventilation.
Other factors can influence the rate of vapour intrusion. For example, vapour concentrations in indoor air may fluctuate depending on:
- weather
- building ventilation
- heating and cooling.
Generally, vapour intrusion does not cause ongoing issues in buildings.
Assess vapour intrusion
Assessing historical vapour intrusion is a highly technical process. Evidence of vapour intrusion might include:
- adjacent current or historical contaminating activity
- poor historical environmental practices – for example, groundwater contamination identified during an environmental audit
- odours reported in indoor air that are caused by nearby contamination
- health effects attributed to nearby contamination
- discovering preferential pathways for volatile chemicals into your building – for example, fractures in building foundations.
If you have evidence to indicate vapour intrusion at your site, you can contact an expert. They can assess the land and recommend next steps.
Control vapour intrusion
Potential vapour intrusion does not mean the land cannot be used.
If a risk to human health from vapour intrusion is identified at your site, you must use controls to prevent and manage the vapour intrusion. For example:
- passive ventilation systems
- vapour control systems
- limitations on digging into the ground to avoid creating pathways for vapours below the soil surface to escape.
If concentrations of subsurface vapours are identified as an elevated risk to human health during site investigation or an environmental audit, you must use engineering controls or remediation to manage the risk.
To learn more about investigating and assessing vapour intrusion, visit Guidance to the duty to manage contaminated land.
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