Soil vapour active sampling

iEnvi has undertaken soil vapour sampling, using the implementation of the ASC NEPM, to identify potential risks of vapour intrusion regarding human exposure on various sites. Vapour intrusion is vapor-forming chemicals migrating from a subsurface source into an overlying building as well as basement carparks, trenches/pipes and conduits. 

The requirement for vapour assessment as part of contaminated site investigations has become more frequent after the ASC NEPM was updated in April 2013 to include soil vapour as part of the standard Tier 1 risk assessment process.

Vapour intrusion is particularly an issue near service station sites with underground petroleum storage systems (UPSS) which commonly leak petroleum hydrocarbons to the subsurface (particularly older systems), and also near old laundromat facilities with chlorinated hydrocarbon solvents and nearby old landfills.

Subsurface vapour intrusion investigations can be sampled using two active sampling methods including USEPATO-15 and USEPATO-17.

The TO-15 method consists of the use of sub-atmospheric (evacuated) canister (1 - 1.5L in volume) which are usually set to approximately between -30”Hg with a flow controller set by the providing analytical lab (usually 200ml/min). The TO-17 method consists of a mixture of thermal desorption tubes and carbon tubes with the use of a rotameter and pump with a calibrated flow rate set by the operator.

The benefits and burdens when using either TO-15 or TO-17 are as per below:

  • TO-15 is more expensive than TO-17 to provide/replace and to transport.
  • TO-17 includes preservation applications including the capping of the exposed thermal desorption and carbon tubes while being cooled at less than 4°C during transport compared to TO-15 has no preservation requirements.
  • TO-15 decontamination process is more labour intensive and lengthy.
  • TO-17 consists of a more involved methodology of sampling. TO-15 is a simpler method with the flow rate set by the analytical laboratory.
  • Assessing hydrocarbon compounds is more beneficial for TO-17 when analysing a greater range of hydrocarbon chains C2-C18 with TO-15 quality limited to the lighter compounds <C10.

In summary, iEnvi identifies that both TO-15 and TO-17 are sampling methods that are suitable for vapour intrusion assessment. The TO-15 method is recommended for sampling events where limited training is required (flow rate is usually set by providing analytical lab) and when the analysis is limited to lighter hydrocarbon compounds <10. The TO-17 method is recommended for operators that are competent with the method and is also less expensive and logistically easier to transport.

Vapour risk intrusion assessment is a standard requirement when developing or managing construction or approvals near petrol stations.  To discuss how to manage vapour intrusion risk contact [email protected]



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