Soil gas – Vapour intrusion
Remediation of brownfield sites and monitoring buildings for vapour intrusion
In many countries, limited availability of land for housing has meant increasing redevelopment of old industrial (brownfield) sites, rather than greenfield sites. However, this requires detailed assessment and removal (‘remediation’) of any residual contamination. This may include inorganics such as asbestos and heavy metals, but also a number of organic pollutants amenable to analysis by gas chromatography (GC) – for example, petroleum hydrocarbons, pesticides and solvents.
However, even after remediation is completed and the new buildings have been constructed, it is often advisable to continue to monitor soil gas for the presence of hazardous pollutants, to ensure that the levels remain low.
In addition, where the presence of hazardous pollutants is unavoidable, steps may need to be taken to avoid migration of VOCs from the soil to air inside the building (‘vapour intrusion’) – for example, by installing impermeable membranes in the basement.
The effectiveness of such methods is another situation where GC can be applied, by monitoring the air inside the building.
What Markes can offer
Gas chromatography (GC) is inherently suitable to monitoring VOCs and SVOCs in soil gas, for example, as part of brownfield site assessment. Popular approaches for this so-called ‘sub-slab’ (vadose) monitoring include:
- Canister sampling, which although convenient, is limited to compounds more volatile than n-C10, and thus excludes many of the heavier organic pollutants that are frequently of concern.
- Pumped or diffusive (passive) sampling onto sorbent tubes, with analysis by thermal desorption (TD)–GC (for example, using Markes’ UNITY-xr or TD100-xr thermal desorbers), is compatible with a wider volatility range than canisters.
Below-ground sampling directly onto sorbent tubes can be carried out using a specialist sampler such as Markes’ VOC-Mole.
In the field of vapour intrusion, many of the same monitoring principles apply as in indoor air monitoring. A number of high-profile incidents in the USA has led to expertise in the monitoring and prevention of vapour intrusion in this country in particular. As a consequence, the USA is leading the way in the development of standard monitoring methods.
Standard monitoring methods
Relevant methods for sub-slab monitoring include:
- For more information on the application of TD technology to contaminated land, see Application Note 029.