CARACTAIR project: a new approach to long-term sampling of soil gases and indoor air
TERA Environnement’s contribution to the CARACTAIR project for enhanced indoor air quality assessment at contaminated sites
TERA Environnement took part in the CARACTAIR research project, funded by ADEME as part of the GESIPOL program, alongside GINGER BURGEAP and IMT Nord Europe. The aim of this project was to improve the assessment of pollution from soil gases and its impact on indoor air quality in buildings.
Soil gases: an invisible source of pollution and their transfer into indoor air
Soil gases refer to the gaseous fraction present in the soil pores.
They consist of:
- gases naturally present in the soil (oxygen, nitrogen, carbon dioxide, etc.)
- water vapor
- and sometimes volatile pollutants resulting from contamination of the subsoil or groundwater
When soil or groundwater is contaminated with volatile substances (hydrocarbons, chlorinated solvents, benzene, etc.), some of these pollutants may evaporate.
These compounds then migrate into the soil in gaseous form: these are soil gases.
They can then:
- stay in the basement
- spread outward
- seep into the buildings through: cracks in the slabs; utility penetrations; crawl spaces; or leaks
Sources and pathways of transfer of volatile pollutants from soil to indoor air. (Source: CARACTAIR Project report)
Since we spend more than 80% of our time indoors, air quality becomes a major public health issue.
Many sources can degrade indoor air quality, including combustion-based heating appliances, cooking systems, building materials, furniture, and smoking. Another source of pollution—less obvious but just as significant—is the intrusion of volatile pollutants from the soil and groundwater through soil gases.
In the context of contaminated sites and soils, it is therefore recommended to conduct measurement campaigns for soil gas, indoor air, and ambient air (NF ISO 18400-204, BRGM-INERIS, 2016), in order to assess the transfer of pollutants into buildings and the risks to occupants. However, commonly used sampling techniques often rely on limited durations, which do not always accurately represent long-term exposures.
Development of methods that better reflect long-term exposure
The project led to the development of an innovative method for long-term sampling of soil gas and indoor air. This approach, which relies on low-flow sampling over periods of up to several weeks, provides a more accurate representation of occupants’ chronic exposure and improves the reliability of assessments at contaminated sites.
Modeling soil-to-indoor-air transfer incorporating biodegradation
The partners have also developed an analytical modeling tool that incorporates the aerobic biodegradation of hydrocarbons. This advancement makes it possible to refine the assessment of pollutant transfer between soil and indoor air and to improve health risk assessments .
Validation of methods and recommendations derived from field measurement campaigns
The research was tested at two experimental sites contaminated with hydrocarbons and chlorinated solvents. Measurement campaigns were conducted in soil gas, subsurface air, and indoor air within buildings (CARACTAIR, p.13-20), to characterize the transfer of pollutants from the soil into occupied spaces.
These campaigns made it possible to validate the methods developed and to provide practical recommendations for the assessment and management of existing buildings.
Analytical report by TERA Environment and development of sampling solutions for soil gases and indoor air
TERA Environnement contributed to the project, particularly in the following areas:
- Analytical development of the method for the various target pollutants (hydrocarbons and chlorinated solvents)
- Analysis of laboratory breakdown tests
- Analysis of samples collected at two actual sites
The results of the CARACTAIR project represent a significant step forward in the management of contaminated sites and the assessment of indoor air quality, offering innovative and practical tools for professionals in the field.
TERA Environnement offers sampling media for long-term, low-flow soil gas sampling (5mL/min ranging from 7 days to several weeks) using 800/200 mg activated carbon tubes for hydrocarbons and chlorinated solvents (LOQ of approximately 20µg/m3 for 1 month of sampling).
For indoor air quality (IAQ) measurements, a sampling method has been developed using triple-bed adsorbent tubes for continuous sampling ranging from 7 days to 4 or even 6 weeks at a flow rate of 5 mL/min. This method is ideal for measuring benzene, toluene, ethylbenzene, and naphthalene, and is very effective for measuring hexane, heptane, and xylene.
For more information on these long-term sampling techniques, please contact us.
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