Flux chambers
Flux chambers are mentioned in the international technical literature as a useful and real tool for estimating the flow of interstitial gases that spread in the air from contaminated sites; the Italian Guidelines on the monitoring of soil gas propose them as a technique for the direct measurements of interstitial gases.
These measurements have assumed a very important value in the risk analysis and in the subsequent decision-making processes within the remediation activities: they allow the evaluation of the “vapor intrusion”, namely the process through which the pollutant chemical substances present in the soil or in the underground water can fill the unsaturated soil thus reaching the above environment and altering indoor and/or outdoor air quality, with potential risk to human health.
A flux chamber can isolate an area from external environmental conditions: the main microclimatic parameters that are monitored inside the chamber are not bound to the weather conditions of the site, especially wind.
By means of two connecting lines positioned on the dome, clean and dry air passes inside the hood at a controlled flow rate. The air in the soil is then “pushed” out of the system and monitored continuously or by sampling to determine the concentration of pollutants. Such measurements thus offer an estimate of the parameters searched for surface unit and time unit.
For example, the main substances that flow chambers can search are aromatic, aliphatic and organ-chloride hydrocarbons, nitrogenous and halogenated hydrocarbons, sulphurates, mercury, etc.
Mérieux NutriSciences owns several flow chambers and has a consolidated experience in their installation and management. When proposing this technique, we consider the geology and hydrogeology of the site as well as the climatic data to better plan the activities. During the quick sampling of the gas leaving the hood and once the conditions of the incoming air and the internal temperature have stabilized, it is possible to proceed in different ways:
- sampling with suitable adsorbing cartridges made of activated carbon or selective resins and subsequent laboratory analysis;
- continuous analysis directly on site by means of portable analyzers in order to recognize a series of compounds in real time and, for some substances, reach very low detection limits;
- sampling of organic VOCs by Canister and subsequent laboratory analysis. The high analytical sensitivity of this technique makes the model applicable to site-specific risk analyzes.
