Soil gas samples are collected from shallow point sources. The soil-gas survey is generally carried out in the summer during a period of stable meteorological conditions. A 1m hollow steel probe with a conic point at the bottom and a sampling port on top is inserted to a depth of 0.5m below the ground surface. Two 50 cc samples of soil gas are extracted with a syringe for cleaning the probe, then a soil-gas sample is extracted and stored in an evacuated 25 ml steel cylinder for laboratory analysis (He, H2, O2, N2, CO2, CH4 and H2S) by means of a Perkin-Elmer AutoSystem XL gas chromatograph.
Furthermore, soil-gas flux measurements have been performed in situ by means of an accumulation chamber (volume: 50 litres) set on the ground in such a way as to eliminate the input of atmospheric air. Every five minutes a gas sample is extracted from an external septum located on the top of the chamber and analysed in loco using a portable gas chromatograph. These measurements result in an accumulation curve which can be used to calculate soil gas flux.
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