WDA Consultants Inc.


GASSYS: A unique in-situ and passive gas sampling system from unsaturated soil and from groundwater.

Weyer, K. U., M. Hamann, and H. Kaiser, 2001
WDA Consultants Inc., 4827 Vienna Drive NW, Calgary, Alberta, Canada

2001



Abstract

Sampling of soil air is applied by the oil industry in exploration and contamination studies. Techniques used range from active collection, where soil gas is gathered by pumping from a borehole, to passive collection over the course of 10 days or more on buried reactive carbon or similar materials as they are exposed to soil air.

Each of those sampling methods has its disadvantages. Active sampling draws soil gas from a large undefined space near the sampling interval. This results in preference to gas flow in higher permeable systems. Hence the results do not reflect the true and undisturbed gas content at the sampling interval. Passive sampling methods usually collect gases by adsorption onto solid material. Analyses using such sampling methods are limited to determining relative gas concentrations as no direct gas sample is taken.

The newly designed passive gas sampling system GASSYS overcomes the aforementioned disadvantages. It takes quantitative and reproducible gas samples from the unsaturated soil. Since the tube of the sampling chamber is permeable to gas but not to water, it also is capable of drawing gas samples from groundwater. Up to four sealed sampling intervals can be installed within an EVA-tube at depths to 30m and more.

In case histories gases from volatile and less volatile hydrocarbons were collected in the EVA-tubes for approximately 20 years without apparent loss of functionality.

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