WDA Consultants Inc. - GASSYS Introduction

GASSYS: a unique, in situ & passive gas sampling system
for unsaturated soil and groundwater

GASSYS measures the characteristics and concentrations of soil gas in the subsurface in a passive, non-pumping manner using ¾" tubes with synthetic EVA permeable membrane tubes. Upon installation the gas content of both the unsaturated and saturated part of the subsurface enters the tube by diffusion until the gas concentration in the tube is equal to the gas concentration outside the tube. While the sampling tube is permeable to gas it is impermeable to water. The type of gas present can be identified within an hour. The time to reach the dynamic equilibrium depends on the characteristics of the gas molecules. It may take from 7 hours to several days. To be on the safe site a sampling time of up to 14 days is often recommended.

After the dynamic equilibrium has been reached the gas contents in the tube is sampled from the surface through fine stainless steel tubes using a calibrated syringe system to collect the gas. The contents of the syringe is then sucked in by an evacuated head space vial with a septum. The sampling can be repeated at exactly the same intake area as often as required for years and decades to come. Membrane tubes can be segmented and hold up to four isolated intake areas with separate stainless steel tubes extending to the surface. GASSYS can easily be assembled in the field and reaches depths of 30 m or more.

GASSYS Schematic
Schematic diagram of a GASSYS installation with 3 sampling segments arranged by layer.

Since 1995 GASSYS has been developed and field tested by KaiserGEOconsult GmbH, Erlangen/Germany (KGC) and the Landesgewerbeanstalt Bayern, Nürnberg/Germany (LGA). The permeable membrane tubes have been developed by Siemens AG, Erlangen, Germany and, for 20 years, proven to perform to expectation in Siemens' leakage detection system LEOS along pipelines worldwide. Field tests against pumping gas sampling systems using reactive carbon for adsorption proved GASSYS to be superior in operation, quality, reproducibility of data, longevity of the installation and low costs.

GASSYS is marketed in Europe by KGC and Röhrenwerke Kupferdreh GmbH (RKG), Essen, Germany, and in the Americas by WDA Consultants Inc., Calgary, Canada (WDA). These companies also offer advice and support in application planning, design, field installation and sampling, if desired. Equipment needed to install GASSYS is manufactured by RKG in Essen, Germany.

An installation and sampling ready system consists of
1. GASSYS-tubes, ready for installation
2. Equipment for installation and gas sampling:
a) removable casing pipe to push the system in place,
b) anvil adapters for connecting casing pipes,
c) lost drive point,
d) connector of lost drive point to casing,
e) rods for removal of the lost drive point,
f) rod to hold GASSYS in place during retrieval of casing,
3. Gas sampling equipment (includes manometer for pressure measurement during gas sampling procedure).

What follows are a number of pictures of the GASSYS apparatus. Click on each thumbnail for a larger version of the picture.

    GASSYS#1 Thumbnail   Detailed view of the GASSYS head assembly with four steel microtubes leading to four segments.
    GASSYS#2 Thumbnail   Scaled view of the tubing assembly displaying the microtubes.
    GASSYS#3 Thumbnail   Use of a syringe to extract the air sample from a segment.
    GASSYS#4 Thumbnail   Evacuating the head-space vial.

For more info contact:

WDA Consultants Inc.
4827 Vienna Drive NW
Calgary, Alberta, Canada T3A 0W7

Tel: +1/403/233-9222
Fax: +1/403/233-9166

Otherwise, see the paper hosted on this website or our slideshow showing a more detailed explanation of the setup, installation, and sampling methodology which is available for download here...