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Direct Sampling Systems Title

An alternative method of soil gas sampling is to collect soil gasses directly through probe rods. Using this method cleanliness of the rod bore is an imperative. If more than one rod length is used, it is also necessary to use the proper size O-rings at all rod connections. As with any soil gas sampling, it is desirable to eliminate any annular space when inserting the probe rods, thus preventing the possible flow of atmospheric air down around the rod and into the sampling train. AT14/AT14AL Expendable Drive Points normally work well for this purpose for both 1.0 in. and 1.25 in. rods. Remember, any of the PRT point holders can also be used for through -the-rod soil gas sampling. When syringe sampling is to be performed, a short length of silicone tubing is often used as a hose connection at the gas sampling cap. This allows a syringe needle to be inserted through the silicone tube section and directly into the rod bore for sampling.

 

Wes McCallTwilight Zone or Vadose Zone, Both Can Be Scary
written by Wes McCall, Geoprobe® Environmental Geologist
taken from the Spring 2006 issue of The Probing Times Newsletter

The first time I used a Geoprobe® machine was in 1988 on a soil gas investigation somewhere in Iowa. My first field project was to track volatile organic contaminant (VOC) plumes in a suburban area and try to locate the potential sources. The area reminded me a little bit of the Twilight Zone but it wasn’t! A Ford van housed the 8M probe unit and boxes of sample bottles, sample coolers, personal protective gear, and of course duct tape and garbage bags. In those days, Geoprobe® and direct push was a brand new concept and most folks were using drill rigs for soil gas investigations or NPT pipe and a slam bar if low-tech and low cost was the need. After using a slam bar and a modified car jack for the extraction process, the Geoprobe® seemed like a dream come true! We pulled more soil gas samples in one day than they used to get in 3 or 4 days with the slam bar!

Soil Gas Contaminants in Residential AreaIn the past we had used soil gas sampling and field analysis as a cost-effective way to track and map VOC contaminant plumes and find the source areas. That was much less expensive than augering to install monitoring wells and collecting groundwater (or soil gas) samples to send to the CLP laboratory for analyses.

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