The following information provides a description of a typical vapor implant installation using a direct push rig. Additional information regarding vapor sampling and analytical requirements is found in the California Regional Water Quality Control Board (Los Angeles Region) Advisory for Active Soil Gas Investigations.
For shallow sampling (<15 ft) in most soils, a two-inch diameter “pre-punch” is first driven to the desired depth of the implant. The pre-punch is removed leaving an open borehole to the proposed implant depth. In collapsing soils that do not leave an “open” borehole or for deeper sampling, steel casing may be required for implant installation. Small diameter tubing (0.25" O.D. x 0.17” I.D.) is then installed in the open borehole or steel casing. Polypropylene or teflon tubing is generally used. For open boreholes, 3/4 inch diameter PVC casing is used as a "guide” to allow easier installation of the flexible tubing. Prior to installation, a small filter (1 inch long, 3/8 inch diameter) is attached to the end of the tubing using a “push on” connector.
Once the implant and tubing is installed to the bottom of the borehole, any casing used is removed. Sand and bentonite are then placed to complete the implant installation. Generally #2/12 sand is slowly poured around the tubing to six inches above the filter. Bentonite is then poured in the borehole as the PVC “guide” casing or steel casing is removed.
The bentonite is hydrated using clean water to ensure an air tight seal is made. The sand and bentonite emplacement depths are checked using a tape measure in the borehole. A small two way valve is attached to the open end of the tubing in a closed position. The valve is opened when sampling is performed. Generally three times the volume of the tubing is purged before a vapor sample is obtained for analysis.
