With Small Volume Sampling, soil vapor is withdrawn from the inert tubing using a syringe connected via a three-way valve. The first 3 to 5 dead volumes of the probe are removed, allowing it to fill with in-situ soil vapor. The next syringe of gas is withdrawn, and immediately transferred to the mobile lab for analysis within minutes of collection. Additional soil vapor samples may be collected and stored in gas-tight containers as desired.
To minimize the potential for cross-contamination between sites, all external probe parts are cleaned of excess dirt and moisture prior to insertion. The internal inert tubing and sampling ports are flushed with hundreds of cubic centimeters of ambient air between samples. If water, dirt, or any material is observed in the tubing, the tubing is replaced with fresh tubing. If concentrations greater than 100ppmv are detected for any compound (except methane), the tubing is replaced.