SECI has conducted soil gas sampling in a wide range of buildings across Illinois. In addition, SECI has installed and sampled soil gas probes in parking lots and on active gasoline filling station sites. In order to complete the soil vapor sampling activities, a three inch in diameter coring is completed through the concrete or asphalt surface with a diamond tip coring machine. After the core is removed, a one inch in diameter direct push sampling device is utilized to remove the soils to a depth of approximately three feet.

After the soils are removed, a one half inch in diameter (outside diameter), stainless steel soil vapor probe with a perforated tip manufactured by SKC Industries is inserted into the borehole. The annulus space around the soil vapor probe is filled with quartz sand to avoid clogging of the perforations on the soil vapor probe.  The sand pack allows for direct transfer of the vapors from the soils to the probe for sampling.

The borehole is then sealed with bentonite.  This installation method most closely models the potential for vapor migration through underground utility lines and/or through cracks or floor drains which is the most likely method of migration on commercial properties.

After the borehole is sealed, a ¼ inch Teflon tube wis attached to the soil vapor probe using a stainless steel barbed fitting. The tube is sealed onto the barbed fitting with a stainless steel hose clamp. The sampling tube is then attached to a SKC Universal Sample Pump. The sample pump is set to operate at a flow rate of 200ml/minute.

After the purging and sampling tubing is attached to the soil vapor probe, a shroud is constructed using a clear plastic bag that was sealed on the floor with sand tubes. Helium is then introduced into the shroud until the plastic bag is fully inflated.

The sampling pump is then started, and the sampling train is monitored with a MGD Model 2002 Helium Leak Detector. The perimeter of the shroud and the exhaust of the air pump used to purge the soil vapor probe are monitored for the presence of Helium to evaluate the integrity of the sampling train. In addition to monitoring for the sampling train integrity with the Helium sensor, the exhaust from the purge pump is monitored with a Photoionization Detector to evaluate for Volatile Organic Compounds.

The air pump is operated for approximately 15 minutes to purge three volumes of air out of the borehole and vapor probe. After the purging is completed, the pump is disconnected, and a laboratory prepared Summa Canister (under vacuum) is connected to collect the representative soil vapor sample. After the canister is filled, it is sealed, labeled and placed into a cooler for transport to the analytical testing laboratory of TO – 15 analysis.