SOIL-GAS SAMPLE COLLECTION – SAMPLING SYSTEM

The soil gas sample for soil gas radon concentration measurement is usually collected using a small-diameter hollow steel probe with a free, sharpened lower end (a lost tip) combined with a large-volume syringe. The entire system must be perfectly sealed. The use of a sampling system that is not perfectly sealed, or that does not reach a sufficient level of vacuum to collect gas samples in soils of low permeability, may result in an underestimated soil gas radon concentration. Therefore, such system must not be used.

The internal volume of the cavity, which is created at the lower end of the sampling probe, must be large enough to enable the sample collection. The soil gas samples are collected from a depth about 1.0 m below the ground surface (the depth of 0.8 m below the ground surface is used in the Czech Republic). If the soil gas samples cannot be collected due to extremely low soil permeability, high groundwater saturation, or presence of shallow, solid rock layers, the following modifications can be used. If the soil permeability is very low, the cavity at the lower end of the sampling probe can be enlarged by retracting the probe about 10 - 15 cm toward the surface. Sometimes (upper soil layers with higher permeability are not reached, the probe remains fixed in the soil, as well as contamination of the soil gas by atmospheric air can be avoided) the probe can be retracted to 0.5 m below the surface, while maintaining the perfect sealing of the whole system. A similar approach is often used when the sampling layer is saturated with water. In cases involving shallow solid rock layers, the minimal sampling depth can be changed to 0.5 m below the surface. However, all deviations from the standard sampling depth should be reported, including an explanation and an estimate of potential influence of these differences to the evaluation results.   

The SAMPLING SYSTEM (standard supply) includes following items:

25 small diameter hollow probes 12/2 mm length 1,10 m, 2000 „lost“ sharp tips, 3 punch wires, 1 retractor (the special one for easy retracting to the surface, two parts), 3 drive in heads, 10 syringes, manual and additional needs (rubber tubes, sampling connector).