Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p56
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 56/117)
Character Range: 502763–505579

in low permeability soils and for shallow probes or sub-slab probes. A number of tracer methods are available to test seal integrity  see API (2005) and ITRC (2007b).
    * Tubing type — the tubing type should be selected to minimise false positives due to outgassing from the tubing materials. Low sorbent materials such as HDPE and nylon are generally preferred. Further information on material properties may be obtained from suppliers or manufacturers.
    * Sample volume — sample volumes should be minimised as far as practicable to meet the requirements of the sampling/analytical method selected. A review of available studies on sample volumes by Hartman (2006) suggested that the sample volume is less important for coarse-grained soil, but in finer grained soils large volumes may be difficult to collect due to the creation of a vacuum during sampling. Large sample volumes increase the likelihood that the sample may originate from different depths and locations, hence sample volumes collected should be minimised. Near ground surface, recovering large sample volumes may result in ambient air being drawn from outside the annulus of the shaft of the probe.
    * Purge volumes — the sample probe, tubing and equipment have an internal volume that must be purged prior to sampling to ensure that only soil vapour is sampled and that the data obtained is representative. Generally, three to four system volumes should be purged where flow rates allow and as long as the purge volume is not large. Whatever calculation is used to estimate the volume purged, this should be consistent for all sample locations. As large purge volumes can result in low pressure/vacuum conditions which may cause contaminant partitioning from the soil to soil vapour, the purge volume should be minimised as far as practicable to ensure that the sample collected is representative. Real-time gas monitoring (using a landfill gas meter to measure oxygen, carbon dioxide and methane or a PID to measure total VOCs) can be useful for assessing the effectiveness of purging (and decrease the purge volume to less than three to four system volumes).
    * Sample flow rates — to minimise the potential for desorption of contaminants from soil to soil vapour in the sampling zone, the assessor should select a sample flow rate appropriate for the soil type. A low sample flow rate (<0.2 L/min) is important where soil vapour is collected from low permeability soil (McAlary et al. 2009); however, higher flow rates may be applicable for coarse-grained soils. Low permeability or high moisture content can induce greater suction pressures when sampling, which can make samples difficult to recover.
    * Equilibration time after installation — the equilibration times for soil vapour sampling is highly dependent on the drilling