Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p57
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 57/117)
Character Range: 505303–508186

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 method. Direct push methods cause minimal disturbance to soil vapour profiles and sampling may be carried out after 30 minutes, whereas 48 hours is recommended for augered installations (API, 2005).

    9.4.3          Passive soil vapour sampling
Source: Davis et al. (2009a)
'Passive' soil vapour sampling or passive implant sampling refers to the burial or placement of an adsorbent or other material in the ground, which is recovered for analysis after an appropriate period of time (hours to days). It is termed passive because no gas sample is actively recovered from the soil profile. The adsorbed mass cannot be equated to a concentration because the volume of air associated with the adsorbed mass is largely unknown.

The method enables a screening level assessment of the presence of vapours in the vadose zone to identify if the vapour pathway is complete and to identify hotspot areas for further sampling using more quantitative methods. Passive samplers may be of benefit in areas where soil vapour probes cannot be installed, in areas where preferential pathways are suspected (or need to be assessed) or where very low permeability soils limit the practicality and integrity of sampling from soil vapour probes (API, 2005).

Since the sorbent can be deployed for long periods (typically 3 to 14 days), this concentrates the mass of contaminants absorbed to the sampler and enhances sensitivity. Longer exposure time does not improve sensitivity except during prolonged rain events which cause soil saturation and interrupt vapour migration in the subsurface (NJDEP, 2005a).

Passive samplers may desorb soil vapours from fine-grained layers that are otherwise not mobile, thus overestimating the amount of soil vapours that are capable of being transported into overlying zones.

More detailed information can be found in Davis et al. (2009a), Baker et al. (2009), ITRC (2007a and 2007b) and NJDEP (2005a and 2005b).

    9.4.4          Flux chamber methods
Source: Davis et al. (2009a)

9.4.4.1         Introduction
A flux chamber (or a flux hood) is a device that is placed on a surface to measure vapour/gas flux (or emission rate) discharging through that surface. The surface may be open ground or be part of a building foundation such as a concrete slab.

Flux chamber methods have generally not been widely used in site assessment or considered a primary vapour intrusion assessment method due to a number of limitations and disadvantages, which are discussed in Davis et al. (2009a) and Baker et al. (2009). However, flux chamber methods may be applicable when a direct measurement