Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p46
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 46/117)
Character Range: 475371–478572

moves along the migration pathways. This requires that chemical, physical and biological interactions between sources and sub-surface materials are taken into account. The CSM should describe the processes that control the movement of contaminants in soil and the unsaturated and saturated zones.

Degradation can be a significant process in decreasing contaminant mass. The actual rate of biodegradation varies according to a range of factors including contaminant type, microbial populations, redox conditions, temperature and the chemical composition of aquifer materials and groundwater. Evidence for the occurrence and efficiency of degradation processes should be considered in the development of the CSM. Where modelling is undertaken, care should be taken to ensure that the biodegradation process(es) being modelled is appropriate and that realistic reaction rate constants are used.

Further information on attenuation processes and their effects can be found in EA (2000a, 2000b), ITRC (1999), ITRC (2010) and Beck and Mann (2010).

    9                   Vapour assessment

9.1              Introduction
This section provides an assessment framework for vapour intrusion (migration of vapours into a building) and basic requirements for measurement of volatile organic compounds (VOCs) in soil vapour, indoor air and outdoor (ambient) air. Primarily, the methods included are applicable to chronic low levels of vapour concentrations as are typically encountered in contaminated site assessments.

Vapours may be generated by biological, chemical and physical decomposition of spilled or dumped wastes. Assessment of ground gases associated with operating or closed landfills ('landfill gas') or buried putrescible wastes is beyond the scope of this guidance. Information on these applications can be found in NJDEP (2005a) and Wilson et al. (2007).

Soil vapour surveys have a wide application in the assessment of volatile contaminants, for example, they may be used when:
    * assessing the presence or absence of VOC contamination
    * delineating VOC contamination in soil and groundwater
    * characterising VOC contamination
    * identifying/differentiating between sources of VOC contamination
    * assessing VOC migration pathways in groundwater
    * monitoring biodegradation of contaminants
    * assessing vapour intrusion risk.
An overview of vapour fate and behaviour processes relevant to VOCs can be found in Davis et al. (2004, 2009a and b). Additional information on assessing vapours in the context of human health risk assessment is provided in Schedule B4.

The assessment of vapours should be undertaken by appropriately qualified and experienced professionals.

If vapour intrusion is suspected of posing an existing or imminent threat to human health, including from inhalation exposure or risk of explosion, then immediate mitigation or management strategies should be implemented.

9.2              Vapour  intrusion assessment framework
Source: API (2005), ITRC (2007a), Davis et al. (2009a) and ODEQ (2010)

    9.2.1          Introduction
For the vapour intrusion pathway to be complete, there must be three components present – a source of sub-surface