Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p49
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 49/117)
Character Range: 483803–486912

space/indoor air
    * biodegradability of vapours and availability of oxygen.

Measurement of indoor or ambient air is the most direct approach to assessment of vapour exposure. However, indoor air sampling can be expensive if many samples over a reasonably long period are needed to obtain representative results. In homes and workplaces, gaining access can be difficult and may lead to unnecessary concern on the part of the occupants. Depending on the volatile compounds considered, ambient and indoor air results may be difficult to interpret since confounding sources of contamination (refer Section 9.3.1) may be present. Where affected by background sources, the collection of indoor or ambient air measurements may not be considered the most appropriate approach.

Soil vapour measurement is the preferred route in most situations where a vapour issue (from a subsurface source) is considered likely to exist.

In the absence of measured soil vapour concentrations, it is also possible to model the generation of vapour from soil, groundwater and non-aqueous phase liquids. This procedure adds another level of uncertainty to the process. The uncertainties associated with the use of a model should be well understood and discussed in relation to the nature of the volatile contaminants assessed. Where unresolved uncertainties or unacceptable risks are predicted by modelling vapour concentrations, direct measurement of soil vapour and/or indoor and ambient air should be obtained.

9.3              Sampling and analysis plan design
Source: API (2005), Davis et al. (2009a), ITRC (2007b), ODEQ (2010) and US EPA (2012a)
When designing an SAQP, consideration should be given to the following:
    * confounding sources of VOCs and SVOCs
    * degradability of vapours and potential presence of daughter compounds
    * land use
    * environmental factors including spatial and temporal variability issues
    * reliability, representativeness, precision and accuracy of available measurement techniques
    * potential for preferential migration pathways.

    9.3.1          Confounding sources of VOCs and SVOCs
Indoor air sampling is the most direct method of measuring VOC exposures where the CSM has identified that vapour intrusion is a potentially complete pathway. In circumstances where very high levels of contamination are present or the contamination has a unique character, the data can provide relatively quick confirmation of vapour intrusion impacts. However, for most sites, simply detecting VOCs inside a building is not definitive evidence of vapour intrusion.

Outdoor or ambient air commonly has detectable levels of VOCs, sometimes exceeding ambient air guideline values. The largest sources of these contaminants include vehicle emissions, fuel storage facilities and emissions from commercial/industrial activities (including service stations). As outdoor air typically makes up 99% to 99.99% of indoor air, ambient VOC levels tend to represent the minimum concentrations in indoor air. Buildings can also contain interior sources of VOCs, which include building materials,