Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p50
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 50/117)
Character Range: 486643–489559

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, paints, dry-cleaned clothes and some commercial and household cleaning products. It is therefore advisable to conduct a survey of the building interior in advance of any indoor sampling to identify potential confounding sources and eliminate them as far as practical prior to sampling and to obtain concurrent ambient air samples.

As it is often not possible to remove all interior sources of VOCs prior to sampling, indoor air results should only be used in the context of a multiple-lines-of-evidence approach. To reduce the frequency of false positives, indoor air sampling is not recommended until other information (lines of evidence) indicates a potential vapour intrusion risk.

Further information including detailed protocols for the collection of indoor air data can be found in ITRC (2007b and 2007c), NYSDOH (2006), and NJDEP (2005b).

    9.3.2          Biodegradation
The concentration of petroleum hydrocarbon (such as TPH and BTEX) vapours in well-oxygenated, generally near-surface soil can be significantly reduced by biodegradation (Davis et al. 2009a, 2009c). However, this is generally not the case in less oxygenated soil such as under large areas of impermeable hardstanding or building foundations.

For petroleum hydrocarbons, the fundamentals of an approach to include an exposure reduction factor due to aerobic biodegradation are discussed in Davis et al. 2009c and included in Schedule B1. The approach is applicable to vapour sources at depths of 2 m or greater and requires the recovery of a soil vapour sample from a depth of at least 1 m below ground in close proximity to the building (or in a similar nearby soil, soil moisture and soil coverage environment). Where the building slab penetrates the ground by more than 0.3 m, then the additional depth of penetration of the slab below 0.3 m should be added to the depth at which the soil vapour sample is recovered for oxygen analysis. It is noted that the measurement of oxygen in the soil profile can be difficult and care should be taken when using this data to support biodegradation.

Halogenated hydrocarbons can also undergo biodegradation, though the process for most halogenated compounds occurs in anaerobic conditions via a number of steps that can be much slower than for the aerobic degradation of petroleum hydrocarbons. The SAQP should address potential degradation products as appropriate.

    9.3.3          Undeveloped land
Assessing the potential for vapour intrusion to a future building on vacant land poses unique challenges. Some of the investigative tools of the vapour intrusion pathway (for example, indoor air and sub-slab sampling)