Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:3:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 3 (pt 3/9)
Character Range: 925929–928956

in Section 2.4.9 of Schedule B5b.

Most organic contaminants of interest at contaminated sites have no natural background concentration, though there are notable exceptions, including polycyclic aromatic hydrocarbons. Therefore, ambient background concentrations should either be measured at a suitable reference site, or a default assumption of zero be made for organic contaminants. There are no equivalent models to that of Hamon et al. (2004) available for organic compounds.

Further information on the establishment of background concentrations in soil and groundwater may be found in SA EPA (2008), ANZECC & ARMCANZ (2000) and US EPA (2002b, 2002c).

    3.2.4          Vapour and particulate (dust) sampling
Direct sampling of ambient air, soil vapour and/or dust can be useful in the risk assessment process, as it provides actual data for inhalation exposure points as opposed to results obtained from fate and transport modelling applied to soil or groundwater data.

Air sampling may be useful in scenarios where human populations are potentially exposed to airborne contaminants over prolonged periods (for example, occupational or residential scenarios).

Australian standards for ambient air quality are provided by the NEPC (2003). Standard methods for sampling and analysis of ambient air and dust are available in various Australian standards (AS 3580 Series; AS 2800-1985; AS 2985-2004; AS 2986-1987; and AS 3640-2009) and US EPA TO Methods (including TO-15 and TO-17, US EPA 1999). Australian guidance on air sampling, analysis, assessment and modelling is available from New South Wales Department of Environment, Climate Change &Water (NSW DECCW, 2010).

Soil vapour sampling guidance is included in Schedule B2 and references therein. Specific guidance on dust sampling for lead is available from US EPA (1995a, 1995b) and ASTM (E1792-03 Standard specification for wipe sampling materials for lead in surface dust, 2011).

3.3              Exposure pathway variables

    3.3.1          Organic carbon content
The potential for a contaminant to volatilise from soil is strongly influenced by the compound's soil partition coefficient (Kd), which is a parameter that estimates the potential for the contaminant to adsorb to soil particles. For organic compounds, which sorb most readily to organic carbon within soil, the partition coefficient is a function of the compound's organic carbon partition coefficient (Koc) and the fraction of organic carbon (Foc) in the soil. The organic carbon partition coefficient represents the chemical partitioning between organic carbon and water in soil. For organic compounds, the relationship between Kd, Koc and Foc is expressed by the following equation:
  Kd = Koc x Foc
Fraction of organic carbon is a soil property that can be measured, and which often has a significant effect on the risk assessment outcome for volatile and persistent contaminants. Samples of uncontaminated soil should be tested for Foc such that the concentration of carbon measured is not