Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p12
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 12/24)
Character Range: 973637–976590

number of components in a solution increases, the individual vapour pressures decrease as the mole fraction of each component decreases with each additional component.

In order to calculate the mole fraction for mixtures, or a solution of compounds, it is necessary to know the concentrations of the individual components comprising the non-aqueous phase liquid. This cannot be achieved by estimating the proportion of components in non-aqueous phase liquid from dissolved phase results. A sample of the free phase liquid should be collected and analysed if practicable.
Mole fraction = Number of moles of compound
   Total number of moles
Number of moles  = Concentration of compound in solution
    Compound molecular weight
The saturation vapour concentration can therefore be calculated by:
Csat  =  X  ρ  MW
           R  T

where:
 Csat =  Saturation vapour concentration (g/cm3)
 X =  Mole fraction of chemical in product
  =  Vapour pressure of the chemical (mm Hg)
 MW =  Molecular weight of compound (g/mole)
 R =  Molar gas constant (62, 361 mm Hg - cm3/mole - k)
 T =  Absolute temperature (293 K for ambient conditions)
Where non-aqueous phase liquid is present, exposure point concentrations may be calculated using models such as NAPL-SCREEN and NAPL-ADV (US EPA (2004a).

4.5              Exposure point concentrations  particulates
Where contamination is present in surface soils or there is potential for near-surface contamination to be brought to surface during construction activities, exposure to particulates (dust) requires consideration.

The concentration of particulates relevant for different exposure scenarios can be determined using either a dust concentration factor or a soil particulate emission factor (PEF). The PEF approach is presented in the soil screening guidance (US EPA 1996) and supplemental soil screening guidance (US EPA 2002a). The methodology uses a fixed conservative soil particulate release rate combined with a box model to determine dust concentrations in air. The PEF assumes loosely packed surface soil so that a relatively large concentration of dust is entrained in air. The entrained soil particles are considered to mix in the ambient air breathing zone directly above the soil source. The calculation of a PEF using the US EPA equations may not be applicable to Australian conditions and hence suitability of the equation should be considered prior to use. In addition, the  model does not address exposures associated with dust that is generated from dry, exposed soil, generated during active use of a site (for example, during use of dry sporting fields) or  mechanically generated (such as during vehicle movements). Dust generated during these scenarios may be better estimated using a dust concentration (loading) relevant to the area and nature of activity assessed or alternatively, exposure may be assessed by conducting air quality monitoring.

4.6              Exposure point