Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:4:p3
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 4 (pt 3/24)
Character Range: 948654–951561

contaminant concentration. This provides a 95% confidence level that the true population mean will be less than, or equal to, this value. The 95% UCL is a useful mechanism to account for uncertainty in whether the data set is large enough for the mean to provide a reliable measure of central tendency. Note that small data sets result in higher 95% UCLs. Further guidance on the use of 95% UCLs can be found in NSW DEC (1995), US EPA (2006) and US EPA (2007a).

Monte Carlo (or other probabilistic) techniques. Refer to Section 2.4.4.

Source input values will normally be soil, groundwater or soil vapour data. In more detailed assessments, more specific sources may be defined, such as dust, bore water or ambient air.

Considerations in this section are also relevant to contaminant source input values derived using fate and transport or other exposure point estimation methods. These are described elsewhere in this Schedule.

    4.2.2          Exposure pathway input values
This stage involves describing the physical environment in terms of the input values that will be used to represent exposure pathways in the model. The scenario being modelled should clearly relate to the existing or proposed land use for which decisions on contamination are required. Depending on the pathways modelled, a number of variables will need to be defined, for example, soil type, soil properties, depth to groundwater, soil and vapour sources, climactic variables and building characteristics and dimensions. Schedule B7 provides a complete list of the exposure pathway variables used to derive the HILs, together with justification of the parameter values selected.

Where the CSM is similar to that used to derive the HILs, exposure pathway input parameters used to conduct a site-specific risk assessment should consider those adopted in the derivation of the HILs, with further consideration of site-specific factors (where relevant). Where the CSM is different from the HIL scenarios, further consideration of site-specific input parameters and variables may be warranted.

Each variable used in a model should be clearly referenced and justified. Some commercially available models do not permit amendment of all the variables listed and the user has to rely on the default values supplied with the software. Where this is the case, it should be demonstrated that the model defaults are applicable to the site. It should be appreciated that models developed for the use in other countries may incorporate assumptions that are not justified in the Australian environment (science policy and physical environment). Reference should be made to the physical setting assumptions outlined in Schedule B7 for guidance on values likely to be suitable for Australian sites. Site-specific data from site investigations should be used wherever possible.

    4.2.3          Exposed population input values
The purpose