Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1:p1
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1 (pt 1/9)
Character Range: 2844256–2847252

1                   Equations for derivation of HILs and interim HILs

1.1         Introduction
This appendix presents the equations used in the derivation of soil health investigation levels (HILs) and interim soil vapour HILs. The appendix does not present all equations and methodologies that may be considered in conducting a site-specific assessment, rather it presents those equations used in deriving the HILs presented in Schedule B7. The derivation of HILs requires the consideration of a number of exposure pathways. With respect to the soil HILs, the following pathways are considered (as relevant for the exposure scenarios and compounds considered):
    * Ingestion of soil and/or dust (indoors). The ingestion rate adopted for the characterisation of this pathway is a combined value reflecting both sources; hence, the calculation undertaken is a combined calculation.
    * Dermal absorption during contact with soil and/or dust (indoors that may be derived from outdoor soil). As with the calculation of ingestion, the calculation of dermal absorption is based on absorption from both sources combined.
    * Inhalation of dust generated from outdoor soil (where surface cover is poor) both outdoors and indoors (including resuspension of dust indoors).
Inhalation of volatile chemicals in soil indoors and outdoors has been considered in the derivation of interim soil vapour HILs.
Worked examples of the HIL A calculations using the equations presented in this Appendix for cadmium and benzo(a)pyrene are included in Attachments A and B respectively.

1.2         General equations
The approach adopted in the derivation of soil HILs is consistent with the approach adopted in the derivation of previous HILs (NEPC 1999) and in other jurisdictions including the USA (in the derivation of preliminary remediation goals (US EPA 1992; US EPA 2002) and regional screening levels (US EPA 2012)) and the UK and New Zealand (in the derivation of soil guideline values (MfE 2011; EA 2009])).
Very generally, a soil health investigation level (HIL) for an exposure pathway (x), where a threshold approach is adopted, can be back-calculated by setting the estimated intake for a chemical (i) to the acceptable intake allowable from soil for that chemical (i), then rearranging the equation as follows:

Equation 1
Similarly, HILs can be derived for other pathways of exposure and for non-threshold carcinogenic effects as relevant. The final HIL is calculated by combining the pathway-specific HILs as noted below:
   Equation 2

where:
              HILingestion  = derived soil guideline associated with the ingestion of soil and dust by young child and/or adult, refer to Equations 3, 4 and 5
              HILdermal  = derived soil guideline associated with dermal absorption of contaminant in soil/dust by young child and/or adult, refer to Equations 6, 7 and 8
              HILplant uptake  = derived soil guideline associated with ingestion of contaminant in home-grown fruit and