The derivation of soil GAC requires the integration of pathway-specific GAC. Although simple in most cases, combining multiple routes of exposure is a complex process which must now be undertaken using ‘the 50% Rule’ on background exposure. The CLEA model relies upon an iterative/repetitive process to search for solutions for the soil GAC by automatically limiting the background exposure to less than that contributed from the soil source under ‘the 50% Rule’.

This paper describes the alternative integration procedures (AIP) which are derived by directly solving three sets of second-order polynomial equations that describe ‘the 50% Rule’ on background exposure. Testing against the CLEA model indicates that the GAC derived using the AIP are identical to those derived by the CLEA model. It is anticipated that the implementation of the AIP would significantly reduce simulation run-time for the CLEA model, as it requires numerous iterations to satisfy a pre-determined closure criterion.

Key words: alternative integration procedures (AIP), average daily exposure (ADE), Contaminated Land Exposure Assessment (CLEA), generic assessment criteria (GAC), median daily intake (MDI), Risk Based Corrective Action (RBCA, tolerable daily intake (TDI)