Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p61
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 61/117)
Character Range: 516174–519085

assessors may wish to use alternative methods, in which case the alternative method should be at least as rigorous and reliable as the TO-methods. For further information on reference methods and alternative methods, see Schedule B3.

    10              Contaminant fate and transport modelling
Source: EA (2000a)

10.1          Overview of contaminant fate and transport modelling
Risk assessments undertaken when groundwater or soil vapour contamination is present may involve the use of quantitative contaminant fate and transport models. Specific expertise and experience are required to carry out this type of modelling because of the highly complex nature of most contaminant fate and transport problems.

In the context of this guidance, a model is defined as a mathematical representation of reality in the form of equations or computer code and values of parameters. Output from this type of modelling may include travel times to receptors and concentrations of contaminants likely to reach receptors.

A model should only be used when it is clear how and why it is to be used. In deciding whether a modelling approach is appropriate, some of the questions that need to be considered are:
    * What is the objective for modelling and what are its benefits?  For example, a model may help in the decision-making process by quantifying the potential impact on a receptor and therefore the need to take action to protect the receptor.
    * Can a model provide reliable answers?  For example, the hydrogeological system may be too complex to be adequately represented by the available modelling resources, in which case the application of a model would serve no purpose.
    * Is the hydrogeological system sufficiently understood to warrant the use of a model?   A model should not be used as an alternative to collecting further site-specific information; however, it may be used to guide further data collection.
If the decision is taken to use a model, then the limitations and assumptions of the model selected should be assessed to determine whether it is fit for the selected purpose.

Modelling is unlikely to be appropriate where preferential migration pathways are present. These pathways may be natural features; for example, solution channels associated with karst development in limestones, weathered shear zones, and permeable geological faults, or anthropogenic in origin; backfill around foundations, backfill in trenching for buried utilities such as sewer, water, gas and electricity lines, and backfill around buried tanks and associated piping.

The key stages in developing a contaminant fate and transport model are:
    * scoping study, comprising a review of existing information and consultation with relevant stakeholders to define the objectives of the study and the scope of work
    * development of a CSM of the saturated and unsaturated zones and consideration of how the