Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p63
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 63/117)
Character Range: 521573–524630

this calibration step, the appropriateness of the model, the need for further site-specific data, and the CSM should be reviewed.
When completed, the model should be fully documented, including the objectives of the model, the model code used and its limitations, description of the conceptual model including all parameters used and any assumptions made, how the model was constructed and calibrated, and information on the accuracy of its predictions.

10.2          Data requirements
The quality and reliability of contaminant transport model results are dependent on the data that has been used to develop the conceptual model and to construct and refine the mathematical model. If the data is inadequate, the model results will be unreliable.

Data requirements vary at different stages in the modelling process but are dependent on the objectives, the complexity of the problem and the sophistication of the analysis. The assessor will need to determine the key parameters for which site-specific data is required and those parameters for which literature values will be acceptable. The ease of collection and relative cost of obtaining site-specific values for flow and transport parameters are summarised in Table 6 below.

In some instances, the collection of site-specific hydrogeological data may not be possible; in which case, reasonable default values should be selected based on geological records.

Rigorous scrutiny should be applied to ensure that input parameters are consistent with the geology, hydrogeology and geochemistry of the site or region modelled. Special care should be taken to ensure that values for hydraulic conductivity, contaminant load and degradation rates (if applicable) are appropriate, and that conclusions drawn on the basis of fate and transport modelling are supported by the available monitoring data.

10.3          Limitations of fate and transport modelling
Problems can arise at different stages of contaminant fate and transport modelling due to:
    * poor sampling and analysis
    * inadequate CSM
    * inappropriate model selection
    * use of inappropriate data sources (literature)
    * (mis)interpretation/use of results.
Further information on generic good practice to avoid these problems can be found in EA (2000a), Middlemis (2000) and Barnett et al. (2012).

10.4          Types of model
The two main types of mathematical model are analytical models and numerical models.

Analytical models use exact solutions to equations that describe the migration of contaminants. In order to produce these exact solutions, the flow/transport equations have to be considerably simplified such that they are typically only applicable to simple flow and contaminant transport systems. Analytical models can be simple formulae, spreadsheets or sequences of calculations packaged up in a piece of software, for example, BIOSCREEN and BIOCHLOR from US EPA.

Numerical models use approximate numerical solutions to the governing equations of groundwater flow and transport. Parameter values are specified at