Model Software Selection
After hydrogeological characterization of the site has been completed, and the conceptual model developed, a computer model software is selected. The selected model should be capable of simulating conditions encountered at the site. The following general guidelines should be used in assessing the appropriateness of a model:
Analytical models should be used where:
- Field data show that groundwater flow or transport processes are relatively simple.
- An initial assessment of hydrogeological conditions or screening of remedial alternatives is needed.
Numerical models should be used where:
- Field data show that groundwater flow or transport processes are relatively complex.
- Groundwater flow directions, hydrogeological or geochemical conditions, and hydraulic or chemical sources and sinks vary with space and time.
A one-dimensional groundwater flow or transport model should be used primarily for:
- Initial assessments where the degree of aquifer heterogeneity or anisotropy is not known.
- Sites where a potential receptor is immediately downgradient of a contaminant source.
Two-dimensional models should be used for:
- Problems which include one or more groundwater sources/sinks (e.g. pumping or injection wells, drains, rivers, etc.).
- Sites where the direction of groundwater flow is obviously in two dimensions(e.g. radial flow to a well, or single aquifer with relatively small vertical hydraulic head or contaminant concentration gradients).
- Sites at which the aquifer has distinct variations in hydraulic properties.
- Contaminant migration problems where the impacts of transverse dispersion are important and the lateral, or vertical, spread of the contaminant plume must be approximated.
Three-dimensional flow and transport models should generally be used where:
- The hydrogeologic conditions are well known.
- Multiple aquifers are present.
- The vertical movement of groundwater or contaminants is important.
The rationale for selection of the appropriate model software should be discussed in the model documentation report. The choice of model software program for use at a site is the responsibility of the modeler. Any appropriate groundwater flow or fate and transport model software may be used provided that the model code has been tested, verified and documented. However, it is recommended that the model developer contact the GMP at the beginning of the investigation to discuss the selection of appropriate model software. In the event that the software is not currently used by the GMP, a copy of the software and the program documentation should be submitted to the GMP along with the model documentation report.