Document ID: chunk:federal_register_of_legislation:F2013C00288:reg:1850:p64
Version: federal_register_of_legislation:F2013C00288
Segment Type: reg
Provision Reference: reg 1850 (pt 64/117)
Character Range: 524354–528711

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 certain points in space and time and provide a more realistic representation of the variation of parameters than is possible with analytical models. Numerical models range from relatively simple one-dimensional steady-state transport models to three-dimensional time-variant models, for example, MODFLOW from the US Geological Survey (USGS), and may consider any or all of advection, dispersion and retardation, biodegradation, multiphase flow and density-driven flow.

A summary of 3-D groundwater modelling codes can be found in Middlemis (2000). When considering using models, advice should be sought from suitably experienced persons in hydrogeology and geochemistry and the application of such models. Comprehensive information and software is available from:
    * US EPA Centre for Subsurface Modelling Support
    *  www.epa.gov/ada/csmos/index.html#download
    * USGS   water.usgs.gov/software/lists/groundwater/.
A comprehensive software catalogue of a wide range of models, which includes information on the advantages and disadvantages of each type, is maintained by the
International Groundwater Modelling Centre at the Colorado School of Mines (www.mines.edu/igwmc/).
Table 6. Summary of site-specific data requirements for contaminant fate and transport modelling
Parameter                                                                    Site-specific       Site-specific      Comments on ease and cost of obtaining site-specific data
                                                                             data essential      data useful
Aquifer depth/geology                                                                                              Easy to obtain but data quality, reliability and cost depends on site-investigation techniques used.
Hydraulic conductivity                                                                                             Relatively easy to obtain but data quality depends on method used. Pump tests provide the best data but can be expensive, particularly where contaminated water needs to be managed.
Hydraulic gradient and direction of groundwater flow/ seasonal variability                                         Relatively easy to obtain but data quality, reliability and cost depend on number and construction of boreholes and frequency of measurement.
Porosity                                                                                                           Intergranular porosity is inexpensive and easy to measure. Generally difficult to measure in fractured aquifers due to factors such as the presence of preferential flow paths e.g. fractures, joints, faults or caverns.
Transport porosity                                                                                                 Difficult to measure – requires tracer test.
Bulk density                                                                                                       Inexpensive and easy to measure.
Partition coefficient (Kd)                                                    for inorganics                       Generally inexpensive and easy to measure but data quality, reliability and cost will depend on methods used.
Cation exchange capacity (CEC)                                                                    for in-organics  Inexpensive and easy to measure.
Moisture content of unsaturated zone                                                                               Inexpensive and easy to measure.
Total organic carbon (TOC)                                                                       for organics      Inexpensive and easy to measure. Representative data can be difficult to obtain in low organic carbon aquifers, in which case, reasonable default values should be selected based on geological records.
Infiltration                                                                                                       Meteorological data is easy and relatively inexpensive to obtain.
Degradation                                                                  