User:Jcreer/MDT Package

Example of the MDT Package dialog.

The Matrix Diffusion Transport package (MDT) works with MODFLOW-USG Transport. The MDT package allow existing flow and chemical transport models of sites to include a full accounting of matrix diffusion effects. The package works with the BCT process.

The MDT Package dialog is divided into two parts: one on the left which shows the main sections, and one on the right which shows the inputs for the current section.

Comments

Comment lines can be added and will appear at the top of the MDT file. Use the Add Row button to create comments. Comments can be removed using the Delete Row button.

Variables

• Cell-by-cell mass flux unit (IMDTCB) – The mass flux between the fracture and the matrix for every cell.
• Immobile domain concentration unit (IMDTCF) – enter a value to activate the immobile domain concentration unit.
• Hydraulic conductivity for fracture only (FRANHK) – Indicates that the hydraulic conductivity and storage terms (for transient simulations) which are input are only for the fracture (mobile) domain. Otherwise, it is assumed that the hydraulic conductivity and storage input for the flow simulation are effective hydraulic conductivity and storage terms for the medium, representative of the entire volume.
• Darcy flux hydraulic conductivity for fracture only (FRADARCY) – Indicates that the Darcy flux should be computed only for the fracture domain by use of this hydraulic conductivity value. Thus, the input hydraulic conductivity is divided by the fracture volume fraction. Also, the storage terms (for transient simulations) which are input are only for the fracture (mobile) domain.
• Shift matrix diffusion start time (TSHIFTMD) – indicates that the MODFLOW start time (t = 0) is not the starting time of matrix diffusion, and the subsequent real variable tshift is the value of time already elapsed since matrix diffusion began.
• Time elapsed since matrix diffusion began (tshift) – Enter the value of time already elapsed since matrix diffusion began.

Aquifer Properties

• Property Name – List of available properties.
  • MDFLAG — The matrix diffusion type flag at any location.
  • VOLFRACMD – The mobile fraction at any location, i.e., the fraction of the total space that is occupied by the fracture/high permeability domain.
  • PORMD – The mobile fraction at any location, i.e., the fraction of the total space that is occupied by the fracture/high permeability domain.
  • RHOBMD – The dry bulk density of the porous matrix of the matrix domain at any location
  • DIFFLENMD – The diffusion length for diffusive transport within the matrix domain at any location (only used for embedded heterogeneity).
  • TORTMD – The tortuosity of the matrix domain at any location.
• Use Constant – Turn on to enter a constant value.
• Constant Value – Enter a constant value for the property.
• Array Editor – Clicking the Edit will open an array editor dialog for the specific property.

Species Properties

• Species ID
• Property Name – List of available properties.
  • KDMD – The adsorption coefficient (Kd) of a contaminant species in the immobile domain at any location.
  • DECAYMD – The first-order decay coefficient in water and on soil (1/time) in the matrix domain at any location.
  • YEILDMD – The yield coefficient for chain decay at any location. The value indicates mass of species generated by decay of the parent component.
  • DIFFMD – The diffusion coefficient of each species component within the matrix domain at any location.
  • AIOLD1MD – The concentration integral (equation 8) of each species in an element associated with matrix diffusion into an infinite acting adjacent aquitard (MDFLAG = 1, 3, 4, 5, 6, or 7). This value is used to restart a simulation with prior matrix diffusion.
  • AIOLD2MD – The concentration integral (equation 8) of each species in an element associated with matrix diffusion in low permeability zones that are embedded in the volume element (MDFLAG = 2, 5, 6, or 7). This value is used to restart a simulation with prior matrix diffusion.
• Use Constant – Turn on to enter a constant value.
• Constant Value – Enter a constant value for the property.
• Array Editor – Clicking the Edit will open an array editor dialog for the specific property.

Related Topics

• MODFLOW-USG Transport