GMS:MF6 MDT Package

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MODFLOW 6
Models & Tools
GWF Model
GWT Model
Cell Properties Dialog
Zone File
Packages
Flow: GNC, HFB, NPF
GWF: BUY, CHD, CSUB,
DRN, EVT, GHB,
LAK, MAW, MVR,
OBS, RCH,RIV,
SFR, STO, UZF,
WEL
GWT: ADV, CNC, DSP
FMI, IC, IST, LKT,
MDT, MST, MVT,
MWT, OBS, SFT,
SRC,SSM, UZT
Other DIS, DISU, DISV,
IMS, OC, TDIS

Example of the MDT Package dialog.

The Matrix Diffusion Transport package (MDT) works with MODFLOW 6. 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.

Note: the MDT package is not an official package released by USGS. The MDT package for MODFLOW 6 provided with GMS is still being developed and may change in the future. Newer versions of the package may not be compatible with older projects.

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.

OPTIONS

  • Print_Input – Print input to listing file.
  • Print_Concentration – Print concentration to listing file.
  • Print_Flows – Print flows to listing file.
  • Save_Flows – Save flows to budget file.
  • Concentration Fileout – Save concentration to file.
  • Budget Fileout – Save budget to file.
  • 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.

GRIDDATA

  • Griddata – 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.
    • 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.
  • Dataset to Array – Clicking the Dataset to Array will open an array editor dialog for the specific property.

Conversion from MODFLOW-USG Transport

When converting a MODFLOW-USG Transport model to MODFLOW 6, use the following table when converting the MDT package:

MODFLOW-USG Transport MODFLOW 6
Package Variable Package Variable
PSB CNC
BCT DIFFNC DSP DIFFC
BCT PRSITY MST POROSITY
BCT BULKD MST BULK_DENSITY
BCT ADSORB MST DISTCOEF
MDT MDFLAG MDT MD_TYPE_FLAG
MDT VOLFRACMD MDT MD_FRACTION
MDT PORMD MDT MD_POROSITY
MDT RHOBMD MDT BULD_DENSITY
MDT DIFFLENMD MDT MD_DIFF_LENGTH
MDT TORTMD MDT MD_TORTUOSITY
MDT DIFFMD MDT MD_DIFF_COEFF

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