While I was trying to run the MT3D, I received an error: Error Reading Flow-Transport Link File Possibly Caused by:

  1. Incompatible Styles of Unformatted Files Used by MODFLOW and MT3D-USGS, ensure usage of FREE in MT3D-USGS name file matches LMT;
  2. Unformatted Flow-Transport Link File Saved by Version 1 of LinkMT3D Package Which Is No Longer Supported by MT3D-USGS.

Based on some initial investigations: https://water.usgs.gov/nrp/gwsoftware/ModelMuse/Help/index.html?lmt6.htm “Unformatted – the flow-transport link file is saved as an unformatted (binary) file, compatible with all versions of MT3D and MT3DMS.”

So I have to convert the input to unformatted. However, doing so will yield another error. This error is basically caused by the undefined variable “FORM” in the source code file lmt8_nwt.f:

IF(ILMTFMT.EQ.0) THEN

      OPEN(IUMT3D,FILE=FNAME,FORM=FORM,ACCESS=ACCESS,

 &      ACTION=ACTION(2),STATUS='REPLACE')

    ELSEIF(ILMTFMT.EQ.1) THEN

      OPEN(IUMT3D,FILE=FNAME,FORM='FORMATTED',ACTION=ACTION(2),

 &      STATUS='REPLACE',DELIM='APOSTROPHE')

ENDIF Another quick investigation: https://docs.oracle.com/cd/E19957-01/805-4939/6j4m0vnaf/index.html We can replaced the FORM to “UNFORMATTED”.

Rebuild the program and the simulation is running again!

Later on it turned out I need to set the LMT to free format in MT3D and MODFLOW should still use FORMATTED.