QUAL-TX v.9.32 is the version currently (as of July 2026) being used by the Modeling Team, Water Quality Assessment Section, Water Quality Division of the TCEQ. QUAL-TX v.9.35, the most current version, includes certain enhancements and was developed for the TMDL Team, Planning and Implementation Section, Water Quality Division of the TCEQ for a project on the Rio Grande.A downloadable version of QUAL_TX does not appear to be available on the TCEQ website.
Known Errors in QUAL-TX: There are some known errors (bugs) in the QUAL-TX model although they are seldom significant.
1) The concentration in the last element of the model will be incorrect if the stream is primarily advective and does not contain Data Type 10 (HYDR-2) or Data Type 27 (LOWER BC) lines. However, there is a work-around for thiis error by including and setting the OCEAN EXCHANGE RATIO line in Data Type 3 to zero (0.0) for primarily advective streams.
2) There is an error in the dispersion flux calculations at junctions. There is no work-around for this, but it will not be noticeable unless there is high dispersion.
3) The interpolation of Initial Conditions may produce undesired results if there is a dam because the model interpolates from the value at the start of one reach to the value at the start of the next lower reach. The model should not be interpolating in this case, but it does. There is no work-around for this.
For any given version, the LA-QUAL model will yield identical results to the QUAL-TX model if the "Model Assumptions" are set to "Texas (TCEQ) defaults" in the menu Preferences/Additional Preferences. LA-QUAL has newer versions than QUAL-TX with additional enhancements and corrections to the errors stated above. These enhancements and corrections are shown in the Version History on the LA-QUAL web page along with additional information. One might want to discuss with TCEQ the possibility of using LA-QUAL instead of QUAL-TX if the last two errors stated above create significant differences in predicted profiles.
Version 9.32 (current version used by TCEQ Modeling Team as of July 2026; see note below)
Note: The executable in the zip file for version 9.32 has been encrypted to avoid browser warnings that the file may be dangerous. The password is 12345678. If you do not trust the executable, do not decrypt it and instead contact the TCEQ Modeling Unit to obtain the executable via email. However, TCEQ's version is the same version in this zip file. The other files in the zip file, including the user's manual, are unencypted.