Hi Jirka,
Thank you very much for this really helpful discussion forum.
I am currently simulating transport of three ionizable pharmaceuticals through an unsaturated column. The transport of these compounds is well described when applying the two-site sorption model (non-equilibrium).
However, I have some doubts about the Frac parameter in Hydrus- 1D. From the many papers I came through, I found out that the frac is a soil parameter reflecting the presence of organic matter and Fe and Al oxides where sorption could occurs by kinetics.
I fit the compound breakthroughs by inverse simulation and I really got nice fits (R2> 0.95), however I allowed the model to fit the frac parameter for each compound although the soil is exactly the same (1 column experiment for the 3 compounds).
Is this correct? I thought that the kinetics of sorption is not only soil dependent but it is also affected by the compounds physic-chemical parameters (e.g. ionization degree) and therefore each compound should have its frac parameter.
Any suggestions will be very welcome.
Thank you very much in advance.
Virtudes