Questions on NAPL volatile and dissolution

Hello everyone and Stefan,

I have several questions on NAPL volatile and dissolution into water. Based on the manual, volatile is controlled by temperature, vapor pressure and concentration in the aqueous phase. If I want to control NAPL not to be volatile, I need to make the vapor pressure lower enough by adjusting the input parameters(TBOILM, VPAM, VPBM,VPCM,VPDM) based the equation of Reid 1987. For temperature, my model is isothermal and I need to make the chemical critical temperature parameter (TCRITM) higher than the input temperature (20C). Am I right? I am not sure about how NAPL dissolve into water. Based on the manual, it seems like mass transfer process instead of equilibrium dissolution. However, there is no parameter for mass transfer coefficient. Is there a way to use equilibrium dissolution (if there is NAPL, aqueous concentration is solubility)? Any clue to clarify will be highly appreciated. Thank you very much!


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  • I am not sure whether I fully understood your question. But, for the last question, doesn't SOLAM define the constant for chemical solubility of organic chemicals in water? With this solubility constant defined, partitioning between water and NAPL phases will be determined, depending on the mole fractions of the component in water and NAPL phases, respectively. I hope this helps, and if not, sorry that I couldn't be any of help to you.
  • Hello everyone, is there anyone who knows about volatile and dissolution? Thank you.


  • Thank you Yoojin. Yes, SOLAM is the solubility of NAPL. Do you mean NAPL dissolution is controlled by the input parameter partition coefficient (OCKM) instead of mass transfer process? I think the partition coefficient is for tracers, but I am not sure. Thank you.


  • Hi Fang,

    No, OCKM is for adsorption of VOCs on the solid grains.

    Mass transfer mechanisms for organic chemicals include dissolution into the aqueous phase AND equilibrium phase partitioning of organic chemicals between the gas, aqueous, and solid phases. Particularly, partitioning of organic chemicals between the aqueous and NAPL phases is dependent on the difference in solubility of the organic chemical compound in these two phases. If you have a single-component NAPL (for instance, only TCE), the solubility of the organic chemical component into the aqueous phase, which controls the dissolution of the single-component NAPL, is the same with the equilibrium constant.


  • Thank you Yoojin. My model only contains one component NAPL (TCE) in the vadose zone and I do not want to consider chemical partitioning on the solid grains and also TCE volatile. Does that mean equilibrium dissolution (aqueous concentration equals solubility if there is NAPL phase in the same cell) based on your explanation)? Thank you.


  • Hi, Fang

    I wonder wether you have clearly known which parameter in TOUGH2 controls the dissolution TCE transport?

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