Fixing solution in PHAST

[18771047611@163.com]

Hi, sorry to post my questions here, because I don't know how to post in right places. Maybe this is my first and biggest questions in phreeqcusers.

Q_Q

The other questions is that I find it's easy to establish a fixed solutions in phreeqc, but it's difficult to establish it in PHAST. I want to uses it instead of the vast seawater which is not effected by other fluids.

Thanks a lot and sorry to post my questions here again!

[dlparkhurst]

The only way to fix a solution composition in PHAST is with a SPECIFIED_HEAD_BC boundary condition. You can chose "fixed solution composition", which means that the concentrations in the cell will not change.

[Hubert]

Hi,dlparkhurst,
The following is a part of my trans.dat file in phast. And the face "250. 1. 1." model the interface of Seawater and Sediment. I can't write  "fixed solution composition" in approprite place, Where could I add "fixed solution composition" ?

HEAD_IC
        -zone   220. 0. 0. 230. 1. 1.
                -head   X   9.95E-07   220   6.70E-07   230
        -zone   230. 0. 0. 240. 1. 1.
                -head   X   6.70E-07   230   3.38E-07   240
        -zone   240. 0. 0. 250. 1. 1.
                -head   X   3.38E-07   240   0.00E+00   250
SPECIFIED_HEAD_BC
        -zone   0. 0. 0. 0.  1.  1.
                -head                           0       0.00000576
                -associated_solution            0       1
        -zone   250. 0. 0. 250.  1.  1.
                -head                           0       0.
                -associated_solution            0       26

But I find I can add a downward fluid of seawater to change the interface of Seawater and Sedimentary to could keep the solution in the interface constant. This treatment method is right?

HEAD_IC
   -zone   220. 0. 0. 230. 1. 1.
                -head   X   9.95E-07   220   6.70E-07   230
        -zone   230. 0. 0. 240. 1. 1.
                -head   X   6.70E-07   230   3.38E-07   240
        -zone   240. 0. 0. 250. 1. 1.
                -head   X   3.38E-07   240   0.00E+00   250
        -zone   250. 0. 0. 350. 1. 1.
                -head   X   0   250   1.   350

SPECIFIED_HEAD_BC
        -zone   0. 0. 0. 0.  1.  1.
                -head                           0       0.00000576
                -associated_solution            0       1
      -fixed solution composition
        -zone   250. 0. 0. 250.  1.  1.
                -head                           0       0.
                -associated_solution            0       26
        -zone   350. 0. 0. 350.  1.  1.
                -head                           0       1.
                -associated_solution            0       27

[dlparkhurst]

What you have is wrong. There is an example of the use of -fixed_solution in SPECEIFIED_HEAD_BC in the PHAST manual, page 100. Check it out.

Alternatively, use the Phast4Windows interface to develop you input for PHAST. You can either run  your model in P4W or export a file that will have the correct formats.

[Hubert]

Thanks for your help. I think I get it!