transport modeling laboratory column

[jennymue]

Hello,
I did some laboratory column Tests with Bromide and Sulfur as tracers and now i want to simulate them with PhreeqC.
I don't know how to put up the columns filled with fine grained sand, medium sand, and coarse sand. I don't know where to specify the kf values in phreeqC. I look for examples quiet Long, but could not find any similiar to my Problem.
This is what i got so far:


SOLUTION 0 Regenwasser (rain water)
    temp      19.5
    pH        6.31
    pe        4.37
    redox     pe
    units     mg/l
    density   1
    Alkalinity 1.22 as HCO3
    Ba        0
    Br        336
    Ca        1.3
    Cl        4.8
    Cu(2)     0.02
    F         0
    Fe(2)     0.03
    K         5
    Mg        0.17
    Mn(2)     0
    N(3)      0.05
    N(5)      1
    Na        0.4
    S(6)      280.2
    Si        0.3
    Sr        0.004
    Zn        0.07
    -water    1 # kg

EQUILIBRIUM_PHASES 0
    CO2(g)    -3.5 10
    O2(g)     -0.699 10

SOLUTION 1-30 Säule (column)
    temp      21.7
    pH        5.97
    pe        4
    redox     pe
    units     mg/l
    density   1
    Alkalinity 109.8 as HCO3
    Ca        3
    Cl        8.3
    F         0.1
    Fe        5.3
    K         1.6
    Mg        1
    Mn(2)     0.9
    N(5)      0
    Na        5.4
    S(6)      7.5
    -water    1 # kg

EQUILIBRIUM_PHASES 1
    Quartz    0 10

END
EXCHANGE 1
    X       0.0015
    -equilibrate with solution 1
    -pitzer_exchange_gammas false
END
TRANSPORT
    -cells                 30
    -shifts                60
    -time_step             1712 # seconds
    -lengths               30*0.005
    -dispersivities        30*0.01
    -correct_disp          true
    -print_cells           30
    -punch_cells           30

SELECTED_OUTPUT 1
    -file                 testmS.cvs
    -reset                true
    -totals               Br  S(6)


USER_GRAPH 1
    -headings               Br S(6)
    -axis_titles            "Sickerwassermenge(amount of leak water) [ml]" "Konzentraion (concentration) [mg/L]" ""
    -chart_title            "Mittelsand Säule 1 08.07.2016"
    -initial_solutions      false
    -connect_simulations    true
    -plot_concentration_vs  t
  -start
10 x = 60*(0.5 + step_no) / cell_no
20 PLOT_XY x, (TOT("Br")* 79.9*1000*100)/ 336, color = red,symbol = Plus, symbol_size = 7
30 PLOT_XY x, (TOT("S(6)")* 96.065*1000*100)/ 279,color = blue, symbol = Diamond, symbol_size = 7
  -end
    -active                 true
END

I would be grateful for every comment/ idea.

 Thanks

Jenny

[dlparkhurst]

For conservative tracers, once you set the lengths of the cells, there are really only two parameters that affect the simulation. The time step gives the average particle velocity, v = l/t, l is length of cell and t is time step; and the dispersivity determines the rate of spreading of the leading edge of the tracer pulse.

I do not know what you mean by kf.

[jennymue]

Yes ok. But how can i tell phreeqc that the column is made out out fine grained sand, medium sand, coarse sand? Do i Need the specific mineral composition? I don't know what to put in to see good breakthrough curves, because Sulfur should be a little slower than Bromide. I am very new to using this program.
Thanks for every help.

[dlparkhurst]

The coarseness of the sand probably has an effect on the hydraulic properties, but in TRANSPORT that is accounted for by the flow velocity and the dispersivity.

For relatively short column experiments, I suspect the sand is basically inert in terms of dissolution of the minerals. If mineral dissolution is important, andf you have analyses of all major ions in the inflow and outflow, you could do inverse modeling to account for the changes in composition.

If you are looking at SO4 and Br, I don't think there will be much difference in their breakthrough, but most likely interactions with surfaces accounts for any difference. If you want a chromatographic effect, you can use either EXCHANGE or SURFACE to allow them to interact with the surface/exchange sites of the minerals.

[jennymue]

ok thank you very much.
i will try it with Exchange/Surface so see if i can get the results that i want.