Mix with transport

[rudolff16]

Hi Phreeqc-forum members,
to simulate gradual mixing between high salinated and fresh water along a 500 m groundwater flow path, and to predict a potential leaching of heavy Metalls from Hosting rocks due to the expected decrease in pH-Value, a draft 5 year Transport Simulation was carried out using 20 cells. Each cell has 25 m width and 0.05 m dispersivity. Any hints or advice to enhance the Input file below?

SOLUTION 1-20 groundwater
    temp      11.9
    pH        7.2
    pe        5.77
    units     mg/l
    density   0.999
    Na        14.5
    K         5.53
    Ca        128
    Mg        34.7
    Cl        127 
    Alkalinity 256 as HCO3
    S(6)      96.5 as SO4
    Fe        0.05
    Al        0.01
    Zn        0.04
    Cd        0.0001
    Pb        0.0001
    -water    0.1 # kg 
END
EQUILIBRIUM_PHASES 5-20
    Alunite   0 0
    Ferryhydrite 0 0
END
SOLUTION 0 High salinated Groundwater
    temp      13.9
    pH        4.5
    pe        5.408
    units     mg/l
    density   1.0920
    Na        17194
    K         5518
    Ca        999
    Mg        15493
    Cl        63485 
    Alkalinity 24 as HCO3
    S(6)      18703 as SO4
    Al        14
    Pb        0.15
    Cu        0.470
    Ni        0.850
    Mn        38
    Zn        2.6
    Fe        0.067
    Cd     0.02
    -water    0.11 # kg
MIX 1
    0    0.01
    1    0.99
MIX 2
    1    0.05
    2    0.95                   
MIX 3
    2    0.1
    3    0.9
MIX 4
    3    0.15
    4    0.85
MIX 5
    4    0.2
    5    0.8
MIX 6
    5    0.25
    6    0.75
MIX 7
    6    0.3
    7    0.7
MIX 8
    7    0.35
    8    0.75
MIX 9
    8    0.4
    9    0.6
MIX 10
    9    0.45
    10   0.65
MIX 11
    10    0.5
    11    0.5
MIX 12
    11    0.5
    12    0.5
MIX 13
    12    0.5
    13    0.5
MIX 14
    13    0.5
    14    0.5
MIX 15
    14    0.5
    15    0.5
MIX 16
    15    0.5
    16    0.5
MIX 17
    16    0.5
    17    0.5
MIX 18
    17    0.5
    18    0.5
MIX 19
    18    0.5
    19    0.5
MIX 20
    19    0.5
    20    0.5
END
EXCHANGE 1-4 Exchange with loam
    AlX3    0.00999
    CaX2    0.22176
    FeX2    0.003915
    KX      0.04392
    MgX2    0.039735
    MnX2    9e-005
    NaX     0.00567
    -pitzer_exchange_gammas true
    -equilibrate 0
END
EXCHANGE 5-20 Exchange with sand formation
    AlX3    0
    CaX2    0.956633333
    FeX2    0.0055
    KX      0.442933333
    MgX2    0.421666667
    MnX2    0.000366667
    NaX     0.044
    -pitzer_exchange_gammas true
    -equilibrate 1
END
PRINT; -reset false
TRANSPORT
    -cells                 20
    -shifts                100
    -time_step             157680000 # seconds
    -lengths               20*25
    -dispersivities        20*0.05
    -punch_cells           20
USER_GRAPH 1
    -headings               S, K, Ca, Cl, Al, pH
    -axis_titles            "Time [Years]" "Concentratios [mg/l]" "pH-Value"
    -axis_scale y_axis      auto auto auto auto log
    -initial_solutions      true
    -connect_simulations    true
    -plot_concentration_vs  t
  -start
10 graph_x (step_no + 0.5)/cell_no
20 graph_y tot("S")*1000/96.1, tot("K")*1000/39.1, tot("Ca")*1000/40, tot("Cl")*1000/35.45, tot("Al")*1000/26.98
30 GRAPH_SY -la("H+")
  -end
    -active                 true
END


# thanks for you help

[rudolff16]

it seems that mixing has no Impact on the results! I am wondering if Transport keyword acts similar to mixing

[dlparkhurst]

Sorry, I am not very good with MIX in combination with TRANSPORT. Look at example 13 for more information.

Also, there is a section on Equations and Numerical Method for Transport Modeling and additional information in the Phreeqc 2 manual, which is in the doc directory of PHREEQC installation directory (for PhreeqcI, it is normally C:\Program Files (x86)\USGS\Phreeqc Interactive 3.6.2-15100\doc).

[John Mahoney]

You appear to be mixing similar solutions or really the same solutions when you use solutions 1 through 20. So you get the same solution except in the first mixing step (soln 0 with soln1) .  You would need to mix two solutions and then  save the mixed solution as another number.  then use that saved mixture in the next step (I think that is what you want?).  So do the mix and then save the new solution and use that in the next mix.  Also END statements might not hurt.
I also am not sure what you intend.

[rudolff16]

Dear John, dear  dlparkhurst,

thank you so much for you hints and advices

[MichaelZ20]

There is an answer to a similar problem in PHREEQC FAQ.

[rfembilejr]

Total simulation time is shift*time step, so in this case your total time is actually 500 years?