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> I am a student at Western Michigan University and I work in the Water
Chemistry Lab for Dr. Michael Barcelona. I am trying to gain some
proficiency with PHREEQC and I have a question for you. I'm using PHREEQC
to model the interaction between ground water, sea water, and limestone
aquifers. The trouble I'm having is that I can't seem to figure out how to
have the limestone interact with the sea water and ground water. I have
input the sea water and ground water with the command SOLUTION. I'm just
not sure what to put the limestone under and then what to do to get the
desired interaction. Do you have any insight to this problem? I would
really appreciate your help.

The following is what should happen in seawater mixing thermodynamically.
You will notice that calcite dissolves and dolomite precipitates in the
mixing zone, however, this does not happen in reality because of the slow
kinetics of dolomite precipitation.


        units   ppm
        pH      8.22
        pe      8.451
        density 1.023
        temp    25.0
        redox   O(0)/O(-2)
        Ca              412.3
        Mg              1291.8
        Na              10768.0
        K               399.1
        Si              4.28
        Cl              19353.0
        Alkalinity      141.682 as HCO3
        S(6)            2712.0
        O(0)            1.0     O2(g) -0.7
SOLUTION 2  Pure water
      pH    7
# Make carbonate ground water
USE solution 2
      Calcite     0     10
      Dolomite    0     10
      CO2(g)      -2.0  10
SAVE solution 2
# Mix G-W and Seawater, equilibrate with carbonates
      1     0.5
      2     0.5
      Calcite     0     10
      Dolomite    0     10

David Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled

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