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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.
David
SOLUTION 1 SEAWATER FROM NORDSTROM ET AL. (1979)
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
END
SOLUTION 2 Pure water
pH 7
END
# Make carbonate ground water
USE solution 2
EQUILIBRIUM_PHASES 2
Calcite 0 10
Dolomite 0 10
CO2(g) -2.0 10
SAVE solution 2
END
# Mix G-W and Seawater, equilibrate with carbonates
MIX
1 0.5
2 0.5
EQUILIBRIUM_PHASES 1
Calcite 0 10
Dolomite 0 10
END
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
David -
I already did the ground water and salt water interaction, but in a different way. However, what I used had different results. I put ion concentrations in according to data obtained from "Geochemical Calculations and Observations on Salt Water Intrusions. II. Validation of a Geochemical Model with Laboratory Experiments", by C.A.J. Appelo, A. Willemsen, H.E. Beekman, and J. Griffioen. Found in the Journal of Hydrology, 120 (1990) 225-250. The specific data I used was on page 238. What I used is as follows:
TITLE Ground water Solution
SOLUTION 1 Ground Water
units mmol/L
pH 7.380
pe -1.738
temp 25.0
Na 21.40
K 0.693
Mg 1.93
Ca 2.95
N(-3) 2.05
Fe 0.320
Mn 0.0092
Cl 21.05
Alkalinity 14.37
S(6) 0.142
N(5) 0.005
N(3) 0.0005
Si 0.470
END
TITLE Seawater solution
SOLUTION 2 Seawater
units ppm
pH 8.22
pe 8.451
density 1.023
temp 25.0
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
END
TITLE Ground Water, & Sea Water
MIX 1
1 .50
2 .50
EQUILIBRIUM_PHASES 1
Calcite 0 10
Dolomite 0 10
END
What's the difference between what you did and what I did? Also, I don't really understand what equilibrium phases does. My understanding is that it is used to model how the minerals act in water at equilibrium under certain conditions.
Then, the final question is, after the sea water and ground water interaction have been taken care of, do I use equilibrium phases to add in the limestone aquifer interaction? Thank you again for your help!
Elizabeth Delaney
Water Chemistry
Chemistry Department
Western Michigan University
Kalamazoo, MI
(260)387-2926