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Re: PHREEQC





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From: "David L Parkhurst"
To: x99delaney1@xxxxxxxxxxx
CC: gs-w_h2osoft@xxxxxxxx
Subject: Re: PHREEQC
Date: Mon, 25 Aug 2003 09:58:55 -0600
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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 1