# Re: a fundamental question!

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The following file is a rough example of uranium rollfront simulation.

David

TITLE  Rollfront

SOLUTION 0 Rainwater
units            mmol/kgw
temp           25.0
pH              7.0     charge
pe               4.0
Ca  1
S(6) 1
EQUILIBRIUM_PHASES 0
CO2(g) -3 10
O2(g)  -0.7 10
Save Solution 0
END

solution 1
EQUILIBRIUM_PHASES 1-2
Schoepite 0.0 0.1
Calcite  0.0 0.1
Goethite 0.0 0.1
SAVE solution 1-10
END
EQUILIBRIUM_PHASES 3-10
Calcite  0.0 0.1
Goethite 0.0 0.1
Uraninite(c)     0     0
KINETICS 3-10
Organic_C
-formula  CH2O
-tol 1e-8
-m0 .005
-m .005

RATES
Organic_C
-start
10 if (m <= 0) then goto 200
20  mO2 = mol("O2")
30  mNO3 = tot("N(5)")
40  mSO4 = tot("S(6)")
50   rate = 1.57e-7*mO2/(2.94e-4 + mO2)
60   rate = rate + 1.e-7*mSO4/(1.e-4 + mSO4)
70  moles = rate * m * (m/m0) * time
80 if (moles > m) then moles = m
200 save moles
-end
END
-cells 10
-shifts 10
-time 5184000
SELECTED_OUTPUT
-file      Roll-front122.csv
-reset     false
-time   false
-distance    true
-totals    U
-pH    true
-pe    true

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

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Complete Water Resources Division Software