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*To*: David L Parkhurst <dlpark@xxxxxxxx>*Subject*: convergence problem*From*: H.Prommer@xxxxxxxx*Date*: Sun, 18 Nov 2001 20:34:10 +0000*Organization*: CLARRC

Hi David, greetings from Edinburgh. I have spend the time after the Golden conference with a nice week of mountainbiking in Utah and then returned home earlier. Inspired by some discussions we had I have modified the pht3d code to write one long input file for each phreeqc step rather than processing cell after cell. It seemed indeed to speed up execution but the difference is by far less substantial than temporally "deactivating" the phreeqc step in regions/cells without chemical gradient (I think I mentioned this). For larger models the input files can become quite big and I had the impression that in those cases the execution was rather slower compared to the cell-by-cell version. I will try to compare it properly one day. Recently I went back to this in situ reducing zone problem that I mentioned in my talk and now included some more metals in addition to zinc for some scenario-type modelling but was unfortunately running into convergence problems. Sometimes when this happened before (very occasionally) it was typically when a component had a very small concentration. However, in the case now, I can't see what the problem is, except that it is caused by Copper. When Cu is removed from the simulation, the model converges in the batch and in the 2D transport simulation. I am not sure if you have any time, but if so, maybe you have an idea what the problem is and how I could avoid it. I have attached the input file (with Cu activated) and the appropriate database file. Thanks & regards Henning

**Attachment:
pht3d_datab.dat**

SOLUTION 13 #GRID 13 units mol/L temp 25.000000 pH 6.676109 charge # comp 29 pe -2.998528 # comp 30 Acetate 7.975427e-05 # comp 1 Molasse 1.878219e-03 # comp 2 O(0) 0.000000e+00 # comp 3 As(3) 2.395640e-09 # comp 4 As(5) 2.871453e-09 # comp 5 C(4) 3.880034e-03 # comp 6 C(-4) 8.380750e-09 # comp 7 Ca 1.286009e-03 # comp 8 Cd 8.428597e-10 # comp 9 Cl 8.471532e-03 # comp 10 Cr(2) 0.000000e+00 # comp 11 Cr(3) 8.004242e-08 # comp 12 Cr(6) 0.000000e+00 # comp 13 Cu(1) 4.582913e-07 # comp 14 Cu(2) 7.206154e-07 # comp 15 Fe(2) 1.514445e-06 # comp 16 Fe(3) 0.000000e+00 # comp 17 K 1.535808e-03 # comp 18 Mg 1.486955e-03 # comp 19 N(-3) 7.330157e-05 # comp 20 N(3) 1.392629e-05 # comp 21 N(5) 0.000000e+00 # comp 22 Na 8.936836e-03 # comp 23 Ni 4.238997e-08 # comp 24 Pb 7.970436e-08 # comp 25 S(-2) 1.009645e-05 # comp 26 S(6) 2.381857e-03 # comp 27 Zn 8.247324e-07 # comp 28 Bacteria 2.422534e-05 # comp 31 imob but no napl EQUILIBRIUM_PHASES 13 Sphalerite 0.0 3.982682e-06 # comp 32 Hematite 0.0 1.999055e-03 # comp 33 Siderite 0.0 0.000000e+00 # comp 34 Covellite 0.0 1.251397e-05 # comp 35 Greenockite 0.0 6.945988e-09 # comp 36 Galena 0.0 6.599528e-07 # comp 37 Millerite 0.0 3.290095e-07 # comp 38 Oripment 0.0 1.618014e-08 # comp 39 Realgar 0.0 0.000000e+00 # comp 40 Cr(OH)3(A) 0.0 9.326369e-07 # comp 41 KINETICS 13 Acetate # 1 -parms 3.250000e+00 1.000000e-04 -formula Acetate -1.0 Acetate -1.0 C2H3O2- 1.0 1.0 Bacteria 0.08 C5H7O2N -0.08^M -steps 2.160000e+04 s(econds) in 1 steps Molasse # 2 -parms 6.000000e+00 -formula Molasse -1.0 C6H12O6 0.33333 Acetate 2.0 H+ 2.0 Bacteria 0.08 C5H7O2N -0.08^M Bacteria # 31 -parms 1.000000e-01 -formula Bacteria -1.0 C5H7O2N 1.0^M FeS(ppt) # 42 -m 0.000000e+00 -parms 1.000000e+00 1.000000e-10 USER_PUNCH 10 PUNCH TOT("Acetate"), TOT("Molasse") 20 PUNCH TOT("O(0)"), TOT("As(3)"), TOT("As(5)"), TOT("C(4)"), TOT("C(-4)"), TOT("Ca"), TOT("Cd"), TOT("Cl"), TOT("Cr(2)"), TOT("Cr(3)"), TOT("Cr(6)"), TOT("Cu(1)"), TOT("Cu(2)"), TOT("Fe(2)"), TOT("Fe(3)"), TOT("K"), TOT("Mg"), TOT("N(-3)"), TOT("N(3)") 25 PUNCH TOT("N(5)"), TOT("Na"), TOT("Ni"), TOT("Pb"), TOT("S(-2)"), TOT("S(6)"), TOT("Zn") 30 PUNCH -LA("H+"), -LA("e-") 40 PUNCH TOT("Bacteria") 60 PUNCH EQUI("Sphalerite"), EQUI("Hematite"), EQUI("Siderite"), EQUI("Covellite"), EQUI("Greenockite"), EQUI("Galena"), EQUI("Millerite"), EQUI("Oripment"), EQUI("Realgar"), EQUI("Cr(OH)3(A)") 90 PUNCH KIN("FeS(ppt)") END

**Follow-Ups**:**Re: convergence problem***From:*David L Parkhurst

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