Error in Percent Error

[Messias]

Hi PHREEQC User's,

I use the Notepad ++ with PHREEQC and found one problem with the values of Percent Error of my data. I used data from groundwater of one landfill from Brazil, and the values of my percent error are presented in 80, 90 %. I don't know if the problem is in my data or in the local contamination. This is a exemple of the output of my data:

Using PHREEQC: version 3.1.7, compiled on January 31, 2015
   Input file: Janeiro 2003.phr
  Output file: Janeiro 2003.phr.out
Database file: c:\phreeqc\database\minteq.v4.dat

------------------
Reading data base.
------------------

   SOLUTION_MASTER_SPECIES
   SOLUTION_SPECIES
   SOLUTION_SPECIES
   PHASES
   PHASES
   SURFACE_MASTER_SPECIES
   SURFACE_SPECIES
   END
------------------------------------
Reading input data for simulation 1.
------------------------------------

   DATABASE c:\phreeqc\database\minteq.v4.dat
   TITLE Poço Um
   SOLUTION 1. AMOSTRA
      units   ppm
      temp   25.30000
      pH   4.64000
      Cd   0.00030
      Cr   0.00250
      Fe   34.50000
      N(-3)    0.15000 as NH4+
      N(3)   0.00100 as NO2-
      N(5)   1.08000 as NO3-
      P   0.04000
      S(-2)   0.00050 as HS-
      S(6)   0.50000 as SO4-2
   END
-----
TITLE
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 Poço Um

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Beginning of initial solution calculations.
-------------------------------------------

Initial solution 1.   AMOSTRA

-----------------------------Solution composition------------------------------

   Elements           Molality       Moles

   Cd                2.669e-09   2.669e-09
   Cr                4.808e-08   4.808e-08
   Fe                6.178e-04   6.178e-04
   N(-3)             8.316e-06   8.316e-06
   N(3)              2.174e-08   2.174e-08
   N(5)              1.742e-05   1.742e-05
   P                 1.291e-06   1.291e-06
   S(-2)             1.512e-08   1.512e-08
   S(6)              5.205e-06   5.205e-06

----------------------------Description of solution----------------------------

                                       pH  =   4.640   
                                       pe  =   4.000   
                        Activity of water  =   1.000
                           Ionic strength  =   1.269e-03
                       Mass of water (kg)  =   1.000e+00
                 Total alkalinity (eq/kg)  =  -2.389e-05
                    Total carbon (mol/kg)  =   0.000e+00
                       Total CO2 (mol/kg)  =   0.000e+00
                         Temperature (°C)  =  25.30
                  Electrical balance (eq)  =   1.239e-03
 Percent error, 100*(Cat-|An|)/(Cat+|An|)  =  95.70
                               Iterations  =   9
                                  Total H  = 1.110137e+02
                                  Total O  = 5.550691e+01

I thought one of the problems can be as one of the elements in the case, iron. In my original data I have the Total Iron, not Fe2+ or Fe3+ as the program input. I wonder if the way I'm entering the data may be causing this problem, since I have not actually isolated concentration of Fe 2+ and Fe 3+. As if anyone would know a solution to this problem.

Thanks,

Best regards

Gabriel

[dlparkhurst]

You have no data for most of the major ions: Ca, Mg, Na, and Cl. You won't get charge balance unless you have a complete analysis including all of the important constituents.

[Messias]

Hi Dear Dlparkhurst,

But this makes my analysis decome less reliable?

and how i can do with the issue of iron?

[dlparkhurst]

Without a complete analysis, you cannot use the charge balance to make any inferences.

As for the iron, it is not clear which redox state is present. In the presence of oxygen and at low pH, it might be Fe(3). There is nitrate in the water, which would indicate more oxidizing conditions. At the same time, there is some ammonia and maybe a trace of sulfide, which would be more consistent with Fe(2). If you really need to know, it is possible to measure the redox states; depends on what your objectives are.

You have not given much information about where the water sample was taken. Perhaps you can make some inferences based on likely contact with oxygen or organic-rich zones, or presence of iron oxyhydroxides.

[Messias]

The objetive of my work is to understand the dynamics of the elements of the contamination in one landfill from Brazil. For this I will use the speciation and saturation for understand how species are formed and the state of this (precipitate/dissolution). This samples are from basaltic aquifier and how much of the Brazilian territory that has a high iron content.

My main concern is to be underestimating or overestimating the concentrations of Fe II or Fe III, since they are one of the elements that stand out as contaminants in the area. Then you would see if the program itself will be able to divide the value of the total iron Fe II and Fe III, or else by some method stoichiometry.

[dlparkhurst]

In an aquifer, where the water is not in contact with the atmosphere, the iron is almost certainly Fe(2).  However, when the water discharges to springs or streams, or is pumped, then the iron will oxidize and form iron oxyhydroxides.

[Messias]

I can consider this as Fe II depending on water analysis? The contact or not of water and oxygen

[dlparkhurst]

You may be able to consider Fe to be Fe(2) depending on the sampling context; that is it from a confined aquifer, has it been exposed to oxygen, is this a low-pH environment, etc. But I am not going to give you any assurances with as little as I know about your environments; it is your job to make the assessment.

[Messias]

Thanks Dlparkhurst for all help