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Error in Percent Error
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Topic: Error in Percent Error (Read 1166 times)
Messias
Contributor
Posts: 5
Error in Percent Error
«
on:
February 03, 2016, 04:33:25 PM »
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
-----
Poço Um
-------------------------------------------
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
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dlparkhurst
Top Contributor
Posts: 1034
Re: Error in Percent Error
«
Reply #1 on:
February 03, 2016, 11:25:10 PM »
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.
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Messias
Contributor
Posts: 5
Re: Error in Percent Error
«
Reply #2 on:
February 04, 2016, 01:09:34 AM »
Hi Dear Dlparkhurst,
But this makes my analysis decome less reliable?
and how i can do with the issue of iron?
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dlparkhurst
Top Contributor
Posts: 1034
Re: Error in Percent Error
«
Reply #3 on:
February 04, 2016, 03:05:57 AM »
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.
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Messias
Contributor
Posts: 5
Re: Error in Percent Error
«
Reply #4 on:
February 04, 2016, 11:42:27 AM »
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.
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dlparkhurst
Top Contributor
Posts: 1034
Re: Error in Percent Error
«
Reply #5 on:
February 04, 2016, 03:54:41 PM »
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.
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Messias
Contributor
Posts: 5
Re: Error in Percent Error
«
Reply #6 on:
February 04, 2016, 06:22:13 PM »
I can consider this as Fe II depending on water analysis? The contact or not of water and oxygen
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dlparkhurst
Top Contributor
Posts: 1034
Re: Error in Percent Error
«
Reply #7 on:
February 04, 2016, 10:39:12 PM »
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.
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Messias
Contributor
Posts: 5
Re: Error in Percent Error
«
Reply #8 on:
February 05, 2016, 12:27:48 PM »
Thanks Dlparkhurst for all help
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