GSS_Calculation error report (bug?)

[Kirkoff Xn]

Hi there,

I am running into an issue. It looks like it's a bug as I am receiving an error message "calculation error report" (see below screenshot)

When trying to calculate mineral saturation or charge imbalance by clicking to "analyte"---> "calculate with specE8", I get this error.

 

 

[Jia Wang]

Hello,

When GSS is asked to calculate an analyte value, it actually calls SpecE8 to do the calculation. When SpecE8 cannot solve the equilibrium system with the given conditions (composition of your sample, temperature, etc) in your GSS sample, the calculation will fail. There can be a variety of issues that cause SpecE8 to fail an equilibrium state calculation and it's not clear based on the screenshot. If you scroll down in the Calculation Error Report pane, you should be able to learn more details regarding the error. I suggest launching a SpecE8 instance with your sample so that you can investigate more closely. For more information on launching GSS samples in SpecE8, please see section 3.5 in the GWB Essentials User Guide.

If you require additional assistance with troubleshooting, please attach the input and thermo file so we can take a closer look.

Hope this helps,
Jia Wang
Aqueous Solutions LLC

[Kirkoff Xn]

Yeah, It's due to large residuals. Can you please advise how to go with this considering there might be a large difference in electroneutrality(?)Injectant.gss

[Jia Wang]

Hello,

The custom thermo dataset was not attached, but I manage to open your GSS file with thermo.tdat. To investigate the issue with convergence, I launched a SpecE8 instance using the sample composition from the attached GSS file. I noticed that your system is relatively oxidized (with an O2 concentration of 4 mg/kg) and at this pH, the dominant species for your arsenic component is going to be the more oxidized form. It would help the program to solve the equilibrium state when a more dominant form is swapped in. In this case, I tried swapping in AsO4--- for As(OH)4-, making sure to convert the concentration in GSS (I did equivalents of As in mmol/l) and use that value, and SpecE8 converged without issues.

If you have only a few samples, it might make sense to launch SpecE8 and perform the swap and run your calculation.

If you wish to carry out the calculation in GSS for a large number of samples, you can edit your dataset and use the exchange feature to swap the position of AsO4--- and As(OH)4- and AsO4-- will be a basis species. This way, you can add the total concentration of As in the spreadsheet by adding AsO4--- to the GSS spreadsheet and maintain equilibrium calculation between arsenic redox species.

Alternatively, you may consider adding the total concentration of As in under the analyte AsO4--- without editing your dataset. This case, you would be decoupling the redox couple AsO4---/As(OH)4-. I am not sure what would be more appropriate for your consideration.

Hope this helps,
Jia

[Jia Wang]

Hello,

Additionally, I also noticed that you had set your O2(aq) as a total concentration instead of a free quantity, which is commonly is. A free quantity means that the amount inputted by the user represents the quantity of that species alone, which O2(aq) almost always is when measured. If you do so, you should be able to run the calculation without swapping basis as mentioned above and still converge with your calculations.

Hope this helps,
Jia

[Kirkoff Xn]

Thank you, Jia!

[Jia Wang]

Glad to hear that was helpful. Hope the rest of your project goes smoothly.

Best,
Jia