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Beginners => PHREEQC basics => Topic started by: d_guse on May 04, 2021, 07:05:19 PM

Title: Definition of saturation index SI/ documentation of version 3
Post by: d_guse on May 04, 2021, 07:05:19 PM
Dear all,

I have a question concerning the definition of the saturation index SI respectively concerning its documentation.

According to the documentation of version 2 of PHREEQC, SI is defined according to the attached screenshot (from: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc/html/final-11.html).

1. Shouldn't this equation read SI = log(IAP / K_SP) with K_SP defined according to eq. (35)? In my opinion, K_SP^(-1) (or a_m,eq^(-1)) is missing in eq. (36).

2. Is there any equivalent documentation for version 3 of PHREEQC concerning the numerical methods and equation definitions?

Thank you very much!


Kind regards
David
Title: Re: Definition of saturation index SI/ documentation of version 3
Post by: dlparkhurst on May 05, 2021, 01:08:12 AM
Yikes. You are right. There should be another term: -log(Kp) or a divisor of Kp inside the log IAP term.

No, the documentation of the numerical method of version 2 is essentially the same for version 3 and was not repeated in the version 3 manual. What can I say, I got tired of writing documentation. Description of numerical methods of new features, particularly TRANSPORT, were added to a limited extent within the description of input for the keywords in the Version 3 manual.
Title: Re: Definition of saturation index SI/ documentation of version 3
Post by: PREETU on August 05, 2022, 10:55:13 AM
Hello Sir,
I have a question relating to the results of saturation index.
I had a dataset of water quality parameters for the month of March and April, I just simply added my database and gave it a run.
The first run was for March dataset, second run for April dataset and the third run was combination of march and april data set.
So, the problem I am facing is that the results of April and combined dataet are same.
So is it possible ?
Title: Re: Definition of saturation index SI/ documentation of version 3
Post by: dlparkhurst on August 05, 2022, 02:28:04 PM
I can't tell if there is a problem or not. I know of no problems with the SI calculations of PHREEQC, but I don't know what is troubling you. Each solution should produce a set of SIs and the results should differ depending on each solution composition.

Try using one of the databases distributed with PHREEQC. If you still have concerns, include an input file (use the # button at the top to include the code in your post) with a couple of solutions that demonstrate the problem.