Charge balance within SpecE8

[Bron]

I have found conflicting charge balances between GWB and PHREEQCI using the same dataset (attached). Results as follows:

 

Method 1: Manual calculation using major ions only = -30.1%

Method 2: PHREEQCI using llnl.dat = -35%

Method 3: SpecE8 using thermo.com.V8.r6+.dat = -70.18%

Method 4: SpecE8 using thermo.dat = -69.78%

 

I expect charge balance to be around 30-35%, not 70%!

 

I have read the thread dated 10/05/2011 entitled, "Charge balance/speciation" where it was commented that discrepancies in charge balances may be attributable to different calculation methods between codes. This does not appear to be the case here as all methods listed above appear to use the following convention:

 

Charge balance = 100*[(Sum cations–Sum anions)/(Sum cations + Sum anions)]

 

The issue within SpecE8 doesn't appear to be related to the database used, or to differences in reported calculation methodologies between codes. Have I loaded the input data incorrectly into GWB? I would greatly appreciate your assistance. Thank you.

TD5_40-60_L1-04.sp8

[Brian Farrell]

Hello Bron,

 

Running your example in GWB 8 (and earlier) I get a charge imbalance error of -70%. In GWB 9, which uses a different convention, I get -35%, which seems to agree with the PHREEQC and hand calculations. I'll look into this further, but I think the explanation offered in the thread you mentioned mixed up the two conventions. Based on a quick spreadsheet I made up, GWB 9 appears to use the same convention that you typed out here, while GWB 8 and earlier versions divide the denominator by 2 (which is the same as multiplying the whole thing by 2).

 

If you'd like to check your own calculations using GWB 9, I think we can arrange to send you a trial version. Just send an email to support@gwb.com.

 

Regards,

 

Brian Farrell

Aqueous Solutions LLC