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Fw: PHREEQC Interactive version 2.8



Hello David,
Just thought I would mention that the problem with F and As still exists in
the LLNL database. I have recently modelled groundwaters for CO2 injection
and formation of Dawsonite (which LLNL has data for) and had to take out
fluoride data to get answers.
regards
Robert Gerritse

----- Original Message ----- 
From: "David L Parkhurst" <dlpark@xxxxxxxx>
To: <geoprocc@xxxxxxxxxxxx>
Cc: <gs-w_h2osoft@xxxxxxxx>
Sent: Saturday, November 24, 2001 2:37 AM
Subject: Re: PHREEQC version 2.3


>
> The problem is with two As-F species, AsO3F-2 and HAsO3F-. The constants
> for these species look much too strong to me. They imply that they account
> for all of the arsenic, with the next species about 1e-10 smaller. The
> convergence problem is caused because under most initial choices of log
> activity F- and H2AsO4-2, these species cause all of the F to be
calculated
> to be in these species as well and the two mass balance equations are the
> same on the left hand side within the numerical precision of the computer.
> Right hand sides are related to the total concentrations, and these
differ.
>
> I would copy the definitions of these two species into your input file in
a
> SOLUTION_SPECIES data block. Then you can either eliminate them by
> decreasing the log K's by 20, or you can decrease the log K's by perhaps 5
> or 10, which will allow the program to converge. For the second case, the
> distribution of species will be effectively the same as the original log
> K's. The concentrations of the minor species will be larger, but with a
> choice of K's, they will still be small relative to the As-F species. I
> suspect there was a sign error or other tabulation error when they
compiled
> the data at LLNL.
>
>
> David
>
>
> David Parkhurst (dlpark@xxxxxxxx)
> U.S. Geological Survey
> Box 25046, MS 413
> Denver Federal Center
> Denver, CO 80225
>
>
>
>                     Michele Y
>                     Crouse               To:     David L
Parkhurst/WRD/USGS/DOI@xxxx
>                                          cc:     h2osoft@xxxxxxxx
>                     11/23/01             Subject:     Re: PHREEQC version
2.3
>                     06:30 AM
>
>
>
>
>
>
> ----- Forwarded by Michele Y Crouse/WRD/USGS/DOI on 11/23/01 08:29 a.m.
> -----
>
>                     "RG&AJ
>                     Gerritse"            To:     <mcrouse@xxxxxxxx>
>                     <geoprocc@xxx        cc:
>                     ce.net.au>           Subject:     Re: PHREEQC version
2.3
>
>                     11/21/01
>                     10:30 p.m.
>
>
>
>
>
> With the attached input file for a recent groundwater sample I get a a
> normal run with the WATEQ database, but with the LLNL database the program
> will not converge. Taking As or F out makes the LLNL run converge. What
can
> the problem be?
>
> regards
> Robert Gerritse
> Geoprocc Pty Ltd
> Wembley Downs
> Western Australia
> (See attached file: Searl5.pqi)
>
>
>



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