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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