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 11/23/01 06:30 cc: h2osoft@xxxxxxxx In-Reply-To: <OF6A7E98F1.E00262C9-ON85256B0D.004A26AA@xxxxxxxx> AM Subject: Re: PHREEQC version 2.3 ----- Forwarded by Michele Y Crouse/WRD/USGS/DOI on 11/23/01 08:29 a.m. ----- "RG&AJ Gerritse" <geoprocc@xxxxxx To: <mcrouse@xxxxxxxx> net.au> cc: In-Reply-To: <OF6A7E98F1.E00262C9-ON85256B0D.004A26AA@xxxxxxxx> 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)
Description: Binary data
Please note that some U.S. Geological Survey (USGS) information accessed through this page may be preliminary in nature and presented prior to final review and approval by the Director of the USGS. This information is provided with the understanding that it is not guaranteed to be correct or complete and conclusions drawn from such information are the sole responsibility of the user.
Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.
The URL of this page is:
Last modified: $Date: 2005-09-13 21:04:21 -0600 (Tue, 13 Sep 2005) $
Visitor number 1878 since Jan 22, 1998.