Tom Meuzelaar

Hi Amy: Received your file via email- the error persists in v8.0.9 - we'll take a look. Regards, Tom Meuzelaar RockWare, Inc.

Dear GWB Users: We have released GWB 8.0.9, which addresses the following issues: Fix error setting anisotropic dispersivities in X2t Correct problem scrolling past hidden rows to the edge of data sheets in GSS Fix several minor glitches in the GUI Resolve all known issues with 8.0 through 8.0.8 All current GWB Essentials, Standard and Pro version 8 users can download the GWB 8.0.9 patch here. Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.

Hi Kathy: Thanks for sending your dataset. It looks like the bicarbonate value in the last column is set to '0.0' - the field should be either blank or set to 'n/d' or similar. I hope that helps, Tom Meuzelaar RockWare, Inc.

Dear Rahul: I don't know much about solubility data for smectite clays. Perhaps another user on this forum can enlighten us, or you can consider going to the library at a local university and searching the literature. Kind regards, Tom Meuzelaar RockWare, Inc.

Dear Rahul: General instructions for adding minerals to thermo databases can be found in the Appendix: Thermo Datasets in the GWB v8 Reference manual. Adding data to a Pitzer database is a far trickier business- for this, I suggest that you refer to the original Harvey-Moller-Weare compilation and PHRQPITZ documentation: Harvie, C.E, N. Møller and J.H. Weare, 1984, The prediction of mineral solubilities in natural waters: The Na-K-Mg-Ca-H-Cl-SO4-OH-HCO3-CO3-CO2-H2O system to high ionic strengths at 25°C. Geochimica et Cosmochimica Acta 48, 723–751. Plummer, L.N., D.L. Parkhurst, G.W. Fleming and S.A. Dunkle, 1988, PHRQPITZ — A computer program incorporating Pitzer’s equations for calculation of geochemical reactions in brines. U.S. Geological Survey Water-Resources Investigations Report 88–4153, 310 p. Regards, Tom Meuzelaar RockWare, Inc.

Hi Kathy: Can you attach your GSS file so I can take a look? Please also specify which sample you are referring to. If your dataset is proprietary, feel free to email it to me. Regards, Tom Meuzelaar RockWare, Inc.

Hi T.C. It looks like your React script did not attach (I only have the .bas custom kinetic file). Can you include this? Regards, Tom Meuzelaar RockWare, Inc.

Hello: You can always look at your scripts in a text editor (ie. Notepad) to see how they differ. The main difference between the two scripts you sent me is that one (confused.ac2) is using the LLNL default database (thermo.dat), while the other (Eh 0.5 HPO4.ac2) is using the extended LLNL database (thermo.com.v8.r6+.dat). The number of uranium species, and the log K values are not the same between the two databases, thus your graphs are different. Hope that helps, Tom Meuzelaar RockWare, Inc.

The trouble is that you have such a high uranium concentration (~1000 mg/kg), and it's difficult to create a model that's initially stable. A couple of things you might try: - cast your concentrations in mg/kg rather than activities - swap other U6+ species in for UO2++ The attached gets you a bit closer. Hope that helps, Tom Meuzelaar RockWare, Inc. SpecE8 basis 1 carbonate_revised.sp8

Hello: Can you attach a script so I can take a look? Regards, Tom Meuzelaar RockWare, Inc.

Hi Amy: Thanks for the additional info- I can reproduce this as follows: 1. open spreadsheet 2. Hide first sample 3. Scroll up and down with mouse I'll forward this to the developers, and let you know when a fix is available. Thanks for the detailed reporting, Tom

Can you attach your data set (or email to me), and tell me what actions are generating the error? Regards, Tom

Hi Amy: What version of GSS are you using? You can find this by going to Help - About GSS... Regards, Tom Meuzelaar RockWare, Inc.

Hi Anke: I received your database and script. The problem with the database is that you've written an entry for HPO4-- in the aqueous species section, not PO4---. Try writing the reaction as it's written in thermo.dat: PO4--- charge= -3.0 ion size= 4.0 A mole wt.= 94.9714 g 2 species in reaction -1.000 H+ 1.000 HPO4-- 12.5908 12.3090 12.1325 12.1305 12.2148 12.3992 12.7240 13.1298 I hope that helps, Tom

Hi Dimin: It looks like the first problem is a charge balance issue. You've chosen to balance on Cl-, but the water defined in the Basis has more anions than cations. If you remove Cl- and balance on Na+, the solution converges. Beyond that, the fast rate constant and the large surface area you've specified causes the reaction to complete within a fraction of a second, rather than over a period of 14 days. Hope that helps, Tom

Hi Dimin: Looks like you're using a modified version of the extended LANL database- can you attach this? If it's proprietary, you can email it to me. Regards, Tom Meuzelaar RockWare, Inc.

Hi Anke: No worries- GWB involves a long and on-going learning curve for all of us, myself included. Can you send me the database with Struvite and with only one Basis entry for phosphate (HPO4-) so I can reproduce the error message you are getting? Regards, Tom

Hi Anke: I've looked at your database- there's a problem with the way you've defined your Basis species- you have both HPO4-- and PO4--- as Basis species. Have a look at Section 3.2 (p. 36) of Craig Bethke's "Geochemical and Biogeochemical Reaction Modeling" text. Regarding your choice of Basis components, from the text: "...the components must be linearly independent of one another. In other words, we should not be able to write a balanced reaction to form one component in terms of the others" In your case, HPO4-- can be formed from H+ and PO4---. The reaction for Struvite in your database is written in terms of the PO4--- basis species, while Hydroxyapatite is written in terms of the other phosphate basis species, HPO4--. Hence, you get the spurious results that you do. I recommend choosing one phosphate basis species (HPO4-- is the default for thermo.dat), and making the other an aqueous species. As far as having only data at 25C, this is not a problem since your model is at 25C (although the dataset you sent me appears to have constants at other temperatures?) I hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Emily: Two points that will hopefully move you in the right direction: It looks like you've put rock mass and not fluid concentration data into the Basis pane. GWB requires that you put an aqueous system of some kind into the Basis pane. One option would be to constrain the concentrations of fluid components initially in equilibrium with your basalt, and then flush water through as a reactant. Your other option would be to titrate the minerals or oxides composing your basalt in as Reactants into your Basis fluid (a reverse titration model). Specifying a beginning and end time does not make a model kinetic, it simply creates an equilibrium model in which the reaction path variable is time. To create a kinetic model, you'll want to add a kinetic mineral in the Reactants pane - have a look at the GWB Reaction Modeling Guide, which has a large section on kinetics. I hope that helps, Tom Meuzelaar RockWare, Inc.

Anne: Just a quick note here to let our users know that we continued our discussions via personal correspondence, and that your questions did not go unanswered. Regards, Tom

Hi Anke: Can you attached your revised database and script for this model? If you wish to keep them confidential, you can email them to my attention. Regards, Tom Meuzelaar RockWare, Inc.

Dear GWB users: We are pleased to announce a workshop in Golden, CO for GWB Essentials, Standard and Professional users this fall. The November 18-19, 2010 workshop is designed for: Current users of GWB Essentials, GWB Standard and GWB Professional who wish to become more familiar with the software's interface and features. Those interested in reviewing the basics of geochemical modeling (speciation models, activity models and activity diagrams) Those interested in learning detailed reaction path modeling (using redox disequilibrium, kinetics, and surface complexation) Those interested in learning the basics of 1D/2D reactive transport modeling Registration fees are $799 (commercial) / $699 (academic). Students can register on stand-by for $299. RockWare will be hosting the workshop in their newly remodeled conference room. The advantage of this venue is a smaller classroom size and teacher to student ratio. This does, however, require that students bring their own laptops. RockWare will provide temporary licenses for GWB Pro v8 to each participant. There conference room seats up to 7 participants. If the course is sold out, and significant interest remains, we will consider holding a second workshop in the late fall. For all the details, visit the GWB workshop page on the RockWare website. Please don't hesitate to contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc. 2221 East Street Golden, CO 80401 ph. 303 640 5526

Ann- the rate constant data in the workbook comes from a variety of sources. However, two current and excellent compilations which contain significant rate constant data are: Palandri, J.L. and Y.K. Kharaka, 2004, A compilation of rate parameters of water-mineral interaction kinetics for application to geochemical modeling, USGS Open File Report 2004-1068, pp. 1-70 Brantley, S.L., Kubicki, J.D. and A.T. White, 2008, Kinetics of water-rock interation, Springer, pp. 737-824 I received your database, and will try to respond within the next day or two, Tom

Hi Ann: When I run the script you give me, I get the same result for both 2 and 30 days- however, I'm not privy to the thermo database you are using, so my pH is higher than what you are calculating. If you want to email me your database (gwb@rockware.com) I can take another look. Let me get back to you on this.... Tom

Hi Ann, Changing the delxi variable won't have much effect in a kinetic run, as GWB chooses it's own timestep. The delxi variable is more suitable to equilibrium models. Part of the problem is likely the fact that you've set exceedingly fast reaction rates for each of the minerals- in the Reaction Modeling Guide, p. 35, rate constants for Quartz and Albite are 2e-16 and 1e-15, respectively. Most rate constants for silicates are around this order of magnitude. In your simulation, all rate constants are close to a value of 1, reflecting very rapid dissolution/precipitation rates. This will force React to choose exceedingly small timesteps. Yes, that's what I'm referring to. Clays (and the Al component) are notoriously difficult when it comes to creating equilibrium models of water-rock systems - in your model, you have 3 clays and 2 feldspars. You might try starting with one, and adding complexity as you go along. This is likely indicative that your kinetic models aren't yet properly configured to begin with. It's almost always better to start with fewer components, and fewer minerals, making sure that you have a stable model first, before adding additional complexity. The (1-Q/K) portion of the rate law is built in, and is simply calculated by GWB based on fluid saturation conditions- in other words, it is implicitly accounted for regardless of what values you use for rate constants and surface areas. Sometimes recreating the actual W/R is important- it really depends on what your modeling objective is. For most models I run, it's more important that I simply include enough mineral mass to reach saturation with the fluid. I think if you revisit your rate constants, you'll get quite a bit further. Have a look at some of the examples in the user's guide and textbook. Hope that helps, Tom