Tom Meuzelaar

Hi Ross: I simplified the script quite a bit, and am still getting a syntax error in line 1, even though the format appears to be correct. I'll need to check with the developers to see if I'm doing something wrong here. However, there's a simple work-around. Save the file in notepad with a .bas extension, and load it in as a Rate law script file. Let me know if that resolves the issue. Regards, Tom Meuzelaar RockWare, Inc.

Hi Ross: Sure- in X2t, choose Config - Second Reaction Interval. Then in Config - Wells, add a well, and you'll notice that you can specify two injection rates. Set the first one to be your injection (positive rate) and the second to be your recovery (negative rate). Be sure to set the Time for both intervals in the Initial pane. Hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Trevor: Have you read pages 13 (and the top of 14) in the Reactive Transport Modeling Guide? This covers heat transfer across medium boundaries. Hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Kelvin: Equilibrium constants for CuCl3- and CuSO4(aq) are only defined at 25C, thus you should either define solubility data for the temperatures you are working at or turn the extrapolate variable off. Hope that helps, 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 July 7-8, 2011 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 later in the year. 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

Hi: Absolutely. Just make sure that you include H+ as a component, and constrain it (swapping) with the variable that controls pH. Hope that helps, Tom Meuzelaar RockWare, Inc.

Hi Laurie: Finally getting around to your question. The issue of charge balance calculation differences among the various codes is a significant one that has not been discussed yet on this forum- so I will post it here for reference. There are two very different methods for calculating charge balance, both with an apparently significant following: Imbalance calculated relative to the sum of anionic and cationic charge, popular among water engineers: Charge balance = 100*[((Sum cations-Sum anions)/(Sum cations + Sum anions))/2)] Example reference: Weight, W.D. (2008), Hydrology Field Manual, McGraw Hill, 751 p. (see Chapter 7) Imbalance calculated as average of anion-cation charge sum: Charge balance = 100*[(Sum cations–Sum anions)/(Sum cations + Sum anions)] Example reference: Zhu, C. and Anderson, G. (2002), Environmental Applications of Geochemical Modeling, Cambridge University Press, 284 p. (see p. 95) I will leave it to other to discuss why this apparent significant discrepancy exists, as I know little about it myself... GWB uses the latter method. I'm not familiar with how other codes calculate this, but it may well be that the other method is used- as you can see, the difference is a factor of two, and you can easily make a correction. The other significant aspect to note is that GWB calculates charge imbalance based on species concentrations after the speciation calculation is performed. If you want to double-check the calculation, simply open the output file, sum the anions and cations and apply formula 2 (above). As far as your input file is concerned, it looks fine. You have chosen to enter your reduced sulfur concentration as total Sulfur. If your laboratory reports S2, you can either enter it as such, or adjust your total Sulfur by a factor of 2. As far as redox is concerned, if you enter a pe value into the GSS spreadsheet, GWB will speciate all coupled redox species according to system O2 values reflected by your pe value, while decoupled redox species do not react with each other, and thus keep their independently constrained values. I hope this helps... Regards, Tom Meuzelaar RockWare, Inc.

Hi: Apologies for the delay. In your first script, as the error message indicates, you run out of Cl- for charge balance, and it is forced to negative concentrations. You can remedy this by either beginning with a higher anion concentration, or better yet, consider a base titration (NaOH for example), rather than a pH slide, as this avoids negative concentration issues. Unless this is a pure solution, it's a good idea to have some background electrolytes (Na, Cl). The issue with the smaller reaction path steps occurs right when Zincite reaches saturation- you are essentially removing 1/10th the proton mass at each step, and this creates an unstable matrix when Zincite becomes supersaturated and React attempts to swap it in for the Zn++ matrix component. I'm not sure exactly why this happens, but this model is being run with a large charge imbalance- I recommend fixing the first model, with charge balance, as this should result in a model that is more stable overall. The same goes for the non-convergence issue at high pH. I hope that helps, Tom Meuzelaar RockWare, Inc. RockWare, Inc.

Hi: Please attach the script you are working with, and I'd be happy to take a look. Regards, Tom Meuzelaar RockWare, Inc.

Hello: Can you please attach a script that shows me your results? If you are using a modified thermodynamic database, please includes this also. If the model and data are proprietary, feel free to email them to me. Regards, Tom Meuzelaar RockWare, Inc.

Hi Ale: The alkalinity reported by GWB is carbonate alkalinity, computed as follows: Alk = 50.0445 * 1000 * (m_HCO3 + 2 m_CO3) * (kg_solv/kg_soln) For computing total alkalinity from the above, refer to Craig Bethke's Geochemical and Biogeochemical Reaction Modeling, page 220 (Chapter 15). I hope that helps, Tom Meuzelaar RockWare, Inc.

Hello: If you want to model changing system chemistry over time, you should take a look at the various kinetic options available in GWB. The best place to start is the Reaction Modeling Guide (starting with page 33). I hope that helps, Tom Meuzelaar RockWare, Inc.

Hello: Please email me, and we'll see if we can get this resolved. Regards, Tom Meuzelaar RockWare, Inc.

Hi Elisabeth: The purpose of a flash diagram is to predict scale and mineral saturation state changes that arise when two fluids are mixed in varying proportions. What GWB actually does is remove fluid from the system in the same proportion that new fluid (in your case, end member groundwater) is titrated in. This allows you to see a range of mixing ratios between your end member groundwater fluid and your mixed fluid. So this approach may not work for your inverse model, as you would essentially be removing water of different compositions twice over. Keep in mind that the water you are 'unmixing' is still likely affected by scaling and volatile removal during fluid ascent. Reconstructing reservoir conditions is a tricky problem that all modelers face. A few things you might add to your approach: Assume that your end member fluid was in equilibrium with local host rock at depth (the Tomichi intrusion, I believe?). If you know the composition of this host rock, you can partially constrain the composition of your thermal end member by titrating these minerals into water at reservoir P/T. If you know that a gas cap exists within the reservoir, you can titrate these gases to saturation into your surface water. With CO2, this will help restore pH/alkalinity. If you have no knowledge of the existence of a gas cap, another approach is to titrate in flashed (exsolved; note that 'flash' here is a different term than what is used in the model) gases. But this requires a measured gas/water ratio, and gas compositions. If you have compositions for surface scale, you can titrate these minerals back into your surface water. There are some difficulties with this, but eventually, your surface water should approach the various saturation states you estimate for your end member thermal water. As far as your model, it doesn't look like you are driving any species concentrations negative. You have some negative components (H+, O2), but that's a mathematical and not a physical phenomena. I hope that helps, Tom

Hi: Try balancing your Basis water on Na- it's the one that is not converging. Your Na/Cl concentrations are extremely low, so you might choose more abundant, nonessential cations and anions for charge balance. Hope that helps, Tom Meuzelaar RockWare, Inc.

Hello: You'll want to use the React module, which is well suited for this: Load the water that you would like to titrate into the React Basis panel Speciate this water (Run) and use the Run - Pickup - Reactants command to load this speciated water into the Reactants tab This water becomes the water that you will mix into your primary water Load your primary water into the Basis tab (Open - React Script) Your mixing model is now set up If you want to experiment with variable mixing ratios, use the Reactants times setting in the Reactants tab Hope that helps. Regards, Tom Meuzelaar RockWare, Inc.

Hello: It looks like you don't have a constraint for the HCO3-, which is necessary for the higher pH range. Some constraints on other dissolved solutes (at a minimum Na and Cl) are going to be helpful as well for maintaining charge balance. Regards, Tom Meuzelaar RockWare, Inc.

Hi Blake: Thanks for your post. Would you mind attaching the script that is generating the singular matrix error so I have a starting point? Regards, Tom Meuzelaar RockWare, Inc.

Dear GWB Users: We have released GWB 8.0.12, which addresses the following issues: Fixes a flaw in React 8.0.11 (but not earlier maintenance releases) introduced by an error in the latest update level of the Intel optimizing compiler; the flaw affected kinetic reaction paths. All current GWB Essentials, Standard and Pro version 8 users can download the GWB 8.0.12 patch here. Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.

Hi Stefan: Attached is an alternate way to set up your problem, which doesn't run into any of the charge balance issues of the first method. Let me know if this is helpful. Regards, Tom Meuzelaar RockWare, Inc.

Dear GWB Users: We have released GWB 8.0.11, which addresses the following issues: corrects a GUI issue in X1t and X2t that can cause the basis panes to freeze or behave oddly. All current GWB Essentials, Standard and Pro version 8 users can download the GWB 8.0.11 patch here. Please contact me with any questions. Regards, Tom Meuzelaar RockWare, Inc.

Hello: Apologies for the late response- I somehow missed notification of your post. Yes, GWB is a great tool for modeling pyrite oxidation. I'd make a couple of changes to your script: You can remove the time constraint, as this is useful only for kinetic modeling, and you do not have a kinetic rate set for pyrite (might be useful to add this to your model...) I would swap Pyrite in for Fe++ in your Basis, and titrate oxygen in from the Reactant panel Those two changes should get you most of the way there. Let me know if you have any further questions. Regards, Tom Meuzelaar RockWare, Inc.

Hi Stefan: In version 8, you can plot charge imbalance error under the System parameters variable type in Gtplot. I wonder if we are looking at different output files- when I run the script you sent me, and look at the last reaction path script in the 'd' output file, charge balance adds up fine. What version are you using? (use the Help - About menu to determine version and sub-version). Regards, Tom

Hi Stefan: The charge imbalance message is not an error, but simply a warning that you are not forcing charge balance. A plot of charge imbalance error shows that your initial system, as you've defined, carries a charge imbalance error of 3.2e-4%. At the end of the simulation, this decreases to 3.2e-5%. Is this significant? Regards, Tom Meuzelaar RockWare, Inc.

Hi: Unfortunately, there is no way to display both the water stability boundaries and show phase stability across your entire axis range. You can do one or the other, but not both. One work-around would simply be to export your second diagram in vector format (using the File - Save image as.. menu option) to a third-party graphics program, and add the water lines in manually. Best regards, Tom Meuzelaar RockWare, Inc.