Brian Farrell

In GWB 2023, TEdit can be used to import any EQ3/6 dataset (including any solid solution definitions) to GWB format. And conversely, GWB datasets using the b-dot and h-m-w models can be exported to EQ3/6 format. For more information, please see 9.3.2 Importing EQ3/6 datasets and 9.3.3 Exporting EQ3/6 datasets in the GWB Essentials Guide.

Hi Tom, With the release of GWB 2023, spaces are allowed in the name of any species in the dataset, basis or secondary. When such a species appears in a reaction, or in a virial pair or triplet, it should appear within quotes in that part of the thermo dataset. For example, the entry for the reaction >CaSeO4 (aq) = CaSeO4 (aq) should appear as: >CaSeO4 (aq) charge= 0 mole wt.= 183.0376 g 1 species in reaction 1.000 "CaSeO4 (aq)" Kd= .01471 Regards, Brian

The minerals actually become undersaturated after each increment of added fluid (and removal of the mixed fluid), but because this is an equilibrium model, the minerals dissolve in response until the fluid re-equilibrates with them (i.e., until they're no longer undersaturated) at the end of the step. If that's not obvious, you can play around with your model to see what's happening. If you use the dump command, which removes minerals from the system before tracing the reaction path, you'll see how the flush model you've configured causes calcite and dolomite to change from saturated to undersaturated when there is no mineral mass available to buffer the fluid chemistry. Or, you can add kinetic rate laws for the Calcite and Dolomite and set their rate constants to small values (for slow reaction), or even 0 (for no reaction), and then if you disable precipitation for other minerals, you'll again see that the flushing fluid causes the minerals to become undersaturated. But since the dissolution rates set are so slow, the minerals don't dissolve to any significant extent. Assuming progressively faster kinetics, however, you should approach the equilibrium behavior in which dissolution is fast enough that the fluid remain in equilibrium with the minerals after each step. Hope this helps, Brian Farrell Aqueous Solutions

Currently the React plugin does not report a description of why a run might have failed. I recommend running the problematic examples directly in React and checking the Results pane for any information that might be helpful. Regards, Brian Farrell Aqueous Solutions

Hi Scott, The reaction progress variable Xi by definition varies from 0 at the start of a reaction path to 1 at the end, but it has meaning only in terms of how you set up the reaction path. If you've set up a simple polythermal path in which temperature varies from 0 to 100 C, for example, then Xi = 0 indicates the initial condition, as always (0 C here), Xi = .5 indicates 50 C, and Xi = 1 is the system heated to 100 C. The program by default takes steps equal to 1/100th of Xi, so here it increases temperature one degree at a time. If the program was instructed to heat water to 200 C, then each step by default would be 2 degrees, and Xi = .5 would correspond to 100 C and Xi = 1 to 200 C. In titration paths (simple reactants), similarly, you specify the amount of a reagent to add over the course of the path, and so adding everything specified corresponds to Xi = 1. Adding half of that corresponds to Xi = .5, and at Xi = 0 you've added nothing. When interpreting the results of a calculation, it's helpful to plot against the variable that actually controls reaction progress. So in a sliding temperature path, you might set temperature as your x axis variable. In a titration, set the mass reacted (under Reactant properties) of the titrated species. And for a sliding fugacity or activity path, you can find the buffered fugacity or activity value under Reactant properties or under Gas fugacity/Species activity. Please let me know if that doesn't clear up your question. Regards, Brian Farrell Aqueous Solutions

Hi Scott, The plotting apps still display Q/K itself, with the option to use a linear or log scale. In other words, the spacing of data points is affected, not the values themselves). You can readily copy numerical values from Gtplot to Excel, however, then transform the values to their logs and make the plot you want in Excel. To export the numerical values from Gtplot, simply choose your desired variables (e.g. Temperature on x axis and Mineral saturation on y axis), then go to Edit > Copy As > Spreadsheet, then paste into Excel. Hope this helps, Brian Farrell Aqueous Solutions

You can use SpecE8 to figure the equilibrium distribution of species given a particular bulk composition and temperature. And you can account for redox disequilibrium as necessary. For more information, please see Chapter 7, Using SpecE8, in the GWB Essentials Guide. In the GWB Standard package, React can account for various kinetic processes, including redox reactions that are catalyzed on mineral surfaces. For more information on modeling kinetic reactions, please see Chapter 4, Kinetic Reaction Paths, in the GWB Reaction Modeling Guide. You’ll likely be particularly interested in sections 4.1 and 4.2, which serve as an introduction to kinetics, as well as 4.6 and 4.6.1, which describe redox transformations and catalysis on mineral surfaces, respectively. You can also scan over a range of temperatures in React; see 3.4 Polythermal reaction paths in the GWB Reaction Modeling Guide. Hope this helps, Brian Farrell Aqueous Solutions

You're welcome.

Modeling is quite often done in steps. It's an iterative process. You can get an estimate of fluid density in React by supplying the major components defined for the fluid: T = 70 pH = 5 Na+ = 1 molal Ca++ = .2 molal Cl- = 1 molal Or, for a more accurate calculation, you can configure a fluid in equilibrium with arbitrary amounts of the reservoir minerals to calculate the density accounting for all the components of the fluid. So, the swapping steps are the same as in the textbook example, but the mineral volume/mass constraints don't matter for that part of the problem. If you'd prefer, you can specify volume% of each mineral, rather than an absolute volume, along with a porosity for the system. As for GSS, you can supply the values of certain analytes or in some cases you can calculate them. If you want to calculate fluid density in GSS from your fluid analysis, choose +analyte > Calculate with SpecE8.... If that's what you're doing and you're still having issues, please attach your spreadsheet. For more information, please see 3.2.5 Calculating analytes in the GWB Essentials Guide. Regards, Brian

Glad to hear this helped. Currently there is no way to change the appearance of analytes. You can right-click on an analyte and see different options, though (e.g. the user analytes and equations have an “edit” option). You might try naming the user analytes and equations to make their type more apparent. As for ignoring “less than” values in user equations, unfortunately GSS is not currently set up to do this. Regards, Brian

Yes, the GWB’s “Carbonate alkalinity” refers to the alkalinity from all carbonates, so it includes what your lab reports separately as “CO3-- alkalinity” and “HCO3- alkalinity”. Looking at your spreadsheet, keep in mind that the user analytes and user equations are just that – analytes for user reference that are disconnected from the program’s speciation calculations. Also, instead of the “concentration” dimension, you might consider using the “alkalinity” dimension, which can be found under the “Chemical parameters” variable type. You can find mg/l_as_CaCO3 among the options. A good use of the feature would be to store your various reported alkalinities as user analytes, then create a user equation to combine your HCO3- and CO3-- alkalinities, then copy the resulting values into GSS’s predefined “Carbonate alkalinity” variable (click +analyte > Chemical parameters > Carbonate alkalinity) that gets used for speciation calculations. As for constraining a speciation calculation in GSS, you can enter the total concentration of the HCO3- component (i.e. the sum of concentrations of CO2, HCO3-, CO3--, and complexes), the free concentration of the HCO3- species (just the concentration of the HCO3- species; do so by choosing the “free” option), or GSS’s Carbonate alkalinity, described above. If both are present, GSS will use whichever of the HCO3- or Carbonate alkalinity is higher up in the order of the spreadsheet. In SpecE8, by contrast, you don’t choose from separate HCO3- or Carbonate alkalinity variables. You only add HCO3- to the basis, then choose appropriate units. The concentration units (e.g. mmol/kg, mg/l, eq/kg, and so on) imply a concentration constraint, whereas the alkalinity units (mmol/kg_as_CaCO3, mg/l_as_CaCO3, eq_acid/kg) imply an alkalinity constraint. For more information, please see the <unit> and alkalinity commands in the SpecE8 chapter of the GWB Command Reference. Hope this helps, Brian Farrell Aqueous Solutions

You're welcome. Like I said, React calculates density (and thus volume) from TDS using either the Phillips or Batzle-Wang methods, both of which are cited in the appendix to the GWB Essentials Guide. You can find various configured and calculated system properties in the output, such as solvent and solution mass, volume, and density, under Chemical parameters and Physical parameters.

The fluid volume comes from an estimate of fluid density based on a NaCl fluid of the same TDS as the fluid in the example. Note, the exact numbers quoted in the forum response for fluid volume refer to a variation of the calculation in which density was calculated according to the Phillips et al method, which was previously the default in the GWB. The new default method starting with GWB14 is the Batzle-Wang equation. The results shouldn’t be too different, though. You can compare them by changing the method on the Config > Options… dialog. For more information, please see Appendix A.10 Fluid density and viscosity in the GWB Essentials Guide, as well the density command in the GWB Command Reference. Regards, Brian Farrell Aqueous Solutions

Hi Ben, GWB 2022 includes more flexibility in how water activity is calculated within the various Debye-Huckel methods (b-dot, phreeqc/wateq4f/minteq, davies). With the B-dot model, specifically, you can now use the method of Wolery from newer versions of EQ3/6, the method of Garrels and Christ used in PhreeqC, or simply set water activity to 1. The methods are notable in that they do not require parameterization of the "H2O" tables as a function of temperature (and pressure) as in the standard method of Helgeson (1969). Note, the tables still need to be included, although the values won't matter if an alternative method is chosen. The methods are set in the thermodynamic dataset following the value for H2O's "ion size" parameter. More information is available in section 3.4.2, Basis species, in the Thermo datasets chapter of the GWB Reference Manual. These options are only available in GWB 2022 and in datasets with the "mar21" format. As a final note, the "debye-huckel" label can be replaced with "b-dot" in GWB 2022 beginning with the "mar21" format. The old label is from a time when the B-dot Debye-Huckel was the only non-virial model included in the GWB. Regards, Brian Farrell Aqueous Solutions

GWB 2022 includes more flexibility in how water activity is calculated within the various Debye-Huckel methods (b-dot, phreeqc/wateq4f/minteq, davies). With the B-dot extended Debye-Huckel model, specifically, you can now use the method of Wolery from newer versions of EQ3/6, the method of Garrels and Christ used in PhreeqC, or simply set water activity to 1. The methods are set in the thermodynamic dataset following the value for H2O's "ion size" parameter. More information is available in section 3.4.2, Basis species, in the Thermo datasets chapter of the GWB Reference Manual. So, to make a closer comparison between the B-dot model used in thermo.tdat and the Davies equation in your modified thermo_phreeqc.tdat, you could set a version of thermo.tdat to use the Garrels and Christ method for water activity, since that is the method which is already used in thermo_phreeqc.tdat. These features are only available in GWB 2022 and in datasets with the "mar21" format. As a final note, the "debye-huckel" label can be replaced with "b-dot" in GWB 2022 beginning with the "mar21" format. The old label is from a time when the B-dot Debye-Huckel was the only non-virial model included in the GWB. Regards, Brian Farrell Aqueous Solutions

For anyone interested in importing SUPCRTBL's PhreeqC-format datasets to GWB-format, several updates in GWB 2022 make this easier. Thermodynamic datasets can now contain an arbitrary number of principal temperatures, so there is no longer any need to alter the LLNL_AQUEOUS_MODEL_PARAMETERS block to limit it to eight temperatures. Additionally, gases in the PHASES block are now recognized as gases (as opposed to minerals) if written with ",g" as well as "(g)" in the name. Finally, the GWB apps can now calculate water activity and "CO2" activity coefficients according to the methods used in PhreeqC's "LLNL" ("B-dot") activity model, in addition to the equations originally prescribed by Helgeson (1969). The PhreeqC methods are now the default for PhreeqC "LLNL" datasets converted to GWB-format using TEdit. For more information, please see section 3.4.2, Basis species, in the Thermo datasets chapter of the GWB Reference Manual, as well as 9.3, Importing PhreeqC datasets, in the Using TEdit chapter of the GWB Essentials Guide. Regards, Brian Farrell Aqueous Solutions

Hi Denis, The GWB 2022 release includes a new "reaction_rate" Custom Rate Law "helper function" that should be of use to you. By using the helper function, the custom rate law for one mineral can reference the current reaction rate for another. For more information, please see Table 5.2 in the GWB Reaction Modeling Guide. Regards, Brian Farrell Aqueous Solutions

As for plotting isopleths or contours of calculated variables, you should look into Phase2. Essentially, it runs a series of React calculations to produce a 2D grid, like you'd see in Act2, but without all of Act2's simplifications. Regards, Brian Farrell Aqueous Solutions

With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen (Act2 and Tact use only the discrete option). Solid solutions can be defined in the thermodynamic dataset or configured by the user at run time. For more information, please see section 2.5, Solid solutions, in the GWB Essentials Guide, as well as relevant sections in the Using Rxn, Using Act2, and Using SpecE8 chapters of that same guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. You can also set a constant non-unity activity value for a mineral in the "in the presence of" section of Act2 and Tact, in case that is of interest. Regards, Brian Farrell Aqueous Solutions

With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen. Solid solutions can be defined in the thermodynamic dataset or configured by the user at run time. For more information, please see section 2.5, Solid solutions, in the GWB Essentials Guide, as well as relevant sections in the Using Rxn, Using Act2, and Using SpecE8 chapters of that same guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. Regards, Brian Farrell Aqueous Solutions

With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen. Solid solutions can be defined in the thermodynamic dataset or configured by the user at run time. For more information, please see section 2.5, Solid solutions, in the GWB Essentials Guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. Regards, Brian Farrell Aqueous Solutions

With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen. Solid solutions can be defined in the thermodynamic dataset or configured by the user at run time. For more information, please see section 2.5, Solid solutions, in the GWB Essentials Guide, as well as relevant sections in the Using Rxn, Using Act2, and Using SpecE8 chapters of that same guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. Regards, Brian Farrell Aqueous Solutions

With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen. Solid solutions can be defined in the thermodynamic dataset or configured by the user at run time. For more information about the model, please see section 2.5, Solid solutions, in the GWB Essentials Guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. Regards, Brian Farrell Aqueous Solutions

With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen. Solid solutions can be defined in the database or configured by the user at run time. In your case, you could define an Olivine solid solution with end members Forsterite and Fayalite. For more information, please see section 2.5, Solid solutions, in the GWB Essentials Guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. Regards, Brian Farrell Aqueous Solutions

Hi Thomas, With the GWB 2022 release, binary solid solutions can now be modeled. Either a Guggenheim or ideal activity model can be used, and either a continuous or discrete implementation can be chosen (in Act2 and Tact, only the discrete option is available). For more information, please see section 2.5, Solid solutions, in the GWB Essentials Guide, as well as relevant sections in the Using Rxn, Using Act2, and Using SpecE8 chapters of that same guide. Please see as well section 3.4.7, Solid solutions, in the Thermo datasets chapter of the GWB Reference Manual. Regards, Brian Farrell Aqueous Solutions