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Geochemist's Workbench Support Forum


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About CShort

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  1. Thanks Brian - very helpful, as always!
  2. Hi GWB Folks, I'm working on an X1T model that should move a contaminated, pH 1 fluid into a clean aquifer (pH 6.8) for 22 years. Then, clean water (pH 6.8) flushes the system back out. Ferrihydrite is distributed through the system in the initial conditions and should allow some sorption of contaminants. I've proved to myself that the model runs without ferrihydrite swapped for Fe+++ in the initial pane. When ferrihydrite is swapped into the model, the model only runs through a few iterations before the fig newton fails to converge - it seems like the solution is becoming unstable in the initial nodes, but no amount of tweaking the stepping parameters seems to make a serious difference. Increasing the pH of the contaminated fluid allows the model to run further; increasing pH to 4 allows the model to run to completion. Any advice or observations are welcome, I've been banging my head against this all night. I'll attach the current version of the model. Unswapping ferrihydrite or removing Fe from the basis will produce a model that runs fine. Removing the surface database doesn't change anything, suggesting to me it's something to do with ferrihydrite stability (?)... or maybe user error. Thanks, Clark SorbModel02.x1t FeOH_minteq_plusU.sdat
  3. Hi Brian, Bryn and I have been talking about this and I'd like to follow up. For a simple model, I'm using REACT to calculate a Kd for uranium at some pH with ferrihydrite present as a sorbent phase. The output is set up to show the Kd. To use that Kd in a subsequent X1T model, I can create a Kd surface dataset. Easy so far. Is it appropriate to use the Kd that REACT spits out in my surface dataset, or does it need to be converted to an activity-Kd? In other words, does REACT provide an activity-Kd or a plain-old-Kd?
  4. Great, thank you Melika!
  5. I've created a GSS using the thermo.com.V8.Rc+.tdat thermo database but want to convert it to the thermo_minteq.tdat. No problem, open -> thermo -> and select thermo_minteq.tdata. Then GWB asks me, through a series of pop up windows, to sort out discrepancies in basis entries. So I start the conversion and, for example for Arsenic, it says AsH3(aq) is unavailable in the new database and suggests I substitute AsO4----. Sure, that's fine, but my AsH3(aq) data are in units of mg/L (as As) in GSS. I want to preserve the same concentration so I can have my new AsO4---- data in units of mg/L (as As). What's strange is that it has a checkbox asking if I want to convert value by elemental equivalent. if I check the box I get what I want - the value stays the same. If i do not check the box, the value is converted to accomodate the difference in unit mass. It seems to me that this should be the opposite - unchecking the box should not do a unit conversion, and checking it SHOULD do a unit conversion. Is this a bug, or do I just have this backwards?
  6. Great, thank you!
  7. Hi GWB, I'm doing some simple charge balance type analyses in React. I've encountered an error where I can't bring in my NH3 data using the MINTEQ database. I set the basis species as NH4+, then try to set the units "as NH3 (aq)". That's when I get an error saying "Error: Don't know keyword: (aq)". It seems like it's having trouble interpreting the (aq) in the unit swap (?). Any suggestions on how to deal with this? Thanks, Clark
  8. I'm attempting to evaluate sorption of several parameters over a range of pH. I attempted to use the "slide" feature in react to do this: the initial solution has a pH of 4, and I slide it to 10. Precipitation is disabled. In this case, at pH 7.3, U is sorbed 99.48%. Great. if I run this same model, instead over the range of 7-10, U is sorbed 12.8% at pH 7.3. I would expect to get similar sorbed fractions at each pH, regardless of the start and end point. I'm expecting that these models should have the same results at every pH. I'm afraid I'm missing something fundamental about how the "slide" function works - what am I missing? Thanks! Clark 20170616_U_Sorption_2005_pH4.rea 20170616_U_Sorption_2005_pH7.rea FeOH_minteq_plusU.sdat
  9. CShort

    Activity-Kd sorption models

    Hi Bryan, Yes that Pb KD is both correct and absurdly high. The measurements are just for the fluid - if the sorbate option is checked, then that's a mistake - it's something I played around but, as you mentioned, isn't appropriate for my model. I too noticed that I can run it using the sorbate option and thought that was curious. I'm not sure I have data handy to add sorbing anions, but that's a good idea. I'm not at all concerned with what the Cl concentration is doing - Na/Cl are both in there just because GWB likes charge balanced solutions. I'm thinking a little bit about creating alternate thermo & surface databases where Pb is not charged to avoid this issue. I'll mess around with sorbing anions as well - maybe I can create a junk anion species with the same KD, concentration, and opposite charge to avoid the issue. I understand these assumptions would misrepresent reality, but the purpose here is to emulate a much older model 1D transport model that doesn't have all the bells and whistles of GWB... actually it has no bells or whistles at all really. It was called SOLUTE ONE-D. It certainly didn't care about charge balancing anything - it didn't even have parameter specific variables. Thank you for your thoguhts Bryan. I'll be messing around with it more today.
  10. I'm working with a relatively simple X1T model in which water 1 is injected into a sandstone containing water 2 for 22 years then chased through the system with water 1. During transport, the only attenuation process operating is an activity-KD retardation model. I'm trying to run this model using different porosity's, assuming that the rest of the volume is just non-reactive quartz. This should be a simple model. This model runs for certain values of concentrations and Kd's, but not others, although the model is fundamentally unchanged. The biggest problem is that the model is unable to initialize because the "Newton-Raphson did not converge...". I've been able to duplicate this issue in React. One issue I've noticed causes this problem is declaring a porosity. The modelled sandstone has a porosity of 0.25. When I run my react code using a blank porosity, blank bulk volume, and 0 inert volume (the default values), it's able to initialize. If I declare a porosity of 0.25, it is unable to initialize. Do you have any thoughts on what might be going on here or what I should look out for when trying to declare porosity values? I've referenced both the reaction guide and the reference guide and have not had much luck sorting this out. Thank you! Clark React_Issue.rea Kd_Ambrosia_Por=25_KD=0.029.sdat
  11. Nailed it - just needed to change the thermo dataset path in the header. Thanks!
  12. I'm working on adding ferrihydrite sorption parameters to the existing FeOH sorption database, but for some reason my reaction, which I believe is charge balanced, throws an error saying that it is not. I'm attempting to add parameter >(s)FeOHRa++, charge = 2, mole weight = 298.8543, log k = -6.66, dlogk/dt = 0, with >(s)FeOH = 1 and Ra++ = 1. Do you have any suggestions here on where I've gone astray? If I run a React sorption model with the equation as written, does GWB still consider it? Edit: I've added Ra++ to the existing Minteq database, and it's charge is set at +2, molar mass 226, element Ra. Thanks, Clark