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Jia Wang

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Jia Wang last won the day on August 19 2019

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  1. Hello Rob, Thank you for the files. The issue here seems having multiple sample entries with same Sample ID. GSS expects each sample to have a unique Sample ID when entered into the spreadsheet. Perhaps you can add a unique identifier to your samples from different dates in the sample ID? Best regards, Jia Wang
  2. Hi Rob, Can you attach a screenshot of your Ternary plot and attach the .xtp file so someone can take a closer look? Thanks, Jia Wang
  3. Hello Rob, You would select samples to plot in the sample pane of your plot of choice. For example, if you're plotting a Piper diagram, you would double click on the center of diagram once it opens from GSS and select the Samples pane. You can select the samples you want to plot by holding down the 'Crtl' button while clicking. Please refer to section 8 Gtplot in the GWB Essentials Guide for more information. Best regards, Jia Wang
  4. Hello Rob, To select samples to display on your Ternary diagram, double click on the diagram to bring up Parameters for Ternary Diagram dialog. Click on the Samples pane and select samples from the available list. You can press 'Crtl' button while clicking to select multiple samples or click on the 'Select All' button if you want to display all samples. If needed, you can add samples to the "Add" or "Add all" button from the Ignore list to the Available list. Please see section 8 Gtplot in the GWB Essentials User Guide for more information. Best regards, Jia Wang
  5. Hello Kevin, Act2 makes calculations for analytical solutions to draw equilibrium lines to show predominant species of the highest activity. Therefore, you should be using the activity of the predominant Fe species in your system for Act2 calculation. Perhaps you might also be interested in Phase2 if you are aiming to investigate a more complex set of reactions? Phase2 draws diagrams that may look similar to Act2 in many cases, but the calculation is a complete solution to the equations describing the distribution of mass, just like in SpecE8 and React. You constrain a fluid in terms of concentration, rather than activity and set up reaction pathways, like in React, along the x and y axis. Please visit the Phase2 webpage for information. Best regards, Jia Wang
  6. Hello Anita, Thank you for the additional information. In Ogata 1970, it was stated that the concentration at x = 0 is maintained at concentration C0 through time to arrive at the analytical solution used in your textbook. Please see example 1 and 2 in the paper for details. Furthermore, the problem prompt from your textbook does not state when the leachate stopped leaking into your system. To accurately treat a solute slug problem, like you described above, you would need that information. Therefore, I think you should approach this problem as if the leachate is leaking continuously for the 1-year duration that you are modeling. A couple of other suggestions that might helpful here. You might want to consider extending the length of your domain by a small distance, maybe by 5 or 10 meters. Dispersion is not evaluated at the boundary condition and therefore introduce a bit of error to the node at the boundary. I would suggest you extend your domain length and look at the concentration at the nearest node to 15 meters. It might also be helpful to increase the number of nodes in your domain. With numerical modeling, there's a certain amount of numerical dispersion associated with grid sizes. Increasing the number of nodes would generally help reduce that numerical dispersion. In your case, I doubled the number of nodes to 300 and it helped. However, at the end of the day, model results will differ slightly from your analytical solution due to the estimations made in the numerical method and also consideration of additional variables that the analytical solution might not. For example, the GWB also considers variables like density changes with varying solute concentration which is not considered in the analytical solution. Hope this helps, Jia Wang
  7. Hello Anita, If you set up your system to have the contaminant flowing into the domain for an interval period of 1 minute, the concentration of Cl- you will see in the system is going to be much lowered than your expected results. To check, you can set the endpoint of your simulation to 10 minutes (before the simulation fails) and see that the maximum concentration of Cl- by plotting the results. You can plot X-position (on X Axis) vs. Cl- in fluid (mg/l) (on Y Axis) and cycle through the time level in the XY configuration dialog. You will see that the concentration of Cl- in your system is only ever as high as 2.18 mg/l. If you are expecting to see a pulse of contaminant in your domain with the Cl- concentration of 725 mg/l, you will need to have a longer interval where the contaminant is flowing into the system. I tried increasing the contaminant interval to 40 days and was able to arrive at 30 mg/l of Cl- at 15 meters from the leaking point. The error you are seeing are associated with stability issues with in your model. You can try to setting your dx_init, initial time step, to a small value (like 1e-5) to help with stability. To change dx_init, go to 'Config' -> 'Stepping' and you will see an option to set a dx_init value. When I tried using 1e-5 for the initial time step, the model ran to completion but again, I am seeing much lower concentration at 15 m than the answer you expected. Can you perhaps clarify what you mean by instantaneous leaking of the contaminant? And is the 30 mg/l of Cl- an analytical solution? Best regards, Jia Wang
  8. Hello Twq, I took a quick look at your script and noticed that all your concentrations besides AsO4--- are extremely low. If you are trying to ask the model to charge balance with such low concentration values concentrations, it might lead to stability issues and I think that is the case here. If you want to preserve charge balance, you might want to set a higher background electrolyte concentration, such as 1 or 0.1 molal for Na+. Alternatively, you can also turn off charge balance. To do so, right click on the unit of a basis species and select 'Do not balance'. You might also want to double check your chemical analysis to make sure your initial system concentrations are correct. I see that you swapped in AsO4--- for As(OH)4- and in doing so, the program calculates the species of other As oxidation states base on redox equilibrium. However, you can disable this by deoupling AsO4--- and adding it as a basis species. By decoupling the redox couple, you can constrained AsO4--- independently in your calculations. You might want to try this if you are interested in the speciation of AsO4--- only. Please refer to section 2.4 Redox Equilibrium for more information on decoupling. In the future, you can also check the equilibrium state of your initial fluid before any reaction path takes place by doing a 'Go initial' run ("Run" --> "Go initial"). This is a useful method to check your basis pane setup before adding in complexities of reactants. If the equilibrated fluid from the initial pane looks correct to you, then issues that occur will likely be due to the reactions from the reaction pathway. Hope this helps, Jia Wang
  9. Hello Dirk, I am glad you got your model up and running. It sounds like your convergence issues might be linked to your model running out of minerals. When you run out of mineral(s) or some other reactant in your system, the model will take smaller time steps to try to calculate the numerical solution, which might explain why you received the error “Step is constrained by rate of increase in length of reaction step at node 0”. In this case, you were trying to sorb solutes onto Fe(OH)3 when it is running out, which is probably why your model couldn’t converge. However, I can’t be sure unless I take a look at your input file but that would be my guess. If you would like someone to help take a closer look, please attach your input and thermo file. Hope this helps, Jia Wang
  10. Hello Rosalyn, Unfortunately, mV is not one of the default available units for Eh in Act2. You can, however, easily make the changes you mentioned above by editing the image in Powerpoint. To do so, you can copy(‘Edit’ -> Copy as ->Enhanced Metafile) and paste the image onto a Powerpoint slide. On your slide, you can right click on the image and ungroup the file and edit the values on the y-axis and change the label to mV. Similarly, you can alter the legend as well to erase any of the sample names and markers you do not want to display. Hope this helps, Jia Wang
  11. Hello Yoshio, Thank you for your question. To calculate Kd' I would use the original sorption isotherm, S = Kd*C, where the sorbed concentration (mole/g dry sediment) is equal to the product of the Kd(cm3/g) and concentration of the free ion (mole/cm3). I would first convert the concentration of dissolved Pb2+ to mole/cm3 which is approximately 10^-8 mole/cm3. Then using the Kd and concentration of dissolved Pb2+, calculate the concentration of Pb sorbed: S = 0.16 [cm3/g] * 10^-8 [mole/cm3] = 1.6 * 10 ^-9 mole of Pb2+ sorbed per gram of sediment. The Kd' term accounts for the activity instead of the concentration. To do so you, you will need to multiply the activity coefficient by the concentration of free ions in solution. Using the activity coefficient (0.66), fraction of free ions in the fluid (0.8), and the concentration of dissolved Pb2+ (~10^-5 molal), you can calculate Kd' like so: 1.6*10^-9 = Kd' * (0.66*0.8*10^-5) where the Kd' is calculated to be approximately 0.0003 mol/g. Hope this helps, Jia Wang
  12. Hello Ulagai, You can enter basis species into the GSS spreadsheet. For your specify question though, HCO3- and CO3-- are both carbonate species. When you enter HCO3- into the database, you are effectively including the sum of the thermodynamic component (e.g. CO2(aq), CO3--, NaHCO3-, etc). If you wish to enter the concentration of HCO3- without the additional species, you will need to enter the species as a free constraint. To do so, you can right click on the unit for HCO3- and select "free". I would not recommend moving CO3-- from aqueous to basis species since components chosen as a basis species must be linearly independent from one another. In this case, HCO3- is the basis species and CO3-- is an aqueous species can be written in terms of HCO3- and H+. You can alternatively add CO3-- as a user defined analyte if you simply want to keep track of how much CO3-- is in your system. But keep in mind, you cannot use user defined analytes in GWB apps for simulations. For more information on how to create your own user analyte, please refer to section 3.3 in the GWB Essentials User guide. Hope this helps, Jia Wang
  13. Hello Ulagai, When you create a new species in the thermo database, in this case H2SiO4, you will need to provide at least one Log K value at one of the 8 principal temperatures. Most commonly, the Log K value is derived at 25 degree Celsius. If you do not enter any Log K values, the GWB programs will not read in the new species you have added. Once you have successfully added in the new species, you should be able to add the species in Rxn and balance reactions. Where the temperature differ from a principal temperature, the application fits non-'500' values to a polynomial. You can expand the results in the Results pane and obtain the temperature polynomial equation the program uses to estimate LogKs with the principal temperature range. While the GWB can extrapolate beyond this range in calculations using the 'extrapolate' option, I would advise to do so cautiously. Please note that starting with GWB14, the thermo database can alternatively carry temperature expansions for log Ks for a range of valid temperature. The method above is for T-table logK approximation for older formatted GWB datasets. Please refer to section 9 in the GWB Essentials Users guide for more information regarding editing thermo datasets in TEdit. Hope this helps, Jia Wang
  14. Hello Mallen, Our records show that your student edition application was approved earlier this month and a new activation code was sent to you. Can you check if you are using the new activation code? If you are still have trouble activating your license, please send an e-mail including your activation code and screenshot of your activation utility to support@gwb.com. Best, Jia Wang
  15. Hello Anita, I took a quick look at your input file and here are a couple of suggestions to help you get started. It seems like you are trying to model a continuously leaking point source contamination for 1 year. However, I notice that in your Intervals pane, you are only setting a one day reaction interval for the 'contaminated' fluid to enter your system at the inlet and the remaining time flushing the system with dilute fluid. If the goal is to simulate a continuously leaking source of contamination at the inlet, then you should remove the second reaction interval from your simulation and allow for the contaminated fluid flow into the system for a full year. To quickly remove any reaction interval period in your Intervals pane, you can simply click to select it and then click the delete button. I deleted the reaction interval that set the inlet fluid as the dilute fluid (named 'fluid 2') and that allow the model to run to completion. For more information on setting boundary conditions and reaction intervals, please refer to section 2.10 and 2.9 in the Reactive Transport User's Guide. You might also be interested in looking at X1t examples listed in section 3.5. The input file corresponding to each example in section 3.5 is available in the GWB installation subdirectory 'Script'. Hope this helps, Jia Wang
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