Gregg W. Jones

That's Jia - I really appreciate it!

Hi Jia - it appears the default unit for Eh on an Eh/pH diagram is volts. Is there a way to change the units to milli volts?

Hi Jia - I'm using react to model mineral saturation in groundwater at a contaminated site. I've entered in the chemical analytes determined from samples collected from a monitor well into the basis. I have attached the react file so you can see the inputs. When I run the simulation, it doesn't run and says residuals too large and shows the largest residuals as Cl-. I know that the simulation is balancing charge on Cl-, so I go into the basis, click on Cl- and select do not balance. When I do that, the simulation runs just fine. However, when I check the output, there is a charge balance error of -24.3%. Here are my questions: 1) Why doesn't the simulation run when I balance on Cl-? 2) When the simulation doesn't run and says, residuals too large, largest residuals as Cl-, what does that mean? 3) Why the large charge balance error? Is it because the simulation is ignoring Cl- because I told it not to balance on Cl-? 4) is the fact that I get a large charge balance error invalidate the results of the simulation in any way? W-3B React Run.rea

Hi Jia - you helped me with this issue a while back but it's still not clear to me. I asked about how to specify units for radioactivity and this was your response: "GSS contains a default list of common units for describing concentrations in water chemistry analyses. Radioactivity units are not among them. If you want to specify a unit for radioactivity you can set a user-defined analyte. To do so, go to "+ analyte" -> 'user analyte...' -> Edit. Enter a name for your analyte and then set the category to 'Chemical parameters' and the dimension to 'Radioactive emission'. The default unit will then be set to pCi/l." You went on to say: "Please note that user analytes are not considered in chemical calculations. For more information, please refer to section 3.3.4 User Analytes of the GWB Essentials Guide. I responded back - One question about your response - you say that user analytes are not considered in chemical calculations. Regarding radium, it is in the thermo data base I'm using - I'm just defining its unit as pCi/L. So if I do that, are you saying Radium won't be considered in chemical calculations? I read section 3.3.4 in the Essentials Guide as you suggested but I don't see anything about the user defined analyte. I didn't see that I got a response from you on this. I have a site where I have exceedances of radium and I need to include it in the model. Surely there's a way for radionuclides entered in pCi/l to be considered in chemical calculations???

Thanks Gia - very helpful!

Hi Jia - I'm interested in determining mineral saturation in shallow groundwater at a well in Colorado. I entered water-quality data from a well using Spec8 and React, making sure to enter everything exactly the same for both input screens, then compared the saturation indices of the supersaturated minerals for the Spec8 vs React output. While the supersaturated minerals are mostly the same, their saturation indices are different at the higher end and then converge as the saturation index gets lower. Why might that be and is it something to be concerned about? See below: Spec8 React CoFe2O4 29.2 23.9 Hematite 23.8 18.5 Jarosite 20.2 12.2 Ferrite-Mg 13.0 7.7 Ferrite- Ca 11.4 6.1 Gothite 11.4 8.7 Alunite 7.4 7.4 Fe(OH)3 6.2 3.5 Dawsonite 3.4 3.5 Diaspore 3.4 3.4 Boehmite 2.9 2.9 Gibbsite 2.8 2.8 Corundum 2.6 2.6 Barite 1.05 1.0 Dolomite 0.331 0.39 Gypsum 0.16 0.16 Well 3B React_output.txt Well 3B SpecE8_output.txt Spec 8 model Well 3B.sp8 W-3B React.rea

Thanks Jia - that's really helpful! Sorry Ive been spelling your name wrong!

Thanks Gia - still don't understand where I get the activity of the species to be diagramed. When making an Eh/pH diagram, the Act 2 program first asks for the activity of the species to be diagramed. When I run the spec 8 model, the model output provides 4 types of information for each aqueous species: molality, concentration in mg/kg, activity coef, and log activity. I have a USGS paper titled Calculation and Use of Ion Activity by John Hem and it says the following: " The activity of the dissolved ions in solution is somewhat less than the concentration of the ions measured and reported in water analyses. To apply the mass-law computation accurately to such solutions, a factor should first be computed by which the reported concentration may be multiplied to yield active concentration or activity. This factor is the activity coefficient". So, I should be able to multiply the concentration of Fe by the activity coefficient to get activity. In my case, the concentration of Fe3+ is 0.2151 mg/kg and its activity coef is .0778. This works out to an activity of 0.0167. I just noticed that in the diagram species box in the Act 2 program, you can also use the log activity of the diagram species which is provided in the model output as I pointed out above.. Am I looking at this correctly?

Gia - I meant to say I can multiply concentration times activity coef, not concentration times concentration.

Hi Gia - after further research, it appears I can multiply concentration of an analyte by its concentration to get its activity. So going back to the question I submitted yesterday: I start by entering analyte concentrations for a water sample in Spec8 then run it and view the results. Under aqueous species, Fe is shown as free iron complexed species and each has the following data:. Molality Mg/kg solution act. coef. log act Fe2+ 2.74e-6 0.1436 0.2296 -2.9621 FeCo3 2.38e-6 0.2589 0.6639 -5.8017 FeCl 1.20e-8 0.001032 0.6639 -8.097 Fe3+ 2.97e-9 .0001562 0.0781 -9.6338 There are more Fe species but I assume their low concentrations make them irrelevant. So the program gives me the activity coeff for each iron complex and Fe2+ and 3+, so can I just multiply the concentration of Fe2+ and Fe3+ by their activity coefficients to get activity then add them together? What about the 2 complexes, FeCO3 and FeCl? Since iron is complexed with them, how do I get the activity of just the iron?

Hi Gia - I'm trying to make an Eh/pH diagram of the iron system so I can see where my water samples plots. The diagram asks for the activity of iron and I'm struggling with how to determine it. I start by entering analyte concentrations for a water sample in Spec8 then run it and view the results. Under aqueous species, Fe is shown as free iron complexed species and each has the following data:. Molality Mg/kg solution act. coef. log act Fe2+ 2.74e-6 0.1436 0.2296 -2.9621 FeCo3 2.38e-6 0.2589 0.6639 -5.8017 FeCl 1.20e-8 0.001032 0.6639 -8.097 Fe3+ 2.97e-9 .0001562 0.0781 -9.6338 There are more Fe species but I assume their low concentrations make them irrelevant? So I assume from this data I can get iron activity but I'm not sure how. Is there a way GWB can just calculate it rather than having to take this data and do a lot of hand calculating? If not, how would I get Fe activity from this data?

I’m working on a contaminated site and am seeing natural attenuation of Cd, Co, and Ra 226+228 contaminants in groundwater. I need to provide evidence of the geochemical mechanisms for these 3 analytes that are causing attenuation. I’m using Spec8 to create an equilibrium model so I can see all the aqueous species and saturation states of minerals. I’m assuming it is possible that supersaturated minerals that contain Cd, Co, and Ra 226+228 precipitate and remove those minerals from solution (at least that’s what I’m trying to demonstrate) and that’s evidence of attenuation mechanisms. Do you think this approach is valid? I’m using the Thermo.comV8.R6t.tdat database. I have the following questions: a) I have data for Al total but not Al3+. There is no Al total in the analyte list but Al3+ is in the analyte list. The groundwater redox conditions are oxidizing so I’m assuming the dominant cation will be Al3+ so is it valid to use the Al3+ concentration for the Al total concentration? b) I have data for Fe total and Fe2+ but not Fe3+. There is no Fe total or Fe3+ in the analyte list but there is Fe2+. I entered the Fe2+ concentration then decoupled the Fe2+/Fe3+ redox couple and that added Fe3+ to the analyte list. Is it valid to do that? Since its an oxidizing environment, Fe3+ is probably the dominant cation so do you think it’s valid for me to use the total Fe concentration for Fe3+? c) I have concentration data for B, Se, and Cr, but these are not in the analyte list. There are however B(OH)3, SeO3, and CrO4 in the analyte list. So for units for each of these I select “as” and for B(OH)3 I select mg/L as B. I do the same for Se and Cr. Is this correct? d) I have ORP data but there is no Eh, pe, or ORP in the analyte list so how does the model know what the redox condition is? I have concentration data for DO, which is 0.57 mg/l and that is in the analyte list. I assume that helps define the redox condition? Is there some other way to define it? e) When I run the model, the resulting pe (which is the same as ORP, I think) is 14.57 but my field ORP reading is 150.5. Why the difference?

Hi Jia - thanks so much for getting back to me on this!! One question about your response - you say that user analytes are not considered in chemical calculations. Regarding radium, it is in the thermo data base I'm using - I'm just defining its unit as pCi/L. So if I do that, are you saying Radium won't be considered in chemical calculations? I read section 3.3.4 in the Essentials Guide as you suggested but I don't see anything about the user defined analyte

Hi! I'm just getting started with GWB and I'm entering a data set into GSS. When I enter radium, which is in pCi/L, I can't find that unit in GSS. What am I missing? Also, I'm trying to understand the themo data sets. I found that the default data set didn't have cadmium, which I'm especially interested in. So I tried a different thermo data file and found one with radium but it didn't have data for some other analytes that the previous thermo data set did have. So am I supposed to keep trying different thermo data sets until I find one that has data for all the analytes I'm trying to enter?