Karen

I am wondering if there are any people on this forum who are more of a "hydrogeologist" than a geochemist who could recommend appropriate parameters for the dual porosity "module" of GWB for a unconsolidated sand aquifer that has an average porosity of 25%.

Nevermind. I sorted this question out.

Brian, I have a questions about an older model/script in x1t that used to run fine on my previous version (version 9) but now seems to get hung up by not converging on the element I chose for charge balance on my new version 11. I know that a general approach for non-conversion is to increase the number of iterations or decrease the tolerance. I am attaching a screenshot. I guess, I am not sure what the best way to fix this general issue in GWB. Suggestions? Karen Johannesson

Thanks again Brian!

Hi Brian, Great! I will pop by the GWB booth and say hi. Quick question, does the BASIC language that GWB employs for such custom rate laws use log for log base 10? When I used to use BASIC decades ago, LOG was for the natural log. I have rate law expression that is given as: log Rate = 0.03*pH2 - 0.073*pH - 10 that I need to "code" for one of the minerals in my hypothetical basalt. Based on what you wrote above, I will need to convert "log R = ..." to "R = ..." using activity("H+") for the pH terms. In my olden days of BASIC programming to code for log base 10, I would have to use "2.303*LOG(argument). Karen

Thanks Brian, This is very, very helpful! Are you planning to attend GSA in Baltimore in a few weeks? If so, hope to see you there. Best wishes, Karen

Thanks Brian! This helps a lot.

Brian, I am interested in writing some custom rate laws into a script for dissolution of some minerals. I have an idea as to how to do this but I think I am possibly missing something critical. Below is a rate law for anorthite dissolution that is one of the simpler expressions I am interested in incorporating into a React model. It has the form: Rate = k+[((aH+3n/aAl3+n)Keq)/(1+Keq(aH+3n/aAl3+n))] where n = 1/3, Keq is a known constant, and k+ is the forward rate constant. "a" represents activities and the parameters with n in them are exponents on the various hydrogen ion and aluminum ion activities. I have attached a file with a better representation of the expression. Also, I have not included the surface area of the (1-Q/K) terms because those are obvious to me as to their implementation. Any suggestions you have would be greatly appreciated. Best wishes, Karen J. Anorthite Rate Law.pdf

Hi Brian, Thanks for your reply. I followed your advice and it worked. So, in case anyone else reads this, the modified scatter data for the case of Mg++ that works is: # Act2 scatter data for activity diagram "SiO2(aq)" "Mg++" "H+" ------------------------------- -4.5052 -1.9982 -8.03 blue blot -3.4015 -2.638 -6.9 green triangle -3.3841 -2.5328 -7.15 red blot -3.3813 -2.74 -7.55 red triangle -3.4283 -2.6321 -6.76 red square -3.3579 -2.8465 -7.7 green square Best wishes, Karen

I am wondering why I can plot scatter data onto an activity diagram (ac2 plot) of log [K+]/[H+] vs. log [siO2(aq)], where [ ] indicates activity, but when I try to plot a similar diagram for log [Ca++]/[H+]^2 vs. log [siO2(aq)], I get the following error "scat: Can't plot scatter data; doesn't contain: log ratio Ca++/H+^2". The scatter data "scripts" that I have been using are the follows: # Act2 scatter data for activity diagram "SiO2(aq)" "K+/H+" --------------------- -4.5052 5.8563 blue blot -3.4015 4.0147 green triangle -3.3841 4.3142 red blot -3.3813 4.6157 red triangle -3.4283 4.0639 red square -3.3579 4.5173 green square and: # Act2 scatter data for activity diagram "SiO2(aq)" "Ca++/(H+)^2" ------------------------------- -4.5052 12.924 blue blot -3.4015 10.2125 green triangle -3.3841 10.6879 red blot -3.3813 11.3482 red triangle -3.4283 9.8096 red square -3.3579 11.6956 green square Again, the one for potassium works fine, but the one for calcium is right out. Thanks, Karen