> My first problem is that when I enter my data into DB and try to speciate it, I get an error message on all those waters with a low pH (i.e pH < 4.2). I have not measured any alkalinity in waters with a pH below 4.3 and therefore have enterred my alkalinity value as <0.01. Could this be the problem ? Is there some way of enterring acidity to compensate for this ? Perhaps a negative alkalinity (to indicate that it is consumed in the reaction) ? Or should I just add a miniscule amount as HCO3, so that it has some value to work with ? NETPATH does not like negative alkalinity. To make it work, try changing the input to total inorganic carbon instead of alkalinity. > Secondly, the .dat file which I have does not offer some of the more important iron and aluminium minerals as a possible phase. The minerals which are not available, and that I need include ferrihydrite, jarosite, jurbanite, melanterite and schwertmannite. I have tried to enter these into the database but am not certain I have done it correctly ....... largely because I have no idea what "I1", "I2" and "I3" are, not to mention my uncertainty regarding the calculation of a redox state for these. Goethite works just as well as ferrihydrite for mole balance modeling. The stoichiometry of the mineral is all that is important. Additional water in the formual also makes no difference. I1, I2, and I3 are isotope values for C13 (permil), C14 (pmc), S34 (permil). > Do you have an updated .dat file ? The one I downloaded from the web is dated August 1997. Alternatively some advice on how to enter these minerals would be greatly appeciated. You probably have the latest version, NETPATH has not been modified in a long time. You can enter more phases in NETPATH with Add on the main screen followed by Phases, followed by a number as listed on the next screen to create a new phase. > Thirdly, I find that if I use an initial (rain water) and a final (mature mine water) water with no iron or aluminium (eg. pH ~7 waters), but include phases such as pyrite, goethite, gibbsite, etc, a mass balance transfer still occurs using these minerals. For example, all the pyrite converts to goethite but I can't figure out where the S goes. ALL into solution ? Similarly with the aluminium .... I can account for most of it: K-spar + kaolinite ~= albite. Is the rest in solution ? I do not want to leave the iron and aluminium phases out, as I know they do exist (XRD traces are evidence). You need to look at the mole transfers and the concentration in solution. The amount of S in the final solution should equal the amount of S in the initial solution plus and minus the transfers from and to the minerals. NETPATH does not automatically perform mole balance on elements, you must specify S as one of the constraints. You also need to specify Redox as a constraint to account for the redox reactions correctly. > Perhaps I should be using PHREEQC (which I used to speciate my waters and calculate SI, but know very little else about) ? I would greatly appreciate any help you can offer. If you are not using isotopic data, you could use the interactive program PhreeqcI. The latest version is a complete interface to PHREEQC that runs under Windows https://wwwbrr.cr.usgs.gov/projects/GWC_coupled/phreeqc). You need to define the beginning and ending solutions with SOLUTION data blocks (flask icon in the interface) and the details of inverse modeling in the INVERSE_MODELING (f-1 icon in interface). Mole balance on all elements included in the phases selected will automatically be enforced. Any conservative elements (not contained in any minerals) will need to be included through the Balances tab. PhreeqcI also enforces charge balance in its calculations by adjusting element concentrations within specified limits. The uncertainties also affect the inverse models that can be found. Good luck, David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225
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