> First, most of the data we are using gives alkalinity in the form of bicarbonate. The question that we have is should this data be entered under the heading of "Alkalinity", "C", or "C(IV)" to produce the best results. You should enter the data as "Alkalinity" and add a field to show that it is as HCO3, default is as CaCO3. I am assuming the units are mg/L. The input file looks like this: -units mg/L Alkalinity 73 as HCO3 > We were also wondering if there was a straight forward way to essentially simulate evaporation on our samples and see what mineral phases precipitate out and at what concentrations. We have tried to do this via the steps outlined in Example 4 (p.209) of the PHREEQC user's guide but were met with little success, and we're unsure if it was due to differences between the programs or whether we were not fully grasping the concept of how to do this type of reaction in PhreeqcI. I can't tell what problem you were having. Evaporation is accomplished by removing water. The initial solution normally has 1 kg water after the initial solution calculation. That is about 55.5 moles of water. If you want to evaporate 90 percent of the water, you must remove about 50 moles of water. Example 2 removes 52.73 moles or 95 percent of the water. For precipitation of solids, you should probably first simulate the evaporation and then look at the saturation indices for minerals that you think might precipitate. Minerals that have positive saturation indices could precipitate. One further complication is that you probably want to stay in equilibrium with atmospheric CO2 during the simulations. You need to add an EQUILIBRIUM_PHASES data block including CO2(g). Once you decide which minerals you want to let precipitate, add them to the EQUILIBRIUM_PHASES data block with 0 moles present initially. PHREEQC will precipitate them when they reach saturation by evaporation. David Any help or suggestions you may be able to offer us would be greatly appreciated.David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: https://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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