> I have been using Netpath to do some weathering calculations in a low TDS, low alkalinity, low pH coastal groundwater. I successfully added some minerals to netpath.dat. My aquifer is primarily a quartz sand and I wanted to use the 1997 Rimstidt quartz Ksp of 10^-3.72, rather than the constant in Netpath's DB.dat. I think that quartz is being dissolved as the water travels down the flowpath, but the program still thinks quartz is oversaturated in most of the waters. Quartz is pretty insoluble, probably about 10 mg/L of dissolved silica. Most waters exceed this concentration. I think it means that there is another source of silica, either alumino silicate minerals (probably feldspar) or a less stable form of silica (chalcedony or microcrystalline quartz, for example). > I changed the constant in that database, but the program is still using the old constant (10^-3.9). Do I need to recompile netpath? I don't think you have to recompile netpath. Db is making the saturation index calculations and changing db.dat should be sufficient (there may be more than one copy of db.dat in different directories, so make sure you change the one that db is actually using. Change a mineral name to quickly test if the db.dat is being used). At a more fundamental level, NETPATH doesn't really care about saturation indices, it only uses mole balance, so it will dissolve quartz if that's what is needed, even if quartz is supersaturated. > The Netpath version I am using is an old one, from 1994, and it's the Mac Netpath. It should be ok. Netpath has not changed much. You may want to consider using PHREEQC. It should be able to handle the same type of inverse problems and NETPATH, however, it does not have the isotope capabilities of NETPATH. David 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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