> 1. Does the program know what oxidation state to designate to metals such as Iron, Manganese and Arsenic given specified parameters such as pe, pH, and Temperature? If you define "Fe", the program will use the pe (or another specified redox couple) to distribute iron between Fe(2) and Fe(3). > Or should I assume that in a reductive environment to use the reduced forms and vice versa for oxidated environment? I am sampling using EPA low flow methods. If you know the state of the iron is ferrous, you should define the iron as "Fe(2)". In general, essentially all of the iron and manganese in solution are Fe(2) (except possibly at low pH) and Mn(2), so specifying the redox state is probably reasonable. > 2. If I have both Alkalinity and Dissolved Inorganic/Organic Carbon values, is there a way I can enter the DOC or DIC? You can specify pH plus either alkalinity or DIC, in which case, the one not defined will be calculated by the program. If you specify both alkalinity and DIC, the pH will be calculated. DOC is essentially not used by PHREEQC. There are definitions for Humate and Fulvate in wateq4f.dat. If you enter the DOC as one of these, then there will be some complexation of metals by the Humate or Fulvate. I think use of these is pretty tenuous. There are other models (GEOCHEM, WHAM, the NICC? model) that are more recent and address metal organic binding more completely. David David Parkhurst (dlpark@xxxxxxxx) U.S. Geological Survey Box 25046, MS 413 Denver Federal Center Denver, CO 80225 Project web page: http://wwwbrr.cr.usgs.gov/projects/GWC_coupled
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