> During the course of my research I have taken samples of groundwater and subjected them to geochemical analysis of: Temperature (Taken in the field with a probe meter), pH (probe meter), SULPHATE (IC (ion chromatography)), CALCIUM (AAS (atomic absorption spectrophotometry)). Hopefully you are analyzing complete major ions as well. > My past reading has shown that saturated sulphate levels It makes more sense to talk about gypsum saturation. You can use PHREEQC to calculate a gypsum saturation index. If gypsum is present, it is common for gypsum saturation indices to approach 0.0, which indicates equilibrium. > are indicative of gypsum dissolution Saturation indices near zero would indicate gypsum dissolution, although pyrite oxidation and calcite dissolution can also produce gypsum saturation indices near zero. > (which is becoming an increasing problem in certain parts of England) Gypsum presumably has been reacting for many millions of years. Perhaps you are saying that you are trying to use more of the water resource, some of which has large sulfate concentrations. > and was wondering if PHREEQ was the correct program for ascertaining this. If not is their anything you could recommend? PHREEQC can be used to calculate saturation indices. It can also be used as an inverse model to try to determine sets of mineral and gas reactants that account for water composition. Both types of calculations are probably appropriate for your study. 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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