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> 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 Parkhurst (dlpark@xxxxxxxx)
U.S. Geological Survey
Box 25046, MS 413
Denver Federal Center
Denver, CO 80225

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