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Re: PHREEQC version 2

> Having started to use the new version of PHREEQC (version 2) in an
modelling mode, I tried running old models (run on version 1.03 PHREEQCi)
check the feasible models were the same. Unfortunately I find that the
number of feasible models produced in version 2 is always less.

It looks like some of the reactions pass your 1e-7 tolerance in one
version, but not the other. If you lower that tolerance (default is around
1e-10, I think), then the two versions give the same number of minimal
models.  I think the differences you are seeing are related to handling
small numbers. The redox reactions that account for the differences are on
the order of 1e-7.  There may have been some changes in the way the
equations were scaled between the two versions that accounts for the
difference. If you are worried about the differences, which are on the
order of 1e-7, then you need to use a smaller tolerance (this is not the
uncertainty). If you do use a smaller tolerance,  it looks like the two
versions are consistent.


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

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