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> I am starting a project that will deal with chemical equilibrium and I
wanted to determine if there is consensus within USGS and USEPA as to which
of these models is most appropriate for problems of this nature.  I was
that the client wants to do the work with MINTEQ but I am not sure of his
rationale.  Are there any pitfalls with using MINTEQ over PHREEQC?

I think the choice is the matter of preference and capability. Minteq has
additional sorption models relative to PHREEQC, triple layer, constant
capacitance, langmuir, and freundlich. minteq has a "sweep" option which
simplifies calculations in some case, for example, if you want to run the
same calculation at multiple pH values. PHREEQC can do the problem, but
requires more input (PHREEQC requires consideration of the reactant that
fixes the pH, which is probably a good thing).

PHREEQC has capabilities for kinetics, 1D-transport, solid-solution, cation
exchange, and gas-phase calculations, which I do not think are present in
Minteq. PHREEQC has only one sorption model, the diffuse double layer model
of Dzombak and Morel, but Freundlich and Langmuir isotherms can be modeled
by using some careful (obscure) definitions. PHREEQC has 4 databases that
are distributed with the code, phreeqc.dat, wateq4f.dat, minteq.dat, and
llnl.dat. phreeqc.dat is a subset of wateq4f.dat, which is essentially
equivalent to the database in wateq4f. minteq.dat is nearly equivalent to
an older minteq database, but I think there has been a release of minteq
with revised thermodynamic data relative to the minteq.dat database that
comes with PHREEQC. llnl.dat is derived from the EQ3/6 and is nearly
identical with the database for EQ3/6 and Geochemists Workbench.

> I have successfully installed a windows version of MINTEQ that was
developed by the
Swedish.  It seems to operate fine.  However the US EPA version of MINTEQ
DOS-based and not compatible with Windows XP.

PhreeqcI is a Windows interface that works with all versions of Windows
from Win95 on. It has screen-driven input for all features of PHREEQC
except some of the isotope extensions.

> Given what you know please provide opinions about the use of one or both
these programs.

Again it is a matter of choice. If the client wants minteq then you may
need to use minteq. I think overall, phreeqc has more capabilities and a
better interface, although I am not familiar with the Swedish version. You
should be able to make most of the calculations of Minteq with PHREEQC, I
don't think the reverse is true.

Did EPA answer your email?


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

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