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Re: inverse model for unsat

Dear Dr. Parkhurst,
Thank you so much for your reply.
This really comes down to geochemistry which I am no expert on. Your input
is very invaluable. I have one more question which is not exactly relating
to PHREEQC. As I mentioned that the locations of the samplings will be in
the unsaturated zone and the aqueous chemistry should be from the
The soil solution, or the water in the pore space, should be extracted
from the soil samples in order to evaluate the chemistry and to test
whether the solution is in equilibrium with the minerals, e.g. jarosite,
albite, montmorillonite and so on. However, I am not certain if the
method should be using just pure water and centrifuging the water to get
all the aqueous ions or using other chemicals. i am thinking of just using
the water. I am reading many papers, e.g. Astrom M and coworkers. They
use HClO4-HNO3-HCl-HF at 200C and dilute the soil sample with diluted aqua
regia to determine the chemistry. Sometimes, researchers use a series of
weak acid to extract metals from the soil solution. However, the ions from
this method are those that were in aqueous phase plus those that were in
solid phase attached to the solid matrix.

I really appreciate your input.

Uma Seeboonruang
Department of Civil Engineering,
King Mongkut's Institute of Technology - Ladkrabang,
Bangkok, Thailand

On Mon, 30 Jun 2003, David L Parkhurst wrote:

> > Currently, I am working on modeling geochemistry for the acid sulfate
> soil
> in Thailand and I am intersted in using the PHREEQC inverse modeling to
> come up with amount of mass transfer between an upper (upgradient) and
> a lower (downgradient) locations. they both are in the same flowpath as
> teh water infiltrates downward. However, both locations are in the unsat
> zone. I am wondering if PHREEQC will be applicable in this case.
> You should be able to use inverse modeling if the downgradient water
> evolves from the upgradient water. It is also possible to consider the
> evolution of rain to each of the waters, if this is the basic situation you
> are considering.
> 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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