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> My selective output file lists steps as specified by "punch_cells" and
"punch_frequency" commands preceded by 15 lines (all numbered "step ?99").
I can trace last 7 lines (out 15 in question) to some parameters of my
seven layers.  The fist 8 lines are conundrum for me.  The PHREEQC manual
for SELECTED_OUTPUT refer to lines "?99" as other calculations.  Would you
please enlighten me what are these calculations whose results are presented
in lines marked -99?

Starting with the simulation in which SELECTED_OUTPUT is defined, every
calculation adds a line to the selected-output file. A calculation includes
initial solution calculations and reaction calculations. I think the -99
for step are probably initial solution calculations. If you move the
SELECTED_OUTPUT definition to the simulation where ADVECTION is defined,
you will not get the initial lines in the selected-output file.

The results for uranium sorbed within each layer after one and two pore
volumes are identical.  It seems to me that the logistics of ADVECTION key
word does not account for the reduced site concentration that exist after
the first pore volume moved through.  Am I interpreting it correctly, and
if so, is there any way to account for the reduction in site concentration
for the advancement of the second pore volume?

I can't tell what your problem is. The sites (SURFACE or EXCHANGE) are
immobile and remain in the cell for which they were defined. However,
sorbants will accumulate on the sites from pore volume to pore volume.
Remember that a time step only advects the solution one cell; a pore volume
would require 46 steps if you have 46 cells.


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

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