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Re: weird phreeqc question




> Something weird is going on with my phreeqc simulations.  Biodegradation
will
work if coupled with dispersion, sorption, and/or gas phase.  It will NOT
work if I take those processes out.  The error I'm getting is that there
are
negative moles in solution after transport step 9.  How can there be
negative
moles in solution if I have the line "If Benzene <= 0 then goto 200?"  I've

changed the 0 to 1e-30, 1e-10, etc.  and it seems that phreeqc isn't even
reading that line.  Any suggestions?

Did the messages say Warning or Error. If it said "Warning", then the
program probably ran ok. If it was "Error", then the program failed. If the
program failed, please send your database and I'll look at the problem.

PHREEQC uses a Runge-Kutta method for integrating rate equations. It
estimates rates at various time points and then combines them to estimate a
rate for the entire time interval. Even if rates result in positive
concentrations at each time point, it is possible to calculate a rate that
causes a negative concentration when all of the estimates are combined.
PHREEQC should go back and use a smaller time interval and re-integrate the
rates.

If the warning messages are a nuisance, you can specify "-warnings false"
in the TRANSPORT data block.

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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