> 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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