To get an interactive shell with 40 processors (20 nodes) do

qsub -I -V -q debug -lwalltime=1:00:00,size=20 -A GEO002

You can then cd to $PBS_O_WORKDIR to get to the place that you launched 
your job from.

From inside the interactive shell, run your job with

yod ./pflotran -use_analytical -use_mph -snes_ls basic
