Dirichlet boundary

Hi all

I am trying to make a boundary with pressure variations. I have two questions:

1- Should I just follow the equation 27 in TOUGH2 manual (ideal gas law)? It means that no need to consider the porosity and pore compressibility?  

2- In order to get the pressure variations between two consecutive times, I should put the the start and end of time interval, and mass rate value of this interval in GENER? The mass rate that was obtained with ideal gas law (my question 1).