Hydrostatic pressure (gravitation equilibrium)

Hello, I'm practicing TOUGH2-ECO2N module with example problem number 4.

I want to simulate CO2 injection and its behavior.

My model which uses just one formation (first figure) is more simpler than ex #4.

In manual, hydrostatic pressure condition is used for initial condition and boundary condition. It means pressure increases as much as pgh as depth of element increases. But my result is quite strange.

May I ask you to let me know why and how to make hydrostatic pressure boundary and initial conditions?

Thank you