Why does Neumann BC applied as source term in OGS?

Hi all,
I am following Geoenergy Modeling I – Geothermal Processes in Fractured Porous Media book where all the Neumann bc are allied in as source term.

(1) How can I apply boundary mass flux boundary (in kg/m2/s) as a Boundary instead of the source term(m3/s)?

(2) For example: Page #72, Left boundary as flow rate Q=3e-7 m3/s but in implementation it’s value is 1e-6 m/s.

I think, It should be 3e-7 m/s ( q = 3e-7 m3/s /1m2). If this is not a typo, would u please explain how this works?

Thank you,
Dinesh P