# Why does Neumann BC applied as source term in OGS?

**URL:** <https://discourse.opengeosys.org/t/why-does-neumann-bc-applied-as-source-term-in-ogs/998>\
**Category:** ogs-users\
**Tags:** ogs5\
**Created:** [April 19, 2022, 6:01am UTC](https://discourse.opengeosys.org/t/why-does-neumann-bc-applied-as-source-term-in-ogs/998 "2022-04-19T06:01:46Z")\
**Posts on this page:** 1\
**Page:** 1

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**Author:** ![Dinesh\_P](https://discourse.opengeosys.org/user_avatar/discourse.opengeosys.org/dinesh_p/32/881_2.png) [@Dinesh\_P](https://discourse.opengeosys.org/u/Dinesh_P)\
**Post date:** [April 19, 2022, 6:01am UTC](https://discourse.opengeosys.org/t/why-does-neumann-bc-applied-as-source-term-in-ogs/998/1 "2022-04-19T06:01:46Z")

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Hi all,  
I am following [Geoenergy Modeling I – Geothermal Processes in Fractured Porous Media](https://www.opengeosys.org/books/geoenergy-modeling-i/) 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.

 ![image](https://discourse.opengeosys.org/uploads/default/original/1X/70395076decb221d702c368189bbee6f4d77db3e.png)

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,  
Regards,  
Dinesh P