About location for .mod files:
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=714730

proposed changes for packages providing gfortran libraries:
http://paste.debian.net/300066/


http://anonscm.debian.org/cgit/debian-science/packages/dh-fortran-mod.git/tree/

Location of gfortran mod files (from the debichem bof):
maybe /usr/include/gfortran-
mod-10 , /usr/include/gfortran-mod-14 ?

sample package:
https://packages.qa.debian.org/libx/libxc.html


http://anonscm.debian.org/cgit/debian-science/packages/dh-fortran-mod.git