ok - you can't currently have "site wide" groups -(I believe someone might have done a hack if you search here) It will be available hopefully in a later version of Moodle. However I suspect your users named engineers/secretary etc are just names of people, not particular roles or permissions and I suggest a workaround would be to include their name in their username as you
upload them (you can re-upload via csv and override whatever you had before) So make the usernames for your engineers something like eng.johnsmith or for your secretary sec.janebrown and then you will be able easily to search for all engineers or secretaries etc to add to a group.