Using ACLs to control access to system files

Preface: I am fairly new to linux in general, as I am a networking / windows admin, so please bear with me.

I am currently attempting to set up a simple SFTP server using Ubuntu Server 14.04.2 LTS and OpenSSH. The machine is a VM with 2 HDDs presented to it (1 for system, 1 for SFTP use). Ideally, what I want is only allow users in a specific group to access anything under the system HDD (mounted as / ) while any other users will use the other HDD (mounted as /sftp/). This means that anybody NOT in a specified group will be unable to even see anything other than things under /sftp/.

Is there a way to set up ACLs to achieve this?

Thanks