You have an airgapped network that prevents remote access, reducing the question of security to one of physical security... which is typically handled with big locks, cameras, 24 hour staffing at the gas station, and maybe men with guns if it comes down to it.
Why would you network these together and create an avenue for simultaneous, surruptitious hacking and attacking of your industrial equipment?
Be thankful you have a job, and don't let the SysAdmin's (natural, and usually good) desire for laziness and efficiency to lead to a future security issue justified by convenience.
ATT had the same idea. In about 1945.
Was gonna say the same thing.... or MCI, this being their entire business model, really.