Subcontractor for Nicor called wants entry to map drain lines

I got a phone call from some guy calling from his cell phone that he is  a sub contractor of a sub contractor for Nicor who is putting new gas lines and he needs to enter my property Monday morning to map out the drain lines before they dig.  Is this legit? I think they said their name is HNO or something like that and they are a sub contractor of pipestrong who is contracted by Nicor. 

I am trying to call Nicor,  but on hold for ever