I don't know of any 'standards' but that doesn't mean they don't exist.
Ask the Contractor to show you where the Standard is 'printed'. If he can't 'match' his point to YOUR particular case, then as far as I'm concerned, the standard is HIS standard; no one else's. At the same time, you can call your local Municipality for an Inspection. Perhaps they can help. Perhaps you should have a few Contractors make a visit for their opinion. (Don't be too excited about this idea - Many COntractors are reluctant to 'bad mouth' the competition either directly, or in writing.)
My best to ya and hope this helps.
Jay J -Moderator
PS: Try contacting a company whose name is on the side of a passing Cement Truck. Maybe they can give you the standard.