Wet well vacuum relief from pump station

[bellmouth]

I am designing for a vacuum relief pipe for a drainage inlet wet well. A couple of 48" dia pipes from a reservoir drain into the wet well, which in turn is piped via a 72" dia pipe to a pump station. The design flow of the pump station is 160 MGD. The vacuum relief design is in anticipation of the either the reservoir inlet valves or pumps misfuctioning so that the pumps are pulling vacuum with the inlet valves closed, requiring inlet air from the top of the wet well to prevent pump or wet well roof damage. The wet well is 90 ft tall and 14 ft dia. What factors would be used to calculate the size of the vacuum relief pipe?