The Port of Charleston, owned and operated by the South Carolina Ports Authority, is one of the largest ports in the United States, ranked in the top 25 by containerized cargo volume in 2014. It consists of five terminals, and a sixth terminal was to open in 2018. Despite occasional labor disputes, the port is ranked number one in customer satisfaction across North America by supply chain executives. Port activity at the two terminals located in the city of Charleston is one of the city's leading sources of revenue, behind tourism. Today, the Port of Charleston boasts the deepest water in the southeast region and regularly handles ships too big to transit through the Panama Canal. A harbor-deepening project is currently underway to take the Port of Charleston's entrance channel to 54 feet and harbor channel to 52 feet at mean low tide.  With an average high tide of 6 feet, the depth clearances will become 60 feet and 58 feet, respectively. Union Pier, in the city of Charleston, is a cruise ship passenger terminal which hosts numerous cruise departures annually. In May 2010, the Carnival Fantasy was permanently stationed in Charleston, offering weekly cruises to the Bahamas and Key West, eventually to include Bermuda. With the addition of the weekly Carnival Fantasy sailings, Union Terminal hosted 67 embarkations and ports of call in 2010. With the closure of the Naval Base and the Charleston Naval Shipyard in 1996, Detyens, Inc. signed a long term lease.  With three dry docks, one floating dock, and six piers, Detyens Shipyard, Inc. is one of the largest commercial marine repair facilities on the East Coast. Projects include military, commercial, and cruise ships.
Question: How many feet difference is there between the Port of Charleston's entrance channel and harbor channel?
Answer: 2