SOUTHERN ILLINOIS — Ameren Illinois is about to start replacing miles of decades-old pipe in a major natural gas project between Jefferson and southern Marion County.

Starting in mid-April, the company will be upgrading 15 miles of six-inch natural gas transmission pipeline that was placed in-service in the 1950s between Centralia and Mount Vernon.

According to Ameren Illinois, crews will be upgrading the pipeline to 10-inch steel for nearly 13.75 miles, while 1.5 miles will be eight-inch steel.

It is one of the longest and largest natural gas upgrades Ameren Illinois has performed in several decades.