WEST WHITELAND >> After falling more than 18 months behind schedule, Sunoco has decided to use a portion of an existing 12-inch pipeline to connect and bypass yet-to-be-completed portions of the 350-mile Mariner East 2 pipeline.Sunoco plans to use a portion of the 12-inch line only in Chester and Delaware counties, from Wallace Township in Chester County to Middletown Township in Delaware County.