Prince William Health System is close to securing a partnership with a larger nonprofit healthcare provider, less than a year after Northern Virginia's largest hospital chain abandoned its plans to merge with the Manassas hospital. Inova Health System walked away from the deal in June, citing a legal challenge from the Federal Trade Commission to block the merger. But the need to expand and modernize its facilities still exists, because the hospital has to keep pace with the fast-growing western Prince William County population it serves, Prince William Health System leaders said.