CHARLESTON, W.Va. -- The parent of Columbia Gas Transmission said Friday it has won federal approval for a plan to spend $300 million a year through 2017 on improvements to its Appalachian pipeline system.Indiana-based NiSource Inc. said the Federal Energy Regulatory Commission approved the plan for Columbia Gas Transmission's lines in West Virginia, Virginia, Pennsylvania, Ohio, Maryland and Kentucky. Columbia Chief Executive Officer Jimmy Staton said the $1.5 billion investment will help ensure safer, more reliable pipeline infrastructure for customers and the communities across the region.The plan stems from a consumer settlement that is unrelated to the December explosion of a Columbia transmission line near Sissonville that destroyed several homes, but it could help prevent similar incidents.NiSource said it will also spend $100 million on maintenance, and its long-term plan is to invest about $4 billion over 10 to 15 years.The work includes replacing about 1,000 miles of transmission lines, including 400 in the first five years, and upgrading 50 critical compressor units. Staton said the work also involves improving Columbia's ability to perform state-of-the-art maintenance and inspections without interrupting service.The cause of the Dec. 11 West Virginia explosion remains under investigation, but the National Transportation Safety Board has said the line showed signs of external corrosion and had thinned to about one-third of the recommended thickness in some spots.The NiSource announcement comes ahead of a Senate Commerce Committee hearing that U.S. Sen. Jay Rockefeller is holding Monday in Charleston on pipeline safety and a recent report by the General Accountability Office.Rockefeller, D-W.Va., scheduled the hearing after a 20-inch line ruptured about 15 miles north of Charleston, triggering a massive fire that cooked a section of Interstate 77. No one was seriously injured.Federal investigators say it took Columbia more than an hour to manually shut off the gas that fueled the fire.The NTSB has long advocated requiring automated valves that could shut off gas in such situations within minutes. Currently, manual valves are required at intervals -- from every 2 1/2 to 10 miles -- based on population density.