Kinder Morgan is doubling down on its preferred route for a proposed Tennessee Gas Pipeline project through central Berkshire County, the Pioneer Valley and a swath of southern New Hampshire, telling federal regulators several alternative proposals are non-starters. In a New Year's Eve filing to the Federal Energy Regulatory Commission, the company's engineers detailed how a suggested hybrid route alongside an existing pipeline through parts of Richmond, the state-protected Kampoosa Bog Drainage Area in Stockbridge and Lee, and towns to the south, then connecting to a 19-mile stretch along the Massachusetts Turnpike, would be impractical and environmentally damaging.