The first lawsuit on behalf of the victims of the Merrimack Valley explosions has been filed against Columbia Gas of Massachusetts...Representing attorneys include environmental attorney Robert F. Kennedy, Jr..."Columbia committed an act of extreme negligence," Kennedy said during a conference call... He accused the company is rapidly building pipelines while not tending to their aging infrastructure, citing several explosions of pipelines operated by NiSource and its subsidiaries...The lawsuit was filed as a class action on behalf of a resident whose home was evacuated following the series of explosions and fires.  The suit does not represent those injured or the family of the teenager killed Thursday, who are expected to be represented separated...Explosions...caused upwards of 70 fires, injured more than two dozen people and resulted in the death of an 18-year-old...Homes in each community were evacuated...Residents were allowed to return home over the weekend though are expected to remain without gas utilities for weeks.  Preliminary investigative reports show over-pressurized gas lines as the believed cause of the disaster.