In an accident reminiscent of last year’s massive oil spill in Calhoun County, a natural gas hydrofracking operation in Pennsylvania suffered an explosion Tuesday evening and spewed huge quantities of chemicals into the surrounding area. Bradford County’s director of public safety said a Chesapeake well went out of control late Tuesday night. That means the well blew near the surface, spilling thousands and thousands of gallons of frack fluid over containment walls, through fields, personal property and farms, even where cattle continue to graze.