Federal and state regulators in North Carolina propose a fix to repair damage caused by more than 50 years of toxic pollution from a pulp mill.By Lisa SorgPLYMOUTH, N.C.—Fall had just arrived when a nor’easter began stewing in the Atlantic Ocean, its gale-force winds carrying the pungent smell of chlorine westward, away from downtown. Against the backdrop of dingy stratus clouds, the Domtar pulp mill loomed.