Shares of Duke Energy Corp. fell 1.0% in afternoon trade Monday, after the electricity generator said based on current estimates and closure timeframes excavation, excavation of its coal ash basins in North Carolina will add $4 billion to $5 billion to the current estimate of $5.6 billion for the Carolinas. "We are making strong progress to permanently close every ash basin in North Carolina in ways that fully protect people and the environment, while keeping costs down as much as possible for our customers," Duke Energy said in a statement.