State: A federal declaration Friday that carbon dioxide endangers public health foreshadows potentially tougher regulation of coal-fired power plants across the country — including one proposed by Santee Cooper for Florence County. Santee Cooper, which plans to spend more than $2 billion on the plant along the Great Pee Dee River, has received a key state air pollution permit to operate the facility. The state permit does not include limits on carbon dioxide pollution, which is …