Tennessean: A deluge of coal ash sludge that broke through a dike at TVA’s Kingston power plant onto a 300-acre stretch of fields, homes and rivers has made the site ground zero in a fight over how “clean” burning coal to produce electricity can be. In this case the focus is on the ash, which can hold even more lead, arsenic and other potentially toxic substances than ever as new technology makes plant air emissions cleaner. Several environmental and health advocacy groups, including Save …