** ADVANCE FOR MONDAY, AUG. 27 - FILE ** This file photo from April 19, 2006, shows bricks made of fly ash, a fine powder loaded with mercury, lead and other toxic chemicals which is the byproduct of coal-burning power plants, in Columbia, Mo. New technology increasingly used at coal-fired power plants that is meant to bring cleaner skies could lead to millions more tons of potentially harmful ash in landfills across the nation, as chemicals injected into many plants' emissions to capture airborne pollutants change the composition of the ash and cut its usefulness. It can't be used in cement, for example, because the interaction of the chemicals may keep the concrete from hardening. (AP Photo/L.G. Patterson)