In a setback for enviros, the U.S. EPA yesterday decided against regulating ash and sludge from coal-burning power plants as a toxic hazardous waste. Instead, the agency will merely develop voluntary coal-ash disposal standards that states could choose to follow, such as a recommendation that disposal sites have liners. About 100 million tons of coal ash — which contains arsenic, mercury, cadmium, and other toxic metals — are produced each year, and enviros have been asking the Clinton administration to regulate its disposal to prevent contamination of water supplies. The coal-power industry, which claimed that federal regulations would cost it billions of dollars a year, is presumably breathing a sigh of relief.