But the Government Accountability Office has said the cleanup standard could affect some of the 200-plus industrial sites in 40 states that also received asbestos-tainted vermiculite from Grace's Montana mine. More than 20 of those sites, posing the highest health risks, have already been cleaned once. Most of those were processing plants where the mineral was heated at high temperatures so it could expand and be used for insulation in millions of homes.The GAO and asbestos experts said the EPA risk assessment could force more cleanups. And Grace representatives and health officials said the EPA proposal could apply to other types of asbestos found in communities across the country. In a letter to the EPA last week, Grace Vice President Karen Ethier said the standard would have "inevitable" consequences beyond Libby. "That broad application will, in turn, result in enormous, unexpected and unnecessary costs to building owners, farmers and other property holders, including the federal government," Ethier said. Manufacturing and trade groups and federal agencies including the White House Office of Management and Budget also have questioned the EPA proposal. They said the low threshold falls below even background asbestos levels seen in parts of the country. Although the sale and manufacture of asbestos-containing materials is tightly regulated, the government has never established a safe level of human exposure for the type of the mineral found in Libby. While there are general cancer-based exposure limits for asbestos set by the Occupational Safety and Health Administration, the EPA proposal for the first time sets a risk level for non-cancer illnesses, such as the debilitating and potentially fatal lung disease asbestosis. That's a crucial issue in Libby, where the Grace mine and processing plants for three decades left the town coated in asbestos dust that has killed an estimated 400 people and sickened at least 1,700 more. Health experts say the death toll is bound to rise because of the long latency period of asbestos-related illness.