The U.S. EPA is investigating why its officials ignored evidence for 18 years that W. R. Grace and Co. used vermiculite ore tainted with asbestos in its building products. An EPA study in 1982, during the Reagan administration, found high levels of asbestos in the company’s vermiculite, contrary to claims made by Grace, but the agency shelved the report and scuttled follow-up studies. As a result, Grace was able to largely avoid government scrutiny, and nearly 200 workers and residents of Libby, Mont., where Grace mined vermiculate until 1990, have died over the past 40 years from ailments likely caused by asbestos.