Approval and Promulgation of Implementation Plans; Indiana

The Indiana Department of Environmental Management (IDEM) submitted a revised opacity rule on October 21, 1999, as a requested revision to its State Implementation Plan (SIP). The revisions amend portions of Indiana's opacity rule concerning the startup and shutdown of operations, terminology used in discussing averaging periods, time periods for temporary exemptions, alternative opacity limits, and conflicts between visible emission readings and continuous opacity monitor (COM) data. A major new component of this rule authorizes the State to incorporate source-specific startup and shutdown provisions into federally enforceable operating permits for certain utility boilers, as long as those provisions fall within a range established in the rule. Indiana provided a modeling analysis showing that the revised startup and shutdown provisions will not have an adverse impact on air quality. In addition, the revisions clarifying averaging periods and resolving conflicts between monitored and visual opacity readings will aid enforcement of the opacity rule.