Two Optional Methods for Relative Accuracy Test Audits of Mercury Monitoring Systems Installed on Combustion Flue Gas Streams and Several Amendments to Related Mercury Monitoring Provisions

EPA is taking direct final action on two optional methods for relative accuracy audits of mercury monitoring systems installed on combustion flue gas streams and several amendments to related mercury monitoring provisions. This action approves two optional mercury (Hg) emissions test methods for potential use in conjunction with an existing regulatory requirement for Hg emissions monitoring, as well as several revisions to the mercury monitoring provisions themselves. This action is in regard to the testing and monitoring requirements for mercury specified in the Federal Register on May 18, 2005. Since that publication, EPA has received numerous comments concerning the desirability of EPA evaluating and allowing use of the measurement techniques addressed in the two optional methods in lieu of the methods identified in the cited Federal Register publication, as they can produce equally acceptable measures of the relative accuracy achieved by Hg monitoring systems. This action allows use of these two optional methods entirely at the discretion of the owner or operator of an affected emission source in place of the two currently specified methods. This direct final rule also amends Performance Specification 12A by adding Methods 30A and 30B to the list of reference methods acceptable for measuring Hg concentration and the Hg monitoring provisions of May 18, 2005, to reflect technical insights since gained by EPA which will help to facilitate implementation including clarification and increased regulatory flexibility for affected sources.