The EPA is issuing revisions to the monitoring requirements to Performance Specification 1 (PS-1) of appendix B to part 60. The revisions clarify and update requirements for source owners and operators who must install and use continuous stack or duct opacity monitoring equipment. The revisions also update design and performance validation requirements for continuous opacity monitoring system (COMS) equipment in appendix B, PS-1. These revisions do not change an affected facility's applicable emission standards or requirements to monitor opacity. However, the revisions do the following: clarify the obligations of owners, operators, and opacity monitor vendors; reaffirm and update COMS design and performance requirements by incorporating by reference American Society for Testing and Materials (ASTM) D 6216-98 (approved February 10, 1998); provide EPA and affected facilities with equipment assurances for carrying out effective monitoring.