EPA is approving a State Implementation Plan (SIP) revision submitted by the State of Maryland. This revision establishes and requires continuous emission monitoring requirements for certain sources of air pollution. The regulation applies to operators of fossil fuel-fired steam generating equipment with a rated heat input capacity of 250 million BTU per hour or greater. The intended effect of this action is to approve an amended regulation submitted by the State of Maryland Department of the Environment as a SIP revision rendering its monitoring requirements as federally enforceable. This action is being taken in accordance with section 110 of the Clean Air Act.