The Environmental Protection Agency (EPA) is partially approving and partially disapproving a revision to the Ohio State Implementation Plan (SIP) intended to provide for attainment of the 2010 primary, health-based 1-hour sulfur dioxide (SO<INF>2</INF>) national ambient air quality standard (NAAQS or ``standard'') for the Muskingum River SO<INF>2</INF> nonattainment area. This SIP revision (hereinafter referred to as the Muskingum River SO<INF>2</INF> plan or plan) includes Ohio's attainment demonstration and other attainment planning elements required under the Clean Air Act (CAA). By this action, EPA is approving the base year emissions inventory and affirming that the nonattainment new source review requirements for the area have been met. EPA is disapproving the attainment plan, since the plan relies on, among other things, acquisition of a parcel of land by a facility located within the nonattainment area, Globe Metallurgical (Globe), that has not occurred. Additionally, EPA is disapproving the plan for failing to meet the requirements for meeting reasonable further progress (RFP) toward attainment of the NAAQS, reasonably available control measures/ reasonably available control technology (RACM/RACT), emission limitations and control measures as necessary to attain the NAAQS, and contingency measures.