EPA is promulgating standards of performance for stationary compression ignition (CI) internal combustion engines (ICE). The standards will implement section 111(b) of the Clean Air Act (CAA) and are based on the Administrator's determination that stationary CI ICE cause, or contribute significantly to, air pollution that may reasonably be anticipated to endanger public health or welfare. The intended effect of the standards is to require all new, modified, and reconstructed stationary CI ICE to use the best demonstrated system of continuous emission reduction, considering costs, non-air quality health, and environmental and energy impacts, not just with add-on controls, but also by eliminating or reducing the formation of these pollutants. The final standards will reduce nitrogen oxides (NO<INF>X</INF>) by an estimated 38,000 tons per year (tpy), particulate matter (PM) by an estimated 3,000 tpy, sulfur dioxide (SO<INF>2</INF>) by an estimated 9,000 tpy, non-methane hydrocarbons (NMHC) by an estimated 600 tpy, and carbon monoxide (CO) by an estimated 18,000 tpy in the year 2015.