The Illinois Environmental Protection Agency (Illinois EPA) finalized revisions to the Sulfur Dioxide (SO2) State Implementation Plan (SIP) in response to the 2010 1-hr SO2 National Ambient Air Quality Standards (NAAQS) on December 7, 2015. The revisions can be found in Section 214 in the Title 35 of the Illinois Administrative Code (IAC). New limits potentially affecting a large portion of Illinois sources become effective on January 1, 2017. This includes hourly source-specific limits as well as state-wide sulfur content limits for distillate fuel oil and residual fuel oil combustion sources (e.g., engines and boilers). Specifically, effective January 1, 2017 the sulfur content of distillate fuel oil is limited to 15 ppm and residual fuel oil is limited to 1,000 ppm. Sources combusting distillate fuel oil and residual fuel oil should ensure that old fuel tanks will contain compliant fuel as of January 1, 2017. Records should be maintained to demonstrate the fuel used by subject emission units meet these limits (e.g., fuel supplier certifications). If a deviation of the new fuel limit or recordkeeping requirements is discovered, the Illinois EPA should be notified within thirty (30) days.