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EPA Approves Iowa's Attainment Plan for Muscatine County

  • 11/18/2020 4:23:00 PM
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The U.S. Environmental Protection Agency (EPA) has approved Iowa’s sulfur dioxide (SO2) attainment plan for Muscatine County. In collaboration with the DNR, facilities in the Muscatine area started reducing their SO2 emissions in 2015 to meet the federal health standard for SO2. EPA’s approval of the plan was published in the Federal Register on November 17, 2020 and will be effective on December 17, 2020. In this action EPA also determined that Iowa’s current regulations related to excess emissions during startup, shutdown, and malfunction (SSM) events do not need revision.


On August 5, 2013, EPA issued a final rule designating a portion of Muscatine County, Iowa, as a nonattainment area for the 1-hour SO2 national ambient air quality standard (NAAQS). The nonattainment designation occurred after EPA revised the SO2 NAAQS in 2010 by adding new health protections for short-term exposures to SO2.

The DNR and facilities in the Muscatine nonattainment area developed a plan to reduce SO2 emissions to attain the new standard as quickly as possible. After public review and comment and Environmental Protection Commission approval, the DNR submitted the plan to EPA on May 26, 2016. The implementation of the plan’s control measures has reduced SO2 emissions in the area by over 10,000 tons per year and, starting with the 2015-2017 time frame, ambient concentrations measured in Muscatine have attained the 1-hour SO2 NAAQS. Now that EPA has finalized the approval of the plan, the DNR is working with EPA to redesignate the area to attainment.

EPA’s final rule approving the Muscatine attainment plan also included a determination that Iowa’s regulations regarding excess emissions during SSM events are consistent with recent federal policy and EPA has withdrawn Iowa from the June 12, 2015, SSM “SIP Call.”

Copies of the DNRs attainment plan and EPA’s final approval are on our website:, under Implementation Plans for Nonattainment and Maintenance Areas, within the "Muscatine 1-hour SO2 Nonattainment Area" subheading. Please contact Matthew Johnson at or Jim McGraw at if you have questions.