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Implementation Plans
This web page provides links to recent State Implementation Plan (SIP) submissions that Iowa has made to EPA. The web page includes links to information about recent Iowa designation recommendations for National Ambient Air Quality Standards (NAAQS) that were promulgated or revised since in 2006.
Questions about the information on this web page may be directed to Matthew Johnson at 515-725-9554 or Matthew.Johnson@dnr.iowa.gov.
Back to topDesignation Recommendations
The Clean Air Act requires the state to submit designation recommendations to EPA within one year of any NAAQS revision. EPA is responsible for issuing the final designations. EPA's final designations can be found in 40 CFR Part 81.
List items for Designation Recommendations
Round 1: Muscatine Nonattainment Area
- Recommendation Letter to EPA (50.62 KB) Archived .pdf
- Amended Recommendation Letter & Technical Support Document (1.68 MB) .pdf
- Public Meeting Presentation (10-3-2013) (1.29 MB) .pdf
- EPA SO2 Designations
1-Hour SO2 Designations Consent Decree
Within three years of any NAAQS revision, the Clean Air Act requires EPA to finalize designations for that pollutant for all areas of the U.S. However, for the 2010 1-hour SO2 NAAQS, by 2013 EPA had only designated areas with ambient monitors measuring NAAQS violations, leaving most of the U.S. undesignated. On March 2, 2015, the U.S. District Court for the Northern District of California accepted a consent decree to resolve the delay. The consent decree required that designations for all remaining undesignated areas in the country be completed in three additional rounds: the first new round by July 2, 2016, the second new round by December 31, 2017, and the final new round by December 31, 2020. Those new rounds would eventually be referred to as rounds 2, 3, and 4, with round 1 representing the initial round of nonattainment designations that occurred in 2013 (which included Muscatine, Iowa).
A summary of state and related actions undertaken in the additional rounds of designation is provided below. Additional information is found on EPA’s website: https://www.epa.gov/sulfur-dioxide-designations.
Round 2: July 2, 2016 Deadline
The State provided to EPA updated designation recommendations for three counties in Iowa (Des Moines, Wapello, and Woodbury) affected by this round of designations.
- Recommendation Letter to EPA with Supporting Documentation (2.89 MB) Archived .pdf
- Updated DNR Technical Support (not considered by EPA in their response letter) (2.79 MB) .pdf
- EPA Response Letter (4.06 MB) .pdf
- DNR Response to EPA Letter (520.57 KB) .pdf
Round 3: December 31, 2017 Deadline
On January 5, 2017, the State provided to EPA an amended designation recommendation for all areas in the State not yet designated for the 2010 1-hour SO2 NAAQS. A technical support document that also addressed information required to be submitted under the Data Requirements Rule accompanied the updated recommendation.
- Recommendation Letter to EPA (218.86 KB) .pdf
- Data Requirements Rule and Round 3 Designations Technical Support Document (3.33 MB) .pdf
- Revised Technical Support Document (3.33 MB) .pdf
- EPA Response to Iowa's Round 3 Recommendation
Round 4: December 31, 2020 Deadline
No areas in Iowa were designated in Round 4. (EPA completed the initial designations process for Iowa in Round 3.)
Data Requirements Rule (DRR)
On August 21, 2015, the U.S. Environmental Protection Agency (EPA) published the "Data Requirements Rule for the 2010 1-Hour Sulfur Dioxide Primary National Ambient Air Quality Standard" (80 FR 51052). The DRR first required states to identify sources not located in a nonattainment area that had actual annual sulfur dioxide (SO2) emissions of at least 2,000 tons, or were deemed by the air agency as requiring further air quality characterization. States were later required to select an evaluation method to characterize SO2 air quality around each affected source, using either modeling, ambient monitoring, or limiting a source’s SO2 emissions to less than 2,000 tons per year. The letters below addressed those requirements for Iowa.
- DRR Source List Letter to EPA (184.34 KB) .pdf
- DRR Source Evaluation Method Letter to EPA (237.74 KB) .pdf
Annual Reporting Requirements
The DRR also added provisions in 40 CFR 51.1205(b) requiring air agencies to submit an annual report to EPA documenting SO2 emissions in areas where modeling of actual SO2 emissions served as the basis for designating the area attainment for the 2010 1-hour SO2 NAAQS. As required, each report below includes an assessment of the cause of any emissions increases from the previous year and a recommendation regarding whether additional modeling is needed in each applicable area.
2017 report
2018 Report
2019 Report
2020 report
2021 Report
2022 Report
2023 Report
2024 Report
2025 Report
Implementation Plans for Maintenance Areas (Formerly Nonattainment)
List items for Implementation Plans for Nonattainment and Maintenance Areas
Iowa has successfully resolved air quality challenges associated with nonattainment designations for portions of Council Bluffs (for the 2008 lead (Pb) NAAQS) and portions of Muscatine County (for the 2010 1-hour sulfur dioxide (SO2) NAAQS). DNR collaborated with local sources to secure meaningful emissions reductions as quickly as possible and developed the necessary state implementation plan (SIP) revisions for EPA approval. These efforts lead to significant air quality improvements and enabled EPA to act on the state’s redesignation requests. As of December 18, 2025, Iowa is free of any nonattainment areas.
Following their redesignation from nonattainment to attainment, Council Bluffs (for lead) and Muscatine (for 1-hour SO2) became maintenance areas (for that given pollutant). As maintenance areas, DNR will continue to monitor their progress to ensure ongoing NAAQS compliance and will submit the required second 10-year maintenance plans when due. Note, “maintenance area” is not an official designation, just a common reference. Also note, the terms “attainment plan” and “nonattainment SIP” as used below are interchangeable, as are the terms “plan” and “SIP.”
In 2011, EPA designated a portion of Council Bluffs as a nonattainment area for the 2008 lead NAAQS after a required new source-oriented ambient air quality monitor measured lead concentrations above that strengthened standard. The nonattainment designation became effective December 31, 2011 (76 FR 72097, November 22, 2011), establishing a 5-year attainment deadline of December 31, 2016.
Attainment Plan: DNR worked cooperatively with two nearby industrial facilities to develop new control measures, such as road paving and sweeping, to reduce emissions and improve air quality. On January 21, 2015, the Environmental Protection Commission (EPC) approved the state’s attainment plan for Council Bluffs. The transmittal letter and plan are both dated January 30, 2015, and were forwarded to EPA on February 3, 2015, for federal review. EPA approved the nonattainment SIP on February 26, 2016 (81 FR 9770).
Initial 10-Year Maintenance SIP: Following EPA’s approval of that attainment plan, and as a prerequisite to redesignation, DNR developed the initial 10-year maintenance SIP for Council Bluffs. The maintenance plan documented the effectiveness of the fully implemented control measures and the ambient air quality monitoring data further demonstrated that timely improvements satisfied the December 31, 2016, attainment deadline. On August 15, 2017, the EPC approved the maintenance SIP and that plan accompanied the Governor’s September 18, 2017, request to redesignate the area to attainment. Redesignation Request & Transmittal Letter (275.95 KB) .pdf
- Redesignation to Attainment: EPA approved the maintenance SIP and redesignated the area from nonattainment to attainment on October 4, 2018 (83 FR 50024). (Note, that rule indicates an effective date of November 5, 2018, but as explained in the preamble, EPA’s intention was that it be effective immediately upon publication.) Pursuant to the Clean Air Act, a second 10-year maintenance is due October 4, 2026 (8 years after the attainment redesignation).
In 2013, EPA designated a portion of Muscatine County as a nonattainment area for the 2010 1-hour SO2 NAAQS after an existing ambient air quality monitor measured hourly SO2 concentrations above that new standard. The nonattainment designation became effective October 4, 2013 (78 FR 4719, August 5, 2013), establishing a 5-year attainment deadline of October 4, 2018.
Attainment Plan: DNR worked cooperatively with three local industrial facilities to develop new control measures, such as adding new scrubbers, complying with more stringent SO2 emissions limits, and relying on recent coal to natural gas fuel conversions, to reduce emissions and improve air quality. On May 17, 2016, the Environmental Protection Commission (EPC) approved the state’s attainment plan for Muscatine and DNR transmitted the plan to EPA that same day for federal review. EPA approved the nonattainment SIP on November 17, 2020 (85 FR 73218).
Transmittal Letter (1.03 MB) .pdf
Muscatine 1-hour SO2 Nonattainment SIP (6.45 MB) .pdf
Attachment B - GPC Permits (46.37 MB) .pdf
Attachment C - MPW Permits (5.01 MB) .pdf
Initial 10-Year Maintenance SIP: Following EPA’s approval of that attainment plan, and as a prerequisite to redesignation, DNR developed the initial 10-year maintenance SIP for Muscatine. The maintenance plan documented the effectiveness of the fully implemented control measures and the ambient air quality monitoring data further demonstrated that timely improvements satisfied the October 4, 2018, attainment deadline. On October 19, 2021, the EPC approved the maintenance SIP and that plan accompanied the Governor’s November 12, 2021, request to redesignate the area to attainment.
Redesignation Request & Transmittal Letter (208.94 KB) .pdf
Muscatine 1-hour SO2 Maintenance SIP (3.23 MB) .pdf
Attachment 1 - GPC Permits (14.77 MB) .pdf
Attachment 2 - MPW Permits (902.52 KB) .pdf
Redesignation to Attainment: EPA approved the maintenance SIP and redesignated the area from nonattainment to attainment effective December 18, 2025 (90 FR 51554, November 18, 2025). Pursuant to the Clean Air Act, a second 10-year maintenance is due December 18, 2033 (8 years after the attainment redesignation).
Muscatine PM2.5 SIP Revision
On February 18, 2014, the Environmental Protection Commission approved a revision to the State Implementation Plan (SIP) to prevent future violations of the 2006 24-hour fine particulate (PM2.5) National Ambient Air Quality Standards (NAAQS) in Muscatine. The SIP revision was forwarded to U.S. EPA on February 18th for federal notice and approval. EPA approved the SIP revision on December 1, 2014.
Supporting Documents
- EPA Call for PM2.5 SIP Review in Muscatine (198.19 KB) .pdf
- SIP for PM2.5 in Muscatine (3.67 MB) .pdf
- Attachment E - MPW Permits (14.96 MB) .pdf
- Attachment G - UTLX Permits (4.6 MB) .pdf
- EPA SIP Revision Approval (266.72 KB) .pdf
Implementation Plans for New or Revised NAAQS
Iowa is required under the Clean Air Act to develop State Implementation Plans (SIPs) for new and revised National Ambient Air Quality Standards (NAAQs), referred to as infrastructure SIPs. Infrastructure SIPs demonstrate that the state has the authority and resources to implement a new or revised NAAQS.
List items for Implementation Plans for New or Revised NAAQS
The infrastructure SIP the 2015 Ozone NAAQS was submitted to EPA on November 30, 2018.
The infrastructure SIP for the 2012 PM2.5 NAAQS was submitted to EPA on December 15, 2015.
The infrastructure SIP for the 2010 NO2 NAAQS was submitted to EPA on July 23, 2013.
A revision to the 2010 NO2 infrastructure SIP to address the interstate transport requirements of Clean Air Act Section 110(a)(2)(D)(i)(I) was submitted to EPA on March 1, 2017.
The infrastructure SIP for the 2010 SO2 NAAQS was submitted to EPA on July 23, 2013.
A revision to the 2010 SO2 infrastructure SIP to address the interstate transport requirements of Clean Air Act Section 110(a)(2)(D)(i)(I) was submitted to EPA on March 26, 2024.
The infrastructure SIP for the 2008 ozone NAAQS was submitted to EPA on December 12, 2012. An amended infrastructure SIP was submitted on January 11, 2013.
The infrastructure SIP for the 2006 PM2.5 NAAQS was submitted to EPA on July 23, 2013.
Regional Haze
In 1999, EPA established rules to improve visibility in federally protected Class I areas, such as larger national parks and wilderness areas. The regional haze regulations require all states to periodically submit State Implementation Plan (SIP) revisions to address emissions of visibility impairing pollutants. The first regional haze SIPs were due in 2007 and comprehensive revisions are generally due approximately every 10 years thereafter (EPA provided a one-time extension for the second regional haze SIPs). At the midpoint of each 10-year plan, a 5-year progress report is due.
List items for Regional Haze
- Iowa's 5-Year Progress Report for the Second Planning Period (1.74 MB) .pdf
- Transmittal Letter (173.74 KB) .pdf
- Appendix A - FLM Consultation (1.3 MB) .pdf
- Final Regional Haze Plan for the Second Implementation Period (2019-2028) (5.94 MB) .pdf
- Transmittal Letter (151.99 KB) .pdf
- Appendix A-1. LADCO TSD (11.31 MB) .pdf
- Appendix A-2. LADCO TSD Supplemental Materials (14.89 MB) .pdf
- Appendix B. Ramboll Area of Influence (AOI) Report (4.74 MB) .pdf
- Appendix C-1. AOI Tool [86 MB Excel file] (86.25 MB) .xlsx
- Appendix C-2. AOI Results [95 MB Excel file] (95.48 MB) .xlsx
- Appendix D-1. Four-Factor Analysis Report (1.05 MB) .pdf
- Appendix D-2. DNR Cost Analysis (489.59 KB) .pdf
- Appendix D-3. Interest Rate Justification Memo (255.33 KB) .pdf
- Appendix E. Air Construction Permits (607.11 KB) .pdf
- Appendix F. FLM Consultation Documents (6.99 MB) .pdf
- Appendix G. Public Comment Letters Received (4.17 MB) .pdf
- Appendix H. Interstate Consultation Documents (2.14 MB) .pdf
- 2019: "Prong 4" SIP Revision (replacing CAIR with CSAPR) - Final SIP (4.03 MB) .pdf
- 2019: "Prong 4" SIP Revision (replacing CAIR with CSAPR) - Transmittal Letter (463.83 KB) .pdf
- 2013: Regional Haze Five-year Review SIP (3.38 MB) .pdf
- 2008: Final Regional Haze (SIP) (2.11 MB) .pdf
- 2008: Final Regional Haze (SIP) - with Appendices (76.38 MB) .pdf