### IDEM INDIANA DEPARTMENT OF ENVIRONMENTAL MANAGEMENT We ProtectHoosiers andOurEnvironlllellt. MitchellE. DanielsJr. 100 North Senate Avenue Governor Indianapolis, Indiana46204 (317) 232-8603 Thomas W. Easterly Toll Free (800) 451-6027 Commissioner www.idem.lN.gov April 8, 2011

Ms. Susan Hedman Regional Administrator U.S. Environmental Protection Agency Region 5 77 West Jackson Boulevard Chicago, IL 60604-3950 Re: Request to Parallel Process the Draft Requestfor Redesignation Petition and Maintenance Plan forthe Indiana Portion (Lake and Porter counties) of the Chicago-Gary-Lake IL-IN NonattainmentArea for Fine Particles Dear Ms. Hedman: The Indiana Department of Environmental Management (IDEM) submits a draft Redesignation Petition and Maintenance Plan forthe Indiana Portion (Lake and Porter counties) ofthe Chicago-Gary-Lake IL-IN NonattainmentArea, which was designated as nonattainment ofthe annual standard for fine particles on April 5, 2005. IDEM will conduct a public hearing concerning the Redesignation Petition and Maintenance Plan on May 18, 2011, and the public comment period will conclude on May 20, 2011. IDEM requests the United States Environmental Protection Agency (U.S. EPA) to proceed with its proposed approval of IDEM's April 3, 2008 submittal and to parallel process this draft submission concurrently.
The attached document consists ofthe following: 

### Redesignation Petition andMaintenance Plan • A formal request that the Indiana Portion (Lake and Portercounties) ofthe Chicago-Gary-Lake IL IN NonattainmentArea for Fine Particles be redesignated to attainment and reclassified as maintenance. It contains and meets the requirements setforth in Section 107 ofthe Clean AirAct and in U.S. EPA Redesignation Guidance. • A maintenance year of2025 is established and 2015 and 2020 are analyzed as interim years.

• The appendices ofthe document contain historical airqualitytrend data, projected emission inventorydataand thorough documentation ofthe mobile emissions analysis.

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### 0Ms. Hedman, Page 2


### Motor Vehicle Emissions Budgets

• Contained in the Redesignation Petition is a new MotorVehicle Emissions Budget for 2016 and 2025. The Northwestern Indiana Regional Planning Commission's (NIRPC's) travel demand forecasting model and the U.S. EPA's software program referred to as MOBILE6.2 were used to determine emissions forthe annual fine particle nonattainmentarea. • A conservative margin ofsafety was applied to the 2016 and 2025 projected emissions.

• The travel demand model was updated with the best available assumptions.

• Vehicle registration data gathered from the Indiana Bureau of MotorVehicles were used to replace the MOBILE6.2 defaultvehicle age distribution. Upon completion ofthe public participation process and documentation, IDEM will forward the official transcript and a summary and response to substantive oral and written comments underseparate cover.
IDEM requests thatthe U.S. EPA proceed with review and approval ofthis submittal. Ifyou have any questions or need additional information, please contact Scott Deloney, Chief, Air Programs Branch, at (317) 233-5694.
Sincerely,

Keith Baugues Assistant Commissioner Office ofAir Quality
KBlsadlghf Enclosures: Draft Request for Redesignation Petition and Maintenance Plan Underthe Annual National AmbientAir Quality Standard for Fine Particles forthe Indiana Portion of the Chicago-Gary-Lake County, IL-IN NonattainmentArea Cc: John Summerhays, U.S. EPA Region 5 

### (wienclosures) Matt Rau, U.S. EPA Region 5 

### (wienclosures) John Mooney, U.S. EPA Region 5 (no enclosures) Cheryl Newlon, U.S. EPA Region 5 (no enclosures) Pat Morris, U.S. EPA Region 5 (no enclosures) Bill Brown, NIRPC 

### (wienclosures) Rob Kaleel, Illinois EPA 

### (wienclosures) Scott Deloney, IDEM (no enclosures) Christine Pedersen, IDEM (no enclosures) Gale Ferris, IDEM 

### (wienclosures)