SIP Steering Committee Meeting March 29, 2012

 In October 2011, EPA issued draft SIP and modeling guidance related to the 1-hour SO2 standard issued in June 2010  EPA’s guidance addresses parameters for dispersion modeling of large sources of SO2 emissions  Refined dispersion modeling must be included in SO2 SIPs that states must submit to EPA in

 NESCAUM states developed a draft dispersion modeling protocol consistent with EPA’s draft guidance; will serve as basis for states’ individual protocols  All NESCAUM states expecting to model emitters of 100 tons or more per year actual emissions as primary sources  Some variability among states as to emission thresholds to determine interactive sources 3

Primary Source Modeling  Required for any source that reported actual emissions >100 tons in one or more years during  Modeling is of full potential or allowable emissions  A primary source must be placed at the center of its own modeling domain  Must include interactive sources in modeling 4

Interactive source modeling  Required for any source within 50 km of a primary source that reported actual emissions >40 tons in one or more years during  Includes sources outside of Massachusetts with actual emissions >40 tons if within 50 km of MA primary source  MassDEP is collecting data from other states 5

Interactive source modeling  Interactive sources must be modeled at full potential or allowable emissions  Sources may be excluded from modeling if screening of the interactive facility demonstrates potential 1-hour SO2 impacts are not greater than 7.8 ug/m3 (3 ppb) 6

Smaller interactive sources  Sources with reported emissions >20 tons per year (but <40 tons) generally not required to be modeled  However, may require modeling based on review of a number of factors: ◦ is source is located in complex terrain ◦ short stacks subject to building downwash ◦ operating parameters ◦ is source captured by background monitor 7

Emissions Data  Will use actual emissions reported by a source to MassDEP’s Air Registration System to determine if source meets threshold for primary and/or interactive sources  Emission data since 2005 will be reviewed as a check on representativeness of recent emissions  Will consider if changes in permit conditions, equipment, or operating parameters may cause future year emissions to vary significantly from reported emissions 8

 MassDEP developing a draft modeling protocol for EPA and stakeholder review  Preparing lists of primary and potential interactive sources and creating 50 km maps  Will schedule an SO2 stakeholder meeting in next 30 days or so  EPA still reviewing comments on its proposed modeling guidance; final EPA guidance date is uncertain 9