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 2013

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NESCAUM states developed a draft dispersion modeling protocol consistent with EPA’s draft guidance; will serve as basis for states’ individual protocols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

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Primary Source Modeling Required for any source that reported

actual emissions >100 tons in one or more years during 2008-2010

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

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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 2008-2010

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

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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)   

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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

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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

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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

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