1999) set forth a framework for reviewing and processing those 1-hour ozone SIPs; one element of

that framework was a commitment for a MCR.2 That proposed rulemaking also noted, “The EPA’s

1996 modeling guidance also recognizes a need to perform a mid-course review as a means for

addressing uncertainty in the modeling results. Because of the uncertainty in long term projections, EPA

believes a viable attainment demonstration that relies on weight of evidence needs to contain provisions

for periodic review of monitoring, emissions, and modeling data to assess the extent to which

refinements to emission control measures are needed.”3

This memorandum covers several topics:

– The overall MCR process and timing, including the potential consequences of findings that

progress toward attainment is or is not being made.

– Guidance for situations where failure to make progress is due to transport.

– Special schedule for other (e.g., moderate or serious) ozone nonattainment areas with

attainment dates of 2004 or earlier.

The Regional Offices should provide this guidance to the appropriate State air pollution control



A mid-course review (MCR) provides for an opportunity to assess if a nonattainment area is or

is not making sufficient progress toward attainment of the one-hour ozone standard. The review will

utilize the most recent monitoring and other data to assess whether the control measures relied on in a

SIPs attainment demonstration have resulted in adequate improvement of the ozone air quality. The

EPA believes that a commitment to perform a MCR is a critical element in any attainment

demonstration that employs a long term projection period and relies on a weight of evidence test.4 In

proposing to approve the attainment demonstration SIPs for ten serious and severe nonattainment areas

for the 1-hour ozone NAAQS on December 16, 1999, EPA indicated that in order for EPA to

approve the SIPs, the States would need to commit to perform a MCR, since they relied on a weight of

evidence test with long term projections. EPA also requested the States to work with EPA in a public

consultative process to develop a methodology for performing the MCR and develop the criteria by

which adequate progress

would be judged. The States have participated in such a consultative process with EPA, which



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