150 SOUTH NINTH STREET EL CENTRO, CA 92243-2850 August 21, 2012

Gerardo Rios AIR POLL

Chief, AirPermits Office (Air-3) EPARegion 9 75 Hawthorne Street SanFrancisco, CA 94105 DISTRICT

SUBJECT: Additional Clarifications for Rule 904 and40 CFR 51.166
DearMr. Rios: TELEPHONE: (760) 482-4606 FAX: (760) 353-9904

This letter is inresponse to your request for additional informationregarding DistrictRule 904. In a letter dated July 10, 2012, we responded to your initial request for clarifications regarding Ru1e 904 and the requirements for a Prevention of Significant Deterioration (PSD) permitting program. Belowweprovide an additional clarificationregarding Rule 904.
To implement the PSD permitting program under the Clean Air Act, Imperial County Air Pollution Control District (District) incorporated section 40 CFR 52.21(k)(2) of EPA's regu1ations byreference into the district'sregulations and included this provision as partofa SIP revision submittedto EPAfor approval. TheDistrictunderstands thatEPAhasrecently stated, in response to litigation, that EPA intends to revise its PSD permitting regulations at 40 CFR 51.166(k)(2) and 40 CFR 52.2l(k)(2) to ensure that these provisions are consistent with EPA statements in the supporting rulemaking record and the Clean Air Act. In light of EPA's response to the litigation and in order to ensure that permitting actions by the District are consistent withthe Clean Air Act, I am writing to clarify thatthe District interprets and intends to apply the PSD programprovisions in the District's portion ofthe California SIP in a manner that is consistentwith certainEPA statements included inthepreamble ofthe 2010 final rule that added section 52.2l(k)(2) to the federal regulations.
Section 52.2l(k)(2) establishes significantimpactlevels (SILs) for PM2.s and reads as follows: (k)(2) Significant impact levels. For purposes of PM2.s, the demonstration required in paragraph (k)(l) ofthis section is deemed to have been made ifthe emissions increase from the new stationary source alone or from the modification alone would cause, in all areas, air quality impacts less thanthe following amounts: Pollutant Averaging time Class I area Class II area Class III area PM2.s

................. Annual

............ 0.06 !!g/m' 0.3 !!g/m' 0.3 !!g/m' 24-hour

........... 0.07 !!g/m' 1.2 !!g/m' 1.2 !!g/m'

AN EQUAL OPPORTUNITY fAFFIRMATIVE ACTION EMPLOYERParagraph (k)(l) requires that sources applying for a new PSD permit demonstrate that any allowable emission increases from the proposed source or modification, in conjunction with all other applicable emissions increases or reductions, will not cause or contribute to a violation of anyNAAQS orany applicable increment. 40 CFR 52.21(k)(l). Inthepreambleto the 2010 final rule adding the (k)(2) provision, EPA advised that, "notwithstanding the existence of a SIL, permitting authorities should determine when it may be appropriate to conclude that even a de minimis impact will 'cause or contribute' to an air quality problem and to seek remedial action from the proposed new source or modification." Prevention ofSignificant Deterioration (PSD) for Particulate Matter Less than 2.5 Micrometers (PM2 .s) -Increments, Significant Impact levels (SILs) and Significant Monitoring Concentration (SMC), 75 Fed. Reg. 64,864, 64,892 (Oct. 20, 2010). In another passage ofthe preamble, EPA also observed that "the use ofa SIL may not be appropriate when a substantial portion ofany NAAQS or increment is known to be consumed." Id. at 64,894.
Consistent withthese statements by EPA inthe preamble to the 2010 final rule, the District does not interpret section 52.21(k)(2) to preclude the District from exercising the discretion to determine when it may be appropriate to conclude that even a de minimis impact on air quality (an impactbelowthe PM2.s SIL values) will cause or contribute to an air quality problem and to seek remedial action from the proposed new source or modification. Based on this interpretation, the District will not read section 52.21(k)(2) as an absolute "safe harbor," but will exercise discretion to determine whether a particular application ofthe PM2.s SILs is appropriate when a substantial portion ofthe PM2.s NAAQS or increment is known to be consumed. The Districtretains the discretionto require additional information from apermit applicant as needed to assure that the source will not cause or contribute to a violation ofany NAAQS or applicable incrementpursuantto paragraph 52.21(k)(l).
Our expectation is that the need for the District to exercise this discretion will only arise in limited circumstances. The District looks forward to receiving additional guidance from EPA on how to identif'y when a permitting authority should exercise this type of discretion before applying the PM2
.5 SILs in section 52.21(k)(2) to support a demonstration that a source will not cause or contribute to aviolation ofthe PM2.s NAAQS and increments. Sincerely,