110 Maple Street, Auburn, CA 95603 • (530) 745-2330 • Fax (530) 745-2373 AIR POLLUTION CONTROL DISTRICT www.placer
.ca.gov/apcd
August 20, 2012
Attn: Gerardo Rios Chief ,AirPermits Office (Air-3) U.S
.EPA Region 9 75 Hawthorne Street San Francisco, CA 94105 Thomas J
. Christofk, Air Pollution Control Officer

Subject: Additional Clarifications for Rule 518 Regarding 40 CFR 51.166 and 40 CFR 52.21(k)(l) Dear Mr. Rios: This letter is in response to your request for additional information regarding District Rule 518, Prevention of Significant Deterioration (PSD) Permit Program. In a letter dated July 6, 2012, we responded to your initial request for clarifications regarding Rule 518 and the requirements for a Prevention of Significant Deterioration (PSD) permitting program. Below we provide an additional clarificationregarding Rule 518
. To implement the PSD permitting program under the Clean Air Act, Placer County Air Pollution Control District (District) incorporated section 40 CFR 52.21(k)(2) ofEPA's regulations by reference into the district's regulations and included this provision as part ofa SIP revision submitted to EPA for approval. The District understands that EPAhas recently stated, in response to litigation,that EPA intends to revise its PSD permitting regulations at 40 CFR 51.166(k)(2) and 40 CFR 52.21(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 with the Clean Air Act, I am writing to clarify that the District interprets and intends to apply the PSD program provisions in the District's portion ofthe California SIP in a manner that is consistent with certain EPA statements included inthe preamble of the 2010 final rule that added section 52.2l(k)(2) to the federal regulations. Section 52.21(k)(2) establishes significant impact levels (SILs) for 

### PM z.s and reads as follows: (k)(2) Significant impact levels. For purposes ofPM2
.s, the demonstration required inparagraph (k)(1) of this section is deemed to have been made if the emissions increase from the new stationary source alone or from the modification alone would cause, in all areas, air quality impacts less than the following amounts: Pollutant Averaging time Class I area Class II area Class III area PMz
.s... ...... ... . Annual.
.... . ...... 0.06 f!g/mJ 0
.3 f!g/m3 0.3 f!g/m3 24-hour
........... 0.07 f!g/mJ 1.2 f!g/mJ 1.2 f!g/mJU.S. EPA Region 9 Additional Clarifications for Rule 518 Regarding 40 CFR 51.1664 and 40 CFR 52.21(k)(1) August 20, 2012 Page2
Paragraph (k)(1) 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 ofany NAAQS or any applicable increment (40 CFR 52.21(k)(1)). In the preamble to the 2010 final rule adding the (k)(2) provision, EPA advised that, "notwithstanding the existence ofa 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 of Significant Deterioration [PSD] for Particulate Matter Less than 2.5 Micrometers [PM2.sl

- Increments, Significant Impact levels [SILs] and Significant Monitoring Concentration [SMC]; 75 Fed. Reg
. 64,864, 64,892 [Oct. 20, 2010])
. In another passage of the preamble, EPA also observed that "the use of a SIL may not be appropriate when a substantial portion ofany NAAQS or increment is known to be consumed" (Id. at 64,894). Consistent with these statements by EPA in the 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 impact below the 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 of the PM2
.s SILs is appropriate when a substantial portion of the PM2
.s NAAQS or increment is known to be consumed. The District retains the discretion to require additional information from a permit applicant as needed to assure that the source will not cause or contribute to a violation ofany NAAQS or applicable increment pursuant to paragraph 52.21(k)(1). 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 identify when a permitting authority should exercise this type ofdiscretion 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 a violation ofthe PM2.s NAAQS and increments. Please contact me, or Don Duffy ofmy staffat (530) 745-2336, ifyou have any questions
.