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, Air Permits 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 

clarification regarding 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) of EPA's regulations by reference 

into the district's regulations and included this provision as part of a SIP revision submitted to EPA 

for approval. The District understands that EPA has 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 of the 

California SIP in a manner that is consistent with certain EPA statements included in the 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 PMz.s and reads as follows: 

(k)(2) Significant impact levels. For purposes of PM2.s, the demonstration required in paragraph 

(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/mJ 
U.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 of any 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 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 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 of any 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 of any 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 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 a 

violation of the PM2.s NAAQS and increments. 

Please contact me, or Don Duffy of my staff at (530) 745-2336, if you have any questions.