February 2, 2012

Mr. Gerardo Rios

Chief, Permits Office

U.S. EPA Region 9

75 Hawthorne Street

San Francisco, CA 94105

Subject: Pio Pico Energy Center PSD Permit Application

1-Hour Ozone Compliance Demonstration 

Dear Mr. Rios:

As requested by EPA during the December 9, 2011 meeting between representatives of 

EPA and Pio Pico Energy Center, LLC (Applicant), we are herein submitting additional 

information on behalf of the Applicant. Specifically, EPA requested additional 

information from the Applicant, using background concentrations from the El Cajon and 

Otay Mesa monitoring stations. 

It should be noted that the Applicant submitted the proposed modeling protocol for the 

Pio Pico Energy Center (Project) to EPA on December 1, 2010, with a request for review 

and comment, consistent with EPA’s policy encouraging early consultation on modeling 

issues.1 EPA did not respond to the Applicant’s request. In the absence of any questions 

or concern expressed by EPA regarding the protocol, the Applicant proceeded with 

modeling and analysis consistent with the protocol, and has expended considerable time 

and effort in reliance on EPA’s tacit approval.2 

Background

The Applicant has previously provided air quality analyses demonstrating compliance 

with federal National Ambient Air Quality Standards (NAAQS) as part of its application 

for a PSD permit. The demonstration of compliance with the new 1-hour NO2 standard 

 

1 Appendix W, Section 10.2.1: “[e]very effort should be made by the Regional Office to meet with all 

parties involved in a SIP revision or a PSD permit application prior to the start of any work on such a 

project. During this meeting, a protocol should be established between the preparing and reviewing parties 

to define the procedures to be followed, the data to be collected, the model to be used, and the analysis of 

the source and concentration data.”

2

It should also be noted that during the December 9 meeting EPA staff indicated that any additional 

concerns regarding modeling issues would be documented in a letter to Applicant on or before December 

16, 2011. To date, no such letter has been received and several calls have been placed to EPA modeling 

staff to confirm that any remaining issues have been resolved. However, no calls have been returned. 

Applicant has therefore proceeded on the assumption that EPA’s requests for additional information about 

modeling issues have been fully addressed. 

sierra

research

1801 J Street

Sacramento, CA 95811

Tel: (916) 444-6666

Fax: (916) 444-8373

Ann Arbor, MI

Tel: (734) 761-6666

Fax: (734) 761-6755
Gerardo Rios -2- February 2, 2012

was made using Chula Vista monitoring data to characterize regional background 

concentrations throughout the entire region. Several non-project sources were also 

explicitly modeled as nearby sources to determine the cumulative impact of the project 

and the existing background. During the December 9 meeting, EPA staff suggested that 

other monitoring sites might provide a more accurate characterization of background 

concentrations. Specifically, EPA suggested El Cajon (because it is located 

approximately the same distance from the ocean as the Project, whereas the Chula Vista 

station is much closer to the ocean) and the station located at the Otay Mesa border 

crossing. 

While the Applicant disagrees with EPA’s belief that these alternate stations offer any 

better characterization of regional background than does the Chula Vista station, the 

Applicant agreed to perform additional analysis to support its PSD application. 

Specifically, the Applicant agreed to perform a compliance demonstration using El Cajon 

data as the background concentration at receptors that are closer to El Cajon than to 

Chula Vista.3 The Applicant also agreed to use Otay Mesa data at receptors within 0.5 

km of the Otay Mesa station. The additional analysis does not require additional 

dispersion modeling, and has been performed by replacing Chula Vista background NO2

data at some receptors with El Cajon data or Otay Mesa data, as appropriate.

El Cajon Data

As noted above, the Applicant agreed to apply El Cajon data to all receptors closer to 

El Cajon than to Chula Vista. As a screening step, the Applicant applied the El Cajon 

data to all receptors. The result was that compliance was demonstrated at all receptors, 

and therefore compliance was demonstrated at the subset closest to El Cajon. The 

highest 5-year average of the 98th percentile cumulative impact (project plus nearby 

sources plus regional background) was 173 μg/m3. This can be compared to the value 

reported in the AFC (179 μg/m3) and the standard (188 μg/m3). Because no noncomplying receptors were identified, it was unnecessary to limit the analysis to any 

particular subset. No further analysis was performed, and additional details are provided 

on the worksheet being provided with this letter.

Otay Mesa Data

The Otay Mesa station is located at the U.S.-Mexico border and is heavily impacted by 

border traffic. This includes a significant number of vehicles that are not equipped with 

California emission controls. The monitor shows significant spikes in concentrations 

during morning and evening rush hours. Because the monitor is directly impacted by 

nearby emissions, it cannot be considered representative of background concentrations. 

Nevertheless, EPA requested that Otay Mesa data be used to evaluate cumulative impacts 

at receptors within 0.5 km of the station.

 

3 Letter, Steve Hill to Gerardo Rios, Pio Pico Energy Center PSD Permit Application Modeling Questions,

December 1, 2011.
Gerardo Rios -3- February 2, 2012

The Otay Mesa station lies just outside the Project’s NO2 impact area. There is only one 

receptor within 0.5 km of the station that has a project impact above the NO2 SIL, and 

there is only one hour in the 5-year evaluation period where the NO2 impact from the 

project exceeds the SIL. 

Synthetic Background Concentration Profile – Previous compliance demonstrations used 

a conservative synthetic background concentration profile. The profile used in previous 

demonstrations was constructed by determining, for each month in the 5-year evaluation 

period, the maximum concentration for each clock hour during a calendar month. These 

values were used to construct 60 daily concentration profiles, one for each calendar 

month in the five-year evaluation period.

For the present analysis, a different procedure was used. Following EPA guidance,

4

multi-year averages of the 98th percentile of available background concentrations were 

calculated by season and hour-of-day. The guidance recommends using the 3rd highest 

value for each season and hour-of-day combination in the evaluation period. The multiyear average for each season is then calculated. This procedure results in four daily 

profiles, one for each season. The modeled project impact for each hour was then added 

to the background concentration in the appropriate seasonal profile. Any resulting value 

above the standard would be a potential violation.

Using this methodology, the maximum cumulative impact (Project plus nearby sources 

plus background) at the receptor was determined to be 164 μg/m3, which is below the 

NAAQS of 188 μg/m3. The cumulative impact during the one hour when the project’s 

impact exceeded the SIL was 148 μg/m3. See the enclosed worksheet for additional 

detail.

If you have any questions regarding this information, please contact the Applicant’s 

representative David Jenkins at (317) 431-1004, or Gary Rubenstein or me at 

(916) 444-6666.

Sincerely,

Steve Hill

cc: John McKinsey, Stoel Rives LLP

David Jenkins, Apex Power Group

Steve Moore, San Diego Air Pollution Control District

Enclosure: CD

 

4

Fox, Tyler, Additional Clarification Regarding Application of Appendix W Modeling Guidance for the 1-

hour NO2 National Ambient Air Quality Standard (March 1, 2011). p. 19