1 Attachment 

Scott –

Please find attached responses to your comments below. Rich Hamel will send you an email with a file transfer 

to download of the modeling files. If you also want the binary files, we can also mail a copy of the memo with a 

CD that contains them as well as the modeling files. Please let us know if you want the binary files, and to whom 

the package should be addressed as well as how many copies. 

We hope that you will find these responses to be sufficient, but please let Rich or I know if you have additional 

questions on this submittal. 

Thanks for your input.

Sara

Sara J. Head, QEP

RE: Palmdale NO2 additional info 

Head, Sara 

to: 

Scott Bohning 

10/08/2010 01:57 PM 

Cc: 

Shirley Rivera, Carol Bohnenkamp, "Hamel, Richard" 

Hide Details 

From: "Head, Sara" <Sara.Head@aecom.com>

To: Scott Bohning/R9/USEPA/US@EPA 

Cc: Shirley Rivera/R9/USEPA/US@EPA, Carol Bohnenkamp/R9/USEPA/US@EPA, 

"Hamel, Richard" <richard.hamel@aecom.com>

History: This message has been replied to. 

Response to EPA Comments on NO2 Modeling.pdf

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Environment

D 805-388-3775 ext 227 M 805-320-8059

sara.head@aecom.com

AECOM 

1220 Avenida Acaso, Camarillo, CA 93012

T 805-388-3775 F 805-388-3577

www.aecom.com 

 

From: Bohning.Scott@epamail.epa.gov [mailto:Bohning.Scott@epamail.epa.gov] 

Sent: Thursday, August 26, 2010 4:07 PM 

To: Head, Sara 

Cc: Rivera.Shirley@epamail.epa.gov; Bohnenkamp.Carol@epamail.epa.gov

Subject: Palmdale NO2 additional info

 

Sara - 

Here are comments I mentioned over the phone, it was good talking to you. I apologize for not getting this to last 

week as I had hoped to. Thanks for your patience. 

As you know, given the newness of the 1-hr NO2 NAAQS, and recent interactions with other PSD applicants, 

there is increased scrutiny of the 1-hr NO2 analysis. EPA will be following "Applicability of Appendix W Modeling 

Guidance for the 1-hour NO2 NAAQS", memorandum from Tyler Fox, Air Quality Modeling Group, EPA OAQPS, 

June 28, 2010 (hereafter "NO2 memo"). The supplemental information provided in "Palmdale Hybrid Power 

Project (PHPP) - Supplemental Information for the Application for PSD Permit", AECOM, July 21, 2010, does not 

appear to meet the requirements of that memo. 

For the 1-hr NO2 analysis in the July 21, 2010 supplemental information for the Palmdale project (PHPP), there 

are several items for which EPA would like additional information. 

- The should be documentation on the representativeness of surface meteorological data for purposes of 

analyzing the 1-hr NO2 impacts, including e.g. comparison of surface characteristics of the meteorological data 

station and facility site, with some reasoning about how they are sufficiently similar for the data to be 

representative, or about how modeling results using the data would expected to be conservative. 

- There should also be some discussion of the representativeness of the upper air meteorological data used. 

- There should additional detail in the assessment of the representativeness or conservatism of the background 

NO2 monitor with respect to background sources. The NO2 memo at p.6 mention raises the issue of background 

being "representative of allowable emission levels under the existing permits" for the background sources. A 

quantitative comparison of the amount of traffic near the monitor and near the project site should be part of the 

assessment. 

- There does not appear to be any cumulative NO2 analysis including background sources, even though the 

project impact (56.8 ppb) is estimated to be well above the draft SIL of 4 ppb. Sources within 50 km beyond the 4 

ppb circle around the source that result in a "significant concentration gradient in the vicinity of the source” should 

be included in the modeling. The emissions rates for those should reflect the recommendations in the Guideline 

on Air Quality models, section 8.1.2. Note that the NO2 memo states that the number of such sources is 

generally expected to be small. 

- It is not clear that the hour by hour addition of modeled to monitored values provides a conservative estimate of 

impacts that could occur, since in future years values may line up differently (e.g. the highest monitored and 

modeled values could occur simultaneously). The NO2 memo at p.5 states that "some level of temporal pairing of 

modeled and monitored values may be considered on a case-by-case basis, with adequate justification and 

documentation". There should be some showing that the hourly method used, along with choice of background 

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site, results in a conservative estimate of total impacts relative to the NAAQS. 

- The NO2 memo specifically notes at pages 3 and 9 that the there is no default in-stack NO2/NOx ratio for either 

the OLM or PVMRM methods for the 1-hr NO2 NAAQS. Rather (p.4), there should be a "case-by-case 

determination based on an assessment of the adequacy of the ozone titration mechanism utilized by these 

options to account for NOx chemistry within the AERMOD model based on 'the chemical environment into which 

the source’s plume is to be emitted' (Appendix W, Section 5.1.j)." 

- There should be some discussion of the representativeness of the Lancaster site for providing ozone data for 

use with OLM. 

- If there is any missing data from the chosen ozone site, then the procedures used for filling in missing data 

should be described, and shown not to bias the modeling results low. 

- Scott B. 

-- 

=+=+=+=+=+=+=+=+=+=+=+=+=+=+= 

"Scott Bohning" <bohning.scott@epa.gov>

U.S. EPA Region 9, AIR-7 

415/947-4127 fax-3579

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