1 

## Response to EPA Comments of August 12, 2010

1-Hour NO 2 

## NAAQS Compliance Demonstration Avenal Energy Project PSD Permit Application

September 13, 2010



### Introduction

On August 12, 2010, EPA sent a letter to Aven al Power Center, LLC (Avenal) regarding the February 2008 application to EPA Region 9 for a PSD permit for the Avenal Energy Project. EPA’s letter contains comments th at describe EPA’s rema ining concerns about Avenal’s analysis of the Project’s compliance with the new 1-hour NO 2 standard. This document contains Avenal’s responses to those comments and information to address EPA’s remaining concerns.



### Revised Modeling Results

Modeling was conducted in accordance with the September 13, 2010 modeling protocol. 1
Screening runs were conducted to determine which operating conditions resulted in peak one-hour impacts. These runs were also used to identify areas where a fine grid of receptors would be located for refined modeling. Results of these screening runs are

shown in Table 1.

Table 1. Screening Results Avenal Energy Project

Operating Scenario Maximum 1-hour

NO 2 impact (μg/m 3 ) Startup/shutdown 508 Full load, high ambient temp with duct firing 38.9

Minimum load, high ambient temp, unfired 23.1 Full load, annual average ambien t temp, with duct firing 40.6

Minimum load, annual average ambient temp, unfired 25.4 Full load, low ambient temp, with duct firing 36.9

Minimum load, low ambient temp, unfired 26.4

1 Sierra Research, Air Dispersion Modeling Protocol, Revised Supplemental NO2 Air Quality Impact Analysis, Avenal Energy Project , September 13, 2010.2 The full load, high ambient temperature case wi th duct firing was selected to represent normal operations, even during seasons wher e those ambient conditions do not apply. Because the normal operation 1-hour impacts ar e so much lower than startup/shutdown 1- hour impacts, the case selected to repr esent normal operation has no effect on demonstration of compliance.

Normal operations

Refined modeling runs were conducted for each of the 5 years of meteorological data. The project impacts for each hour were a dded to the corresponding background ambient concentration to obtain the predicted con centration for comparison with the National Ambient Air Quality Standard (NAAQS).

For each year, the eighth highest value (98 th percentile) was determined for each receptor in the modeling domain. These five values were averaged for each receptor. The highest result out of all of the receptors was selected for comparison with the NAAQS. The results are presented in Table 2.

Startup/shutdown

Refined modeling runs were conducted for each of the 5 years of meteorological data. The project impacts for each hour were a dded to the corresponding background ambient concentration to obtain the predicted concentration for comparison with the NAAQS.

For each year, the eighth highest value (98 th percentile) was determined for each receptor in the modeling domain. These five values were averaged for each receptor. The highest result out of all of the receptors was selected for comparison with the NAAQS. The results are presented in Table 2.

Table 2. Refined Results Avenal Energy Project

Operating Scenario Highest Result for comparison with NAAQS (μg/m 3 ) Highest Result for comparison with NAAQS (ppb) 1-hour NO 2 Standard

(ppb)

Startup/shutdown 150.3 80 100 Normal operation 108.3 57 100

The modeling demonstrates that the project wi ll comply with the federal 1-hour standard

for NO 2

.3 

## Responses to EPA Comments

General Comments

EPA COMMENT: As a technical and a legal matter, the information, data, protocols and analyses previously provided by Avenal to EPA and/or other regulatory agencies for the purposes of demonstrating comp liance with the Federal annual NO 2 standard or the

State 1-hour NO 2 standard cannot simply be assu med to demonstrate the AEP's compliance under the Clean Air Act PSD program with the Federal 1-hour NO 2 standard. Further, EPA did not previously ac cept or approve Avenal's use of such information, data, protocols and analyses for the purposes of demonstrating compliance

with the Federal 1-hour NO 2 standard; indeed, that standar d had not been finalized at the time such information was initially subm itted and thus would not have been reviewed for that purpose.

RESPONSE:

Avenal understands that the data and analys is it previously submitted to demonstrate compliance with EPA’s annual NO 2 standard and Ca lifornia’s 1-hour NO 2 standard

cannot be assumed to demonstrate compliance with EPA’s new 1-hour NO 2 standard. As a technical matter, however, much of the in formation, data, and analysis that Avenal previously submitted necessarily serves as the starting point for evaluating compliance

with the new 1-hour NO 2 standard. Avenal simply notes that significant portions of the underlying information necessary to complete the new analytical requirement were previously submitted to EPA. These in clude ambient background data for use in modeling, discussions of the proc ess used to identify nearby s ources, and other materials. In fact, much of the information previously submitted is as relevant to an analysis of 1-

hour NO 2 impacts as it is to analyses of the Project’s impacts on 1-hour and 8-hour average CO, 24-hour and annual average PM 10 , and annual average NO 2 ambient air quality standards.

It is misleading to suggest that “Avenal c hose to forego EPA input on the protocol” that Avenal used to analyze the project’s 1-hour NO2 impacts, when Avenal specifically sought EPA’s input but did not receive it. On May 5, 2010, shortly after EPA notified Avenal that it would not issue the permit until APC could demonstrate compliance with

the new NO 2 standard, APC resubmitted to EPA the Project’s August 2007 modeling protocol and specifically sought EPA concurrence to use four elements of that prior protocol in the supplemental an alysis of the 1-hour average NO 2 standard:

 Emission sources to be included in the analysis

 Meteorological data

 Background ozone concentrations

 Background NO 2 concentrations4 Because EPA did not respond to or comment on the submitted protocol requests, APC proceeded with its analysis of the Project’s impacts on the 1-hour NO 2 standard based on existing EPA guidance documents (which are clearly relevant even though they do not deal specifically with the new standard) a nd protocols that California agencies have accepted for modeling 1-hour NO 2 impacts. Since that time, EPA has requested additional analyses, discussion, and documentati on in order to allow it to complete its review of the Project’s co mpliance with the 1-hour NO 2 standard. Although EPA’s requests seek additional information, these re quests lack specific guidance on how such analyses should be prepared. At the same ti me, several of the requests appear to include a scope and breadth never before seen in a PSD review.

Because EPA has only provided general guidance and has not addressed a number of key

details as to the criteria it will apply in its review, we have based the following responses on two basic sources: (1) existing, written EPA guidance documents; and (2) past PSD permits issued by EPA or EPA delegates. For some issues, we have not been able to find relevant guidance from either source. In thos e cases, we propose cr iteria and explain why

we believe those crit eria should be used.



### Nearby Sources

EPA COMMENT: Avenal's May 13, 2010 1-hour NO 2 submittal did not include necessary information indicating which, if any , nearby sources were modeled or the process used to determine which nearby sources should be included.

RESPONSE: The May 13, 2010 submittal was a supplement to previous submittals. It described in detail the additional work that was done to demonstrate compliance with the

1-hour NO 2 NAAQS. As a supplemental analysis, it built on previously submitted information. The process used to determin e which nearby sources to include in the modeling was described in the orig inal (February 2008) application.

EPA COMMENT: Please provide a description of the process used for determining which nearby sources should be included in the modeling, as well as the modeling analysis for any such sources.

RESPONSE: The process that was used to make that determination was described in previous documents. EPA accurately desc ribed the process in its August 12, 2010 letter

and attachments:

“The applicant's June 28, 2010 respons e states that APC Section 6.2.7.1.2 (Localized Impacts) thoroughly discussed th e criteria used to evaluate whether any stationary sources existed within six m iles that would qualify to be explicitly included in a cumulative air quality m odeling impact analysis. None were identified by either the Applicant or the SJVAPCD.

“APC Section 6.2.7.1.2 (Localized Impacts) is presented here:5 “6.2.7.1.2 Localized Impacts

“The CEC has defined this local analysis as "a cumulative air quality modeling impacts analysis of the pr oject's typical operating mode in combination with other stationary so urce emissions sources within a sixmile radius which have received construction permits but are not yet operating, or are in the permitting pro cess."[footnote omitted] Within the distance of six miles, three categorie s of projects with combustion sources

were evaluated:

 Existing projects that have been in operation since at least January 2006.

 Projects for which air pollution permits to construct have been issued and that began operation after 2006.

 Projects for which air pollution permits to construct have not been issued, but are reasonably foreseeable.

“Existing projects that have been in operation since at least January 2006 are reflected in the ambient air quality data that have been used to represent background concentrations for the proposed project; consequently, no further analysis of the emissions from this category of facilities was performed.

“The District was requested on Ju ly 19, 2007, to provide information on any sources that might be appropriate (i.e., within 6 miles and with an emission increase of at least 5 tons pe r year for a criteria pollutant) for a cumulative air quality impact anal ysis, but has not identified any. Consequently, no localized cumulativ e impact modeling analysis was performed for the proposed project.” 2

The same screening process was used to iden tify nearby sources for the Class II impacts analysis.

The applicant screened nearby sources for th e purpose of preparation of a cumulative impact analysis as part of its application for a license from the California Energy Commission (CEC). Because the purpose and elem ents of the CEC analysis are similar to elements of the PSD compliance demonstrati on, the CEC analysis was submitted to EPA as part of its PSD application.

The portion of that analysis that is relevant here is the iden tification of sources that are not adequately represented by ambient monitori ng data, and must therefore be explicitly modeled. The applicant contacted the District and requested a li st of all projects within 6

2 Gerardo Rios letter to Jim Rexroad, Attachment 1, August 12, 2010. p. 3:6 miles of the project site 3 for which permits had been reque sted or issued that had not begun operating prior to January 2006. This date was select ed because impacts from sources operating before that date were pr esumed to be reflected in the ambient monitoring data. Sources with permitted emission s of less than 5 tons per year were also

excluded. 4

No nearby sources were identified using this approach that were not already included in the underlying ambient monitoring data. Becau se no nearby sources were identified, no nearby sources were modeled in either our or iginal February 2008 a pplication nor in our May 2010 supplemental submission.

EPA COMMENT: The sources to be considered for inclusion in the PSD nearby source analysis are not limited to a six mile radius.

RESPONSE: EPA has not established any clear guida nce as to the relevant distance to be considered in evaluating the potential fo r nearby sources to contribute to impacts associated with a proposed project. The sour ces to be considered for inclusion in the PSD nearby source have, in most previous pe rmit reviews, been limited to the impact

area itself. 5,6, 7,8,9,10,11,12,13 At the time that the PSD application was submitted, all offsite

3 CEC staff has determined, based on its modeling experience, that there is no statistically significant concentration overlap for non-reactive pollutant concentrations between two stationary emission sources beyond six miles. See, for example, CEC, Hanford Energy Park Peaker Staff Report , Oct. 2009, p. 4.1-25.

4 CEC staff has determined, based on its modeling experience, that emission sources with emissions below 5 tons per year are unlikely to significantly contribu te to cumulative air quality emission impacts. See, for example, CEC, Modesto Irrigation District Woodland Generation Station 2 Commission Decision , Sep. 2001, p. 4-24.

5 Russell City, (BAAQMD Additional Statement of Basis, August 2009, p.87): only sources within a radius of six miles around the facility that had been permitted since January 1, 2007 were considered.

6 Sierra Pacific Loyalton (SPI-Loyalton Ambient Air Qu ality Impact Report 3/19/10): No comparison of annual or 1-hour impacts with SIL; therefore no impact area determin ed; no nearby sources reviewed

7 Navajo Generating Station (Statement of Basis October 2008): CO impacts above SIL. Sources within 100 km of the project were considered for modeling. Largest source identified in that area was 0.04 tpy (Applicant’s Modeling Protocol and Report p. 25); no additional sources were modeled.

8 Morro Bay (Ambient Air Quality Impact Report, May 2006): 24-hour and annual PM 10 impacts were above the SIL. No existing nearby sources were considered for inclusion in the modeling.

9 Calpine-Sutter (Ambient Air Quality Impact Report, July 2009): Annual NO 2 impacts exceeded the SIL. The adjacent Greenleaf facility was incl uded in the modeling. EPA’s analys is is silent as to whether any other sources were modeled, as well as the proces s used to screen nearby facilities for inclusion.

10 Avenal (Statement of Basis, June 2009): 1-hour CO impacts exceede d SIL; EPA accepted the applicant’s analysis (using the CEC cumulative im pact procedure) for identification of nearby sources; no existing sources were considered, and only sources within 6 miles were considered.

11 Colusa Generating Station (Ambient Air Qu ality Impact Report, May 2008): 24-hour PM 10 impacts were above the SIL. All major and minor so urces within 54 km (i.e., distance to edge of impact area plus 50 km) of the project were screened for inclusion in cumula tive impact modeling. The only nearby source that was identified was the adjacent Delevan Compressor Station. This source was included in the cumulative impact modeling performed for the PSD application. See email from Mark Strehlow (URS) to Scott Bohning (EPA), Re: Colusa Generating Station PSD Application , 9/20/2007.

12 Big West (Statement of Basis November 2007): No impacts above SIL, therefore no further consideration of nearby sources7 impacts from the Project were below the relevant SILs with the ex ception of the 1-hour CO standard EPA accepted the APC’s analysis, based on the CEC methodology, for concluding there were no nearby sources that n eeded to be added to the analysis of the Project’s impacts on the 1-hour CO standard. (Both CO a nd NOx emissions are almost exclusively associated with combustion s ources; hence a conclusion that there are no nearby sources of CO that warrant analysis would logically extend to NOx sources as well.)

No SIL has been promulgated for the 1-hour NO 2 NAAQS. 14 At the time that EPA first requested that APC conduct an analysis of the new standard, no guidance existed as to how such an analysis should be performed, and an interim SIL had not been proposed. However, while EPA contemplates a proposal for a SIL, on June 28, 2010, the agency suggested use of an interim level of 4 ppb (m aximum predicted 1-hour concentration) as

a SIL. 15 Using this level, the Project’ s impact area extends to 50 km. 16

The 1990 Draft Guidance recommends extend ing the search for nearby sources beyond the impact area. 17 However, as discussed above, EPA Region 9 has frequently excluded consideration of point sources outside of the impact area as “nearby sources.”

To respond to EPA’s most recent request, and to be even more conservative in approaching this issue, we have performed a new analysis considering point sources within 100 km of the project site for incl usion in the NAAQS inventory for the 1-hour

NO 2 standard.

EPA has considered and accepted several methods for screening sources for inclusion in the NAAQS inventory. These are summari zed in the meeting notes for an EPA/State/Local PSD Workshop he ld in New Orleans in May 2005.

As discussed in the workshop notes:

“The concept of “significant concentration gradient” is used to catch all instances not represented by “regional” monitored concentrations, added to the combined sources’ impacts to determine total impacts, which could interact with the proposed source’s impacts. However, w ithout some practical limitations, such gradients can occur anywhere in the “vic inity” of the sources defined by the SIA and could lead to a large and, at times, unnecessary resource expenditures. Thus,

13 Victorville 2 (Statement of Basis June 2008): No im pacts above SIL, therefore no further consideration of nearby sources

14 75 FR 6525

15 EPA. “General Guidance fo r Implementing the 1-hour NO 2 National Ambient Air Quality Standard in Prevention of Significant Deterioration Permits, Including an Interim 1-hour NO 2 Significant Impact Level”. June 28, 2010.

16 “The impact area is a circular area with a radius extending from the source to (1) the most distant point where approved dispersion modeling predicts a signif icant ambient impact will occur, or (2) a modeling receptor distance of 50 km, whichever is less.” EPA, New Source Review Workshop Manual (Draft),

October 1990 p. C-26. For the Project, this is based on all post-commissioning emission scenarios.

17 EPA, New Source Review Workshop Manual (Draft), October 1990 p. C-328 in order to balance the need for identify ing all sources which meet the criteria in

the Guideline and also to achieve a wo rkable inventory of sources, various permitting agencies have developed and used objective tools to assist in the

determination of an emission inventor y. A 1992 EPA/States modelers workgroup considered some of these approaches and concluded that all such tools should be used by the reviewing authority on a case by case basis to compliment [sic] their professional judgment in developing an inventory of nearby sources.” 18

The “20D Method”, developed by North Ca rolina and discussed at the May 2005 PSD Workshop, is one regulatory method developed for identifying nearby sources with the potential to result in impacts not captured by regional monitoring. The method relies on a

formula derived as 20 times the distance to the source. The method suggests including those sources within the screening area fo r which Q > 20D, where Q is the maximum emission (in tons per year) for the source bei ng screened, and, for short-term analyses, D is the distance (in kilometers) from the sour ce being screened to the PSD source.. For the purposes of this method, the source is defi ned as the facility or complex, not an individual stack or other emission point; therefore, cumulative emissions of each pertinent pollutant go thr ough the screening process.

We considered using the PSD definition of a significant emissions increase for NOx emissions (40 TPY) as the de minimis threshold for excluding a source from consideration. However, we chose to use a much lower threshold of 5 TPY in order to be

consistent with the CEC criteria for cumula tive impact analyses, and to ensure that the analysis was sufficiently conservative to address EPA’s concerns. This value is consistent with past guidance from EPA Region 9. 19

Emission sources were located using the California ARB CHAPIS web site (www.arb.ca.gov/chapis), which graphically displa ys all sources that met one or more of the following in 2001:

a. Sources that emitted at least 10 to ns of VOC, NOx, SOx, CO, or PM10; b. Power plants rated at 50 MW or greater; or c. Air Toxic “Hot Spots” f acilities in the categories of 1) metal fabrication; 2) aerospace/electronics; and 3) chemical plants.

ARB’s Facility Search Tool (http://www. arb.ca.gov/app/emsinv/facinfo/facinfo.php?dd) was used to determine whether any relevant sources in the 2008 inventory had been

overlooked.

The results of this analys is are shown in Table 3.

18 PSD Modeling Workgroup. EPA/State/Local Workshop. New Orleans, May 17, 2005.

19 Memo Scott Bohning (EPA) to Mark Strehlow (URS), CGS status note , October 3, 2007.9 Table 3

Identification of Potential Sources Considered for Inclusion in the 1-hour NO 2 Impact Analysis

Facility 2008

NOx emissions (TPY) Distance

from Project Site (km) Q/D (TPY/Km) Include as Nearby

Source? *

PG&E 25.2 3 8.4 No

Avenal State Prison 9.3 14 0.7 No

Los Gatos Tomato 9.7 13 0.7 No

NAS Lemoore 30.9 24 1.3 No Shell Pipeline Co. 16.1 27 0.6 No Aera Energy LLC 66.6 29 2.3 No

Coalinga Cogen 23.8 29 0.8 No

Chevron USA Inc. 169.5 31 5.5 No

Paramount Farms 11.0 34 0.3 No Del Monte Corporation 11.4 40 0.3 No

Hanford L P 36.5 42 0.9 No

Nichols Pistachio 5.8 43 0.1 No

Samson Resources Company 15.7 42 0.4 No

Sources > 50 km and < 100 km and > 100 TPY Madera County

No sources San Benito County

No sources Monterey County

No sources Fresno County

Guardian Industries 193.2 66 2.9 No

PPG Industries 280.9 73 3.8 No Tulare County

No sources Kern County AERA Energy 386.9 78 5.0 No

Chevron USA 370.4 100 3.7 No

Chevron USA 104.9 80 1.3 No

Covanta Delano 169.9 84 2.0 No La Paloma Generating Co. 135.6 98 1.4 No Plains Exploration &

Production 228.2 <4.6 No

Rio Bravo Jasmin 140.6 62 2.3 No

Rio Bravo Poso 143.9 62 2.3 No

* Sources are included as a nearby source if Q/D > 20, which is mathematically identical to Q > 20D.10 Table 1 shows that there are no facilities both large enough and close enough to the project to be included in th e NAAQS inventory. All sources ar e far enough away that it is unlikely that impacts will interact appreciab ly with project’s short term impacts.

EPA COMMENT: The sources to be considered for inclusion in the PSD nearby source analysis are not limited to new sources (i.e., sources not constructed or operated during the period that monitoring data were collected).

RESPONSE: As discussed above, the PSD nearby s ource analysis has been revised to include existing point sources.

EPA COMMENT: The sources to be considered for inclusion in the PSD nearby source analysis are not limited to stationary sources.

RESPONSE: This comment is puzzling and appears to be inconsistent with EPA’s longstanding written guidance and practice. No r can we discern any reason why the 1-hour

NO 2 standard would warrant a departure from the Agency’s long-standing approach to PSD modeling. For many years, there has been a 1-hour CO standar d, and mobile source emissions in most parts of the county repres ent the largest portion of the CO emissions inventory. Yet, to the best of our knowle dge, EPA does not require, and has not required, modeling of mobile source CO emissions fo r PSD compliance determinations. This is obviously sensible, as the impact of mobile sources is alread y reflected in the monitoring data. Whether the pollutant at issue is CO or NOx is not relevant to this matter.

In addition, the Draft NSR Workshop Ma nual provides the following guidance on determining the ambient background concentr ation for PSD compliance determinations:

“The Modeling Guideline defines a "nearby" source as any point source expected to cause a significant concen tration gradient in the vi cinity of the proposed new

source or modification.” 20 (emphasis added)

“Also, if the location of the proposed s ource or modification is not affected by

other major stationary point sources , the assessment of existing ambient concentrations may be done by evalua ting available monitoring data. It is generally preferable to use data collecte d within the area of concern; however, the possibility of using measured concentrations from representative "regional" sites may be discussed with the permitting agency. The PSD Monitoring Guideline provides additional guidance on the use of such regional sites.” 21 (emphasis added)

Appendix W contains the following requirement to include nearby sources in modeling to demonstrate compliance with ambient standard s: “For compliance with the short-term and annual ambient standards, the nearby source s as well as the primary source(s) should

20 EPA, New Source Review Workshop Manual (Draft), October 1990 p. C.32

21 EPA, New Source Review Workshop Manual (Draft), October 1990 p. C.1811 be evaluated using an appropriate Appendix A model with the emi ssion input data shown

in Table 8-1 or 8-2.” 22

Table 8-1 is entitled “Model Emission Input Data for Point Sources” [emphasis added]. 23

Table 8-2 is entitled “ Point Source Model Input Data for NAAQS Compliance in PSD Demonstrations” [emphasis added]. 24

EPA recently issued guidance on how to address the new 1-hour NO 2 standard in PSD permit applications. 25 This guidance includes an extens ive discussion on construction of the inventory for PSD analysis. There is no thing in this discussion to suggest an expansion of the PSD NAAQS modeling requi rements to include non-point sources.

In addition to this guidance, we can fi nd no evidence that EPA Region 9 has included sources other than stationary sources in an analysis of “nearby sources” for a NAAQS inventory

EPA COMMENT: In addition, background monitoring data may not reflect existing sources operating at their full operating capacity. 40 CFR Part 51, Appendix W, Subsection 8.2.1.c. states that "[s]ince sources don't typically operate at their maximum allowable capacity (which may include the use of 'dirtier' fuels), modeling is necessary to express the potential contribution of backgr ound sources, and this impact would not be captured via monitoring. Background concen trations should be determined for each critical (concentrati on) averaging time."

RESPONSE: The language cited by EPA refers to the operating parame ters that should

be modeled once a point source has been determined to be a nearby source, not the basis for determining whether the point source is a nearby source in the first place. This therefore becomes an issue only after an existi ng point source has been identified to be a nearby source, due to its potenti al to create a significant concentration gradient in the impact area.

For example, the modeling protocol for the Co lusa Generating Station first identified the adjacent Delevan Compression Station as an existing major source, containing three gas turbine-driven compressors li censed for full-year operation. Hi storical usage records for the turbines were used to estimate past ac tual emissions. Because impacts from past

actual emissions were included in ambien t monitoring data, the cumulative modeling

included the difference between estimated past actual emissions and the maximum potential emissions allowed by permit. 26

22 Guideline on Air Quality Models (40 CFR Part 51, Appendix W), Section 8.2.3.c

23 Guideline on Air Quality Models (40 CFR Part 51, Appendix W), Table 8-1

24 Guideline on Air Quality Models (40 CFR Part 51, Appendix W), Table 8-2

25 EPA. “General Guidance fo r Implementing the 1-hour NO 2 National Ambient Air Quality Standard in Prevention of Significant Deterioration Permits, Including an Interim 1-hour NO 2 Significant Impact Level”. June 28, 2010

26 URS, Modeling Protocol for the Colusa Generating Station, July 12, 2006, p. 4-1212 As discussed above, there are no nearby sour ces relevant to the analysis of AEP’s impacts on the 1-hour NO 2 standard.

EPA COMMENT: Adequate documentation of the Distri ct's response [to the request for information about local sour ces] is not provided.

RESPONSE: The inventory data for the few sour ces in the vicinity of the proposed project site identified by the Di strict are attached as Att achment 1, along with the letter requesting the information and the District’s response (the last three pages of the attachment). This attachment formed Appendix 6.2-6 in the original February 2008 submittal of the application for a PSD permit.



### Modeling

Responses to EPA’s comments on the justification for use of the non-regulatory-default PVMRM option in AERMOD are provided below.

Provision i

EPA COMMENT: The model has received a scientific peer review: This provision is adequately addressed.

RESPONSE: Noted.

Provision ii

EPA COMMENT: The model can be demonstrated to be applicable to the problem on a theoretical basis: This provision is not ade quately addressed. That th e project is located in an area of high ozone concentrations doe s not necessarily just ify the use of PVMRM, nor does it necessarily imply a particular bias or lack of bias in the results.

RESPONSE: AERMOD without PVMRM is a disp ersion model. It predicts groundlevel concentrations ba sed on distribution of emissions fr om the sources being modeled. However, the NOx emitted at the stack is a mixture of (primarily) NO and NO 2 . If

conversion of stack NO to NO 2 in the atmosphere is not ta ken into account, the model will underpredict NO 2 impacts. At the same time, if the unrealistic assumption is made that 100% of stack NO is converted to ground-level NO 2 at all receptors, regardless of transport time, transport distance, or ambien t ozone concentrations, the dispersion model will overpredict NO 2 impacts. Conservative assumptions are initially used in compliance screening methodologies in order to assure compliance. As the compliance evaluation methodology becomes more sophisticated, the greater accuracy co ntinues to assure compliance while allowing less conservative a ssumptions. EPA addresses this process, in

the context of the 1-hour NO 2 standard, through increasingly sophisticated (and less conservative) tiers of analysis.13 The regulatory default modeling methodologies for the 1-hour NO 2 standard are screening methodologies. 27

Tier 1: Assume full conversion of NO to NO 2 based on application of an appropriate refined modeling technique under Section 4.2.2 of Appendix W to

estimate ambient NOx concentrations.

Tier 2: Multiply Tier 1 re sult by empirically-derived NO 2 /NOx ratio, with 0.75 as

the annual national default ratio.

Tier 3: Detailed screening methods may be considered on a case-by-case basis, with the Ozone Limiting Method (OLM) identified as a detailed screening technique for point sources. PVMRM is al so considered by EPA to be in this category at this time. 28

Consistent with USEPA guidelines, the District has issued more detailed guidance that provides a four tier approach to modeli ng that tests compliance with the 1-hour NO 2 NAAQS. The District applied Tiers I thr ough III to the Project’s emissions during normal operation and startup to demons trate compliance with the 1-hour NO 2 NAAQS, and also applied Tier IV to commissioning emissions to demonstrate compliance. The detailed descriptions of the tiered approaches follow: 29

1. Tier I

a. The maximum 1-hour NO 2 concentration is modeled from all sources in a project using AERMOD, five years of meteorological data, and the assumption of complete conversion of NO to NO 2 . The maximum

modeled concentration is added to the representative background concentration provided by the District.

i. If the maximum combined concentration is less than the 1-hour

NO 2 NAAQS, the analysis is complete and compliance with the

standard has been demonstrated.

ii. If the maximum combined concentration exceeds the 1-hour NO 2 NAAQS, then the maximum mode led concentration alone is compared to the interim SIL of 4 ppb.

1. If the maximum modeled concentr ation is less than the SIL, then the analysis is comple te and compliance with the

standard has been demonstrated.

2. If the maximum modeled concentration exceeds the SIL, then the analysis must continue as described next using the

27 EPA, Appendix W Section 5.2.4. See also Memorandum from Wood to Regional Air Division Directors, General Guidance for Implementing the 1-hour NO 2 Standard in Prevention of Significant Deterioration

Permits , June 28, 2010, p.14.

28 Memorandum from Wood to Regional Air Division Directors, Applicability of Appendix W Modeling Guidance for the 1-hour NO 2 NAAQS , June 28, 2010, p.2

29 SJVAPCD. Assessment of Non-Regulatory Options in AERMOD, Specifically OLM and PVMRM, August 19, 2010. Appendix A, Modeling Protocol.14 Ambient Ratio Method (ARM) value of 0.9 for the

conversion of NO to NO 2

. b. The maximum 1-hour NO 2 concentration is modeled from all sources in a project using AERMOD, five years of meteorological data, and the application of a default Ambien t Ratio Method (ARM) value of 0.9 instead of complete conversion of NO to NO 2 . Again, the maximum

modeled concentration is added to the representative background concentration provided by the District.

i. If the maximum combined concentration is less than the 1-hour

NO 2 NAAQS, the analysis is complete and compliance with the

standard has been demonstrated.

ii. If the maximum combined concentration exceeds the 1-hour NO 2 NAAQS, then the maximum mode led concentration alone is compared to the interim SIL of 4 ppb.

1. If the maximum modeled concentr ation is less than the SIL, then the analysis is comple te and compliance with the

standard has been demonstrated.

2. If the maximum modeled concentration exceeds the SIL, then the analysis must conti nue as described next using

AERMOD PVMRM or OLM.

c. The maximum 1-hour NO 2 concentration is modeled from all sources in a project using AERMOD PVMRM or OLM, and five years of meteorological data. The maximum m odeled concentration is added to the representative background concen tration provided by the District.

i. If the maximum combined concentr ation is less than the 1-hour

NO 2 NAAQS, the analysis is complete and compliance with the

standard has been demonstrated.

ii. If the maximum combined concentration exceeds the 1-hour NO 2 NAAQS, then the maximum mode led concentration alone is compared to the interim SIL of 4 ppb.

1. If the maximum modeled concentr ation is less than the SIL, then the analysis is comple te and compliance with the

standard has been demonstrated.

2. If the maximum modeled concentration exceeds the SIL, then the analysis must continue as described next in Tier

II.

2. Tier II: The Tier II method is iden tical to Tier I ex cept that the 8 th highest

modeled concentration re places the maximum modele d concentration in the analysis.

3. Tier III: The 98th percen tile 1-hour predicted concentr ation is determined using the post-processor developed by the Distri ct, third-party software developers, 30 or an EPA-revised version of AERMOD. This concentrati on is used in the same stepwise approach described for Tier I above.

30 Sierra Research developed and used such a post-p rocessor in preparing the May 13, 2010 submittal to

EPA.15 4. Tier IV: The predicted 1-hour NO 2 concentrations from the model are paired in

time with the monitored 1-hour NO 2 concentrations. The same approach as

identified above for Tier III is used to calculate a final concentration to compare

with the standard.

The Project’s May 13, 2010 submittal of the supplemental 1-hour NO 2 air quality impact analysis used a Tier IV approach. The only difference between the May 13, 2010 submission and the enclosed, revised submissi on is that meteorological and background

ozone and NO 2 data are based on more recent da ta prepared (and required) by the SJVAPCD, reflecting an updated data substitution methodology that complies with EPA and District requirements.

Under EPA’s interim guidance for eval uating compliance with the 1-hour NO 2 NAAQS, the SIL-equivalent is so low that almost any moderate-to-large combustion source will have difficulty passing a screen ing assessment. It is ther efore necessary to use more sophisticated analytical tools, as provided for in EPA guidance. One such tool identified by both EPA and the District, and selected for use with the Project, is the PVMRM option

within AERMOD.

AERMOD-PVMRM has been tested specifica lly for its ability to compute unbiased results. One of the key studies was conduc ted by a senior modeler currently in OAQPS at EPA, and conducted on large natural gas-fired power plants. 31 The study concluded the following: “Based on all of the data available, the AERMOD-PVMRM algorithm is judged to provide unbiased estimates of the NO 2 /NO x ratio based on criteria that are comparable to, or more rigorous than, evaluations performed for other dispersion models that are judged to be refined,”

In addition, the District conducted a caref ul review of both the PVMRM and OLM options in the implementation of AERMOD to demonstrate regulatory compliance of

new sources. 32 The District evaluation took into account and described compliance of the PVMRM option with the fo llowing five requirements 33 for approval to use an “alternative refined model”, as PVMRM is defined by EPA:

“i. The model has received a scientific peer review; ii. The model can be demonstrated to be applicable to the problem on a theoretical basis; iii. The data bases which are necessary to perform the analysis are available and adequate; iv. Appropriate performance evaluations of the model have shown that the model is not biased toward underestimates; and

31 Brode, Roger W. Final Report, Evaluation of Bias in AERMOD-PVMRM, MACTEC report on Alaska Department of Environmental Conservation Contract No. 18-9010-12, June 2005.

32 SJVAPCD. Assessment of Non-Regulatory Options in AERMOD, Specifically OLM and PVMRM, August 19, 2010.

33 USEPA. Guideline on Air Quality Models (40 CFR Part 51, Appendix W), Section 3.2.2.e16 v. A protocol on methods and procedures to be followed has been established.” 34

The District evaluation of AERMOD-PVMRM concluded th e following: “Based on the information provided above, the District has determined that the method for determining hourly NO 2 concentrations using AERMOD in c onjunction with the non-regulatory OLM or PVMRM options is acceptable based on the requirements in 40 CFR Part 51, Appendix W, 3.2.2(e)...” 35

For all of the above reas ons, the PVMRM option within AERMOD is demonstrably applicable to a refined an alysis of 1-hour average NO 2 impacts from the Project on a

theoretical basis.

Provision iii

EPA COMMENT: The data bases which are necessa ry to perform the analysis are available and adequate: The info rmation provided in paragra ph 2 in Avenal's June 28, 2010 letter discusses the use of the ozone dat a submitted by Avenal in the PVMRM option within AERMOD, but does not provide adequate ju stification for use of the ozone data in this context for purposes of the PSD program.

RESPONSE: This comment is addressed in the di scussion of ambient monitoring data,

below.

EPA COMMENT: "This analysis should include a disc ussion of the representativeness of the surface characteristics. The surfa ce characteristics input to AERMET should be

based on the land cover characteristics in the vicinity of the meteorological tower. The information provided in the response doe s not adequately address EPA's comment. The response does not provide (1) information about the surface characteri stics at the project site, (2) specific informati on about the surface characteri stics for the meteorological station that were computed by the District, or (3) a discussi on of how the specific surface

characteristics at the meteor ological station are representa tive of the specific surface characteristics at the project site. Avenal should prov ide this information.

RESPONSE: As stated in our May 13, 2010 submittal of the Supplemental NO 2 Air Quality Impact Analysis, the District required use of, and the analysis used, meteorological data collected and prepared by the District from their Hanford monitoring station. The District, not the applicant, preprocessed the meteorological data using

AERMET for use in AERMOD. As stated in the May 13 submittal, “The surface characteristics appropriate for the land uses surrounding the meteorological station at Hanford—namely surface roughness length, albedo, and Bowen Ratio—were computed by the District. The meteorologi cal data set used for this anal ysis is unchanged from that

34 SJVAPCD. Assessment of Non-Regulatory Options in AERMOD, Specifically OLM and PVMRM, pp. 2- 6, August 19, 2010.

35 SJVAPCD. Assessment of Non-Regulatory Options in AERMOD, Specifically OLM and PVMRM, p. 5, August 19, 2010.17 used to develop the air quality impact an alysis in the February 2008 PSD and FDOC permit applications.”

The District has provided the detailed surface characteristic information EPA requests for the Hanford meteorological station on pages 37-47 and 96 in Version 1.2 of their August

2006 Guidance for Air Dispersion Modeling. (The indicated pages are attached to this submittal as Attachment 2.) The District believes that, the procedure and resulting

surface characteristic information for AERMET “in the vicinity of the meteorological tower” described therein was fully compliant with USEPA requirements existing in 2006 for the 2000-2004 meteorological data used in the project modeling and ambient air quality impact analysis. 36 The meteorological tower is located near the center of the north-northwest south-southeast aligned runway. Roughly two-thirds of the area surrounding the tower is agriculture as can be seen in the aerial image on page 96 of the attached District guidance pages.

The District believes that the surface ch aracteristics (surface roughness, albedo and Bowen ratio) near the project site are similar to those around the meteorological tower because the area on and around the project site is agricultural in use, as is the dominant portion (i.e., two-thirds) of the area around the meteorological tower. The similarity between the two locations, in terms of the three basic para meters required by AERMET, increased for the processing of the more recent meteorological data (i.e., 2005-2009) provided by the District because USEPA reduced the radius for the evaluation of surface characteristics from the 3 km used in pr ocessing the original, 2000-2004 meteorological data set to 1 km, which was used to pro cess the revised 2005-2009 meteorological data

set. This reduction in radius removed much of the land use that was different between the two locations (i.e., suburban and urban land use). 37

Both locations have similar se asonal distributions of rainfa ll as shown in Table 4, with the maximum monthly rainfall occurring in Ja nuary and no monthly ra infall in July and August.

36 The District informed Carol Bohnenkanp of EPA Region 9 about its methodology through several telephone conversations with Leland Villalvazo during the period of May through December 2006 (SJVAPCD. Email from Glenn Reed to Eric Walther of Sierra Research, August 30, 2010.)

37 SJVAPCD. Telephone conversation between Leland Villalvazo and Eric Walther of Sierra Research, August 30, 2010.18 Table 4 Average Rainfall a (inches)

Month Avenal b Hanford c

January 1.6 1,6 February 1.4 1.6

March 1.0 1.4 April 1.1 0.8 May 0.6 0.2

June 0.0 0.1 July 0.0 0.0 August 0.0 0.0 September 0.1 0.1

October 0.2 0.4

November 0.6 0.8

December 0.3 1.3

Year 6.9 8.4

a Correlation coefficient = 0.99

b Avenal rainfall data (National Climatic Data Center [NCDC] Cooperative Stations, 1955-1961, http://www.worldclimate.com/cgi-bin/da ta.pl?ref=N35W120+2200+040398C).

c Hanford rainfall data (NCDC Cooperative Sta tions, 1931-1995, http://www.worldclimate.com/cgibin/data.pl?ref=N36W119+2200+043747C).

EPA COMMENT: The response does not provide an analysis supporting the conclusion that the project site and the Camp Pendl eton meteorological monitoring station are climatologically similar; this analysis should be provided.

RESPONSE: The sentence at the top of page 222 in the applicant’s June 28, 2010 submittal erroneously referred to Camp Pendleton. The sentence should have said “Hanford meteorological data”, not “C amp Pendleton meteorological data”.

Relative to the Hanford meteorological mon itoring site, the climatology of Hanford and the Avenal Energy Project site are closely similar because of the following:

1. Both sites are in the same county (Ki ngs County) and the same flat Central Valley, separated by only 28 miles.

2. Both sites are accurately described by the same climatology contained in the original February 2008 application subm itted to the USEPA, CEC and SJVAPCD,

as follows:

“USEPA defines the term ‘on-site data’ to mean data that would be representative of atmospheric dispersion conditions at the source and at locations where the source may have a significant impact on air quality. Specifically, the meteorological data requirement originates in the Clean Air Act at Section 165(e)(1), which requires an analysis ‘of the ambient air quality at the proposed site and in areas which may be affected by emissions from such facility for each19 pollutant subject to regulation under [the Act] which will be emitted from such facility.’

“This requirement and USEPA’s guidance on the use of on-site monitoring data

are also outlined in the ‘ On-Site Meteorological Program Guidance for Regulatory Modeling Applications ’ (1987a). The represen tativeness of the data depends on (a) the proximity of the mete orological monitoring site to the area under consideration, (b) the complexity of the topography of the area, (c) the exposure of the meteorological sensors, and (d) the period of time during which

the data are collected. The District ’s Hanford meteorological data are representative of conditions at the project site relative to these four factors as

follows:

a) The meteorological monitoring station is 28 miles from the project site on a flat valley; b) The topography at and between the two sites is flat; c) The meteorological sensors are locate d near the center of the northnorthwest/south-southeast aligned runw ay at the Hanford airport, giving them the same unobstructed exposure to wind that would be experienced at the Project site; and d) The five years of meteorological data used in the original supplemental modeling submissions (2000-2004) were coincident with the ambient ozone data used therein, and the five y ears of meteorological data used in the new modeling submittal herein ( 2005-2009) is coincident with the

ambient ozone and NO 2 data used for the 1-hour NO 2 analysis.

“Representativeness has also been defined in the ‘ Workshop on the Representativeness of Me teorological Observations ’ (Nappo et. al., 1982) as ‘the

extent to which a set of measurements taken in a space-time domain reflects the

actual conditions in the same or differe nt space-time domain taken on a scale appropriate for a specific application.’ Re presentativeness is best evaluated when sites are climatologically similar, as are the project site and the Hanford meteorological monitoring station. Repr esentativeness has additionally been defined in the PSD Monitoring Guid eline (USEPA 1987b) as data that characterize the air quality for the gene ral area in which the proposed project would be constructed and operated. Becau se of the relative proximity of the Hanford meteorological data site to the proposed project site, the same large-scale topographic features that influence the meteorological data monitoring station also influence the proposed projec t site in the same manner. “ 38

38 Sierra Research. Air Dispersion Modeling and Health Risk Assessment Protocol, Avenal Energy Project, Kings County, California, Section 5, p. 5, August 2007.20 Further to the EPA question about the climatological similarity of the project site and the meteorological monitoring site is the followi ng climate information, taken from Section 6.2.1.2 of the February 2008 application: 39

“The climate of the San Joaquin Valley is characterized by hot summers, mild winters, and small amounts of precipitati on. The major climatic controls in the Valley are the mountains on three sides and the semi-permanent Pacific High pressure system over the eastern Pacific Ocean. The Great Basin High pressure system to the east also affects the Valle y, primarily during the winter months. These synoptic scale influences result in distinct seasonal weat her characteristics,

as discussed below.

“The Pacific High is a semi-permanent s ubtropical high pressure system located

off the Pacific Coast. It is centere d between the 140°W and 150°W meridians,

and oscillates in a north-south direction seasonally. During the summer, it moves northward and dominates the regional clim ate, producing persistent temperature inversions and a predominantly southw esterly wind field. Clear skies, high temperatures, and low humidity character ize this season. Precipitation rarely occurs during summer months, because migrating storm systems are blocked by the Pacific High. Occasionally, however, tropical air moves into the area and thunderstorms may occur over the adjacent mountains.

“In the fall, the Pacific High weakens and shifts southwestward toward Hawaii,

and its dominance is diminished in the San Joaquin Valley. During the transition period, the storm belt and zone of strong westerly winds also moves southward into California. The prevailing weather pa tterns during this time of year include storm periods with rain and gusty winds , clear weather that can occur after a storm or because of the Great Basin High pr essure area, or persistent fog caused by temperature inversion. The average annua l rainfall at the site is approximately 7 inches, of which approximately 70% falls in the four months of December through March. Temperature, winds, and rainfall are more variable during the fall and winter months, but al so stagnant conditions occur more frequently than during summer. ( Climates of the States – Ca lifornia, U.S. Department of Commerce, Weather Bureau , 1959.)

“Wind and mixing height are two key mete orological parameters that govern the potential for air pollution problems. The predominant winds in California are shown in Figures 6.2-1 through 6.2-4. ( The Uses of Meteorological Data in Large-Scale Air Pollution Surveys , Stanford Research Institute, 1958). As the figures indicate, winds in Ca lifornia are generally light and easterly in the winter, but strong and westerly in the spring, summer, and fall.

“Wind patterns in the genera l area of the project site are presented in Figures 6.2- 5a through 5y, which show annual and quarterly wind roses for the Hanford,

39 Application to the U.S. EPA for a Pr evention of Significant Deterioration Permit, Avenal Energy Project, Kings County, California. Section 6.2.1.2, pp. 6.2-2 through 6.2-4, February 2008.21 California monitoring station. Hanford is approximately 28 mile s northeast of the site, and is the closest station for ai r quality and meteorological monitoring (discussed in more detail in Sections 6.2.3 and 6.2.5, respectively. Approximately half of all winds come from the northwest quadrant, and calm winds occur approximately one-quarter of the time.

“Concerning mixing heights, inland areas, where marine influence is weak or nonexistent, experience strong ground-base d inversions, which inhibit mixing and can result in high pollutant concentrations. An example case available from the central part of the San Joaquin Valley is Fresno. Smith, et al (1984), reported that at Fresno, 50th percentile morning mi xing heights for the period 1979-80 were 115-150 meters (approximately 375-495 feet ) in the fall and winter, 230 meters (755 feet) in the spring, and 175 meters (575 feet) in the summer. Such low morning mixing heights trap pollutants, at least during the morning. The 50th percentile afternoon mixing heights, how ever, were unlimited in spring and summer, 1135 meters (3,725 feet) in the fa ll, and 630 meters (2,065 feet) in the winter. Such mixing heights provide generally favorable conditions for the dispersion of pollutants.”

EPA COMMENT: Since the spatial scope of each variable could be different, representativeness should be judged for each variable separately. For example, for a variable such as wind direction, the data may need to be collected very near plume height to be adequately representative, whereas, for a variable such as temperature, data from a station several kilometers away from the sour ce may in some cases be considered to be adequately representative. Avenal should address this issue in its analysis.

RESPONSE: The representativeness of the Hanford meteorological data was justified in the discussion contained in the air dispersion modeling protocol submitted to Region 9 in August 2007. Please refer to that document fo r details. The analysis is summarized

below.

“The meteorological data from the Hanfor d monitoring station are representative of conditions at the Project because the area is extremely flat both between the two locations and over a much larger ar ea to the northwest and southeast along the alignment of the San Joaquin Valley. Air flow in the valley (including both locations) can be characterized by up-v alley and down-valley winds. The downvalley winds are generally a result of airf low into the Valley from the Carquinez

Strait and the Altamont Pass that then flow south. Strong diurnal wind regimes markedly affect the horizontal transport of ai r in the project area. This results in a pronounced north-northwest component to the wind roses shown in Figures 2A through 2E for 2000-2004, respectively. Modeling for each of the five years of22 available data 40 will not vary much because the meteorological data are so constant between the years.” 41

Because of the relative proximity of the Hanf ord meteorological data site to the proposed project site, the same large-scale topographi c features that influe nce the meteorological data monitoring station also influence the proposed project site in the same manner.

The upper air data is necessarily representa tive of a large geographic domain because of the large distances between upper air meteorological monitoring stat ions. The upper air data also reasonably represents conditions at the higher altitudes of plumes from large sources such as the proposed F-Class combustion gas turbines.

This analysis, and the use of the Hanford stat ion meteorological data as representative of the Project site, was accepted by EPA for purpos es of analysis of the Project’s impacts on the 1-hour and 8-hour CO standards, the 24-hour and annual average PM 10 standards, and the annual average NO 2 standard. We are unaware of any scientific reason why meteorological data which are acceptably repr esentative for these pollutants would not also be representative in the context of a 1-hour NO 2 standard.

Provision iv

EPA COMMENT: Appropriate performance evaluations of the model have shown that

the model is not biased toward underestimates : This provision is ade quately addressed.

RESPONSE: Noted.

Provision v

EPA COMMENT: A protocol on methods and procedures to be followed has been established: This provision is not adequat ely addressed, and was not approved in the previous submittals. Please provide a protoc ol that is consistent with the comments

stated above.

RESPONSE: The August 2007 modeling protocol for the project was resubmitted to EPA on May 5, 2010, with a request for EPA comme nts regarding four elements of that protocol proposed to be car ried forward to the 1-hour NO 2 analysis. EPA did not respond to that request. Nonetheless, a supplementa l protocol for demonstration of compliance

with the 1-hour NO 2 standard is attached.

40 SJVAPCD. Hanford meteorological data in AERMOD-compatible format, http://www.valleyair.org/busind/pto/Tox_Resources/AirQualityMonitoring.htm

41 Sierra Research. Air Dispersion Modeling and Health Risk Assessment Protocol, Avenal Energy Project, Kings County, California, Section 4, p. 4, August 2007.23 Scenario Selection

EPA COMMENT: We note that the 1-hour scenario is based on a combination of the following: (a) Case 4 (from vendor data) t hat represents 50% load and 101 degrees F; and (b) a cold start estimate of 80 lbs/hour (each), which appears to be based on a compilation of other facilities' cold start data. The information provided to date is insufficient and should demonstrate why th e parameters for the proposed 50% load and 101 degrees F case represent the worst-case 1- hour NOx scenario; i.e., why other loads (e.g., 60%, 75%) and other ambient conditions were not considered or demonstrative of

the worst-case 1-hour NOx emission rate.

RESPONSE: The worst-case 1-hour NOx emission rate from the Project was shown in the February 2008 PSD applica tion to be 160 lbs/hr per uni t during a turbine startup. 42
The analysis in the February 2008 PSD app lication went beyond identification of the worst-case 1-hour emission rate to identify combinations of emission rates and operatingscenarios that result in the worst case 1-hour impacts. The demonstration of the worstcase scenarios for the 1-hour NOx analysis was contained in the February 2008 PSD application. The maximum 1-hour NOx emi ssion case for one turb ine occurs during a cold startup. 43 The maximum 1-hour NOx emission case for two turbines occurs during the simultaneous cold startup of two turbines. 44 A screening air dispersion modeling analysis was conducted to determine the co mbination of turbine operation and ambient temperature which resulted in the maximum impact. In this analysis, the following

combinations were evaluated:

 100% and 50% load (i.e., these two loads bracket the infinite number of possible intermediate loads; there are no known non-linearities in turbine emissions

characteristics which would render thes e two conditions unrepresentative of extremes in project operations)

 With and without duct burner firing

 Three bracketing ambient temperatures:

o Extreme hot (101F)

o Annual average ( 63°F)

o Extreme cold (32°F)

EPA correctly notes that the maximum start up impact occurred with the combination of 50% load (startup conditions) and extreme hot ambient temperature.

Note that the use of cold st artup emission characteristics (abnormally high emission rates, low stack velocity, low stack temperature) results in a signifi cantly conservative

estimation of the 98 th percentile ground level impact. A cold startup is a rare event

42 Application to the U.S. EPA for a Pr evention of Significant Deterioration Permit, Avenal Energy Project, Kings County, California, Table 6.2-23. February 2008.

43 Application to the U.S. EPA for a Pr evention of Significant Deterioration Permit, Avenal Energy Project, Kings County, California, Appendix 6.2-1 Table 6.2-1.8 and Appendix 6.2-2 Table 6.2-2.5,February 2008.

44 Id.24 relative to other operating c onditions. The compliance demonstration assumes that both turbines are in cold startup mode at the same time, and not merely during the worst possible hour of the year from the standpoint of project imp act; this operating condition is assumed to occur during each of the next 6 or 7 worst possible hours of the year when, in fact, it is unlikely that such an event would occur more than once or twice per year.

The suitability of this screening analysis for defining worst case emission rates and dispersion characteristics was accepted by EPA fo r purposes of analysis of the Project’s impacts on the 1-hour and 8-hour CO sta ndards, the 24-hour and annual average PM 10 standards, and the annual average NO 2 standard. We are unaware of any scientific reason why the worst case emission rates and disper sion characteristics which are acceptably representative for these pollutants would not al so be representative in the context of a 1-

hour NO 2 standard.

Stack NO 2 /NOx ratios

EPA COMMENT: Avenal has selected the in-stack NO 2 /NOx ratio for the two combustion turbines as follows: equal to 0.25 for normal operations and equal to 0.4 for startup and commissioning operations. Avenal did not provide the specific background information cited for EPA in support of the se lection process. Ave nal stated that the ratios were "derived from source test dat a." EPA needs to confirm the proposed conservative ratios for use in the 1-hour NO 2 NAAQS air quality modeling

.

The applicant should provide the source test data, which the SDAPCD furnished, that Avenal has relied upon to develop the 0.25 and 0.4 ratios. This should include, at a minimum, source test results, source test suppo rt information to c onfirm test conditions and equipment operations, and the source te st methodology. The applicant should confirm if the source test data relied upon is a result of emissions co mpliance testing or a result of other circumstances. Based on this information, the applic ant should provide a discussion that demonstrates the repres entativeness and compar ability of this information for Avenal's selection of the proposed ratios for normal, startup and commissioning operations.

RESPONSE: The SDAPCD based its recommendation regarding NO 2 /NOx ratios on the

results of source tests conducted under S DAPCD supervision at the Palomar Energy Center. The emission compliance tests c onducted on January 25 and 27, 2006 for Units 2 and 1, respectively (see Attachment 3) provide d the basis for the recommended ratio of 0.25 during normal operation of F-Class gas tu rbines burning natu ral gas and equipped with dry low-NOx combustors, selective cataly tic reduction and oxidati on catalysts. The SDAPCD analyzed the results of startup tests at the same facility conducted on May 3, 4, 18, and 23, 2006 (see Attachment 4) to deve lop the recommended ratio of 0.40 during startup operation. These recommendations were contained in a November 13, 2006

internal email from Steve Moore of the S DAPCD (Attachment 5). A later, confirming source test (Attachment 6), which was focused on the first hour of startup, indicated a

lower NO 2 /NOx ratio of close to 5% but the Dist rict decided to keep their conservative25 recommendation of 0.40 for the NO 2 /NOx ratio during startups. 45 The latter test was specifically requested by the SDAPCD to determine emissions during the first hour of a cold start, which would produce the highest hourly NOx emission rates. All of these tests were performed on a GE F-Class turbine, es sentially identical to the gas turbines proposed for the Avenal Energy Project.

Estimates of impacts during commissioning ac tivities were performed in support of the application for certification from the CEC. Commissioning impacts are not reviewed as part of the PSD permit process. 46

EPA COMMENT: If the development of the normal, startup, and commissioning ratios

also were based on another method other than source testing, the applicant should provide the information that Avenal has relied upon. For instance, if continuous emissions monitoring also was relied upon, pl ease provide a discussion that also demonstrates the representative and comparab ility of this information for Avenal's selection of the proposed ratios.

RESPONSE: The ratios were developed by the SDAPCD from the indicated source tests, not from another method.

EPA COMMENT: San Diego APCD Recommendations: Avenal stated that the proposed instack ratio values of 0.25 and 0.4 were" ... recommended by San Diego Air Pollution Control District for the m odeling on another large-scale combined-cycle gas turbine project." The applicant should include th e SDAPCD's recommendation and rationale.

RESPONSE: The SDAPCD rationale was that the performance of the Palomar Energy Center GE F-Class gas turbines would be indicative of the performance of F-Class turbines proposed for other projects. The November 13, 2006 internal email from Steve Moore, Senior Engineer at the SDAPCD , recommending use of the indicated NO 2 /NOx

ratios is attached as Attachment 5.



### Ambient Monitoring Data

Responses to EPA’s comments on the represen tativeness of ambient monitoring data are presented below.

General

EPA COMMENT: The statements that the source is 28 miles northeast of the project site, is the closest sour ce, and is adequately close, are not su fficient to show that the data

45 SDAPCD. Telephone conversation between Steven Moore, Senior Engineer, and Eric Walther of Sierra Research, August 26, 2010.

46 See, e.g., memorandum from P. Culver, EPA to file dated 9/25/1978 indicating that “boil-out” of a coalfired steam generator was a part of source construction, and did not constitute startup for purposes of PSD. The high-emission rate aspects of commissioning a combined cycle power plant are analogous to boiler “boil-out”. Air quality impacts during commissioning were not addressed in EPA’s June 2009 Statement of Basis and Air Quality Impact Report for the Project.26 is representative. The discussion of repr esentativeness for ambient air quality data should be specific to the pollutant for the appropriate averaging time.

RESPONSE: In addition to the factors already lis ted in EPA’s comment (i.e., that the monitoring stations used are th e closest stations, and are adeq uately close, to the Project site), we have discussed above the similarity between the sites with regard to land use, and the presence of nearby sources of pollutant s that might affect one site but not the

other.

Furthermore, EPA had previously accepted this discussion as adequa te justification for the use of representative bac kground air quality data from th e Corcoran and Hanford sites for purposes of evaluating compliance with th e 1-hour and 8-hour av erage CO standards, the 24-hour average PM 10 standard, and the annual average NO 2 standard. We are unaware of any scientific reason why data that are acceptably representative for these purposes would not also be represen tative with respect to the 1-hour NO 2 standard.

Ozone

EPA COMMENT: The discussion of representativen ess for hourly ozone data in the San Joaquin Valley should consider the regional pa ttern of ozone in the San Joaquin Valley. The effect of local sources on the forma tion and destruction of ozone should be considered. For example, is the monitoring st ation near a roadway that may be a local sink of ozone? Conditions at the project site should be compared to conditions at monitoring sites in the San Joaquin Valley.

RESPONSE: Section 5 of the SJVACPD Extreme Ozone Attainment Demonstration

Plan describes the modeled pattern of future ozone impacts in the San Joaquin Valley. 47
These predictions form the basis of the District’s SIP for attainment of the federal ozone NAAQS. Figure 5-2 of the Plan shows the peak ozone distribution in the base case for the plan, July/August 2000. The pred icted ozone concentrations throughout Kings County are similar; predicted concentrations at Hanford and at the project site are within 10% of each other. Projections of future ozone concentr ations are shown in Fi gure 5-4, and again the peak ozone concentrations at the two sites ar e expected to be with 10% of each other. Because the conditions that give rise to peak ozone concentrations feature low wind speeds, comparison of peak ozone concentra tions would be expected to maximize the isolation of the two sites and emphasize differe nces between the two sites. Consequently,

we believe the ozone data from the Ha nford monitoring sta tion are reasonably representative of concentrations at the Project site. With respect to roadway traffic, the Hanford monitoring station is located near to California Route 43, but it is located approximately 12 miles from the nearest major freeway, California Route 99. In comparison, the Project site is located approxi mately two miles from Interstate 5. Thus, with respect to this one narrow issue, ozone concentrations at the Hanford site would be expected to be less impacted by roadway traffic than the Project site, and hence ozone concentrations would be expected to be slightly lower (all el se being equal) at the Project

47 SJVAPCD, Extreme Ozone Attainme nt Demonstration Plan , October 8, 2004.27 site. In the context of the ozone limiting f unctions of AERMOD, this means that the use

of ozone data from Hanford is health-conservative.

EPA COMMENT: The method for substituting missing oz one concentrations should be replaced with a clearly defined approach that includes a reasonable assurance that

substituted values will not result in underestimat es of ambient NO 2 concentrations. Avenal has not provided reasonable assurance that the method used—substituting concentrations with "hour-appr opriate" values (e.g., from th e previous day, or the next day, for the same hour)—will not result in underestimates of ambient NO 2 concentrations. For example, Avenal has not indicated whether there were instances in which there were "hour appropriate" data for bo th the day before and day after the date on which data was missing, and whether in any such cases it took the higher of the two

values.

RESPONSE: In general, the ozone concentration substi tuted for a missing hourly value

was the arithmetic mean of th e ozone concentrations measured during the hour before and the hour after the missing value. In a fe w cases, the ozone concentration substituted for a missing hourly value was the arithmetic m ean of the ozone concentrations measured during the same hour on the previous and fo llowing days. Because ozone is generated by reactions that depend on incoming solar energy, ambient temperature, and the availability of nitric oxide, nitrogen dioxide, and other reactive molecules, resulting in a typical diurnal pattern of growth in the morning hours and loss after sunset, th e choice of the best value for substitution depends on the time of day of the missing concentration and the relative magnitude of the ozone concentrati ons successfully measur ed during the same hour on the previous and following days, and the ozone concentrations measured during

the hour before and the hour after the missing value.

The revised supplemental 1-hour NO 2 impacts analysis enclosed with this submission relies on background ozone concentra tions provided by the District.

NO 2

EPA COMMENT: The discussion on representativeness presented by Avenal, i.e., that there is a lack of any large local industrial sources in the Hanford area, and that the Hanford site is nearest to the facility, is not an adequate discussion of representativeness. The discussion of representativeness for ambient air quality dat a should include a discussion of why the ambient pollution levels monitored at the Hanford monitoring station represent area-wide ambient conditions, not simply that they do not represent localized impacts.

RESPONSE: As EPA noted in its comment, ambi ent monitoring data is assumed to represent regional concentrations. One element of this assumption is that the monitor is not impacted significantly by local sources of emissions. EPA accepted the background ambient monitoring data from Corcoran and Hanford in the context of the 1-hour and 8- hour CO standards, the 24-hour PM 10 standard, and the annual average NO2 standard.28 Since both the CO and NO 2 concentrations are principa lly influenced by combustion sources, we are unaware of a ny scientific reason why data from these two monitoring sites would not also be repres entative of regional background concentrations for purposes

of the 1-hour NO 2 standard.

EPA COMMENT: The discussion should be appropr iate for the pol lutant for the appropriate averaging time. For example, th e discussion of representativeness for hourly NO 2 data in the San Joaquin Valley should include a discussion of the sources and conditions likely to contribute to high hourly levels of NO 2 in the San Joaquin Valley. The project site should be compared to various monitoring sites in the San Joaquin Valley. This type of informa tion has not been provided.

RESPONSE: The Hanford site was se lected for background NO 2 concentrations for

several reasons:

 It is the closest NO 2 monitor to the project site.

 The nearby land use is similar at the Hanford site and the Project site;

 The topography near both sites is similar

 The climatology affecting both sites is similar.

In contrast with the Hanford site, urban m onitoring sites in the District have very different surrounding sources. The other rural site s in the area have characteristics similar

to those of Hanford and the Pr oject site, but all are farther away from the project than Hanford. Hanford thus provides the best available characterization of project conditions

The question of whether there are sources that might impact the project site, but are not adequately represented by the ambient data, is essentially the same as the analysis for nearby sources that must be modeled.

Table 5 lists point sources and NOx emissions for sources in the vici nity of the project

and the Hanford monitor. This table shows th at the there are no major sources, and few large sources, in the vicinity of either lo cation. Because there are more NOx emissions in the immediate vicinity of Hanford, using ambi ent data from that site to represent the regional background is conservative, to the ex tent that the monitor site is directly impacted by nearby sources.29 Table 5 Comparison of NOx Sources Aro und Project and Monitoring Sites

Range Project Hanford Monitoring Site

Facilities 2008

NOx

emissions (TPY as NO 2 ) Facilities 2008

NOx emissions (TPY as NO 2 )

<= 5 km PG&E 25.2 Hanford LP

Samson Resources 52.2

<= 10 km PG&E 25.2 Hanford LP

Samson Resources 63.6

EPA COMMENT: The NO 2 ambient data used for the annual NO 2 NAAQS analysis were not evaluated by EPA in that context in light of the fact that th e analysis did not use

ambient NO 2 data, and the fact that the analys is had a project impact below the monitoring de minimis level. These factors ar e not present in the context of the 1-hour

NO 2 NAAQS. Thus, EPA did not review or approve the information submitted at that time with respect to repres entativeness fo r the 1-hour NO 2 NAAQS.

RESPONSE: In light of Avenal’s reference to the use of previously submitted

information in the NO 2 analysis, Avenal assumes that EPA will review the previously

submitted data as referenced and modified by this and other recent submissions.



### Compliance Demonstration

EPA COMMENT: We note that the EPA guidance document issued by EPA's Office of Air Quality Planning and Standar ds entitled General Guidan ce for Implementing the 1-

hour NO 2 National Ambient Air Quality Standard in Prevention of Significant Deterioration Permits, Incl uding an Interim 1-hour NO 2 Significant Impact Level, dated June 28, 2010, provides a recommended interim as for the 1-hour NO 2 NAAQS of 4 ppb.

RESPONSE:

The June 28 th guidance document was not issued until after EPA requested that the applicant conduct an analysis to demons trate compliance with the new 1-hour NO2 standard, and after the requested analysis had been submitted. In light of EPA’s new guidance on this issue, Avenal has used the interim suggested leve l of 4 ppb as a SILequivalent to determine the impact area for the 1-hour NO 2 standard, and to determine whether impacts are significant for the purposes of this analysis.

EPA COMMENT: EPA's June 28, 2010 NO 2 clarification memorandum acknowledges that some level of temporal pai ring of modeled and monitored NO 2 concentrations may be appropriate in some situations, the just ification regarding pairing on an hour-by-hour basis provided in Avenal's response, wh ich states that the "approach guarantees30 meteorological consistency for each pair of background and modeled concentrations combined in each hour of the year," does not provide a sufficient rationale to support that approach in this case. There may be sound technical argumen ts to account for consistency in terms of the meteorol ogy affecting both background and modeled concentrations, but the justific ation also needs to consider the spatial representativeness of the monitored data as well, which is not addressed in Avenal's response to this

comment.

RESPONSE: The spatial representativeness of th e ambient monitoring data used to assess the Project’s im pacts on the 1-hour NO 2 standard is discussed above.

EPA COMMENT: The aspect of temporal pairing of modeled and monitored concentrations is also acknowledge d in EPA's March 23, 2010 memorandum from Stephen Page regarding Modeling Procedur es for Demonstrating Compliance with PM2.5 NAAQS, where EPA indicates on page 8 that a Second Tier approach for combining modeled and monitored PM 2.5 concentrations on a seasonal or quarterly basis may be considered when the modeled primary PM 2.5 impacts and background PM 2.5 levels (including secondary PM 2.5 formation) are not correlated on that time scale. Although the March 23, 2010 memo does not pr ovide details regarding the recommended method for combining modeled and monitored PM 2.5 concentrations on a seasonal or quarterly basis, the recent draft PM 2.5 Hot Spot Conformity Guidance (EPA, 2010) recommends combining the average of the highest modeled 24-hour concentrations within each season/quarter to each of the eight highest 24-hour monitored background concentrations for that season/quarter, and th en sorting the combined distribution to determine the cumulative design value (see A ppendix K of the draft Hot Spot guidance).

Note that the modeled and m onitored concentrations are not paired on a day-by-day (or hour-by-hour) basis in this Second Tier approach for PM 2.5 , even though the spatial homogeneity of background levels of PM 2.5 on a daily basis is likely to be much greater than the spatial homogeneity of background levels of NO 2 on an hourly basis.

RESPONSE: The example cited by EPA is a screening level analysis applicable to 24- hour average concentrations of a pollutant other than NO2. EPA has argued extensively in its Aug. 12, 2010 comments that guidance and analyses relative to other pollutants and/or averaging periods ar e not relevant to a discu ssion of the new 1-hour NO2 standard, so we are uncertain as to why EPA believes, in this particular instance, that guidance relative to the 24-hour PM2.5 standard is relative to the 1-hour NO2 standard. Nonetheless, with respect to the substance of EPA’s comment, the statistical form of the

1-hour NO2 standard does not lend itself to the approach proposed for the 24-hour PM2.5 standard. Such an approach would invariably result in a predicted violation of the 1-hour NO2 standard when, in fact, none would be expected. The existence of a more conservative mathematical approach for combining modeled and background concentrations should not preclude the use of technically defensible, less conservative approach.

EPA COMMENT: Pairing the monitored background values with modeled concentrations on an hour-by-hour basis im plies an assumption that the monitored31 concentrations are equally representative at each location within the modeling domain for each hour of the simulation.

RESPONSE: Avenal would propose the following cl arification to EPA’s comment: the monitored concentrations are equally representative of the regional background

concentration at each location within th e modeling domain for each hour of the simulation. This assumption is inherently co nservative. As discussed previously, we assume that every point in the region is impacted by the same regional background concentration plus the impact of local source s. Any monitor will reflect that background plus the local sources that impact it.

Because the monitor data is the sum of regional background plus local impacts, any monitor’s data from the region can never be lower than the background. Because the monitor’s data must, by definition, be as high as or higher than the regional background, the assumption that the monitor data is equally representative at each location within the modeling domain is a conservative one. EPA’s concern about “spatial representativeness” (that is, local sources that impact the modeling domain) is addressed through the nearby source analysis.

EPA COMMENT: There is no technical or even rati onal basis to support such a degree of representativeness in this case or any other case.

RESPONSE: This comment is puzzling, because there is no basis to distinguish between the use of ambient monitoring data in this case and its use in other cases. The approach used in our analysis is consistent with th e approach that EPA and other environmental agencies have used for many years, and the assumption is the same for all uses of ambient monitoring data in compliance determ ination. The technique used to combine background and modeled concentrations on an hour ly basis for the Project is the same as that used by the District.

EPA COMMENT: Such a degree of representativene ss would also be unreasonable to impose as a general requirement for use of background monitored dat a, given the limited number of monitors available. However , any modeling approach developed regarding the use of monitored background concentr ations as part of a cumulative impact

assessment must take into account th ese limitations of monitored data.

RESPONSE: It is unnecessary to attempt to distinguish between “degrees of representativeness.” As disc ussed above, given an adequa te demonstration that the monitor and the impact area are in the sa me region, subject to the same regional background, then the assumption that the monitor represents regional background is necessarily conservative. The possible eff ects of local sources on the impact area are addressed by the nearby source analysis.

EPA COMMENT: The results from the 1-hour NO 2 CAAQS comparison summarized in Table 6.2-31 (6.2-66) of the APC show maximu m 1-hour Avenal facili ty impacts of 190 μg/m3, combined with a background concentration of 137.2 μg/m 3 to give a total impact of 327.2 μg/m 3 . This cumulative 1-hour NO 2 impact is well above the EPA 1-hour NO 232 standard, although we recognize that the 1-hour modeled NO 2 concentration documented in the APC is likely to be higher than the 98th-percentile of the annual distribution of maximum daily 1-hour values used as the form of the 1-hour EPA standard. However,

the AFC results are also about 2.7 time s higher than the cumulative 1-hour NO 2 impact reported in the May 13, 2010 submittal, which se rves to highlight th e significance of the issue raised by EPA in this comment, and to emphasize the importance of having clear justification and documentation of the approach taken for combining modeled and monitored concentrations for comparison to the NAAQS.

RESPONSE: On the contrary, the extremely hi gh values predicted by a screening analysis emphasize the conservativ e nature of such an analysis, and justify the level of comfort that a demonstration of compliance using such a method provides. It says nothing, however, about the significance of the issue raised by EPA in its comment, because it says nothing about the degree of conservatism represented by the more realistic model. As shown in the supplemental 1-hour NO 2 impact analysis submitted on May 14, 2010, as well as the revised supplemental 1-hour NO 2 impact analysis enclosed herewith, the Project will not cau se or contribute to violations of this new standard, even if such a requirement were applicable to the Project.

EPA COMMENT: EPA disagrees that it is suitable to apply the currently available monitoring guidance for the 1-hour NO 2 standard to modeling applic ations, as suggested by Avenal. EPA's comment obj ects to discarding valid modeled data. The applicant should choose a method for combining modele d and monitored data that does not discard

valid modeled data and which is consistent with Appendix W. EPA's guidance entitled Applicability of Appendix W Mode ling Guidance for the 1-hour NO 2 National Ambient Air Quality Standard (June 28, 2010) may be us eful in preparing an analysis of the

1-hour NO 2 NAAQS.

RESPONSE: We have reviewed The Appendix W modeling guidance document again, and it does not provide useful guidance to ad dress this issue. This is because the modeling guidance document only describes co mpliance demonstrations using screening approaches, and not a full compliance de monstration that simulates siting a NAAQS compliance monitor at every single point in the modeling domain.

Because the compliance demonstration uses all available data in a way that replicates exactly the way those data would be used to determine the region’s attainment status, it is the most direct demonstration of compliance with the NAAQS.

Nonetheless, in the revi sed supplemental 1-hour NO 2 impact analysis provided with this response, background concentrations were provided by the District, and were not developed using the method objected to by EPA.33 

### Conclusion

We believe that this document and the attached materials address all of EPA’s remaining concerns. If there are any questions, they can be directed to Gary Rubenstein of Sierra Research at (916) 273-5126.