1 

Response to EPA Comments 

of August 12, 2010 

1-Hour NO2 NAAQS Compliance Demonstration 

Avenal Energy Project 

PSD Permit Application

September 13, 2010 

 

Introduction 

On August 12, 2010, EPA sent a letter to Avenal 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 that describe EPA’s remaining concerns about 

Avenal’s analysis of the Project’s compliance with the new 1-hour NO2 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 

NO2 impact 

(μg/m3

) 

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 ambient 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 with duct firing was selected to represent 

normal operations, even during seasons where those ambient conditions do not apply. 

Because the normal operation 1-hour impacts are so much lower than startup/shutdown 1-

hour impacts, the case selected to represent 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 added to the corresponding background ambient 

concentration to obtain the predicted concentration for comparison with the National 

Ambient Air Quality Standard (NAAQS). 

For each year, the eighth highest value (98th 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 added to the corresponding background ambient 

concentration to obtain the predicted concentration for comparison with the NAAQS. 

For each year, the eighth highest value (98th 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/m3

) 

Highest Result 

for comparison 

with NAAQS 

(ppb) 

1-hour NO2

Standard 

(ppb) 

Startup/shutdown 150.3 80 100 

Normal operation 108.3 57 100 

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

for NO2. 
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 compliance with the Federal annual NO2 standard or the 

State 1-hour NO2 standard cannot simply be assumed to demonstrate the AEP's 

compliance under the Clean Air Act PSD program with the Federal 1-hour NO2

standard. Further, EPA did not previously accept or approve Avenal's use of such 

information, data, protocols and analyses for the purposes of demonstrating compliance 

with the Federal 1-hour NO2 standard; indeed, that standard had not been finalized at 

the time such information was initially submitted and thus would not have been reviewed 

for that purpose. 

RESPONSE: 

Avenal understands that the data and analysis it previously submitted to demonstrate 

compliance with EPA’s annual NO2 standard and California’s 1-hour NO2 standard 

cannot be assumed to demonstrate compliance with EPA’s new 1-hour NO2 standard. As 

a technical matter, however, much of the information, data, and analysis that Avenal 

previously submitted necessarily serves as the starting point for evaluating compliance 

with the new 1-hour NO2 standard. Avenal simply notes that significant portions of the 

underlying information necessary to complete the new analytical requirement were 

previously submitted to EPA. These include ambient background data for use in 

modeling, discussions of the process used to identify nearby sources, and other materials. 

In fact, much of the information previously submitted is as relevant to an analysis of 1-

hour NO2 impacts as it is to analyses of the Project’s impacts on 1-hour and 8-hour 

average CO, 24-hour and annual average PM10, and annual average NO2 ambient air 

quality standards. 

It is misleading to suggest that “Avenal chose 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 NO2 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 analysis of the 1-hour average NO2 standard: 

 Emission sources to be included in the analysis 

 Meteorological data 

 Background ozone concentrations 

 Background NO2 concentrations 
4 

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 NO2 standard based on 

existing EPA guidance documents (which are clearly relevant even though they do not 

deal specifically with the new standard) and protocols that California agencies have 

accepted for modeling 1-hour NO2 impacts. Since that time, EPA has requested 

additional analyses, discussion, and documentation in order to allow it to complete its 

review of the Project’s compliance with the 1-hour NO2 standard. Although EPA’s 

requests seek additional information, these requests lack specific guidance on how such 

analyses should be prepared. At the same time, 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 those cases, we propose criteria and explain why 

we believe those criteria should be used. 

Nearby Sources 

EPA COMMENT: Avenal's May 13, 2010 1-hour NO2 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 NO2 NAAQS. As a supplemental analysis, it built on previously submitted 

information. The process used to determine which nearby sources to include in the 

modeling was described in the original (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 described the process in its August 12, 2010 letter 

and attachments: 

“The applicant's June 28, 2010 response states that APC Section 6.2.7.1.2 

(Localized Impacts) thoroughly discussed the criteria used to evaluate whether 

any stationary sources existed within six miles that would qualify to be explicitly 

included in a cumulative air quality modeling 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 project's typical operating mode in 

combination with other stationary source emissions sources within a sixmile radius which have received construction permits but are not yet 

operating, or are in the permitting process."[footnote omitted] Within the 

distance of six miles, three categories 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 July 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 per year for a criteria pollutant) for a 

cumulative air quality impact analysis, but has not identified any. 

Consequently, no localized cumulative impact modeling analysis was 

performed for the proposed project.”2

The same screening process was used to identify nearby sources for the Class II impacts 

analysis. 

The applicant screened nearby sources for the 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 elements of the CEC analysis are similar to 

elements of the PSD compliance demonstration, the CEC analysis was submitted to EPA 

as part of its PSD application. 

The portion of that analysis that is relevant here is the identification of sources that are 

not adequately represented by ambient monitoring data, and must therefore be explicitly 

modeled. The applicant contacted the District and requested a list of all projects within 6 

 

2

 Gerardo Rios letter to Jim Rexroad, Attachment 1, August 12, 2010. p. 3: 
6 

miles of the project site3

 for which permits had been requested or issued that had not 

begun operating prior to January 2006. This date was selected because impacts from 

sources operating before that date were presumed to be reflected in the ambient 

monitoring data. Sources with permitted emissions 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. Because no nearby sources were identified, no 

nearby sources were modeled in either our original February 2008 application 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 guidance as to the relevant distance to 

be considered in evaluating the potential for nearby sources to contribute to impacts 

associated with a proposed project. The sources to be considered for inclusion in the 

PSD nearby source have, in most previous permit 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 contribute 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 Quality Impact Report 3/19/10): No comparison of 

annual or 1-hour impacts with SIL; therefore no impact area determined; 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 PM10 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 NO2 impacts exceeded the SIL. 

The adjacent Greenleaf facility was included in the modeling. EPA’s analysis is silent as to whether any 

other sources were modeled, as well as the process used to screen nearby facilities for inclusion. 10 Avenal (Statement of Basis, June 2009): 1-hour CO impacts exceeded SIL; EPA accepted the applicant’s 

analysis (using the CEC cumulative impact 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 Quality Impact Report, May 2008): 24-hour PM10 impacts were 

above the SIL. All major and minor sources within 54 km (i.e., distance to edge of impact area plus 50 km) 

of the project were screened for inclusion in cumulative 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 sources 
7 

impacts from the Project were below the relevant SILs with the exception 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 needed to be added to the analysis of the 

Project’s impacts on the 1-hour CO standard. (Both CO and NOx emissions are almost 

exclusively associated with combustion sources; 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 NO2 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 (maximum 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 extending 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 inclusion in the NAAQS inventory for the 1-hour 

NO2 standard. 

EPA has considered and accepted several methods for screening sources for inclusion in 

the NAAQS inventory. These are summarized in the meeting notes for an 

EPA/State/Local PSD Workshop held 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, without some practical limitations, such 

gradients can occur anywhere in the “vicinity” 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 impacts above SIL, therefore no further consideration 

of nearby sources 

14 75 FR 6525 

15 EPA. “General Guidance for Implementing the 1-hour NO2 National Ambient Air Quality Standard in 

Prevention of Significant Deterioration Permits, Including an Interim 1-hour NO2 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 significant 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-32 
8 

in order to balance the need for identifying all sources which meet the criteria in 

the Guideline and also to achieve a workable inventory of sources, various 

permitting agencies have developed and used objective tools to assist in the 

determination of an emission inventory. 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 Carolina 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 for which Q > 20D, where Q is the maximum 

emission (in tons per year) for the source being screened, and, for short-term analyses, D 

is the distance (in kilometers) from the source being screened to the PSD source.. For the 

purposes of this method, the source is defined as the facility or complex, not an 

individual stack or other emission point; therefore, cumulative emissions of each 

pertinent pollutant go through 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 cumulative 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 displays all sources that met one or more of 

the following in 2001: 

a. Sources that emitted at least 10 tons of VOC, NOx, SOx, CO, or PM10; 

b. Power plants rated at 50 MW or greater; or 

c. Air Toxic “Hot Spots” facilities 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 analysis 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 NO2

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 the NAAQS inventory. All sources are far enough away that it is 

unlikely that impacts will interact appreciably 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 source 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. Nor can we discern any reason why the 1-hour 

NO2 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 standard, and mobile source 

emissions in most parts of the county represent the largest portion of the CO emissions 

inventory. Yet, to the best of our knowledge, EPA does not require, and has not required, 

modeling of mobile source CO emissions for PSD compliance determinations. This is 

obviously sensible, as the impact of mobile sources is already 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 Manual provides the following guidance on 

determining the ambient background concentration for PSD compliance determinations: 

“The Modeling Guideline defines a "nearby" source as any point source expected 

to cause a significant concentration gradient in the vicinity of the proposed new 

source or modification.”20 (emphasis added) 

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

other major stationary point sources, the assessment of existing ambient 

concentrations may be done by evaluating available monitoring data. It is 

generally preferable to use data collected 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 standards: “For compliance with the short-term 

and annual ambient standards, the nearby sources 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.18 
11 

be evaluated using an appropriate Appendix A model with the emission 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 NO2 standard in PSD 

permit applications.25 This guidance includes an extensive discussion on construction of 

the inventory for PSD analysis. There is nothing in this discussion to suggest an 

expansion of the PSD NAAQS modeling requirements to include non-point sources. 

In addition to this guidance, we can find 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 background sources, and this impact would not be 

captured via monitoring. Background concentrations should be determined for each 

critical (concentration) averaging time." 

RESPONSE: The language cited by EPA refers to the operating parameters 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 existing point source has been identified to be a 

nearby source, due to its potential to create a significant concentration gradient in the 

impact area. 

 

For example, the modeling protocol for the Colusa Generating Station first identified the 

adjacent Delevan Compression Station as an existing major source, containing three gas 

turbine-driven compressors licensed for full-year operation. Historical usage records for 

the turbines were used to estimate past actual emissions. Because impacts from past 

actual emissions were included in ambient 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 for Implementing the 1-hour NO2 National Ambient Air Quality Standard in 

Prevention of Significant Deterioration Permits, Including an Interim 1-hour NO2 Significant Impact 

Level”. June 28, 2010 

26 URS, Modeling Protocol for the Colusa Generating Station, July 12, 2006, p. 4-12 
12 

As discussed above, there are no nearby sources relevant to the analysis of AEP’s 

impacts on the 1-hour NO2 standard. 

EPA COMMENT: Adequate documentation of the District's response [to the request for 

information about local sources] is not provided. 

RESPONSE: The inventory data for the few sources in the vicinity of the proposed 

project site identified by the District are attached as Attachment 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 adequately addressed. That the project is located 

in an area of high ozone concentrations does not necessarily justify 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 dispersion model. It predicts groundlevel concentrations based on distribution of emissions from the sources being modeled. 

However, the NOx emitted at the stack is a mixture of (primarily) NO and NO2. If 

conversion of stack NO to NO2 in the atmosphere is not taken into account, the model 

will underpredict NO2 impacts. At the same time, if the unrealistic assumption is made 

that 100% of stack NO is converted to ground-level NO2 at all receptors, regardless of 

transport time, transport distance, or ambient ozone concentrations, the dispersion model 

will overpredict NO2 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 continues to assure 

compliance while allowing less conservative assumptions. EPA addresses this process, in 

the context of the 1-hour NO2 standard, through increasingly sophisticated (and less 

conservative) tiers of analysis. 
13 

The regulatory default modeling methodologies for the 1-hour NO2 standard are 

screening methodologies.27 

Tier 1: Assume full conversion of NO to NO2 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 result by empirically-derived NO2/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 also 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 modeling that tests compliance with the 1-hour NO2

NAAQS. The District applied Tiers I through III to the Project’s emissions during 

normal operation and startup to demonstrate compliance with the 1-hour NO2 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 NO2 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 NO2. 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 

NO2 NAAQS, the analysis is complete and compliance with the 

standard has been demonstrated. 

ii. If the maximum combined concentration exceeds the 1-hour NO2

NAAQS, then the maximum modeled concentration alone is 

compared to the interim SIL of 4 ppb. 

1. If the maximum modeled concentration is less than the SIL, 

then the analysis is complete 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 

 

27EPA, Appendix W Section 5.2.4. See also Memorandum from Wood to Regional Air Division Directors, 

General Guidance for Implementing the 1-hour NO2 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 NO2 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 NO2. 

b. The maximum 1-hour NO2 concentration is modeled from all sources in a 

project using AERMOD, five years of meteorological data, and the 

application of a default Ambient Ratio Method (ARM) value of 0.9 

instead of complete conversion of NO to NO2. 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 

NO2 NAAQS, the analysis is complete and compliance with the 

standard has been demonstrated. 

ii. If the maximum combined concentration exceeds the 1-hour NO2

NAAQS, then the maximum modeled concentration alone is 

compared to the interim SIL of 4 ppb. 

1. If the maximum modeled concentration is less than the SIL, 

then the analysis is complete 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 

AERMOD PVMRM or OLM. 

c. The maximum 1-hour NO2 concentration is modeled from all sources in a 

project using AERMOD PVMRM or OLM, and five years of 

meteorological data. 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 

NO2 NAAQS, the analysis is complete and compliance with the 

standard has been demonstrated. 

ii. If the maximum combined concentration exceeds the 1-hour NO2

NAAQS, then the maximum modeled concentration alone is 

compared to the interim SIL of 4 ppb. 

1. If the maximum modeled concentration is less than the SIL, 

then the analysis is complete 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 identical to Tier I except that the 8th highest 

modeled concentration replaces the maximum modeled concentration in the 

analysis. 

3. Tier III: The 98th percentile 1-hour predicted concentration is determined using 

the post-processor developed by the District, third-party software developers,30 or 

an EPA-revised version of AERMOD. This concentration is used in the same 

stepwise approach described for Tier I above. 

 

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

EPA. 
15 

4. Tier IV: The predicted 1-hour NO2 concentrations from the model are paired in 

time with the monitored 1-hour NO2 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 NO2 air quality impact 

analysis used a Tier IV approach. The only difference between the May 13, 2010 

submission and the enclosed, revised submission is that meteorological and background 

ozone and NO2 data are based on more recent data 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 evaluating compliance with the 1-hour NO2 NAAQS, 

the SIL-equivalent is so low that almost any moderate-to-large combustion source will 

have difficulty passing a screening assessment. It is therefore 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 specifically for its ability to compute unbiased 

results. One of the key studies was conducted 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 NO2/NOx 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 careful 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 following five requirements33 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.e 
16 

v. A protocol on methods and procedures to be followed has been established.”34

The District evaluation of AERMOD-PVMRM concluded the following: “Based on the 

information provided above, the District has determined that the method for determining 

hourly NO2 concentrations using AERMOD in conjunction 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 reasons, the PVMRM option within AERMOD is demonstrably 

applicable to a refined analysis of 1-hour average NO2 impacts from the Project on a 

theoretical basis. 

 Provision iii 

EPA COMMENT: The data bases which are necessary to perform the analysis are 

available and adequate: The information provided in paragraph 2 in Avenal's June 28, 

2010 letter discusses the use of the ozone data submitted by Avenal in the PVMRM option 

within AERMOD, but does not provide adequate justification for use of the ozone data in 

this context for purposes of the PSD program. 

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

below. 

EPA COMMENT: "This analysis should include a discussion of the representativeness 

of the surface characteristics. The surface 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 does not adequately address EPA's comment. The 

response does not provide (1) information about the surface characteristics at the project 

site, (2) specific information about the surface characteristics for the meteorological 

station that were computed by the District, or (3) a discussion of how the specific surface 

characteristics at the meteorological station are representative of the specific surface 

characteristics at the project site. Avenal should provide this information. 

RESPONSE: As stated in our May 13, 2010 submittal of the Supplemental NO2 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 meteorological data set used for this analysis 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 analysis 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 characteristics (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 parameters 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 processing the original, 2000-2004 meteorological 

data set to 1 km, which was used to process 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 seasonal distributions of rainfall as shown in Table 4, with 

the maximum monthly rainfall occurring in January and no monthly rainfall 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 Rainfalla

 (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/data.pl?ref=N35W120+2200+040398C). c

 Hanford rainfall data (NCDC Cooperative Stations, 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 Pendleton 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 “Camp Pendleton meteorological data”. 

Relative to the Hanford meteorological monitoring 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 (Kings 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 submitted 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 each 
19 

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 representativeness of the data 

depends on (a) the proximity of the meteorological 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 located near the center of the northnorthwest/south-southeast aligned runway 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 years of meteorological data used in 

the new modeling submittal herein (2005-2009) is coincident with the 

ambient ozone and NO2 data used for the 1-hour NO2 analysis. 

“Representativeness has also been defined in the ‘Workshop on the 

Representativeness of Meteorological 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 different space-time domain taken on a scale 

appropriate for a specific application.’ Representativeness is best evaluated when 

sites are climatologically similar, as are the project site and the Hanford 

meteorological monitoring station. Representativeness has additionally been 

defined in the PSD Monitoring Guideline (USEPA 1987b) as data that 

characterize the air quality for the general area in which the proposed project 

would be constructed and operated. Because 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 project 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 following 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 precipitation. 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 Valley, primarily during the winter months. 

These synoptic scale influences result in distinct seasonal weather characteristics, 

as discussed below. 

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

off the Pacific Coast. It is centered 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 climate, producing persistent temperature 

inversions and a predominantly southwesterly wind field. Clear skies, high 

temperatures, and low humidity characterize 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 patterns 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 pressure area, or persistent fog caused 

by temperature inversion. The average annual 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 also stagnant conditions occur more frequently than 

during summer. (Climates of the States – California, U.S. Department of 

Commerce, Weather Bureau, 1959.) 

“Wind and mixing height are two key meteorological 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 California are generally light and easterly in the winter, 

but strong and westerly in the spring, summer, and fall. 

“Wind patterns in the general 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 Prevention 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 miles northeast of the 

site, and is the closest station for air 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-based 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 mixing 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, however, were unlimited in spring and 

summer, 1135 meters (3,725 feet) in the fall, 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 source 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 for details. The analysis is summarized 

below. 

“The meteorological data from the Hanford 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 area 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-valley and down-valley winds. The downvalley winds are generally a result of airflow 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 air 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 of 
22 

available data40 will not vary much because the meteorological data are so 

constant between the years.” 41

Because 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 project site in the same manner. 

The upper air data is necessarily representative of a large geographic domain because of 

the large distances between upper air meteorological monitoring stations. 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 station meteorological data as representative of 

the Project site, was accepted by EPA for purposes of analysis of the Project’s impacts on 

the 1-hour and 8-hour CO standards, the 24-hour and annual average PM10 standards, and 

the annual average NO2 standard. We are unaware of any scientific reason why 

meteorological data which are acceptably representative for these pollutants would not 

also be representative in the context of a 1-hour NO2 standard. 

 Provision iv

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

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

RESPONSE: Noted. 

 Provision v 

EPA COMMENT: A protocol on methods and procedures to be followed has been 

established: This provision is not adequately addressed, and was not approved in the 

previous submittals. Please provide a protocol 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 comments regarding four elements of that 

protocol proposed to be carried forward to the 1-hour NO2 analysis. EPA did not respond 

to that request. Nonetheless, a supplemental protocol for demonstration of compliance 

with the 1-hour NO2 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) that 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 the 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 application to be 160 lbs/hr per unit during a turbine startup.42 

The analysis in the February 2008 PSD application went beyond identification of the 

worst-case 1-hour emission rate to identify combinations of emission rates and operating 

scenarios 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 emission case for one turbine 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 combination 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 these 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 startup impact occurred with the combination of 

50% load (startup conditions) and extreme hot ambient temperature. 

Note that the use of cold startup emission characteristics (abnormally high emission rates, 

low stack velocity, low stack temperature) results in a significantly conservative 

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

 

42 Application to the U.S. EPA for a Prevention 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 Prevention 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 conditions. 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 impact; 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 for purposes of analysis of the Project’s 

impacts on the 1-hour and 8-hour CO standards, the 24-hour and annual average PM10

standards, and the annual average NO2 standard. We are unaware of any scientific reason 

why the worst case emission rates and dispersion characteristics which are acceptably 

representative for these pollutants would not also be representative in the context of a 1-

hour NO2 standard. 

 Stack NO2/NOx ratios 

EPA COMMENT: Avenal has selected the in-stack NO2/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 selection process. Avenal stated that the 

ratios were "derived from source test data." EPA needs to confirm the proposed 

conservative ratios for use in the 1-hour NO2 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 support information to confirm test conditions 

and equipment operations, and the source test methodology. The applicant should 

confirm if the source test data relied upon is a result of emissions compliance testing or a 

result of other circumstances. Based on this information, the applicant should provide a 

discussion that demonstrates the representativeness and comparability of this 

information for Avenal's selection of the proposed ratios for normal, startup and 

commissioning operations. 

RESPONSE: The SDAPCD based its recommendation regarding NO2/NOx ratios on the 

results of source tests conducted under SDAPCD supervision at the Palomar Energy 

Center. The emission compliance tests conducted on January 25 and 27, 2006 for Units 2 

and 1, respectively (see Attachment 3) provided the basis for the recommended ratio of 

0.25 during normal operation of F-Class gas turbines burning natural gas and equipped 

with dry low-NOx combustors, selective catalytic reduction and oxidation 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 develop 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 SDAPCD (Attachment 5). A later, confirming 

source test (Attachment 6), which was focused on the first hour of startup, indicated a 

lower NO2/NOx ratio of close to 5% but the District decided to keep their conservative 
25 

recommendation of 0.40 for the NO2/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, essentially identical to the gas turbines 

proposed for the Avenal Energy Project. 

Estimates of impacts during commissioning activities 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, please provide a discussion that also 

demonstrates the representative and comparability 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 modeling on another large-scale combined-cycle gas turbine 

project." The applicant should include the 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 NO2/NOx 

ratios is attached as Attachment 5. 

Ambient Monitoring Data 

Responses to EPA’s comments on the representativeness 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 source, and is adequately close, are not sufficient 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 representativeness for ambient air quality data 

should be specific to the pollutant for the appropriate averaging time. 

RESPONSE: In addition to the factors already listed in EPA’s comment (i.e., that the 

monitoring stations used are the closest stations, and are adequately 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 pollutants that might affect one site but not the 

other. 

Furthermore, EPA had previously accepted this discussion as adequate justification for 

the use of representative background air quality data from the Corcoran and Hanford sites 

for purposes of evaluating compliance with the 1-hour and 8-hour average CO standards, 

the 24-hour average PM10 standard, and the annual average NO2 standard. We are 

unaware of any scientific reason why data that are acceptably representative for these 

purposes would not also be representative with respect to the 1-hour NO2 standard. 

Ozone 

EPA COMMENT: The discussion of representativeness for hourly ozone data in the San 

Joaquin Valley should consider the regional pattern of ozone in the San Joaquin Valley. 

The effect of local sources on the formation and destruction of ozone should be 

considered. For example, is the monitoring station 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 predicted 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 concentrations are shown in Figure 5-4, and again the 

peak ozone concentrations at the two sites are 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 concentrations would be expected to maximize the 

isolation of the two sites and emphasize differences between the two sites. Consequently, 

we believe the ozone data from the Hanford monitoring station 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 approximately 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 else being equal) at the Project 

 

47 SJVAPCD, Extreme Ozone Attainment Demonstration Plan, October 8, 2004. 
27 

site. In the context of the ozone limiting functions of AERMOD, this means that the use 

of ozone data from Hanford is health-conservative. 

EPA COMMENT: The method for substituting missing ozone concentrations should be 

replaced with a clearly defined approach that includes a reasonable assurance that 

substituted values will not result in underestimates of ambient NO2 concentrations. 

Avenal has not provided reasonable assurance that the method used—substituting 

concentrations with "hour-appropriate" values (e.g., from the previous day, or the next 

day, for the same hour)—will not result in underestimates of ambient NO2

concentrations. For example, Avenal has not indicated whether there were instances in 

which there were "hour appropriate" data for both 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 substituted for a missing hourly value 

was the arithmetic mean of the ozone concentrations measured during the hour before 

and the hour after the missing value. In a few cases, the ozone concentration substituted 

for a missing hourly value was the arithmetic mean of the ozone concentrations measured 

during the same hour on the previous and following 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, the choice of the best 

value for substitution depends on the time of day of the missing concentration and the 

relative magnitude of the ozone concentrations successfully measured 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 NO2 impacts analysis enclosed with this submission 

relies on background ozone concentrations provided by the District. 

NO2

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 data 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, ambient 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 PM10 standard, and the annual average NO2 standard. 
28 

Since both the CO and NO2 concentrations are principally influenced by combustion 

sources, we are unaware of any scientific reason why data from these two monitoring 

sites would not also be representative of regional background concentrations for purposes 

of the 1-hour NO2 standard. 

EPA COMMENT: The discussion should be appropriate for the pollutant for the 

appropriate averaging time. For example, the discussion of representativeness for 

hourly NO2 data in the San Joaquin Valley should include a discussion of the sources and 

conditions likely to contribute to high hourly levels of NO2 in the San Joaquin Valley. 

The project site should be compared to various monitoring sites in the San Joaquin 

Valley. This type of information has not been provided. 

RESPONSE: The Hanford site was selected for background NO2 concentrations for 

several reasons: 

 It is the closest NO2 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 monitoring sites in the District have very 

different surrounding sources. The other rural sites in the area have characteristics similar 

to those of Hanford and the Project 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 vicinity of the project 

and the Hanford monitor. This table shows that the there are no major sources, and few 

large sources, in the vicinity of either location. Because there are more NOx emissions in 

the immediate vicinity of Hanford, using ambient data from that site to represent the 

regional background is conservative, to the extent that the monitor site is directly 

impacted by nearby sources. 
29 

Table 5 

Comparison of NOx Sources Around Project and Monitoring Sites 

Range 

Project Hanford Monitoring Site 

Facilities 

2008 

NOx 

emissions 

(TPY as NO2) 

Facilities 

2008 

NOx emissions 

(TPY as NO2) 

<= 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 NO2 ambient data used for the annual NO2 NAAQS analysis were 

not evaluated by EPA in that context in light of the fact that the analysis did not use 

ambient NO2 data, and the fact that the analysis had a project impact below the 

monitoring de minimis level. These factors are not present in the context of the 1-hour 

NO2 NAAQS. Thus, EPA did not review or approve the information submitted at that 

time with respect to representativeness for the 1-hour NO2 NAAQS. 

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

information in the NO2 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 Standards entitled General Guidance for Implementing the 1-

hour NO2 National Ambient Air Quality Standard in Prevention of Significant 

Deterioration Permits, Including an Interim 1-hour NO2 Significant Impact Level, dated 

June 28, 2010, provides a recommended interim as for the 1-hour NO2 NAAQS of 4 ppb. 

RESPONSE: 

The June 28th guidance document was not issued until after EPA requested that the 

applicant conduct an analysis to demonstrate 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 level of 4 ppb as a SILequivalent to determine the impact area for the 1-hour NO2 standard, and to determine 

whether impacts are significant for the purposes of this analysis. 

EPA COMMENT: EPA's June 28, 2010 NO2 clarification memorandum acknowledges 

that some level of temporal pairing of modeled and monitored NO2 concentrations may 

be appropriate in some situations, the justification regarding pairing on an hour-by-hour 

basis provided in Avenal's response, which states that the "approach guarantees 
30 

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 arguments to account for 

consistency in terms of the meteorology affecting both background and modeled 

concentrations, but the justification 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 the ambient monitoring data used to 

assess the Project’s impacts on the 1-hour NO2 standard is discussed above. 

EPA COMMENT: The aspect of temporal pairing of modeled and monitored 

concentrations is also acknowledged in EPA's March 23, 2010 memorandum from 

Stephen Page regarding Modeling Procedures for Demonstrating Compliance with 

PM2.5 NAAQS, where EPA indicates on page 8 that a Second Tier approach for 

combining modeled and monitored PM2.5 concentrations on a seasonal or quarterly basis 

may be considered when the modeled primary PM2.5 impacts and background PM2.5

levels (including secondary PM2.5 formation) are not correlated on that time scale. 

Although the March 23, 2010 memo does not provide details regarding the recommended 

method for combining modeled and monitored PM2.5 concentrations on a seasonal or 

quarterly basis, the recent draft PM2.5 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 then sorting the combined distribution to 

determine the cumulative design value (see Appendix K of the draft Hot Spot guidance). 

Note that the modeled and monitored concentrations are not paired on a day-by-day (or 

hour-by-hour) basis in this Second Tier approach for PM2.5, even though the spatial 

homogeneity of background levels of PM2.5 on a daily basis is likely to be much greater 

than the spatial homogeneity of background levels of NO2 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 are not relevant to a discussion 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 implies an assumption that the monitored 
31 

concentrations are equally representative at each location within the modeling domain 

for each hour of the simulation. 

RESPONSE: Avenal would propose the following clarification to EPA’s comment: the 

monitored concentrations are equally representative of the regional background

concentration at each location within the modeling domain for each hour of the 

simulation. This assumption is inherently conservative. As discussed previously, we 

assume that every point in the region is impacted by the same regional background 

concentration plus the impact of local sources. 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 rational 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 the 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 determination. The technique used to combine 

background and modeled concentrations on an hourly basis for the Project is the same as 

that used by the District. 

EPA COMMENT: Such a degree of representativeness would also be unreasonable to 

impose as a general requirement for use of background monitored data, given the limited 

number of monitors available. However, any modeling approach developed regarding 

the use of monitored background concentrations as part of a cumulative impact 

assessment must take into account these limitations of monitored data. 

RESPONSE: It is unnecessary to attempt to distinguish between “degrees of 

representativeness.” As discussed above, given an adequate demonstration that the 

monitor and the impact area are in the same region, subject to the same regional 

background, then the assumption that the monitor represents regional background is 

necessarily conservative. The possible effects of local sources on the impact area are 

addressed by the nearby source analysis. 

EPA COMMENT: The results from the 1-hour NO2 CAAQS comparison summarized in 

Table 6.2-31 (6.2-66) of the APC show maximum 1-hour Avenal facility impacts of 190 

μg/m3, combined with a background concentration of 137.2 μg/m3

 to give a total impact 

of 327.2 μg/m3. This cumulative 1-hour NO2 impact is well above the EPA 1-hour NO2
32 

standard, although we recognize that the 1-hour modeled NO2 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 times higher than the cumulative 1-hour NO2 impact 

reported in the May 13, 2010 submittal, which serves to highlight the 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 high values predicted by a screening 

analysis emphasize the conservative 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 NO2 impact analysis submitted on 

May 14, 2010, as well as the revised supplemental 1-hour NO2 impact analysis enclosed 

herewith, the Project will not cause 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 NO2 standard to modeling applications, as suggested 

by Avenal. EPA's comment objects to discarding valid modeled data. The applicant 

should choose a method for combining modeled 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 Modeling Guidance for the 1-hour NO2 National Ambient 

Air Quality Standard (June 28, 2010) may be useful in preparing an analysis of the 

1-hour NO2 NAAQS. 

RESPONSE: We have reviewed The Appendix W modeling guidance document again, 

and it does not provide useful guidance to address this issue. This is because the 

modeling guidance document only describes compliance demonstrations using screening 

approaches, and not a full compliance demonstration 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 revised supplemental 1-hour NO2 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.