# Supplemental NO 2 

# Air Quality Impact Analysis

Avenal Energy Project

prepared for:



## Avenal Power Center, LLC

May 13, 2010

prepared by:

Sierra Research, Inc.
1801 J Street Sacramento, California 95811 (916) 444-6666

### Supplemental NO 2 

### Air Quality Impact Analysis Avenal Energy Project

prepared for:

Avenal Power Center, LLC

May 13, 2010

Principal author:

Eric Walther

Sierra Research, Inc.

1801 J Street Sacramento, CA 95811 (916) 444-6666

### Supplemental NO 2 

### Air Quality Impact Analysis Avenal Energy Project

Table of Contents

Page

1. Background................................................................................................................. 1

1.1 Project Description.............................................................................................. 1 1.2 History of Demonstrating Compliance w ith Ambient Air Quality Standards.... 1

1.3 The New NO 2 National Ambient Air Quality Standard ..................................... 2

2. Methodology............................................................................................................... 3

2.1 Overview of Methodology.................................................................................. 3 2.2 AERMOD Modeling........................................................................................... 4 2.3 Receptor Grids .................................................................................................... 4 2.4 Data Requirements—Me teorological Data......................................................... 5 2.5 Data Requirements—Ambient Monitoring Data................................................ 6 2.6 Combining Existing Ambient Air Qual ity Data with Modeled Impacts ............ 7

3. Results..................................................................................................................... .. 10-1- 

## 1. BACKGROUND

1.1 Project Description

The Avenal Energy Project will be a combined-cycle 600-megawatt (MW) power generation facility consisting of two GE Energy Frame 7FA natural gas-fired turbinegenerators, a single condensing steam turb ine (STG), air-cooled condenser, and associated balance-of-plant equipment. The f acility will be located on a 148-acre site at the eastern edge of th e city limits of Avenal, Kings County, California, adjacent to the San Luis Canal. Agricultural land uses currently occupy and surround the site.



### 1.2 History of Demonstrating Compliance with Ambient Air Quality

Standards

Key dates in the history of demonstrating co mpliance with ambient air quality standards in the applications to the USEPA for a PSD permit and to the San Joaquin Valley Air Pollution Control District (SJVAPCD or District) for a Final Determination of Compliance (FDOC) are the following:

 February 15, 2008 PSD and ATC permit applications submitted to USEPA and SJVAPCD, respectively

 October 30, 2008 District FDOC issued

 June 16, 2009 EPA draft PSD permit issued

An ambient air quality impact analysis was prepared to support the February 2008 PSD permit and FDOC applications. The air disp ersion modeling indicated that the maximum annual nitrogen dioxide (NO 2 ) impact from the project of 0.5 μg/m 3 would not exceed the Significant Impact Level of 1.0 μg.m 3 for the annual NO 2 National Ambient Air Quality Standard (NAAQS).

A full impact analysis demonstrating compliance with the annual NO 2 NAAQS was included in the February 2008 application. EPA confirmed that the Project’s maximum potential annual NO 2 impact of 0.6 μg/m 3 was below the applicable Significant Impact Level of 1 μg/m 3 and, hence, that no further analysis was required for potential NO 2-2- impacts from the Project’s NOx emissions. 1 At the time that the application was submitted, there was no hourly NO 2 NAAQS.



### 1.3 The New NO 2 

### National Ambient Air Quality Standard

On February 9, 2010, EPA revised the primary NO 2 NAAQS, establishing a new onehour NO 2 standard to supplement the existing annual standard (75 FR 6473). The new standard became effective on April 12, 2010. It is a statistically base d standard at a level of 100 ppb, based on the 3-year average of the 98 th percentile of the yearly distribution 2
of 1-hour daily maximum concentrations, and will supplement the existing annual

standard. 3

This report demonstrates that the Avenal Ener gy Project will not interfere with attainment

of the new NO 2 standard. The following guidance doc uments were used to develop the methodology for this analysis:

 USEPA. Notice Regarding Modeling for New Hourly NO 2 NAAQS , updated February 25, 2010;

 Federal Register, Volume 75, Number 26, Part III, Environmental Protection Agency, 40 CFR Parts 50 and 58, Primary National Am bient Air Quality Standards for Nitrogen Dioxide; Final Rule, Appendix S, pages 6532-6534, February 9, 2010;

 USEPA. Guideline on Air Quality Models, published as Appendix W of 40 CFR Part 51, Federal Register, Volume 70, Number 216, November 9, 2005; and

 USEPA. On-Site Meteorological Program Guidance for Regulatory Model Applications, report EPA 450/4-87-013, August 1995.

###

1 USEPA. Draft PSD Permit Statement of Basis and Ambient Air Quality Impact Report , Tables 8-1 and 8- 2, pp.25 and 26, respectively, June 2009.

2 For a reasonably complete annual set of daily measurements (i.e., at least 351 valid days), the 98 th
percentile is the 8 th highest measurement.

3 75 FR 6474-3- 

## 2. METHODOLOGY

2.1 Overview of Methodology

This full impact analysis considers project emissions and regional background

concentrations. The NO 2 impacts in the study area from project sources were estimated using AERMOD and the Plume Volume Molar Ratio Method (PVMRM) for each hour in the five-year analysis period (2000–2004).

The representative background concentrati on for each hour was added to the modeled impact from the Project plus nearby sources to get a predicted concentration for each hour in the study period, for each receptor.

EPA’s guidance on the use of AERMOD modeling results to calculate NO 2 impacts for comparison to the new standard was followed, as outlined below. 4

 For each day in the study period, the highest one-hour concentration was determined for each receptor in the mode ling domain. This is the daily maximum

concentration.

 At each receptor, for each calendar year in the five-year analysis period, the 98 th
percentile daily maximum concentration was determined. If the annual data set is essentially complete (i.e., at least 351 valid days), the 98 th percentile corresponds

to the 8 th highest daily maximum. If the annual data set is complete to at least the required 75% for all four quarters, and th e number of valid daily measurements is between 301 and 350, the 98 th percentile concentration for each receptor was the

7 th highest daily one-hour maximum. A si milar scale is provided in Appendix S

Table 1 of the Final Rule for fewer valid daily measurements in an otherwise “complete” year.

 At each receptor, the 98 th percentile daily maximum concentrations were averaged across each of the 3 consecutive three-ye ar periods in the five-year analysis period. 5

 The highest three-year average 98 th percentile concentratio n across all receptors represents the modeled 1-hour NO 2 concentration for comparison with the NAAQS.

4 Notice Regarding Modeling for New Hourly NO 2 NAAQS ; EPA (Updated February 25, 2010).

5 This approach is more conservative (results in a higher maximum value) than the approach described in the EPA guidance, which calls for an average across all modeled years. This approach was taken to make the result more closely match the form of the standard.-4-  The design value was converted from μg/m 3 (the units used by AERMOD) to ppb (the units in the standa rd) using the ratio 100 μg/m 3 = 53 ppb, following EPA guidance; the result was rounded to the n earest ppb and compared to the standard.



### 2.2 AERMOD Modeling

The following USEPA air dispersion models we re used to quantify pollutant impacts on the surrounding environment based on the em ission sources’ operating parameters and

their locations:

 American Meteorological So ciety/Environmental Prot ection Agency Regulatory Model Improvement Committee (AERMIC) model, also known as AERMOD (Version 09292); and

 Building Profile Input Program – Plume Rise Model Enhancements (BPIP-PRIME, Version 04274).

The original air dispersion modeling for the Project was conducted with AERMOD Version 07026, but this supplemental air dispersion modeling analysis has been conducted using AERMOD Version 09292. The ai r quality modeling analysis followed the January 2008 USEPA AERMOD Implemen tation Guide and EPA’s 2005 “Guideline on Air Quality Models.” USEPA default op tions for AERMOD were used (model option DFAULT). Standard AERMOD control parame ters were used, including stack tip downwash, non-screening mode, non-flat terrai n, and sequential meteorological data check. The modeled hourly NO 2 concentrations were limited by the available ozone according to the use of AERMOD with the PVMRM option. To the extent that the meteorological data set contained missing va lues for any hour such that a valid NO 2 concentration could not be modeled, the re sults for that hour were coded as missing.



### 2.3 Receptor Grids

Receptor and source base elevations were determined from USGS Digital Elevation Model (DEM) data using the 71⁄2-minute format (10- to 30-meter spacing between grid nodes). All coordinates were referen ced to UTM North American Datum 1927 (NAD27), Zone 10. The AERMOD receptor el evations were interpolated among the DEM nodes according to standard AERMAP pro cedure. For determining concentrations in elevated terrain, the AERMAP terrain pr eprocessor receptor-outpu t (ROU) file option

was chosen.

Nested Cartesian coordinate receptor grids we re developed to provide adequate spatial coverage surrounding the project area for assessing ground-level pollution concentrations, to identify the spatial extent of significant impacts, and to identify maximum impact locations. The resolution a nd extent of each nested grids were as

follows:-5-  25-meter resolution along the facility fe nce line in a single tier of receptors composed of four segments extending out to 100 meters from the fence line;

 100-meter resolution from 100 meters to 1,000 meters from the fence line; and

 250-meter resolution from 1 km out to approximately 10 km from the site.

When maximum first-high or maximum second-high impacts occurred in the 100- or 250-meter spaced areas, an additional refined receptor grid with 25-meter resolution was placed around each maximum coarse grid impact in the form of a circular area extending out to a distance of 500 meters (i.e., two coarse grid “spacings”) from the location of each coarse grid maximum. Concentrations within the facility fence line were not calculated.

The following 7.5-minute USGS Digital El evation Model (DEM) quadrangles in California were employed for modeling the Project:

 Guijarral Hills;

 Huron;

 Westhaven;

 Avenal;

 La Cima;

 Kettleman City;

 Garza Peak;

 Kettleman Plain; and

 Los Viejos.

The approach used for selecting receptor grids fo r this analysis is identical to that used in the air quality impact analysis containe d in the February 2008 PSD and FDOC permit applications.



### 2.4 Data Requirement s—Meteorological Data

AERMOD uses hourly meteorological data to characterize plume dispersion. The representativeness of the da ta is dependent on the proximity of the meteorological monitoring site to the area under consider ation, the complexity of the terrain, the exposure of the meteorological monitoring site , and the period during which the data are collected. The meteorological data used in th is analysis were collected at the Hanford monitoring station, located 28 miles northeast of th e site. This data set was selected to be representative of meteorol ogical conditions at the proj ect site and to meet the requirements of the EPA On Site Meteor ological Program Guidance for Regulatory Model Applications (EPA 450/4 87 013, August 1995). The analysis used meteorological data collect ed during 2000-2004, and prepared by the District in AERMOD-compatible format.-6- The District had preprocessed the meteorological data from Hanford into the format required by AERMOD. The surface characteri stics 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 mete orological data set used for this analysis is unchanged from th at used to develop the air quality impact analysis in the February 2008 PSD and FDOC permit applications.



### 2.5 Data Requirements— Ambient Monitoring Data

Ambient NO 2 data collected during the five-y ear modeling period of 2000-2004 at the Hanford monitoring station were used to characterize the re presentative ambient background concentrations. The ambient po llution levels monitored at the Hanford monitoring station represent area-wide ambi ent conditions rather than the localized impacts of any particular facili ty due to the lack of any larg e local industrial sources in

the Hanford area.

Computation of hourly NO 2 impacts from the Project also requires use of ambient monitored hourly ozone concentrations. The PVMRM adaptation of the Ozone Limiting

Method 6 was used to determine the extent to which the NO emitted from the exhaust

stacks is converted to NO 2 when it reaches the ground. AERMOD PVMRM calculates

the NO 2 concentration using hourly oz one data. Hourly ozone da ta collected at the same Hanford monitoring station during the year s 2000-2004 were used in conjunction with PVMRM to calculate hourly NO 2 concentrations from hourly NOx concentrations, as described in the modeling protocol submitted to EPA on August 14, 2007.

The hourly ambient monitoring data are identical to those used in the air quality impact analysis in the February 2008 PSD and FDOC permit applications

2.5.1 Data Substitution—Ozone

Data substitution for missing hourly O 3 and NO 2 ambient monitoring data requires different data substitution procedures because the two data sets serve different purposes. The hourly O 3 data are used within the AERMOD air dispersion model when operated using the PVMRM option that simulates the atmospheric chemistry of O 3 reacting with initially emitted nitric oxide (NO) to form NO 2 . If the amount of O 3 in the plume is insufficient to completely react the NO to NO 2 , then the reaction is limited, forming less

NO 2 than occurs with the simplifying defau lt assumption of complete conversion. The model disperses the initial NOx emissions, which are mostly NO, during each of the 8,760 hours in a 365-day year. Missing hourly ambient O 3 concentrations from the

6 Cole, Henry S. and John E. Summerhays. The Application of reactive plume models to the estimation of

short-term NO 2 concentration , presentation at the Annual Meeting of the Air Pollution Control Association, Houston, Texas, June 1978, and A review of techniques available for estimating short-term NO 2 concentrations , Journal of the Air Pollution Control Association, Volume 29, Number 8, pages 812-817, August 1979.-7- Hanford monitoring station were given substi tuted concentrations with hour-appropriate values (e.g., from the previous day, or the ne xt day, for the same hour) as stated in the August 14, 2007 modeling protocol.

2.5.2 Data Substitution—NO 2

Unlike the O 3 data that are used by the dispersion model to determine modeled impacts,

the NO 2 ambient data are used to establish the baseline ambien t conditions for the Project impact area. As such, based on EPA guidan ce related to determinations of compliance with the new one-hour average NO 2 NAAQS, 7 no data substitution was performed for the

NO 2 data; instead, it was necessary to determin e whether there are sufficient hourly data available for a complete day, quart er, and year. Under EPA guidance, 8 a day is classified as complete if it has at least 75% of the hourly concentrations recorded (i.e., at least 18 hourly readings per day). A quart er is classified as complete if it has at least 75% of the sampling days with complete data (i.e., at l east 67 to 69 depending on quarter). A year is classified as complete if it has four comple te quarters. An incomplete year cannot be used to demonstrate compliance (although under cer tain circumstances it could be used to demonstrate noncompliance).

To determine whether a day, quarter, or year is complete, missing hourly NO 2 data were identified. Missing hourly NO 2 ambient concentrations were replaced with the value -99, which informs the computation algorithm that no valid NO 2 concentration was measured for that hour. If more than six hourly con centrations were missing in the same day, the entire day was identified as invalid, agai n following the same EPA regulatory guidance. 9



### 2.6 Combining Existing Ambient Air Quality Data with Modeled Impacts

Modeled concentrations we re added to background NO 2 concentrations to determine total concentrations for comparison with the new NAAQS using the procedure summarized

below.

The modeled and monitored 1-hour NO 2 concentrations were combined as outlined

below.

 As described above, the impacts of the proj ect at each receptor in the study area and for each hour in the analysis pe riod were modeled using AERMOD.

 The predicted total hourly NO 2 concentration at each receptor was calculated by adding the modeled hourly project impact at the receptor to the corresponding

hour NO 2 concentration measured at the Ha nford ambient monitoring station.

7 Federal Register, Volume 75, Number 26, Part III, Environmental Protection Agency, 40 CFR Parts 50 and 58, Primary National Ambient Air Quality Standards for Nitrogen Dioxide; Final Rule, Appendix S, pages 6532-6533, February 9, 2010.

8 Ibid, p. 6532.

9 Ibid.-8-  For hours with missing ambient monitored background NO 2 concentrations, the resulting total hourly co ncentrations (modeled impacts plus background concentrations) were labeled as missing us ing the value -99 at every receptor.

 The daily maximum total hourly NO 2 concentration for each day was determined for each receptor. If there were fewer th an 18 complete hours for a day, the value for that day was labeled as missing using the value of -99.

 If there were four complete quarter s for a given complete year, the 98 th percentile daily maximum total hourly NO 2 concentration was determined for that year for each receptor as follows from EPA guidance:

- 8 th highest value if the annual number of valid daily maximum total hourly

NO 2 concentrations is at least 351;

- 7 th highest value if the annual number of valid daily maximum total hourly

NO 2 concentrations is between 301 and 350; and

- 6 th highest value if the annual number of valid daily maximum total hourly

NO 2 concentrations is between 251 and 300.

 At each receptor, the 98 th percentile daily maximum concentrations were averaged across each three-year period in the analysis period.

 From the field of receptors, the receptor with the highest three-year average was selected to represent the maximum total hourly NO 2 concentration for the project impact area. This maximum total hourly NO 2 concentration was converted from μg/m 3 to ppb (using the annual NO 2 NAAQS conversion ratio of 100 μg/m 3 = 53 ppb); the result was rounded to the nearest ppb and compared to the new

one-hour NO 2 NAAQS.

Sierra Research developed a postprocessor in FORTRAN to perform these calculations. The postprocessor uses the two following input files:

 AERMOD 1-hour average NO 2 DAYTABLE 10 output file (processed with PVMRM); and

 Hourly ambient background NO 2 concentrations (in units of μg/m 3 ).

To allow the postprocessor to handle th e large DAYTABLE output files for tens of thousands of receptors in the grids and the fi ve years of hourly mete orological data, the postprocessor reads and proce sses concentrations from bot h files in 24-hour blocks.

10 A February 25, 2010 USEPA Notice Regarding Modeling for New Hourly NO 2 NAAQS, suggests the same computational post-processing with the AERMOD-generated POSTFILE ( http://www.epa.gov/scram001/no2_hourly_NAAQS_aermod_02-25-10.pdf ). The AERMOD generated DAYTABLE and POSTFILE contain identical data, but in different formats.-9- The AERMOD output file is read, receptor by receptor, for each hour. Then the background concentration is read for that hour and added to the modeled concentrations. By the end of a day’s values, if 75% comp leteness is not achieved, then the hourly maxima at all the receptors for that day ar e replaced with an incompleteness indicator (-99).

Once the daily maxima are determined for each receptor for the entire year, two tables are generated. The first table calculated is th e daily maxima for all receptors, and becomes the first output table from the postprocessor.

The daily maxima for each receptor are sort ed by the postprocessor through use of the HEAPSORT utility from Numerical Recipes. 11 The second table is calculated, and output for the eight highest daily maximum concentrations for each receptor (tagged by Julian day) is generated.

At each receptor, the 98 th percentile daily maximum concentrations were averaged across each of the 3 three-year periods in the 2000- 2004 analysis period. Examination of the second table yields the highest 8 th -highest concentration from among all the receptors, for comparison to the federal standard.

###

11 The HEAPSORT sorting routine is taken from Press, W.H., B.P. Flannery, S.A. Teukolsky, and W.T. Vetterling,, Numerical Recipes, The Art of Scientific Computing (FORTRAN Version) , Section 8.2, page 229, Cambridge University Press, New York, 1989.-10- 

## 3. RESULTS

The three-year average of 98 th percentile concentrations at any receptor was 119.8 μg/m 3

, or 63 ppbv, and occurred during startup conditio ns. This is lower than the one-hour NO 2 NAAQS of 100 ppb. The project will therefore not cause or contribute to an exceedance

of the standard.

Except for the last two quarters of 2001, each quarter in the study an alysis period met the validity requirements for a compliance de monstration under EPA guidelines. For 2000, 2002, and 2004, more than 350 of the daily measurements were valid; thus the 98 th
percentile concentration for each receptor was the 8 th highest daily one-hour maximum. The year 2001 was invalid for compliance calc ulation because of the invalid last two quarters. For 2003, the 342 valid daily measurements were between 301 and 350; therefore, the 98 th percentile concentration for each receptor was the 7 th highest daily onehour maximum. Failure of the year 2001 left only one consecutive three-year period over which to calculate the three-year average of 98 th percentile concen trations—2002-2004; this was the period used to determine the three-year average 98 th percentile value of 63 ppbv.