# Air Dispersion Modeling and
Health Risk Assessment
Protocol

Avenal Energy Project Kings County, California

Submitted to:



### San Joaquin Valley Air Pollution Control District California Energy Commission U.S. Environmental Protection Agency, Region 9

Federal Power Avenal LLC prepared for:



### August 2007

prepared by:

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

## Air Dispersion Modeling and Health Risk Assessment Protocol Avenal Energy Project

Submitted to San Joaquin Valley Air Quality Management District California Energy Commission U.S. Environmental Protection Agency, Region 9

August 2007

Sierra Research, Inc.

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

### Air Dispersion Modeling and Health Risk Assessment Protocol Avenal Energy Project

Table of Contents

Section Page 1. Purpose and Background ..................................................................................................... ...... 1 2. Project Location........................................................................................................... .............. 3 3. Proposed Emission Sources .................................................................................................. ..... 3

4. Meteorol ogical Data ........................................................................................................ .......... 4 5. Site Representation – Meteorological Data ............................................................................... 4 6. Existing Ambient Air Quality Data .......................................................................................... . 5 7. Air Quality Dispersion Models.............................................................................................. .... 6 8. Good Engineering Practice (GEP) Stack Height and Downwash ............................................. 8 9. Receptor Selection ......................................................................................................... ............ 8 10. Modeling Scenarios ......................................................................................................... ....... 10 11. Class I Area Impact Analysis and Class II PSD Significance Thresholds ............................. 11 12. Ambient Air Quality Impact Analyses .................................................................................. 12

13. Health Risk Assessment..................................................................................................... ..... 14 14. Construction Air Quality Impact Analysis ............................................................................. 16 15. Cumulative Air Quality Impact Analysis ............................................................................... 17 16. Final Modeling Submittal ................................................................................................... .... 17

17. References............................................................................................................................... 18

Appendix A: Location Figures Appendix B: Information on CTDMPLUS Model

List of Tables

Page 1. Air Quality Impact Analysis Significance Thresholds..........................................................3 2. Operating Modes of the Combustion Gas Turbines............................................................11 3. Significance Levels for Air Quality Impacts in Class II Areas...........................................13

List of Figures

Page 1. Locations of Project and Surface Meteorological Monitoring Station ...............................20 2A. Wind Rose for Hanford, CA – Calendar Year 2000 ...........................................................21 2B. Wind Rose for Hanford, CA – Calendar Year 2001 ...........................................................22 2C. Wind Rose for Hanford, CA – Calendar Year 2002 ...........................................................23 2D. Wind Rose for Hanford, CA – Calendar Year 2003 ...........................................................24 2E. Wind Rose for Hanford, CA – Calendar Year 2004 ...........................................................25-1- 

## Avenal Energy Project Modeling Protocol July 2007

1. P URPOSE AND B ACKGROUND

On behalf of Federal Power Avenal LLC (Applicant), Sierra Research is submitting this modeling protocol to the San Joaquin Valley Air Pollution Control District (SJVAPCD or District), California Energy Commission (CEC), a nd U.S. Environmental Protection Agency (US EPA) for approval of the air dispersion and health risk assessment modeling proposed to be conducted in support of the Avenal Energy Project (Project) Application for a Determination of Compliance (DOC) from the District, Applicati on for Certification (AFC) from the CEC, and Prevention of Significant Deterioration (PSD) Permit from the EPA.

The proposed air-cooled combined-cycle power plant project will consist of constructing and operating the following equipment:

• Two General Electric PG7241 (FA) combustion turbines (or equivalent), rated at 180 MW (nominal net, at site design conditions);

• Two heat recovery steam generators (HRSGs) equipped with duct burners;

• One 300-MW (nominal) condensing steam turbine;

• One natural gas-fueled auxiliary boiler;

• Three inlet air chillers with associated air cooling;

• One closed cooling water air cooler;

• One fire water pump engine; and

• One emergency generator engine.

The project site is located six miles northeast of the residential and business districts of the City of Avenal in Kings County, between the California Aqueduct and the Avenal Cutoff Road (see location figures in Appendix A).

Because the Project will generate more than 50 MW of electric power, certification by the CEC will be needed to satisfy requirements for public disclosure of potential environmental impacts under the California Environmental Quality Act (CEQA). Criteria pollutant emissions of nitrogen oxides (NOx), carbon monoxide (CO), and particulate matter with nominal aerodynamic diameter less than or equal to 10 microns (PM 10 ) will exceed 50 tons per year, and hence, classify the Project as a new major source under District New Source Review regulations,Rule 2201. Project emissions of these same pollutants are also expected to exceed the 100 tonper-year major source threshold for the federal Prevention of Significant Deterioration (PSD) requirements (40 CFR 52.21) pertaining to federal attainment 1 pollutants nitrogen dioxide (NO 2 ),

1 Sulfur dioxide (SO 2 ) is also an attainment pollutant, while ozone and particulate matter with nominal aerodynamic diameter less than or equal to 2.5 microns (PM 2.5 ) are nonattainment pollutants in the project area of the San Joaquin Valley Air Basin.-2- CO, and PM 10 emitted from the fossil fuel-fired steam-electric plant category 2 listed in the federal PSD regulations. Therefore, the permit application will include a demonstration of compliance with all applicable portions of the PSD requirements. Emissions of volatile organic compounds (VOCs) and sulfur dioxide (SO 2 ) will be below major source levels.

The Applicant will submit air quality impact analyses to the SJVAPCD, CEC, and US EPA. The modeling analyses will include pollutants as required by District Rule 2201, Section 4.3.2;,CEC requirements 3 for evaluation of project air quality impacts; and applicable US EPA requirements for PSD permits. The purpose of this document is to establish the procedure for meeting District, CEC and US EPA air quality modeli ng requirements for the proposed project.

This protocol follows modeling guidance provide d by the U.S. Environmental Protection Agency (USEPA) in its “ Guideline on Air Quality Models ” (including supplements), the National Park

Service’s “ Permit Application Guidance for New Air Pollution Sources ” (Bunyak, 1993), the Federal Land Managers’ “ Air Quality Related Values Workgroup (FLAG) Draft Phase I Report ” (October 1999), the “ Interagency Workgroup on Air Quality Modeling (IWAQM) Phase II

Recommendations ” (1998), and the SJVAPCD Guidance for Air Dispersion Modeling, Version

1.2 (August 2006).

The air quality impact analysis will address the proposed facility operation in terms of the following modes:

• Baseload (100%) operation without duct firing

• Baseload (100%) operation with duct firing

• Startup/shutdown operations.

Impacts from operation of the facility will be compared to the thresholds shown in Table 1:

2 Fossil fuel-fired steam-electric plant with heat input greater than 250 MMBtu/hour.

3 Summarized in CEC Data Adequacy Worksheets, revised March 28, 2007, and available at http://www.energy.ca.gov/sitingcases/documents/index.html

.-3- Table 1 Air Quality Impact Analysis Significance Thresholds

Air Quality Criteria VOC a NO 2 PM 10 PM 2.5 CO SO 2

PSD Significant Impact Levels NA b √ √ NA √ NA

PSD Monitoring Exemption Levels NA √ √ √ NA

Ambient Air Quality Standards (AAQS) √ √ √ √ c √ √

Class I and Class II Visibility √ √ √

Impacts to Soils and Vegetation √ √ √

Class I Area Acid Deposition √ √ √

Notes: a. VOC emissions are used as a surrogate for ozone impacts in the PSD review process; no ozone modeling will be

carried out. b. Not applicable. c. USEPA guidance (71 FR 6727) provides that compliance with the federal PM 2.5 NAAQS should be evaluated using the PM 10 NAAQS and not modeled directly. At the request of the California Air Resources Board (ARB), compliance with both the federal 24-hour average AAQS and the state and federal annual average AAQS for

PM 2.5 will be addressed based on PM 2.5 for non-PSD purposes.

2. P ROJECT L OCATION

The location of the site is approximately the following:

• Latitude: 36.088394° North

• Longitude: 120.061141° West

or, in Universal Transverse Mercator (UTM) coordinates,

• Northing: 3,997.742 kilometers (km) and

• Easting: 764.616 kilometers (North American Datum [NAD] 27, Zone 10).

The nominal site elevation is 340 feet (104 meters) above mean sea level.

3. P ROPOSED E MISSION S OURCES

The new emission sources for the Project will be the two natural gas-fired combustion turbines in combined-cycle mode, one natural gas-fired auxiliary boiler, one natural gas-fueled emergency generator engine, and one Diesel-fueled fire water pump engine. The turbines will utilize advanced combustion design and emission controls to limit emissions of NOx, CO, and

VOC. Emissions of PM 10 and particulate matter with nominal aerodynamic diameter less than or equal to 2.5 microns (PM 2.5 ), and SOx will be kept to a minimum through the exclusive use of natural gas in the turbines. The layout of the emitting units is shown in the last three figures in Appendix A.-4- 4. M ETEOROLOGICAL D ATA

The Project area has no on-site meteorological monitoring. The District has developed and posted on its website five years of meteorological data from its monitoring station at Hanford, CA, located 28 miles to the northeast of the project site (see Figure 1), and appropriate for use on this project with the model AERMOD 4 (current version 07026). Data from the Hanford station 5 have been processed by AERMET software, which formats the data for use in AERMOD. 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 can be characterized by up-valley and down-valley winds. The down-valley 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 mark edly 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 available data 6 will not vary much because the meteorological data are so constant between the years.

It is expected that the main modeling for the project will be accomplished with AERMOD. If needed for supplemental modeling of air dispersion to receptors in terrain above stack-top height, Appendix A contains information on the following two additional models and the meteorological data needed to run them: Complex Terrain Screening Model (CTSCREEN) and the Complex Terrain Dispersion Model PLUS (CTDMPLUS).

5. S ITE R EPRESENTATION

– M ETEOROLOGICAL D ATA

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 meteorologi cal 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 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

4 AERMOD stands for American Meteorological Society/Environmental Protection Agency Regulatory Model, and was developed by the American Meteorological Society/Environmental Protection Agency Regulatory Model Improvement Committee (AERMIC).

5 SJVAPCD. Meteorological data from Hanford during 2000-2004, http://www.valleyair.org/busind/pto/Tox_Resources/AirQualityMonitoring.htm.

6 SJVAPCD. Hanford meteorological data in AERMOD-compatible format, http://www.valleyair.org/busind/pto/Tox_Resources/AirQualityMonitoring.htm-5- are collected. The District’s proposed Camp Pe ndleton meteorological data are representative of conditions at the project site.

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 Camp Pendleton 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.

6. E XISTING A MBIENT A IR Q UALITY D ATA

Background ambient air quality data for the project area during 2004-2006 will be obtained from the following monitoring sites that are nearest to the project site by pollutant:

• Corcoran- Patterson Avenue 7 : PM 10 and PM 2.5

• Visalia-North Church Street: CO

• Hanford-South Irwin Street: O 3 and NO 2

• Sacramento-Del Paso Manor: SO 2

Modeled concentrations will be added to these representative background concentrations to determine compliance with the CAAQS and NAAQS.

For PM 10 and PM 2.5 , the following data will be used to represent project background:

• For PM 10 , the highest 24-hour average and annual average values between 2004 and 2006 will be used to represent project background.

• For PM 2.5 24-hour impacts, the three-year average of the 98 th percentile 24-hour monitored levels for the period between 2004 and 2006 will be used to represent project background. For annual impacts, the highest monitored annual average between 2004 and 2006 will be used to represent project background. The maximum modeled 24-hr

and annual PM 2.5 impacts for the project will be added to the above project background levels to confirm that the project will not cause or contribute to a violation of an air quality standard. The most recent three calendar-year period available, 2004-2006, is used to most accurately represent future background levels in the AQIA.

• If a more refined analysis of potential PM 2.5 impacts is needed, then the following procedure would be followed to combine background concentrations of 24-hour average

PM 2.5 concentrations during the period 2000 through 2004 (contemporaneous with meteorological data) with modeled impact concentrations. Because PM 2.5 measurements

7 http://www.arb.ca.gov/adam/cgi -bin/db2www/adamtop4b.d2w/Branch-6- are taken on a once-in-six-day basis, each PM 2.5 measurement would be presumed to represent the day of measurement and each of the five subsequent days. Missing data would be filled in by interpolation using da ta from the data immediately preceding and following the missing data point. These day- specific project background data would be combined with contemporaneous modeled project impacts to evaluate compliance with

the PM 2.5 AAQS for non-PSD purposes. The highest three-year average of the combined project plus background 98 th percentile 24-hour average concentrations would then be used to evaluate compliance with the 24-hour average PM 2.5 AAQS for non-PSD purposes. The highest three-year average of the combined project plus background annual average concentrations would be used to evaluate compliance with the annual average PM 2.5 AAQS for non-PSD purposes.

7. A IR Q UALITY D ISPERSION M ODELS

Overview

The following USEPA air dispersion models are proposed for use to quantify pollutant impacts on the surrounding environment based on the emission sources’ operating parameters and their

locations:

• American Meteorological Society/Environmental Protection Agency Regulatory Model Improvement Committee (AERMIC) model, also known as AERMOD (Version 07026);

• Building Profile Input Program – Plume Rise Model Enhancements (BPIP-PRIME, current version 04274); and

• SCREEN3 (Version 96043).

The following models are not expected to be used, but they are listed in the event that an optional specialized modeling analysis is necessary for the project. In addition to the information listed below, further information on the use of CTDMPLUS is provided in Appendix

A.

• Complex Terrain SCREEN (CTSCREEN, Version 94111)

• Complex Terrain Dispersion Model (CTDMPLUS, Version 93228)

• Visibility Screening Model (VISCREEN (Version 88341)

The first three primary models listed above, and how they are used, are discussed below.

Simple, Complex, and Intermediate Terrain Impacts

For modeling project emissions in simple, complex, and intermediate terrain, the USEPArecommended guideline model AERMOD will be used with the AERMET-processed hourly meteorological data from the Hanford monitoring station during 2000-2004 provided by the District on its website. The AERMOD model requi res hourly meteorological data consisting ofwind vector and speed (with reference height), temperature (with reference height), MoninObukhov length, surface roughness length, heights of the mechanically and convectively-7- generated boundary layers, surface friction velocity, convective velocity scale, and vertical potential temperature gradient in the 500-meter layer above the planetary boundary layer. The model assumes that there is no variability in meteorological parameters over a one-hour time period, hence the term “steady-state.” The AERMOD model allows input of multiple sources and source groupings, eliminating the need for multiple model runs. Complex phenomena such as building-induced plume downwash are treated in this model.

Standard AERMOD control parameters will be used (stack tip downwash, non-screening mode, non-flat terrain, sequential meteorological data check employed). Stack-tip downwash, which adjusts the effective stack height downward following the methods of Briggs (1972) for cases where the stack exit velocity is less than 1.5 times the wind speed at stack top, will be selected per USEPA guidance. The rural default option will be used by not invoking the URBANOPT option. 8

Ambient Ratio Method and Ozone Limiting Method

Annual NO 2 concentrations will be calculated using the Ambient Ratio Method (ARM), adopted in Supplement C to the Guideline on Air Quality Models (USEPA, 1995). The Guideline allows a nationwide default of 75% for the conversion of nitric oxide (NO) to NO 2 on an annual basis

and the calculation of NO 2 /NOx ratios.

If NO 2 concentrations need to be examined in more detail, the Plume Volume Molar Ratio Method (PVMRM) adaptation of the Ozone Limiting Method (Cole and Summerhays, 1979) will be used.

AERMOD PVMRM calculates the NO 2 concentration using hourly ozone data. Hourly ozone data collected at the Hanford monitoring station dur ing the years 2000-2004 will be used in conjunction with PVMRM to calculate hourly NO 2 concentrations from hourly NOx concentrations. Missing hourly ozone data will be substituted prior to use with day-appropriate values (e.g., from the previous day, or the next day, for the same hour). Any other missing hourly ozone data will be substituted with 40 ppb ozone (typical ozone tropospheric background level). The PVMRM involves an initial comparison of the estimated maximum NOx concentration and the ambient O 3 concentration left in the plume after reaction of NO with O 3 to determine which is the limiting factor

to NO 2 formation. If the remaining O 3 concentration is greater than the maximum NOx concentration, total conversion is assumed. If the NOx concentration is greater than the remaining

O 3 concentration, the formation of NO 2 is limited by the remaining ambient O 3 concentration. In this case, the NO 2 concentration is set equal to the O 3 concentration plus a correction factor that

accounts for in-stack and near-stack thermal conversion.

Fumigation

The SCREEN3 model will be used to evaluate inversion breakup fumigation impacts for shortterm averaging periods (24 hours or less), as appropriate. The methodology in USEPA, 1992 (Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, Revised) will be followed for these analyses. Combined impacts for all sources under fumigation

8 The rural vs. urban option in AERMOD is primarily designed to set the fraction of incident heat flux that is transferred into the atmosphere. This fraction becomes im portant in urban areas having an appreciable “urban heat island” effect due to a large presence of land covered by concrete, asphalt, and buildi ngs. This situation does not exist for the proposed project site.-8- conditions will be evaluated, based on USEPA and any applicable SJVAPCD modeling guidelines.

8. G OOD E NGINEERING P RACTICE (GEP) S TACK H EIGHT AND D OWNWASH

AERMOD can account for building downwash effects on dispersing plumes. Stack locations and heights and building locations and dimensions will be input to BPIP-PRIME. The first part of BPIP-PRIME determines and reports on whether a stack is being subjected to wake effects from a structure or structures. The second part calculates direction-specific building dimensions for each structure that are used by AERMOD to ev aluate wake effects. The BPIP-PRIME output is formatted for use in AERMOD input files.

9. R ECEPTOR S ELECTION

Receptor and source base elevations will be determined from USGS Digital Elevation Model (DEM) data using the 71⁄2-minute format (10- to 30-meter spacing between grid nodes). All coordinates will be referenced to UTM North American Datum 1927 (NAD27), Zone 10. The AERMOD receptor elevations will be interpolated among the DEM nodes according to standard AERMAP procedure. For determining concentrations in elevated terrain, the AERMAP terrain preprocessor receptor-output (ROU) file option w ill be chosen; hills will not be imported into AERMOD for CTDM-like processing.

Cartesian coordinate receptor grids will be used to provide adequate spatial coverage surrounding the project area for assessing ground-level pollution concentrations, to identify the extent of significant impacts, and to identify maximum impact locations. A 250-meter resolution coarse receptor grid will be developed and will extend outwards at least 10 km (or more as necessary to calculate the significant impact area).

For the full impact analyses, a nested grid will be developed to fully represent the maximum impact area(s). This nested grid will have the following resolutions:

• 25-meter resolution along the facility fence-line in a single tier of receptors composed of four segments extending out to 100 meters from the fenceline

• 100-meter resolution from 100 meters to 1,000 meters from the fenceline

• 250-meter resolution from 1 km out to at least 10 km from the site.

When maximum first-high or maximum second-high impacts occur in the 100- or 250-meter spaced areas, an additional refined receptor grid with 25-meter resolution will be placed around each maximum coarse grid impact and extended out 1,000 meters in all directions from that point of impact. Concentrations within the facility fenceline will not be calculated.

The following 7.5-minute USGS Digital Elevation Model (DEM) quadrangles in California will be employed for modeling the Project:

• Guijarral Hills,

• Huron,

• Westhaven,

• Avenal,-9- • La Cima,

• Kettleman City,

• Garza Peak,

• Kettleman Plain; and

• Los Viejos.

If more distant impacts are encountered in the AERMOD results, then other quadrangles that may be needed include the following (listed from approximately nearest, to farthest):

• The Dark Hole,

• Kreyenhaugen Hills,

• Coalinga,

• Domengine Ranch,

• Harris Ranch,

• Calflax,

• Vanguard,

• Lemoore,

• Stratford,

• Alcalde Hills,

• Joaquin Rocks,

• Lillis Ranch,

• Tres Picos Farms,

• Westside,

• Five Points,

• Burrel,

• Riverdale,

• Ciervo Mountain,

• Tumey Hills,

• Monocline Ridge,

• Levis,

• Cantua Creek,

• San Joaquin,

• Helm,

• Raisin,

• Mercey Hot Springs,

• Chounet Ranch,

• Chaney Ranch,

• Coit Ranch,

• Tranquility,

• Jam esan,

• Kerman,

• Kearney Park,

• Laguna Seca Ranch,

• Hammonds Ranch; and

• Charleston School.-10- 10. M ODELING S CENARIOS

Pollutant emissions to the atmosphere from the proposed project will be dominated by the products of combustion of natural gas in the combustion turbines. Emission rates will be included in the Application for Certification and Application for a Determination of Compliance for the project and will be based on vendor data and additional conservative assumptions of equipment performance. Turbine emissions and stack parameters, such as flow rate and exit temperature, depend on ambient temperature and operating load. To calculate the maximum air quality impacts, a screening analysis will be performed to determine which combination of operating load and atmospheric temperature produces the maximum ground-level concentration (i.e., impact) for each combination of pollutant and averaging time used in an ambient air quality

standard.

In the modeling analysis, maximum impacts will be predicted for base load (100%) and reduced load (50%) conditions. In addition, design extreme hot, annual average, and extreme cold ambient temperatures will be evaluated for each load condition. Each of these conditions has unique performance characteristics that affect plume dispersion and thus predicted impacts. The results of this screening analysis will be used to select the maximum-impact operational scenarios for the modeling analyses. Refined modeling of these maximum-impact scenarios will be based on the five years of available meteorological data and will identify the general locations of maximum impacts on the coarse grid of receptors, around which fine grids will be used to identify the locations of maximum impacts within 25 meters.

Details of Operating Scenarios

Maximum emissions during normal operation woul d occur during periods of maximum fuel consumption, which would occur at peak load (with steam power augmentation). Besides normal operation, three other modes of operation would occur: commissioning (one initial period), startup, and shutdown. In addition to the impacts associated with normal operation, the modeling analysis for the project will examine the short-term impacts associated with commissioning and gas turbine startup/shutdown activities. Table 2 gives more detail on all four operating modes.-11- Table 2 Operating Modes of the Combustion Gas Turbines

Mode Description

Commissioning The process of fine-tuning each of the turbines and their associated emission control systems. The facility will follow a systematic approach to optimize performance of the turbines and the associated control equipment. NOx, CO, and VOC emissions are expected to be greater during commissioning than during normal operation. This one-time mode affects only the initial year of operation.

Start-up Startup NOx and CO emissions are higher because the combustors are not fully optimized, and catalyst systems have not reached optimal temperatures.

Normal Operation Normal operation begins after the turbines and the control equipment are working optimally, at their designated levels. Emissions may vary between the extreme hot, annual average,

and extreme cold ambient conditions.

Shutdown Shutdown occurs at the initiation of the turbine shutdown sequence and ends with the cessation of turbine firing.Typically, the shutdown process will emit less than the startup process, and thus this mode will be represented by the analysis of start-up emissions.

11. C LASS I A REA I MPACT A NALYSIS AND C LASS II PSD S IGNIFICANCE T HRESHOLDS

The project is not located within 100 km of Class I areas, the nearest being the following:

• Pinnacles National Monument: 113 km

• Sequoia National Park: 113 km

• Ventana Wilderness: 127 km

Therefore, the Project, although a major source, will not need to evaluate impacts to visibility and other air quality related values at Class I areas.-12- 12. A MBIENT A IR Q UALITY I MPACT A NALYSES

In evaluating the impacts of the proposed project on ambient air quality, we will model the ambient impacts of the project, add those impacts to background concentrations, and compare

the results to the state and federal ambient standards for SO 2 , NO 2 , PM 10 , PM 2.5, 9 and CO.

In accordance with USEPA guidelines, 10 the highest second-highest modeled concentrations will be used to demonstrate compliance with the short-term federal standards and the highest modeled concentration will be used to demonstrate compliance with the federal annual and all

state standards.

Based on the results of the screening procedure, the operating case that produces the highest modeled ambient concentration for each individual pollutant and averaging period will be used in the refined air quality impact analysis. The screening analysis will identify the operating cases that produce the highest concentration for each pollutant and averaging period, and will provide the specific stack parameters (stack height, stack diameter, exhaust temperature and exhaust velocity) that will be used to evaluate compliance with applicable PSD increments and compliance with the AAQS for all applicable pollutants and averaging periods.

Compliance with ambient air quality standards will be demonstrated in accordance with the three-step process outlined in the October 1990 Draft NSR/PSD Workshop Manual (p. C.51, “The Compliance Demonstration”). The first step in the compliance demonstration is to determine, for each pollutant and averaging period, whether the proposed new equipment will cause a significant ambient impact anywhere. As indicated in the Workshop Manual, “If the significant net emissions increase 11 from a proposed source would not result in a significant ambient impact anywhere, the application is usually not required to go beyond a preliminary analysis in order to make the necessary showing of compliance for a particular pollutant.” The significance levels for air quality impacts are shown in the Table 3. If the maximum modeled impact for any pollutant and averaging period is below the appropriate significance level, no further analysis is necessary.

If the modeled impacts from the Project are above the PSD significance thresholds shown in Table 3, the second step of the compliance demonstration is required to show that the proposed new source, in conjunction with existing sources, will not cause or contribute to a violation of any ambient air quality standard. 12

9 As noted above, comparisons to the federal PM 2.5 AAQS are for non-PSD purposes.

10 40 CFR part 51, Appendix W, Sections 11.2.3.2 and 11.2.3.3

11 Note that this guidance requires modeling only for pollutants for which there is a significant net increase.

12 Because the applicable EPA guidance doe s not define signifi cance levels for PM 2.5 , PM 2.5 impacts will be presumed to be above any applicable significance level regardless of the modeled concentration, and the second step of the process will be performed.-13- Table 3 Significance Levels for Air Quality Impacts in Class II Areas a ( μ g/m 3 ) Averaging Period

Pollutant Annual 24-hour 8-hour 3-hour 1-hour

SO 2 1 5 -- 25 --

PM 10 1 5 -- -- --

NOx 1 -- -- -- --

CO -- -- 500 -- 2000
a. From 40 CFR 51.165, shown as Table C-4 in the 1990 draft PSD Workshop Manual.

If the modeled impacts from the project alone are above the PSD significance thresholds shown in Table 3, the second step of the compliance demonstration is required to show that the proposed new source, in conjunction with existing sources, will not cause or contribute to a violation of any ambient air quality standard. 13 As discussed in more detail in Section 6 of this protocol, the impacts of existing sources are represented by the existing ambient air quality data. In accordance with Section 8.2.1 of Appendix W to 40 CFR Part 51,

Background concentrations are an essential part of the total air quality concentration to be considered in determining source impacts. Background air quality includes pollutant concentrations due to: (1) Natural sources; (2) nearby sources other than the one(s) currently under consideration; and (3) unidentified sources. Typically, air quality data should be used to establish background concentrations in the vicinity of the source(s)

under consideration.

Because ambient PM 10 and PM 2.5 levels result from both secondary pollutant formation as well as directly emitted particulate matter, it is appropriate to rely on the locally monitored air quality

data for PM 10 and PM 2.5 to represent background concentrations in the project area.

The impact of the proposed new equipment will be modeled using the maximum allowable emission limits as proposed in the application and the design capacities of the turbines, assuming continuous operation, in accordance with the guidance in Table 8-2 of Appendix W. If the predicted total ground-level concentration obtained by adding the maximum impact of the proposed new equipment to the monitored background concentrations is below the state or federal ambient air quality standard for each pollutant and averaging period, no further analysis is required for that pollutant and averaging period.

If the proposed new equipment, combined with existing background concentrations, will result in predicted total ground-level concentration in excess of an applicable ambient air quality standard, then the third step of the compliance demonstration procedure will be undertaken. According to the 1990 draft Workshop Manual,

For a NAAQS violation to which an applicant contributes significantly, a PSD permit may be granted only if sufficient emissions reductions are obtained to compensate for the

13 Because the applicable EPA guidance doe s not define signifi cance levels for PM 2.5 , PM 2.5 impacts will be presumed to be above any applicable significance level regardless of the modeled concentration, and the second step of the process will be performed.-14- adverse ambient impacts caused by the proposed source. Emissions reductions are considered to compensate for the proposed source’s adverse impact when, at a minimum, (1) the modeled net concentration, resulting from the proposed emissions increase and the federally enforceable emissions reduction, is less than the applicable significant ambient impact level at each affected receptor

, and (2) no new violations will occur

. [emphasis added]

In accordance with this guidance, only if the modeled impacts from the proposed new equipment, combined with existing background concentrations, are predicted to cause a new violation of a standard for which the District is currently in attainment will this netting procedure be used. The federally enforceable emissions reductions to be used in the netting procedure will be provided by emission reduction credits (ERCs) already acquired and certified by the District.

13. H EALTH R ISK A SSESSMENT

A health risk assessment (HRA) will be perfor med according to the Office of Environmental Health Hazard Analysis “Air Toxics Hot Spots Program Guidance Manual for Preparation of Health Risk Assessments” (August 2003). The HRA modeling will be prepared using the ARB’s Hotspots Analysis and Reporting Program (HAR P) computer program (Version 1.3, October 18, 2005). The HARP model will be used to assess cancer risk as well as non-cancer chronic and

acute health hazards. The HRA w ill include the four following pathways: inhalation, dermal absorption, and soil and mother’s milk ingestion.

Because the HARP model incorporates the previously USEPA-approved model ISCST3, a special methodology will be employed to be consistent with using AERMOD for the air dispersion modeling and retain the health values and risk computations provided by HARP Version 1.3. The methodology used to prepare the HRA has been described by the ARB 14 and is described below. Its use has been approved by the CEC, the SJVAPCD and several other

Districts 15 on previous power plant projects.

The risk assessment module of the HARP model is run using unit ground level impacts to obtain derived cancer risks for each toxic air contaminant (TAC). Cancer risks are obtained for the derived (OEHHA) method, the derived (adjuste d) method, average point estimate, high-end point estimate, and derived (OEHHA) method for worker exposure. The HARP model output is cancer risk by TAC and pathway for each type of analysis, based on an exposure of 1.0 μ g/m 3

. Individual cancer risks are expressed in units of risk per μ g/m 3 of exposure. To calculate the weighted risk for each source, the annual average emission rate in grams per second for each TAC will be multiplied by the individual cancer risk for that TAC in units of ( μ g/m 3 ) -1 . The resulting weighted cancer risks for each TAC will then be summed for the source. The same approach will be used to determine the non-cancer acute and chronic health hazards associated with the Project.

14 Procedure is described in Part B of Topic 8 of the HARP How-To Guides: How to Perform Health Analyses Using a Ground Level Concentration.

15 San Diego APCD, Bay Area AQMD, North Coast Unified AQMD-15- Health risk from exposure to a carcinogenic TAC is calculated as the product of the exposure concentration times a factor representing the risk per unit concentration (i.e., unit risk) for the TAC. In the case of cancer risk, the unit risk depends on breathing rate, the cancer potency factor of the TAC, dimensional factors, a nd other terms involving non-inhalation pathways, when relevant. In the case of chronic and acute non-cancer impacts, the health hazard per unit concentration (i.e., unit impact) is normally calculated as 1 divided by the Reference Exposure Level (REL, expressed as a concentration in μg/m 3 ) for the TAC.

Exposure concentration is calculated as the product of the actual emission rate (in grams per second) 16 of the TAC times the concentration per unit of emission (i.e., χ /Q for an emission rate of 1 g/s), which is the output from the AE RMOD air dispersion modeling calculation. This exposure concentration is the “Unit Concentration.”

HARP automatically passes the “Unit Concentration” for a given source and receptor into its risk module where it is multiplied by the actual emission rate (in g/s) for each TAC and the “Unit Risk” for the TAC to produce the calculated risk for the TAC. This is done for all the TACs emitted by a source and the summed cancer risk, or non-cancer health impact for common toxic endpoints in the case of chronic and acute risk, is the total risk or non-cancer health impact at that receptor from that source. The total cancer risk or non-cancer health impact at a receptor is the sum of the risks or health impacts from all of the sources.

Because HARP is not designed to pass AERMOD “Unit Concentration” outputs to its Risk Module, an alternative procedure will be used. The calculation of cancer risk or non-cancer health impact does not require the variables to be multiplied in any particular order. Therefore, the final result will be the same if, for a given source, the “Unit Risk” for a TAC is multiplied by the actual emissions (g/s) for the TAC, and these products are added together to give a “Source Strength”. The “Source Strength” is then used as the source emission rate in AERMOD.

This methodology thus uses HARP to calculate the “Unit Risks” for all carcinogenic TACs and unit chronic and acute health impacts for all non-carcinogenic TACs, including all required exposure pathways and toxic end points as well as receptor types, including residents and workers. The unit risk or unit health impact for each TAC from a source is multiplied by the emission rate of that TAC from the source. These products are summed for all the TACs emitted by the source. This is done for each source. Finally, the resulting “Source Strength” for all project sources are used as emission rates in AERMOD. The AERMOD output contains the resulting cancer risks and non-cancer chronic and acute health impacts.

16 The annual emission rate is the actual long-term emission rate used for analysis of cancer risk and chronic noncancer health impact, and the one-hour emission rate is the actual short-term emission rate used for analysis of acute non-cancer health impact.-16- 14. C ONSTRUCTION A IR Q UALITY I MPACT A NALYSIS

The potential ambient impacts from air pollutant emissions during the construction of the Project will be evaluated by air quality modeling that will account for the construction site location and the surrounding topography; the sources of emissions during construction, including vehicle and equipment exhaust emissions; and fugitive dust.

Types of Emission Sources

− Construction of the Project will require 27 months, and can be viewed as three main sequential phases: site preparation; construction of foundations; and installation and assembly of the Project turbines and associated equipment. The construction impacts analysis will include a schedule for construction operation activities. Site preparation includes site excavation, excavation of footings and foundations, and backfilling operations.

Fugitive dust emissions from the construction of the project result from the following activities:

• Excavation and grading at the construction site;

• Onsite travel on paved and unpaved roads and across the unpaved construction site;

• Aggregate and soil loading and unloading operations;

• Raw material transfer to and from material stockpiles; and

• Wind erosion of areas disturbed during construction activities.

Engine exhaust will be emitted from the following sources:

• Heavy equipment used for excavation, grading, and construction of onsite structures;

• Water truck used to control construction dust emissions;

• Diesel-fueled welding machines, gasoline-powered generators, air compressors, and

water pumps;

• Gasoline-fueled pickup trucks and Diesel-fuele d flatbed trucks used onsite to transport workers and materials around the construction site;

• Transport of mechanical and electrical equipment to the project site;

• Transport of rubble and debris from the site to an appropriate landfill; and

• Transport of raw materials to and from stockpiles.

Emissions from a peak activity day will be modeled. Annual average emissions over the 27- month construction period will also be calculated and modeled for comparison with annual

standards.

Existing Ambient Levels – The background data discussed earlier will be used to represent existing ambient levels for the construction analysis as well as the analysis of the impacts of project operations.

Model Type

− The USEPA model, ISCST3, has been approved by the CEC for use in construction modeling, and will be used to estimate ambient impacts from construction emissions. The modeling options and meteorological data described above will be used for the modeling analysis.-17- The construction site will be represented as both a set of volume sources and a separate set of area sources in the modeling analysis. Emissions will be divided into two categories: exhaust emissions and dust emissions. For exhaust emissions, a plume height of 4.6 meters (15 feet) will be used. Plume height refers to the distance measured from ground level to the centerline of the emissions plume. For dust emissions, a release height of two meters will be used due to the ambient plume temperatures and negligible plume velocities.

For the construction modeling analysis, the receptor grid will begin at the property boundary and will extend approximately one kilometer in all directions. Receptor spacing will be 60 meters, except for three tiers of receptors spaced along the project boundary at 25-meter spacing.

15. C UMULATIVE A IR Q UALITY I MPACT A NALYSIS

The CEC has defined this 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 six-mile radius which have received construction permits but are not yet operating, or are in the permitting process.” For each criteria pollutant the CEC staff considers facilities having an emission increase of less than five tons per year to be de minimis , so such facilities may be excluded. The District has already been requested to provide information on any sources that might be appropriate for a cumulative air quality impact analysis, as defined above.

Upon receipt of sufficient information from the Di strict to allow air dispersion modeling of the non-project sources to be included in the cumulative air quality impact analysis, AERMOD will be used in a procedure similar to that described earlier in this protocol.

16. F INAL M ODELING S UBMITTAL

The final modeling analyses will include the following materials:



### • Summaries of maximum modeled impacts for each air quality scenario showing meteorological conditions and receptor location and elevation;



### • All modeling inputs and outputs (including BPIP-PRIME and meteorological files) in electronic format, together with a description of all filenames;



### • Plot plan showing emission points, nearby buildings (including dimensions), crosssection lines, property lines, fencelines, roads, and UTM coordinates; and



### • A table showing building heights used in the modeling analysis.

The HRA results will include AERMOD output plot files, spreadsheets that relate the computed risks with UTM coordinates, and textual discussion that explains the methodology to the lay public.-18- 17. R EFERENCES

Briggs, G.A. (1972). Discussion on Chimney Plumes in Neutral and Stable Surroundings

. Atmos. Environ. 6:507-510.

Bunyak, John, 1993. Permit Application Guidance for New Air Pollution Sources . Natural Resources Report NPS/NRAQD/NRR- 93/09, US Dept. of the Interior, National Park Service.

Cole, H.S. and J.E. Summerhays (1979). A review of techniques available for estimating

short-term NO 2 concentrations . Journal of the Air Pollution Control Association 29(8) 790-888.

Irwin, J.S. (1978). Proposed Criteria for Selection of Urban Versus Rural Dispersion Coefficients . Staff Report. Meteorology and A ssessment Division, U.S. Environmental Protection Agency, Research Triangle Park, NC. (Air Docket Reference No. II-B-8 for the Fourth Conference on Air Quality Modeling).

Nappo, C. J. et al. (1982). The Workshop on the Representativeness of Meteorological

Observations , June 1981, Boulder, Co. Bull. Amer. Meteor. Soc., Vol. 63, No. 7, pp. 761-764. American Meteorological Society, Boston, MA.

San Diego APCD (2005). Supplemental Guidelines for Submission of Air Toxics “Hot Spots” Program Health Risk Assessments (HRAs) , Version 1.0, March 1, 2005.

USEPA, 1985. Guideline for Determination of Good Engineering Practice Stack Height (Technical Support Document for the Stack He ight Regulations) - Revised. EPA-450/4-80-

023R.

USEPA (1986). Guideline on Air Quality Models (Revised) . U.S. EPA-45/2-78-027R, Office of Air Quality Planning and Standards, Research Triangle Park, NC.

USEPA (1987a). Supplement A to the Guideline on Air Quality Models (Revised) . Office of Air Quality Planning and Standards, Research Triangle Park, NC.

USEPA (1987b). Ambient Monitoring Guidelines for Prevention of Significant Deterioration (PSD) . Office of Air Quality Planning and Standards, and Office of Research and Development, Research Triangle Park, NC.

USEPA (1988). Workbook for Plume Visual Impact Screening and Analysis . Office of Air Quality Planning and Standards, Research Triangle Park, NC. EPA-450/4-88-015 (Including October 1992 Revisions).

USEPA, 1990. Supplement B to the Guideline on Air Quality Models (Revised). Office of Air Quality Planning and Standards, Research Triangle Park, NC.

USEPA, 1990. New Source Review Workshop Manual

− Draft . Office of Air Quality Planning and Standards, Research Triangle Park, NC.-19- USEPA, 1992. Procedures for Substituting Values for Missing NWS Meteorological Data for Use in Regulatory Air Quality Models . Dennis Atkinson and Russell F. Lee, Office of Air Quality Planning and Standards, Research Triangle Park, NC. July 7, 1992.

USEPA (1992). Screening Procedures for Estimating the Air Quality Impact of Stationary Sources, (Revised). Office of Air Quality Planning and Standards, Research Triangle Park, NC.

USEPA (1995). Supplement C to the Guideline on Air Quality Models (revised) . Office of Air Quality Planning and Standards, Research Triangle Park, NC.

USEPA (1998). Interagency Workgroup on Air Quality Modeling (IWAQM) Phase 2 Summary Report and Recommendations for Modeling Long-Range Transport Impacts . Air Quality Modeling Group (MD-14), Research Triangle Par k. National Park Service - Air Resource Division, Denver, Colorado. USDA Forest Service - Air Quality Program, Fort Collins, Colorado. US Fish and Wildlife Service Air Quality Branch, Denver, Colorado.

USEPA (2000). Meteorological Monitoring Guidance for Regulatory Modeling Applications

. Publication No. EPA-454/R-99-005. Office of Ai r Quality Planning & Standards, Research Triangle Park, NC. (PB 2001-103606) (Available at www.epa.gov/scram001/ )

USEPA (2003). 40 CFR Part 51, Appendix W. Guideline on Air Quality Models . Last update

5/13/2003.

USDA Forest Service Air Quality Program, Nati onal Park Service Air Resource Division, US Fish and Wildlife Service - Air Quality Branch (2000). Federal Land Managers’ Air Quality Related Values Workgroup (FLAG) Phase I Report. December 2000.-20- Figure 1 Locations of Project and Surface Meteorological Monitoring Station Avenal Energy Project-21- NORTH

SOUTH WEST EAST 5% 10% 15% 20% 25%

W I N D S P E E D ( K n o t s )

> = 2 2

1 7

- 2 1

1 1

- 1 7

7

- 1 1

4

- 7

1

- 4

C a l m s : 2 5

. 8 8 %

Figure 2A: Wind Rose for Hanford, CA – Calendar Year 2000-22- NORTH

SOUTH WEST EAST 6% 12% 18% 24% 30%

W I N D S P E E D ( K n o t s )

> = 2 2

1 7

- 2 1

1 1

- 1 7

7

- 1 1

4

- 7

1

- 4

C a l m s : 1 2

. 6 9 %

Figure 2B: Wind Rose for Hanford, CA – Calendar Year 2001-23- NORTH

SOUTH WEST EAST 6% 12% 18% 24% 30%

W I N D S P E E D ( K n o t s )

> = 2 2

1 7

- 2 1

1 1

- 1 7

7

- 1 1

4

- 7

1

- 4

C a l m s : 2 3

. 3 9 %

Figure 2C: Wind Rose for Hanford, CA – Calendar Year 2002-24- NORTH

SOUTH WEST EAST 5% 10% 15% 20% 25%

W I N D S P E E D ( K n o t s )

> = 2 2

1 7

- 2 1

1 1

- 1 7

7

- 1 1

4

- 7

1

- 4

C a l m s : 2 1

. 3 2 %

Figure 2D: Wind Rose for Hanford, CA – Calendar Year 2003-25- NORTH

SOUTH WEST EAST 5% 10% 15% 20% 25%

W I N D S P E E D ( K n o t s )

> = 2 2

1 7

- 2 1

1 1

- 1 7

7

- 1 1

4

- 7

1

- 4

C a l m s : 2 1

. 9 0 %

Figure 2E: Wind Rose for Hanford, CA – Calendar Year 2004

### Appendix A

Location Figures**SITE BOUNDARY** 5 AVENAL CUTOFF ROAD**GAS PIPELINE SAN LUIS** **CANAL**

**G G**  **G G**  **E ELECTRIC** **TRANSMISSION LINE E** **E**

**G ALTERNATE** **GAS PIPELINE ROUTE** **EXISTING PG&E 230 KV TRANSMISSION LINE** **EXISTING PG&E 500 KV TRANSMISSION LINES** 

**E**

**E**02,000 4,000 FEETSCALEREFERENCE:U.S.G.S 7.5 MINUTE TOPOGRAPHIC SERIES MAPOF LA CIMA, CALIFORNIA, DATED 1978.290317-AFC-2.1-1A REV. 09/05/06**FIGURE 2.1-1A NATURAL GAS AND ELECTRICAL** **INTERCONNECTION ROUTES FEDERAL POWER AVENAL LLC** AVENAL ENERGY

### Appendix B

Information on CTDMPLUS Model

The CTDMPLUS and CTSCREEN Models

Complex terrain impacts may need to be modeled with more accuracy than that provided by AERMOD. The use of more refined modeling t echniques is specifically addressed in EPA’s Appendix W 1 modeling guidance, as follows:

Since AERMOD treats dispersion in complex terrain, we have merged sections 4 and 5 of appendix W, as proposed in the April 2000 NPR [Notice of Proposed Rulemaking]. And while AERMOD produces acceptable regulatory design concentrations in complex terrain, it does not replace CTDMPLUS for detailed or receptor-oriented complex terrain analysis, as we have made clear in Guideline section 4.2.2. CTDMPLUS remains available for use in complex terrain. [p. 68225]

4.2.2 Refined Analytical Techniques
d. If the modeling application involves a well defined hill or ridge and a detailed dispersion analysis of the spatial pattern of plume impacts is of interest, CTDMPLUS, listed in Appendix A, is available. CTDMPLUS provides greater resolution of concentrations about the contour of the hill feature than does AERMOD through a different plume-terrain interaction algorithm. [p. 68233]

CTSCREEN is the same basic model as CTDMPLUS, except that meteorological data are handled internally in a simplified manner. As discussed in the CTSCREEN users guide, 2

Since [CTDMPLUS] accounts for the three-dimensional nature of plume and terrain interaction, it requires detailed terrain and meteorological data that are representative of the modeling domain. Although the terrain data may be readily obtained from topographic maps and digitized for use in the CTDMPLUS, the required meteorological data may not be as readily available.

Since the meteorological input requirements of the CTDMPLUS can limit its application, the EPA's Complex-Terrain-Modeling, Technology-Transfer Workgroup developed a methodology to use the advanced techniques of CTDMPLUS in situations where on-site meteorological measurements are limited or unavailable. This approach uses CTDMPLUS in a "screening" mode--actual source and terrain characteristics are modeled with an extensive array of predetermined meteorological conditions.

1 40 CFR 51 Subpart W, as amended November 9, 2005 at 70 FR 68218, “Revision to th e Guideline on Air Quality Models: Adoption of a Preferred General Purpose (F lat and Complex Terrain) Dispersion Model and Other

Revisions.”

2 USEPA, EPA-600/8-90-087, “User’s Guide to CTDMPLUS: Volume 2. The Screening Mode (CTSCREEN),”

October 1990.This CTDMPLUS screening mode (CTSCREEN) serves several purposes in regulatory applications. When meteorological data are unavailable, CTSCREEN can be used to obtain conservative (safely above those of refined models), yet realistic, impact estimates for particular sources.

Therefore, the use of the CTSCREEN version of CTDMPLUS is consistent with EPA guidance.

Meteorological Data for CTDMPLUS

The discussion in Section 6 of the text focuse d on meteorological data needed to run AERMOD. As discussed in a later section, an additional model, Complex Terrain Dispersion Model PLUS (CTDMPLUS), may be used in lieu of the model Complex Terrain Screening Model(CTSCREEN) for receptors in the terrain above stack-top height. CTDMPLUS is a USEPAapproved air dispersion model, and is fully supported with user guidance documentation. 3

CTDMPLUS requires an extensive suite of meteorological data composed of not only wind speed, direction, and temperature, but also hor izontal and vertical wind direction standard deviations (sigma theta and sigma phi, respectivel y), and vertical wind speed standard deviation (sigma w). The AERMOD-compatible meteorological data set provided by the SJVAPCD,
derived from measurements taken at Hanford, CA, does not include these non-standard

measurements.

It is possible to develop conservative values for the standard deviation parameters sigma theta, sigma phi, and sigma w that are consistent with the available meteorological data, and use them to prepare a meteorological data set that is usable in CTDMPLUS and yields conservative (i.e., high) ground-level concentrations.

If modeling with CTDMPLUS is required, the District will be requested to develop ISCST3- compatible meteorological data sets for the same three years of 2003-2005. The ISCST3 meteorological data set would be used to create the CTDMPLUS-compatible meteorological data set. Because all three of these Gaussian dispersion models—ISCST3, AERMOD, and CTDMPLUS—require upper air data as well as surface data, the upper air data from the Oakland Metropolitan Airport (ID No. 23230) would be used because it is the same station used by the SJVAPCD to develop the AERMOD-compatible meteorological dataset.

The following meteorological parameters are needed for CTDMPLUS and would be taken directly from the AERMET files:

• Observed mixing height, provided as the height of the convective or planetary boundary layer (PBL);

3 USEPA. Technology Transfer Network, Support Center for Regulatory Atmospheric Modeling, http://www.epa.gov/scram001/di spersion_prefrec.htm#ctdmplus• Calculated mixing height, provided as the height of the mechanical, or surface, boundary layer (SBL);

• Friction velocity (USTAR);

• Monin-Obukhov length (L); and

• Roughness length (Z O ).

The remaining standard deviations (sigma values) are not available from AERMOD and must be obtained from ISCST3-compatible files that would be developed from the Hanford, CA meteorological data. Stability classes determined by MPRM 4 or PCRAMMET 5 from the measured Hanford meteorological data would be used to select the most conservative values from the following ranges recommended in USEPA’s Meteorological Monitoring Guidance

document: 6

Sigma Phi ( σ Φ )/ Sigma Theta ( σ θ )/ Stability Regulatory Range Regulatory Range Category (degrees) (degrees)

A 11.5 22.5

B 10.0 – 11.5 17.5 – 22.5

C 7.8 – 10.0 12.5 – 17.5

D 5.0 – 7.8 7.5 – 12.5

E 2.4 – 5.0 3.8 – 7.5

F < 2.4 < 3.8

The most conservative values (that is, the values that produce the highest modeled impacts) for sigma theta and sigma phi within each range would be determined by conducting a sensitivity analysis for all combinations of stack conditions to be modeled using CTDMPLUS and receptor locations for which CTDMPLUS would be used (that is, receptors above stack height). The sensitivity analysis would use the upper and lower values of each range for each stability category. For example, for stability category D, four combinations would be evaluated as

follows:

σ Φ σ θ
5.0 7.5

5.0 12.5

7.8 7.5

7.8 12.5

4 The Meteorological Processor for Regulatory Models

5 EPA meteorological preprocessor

6 Tables 6-8a and 6-9a in Meteorological Monitoring Guidance for Regulatory Modeling Applications, EPA-454/R99-005, US EPA Office of Air and Radi ation, Office of Air Quality Pla nning and Standards, February 2000.For stability category A, maximum values for σ Φ and σ θ of 15.0 and 27.0, respectively, would be evaluated. For stability category F, minimum values for σ Φ and σ θ of 1.0 and 2.0, respectively,

would be evaluated

.

Sigma-w would be estimated by multiplying sigma-phi (after conversion from degrees to radians) by the horizontal wind speed.