Prepared for: 

City of Palmdale, California 

Class II Area Dispersion Modeling 

Protocol for the Proposed 

Palmdale Hybrid Power Project 

ENSR Corporation 

July 2008 

Document No.: 10855-002-040C2MP 
Prepared for: 

City of Palmdale, California 

Class II Area Dispersion Modeling 

Protocol for the Proposed 

Palmdale Hybrid Power Project 

_________________________________ 

Prepared By: Richard P. Hamel 

_________________________________ 

Reviewed By: Brian Stormwind 

ENSR Corporation 

July 2008 

Document No.: 10855-002-040C2MP 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol i July 2008 

Contents 

1.0 Introduction .............................................................................................................................................1-1

2.0 Dispersion Modeling Analysis..............................................................................................................2-1

2.1 Model Selection Criteria...................................................................................................................2-1

2.1.1 Good Engineering Practice Stack Height Analysis ...........................................................2-1

2.1.2 Dispersion Environment.....................................................................................................2-2

2.1.3 Local Terrain.......................................................................................................................2-2

2.1.4 Representative Meteorological Data .................................................................................2-4

2.2 Dispersion Model Selection and Application...................................................................................2-4

2.2.1 Terrain and Receptor Data Processing with AERMAP.....................................................2-6

2.2.2 Meteorological Data Processing with AERMET................................................................2-9

2.2.3 Model Options ..................................................................................................................2-14

2.3 Characterization of Sources to be Modeled..................................................................................2-14

2.3.1 Combustion Turbines .......................................................................................................2-14

2.3.2 Ancillary Combustion Units ..............................................................................................2-16

2.3.3 Cooling Towers.................................................................................................................2-16

2.3.4 Construction Sources.......................................................................................................2-16

2.4 Evaluation of Air Quality Impacts...................................................................................................2-17

2.4.1 Project Operation Impacts................................................................................................2-17

2.4.2 Ambient Background Concentrations..............................................................................2-19

2.4.3 NO2 Modeling ...................................................................................................................2-20

3.0 Additional Impact Analyses ..................................................................................................................3-1

3.1 Vegetation and Soils ........................................................................................................................3-1

3.2 Associated Growth...........................................................................................................................3-2

4.0 References...............................................................................................................................................4-1

List of Attachments 

Attachment 1 AVAQMD Correspondence Related to the Cumulative Modeling Inventory
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol ii July 2008 

List of Tables 

Table 2-1 AERSURFACE Season and Bowen Ratio Condition Designations......................................2-12

Table 2-2 Ambient Air Impact Criteria (μg/m3)........................................................................................2-19

Table 2-3 Annual Monitoring Data for Background Concentrations ......................................................2-20

Table 3-1 EPA Criteria for Gaseous Pollutant Impacts on Natural Vegetation and Crops .....................3-1

List of Figures 

Figure 2-1 Land-Use and Topography in the Vicinity of the Proposed PHPP Power Block ....................2-3

Figure 2-2 Location of the Palmdale Regional Airport Met Tower ............................................................2-5

Figure 2-3 Near Field Cartesian Receptor Field Used in the PHPP AERMOD Analysis.........................2-7

Figure 2-4 Far Field Cartesian Receptors Field Used in the PHPP AERMOD Analysis..........................2-8

Figure 2-5 Aerial Photo of the Area Surrounding the Palmdale Regional Airport ..................................2-10

Figure 2-6 1992 NLCD Data Image of the Region Surrounding the Palmdale Regional Airport...........2-11

Figure 2-7 One km Radius Circle Around the Palmdale Regional Airport with Surface 

Roughness Sectors Shown ....................................................................................................2-13

Figure 2-8 Palmdale Regional Airport 2002-2004 Wind Rose ................................................................2-15

Figure 2-9 Location of Emission Sources Used In Construction Modeling.............................................2-18
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 1-1 July 2008 

1.0 Introduction 

The City of Palmdale, California, is proposing to build a hybrid combined-cycle / solar-thermal power plant in 

the City of Palmdale to the northwest of the Air Force Plant 42 / Palmdale Regional Airport. The Project will 

feature a 2 on 1 combined-cycle configuration with two GE 7FA gas turbines and one steam turbine 

producing a nominal electrical output of 570 megawatts (MW) along with a 250-acre solar thermal collection 

field, capable of producing 50 MW. The hybrid power plant will be owned by the City of Palmdale and the 

development managed by Inland Energy and will be known as the Palmdale Hybrid Power Project (PHPP or 

Project). The combustion turbine trains will include heat recovery steam generators and will be fueled with 

natural gas only. In addition to the combustion turbines, the facility will contain ancillary combustion 

equipment including a natural gas-fired auxiliary boiler, a natural gas-fired heat transfer fluid (HTF) heater, a 

diesel-fired emergency generator, and a diesel-fired fire water pump engine. The facility will also include a 

wet mechanical draft cooling tower. 

The proposed facility will be located in an area that is designated federal non-attainment for respirable 

particulate matter (PM10) and ozone (O3), and attainment or unclassified for sulfur dioxide (SO2), nitrogen 

dioxide (NO2), carbon monoxide (CO), and fine particulate matter (PM2.5). Based on an estimate of 

preliminary facility air emissions, the Project will be a major source with respect to New Source Review 

(NSR) regulations, will trigger Prevention Significant Deterioration (PSD) review for NO2, CO, PM10, and 

PM2.5 and will be subject to non-attainment new source review (NANSR) for PM10 and ozone precursors 

NOX and volatile organic compounds (VOC). The facility will be a minor source of SOx, lead, and other PSD 

pollutants. Therefore, as required by the PSD regulations, Inland Energy will conduct a Best Available 

Control Technology (BACT) evaluation to determine the best level of control for CO, taking into account the 

environmental, economic and energy consumption impacts. Per NANSR, a Lowest Achievable Emission 

Rate (LAER) review for NOX (as an ozone precursor) and PM10/PM2.5 will be conducted. The U.S. 

Environmental Protection Agency (EPA) administers the PSD program in this area and the Antelope Valley 

Air Quality Management District (AVAQMD) manages the local NANSR program. 

Air quality modeling will be performed in accordance with EPA modeling guidelines (EPA, 2005) for all 

sources and will be conducted with the EPA’s AERMOD dispersion model to demonstrate compliance with 

the National Ambient Air Quality Standards (NAAQS), California Ambient Air Quality Standards (CAAQS) 

and Prevention Significant Deterioration (PSD) increments in the local (Class II) area. 

Dispersion modeling will also be conducted to assess potential impacts at Class I Areas in accordance with 

PSD modeling requirements. The details of the proposed modeling approach for Class I Areas is 

documented in a separate modeling protocol. This Class II Area modeling protocol also does not address 

the procedures or methodology that will be used in evaluating potential health risks from air toxics 

emissions. The proposed approach for conducting a health risk assessment (HRA) will be provided in the 

Application for Certification (AFC). 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-1 July 2008 

2.0 Dispersion Modeling Analysis 

This section presents the modeling analysis that will be conducted to assess ambient air quality impacts 

which will ultimately demonstrate compliance with applicable State and Federal ambient air quality 

standards. The analyses will be conducted in accordance with the EPA Guideline on Air Quality Models 

(GAQM; as incorporated in Appendix W of 40 CFR Part 51 Revised November 9, 2005). The revised 

version of GAQM adopts AERMOD as a preferred general purpose dispersion model for both flat and 

complex terrain. 

2.1 Model Selection Criteria 

The suitability of an air quality dispersion model for a particular application is dependent upon several 

factors. For this study, the following selection criteria have been evaluated: 

• Stack heights relative to nearby buildings/structures; 

• Dispersion environment; 

• Local terrain; and 

• Availability of representative meteorological data. 

2.1.1 Good Engineering Practice Stack Height Analysis 

The EPA modeling guidelines require the evaluation of the potential for physical structures to affect the 

dispersion of emissions from stack sources. The exhaust from stacks that are located within specified 

distances of buildings, and whose physical heights are below specified levels, may be subject to 

“aerodynamic building downwash” under certain meteorological conditions. If this is the case, a model 

capable of simulating this effect must be employed. 

The analysis used to evaluate the potential for building downwash is referred to as a Good Engineering 

Practice (GEP) stack height analysis. Stacks with heights below physical GEP are considered to be subject 

to building downwash. In the absence of structural effects, EPA has established a default GEP height of 

213 feet (65 meters). Any portion of a stack above the maximum of the physical or default GEP height 

cannot be used in the dispersion modeling analysis for purposes of comparison to ambient impact criteria. 

A GEP stack height analysis will be performed for the proposed ancillary equipment stacks in accordance 

with EPA’s GEP stack height guidelines (EPA, 1985). Per the guidelines, the physical GEP height, HGEP, is 

determined from the dimensions of all buildings which are within the region of influence using the following 

equation: 

HGEP = HB + 1.5L 

Where: HB = height of the structure within 5L of the stack which maximizes HGEP, and 

 L = lesser dimension (height or projected width) of the structure. 

For a squat structure, i.e., height less than projected width, the formula reduces to: 

HGEP = 2.5HB

In the absence of influencing structures, a default GEP stack height is credited up to 213 feet (65 m). 

The GEP stack height for all proposed stacks will be determined using the EPA Building Profile Input 

Program (BPIP) that performs the GEP calculation for a multi-building complex on a stack-by-stack basis. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-2 July 2008 

The stack heights of the ancillary equipment have not been determined at this time but it is anticipated that 

these stacks will be less than their respective GEP formula heights and, therefore, subject to building 

downwash. Therefore, building dimensions developed by BPIP for all stacks will be input to the dispersion 

model as necessary. 

The results of the GEP analysis will be documented in the AFC and the BPIP input and output files will be 

provided in the modeling archive submitted with the AFC (Appendix G.6). 

2.1.2 Dispersion Environment 

The application of the dispersion model requires characterization of the local dispersion environment (within 

three kilometers [km]) as either urban or rural, based on an EPA-recommended procedure (Auer, 1978) that 

characterizes an area by prevalent land use. This land use approach classifies an area according to 12 

land use types. In this scheme, areas of industrial, commercial, and compact residential land use are 

designated urban. According to the GAQM, if more than 50 percent of an area within a three-km radius of 

the proposed facility is classified as rural, then rural dispersion assumptions are to be used in the dispersion 

modeling analysis. Conversely, if more than 50 percent of the area is urban, urban dispersion is assumed. 

As shown in Figure 2-1, the land-use within three km of the proposed facility is characterized as rural based 

on the EPA-recommended procedure. AERMOD does not require any specification for rural applications 

since rural dispersion is the default dispersion mode. 

2.1.3 Local Terrain 

The EPA modeling guidelines require that the differences in terrain elevations between the stack base and 

model receptor locations be considered in the modeling analyses. For dispersion modeling purposes, there 

are three types of terrain: 

• Simple terrain – locations where the terrain elevation is at or below the exhaust height of the stacks 

to be modeled; 

• Intermediate terrain – locations where the terrain is between the top of the stack and the modeled 

exhaust “plume” centerline (this varies as a function of plume rise, which in turn, varies as a function 

of meteorological condition); and 

• Complex terrain – locations where the terrain is above the plume centerline. 

Prior to the introduction of AERMOD, these terrain types had to be modeled in different ways that were not 

necessarily consistent. One advantage of using AERMOD is that there is a seamless and consistent 

approach to all terrain types. 

The terrain immediately surrounding the proposed site location is primarily flat, desert scrubland. The 

terrain to the south and west of the Project site is mountainous with elevations exceeding 4,500 feet 

(compared to the Project base elevation of 2,513 feet). The terrain gradually slopes upward to the south 

and west for the first 10 kilometers away from the Project then rapidly rises to elevations in the 3,000-4,000 

foot range. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-3 July 2008 

Figure 2-1 Land-Use and Topography in the Vicinity of the Proposed PHPP Power Block 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-4 July 2008 

2.1.4 Representative Meteorological Data 

The Project modeling will use a three-year sequential hourly meteorological data set, consistent with 

Appendix B of the California Energy Commission’s Rules of Practice and Procedure & Power Plant Site 

Certification Regulations (2000). Three years (2002-2004) of surface meteorological data are available from 

the Automatic Surface Observing System (ASOS) tower at nearby Palmdale Regional Airport and are 

proposed for this application. Per discussion with Brett Banks of the Antelope Valley Air Quality 

Management District (AVAQMD), this was the preferred option if the data were available. A review of the 

completeness of the data at Palmdale Regional Airport showed that the data capture was slightly below the 

90% completeness per quarter for all required data types recommended in the Meteorological Monitoring 

Guidance for Regulatory Modeling Applications (EPA, 2000) for the following quarters: 

2002: Q1 Wind direction 86.5% complete 

2002: Q2 Wind direction 89.1% complete 

2003: Q3 Wind direction 83.3% complete 

All other quarterly values exceeded the recommended 90% threshold. Two other sources of meteorological 

data were considered as alternatives: The Lancaster Division Street Met Tower in Lancaster, CA, and 

William J. Fox Field north of Lancaster. A data completeness study of these two locations revealed that the 

data capture at each was lower than that of Palmdale Regional Airport. Palmdale Regional Airport is 

therefore the best option for this analysis because of a) superior data capture, b) it’s close proximity to the 

Project site (the met tower is less than 2 miles from the proposed turbine stack locations) c) the similarity in 

surface characteristics between the airport and the Project site, and d) AVAQMD’s preference to use the 

Palmdale Regional Airport Data. 

The location of the Palmdale Regional Airport relative to the proposed Project location is shown in Figure 2-2. 

The anemometer height at Palmdale Regional Airport is 10 meters. Concurrent upper air data from 

Mercury Desert Rock Airport in Mercury, Nevada will also be used as required for the dispersion modeling. 

Use of 2005, 2006, and 2007 data is not proposed because of the poor data recovery of the upper air data 

at Mercury Desert Rock Airport during these years. Surface data will be acquired from Trinity Consultants, 

Inc., filled per the Procedures for Substituting Values for Missing NWS Meteorological Data for Use in 

Regulatory Air Quality Models memo by Atkinson and Lee (EPA, 1992). The upper air data will be 

downloaded from the NCDC RAOB Database website (http://raob.fsl.noaa.gov/). 

2.2 Dispersion Model Selection and Application 

The EPA GAQM prescribes a set of approved models for regulatory applications for a wide range of source 

types and dispersion environments. Based on a review of the factors discussed above, the AERMOD 

model is proposed to assess air quality impacts for the Project. AERMOD is a state-of-the-art dispersion 

model that incorporates modeling improvements especially for applications involving building downwash 

and complex terrain. AERMOD has become the recommended model by the EPA for general use to 

replace the Industrial Source Complex - Short Term 3 model. The latest version of AERMOD (07026), the 

AERMET (06341) meteorological preprocessor, and the AERMAP (06341) terrain preprocessor will be used 

in this application. 

AERMOD will be applied with the three years of meteorological data discussed above for all receptors 

(simple and complex terrain) in the modeling domain (see Section 2.3.1) to assess air quality impacts 

from the Project. AERMOD will be applied to assess the maximum criteria pollutant concentrations 

including 1-hour and annual NO2, 24-hour and annual PM10/PM2.5, 1-hour and 8-hour CO, and 1-hour, 

3-hour, 24-hour and annual SO2. The proposed meteorological data processing with AERMET and 

development of the receptor grid with AERMAP are discussed below. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-5 July 2008 

Figure 2-2 Location of the Palmdale Regional Airport Met Tower 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-6 July 2008 

2.2.1 Terrain and Receptor Data Processing with AERMAP 

A comprehensive Cartesian receptor grid extending to 20 km from the center of the power block will be used 

in the AERMOD modeling to assess maximum ground-level pollutant concentrations. Based on preliminary 

modeling, the 20-km receptor grid will be sufficient to resolve the maximum impacts and any significant 

impact area(s). 

The Cartesian receptor grid will consist of the following receptor spacing: 

• Fenceline to 3,000 meters at 100 meter increments 

• Beyond 3,000 meters to 5,000 meters at 200 meter increments 

• Beyond 5 kilometers to 10 kilometers at 500 meter increments 

• Beyond 10 kilometers to 20 kilometers meters at 1,000 meter increments 

Discrete receptors will be placed approximately every 50 meters along the Project fence line for increased 

resolution of impacts along this boundary. 

The AERMAP receptor locations and the proposed AERMAP domain are shown in Figure 2-3 (near-field 

portion of the receptor grid) and Figure 2-4 (far-field receptors and AERMAP domain). An additional five km 

was added to the AERMAP domain beyond the 20 km receptor grid shown in Figure 2-4. This additional 

area is included in order to provide sufficient resolution of the hill height scale required for each receptor. 

Terrain elevations from Digital Elevation Model (DEM) data acquired from United States Geological Service 

(USGS) will be processed with AERMAP to develop the receptor terrain elevations and corresponding hill 

height scale required by AERMOD. All of the DEM files will be from Universal Transverse Mercator (UTM) 

Zone 11 and referenced to North American Datum (NAD) 27 (Note that the receptors shown in Figures 2-3 

and 2-4 are referenced to NAD27). The DEM files will also be included in the modeling archive that will be 

submitted along with the AFC. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-7 July 2008 

Figure 2-3 Near Field Cartesian Receptor Field Used in the PHPP AERMOD Analysis 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-8 July 2008 

Figure 2-4 Far Field Cartesian Receptors Field Used in the PHPP AERMOD Analysis 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-9 July 2008 

2.2.2 Meteorological Data Processing with AERMET 

Three years (2002-2004) of surface observations from the NWS tower at Palmdale Regional Airport in 

Palmdale, and concurrent upper air data from Mercury Desert Rock Airport in Mercury will be processed 

with AERMET, the meteorological preprocessor for AERMOD. 

AERMET will be applied to create two meteorological data files required for input to AERMOD: 

Surface: A file with boundary layer parameters such as sensible heat flux, surface friction velocity, 

convective velocity scale, vertical potential temperature gradient in the 500-meter layer 

above the planetary boundary layer, and convective and mechanical mixing heights. Also 

provided are values of Monin-Obukhov length, surface roughness, albedo, Bowen ratio, 

wind speed, wind direction, temperature, and heights at which measurements were taken. 

Profile: A file containing multi-level meteorological data with wind speed, wind direction, 

temperature, sigma-theta (σθ) and sigma-w (σw) when such data are available. For this 

application involving the Lancaster tower data, the profile file will contain a single level of 

wind data (9.3 meters) and the temperature data only. 

AERMET requires specification of site characteristics including surface roughness (zo), albedo (r), and 

Bowen ratio (Bo). These parameters were developed according to the guidance provided by EPA in the 

recently revised AERMOD Implementation Guide (AIG) (EPA, 2008a). 

The revised AIG provides the following recommendations for determining the site characteristics: 

1. The determination of the surface roughness length should be based on an inverse distance 

weighted geometric mean for a default upwind distance of one km relative to the measurement site. 

Surface roughness length may be varied by sector to account for variations in land cover near the 

measurement site; however, the sector widths should be no smaller than 30 degrees. As discussed 

further below, three sectors were used in this application. 

2. The determination of the Bowen ratio will be based on a simple unweighted geometric mean (i.e., 

no direction or distance dependency) for a representative domain, with a default domain defined by 

a 10 km by 10 km region centered on the measurement site. 

3. The determination of the albedo should be based on a simple unweighted arithmetic mean (i.e., no 

direction or distance dependency) for the same representative domain as defined for Bowen ratio, 

with a default domain defined by a 10 km by 10 km region centered on the measurement site. 

The AIG recommends that the surface characteristics be determined based on digitized land cover data. 

EPA has developed the AERSURFACE tool that will be used to determine the site characteristics based on 

digitized land cover data in accordance with the recommendations from the AIG discussed above. 

AERSURFACE incorporates look-up tables of representative surface characteristic values by land cover 

category and seasonal category. AERSURFACE will be applied with the instructions provided in the 

AERSURFACE User’s Guide (EPA, 2008b). 

The current version of AERSURFACE (Version 08009) supports the use of land cover data from the USGS 

National Land Cover Data 1992 archives (NLCD92) (http://edcftp.cr.usgs.gov/pub/data/landcover/states/). 

The NLCD92 archive provides data at a spatial resolution of 30 meter based on a 21-category classification 

scheme applied over the continental U.S. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-10 July 2008 

Figure 2-5 Aerial Photo of the Area Surrounding the Palmdale Regional Airport 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-11 July 2008 

 Figure 2-6 1992 NLCD Data Image of the Region Surrounding the 

Palmdale Regional Airport 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-12 July 2008 

Visual inspection of recent satellite images (2005) in the area of the measurement site (see Figure 2-6), 

compared to the 19921 land cover images (Figure 2-7) indicate that there have been no significant changes 

in land use cover confirming the use of the 1992 data will be reasonable. As recommended in the AIG for 

surface roughness, the one kilometer area was broken down into sectors for the analysis. Two sectors were 

identified for this analysis based upon visual observation of the land-use around the monitoring station as 

shown on aerial photographs (see Figure 2-7). 

In AERSURFACE, the various land cover categories are linked to a set of seasonal surface characteristics. 

As such, AERSURFACE requires specification of the seasonal category for each month of the year. The 

following five seasonal categories are offered by AERSURFACE: 

1. Midsummer with lush vegetation; 

2. Autumn with unharvested cropland; 

3. Late autumn after frost and harvest, or winter with no snow; 

4. Winter with continuous snow on ground; and 

5. Transitional spring with partial green coverage or short annuals. 

The designations used in this application are summarized in Table 2-1. 

Table 2-1 AERSURFACE Season and Bowen Ratio Condition Designations 

Season Bowen Ratio Category 

Month 

2002-2004 2002 2003 2004 

January Winter * Dry Dry Dry 

February Winter * Dry Dry Wet 

March Autumn Dry Wet Average 

April Autumn Average Wet Average 

May Summer Average Wet Average 

June Summer Average Average Average 

July Summer Average Wet Average 

August Summer Average Average Average 

September Summer Average Average Average 

October Summer Average Average Wet 

November Autumn Average Average Wet 

December Autumn Wet Average Wet 

* The “Late autumn after frost and harvest or winter with no snow” category will be used for January and 

February season. 

 

1

 1992 is the data set that the EPA uses for AERSURFACE. This data set is reviewed to verify that the area hasn’t 

significantly changed over time. Aerial photos of this Palmdale area show that there has been no major development in 

this period. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-13 July 2008 

Figure 2-7 One km Radius Circle Around the Palmdale Regional Airport with 

Surface Roughness Sectors Shown 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-14 July 2008 

In addition, for Bowen ratio, the land use values are linked to three categories of surface moisture 

corresponding to average, wet and dry conditions. The surface moisture condition for the site may vary 

depending on the meteorological data period for which the surface characteristics will be applied. 

AERSURFACE applies the surface moisture condition for the entire data period. Therefore, if the surface 

moisture condition varies significantly across the data period, then AERSURFACE can be applied multiple 

times to account for those variations. As recommended in the AERSURFACE User’s Guide, the surface 

moisture condition for each month will be determined by comparing precipitation for the period of data to be 

processed to the 30-year climatological record, selecting “wet” conditions if precipitation was in the upper 

30th-percentile, “dry” conditions if precipitation was in the lower 30th-percentile, and “average” conditions if 

precipitation was in the middle 40th-percentile. The monthly designations of surface moisture input to 

AERSURFACE are also summarized in Table 2-1. 

The base elevation used for the Palmdale Regional Airport will be 769.3 meters (2,524 feet) above sea 

level. A three-year wind rose is provided as Figure 2-8. 

2.2.3 Model Options 

AERMOD will be applied with the EPA recommended default options. Model iterations will be conducted for 

each year of meteorological data to identify the maximum impacts over all three years for the pertinent 

averaging periods. 

2.3 Characterization of Sources to be Modeled 

The Project will include the following air emission sources that will be included in the modeling analysis: 

• Two combined cycle combustion turbines, each with heat recovery steam generators (HRSGs) 

• Auxiliary boiler 

• Emergency generator engine 

• Fire-water pump engine 

• Heat transfer fluid heater 

• Cooling tower 

A preliminary plot plan of this equipment is shown in Figure 2-9. Calculation of emissions, including 

proposed control technology, will be provided in the AFC, PSD and NANSR permit applications. 

2.3.1 Combustion Turbines 

2.3.1.1 Normal Turbine Operations 

The dispersion modeling analysis will be conducted with emission rates and flue gas exhaust characteristics 

(flow rate and temperature) that are expected to represent the range of possible values for the natural gasfired turbines under consideration. Because turbine emission rates and flue gas characteristics for a given 

turbine load vary as a function of ambient temperature and operational load, data will be derived for three 

ambient temperatures for natural gas fuel at each of the three operating load points (100%, 75% and 50%). 

The temperatures will cover a representative minimum, annual average and a representative maximum. 

The 100% load case will also include maximum duct firing of the HRSGs. Although maximum emissions will 

occur during 100% load operation, plume rise will be lower and hence impacts could be greater during 

partial load conditions. Therefore, modeling will be conducted for all cases to define the worst-case 

scenario for each pollutant. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-15 July 2008 

Figure 2-8 Palmdale Regional Airport 2002-2004 Wind Rose 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-16 July 2008 

2.3.1.2 Startup/Shutdown Turbine Operations 

During startup and shutdown of the combustion turbines, emissions of NOX and CO will be higher than 

normal operations. As such, worst-case startup and shutdown conditions will be modeled with AERMOD for 

comparison to the 1-hour NO2 CAAQS of 339 μg/m3

 and the 1-hour CO CAAQS of 23,000 μg/m3. An 

analysis of maximum 8-hour CO impacts for comparison to the CAAQS of 10,000 μg/m3, including 

startup/shutdown, will also be conducted. Stack parameters and emissions data required for modeling 

short-term startup/shutdown scenarios will be provided in the modeling report. It is anticipated that stack 

parameters corresponding to a 20 percent load will be used as representative of this operating mode. If 

required, application of the ozone limiting method (OLM) as described in Section 2.4.3 will be used to 

account for the oxidizing potential of background ozone to convert NOX to NO2 on an hourly basis. Startup 

and shutdown emissions will be accounted for in the annual average modeling by developing scenarios, 

such as base load and daily cycling cases, to determine the worst case emissions. To assess annual 

average impacts, the maximum annual potential emissions will be modeled with 100% load stack 

parameters and annual average temperature as this case will be most representative of annual average 

conditions. 

2.3.1.3 Turbine Commissioning 

Maximum emissions during the initial tuning and testing of the combustion turbines at the end of 

construction of the power plant will be similar to emissions during startup and shutdown operations. To the 

extent where there are differences, short-term modeling of NOX and CO emissions will also be performed to 

determine impacts from this phase. 

2.3.2 Ancillary Combustion Units 

The Project will include an auxiliary boiler, emergency generator engine, fire-water pump engine and heat 

transfer fluid heater. These units will each have a dedicated stack. The modeling of these sources will be 

based on maximum (short-term and annual) emissions of the criteria pollutants and appropriate stack 

parameters based on the size of the units proposed. The stack parameters and air emissions of all the units 

will be documented within the modeling report. 

2.3.3 Cooling Towers 

The Project will include a wet mechanical draft cooling tower. Drift eliminators will be utilized to minimize 

cooling tower drift. Cooling tower drift consists of water droplets containing dissolved solids which are 

entrained in the airflow through the tower and carried out to the atmosphere. As such, the cooling tower will 

be a source of particulate matter emissions and will be included in the modeling analysis to assess Project 

PM10/PM2.5 air quality impacts. 

The PHPP cooling tower will consist of 10 cells. Each cell will be modeled as an individual point source. 

The modeling report will document the source parameters including the fan stack height, inside diameter, 

exhaust temperature and velocity. 

2.3.4 Construction Sources 

Construction of the PHPP is anticipated to take 27 months. Construction-related air emissions will include 

exhaust and fugitive dust from vehicle and construction equipment and windblown fugitive dust from grading 

and other soil disturbing activities. Criteria pollutant emissions will be modeled to determine maximum air 

quality impacts. Modeling will reflect that construction will primarily occur during daylight hours. The 

maximum modeled concentrations will then be added to background concentrations and compared to the 

applicable standards. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-17 July 2008 

Construction-related emissions will be modeled using the AERMOD model (version 07026). Emissions of 

criteria pollutants for the construction sources will be modeled as layered area sources, with one layered 

area source representing power block construction, and another representing solar array construction. 

Buoyancy and mechanical turbulence from the hot exhaust and mobility of the construction equipment will 

be included as an initial vertical dimension in the area source algorithm. Fugitive dust emissions and onsite 

motor vehicles will be modeled as a separate low-level area source since these emissions would almost all 

occur near ground level. 

For the emission source associated with the power block construction, an area polygon source with a total 

area of about 95,260 square meters (m2

) will be used. This area represents the size of the power block and 

will be used to compute the emission flux for the power block area. For the construction sources associated 

with the solar array construction, a rectangular area source with an area of about 100,700 m2

 will be used. 

The solar array area source represents the largest area that is expected to be under construction at a given 

time and the solar array construction emission flux will be calculated based on this area. The power block 

sources will be located over the proposed footprint for the power block equipment, while the solar array 

construction sources will be placed just to the west of the power block to allow for potential interaction of 

plumes from both area sources. Each of these locations, shown in Figure 2-9, will have two overlaid area 

sources, one for the windblown fugitive and on-site vehicle emissions, and a second for the construction 

equipment with vertical exhaust pipes. 

A release height of 2.0 meters will be assumed for the fugitive / onsite vehicles sources, with an initial plume 

height of 15 feet (4.57 m). Following EPA AERMOD guidance (EPA, 2004), the initial area source vertical 

standard deviation for construction combustion emissions is estimated as the plume depth divided by 2.15, 

or 2.13 m. 

The large construction equipment will be assumed to have a release height of 3.7 m. The initial vertical 

depth of the diesel exhaust plume for construction activities will be estimated as four times the release 

(exhaust) height. This height (14.8 m) takes into account the plume rise of the hot diesel exhaust, 

mechanical mixing on the site introduced by the movement of heavy equipment, and structure wake 

turbulence introduced by buildings and structures on the Project site. The initial area source vertical 

standard deviation for the construction equipment is calculated by taking this vertical depth and dividing by 

2.15 for an initial sigma-z of 6.88 meters. 

2.4 Evaluation of Air Quality Impacts 

2.4.1 Project Operation Impacts 

The modeling of normal plant operations using AERMOD will be done as a multi-step process. First, the 

worst-case impacts for the combustion turbines (based on different load and temperature profiles) will be 

identified. Next, the worst-case combustion turbine impacts will be combined with normal operations of the 

other facility sources. The maximum air quality impacts due to emissions from the Project sources will be 

compared to the EPA Significant Impact Levels (SILs) (see Table 2-2). For criteria pollutants and averaging 

periods where the modeled Project impacts are below their respective SILs, no further analysis will be 

required to demonstrate compliance with the PSD increments. For pollutants and averaging periods where 

modeled impacts are greater than the SILs, multi-source modeling will be required to determine the 

cumulative impacts of the Project and nearby major background sources to demonstrate compliance with 

the PSD increments. In addition, the CEC requires a cumulative analysis to demonstrate compliance with 

the NAAQS/CAAQS. 

ENSR submitted a letter to the AVAQMD on July 2, 2008 requesting a background inventory for sources to 

be included in the cumulative modeling. ENSR was contacted by Chris Anderson and recommended that 

two facilities close to the Project site, Lockheed-Martin Aeronautics and Northrop-Grumman Corporation, be 

included in the cumulative analysis. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-18 July 2008 

Figure 2-9 Location of Emission Sources Used In Construction Modeling 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-19 July 2008 

Table 2-2 Ambient Air Impact Criteria (μg/m3) 

NAAQS 

Pollutant Averaging 

Period 

PSD Class II 

Significant 

Impact Levels 

PSD Class II 

Increments CAAQS 

Primary Secondary 

1-hour -- -- 3391 -- -- NO2

Annual 1 25 57 100 100 

1-hour 2,000 -- 23,000 40,000 NA 

CO 

8-hour 500 -- 10,000 10,000 NA 

24-hour 5 30 50 150 150 

PM10 

Annual 1 17 20 -- -- 

24-hour -- -- -- 35 35 

PM2.5 

Annual -- -- 12 15 15 

1-hour -- -- 655 -- -- 

3-hour 25 512 -- NA 1300 

24-hour 5 91 105 365 NA 

SO2

Annual 1 20 -- 80 NA 

1 The California Office of Administrative Law (OAL) approved the rulemaking on February 19, 2008, and the revised 

NO2 standard became March 20, 2008. 

The cumulative source database was received in the form of a Hotspots Analysis and Recording Program 

(HARP) modeling file for the two facilities which included the sources the be modeled and included the 

necessary stack parameters and emissions data. 

The HARP data included 284 sources (129 at Lockheed, 155 at Northrop), the vast majority of which had 

very small emissions. Because of the large number of sources, AERMOD runs would take an extremely 

long time to complete. Therefore, following consultation with the AVAQMD, it was determined that the 

modeling would only explicitly include the sources that emit 5% or greater of the total facility emissions for 

each pollutant. The emissions from sources not modeled (i.e., sources with emissions less than 5% of the 

total) will be added to the highest emitting source for that pollutant. In the case where there are multiple 

sources with the highest emission rate, the emissions from sources not modeled will be added to the with 

source closest to the Project site. This approach will provide a reasonable simplification to the modeling that 

will result in more manageable modeling run times while ensuring that the emissions from the non-Project 

facilities are properly accounted for in the cumulative modeling. 

The correspondence related to the cumulative inventory is contained in Attachment 1 to this protocol.. 

2.4.2 Ambient Background Concentrations 

An ambient regional background component representing non-modeled source contributions will be 

added to the modeled concentrations to demonstrate compliance with the CAAQS/NAAQS. Regional 

background concentrations from available ambient monitoring data most representative of current air 

quality in the proposed project impact area are shown in Table 2-3. These data represent the three most 

recent years (2005-2007) available from the Lancaster Division Street monitor (same location as the 

meteorological data), except for the SO2 background data, which represents the three most recent years 

(2005-2007) available from the Burbank West Palm Avenue monitor in Burbank, CA. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 2-20 July 2008 

Table 2-3 Annual Monitoring Data for Background Concentrations 

Maximum Observed Concentrations (μg/m3

) Pollutant Period 

2005 2006 2007 

1-hour 139.2 124.1 120.4 

NO2

Annual 28.2 28.2 26.3 

1-hour 3,335 3,680 2,875 

CO 

8-hour 1,725 1,840 1,495 

24-hour 55 65 86 

PM10 

Annual 22 23 25 

24-hour 16 13 20 

PM2.5 

Annual 8.9 7.4 8.0 

1-hour 34.1 23.6 21.0 

3-hour 23.6 13.1 13.1 

24-hour 15.7 10.5 7.9 

SO2

Annual 5.2 2.6 2.6 

All short term values are the maximum concentration with the exception of PM2.5 which is the 98th

percentile. Annual values are mean annual concentrations. 

2.4.3 NO2 Modeling 

To complete the Ambient Air Quality Impacts Analysis (AQIA) for NO2, the modeled ground-level 

concentrations resulting from NOX emissions must be converted to NO2. For the PHPP AQIA, initially the 

EPA national default conversion factor of 75 percent will be applied to the modeled NOX concentrations to 

estimate NO2. If further refinement of the NO2 concentrations is necessary, the ozone limiting method 

(OLM) will be applied as implemented in AERMOD with the use of hourly ozone concentrations from the 

most representative monitor. In using the OLM in AERMOD, conversion of NOX emissions to NO2

concentrations are limited based on the availability of ozone as determined by the ambient background 

levels. If necessary, background ozone levels will be obtained from the EPA AirData website for the 

Lancaster monitoring station. 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 3-1 July 2008 

3.0 Additional Impact Analyses 

PSD regulations require a review of the following additional potential impacts which may result from the 

proposed project with respect to the following: 

• Vegetation and Soils 

• Associated Growth 

• PSD Class I Area Impacts 

Potential impacts to PSD Class I Areas are addressed in a separate modeling protocol. 

3.1 Vegetation and Soils 

The project lies in an area of primarily consisting of desert and desert shrub-land, with much of the nearby 

area covered by the Palmdale Regional Airport. No significant off-site impacts are expected from the 

proposed action. Therefore, the potential for adverse impacts to either soils or vegetation is minimal. 

Criteria for evaluating impacts on soils and vegetation are provided in EPA's A Screening Procedure for the 

Impacts of Air Pollution Sources on Plants, Soils and Animals (EPA 1980). Table 3-1 lists the EPA 

suggested criteria for the gaseous pollutants emitted directly from the proposed facility. These criteria are 

established for sensitive vegetation and crops exposed to the effects of the gaseous pollutants through 

direct exposure. Adverse impacts on soil systems result more readily from the secondary effects of these 

pollutants' impacts on the stability of the soil system. These impacts could include increased soil 

temperature and moisture stress and/or increased runoff and erosion resulting from damage to vegetative 

cover. The modeled air concentrations for the proposed facility will be compared to these criteria to 

evaluate impacts on both soils and vegetation. 

Table 3-1 EPA Criteria for Gaseous Pollutant Impacts on Natural Vegetation and Crops 

Pollutant Averaging Time 

Minimum Impact Level for 

Affects on Sensitive Plants 

(μg/m3) 

4 hours 3,760 

8 hours 3,760 

1 month 564 

NO2

Annual 94 

CO 1 week 1,800,000 

1 hour 917 

SO2 3 hours 786 

Annual 18 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 3-2 July 2008 

3.2 Associated Growth 

PSD requires an assessment of the secondary impacts from applicable projects. There will be minimal 

associated growth expected during Project construction due to the relatively short-term (two year) duration 

and existence of a large construction labor force in the region. Additionally, no long-term growth (i.e., 

general commercial, residential, industrial or other secondary growth in the area) is expected during 

operations due to the small labor force that will be required to operate this hybrid power plant. Therefore, no 

analysis of secondary impacts from associated growth is needed for this Project.
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol 4-1 July 2008 

4.0 References 

Auer, A. H., 1978. Correlation of Land Use and Cover with Meteorological Anomalies. J. Appl. Meteor., 

Vol 17, pp 636-643. 

Dennis, Richard, Handbook on Aerosols, 1976. Energy Research and Development Administration 

Publication TID-26608, page 50. 

EPA, 1980. A Screening Procedure for the Impacts of Air Pollution Sources on Plants, Soils and Animals. 

OAQPS/EPA 450/2-81-078. 

EPA, 1985. Guideline for Determination of Good Engineering Practice Stack Height (Technical Support 

Document for the Stack Height Regulations), Revised. EPA Publication No. EPA-450/4/80-023R. 

Office of Air Quality Planning and Standards (OAQPS), Research Triangle Park, NC. 

EPA, 1992 Procedures for Substituting Values for Missing NWS Meteorological Data for Use in Regulatory 

Air Quality Models. D. Atkinson and R.F. Lee Research Triangle Park, NC 27711. July 

EPA, 1995. Compilation of Air Pollution Emission Factors. Volume I: Stationary Point and Area Sources. 

AP-42 Fifth Edition. OAQPS, Research Triangle Park, NC 27711. 

EPA, 1998. AERMET Users Guide (http://www.epa.gov/scram001/metobsdata_procaccprogs.htm#aermet) 

EPA, 2000 Meteorological Monitoring Guidance for Regulatory Modeling Applications 

(http://www.epa.gov/scram001/guidance/met/mmgrma.pdf) 

EPA, 2004. User's Guide for the AMS/EPA Regulatory Model - AERMOD, EPA Publication Nos. 

EPA-454/B-03-001. OAQPS, Research Triangle Park, NC 27711. 

EPA, 2005. Guideline on Air Quality Models (Revised). Codified in the Appendix W to 40 CFR Part 51. 

OAQPS, Research Triangle Park, NC 27711. November. 

EPA, 2008a. AERMOD Implementation Guide. http://www.epa.gov/scram001/7thconf/aermod/

aermod_implmtn_guide_09jan2008.pdf. 

EPA, 2008b. AERSURFACE Users Guide 

(http://www.epa.gov/scram001/7thconf/aermod/aersurface_userguide.pdf) 

Hinds, William, C., 1982. Aerosol Technology, John Wiley & Sons, New York, NY, Page 381. 

U.S. Federal Aviation Administration, 2005. Electronic Code of Federal Regulations - 14 CFR 77.28: 

Objects Affecting Navigable Airspace. 

http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?&c=ecfr&tpl=/ecfrbrowse/Title14/14tab_02.tpl
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol July 2008 

Attachment 1 

AVAQMD Correspondence Related to the Cumulative Modeling 

Inventory 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol July 2008 
PHPP Appendix G.4, Class II Area Dispersion Modeling Protocol July 2008