Submitted to: Submitted by:

Arizona Public Service AECOM

Phoenix, AZ Fort Collins, Colorado 

60221977

July 2013

Environment

Four Corners Power Plant and Navajo 

Mine Energy Project Environmental 

Impact Statement Ozone Impact 

Assessment
AECOM Environment ES-1

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Executive Summary

The Arizona Power Service (APS) operates the Four Corners Power Plant (FCPP), a privately owned 

and operated coal-fired power plant located on the Navajo Nation, about 25 miles west of Farmington, 

New Mexico. The APS contracted AECOM to assist in gathering data in support of the preparation of an 

Environmental Impact Statement (EIS). The EIS will be prepared to analyze the effects of related 

proposed federal undertakings in accordance with the National Environmental Policy Act of 1969 

(NEPA), 42 United States Code 4231–4347; the Council on Environmental Quality’s regulations for 

implementing NEPA, 40 CFR Parts 1500 through 1508; and the Department of the Interior’s (DOI) NEPA 

regulations, 43 CFR Part 46, the Office of Surface Mining Reclamation and Enforcement (OSM), 

Western Region (WR), Denver, Colorado. The OSM is the lead federal agency.

APS’ proposed action to be analyzed in the EIS includes a lease amendment for the FCPP, rights-of-way

(ROWs) renewals, ceasing operations of Units 1, 2, and 3, installing SCR controls on the two remaining 

operating units (4 and 5), and continuing operations of the transmission lines and ancillary facilities. 

Other connected actions include development of a new coal mine permit area, called the Pinabete 

Permit, located adjacent to the FCPP on the Navajo Nation by BHP Navajo Coal Company (BNCC) and 

continued operations of transmission lines associated with the FCPP that are operated by Public Service 

Company of New Mexico (PNM).

This EIS is in response to the proposed Lease Amendment No. 3 for the FCPP site and renewal of ROW

for existing FCPP facilities. This modeling work focuses exclusively on the assessment of ozone air 

quality impacts associated with the proposed lease renewal and grant issuance. The assessment is 

conducted by modeling the FCPP emissions in combination with other regional emissions sources and 

comparing the resulting ozone concentrations to the United States Environmental Protection Agency’s 

(USEPA) 2008 8-hour ozone National Ambient Air Quality Standard (NAAQS). Ozone impacts were 

assessed near the FCPP, at existing ozone monitors, and at 88 Class I and sensitive Class II areas.

The approach used in this modeling work relies on the input data, configurations, supporting information, 

and modeling platform developed for the Four Corners Air Quality Study (FCAQS). The FCAQS, which 

encompasses the FCPP project area, was conducted with the Comprehensive Air Quality model with 

extensions (CAMx) to assess air quality conditions in the Four Corners region and evaluate the potential 

future impacts of various control scenarios in 2018. The FCAQS modeling was performed using 

12-kilometer (km), and 4-km grid cell resolution for two modeling domains. The FCAQS also performed a 

model performance evaluation of CAMx results by comparing modeled concentrations to ambient 

measurements. This evaluation found that model performance for ozone was within the established 

USEPA acceptance criteria for most months, indicating CAMx is adequate for ozone modeling.

Using the FCAQS modeling platform, AECOM simulated ozone concentrations for the year 2005 and 

two future year 2018 scenarios to assess the impacts of the proposed FCPP proposed action. The 2005 

Baseline simulation was conducted using the 2005 FCAQS regional emissions inventory to provide an 

assessment of current air quality conditions and for comparison to future year model-predictions. 

The 2018 No Action (NA) Alternative simulation was developed to reflect the scenario that the FCPP 

lease is not renewed and the FCPP would be shut down. Therefore, the FCPP has zero emissions for 

the 2018 NA Alternative emissions inventory. The other regional emissions for the 2018 NA Alternative 

emissions inventory were based on FCAQS Mitigation Scenario #4 which applies control measures to 

nitrogen oxides (NOX) and sulfur dioxide (SO2) from coal-fired power plants, as well as NOX and Volatile 

Organic Compounds (VOC) controls to oil and gas sources in San Juan and Rio Arriba counties in New 

Mexico. In addition, FCAQS Mitigation Scenario #4 was updated with the most current information 

available for Electric Generating Units (EGU) in the 4-km domain, including the San Juan Generating 

Station (SJGS). 

The 2018 Proposed Action (PA) emissions are identical to the NA Alternative, except for the FCPP. The 

modeled emissions for the FCPP were provided by APS.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

The emissions inventories for the 2005 Baseline, 2018 NA Alternative, and 2018 PA were processed 

through the Sparse Matrix Operator Kernel Emissions (SMOKE) model to produce surface and elevated 

hourly, gridded, speciated, emissions for the CAMx air quality model. Using the SMOKE processed 

emissions and FCAQS model-ready meteorological inputs and ancillary data, CAMx was used to 

perform ozone modeling to assess the FCPP PA impacts on the Four Corners region. Ozone was 

modeled from May through August as the observed ozone concentrations are highest during the 

summer months in this region. The CAMx configuration options used in this modeling work were based 

on the FCAQS, except for the Plume-in-Grid (PiG) sub-model setting. The PiG sub-model was required 

for FCPP and SJGS to better represent the early chemical and transport evolution of the NOX plumes 

associated with these sources. 

The results of these three CAMx simulations were post-processed to perform the following analyses: 

1) comparison of modeled concentrations to the 8-hour ozone NAAQS, 2) model attainment tests for 

monitored and unmonitored areas, and 3) assessment of the ozone impacts due to the PA. 

Model-predicted ozone concentrations were further post-processed with AECOM’s Impact Assessment 

Suite (IAS) and USEPA’s Model Attainment Test Software (MATS). The IAS was designed to read 

model predicted concentrations at specified receptor sites and produce values that could be compared to 

the ozone NAAQS and also to provide suitable input files for MATS. The IAS calculated the modelpredicted fourth highest daily maximum 8-hour average ozone concentrations at Class I and sensitive 

Class II areas for comparison to the NAAQS for the 2005 Baseline, 2018 NA Alternative, and 2018 PA 

simulations. The IAS results are referred to as the absolute model-predicted impacts.

Ozone model attainment demonstration was performed using MATS. The model-predicted impacts are 

adjusted for monitored concentrations. MATS results are referred to as model-adjusted impacts. The 

MATS tool was designed to project future ozone concentrations at locations of ozone monitors and also 

locations removed from monitors based on ambient ozone measurements. Projections were based on 

applying a RRF to an ozone design value, which is estimated from the 5-year weighted average of the 

fourth highest daily maximum 8-hour average monitored values. The MATS also calculated ozone 

concentrations for sites removed from monitor locations by using two types of spatial interpolation:

1) between “neighbor” monitors and 2) between “neighbor” monitors but relying on model data to perform 

gradient adjustments. This analysis provides the MATS calculated fourth-highest daily maximum 8-hour 

average ozone concentrations for monitor locations and also spatial interpolation values for unmonitored 

Class I and sensitive Class II areas. The MATS was run for the 4-km domain for both the 2018 NA 

Alternative and PA scenarios for comparison to the NAAQS.

Model results and comparisons were presented in different tabular and graphical format analysis. 

Regional comparisons showed that there is an overall decrease in cumulative ozone concentrations for 

the 2018 year simulations relative the 2005 Baseline. The largest changes occur in the western and 

central areas of the 4-km domain where the model-predicted fourth-highest daily maximum 8-hour 

average ozone concentrations decrease by 5 to 7 parts per billion (ppb). The only locations where ozone 

is observed to increase occur in San Juan County in New Mexico, in an area immediately downwind of 

the FCPP. The maximum increase in the fourth-highest 8-hour ozone concentrations between the 2018 

NA Alternative and 2005 Baseline was 3.5 ppb. This increase occurs in a region where ozone 

concentrations do not exceed the NAAQS. 

The PA ozone impacts were estimated as the difference between 2018 PA and the 2018 NA Alternative 

simulations. This difference in the model concentrations was examined using three methods: 1) absolute 

values, 2) monitored area analysis, and 3) unmonitored area analysis. In general, the largest impacts 

range between 2 to 4.7 ppb. These impacts occur almost entirely in San Juan County, New Mexico 

about 11 miles southeast of the FCPP and about 16 miles southwest of Farmington. The absolute model 

predicted results indicate that in 2005, twelve Class I and sensitive Class II areas exceeded the NAAQS, 

but by 2018 only three of these areas may exceed the NAAQS. These areas include La Garita 

Wilderness Area, Grande Messa National Forest, and Rio Grande National Forest. The FCPP does not 

contribute to the ozone concentrations in any of these areas (i.e., the FCPP contribution in these areas is 

0.0 ppb). Importantly, the absolute model predicted ozone concentration for the PA at the Navajo Nation 

is just below the NAAQS. The model-predicted FCPP contribution to this area is 0.7 ppb of ozone.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

The monitored area analysis indicates that in 2005 one monitor exceeded the NAAQS, but that by 2018 

no monitors in the 4-km modeling domain would exceed the NAAQS. 

Similar to the absolute model-predicted impacts, the unmonitored area analysis indicates that in 2005 

there were nine Class I and sensitive Class II areas with modeled ozone exceedences, but that by 2018 

the ozone concentrations in these areas will decrease and only one area (Sandia Mountain Wilderness 

Area) may have ozone exceedences. The FCPP contributes 0.1 ppb at Sandia Mountain. Importantly, 

using this method to predict future ozone concentrations, the ozone levels at the Navajo Nation are 

notably lower than the absolute model impacts and the contribution of the FCPP to this area is between 

0.0 and 0.1 ppb.

Overall, the model-predicted future ozone concentrations are similar regardless of the methods used to 

analyze the results. In general, ozone concentrations are predicted to decrease in 2018 throughout the 

4-km modeling domain relative to conditions in 2005. Ozone impacts from the FCPP under the Proposed 

Action do not contribute to areas that may continue to have ozone concentrations that exceed the 

NAAQS in 2018. 
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

List of Acronyms

APS Arizona Public Service Company

BART Best Available Retrofit Technology

BC boundary concentration

BIA Bureau of Indian Affairs

BLM Bureau of Land Management

BNCC BHP Navajo Coal Company

CAMx comprehensive air quality model with extensions

CB05 Carbon Bond 2005

CEMS Continuous Emissions Monitoring System

CFR Code of Federal Register

CO carbon monoxide

°C degrees Celsius

dd decimal degrees

DVC current year design value

DVF future year design value

EGU electric generating units

EIS Environmental Impact Statement

FCAQS Four Corners Air Quality Study

FCPP Four Corners Power Plant

GEOS-Chem Goddard Earth Observing System - Chemical

GREASD Greatly Reduced Execution and Simplified Dynamics

g/kg grams per kilogram

g/m3 grams per meter cubed

IA Index of Agreement

IAS Impact Assessment Suite

IC initial concentration

IMPROVE Interagency Monitoring of Protected Visual Environments

IR Indian Reservation

ISORROPIA Inorganic Aerosol Thermodynamics/Partitioning scheme

K degrees Kelvin

km kilometer

LCC Lambert Conformal Conic

m meter

MATS Model Attainment Test Software

MEGAN Model Emissions of Gases and Aerosols from Nature

mb millibars

MM5 Mesoscale Model version 5

MSL mean sea level

MW megawatt

m/h meters per hour
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

m/s meters per second

m2

/s meters squared per second

NA No Action

NAAQS National Ambient Air Quality Standards

NASA National Aeronautics and Space Administration

NCAR National Center for Atmospheric Research

NEPA National Environmental Policy Act

NH3 ammonia

NM National Monument

NNEPA Navajo Nation Environmental Protection Agency

NP National Park

NPDES National Pollutant Discharge Elimination System

NOAA National Oceanic and Atmospheric Administration

NO nitrogen oxide

NO2 nitrogen dioxide

NO3 nitrate

NOX nitrogen oxides

NWS National Weather Service

O2 molecular oxygen

O3 ozone

OSM Office of Surface Mining Reclamation and Enforcement

PA Proposed Action

PGM photochemical grid model

PiG Plume-in-Grid

PM particulate matter

PM2.5 particulate matter with an aerodynamic diameter if 2.5 microns or less

PM10 particulate matter with an aerodynamic diameter if 10 microns or less

PNM Public Service Company of New Mexico

ppb parts per billion

ppm parts per million

PPM Piecewise Parabolic Method

PSU Pennsylvania State University

QA quality assurance

RADM Regional Acid Deposition Model

ROW right-of-way

RPO Regional Planning Organization

RRFs relative response factors

SCC source classification code

SCR Selective Catalytic Reduction

SIP State Implementation Plan

SJGS San Juan Generating Station

SMCRA Surface Mining Control and Reclamation Act

SMOKE Sparse Matrix Operator Kernel Emissions

SOAP Secondary Organic Aerosol Formation/Partitioning scheme
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SO2 sulfur dioxide

SO4 sulfate

TDL Techniques Development Lab

TOMS Total Ozone Mapping Spectrometer

tpy tons per year

USACE U.S. Army Corps of Engineers

USEPA U.S. Environmental Protection Agency

VOC volatile organic compound

WA Wilderness Area

WRAP Western Regional Air Partnership

WSA Wilderness Study Area

2-D two-dimensional

3-D three-dimensional
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Contents

Executive Summary ...............................................................................................................................ES-1

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

1.1 Modeling Overview................................................................................................................1-2

1.2 Contents of the Modeling Report..........................................................................................1-4

2.0 Regional Emissions Inventory......................................................................................................2-1

2.1 2005 Baseline........................................................................................................................2-3

2.2 2018 No Action Alternative ...................................................................................................2-6

2.3 2018 Proposed Action Alternative ........................................................................................2-7

3.0 Modeling Approach........................................................................................................................3-1

3.1 Gridded Meteorological Data................................................................................................3-1

3.2 Emissions Modeling ..............................................................................................................3-1

3.3 CAMx Modeling.....................................................................................................................3-3

3.4 CAMx Post-Processing.........................................................................................................3-5

3.4.1 Assessment Areas .................................................................................................3-5

3.4.2 Ozone Impact Assessment....................................................................................3-7

3.4.3 Ozone Model Attainment Test at Monitored Locations ........................................3-9

3.4.4 Ozone Model Attainment Test Removed from Monitors ......................................3-9

4.0 Modeling Results............................................................................................................................4-1

4.1 Absolute Model-Predicted Ozone Concentrations...............................................................4-2

4.1.1 2005 Baseline Compared to the 2018 No Action Alternative...............................4-2

4.1.2 2005 Baseline Compared to the 2018 Proposed Action ......................................4-4

4.1.3 2018 Proposed Action Compared to the 2018 No Action Alternative..................4-4

4.1.4 Ozone Concentrations at Class I and Sensitive Class II Areas .........................4-10

4.2 Model-Adjusted Ozone Concentrations .............................................................................4-13

5.0 Summary..........................................................................................................................................5-1

6.0 References.......................................................................................................................................6-1
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

List of Appendices

Appendix A - Analysis of FCAQS Emissions Inventory and CAMx Model Sensitivity

List of Tables

Table 1-1 MM5 and CAMx Domain Dimensions.................................................................................1-3

Table 1-2 RPO Unified Grid Definition ................................................................................................1-3

Table 2-1 FCAQS Regional Emissions Inventory Summary..............................................................2-2

Table 2-2 2005 Baseline 4-km Domain Major EGUs Emissions........................................................2-4

Table 2-3 FCPP Units 1-5 Stack Parameters .....................................................................................2-4

Table 2-4 2005 Baseline 4-km Domain Emissions by Source Category ...........................................2-4

Table 2-5 SJGS 2018 Emissions.........................................................................................................2-6

Table 2-6 2018 NA Alternative 4-km Domain Emissions by Source Category..................................2-7

Table 2-7 FCPP 2018 PA Emissions ..................................................................................................2-7

Table 2-8 FCPP Unit 4-5 Stack Parameters .......................................................................................2-8

Table 2-9 2018 PA 4-km Domain Emissions by Source Category ....................................................2-8

Table 3-1 CAMx-Required Meteorological Data .................................................................................3-1

Table 3-2 CAMx Air Quality Model Configurations .............................................................................3-4

Table 4-1 Maximum 1-hour daily Ozone Difference between 2018 PA and NA Alternative.............4-7

Table 4-2 Fourth-Highest Daily Maximum 8-hour Average Ozone Concentrations at Class I 

and Sensitive Class II Areas .............................................................................................4-10

Table 4-3 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Monitoring Sites 

Located within the 4-km Domain.......................................................................................4-15

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored 

Sensitive Class I and II Areas Located within the 4-km Domain .....................................4-16
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

List of Figures

Figure 1-1 FCAQS MM5 and CAMx Model Domains ..........................................................................1-5

Figure 1-2 FCPP with the CAMx 12-km and 4-km Domains ...............................................................1-6

Figure 2-1 4-km CAMx Domain and EGUs ..........................................................................................2-5

Figure 3-1 Class I and Sensitive Class II Areas of Concern................................................................3-8

Figure 3-2 MATS Ozone Monitors in the Four Corners States .........................................................3-10

Figure 4-1 Model-predicted Fourth-Highest Daily Maximum 8-hour Average Ozone 

Concentrations: 2005 Baseline and 2018 NA Alternative..................................................4-3

Figure 4-2 Model-predicted Fourth-Highest Daily Maximum 8-hour Average Ozone 

Concentrations: 2005 Baseline and 2018 PA.....................................................................4-5

Figure 4-3 Model-predicted Fourth-Highest Daily Maximum 8-hour Average Ozone 

Concentrations: 2018 NA Alternative and PA ....................................................................4-6

Figure 4-4 2018 NA Alternative and PA Model-Predicted Hourly Average Ozone and 

NOX on July 16 ....................................................................................................................4-8

Figure 4-5 2018 NA Alternative and PA Model-Predicted Hourly Average Ozone and 

NOX on August 2 .................................................................................................................4-9
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

1.0 Introduction

The Arizona Public Service Company (APS) operates the Four Corners Power Plant (FCPP), a privately 

owned and operated coal-fired power plant located on the Navajo Nation, about 25 miles west of 

Farmington, New Mexico. The facility currently consists of five boiler electric generating units (Units 1-5), 

with a total capacity of approximately 2,100 megawatts (MW). The current FCPP lease expires in 2016.

Under the proposed action, Units 1, 2, and 3 will be permanently retired prior to the FCPP lease 

expiration. Units 4 and 5 with a total capacity of 1,540 MW will continue to operate after 2016.

The APS contracted AECOM to assist APS in gathering data to submit to Office of Surface Mining 

Reclamation and Enforcement (OSM) to be used in preparation of an environmental impact statement 

(EIS). The EIS is needed to support the following proposed Federal actions:

• Approval from Bureau of Indian Affairs (BIA) of Lease Amendment No.3 for the FCPP site, which 

has been signed by the Navajo Nation after Navajo Nation Council approval.

• Issuance by BIA of renewed right-of-way (ROWs) for existing facilities for the FCPP and its 

switchyards, and ancillary facilities, a 500-kilovolt (kV) transmission line and two 345-kV 

transmission lines and ancillary transmission line facilities (including the Moenkopi Switchyard), 

an associated 12-kV line, and access road.

Concurrent with the proposed FCPP lease amendment approval and renewed ROWs grant actions, 

BHP Navajo Coal Company (BNCC) proposes to develop a new permit area, called the Pinabete Permit, 

which is located adjacent to the FCPP on tribal trust lands on the Navajo Nation. The new Pinabete 

Permit area would, in conjunction with the mining of any reserves remaining within the existing Navajo 

Mine Permit area (Federal Surface Mining Control and Reclamation Act [SMCRA] Permit NM0003F), 

supply low-sulfur coal to the FCPP at a rate of approximately 5.8 million tons per year. Development of 

the Pinabete Permit area and associated coal reserves would use surface mining methods and, based 

on current projected customer needs, would supply coal to FCPP for up to 25 years beginning in 2016. 

The proposed Pinabete Permit area would include previously permitted but undeveloped coal reserves 

within Area IV North of the Navajo Mine Lease, and unpermitted and undeveloped coal reserves in a 

portion of Area IV South of the existing Navajo Mine Lease. Full implementation of the proposed 

Pinabete Permit is expected to require specific federal actions that will be addressed in the EIS, 

including: 

• Approval from the OSM of the new SMCRA permit.

• Approval from the Bureau of Land Management (BLM) of a revised Mine Plan developed for the 

proposed maximum economic recovery of coal reserves.

• Approval of a Section 404 Individual Permit from the U.S. Army Corps of Engineers (USACE) for 

the impacts to waters of the United States from proposed mining activities.

• Approval of a Section 402 National Pollutant Discharge Elimination System (NPDES) permit or 

permit revision from the U.S. Environmental Protection Agency (USEPA).

• Approval by the BIA of a proposed realignment for approximately 2.8 miles of BIA 3005/Navajo 

Road N-5082 (Burnham Road) in Area IV South to avoid proposed mining areas.

• Approval or grant of other associated facilities, permits, or ROWs for access and haul roads, 

power supply for operations, and related facilities.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

This report focuses exclusively on the assessment of the ozone ambient air quality impacts associated 

with the proposed lease renewal and grant issuance. The assessment was conducted by modeling the 

FCPP emissions in combination with other regional emissions sources and comparing the resulting 

ozone concentration to the USEPA’s 2008 8-hour ozone National Ambient Air Quality Standards 

(NAAQS). Assessment of sulfur dioxide (SO2), nitrogen dioxide (NO2), particulate matter (PM) with 

aerodynamic diameters less than or equal to 2.5 and 10 microns (PM2.5, PM10, respectively), carbon 

monoxide (CO), and lead impacts are addressed in a separate report (AECOM 2013).

1.1 Modeling Overview

The objective of this modeling work was to estimate the change in ozone air quality impacts associated

with the proposed future operations of the FCPP relative to current conditions. Ozone impacts were 

assessed near the FCPP, at existing ozone monitors; at Class I areas identified in the Clean Air Act 

(CAA) Amendments of 1977, and at sensitive Class II areas. This assessment was performed with the 

Comprehensive Air Quality Model with Extensions (CAMx) (ENVIRON 2008). 

The use of the CAMx model for analyzing air quality impacts has been well established in the scientific 

community, and the model has been used for many previous modeling studies in the western U.S., 

including the Four Corners Air Quality Study (FCAQS) (ENVIRON 2009). The Pennsylvania State 

University/National Center for Atmospheric Research (PSU/NCAR) Mesoscale Model version 5 (MM5) 

and the Sparse Matrix Operator Kernel Emissions (SMOKE) (Coats 1995; Houyoux and Vukovich 1999) 

models were used in combination with CAMx for this project. Collectively, these models will be referred 

to hereafter as the CAMx modeling system. The version of the CAMx modeling system used for this work 

includes:

• The MM5 (version 5) is a meteorological model that generates hourly, gridded meteorological 

data required as inputs to the CAMx and SMOKE models.

• The SMOKE modeling system (version 2.4) is an emissions modeling system that generates 

hourly, gridded, and speciated emissions inputs of mobile, non-road, area, point, fire, and 

biogenic emissions sources for photochemical grid models.

• The CAMx modeling system (version 4.51) is a ‘One-Atmosphere’ photochemical grid model 

(PGM) capable of addressing ozone and other criteria pollutants, visibility, and acid deposition at 

the regional and urban scale.

To be consistent with previous regional modeling and publicly available information, the project approach 

relied on the input data, configurations, and supporting information developed for the FCAQS

(ENVIRON 2009). The FCAQS was developed specifically to assess air quality conditions in the Four 

Corners region and evaluate potential changes in year 2018 due to various control scenarios.

The FCAQS provided an ozone modeling platform that encompasses the FCPP project area and is 

appropriate for use in an EIS. All model domains in the FCAQS CAMx modeling system, which also are

used for this project, are shown in Figure 1-1 and listed in Table 1-1. The CAMx nested system uses 

domains with 36-kilometer (km), 12-km, and 4-km nested grid cells, hereafter referred to as the 36-km, 

12-km, and 4-km domains. All model domains used the map projection from the Regional Planning 

Organizations’ (RPO) unified grid. The RPO unified grid consists of a Lambert Conformal Conic (LCC) 

map projection using the projection parameters listed in Table 1-2. The location of the FCPP is shown 

relative to the 12-km and 4-km CAMx domains in Figure 1-2.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 1-2 RPO Unified Grid Definition

Parameter Value

Projection LCC

Datum World Geodetic System 1984

Standard Parallel 1 33° latitude

Standard Parallel 2 45° latitude

Central Meridian -97° longitude

Latitude of Origin 40° latitude

Consistent with the FCPP EIS project objectives, AECOM simulated the ozone concentrations for the 

year 2005 as well as two future year simulations for 2018 using the FCAQS modeling platform. As part of 

this modeling work, the FCAQS emissions inventory was reviewed and updated if more recent data were 

available. The details of the model simulations are summarized below:

• 2005 Baseline. The analysis of current air quality conditions used the FCAQS 2005 (ENVIRON 

2009) emissions inventory for the model domain described in more detail in Section 2.1. 

Modeling year 2005 emissions established baseline air quality levels against which future year 

project and cumulative impacts were evaluated. In addition, the baseline run was critical for 

establishing any potential model bias and errors that may exist relative to observations so that 

the bias and errors in model-predicted future year impacts can be assessed.

• 2018 No Action Alternative. The No Action (NA) Alternative used the same regional emissions 

as the Proposed Action (PA) but without any emissions contribution from the FCPP. The 

emissions inventory for this analysis is described in more detail in Section 2.2. This modeling 

scenario included all other regional emissions sources in order to assess cumulative future air 

quality impacts for comparison to the PA.

• 2018 Proposed Action. A project-specific emissions inventory was developed for the PA. The 

development of this emissions inventory is described in more detail in Section 2.3. The PA 

emissions inventory was modeled in conjunction with other regional emissions sources, identical 

to the NA Alternative. The potential air quality impacts due to the FCPP proposed emissions

were assessed by comparing the modeled impacts for the PA to the NA Alternative.

Table 1-1 MM5 and CAMx Domain Dimensions

Model Model Domain

Number of Grid 

Cells (X,Y)

Domain Coordinates (Southwest 

to Northeast Corner in km)

MM5 36-km 165x129 (-2952, -2304) to (2592, 2304)

12-km 178x157 (-2376, -1080) to ( -252, 792)

4-km 172x167 (-1272, -672) to ( -588, -8)

CAMx and

SMOKE

36-km 148x112 (-2736, -2088) to (2592, 1944)

12-km 167x137* (-2316, -912) to ( -312, 732)

4-km 101x 92* (-1192, -508) to ( -788, -140)

* These values include buffer cells. 
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

The CAMx model results were post-processed to derive results: 1) for comparison to the 8-hour ozone 

NAAQS; 2) for conducting the ozone model attainment tests for both monitored and unmonitored areas;

and 3) to analyze the ozone impacts due to the PA. Section 3.4 provides additional information on how 

model results were post-processed for future year impacts assessment.

1.2 Contents of the Modeling Report

In a very simplified sense, ozone impacts were evaluated using a three-step process: 1) estimate and 

process all regional emissions; 2) model the emissions; and 3) compare the modeled impacts to 

applicable standards. The first step in the process was the emissions development; Chapter 2.0

describes the regional emissions inventory developed for the baseline and future emissions scenarios. 

Chapter 3.0 describes the photochemical grid model system inputs, procedures and options used in this 

analysis, and methods used to post-process model results. Chapter 4.0 presents the model results and 

compares results to the 8-hour ozone NAAQS. Chapter 5.0 summarizes the ozone impacts. References 

are provided in Chapter 6.0. 
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C A N A D A

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Legend

APS Four Corners Power Plant

36-km CAMx Domain

12-km CAMx Domain

4-km CAMx Domain

36-km MM5 Domain

12-km MM5 Domain

4-km MM5 Domain

Four Corners Power Plant

Ozone Modeling Study

Figure 1-1

FCAQS MM5 and

CAMx Model Domains

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1:29,000,000

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§ ̈¦90

§ ̈¦5

§ ̈¦5

San

Francisco

San Jose Denver

Los Angeles

San Diego

Phoenix

El Paso

Las Vegas

Salt Lake City

Casper

Rapid City

Billings

Arizona

California

Colorado

Idaho

Montana

North

Dakota

Nebraska

New

Mexico

Nevada

Oregon

Utah

Wyoming
AECOM Environment 2-1

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

2.0 Regional Emissions Inventory

For regional photochemical modeling, it is essential to model the emissions from all source categories in 

the model domains. The performance of the air quality model depends on its ability to simulate the 

complex interactions between primary emissions sources and meteorological conditions. For this 

analysis, the FCPP emissions for both the 2005 Baseline and future years were obtained in consultation 

with APS. Regional emissions for all other sources were obtained from the FCAQS.

For the FCAQS, emissions from 2005 were modeled as well as multiple emissions scenarios for year 

2018 (ENVIRON 2009). The following is a summary of the FCAQS emissions inventories that are 

relevant to the FCPP EIS project: 

• 2005 Base Case emissions:

− Emissions for all area and point sources outside the 4-km domain were obtained by linearly

interpolating between Western Regional Air Partnership (WRAP) 2002 emissions inventory 

and the WRAP 2018 Preliminary Reasonable Progress 2018 (PRP18) emissions inventory

(Fields et al. 2007). 

− The 4-km domain emissions inventories were updated for the following emission categories: 

oil and gas, electric generating units (EGUs), non-EGUs, mobile, and fugitive dust.

• 2018 Base Case emissions:

− Emissions for all point and area sources outside the 4-km domain were obtained directly 

from the WRAP PRP18.1

− The 4-km domain emissions inventories were updated for the following emission categories: 

oil and gas, EGUs, non-EGUs, mobile, and fugitive dust.

• 2018 Mitigation Scenario #4:

− Application of control measures for nitrogen oxide (NOX) and SO2 emissions from coal-fired 

power plants in the Four Corners region. 

− Application of control measures for NOX and volatile organic compound (VOC) emissions 

from oil and gas sources in San Juan and Rio Arriba counties in New Mexico. The controls

were applied to both area and point source emissions from oil and gas equipment.

• The following emission categories remained constant between all model scenarios:

− The emissions inventories for ammonia. The 4-km domain emissions were developed 

specifically for FCAQS.

− The biogenic emissions. These emissions were developed for all three modeling domains

using the Model Emissions of Gases and Aerosols from Nature (MEGAN) version 2.0.

− Wildfires and prescribed fires. These emissions were obtained for the 12-km and 4-km 

domains from National Center for Atmospheric Research (NCAR) 2005 fire database 

(NCAR 2005).

Table 2-1 summarizes the FCAQS regional emissions inventories for years 2005 and 2018. 

 

1 Additional processing was required to convert the 36-km gridded area source emissions into 12-km grid cells in 

the 12-km domain. The 36-km gridded area source emissions were evenly divided into each of the nine 12-km grid 

cells contained within a single 36-km grid cell.
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Table 2-1 FCAQS Regional Emissions Inventory Summary

Emissions 

Component Domain

FCAQS Data Sources and Supporting 

Information

2005 Base Case

Area 

36-km domain

Linear interpolation between WRAP 

Plan02d and WRAP PRP18; includes road 

dust and fugitive dust emissions

12-km domain, excluding the 4-

km domain

Disaggregated 36-km resolution emissions

to 12-km x 12-km grid cells 

4-km domain Updated emissions including oil and gas 

sources from WRAP Phase II

On-Road 36-km, 12-km, and 4-km domains SMOKE-MOBILE6

Off-Road 36-km, 12-km, and 4-km domains

Linear interpolation between WRAP 

Plan02d and WRAP PRP18; include 

locomotive, aircraft and other non-road 

sources

Biogenic 36-km, 12-km, and 4-km domains SMOKE-MEGAN

Point 

36-km domain

EGU, non-EGU, and Oil and Gas emissions 

from both Tribal and State sources with 

revised sources in 4-km region

36-km domain 2005 NCAR fire database

2018 Base Case and Mitigation Scenario #4

Area 

36-km domain WRAP PRP18; includes road dust and 

fugitive dust emissions

12-km domain, excluding the 4-

km domain

Disaggregated 36-km resolution emissions

to 12-km x 12-km grid cells

4-km domain Revised emissions including oil and gas 

sources

On-Road 36-km, 12-km, and 4-km domains SMOKE-MOBILE6

Off-Road 36-km, 12-km, and 4-km domains WRAP PRP18; includes locomotive, aircraft 

and other non-road sources

Biogenic 36-km, 12-km, and 4-km domains SMOKE-MEGAN; same as 2005

Point 

36-km domain

EGU, non-EGU, and Oil and Gas from both 

Tribal and State sources with revised 

sources in 4-km domain

36-km domain 2005 NCAR fire database; same as 2005

The FCAQS regional emissions inventories were updated for the FCPP EIS to include more recent 

information. The FCAQS 2005 Base Case emissions inventory is the basis for the FCPP EIS 2005 

Baseline emissions inventory and the FCAQS 2018 Mitigation Scenario #4 is the basis for the FCPP EIS 

2018 NA Alternative and PA emissions inventories. The updates that were made to the FCAQS were 

limited to those changes that are relevant for evaluating ozone impacts in the vicinity of the FCPP.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Given the objectives of this project and availability of more recent information, AECOM updated the 

FCAQS 4-km domain EGU point source inventory. The updates were limited to the 4-km domain since 

this is the area most relevant for the FCPP. The updates were based on the most current information for 

both 2005 and projected future EGU operations. The following changes were made to the FCAQS 4-km 

EGU inventory:

• FCPP annual emissions were updated for all model scenarios;

• The temporal variably of the FCPP emissions were adjusted to have a constant emission rate for 

all model scenarios (APS 2013);

• The stack parameters for FCPP Units 1-5 were updated for all model scenarios;

• The locations of all the major EGU point sources in the 4-km domain were revised to reflect their 

correct latitude and longitude values for all model scenarios; and

• San Juan Generating Station (SJGS) annual emissions were updated for the 2018 NA 

Alternative and PA.

Since the emissions inventory was revised for assessing ozone impacts, the emissions inventory 

improvements focused on ozone precursors (NOx and VOC). As part of this effort, the Navajo Mine 

emissions for the PA were reviewed. Importantly, the proposed activities and operations at the Navajo 

Mine would not emit ozone precursors (NOx and VOC) in sufficient quantities to impact ozone formation 

(AECOM 2013). Therefore, the Navajo Mine emissions were not explicitly modified for the NA Alternative 

and PA.

The following sections provide more detailed information about the updates made to the FCAQS 

emissions inventories for the purposes of assessing FCPP ozone impacts. 

2.1 2005 Baseline

The 2005 Baseline regional emissions inventory was based on the 2005 FCAQS Base Case emissions 

inventory for all source categories, except that the FCPP emissions were updated based on data from 

APS (2013). The ozone precursors emitted from the FCPP primarily occur due to the combustion of coal 

in the main coal-fired boilers (Units 1-5). Smaller amounts of precursor emissions also are emitted from 

the ancillary equipment, such as the recently permitted gas-fired auxiliary boiler and vehicle exhaust. 

The modeled FCPP 2005 Baseline emissions are shown in Table 2-2 with the emissions for the largest 

EGUs in 4-km domain. The Mohave Generating Station was shut down on 2005. Therefore, this EGU 

was removed from the modeled emissions inventory. All emissions are provided in tons per year (tpy). 

While this project focused on ozone impacts, the FCAQS assessed the impacts of multiple pollutants. 

For completeness, all modeled emissions are shown in Table 2-2. The locations of the EGUs within the 

4-km domain are shown in Figure 2-1.

In addition to updating the total FCPP emissions, the temporal variability of the FCPP emissions and the 

stack parameters also were revised for the purposes of this project. Based on information from APS 

(2013), the FCPP emissions were modeled with a constant emissions rate throughout the model period.

The exhaust gases from Units 1-5 were modeled as one single stack with an effective average diameter 

calculated from the values from all the units. Table 2-3 summarizes the exhaust stack parameters 

provided by engineers at APS, which are used for the 2005 Baseline model simulation (APS 2013).

The modeled 2005 Baseline 4-km domain emissions are summarized in Table 2-4 for all source 

categories. 
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Table 2-2 2005 Baseline 4-km Domain Major EGUs Emissions

Facility Name

Latitude

(dd)

Longitude

(dd)

2005 Emissions (tpy)1

CO NH3 NOX PM10 PM2.5 SO2 VOC

Four Corners Power 

Plant

36.689162 -108.479631 2,411 0 44,587 1,408 704 13,712 12

San Juan Generating 

Station

36.802150 -108.438205 1,534 0 26,829 1,520 393 16,636 185

Escalante Station 35.415965 -108.082289 203 4 3,799 19 7 1,293 0

Reeves Generating 

Station

35.171700 -106.599700 1,406 5 151 0 5 0 8

Milagro Cogeneration 

Plant

36.736700 -107.941700 0 0 110 0 0 3 0

Animas Power Plant 36.724885 -108.191808 16 0 61 0 0 0 58

Delta Person 

Generating Station

35.027592 -106.643502 1 1 4 4 0 0 0

1 For the assessment of ozone impacts, 2005 is selected as the “baseline year” based on availability of input data. A baseline 

year is necessary to conduct an ozone attainment test in accord with USEPA guidance (2007). This is not an increment 

consuming baseline assessment.

Table 2-3 FCPP Units 1-5 Stack Parameters

Parameter Units Units 1-5 Merged Stack

Latitude decimal degrees (dd) 36.689162

Longitude dd -108.479631

Stack Height meters (m) 115.824

Effective Diameter m 8.6868

Gas Exit Velocity meters per hour (m/h) 87782.4

Stack Gas Exit Temperature degrees Kelvin (K) 327.00

Table 2-4 2005 Baseline 4-km Domain Emissions by Source Category

Pollutant 

(tpy) Area

OnroadOffroad BiogenicArea Oil 

& Gas

Point 

Oil & 

Gas EGU

NonEGU Total

NOX 16,477 39,340 15,717 1,834 38,832 29,998 72,668 6,997 221,863

SO2 5,789 669 809 0 136 602 30,518 4,938 43,461

VOC 32,989 23,499 11,690 238,471 110,862 11,410 299 2,429 431,649

PM10 37,224 1,197 1,224 98,640 24 168 990 3,018 142,485
XW

XW

XW

XW XW

XW

6

6

6

6

6

6

6

6

6

X

FCPP

§ ̈¦40

§ ̈¦25

Arizona

Colorado

New Mexico

Utah

Durango

Shiprock

Farmington

Window Rock

Gallup

Santa Fe

Rio Rancho

Albuquerque

Los Lunas

San Juan

Generating

Station

Escalante

Station

Reeves Generating Station

Milagro

Cogeneration

Plant Animas

Power

Plant

Delta Person Generating Station

San Juan

Navajo

Coconino

Apache

Cibola

San Juan

McKinley

Garfield

Kane

San Juan

Dolores

La Plata

Montezuma

Catron

San

Miguel

Montrose

Ouray

Saguache

Gunnison

Chaffee

Fremont

Torrance

Hinsdale

Rio

Arriba

Taos

San

Miguel

Valencia

Mora

Santa Fe

Los

Alamos

Sandoval

Bernalillo

Mineral

Rio

Grande

Alamosa

Costilla

Archuleta

Conejos

Legend

X APS Four Corners Power Plant

XW EGUs in 4-km Domain

6 City

4-km CAMx Domain

Interstate Highway

County

Four Corners Power Plant

Ozone Modeling Study

Figure 2-1

4-km CAMx Domain

and EGUs

0 20 40 80

Kilometers

0 10 20 40

Miles

1:2,100,000

o

AZ

CA CO

ID

KS

MT

ND

NE

NM

NV

OK

OR

SD

TX

UT

WA

WY

CANADA

2-5
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

2.2 2018 No Action Alternative

The 2018 NA Alternative emissions inventory was developed to reflect the scenario that the FCPP lease 

is not renewed and the FCPP would be shut down. Therefore, the FCPP has zero emissions for the 

2018 NA Alternative emissions inventory.

As described previously, an assessment of ozone impacts requires inclusion of all regional emissions 

sources. For the purposes of assessing the NA Alternative ozone concentrations, the FCAQS 2018 

Mitigation Scenario #4 was selected. As described in Appendix A, the emissions inventory for the 

FCAQS Mitigation Scenario #4 is potentially more accurate for the Four Corners area than the original 

2018 Base Case emissions inventory. As summarized previously, the FCAQS Mitigation Scenario #4

contains the following differences from the 2018 Base Case inventory:

• Application of control measures for NOX and SO2 emissions from coal-fired power plants in the 

Four Corners region. 

• Application of control technologies to oil and gas sources for NOX and VOC emissions in San 

Juan and Rio Arriba counties in New Mexico. The changes include both area and point sources 

for oil and gas inventories. 

Since the FCAQS was finalized, updated emissions information has become available for the oil and gas 

sources in the Four Corners area. Appendix A presents a comparison of the FCAQS modeled oil and 

gas emissions relative to the most recent oil and gas emissions inventory data. 

The only updates made to FCAQS Mitigation Scenario #4 for the NA Alternative are: 1) removal of the 

FCPP emissions; 2) revised SJGS 2018 emissions provided by Public Service Company of New Mexico 

(PNM) as summarized in Table 2-5 (PNM 2013); and 3) the locations (latitude and longitude) of EGUs 

located in the 4-km domain (as shown in Table 2-2 and Figure 2-1).

The SJGS emissions were updated for both the 2018 NA Alternative and PA emissions inventories. The 

SJGS 2018 annual emissions were obtained from PNM (2013). The modeled 2018 SJGS emissions 

inventory is shown in Table 2-5. These emissions were based on the August 22, 2011 New Mexico 

Regional Haze Federal Implementation Plan and conservatively assumes an 85 percent capacity factor. 

After the modeling was initiated for this project, PNM signed a tentative agreement with New Mexico

Environmental Department and USEPA to develop an alternative State Implementation Plan (SIP) to 

revise the SGJS emissions by 2018. The SGJS emissions under this revised plan were expected to be 

similar to the data shown in Table 2-5 for SIP potential future emissions. The SJGS potential future SIP 

emissions are provided for informational purposes only.

Table 2-5 SJGS 2018 Emissions 

2018 (tpy)

CO NH3 NOX PM10 PM2.5 SO2 VOC

Modeled 2018 Emissions 33,507 90 3,500 3,884 2,800 10,500 210

SIP Potential Future 

Emissions

18,615 ND 8,011 1,185 1,185 3,483 105

Note: ND = No Data.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 2-6 summarizes the modeled 2018 NA Alternative 4-km domain emissions by source category.

Table 2-6 2018 NA Alternative 4-km Domain Emissions by Source Category

Pollutant 

(tpy) Area

OnroadOffroad Biogenic

Area 

Oil & 

Gas

Point 

Oil & 

Gas EGU

NonEGU Total

NOX 21,231 13,385 8,743 1,834 39,639 26,216 10,054 7,770 142,210

SO2 13,428 180 66 0 142 715 8,027 5,763 50,127

VOC 41,906 11,094 8,193 238,471 65,950 15,945 581 2,738 421,134

PM10 54,934 883 655 98,640 26 116 5,889 1,814 162,957

2.3 2018 Proposed Action Alternative

The PA emissions are identical to the NA Alternative, except for the FCPP. The modeled emissions for 

the FCPP were obtained by personal communication with APS and are consistent with the EIS NAAQS 

study (AECOM 2013). Units 4 and 5 are cell burner, pulverized coal-fired boilers equipped with lime 

spray towers and baghouses for SO2 and PM control. Under the PA, SCR controls will be installed as 

part of the Best Available Retrofit Technology (BART) agreement (USEPA 2012). Emission rates from 

Units 4 and 5 were derived based on actual hourly data, the current Title V operating permit (NNEPA 

2008) for FCPP, as well as from the final BART rule (USEPA 2012) for NOX and PM. The emission rates 

for NOX, SO2, PM10, PM2.5, and CO emissions were consistent with the NAAQS compliance assessment 

(AECOM 2013). Ammonia (NH3) and VOC emissions were provided by personal communication with 

APS (APS 2013). The modeled FCPP 2018 PA emissions are shown in Table 2-7.

Table 2-7 FCPP 2018 PA Emissions

Facility Name

2018 (tpy)

CO NH3 NOX PM10 PM2.5 SO2 VOC

Four Corners Power Plant 1654.2 87 5789.6 1075.4 729.7 11224.7 8

Table 2-8 summarizes the PA modeled stack parameters for Units 4 and 5. Similar to the 2005 Baseline

scenario, the exhaust gases from Units 4 and 5 were modeled as one single stack with an effective 

average diameter calculated from the values of both units. The stack location and height are identical to 

the 2005 Baseline modeling; however, the temperature and exhaust velocity are based on actual hourly 

data measured from 2009 through 2011.
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 2-8 FCPP Unit 4-5 Stack Parameters

Units Units 4-5 Merged Stack

Latitude dd 36.689162

Longitude dd -108.479631

Stack Height m 115.824

Effective Diameter m 12.28

Gas Exit Velocity1 m/h 74160

Stack Gas Exit Temperature1 K 327.00

1 The exhaust parameters coincide with a 99th percentile heat input rate of 7,411 MMBtu/hr for 

each of Units 4 and 5.

The modeled 2018 PA emissions inventory is shown for all sources within the 4-km domain in Table 2-9.

Table 2-9 2018 PA 4-km Domain Emissions by Source Category

Pollutant 

(tpy) Area

OnroadOffroad BiogenicArea Oil 

& Gas

Point 

Oil & 

Gas EGU*

NonEGU Total

NOX 21,231 13,385 8,743 1,834 39,639 26,216 19,344 7,770 142,210

SO2 13,428 180 66 0 142 715 29,752 5,763 50,127

VOC 41,906 11,094 8,193 238,471 65,950 15,945 799 2,738 421,134

PM10 54,934 883 655 98,640 26 116 9,419 1,814 162,957

* The values include PA emissions for FCPP.
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3.0 Modeling Approach

The air quality modeling and input data used the FCAQS modeling platform, as mentioned previously. 

This modeling platform consisted of the following key components: 1) a meteorological modeling 

simulation using the PSU /NCAR Mesoscale Model version 5 (MM5) (Dudhia 1993); 2) emission 

inventories processed with the SMOKE emission processing system; and 3) air quality modeling 

simulations using the CAMx model. 

The modeling domains used in this modeling work were identical to those in the FCAQS, which were 

comprised of a 36-km, 12-km, and 4-km nested grids (Figure 1-1). The modeling conducted for this 

analysis was only performed for the nested12-km and 4-km domains because: a) the FCAQS analysis 

and most of the important updates to the emissions inventory were done for these two domains; b) the 

12-km domain encompasses most of the western U.S., which captures any potential regional effects that 

could impact the 4-km domain; and c) the FCPP is located within the 4-km domain. The following 

sections provide more detailed information about the setup, configuration, and data sources for each 

model used for this modeling work.

3.1 Gridded Meteorological Data

The FCAQS developed gridded meteorological data for the year 2005 using the MM5. These gridded 

meteorological data were processed for CAMx modeling using the MM5CAMx processor. The 2005 

gridded meteorological files were used for all modeling scenarios for this project (i.e., the 2005 Baseline, 

2018 NA Alternative, and 2018 PA). The meteorological data are consistent with the parameters required 

for CAMx as shown in Table 3-1. Detailed information about the set up and results of the MM5 modeling 

and the post-processing to CAMx-ready meteorological input can be found in the FCAQS (ENVIRON 

2009).

Table 3-1 CAMx-Required Meteorological Data 

CAMx Input Parameter Description

Layer interface height (m) three-dimensional (3-D), hourly, gridded, time-varying layer heights

Winds (m/s) 3-D, hourly, gridded wind vectors

Temperature (K) 3-D, hourly, gridded temperature and 2D, hourly, gridded surface 

temperature 

Pressure (mb) 3-D, hourly, gridded pressure

Vertical Diffusivity (m2/s) 3-D, hourly, gridded vertical exchange coefficients

Water Vapor (ppm) 3-D, hourly, gridded water vapor mixing ratio

Clouds and Rainfall (g/m3) 3-D, hourly, gridded cloud and rain liquid water content 

Land use types two-dimensional (2-D) gridded land use/land cover distribution

3.2 Emissions Modeling

The SMOKE emissions modeling system (Coats 1995; Houyoux and Vukovich 1999) was used to 

generate the hourly, gridded, speciated model-ready emissions inputs for the 2005 Baseline, the 2018 

NA Alternative, and 2018 PA modeling scenarios. The emissions described in Chapter 2.0 were 

processed and formatted in two types of emissions input files: surface and elevated emissions. Surface 

emissions consist of area sources, on-road and non-road (mobile) sources, as well as fugitive dust, 
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

ammonia, and biogenic emissions. These sources were then gridded for the CAMx nested system for 

domains with 36-km, 12-km, and 4-km grid cells. Elevated emissions consist of major point sources 

including EGU, non-EGU point sources (including oil and gas sources), and fires. For elevated sources, 

the plume rise for each source was calculated by CAMx from stack parameters and hourly 

meteorological conditions to place the emissions in the appropriate vertical layer.

For this project, the SMOKE configuration parameters and data inputs were consistent with FCAQS. The 

following SMOKE processing routines that were used for this work:

• Spatial Allocation. The spatial resolution of the emissions must match the CAMx grid cells for 

each domain. Initial area, on-road, and non-road emission inventories were spatially resolved at 

the county level, and county-level emissions were allocated to the grid cells within each county 

based on spatial surrogates. Spatial surrogates were based on attributes such as population, 

land use category, and economic activity. The USEPA has developed spatial surrogates which 

were used for spatially allocating all non-oil and gas emissions. Oil and gas area emissions were 

spatially allocated based on well location and production information.

• Temporal Allocation. Initial emissions data were provided for different averaging periods 

depending on each source type. Source types with annual or short-term emission rates were 

adjusted to seasonal or monthly profiles accounting for day-of-week and hour-of-day differences. 

Area sources, including non-road and dust emissions were allocated by monthly, daily, and 

hourly profiles provided by the USEPA. Biogenic and on-road emissions were modeled using 

hourly meteorological data. Point sources, including continuous emissions monitoring system 

(CEMS) and fire emissions, were modeled with available day-specific, or hour-specific emissions 

and meteorology. In this modeling work, the emissions rates from the FCPP were assumed 

constant throughout the modeling period to reflect an expected constant capacity factor of 91 

percent.

• Chemical Speciation. Emission inventories do not routinely include estimates of every chemical 

species emitted; rather, total emissions are reported for similar pollutants. Emissions of total 

VOC were converted to estimates of carbon bond types as required by the Carbon Bond 2005 

(CB05) chemical mechanism (Yarwood et al. 2005). Total NOX emissions were allocated to 

nitrogen oxide (NO) and NO2 components. The PM was allocated to coarse PM, nitrate, sulfate, 

organic carbon, elemental carbon, and other fine particulates. The SMOKE model includes 

default speciation profiles by source classification codes (SCC). These profiles are based on 

USEPA’s default data as well as on various updates and improvements incorporated to account 

for variations in fuels, solvent composition, and chemical mechanisms used in air quality models.

• Elevated Sources. All sources were treated by SMOKE as potentially elevated. The Plume-inGrid (PiG) sub-model that tracks the dispersion and chemical evolution of individual plume 

segments within the larger grid model framework was invoked to handle large stationary sources 

in the 4-km domain such as FCPP and SJGS.

• Quality Assurance. The SMOKE model includes quality assurance (QA) and reporting features 

to keep track of the adjustments at each processing stage and ensure that data integrity is not 

compromised. The QA tools from SMOKE were used to provide summary plots and tables of 

emissions.

Importantly, the revisions to the FCAQS emissions described in Chapter 2.0 only affected the elevated 

point source emissions, the surface level emissions files from the FCAQS were used without any 

modifications. Additional SMOKE processing steps were performed for the elevated point sources 

described in Chapter 2.0. The following steps were performed for all elevated emissions files modeled 

for this project:
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

1. Removing (zeroing out) point sources emissions in the 4-km domain from the original 36-km 

binary point source files.

2. Processing point source emissions for sectors, including EGU, non-EGU, and point oil and gas,

through SMOKE to create pre-CAMx point source files in ASCII format.

3. Converting non-PiG point sources in ASCII into CAMx-ready binary format.

4. Processing FCPP and SJGS to setup their emissions to be handled by the PiG sub-model and 

converting them to CAMx-ready binary format. 

5. Merging PiG, non-PiG and point, fire emissions into final merged CAMx-ready point source 

emissions.

Given the complexity involved in the modification of the point sources in the 4-km domain, these steps 

were followed to first reproduce the FCAQS inventories identically. This served as a verification step to 

ensure the results from FCAQS were reproducible and make sure there were no oversights in the 

generation of the updated inventory. Once verified, the same steps were applied to the revisions of the 

point sources emissions in the 4-km domain as described in Chapter 2.0.

3.3 CAMx Modeling

The ozone modeling performed was conducted with CAMx. In addition to appropriate meteorological and 

emissions input data described in previous sections, the PGM requires input files that configure and 

setup each simulation, define the chemical mechanism to be used, and describe the photochemical 

conditions, surface characteristics, initial/boundary conditions, emissions rates, and various 

meteorological fields over the entire modeling domain. Relevant CAMx model inputs include:

• Three-dimensional, hourly meteorological fields generated, which for this modeling work were 

generated by the FCAQS with the MM5CAMx processor.

• Two-dimensional, low-level (surface layer) emissions and elevated point source emissions 

generated by the SMOKE emissions processor.

• Initial concentration (IC) and boundary concentration (BC) inputs generated by the CAMx IC/BC 

processors.

• Albedo/Haze/Ozone Column input file.

• Photolysis rates look up table.

• Land use and topography data.

The main CAMx configuration options in this modeling work were identical to those used in the FCAQS. 

These options are summarized in Table 3-2. The CAMx model was set up on the 12-km and 4-km 

domains using two-way grid nesting. The base configuration of CAMx used the vertical layers that are 

aggregated from 34 MM5 layers to 19 CAMx layers spanning the depth between the surface and 

approximately 15 km above mean seal level (MSL). The Piecewise Parabolic Method (PPM) advection 

solver was used along with the spatially varying horizontal diffusion approach. Vertical diffusion in CAMx 

was modeled by K-theory. 
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Table 3-2 CAMx Air Quality Model Configurations

Science Options Configuration Details

Vertical Grid Mesh 19 layers Aggregated from 34 MM5 layers

Grid Interaction One-way nesting from the 36-km 

domain to the 12-km domain

Two-way nesting between the 12-

km domain and 4-km domain

Initial Conditions 5 days full spin-up for 12-km and 

4-km domains using initial 

concentration derived from 36-km 

results 

Started on April 25, 2005

Boundary Conditions Goddard Earth Observing System 

- chemical (GEOS-Chem) 2002 

annual run as prepared by WRAP

Contains daily 3-hour averages 

gridded concentrations

Chemistry

Gas Phase Chemistry CB05

Aerosol Chemistry ISORROPIA equilibrium

Cloud Chemistry RADM-type aqueous chemistry

Meteorological Processor MM5CAMx

Horizontal Transport K-theory with grid size dependent 

on coefficient of horizontal eddy 

diffusion

Vertical Transport K-theory Lower limit of vertical eddy 

diffusivity = 1.0

Deposition Scheme Zhang wet and dry deposition

Plume-in-Grid Greatly Reduced Execution and 

Simplified Dynamics (GREASD) 

PiG

PiG approach aimed at treating 

the early chemical evolution of 

large NOX plumes. Applied to 

FCPP and SJGS point sources 

only.

Numerics

Gas Phase Chemistry Solver Chemical Mechanism Compiler 

Fast Solver

Horizontal Advection Scheme PPM scheme

Integration Time Step Wind speed dependent

The CAMx configuration also includes the CB05 gas phase photochemical mechanism (Yarwood et al. 

2005). The CB05 gas-phase photochemical mechanism contains 156 reactions involving 52 chemical 

species. The VOC species were treated using a lumped bond approach in which actual VOC species are 

represented in the CB05 mechanism by model species that are designed to represent certain carbon 

bond types. This approach was used to reduce the total number of VOC species represented in the 

photochemical model. The CAMx is a ‘one-atmosphere’ model which means that in addition to the 
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

algorithms that estimate the fate of ozone, PM formation also is included through aqueous chemistry 

(Regional Acid Deposition Model [RADM]), Inorganic Aerosol Thermodynamics/partitioning 

(ISORROPIA), and Secondary Organic Aerosol Formation/partitioning (SOAP) schemes. The particulate 

chemistry mechanism utilizes products from the gas phase photochemistry for production of sulfate 

(SO4), nitrate (NO3), condensable organic gases, and chloride. Mineral NO3 is included in the calculation 

of aerosol NO3 formation. None of the other PM or gas-phase species, however, were reported in this 

analysis. 

An important aspect of the FCAQS was the comprehensive model evaluation of CAMx results by 

comparing model predictions to measurements of ambient air pollutant concentrations. The FCAQS 

found that the model performance for ozone for most months was within the established USEPA 

acceptance criteria of ±15 percent bias envelope and that all months were within the 35 percent error 

envelope. The bias also decreased during summer months, which indicates that CAMx exhibits the 

largest under predictions for the highest ozone concentrations. Overall the model performance for ozone, 

however, was adequate in replicating rural levels of ozone throughout the modeling of the 2005 Baseline 

and over the 4-km domain that covered the Four Corners area. 

The focus of this analysis was on the periods when ozone formation is the largest; as a result, the 

modeling period of May through August was selected to evaluate the ozone impacts that can be 

attributed to the FCPP since maximum ozone concentrations typically occur during summer season in 

this region.

The PiG sub-model was invoked to adequately simulate the chemistry and transport of concentrated 

point source plumes within the grid model framework. The PiG was invoked to handle the emissions 

from FCPP and SJGS. The PiG option has been primarily used for simulating elevated point source 

plumes within a grid model.

In addition to the meteorology and emissions inputs, the CAMx model requires ancillary data, including 

initial and boundary concentrations for all chemical species, and ozone column data for calculating 

photolysis rates. The source of all the ancillary data used in this modeling work are described in detail in 

the FCAQS report (ENVIRON 2009). 

3.4 CAMx Post-Processing

The USEPA metrics for predicting future attainment of the ozone NAAQS are based on the modeled 

ozone concentrations at a monitor location. For this analysis, the project area contains some available 

ozone measurements, but not near the sensitive areas. Therefore, it is desirable to examine the ozone 

impacts both at the monitors and at areas removed from monitors. The ozone impacts were analyzed at 

Class I and sensitive Class II areas shown in Figure 3-1. The ozone model attainment test was

performed through the use of the Model Attainment Test Software (MATS) (Abt Associates, Inc. 2009) as 

well as AECOM’s Impact Assessment Suite (IAS); both assessment tools and methodologies are 

described in the following sections.

3.4.1 Assessment Areas

Ozone impacts will be evaluated at the following Class I and sensitive Class II areas:

Class I Areas

• Bandelier Wilderness Area (WA)

• Canyonlands National Park (NP)

• La Garita WA

• Mesa Verde NP

• Pecos WA

• Petrified Forest NP

• San Pedro Parks WA

• Weminuche WA
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Class II Areas

• Acoma Indian Reservation (IR)

• American Flats

• Aztec Ruins National Monument (NM)

• Bisti/De-Na-Zin WA

• Bridger Jack Mesa Wilderness Study 

Area (WSA)

• Butler Wash WSA

• Cahone Canyon WSA

• Canoncito IR

• Canyon de Chelly NM

• Carson NF

• Chaco Culture National Historic Park

• Chama Rover Canyon WA

• Cheese Box Canyon WSA

• Cibola NF

• Cochiti IR

• Cross Canyon WSA

• Cruces Basin WA

• Dark Canyon WA

• Dome WA

• El Malpais NM

• El Morro NM

• Fish Creek Canyon WSA

• Glen Canyon National Recreation Area

• Grand Mesa, Uncompahgre, and 

Gunnison NFs

• Handies Peak WSA

• Hopi IR

• Hovenweep NM

• Hubbell Trading Post National Historic 

Site

• Jemez IR

• Jemez National Recreation Area

• Jicarilla Apache IR

• Laguna IR

• Little Rockies WSA

• Lizard Head WA

• Mancos Mesa WSA

• Manti-Lasal NF

• McKenna Peak WSA

• Menefee Mountain WSA

• Mesa Verde WA

• Middle Point WSA

• Monte Vista National Wildlife Refuge

• Mount Sneffels WA

• Nambe IR

• Natural Bridges NM

• Navajo Nation

• Ojito WA

• Pecos National Historical Park

• Petrified Forest National WA

• Petroglyph NM

• Pojoaque IR

• Powderhorn WA (BLM)

• Powderhorn WA (USFS)

• Powderhorn WSA (BLM)

• Ramah Navajo IR

• Redcloud Peak WSA

• Rio Grande NF

• Road Canyon WSA

• San Felipe IR

• San Ildefonso IR

• San Juan NF

• San Juan IR

• Sandia IR

• Sandia Mountain WA

• Santa Ana IR

• Santa Clara IR

• Santo Domingo IR

• Slickhorn Canyon WSA

• Santa Fe NF

• South San Juan WA

• Southern Ute IR

• Squaw/Papoose Canyon WSA

• Tesuque IR

• Uncompahgre WA (BLM)

• Uncompahgre WA (USFS)

• Ute Mountain IR

• Weber Mountain WSA

• West Malpais WA

• Yucca House NM

• Zia IR

• Zuni IR
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The locations of these Class I and Class II sensitive areas within the 4-km domains are shown in 

Figure 3-1. These areas are managed by a number of Federal Agencies and include National Parks, 

Wilderness Areas and tribal lands among others. Ambient ozone concentrations for both the 2005 

Baseline and 2018 future year modeling results are reported in Chapter 4.0 for all of these areas. Model 

results and comparisons also are presented in both tabular and graphical format.

3.4.2 Ozone Impact Assessment

AECOM’s IAS was developed to post-process model results into the format required for assessment and 

comparison with applicable standards and thresholds. Photochemical models produce hourly values of 

pollutant concentrations, such as ozone, at each grid cell. These results often need to be evaluated over 

different spatial and temporal scales, such as Class I or sensitive Class II areas, and various averaging 

periods like 8-hour averages or annual averages. The IAS was designed to post-process CAMx model 

results. The following processing methods were used for this project:

a) Selecting model-predicted hourly concentrations for applicable species to compute appropriate 

temporal average concentrations. The hourly concentrations and averages can be compared to 

applicable NAAQS for a given set of receptors within a modeling domain. The results from this 

step are reported and referred to as the “absolute” model-predicted impacts.

b) Selecting model-predicted hourly concentrations and processing the data to produce files for 

input into the MATS tool. The MATS tool requires model estimated daily maximum 8-hour ozone

concentrations for each grid cell in the modeling domains. The results from the MATS tools are 

referred to as the “model-adjusted” impacts. More information about the MATS tool is provided 

in the following section.

In addition to the CAMx output files, the only data required by the IAS is a file containing the locations of 

the assessment areas. This file was prepared using ESRI’s ArcGIS software by intersecting the Class I 

and sensitive Class II areas shown in Figure 3-1 with the 4-km domain grid cells.

To calculate the absolute model-predicted impacts for each assessment area, the IAS calculates the 8-

hour ozone NAAQS following this process:

1. Calculate rolling 8-hour averages from the hourly model-predicted ozone concentrations for 

each model grid cell within an assessment area;

2. Obtain the daily maximum value from step 1 for each assessment area in model grid; and

3. Rank all the values calculated in step 2 from largest to smallest for each assessment area and 

select the fourth-highest value. This provides the model-predicted fourth highest daily maximum 

8-hour average ozone concentration for each assessment area. This value is consistent with the 

statistical form of the 8-hour ozone NAAQS.

To calculate the model-predicted impacts for the MATS tool, steps 1 and 2 were conducted for the full 

4-km model domain and the results are formatted to be compatible with the MATS tool. 
6

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Mount

Sneffels

Wilderness

Powderhorn Wilderness

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Arizona

Colorado

New Mexico

Utah

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Acoma IR

Canoncito IR

Cochiti IR

Hopi IR

Isleta IR

Jemez IR

Jicarilla

Apache IR

Laguna IR

Nambe IR

Navajo IR

Picuris IR

Pojoaque IR

Ramah Navajo IR

San Felipe IR

San Ildefonso IR

San Juan

IR

Sandia IR

Santa Ana IR

Santa Clara IR

Santo Domingo IR

Southern

Ute IR

Taos IR

Tesuque IR

Ute Mountain IR

Zia IR

Zuni IR

Carson NF

Cibola NF

Grand Mesa, Uncompahgre

and Gunnison NFs

Manti-Lasal NF

Pike and

San Isabel NFs

Rio Grande NF

San Juan NF

Santa Fe NF

Hubbell Trading

Post National

Historic Site

Chaco Culture

National

Historical Park

Pecos National

Historical Park

Aztec Ruins NM

Canyon

de Chelly

El Malpais El Morro NM

Hovenweep NM

Natural Bridges NM

Navajo NM

Petroglyph

Canyonlands NP

Capitol

Reef NP

Mesa

Verde NP

Petrified

Forest NP

Glen Canyon

National

Recreation

Area

Jemez National

Recreation Area

Monte Vista

National

Wildlife Refuge

Bisti/De-Na-Zin

Wilderness

Cebolla

Wilderness

Ojito

Wilderness

West Malpais

Wilderness

Bandelier

Wilderness

Mesa Verde

Wilderness

Petrified

Forest National

Wilderness Area

Chama River

Canyon

Wilderness

Cruces

Basin

Wilderness

Dark Canyon

Wilderness

Dome Wilderness

La Garita Wilderness

Lizard Head Wilderness

Manzano Mountain Wilderness

Pecos

Wilderness

San Pedro Parks

Wilderness

Sandia Mountain

Wilderness

South

San Juan

Wilderness

Weminuche

Wilderness

Amercian Flats

Bridger Jack Mesa

Wilderness SA

Butler Wash

Wilderness SA

Cahone Canyon

Wilderness SA

Cheese Box Canyon

Wilderness SA

Cross Canyon

Wilderness SA

Fiddler Butte

Wilderness SA

Fish Creek Canyon

Wilderness SA

Handies Peak

Wilderness SA

Little Rockies

Wilderness SA

Mancos Mesa

Wilderness SA

McKenna Peak

Wilderness SA

Menefee Mountain

Wilderness SA

Middle Point

Wilderness SA

Mount Hillers

Wilderness SA

Redcloud Peak

Wilderness SA

Road Canyoon

Wilderness SA

San Luis Hills

Wilderness SA

Slickhorn Canyon

Wilderness SA

Squaw/Papoose Canyon

Wilderness SA

Weber Mountain

Wilderness SA

Santa Fe NF

Santa Fe NF

Carson NF

Cibola NF

Cibola NF

Uncompahgre Wilderness

Laguna IR

San Juan NF

Carson NF

Santa Fe NF

Legend

X APS Four Corners Power Plant

6 City

Interstate Highway

4-km CAMx Domain

Class I Area of Concern

Class II Area of Concern

Four Corners Power Plant

Ozone Modeling Study

Figure 3-1

Class I and Sensitive

Class II Areas of Concern

0 20 40 80

Kilometers

0 10 20 40

Miles

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3.4.3 Ozone Model Attainment Test at Monitored Locations

The USEPA guidance for projecting future 8-hour ozone concentrations recommends using the PGM in 

a relative sense to scale current observed 8-hour design values (USEPA 2007). A design value is 

defined as a 5-year average of the fourth-highest daily maximum 8-hour ozone concentration at a 

monitor. The locations of all monitors used for this assessment are shown in Figure 3-2. Model scaling 

factors called relative response factors (RRFs) were used to scale the observed design values in order 

to predict future year design values. The RRFs are the ratio of the future year (or the control case) to the 

current year modeled 8-hour ozone concentrations near a monitor site. The USEPA has defined “near 

the monitor” to be approximately 15 km from the monitor location. The future year design value (DVF) is 

obtained from the current year design value (DVC) using the relationship:

DVF = DVC x RRF

The RRFs were calculated for all days in which the current year modeled 8-hour ozone value is above a 

threshold. The USEPA currently recommends a threshold between 70 and 85 ppb; this modeling work, 

however, set a lower threshold of 40 ppb to accommodate an adequate number of days and to 

accommodate a potentially lower ambient standard for ozone. This was done so that the model response 

to future changes in emissions is considered only on high ozone days of comparable conditions to the 

days used to produce the DVC. The USEPA allows a reduction of the threshold value to 70 ppb to meet 

the minimum day requirements. These procedures were developed mainly for urban ozone 

non-attainment areas where ozone concentrations are much higher than those measured in this project 

area.

To perform the 8-hour projections, the USEPA has developed the MATS (Abt Associates Inc. 2009) tool 

that uses modeling results, 8-hour ozone design values, and follows USEPA guidance (USEPA 2007) to 

project 8-hour ozone concentrations that reflect the change in emissions from the baseline to an 

alternative emissions scenario. The MATS ozone design values were calculated in accordance with 

40 CFR Part 50.10, and Appendix I to Part 50.

The USEPA modeling guidance procedures (USEPA 2007) recommends using a DVC based on a 

5-year average of 8-hour ozone design values centered on the modeling year. For the 2005 Baseline

modeling, this means the DVC was the weighted average of the fourth-highest 8-hour ozone value at a 

monitor from 2003, 2004, 2005, 2006, and 2007. To develop RRFs, USEPA guidance recommends 

using current and future modeling results for all days in which the current year daily maximum 8-hour 

ozone concentration near the monitor exceeds a threshold value. The maximum modeled daily 

maximum 8-hour ozone concentration was picked from a 7x7 array of grid cells centered on the monitor

in the 4-km domain. This analysis follows the USEPA recommendation of using an 8-hour ozone 

threshold based on a minimum of 5 days, although greater than 10 days is preferred. The 8-hour ozone 

projections using the MATS tool were performed twice using the 2005 Baseline simulation to forecast 

ozone concentrations for the 2018 NA Alternative and PA scenarios.

3.4.4 Ozone Model Attainment Test Removed from Monitors

The USEPA’s guidance on model attainment demonstration (USEPA 2007) suggests that an 

assessment of the impacts in areas removed from monitor locations is a recommended supplemental 

analysis that needs to be performed as part of the demonstration. The information from this type of test 

can help to determine if further action is required despite passing the modeled attainment test at all 

monitoring sites. Additionally, it also helps to determine if any unmonitored sensitive areas could be 

subjected to potential exceedences to the NAAQS. It is important, however, to emphasize that this type 

of analysis is subject to larger uncertainty than the analysis of monitored areas. The MATS unmonitored 

screening analysis was used to prepare spatial fields of the projected future year ozone design values 

throughout the 4-km. 
6

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X APS Four Corners Power Plant

!( Ozone Monitor

6 City

4-km CAMx Domain

Interstate Highway

County

Four Corners Power Plant

Ozone Modeling Study

Figure 3-2

MATS Ozone Monitors

in 4-km Domain

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Kilometers

0 10 20 40

Miles

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o

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CA CO

ID

KS

MT

ND

NE

NM

NV

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UT

WA

WY

CANADA

3-10
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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Further details on this type of analysis can be found on the MATS user’s guide (Abt Associates, Inc. 

2009), but MATS can provide spatial field results. That is, MATS can provide air pollution estimates 

made at the center of each grid cell in a specified modeling domain. 

The following types of spatial fields were calculated for ozone:

• Baseline – interpolate monitor data to spatial field. This is an interpolation of baseline monitor 

values at each grid cell. The MATS identifies the “neighbor” monitors for each grid cell and then 

calculates an inverse-distance-weighted average of the monitor values at each grid cell.

• Baseline – interpolate gradient-adjusted monitor data to spatial field. This is an interpolation of 

model-adjusted baseline monitor values at each grid cell. The MATS identifies the “neighbor”

monitors for each grid cell, it adjusts the monitor values to account for the modeled spatial 

gradient, and then calculates an inverse-distance weighted average of the monitor values.

• Forecast – interpolate monitor data to spatial field. Temporally adjust. This is an interpolation of 

baseline monitor values at each grid cell that are then temporally adjusted to a future year. The 

MATS calculates the Baseline - interpolate monitor data to spatial field and multiplies it with a 

RRF.

• Forecast – interpolate gradient-adjusted monitor data to spatial field. Temporally adjust. This is 

an interpolation of model-adjusted baseline monitor values at each grid cell that are then 

temporally adjusted to a future year. The MATS calculates the Baseline interpolate gradientadjusted monitor data to spatial field and multiplies it with a RRF.

The MATS tool was used to obtain estimates of the spatial fields described above for each of the 

modeling scenarios considered in this project. Although the information provided by MATS is gridded 

data for the entire 4-km domain, only a subset is presented for this analysis. Chapter 4.0, summarizes 

the spatial field ozone design values for 2005 and 2018 at the unmonitored Class I and sensitive Class II 

areas listed on Section 3.4.1. These values were obtained with the help of Esri’s ArcGIS software and 

MATS output. ArcGIS was used to locate the centroid of each sensitive area that intersects the 4-km 

domain and identify the nearest MATS’s spatial field values to each sensitive area centroid. 
AECOM Environment 4-1

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

4.0 Modeling Results

In order to evaluate the impacts of the PA and compare the results to ozone NAAQS, the model 

scenarios described in Chapter 1.0 were modeled using the emission inventory described in Chapter 2.0. 

Model results were processed using the methods described in Chapter 3.0 to compare results with the 

8-hour ozone NAAQS. Model results were processed and presented in two different ways. The absolute 

model results are model-predicted concentrations without any adjustment from actual monitored values. 

These results were processed with the IAS tool to put model values in a form that can be directly 

compared to the ozone NAAQS. The second processing method uses the MATS tool to adjust model 

results with actual monitoring values. This second method accounts for model bias and the inter-annual 

variability in ozone concentrations at monitoring locations. Results from both methods are reported and 

analyzed in the following subsections. 

In this section, the predicted model concentrations are compared to the ozone NAAQS. The primary and 

secondary NAAQS are defined as the 3-year average of the annual fourth-highest daily maximum 8-hour 

ozone concentration may not exceed a level of 75 ppb (CFR 2008). Although modeling results were only 

available for less than a 3-year period, the averaging form required by the standard has been taken into 

account to perform these comparisons. 

Modeled results should be interpreted in consideration of know model limitations. The FCAQS performed 

a comprehensive model evaluation by comparing CAMx model predictions to measurements of ambient 

air pollutant concentrations. The FCAQS found that the ozone model performance for most months was 

within the established USEPA acceptance criteria of ±15 percent bias envelope and that all months were 

within the 35 percent error envelope. The bias also decreased during summer months, which indicates 

that CAMx exhibits the largest under predictions for the highest ozone concentrations. Overall the model 

performance for ozone, however, was adequate in replicating rural levels of ozone throughout the 2005 

Baseline modeling over the 4-km domain that covered the Four Corners area.

The following analyses are presented in this section:

• Absolute model concentrations were compared between:

− The 2005 Baseline and the 2018 NA Alternative for the fourth-highest daily maximum 8-hour 

concentrations.

− The 2005 Baseline and the 2018 PA for the fourth-highest daily maximum 8-hour 

concentrations.

− The 2018 NA Alternative and the 2018 PA for both the fourth-highest daily maximum 8-hour 

concentrations and the overall daily maximum 1-hour concentrations.

− The 2018 NA Alternative and the 2018 PA at Class I and sensitive Class II areas. Results 

also are compared to NAAQS.

• Model-adjusted concentrations were compared between:

− The 2018 NA Alternative and the 2018 PA at monitored locations. Results also are 

compared to NAAQS and the 2005 design values.

− The 2018 NA Alternative and the 2018 PA at unmonitored Class I and sensitive Class II 

areas. Results also are compared to NAAQS and the 2005 design values.
AECOM Environment 4-2

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

4.1 Absolute Model-Predicted Ozone Concentrations

This section reports and analyzes the absolute model-predicted ozone concentrations from all modeling 

scenarios. Model-adjusted ozone concentrations that are consistent with USEPA’s guidance on ozone 

model attainment demonstrations are reported and analyzed in Section 4.2.

4.1.1 2005 Baseline Compared to the 2018 No Action Alternative

Figure 4-1 depicts the spatial extent of model-predicted cumulative ozone concentrations including the 

2005 Baseline, the 2018 NA Alternative, and the differences between these scenarios. The figure 

provides the model-predicted fourth-highest daily maximum 8-hour average ozone concentrations at the 

surface layer for each grid cell. The model results presented in this spatial figure are consistent with the 

form of the 8-hour ozone NAAQS, except that the model estimates only include the values from May to 

August. A direct comparison to the NAAQS would require an average over a 3-year period. Importantly,

the timing of the fourth-highest value in the figure can vary from one grid cell to the next, and thus the 

values shown in the figures are not matched in time. The model results from the NA Alternative scenario 

represent the estimated future 2018 ozone concentrations that result from changes of all the domainwide emissions except for the FCPP, whose contributions were entirely removed from the inventory as 

explained in Section 2.2.

The modeled spatial concentrations in 2005 are shown in Figure 4-1a. Figure 4-1a illustrates that the 

modeled peak fourth-highest daily maximum 8-hour average ozone concentration in the 4-km domain in 

2005 was 73.1 ppb and occur in Rio Arriba County, New Mexico (36.97°N, 107.38°W) right on the 

northeast edge of the San Juan Basin oil and gas field. In general, the largest concentrations occur in 

San Juan and Rio Arriba counties in New Mexico where model-predicted ozone exceeds 70 ppb. Other 

regions with relatively high concentrations were La Plata, Archuleta, Conejos, Mineral and Rio Grande 

counties in Colorado where ozone can reach up to 70 ppb. In general for the 2005 Baseline, Figure 4-1a

shows spatial patterns that reflect ozone formation downwind from, or to the east of, important NOX and 

VOC (ozone precursors) sources. This is consistent with both the location of EGU and oil and gas 

emissions sources in the 4-km domain and the typical synoptic westerly transport in the region. It is 

important to remember that the ozone concentrations for this figure represent the cumulative effect of all 

the sources in the region and not just sources from FCPP during the 2005 Baseline year.

Figure 4-1b shows the model-predicted fourth-highest daily maximum 8-hour average ozone 

concentrations at the surface layer for each grid cell for the 2018 NA Alternative. Figure 4-1b illustrates 

that the modeled peak fourth-highest daily maximum 8-hour average ozone concentration in the 4-km 

domain in 2018 was 69.9 ppb and occur at about 16 miles southeast of the maximum concentrations for 

the 2005 Baseline. A qualitative assessment of Figures 4-1a and 4-1b show that although the spatial 

distribution of ozone concentrations are very similar in both figures, the 2018 NA Alternative 

concentrations show an overall decrease relative to the 2005 Baseline. For instance, the modeled peak 

fourth-highest concentration within the 4-km domain decreases by 3 pbb in 2018 relative to 2005, while 

the domain-wide average concentration decreases from 63.9 ppb in 2005 to 61.6 ppb in 2018. 

To examine in more detail the changes that occur between the base year and the NA Alternative 

scenario, Figure 4-1c shows the spatial difference between model-predicted fourth-highest daily 

maximum 8-hour average ozone concentration in the 2018 NA Alternative and the 2005 Baseline model 

simulations (i.e., the difference between Figure 4-1b and 4-1a). Figure 4-1c confirms that there is an 

overall domain-wide decrease in ozone concentrations in 2018 relative to 2005. The most notable 

changes occur in the western and central areas of the domain where there is a 5 to 7 ppb decrease in 

the model-predicted fourth-highest daily maximum 8-hour average ozone concentrations. The only 

locations with increases in ozone occur in San Juan County in New Mexico, which are immediately 
Four Corners Power Plant

Ozone Modeling Study

Figure 4-1

Model-predicted Fourth Highest 

Daily Maximum 8-hour Average 

Ozone Concentrations:

2005 Baseline and 

2018 NA Alternative

25

40

Weminuche

Wilderness

San Pedro

Parks

Wilderness

La Garita

Wilderness

Bandelier

Wilderness

Petrified

Forest NP

Mesa

Verde NP

Albuquerque

Santa Fe

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Miles 0 8 40 0 160

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Mesa

Verde NP

Albuquerque

Santa Fe

Farmington

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Legend

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Power Plant

City

Class I Areas

Interstate Highway

State Boundary

County Boundary

25

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Wilderness

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a) 2005 Baseline b) 2018 NA Alternative

c) 2018 NA Alternative - 2005 Baseline

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FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

downwind of the location of FCPP. The main reason for the increase in ozone concentrations in 2018 

relative to 2005 is the reduction in the NO emissions from the FCPP. In fact, this decrease is such that 

FCPP’s NOX emissions for the NA Alternative are exactly zero. During 2005, the ozone concentrations 

were lower in the area surrounding the FCPP due to the chemical reaction of ozone with NO emitted 

from the power plant. In the presence of NO, ozone is chemically transformed into oxygen (O2), and NO 

is converted into NO2. When the emissions of NO decrease in the future year 2018, ozone is no longer 

converted into O2, and the net effect is an increase in the ozone concentrations immediately downwind 

from the source. The maximum increase in the fourth-highest 8-hour ozone concentrations between the 

2018 NA Alternative and 2005 Baseline is 3.5 ppb. It is important to note, however, that this increase 

occurs in an area where ozone concentrations range only from 65 to 70 ppb and that model-predicted 

ozone concentrations in the vicinity of the FCPP peaks at 69 ppb.

4.1.2 2005 Baseline Compared to the 2018 Proposed Action

Figure 4-2 depicts the spatial extent of model-predicted cumulative ozone concentrations including the 

2005 Baseline, the 2018 PA, and the differences between these scenarios. The figure provides the 

model-predicted fourth-highest daily maximum 8-hour average ozone concentrations at the surface layer 

for each grid cell. The model results presented in this spatial figure are consistent with the form of the 8-

hour ozone NAAQS, except that the model estimates only include the values from May to August. A 

direct comparison to the NAAQS would require an average over a three year period. Importantly, the 

timing of the fourth-highest value in the figure can vary from one grid cell to the next, and thus the values 

shown in the figures are not matched in time. The model results from the PA scenario represent the 

estimated future (2018) ozone concentrations that result from changes of all the domain-wide emissions 

including those from the FCPP, whose contributions are detailed in Section 2.3.

Comparison between Figures 4-1 and 4-2 shows that domain-wide ozone concentrations for the future 

year 2018 are very similar indicating that the FCPP contribution is minor. This is confirmed by comparing 

Figures 4-1c and Figure 4-2c. Each of these figures presents the difference between PA and NA 

Alternative to the 2005 Baseline, respectively. The domain-wide spatial patterns in these figures are 

similar with the exception of larger differences immediately downwind of the FCPP. The spatial extent of 

ozone concentrations subject to the largest impacts from the FCPP can be estimated from these figures 

to be no larger than approximately 32 km east of the power plant.

4.1.3 2018 Proposed Action Compared to the 2018 No Action Alternative

The following sections present several analyses that estimated the potential future impacts for the 2018 

PA. These estimates were based on the evaluation of absolute modeling results from both the 2018 NA 

Alternative and PA scenarios. Since the 2018 NA Alternative and the 2018 PA model simulations were 

identical except for the change in the FCPP emissions, the impacts of the power plant can be isolated by 

comparing these results. 

4.1.3.1 Fourth-Highest 8-Hour Average Ozone Concentrations

Similar to Figure 4-1, Figure 4-3 depicts the spatial extent of model-predicted fourth-highest daily 

maximum 8-hour average ozone concentrations for three analyses: the 2018 NA Alternative, the 2018 

PA, and the differences between the 2018 PA and the 2018 NA Alternative. 

Comparison of Figure 4-3a and 4-3b shows that the spatial patterns of the fourth-highest daily maximum 

8-hour average ozone concentrations are very similar between the PA and the NA Alternative. For both 

modeling scenarios, the highest ozone concentrations, ranging from 60 to 70 ppb, are found mostly in 

the northeastern portion of the 4-km domain. The fourth-highest daily maximum 8-hour average ozone 

concentration in the vicinity of the FCPP ranges from 65 to 70 ppb. Additionally, the largest and smallest 

values of the fourth-highest daily maximum 8-hour average ozone concentrations throughout the 4-km 

model domain are 70.1 ppb and 43.6 ppb, respectively.
Four Corners Power Plant

Ozone Modeling Study

Figure 4-2

Model-predicted Fourth Highest 

Daily Maximum 8-hour Average 

Ozone Concentrations:

2005 Baseline and 

2018 PA

25

40

Weminuche

Wilderness

San Pedro

Parks

Wilderness

La Garita

Wilderness

Bandelier

Wilderness

Petrified

Forest NP

Mesa

Verde NP

Albuquerque

Santa Fe

Farmington

0 5 25 0 100

Miles 0 8 40 0 160

Kilometers

TX

CA

MT

AZ

ID

NV

NM

CO

OR

UT

WY

KS

SD

NE

ND

OK

WA

25

40

Weminuche

Wilderness

San Pedro

Parks

Wilderness

La Garita

Wilderness

Bandelier

Wilderness

Petrified

Forest NP

Mesa

Verde NP

Albuquerque

Santa Fe

Farmington

1:4,500,000

Legend

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Power Plant

City

Class I Areas

Interstate Highway

State Boundary

County Boundary

25

40

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Wilderness

San Pedro

Parks

Wilderness

La Garita

Wilderness

Bandelier

Wilderness

Petrified

Forest NP

Mesa

Verde NP

Albuquerque

Santa Fe

Farmington

ppb

70

67.5

65

62.5

60

57.5

55

ppb

70

67.5

65

62.5

60

57.5

55

ppb

5

4

3

2

1

0

-1

-2

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-4

-5

a) 2005 Baseline b) 2018 PA

c) 2018 PA - 2005 Baseline

4-5
Four Corners Power Plant

Ozone Modeling Study

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AECOM Environment 4-7

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Figure 4-3c depicts the spatial differences between model-predicted fourth-highest daily maximum 

8-hour average ozone concentration in 2018 PA and the 2018 NA Alternative (i.e., the difference 

between Figure 4-3b and 4-3a). The maximum model-predicted difference between the PA and the NA 

Alternative is 4.7 ppb, which occurs downwind of the FCPP. This maximum difference is located about 

11 miles southeast of the FCPP and about 16 miles southwest of Farmington, New Mexico. Most of the 

impacted areas show a 2 to 4 ppb increase in ozone concentrations and are located entirely in San Juan 

and McKinley counties in New Mexico. Figure 4-3c also demonstrates that the largest impacts from the 

FCPP are more likely to be located east of the FCPP, which reflects the typical westerly transport in the 

region.

4.1.3.2 Daily Maximum 1-Hour Average Ozone Concentrations 

In order to evaluate the maximum model-predicted ozone impact attributable to the FCPP, the 2018 NA 

Alternative 1-hour average ozone concentrations were subtracted from the 2018 PA 1-hour average 

ozone concentrations. Table 4-1 shows the five largest values of the daily 1-hour difference between the 

2018 future scenarios for the entire modeling period along with the date when they occur and their 

approximate location. The maximum model-predicted ozone impacts attributable to the FCPP occurs

during the summer mostly in July and August. The impacts are located to the east of the FCPP, with the 

largest impact (15.8 ppb) at about 12 miles to the southeast of FCPP, while the fifth largest impact 

(13.1 ppb) is located approximately 29 miles southeast of the FCPP.

Table 4-1 Maximum 1-hour daily Ozone Difference between 2018 PA and NA Alternative

Difference between 

2018 PA and NA 

Alternatives Ozone 

Values (ppb)

Date Associated to 

Largest Difference

Latitude

(degrees)

Longitude

(degrees)

15.8 July 16 36.58811 -108.32195

15.1 August 2 36.67785 -108.15470

14.9 August 9 36.76324 -108.39458-

13.3 July 13 36.54767 -108.36091

13.1 August 26 36.43069 -108.07183

In order to examine the spatial extent of the potential impacts from the FCPP, isopleths of absolute 

model-predicted ozone concentration for 2018 NA Alternative and PA and their difference for the two 

largest episodes identified in Table 4-1 are presented in Figures 4-4 and 4-5. Figure 4-4 presents 

model results for July 16 at 14:00 MST while Figure 4-5 presents results for August 2 at 13:00 MST. 

Both figures show ozone concentrations on the upper panel and NOX concentrations on the lower panel. 

On July 16, the maximum modeled 1-hour ozone concentration in the 4-km domain is 78.6 ppb for both 

the 2018 NA Alternative and PA. Figure 4-4c shows that the FCPP contributes 15.8 ppb to the modeled 

ozone concentrations. Although this region generally has westerly transport for this period, Figure 4-4c

indicates southeasterly transport occurs during July 16 as shown by the direction of the ozone plume. 

On August 2, the maximum modeled 1-hour ozone concentration in the 4-km domain is 69.3 ppb for both 

the 2018 PA and the NA Alternative. Figure 4-5c shows that the FCPP contributes 15.1 ppb to the 

modeled ozone concentrations. It is likely the meteorological conditions during August 2 were more 

stagnant than the July 16 period due to the spatial concentrations of ozone in the vicinity of the FCPP.
AECOM Environment 4-8

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

(a) NA Alternative (b) PA (c) PA - NA

Figure 4-4 2018 NA Alternative and PA Model-Predicted Hourly Average Ozone and NOX on July 16
AECOM Environment 4-9

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

(a) NA Alternative (b) PA (c) PA - NA

Figure 4-5 2018 NA Alternative and PA Model-Predicted Hourly Average Ozone and NOX on August 2
AECOM Environment 4-10

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

4.1.4 Ozone Concentrations at Class I and Sensitive Class II Areas

Table 4-2 presents the absolute model-predicted ozone concentrations for the Class I and sensitive 

Class II areas listed in Section 3.4.1 and shown in Figure 3-1. The reported ozone values are the 

model-predicted fourth-highest daily maximum 8-hour average concentrations that occur in any grid cell 

that contains the Class I or sensitive Class II area and were estimated with the IAS tool. As shown in 

Table 4-2, there are 12 sensitive areas with model-predicted ozone concentrations that exceed the 

NAAQS in 2005. Consistent with the results discussed previously, overall ozone concentrations 

decrease in 2018 relative to 2005. The number of sensitive areas with predicted NAAQS exceedences 

decreases from 12 areas in 2005 to only four areas in the 2018 PA and three areas in the NA Alternative 

model scenarios. These four areas with model-predicted ozone concentrations that exceed the NAAQS 

in the PA are La Garita WA, Grand Mesa, Uncompahgre, and Gunnison NFs, Navajo Nation, and Rio 

Grande NF. The contribution of the FCPP to these exceedences can be estimated by evaluating the 

difference between the 2018 PA and NA Alternative. In La Garita WA, Grand Mesa, Uncompahgre, and 

Gunnison NFs, and Rio Grande NF, the difference between the 2018 PA and NA Alternative is 0.0 ppb, 

indicating that the FCPP does not contribute to any modeled ozone impacts that exceed the NAAQS.

Importantly, the absolute model predicted ozone concentration for the PA at the Navajo Nation is just 

below the NAAQS. The model-predicted FCPP contribution to the Navajo Nation is 0.7 ppb of ozone.

For all other areas in Table 4-2, the difference between the model-predicted 2018 PA and NA Alternative

is 0.0 ppb with the exception of 43 sensitive areas where the model-predicted impacts due to the PA 

range from 0.1 to 0.9 ppb. The maximum impact of the PA (0.9 ppb) occurs at Ute Mountain IR in 

Colorado and New Mexico and also at Chaco Culture National Historic Park in New Mexico. The modelpredicted fourth-highest daily average 8-hour ozone concentrations at Ute Mountain and Chaco Culture 

National Historic Park are 63.8 ppb and 67.8 ppb respectively under the 2018 PA, which is well below 

the 75 ppb NAAQS. 

Table 4-2 Fourth-Highest Daily Maximum 8-hour Average Ozone Concentrations at Class I 

and Sensitive Class II Areas

Receptor Site

2005 Ozone 

Values (ppb)

2018 PA 

Ozone Values 

(ppb)

2018 NA 

Alternative 

Ozone Values 

(ppb)

Difference 

Between PA 

and NA 

Alternative 

Ozone Values 

(ppb)

CLASS I AREAS

Bandelier WA1 69.1 66.8 66.4 0.4

Canyonlands NP2 62.5 61.0 61.0 0.0

La Garita WA 76.3 75.4 75.4 0.0

Mesa Verde NP 67.3 65.0 64.7 0.3

Pecos WA 69.0 66.9 66.9 0.0

Petrified Forest NP 69.9 68.0 68.0 0.0

San Pedro Parks WA 70.1 67.5 67.5 0.1

Weminuche WA 75.6 74.8 74.8 0.0

CLASS II AREAS

Acoma IR3 66.6 63.3 63.1 0.2

American Flats 74.7 73.9 73.9 0.0
AECOM Environment 4-11

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-2 Fourth-Highest Daily Maximum 8-hour Average Ozone Concentrations at Class I 

and Sensitive Class II Areas

Receptor Site

2005 Ozone 

Values (ppb)

2018 PA 

Ozone Values 

(ppb)

2018 NA 

Alternative 

Ozone Values 

(ppb)

Difference 

Between PA 

and NA 

Alternative 

Ozone Values 

(ppb)

Aztec Ruins NM4 71.0 68.7 68.7 0.0

Bisti/De-Na-Zin WA 68.0 62.9 62.2 0.7

Bridger Jack Mesa WSA5 62.5 61.2 61.2 0.0

Butler Wash WSA 62.7 61.1 61.1 0.0

Cahone Canyon WSA 64.9 61.6 61.4 0.2

Canoncito IR 65.7 62.9 62.8 0.2

Canyon de Chelly NM 65.8 61.9 61.9 0.0

Carson NF 75.3 72.1 71.9 0.1

Chaco Culture National Historic Park 68.9 63.8 62.9 0.9

Chama Rover Canyon WA 72.6 69.6 69.6 0.1

Cheese Box Canyon WSA 62.9 62.0 62.0 0.0

Cibola NF 72.3 70.5 70.3 0.1

Cochiti IR 70.9 69.2 69.1 0.1

Cross Canyon WSA 64.5 61.4 61.1 0.3

Cruces Basin WA 73.0 70.0 69.8 0.2

Dark Canyon WA 65.3 64.2 64.2 0.0

Dome WA 68.2 66.0 65.5 0.5

El Malpais NM 66.0 63.4 63.3 0.1

El Morro NM 65.0 63.2 63.1 0.1

Fish Creek Canyon WSA 65.0 62.3 62.3 0.0

Glen Canyon National Recreation Area 67.7 65.5 65.5 0.0

Grand Mesa, Uncompahgre, and 

Gunnison NF

76.3 75.4 75.4 0.0

Handies Peak WSA 75.2 74.3 74.3 0.0

Hopi IR 62.7 60.5 60.5 0.0

Hovenweep NM 65.7 62.0 61.6 0.4

Hubbell Trading Post National Historic 

Site

58.9 56.6 56.6 0.0

Jemez IR 67.3 65.5 65.2 0.3

Jemez National Recreation Area 68.6 66.3 66.0 0.3

Jicarilla Apache IR 75.3 72.4 71.9 0.5
AECOM Environment 4-12

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-2 Fourth-Highest Daily Maximum 8-hour Average Ozone Concentrations at Class I 

and Sensitive Class II Areas

Receptor Site

2005 Ozone 

Values (ppb)

2018 PA 

Ozone Values 

(ppb)

2018 NA 

Alternative 

Ozone Values 

(ppb)

Difference 

Between PA 

and NA 

Alternative 

Ozone Values 

(ppb)

Laguna IR 68.1 64.9 64.6 0.3

Little Rockies WSA 67.3 65.2 65.2 0.0

Lizard Head WA 72.2 71.4 71.4 0.0

Mancos Mesa WSA 66.7 64.5 64.5 0.0

Manti-Lasal NF 66.3 65.4 65.4 0.0

McKenna Peak WSA 66.2 65.1 65.1 0.0

Menefee Mountain WSA 65.9 64.8 64.6 0.2

Mesa Verde WA 66.1 65.0 64.6 0.5

Middle Point WSA 64.7 62.7 62.7 0.0

Monte Vista National Wildlife Refuge 69.4 68.4 68.4 0.0

Mount Sneffels WA 72.8 71.8 71.8 0.0

Nambe IR 69.7 67.5 67.4 0.1

Natural Bridges NM 64.0 63.2 63.2 0.0

Navajo Nation 78.7 74.9 74.3 0.7

Ojito WA 64.1 61.8 61.8 0.0

Pecos National Historical Park 65.3 63.1 63.0 0.0

Petrified Forest National WA 68.7 66.9 66.9 0.0

Petroglyph NM 69.4 67.7 67.7 0.1

Pojoaque IR 65.1 63.0 62.9 0.1

Powderhorn WA (BLM) 74.0 73.0 73.0 0.0

Powderhorn WA (USFS) 73.9 72.9 72.9 0.0

Powderhorn WSA (BLM) 71.8 70.8 70.8 0.0

Ramah Navajo IR 67.3 66.5 66.5 0.0

Redcloud Peak WSA 75.0 74.1 74.1 0.0

Rio Grande NF 76.1 75.2 75.2 0.0

Road Canyon WSA 65.1 61.1 61.1 0.0

San Felipe IR 72.4 70.4 70.4 0.1

San Ildefonso IR 66.0 63.9 63.6 0.3

San Juan NF 75.1 74.3 74.3 0.0

San Juan IR 67.3 66.1 66.1 0.0
AECOM Environment 4-13

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-2 Fourth-Highest Daily Maximum 8-hour Average Ozone Concentrations at Class I 

and Sensitive Class II Areas

Receptor Site

2005 Ozone 

Values (ppb)

2018 PA 

Ozone Values 

(ppb)

2018 NA 

Alternative 

Ozone Values 

(ppb)

Difference 

Between PA 

and NA 

Alternative 

Ozone Values 

(ppb)

Sandia IR 71.9 70.7 70.6 0.1

Sandia Mountain WA 72.0 70.1 70.0 0.1

Santa Ana IR 72.6 70.7 70.7 0.1

Santa Clara IR 71.1 68.3 67.9 0.3

Santo Domingo IR 70.9 68.6 68.5 0.1

Slickhorn Canyon WSA 65.4 62.3 62.3 0.0

Santa Fe NF 73.5 70.6 70.5 0.1

South San Juan WA 74.6 73.8 73.8 0.0

Southern Ute IR 74.6 72.0 71.7 0.3

Squaw/Papoose Canyon WSA 65.1 61.0 60.8 0.2

Tesuque IR 67.4 65.5 65.4 0.1

Uncompahgre WA (BLM) 75.0 74.2 74.2 0.0

Uncompahgre WA (USFS) 75.0 74.1 74.1 0.0

Ute Mountain IR 73.8 67.8 67.0 0.9

Weber Mountain WSA 66.3 65.0 64.5 0.4

West Malpais WA 62.1 61.3 61.3 0.0

Yucca House NM 65.2 60.5 60.5 0.1

Zia IR 67.2 65.2 65.1 0.1

Zuni IR 66.5 64.8 64.8 0.0

1 WA = Wilderness Area.

2 NP = National Park.

3 IR = Indian Reservation.

4 NM = National Monument.

5 WSA = Wilderness Study Area.

Notes: Model-predicted concentrations that exceed 75 ppb are shown in red text. Information in parentheses indicates agency 

managing sensitive area.

4.2 Model-Adjusted Ozone Concentrations 

The 2005 design values were calculated based on actual monitoring data over a 5-year monitoring 

record. Application of design value concentrations to model results was used to present the modeling 

results in a form consistent with the NAAQS and reduces model uncertainty and biases that could result 

from using absolute model predictions alone.
AECOM Environment 4-14

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

4.2.1.1 Ozone Impact Assessment in Monitored Areas

Table 4-3 provides the ozone design values estimated by MATS for 2005 and 2018 at 16 monitoring 

sites located within the 4-km modeling domain. Note that red text in the table indicates design values that 

exceed 75 ppb. The 2005 design values were calculated exclusively from measured ozone 

concentrations. As shown in Table 4-3, there is only one monitor (site ID 350011012) with design values 

in 2005 that exceed the 8-hour ozone NAAQS (77 ppb). This site is located northeast of Albuquerque in 

Bernalillo County, New Mexico. In general, the future year design values decrease relative to 2005, and 

this is consistent with the results presented in Section 4.1 for absolute model predictions. As shown in 

Table 4-3, there are no monitors within the 4-km domain with design values that exceed the 8-hour 

ozone NAAQS under both the 2018 NA Alternative and PA. This reduction in ozone levels is attributable 

to reduced regional emissions, including those from the FCPP, relative to 2005.

For all monitor locations, the contribution from the FCPP was calculated as the difference between the 

PA and NA Alternative design values, and these results also are shown in Table 4-3. The ozone 

contribution attributable to FCPP is 0.0 ppb for all monitors close to exceeding the NAAQS in 2018, such 

as the aforementioned Albuquerque, New Mexico monitor (site ID 350011012). Furthermore, this monitor 

is located at a considerable distance from the FCPP. There are 11 monitors with a predicted non-zero 

contribution to ozone that is attributable to the PA. These contributions range from 0.1 to 1.0 ppb. The 

largest impact of the PA at an existing monitor is 1.0 ppb, which occurs in Farmington, New Mexico (site 

ID 350451005). Importantly, none of the monitoring sites that are predicted to have an increase in ozone 

concentrations under the PA have a design value that exceeds the NAAQS either in 2005 or in 2018. 

4.2.1.2 Ozone Impact Assessment in Unmonitored Areas

In addition to assessing the ozone impacts in areas with monitors, areas without monitors were 

assessed using the MATS tool in order to evaluate all areas where future year design values could be 

greater than the NAAQS. It should be noted that due to lack of measurement data, the analysis of ozone 

attainment test in the unmonitored areas can be more uncertain than in places where monitoring data 

are available. As a result, the unmonitored area analysis should be treated as a separate test from the 

monitor based attainment test. The current work provides results from the unmonitored area analysis as 

a supplemental analysis. The receptors chosen for this analysis include the Class I and sensitive Class II 

areas listed in Section 3.4.1 that are within the 4-km domain. The methodology used to obtain the values 

presented in Table 4-4 is detailed in Section 3.4.4.

Table 4-4 shows ozone design values estimated by MATS for 2005 and 2018 at unmonitored areas. The 

2005 Baseline column represents ozone concentrations at 88 sensitive areas from the interpolation of 

available monitor data for 2005 (spatial field baseline). In 2005, there are no receptors that exceed the 

ozone NAAQS. Because 2018 ozone design values generally decrease from 2005, there are no 

receptors that exceed the ozone NAAQS in the future year either. The difference between PA and NA 

Alternative is seen in 60 sensitive areas with differences ranging from 0.1 to 1.0 ppb due to impacts from 

the FCPP. The maximum impact of 1.0 ppb occurs at Bisti/De-Na-Zin WA, which has a future design 

value of 65.8 ppb.

Table 4-4 also shows interpolated gradient-adjusted ozone concentrations for Class l and sensitive 

Class II areas. When these gradient-adjusted values are examined, the baseline 2005 ozone 

concentrations exceed the NAAQS at only nine receptors. Only one site, Sandia Mountain WA, shows 

ozone exceedences of the NAAQS in the 2018 future year scenarios. The difference between the 2018 

PA and NA Alternative for Sandia Mountain WA is 0.1 ppb, indicating some impacts from the FCPP. The 

ozone values for both the 2018 NA Alternative and PA, however, exceed the NAAQS. The difference 

between PA and NA Alternative are non-zero for 60 sensitive areas with predicted FCPP contributions 

ranging from 0.1 to 1.0 ppb. The maximum impact of 1.0 ppb occurs at Bisti/De-Na-Zin WA, which has a 

future ozone design value of 62 ppb.
AECOM Environment 4-15

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-3 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Monitoring Sites Located within the 4-km Domain

Location Site ID

Latitude

(degrees)

Longitude

(degrees)

2005 Baseline 

Ozone Design 

Value

(ppb)

2018 PA 

Ozone Value

(ppb)

2018 NA 

Alternative 

Ozone Value

(ppb)

Difference between 

PA and NA 

Alternative Ozone 

Values

(ppb)

Bernalillo County, New Mexico 350010019 35.10728 -106.56359 72.3 70.6 70.5 0.1

Bernalillo County, New Mexico 350010023 35.13430 -106.58520 71.0 69.0 68.9 0.1

Bernalillo County, New Mexico 350010024 35.06310 -106.57879 72.3 70.6 70.5 0.1

Bernalillo County, New Mexico 350010027 35.15390 -106.69715 71.7 69.5 69.4 0.1

Bernalillo County, New Mexico 350010029 35.01708 -106.65739 69.0 67.1 67.1 0.0

Bernalillo County, New Mexico 350011012 35.18520 -106.50815 77.0 74.9 74.9 0.0

Bernalillo County, New Mexico 350011013 35.19324 -106.61382 73.7 71.7 71.7 0.0

Bernalillo County, New Mexico 350011014 35.20220 -106.64927 70.3 68.0 68.0 0.0

La Plata County, Colorado 80671004 37.30389 -107.48417 72.0 69.8 69.6 0.2

La Plata County, Colorado 80677003 37.10258 -107.87022 63.7 60.3 60.1 0.2

Montezuma County, Colorado 80830101 37.19833 -108.49028 72.0 65.1 64.7 0.4

Sandoval County, New Mexico 350431001 35.29944 -106.54833 67.7 65.6 65.5 0.1

Sandoval County, New Mexico 350431003 35.23806 -106.64944 73.3 70.9 70.9 0.0

Sandoval County, New Mexico 350439004 35.61528 -106.72444 71.0 68.6 68.3 0.3

San Juan County, New Mexico 350450009 36.74222 -107.97694 69.7 66.5 66.2 0.3

San Juan County, New Mexico 350451005 36.79667 -108.47250 71.3 68.1 67.1 1.0

Note: Design value concentrations that exceed 75 ppb are shown in red text.
AECOM Environment 4-16

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored Sensitive Class I and II Areas Located within the 4-km

Domain

Site Name

Interpolated Ozone Concentration (ppb) Interpolated Gradient-Adjusted Ozone Concentration (ppb)

2005 

Baseline 2018 PA 

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

2005 

Baseline 2018 PA

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

CLASS I AREAS

Bandelier WA1 71.4 68.6 68.4 0.2 71.5 68.7 68.5 0.2

Canyonlands NP2 71.8 69.4 69.4 0.0 65.4 63.2 63.2 0.0

La Garita WA 71.9 70.7 70.7 0.0 75.4 74.2 74.1 0.1

Mesa Verde NP 71.4 68.4 68.1 0.3 69.5 66.5 66.3 0.2

Pecos WA 71.8 69.3 69.2 0.1 75.0 72.4 72.3 0.1

Petrified Forest NP 70.8 67.9 67.9 0.0 68.1 65.3 65.3 0.0

San Pedro Parks WA 71.3 68.6 68.3 0.3 73.4 70.6 70.3 0.3

Weminuche WA 69.5 68.0 67.9 0.1 70.1 68.6 68.5 0.1

CLASS II AREAS

Acoma IR3 70.5 68.2 68.1 0.1 66.5 64.3 64.2 0.1

American Flats 70.0 68.8 68.7 0.1 72.3 71.0 71.0 0.0

Aztec Ruins NM4 69.0 65.8 65.5 0.3 70.9 67.6 67.3 0.3

Bisti/De-Na-Zin WA 70.5 65.8 64.8 1.0 66.4 62.0 61.0 1.0

Bridger Jack Mesa WSA5 71.8 69.0 68.9 0.1 65.2 62.7 62.6 0.1

Butler Wash WSA 71.8 69.7 69.7 0.0 66.7 64.7 64.7 0.0

Cahone Canyon WSA 71.8 67.5 67.3 0.2 67.5 63.5 63.2 0.3

Canoncito IR 70.5 67.9 67.8 0.1 67.8 65.3 65.2 0.1
AECOM Environment 4-17

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored Sensitive Class I and II Areas Located within the 4-km

Domain

Site Name

Interpolated Ozone Concentration (ppb) Interpolated Gradient-Adjusted Ozone Concentration (ppb)

2005 

Baseline 2018 PA 

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

2005 

Baseline 2018 PA

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

Canyon de Chelly NM 70.9 67.7 67.6 0.1 64.6 61.7 61.6 0.1

Carson NF 70.1 66.8 66.6 0.3 72.6 69.1 68.9 0.3

Chaco Culture National Historic 

Park

70.5 67.3 66.9 0.4 67.1 64.0 63.6 0.4

Chama Rover Canyon WA 71.3 67.3 67.0 0.3 73.8 69.7 69.4 0.3

Cheese Box Canyon WSA 71.4 69.0 69.0 0.0 66.3 64.1 64.1 0.0

Cibola NF 71.5 69.6 69.6 0.1 72.0 70.1 70.1 0.0

Cochiti IR 71.6 68.6 68.4 0.2 73.1 70.0 69.9 0.1

Cross Canyon WSA 71.8 66.2 65.7 0.5 67.3 62.0 61.6 0.4

Cruces Basin WA 71.4 69.2 69.1 0.1 75.8 73.5 73.4 0.1

Dark Canyon WA 71.5 69.9 69.9 0.0 68.9 67.4 67.4 0.0

Dome WA 71.4 68.6 68.3 0.3 72.0 69.2 68.9 0.3

El Malpais NM 70.5 68.1 68.1 0.0 66.9 64.6 64.6 0.0

El Morro NM 70.5 68.0 68.0 0.0 65.2 62.9 62.9 0.0

Fish Creek Canyon WSA 71.5 68.1 67.9 0.1 66.7 63.5 63.4 0.1

Glen Canyon National Recreation 

Area

71.4 68.5 68.5 0.0 66.8 64.1 64.1 0.0

Grand Mesa, Uncompahgre, and 

Gunnison NFs

70.7 68.9 68.8 0.1 69.1 67.3 67.2 0.1
AECOM Environment 4-18

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored Sensitive Class I and II Areas Located within the 4-km

Domain

Site Name

Interpolated Ozone Concentration (ppb) Interpolated Gradient-Adjusted Ozone Concentration (ppb)

2005 

Baseline 2018 PA 

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

2005 

Baseline 2018 PA

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

Handies Peak WSA 70.0 69.0 68.8 0.2 72.0 70.9 70.8 0.1

Hopi IR 70.8 68.0 68.0 0.0 63.4 60.9 60.9 0.0

Hovenweep NM 71.8 65.3 64.6 0.7 68.7 62.5 61.8 0.7

Hubbell Trading Post National 

Historic Site

70.8 68.3 68.3 0.0 65.1 62.8 62.8 0.0

Jemez IR 71.1 68.6 68.3 0.3 70.8 68.3 68.0 0.2

Jemez National Recreation Area 70.2 68.0 67.8 0.2 70.8 68.6 68.4 0.2

Jicarilla Apache IR 70.6 67.6 67.4 0.3 74.7 71.5 71.3 0.2

Laguna IR 70.5 67.8 67.7 0.1 68.3 65.7 65.6 0.1

Little Rockies WSA 71.4 69.1 69.1 0.0 67.0 64.9 64.8 0.1

Lizard Head WA 69.3 67.4 67.3 0.1 68.5 66.6 66.5 0.1

Mancos Mesa WSA 71.4 68.3 68.3 0.0 67.6 64.7 64.6 0.1

Manti-Lasal NF 71.5 69.9 69.9 0.0 68.4 66.8 66.8 0.0

McKenna Peak WSA 69.9 67.1 66.9 0.2 65.1 62.5 62.3 0.2

Menefee Mountain WSA 69.8 67.7 67.6 0.1 66.9 64.9 64.8 0.1

Mesa Verde WA 70.9 68.4 68.3 0.1 69.4 67.0 66.8 0.1

Middle Point WSA 71.4 69.5 69.5 0.0 65.5 63.7 63.7 0.0

Monte Vista National Wildlife 

Refuge

71.9 70.7 70.5 0.2 73.3 72.1 71.9 0.2
AECOM Environment 4-19

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored Sensitive Class I and II Areas Located within the 4-km

Domain

Site Name

Interpolated Ozone Concentration (ppb) Interpolated Gradient-Adjusted Ozone Concentration (ppb)

2005 

Baseline 2018 PA 

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

2005 

Baseline 2018 PA

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

Mount Sneffels WA 69.3 67.8 67.7 0.1 68.4 66.9 66.9 0.0

Nambe IR 71.7 69.4 69.3 0.1 70.4 68.1 68.0 0.1

Natural Bridges NM 71.4 68.6 68.6 0.0 66.4 63.8 63.8 0.0

Navajo Nation 71.0 68.5 68.5 0.1 65.6 63.3 63.3 0.0

Ojito WA 70.7 68.2 68.2 0.0 67.8 65.4 65.4 0.0

Pecos National Historical Park 72.2 70.5 70.4 0.1 75.1 73.3 73.2 0.1

Petrified Forest National WA 70.8 67.7 67.7 0.0 68.2 65.2 65.2 0.0

Petroglyph NM 71.6 69.1 69.0 0.1 72.4 69.9 69.9 0.0

Pojoaque IR 71.7 69.5 69.5 0.0 70.1 68.0 67.9 0.1

Powderhorn WA (BLM) 71.9 70.7 70.7 0.0 75.2 73.9 73.9 0.0

Powderhorn WA (USFS) 71.9 70.8 70.8 0.0 75.5 74.4 74.4 0.0

Powderhorn WSA (BLM) 71.9 70.5 70.5 0.0 73.6 72.2 72.2 0.0

Ramah Navajo IR 70.7 67.7 67.7 0.0 66.2 63.4 63.4 0.0

Redcloud Peak WSA 71.9 70.7 70.6 0.1 74.9 73.6 73.5 0.1

Rio Grande NF 71.9 70.6 70.5 0.1 74.8 73.5 73.4 0.1

Road Canyon WSA 71.4 67.8 67.7 0.1 66.8 63.5 63.3 0.2

San Felipe IR 71.3 68.1 68.1 0.0 73.9 70.6 70.6 0.0

San Ildefonso IR 71.5 69.1 69.0 0.1 69.1 66.8 66.7 0.1
AECOM Environment 4-20

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored Sensitive Class I and II Areas Located within the 4-km

Domain

Site Name

Interpolated Ozone Concentration (ppb) Interpolated Gradient-Adjusted Ozone Concentration (ppb)

2005 

Baseline 2018 PA 

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

2005 

Baseline 2018 PA

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

San Juan IR 71.5 68.7 68.5 0.2 69.7 67.0 66.8 0.2

San Juan NF 71.9 69.9 69.8 0.1 72.9 70.9 70.7 0.2

Sandia IR 71.8 69.4 69.4 0.0 73.6 71.2 71.1 0.1

Sandia Mountain WA 72.4 70.3 70.2 0.1 78.8 76.5 76.4 0.1

Santa Ana IR 70.3 67.8 67.8 0.0 72.0 69.5 69.4 0.1

Santa Clara IR 71.4 69.1 68.8 0.3 72.4 70.0 69.7 0.3

Santa Fe NF 71.5 68.9 68.7 0.2 72.1 69.5 69.3 0.2

Santo Domingo IR 71.5 68.2 68.0 0.2 72.4 69.1 68.9 0.2

Slickhorn Canyon WSA 71.4 67.6 67.5 0.1 67.5 63.9 63.8 0.1

South San Juan WA 71.4 69.1 68.9 0.2 75.0 72.6 72.3 0.3

Southern Ute IR 67.3 64.4 64.3 0.1 67.1 64.2 64.1 0.1

Squaw/Papoose Canyon WSA 71.8 66.5 65.9 0.6 67.7 62.7 62.2 0.5

Tesuque IR 71.7 69.4 69.4 0.0 70.4 68.1 68.1 0.0

Uncompahgre WA (BLM) 69.4 68.1 68.0 0.1 71.4 70.0 70.0 0.0

Uncompahgre WA (USFS) 71.9 70.7 70.7 0.0 75.2 74.0 74.0 0.0

Ute Mountain IR 71.8 65.1 64.3 0.8 74.5 67.5 66.7 0.8

Weber Mountain WSA 70.4 67.9 67.8 0.1 68.6 66.2 66.1 0.1

West Malpais WA 70.5 68.3 68.2 0.1 66.3 64.2 64.1 0.1
AECOM Environment 4-21

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 4-4 MATS 8-Hour Ozone Design Values for 2005 and 2018 at Unmonitored Sensitive Class I and II Areas Located within the 4-km

Domain

Site Name

Interpolated Ozone Concentration (ppb) Interpolated Gradient-Adjusted Ozone Concentration (ppb)

2005 

Baseline 2018 PA 

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

2005 

Baseline 2018 PA

2018 NA 

Alternative

Difference 

between 2018 

PA and NA 

Alternative

Yucca House NM 71.8 66.6 66.2 0.4 71.1 66.0 65.5 0.5

Zia IR 71.2 68.6 68.4 0.2 69.8 67.3 67.1 0.2

Zuni IR 70.8 67.7 67.6 0.1 64.5 61.7 61.6 0.1

1 WA = Wilderness Area.

2 NP = National Park.

3 IR = Indian Reservation.

4 NM = National Monument.

5 WSA = Wilderness Study Area.

Notes: Model-predicted concentrations that exceed 75 ppb are shown in red text. Information in parentheses indicates agency managing sensitive area.
AECOM Environment 5-1

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

5.0 Summary

The APS operates the FCPP, a privately owned and operated coal-fired power plant located on the 

Navajo Nation, about 25 miles west of Farmington, New Mexico. The APS contracted AECOM to assist 

in gathering data to submit to the OSM for the preparation of an EIS. This EIS is in response to the 

proposed Lease Amendment No. 3 for the FCPP site and renewal of ROWs for existing FCPP facilities. 

This modeling work focuses exclusively on the assessment of ozone ambient air quality impacts 

associated with the proposed lease renewal and grant issuance. The assessment is conducted by 

modeling the FCPP emissions in combination with other regional emissions sources and comparing the 

resulting ozone concentrations to the USEPA’s 2008 8-hour ozone NAAQS. Ozone impacts were 

assessed near the FCPP, at existing ozone monitors, at Class I areas, and sensitive Class II areas.

The approach used in this modeling work relies on the input data, configurations, supporting information, 

and modeling platform developed for the FCAQS (ENVIRON 2009). The FCAQS, which encompasses 

the FCPP project area, was conducted to assess air quality conditions in the Four Corners region and 

evaluate the potential future impacts of various control scenarios in 2018. The FCAQS modeling used 

the CAMx modeling system, a modeling platform that includes the MM5 meteorological model, the 

SMOKE emissions processing system, and the CAMx photochemical grid model. The FCAQS also 

provided the modeling domains that consist of 12-km and 4-km nested grid cells that were used for all 

simulations.

AECOM estimated the impacts on ozone concentrations due to the emissions from the FCPP by using 

this modeling platform to simulate the following scenarios:

• 2005 Baseline. The 2005 Baseline simulation used the FCAQS 2005 (ENVIRON 2009) 

emissions inventory for an analysis of current air quality conditions. Modeling emissions in the 

year 2005 established baseline air quality levels against which future year project and 

cumulative impacts were evaluated.

• 2018 No Action Alternative. The NA Alternative simulation was based on the FCAQS 2018 

Mitigation Scenario #4 and included impacts all regional emissions except for contributions from 

the FCPP. Mitigation Scenario #4 applied aggressive control measures for NOX and SO2 from 

coal-fired power plants in the Four Corner’s region as well as control technologies for oil and gas 

sources of NOX and VOCs in San Juan and Rio Arriba counties in New Mexico.

• 2018 Proposed Action. The PA simulation also was based on the FCAQS 2018 Mitigation 

Scenario #4 and included contributions from the proposed future emissions of the FCPP. 

Potential air quality impacts from the FCPP proposed emissions were assessed by comparing 

modeled impacts of the PA to the NA Alternative.

As part of this modeling work, the FCAQS emissions inventories were reviewed and updated for these 

three scenarios. APS provided updated emissions for the FCPP that are consistent with the final BART 

rule. The FCAQS regional emissions inventory was updated with emissions and parameter information 

for other EGUs in the 4-km domain as well, particularly the SJGS.

Updated FCAQS emissions inventories were processed through SMOKE to produce surface and 

elevated hourly, gridded, and speciated model-ready emissions for the three scenarios described. The 

CAMx then used these SMOKE processed emissions and FCAQS model-ready meteorological inputs 

and ancillary data to perform ozone modeling to assess the FCPP PA impacts on the Four Corners 

region. The selected modeling period spans from May through August because observed ozone 

concentrations are usually the highest during the summer months in this region. Most of the main CAMx 

configuration options used in this modeling work were based on the FCAQS, except for the PiG 

sub-model setting. The PiG sub-model was required for FCPP and SJGS to better represent the early 

chemical and transport evolution of large NOx plumes associated with these sources. 
AECOM Environment 5-2

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

The CAMx was shown to be appropriate for this modeling work by a comprehensive model evaluation of 

CAMx results in the FCAQS. The FCAQS evaluated model performance by comparing modeled 

concentrations to ambient measurements. This evaluation found that model performance for ozone was 

within the established USEPA acceptance criteria for most months, indicating CAMx is adequate for 

modeling ozone for the 2005 Baseline simulation.

The results of the three CAMx simulations were post-processed to perform the following analyses: 

1) comparison of modeled concentrations to the 8-hour ozone NAAQS, 2) model attainment tests for

monitored and unmonitored areas, and 3) assessment of the ozone impacts due to the PA. Ozone 

impacts were assessed at ozone monitor locations as well as 88 unmonitored Class I and sensitive 

Class II areas in the 4-km domain.

Model-predicted ozone concentrations were further post-processed with AECOM’s IAS and EPA’s MATS 

tools. The IAS was designed to read model predicted concentrations at specified receptor sites and 

produce values that could be compared to the ozone NAAQS and also to provide suitable input files for 

MATS. The IAS calculated the model-predicted fourth highest daily maximum 8-hour average ozone 

concentrations at Class I and sensitive Class II areas for comparison to the NAAQS for the 2005 

Baseline, 2018 NA Alternative, and 2018 PA simulations. 

Ozone model attainment demonstration was performed using MATS. The MATS tool was designed to 

project future ozone concentrations at locations of ozone monitors and also locations removed from 

monitors based on ambient ozone measurements. Projections were based on applying a RRF to an 

ozone design value, which is estimated from the 5-year weighted average of the fourth highest daily 

maximum 8-hour average monitored values. The MATS also calculated ozone concentrations for sites 

removed from monitor locations by using two types of spatial interpolation: 1) between “neighbor”

monitors, and 2) between “neighbor” monitors but relying on model data to perform gradient 

adjustments. This analysis provides the MATS calculated fourth-highest daily maximum 8-hour average 

ozone concentrations for monitor locations and also spatial interpolation values for unmonitored Class I 

and sensitive Class II areas. The MATS was run for the 4-km domain for both the 2018 NA Alternative 

and PA scenarios for comparison to the NAAQS.

Qualitative assessment of the spatial distribution of ozone concentrations between the baseline and 

future simulations indicated an overall decrease in ozone levels in 2018 relative to 2005. In particular for 

the NA Alternative simulations, domain-wide average concentration decreased from 63.9 ppb in 2005 to 

61.6 ppb in 2018. The most notable changes occur in the western and central areas of the 4-km domain 

where the model-predicted fourth-highest daily maximum 8-hour average ozone concentrations 

decreased by 5 to 7 ppb. The only locations where ozone is observed to increase occur in San Juan 

County in New Mexico, which are immediately downwind of the location of FCPP. The maximum 

increase in the fourth-highest 8-hour ozone concentrations between the 2018 NA Alternative and 2005 

Baseline was 3.5 ppb. This increase occurs in an area where ozone concentrations do not exceed the 

NAAQS (values range between 65 to 70 ppb) and concentrations in the vicinity of the FCPP peaks at 

69 ppb. 

Results show that the FCPP contributions generally range from 0.0 to 0.9 ppb over the 4-km domain.

Qualitative assessment of the spatial distribution of ozone concentrations between the baseline and both 

future simulations yield similar spatial patterns, with the exception of some differences immediately 

downwind of the FCPP. 

The impacts of the FCPP under the PA were estimated as the difference between 2018 PA and the 2018 

NA Alternative simulations. For both modeling scenarios, the highest ozone concentrations, ranging from 

60 to 70 ppb, are found mostly in the northeastern portion of the 4-km domain. The maximum modelpredicted difference between the PA and the NA Alternative is 4.7 ppb, which occurs downwind of the 

FCPP. This maximum difference is located about 11 miles southeast of the FCPP and about 16 miles 
AECOM Environment 5-3

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

southwest of Farmington, New Mexico. Most of the impacted areas show a 2 to 4 ppb increase in ozone 

concentrations and are located entirely in San Juan and McKinley counties in New Mexico.

The impacts on receptors defined as Class I and sensitive Class II areas in this analysis was examined 

with various approaches. Examination of absolute model concentrations indicates that in general the 

number of sensitive areas with predicted NAAQS exceedences decrease from 12 areas in 2005 to only 

three areas in the NA Alternative model scenarios. The affected areas are La Garita WA, Grand Mesa, 

Uncompahgre, and Gunnison NFs, and Rio Grande NF. The FCPP, however, does not contribute to 

their modeled impacts since the difference between the 2018 PA and NA Alternative is 0.0 ppb. 

Importantly, the absolute model predicted ozone concentration for the PA at the Navajo Nation is just 

below the NAAQS. The model-predicted FCPP contribution to the Navajo Nation is 0.7 ppb of ozone. For 

all other areas the impacts from the FCPP are 0.0 ppb except for 43 sensitive areas where the 

model-predicted impacts due to the FCPP range from 0.1 to 0.9 ppb. The maximum impact (0.9 ppb) 

occurs at Ute Mountain IR in Colorado and New Mexico and also at Chaco Culture National Historic Park 

in New Mexico. In both areas, however, the model concentrations are well below the NAAQS.

Examination of model concentrations adjusted with monitored data as provided by MATS indicate that 

there is only one monitor (site ID 350011012) with design values in 2005 that exceed the 8-hour ozone 

NAAQS (77 ppb). This site is located northeast of Albuquerque in Bernalillo County, New Mexico. The 

analysis indicates that there are no monitors within the 4-km domain with design values that exceed the 

8-hour ozone NAAQS under both the 2018 NA Alternative and PA. There are 11 monitors with a 

predicted non-zero contribution to ozone that is attributable to the PA. These contributions range from 

0.1 to 1.0 ppb. The largest impact of the PA at an existing monitor is 1.0 ppb, which occurs in 

Farmington, New Mexico (site ID 350451005). Importantly, none of the monitoring sites that are 

predicted to have an increase in ozone concentrations under the PA have a design value that exceeds 

the NAAQS either in 2005 or in 2018.

Finally, the examination of ozone impacts in unmonitored areas shows that in 2005 there are no 

sensitive areas that exceed the ozone NAAQS. This analysis is subject to more uncertainty relative to 

the monitored analysis, but it does show similar conclusions as the other types of results presented. 

Because 2018 ozone design values generally decrease from 2005, there are no receptors that exceed 

the ozone NAAQS in the future year either. The difference between PA and NA Alternative is seen in

60 sensitive areas with differences ranging from 0.1 to 1.0 ppb due to impacts from the FCPP. The 

maximum impact of 1.0 ppb occurs at Bisti/De-Na-Zin WA, which has a future design value of 65.8 ppb.

Overall, the model-predicted future ozone concentrations are similar regardless of the methods used to 

analyze the results. In general, ozone concentrations are predicted to decrease in 2018 throughout the 

4-km modeling domain relative to conditions in 2005. Ozone impacts from the FCPP under the Proposed 

Action do not contribute to areas that may continue to have ozone concentrations that exceed the 

NAAQS in 2018.
AECOM Environment 6-1

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

6.0 References

Abt Associates Inc. 2009. Modeled Attainment Test Software User's Manual. Prepared for Office of Air 

Quality Planning and Standards, USEPA, Research Triangle Park, North Carolina. March 2009.

AECOM. 2013. Four Corners Power Plant and Navajo Mine Environmental Impact Statement NAAQS 

Compliance Modeling Study. Prepared for Arizona Public Service. May 2013.

Arizona Public Service. 2013. Personal communication between Alan Papp, Richard Grimes (APS) and 

Marco Rodriguez (AECOM). February 2013.

Code of Federal Registrations (CFR). 2008. Ozone National Ambient Air Quality Standard. 73 FR 16436. 

March 27, 2008. 

Coats, C. J., Jr. 1995. High Performance Algorithms in the Sparse Matrix Operator Kernel Emissions 

(SMOKE) Modeling System, MCNC Environmental Programs, Research Triangle Park, North 

Carolina. 1995.

ENVIRON International Corporation (ENVIRON). 2009. Air Quality Modeling Study for the Four Corners. 

Prepared for New Mexico Environment Department Air Quality Bureau. June 2009. Internet 

website: http://www.nmenv.state.nm.us/aqb/4C/Modeling.html. 

ENVIRON International Corporation (ENVIRON). 2008. User’s Guide Comprehensive Air Quality Model 

with Extensions Version 4.50. ENVIRON International Corporation, Novato, California. September 

2008.

Fields, P. G., M. E. Wolf, T. Moore, and L. Gribovice. 2007. Developing the WRAP Point and Area 

Source Emissions Projects for the 2018 Reasonable Progress Milestone for Regional Haze 

Planning. Presented at 16th Annual International Emission Inventory Conference Emission 

Inventories: “Integration, Analysis, and Communications.” May 14-17, 2007.

Houyoux, M. R. and J. M. Vukovich. 1999. Updates to the Sparse Matrix Operator Kernel Emissions 

(SMOKE) Modeling System and Integration with Models-3. Presented at The Emission Inventory: 

Regional Strategies for the Future, Raleigh, North Carolina, Air & Waste Management Association.

October 26-28, 1999.

National Aeronautics and Space Administration (NASA). 2013. GEOS-Chem Model. April 2013. Internet 

website: http://acmg.seas.harvard.edu/geos/.

National Center for Atmospheric Research (NCAR). 2005. Fire Emission Factors and Emission 

Inventories. 2005. Internet website: http://bai.acd.ucar.edu/Data/fire/.

Navajo Nation Environmental Protection Agency (NNEPA). 2008. Arizona Public Service Four Corners 

Power Plant Title V Operating Permit. August 2008. Internet website: 

http://www.navajonationepa.org/airqty/Pdf_files/FCPPpermit8-1-2008.pdf.

Public Service Company of New Mexico (PNM). 2013. Personal communication between Mark Williams 

(PNM) and Marco Rodriguez (AECOM). February 2013.

United States Environmental Protection Agency (USEPA). 2012. Source Specific Federal 

Implementation Plan for Implementing Best Available Retrofit Technology for Four Corners Power 

Plant. 77FR 51620. August 24, 2012.
AECOM Environment 6-2

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

United States Environmental Protection Agency (USEPA). 2007. Guidance on the Use of Models and 

Other Analyses for Demonstrating Attainment of Air Quality Goals for Ozone, PM2.5, and Regional 

Haze. USEPA, Office of Air Quality and Planning Standards, Research Triangle Park, North 

Carolina. EPA 454/B-07-002. April 2007.

Yarwood, G., S. Rao, M. Yocke, and G. Z. Whitten. 2005. Updates to the Carbon Bond Mechanism: 

CB05. USEPA Final Report, 161 pp. 2005. Internet website: 

http://www.camx.com/publ/pdfs/CB05_Final_Report_120805.pdf.
AECOM Environment

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Appendix A

Analysis of FCAQS 

Emissions Inventory and 

CAMx Model Sensitivity
AECOM Environment A-1

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Updated emissions information has become available for the oil and gas sources in the Four Corners 

area since the FCAQS was finalized. This appendix presents a comparison of the oil and gas emissions 

modeled in the FCAQS and the most recent oil and gas emissions inventory data. This information is 

used to support two points: 

1. That the Mitigation Scenario #4 emissions inventory is potentially a more accurate assessment 

of potential future emissions in the Four Corners area than the original 2018 Base Case 

emissions inventory; and

2. A revised model performance evaluation is not required based on results that the FCAQS 2018 

model impacts are relatively insensitive to the changes in the base year oil and gas emissions 

inventory. 

Emissions Inventory Comparison

The oil and gas emissions inventory modeled in the FCAQS 2005 Base Case is shown in Table 1. 

These emissions are compared to the latest available emissions inventory for this area, which is the 

Western Regional Air Partnership (WRAP) Phase III Emissions Inventory for the North and South San 

Juan Basins for year 2006. Since the FCAQS was completed, the estimated emissions from oil and gas 

sources near the Four Corners Power Plant have decreased by approximately 50 percent for Volatile 

Organic Compounds (VOC), carbon monoxide (CO), and sulfur dioxide (SO2); decreased by 

approximately 25 percent for nitrogen oxides (NOx); and increased by approximately 250 percent for 

particulate matter with an aerodynamic diameter of 10 microns or less (PM10).

Table 1 Comparison of the North and South San Juan Basins Oil and Gas Emissions 

Inventories for the FCAQS 2005 Base Case and 2006 WRAP Phase III 

Oil and Gas Emissions

VOC 

(tpy)

NOx

(tpy) CO (tpy)

SO2

(tpy)

PM10

(tpy)

FCAQS 2005 Base Case (Phase II) 119,959 64,252 53,292 686 171

WRAP Phase III 2006 62,296 46,270 28,132 306 620

Difference (tpy) -57,664 -17,982 -25,161 -380 449

Percent Change (%) -48 -28 -47 -55 262

Table 2 shows how the entire FCAQS 2005 Base Case emissions inventory would change (i.e. the 

emissions from all sources in the 4-kilometer (km) modeling domain, not just the emissions from the oil 

and gas sector) if the study had used the WRAP Phase III oil and gas emissions in Table 1 instead of 

the Phase II emissions. As shown in Table 2, the total emissions in the 4-km modeling domain would be 

approximately 13 percent lower for VOC, 8 percent lower for NOx, and less than 1 percent different for 

SO2 and PM10. 

Table 2 Comparison of the FCAQS 2005 Base Case Emissions between the Phase II 

Emissions and the Phase III Emissions 

4-km Domain

VOC 

(tpy)

NOx

(tpy)

CO

(tpy)

SO2

(tpy)

PM10

(tpy)

Modeled FCAQS 2005 Base Case (Phase II) 431,649 221,863 NA 43,461 142,485

FCAQS 2005 Base Case Replaced with Phase III 373,985 203,881 NA 43,081 142,934

Percent Change (%) -13.4 -8.1 NA -0.9 0.3
AECOM Environment A-2

FCPP/Navajo Mine EIS Ozone Impact Assessment July 2013

Table 3 compares the 4-km Domain Oil and Gas emissions for the 2018 Base Case to the 2018 

Mitigation Scenario #4. As shown in Table 3, the 4-km domain oil and gas emissions would be 

approximately 45 percent lower for VOC, and 15 percent lower for NOx. These percent changes are 

relatively similar to the estimated changes in the 2005/2006 emissions inventory shown in Table 1.

Table 3 Comparison of the 4-km Domain Oil and Gas Emissions Inventories for the 2018 

Base Case and 2018 Mitigation Scenario #4 

Oil and Gas Emissions

VOC

(tpy)

NOx

(tpy)

SO2

(tpy)

PM10

(tpy)

2018 Base Case 149,227 78,040 857 162

2018 Mitigation Scenario #4 81,895 65,855 857 142

Difference (tpy) -67,332 12,185 0 20

Percent Change (%) -45.12 15.61 0.00 12.35

Implications of Emissions Inventory on Ozone Concentrations

Since the objective of the ozone modeling is to assess the changes in the concentration of ozone that is 

attributable to the project, it is important to understand how the changes in the emissions inventory relate 

to changes in the modeled ozone concentrations. As part of the FCAQS, the sensitivity of ozone 

concentrations to changes in NOx and VOC ratios were investigated using a Higher-Order Direct 

Decoupled (HDDM) method2

. Importantly, the HDDM analysis was performed only on the days and 

locations with the highest modeled impact, so the applicability of the results of the HDDM is limited to 

these conditions3

. HDDM results from the FCAQS shows that a potential reduction of 13% in VOC and 

8% in NOx emissions4 would result in ozone reductions of 2 ppb in Navajo Lake area when ozone 

exceeds 65 ppb on average, and no change in ozone concentrations at Mesa Verde.

 

2 ENVIRON International Corporation (ENVIRON). 2010.Addendum to the Air Quality Modeling Study for the Four 

Corners. Prepared for New Mexico Environment Department Air Quality Bureau. April 2010. Internet website: 

http://www.nmenv.state.nm.us/aqb/4C/Documents/FourCornersModelingAddendum_5April2010.pdf 3 HDDM was performed for only the days when ozone exceeded 65 ppb in July 2005 at Navajo Lake and Mesa 

Verde.

4 Note that these percent changes in emissions are consistent with the emission differences that would occur if the 

FCAQS were to be revised to include the updated oil and gas emissions inventory, as shown in Table 2.