March 2014 Affected Environment, Impacts, and Mitigation 4-1

4 Affected Environment, Impacts, and Mitigation 

Approach to Environmental Analysis

In the environmental analysis, each environmental resource is addressed in its own section. Each section 

includes the description of affected environment for that resource, the environmental consequences of the 

Proposed Action and alternatives on that resource, and proposed mitigation for any identified major 

environmental consequences. 

Many of the environmental effects of the Project analyzed in this EIS are attributed to the continued 

operation of existing facilities (Navajo Mine, FCPP, transmission lines). These continuing operations are 

described in Section 2. The Council on Environmental Quality provides guidance on this approach:

“The current condition is frequently used as the benchmark for comparing the 

environmental effects of the alternatives. However, in cases of continued operations, the 

current condition may not adequately represent how actions have impacted resources in 

the past, are currently impacting resources, or how resources might respond to future 

impacts. Designating existing environmental conditions as a benchmark may focus the 

environmental impact assessment too narrowly, overlooking cumulative impacts of past 

and present actions or limiting assessment to the Proposed Action and future actions. For 

example, if the current environmental condition were to serve as the condition for 

assessing the impacts of relicensing a dam, the analysis would only identify the marginal 

environmental changes between the continued operation of the dam and the existing 

degraded state of the environment. In this hypothetical case, the affected environment 

has been affected for more than 50 years with accompanying declines in flows, 

reductions in fish stocks, habitat loss, and disruption of hydrologic functions. If the 

assessment took into account the full extent of continued impacts, the significance of the 

continued operation would more accurately express the state of the environment and 

thereby better predict the consequences of relicensing the dam (CEQ 1997).” 

Following this guidance, for each environmental resource, the analysis of the effects of continuing 

operations (described in Section 2) and of the alternatives including the Proposed Action (described in 

Section 3), are measured relative to environmental benchmarks specific to each resource category. The 

analysis identifies environmental impairments, either existing or ongoing, that would be addressed 

through mitigation measures or other means.

There have been two completed federal actions that may affect the continuing operations at FCPP, and at 

Navajo Mine. At FCPP, the EPA has made its ruling with respect to BART to control air emissions 

(Section 2.4.2). For Navajo Mine, OSMRE has approved the SMCRA permit transfer from BNCC to NTEC 

(Section 2.4.1). These completed federal actions form part of the environmental baseline to which the 

effects of continuing operations and the Proposed Actions are compared. In each description of the 

environmental setting, the measured current conditions (prior to 2014) are described first. This description 

is followed by the expected conditions as a result of BART compliance or as a result of the SMCRA

(interim period: 2014-2018) permit transfer. Environmental consequences are then determined relative to 

this baseline condition. 

In some cases, the two completed federal actions do have long-term consequences to continuing 

operations that are considered in this EIS. For example, installation of SCR equipment on Units 4 and 5 

requires the transport of large quantities of ammonia to FCPP; the environmental consequences of the

ammonia transport, storage, and use are analyzed in the EIS as the continuing operations of FCPP, even 

though this requirement has not yet commenced. Further, the transfer of the SMCRA permit to NTEC may 
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4-2 Affected Environment, Impacts, and Mitigation March 2014

have long-term socioeconomic effects to the Navajo Nation, the State of New Mexico, and San Juan 

County. These long-term effects are analyzed in this EIS.

The environmental consequences would vary in duration and significance among the environmental 

resources. At the Navajo Mine and Pinabete Permit Areas, short-term impacts would occur during and/or 

immediately following construction activities and mining operations and would persist up to the reclamation 

phase. Based on historic operations at the Navajo Mine, a mined area is typically disturbed for 5 years prior 

to reclamation. Long-term impacts persist for the duration of the mining permit period (through 2041) and 

account for post-reclamation activities. Permanent impacts persist beyond or occur after reclamation (post 

2041). For the FCPP and transmission lines, short-term impacts are those that would occur immediately 

following approval of the lease renewals plus a reasonable period afterwards (i.e., a total of about 5 years). 

Long-term impacts are those that would persist beyond or occur after the 5-year period.

The levels of significance of impacts are classified as major, moderate, minor, negligible or “no impact.” 

An impact is considered major if it would result in a substantial adverse change to the environment. An 

impact is considered moderate or minor if it would not result in substantial adverse environmental effects 

but could still have some effect. The determination of whether an impact is moderate or minor is 

described within each resource category. In contrast to “no impact”, a negligible impact could occur but at 

the lowest limits of detection of an effect. In cases where no impact would occur, this conclusion is noted. 

Quantitative thresholds are applied, where appropriate, to determine the level of significance (for 

example, quantitative thresholds are commonly used to determine impact levels in the areas of noise and 

air quality). Other issues are assessed qualitatively based on context and intensity. A summary of 

unavoidable adverse impacts is provided following the analyses of individual resource areas.

As part of its SMCRA permit application, BNCC included measures to reduce or avoid potential impacts.

These measures are incorporated into the description of the Proposed Action and mine alternatives. 

These measures, as well as compliance with environmental regulations, are therefore not considered to 

be mitigation measures in this EIS. These measures were evaluated when considering the significance 

and duration of impacts, and, in some instances, the EIS identifies additional measures that would be 

necessary to avoid or further reduce potential impacts. Mitigation measures are agency-determined 

protections beyond those already proposed by the applicants or required by regulatory compliance.

The scope of the EIS was developed based on input from many sources, including the SMCRA permit 

applications; the cooperating agencies; open houses and public scoping and comment meetings; letters 

received from the public; and field inspections, research, and analyses. Conclusions and 

recommendations in this EIS are subject to the following assumptions:

Project proponents would comply with all applicable laws and regulations;

The proposed Project facilities would be constructed and operated as described in Sections 2 and

3 of this EIS;

Project proponents would implement the measures included in the respective applications; and 

Project proponents would implement the recommendations and mitigation measures included in 

this EIS.
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March 2014 Air Quality 4.1-1

4.1 Air Quality

The proposed project is located in the Four Corners region of northwestern New Mexico within the San 

Juan Air Basin (Figure 4.1-1). This air basin comprises the Four Corners region of northwest New Mexico, 

southwest Colorado, southeast Utah, and northeast Arizona. For the purposes of this EIS, the Proposed 

Action area encompasses a 300-km (km) (186-mile) radius from FCPP, which includes the Navajo Nation 

and Hopi tribal lands. San Juan Basin air quality is generally good and meets EPA ambient air quality 

standards. Primary issues of concern in this region include regional haze and visibility issues, as well as 

the potential deposition of metals from air to soil and water as a result of industrial air emissions.

The Navajo Mine and FCPP are located on Navajo sovereign tribal land; therefore, air emissions and air 

quality are under the jurisdiction of the Navajo Nation Environmental Protection Agency (NNEPA) and 

overseen by the EPA Region IX in San Francisco.1 Federal and tribal law defines criteria emissions to 

include the following: reactive or volatile organic compounds (ROCs or VOCs), nitrogen oxides (NOX as 

NO and NO2), carbon monoxide (CO), sulfur dioxide (SO2), respirable particulate matter (PM10), and fine 

particulate matter (PM2.5). Of these, VOCs and NOX are precursors of ground-level photochemical ozone 

(O3), which can result in decreased visibility and haze.

In addition, the EPA published a Final Ruling regarding the Source Specific Federal Implementation Plan 

(FIP) to Implement Best Available Retrofit Technology (BART) at the FCPP in August 2012, which 

provides requirements for future operation of the plant. The FIP and associated BART requirements have 

been determined and as such comprise part of the environmental baseline for assessing the 

consequences of the Proposed Action and alternatives. A detailed discussion of the regulatory framework 

regarding air quality and air emissions as applicable to the proposed Project is provided below.

Coal mining would cause air emissions from combustion of motor fuels (diesel and gasoline) used to 

operate mining equipment, portable equipment, and support vehicles. Mining activities also cause air 

emissions from explosives detonation (NO2, SO2, and CO) and fugitive dust (PM10 and PM2.5) from 

earthmoving activities. Power plant operation and maintenance would cause air emissions from the 

combustion of coal in boilers as well as motor fuels (diesel and gasoline) used in offroad equipment, 

portable equipment, and support vehicles. Support activities include switchyard and transmission line 

maintenance near the plant. Several quantitative models were conducted to evaluate the potential air 

quality impacts of the Proposed Action and alternatives. These include calculations of mobile and 

stationary source emissions in comparison to federal standards; air deposition modeling; Ozone 

Assessment; and plume visibility. Each of these models, their results, and implications with regard to 

potential impacts are described in the environmental consequences section. 

Human health risk assessment of HAPs, diesel particulate matter, and fugitive dust are presented in 

Section 4.17, Health and Safety. These issues are also mentioned in this section.

4.1.1 Regulatory Compliance Framework

4.1.1.1 Air Quality Standards

Air quality in a given location is determined by the concentration of various pollutants in the atmosphere. 

National Ambient Air Quality Standards (NAAQS) have been established by the EPA under the Clean Air 

Act of 1970 (CAA, amended 1977 and 1990, 42 United States Code 7401 et seq.). The NAAQS represent 

maximum levels of background pollution that are considered safe, with an adequate margin of safety, to 

protect public health (primary standards) and welfare (secondary standards such as diminished 

production and quality of agricultural crops, reduced visibility, degraded soils, materials and infrastructure 

1

In 2005, the NNEPA and owners of the FCPP entered into a Voluntary Compliance Agreement that resolves jurisdictional authority

dispute and states that the administration and enforcement of the NNEPA permit cannot be more stringent than EPA limits and

federal court decisions; thereby, limiting the tribe’s ability to enforce more stringent limits than that established by the EPA.
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Draft Environmental Impact Statement

4.1-2 Air Quality March 2014

damage, and damaged vegetation). Recently, the EPA has proposed developing new secondary 

standards aimed at reducing the impacts of atmospheric deposition on surface waters (GAO 2013). 

Individual states have the option to adopt more stringent standards and to include other pollution sources. 

However, all states in the Four Corners region – New Mexico, Arizona, Utah, and Colorado – have 

adopted NAAQS in lieu of adopting more stringent state standards. Also, the sovereign nations – Navajo 

Nation, Hopi Tribe, and Southern Ute Indian Tribe – use NAAQS as tribal standards.

The EPA has defined six criteria pollutants for which NAAQS have been established: ozone (O3), carbon 

monoxide (CO), nitrogen dioxide (NO2), sulfur dioxide (SO2), respirable and fine particulate matter (PM10

and PM2.5, respectively), and airborne lead (Pb). Each of these is described below.

Ozone (O3)

Ground-level ozone is a secondary pollutant formed in the atmosphere by a series of complex chemical 

reactions and transformations in the presence of sunlight. NOX and volatile organic compounds (VOCs) 

are the principal constituents in these reactions. The greatest source of NOX and VOC emissions is the 

high-temperature combustion of fossil fuels such as in motor vehicle engines and power plant boilers.

Thus, regulation and control of NOX and VOCs from these sources is essential to reduce the formation of 

ground-level ozone.

Ozone is a strong irritating gas that can chemically burn and cause narrowing of airways, forcing the 

lungs and heart to work harder to provide oxygen to the body. A powerful oxidant, ozone is capable of 

destroying organic matter, including human lung and airway tissue. Ozone damages cells in the lungs, 

making the passages inflamed and swollen. Ozone also causes shortness of breath, nasal congestion, 

coughing, eye irritation, sore throat, headache, chest discomfort, breathing pain, throat dryness, 

wheezing, fatigue, and nausea. It can damage alveoli, the individual air sacs in the lungs where oxygen 

and carbon dioxide are exchanged. Ozone has been associated with a decrease in resistance to 

infections. People most likely to be affected by ozone include the elderly, the young, and athletes. Ozone 

may pose its worst health threat to people who already suffer from respiratory diseases such as asthma, 

emphysema, and chronic bronchitis (VCAPCD 2003).

Nitrogen Dioxide (NO2)

NO2 is formed in the atmosphere primarily by the rapid reaction of the colorless gas nitric oxide (NO) with 

atmospheric oxygen. It is a reddish brown gas with an odor similar to that of bleach. NO2 participates in 

the photochemical reactions that result in O3. The greatest source of NO, and subsequently NO2, is the 

high-temperature combustion of fossil fuels such as in motor vehicle engines and power plant boilers. 

NO2 and NO are referred to collectively as NOX. NO2 can irritate and damage the lungs, cause bronchitis 

and pneumonia, and lower resistance to respiratory infections such as influenza. Researchers have 

identified harmful effects, similar to those caused by ozone, with progressive changes over four hours of 

exposure causing impaired pulmonary function, increased incidence of acute respiratory disease, and 

difficult breathing for both bronchitis sufferers and healthy persons (VCAPCD 2003).
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Carbon Monoxide (CO)

CO is a common, colorless, odorless, highly toxic gas. It is produced by natural and anthropogenic 

(caused by human activity) combustion processes. The major source of CO is incomplete combustion of 

carbon-containing fuels (primarily gasoline, diesel fuel, natural gas, and coal). However, it also results 

from combustion processes including forest fires and agricultural burning. Ambient CO concentrations are 

generally higher in the winter, usually on cold, clear days and nights with little or no wind. Low wind 

speeds inhibit horizontal dispersion, and surface inversions inhibit vertical mixing. Traffic-congested 

intersections have the potential to result in localized high CO levels.

When inhaled, CO does not directly harm the lungs. The impact from CO is on oxygenation of the entire 

body. CO combines chemically with hemoglobin, the oxygen transporting component of blood. This 

diminishes the ability of blood to carry oxygen to the brain, heart, and other vital organs. Red blood cells 

have 220 times the attraction for CO as for oxygen. This affinity interferes with movement of oxygen to the 

body’s tissues. Effects from CO exposure include headaches, nausea, and death. People with heart 

ailments are at risk from low-level exposure to CO. Also sensitive are people with chronic respiratory 

disease, the elderly, infants and fetuses, and people suffering from anemia and other conditions that 

affect the oxygen carrying capacity of blood. High CO levels in a concentrated area can result in 

asphyxiation. Studies show a synergistic effect (an effect that is greater than just the sums of the two 

constituents) when CO and O3 are combined (VCAPCD 2003).

Sulfur Dioxide (SO2)

SO2 is a colorless gas with a sharp, irritating odor. It can react in the atmosphere to produce sulfuric acid 

and sulfates, which contribute to acid deposition and atmospheric visibility reduction. It also contributes to 

the formation of PM10. Most of the SO2 emitted into the atmosphere is from burning sulfur-containing 

fossil fuels by mobile sources such as marine vessels and farm equipment and stationary fuel 

combustion, such as coal-fired power plants. SO2 irritates the mucous membranes of the eyes and nose 

and may also affect the mouth, trachea, and lungs. Healthy people may experience sore throats, 

coughing, and breathing difficulties when exposed to high concentrations. SO2 causes constriction of the 

airways and poses a health hazard to asthmatics, which are very sensitive to SO2. Children often 

experience more respiratory tract infections when they are exposed to SO2 (VCAPCD 2003).

Respirable Particulate Matter, 10 Microns (PM10)

PM10 consists of particulate matter, fine dusts and aerosols, 10 microns or smaller in diameter. When 

inhaled, particles larger than 10 microns generally are caught in the nose and throat and do not enter the 

lungs. PM10 can enter the large upper branches of the lungs just below the throat, where they are caught 

and removed (by coughing, spitting, or swallowing).

The primary sources of PM10 include dust from paved and unpaved roads and construction and 

demolition operations. Lesser sources of PM10 include wind erosion, agricultural operations, residential 

wood combustion, smoke, tailpipe emissions, and industrial sources. These sources have different 

constituents and, therefore, varying effects on health. Road dust is composed of many particles other 

than soil dust. It also includes engine exhaust, tire rubber, oil, and truck load spills. Airborne particles 

absorb and adsorb toxic substances and can be inhaled and lodge in the lungs. Once in the lungs, the 

toxic substances can be absorbed into the bloodstream and carried throughout the body. PM10

concentrations tend to be lower during the winter months because weather greatly affects PM10

concentrations. During rain, concentrations are relatively low, and on windy days, PM10 levels can be 

high. Photochemical aerosols, formed by chemical reactions with manmade emissions, may also 

influence PM10 concentrations.

Elevated ambient particulate levels are associated with premature death, an increased number of asthma 

attacks, reduced lung function, aggravation of bronchitis, respiratory disease, cancer, and other serious 
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Draft Environmental Impact Statement

4.1-6 Air Quality March 2014

health effects. Short-term exposure to particulates can lead to coughing, minor throat irritation, and a 

reduction in lung function. Long-term exposure can be more harmful. EPA estimates that 8 percent of 

urban nonsmoker lung cancer risk is due to PM10 in soot from diesel trucks, buses, and cars. Additional 

studies by EPA and the Harvard School of Public Health estimate that 50,000 to 60,000 deaths per year 

in the United States are caused by particulates. PM10 particles collect in the upper portion of the 

respiratory system, affecting the bronchial tubes, nose, and throat. They contribute to aggravation of 

asthma, premature death, increased number of asthma attacks, bronchitis, reduced lung function, 

respiratory disease, aggravation of respiratory and cardiovascular disease, alteration of lung tissue and 

structure, changes in respiratory defense mechanisms, and cancer (VCAPCD 2003).

Fine Particulate Matter, 2.5 Microns (PM2.5)

PM2.5 is a mixture of particulate matter fine dusts and aerosols 2.5 microns or smaller in aerodynamic 

diameter. PM2.5 can enter the deepest portions of the lungs where gas exchange occurs between the air 

and the blood stream. These are the most dangerous particles because the lungs have no efficient 

mechanisms for removing them. If these particles are soluble in water, they pass directly into the blood 

stream within minutes. If they are not soluble in water, they are retained deep in the lungs and can remain 

there permanently. This increases the risks of long-term disease including chronic respiratory disease, 

cancer, and increased and premature death. Other effects include increased respiratory stress and 

disease, decreased lung function, alterations in lung tissue and structure, and alterations in respiratory 

tract defense mechanisms.

EPA’s PM Integrated Science Assessment concluded that “many constituents of PM2.5 can be linked with 

multiple health effects, and the evidence is not yet sufficient to allow differentiation of those constituents 

or sources that are more closely related to specific outcomes” (EPA, 2009c). While some particles may 

have higher or lower toxicity than the average for all fine particles, the body of scientific evidence supports 

the conclusion that reducing all fine particles will result in substantial public health benefits.

PM2.5 particles are emitted from activities such as industrial and residential combustion processes, wood 

burning, and from diesel and gasoline-powered vehicles. They are also formed in the atmosphere from 

gases such as SO2, NOX, ammonia, and VOCs that are emitted from combustion activities and then 

become particles as a result of chemical transformations in the air (secondary particles) (VCAPCD 2003).

4.1.1.2 Attainment Status

Table 4.1-1 displays the NAAQS (EPA 2012f). States and county or regional air districts are required to 

monitor air pollutant levels to ensure that NAAQS are met and, in the event that they are not, to develop 

strategies to meet these standards. Sovereign nations (e.g., Navajo, Southern Ute) also monitor air 

pollutant levels as required. Depending on whether the standards are met or exceeded, the local air basin 

or air quality control region is classified as being in “attainment” or “nonattainment.” Where insufficient 

data exist to make a determination, an area is deemed “unclassified.” A General Conformity determination 

is required for Federally-sponsored, permitted, or funded actions in NAAQS nonattainment areas or in 

certain maintenance areas when the total direct and indirect net emissions of nonattainment pollutants (or 

their precursors) exceed specified thresholds (Clean Air Act Amendments of 1990 Section 176[c]).

The states which comprise the Four Corners region (New Mexico, Arizona, Colorado and Utah) are all 

classified as in attainment for all federal NAAQS (EPA 2012f). In general, the Four Corners region 

experiences low concentrations of most pollutants when compared to Federal standards; however, 

ambient concentrations of ozone and particulate matter have sometimes approached, but not exceeded, 

Federal standards in the three most recent years for which validated data are available. Since the Action 

area is presently in NAAQS attainment or unclassified for all pollutants, a General Conformity 

determination is not applicable to the proposed project.
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Table 4.1-1 National Ambient Air Quality Standards (NAAQS)

Pollutant Type

Averaging 

Time

Concentration

ppmv ppbv μg/m Statistical Form 3

Ozone (O3)

Primary and 

Secondary

8-hour 0.075 75 147

Annual 4th-highest daily maximum 

8-hour concentration averaged over 

3 years

Nitrogen 

Dioxide (NO2)

Primary 1-hour 0.100 100 188 98th percentile averaged over 3 years

Primary and 

Secondary

Annual 0.053 53 100 Annual mean

Sulfur Dioxide 

(SO2)

Primary 1-hour 0.075 75 196 99th percentile of 1-hour daily maximum 

concentrations averaged over 3 years

Secondary 3-hour 0.5 500 1,309 Not to be exceeded more than once 

per year

Carbon 

Monoxide (CO) Primary

1-hour 35 35,000 40,072 Not to be exceeded more than once 

per year 8-hour 9 9,000 10,304

Particulates

(as PM10)

Primary and 

Secondary

24-hour 150 Not to be exceeded more than once per 

year on average over 3 years

Particulates

(as PM2.5)

Primary and 

Secondary

24-hour 35 98th percentile averaged over 3 years

Primary Annual 12 Annual mean averaged over 3 years

Secondary Annual 15 Annual mean averaged over 3 years

Lead (Pb) Primary and 

Secondary

3-month 

rolling

0.15 Not to be exceeded at any time

Source: EPA 2012f

Notes:

All NAAQS generally correspond to an Air Quality Index (AQI) of 100

μg/m3= micrograms per cubic meter (10-6 g/m3)

ppbv = parts per billion by volume (cc/103 m

3

)

ppmv = parts per million by volume (cc/m3)

For gases, equivalent μg/m3calculated from ppmv based on molecular weight and standard conditions:

Standard Ambient Temperature 25°C

Standard Barometric Pressure 760 mm Hg

Standard Molar Volume 24.465 liters/g-mole

4.1.1.3 Hazardous Air Pollutants

Hazardous Air Pollutants (HAPs), also known as toxic air pollutants or air toxics, are those pollutants that 

cause or may cause cancer or other serious health effects, such as reproductive effects or birth defects, 

or adverse environmental and ecological effects. Title III of the CAA Amendments of 1990 currently 

identifies 187 pollutants as HAPs, the Federal term for air toxics. In 2001, the EPA identified 21 HAPs as 

mobile source air toxics, six of which are designated priority pollutants (66 FR 17235): acetaldehyde, 

acrolein, benzene,1, 3-butadiene, diesel exhaust (particulate matter and organic gases), and 

formaldehyde. Diesel particulate matter (DPM, as PM10) is considered a carcinogenic air toxic. An EPA 

assessment “examined information regarding the possible health hazards associated with exposure to 

diesel engine exhaust (DE), which is a mixture of gases and particles. The assessment concludes that 

long-term (i.e., chronic) inhalation exposure is likely to pose a lung cancer hazard to humans, as well as 
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4.1-8 Air Quality March 2014

damage the lung in other ways depending on exposure. Short-term (i.e., acute) exposures can cause 

irritation and inflammatory symptoms of a transient nature, these being highly variable across the 

population” (EPA 2002). However, no EPA standard exists for DPM. 

In addition to DPM from mining equipment and heavy trucks, coal combustion in power plant boilers emits 

a wide range of inorganic and organic HAPs from stacks, according to the EPA (EPA 2011a, 40 CFR 63 

Subpart UUUUU). Inorganic metals include: antimony (Sb), arsenic (As), beryllium (Be), cadmium (Cd), 

chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), manganese (Mn), mercury (Hg), nickel (Ni), and 

selenium (Se). Organics and nonmetallic inorganics include: acetaldehyde, acetophenone, acrolein, 

benzene, benzyl chloride, bis(2-ethylhexyl)phthalate (DEHP), carbon disulfide, chlorobenzene, 

chloroform, cyanide, 2,4-dinitrotoluene, ethyl benzene, ethyl chloride, formaldehyde, hexane, hydrogen 

chloride, hydrogen fluoride, isophorone, methyl bromide, methyl chloride, methyl ethyl ketone, methylene 

chloride, PAHs, phenol, propionaldehyde, tetrachloroethylene, toluene, styrene, and xylenes (ortho-,

meta-, para- isomers).

Mercury and Air Toxics Standards

Coal-fired power plants are the largest source of mercury and acid gas emissions in the United States 

and are responsible for about 50 percent of mercury emissions and about 77 percent of acid gas 

emissions. Most mercury deposited in the western US, however, originates in Asia (Strode et al. 2008). 

Peer-reviewed scientific literature shows that mercury emissions from Electric Generating Units in the 

U.S. enhance mercury deposition and the response of ecosystems in the U.S. (77 FR 9339). Other toxic 

metals emitted from power plants include arsenic, chromium, hexavalent chromium, nickel, and selenium 

(EPA 2013a).

When elemental mercury from the air reaches surface waters via direct and indirect deposition, 

microorganisms can convert it into methylmercury, a highly toxic form that bio-accumulates in fish. 

Humans are primarily exposed to mercury by eating contaminated fish. Methylmercury exposure is a 

particular concern for women of childbearing age, fetuses, and young children because studies have 

linked high levels of methylmercury to damage to the developing nervous system, which can impair 

children’s’ ability to think and learn. Mercury and other power plant emissions also damage the ecological 

environment (EPA 2013a).

On December 16, 2011, the EPA issued the final Mercury and Air Toxics Standards (MATS) and Utility 

New Source Performance Standards (Utility NSPS) rulemakings which were published in the Federal 

Register on February 16, 2012 (77 FR 9304). Promulgated as 40 CFR 63 Subpart UUUUU – National 

Emission Standards for Hazardous Air Pollutants (NESHAPS) for Coal- and Oil-Fired Electric Utility 

Steam Generating Units, the MATS rule establishes emission limitations and work practice standards for 

HAPs emitted from coal- and oil-fired electric utility steam generating units along with requirements to 

demonstrate initial and continuing compliance with the HAP emission limits.

The EPA estimates there are about 1,400 existing generating units affected by the MATS rule –

1,100 coal-fired units and 300 oil-fired units – at about 600 power plants nationwide. As an existing coalfired generating facility, FCPP must comply with specific HAP emissions limits for the following pollutants:

a) Filterable particulate matter (PM) or total nonmercury HAP metals or individual HAP metals 

(antimony, arsenic, beryllium, cadmium, chromium, cobalt, copper, lead, manganese, nickel, 

selenium);

b) Hydrogen chloride or sulfur dioxide; and 

c) Mercury.

The MATS emissions limits are based on existing control technologies that are widely available and 

commonly used in the electric utility industry such as electrostatic precipitators, fabric filters (baghouses), 

flue gas desulfurization (scrubbers), or dry sorbent injection. For existing controlled units such as FCPP 
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Units 4 and 5 which are equipped with baghouses and scrubbers, compliance can be achieved by April 

16, 2015, and maintained as follows (EPA 2013a): 

Operations and Maintenance. Emissions and operating limits apply at all times except during 

periods of startup and shutdown. The plant must operate and maintain all equipment, including air 

pollution control equipment and monitoring equipment, in a manner consistent with safety and 

good air pollution control practices for minimizing emissions. Determination of whether such 

operation and maintenance procedures are being used is based on information available to the 

EPA which may include, but is not limited to, monitoring results, review of operation and 

maintenance procedures, review of operation and maintenance records, and inspection of the 

source.

Testing and Monitoring of PM and non-Mercury Metals. Initial performance testing is required for 

all pollutants to demonstrate compliance with the applicable emission limits. In certain 

circumstances, such as when a unit does not qualify as a low-emissions unit for total nonmercury 

HAP metals, individual nonmercury HAP metals, or filterable PM, compliance with applicable 

emissions limits must be demonstrated through an initial source compliance demonstration test 

and ongoing continuous monitoring through use of either a PM continuous parametric monitoring 

system, a PM continuous emission monitoring system, or quarterly source compliance 

demonstration testing. Units which use PM continuous parametric monitoring system must 

establish a site-specific operating limit corresponding to the results of the source compliance 

demonstration test for the applicable pollutant profile. Alternatively, a source can opt to install and 

operate a PM continuous emission monitoring system.

Testing and Monitoring of Hydrogen Chloride and Mercury. If a unit does not qualify as lowemitter of the acid gas hydrogen chloride (HCl), a source may demonstrate initial and ongoing 

compliance through use of an HCl continuous emission monitoring system, conducting initial and 

quarterly source compliance demonstration testing, or if the unit uses wet or dry flue gas 

desulfurization technology, it may install and operate an SO2 continuous emissions monitoring 

system. If a unit does not qualify as a low-emitter of mercury, a source must demonstrate initial 

and ongoing compliance through use of an approved mercury continuous emissions monitoring 

system or a sorbent trap monitoring system.

Recordkeeping and Reporting. A source must monitor and collect data according to EPA 

specifications and a site-specific monitoring plan and periodically submit electronic reports to the 

EPA. As MATS sources are also Title V (Federal Operating Permit) sources, all monitoring and 

operating data records must be retained for a minimum of 5 years.

On March 28, 2013, the EPA finalized updates to certain emission limits for new power plants under the 

MATS rule, including mercury, PM, SO2, acid gases and certain individual metals. Additionally, certain 

testing and monitoring requirements that apply to new sources were adjusted. The new standards affect 

only new coal- and oil-fired units that will be built in the future (78 FR 24073). The update does not 

change the final emission limits or other requirements for existing power plants such as FCPP. 

4.1.1.4 Federal Visibility Protection and Atmospheric Deposition Control Programs 

Protection of Visibility (Regional Haze Rule)

Visibility and haze are regulated under the Regional Haze Rule of the CAA (40 CFR 51 Subpart P). Under 

the CAA, Class I areas are those in which visibility is protected more stringently than under NAAQS. 

Class I areas include national parks and monuments, wilderness areas, and other areas of special 

national and cultural significance. Section 169A (42 USC Part 7491) of the CAA sets forth a national goal 

for visibility which is the ‘‘prevention of any future, and the remedying of any existing, impairment of 

visibility in Class I areas which impairment results from manmade air pollution’’ (64 FR 35714). 
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Draft Environmental Impact Statement

4.1-10 Air Quality March 2014

There are 156 Class I areas in the United States, 49 of which are national parks and monuments. The 

Regional Haze Rule, enacted in 1999, requires states to establish goals and emission reduction 

strategies for improving visibility in all Class I areas as part of State Implementation Plans (SIPs) as 

geographically applicable. In addition, the EPA encourages states to work together in regional 

partnerships to develop and implement multistate strategies to reduce emissions of visibility-impairing fine 

particle (PM2.5) pollution (64 FR 35714).

Due to long range transport of visibility-impairing fine particles, all 50 states are required to participate in 

planning, analysis, and in many cases, emission control programs. Each state must develop coordinated 

strategies and implement programs to make reasonable progress toward the goal of no “man-made 

impairment” in Class I areas by reducing emissions that contribute to haze. The Regional Haze Rule 

requires states to establish goals for each affected Class I area which improve visibility on the haziest 

days (20 percent most-impaired days) and ensure no degradation occurs on the clearest days (20 percent 

least-impaired days). The reasonable progress goals are designed to reach natural conditions by 2060. 

States are required to conduct certain analyses, including analyses of improvement rates, to ensure that 

they set reasonable progress goals (64 FR 35714, CSU 2013a).

Relationship to NAAQS 

On December 14, 2012, the EPA established the current primary and secondary NAAQS for PM2.5 (see 

Table 4.1-1) as ‘‘requisite to protect the public welfare’’ against visibility impairment on a nationally 

uniform basis as provided in CAA Section 109B. However, consistent with the purposes of Section 169A 

of the CAA, the EPA recognizes that uniform NAAQS cannot eliminate visibility impairment in all parts of 

the country. The regional haze program contributes to improvement of local visibility impacts outside of 

Class I areas that may persist after attainment of the secondary standard (64 FR 35714).

Relationship to BART

The Regional Haze Rule (40 CFR 51 Subpart P) requires the use of Best Available Retrofit Technology 

(BART) at older coal-fired power plants to reduce haze and improve visibility. The BART provision in 

Section 169A(b)(2)(A) addresses the pollution from a specific set of existing sources, such as coal-fired 

power plants near Class I areas (e.g., FCPP, San Juan Generating Station, Navajo Generating Station). 

The BART provision requires EPA to promulgate regulations requiring states to revise their SIPs to 

contain measures to make reasonable progress toward the national visibility goal, including a requirement 

that certain existing stationary sources procure, install, and operate BART (64 FR 35714).

The CAA defines the sources potentially subject to BART as major stationary sources, including 

reconstructed sources, from one of 26 identified source categories which have the potential to emit 250 

tons per year or more of any air pollutant, and which were placed into operation between August 1962 

and August 1977. This set of sources potentially subject to BART was defined in the 1977 amendments to 

the CAA and the 2012 Regional Haze Rule is consistent with these amendments, 35 years later. Chief 

among the 26 source categories are fossil-fuel fired steam electric plants of more than 250 mmBTU/hr 

heat input such as FCPP.

Consistent with the Regional Haze Rule, the Source Specific Federal Implementation Plan for Implementing 

Best Available Retrofit Technology for Four Corners Power Plant: Navajo Nation (40 CFR 49) requires 

FCPP to reduce emissions of NOX and defines emission limits for PM based on emission rates currently 

achieved at FCPP. The FIP requires that Units 4 and 5 meet a BART emission limit of 0.015 lb/MMBtu 

within 60 days after restart following the scheduled major outages for Units 4 and 5 in 2013 and 2014, 

suggesting that the emission limit is achievable through the proper operation of the existing baghouses. 

FCPP must continue to meet the existing 20 percent opacity limit on Units 4 and 5 and is required to comply 

with a 20 percent opacity limit on its material handling operations, including coal handling.
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-11

NOX and PM pollutants contribute to visibility impairment in the mandatory Class I Federal areas 

surrounding FCPP. These pollutants contribute to visibility impairment in the mandatory Class I Federal 

areas surrounding FCPP, of which there are 16 within the 300 km radius as shown in Appendix A, 

Section A3. For NOX emissions, APS has opted to close Units 1, 2, and 3 and install selective catalytic 

reduction (SCR) controls on Units 4 and 5 to meet an emission limit of 0.098 pound NOX per million BTU2

(lbs/mmBTU) heat input each (30-day rolling average), which is an 80 percent reduction from 

0.49 lb/mmBTU. For PM, Units 4 and 5 must meet an emission limit of 0.015 lb/mmBTU, while retaining 

the existing 20 percent opacity limit, through the proper operation of the existing baghouses. EPA is also 

requiring FCPP to comply with a 20 percent opacity limit on its coal and material handling operations 

(77 FR 51620) (Refer to Section 4.1.3).

Atmospheric Deposition

Since the 1970s, implementation of CAA regulations has reduced emissions of NOX, SO2, and mercury 

and reduced the impact of atmospheric deposition on water quality and aquatic ecosystems. However, in 

spite of progress, atmospheric deposition continues to affect water quality and harm aquatic ecosystems 

(GAO 2013).

According to EPA’s 2008 National Emissions Inventory, domestic emissions of NOX declined from about 

26 million tons in 1990 to about 17 million tons in 2008. About 74 percent of this reduction came from 

reduced emissions from power plants and vehicles. Also according to the inventory, emissions of SO2

declined from 23 million tons in 1990 to 10 million tons in 2008, and about 64 percent of this reduction 

came from reduced emissions from power plants (EPA 2011b, GAO 2013).

Three key regulations or programs have contributed to reductions in acid rain precursors: (1) Title II 

emission standards for mobile sources (motor vehicles), (2) actions designed to meet primary NAAQS, and 

(3) the Acid Rain Program. Although neither vehicle emissions standards nor actions to meet primary 

NAAQS are designed to address the deposition effects of NOX and SO2 emissions on surface waters, these 

standards have contributed to overall reductions in these criteria pollutants. In contrast, the Acid Rain 

Program was designed, in part, to address the effect of NOX and SO2 on surface waters (GAO 2013).

The Acid Rain program implements requirements for significant decreases in the emissions of NOX and

SO2 from power plants to improve air quality and protect ecosystems that have been damaged by acid 

rain, including aquatic ecosystems. According to the 2011 National Acid Rain Precipitation Assessment 

Program report, the Acid Rain Program has been successful in reducing NOX and SO2 emissions from 

electric power generation to below levels set by Congress in 1990. By 2009, SO2 emissions from power 

plants were 3.25 million tons lower than the final 2010 cap level of 8.95 million tons, and NOX emissions 

were 6.1 million tons less than the levels projected for 2000. As a result of these reductions, air quality 

has improved and acid deposition has decreased to the extent that some acid-sensitive areas are 

beginning to show signs of recovery. However, current emission reductions pursuant to rules finalized in 

2005 are not sufficient to allow full recovery of acid-sensitive ecosystems. Estimates from modeling 

presented in the National Acid Rain Precipitation Assessment Program report show that additional 

emission reductions are necessary to protect and recover acid-sensitive ecosystems. However, since the 

mandated emission reductions have been achieved, no additional reductions in emissions can reasonably 

be expected from the Acid Rain Program as currently designed (NSTC 2011).

2 One British Thermal Unit (BTU) is the amount of heat required to raise the temperature of one pound (453.6 grams) of pure 

water from 39 to 40 °F (3.9 to 4.4 °C) 
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Draft Environmental Impact Statement

4.1-12 Air Quality March 2014

Two recent developments–new environmental regulations and changing market conditions – could affect 

future NOX and SO2 emissions from power plants (EPA 2013b, GAO 2013): 

The Cross-State Air Pollution Rule promulgated by EPA on July 6, 2011, was challenged in the 

DC Circuit Court of Appeals (Case No. 11-1302, August 21, 2012) on the grounds that the CrossState Air Pollution Rule exceeds the EPA’s statutory authority in two independent respects. For 

each of those two independent reasons, the Court ruled that the Cross-State Air Pollution Rule 

violates federal law and therefore must be vacated. On October 5, 2012, the EPA filed a petition 

with the Court seeking en banc rehearing of the case, and on January 24, 2013, the Court denied 

EPA's petition. On March 29, 2013 the U.S. Solicitor General petitioned the Supreme Court to 

review the DC Circuit Court's decision. The Supreme Court granted certiorari and heard 

arguments for the case on December 11, 2013.

Contemporaneous (occurring at the same time) changes in energy market conditions have been 

weighing on the future viability of coal-fired power plants. Key among these has been the decline in 

the price of natural gas due to increased supply, which has made it more attractive to electric power 

providers in lieu of burning coal. Natural gas emits far less NOX and SO2 than coal, and about half 

as much GHGs for the same level of generating efficiency, and even less in new high-efficiency 

(i.e., combined-cycle) generating units. Thus, as more new power plants opt for natural gas in lieu 

of coal, acid deposition would be expected to continue to decrease overall (GAO 2013).

Similar to NOX and SO2 emission reductions, mercury emissions from domestic anthropogenic (caused 

by human activity) sources declined from about 246 tons in 1990 to about 61 tons in 2008, according to 

the 2008 National Emissions Inventory (NEI). More than half of this decline can be attributed to reduced 

emissions from municipal waste combustors and medical waste incineration. According to the inventory, 

in 1990, these two sources emitted about 108 tons of mercury; in 2008, they emitted less than 2 tons of 

mercury (an approximately 98 percent decrease). Mercury emissions from power plants also declined 

from about 59 tons of mercury in 1990 to about 30 tons of mercury in 2008 (EPA 2011b, GAO 2013).

On February 16, 2012, EPA promulgated the Mercury and Air Toxics Standards establishing for the first 

time emission limitations on mercury and other toxic pollutants, mainly metals, from existing and new 

power plants. Legal challenges are pending before the DC Circuit Court of Appeals; however, 

proceedings have been delayed until EPA, in response to a petition for reconsideration, updates certain 

emission limits for new power plants, which were finalized on March 28, 2013. EPA reopened the public 

comment period on reconsideration of startup and shutdown provisions on June 25, 2013 and argued the 

case before the Court of Appeals on December 10, 2013. Existing sources have 3 years to comply with 

the new standards but can seek an additional year from the permitting authority. When fully implemented, 

EPA projects that the Mercury and Air Toxics Standards will reduce future mercury emissions from 

domestic power plants to about 9 tons by 2016, a 70 percent reduction from 2008 (GAO 2013). 

Acid Rain Program

The EPA’s Acid Rain Program (40 CFR Parts 72 through 78) is the principal regulatory mechanism 

designed to achieve significant environmental and public health benefits through reductions in emissions 

of SO2 and NOX which are the primary causes of acid deposition. To achieve this goal in a cost-effective 

manner the program employs both traditional command-and-control and innovative market-based 

approaches for controlling air pollution. The program also encourages energy efficiency and pollution 

prevention. The Acid Rain Program was developed with consultation from various stakeholders including 

electric utilities, energy companies, pollution control equipment vendors, labor, academia, public utility 

commissions, state environmental agencies, and conservation groups. As an affected source, FCPP is a 

participant in the Acid Rain Program. 

Title IV of the Clean Air Act Amendments of 1990 set the goal of reducing annual SO2 emissions by 

10 million tons per year below 1980 levels. To achieve these reductions, the Act required a two-phase 
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-13

approach to reducing SO2 and NOX emissions from fossil fuel power plants. Phase I began in 1995 and 

affected 445 generating units, mainly at coal-fired electric utility plants located in eastern and mid-western 

states. Phase II began in 2000 and lowered annual emissions limits imposed on large, higher emitting plants 

and also set limits on smaller, cleaner plants fired by coal, oil, and gas, encompassing over 

2,000 generating units rated 25 megawatts or greater nationwide. The Act also required a 2 million ton per 

year reduction in NOX emissions by 2000 using technology such as low-NOX burners in coal-fired units.

FCPP is subject to the principal provisions of the Acid Rain Program, under the authority of the NNEPA and 

EPA Region IX, respectively. This includes appointing a Designated Representative, filing an Acid Rain 

permit application and compliance plan, and monitoring and recording emissions. FCPP is also able to take 

part in allowance trading, and is required to hold sufficient SO2 allowances to cover annual emissions (EPA 

2013b). These provisions are described in detail in Appendix A.

4.1.1.5 Federal Prevention of Significant Deterioration (PSD) Program

Prevention of Significant Deterioration (40 CFR 51.166 and 40 CFR 52.21) provides the overall regulatory 

framework for the permitted operation of FCPP. The PSD Program is designed to: 

Protect public health and welfare;

Preserve, protect, and enhance the air quality in national parks, national wilderness areas, 

national monuments, national seashores, and other areas of special national or regional natural, 

recreational, scenic, or historic value;

Ensure that economic growth will occur in a manner consistent with the preservation of existing 

clean air resources; and

Ensure that any decision to permit increased air pollution in any area to which this section applies is 

made only after careful evaluation of all the consequences of such a decision and after adequate 

procedural opportunities for informed public participation in the decision making process.

PSD does not prohibit new or existing stationary sources, such as oil refineries, factories, or power plants, 

from increasing emissions; rather, PSD is designed to ensure that emissions increases would have no 

significant effect on regional air quality (EPA 2013d).

PSD permitting applies to new major sources or major modifications at existing sources (e.g., FCPP) 

located in NAAQS attainment or unclassified areas for applicable pollutants. Since FCPP is located in an 

NAAQS attainment area for all criteria pollutants (see Table 4.1-4), PSD applies to emissions of NOX,

VOC, CO, SO2, PM10, PM2.5, and lead (EPA 2013d). Details of the requirements of PSD permitting are 

provided in Appendix A. 

A PSD permit would be required for a major modification at FCPP. A recent DC Circuit Court decision on 

PSD rules related to PM2.5 increments and baselines could affect FCPP in the future. On January 22, 

2013, the US Court of Appeals for the District of Columbia Circuit granted a request from the EPA to 

vacate and remand portions of two PSD PM2.5 rules which addressed the Significant Impact Levels so 

that the EPA could correct errors in the rules. The Court also vacated parts of rules establishing PM2.5

Significant Monitoring Concentrations due to regulatory errors. The Court’s decision became final on 

March 15, 2013, and the affected provisions of 40 CFR 51.166 and 52.21 were vacated. The EPA will 

develop replacement PSD PM2.5 rules to correct errors and address the Court’s decision (EPA 2013d).

Specific to the Proposed Action, APS is planning to install SCR NOX control equipment on FCPP Units 4 

and 5 in compliance with 40 CFR 49 BART requirements. Preliminary engineering calculations have 

shown that this would result in byproduct emissions of sulfuric acid gas (H2SO4) in excess of the 7 ton 

per year threshold. APS has prepared the PSD permit application for the Proposed Action, including PSD 

increments modeling. The PSD permitting action is exempt from NEPA; but not from Endangered Species 

Act (ESA) Section 7 reviews. As such, APS is also preparing an ESA impacts analysis (discussed in 
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Draft Environmental Impact Statement

4.1-14 Air Quality March 2014

detail in Section 4.8 Special Status Species). Engineering estimates for NOX and H2SO4 emissions used 

in the impacts analyses were done prior to installation of the SCR equipment. These estimated values 

were conservative and subsequent analyses are expected to result in lower values and lower impacts 

once actual SCR performance is known. The PSD permit will ultimately contain actual values determined 

after the SCR equipment is installed and operating. For Section 7 ESA compliance, EPA has its own 

permitting process, commencing with publication of the draft PSD permit and the public comment period. 

Before EPA can take further action on the PSD permit, it must comply with ESA requirements.

4.1.1.6 Federal Stationary Source Regulations

The NNEPA and EPA are both cooperating agencies in the review of the continued operations of FCPP. 

As described above, the Regional Haze Rule requires the use of BART at older coal-fired power plants to 

reduce haze and improve visibility. In August 2012, EPA issued its final rule for BART compliance at 

FCPP. The final rule allows APS the choice in either complying with the EPA’s 2010 draft rule or the APS 

counter-proposal to meet stated NOX and particulate matter emissions limits. In compliance with the first 

of the options provided by EPA, APS shut down Units 1, 2, and 3 on December 30, 2013 and plans to 

install selective catalytic reduction devices on Units 4 and 5 by July 31, 2018. Because EPA’s decision 

precedes this EIS, the compliance actions are considered part of the environmental baseline for analysis 

of the consequences of the Proposed Action and alternatives. 

Source Specific Federal Implementation Plan (FIP) for Implementing BART for FCPP 

The primary goal of the Source Specific FIP for Implementing Best Available Retrofit Technology for Four 

Corners Power Plant: Navajo Nation [EPA-R09-OAR-2010-0683; FRL-9703-2] is reducing emissions of 

the PM2.5 precursor NOX, thereby improving visibility in the region. The FIP requires FCPP to meet new 

emissions limits required by the BART provision of the CAA for NOX and PM. These pollutants contribute 

to visibility impairment in the 16 mandatory Class I Federal areas surrounding FCPP. Under the FIP, 

FCPP could choose between two emissions control strategies (options) and notify EPA of its choice by 

July 1, 2013 (EPA 2012g), which was extended by EPA to December 31, 2013. The final BART 

determination requires FCPP to meet a plant-wide heat input-weighted emission limit of 0.11 pound per 

million BTU (lb/mmBTU) on a rolling 30-day average, which represents an 80 percent reduction from 

historic NOX emission rates in one of two ways:

FCPP could implement post-combustion NOX controls (i.e., SCR) on Units 1 through 5, with 

implementation of SCR devices on one of the 750 MW units (i.e., 4 or 5) completed within 4 years 

of promulgation, and SCR devices on the remaining units completed within 5 years of 

promulgation.

FCPP could implement an alternative emissions control strategy which required permanent 

closure of Units 1, 2, and 3 by December 31, 2013, and implementation of SCR on Units 4 and 5 

by July 31, 2018, to meet a NOX emission limit of 0.098 lb/mmBTU each on a 30-day rolling 

average. This represents an 80 percent reduction of NOX, down from 0.49 lb/mmBTU. For PM, 

the Rule requires Units 4 and 5 to meet a BART emission limit of 0.015 lb/mmBTU within 60 days 

after restart following the scheduled major outages for Units 4 and 5 in 2013 and 2014. This 

emission limit is achievable through the proper operation of the existing baghouses and FCPP 

must continue to meet the existing 20 percent plantwide opacity limit, which also applies to 

material handling operations, including coal handling.

On December 31, 2013, APS notified EPA that it preferred the alternative FIP emissions control strategy. As 

such, Units 1, 2, and 3 were shut down on December 30, 2013. Thus, emissions from Units 1, 2, and 3 

permanently ceased. In addition, APS will install SCR devices on Units 4 and 5 by July 31, 2018. As a 

result, there would be a transition period from 2014 to mid-2018 during which Units 1, 2, and 3 are shutdown and Units 4 and 5 operate without SCR (refer to Section 4.1.3).
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-15

Title V Operating Permits

Parts 70 and 71 implement Title V of the CAA, 42 U.S.C. 7661, et seq. Title V operating permits are 

legally enforceable documents that permitting authorities issue to major stationary sources of air pollution 

regulating their emissions. Title V major source thresholds are defined by the NAAQS attainment status of 

the jurisdiction, with progressively lower (more stringent) thresholds in moderate, serious, severe, and 

extreme nonattainment areas. Part 70 permits are issued by state and local (county or district) permitting 

authorities. Part 71 permits are issued either directly by the EPA or through tribal EPAs on sovereign 

tribal lands. The Part 71 permit for FCPP is issued by the NNEPA.

Section II.A.2 of the current Part 71 permit for FCPP (NN-ROP-05-07, expires August 1, 2013) contains 

the following enforceable limitations on SO2, NOX, PM, and opacity emissions (40 CFR 49.23):

Minimum 88 percent SO2 control efficiency (reduction) on a plantwide weighted annual average 

basis, calculated daily using heat input data (this is stated as a maximum 12 percent post-control 

residual SO2 emissions compared to pre-control uncontrolled emissions).

Maximum 17,900 pounds per hour SO2 emissions on a plantwide 3-hour rolling average basis.

Maximum 0.050 pound per million BTU particulate matter emission rate from any unit, determined 

by source testing.

Maximum plume opacity of 20 percent from Units 4 and 5, except for brief periods of not more 

than 27 percent opacity lasting not more than six minutes in an hour.

Maximum 0.85 pound per million BTU NOX emission rate from Units 1 and 2 on a 30-day rolling 

average basis.

Maximum 0.65 pound per million BTU NOX emission rate from Units 3, 4 and 5 on a 30-day 

rolling average basis.

Maximum 335,000 pounds per day NOX emissions on a plantwide 24-hour basis, discounted by 

1,542 pounds per hour for any of Units 1, 2, or 3 not operating and discounted by 4,667 pounds 

per hour for any of Units 4 or 5 not operating.

Section II.A.3 of the Part 71 permit contains testing and monitoring requirements to quantify the above 

emissions limitations, and Section II.A.4 contains emissions recordkeeping and reporting requirements. 

Section II.B incorporates by reference provisions of the Phase II Acid Rain permit (40 CFR Parts 72, 72, 

and 75). Section II.C defines Compliance Assurance Monitoring (CAM, 40 CFR Part 64) requirements for 

monitoring particulate matter emissions from Units 1, 2, 3, 4 and 5 per the above limitation. 

Continuous Emissions Monitoring

The FCPP is subject to Part 75 requirements for the monitoring, recordkeeping, and reporting of SO2,

NOX, CO2 emissions, volumetric flow, and opacity data from affected units under the Acid Rain Program 

pursuant to Sections 412 and 821 of the Clean Air Act, 42 U.S.C. 7401-7671, et seq. Part 75 also sets

forth provisions for the monitoring, recordkeeping, and reporting of NOX mass emissions, which are 

required to be controlled to demonstrate compliance with a NOX mass emission reduction program. For 

FCPP, this is consistent with the Source Specific Federal Implementation Plan for Implementing Best 

Available Retrofit Technology for Four Corners Power Plant: Navajo Nation. Under Part 75 operating and 

emissions records must be retained for a minimum of 5 years. 
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Draft Environmental Impact Statement

4.1-16 Air Quality March 2014

4.1.1.7 Mobile Source Regulations

The EPA regulates mobile sources of air pollution in the State of New Mexico and Navajo Nation via 

Federal mobile source standards. In most jurisdictions, self-propelled nonroad mining and construction 

equipment is considered a vehicle, as defined by vehicle codes. Operations at both the FCPP and Navajo 

Mine are subject to mobile source emissions standards.

A vehicle may have an engine that both propels the vehicle and powers equipment mounted on the 

vehicle, typically via hydraulics. As such, single-engine vehicles are generally exempt from direct 

regulation by states, air districts, or sovereign tribes. However, not included in most exemption provisions 

is any nondriveline engine-powered equipment mounted on a vehicle that would otherwise require a 

permit under state, air district, or tribal regulations. An example of this dual-engine configuration would be 

a vacuum street sweeper where an auxiliary engine drives the vacuum blower. Another example would be 

a mobile crane or drilling rig with an independent hoist or draw-works engine, respectively. 

Federal Tier 1 standards for offroad diesel engines were adopted in 1995. Federal Tier 2 and Tier 3 

standards were adopted in 2000 and selectively apply to the full range of diesel offroad engine power 

categories. Both Tier 2 and Tier 3 standards include durability requirements to ensure compliance with 

the standards throughout the useful life of the engine (40 CFR 89.112).

On May 11, 2004, the EPA signed the final rule implementing Tier 4 emission standards which are to be 

phased-in over the period of 2008-2015 (69 FR 38957-39273, June 29, 2004). The Tier 4 standards

require that emissions of PM and NOX be further reduced by about 90 percent. Such emission reductions 

can be achieved through the use of advanced control technologies – including advanced exhaust gas 

after treatment similar to those required by the 2007-2010 standards for highway diesel engines.

4.1.2 Affected Environment Pre-2014

4.1.2.1 Area Climate

The Four Corners area is located in a high desert region averaging over 5,000 feet elevation and over 

270 clear days per year with low humidity and generally warm daytime temperatures. As shown in 

Table 4.1-2, average summer daytime high temperatures in Shiprock and Fruitland are about 93 °F and 

average winter nighttime low temperatures are about 15 °F, with an average year-round temperature of 

about 52 °F. Average annual precipitation is typically 7.8 inches with light snowfalls in winter (WC 2013). 

Average high desert wind speed is about 9 miles per hour with a typical east-by-northeast and west-bysouthwest diurnal wind direction pattern (NOAA 2008, 2013). Due to the area’s aridity, climate change 

could have a substantial impact if the already low precipitation amounts decrease in the future (NM 2005).

Table 4.1-2 Climate Data for the Navajo Nation (Based on Measurements in Shiprock and 

Fruitland)

Month

Maximums

°F

Minimums

°F

Averages

°F

Precipitation

inches

Wind

mph

January 41.6 15.4 28.6 0.6 8.0

February 50.5 21.8 36.1 0.6 8.8

March 59.5 27.2 43.3 0.6 9.9

April 69.0 33.0 51.0 0.5 10.7

May 78.5 41.5 60.0 0.5 10.5

June 88.5 49.9 69.2 0.3 9.8

July 93.0 57.5 75.2 0.7 8.9

August 90.3 56.0 73.3 1.0 8.1
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-17

Month

Maximums

°F

Minimums

°F

Averages

°F

Precipitation

inches

Wind

mph

September 82.9 47.1 65.0 1.0 8.4

October 71.1 35.5 53.4 1.0 8.2

November 55.7 26.2 40.8 0.8 7.9

December 43.7 17.4 30.7 0.7 7.6

Annual 93.0 15.4 52.2 8.3 8.9

Sources: WC 2013, NOAA 2008

4.1.2.2 Ambient Air Quality

Air quality is affected by a variety of sources in the Project Area. Large stationary sources such as FCPP 

and San Juan Generating Station emit substantial amounts of NOX and SO2, along with PM10 and PM2.5.

Oil and gas production facilities in the region emit mainly NOX and VOCs along with some SO2, PM10,

and PM2.5. Light motor vehicles, diesel powered construction equipment, and commercial trucks used in 

the region are another source of these pollutants. Non-combustion sources of PM10 and PM2.5 include 

fugitive dust from roads, construction, demolition, and earthmoving. Finally, commercial and general 

aviation aircraft operating at nearby airports generate emissions that affect air quality.

O3 is a secondary pollutant that is not emitted directly by sources, but rather is formed by a reaction 

between NOX and VOCs in the presence of sunlight. Reductions in O3 concentrations are dependent 

upon reducing emissions of these precursors. Principal sources of O3 precursors are motor vehicles and 

other mobile equipment (including agricultural equipment), solvent use, petroleum industry activities, 

nonelectric agricultural water pumping, and electric utilities operation such as power plant boilers. Another 

secondary pollutant is condensable PM2.5, which is formed by precursors SO2, NOX, VOCs, and 

ammonia (CARB 2005). Condensable PM2.5 is a principal driver of regional haze (visibility degradation); 

therefore, reductions in regional levels of NOX and SO2 would also reduce the amount of haze.

The New Mexico Environmental Department (NMED), Navajo Nation, Southern Ute Indian Tribe, 

Colorado Department of Public Health and Environment, US Forest Service (USFS), and National Park 

Service (NPS) in combination operate an extensive regional air monitoring network composed of 

17 stations that collectively measure the ambient concentrations of six criteria air pollutants: O3, NO2,

SO2, CO, PM10, and PM2.5. Not all monitoring stations are fully instrumented for these pollutants, while 

some sites have not been operating for adequate periods of time to provide representative data for 

determination of attainment status. In addition, one site measures lead (Pb) and sulfate (SO4) within total 

suspended particulate matter (TSP). Each site listed in Table 4.1-3 and shown on Figure 4.1-2 is 

categorized by the monitoring program it operates under (EPA 2012e):

State and Local Air Monitoring Stations (SLAMS) (New Mexico, Colorado)

Tribal Monitors (Navajo Nation, Southern Ute Indian Tribe)

Non-EPA Federal Monitors (USFS, NPS)

Special Purpose Monitors (Colorado)

Interagency Monitoring of Protected Visual Environments (IMPROVE) (NPS)

Data collected by the various monitoring programs is ultimately reported to the EPA, which oversees the 

programs and provides technical support, quality assurance, data processing, and public access (EPA 

2012e). Ambient air monitoring data summaries are presented in Table 4.1-4.
Table 4.1-3 Ambient Monitoring Site Descriptions and Parameters – Four Corners Region

3 2 2 10 2.5
3 2 2 10 2.5
This Page Intentionally Left Blank
A N OZI R A

OCI X E M WE N

A D O

T

"N 34' 0 39°

"N 34' 0 39°

"N 24' 0 36°

"N 24' 0° 63

Table 4.1-4 Ambient Air Monitoring Sites and Parameters in Vicinity of Proposed Action - Four Corners Region

3

2X

2

10

33

10 3
2.5

3

2.5

3

2.5 3

3

4 3

3
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-25

4.1.2.3 Stationary Sources of Air Pollutants – Electric Power Generation 

The electric utility sector involves the generation, transmission, and distribution of electricity. The main 

source of emissions from the sector is power plants. Stack criteria emissions include NOX, SO2, CO, 

VOC, PM10, and PM2.5. Air toxics (HAPs) are emitted in relatively small quantities compared to criteria 

pollutants or greenhouse gases (GHGs). These gases and particulates are released during the 

combustion of fossil fuels, such as coal, oil, and natural gas (EPA 2011a).

Fossil fuel combustion to generate electricity accounts for about 70 percent of SO2 emissions and about 

20 percent of NOX emissions nationwide (EPA 2012c), and coal combustion emits significantly more air 

contaminants, SO2 in particular, than burning natural gas or petroleum to generate electricity (EPA 

2011a). In 2010, about 45 percent of electricity was generated using coal and about 25 percent was 

generated using natural gas. The percentage of natural gas generation has grown in recent years due to 

its reputation as a “clean” fuel and increased supply, which has driven down prices. Petroleum accounts 

for less than 1 percent of electricity generation, down significantly from the past. The remaining 

generation comes from nuclear plants (about 20 percent) and renewable sources (about 10 percent), 

which includes hydroelectric, geothermal, biomass (wood and agricultural wastes), wind, and solar 

(photovoltaic and thermal) (EPA 2012d). Nuclear, hydroelectric, wind, and solar emit no criteria pollutants.

Geothermal may emit some SO2, depending on the resource being tapped, and biomass emits NOX,

SO2, CO, VOC, PM10, and PM2.5 because it involves combustion of nonfossil fuels.

Although PM2.5 is a subset of PM10, it differs from the rest of PM10. While most of ambient PM10 results 

from direct emissions of the pollutant, a significant amount of the ambient PM2.5 results from 

transformation of precursors and condensing of gaseous pollutants in the atmosphere. Other than direct 

PM2.5 emissions, the key pollutants contributing to PM2.5 concentrations in the atmosphere are SO2,

NOX, VOCs, and ammonia (CARB 2005). Pursuant to 40 CFR 49, Source Specific Federal 

Implementation Plan for Implementing Best Available Retrofit Technology for Four Corners Power Plant: 

Navajo Nation, the primary goal of controlling NOX emissions from FCPP is to reduce PM2.5 precursors 

and thereby improve visibility in the region.

Electric power generating resources are rated terms of kilowatts (KW) or megawatts (MW) output 

capacity. As a point of reference, at an average peak load of 10 kilowatts each, 1 megawatt would power 

100 homes. Except for photovoltaic “solar panels” which have no moving parts, all generation of 50 or 60 

Hertz (Hz) sine-wave alternating current (AC) power involves spinning a synchronous generator 

(alternator) from a source of rotational energy (turbine or engine). Utility-scale turbines include hydraulic 

turbines, steam turbines, gas or combustion turbines, and wind turbines. Utility-scale engines include 

spark-ignition natural gas, compression-ignition diesel, or dual fuel.

Steam turbines, due to their ability to use a wide range of heat sources (fuels), are a principal means of 

generating base load3electric power in the U.S. and worldwide. Four Corners is a coal-fired steam 

turbine power plant, as are other large generating stations in the region, such as San Juan and Navajo 

generating stations (San Juan Generating Station and Navajo Generating Station, respectively). While 

turbine-generator arrangements are basically the same, i.e., synchronous direct drive operating at 

3,600 or 1,800 revolutions per minute (rpm) in 60 Hz systems, the source of steam can be a boiler or 

steam generator heated by combustion of fossil fuel, biomass, solar thermal energy, or nuclear fission; 

geothermal energy also powers steam turbines, either directly or indirectly.

3 Base load is continuous generation operating at or near full capacity 24 hours per day for optimum efficiency 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-26 Air Quality March 2014

Four Corners Power Plant

Turbine-generator nameplate capacities at FCPP are 170 megawatts each for Units 1 and 2, 

220 megawatts for Unit 3, and 770 megawatts each for Units 4 and 5. The boilers are rated at 

2,551 million BTU4per hour (mmBTU/hr) each for Units 1 and 2, 3,387 mmBTU/hr for Unit 3, and 

8,612 mmBTU/hr each for Units 4 and 5. Total installed generator capacity is 2,100 megawatts and 

combined boiler ratings are 25,713 mmBTU/hr.

Air pollution control equipment installed on FCPP Units 4 and 5 consists of baghouses (fabric filters) for 

particulate matter (fly ash) control, low-NOX burners designed to reduce NOX emissions, and caustic wet 

scrubbers (i.e., flue gas desulfurization, FGD) which use hydrated lime (calcium hydroxide, Ca(OH)2) in 

solution to control SO2 and acid gases via absorption. Commissioned in 2005, the FGD system consists of 

ten 100-foot tall absorber towers for reduction of SO2 and acid gases to base salts (e.g., CaSO4, CaCl2). 

Mercury (Hg) is incidentally captured by the baghouses and FGD. During operation, boiler exhaust (flue 

gas) passes through the baghouses and then FGD before being released to the atmosphere via the 

auxiliary stacks, bypassing the original Units 4 and 5 stacks. The Units 4 and 5 baghouses trap over 99 

percent of particulate matter and FGD removes approximately 90 percent of SO2 from the flue gas.

The following summarizes stationary sources of emissions from the FCPP. For the representative 

12-year5

period 2000 to 2011, Table 4.1-5 shows historic plantwide generation (megawatt-hours per 

year), SO2 and NOX emissions (short tons per year), and emission rates (kilograms per megawatt-hour, 

same as grams per kilowatt-hour) from FCPP Units 1, 2, 3, 4, and 5, as reported to EPA pursuant to the 

CAA. Emissions of PM are estimated by applying EPA emission factors as noted. 

Projected future emissions from FCPP and regional plants are estimated in Section 4.1.4 referencing the 

7-year historic baseline period of 2005 to 2011 when FGD became active on Units 4 and 5. It is 

necessary to define this historic baseline period because FGD affects boiler performance by a small 

amount, mainly due to increased exhaust back-pressure. In turn, this affects turbine-generator output by a 

small amount. For analysis of future emissions impacts in Section 4.1.4, the continuing operation of Units 

4 and 5 with FGD and SCR represents the future baseline condition of the Proposed Action.

In addition to criteria pollutants, HAP emissions from coal combustion are estimated in Section 4.1.3

based on historic operating data for Units 1, 2, 3, 4 and 5 and projected future utilization of Units 4 and 5 

using EPA emission factors (EPA 2011a, 40 CFR 63 Subpart UUUUU).

Table 4.1-5 Historic Aggregated Part 75 Emissions - ORISPL 2442 Units 1, 2, 3, 4, and 5

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2000 16,109,134 38,332 2.16 46,513 2.62 2,107 0.12

2001 16,472,108 39,564 2.18 47,300 2.60 2,170 0.12

2002 14,768,989 32,847 2.02 41,577 2.55 1,972 0.12

2003 16,857,882 35,094 1.89 45,197 2.43 1,998 0.11

2004 16,134,118 20,943 1.18 40,742 2.29 1,964 0.11

2005 16,829,089 12,653 0.68 41,743 2.25 2,051 0.11

2006 17,162,615 15,192 0.80 44,649 2.36 2,040 0.11

2007 15,700,442 10,239 0.59 41,083 2.37 1,979 0.11

2008 15,821,299 10,398 0.60 40,311 2.31 1,969 0.11

4 British Thermal Unit (BTU): the amount of heat required to raise the temperature of 1 pound of water 1°F, from 39 to 40°F

5

The Title V recordkeeping requirement is 5 years.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-27

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2009 16,804,764 12,450 0.67 42,511 2.29 2,030 0.11

2010 14,955,046 11,043 0.67 38,837 2.36 1,908 0.12

2011 15,066,283 11,822 0.71 38,712 2.33 1,852 0.11

Historic Baseline 16,048,505 11,971 0.68 41,121 2.32 1,976 0.11

Plantwide Share 100% 100% 100% 100%

Source: EPA 2012h

Notes:

PM calculated per AP-42 Chapter 1.1 support document Tables 4-7 and A-3; Title V permit condition (Units 1, 2, and 3); 40 CFR 49 

final rule (Units 4 and 5)

Baseline period is 2005-11 (flue gas desulfurization, FGD, installed on Units 4 and 5)

Navajo Mine

No stationary sources are present at the Navajo Mine; therefore, this discussion is only applicable to 

the FCPP.

Transmission Lines

No stationary sources are present at any of the subject transmission lines; therefore, this discussion is 

only applicable to the FCPP.

4.1.2.4 Mobile Sources of Air Pollutants 

While stationary sources such as power plants and oil refineries emit large quantities of criteria pollutants, 

mobile sources, due to their sheer numbers nationwide, also emit significant amounts. Mobile sources 

include onroad vehicles (e.g., automobiles, trucks, motorcycles), offroad equipment (e.g., earthmovers, 

cranes, portable pumps and generators), trains (e.g., freight, passenger, light rail), vessels (e.g., boats, 

ships, watercraft), and aircraft (e.g., general aviation, commercial, military). Mobile source fuels include 

gasoline, diesel, heavy fuel oil, and jet fuel, all of which emit NOX, SO2, CO, VOC, PM10, and PM2.5 when 

combusted, also HAPs. 

Four Corners Power Plant

Mobile sources associated with FCPP include materials handling equipment, maintenance equipment, 

and support vehicles, as well as employee personal vehicles. Similar to the Navajo Mine, the dominant 

fuel used for mobile sources is diesel fuel and some gasoline. Emissions of fugitive dust occur through 

earthmoving activities and unpaved road travel within the FCPP lease area. Table 4.1-6 below displays 

estimated criteria emissions from mobile sources at FCPP.

Table 4.1-6 Estimated Criteria Emissions from FCPP Mobile Sources

Mobile Sources

VOC

tons/yr

CO

tons/yr

NOX

tons/yr

SOX

tons/yr

PM10

tons/yr

PM2.5

tons/yr

Power Plant Offroad Equipment 0.31 3.69 2.05 0.004 0.13 0.11

Power Plant Onroad Vehicles 0.11 0.76 0.86 0.002 0.04 0.03

Annual Totals 0.42 4.46 2.90 0.006 0.16 0.14

Sources: APS 2012a, EPA 2011a, SCAQMD 2008

Note:

PM10 and PM2.5 for exhaust only, fugitive dust accounted for in BNCC FONSI
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-28 Air Quality March 2014

Navajo Mine

All emissions from the Navajo Mine operations (within the Navajo Mine Permit Area) are considered mobile 

source emissions. Mobile sources associated with Navajo Mine operations include diesel-powered 

draglines, loaders, coal haul trucks, support vehicles, and explosives detonation. The dominant fuel used for 

mobile sources at Navajo Mine is diesel fuel, also referred to as distillate fuel oil no. 2, along with some 

gasoline. In addition to engine exhaust, emissions of fugitive dust, as PM10 and PM2.5, is caused by 

earthmoving and unpaved road travel at primarily at Navajo Mine. Coarser particles (e.g., PM30) also may 

be emitted from activities that disturb topsoil, such as overburden removal at the mine. Other localized 

sources include agriculture, construction, wind-blown dust, pollen, salts, brake dust, and tire wear. Fugitive

dust is the largest component of mining emissions. Table 4.1-7 below summarizes these emissions. 

Table 4.1-7 Estimated Criteria and DPM Emissions from Navajo Mine Operations

Mobile and Fugitive Sources

VOC

tons/yr

CO

tons/yr

NOX

tons/yr

SOX

tons/yr

PM10

tons/yr

PM2.5

tons/yr

DPM

tons/yr

Overburden Drilling and Blasting 19.67 4.99 0.59 3.36 0.97

Coal Seam Drilling and Blasting 241.96 61.39 7.22 4.82 1.40

Overburden Dragline Stripping 62.96 5.56

Mine Extraction Operations and Loading 15.44 65.57 141.75 0.20 183.59 20.58 5.11

Coal Hauling Trucks to Stockpiles 14.16 68.08 125.40 0.18 276.47 27.65 5.31

Mining Support Vehicle Travel 3.36 9.91 33.73 0.05 180.73 18.07 0.77

Unloading at Stockpiles and Railcar Loading 0.71 0.22

Reclamation 124.50 24.90

Coal Preparation Plant (except stockpile) 13.89 4.05

Wind Erosion (coal and spoils piles) 58.82 21.03

Annual Totals 32.96 405.19 367.26 8.23 909.85 124.43 11.20

Source: OSMRE 2012b

Notes:

SOX emissions estimated from FONSI supporting data

PM10 and PM2.5 includes exhaust and fugitive dust as determined in FONSI

For diesels, DPM estimated as 7.8% of CO emissions per offroad emissions factors (SCAQMD 2008)

As shown in Table 4.1-7, mining mobile and fugitive source NOX emissions are a small fraction of FCPP 

stack emissions, about 370 tons per year (OSMRE 2012a, APS 2012a). As FCPP baseline NOX

emissions are about 41,100 tons per year, mining mobile and fugitive sources represent only 0.9 percent 

of total NOX emissions from the combined operations. Also as shown in the table, mining mobile and 

fugitive source PM10 emissions are about 910 tons per year and FCPP baseline PM10 emissions are 

about 1,980 tons per year. 

Transmission Line Mobile Sources

Mobile source emissions associated with transmission line maintenance are included with FCPP offroad 

equipment and onroad vehicle usage shown in Table 4.1-6 and represent a very small fraction of 

overall emissions.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-29

Hazardous Air Pollutants

Coal combustion in power plant boilers emits a wide variety of inorganic and organic HAPs. Tables 4.1-8

and 4.1-9 show estimated average annual HAP emissions from FCPP based on historic (pre-Project) 

operating data prior to implementation of 40 CFR 63 Subpart UUUUU for Units 1, 2, 3, 4, and 5.

Table 4.1-8 Estimated Historic HAP Metals Emissions - ORISPL 2442

HAP (Metals)

2000-11

Units 1 – 5

Average lbs/yr

Antimony (Sb) 156

Arsenic (As) 3,552 

Beryllium (Be) 182

Cadmium (Cd) 442

Chromium (Cr) 2,252 

Cobalt (Co) 866

Copper (Cu) 4,938 

Lead (Pb) 3,639 

Manganese (Mn) 4,245 

Mercury (Hg) 719

Nickel (Ni) 2,426 

Selenium (Se) 11,262 

Average FCPP Generation (MW-hrs/yr) 16,056,814 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-30 Air Quality March 2014

Table 4.1-9 Estimated Historic HAP Nonmetals Emissions - ORISPL 2442

HAP

(Organics and Inorganics)

2000-11

Units 1 – 5

Average lbs/yr

Acetaldehyde 4,938

Acetophenone 130

Acrolein 2,512

Benzene 11,262

Benzyl chloride 6,064

Bis (2-ethylhexyl)phthalate (DEHP) 632

Carbon disulfide 1,126

Chlorobenzene 191

Chloroform 511

Cyanide 21,659

2,4-Dinitrotoluene 2

Ethyl benzene 814

Ethyl chloride 364

Formaldehyde 2,079

Hexane 580

Hydrogen chloride 10,396,140

Hydrogen fluoride 1,299,518

Isophorone 5,025

Methyl bromide 1,386

Methyl chloride 4,592

Methyl ethyl ketone 3,379

Methylene chloride 2,512

PAHs (composite total) 180

Phenol 139

Propionaldehyde 3,292

Tetrachloroethylene 373

Toluene 2,079

Styrene 217

Xylenes (o,m,p) 321

Average Generation (MW-hrs/yr) 16,056,814
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-31

4.1.2.5 Visibility / Regional Haze

Regional haze is visibility impairment caused by multiple sources and activities which emit fine particles 

and their precursors and which are located across a broad geographic area. In 1980, when adopting the 

initial visibility protection provisions of the CAA, Congress specifically recognized that the ‘‘visibility 

problem is caused primarily by emission into the atmosphere of SO2, NOX, and particulate matter (PM), 

especially fine particulate matter (PM2.5), from inadequately controlled sources.’’ Fine particulate matter 

such as sulfates, nitrates, organic carbon, elemental carbon, and soil dust impairs visibility by scattering 

and absorbing sunlight, can cause health effects and increase mortality in humans, and contributes to 

environmental effects such as acid deposition (acid rain) and eutrophication (depletion of oxygen in lakes 

and ponds) (64 FR 35714).

Visibility has been defined as “the greatest distance at which an observer can just see a black object viewed 

against the horizon sky.” An object is usually referred to as at “threshold contrast” when the difference 

between the brightness of the sky and the brightness of the object is reduced to such a degree that an 

observer can just barely see the object. Visibility is closely associated with conditions that allow appreciation 

of landscape features, which is especially true in the desert southwest, where recognition and appreciation 

of the form, contrast detail, and color of near and distant features is valued by society (CIRA 1999).

Visibility degradation is caused by diffraction, refraction, phase-shift, and absorption of light by 

atmospheric particles, aerosols, and gases that are nearly the same size as the wavelengths of the visible 

light spectrum. Without the effects of anthropogenic (caused by human activity) air pollution, maximum 

natural visual range in the western United States is about 120 miles (180 km) and about 80 miles 

(110 km) in the east. Sulfates, including ammonium sulfate, comprise about 70 percent of visibility 

impacts in the east and about 30 percent in the west. Due to photochemistry, the visibility impacts of 

nitrates tend to be highest during the winter (less sunlight) and lowest during the summer (more sunlight) 

(CIRA 1999).

Sulfates and nitrates resulting from SO2 and NOX emissions also contribute to visibility impairment. 

Sulfates, including ammonium sulfate, comprise about 70 percent of visibility impacts in the East and 

about 30 percent in the West. Due to photochemistry, the visibility impacts of nitrates tend to be highest 

during the winter and lowest during the summer. In the West, nitrates and carbon are factors, but sulfates 

have been implicated as a cause of visibility impairment in many of the Colorado River Plateau national 

parks, including the Grand Canyon, Canyonlands, and Bryce Canyon (EPA 2013c, CIRA 1999).

The role of regional transport of fine particles and aerosols which contribute to elevated PM levels and 

regional haze impairment has been well-documented through decades of research. Data from the 

Interagency Monitoring of Protected Visual Environments (IMPROVE) network (described below) shows 

that chronic visibility impairment occurs at most national park, national monument, and wilderness area 

monitoring sites in the west. Average visual range in many Class I areas in the West is 60 to 90 miles 

(100 to 150 km) equivalent to 13.6 to 9.6 deciviews, 6or about 50 to 70 percent of the visual range that 

would exist without anthropogenic air pollution from stationary and mobile sources (64 FR 35714). 

Table 4.1-10 through 4.1-16 provide historic ozone and ozone precursor levels in the Four Corners 

Region. Table 4.1-17a shows trends in regional visibility over the same time period.

6 One deciview represents the minimal perceptible change in visibility to the human eye and is proportional to the logarithm of the 

light extinction coefficient. As such, it is linear with respect to perceived visual changes over its entire range, analogous to the 

decibel scale for sound. A 1 dv change represents about a 10 percent change in the extinction coefficient. The higher the 

deciview value, the poorer the visibility.
Table 4.1-10 Historic Ozone Trends

Table 4.1-11 Historic Nitrogen Dioxide Trends

Table 4.1-12 Historic Sulfur Dioxide Trends
Table 4.1-13 Historic Carbon Monoxide Trends
T

abl

e

4.1-14

Historic

Res

pira

ble

P

articulate (PM ) Trends

3

3
3

3
T

abl

e

4.1-15

Historic

Fin

e

P

articul

ate (PM ) Trends

3

3
T

abl

e

4.1-16

T

S

P /

L

e

a

d / Sulfate

3 3

4

3
Table 4.1-17a Historic Composite Visibility - 10 IMPROVE Sites
Table 4.1-17b Historic Visibility - 10 IMPROVE Sites
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-44 Air Quality March 2014

Visibility conditions are presented by individual park or wilderness in Table 4.1-17b to show how conditions 

vary geographically. The trends shown on Table 4.1-17a are represented graphically on Figure 4.1-3. As 

can been seen in the graphic, deciviews have steadily decreased; thus, regional visibility has improved 

during the 11-year period, apparently due to improved control of air pollution from sources such as power 

plants. Thus, progress is apparent toward the future goal of the Regional Haze Rule, i.e., achieving natural 

conditions by 2060.

Figure 4.1-3 Historic Composite Visibility Trend

Four Corners Air Quality Study

In 2009, the NMED Air Quality Bureau released the Air Quality Modeling Study for the Four Corners Region

(NMED 2009). The main study was conducted during the latter half of 2007 in response to concerns about 

the air quality impacts of growth comprising many types of sources, especially the oil and gas industry and 

electric power generation, on Class I and surrounding Class II areas in the Four Corners region. The 

speculative study examined five conceptual emissions mitigation scenarios that could be implemented in the 

future with the aim of halting further deterioration of regional air quality and possibly improving it. 

The NMED, in coordination with the Colorado Department of Public Health and Environment, convened 

the Four Corners Air Quality Task Force comprised of states, tribes, Federal land managers and other 

stakeholders to develop strategies for air quality management in the region. As part of the effort, the Four 

Corners Air Quality Task Force identified the need to model the air quality impacts of various proposed 

mitigation strategies being developed by Task Force working groups. Estimates of mitigation scenario 

effects on ozone, particulate matter, visibility (regional haze), and atmospheric deposition (acid rain, 

metals) were needed. In addition, peak ozone and visibility impacts in the Mesa Verde, San Pedro Parks, 

and Weminuche Class I areas and surrounding Class II areas were of primary interest. In response to 

these requirements, NMED conducted a comprehensive atmospheric modeling study.

As a result, a high resolution (4 x 4 km [2.5 x 2.5 mile] horizontal grid cell size) regional scale dispersion 

model of the Four Corners region was developed. This effort produced a regional air quality planning tool 

which can be used to evaluate impacts of both future development projects and alternative emission 

0.00

2.00

4.00

6.00

8.00

10.00

12.00

14.00

2000 2002 2004 2006 2008 2010

Deciviews (dV)

Year

Lowest 20% of Days

Highest 20% of Days

Average of all Days
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-45

Section 4 1_Air Quality_031014.docx

reduction strategies. Results of the modeling study are intended to inform the direction of future air quality 

management efforts in the Four Corners region.

An updated emissions inventory for 2005 and a projected inventory for 2018 were developed for use in 

this study. Inventories previously developed for the Western Regional Air Partnership were used as the 

main starting points for these inventories. The 2005 and 2018 inventories comprised emissions from 

electric power generation, oil and gas exploration and production, other proximate anthropogenic sources, 

along with applicable mobile source, fugitive dust, biogenic, and wildfire emissions. The resulting modelready emissions were used to estimate the air quality impacts of five alternative mitigation scenarios 

focused on various combinations of emissions reductions from electric power generation and oil and gas 

activities in the Four Corners region.

Emissions in the CAMx model changed very little overall between the 2005 base case and the 2018 base 

case; the ozone results are nearly identical. Annual fourth-highest daily maximum 8-hour average ozone 

values predicted show either no change or a decline of 1 or 2 ppb in the fourth-highest modeled daily 

maximum 8-hour ozone concentrations at most locations. Results of an ozone source apportionment 

analysis performed on the 2018 base case scenario showed that local oil & gas and electric generating 

unit (EGU) sources are the biggest contributors to local ozone episodes.

Ozone concentrations predicted under the 2018 base case with each of five mitigation scenarios were 

compared for two key months; April (when high ozone is predicted at higher elevations in the San Juan 

and other mountain ranges) and July (when high ozone is predicted at lower elevations). Time series of 

hourly predicted ozone show that ozone reductions under the mitigation scenarios are generally less than 

5 ppb. Some increases in ozone are evident during some off-peak hours due to negative benefits of NOx

reductions under VOC limited conditions. Seasonal differences showed that the higher ozone values 

observed during the late spring are more heavily influenced by precursor sources and ozone transport 

from outside the 4 km domain, compared to summer values. 

The five emissions mitigation scenarios focused on EGU and oil and gas sources in the Four Corners area. 

Results in the 2018 base case inventory included a 70% NOx reduction and a 16% SO2 reduction from local 

(i.e., 4 km domain) EGU sources as well as an approximate 50% VOC reduction and a 16% NOx reduction 

from local oil and gas sources. EGU and oil & gas together account for 75% of 4 km domain NOx emissions 

(oil and gas alone accounts for 37% of 4 km domain NOx emissions) and 33% of 4 km domain VOC 

emissions. Thus, the combined EGU and oil and gas NOx controls considered here amount to roughly a 

50% reduction in local NOx emissions and a 16% reduction in local VOC emissions. These mitigation 

scenarios resulted in peak predicted ozone changes generally limited to less than about 5 ppb. 

A combination of VOC and NOx controls on oil and gas sources is more effective at reducing ozone than 

VOC or NOx controls alone. There also appears to be a synergistic effect resulting in enhanced ozone 

reduction when the EGU controls are combined with the oil and gas controls: EGU controls alone result in 

inconsistent reductions from day to day depending on meteorological conditions but combining them with 

the oil and gas controls appears to put a “floor” under the reductions resulting in larger and more 

consistent reductions. 

4.1.2.6 Atmospheric Deposition / Acid Rain

Atmospheric deposition transfers air pollutants such as NOX, SO2, and mercury (Hg) from the air to the 

earth’s surface and affects water quality due to precipitation runoff into waterbodies. Nitrogen compounds 

such as ammonia (NH3) contribute to nutrient over-enrichment (i.e., algae blooms) which can result in 

oxygen depleted areas known as “dead zones,” where fish and other organisms cannot survive. Once in 

water, mercury becomes concentrated in fish and can harm the health of individuals who consume these 

fish, particularly children. Further, acid rain threatens certain aquatic ecosystems, especially in highaltitude mountain lakes and streams with limited buffering capacity (EPA 2013c, GAO 2013).
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-46 Air Quality March 2014

Nitrogen oxides react with moisture and oxygen in the atmosphere to form nitric acid (HNO3), nitrates (NO3

-

), and nitrites (NO2

-

) while sulfur dioxide reacts to form sulfuric acid (H2SO4), sulfates (SO4

2-), and sulfites 

(SO3

2-). Other inorganic pollutants include ammonium ion (NH4+

), chloride ion (Cl-), light metals such as 

beryllium (Be), calcium (Ca), magnesium (Mg), potassium (K), and sodium (Na), and heavy metals such as 

antimony (Sb), arsenic (As), cadmium (Cd), chromium (Cr), cobalt (Co), copper (Cu), lead (Pb), manganese 

(Mn), mercury (Hg), nickel (Ni), and selenium (Se). Organic pollutants can include polychlorinated biphenyls 

(PCBs) and PAHs, both of which are carcinogenic, along with some metals listed above.

The term “acid rain” is a broad reference to mixtures of wet and dry deposition containing higher than 

normal amounts of sulfuric and nitric acids. The main anthropogenic precursors of acid rain are SO2 and 

NOX emissions from fossil fuel combustion. In the United States, about 67 percent of all SO2 and about 

25 percent all NOX is emitted from fossil fuel electric power generation, in particular, coal-fired power 

plants. Acid rain occurs when these gases react (hydrolyze) in the atmosphere with water, oxygen, and 

other chemicals to form a weak solution of sulfuric and nitric acids, typically pH73 to 5. When SO2 and 

NOX are released from power plant stacks and other sources, prevailing winds transport these 

compounds across state and national borders, sometimes over hundreds of miles, resulting in 

environmental impacts far away from the pollution source. Acid rain causes acidification of lakes and 

streams and contributes to damage to trees and many sensitive forest soils. It also accelerates the decay 

of building materials and paints, including irreplaceable buildings, statues, and sculptures which are part 

of the national cultural heritage (EPA 2013c).

The EPA and National Acid Deposition Program (NADP) operate nationwide networks of depositionoriented monitoring sites. Sites in the vicinity of the Project area are listed in Table 4.1-18 and shown on

Figure 4.1-4. Descriptions of applicable monitoring projects are provided in Appendix A.

CASTNET Data

For the historic 12-year period from 2000 through 2011, Tables 4.1-19a (metric units) and 4.1-19b (English 

units) show measured precipitation, wet and dry ammonium (NH4

+

), wet and dry nitrate (NO3

-

), wet and dry 

sulfate (SO4

2-), dry nitric acid (HNO3), and dry sulfur dioxide (SO2) as reported by CASTNET for cumulative 

annual periods (EPA 2013e). Precipitation units are depth in centimeters (cm) and inches (in); deposition 

units are mass per unit area in kilograms per hectare (kg/ha) and pounds per acre (lb/acre). 

Table 4.1-20 shows total nitrogen compounds and total sulfur compounds deposition rates versus annual 

precipitation amounts. Total deposition is expressed two ways, absolute in units of kilograms per hectare 

(kg/ha) and normalized in units of kilograms per hectare per decimeter precipitation (kg/ha-dm). 

7

pH is defined as the negative (base 10) logarithm of the hydrogen ion concentration (moles per liter). For example, if [H+] = 

0.0001 moles/liter, then pH = 4.
Table 4.1-18 Deposition Monitoring Sites - Four Corners Region and Vicinity

1

1

2

3

4
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"N 0' 0° 53

"N 0' 0° 53

T

able

4.1-19a

Historic

S

p

e

ciated 

D

epo

sition - 4

C

A

S

T

N

E

T

Site

s (m

etric units)

4 3 3 3 4 4 2 4
T

able

4.1-19b

Historic

S

p

e

ciated 

D

epo

sition - 4

C

A

S

T

N

E

T

Site

s (English units)

4 3 3 3 4 4 2 4
Table 4.1-20 Historic Composite Deposition Rates - 4 CASTNET Sites
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-54 Air Quality March 2014

Deposition is normalized in units of kilograms per hectare per decimeter precipitation (kg/ha-dm) to 

eliminate the variability of precipitation amounts and discern the actual deposition contents of precipitation 

(i.e., concentrations). 

Figures 4.1-5 and 4.1-6 illustrate historic deposition trends as measured by the CASTNET monitoring 

program. Figure 4.1-5 shows absolute amounts of precipitation, total nitrogen compounds, and total sulfur 

compounds over the 12-year period. Since the amount of deposition is proportional to the amount of 

precipitation received, Figure 4.1-6 shows normalized total nitrogen compounds and total sulfur 

compounds where normalized precipitation is expressed as unity.

Figure 4.1-5 Historic CASTNET Precipitation and Deposition

Figure 4.1-6 Historic CASTNET Deposition Rates - Normalized

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

4.5

5.0

2000 2002 2004 2006 2008 2010 2012

Precip, dm

or Dep, kg/ha

Year

Precip, dm

Total N, kg/ha

Total S, kg/ha

0.0

0.2

0.4

0.6

0.8

1.0

1.2

2000 2002 2004 2006 2008 2010 2012

Dep Rate, kg/ha-dm

Year

Normalized Precip

Total N, kg/ha-dm

Total S, kg/ha-dm
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-55

As shown in Table 4.1-20 and Figure 4.1-7, the data suggests the average rate of nitrogen and sulfur 

deposition in the Four Corners region has been trending downward over the 12-year period. The data 

also suggests that total nitrogen compound deposition has decreased by about 30 percent and total sulfur 

compound deposition has decreased by about 24 percent, as measured by CASTNET from 2000 to 2011. 

These apparent downward trends suggest that regional emissions of NOX and SO2 from stationary and 

mobile sources may have decreased overall due to improved emission controls, lower-polluting fuels, and 

changes in economic activity, among other factors.

National Trends Network

Annual summary data from seven NTN sites located at Canyonlands, Grand Canyon, Mesa Verde, 

Petrified Forest, Alamosa, Bandelier, and Green River is aggregated to provide a general estimate of 

historic deposition in the Four Corners region. Deposition is calculated by NADP based on the NTN wet 

bucket method and measured precipitation. (NADP 2013) 

For the historic 12-year period from 2000 through 2011, Tables 4.1-21a (metric units, kg/ha) and 4.1-21b

(English units, lb/acre) show measured precipitation, free acidity (H+as pH), calcium (Ca2+), magnesium 

(Mg2+), sodium (Na+), potassium (K+), sulfate (SO4

2-), nitrate (NO3-

), chloride (Cl-), and ammonium (NH4

+

)

ions, also total inorganic nitrogen (N) as reported by NTN for cumulative annual periods (NADP 2013).

Table 4.1-22 shows absolute and normalized acid/base ion deposition rates in metric units for sulfate, 

nitrate, chloride, and ammonium. Table 4.1-23 shows absolute and normalized light metal ion deposition 

rates in metric units for calcium, magnesium, potassium, and sodium.

Table 4.1-21a Historic Speciated Deposition - 7 NTN Sites (metric units)

Year

Precip

cm

Ca

kg/ha

Mg

kg/ha

K

kg/ha

Na

kg/ha

NH4

kg/ha

NO3

kg/ha

Inorg N

kg/ha

Cl

kg/ha

SO4

kg/ha

H

+

kg/ha

2000 23.7 1.96 0.19 0.16 0.33 1.30 7.99 2.82 0.52 4.52 0.06

2001 25.9 2.34 0.25 0.14 0.42 1.64 8.59 3.22 0.60 5.10 0.05

2002 16.3 1.76 0.15 0.08 0.21 0.98 3.53 1.56 0.30 2.26 0.01

2003 18.7 1.56 0.15 0.10 0.17 1.04 4.37 1.80 0.27 2.41 0.02

2004 28.1 3.38 0.33 0.23 0.58 2.47 10.58 4.32 0.91 6.45 0.06

2005 33.6 3.30 0.30 0.23 0.52 2.66 10.43 4.42 0.72 7.65 0.09

2006 26.8 3.18 0.32 0.18 0.41 2.01 8.33 3.45 0.61 4.85 0.04

2007 26.6 3.49 0.31 0.20 0.50 1.99 8.32 3.43 0.77 5.10 0.05

2008 25.9 3.05 0.30 0.18 0.43 1.58 7.02 2.81 0.65 4.09 0.04

2009 21.1 5.87 0.34 0.29 0.48 1.35 5.10 2.20 0.61 4.19 0.02

2010 34.7 6.12 0.73 0.37 0.93 3.77 13.89 6.07 1.46 7.70 0.07

2011 25.0 3.79 0.38 0.21 0.52 2.05 7.80 3.36 0.72 4.76 0.03

Mean 25.5 3.32 0.31 0.20 0.46 1.91 8.00 3.29 0.68 4.92 0.05

Median 25.9 3.24 0.31 0.19 0.46 1.82 8.15 3.29 0.63 4.81 0.04

Cumulative 306.4 39.80 3.75 2.37 5.51 22.86 95.96 39.45 8.12 59.07 0.54

Source: NADP 2013

Notes:

Aggregated data for 7 sites: AZ03, AZ97, CO00, CO99, NM07, UT09, UT98; Site AZ97 commenced operation 2003 (no data for 

2000, 2001, 2002)
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Draft Environmental Impact Statement

4.1-56 Air Quality March 2014

Table 4.1-21b Historic Speciated Deposition - 7 NTN Sites (English units)

Year

Precip

in

Ca

lb/acre

Mg

lb/acre

K

lb/acre

Na

lb/acre

NH4

lb/acre

NO3

lb/acre

Inorg N

lb/acre

Cl

lb/acre

SO4

lb/acre

H

+

lb/acre

2000 9.3 1.75 0.17 0.14 0.30 1.16 7.13 2.52 0.46 4.03 0.06

2001 10.2 2.09 0.22 0.12 0.38 1.46 7.67 2.87 0.54 4.55 0.05

2002 6.4 1.57 0.14 0.07 0.19 0.87 3.15 1.39 0.27 2.01 0.01

2003 7.4 1.39 0.13 0.09 0.15 0.93 3.90 1.61 0.24 2.15 0.02

2004 11.0 3.02 0.30 0.20 0.52 2.21 9.44 3.85 0.81 5.75 0.05

2005 13.2 2.94 0.27 0.20 0.46 2.38 9.30 3.94 0.64 6.83 0.08

2006 10.6 2.84 0.29 0.16 0.36 1.79 7.44 3.07 0.55 4.33 0.04

2007 10.5 3.11 0.27 0.18 0.45 1.78 7.42 3.06 0.69 4.55 0.04

2008 10.2 2.72 0.27 0.16 0.38 1.41 6.27 2.51 0.58 3.65 0.04

2009 8.3 5.23 0.31 0.26 0.43 1.21 4.55 1.97 0.55 3.74 0.02

2010 13.7 5.46 0.65 0.33 0.83 3.36 12.40 5.42 1.30 6.87 0.06

2011 9.9 3.38 0.34 0.19 0.46 1.83 6.96 2.99 0.64 4.25 0.03

Mean 10.1 2.96 0.28 0.18 0.41 1.70 7.13 2.93 0.60 4.39 0.04

Median 10.2 2.89 0.27 0.17 0.41 1.62 7.28 2.93 0.56 4.29 0.04

Cumulative 120.6 35.50 3.34 2.11 4.91 20.40 85.62 35.20 7.25 52.70 0.49

Source: NADP 2013

Notes:

Aggregated data for 7 sites: AZ03, AZ97, CO00, CO99, NM07, UT09, UT98

Site AZ97 commenced operation 2003 (no data for 2000, 2001, 2002)

Table 4.1-22 Historic Acid/Base Ion Deposition Rates - 7 NTN Sites

Year

Precipitation

Sulfate

Composite

Nitrate

Composite

Chloride

Composite

Ammonium

Composite

cm dm kg/ha kg/ha-dm kg/ha kg/ha-dm kg/ha kg/ha-dm kg/ha kg/ha-dm

2000 23.7 2.37 4.52 1.90 7.99 3.37 0.52 0.22 1.30 0.55

2001 25.9 2.59 5.10 1.97 8.59 3.32 0.60 0.23 1.64 0.63

2002 16.3 1.63 2.26 1.39 3.53 2.17 0.30 0.18 0.98 0.60

2003 18.7 1.87 2.41 1.29 4.37 2.33 0.27 0.14 1.04 0.56

2004 28.1 2.81 6.45 2.30 10.58 3.77 0.91 0.32 2.47 0.88

2005 33.6 3.36 7.65 2.28 10.43 3.10 0.72 0.21 2.66 0.79

2006 26.8 2.68 4.85 1.81 8.33 3.11 0.61 0.23 2.01 0.75

2007 26.6 2.66 5.10 1.92 8.32 3.13 0.77 0.29 1.99 0.75

2008 25.9 2.59 4.09 1.58 7.02 2.72 0.65 0.25 1.58 0.61

2009 21.1 2.11 4.19 1.98 5.10 2.41 0.61 0.29 1.35 0.64

2010 34.7 3.47 7.70 2.22 13.89 4.00 1.46 0.42 3.77 1.09

2011 25.0 2.50 4.76 1.90 7.80 3.12 0.72 0.29 2.05 0.82

Trend 0.24 0.19 0.14 0.27

Change 14% 7% 75% 47%

Source: NADP 2013

Notes:

Aggregated data for 7 sites: AZ03, AZ97, CO00, CO99, NM07, UT09, UT98; Site AZ97 commenced operation 2003 (no data for 

2000, 2001, 2002)
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-57

Table 4.1-23 Historic Light Metal Ion Deposition Rates - 7 NTN Sites

Year

Precipitation

Calcium

Composite

Magnesium

Composite

Potassium

Composite

Sodium

Composite

cm dm kg/ha kg/ha-dm kg/ha kg/ha-dm kg/ha kg/ha-dm kg/ha kg/ha-dm

2000 23.7 2.37 1.96 0.83 0.19 0.08 0.16 0.07 0.33 0.14

2001 25.9 2.59 2.34 0.90 0.25 0.09 0.14 0.05 0.42 0.16

2002 16.3 1.63 1.76 1.08 0.15 0.09 0.08 0.05 0.21 0.13

2003 18.7 1.87 1.56 0.83 0.15 0.08 0.10 0.05 0.17 0.09

2004 28.1 2.81 3.38 1.21 0.33 0.12 0.23 0.08 0.58 0.21

2005 33.6 3.36 3.30 0.98 0.30 0.09 0.23 0.07 0.52 0.15

2006 26.8 2.68 3.18 1.19 0.32 0.12 0.18 0.07 0.41 0.15

2007 26.6 2.66 3.49 1.31 0.31 0.12 0.20 0.08 0.50 0.19

2008 25.9 2.59 3.05 1.18 0.30 0.12 0.18 0.07 0.43 0.17

2009 21.1 2.11 5.87 2.77 0.34 0.16 0.29 0.14 0.48 0.23

2010 34.7 3.47 6.12 1.76 0.73 0.21 0.37 0.11 0.93 0.27

2011 25.0 2.50 3.79 1.51 0.38 0.15 0.21 0.09 0.52 0.21

Trend 1.13 0.10 0.05 0.10

Change 155% 139% 108% 84%

Source: NADP 2013

Notes:

Aggregated data for 7 sites: AZ03, AZ97, CO00, CO99, NM07, UT09, UT98; Site AZ97 commenced operation 2003 (no data for 

2000, 2001, 2002)

Figures 4.1-7a, 4.1-7b, and 4.1-7c illustrate the normalized rates shown in Tables 4.1-22 and 4.1-23 using 

compatible Y-axis scales (i.e., 0-1, 0-2, 0-4). Figure 4.1-7a shows normalized magnesium, potassium, 

sodium, chloride, and acidity. Figure 4.1-7b shows ammonium and total inorganic nitrogen. Figure 4.1-7c 

shows calcium, nitrate, and sulfate. In each of these normalized figures, precipitation is expressed as unity.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-58 Air Quality March 2014

Figure 4.1-7a Historic NTN Deposition Rates – Normalized (Mg, K, Na, Cl, H+)

Figure 4.1-7b Historic NTN Deposition Rates – Normalized (Ammonia)

0.00

0.20

0.40

0.60

0.80

1.00

1.20

2000 2002 2004 2006 2008 2010 2012

Dep Rate, kg/ha-dm

Year

Normalized Precip

Mg, kg/ha-dm

K, kg/ha-dm

Na, kg/ha-dm

Cl, kg/ha-dm

H+, kg/ha-dm

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

2000 2002 2004 2006 2008 2010 2012

Dep Rate, kg/ha-dm

Year

Normalized Precip

NH4, kg/ha-dm

Inorg N, kg/ha-dm
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-59

Figure 4.1-7c Historic NTN Deposition Rates – Normalized (Ca, NO3, SO4)

As shown in Tables 4.1-22 and 4.1-23 and Figures 4.1-7a, 4.1-7b, and 4.1-7c, NTN data suggests the 

average rate of deposition for all analytes in the Four Corners region has been trending upward over the 

12-year period. The data also suggests that sulfate, nitrate, chloride, and ammonium deposition has 

increased by about 14 percent, 7 percent, 75 percent, and 47 percent, respectively, over the 12-year 

period. Further, calcium, magnesium, potassium, and sodium deposition has increased by an average of 

about 120 percent, as measured by NTN from 2000 to 2011.

The lower rates of increase for sulfate and nitrate suggests that regional emissions of NOX and SO2 from 

stationary and mobile sources may not be increasing as rapidly overall due to improved emission controls 

and lower-polluting fuels; however, these factors could be offset by use of agricultural chemicals such as 

fertilizers which can contain these compounds. The higher rate of increase for the metallic analytes 

(calcium, magnesium, potassium, sodium) suggests that drought conditions in the region could be 

responsible for increased airborne soil dusts which can contain these minerals. For the remaining 

analytes chloride and ammonium, increases are moderate, which suggests that while chloride could be 

attributable to soil dust, ammonium could be attributable to fertilizer application, animal husbandry, or 

NOX emissions controls on stationary sources.

Because CASTNET and NTN employ very different measurement principles, results from the two 

networks are not directly comparable and differences in results and trends cannot be strictly viewed as 

inconsistent or contradictory. Rather, the two different methods should be considered complimentary as 

they each provide insight into the complexities of atmospheric deposition.

Mercury Deposition Network

Annual sampling data from four MDN sites located at Sycamore Canyon, Molas Pass, Mesa Verde, and 

Navajo Lake is compared and aggregated to provide a general estimate of historic mercury deposition in 

the Four Corners region. Total mercury (Hg) deposition (organic + elemental) is calculated by NADP in 

units of nanograms per square meter (ng/m2) based on the amount of sample collected in the wet bottle in 

equivalent millimeters (mm) times its mercury concentration in nanograms per liter (ng/l). In contrast to

0.00

0.50

1.00

1.50

2.00

2.50

3.00

3.50

4.00

4.50

2000 2002 2004 2006 2008 2010 2012

Dep Rate, kg/ha-dm

Year

Normalized Precip

Ca, kg/ha-dm

NO3, kg/ha-dm

SO4, kg/ha-dm
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-60 Air Quality March 2014

NTN, precipitation gage data are not used for data reduction since the bottle quantity is a more precise 

measurement for trace quantities (NADP 2013).

For the historic 10-year period from 2002 through 2011, individual site results are shown in Table 4.1-24

comprising absolute units of ng/m2and kg/ha, and normalized units of ng/m2-mm as reported by MDN on 

a discrete sample basis (NADP 2013). Since the number of sites and samples is not large, absolute 

percent difference (variation) about the weighted arithmetic mean is shown to assess measurement 

variability (consistency) from year-to-year.

Table 4.1-24 Historic Mercury Deposition - 4 MDN Sites

Site ID 

Code Year

Months 

Operation

Valid 

Samples

Precipitation 

Collected

Measured

Mercury Deposition

mm cm ng/m2kg/ha ng/m2-mm variation

AZ02* 2006 10 29 429 42.9 8,678 8.68E-05 20.2 13%

AZ02* 2007 12 21 401 40.1 10,358 1.04E-04 25.8 10%

AZ02* 2008 12 22 459 45.9 8,567 8.57E-05 18.7 20%

AZ02* 2009 12 25 178 17.8 5,384 5.38E-05 30.3 30%

AZ02* 2010 12 23 313 31.3 7,859 7.86E-05 25.1 8%

AZ02* 2011 12 28 287 28.7 7,436 7.44E-05 25.9 11%

AZ02 Cumulative 148 2067 206.7 48,282 4.83E-04 23.4 14%

NM98 2009 8 18 151 15.1 3,762 3.76E-05 24.9 5%

NM98 2010 12 20 241 24.1 7,126 7.13E-05 29.6 25%

NM98 2011 12 24 231 23.1 4,294 4.29E-05 18.6 22%

NM98 2012 9 18 152 15.2 3,179 3.18E-05 20.9 12%

NM98 Cumulative 80 775 77.5 18,360 1.84E-04 23.7 16%

CO96** 2009 6 22 331 33.1 4,928 4.93E-05 14.9 14%

CO96** 2010 12 39 614 61.4 8,475 8.47E-05 13.8 5%

CO96** 2011 12 44 790 79.0 9,307 9.31E-05 11.8 10%

CO96 Cumulative 105 1735 173.5 22,709 2.27E-04 13.1 9%

CO99 2002 11 23 190 19.0 3,471 3.47E-05 18.3 3%

CO99 2003 12 29 301 30.1 4,914 4.91E-05 16.3 8%

CO99 2004 12 27 327 32.7 3,161 3.16E-05 9.7 45%

CO99 2005 12 30 481 48.1 5,433 5.43E-05 11.3 36%

CO99 2006 12 30 310 31.0 4,963 4.96E-05 16.0 9%

CO99 2007 12 33 380 38.0 6,708 6.71E-05 17.6 0%

CO99 2008 12 28 404 40.4 6,021 6.02E-05 14.9 16%

CO99 2009 12 25 321 32.1 10,100 1.01E-04 31.5 79%

CO99 2010 12 30 458 45.8 10,583 1.06E-04 23.1 31%

CO99 2011 12 28 373 37.3 7,203 7.20E-05 19.3 9%

CO99 Cumulative 283 3545 354.5 62,558 6.26E-04 17.6 24%

Source: NADP 2013

Notes: 

* Indicates location is outside 300 km radius of FCPP

** Indicates location is nondesert characteristic (mountains); 

Site NM98 ceased operation September 2012; 

Variation is absolute difference between annual value and cumulative mean of annual values 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-61

Table 4.1-25 aggregates the results shown in Table 4.1-24 to provide a general estimate of region-wide 

mercury deposition rates over the 10-year period. Figure 4.1-8 illustrates these normalized mercury 

deposition rates in units of ng/m2-mm. For consistency with NTN precipitation data from multiple (7) rain

gages over 12 years, Table 4.1-26 correlates MDN trending results against NTN precipitation amounts to 

obtain estimated mercury deposition as if it were an NTN parameter, as illustrated on Figure 4.1-9.

The normalized MDN results shown in Table 4.1-25 and Figure 4.1-8 suggest an upward trend in the rate 

of mercury deposition in the region over a decade. As shown in Table 4.1-26, from 2000 to 2011, the 

estimated average trending deposition rate increased by about 6 ng/m2-mm or about 40 percent overall 

with an average annual variability of less than 20 percent, which indicates that results are reasonably 

consistent overall. The trending analysis suggests that mercury deposition in the Western region has 

been increasing.

While increases are due in part to trans-Pacific transport of mercury from sources in Asia (refer to Section 

4.8, Special-Status Species for a more detailed discussion), coal-fired power plants are the largest source 

of mercury emissions in the United States. Mercury is emitted from EGUs in three forms; each of which 

has specific physical and chemical properties that determine how far it travels in the atmosphere before 

depositing to the landscape. Although gaseous oxidized mercury and particle-bound mercury are 

generally local/regional mercury deposition concerns, all forms of mercury may deposit to local or regional 

watersheds. U.S. coal-fired power plants account for over half of the U.S. controllable emissions of the 

quickly depositing forms of mercury (Federal Register 2012).According to the EPRI baseline scenario 

modeling results, the maximum contribution of FCPP mercury emissions to mercury total deposition is 

about 28 percent in San Juan County near the FCPP and contributions from FCPP range from 2 to 28

percent in the vicinity of the plant; however, the contributions from FCPP are less than 2 percent over the 

remainder of the San Juan basin (EPRI 2013).
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-62 Air Quality March 2014

Table 4.1-25 Historic Annual Mercury Deposition - 4 MDN Sites

Year

Sites 

Operating

Valid

Samples

Precipitation Collected Deposition Rate

mm cm ng/m2-mm variation

2002 1 23 190 19.0 18.3 2%

2003 1 29 301 30.1 16.3 13%

2004 1 27 327 32.7 9.7 48%

2005 1 30 481 48.1 11.3 39%

2006 2 59 739 73.9 18.5 1%

2007 2 54 782 78.2 21.8 17%

2008 2 50 863 86.3 16.9 9%

2009 4 90 980 98.0 24.7 32%

2010 4 112 1,626 162.6 20.9 12%

2011 4 124 1,681 168.1 16.8 10%

Cumulative 598 7,969 796.9 18.7 18%

Trend 6.2

Change 43%

Source: NADP 2013

Notes: Aggregated data for 4 sites: AZ02, NM98, CO96, CO99; Site NM98 ceased operation September 2012. Variation is absolute 

difference between annual value and cumulative mean of annual values 

Figure 4.1-8 Historic MDN Deposition Rates – Normalized
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-63

Table 4.1-26 Estimated NTN-Correlated Annual Mercury Deposition

Year

NTN Precipitation Average Deposition

cm mm ng/m2-mm ng/m2kg/ha

2000 23.7 237 13.0 3,086 3.09E-05

2001 25.9 259 13.7 3,546 3.55E-05

2002 16.3 163 14.4 2,341 2.34E-05

2003 18.7 187 15.1 2,827 2.83E-05

2004 28.1 281 15.8 4,430 4.43E-05

2005 33.6 336 16.5 5,540 5.54E-05

2006 26.8 268 17.2 4,604 4.60E-05

2007 26.6 266 17.9 4,751 4.75E-05

2008 25.9 259 18.6 4,798 4.80E-05

2009 21.1 211 19.2 4,070 4.07E-05

2010 34.7 347 19.9 6,923 6.92E-05

2011 25.0 250 20.6 5,165 5.16E-05

Mean 25.5 255 4,340 4.34E-05

Median 25.9 259 4,517 4.52E-05

Cumulative 306.4 3064 52,080 5.21E-04

Source: NADP 2013

Notes:

Aggregated precip data for 7 NTN sites: AZ03, AZ97, CO00, CO99, NM07, UT09, UT98; Aggregated Hg dep data for 4 MDN sites: 

AZ02, NM98, CO96, CO99; Average deposition rate determined from 10-year trend line 

Figure 4.1-9 Estimated NTN-Correlated Annual Mercury Deposition

0

1

2

3

4

5

6

7

8

2000 2002 2004 2006 2008 2010 2012

Precip, dm or Dep, ug/m2

Year

Precip, dm

Hg, ug/m2
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Draft Environmental Impact Statement

4.1-64 Air Quality March 2014

Ammonia Monitoring Network

Annual sampling data from two AMoN sites located in Navajo Lake and Farmington are compared and 

aggregated to provide a general estimate of historic ambient ammonia concentrations in the Four Corners 

region. Concentrations are calculated by NADP based on the AMoN diffusion filter method and measured 

air flow rates (NADP 2013).

For the historic 4-year 8-month period from January 2008 through August 2012, individual and 

aggregated site results are shown in Table 4.1-27 comprising units of nanograms per cubic meter (ng/m3)

and parts per billion by volume (ppbv) as reported by AMoN on a discrete sample basis (NADP 2013). 

Since the number of sites and samples is not large, absolute percent difference (variation) about the 

weighted arithmetic means are shown to assess measurement variability (consistency) from year-to-year. 

Figure 4.1-10 illustrates the results shown in Table 4.1-27 and contrasts them against the overall mean 

value obtained by averaging all samples overall years at both sites.

The trending results shown in Table 4.1-27 and Figure 4.1-10 indicate an apparent rise in mean ambient 

ammonia concentration of about 240 μg/m3or about 0.3 ppbv, which is about a 40 percent increase, with 

an average annual variability of 15 percent over the course of the active monitoring period. This suggests 

that changes in ambient ammonia concentrations could be attributable to changes in fertilizer application, 

animal husbandry, or NOX emissions controls on stationary sources. Another possible explanation for 

these changes is overall improvement in the relatively new measurement technique over time, from field 

procedures to laboratory analysis. This could have resulted in better sensitivity and data capture as the 

program progressed, which would tend to detect an analyte, which may have previously been underdetected or undetected; i.e., a lowering of the method detection limit (MDL).

Table 4.1-27 Historic Ambient Ammonia Concentration - 2 AMoN Sites

Site ID 

Code Year

Months 

Operation

Valid 

Samples

Days of 

Data

Measured Ammonia

ng/m3ppbv variation

NM98 2008 12 18 246 331 0.48 14%

NM98 2009 12 26 356 354 0.51 8%

NM98 2010 10 20 270 463 0.67 20%

NM98 2011 12 26 348 330 0.47 14%

NM98 2012 8 17 236 483 0.70 25%

NM98 Weighted Average 107 1456 385 0.55 17%

Trend 112 0.16

Change 33% 33%

NM99 2008 12 18 253 844 1.21 22%

NM99 2009 12 24 309 1,008 1.45 7%

NM99 2010 12 26 354 1,213 1.75 12%

NM99 2011 12 26 356 1,054 1.52 3%

NM99 2012 8 14 195 1,341 1.93 24%

NM99 Weighted Average 108 1467 1,084 1.56 14%

Trend 416 0.60

Change 47% 47%
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-65

Site ID 

Code Year

Months 

Operation

Valid 

Samples

Days of 

Data

Measured Ammonia

ng/m3ppbv variation

NM98/99 2008 24 36 499 592 0.85 20%

NM98/99 2009 24 50 665 658 0.95 11%

NM98/99 2010 22 46 624 887 1.28 21%

NM98/99 2011 24 52 704 696 1.00 5%

NM98/99 2012 16 31 431 870 1.25 18%

NM98/99 Composite Average 215 2923 736 1.06 15%

Trend 238 0.34

Change 38% 38%

Source: NADP 2013

Note:

Variation is absolute difference between annual value and cumulative mean of annual values 

Figure 4.1-10 Historic Ambient Ammonia – Northwest New Mexico

0

200

400

600

800

1000

1200

1400

1600

2008 2009 2010 2011 2012

Ammonia Concentration, ng/m3

Year 

Mean NH3, ng/m3

Composite NH3, ng/m3

NM98 NH3, ng/m3

NM99 NH3, ng/m3
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-66 Air Quality March 2014

4.1.2.7 Sensitive Receptors

Certain population groups are considered more sensitive to air pollution and odors than others; those that 

are particularly sensitive include children, elderly, and acutely ill and chronically ill persons, especially 

those with cardio respiratory diseases such as asthma and bronchitis. Sensitive receptors (land uses) 

indicate locations where such individuals are typically found, namely schools, daycare centers, hospitals, 

senior citizen centers, residences of sensitive persons, and parks with active recreational uses, such as 

youth sports.

Persons engaged in strenuous work or physical exercise also have increased sensitivity to poor air 

quality. Residential areas are considered more sensitive to air quality conditions than commercial and 

industrial areas, because people generally spend longer periods of time at their residences, resulting in 

greater exposure to ambient air quality conditions. Recreational uses such as parks are also considered 

sensitive, due to the greater exposure to ambient air quality conditions and because the presence of 

pollution detracts from the recreational experience.

Four Corners Power Plant

The FCPP generating units are located more than 1⁄2 mile from any sensitive land uses such as schools, 

hospitals, and senior citizen centers. The nearest sensitive receptors are homes located greater than 

1 mile from the FCPP (see Figure 4.14-2).

Navajo Mine

Five residences are within 1⁄2 mile (800 meters) of the Pinabete Permit Area. Of these five residences, 

three are located within the Area IV boundary. Navajo Mine has begun negotiations with two of these 

residents to relocate out of the proposed mining area. Several other isolated single-family residences are 

in the vicinity of the proposed mining disturbance zone of Area IV North, the nearest of which is about 

4,500 feet (1,370 meters) away. Three residences are within 1 mile (1,600 meters) of the edge of the 

disturbance area. Four additional residences lie within 1 mile (1,600 meters) of the mining disturbance 

zone of Area III within the Navajo Mine Permit Area. The nearest structure is approximately 3,900 feet 

(1,190 meters) north of Area III (see Figure 4.14-2).

Transmission Lines

Numerous residences and other sensitive receptors, including parks, and schools, are located in close 

proximity (within 1⁄2 mile) to the transmission line ROWs. 

4.1.3 Changes to Air Quality Affected Environment Post-2014

Two completed federal actions may lead to changes in the affected environment: (1) the EPA has made 

its ruling with respect to BART to control air emissions; and (2) OSMRE has approved the SMCRA permit 

transfer from BNCC to NTEC (Section 2.4). These completed federal actions are considered part of the 

environmental baseline to which the effects of continuing operations and the Proposed Actions are 

compared in the following Section. 

The transfer of the SMCRA permit for the Navajo Mine from BNCC to NTEC would not affect the air 

quality baseline. 

The implementation of BART at FCPP would cause a substantial change to the environmental baseline. 

As part of a separate action, Southern California Edison divested its 48 percent share of Units 4 and 5 to 

APS. The sale was finalized December 30 2013. APS notified EPA that the alternative emissions control 

strategy is preferred and subsequently APS shut down Units 1, 2, and 3 on December 30, 2013. Thus, 

emissions from Units 1, 2, and 3 have permanently ceased as of that date. As a result, there would be a 

transition period from 2014 to mid-2018 after which Units 1, 2, and 3 have been shut down and during 

which Units 4 and 5 would operate without SCR. This interim air quality baseline is presented in this 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-67

section. Once BART is fully implemented, the reduction in air emissions from FCPP would decrease 

substantially. Table 4.1-28 summarizes the reductions.

Table 4.1-28 Summary of Air Emission Reductions from BART Compliance at FCPP

Criteria Pollutants, Greenhouse 

Gases and Target Metals

Historic Pre-2014 

Baseline Emissions

Units 1, 2, 3, 4, 5

tons/yr

Estimated Post-2014

Baseline Emissions

Units 4 & 5

tons/yr

Post-2014 versus 

Pre-2014 Baseline

Reduction

Percent

Sulfur Dioxide (SO2) 11,971 9,800 18%

Nitrogen Oxides (NOX) 41,121 5,420 87%

Carbon Monoxide (CO) 2,096 1,580 25%

Filterable Particulate (PM) 1,976 830 58%

Carbon Dioxide Equivalents (CO2e) 15,439,236 11,396,710 26%

Arsenic (As) 1.78 0.06 96%

Lead (Pb) 1.82 0.07 96%

Mercury (Hg) 0.36 0.07 81%

Selenium (Se) 5.63 0.28 95%

4.1.3.1 Stationary Source Emissions

Pursuant to 40 CFR 49, Source Specific Federal Implementation Plan for Implementing Best Available 

Retrofit Technology for Four Corners Power Plant: Navajo Nation, the primary goal of controlling NOx

emissions from FCPP is to reduce PM2.5 precursors and thereby improve visibility in the region. Table 4.1-29

shows historic generation (kilograms per megawatt/hour, same as grams per kilowatt-hour) from Units 1, 2, 

and 3 for the representative 12-year period 2000-2011; and Table 4.1-28 shows historic generation from 

Units 4 and 5. These two tables split SO2, NOx and PM data illustrate the relative contributions of the older, 

less efficient generating units (1, 2, and 3) and the newer, more efficient generating units (4 and 5).

Table 4.1-29 Historic Grouped Part 75 Emissions - ORISPL 2442 Units 1, 2, and 3 (to be 

decommissioned)

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2000 4,550,595 11,387 2.27 15,201 3.03 1,240 0.25

2001 4,642,272 12,779 2.50 16,997 3.32 1,299 0.25

2002 4,664,651 10,783 2.10 16,403 3.19 1,256 0.24

2003 4,503,798 9,887 1.99 15,316 3.09 1,152 0.23

2004 4,799,830 4,966 0.94 16,798 3.17 1,227 0.23

2005 4,936,157 3,501 0.64 16,743 3.08 1,254 0.23

2006 4,683,715 3,170 0.61 16,722 3.24 1,202 0.23

2007 4,851,740 2,643 0.49 17,079 3.19 1,252 0.23

2008 4,823,075 2,853 0.54 16,390 3.08 1,245 0.23

2009 4,780,246 2,736 0.52 16,008 3.04 1,220 0.23

2010 4,646,445 2,914 0.57 16,301 3.18 1,221 0.24
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-68 Air Quality March 2014

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2011 4,258,209 3,052 0.65 15,315 3.26 1,133 0.24

Historic Baseline 4,711,369 2,981 0.57 16,365 3.15 1,218 0.23

Plantwide Share 29% 25% 40% 62%

Source: EPA 2012h

Notes:

PM calculated per AP-42 Chapter 1.1 support document Tables 4-7 and A-3; Title V permit condition (Units 1, 2, and 3)

Baseline period is 2005-11 (flue gas desulfurization, FGD, installed on Units 4 and 5)

Table 4.1-30 Historic Grouped Part 75 Emissions - ORISPL 2442 Units 4 and 5

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2000 11,558,538 26,945 2.11 31,312 2.46 867 0.07

2001 11,829,836 26,785 2.05 30,303 2.32 870 0.07

2002 10,104,338 22,064 1.98 25,174 2.26 715 0.06

2003 12,354,084 25,207 1.85 29,880 2.19 846 0.06

2004 11,334,289 15,976 1.28 23,944 1.92 737 0.06

2005 11,892,933 9,152 0.70 25,000 1.91 796 0.06

2006 12,478,900 12,022 0.87 27,927 2.03 838 0.06

2007 10,848,702 7,596 0.64 24,004 2.01 728 0.06

2008 10,998,224 7,546 0.62 23,922 1.97 724 0.06

2009 12,024,518 9,714 0.73 26,503 2.00 810 0.06

2010 10,308,601 8,129 0.72 22,536 1.98 687 0.06

2011 10,808,075 8,770 0.74 23,397 1.96 719 0.06

Historic Baseline 11,337,136 8,990 0.72 24,756 1.98 757 0.06

Plantwide Share 71% 75% 60% 38%

Source: EPA 2012h

Notes:

PM calculated per AP-42 Chapter 1.1 support document Tables 4-7 and A-3; 40 CFR 49 final rule (Units 4, 5)

Baseline period is 2005-11 (flue gas desulfurization, FGD, installed on Units 4 and 5)

As shown in Tables 4.1-29 and 4.1-30, Units 1, 2, and 3 generated 29 percent of electric power at FCPP 

during the baseline period but emitted 40 percent of NOX and 62 percent of PM while Units 4 and 5 

generated 71 percent of electric power but emitted 60 percent of NOX and 38 percent of PM. Emissions of 

SO2 are about on-par with generation percentages. This demonstrates that Units 4 and 5 are more 

efficient and have lower NOX and PM emission rates in units of kilograms per megawatt-hour (kg/MW-hr). 

4.1.3.2 Hazardous Air Pollutants

Coal combustion in power plant boilers emits a wide variety of inorganic and organic HAPs. Tables 4.1-31

and 4.1-32 show estimated average annual HAP emissions from FCPP based on historic (pre-2014)

operating data prior to implementation of 40 CFR 63 Subpart UUUUU for Units 1, 2, 3, 4, and 5, and 

projected (post-2014) average annual HAP emissions from Units 4 and 5 operating in compliance with 40 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-69

CFR 63 Subpart UUUUU. For the pre-2014 condition, emissions are totaled for Units 1 through 5, Units 1, 

2, and 3 (decommissioned in 2013), and Units 4 and 5 to show the relative contributions of the grouped 

units. Estimated HAP emissions are based on historic operating data, projected operating data, and 

regulatory default emission factors published by the EPA (EPA 2011a, 40 CFR 63 Subpart UUUUU). 

As shown in Table 4.1-31, the shutdown of Units 1, 2, and 3 and compliance with 40 CFR 63 Subpart 

UUUUU for Units 4 and 5 would reduce estimated annual metal HAP emissions by about 91 percent 

overall compared to estimated historic regulatory default emissions. As shown in Table 4.1-32, except for 

hydrogen chloride (an acid gas), estimated emissions of nonmetal HAPs would be reduced by about 

26 percent overall compared to estimated historic emissions. However, beginning in 2014, nonmetal 

inorganic and organic HAP emissions from Units 4 and 5 specifically may increase about 9 percent 

compared to recent 12-year historic levels for these Units due to the potential for increased generation 

following the shutdown of Units 1, 2, and 3.

Table 4.1-31 Estimated Historic and Future HAP Metals Emissions - ORISPL 2442

HAP (Metals)

2000-11 2000-11 2000-11 2014 Comparison of 

Historic Levels to 

Baseline Units

1 - 5

Average 

lbs/yr

Units

1, 2, and 3

Average 

lbs/yr

Units

4 and 5

Average 

lbs/yr

Units

4 and 5

Average 

lbs/yr

Reduction

Percent

Antimony (Sb) 156 50 106 91 42%

Arsenic (As) 3,552 1,140 2,412 124 96%

Beryllium (Be) 182 58 124 23 88%

Cadmium (Cd) 442 142 300 34 92%

Chromium (Cr) 2,252 723 1,530 317 86%

Cobalt (Co) 866 278 588 91 90%

Copper (Cu) 4,938 1,584 3,354 702 86%

Lead (Pb) 3,639 1,167 2,471 136 96%

Manganese (Mn) 4,245 1,362 2,883 453 89%

Mercury (Hg) 719 231 488 136 81%

Nickel (Ni) 2,426 778 1,648 396 84%

Selenium (Se) 11,262 3,613 7,649 566 95%

Overall Reduction (all metals) 91%

Average FCPP 

Generation (MW-hrs/yr) 16,056,814 4,678,394 11,378,420 12,410,900 23%

Sources: 77 FR 32 Tables 3 and 5; 40 CFR 63 Subpart UUUUU Table 2; EPA 2011a (AP-42 Tables 1.1-13, -14, -15, -18)

Notes:

For metals, pre-Project (2000-11) AP-42 Table 1.1-18, post-Project (2014-25) Part 63 Subpart UUUUU Table 2 

For coal-fired units not low rank virgin coal

Megawatts (MW) gross electric power output

Part 63 regulation assumes heat rate = 10,000 BTU/KW-hr = 34.13% conversion efficiency

Higher heating value (HHV) of Navajo coal = 17.632 mmBTU/ton (AP-42 Section 1.1 Background Table A-3)

AP-42 emission factors rated “E” (poor) not used

Assumed future annual gross heat input based on 2000-11 historic actual capacity factors plus contingency margin

Capacity factor contingency margin = 9%

Copper not a 40 CFR 63 Subpart UUUUU metal; included here for consistency with ERA modeling protocol

Copper estimated based on chromium (metal with closest boiling point) and 2010 FCPP TRI Cu/Cr ratio of 2.21
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-70 Air Quality March 2014

Table 4.1-32 Estimated Historic and Future HAP Nonmetals Emissions - ORISPL 2442

HAP

(Organics and Inorganics)

2000-11 2014 Comparison of 

Historic Levels 

to Baseline

Reduction

Percent

Units

1 - 5

Average 

lbs/yr

Units

1, 2, and 3

Average 

lbs/yr

Units

4 and 5

Average 

lbs/yr

Units

4 and 5

Average 

lbs/yr

Acetaldehyde 4,938 1,584 3,354 3,658 26%

Acetophenone 130 42 88 96 26%

Acrolein 2,512 806 1,706 1,861 26%

Benzene 11,262 3,613 7,649 8,343 26%

Benzyl chloride 6,064 1,946 4,119 4,493 26%

Bis (2-ethylhexyl)phthalate (DEHP) 632 203 430 469 26%

Carbon disulfide 1,126 361 765 834 26%

Chlorobenzene 191 61 129 141 26%

Chloroform 511 164 347 379 26%

Cyanide 21,659 6,949 14,710 16,045 26%

2,4-Dinitrotoluene 3 1 2 2 26%

Ethyl benzene 814 261 553 603 26%

Ethyl chloride 364 117 247 270 26%

Formaldehyde 2,079 667 1,412 1,540 26%

Hexane 580 186 394 430 26%

Hydrogen chloride 10,396,140 3,335,293 7,060,847 226,323 98%

Hydrogen fluoride 1,299,518 416,912 882,606 962,694 26%

Isophorone 5,025 1,612 3,413 3,722 26%

Methyl bromide 1,386 445 941 1,027 26%

Methyl chloride 4,592 1,473 3,119 3,402 26%

Methyl ethyl ketone 3,379 1,084 2,295 2,503 26%

Methylene chloride 2,512 806 1,706 1,861 26%

PAHs (composite total) 180 58 122 133 26%

Phenol 139 44 94 103 26%

Propionaldehyde 3,292 1,056 2,236 2,439 26%

Tetrachloroethylene 373 120 253 276 26%
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-71

HAP

(Organics and Inorganics)

2000-11 2014 Comparison of 

Historic Levels 

to Baseline

Reduction

Percent

Units

1 - 5

Average 

lbs/yr

Units

1, 2, and 3

Average 

lbs/yr

Units

4 and 5

Average 

lbs/yr

Units

4 and 5

Average 

lbs/yr

Toluene 2,079 667 1,412 1,540 26%

Styrene 217 69 147 160 26%

Xylenes (o,m,p) 321 103 218 237 26%

Average Generation (MW-hrs/yr) 16,056,814 4,678,394 11,378,420 12,410,900 23%

Sources: 77 FR 32 Tables 3 and 5; 40 CFR 63 Subpart UUUUU Table 2; EPA 2011a (AP-42 Tables 1.1-13, -14, -15, -18)

Notes:

For HCl, pre-Project (2000-11) AP-42 Table 1.1-15, post-Project (2014-25) Part 63 Subpart UUUUU Table 2 

For coal-fired units not low rank virgin coal

MW gross electric power output

Part 63 regulation assumes heat rate = 10,000 BTU/KW-hr = 34.13% conversion efficiency

Higher heating value (HHV) of Navajo coal = 17.632 mmBTU/ton (AP-42 Section 1.1 Background Table A-3)

AP-42 emission factors rated “E” (poor) not used

Assumed future annual gross heat input based on 2000-11 historic actual capacity factors plus contingency margin

Capacity factor contingency margin = 9%

4.1.3.3 Visibility/Regional Haze

Closure of Units 1, 2, and 3 and implementation of SCR on Units 4 and 5 would yield a compound NOX

reduction of about 87 percent on a plantwide basis. Because NOX is an ozone precursor, elimination of 

up to 35,700 tons per year (98 tons per day) of NOX emissions8 would result in a clean air benefit for the 

region in addition to an incremental improvement in regional haze and visibility.

An assessment of ozone emissions from the FCPP was conducted to show the predicted fourth-highest 

maximum 8-hour impacts for PSD Class I and affected sensitive Class II areas. Tables 4.1-33 through

4.1-35 summarize the decrease in ozone levels at Class I and Class II areas in the region that would 

occur by the end of the baseline period, in comparison to historic levels.

Table 4.1-33 Fourth-Highest Maximum 8-Hour Ozone Impacts - PSD Class I Areas

Sixteen Class I Areas

Historic

Ozone1

Baseline

Ozone2

Endpoint 

NAAQS

ppbv ppbv status

Petrified Forest National Park (AZ) 69.9 67.9 Meet

Grand Canyon National Park (AZ)

Capitol Reef National Park (UT)

Canyonlands National Park (UT) 62.4 61.0 Meet

Arches National Park (UT)

Mesa Verde National Park (CO) 67.3 65.0 Meet

Black Canyon of the Gunnison Wilderness (CO)

Weminuche Wilderness (CO) 75.5 74.7 Meet

8 Potential reduction from 41,100 tons per year (pre-Project) to 5,400 tons per year (post-Project).
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-72 Air Quality March 2014

Sixteen Class I Areas

Historic

Ozone1

Baseline

Ozone2

Endpoint 

NAAQS

ppbv ppbv status

La Garita Wilderness (CO) 76.2 75.4 Exceed

West Elk Wilderness (CO)

Maroon Bells – Snowmass Wilderness (CO)

Great Sand Dunes National Monument (CO)

Wheeler Peak Wilderness (NM)

Pecos Wilderness (NM) 69.0 66.8 Meet

Bandelier National Monument (NM) 69.1 66.8 Meet

San Pedro Parks Wilderness (NM) 70.0 67.5 Meet

Note: bolded values indicate exceedances

1 Year 2005

2 Year 2018 (note that modeling results were not available for 2013. 2018 represents the period wherein Units 1, 2, and 3 have 

been shut-down and SCR has been installed on Units 4 and 5.

Table 4.1-34 Fourth-Highest Maximum 8-Hour Ozone Impacts - Affected Sensitive Class II Areas

Affected Sensitive Class II Areas

Historic

Ozone1

Baseline 

Ozone2

Endpoint 

NAAQS

ppbv ppbv status

Carson National Forest 75.2 72.0 Meet

Grand Mesa, Uncompahgre, and Gunnison National 

Forests 76.2 75.4 Exceed

Handies Peak Wilderness Study Area 75.1 74.3 Meet

Jicarilla Apache Indian Reservation 75.2 72.3 Meet

Navajo Nation 78.7 74.9 Meet

Redcloud Peak Wilderness Study Area 74.9 74.0 Meet

Rio Grande National Forest 76.0 75.2 Exceed

San Juan National Forest 75.1 74.2 Meet

Uncompahgre Wilderness Area (BLM managed) 75.0 74.1 Meet

Uncompahgre Wilderness Area (USFS managed) 74.9 74.1 Meet

Note: bolded values indicate exceedances

1 Year 2005

2 Year 2018 (note that modeling results were not available for 2013. 2018 represents the period wherein Units 1, 2, and 3 have 

been shut-down and SCR has been installed on Units 4 and 5.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-73

Table 4.1-35 Attainment Test 8-Hour Ozone Design Values - Four Corners Region

Areas and Monitoring Sites

Historic

Ozone1

Baseline Action 

Ozone2

Endpoint 

NAAQS

ppbv ppbv status

San Juan County, New Mexico (35-45-0009) 69.7 66.5 Meet

San Juan County, New Mexico (35-45-1005) 71.3 68.1 Meet

La Plata County, Colorado (08-67-1004) 72.0 69.8 Meet

La Plata County, Colorado (08-67-7003) 63.7 60.3 Meet

Montezuma County, Colorado (08-83-0101) 72.0 65.1 Meet

Source: AECOM 2013b

Notes:

1 Year 2005

2 Year 2018 (note that modeling results were not available for 2013. 2018 represents the period wherein Units 1, 2, and 3 have 

been shut-down and SCR has been installed on Units 4 and 5.

The 2005 Baseline simulation was conducted using the 2005 FCAQS regional emissions inventory from 

SLAMS and NADP sites Part 75 data for FCPP (AECOM 2013b). The report is also the source of the two 

future year 2018 scenarios developed to assess the impacts of the proposed FCPP proposed action. 

Regional comparisons show an overall decrease in cumulative ozone concentrations for the 2018 year 

simulations relative to 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 to 7 ppbv. The only locations where ozone is observed to increase are 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 occurs in a region where ozone concentrations do not exceed the 

NAAQS. 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.

In 2005, four Class I and Class II areas exceeded the NAAQS; La Garita Wilderness Area, Grand Mesa 

National Forest, Navajo Nation, and Rio Grande National Forest. The 2018 model-predicted results 

indicate none of these areas would exceed the NAAQS. The FCPP does not contribute to the ozone 

concentrations in any of these areas, as the FCPP contribution in these areas is 0.0 ppbv. The 

unmonitored area analysis indicated that in 2005 there was one sensitive Class II area, Sandia Mountain 

Wilderness Area, with modeled ozone exceedences. By 2018 the ozone concentrations in this area will 

decrease but ozone exceedences may still occur episodically. The FCPP contributes 0.1 ppbv at Sandia 

Mountain.

The model-predicted FCPP ozone contribution at the Navajo Nation is 0.6 ppb. The monitored area 

analysis indicates that in 2005 one monitor exceeded the NAAQS, but by 2018, no monitors in the 4-km 

modeling domain would exceed the NAAQS. 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 ppbv.

Ozone concentrations are predicted to decrease in 2018 throughout the 4-km modeling domain relative to 

conditions in 2005. Overall, the model-predicted future ozone concentrations are similar regardless of the 

methods used to analyze the results. Modeled ozone impacts from the FCPP in 2018 under the Proposed 

Action do not contribute to areas that may continue to have ozone concentrations that exceed the NAAQS.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-74 Air Quality March 2014

The analysis indicates that under baseline conditions, after implementation of the new BART upgrades to 

FCPP, no monitoring sites are expected to exceed the 8-hour ozone NAAQS. Five ozone monitors are in 

the vicinity with predicted nonzero impacts ranging from 0.2 to 1.0 ppbv. In general, ambient ozone 

concentrations are predicted to decrease under baseline conditions relative to historic conditions in 2005 

(AECOM 2013b).

4.1.3.4 Atmospheric Deposition

Under the FIP for FCPP, APS shut down Units 1, 2 and 3 on December 30, 2013. As shown in Table 4.1-

29, the shut-down of these units reduced the SO2 and NOX emissions by 18 and 87 percent, respectively, 

on a plantwide basis, and 4 and 34 percent, respectively, on a regional basis. In general, these emissions 

reductions could incrementally lower acid deposition impacts downwind of FCPP to some extent, subject 

to assessment through long-term monitoring.

As shown in Table 4.1-29, shut-down of Units 1, 2, and 3 resulted in an approximate 90 percent overall 

reduction in metals emissions, when considered in combination with Units 4 and 5 operating in 

compliance with 40 CFR 63 Subpart UUUUU and Part 71 permit conditions. In particular, emissions of 

mercury are about 80 percent lower than uncontrolled regulatory default levels. Similarly, other large 

emissions reductions (over 90 percent) would include arsenic, cadmium, lead, and selenium.

As shown in Table 4.1-13, there is an approximate 25 percent overall reduction in nonmetal inorganic and 

organic HAP emissions due to closure of Units 1, 2, and 3 in combination with Units 4 and 5 operating in 

compliance with 40 CFR 63 Subpart UUUUU and Part 71 permit conditions. Subpart UUUUU hydrogen 

chloride acid gas (a precursor to chloride ion, Cl-) emissions are over 90 percent lower than uncontrolled 

regulatory default levels due to absorption in the caustic wet scrubbers used to control SO2 emissions 

from Units 4 and 5.

4.1.4 Environmental Consequences

The following sections present the results of the quantitative assessment of emissions from FCPP and the 

Navajo Mine from 2016 to 2041. Emissions from continued operation of the transmission lines would have 

minor impact compared to any potential impact from the FCPP and Navajo Mine; therefore, these are 

described qualitatively. Predicted emissions from FCPP are based on historic operating data reported to 

the EPA and estimated mining emissions are cited from the recent Area IV North EA/Finding of No 

Significant Impact (OSMRE 2012b). For FCPP, projected PM emissions are calculated based on EPA 

data, permit conditions, and process rates. In addition to criteria pollutants, estimated future emissions of 

noncriteria HAPs from FCPP are based on historic operating data and regulatory air emission factors 

published by the EPA.

Modeling

Extensive modeling efforts were conducted in order to assess the potential effects to air quality. This 

includes a NAAQS Modeling Study (2013a) and an Ozone Impact Assessment (2013b). Also conducted 

was a plume visibility assessment to evaluate the potential contributions of the Proposed Action on

regional haze. The results of these models have been critically reviewed by federal agencies (e.g., NPS, 

EPA), and where applicable, are incorporated into the impact analyses for each alternative. A brief 

summary description of the methodology of each model is provided below.

NAAQS Modeling Study Summary

The NAAQS Modeling Study (2013a) evaluated the effects of criteria emissions from FCPP Units 4 and 5 

on local ambient air quality, along with fugitive dust emissions from mining, coal handling, lime handling, 

ash placement, and vehicle traffic on mine and plant roads, including employee vehicles. The objective of 

the study was to determine whether criteria emissions from FCPP and Navajo Mine would cause an 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-75

exceedance of NAAQS. This is particularly important for SO2 and NO2 because current NAAQS are more 

stringent (lower) than when prior air quality studies (NMED 2009) were performed.

The modeling analyses for the power plant and mine were based on procedures contained in the 

Guideline on Air Quality Models, which is codified in 40 CFR Part 51, Appendix W (EPA 2005a). The 

guideline asserts that the suitability of an air quality dispersion model for a particular application is 

dependent upon several criteria, which include (1) stack height relative to nearby structures, 

(2) dispersion environment, (3) local terrain, and (4) availability of representative meteorological data. 

Based on a review of these factors, the most current version of the AERMOD9 program was used to 

quantify emissions from the FCPP and Navajo Mine (AECOM 2013a).

The NAAQS Modeling Study was performed using EPA’s AERMOD dispersion model. Upon review, the 

NPS commented on the applicability of certain meteorological data pre-processing options available in 

AERMOD and used in the study. In response to these comments and with the EPA’s concurrence: 1) the 

model will be re-run using EPA’s newest version of the pre-processing software when it becomes 

available; 2) a sensitivity analysis will be performed that compared the previous (old) modeling results to 

the new modeling results; 3) a conclusion will be formed on the significance of the differences in modeling 

results; and 4) the NAAQS Modeling Study report will be amended to include a discussion of the 

differences and their relevance to the results of the study. While the EPA determined that the model could 

not be used with certain options for permitting, a distinction was made between modeling for an EIS 

versus modeling for a permit application. Thus, since there should be no significant differences in the 

modeling results between the old and new versions, the NAAQS modeling methodology should be 

deemed acceptable by the NPS and EPA.

Ozone Impact Assessment Summary

As part of the NAAQS assessment, APS conducted photochemical modeling on a regional level to assess 

the effects of NOX emissions from FCPP. The assessment was conducted by modeling FCPP emissions 

in combination with other regional sources and comparing the resulting ozone concentrations to the 

current 8-hour ozone NAAQS and also the former (1979-97) 1-hour ozone NAAQS. Ozone impacts were 

assessed near FCPP (maxima), in nearby PSD Class I and sensitive Class II areas, and at existing ozone 

monitoring sites (AECOM 2013b).

For consistency and economy, APS utilized input data, configurations, and supporting information for the 

CAMx (Comprehensive Air Quality Model with eXtensions) modeling program10,, which was used for the 

Four Corners Air Quality Study (NMED 2009). As part of the modeling procedure, the Four Corners Air 

Quality Study regional emissions inventory was updated with current data for other sources in the 4-km 

domain, and APS provided updated emissions for FCPP consistent with the final BART rule. The 

modeling period spanned May through August because monitored ozone concentrations are highest 

during the summer months due to stronger sunlight, which drives photochemical reactions. 

Impacts on regional ozone concentrations were evaluated by using CAMx to simulate three scenarios for 

the years 2005 and 2018:

1. The 2005 Baseline simulation used the updated Four Corners Air Quality Study 2005 emissions 

inventory for an analysis of current air quality conditions. Modeling emissions for 2005 

established historic air quality levels against which the alternatives were evaluated.

2. The 2018 No Action Alternative simulation was based on Four Corners Air Quality Study 2018 

Mitigation Scenario No. 4 and included impacts for all regional emissions except those from 

FCPP. This scenario hypothetically applied aggressive NOX and SO2 control measures at coal9 AERMOD is a steady-state plume model that incorporates air dispersion based on planetary boundary layer turbulence structure 

and scaling concepts, including treatment of both surface and elevated sources and both simple and complex terrain. It is the 

regulatory default model required to be used for SIP revisions for existing sources, and for NSR and PSD programs.

10 The CAMx modeling system includes a meteorological model, an emissions data processor, and a photochemical grid model.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-76 Air Quality March 2014

fired power plants in the region as well as new controls on oil and gas industry NOX and VOC 

sources in San Juan and Rio Arriba counties.

3. The 2018 Proposed Action was also based on Four Corners Air Quality Study 2018 Mitigation 

Scenario No. 4 and includes contributions from estimated future emissions from Units 4 and 5. 

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

(1) assessment of maximum ozone impacts due to the Proposed Action; (2) comparison of modeled 

concentrations to the 8-hour ozone NAAQS; and (3) attainment tests for monitored and unmonitored 

areas, including PSD Class I and sensitive Class II areas.

The NPS has expressed concern that a 5-year old estimated regional future emissions scenario developed 

as part of the Four Corners Air Quality Study (NMED 2009) and used to predict ozone levels for 2018 may 

have overestimated future NOX emissions from FCPP and San Juan Generating Station while possibly 

underestimating future VOC emissions from the oil & gas industry in the region. This suggested that the 

2018 emissions scenario may not have been totally credible with respect to today’s view of the near future 

(i.e., generating unit shutdowns and slower growth in the oil and gas industry). However, due to 

conservative assumptions made for the ozone impact modeling, any re-modeled ozone impacts would not 

be significantly different from the original impacts and overall conclusions would remain the same.

Deposition Effects – Monitoring Networks 

Estimates or assumptions used to predict future conditions can introduce some level of uncertainty into 

forecasts. In Guidelines for Ecological Risk Assessment, the EPA notes that a major source of uncertainty 

is extrapolation (i.e., the greater [or longer]) the extrapolation, the greater the uncertainty) (EPA 1998a). 

This point is particularly true for screening-level forecasts or assessments, where assumptions are 

generally intended to provide conservative upper-bound estimates. However, it is important to recognize 

that findings made using these techniques do not necessarily mean that predicted conditions would 

actually occur under real circumstances. The following predictions of deposition monitoring network 

observations are based on extrapolation of historic data while taking into account the anticipated effects 

of the alternatives and other changes in the region (i.e., emissions reductions). Thus, the results are

somewhat uncertain, but provide an upper bound to the impacts.

To delineate the area to be evaluated in the Ecological Risk Assessment (discussed in detail in Section 4.8,

Threatened and Endangered Species), deposition modeling was conducted using the CALPUFF11 model. A 

screening procedure was applied to estimate potential changes to soil concentrations of selected metals 

associated with 25 years of cumulative deposition from future FCPP operations. The estimated 

concentrations of emitted metals in ambient air and the amount deposited to surface soil were calculated 

and compared to measured soil concentrations within San Juan County (AECOM 2013c).

Eight metals were selected for initial modeling in the FCPP/Navajo screening procedure: arsenic, 

cadmium, chromium, mercury, antimony, lead, copper, and selenium (AECOM 2013c). The CALPUFF 

model was applied within a 300-km (186-mile) radius of FCPP to simulate dispersion and deposition of 

the eight metals due to continuous full load (99th percentile) operation of FCPP for 25 years. The 

deposition area was determined by predicting where incremental increases in soil concentrations of any 

of the eight metals was more than 1 percent of present-day concentrations per data provided by the U.S. 

Geological Survey (USGS). This procedure determined that the deposition area extended less than 50 km 

(31 miles) from FCPP; therefore, more detailed air dispersion and deposition modeling was performed 

using AERMOD12 and refined emissions estimates. The same comparative procedures were used to 

estimate impacted soil concentrations against the USGS data, and it was found that the deposition 

11 CALPUFF is the EPA-approved model to simulate dispersion and deposition over a large area for long-range transport and 

complex terrain on scales of tens to hundreds of kilometers. The 300 km (186-mile) radius was selected to encompass a large 

distance from FCPP for screening purposes.

12 AERMOD is the EPA-approved steady-state plume model that incorporates air dispersion for simple and complex terrains and is 

designed for short-range modeling up to 50 km (31 miles).
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-77

patterns of the CALPUFF and AERMOD analyses were similar in shape and overlapped significantly, thus 

providing a validation of the modeling results (AECOM 2013c).

Significance Thresholds

Significance thresholds for evaluating air quality impacts with regard to criteria pollutants are defined in 

the Clean Air Act. With regard to visibility, significance thresholds have been defined by the EPA. In terms 

of potential impacts of HAPs on sensitive receptors, no EPA, NNEPA or other local regulatory threshold 

has been defined; therefore, the threshold used by air quality agencies outside of the Four Corners region 

is used to evaluate potential impacts. No significance thresholds are defined with regard to deposition of 

air emissions. This information is presented within this impacts chapter to provide data regarding the area 

of deposition under each alternative; however, impacts of deposition are assessed in Section 4.5, Water 

Resources, and Section 4.8, Special-Status Species, as applicable.

Criteria Emissions

Pursuant to 40 CFR 51.166(23)(i), PSD significance thresholds related to NAAQS are shown below. Per 

the regulatory definition, significant means a net emissions increase at an existing source (e.g., FCPP) or 

the potential of a new source to emit air pollutants that would equal or exceed any of the mass rates in 

units of short tons per year (tpy) as listed in Table 4.1-36.

Table 4.1-36 Criteria Emission Significance Thresholds

Criteria Pollutant Significance Threshold

Carbon monoxide 100 tpy

Nitrogen oxides 40 tpy

Sulfur dioxide 40 tpy

Particulate matter 25 tpy (total) or 15 tpy of PM10

PM2.5 10 tpy of direct PM2.5 emissions; 40 tpy of SO2 emissions; 40 tpy of 

NOX emissions unless demonstrated not to be a PM2.5 precursor

Ozone 40 tpy VOCs or NOX precursors

Lead 0.6 tpy

Fluorides 3 tpy

Sulfuric acid mist (H2SO4) 7 tpy

Hydrogen sulphide 10 tpy

Total reduced sulphur (including H2S) 10 tpy

Reduced sulphur compounds (including H2S) 10 tpy
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Draft Environmental Impact Statement

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Key concepts in projecting future emissions are capacity factor and potential-to-emit (PTE), as 

defined below: 

Capacity factor is defined as actual utilization divided by theoretical design capacity. For 

generating units, this factor is typically expressed as actual megawatt-hours (MW-hrs) generated 

in a year versus design rating in megawatts times 8,760 hours per year (maximum theoretical 

MW-hrs). Since generating units must be periodically shut down for maintenance and seldom 

operate at full design rating (load) to extend equipment life, capacity factor is always less than 

100 percent, typically in the range of 80 to 95 percent for base load generating units, depending 

on overall reliability.

PTE is defined as maximum theoretical emissions for a pollutant at permitted operating 

conditions. Traditionally, PTE is determined assuming maximum allowable emission rate at 100 

percent capacity factor; however, since actual capacity factor is less than 100 percent, theoretical 

PTE is never normally achieved unless limited by permit condition. 

Four Corners Power Plant

Stack Emissions – SO2 , NOX, CO, Pb, Filterable PM10, and PM2.5, Condensable H2SO4, and Organics

Modeled mass emission rates from the Units 4 and 5 stacks were based on historic hourly data, Title V 

permit conditions, EPA emission estimation techniques (EETs), and BART limits for NOX and PM. 

Modeled stack temperature and exhaust velocity were based on actual hourly data recorded from 2009 

through 2011. Per guidance received from the EPA, APS modeled 3 years of actual 1-hour SO2

emissions from Units 4 and 5. Since the BART emission rate for NOX is based on a 30-day rolling 

average, which is appropriate for visibility impacts, both 30-day and 1-hour average emission rates for 

NOX were modeled. In addition, modeled PM10 and PM2.5 emission rates included condensable 

emissions consistent with increased sulfuric acid mist (H2SO4) conversion, a byproduct of SCR operation. 

Table 4.1-37 reproduces the mass emission rates used for modeling future operations of Units 4 and 5 

assuming an average historic annual capacity factor of 86 percent. 13 Surface meteorological data 

comprised 5 years (2006 through 2010) from Navajo Met Towers 1 and 3 along with concurrent upper air 

data from Albuquerque International Airport.

Table 4.1-37 Modeled Future Criteria Pollutant Emissions Rates - ORISPL 2442 Units 4 and 5

Criteria Pollutant

Factor

lb/mmBTU Factor Reference Notes

Units 4 and 5 Combined

mmBTU/hr lbs/hr g/sec

Sulfur Dioxide (SO2) 0.190 40 CFR 75 historic average (1-hour) 14,822 2,816 354.83

Nitrogen Oxides (NOX), 

average

0.098 40 CFR 49 BART Rule (30-day 

rolling average) 14,822 1,453 183.02

Nitrogen Oxides (NOX), 

maximum

0.190 1-hour average 14,822 2,816 354.83

Carbon Monoxide (CO) 0.028 AP-42 Table 1.1-3; 17.632 

mmBTU/ton

14,822 415 52.29

Lead (Pb) 1.2E-06 40 CFR 63 Subpart UUUUU Table 2 14,822 0.02 0.0022

Filterable Particulate (PM) 0.01500 40 CFR 49 BART Rule 14,822 222.33 28.01

Total Filterable PM10 0.01380 AP-42 Table 1.1-6; 92% of 

filterable PM 14,822 204.54 25.77

13 Expressed as a continuous heat input of 7,411 mmBTU/hr for each generating unit rated at 8,612 mmBTU/hr, determined as the 

99th percentile of boiler operating data for the 3-year period 2009 through 2011. 
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-79

Criteria Pollutant

Factor

lb/mmBTU Factor Reference Notes

Units 4 and 5 Combined

mmBTU/hr lbs/hr g/sec

“Coarse” Filterable PM10 0.00585 difference (total filterable - fine

filterable) 14,822 86.71 10.93

Fine Filterable PM2.5 0.00795 AP-42 Table 1.1-6; 53% of filterable 

PM 14,822 117.83 14.85

Fine “Soil” PM2.5 0.00766 difference (fine filterable - fine 

elemental carbon) 14,822 113.48 14.30

Fine Elemental Carbon 

PM2.5

0.00029 EPA 68-D-98-046 Table 6; 3.7% of 

PM2.5

14,822 4.36 0.55

Total Condensable PM10 /

PM2.5

0.00835 sum (sulfuric acid + organics) 14,822 123.81 15.60

Condensable Sulfuric Acid 

(H2SO4)

0.00435 Stack test and EPRI removal 

efficiency (%) 14,822 64.52 8.13

Condensable Organics 0.00400 AP-42 Table 1.1-5; 20% of 

0.02 lb/mmBTU 14,822 59.29 7.47

Grand Total PM10 0.02215 Total Filterable + Total Condensable 14,822 328.35 41.37

Grand Total PM2.5 0.01630 Fine Filterable + Total Condensable 14,822 241.64 30.45

Source: AECOM 2013a

Materials Handing Emissions – PM10 and PM2.5

For the two lime silos equipped with baghouses for dust control, PM emissions were estimated using the 

permissible outlet loading in units of grains 14 per cubic foot of exhaust air from the baghouses and the 

volumetric displacement of air when lime is loaded into a silo. The fly ash waste disposal area has five silos, 

all equipped with baghouses, and three pug mills with scrubbers for processing fly ash. Fly ash baghouse 

and scrubber emissions were estimated and modeled using the outlet grain loading and air flowrate for each 

control device. For the lime slurry mixing process, fugitive droplets were modeled as volume sources. Open 

transfer points within the coal transport system were also modeled as volume sources.

Plant Traffic – PM10 and PM2.5

Paved and unpaved road source characteristics were developed to represent vehicular traffic at FCPP. 

Based on EPA guidance, roads were represented by lines of volume sources. For daytime operations, fly 

ash disposal trucks, fly ash sales trucks, lime delivery trucks, SCR reagent (ammonia or urea) delivery 

trucks, road-watering trucks, and company and employee vehicles (autos, pickups, SUVs, vans) were 

included. Vehicular traffic during overnight hours was assumed to be minimal, and roads are watered 

several times a day. Fugitive dust from paved and unpaved roads was calculated using EETs published 

by the EPA, taking into account road watering as an effective dust control method. Fugitive dust controls 

can cut emissions by at least 50 percent and up to 90 percent if applied copiously (EPA 2006). 

Lime and Ash Piles – PM10 and PM2.5

Area sources at FCPP consist of stockpiles located at the lime processing area and the ash disposal 

area. Wind erosion of stockpiles is highly intermittent due to the relatively high threshold wind speeds 

needed to entrain lime and ash. To facilitate modeling, triggered wind events were evaluated by reviewing 

on-site wind speed data correlated to threshold friction velocity guidance and EETs published by the EPA. 

The fly ash has high moisture content when transported and unloaded by the haul trucks. Over time, it 

14 One pound of material has 7,000 grains , or 1 gram of material has 15.432 grains.
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Draft Environmental Impact Statement

4.1-80 Air Quality March 2014

dries into a cement-like solid. Surfactant is applied regularly to reduce the amount of fugitive dust that can 

become airborne during triggering wind events.

Navajo Mine

Navajo Mine North – PM10 and PM2.5

The Navajo Mine coal preparation plant is in the northern portion of the lease area and adjacent to FCPP 

on the eastern side. A train transports coal from Lowe Stockpile to the processing area where the railcars 

are unloaded into one of two hoppers, displacing air upward, which entrains some coal dust. Water 

sprays inside each receiving hopper are activated when a railcar is unloaded, reducing entrained coal 

dust by about 50 percent. For modeling, particulate emissions from the coal hoppers were estimated by 

APS per published EPA guidance taking into account site-specific factors such as drop distance. Other 

principal components of the coal preparation plant modeled by APS include towers silos, crushers, and 

conveyors. Coal stockpiles were evaluated in a similar manner to lime and ash stockpiles described 

above (AECOM 2013a).

Navajo Mine South (Area IV) – NOX, SO2, CO, PM10, and PM2.5

Sources in the southern portion of the Navajo Mine include the Pinabete Permit Area, transport of coal 

from the Pinabete Permit Area to Lowe Stockpile, unloading at the pile and loading into railcars, blasting, 

and overburden replacement. Emission factors, control efficiencies, and equipment lists were provided to 

APS by Navajo Mine. Mining emissions comprise diesel engine exhaust and fugitive dust. Mobile sources 

modeled by APS included shot hole drilling, dragline activity, bulldozing, loading coal into trucks with 

front-end loaders, scraping, and road grading.

Coal and overburden blasting emits CO, NO2, and SO2 from detonation of ANFO explosive. Emission 

factors published by the EPA were used to calculate emissions of CO and NO2. Since Navajo Mine uses 

ultralow sulfur diesel fuel in its ANFO mixture, SO2 emissions are significantly less than cited in the EPA 

emission factors, which were adjusted accordingly. Coal blasting routinely occurs 3 days per week about 

mid-day within a 4-hour time window; however, the ANFO emission rate was conservatively modeled for 

4 hours per day, 5 days per week, for a total of 20 hours per week to simplify the modeling. Each blast is in 

a different location and meteorological conditions vary; therefore, the modeled concentrations were 

conservative. In contrast, overburden blasting occurs only once per month over a larger area and never 

occurs in the same location twice. Due to the transient and temporal nature of overburden blasting, it was 

not included in the NAAQS modeling based on specific EPA guidance for intermittent sources (EPA 2011a).

Mine Traffic – PM10 and PM2.5

Traffic impacts from coal haul trucks, watering trucks, scrapers, end dump trucks, and pickups on the 

roads between the active mining areas and Lowe Stockpile were characterized by modeling activities 

occurring 24 hours per day (AECOM 2013a). Fugitive dust was calculated using EETs published by the 

EPA, taking into account road watering as an effective dust control method, supplemented by a nontoxic 

chemical dust suppressant applied to major unpaved roads annually.

Mine Coal Stockpiles – PM10 and PM2.5

Coal from the active mining areas is transported and unloaded onto Lowe Stockpile and compacted using 

bulldozers. As modeled by APS, unloading and bulldozing activities occur 24 hours per day, and coal is 

loaded from the pile into railcars for transport to the coal preparation plant. Wind erosion of stockpiles was 

modeled by APS by evaluating triggering wind events correlated to threshold friction velocity guidance 

and EETs published by the EPA. Wind erosion of overburden reclaim piles was modeled in the same 

manner (AECOM 2013a).
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-81

HAPs

Air toxics are pollutants that may result in an increase in mortality or serious illness, or that may pose a 

present or potential hazard to human health. Health effects of air toxics include cancer, birth defects, 

neurological damage, damage to the body’s natural defense system, and diseases that can lead to 

premature death. 

A screening-level Health Risk Assessment (HRA) for DPM was performed using conservative 

methodology for upper-bound mining activity levels and timeframes. Detailed results of the HRA are 

provided in Section 4.17, Public Health. In general, due to the broad geographic dispersion of mining 

activities, their short-term temporary nature at any particular location, and lack of proximate receptors 

within 1,000 feet (300 meters), no significant risk to sensitive receptors or the general public would be 

posed by mining-related HAP emissions.

Plume Visibility

The screening analysis was conducted per guidance contained in the Workbook for Plume Visual Impact 

Screening and Analysis (EPA 1992a), with additional recommendations provided by the NPS. EPA’s 

screening-level plume visibility model VISCREEN was used with site-specific meteorological data to 

calculate plume visibility parameters corresponding to worst-case conditions. As a screening model,

VISCREEN does not calculate plume height above the ground, but hypothetically places the observer at 

plume height, looking horizontally at various sun-time intervals through the plume centerline. VISCREEN 

then computes the combinations of sun-plume-observer geometry that the result in the largest degree of 

plume visual impact. Because of this simplified line-of-sight geometry, the results from VISCREEN are 

conservative; thus, actual visual impacts would be less than otherwise predicted.

The model calculates linear Gaussian15 dispersion of PM and NO2, the two pollutants known to contribute 

most to visible plumes, notwithstanding condensing water vapor in cold weather. However, as a near-field 

model, VISCREEN does not address the secondary formation of nitrate (NO3

-

) and sulfate (SO4

2-)

particles which are known to contribute to regional haze at longer distances. The model outputs two visual 

impact parameters: plume contrast and plume perceptibility. According to the EPA, plume contrast (Cp) 

values exceeding an absolute value of 0.05 should be used as a screening threshold, inferring that a 

5 percent change in intensity is likely to be noticed by a casual observer, 16

evaluates the degree to which a plume can be seen either against a background sky or terrain. The EPA 

st a background 

sky or terrain (EPA 1992a).

The EPA has determined that plume contrast (Cp) values exceeding an absolute value of 0.05 should be 

used as a screening threshold for sources located within federally-designated Class I areas, inferring that 

a 5 percent change in intensity is likely to be noticed by a casual observer, 17

evaluates the degree to which a plume can be seen either against a background sky or terrain. The EPA 

sky or terrain (EPA 1992a). Therefore, for the purposes of this analysis, a vista is significantly improved if 

No criteria exist for evaluating visible plumes from sources beyond the boundaries of Federal Class I 

areas; therefore, this criteria was used to determine if emissions from the Proposed Action would affect 

visibility within Class I areas.

15 Normal functions developed by German mathematician Karl Friedrich Gauss (1777-1855) that express natural phenomena.

16 A positive Cp means the plume is a lighter color than the sky, a negative Cp means the plume looks darker than the sky.

17 A positive Cp means the plume is a lighter color than the sky, a negative Cp means the plume looks darker than the sky.
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Draft Environmental Impact Statement

4.1-82 Air Quality March 2014

4.1.4.1 Alternative A – Proposed Action

Future Criteria Emissions

Under the Proposed Action, Units 4 and 5 at the FCPP and the Navajo Mine would continue to operate 

and emit criteria and noncriteria pollutants, including HAPs, for the duration of the 25-year lease 

agreement, with the required installation and commissioning of SCR equipment by July 2018. Since SCR 

requires ammonia reagent (either anhydrous, aqueous, or from urea) to reduce NOX to nitrogen (N2) and 

water vapor (H2O), some unreacted (residual) ammonia (NH3) would be emitted from the boiler stacks as 

“ammonia slip,” typically 5 to 10 ppmv for BART installations.

Onroad vehicles and offroad equipment owned by FCPP are used for plant and switchyard maintenance. 

Segments of the transmission lines nearest FCPP are also maintained using plant vehicles and 

equipment. These vehicles and equipment emit air contaminants in engine exhaust during normal use. All 

equipment and vehicle engines used at the plant meet Federal emissions standards applicable on the 

date of manufacture. 

Four Corners Power Plant

Emissions from Units 4 and 5 would continue through 2041, supplied with coal from the Navajo Mine.

Table 4.1-38 shows estimated future (2014 through 2026) potential criteria emissions (SO2, NOX

,

and

calculated PM) from Units 4 and 5 assuming a maximum annual generation capacity factor of 92 percent 

based on the 7-year period from 2005 to 2011 when FGD became active on Units 4 and 5. Pre-project 

metals emissions are based on historical capacity factor of 84 percent and AP-42 regulatory default 

emission factors as “uncontrolled” emissions. Post-project metal emissions are based on projected 

maximum capacity factor of 92 percent and 40 CFR 63 Subpart UUUUU emission factors as “controlled” 

emissions. The large reductions in metals emissions are because the Subpart UUUUU controlled factors 

are much lower than the AP-42 uncontrolled factors. For nonmetal HAPs, the same set of AP-42

regulatory default emission factors are used for both pre- and post-project emissions estimates as these 

are not subject to Subpart UUUUU (except HCl). Because the maximum annual capacity factor (92 

percent) is 9 percent higher than the historic capacity factor (84 percent), the nonmetal HAPs potential-toemit is also 9 percent higher. To be conservative, this 92 percent capacity factor is 9 percent higher than 

the historic average of 84 percent for the same period. For the 12-year period beginning in 2000, a 92 

percent capacity factor was achieved only during 2 years, 2003 and 2006, all other years were less. Thus, 

the probability of achieving 92 percent capacity factor is estimated to be 1 in 6 or about 17 percent 

overall, which is a reasonable contingency over the long run. Projected annual emissions for years 2027 

through 2041 are assumed to be the same as year 2026 (12 years from now) due to potential loaddemand maturity over the long-term.

Table 4.1-38 Estimated Future Maximum Part 75 Emissions - ORISPL 2442 Units 4 and 5 

(with phased SCR controls)

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2014 12,410,900 9,800 0.72 27,100 1.98 830 0.06

2015 12,410,900 9,800 0.72 27,100 1.98 830 0.06

2016 12,410,900 9,800 0.72 27,100 1.98 830 0.06

2017 12,410,900 9,800 0.72 19,870 1.45 830 0.06

2018 12,410,900 9,800 0.72 12,640 0.92 830 0.06

2019 12,410,900 9,800 0.72 5,420 0.40 830 0.06

2020 12,410,900 9,800 0.72 5,420 0.40 830 0.06

2021 12,410,900 9,800 0.72 5,420 0.40 830 0.06
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March 2014 Air Quality 4.1-83

Year

Generation Sulfur Dioxide Nitrogen Oxides Particulate Matter

MW-hrs/yr tons/yr kg/MW-hr tons/yr kg/MW-hr tons/yr kg/MW-hr

2022 12,410,900 9,800 0.72 5,420 0.40 830 0.06

2023 12,410,900 9,800 0.72 5,420 0.40 830 0.06

2024 12,410,900 9,800 0.72 5,420 0.40 830 0.06

2025 12,410,900 9,800 0.72 5,420 0.40 830 0.06

2026 12,410,900 9,800 0.72 5,420 0.40 830 0.06

Source: EPA 2012h Notes: Projected emissions for years 2027 through 2041 same as year 2026 (flat extrapolation assumed) 

PM calculated per AP-42 Chapter 1.1 support document Tables 4-7 and A-3; 40 CFR 49 final rule (Units 4 and 5) 

Maximum annual capacity factor = 92% based on historic operations (average historic annual capacity factor = 84%)

All air emissions from FCPP would remain as described in the baseline, which accounts for the decreased 

emissions due to the shutdown of Units 1, 2, and 3 and application of BART. PSD thresholds for sulfuric 

acid mist would be exceeded by the Proposed Action; ammonia slip emissions from SCR operation do not 

fall under PSD because ammonia is not a regulated criteria pollutant.

Table 4.1-39 shows estimated criteria emissions from FCPP vehicles and mobile equipment (APS 

2012a), a very small portion of which is attributable to transmission line maintenance. In comparison to 

boiler (stack) emissions, FCPP mobile source NOX emissions are only 0.05 percent, which would result 

minor impact in the short- or long-term.

Table 4.1-39 Estimated Criteria Emissions from FCPP Mobile Sources

Mobile Sources

VOC CO NOX SOX PM10 PM2.5

tons/yr tons/yr tons/yr tons/yr tons/yr tons/yr

Power Plant Offroad Equipment 0.31 3.69 2.05 0.004 0.13 0.11

Power Plant Onroad Vehicles 0.11 0.76 0.86 0.002 0.04 0.03

Annual Totals 0.42 4.46 2.90 0.006 0.16 0.14

Sources: APS 2012a, EPA 2011a, SCAQMD 2008

Note:

PM10 and PM2.5 for exhaust only, fugitive dust accounted for in OSMRE 2012b

Navajo Mine

Development of the Pinabete Permit Area (Area IV North and South) and associated coal reserves under 

the Proposed Action would use best-practice surface mining methods and equipment to supply coal to 

FCPP for up to 25 years beginning in 2016 and ending in 2041. Mining activity would cause emissions 

from diesel-powered offroad equipment and onroad vehicles, explosives detonation, fugitive methane 

liberated from coal seams, and fugitive dust. All equipment and vehicle engines used at the mine meet 

Federal emissions standards applicable on the date of manufacture. 

Table 4.1-40 shows estimated criteria emissions and DPM from Navajo mining operations in the existing

Navajo Mine Permit Area and the proposed Pinabete Permit Area and related activities. These

quantifiable sources contribute about 6.8 percent of NOX PTE and about 0.1 percent of SO2 PTE. 

Reasonable variations in mining-related mobile source estimates for NOX and SO2 would have minor

impact in the short- or long-term because a 10 percent change in mining-related NOX or SO2 emissions 

would represent only 0.7 percent of total project NOX emissions and 0.01 percent of SO2 emissions, 

which is well within EPA precision limits of -2 to +5 percent for fossil fuel combustion (EPA 2012b).
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-84 Air Quality March 2014

Fugitive dust emissions from coal mining and coal handling are estimated at 910 tons per year, which is

about 10 percent greater than power plant stack emissions (830 tons per year). Mining PM emissions are 

mainly in the form of relatively uncontrolled fugitive dust; therefore, are highly variable. Power plant PM 

emissions are controlled using baghouses; therefore are highly controlled and less variable. Because of 

the variability, fugitive dust emissions cannot be directly compared to power plant stack PM emissions.

Table 4.1-40 Estimated Criteria and DPM Emissions from Navajo Mine Operations (both Navajo 

Mine and Pinabete Permit Areas)

Mobile and Fugitive Sources

VOC CO NOX SOX PM10 PM2.5 DPM

tons/yr tons/yr tons/yr tons/yr tons/yr tons/yr tons/yr

Overburden Drilling and Blasting 19.67 4.99 0.59 3.36 0.97

Coal Seam Drilling and Blasting 241.96 61.39 7.22 4.82 1.40

Overburden Dragline Stripping 62.96 5.56

Mine Extraction Operations and Loading 15.44 65.57 141.75 0.20 183.59 20.58 5.11

Coal Hauling Trucks to Stockpiles 14.16 68.08 125.40 0.18 276.47 27.65 5.31

Mining Support Vehicle Travel 3.36 9.91 33.73 0.05 180.73 18.07 0.77

Unloading at Stockpiles and Railcar Loading 0.71 0.22

Reclamation 124.50 24.90

Coal Preparation Plant (except stockpile) 13.89 4.05

Wind Erosion (coal and spoils piles) 58.82 21.03

Annual Totals 32.96 405.19 367.26 8.23 909.85 124.43 11.20

Source: OSMRE 2012b

Notes:

SOX emissions estimated from FONSI supporting data

PM10 and PM2.5 includes exhaust and fugitive dust as determined in FONSI

For diesels, DPM estimated as 7.8% of CO emissions per offroad emissions factors (SCAQMD 2008)

Transmission Lines 

Mobile source emissions from maintenance of transmission lines would include diesel exhaust from truck 

trips. Maintenance would occur at various points along each of the transmission lines, on less than an 

annual basis at each site. Therefore, emissions would have minor impact in the short- or long-term (less 

than 1 percent of aggregated mobile sources) and would not result in exceedances of any NAAQS.

Combined Emissions Summary

Table 4.1-41 summarizes the NAAQS modeling results for all pollutants with monitored (existing) ambient 

background concentrations added in. As shown in Table 4.1-41, future total concentrations for all 

pollutants and averaging times would be expected to meet current NAAQS (AECOM 2013a):

Quarterly lead, 1-hour and 3-hour SO2, 1-hour and annual NO2 impacts would be from Units 4 

and 5 stack emissions. 

Annual and 24-hour PM2.5 impacts would be dominated by low elevation sources such as coal 

preparation, lime and ash handling, and road dust.

Active mining and mine vehicle traffic emissions would dominate the impact for 24-hour PM10.

1-hour and 8-hour CO impacts would be driven by the coal blasting emissions, which were 

modeled for 4 hours per day even though these emissions occur less than 1 hour per day.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-85

Modeling using conservative assumptions for elevated stack or ground-level fugitive sources at FCPP or 

Navajo Mine show that NAAQS would not be exceeded (AECOM 2013d). Air quality regulations require that 

NAAQS be measured at the site boundary, where no densely populated areas exist near the plant or mine. 

In addition to stack emissions, modeling of fugitive dust emissions from road traffic, materials handling, 

and mining operations determined that the Proposed Action would not cause local exceedances of 

NAAQS for PM10 (respirable particulate) and PM2.5 (fine particulate); however, the estimate of PM2.5

emissions from the Proposed Action approaches the NAAQS (33.2 μg/m3 as compared with the 35 μg/m3

NAAQS). Refer to Section 4.1.4 for the modeling assumptions, including operational control factors 

assumed in the modeling. For PM2.5, the guidance in the March 23, 2010 EPA/Stephen Page memo for 

adding modeled to background concentrations was followed. This guidance indicates that the peak 24-

hour modeled concentration should be added to the 98th percentile background concentration. However, 

the new EPA draft procedure for PM2.5 modeling released on March 4, 2013, indicates that the 98th

percentile modeled 24-hour concentration should be added to the 98th percentile background 

concentration in certain situations. This proposed procedure would be applicable in the FCPP case due to 

the fact that the peak modeled concentration is due to fugitive emissions (no precursor emissions). Using 

the recent draft guidance, the 24-hour PM2.5 design concentration would be reduced from about 33 μg/m3

to about 26 μg/m3. Therefore, for both SO and PM, the design concentrations are on the order of 75 

percent of the NAAQS, leaving considerable room for uncertainties in background concentrations.

Attainment of primary NAAQS is protective of public health, including sensitive receptors (see also 

Section 4.17, Public Health, for justification that NAAQS are protective); therefore, impacts in the short- or 

long-term operation of the FCPP and Navajo Mine are estimated to be minor.

Table 4.1-41 NAAQS Modeling Results - FCPP & Navajo Mine Vicinity 

Pollutant Standard

Averaging 

Time

Modeled 

Impact

Monitored 

Background

Total 

Impact NAAQS

μg/m3μg/m3μg/m3μg/m3status

Ozone (O3)* Primary & 

Secondary

8-hour -6.3 139.7 133.5 147 Meet

Nitrogen Dioxide (NO2)

Primary 1-hour 169.0 188 Meet

Primary & 

Secondary

Annual 3.4 37.4 40.8 100 Meet

Sulfur Dioxide (SO2)

Primary 1-hour 194.5 196.4 Meet

Secondary 3-hour 186.1 44.5 230.6 1,309 Meet

Carbon Monoxide (CO) Primary

1-hour 955 1610 2,565 40,072 Meet

8-hour 181 1035 1,216 10,304 Meet

Particulates (as PM10)

Primary & 

Secondary

24-hour 43.4 44.0 87.4 150 Meet
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-86 Air Quality March 2014

Pollutant Standard

Averaging 

Time

Modeled 

Impact

Monitored 

Background

Total 

Impact NAAQS

μg/m3μg/m3μg/m3μg/m3status

Particulates

(as PM2.5)

Primary & 

Secondary

24-hour 19.6 13.6 33.2 35 Meet

Primary Annual 3.8 4.4 8.2 12 Meet

Secondary Annual 3.8 4.4 8.2 15 Meet

Lead (Pb) Primary & 

Secondary

3-month 

rolling

0.001 0.006 0.007 0.15 Meet

Sources: AECOM 2013a, AECOM 2013b, EPA 2012f

Notes:

Primary standards provide public health protection, including protecting the health of “sensitive” populations such as asthmatics, 

children, and the elderly.

Secondary standards provide public welfare protection, including protection against decreased visibility and damage to animals, 

crops, vegetation, and buildings.

*Site 35-045-1005 (Farmington, San Juan County, New Mexico)

All NAAQS generally correspond to an Air Quality Index (AQI) of 100

μg/m3= micrograms per cubic meter (10-6 g/m3)

Future HAP Emissions

Four Corners Power Plant

Coal combustion in power plant boilers emits a wide variety of inorganic and organic HAPs. Tables 4.1-42

and 4.1-43 show estimated average annual HAP emissions from FCPP under baseline conditions (Units 

1, 2, and 3 shut-down) and projected average annual HAP emissions from Units 4 and 5 operating in 

compliance with 40 CFR 63 Subpart UUUUU. Estimated HAP emissions are based on historic operating 

data, projected operating data, and regulatory defined emission factors published by the EPA (EPA

2011a). As shown in the tables, compliance with 40 CFR 63 Subpart UUUUU for Units 4 and 5 would 

reduce estimated annual hydrogen chloride emissions by about 98 percent due to acid gas removal 

(absorption and neutralization) by the caustic wet scrubbers used to control SO2 emissions. Emissions of 

metals from FCPP under the Proposed Action decrease substantially with the installation of SCR on Units 

4 and 5. In contrast, non-metal emissions would increase by approximately 9 percent due to the projected 

increase in annual capacity factor applicable to HAPs not subject to Subpart UUUUU.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-87

Table 4.1-42 Estimated Historic and Future HAP Metals Emissions - ORISPL 2442

Hazardous Air Pollutants

Metals

2000-11

Units 4 and 5

Average lbs/yr

2014-25

Units 4 and 5

Average lbs/yr

Comparison of Baseline to Emissions 

under the Proposed Action

Change Percent

Average Generation, MW-hrs/yr 11,378,420 12,410,900 9%

Antimony (Sb) 106 91 -16%

Arsenic (As) 2,412 124 -94%

Beryllium (Be) 124 23 -81%

Cadmium (Cd) 300 34 -89%

Chromium (Cr) 1,530 317 -79%

Cobalt (Co) 588 91 -85%

Copper (Cu) 3,354 702 -79%

Lead (Pb) 2,471 136 -94%

Manganese (Mn) 2,883 453 -84%

Mercury (Hg) 488 136 -72%

Nickel (Ni) 1,648 396 -76%

Selenium (Se) 7,649 566 -93%

Table 4.1-43 Estimated Historic and Future HAP Nonmetals Emissions - ORISPL 2442

Hazardous Air Pollutants 

(Organics and Inorganics)

2000-11

Units 4 and 5

Average lbs/yr

2014-25

Units 4 and 5

Average lbs/yr

Comparison of Baseline to Emissions 

under the Proposed Action

Change Percent

Average Generation, MW-hrs/yr 11,378,420 12,410,900 +9%

Acetaldehyde 3,354 3,658 +9%

Acetophenone 88 96 +9%

Acrolein 1,706 1,861 +9%

Benzene 7,649 8,343 +9%

Benzyl chloride 4,119 4,493 +9%

Bis(2-ethylhexyl)phthalate 

(DEHP) 430 469 +9%

Carbon disulfide 765 834 +9%

Chlorobenzene 129 141 +9%

Chloroform 347 379 +9%

Cyanide 14,710 16,045 +9%

2,4-Dinitrotoluene 2 2 0%

Ethyl benzene 553 603 +9%

Ethyl chloride 247 270 +9%

Formaldehyde 1,412 1,540 +9%

Hexane 394 430 +9%

Hydrogen chloride 7,060,847 226,323 -96%
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-88 Air Quality March 2014

Hazardous Air Pollutants 

(Organics and Inorganics)

2000-11

Units 4 and 5

Average lbs/yr

2014-25

Units 4 and 5

Average lbs/yr

Comparison of Baseline to Emissions 

under the Proposed Action

Change Percent

Hydrogen fluoride 882,606 962,694 +9%

Isophorone 3,413 3,722 +9%

Methyl bromide 941 1,027 +9%

Methyl chloride 3,119 3,402 +9%

Methyl ethyl ketone 2,295 2,503 +9%

Methylene chloride 1,706 1,861 +9%

PAHs (composite total) 122 133 +9%

Phenol 94 103 +9%

Propionaldehyde 2,236 2,439 +9%

Tetrachloroethylene 253 276 +9%

Toluene 1,412 1,540 +9%

Styrene 147 160 +9%

Xylenes (o,m,p) 218 237 +9%

Navajo Mine

As described in Sections 3.1.2.3 and 3.1.2.7, diesel particulate matter is considered a HAP; thus, larger 

and more persistent sources of DPM could present a health risk to nearby sensitive receptors. An 

example of this situation would be mining operations where large diesel-powered equipment and vehicles 

are used in active areas for extended lengths of time, months or years; however, such use does not meet 

the definition of a stationary source of air contaminants.

Any residences (i.e., sensitive receptors) in the vicinity of the Pinabete Permit Area could be affected by 

mining-related emissions such as DPM, fugitive dust, and blasting gases (NO2, SO2, and CO). As described 

above, the nearest sensitive receptor would be approximately 1⁄2 mile (800 meters) from proposed Area IV

mining activities. However, no agency-published guidelines for significance criteria exist to assess these 

impacts. Further, due to the broad geographic dispersion of mining activities, their short-term temporary 

nature at any particular location, and lack of proximate receptors within 1,000 feet (300 meters), minor

impacts to sensitive receptors or the general public would be posed by short- and long-term mining-related 

HAP emissions since the cited public health risk thresholds would not be exceeded (BAAQMD 1999, 2010).

Transmission Lines

No emissions of HAPs are anticipated to result from maintenance activities associated with continued 

operation of the subject transmission lines.

Deposition Modeling Results

The following discussion applies to emissions from the FCPP. No short- or long-term impacts related to 

deposition of air emissions would result from continued operation of the Navajo Mine or transmission lines

since the principal source of long-range deposition pollutants is power plant stacks, not mining activities.

Four Corners Power Plant

The refined deposition area identified using AERMOD extended less than 50 km from FCPP in all 

directions. However, to allow the fate and transport modeling software to predict the contributions of 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-89

contaminants to water bodies within the deposition area from upstream watersheds, it was necessary to 

extend the AERMOD domain to a 50-km radius in all directions, the maximum distance recommended by 

the EPA. This extension was necessary because contributions to water bodies from upstream watersheds 

can enter the deposition area by leaching through the soil profile and entering the shallow groundwater 

system, or through soil erosion and surface water runoff into the San Juan River system (AECOM 2013c).

Clean Air Status and Trends Network

Continued operation of the FCPP under the Proposed Action would be expected to contribute to overall 

downward trends in regional deposition rates measured by CASTNET over the last decade because of 

the emission reductions required by BART (see Section 4.1.3). Assuming that these trends would be 

consistent over time, Table 4.1-44 and Figure 4.1-11 show projected sulfur and nitrogen compound 

deposition rates from 2014 to 2026, the same timeframe as projected by the IMPROVE program 

described in Section 4.1.2.5.

Table 4.1-44 Projected Normalized CASTNET Deposition Rates for Region

Year

Normalized Precipitation

dm

Total Nitrogen

kg/ha-dm

Total Sulfur

kg/ha-dm

2014 1.0 0.57 0.26

2015 1.0 0.55 0.25

2016 1.0 0.52 0.24

2017 1.0 0.50 0.23

2018 1.0 0.47 0.22

2019 1.0 0.45 0.22

2020 1.0 0.42 0.21

2021 1.0 0.40 0.20

2022 1.0 0.37 0.19

2023 1.0 0.35 0.18

2024 1.0 0.32 0.18

2025 1.0 0.30 0.17

2026 1.0 0.27 0.16

Trend -0.30 -0.10

Change -53% -38%

Source: EPA 2013e

Note:

Based on aggregated historic data for four existing sites: CAN407, GRC474, MEV405, PET427
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-90 Air Quality March 2014

Figure 4.1-11 Projected Normalized CASTNET Deposition Rates

As shown in Table 4.1-44 and on Figure 4.1-11, projected nitrogen compounds deposition could decrease 

by about 0.3 kg/ha-dm and sulfur compounds deposition could decrease by about 0.1 kg/ha-dm. These 

projected changes in deposition rates could represent decreases of about 50 and 40 percent, 

respectively, from 2014 to 2026.

National Trends Network

As described in Section 4.1.2.6, the NTN measures free acidity (H+as pH), calcium (Ca2+), magnesium 

(Mg2+), sodium (Na+), potassium (K+), sulfate (SO4

2-), nitrate (NO3-

), chloride (Cl-), and ammonium (NH4

+

)

ions, also total inorganic nitrogen (N). As shown on Figures 4.1-7a, 4.1.7b, and 4.1.7c, these 10 analytes 

have been trending upward over the past 12 years; however, the lower rates of increase for sulfate and 

nitrate, 14 and 7 percent, respectively, suggests that regional emissions of SO2 and NOX from stationary 

and mobile sources may not be increasing as rapidly overall due to improved emission controls and lowerpolluting fuels in the region which could reduce future NOX emissions by about 20 percent (NMED 2009).

Similarly, reduced NOX and SO2 emissions from FCPP (also San Juan and Navajo Generating Stations) not 

fully accounted for in the Four Corners Air Quality Study as a result of compliance with BART could 

also marginally contribute to lowering regional nitrogen and sulfur acid deposition rates measured by NTN

by several percent, as conservatively projected in Table 4.1-45 and on Figure 4.1-12 for 2014 to 2026. 

However, the apparently increasing deposition of calcium, magnesium, sodium, potassium, and chloride 

may be attributable to increased soil dust transport brought on by drought conditions. Also, increased 

ammonia emissions from Units 4 and 5 due to SCR operation could increase deposition of ammonium ion 

and inorganic nitrogen to some extent (see AMoN discussion below for further context). Specifically, with 

respect to sulfate and nitrate deposition in the region, implementation of BART or approved alternatives 

would reduce nitrate precursor (NOX) emissions by approximately 87 percent at FCPP, 62 percent at SJGS, 

and 84 percent at NGS. Similarly, BART or approved alternatives would reduce sulfate precursor (SO2)

emissions by approximately 18 percent at FCPP and 67 percent at SJGS. However, NGS is currently 

emitting approximately 90 percent less SO2 than in the past due to installation and operation of FGD 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-91

scrubbers and no further reductions are planned. Thus, due to the potential for large decreases in future 

mass emissions of SO2 and NOX from power plants in the region, mass deposition rates of sulfates and 

nitrates in the region could nominally decrease by several percent with respect to the past (EPA 2012h, 

2012i, 2013g; PNM 2013; NGS 2013).

Table 4.1-45 Projected Normalized NTN Deposition Rates for Region

Year

Normalized Precipitation

dm

Total Nitrate

kg/ha-dm

Total Sulfate

kg/ha-dm

2014 1.0 3.12 2.02

2015 1.0 3.06 2.00

2016 1.0 3.00 1.98

2017 1.0 2.94 1.96

2018 1.0 2.88 1.94

2019 1.0 2.82 1.92

2020 1.0 2.76 1.90

2021 1.0 2.70 1.88

2022 1.0 2.64 1.86

2023 1.0 2.58 1.84

2024 1.0 2.52 1.82

2025 1.0 2.46 1.80

2026 1.0 2.40 1.78

Trend -0.72 -0.24

Change -23% -12%

Sources: NADP 2013, EPA 2013e

Note:

Based on aggregated historic data for seven existing sites: AZ03, AZ97, CO00, CO99, NM07, UT09, UT98
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-92 Air Quality March 2014

Figure 4.1-12 Projected Normalized NTN Deposition Rates

Mercury Deposition Network

As described in Section 4.1.2.6, normalized MDN results shown in Table 4.1-46 and on Figure 4.1-13

suggest an upward trend in the measured rate of mercury deposition in the region over a decade. The 

trending analysis suggests that mercury deposition measured in the western region has been increasing, 

due in large part to trans-Pacific transport from sources in Asia. EPRI (2013) indicate that “Baseline 

contributions of Hg emissions from non-U.S. sources to Hg deposition in the San Juan basin range from 

70% to 98%. Hg emissions from China contribute from 13 to 16% to Hg deposition in the basin in the 

post-2014 scenario.” Table 4.1-46 and Figure 4.1-13 show projected mercury deposition rates, which 

could be measured by MDN from 2014 to 2026 based on the following assumed conditions: (1) transPacific transport continues historic trend due to economic growth in Asia, (2) regional power plants 

continue to emit proportionally, and (3) FCPP achieves MATS compliance in concert with the Proposed 

Action. The latter two conditions help define conservative upper and lower bounds for broadly estimating 

regional and local effects of reduced mercury emissions from FCPP against apparent transport from 

outside the region:

The historic trend extrapolates historic data as described in Section 4.1.2.6, which could 

represent a worst-case scenario, however unlikely.

The upper bounding estimate assumes an 80 percent reduction of 19 percent of emissions, the 

FCPP regional share.

The lower bounding estimate assumes an 80 percent reduction of 45 percent of emissions, the 

FCPP state/local share.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-93

Based on historic trends, the zone between the estimated upper and lower bounds could represent a 

2

-dm), 18 which could be measured in aggregate by MDN 

over the long term as a result of the Proposed Action.

Table 4.1-46 Projected Normalized MDN Deposition Rates for Region

Year

Normalized 

Precipitation

dm

Historic Trend

μg/m2-dm

Proposed Action Range

Upper

μg/m2-dm

Lower

μg/m2-dm

2014 1.0 2.27 1.93 1.45

2015 1.0 2.34 1.98 1.50

2016 1.0 2.41 2.04 1.54

2017 1.0 2.48 2.10 1.59

2018 1.0 2.55 2.16 1.63

2019 1.0 2.62 2.22 1.68

2020 1.0 2.69 2.28 1.72

2021 1.0 2.76 2.34 1.76

2022 1.0 2.83 2.40 1.81

2023 1.0 2.90 2.46 1.85

2024 1.0 2.96 2.51 1.90

2025 1.0 3.03 2.57 1.94

2026 1.0 3.10 2.63 1.99

Trend 0.83 0.36 -0.29

Change 37% 16% -13%

Sources: NADP 2013; EPA 2012a, 2011a; 40 CFR 63 Subpart UUUUU

Notes:

Based on aggregated historic data for 4 MDN sites: AZ02, NM98, CO96, CO99. Historic trend assumes ongoing status quo, 

including trans-Pacific transport. Estimated action assumes 80% reduction of Hg emissions from FCPP in compliance with MATS; 

upper and lower ranges reflecting regional and local shares. 

18 2

-dm to ng/m2-mm multiply by 10.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-94 Air Quality March 2014

Figure 4.1-13 Projected Normalized MDN Deposition Rates

Ammonia Monitoring Network

The Proposed Action, by implementing SCR on Units 4 and 5 to reduce NOX emissions, would increase 

emissions of ammonia (NH3) as unreacted “ammonia slip” in stack gas by about 140 tons per year;

however, there is no applicable significance criteria for ammonia mass emissions, only concentrations in 

ambient air, as discussed below19. In addition to ammonia slip, SCR operation would also cause formation 

of about 280 tons per year of sulfuric acid mist (H2SO4) in stack gas, which is significant pursuant to 40 

CFR 51.166(23)(i) which defines the PSD significance threshold for sulfuric acid mist emissions as 7 tons 

per year. Under certain conditions, NH3 and H2SO4 can combine to form ammonium sulfate ([NH4]2SO4), 

a crystalline salt and a source of nitrogen nutrient deposition measured by NTN.

Table 4.1-47 and Figure 4.1-14 show projected ambient ammonia concentrations in northwestern New 

Mexico based on measurement data collected at AMoN sites in Navajo Lake (NM98) and Farmington 

(NM99) during the 2008 through 2012 timeframe, which is shorter than the 12-year data timeframes 

available for other deposition analytes.

19 Assumes 5 ppmv ammonia slip at 3 percent oxygen in stack gas, to be determined by BART permit condition.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-95

Table 4.1-47 Projected AMoN Ambient Concentrations - Northwestern New Mexico

Year

Historic Composite

ng/m3

Proposed Action Range

Upper

ng/m3

Lower

ng/m3

2014 979 1,509 504

2015 1,038 1,613 532

2016 1,098 1,717 560

2017 1,157 1,821 588

2018 1,217 1,925 617

2019 1,277 2,029 645

2020 1,336 2,133 673

2021 1,396 2,237 701

2022 1,455 2,341 729

2023 1,515 2,445 757

2024 1,574 2,549 785

2025 1,634 2,653 813

2026 1,693 2,757 841

Trend 715 1,248 336

Change 73% 83% 67%

Source: NADP 2013; EPA 2011b, 1992b; CDC 2013

Notes:

Based on aggregated historic data for 2 AMoN sites: NM98 Navajo Lake (lower), NM99 Farmington (upper).

Historic composite trend assumes ongoing status quo.

NIOSH 3

= 17,370,000 ng/m3

.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-96 Air Quality March 2014

Figure 4.1-14 Projected AMoN Ambient Concentrations - Northwestern New Mexico

As discussed in Section 4.17, Public Health and Safety, in more detail, for occupational exposure to 

ammonia, the National Institute of Occupational Safety and Health (NIOSH) reference exposure level 

(REL) for ammonia (CAS No. 7664-41- 3

on a time-weighted average basis 

(CDC 2013). No EPA standard has been adopted for public exposure to ammonia; therefore, the 

California Office of Environmental Health and Hazard Assessment (2013) REL is provided as a 

conservative benchmark from which to compare the project concentrations. As such, acute (1 hour) REL 

3

and the chronic (long- 3.

As shown on Figure 4.1-14, measured mean ambient ammonia concentrations range from about 

0.74 3 3(projected). These airborne concentrations represent less than 1 

percent of the 20 3 chronic REL; thus, no significant risk to public health from airborne ammonia is 

indicated for northwestern New Mexico since the chronic REL is not exceeded.

Visibility Effects

The following discussion applies only to emissions from the FCPP. Because long-range visibility impacts 

are principally caused by emissions of NOX and PM from power plant stacks (the regulatory aim of 40 

CFR Part 49), visibility impacts from continued operation of the Navajo Mine (ground-level fugitive dust) 

and transmission lines (mobile sources) would be minor in comparison to the FCPP; therefore, 

implementation of these aspects (i.e., mine and transmission lines) of the Proposed Action would not 

have any effects on long-range regional visibility or ozone levels.

Four Corners Power Plant

Regional Haze

As discussed in Section 4.1.6, the Source Specific Federal Implementation Plan for Implementing Best 

Available Retrofit Technology for Four Corners Power Plant: Navajo Nation (40 CFR 49) requires FCPP 

to reduce emissions of NOX and defines emission limits for PM based on emission rates currently 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-97

achieved at FCPP. These pollutants contribute to visibility impairment (regional haze) in the 16 mandatory 

Class I Federal areas surrounding FCPP within a 300-km (186-mile) radius. Installation of SCR controls 

on Units 4 and 5 will reduce NOX emissions 80 percent from 0.49 to 0.098 lb/mmBTU on a 30-day rolling 

average basis. For PM, Units 4 and 5 must meet an emission limit of 0.015 lb/mmBTU, while retaining the 

existing 20 percent opacity limit (77 FR 51620).

Compared to plantwide historic levels, implementation of 40 CFR 49 will reduce potential NOX emissions 

87 percent, from about 41,100 to 5,400 tons per year over the long term, and will reduce potential PM 

emissions 58 percent, from about 1,980 to 830 tons per year. While these reductions are very significant 

on a plantwide basis, they are somewhat less significant on a regional scale. Controlled NOX emissions 

from FCPP would presumably comprise about 5 percent of regional NOX emissions by 2020, and about 

3 to 8 percent of regional PM emissions, depending on future control actions taken at other power plants. 

These regional percentages suggest that reducing emissions from FCPP would result in an incremental 

improvement in regional haze and visibility; however, a major improvement would also require effective 

control efforts at other power plants in the region.20

As described in Section 4.1.6.4 and shown on Figure 4.1-5, average visibility in the region has improved by 

about 15 percent over the 11-year period from 2000 to 2010, apparently due to improved control of air 

pollution from sources such as power plants. If this historic trend continues into the future, average 

deciviews could improve at a rate of about -0.12 per year. Thus, during the first half of the 25-year 

relicensure period (2014 to 2026), an average improvement of about -1.5 deciviews could be possible, as 

projected in Table 4.1-48 and illustrated on Figure 4.1-15 for the IMPROVE program (see Section 4.1.6.3).

Figure 4.1-15 Projected Composite Visibility Trends

20 Assessing future control strategies elsewhere is beyond the scope of this analysis.
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

4.1-98 Air Quality March 2014

Table 4.1-48 Projected Regional Visibility

Year

Lowest

Mean

dV

Highest

Mean

dV

Average

Mean

dV

2014 1.9 9.9 5.8

2015 1.8 9.8 5.6

2016 1.7 9.7 5.5

2017 1.6 9.5 5.4

2018 1.5 9.4 5.3

2019 1.3 9.2 5.2

2020 1.2 9.1 5.0

2021 1.1 9.0 4.9

2022 1.0 8.8 4.8

2023 0.9 8.7 4.7

2024 0.8 8.5 4.5

2025 0.6 8.4 4.4

2026 0.5 8.3 4.3

13-Year Trend Change -1.4 -1.7 -1.5

Relative Improvement 73% 17% 25%

Source: CSU 2013c

Plume Visibility Assessment Summary

A screening-level plume visibility analysis for a land area within 50 km (31 miles) of FCPP was conducted 

(AECOM 2013d) to assess whether a plume from the Units 4 and 5 stack would be visible to casual 

observers during daylight hours in fair weather, and to what extent. For the study, 16 roadside viewpoints 

were identified that provide vistas of natural landmarks in the vicinity of FCPP:

1. Ford Butte West Viewpoint (US Route 491)

2. Bennet Rock East Viewpoint (US Route 491)

3. Barber Peak West Viewpoint (US Route 491)

4. Table Mesa East Viewpoint (US Route 491)

5. Cathedral Cliff South Viewpoint (US Route 491)

6. Shiprock South Viewpoint (Red Rock Highway/Indian Route 13)

7. Shiprock North Viewpoint (US Route 64)

8. Chimney Rock West Viewpoint (US Route 491)

9. Chimney Rock East Viewpoint (Mancos Canyon Road)

10. Hogback West Viewpoint (US Route 64)

11. Hogback East Viewpoint (US Route 64)

12. Piñon Mesa East Viewpoint (NM State Route 170)
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-99

13. Piñon Mesa South Viewpoint (NM State Route 170)

14. Angel Peak West Viewpoint (US Route 550)

15. Bisti Badlands West Viewpoint (County Road 7260)

16. Bisti Badlands West Viewpoint (NM State Route 371)

Tables 4.1-49 and 4.1-50 summarize the screening-level results in terms of the vistas with greatest 

change, the least change as a percent of significance threshold for each parameter, and the number of 

vistas for which the visibility parameters would be improved or be degraded. 

Note that controlling emissions of PM and NOX from Units 4 and 5 would not contribute proportionally to 

reductions in plume visibility for all viewpoints and vistas due to the predicted increase in sulfate 

emissions from Units 4 and 5 SCR operation, which would result in a slight increase in light scattering and 

minor degradation of some vistas (AECOM 2013e).

As shown in Tables 4.1-49 and 4.1-50, the assessment of plume visibility from Units 4 and 5 indicates 

likely times when a downwind plume would be perceptible from various viewpoints in the area. This 

indication -case 

meteorological conditions would exceed the contrast and perceptibility thresholds established by the EPA. 

The overall results suggest that the Proposed Action would improve view aesthetics in the area 

surrounding FCPP due to reduced visible plumes compared to present-day conditions. However, at 

present, no criteria exist for evaluating visible plumes from sources beyond the boundaries of Federal 

Class I areas. (AECOM 2013e)
T

able

4.1-49

5 5

11

2

3

4
Table 4.1-50 Plume Contrast (Cp) Modeling Results

5 5

11

2

3

4
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4.1-102 Air Quality March 2014

Ozone Effects

Upon implementation of the Proposed Action, local ozone would be expected to decrease by about 

3

3

on an 8-hour basis. Based on the Ozone Impact Assessment conducted for the project, 

ozone impacts under the Proposed Action would be the same as described for the baseline. As described 

in the environmental setting section, the primary reduction in ozone emissions would occur upon shutdown of Units 1, 2, 3, prior to implementation of the Proposed Action.

The Four Corners area is currently in NAAQS attainment for ozone. Decreasing or unchanged ozone 

levels would support continuing NAAQS attainment, notwithstanding unpredicted meteorological 

conditions or significant new sources of precursors NOX and VOC originating elsewhere which is beyond 

the scope of the modeling study. Thus, effects on ozone are minor due to NAAQS attainment status 

remaining unchanged.

The analysis indicates that no monitoring sites would be expected to exceed the 8-hour ozone NAAQS 

under the Proposed Action. Five ozone monitors are in the vicinity with predicted nonzero impacts ranging 

from 0.2 to 1.0 ppbv. The largest impact of the Proposed Action at an existing monitor is 1.0 ppbv in 

Farmington (Site ID 35-45-1005). None of the monitoring sites predicted to have an increase in ozone 

concentrations under the Proposed Action would have design values that exceed NAAQS. Ozone impacts 

caused by FCPP emissions under the Proposed Action would not be the sole cause of NAAQS 

exceedances in those areas (i.e., La Garita Wilderness in Colorado; Grand Mesa in Uncompahgre and 

Gunnison National Forests; and Rio Grande National Forest) that may continue to exceed NAAQS in or 

after 2018 (possibly due to new precursor source contributions originating elsewhere or unpredicted 

meteorological conditions) (AECOM 2013b).

4.1.4.2 Alternative B – Navajo Mine Extension Project Plan

Under Alternative B with FIP Alternative A, impacts would be essentially the same as for the Proposed 

Action. Emissions and effects would be essentially the same as described in Section 4.1.1.2.

Four Corners Power Plant

Since the operating scenario would be the same, effects would be the same as described in 

Section 4.1.1.2, stack criteria emissions would be the same as shown in Tables 4.1-1 through 4.1-3 and 

HAP emissions would be the same as shown in Tables 4.1-4a and 4.1-4b.

Navajo Mine 

The proposed mining area would be slightly altered from the Proposed Action, resulting in increased coal 

hauling distances and the associated emissions and dust would result in greater impacts on localized air 

quality. However, this increase in emissions and dust is within estimation and precision, therefore effects 

would be essentially the same as described in Section 4.1.1.2 (OSMRE 2011).

Transmission Lines

FCPP mobile source emissions would be essentially the same as shown in Table 4.1-39, within 

estimation precision (APS 2012). A very small portion of these emissions (less than 1 percent) would be 

associated with transmission line maintenance.

4.1.4.3 Alternative C – Alternative Pinabete Mine Plan

Under Alternative C, OSMRE would disapprove the Pinabete permit application and issue a new 10,094-

acre SMCRA permit area for a proposed mining disturbance in approximately 6,492 acres. Mining would 

be located in both Areas IV North and South. The BIA would approve the lease amendment for FCPP, 

and FCPP would operate as described under the Proposed Action. Under Alternative C impacts would be 
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Draft Environmental Impact Statement

March 2014 Air Quality 4.1-103

essentially the same as for the Proposed Action. Emissions and effects would be the same as described 

in Section 4.1.1.2.

Four Corners Power Plant

Effects would be the same as described in Section 4.1.1.2.

Navajo Mine 

Although the mining area would be slightly altered from the Proposed Action, effects would be the same 

as described in Section 4.1.1.2.

Transmission Lines

FCPP mobile source emissions would be the same as shown in Table 4.1-39. A very small portion of 

these emissions (less than 1 percent) would be associated with transmission line maintenance.

4.1.4.4 Alternative D – Alternative Ash Disposal Area Configuration

Navajo Mine 

Under this alternative, OSMRE would approve the Pinabete permit application and renew the SMCRA 

permit for the Navajo Mine permit. The Navajo Mine would operate as described under the Proposed 

Action. Impacts would be the same as described for the Proposed Action.

Four Corners Power Plant

Since the operating scenario would be the same, effects would be the same as described in the proposed 

action. Although the DFADA disturbance area would be slightly reduced from the Proposed Action, 

effects would be the same as described in the Proposed Action. 

Transmission Lines

FCPP mobile source emissions would be essentially the same as Described for the Proposed Action. A 

very small portion of these emissions (less than 1 percent) would be associated with transmission line 

maintenance.

4.1.4.5 Alternative E – No Action Alternative

Under the No Action Alternative, criteria emissions would continue through 2015 until the FCPP shuts 

down. The following section provides a summary of estimated emissions under this alternative. 

Deposition effects under the No Action Alternative would be the same as described in the environmental 

setting; therefore, no additional analysis is provided. Ozone emissions from the FCPP would continue 

through 2015. An analysis of regional visibility as a result of the No Action Alternative is provided below.

Future Criteria Emissions

Table 4.1-51 below shows estimated stationary and mobile source emissions of SO2, NOX, and PM under 

this scenario during 2014 and 2015. 
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4.1-104 Air Quality March 2014

Table 4.1-51 Estimated No Action Criteria Emissions - FCPP and Navajo Mine

Year

Stationary Sources Mobile Sources

SO2

tons/yr

NOX

tons/yr

PM

tons/yr

SO2

tons/yr

NOX

tons/yr

PM

tons/yr

2014 12,000 41,100 2,000 12 550 1,350

2015 12,000 41,100 2,000 12 550 1,350

2-Year Total 24,000 82,200 4,000 24 1,100 2,700

Sources: EPA 2012h, 2011a; OSMRE 2011; APS 2012; SCAQMD 2008

Notes:

Stationary - power plant emissions per 2005-11 baseline period (Units 1, 2, 3, 4, and 5)

Mobile - mining equipment and mine and power plant support vehicles (includes fugitive dust)

Stationary sources rounded to nearest 100 tons; mobile sources NOX and PM rounded to nearest 10 tons

Four Corners Power Plant

Under the No Action Alternative, FCPP would continue to operate in 2014 and 2015. Beginning in 2016, 

power plant decommissioning would involve dismantling and salvage work. Estimated stationary source 

emissions for the preceding 2 years are shown in Table 4.1-51.

Navajo Mine 

Beginning in 2016, mine closure would involve land reclamation and equipment removal activities, along 

with disposition of water rights. Reclamation would occur as described for the Proposed Action; however at 

an earlier time. Estimated mobile source emissions for the preceding 2 years are shown in Table 4.1-51.

Transmission Lines

Following shut-down of the FCPP in 2015, power from the FCPP would no longer be transported via the 

subject transmission lines. Beginning in 2016, transmission line decommissioning may involve 

dismantling and salvage work; however, these tasks are presently undefined and beyond the scope of 

this study. A very small portion of the mobile source emissions shown in Table 4.1-51 would be 

associated with transmission line maintenance.

Visibility Effects

Four Corners Power Plant

As discussed above, under the No Action Alternative, following 2015, all stationary source emissions from 

the FCPP would cease. The Ozone Impact Assessment conducted for the proposed Project included a

comparison of the regional ozone emissions between the Proposed Action and the No Action Alternative. 

Table 4.1-52 shows the five largest differences in regional ozone levels between the Proposed Action and 

No Action scenarios for 1-hour averaging times. The maximum predicted ozone impacts attributable to 

FCPP would occur in July and August. The largest impact (16 ppbv) would be about 12 miles southeast of 

FCPP, while the fifth largest impact (13 ppbv) would be located about 29 miles southeast of FCPP.

Tables 4.1-53 and 4.1-54 show predicted fourth-highest maximum 8-hour impacts for PSD Class I and 

affected sensitive Class II areas as defined by the NAAQS. Table 4.1-55 shows 8-hour EPA design 

values for five ozone monitoring sites in the vicinity as predicted by the NAAQS attainment test 

methodology. For the No Action Alternative, regional average ozone concentrations decreased from 64 to 

62 ppbv. The greatest changes occurred in the western and central areas of the region where predicted 

fourth-highest daily maximum 8-hour average ozone concentrations decreased by about 5 to 7 ppbv. In 
Four Corners Power Plant and Navajo Mine Energy Project

Draft Environmental Impact Statement

March 2014 Air Quality 4.1-105

contrast, under the Proposed Action, the only locations where ozone increased were immediately 

downwind of FCPP [possibly due in part to predicted meteorological conditions used for the modeling and 

increased utilization of Units 4 and 5]. The maximum increase in the fourth-highest 8-hour ozone 

concentrations was less than 4 ppbv (AECOM 2013b). Thus, since predicted ozone concentrations in the 

region are expected to decrease or remain about the same and the overall region is currently in NAAQS 

attainment, the Proposed Action would have minor impact on ambient ozone in the region in the short- or 

long-term.

Table 4.1-52 Maximum 1-Hour Ozone Impacts - Five Largest Differences

Difference Between 

Proposed Action and 

No Action1

Former NAAQS2

Nearest Local 

Maximum3

Furthest Local 

Maximum4

Former NAAQS

ppbv month ppbv ppbv ppbv status

15.8 July 120 77 90 Meet

15.1 August 120 77 90 Meet

14.9 August 120 77 90 Meet

13.3 July 120 77 90 Meet

13.1 August 120 77 90 Meet

Source: AECOM 2013b

Notes:

1 Maxima occur between 12 and 29 miles (19 and 46 km) southeast of FCPP 

2

The 1979 1-hour NAAQS for ozone was rescinded in 1997 (attainment was defined as one or fewer days per calendar year where 

the maximum hourly average ozone concentration was greater than 120 ppbv)

3 Site 35-45-0009: 28 miles (45 km) east of FCPP monitored maximum for 2011

4 Site 35-45-0018: 47 miles (75 km) east of FCPP monitored maximum for 2011

Table 4.1-53 Fourth-Highest Maximum 8-Hour Ozone Impacts - PSD Class I Areas

Sixteen Class I Areas

Proposed 

Action 

Ozone1

ppbv

No Action 

Ozone1

ppbv

Difference Between 

Proposed Action and 

No Action

ppbv

Endpoint 

NAAQS

status

Petrified Forest National Park (AZ) 67.9 67.9 0.0 Meet

Grand Canyon National Park (AZ)

Capitol Reef National Park (UT)

Canyonlands National Park (UT) 61.0 61.0 0.0 Meet

Arches National Park (UT)

Mesa Verde National Park (CO) 65.0 64.7 0.3 Meet

Black Canyon of the Gunnison Wilderness 

(CO)

Weminuche Wilderness (CO) 74.7 74.7 0.0 Meet

La Garita Wilderness (CO) 75.4 75.4 0.0 Exceed

West Elk Wilderness (CO)

Maroon Bells – Snowmass Wilderness (CO)

Great Sand Dunes National Monument (CO)

Wheeler Peak Wilderness (NM)
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4.1-106 Air Quality March 2014

Sixteen Class I Areas

Proposed 

Action 

Ozone1

ppbv

No Action 

Ozone1

ppbv

Difference Between 

Proposed Action and 

No Action

ppbv

Endpoint 

NAAQS

status

Pecos Wilderness (NM) 66.8 66.8 0.0 Meet

Bandelier National Monument (NM) 66.8 66.3 0.5 Meet

San Pedro Parks Wilderness (NM) 67.5 67.4 0.1 Meet

1 Year 2018

Table 4.1-54 Fourth-Highest Maximum 8-Hour Ozone Impacts - Affected Sensitive Class II Areas

Affected Sensitive Class II Areas

Proposed 

Action 

Ozone1

ppbv

No Action 

Ozone1

ppbv

Difference Between 

Proposed Action and 

No Action

ppbv

Endpoint 

NAAQS

status

Carson National Forest 72.0 71.9 0.1 Meet

Grand Mesa, Uncompahgre, and Gunnison 

National Forests 75.4 75.4 0.0 Exceed

Handies Peak Wilderness Study Area 74.3 74.3 0.0 Meet

Jicarilla Apache Indian Reservation 72.3 71.8 0.5 Meet

Navajo Nation 74.9 74.3 0.6 Exceed

Redcloud Peak Wilderness Study Area 74.0 74.0 0.0 Meet

Rio Grande National Forest 75.2 75.2 0.0 Exceed

San Juan National Forest 74.2 74.2 0.0 Meet

Uncompahgre Wilderness Area (BLM 

managed) 74.1 74.1 0.0 Meet

Uncompahgre Wilderness Area (USFS 

managed) 74.1 74.1 0.0 Meet

1 Year 2018

Table 4.1-55 Attainment Test 8-Hour Ozone Design Values - Four Corners Region

Areas and Monitoring Sites

Proposed 

Action 

Ozone1

ppbv

No Action 

Ozone1

ppbv

Difference 

Between 

Proposed 

Action and 

No Action

ppbv

Endpoint 

NAAQS

status

San Juan County, New Mexico (35-45-0009) 66.5 66.2 0.3 Meet

San Juan County, New Mexico (35-45-1005) 68.1 67.1 1.0 Meet

La Plata County, Colorado (08-67-1004) 69.8 69.6 0.2 Meet

La Plata County, Colorado (08-67-7003) 60.3 60.1 0.2 Meet

Montezuma County, Colorado (08-83-0101) 65.1 64.7 0.4 Meet

Source: AECOM 2013b

1 Year 2018
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March 2014 Air Quality 4.1-107

4.1.5 Air Quality Mitigation Measures

The Project Applicants have proposed measures that would be implemented to reduce or eliminate some 

of the environmental impacts of the Proposed Action. These measures include specific mitigating 

measures for certain environmental impacts, standard operating procedures that reduce or avoid 

environmental impacts, and best management practices for specific activities. These are described in 

Section 3.2.6.1. These measures are part of their application materials and are enforceable through 

permit or lease conditions. In addition, the Project Applicants must comply with additional protective 

regulatory requirements including laws, ordinances, regulations, and standards that are enforceable by 

the responsible agency over that activity. These are described in the Regulatory Compliance Framework 

Section for each resource category. Moreover, EPA issued its FIP for BART at FCPP to control air 

emissions, which led to changes in the affected environment. This completed federal action is considered 

part of the environmental baseline to which the effects of continuing operations and the Proposed Actions 

are compared. As a result of the BART ruling, APS shut down Units 1, 2, and 3 on December 30, 2013, 

and will install SCR on the remaining Units 4 and 5. Although the BART rules specifically address NOx

and particulate matter, the implementation of BART would result in a decrease of all air pollutants emitted 

as shown in Table 4.1-39.

Where the environmental analysis in this EIS recommends additional protective measures, over and 

above the applicant proposed measures, regulatory compliance, and emissions reductions resulting from 

BART compliance, they are listed below as specific mitigation measures. In this instance, the Proposed 

Action, including the continuing operations of Navajo Mine, FCPP, and the transmission lines, would not 

result in major adverse effects to air quality. Therefore, no additional mitigation is recommended.
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4.1-108 Air Quality March 2014

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