Analysis Topics: Natural Resources 

Air Quality 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-697

Air Quality 

Affected Environment 

The primary factors that influence air quality are the locations of air pollutant sources, the types and 

amounts of pollutants emitted, meteorological conditions, and topographic features. Atmospheric 

conditions, such as wind speed, wind direction, and air temperature gradients, interact with the 

physical features of the landscape to determine the movement and dispersal of air pollutants. Air 

quality in the Merced River corridor and potential impacts associated with the project alternatives are 

discussed below. 

Regulatory Context 

Regulation of air pollution is achieved through both national and state ambient air quality standards 

and emissions limits for individual sources of air pollutants. 

Federal and State Ambient Air Quality Standards 

The Clean Air Act of 1970 (42 USC 7401 et seq.) tasked the U.S. Environmental Protection Agency 

(EPA) with establishing national ambient air quality standards (NAAQS) and periodically reassessing 

whether these standards are adequate to protect public health and the national welfare, including 

those resources and values associated with national parks and wilderness areas. The NAAQS set 

thresholds for criteria pollutants, including ozone (O3), carbon monoxide (CO), nitrogen oxides 

(NOX), sulfur dioxide (SO2), suspended particulate matter (PM), and lead (Pb). Since that time, subsets 

of particulate matter have been identified for which permissible levels have been established. These 

include particulate matter of 10 microns in diameter or less (PM10) and particulate matter of 

2.5 microns in diameter or less (PM2.5). 

Under the 1988 California Clean Air Act, the California Air Resources Board has also adopted 

standards for these criteria pollutants (called California Ambient Air Quality Standards, or CAAQS) 

and applies additional standards for pollutants that are not currently included in the national 

standards. The federal and state ambient standards differ in some cases; in general, the California 

standards are more stringent, particularly for ozone and PM10. Both the EPA and the California Air 

Resources Board classify air basins in California as either in “attainment” or “nonattainment” with 

their respective standards. Areas that were once designated as nonattainment, but are now achieving 

the NAAQS, are termed “maintenance areas.” Table 9-131 shows the current state and federal 

ambient air quality standards. 

The federal government delegates the inventory of all criteria pollutants to the state, which performs 

this regulatory function and assesses air quality under NAAQS and CAAQS by inventorying emissions 

and regulating the concentrations of primary pollutants. Some of these standards contain both primary 

standards for human health and secondary standards for more indirect (e.g., ecological) endpoints, 

including acidification and eutrophication of lakes. The National Park Service (NPS) assists the State 

of California by measuring concentrations of pollutants and monitoring ecological endpoints to help 

evaluate the effectiveness of secondary NAAQS and CAAQS. 
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TABLE 9-131: AMBIENT AIR QUALITY STANDARDS

Pollutant 

Averaging 

Time 

State 

Standard 

Federal 

Primary 

Standard 

Federal 

Secondary 

Standard Major Pollutant Sources 

Ozone 

8 hour 0.070 ppm 0.075 ppm Same as 

primary 

standard 

Formed when ROG and NOx react in the presence 

of sunlight. Major sources include on-road motor 

vehicles, solvent evaporation, and 

commercial/industrial mobile equipment 1 hour 0.090 ppm --- 

Carbon 

Monoxide 

8 hour 9.0 ppm 9.0 ppm 

None Internal combustion engines, primarily gasolinepowered motor vehicles 1 Hour 20 ppm 35 ppm 

Nitrogen 

Dioxide 

Annual 

Average 0.030 ppm 0.053 ppm Same as 

primary 

standard 

Motor vehicles, petroleum refining operations, 

industrial sources, aircraft, ships, and railroads 

1 Hour 0.180 ppm 0.100 ppm 

Sulfur 

Dioxide 

Annual 

Average --- --- -- 

Fuel combustion, chemical plants, sulfur recovery 

plants, and metal processing 

24 Hour 0.04 ppm --- 

3 Hour --- --- 0.5 ppm 

1 Hour 0.25 ppm 0.075 ppm -- 

Particulate 

Matter 

(PM10) 

Annual 

Arithmetic 

Mean 

20 g/m3 --- Same as 

primary 

standard 

Dust- and fume-producing industrial and 

agricultural operations, combustion, atmospheric 

photochemical reactions, prescribed and wildland 

fires, and natural activities (e.g., wind-raised dust 

24 hour 50 g/m3 150 g/m3 and ocean sprays) 

Particulate 

Matter 

(PM2.5) 

Annual 

Arithmetic 

Mean 

12 g/m3 15 g/m3 Same as 

primary 

standard 

Fuel combustion in motor vehicles, equipment, 

and industrial sources; residential and agricultural 

burning; prescribed and wildland fires; also, 

formed from photochemical reactions of other 

pollutants, including NOx, sulfur oxides, and 

organics 24 hour --- 35 g/m3 

Lead 

Calendar 

Quarter --- 1.5 g/m3 

Same as 

primary 

standard Present source: lead smelters, battery 

manufacturing and recycling facilities. Past source: 

combustion of leaded gasoline. 30-Day 

Average 1.5 g/m3 --- --- 

Hydrogen 

Sulfide 1 hour 0.03 ppm 

No Federal Standard 

Geothermal power plants, petroleum production 

and refining 

VisibilityReducing 

Particles 

8 hour 

Extinction of 

0.23/km; 

visibility of 10 

miles or more 

See PM2.5. 

NOTE: ppm = parts per million; g/m3 = micrograms per cubic meter; km = kilometers 

SOURCE: CARB 2009a, 2011a. 
Analysis Topics: Natural Resources 

Air Quality 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-699

The State Implementation Plans 

The state and federal Clean Air Acts require nonattainment air districts to develop plans, known as 

State Implementation Plans (SIPs). SIPs are comprehensive plans that describe how the district would 

attain NAAQS. The 1990 amendments to the federal Clean Air Act set deadlines for attainment based on 

the severity of an area’s air pollution problem. SIPs are not single documents. They are a compilation of 

new and previously submitted plans, programs (e.g., monitoring, modeling, permitting), district rules, 

state regulations, and federal controls. Many of California’s SIPs rely on the same core set of control 

strategies, including emission standards for cars and heavy trucks, fuel regulations, and limits on 

emissions from consumer products. State law makes the California Air Resources Board the lead agency 

for all purposes related to the SIP. Local air districts and other agencies prepare SIP elements and submit 

them to the California Air Resources Board for review and approval. The California Air Resources Board 

forwards SIP revisions to the EPA for approval and publication in the Federal Register. The Code of 

Federal Regulations, title 40, chapter I, part 52, subpart F, section 52.220 lists all of the items that are 

included in the California SIP. At any one time, several California submittals are pending EPA approval. 

The portion of the South Fork Merced River corridor within Yosemite National Park crosses into 

both Mariposa and Madera counties, which are located in the Mountain Counties Air Basin and the 

San Joaquin Valley Air Basin, respectively. The Mountain Counties Air Basin has been designated as 

nonattainment for state and federal ozone standards. Only the Yosemite National Park portion of 

Mariposa County is designated as nonattainment for the state PM10 standard, primarily due to local 

sources near the Yosemite Valley Visitor Center monitoring site. Similarly, the San Joaquin Valley Air 

Basin has also been designated as nonattainment for state and federal ozone standards, state PM10 

standards, and state and federal PM2.5 standards. The Mariposa County Air Pollution Control District 

(MCAPCD) is the regional agency responsible for rulemaking, permitting, and enforcement activities 

affecting stationary sources in Mariposa County. No air quality plans have been prepared for the 

Mariposa County portion of the Mountain Counties Air Basin. The state has not required an ozone 

plan because of the overwhelming influence of pollutant transport on ozone conditions in Mariposa 

County. With regard to the Madera County portion of the San Joaquin Valley Air Basin, the 

San Joaquin Valley Air Pollution Control District (SJVAPCD) has developed air quality plans for 

1-hour and 8-hour ozone, as well as for PM10 and PM2.5. 

General Conformity 

Under the 1990 amendment to the Clean Air Act (section 176(c)(4)), a general conformity rule was 

established to ensure that actions taken by federal agencies in nonattainment areas conform to state 

goals for the attainment and maintenance of the NAAQS. In 1993 the EPA published guidance on this 

rule that assists federal agencies in deciding whether a conformity determination is required, and if so, 

how to make such a determination (EPA 1993). The general conformity rule is currently undergoing 

revision. 

Management actions identified herein that would occur in Mariposa County would likely be subject to 

the General Conformity Rule, given that the county is now a nonattainment area for the national 8-hour 

ozone standard. The de minimus thresholds1

 for ozone are 50 tons per year of volatile organic 

 

1 The minimum threshold for which a conformity determination must be performed. 
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compounds (VOC) and 100 tons per year of nitrogen oxides (NOx). Actions that would occur in Madera 

County are currently, and would continue to be, subject to the rule because the county lies in an area 

(San Joaquin Valley Air Basin) that has been designated as nonattainment for national ozone and PM10 

standards, which is the subject of the ozone SIP and a PM10 SIP. As a result of the San Joaquin Valley Air 

Basin’s recent designation as an extreme nonattainment area, the applicable de minimis standards for 

ozone are lower — 10 tons per year of VOC and 10 tons per year of NOx. With respect to particulates, 

Madera County’s applicable de minimis threshold for PM2.5 is 100 tons per year. 

Mandatory Class I Areas 

In addition to the state and federal requirements described above for nonattainment areas, 

section 162(a) of the federal Clean Air Act sets forth additional provisions for the protection of air 

quality across certain federal lands, such as national parks, national wilderness areas, and national 

monuments. Yosemite National Park was designated as a Class I area in 1977. This designation gives 

Federal Land Managers (FLMs) the responsibility for protecting air quality related values (AQRVs) 

from the adverse impacts of new or modified sources of emissions. Generally, an AQRV is a resource, 

as identified by the FLM, that may be adversely affected by a change in air quality and may include 

visibility or a specific scenic, cultural, physical, biological, ecological, or recreational resource 

identified by the FLM for a particular federal area (NPS, 2011t). In order to achieve greater 

consistency in the approach each agency uses to identify and evaluate AQRVs, air resource managers 

from the U.S. Forest Service (USFS), the NPS, and the U.S. Fish and Wildlife Service (FWS) FLMs 

established the Federal Land Managers’ Air Quality Related Values Work Group (FLAG) in order to: 

 Define sensitive AQRVs, 

 Identify the critical loads (or pollutant levels) that would protect an area and identify the 

criteria that define adverse impacts, and 

 Standardize the methods and procedures for conducting AQRV analyses. (USFS et al. 2010) 

AQRVs that have been identified for Yosemite National Park include visibility, pine (injury from 

ozone), high elevation lakes (acidity), and lichen (sensitive to vehicle-derived reactive nitrogen 

deposition) (Tarnay 2012). 

In 1999, the EPA published a regional haze rule to guide the preparation of state regional haze plans to 

improve air quality and reduce haze in Class I federal areas. The ultimate goal of the rule is to restore 

natural visibility conditions in Class I areas, such as Yosemite National Park, by 2064. Under the 

regulations, all states are required to develop implementation plans that demonstrate reasonable 

progress toward this goal. In January of 2009, the California Air Resources Board adopted the 

California Regional Haze Plan, which sets forth specific visibility goals for the state. The plan is part of 

a broader multi-state effort to improve visibility throughout the western region. The plan details 

baseline conditions of individual Class I areas, including Yosemite National Park, and sets a path 

toward achieving interim, reasonable progress goals statewide by 2018 (CARB 2009b). The El Portal 

Administrative Site is located within a Class II area, in which less stringent standards apply. 
Analysis Topics: Natural Resources 

Air Quality 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-701

Federal Policies 

Executive Order 13423, Issued by President George W. Bush, Jan. 24, 2007. This executive order 

sets as a policy of the United States that “Federal agencies conduct their environmental, transportation, 

and energy-related activities under the law in support of their respective missions in an environmentally, 

economically and fiscally sound, integrated, continuously improving, efficient, and sustainable manner” 

(section 1, Policy). Goals for agencies include such measures as improving energy efficiency and reducing 

greenhouse gases generated by agency operations and actions, reducing energy intensity and requiring 

that energy consumed by the agency comes from new renewable sources, reducing water consumption, 

and ensuring that agencies reduce their fleet’s total consumption of petroleum products (NPS 2007h). 

National Park Service Management Policies 

The NPS has a responsibility to protect air quality under both the 1916 Organic Act and the Clean 

Air Act. Accordingly, the service would seek to perpetuate the best possible air quality in parks to 

(1) preserve natural resources and systems; (2) preserve cultural resources; and (3) sustain visitor 

enjoyment, human health, and scenic vistas. Through the NPS Management Policies 2006, the park has 

committed to actively promoting and pursuing measures to protect AQRVs from the adverse impacts of 

air pollution. In cases of doubt as to the impacts of existing or potential air pollution on park resources, 

the park would err on the side of protecting air quality and related values for future generations (NPS 

2006a). 

It is also NPS policy that internal activities at parks must comply with all applicable federal, state, and 

local air pollution laws and regulations (NPS 2004a). To meet these goals, parks may be required to 

obtain air quality permits before conducting activities, such as prescribed burning, that emit pollutants. 

Likewise, operating permits may be required for some emission sources, such as wastewater treatment 

facilities. 

Environmental Context 

Climate and Meteorology 

California is divided into air basins that are defined partly by their meteorological and topographical 

characteristics. As previously noted, the portions of the Merced River and South Fork Merced River 

that traverse Yosemite National Park are located within two air basins: Mountain Counties Air Basin 

and San Joaquin Valley Air Basin. Generally, the uppermost reaches of the Merced River and South 

Fork Merced River lie within San Joaquin Valley Air Basin, and the lower reaches lie within Mountain 

Counties Air Basin. 

The portions of the Merced River and South Fork Merced River that traverse the park lie within the 

Sierra Nevada mountain range, which roughly parallels the eastern boundary of California and extends 

from the Cascades Range in the north to the Tehachapi Mountains in the south. Cooler climates with 

more wind are, in general, characteristic of the mountains, as contrasted with the nearby valleys. 

Mountain climatic zones are characterized by considerable vertical wind motion and by winds and 

temperatures different from those in the valleys. The Yosemite Valley, for instance, experiences 
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inversions, which occur when air temperature increases with altitude. Flat topography traps 

descending cold air at night, creating a shallow inversion layer that inhibits air pollutant dispersion and 

results in high pollutant concentrations. 

Air Quality Monitoring Data 

Federal, state, and local agencies operate a network of monitoring stations throughout California to 

collect data on ambient concentrations of air pollutants. Table 9-132 summarizes recent monitoring 

data from the monitoring stations in the project vicinity. Three of the stations are in Yosemite National 

Park (Turtleback Dome, Merced River, and Yosemite Valley Visitor Center) and one is outside of the 

park, in the Sierra National Forest (Jerseydale). The Merced River, Yosemite Valley Visitor Center (in 

Yosemite Village), and Jerseydale stations are approximately 4,000 feet above sea level, and Turtleback 

Dome is approximately 5,300 feet above sea level. As shown in table 9-131, exceedances of state and 

national standards for ozone and PM10 are recorded on occasion within the park and in the park 

vicinity. 

Ozone. Ozone is a reactive pollutant that is not emitted directly into the atmosphere, but is a 

secondary air pollutant produced in the atmosphere through a complex series of photochemical 

reactions involving volatile organic compounds (VOCs) and nitrogen oxides (NOx). These pollutants 

are known as precursor compounds for ozone. Significant ozone production generally requires ozone 

precursors to be present in a stable atmosphere with strong sunlight for approximately three hours. 

Ozone is a regional air pollutant because it is not emitted directly by sources but is formed downwind 

of sources of VOC and NOx. Short-term exposure to ozone can irritate the eyes and cause constriction 

of the airways. Besides causing shortness of breath, ozone can aggravate respiratory diseases such as 

asthma, bronchitis, and emphysema. Exposure to ozone is also associated with a wide range of effects 

on vegetation AQRVs, such as visible foliar injury, growth reductions and yield loss in annual crops, 

growth reductions in tree seedlings and mature trees, and effects that can have impacts at the forest 

stand and ecosystem level (EPA 1997). 

Particulate Matter (PM10 and PM2.5). PM10 consists of particulate matter that is 10 microns or less 

in diameter (a micron is 1 one-millionth of a meter), and PM2.5 consists of particulate matter 

2.5 microns or less in diameter. Both PM10 and PM2.5 can be inhaled into the air passages and the 

lungs and can cause lung irritation, but PM2.5 can penetrate more deeply into alveolar passages where 

diffusion into the blood stream is possible, which can result in additional adverse cardiovascular health 

effects. Particulate matter in the atmosphere results from many kinds of dust- and fume-producing 

industrial and agricultural operations, combustion, and atmospheric photochemical reactions. For 

instance, in Mariposa County, the principal sources of direct emissions of PM10 include entrainment 

of dust through vehicle travel over paved and unpaved roads, residential fuel combustion, and 

wildfires. However, PM10 and PM2.5 concentrations also reflect secondary pollutant formation 

derived from photochemical reactions involving pollutants such as VOC and NOx. As described above 

in connection with ozone, on-road motor vehicles are a principal source of regional VOC and NOx 

emissions. 
Analysis Topics: Natural Resources 

Air Quality 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-703

TABLE 9-132: AIR QUALITY DATA SUMMARY (2006-2010) FOR THE STUDY AREA

Pollutant Standarda

Monitoring Data by Year 

2006 2007 2008 2009 2010 

Ozone (Yosemite National Park — Turtleback Dome Station) 

Highest 1-Hour Average (ppm)b 0.100 0.100 0.108 0.096 0.091 

Days over State Standard 0.09 4 3 11 1 0 

Highest 8-Hour Average (ppm)b 0.094 0.097 0.102 0.086 0.085 

Days over State Standard 0.07 52 49 56 8 23 

Days over National Standard 0.075 30 25 33 26 5 

Ozone (Sierra National Forest — 6440 Jerseydale) 

Highest 1-Hour Average (ppm)b 0.101 0.099 0.108 0.096 0.109 

Days over State Standard 0.09 3 1 5 1 2 

Highest 8-Hour Average (ppm)b 0.092 0.092 0.093 0.084 0.101 

Days over State Standard 0.07 41 26 30 18 6 

Days over National Standard 0.075 13 12 17 5 3 

Particulate Matter (PM10) (Yosemite Village — Visitor Center) 

Highest 24-Hour Average – State/National 

(g/m3

)

b Highest 1-Hour Average, ppmc 

97.0 116.0 118.4 82.2 74.3 

Estimated days over State Standardc 50 2 1 2 3 2 

Estimated days over National Standardc 150 0 0 0 0 0 

State Annual Averaged 20 NA NA NA 23.6 20.3 

Particulate Matter (PM2.5) (Yosemite Village — Visitor Center) 

Highest 24-Hour Average – National 

(g/m3

)

b Highest 1-Hour Average, ppmc

36.1 134.0 130.1 47.2 61.0 

Estimated days over National Standardc 35 NA NA NA NA NA 

State Annual Averaged 12 NA 14.2 NA NA NA 

National Annual Averaged 15 NA NA NA NA NA 

NOTE: NA = Adequate data was not available. Values in bold exceed the respective air quality standard. 

a Generally, state standards are not to be exceeded and federal standards are not to be exceeded more than once per year. 

b ppm = parts per million; g/m3 = micrograms per cubic meter. c

 PM10 and PM2.5 are not measured every day of the year. 

d State statistics are based on California-approved samplers, whereas national statistics are based on samplers using federal reference 

or equivalent methods. 

SOURCE: CARB 2011b 

On occasion, concentrations of PM10/PM2.5 in the park reflect pollutant transport from upwind 

areas, such as San Joaquin Valley Air Basin; under other conditions, ambient concentrations reflect 

local sources such as campfires, entrainment of dust from vehicle movement over paved roads 

(particularly from wintertime sanding of roads for traction), and wildland and prescribed fires. 

Regional emissions of PM10/PM2.5 and their precursors within the San Joaquin Valley are expected to 

decrease over the next decade or so, largely as a result of reductions in emissions due to state and 

federal motor-vehicle emissions control standards and programs. Local emissions of PM10/PM2.5 

would continue to be proportional to the number of campsites; the level of construction-related 

activity; the extent of vehicle travel on park roads; and the frequency and extent of prescribed fires. 
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Visibility-Reducing Particles and Gases. Visibility impairment occurs as a result of the scattering and 

absorption of light by particles and gases in the atmosphere. Both primary and secondary formations 

of particles contribute to visibility impairment. Primary particles, such as elemental carbon from diesel 

and wood combustion or dust from certain industrial activities or natural sources, are emitted directly 

into the atmosphere. Secondary particles that are formed in the atmosphere from primary gaseous 

emissions include sulfate from sulfur dioxide emissions, nitrates from NOx emissions (which can also 

adversely impact lichen AQRVs from nitrogen deposition), and organic carbon particles formed from 

VOC emissions. The only primary gaseous pollutant that directly reduces visibility is nitrogen dioxide, 

which is the brown-colored gas readily visible during periods of heavy air pollution. 

Visibility conditions are commonly expressed in terms of three mathematically related metrics: visual 

range, light extinction, and deciviews. Visual range is the maximum distance at which one can identify a 

black object against the horizon and is typically described in miles or kilometers. Light extinction, which 

is inversely related to visual range, is the sum of light scattering and light absorption by particles and gases 

in the atmosphere and is expressed in terms of inverse megameters, with large values representing poorer 

visibility. Unlike visual range, the light extinction coefficient expresses the relative contribution of one 

particulate constituent (e.g., sulfates or nitrates) versus another to overall visibility impairment. The 

deciview metric was developed because changes in visual range and light extinction are not proportional 

to human perception. For example, a 5-mile change in visual range can be either very apparent or not 

perceptible, depending on the baseline level of ambient pollution. The deciview metric provides a linear 

scale for perceived visual changes over the entire range of conditions, from clear to hazy, analogous to 

the decibel scale for sound. Under many scenic conditions, a change of 1 deciview is considered to be 

perceptible by the average person. A deciview of zero represents pristine conditions. 

Current visibility impairment in Yosemite National Park ranged from 4.6 deciviews for the clearest 

20% of days during the 1990–1999 period, to 22 deciviews for the haziest 20% of days during that 

period (NPS 2002). In contrast, the corresponding range of deciview values was 3.9 (clearest 20%) to 

13.9 (haziest 20%) and 13.6 to 31.8 in Rocky Mountain National Park and Great Smoky Mountains 

National Park, respectively. Yosemite National Park visibility for the clearest 20% of days is much 

better than the NPS average, whereas visibility for the haziest 20% of days is about average. Organic 

carbon, elemental carbon, crustal matter (fugitive dust originating from the earth’s crust), nitrates, and 

sulfates are primarily responsible for visibility impairment in Yosemite Valley. 

Emission Sources. Sources of pollution generally fall into one of three categories: stationary, mobile, 

or area. Stationary sources refer to emissions sources associated with industrial or commercial 

processes. Mobile sources refer to on-road and off-road vehicles, among other nonstationary sources. 

Area sources refer to a wide range of sources that are individually minor, but are more substantial in 

aggregate. A summary of the potential emissions sources within the project area, arranged by source 

category, is shown in table 9-133. 

While air quality in a given air basin is usually determined by emission sources within the basin, it also 

can be affected by pollutants transported from upwind air basins by prevailing winds. A study of 

surface ozone in the summers of 2003 and 2005 identified the San Francisco Bay Area and eastern 

Nevada to be contributing sources of ozone pollution (Burley and Ray 2007). A similar study examined 

the potential sources of fine particulate matter within the park during the summer of 2002 and found 
Analysis Topics: Natural Resources 

Air Quality 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-705

TABLE 9-133: POTENTIAL EMISSIONS SOURCES WITHIN THE PROJECT AREA

Stationary Sources 

Air conditioners and refrigeration units Wastewater Treatment Plants 

Food Preparation (e.g., grills, stoves) Storage Tanks 

Commercial/Institutional Boilers, Heaters, and 

Fireplaces 

Stationary Pumps/Compressors/Generators 

Mobile Sources 

Landscape maintenance equipment NPS snowmobiles 

NPS aircraft NPS on-road vehicles 

Visitor vehicles Buses 

Area Sources 

Landscape maintenance equipment Campfires 

Welding Charcoal and lighter fluid consumption 

Demolition activities Consumer solvents 

Road Maintenance Dust from paved roads 

Prescribed and Wild Fire LPG Gas Combustion 

Herbicides/pesticides Solvent Use 

Livestock Surface Coating (e.g., paints/solvents) 

Waste disposal Woodworking/wood finishing 

NPS = National Park Service; LPG = liquefied petroleum gas 

SOURCE: NPS 1999d 

that although local sources contributed, wildfires as far away as western and southern Oregon were 

primarily responsible for haze within Yosemite National Park during that summer (McMeeking et al. 

2006). The California EPA concluded that all of the ozone exceedances in 1995 in the southern portion 

of the Mountain Counties Air Basin (i.e., Tuolumne and Mariposa counties) were caused by transport 

of ozone and ozone precursors from the San Joaquin Valley Air Basin (CARB 1996). 

Sensitive Receptors 

Air quality does not affect every individual in the population in the same way, and some groups are 

more sensitive to adverse health effects than others. Population subgroups sensitive to the health 

effects of air pollutants include the elderly and the young; population subgroups with higher rates of 

respiratory disease, such as asthma and chronic obstructive pulmonary disease; and populations with 

other environmental or occupational health exposures (e.g., indoor air quality) that affect 

cardiovascular or respiratory diseases. 

Such land uses and facilities as schools, children’s day care centers, hospitals, and nursing and 

convalescent homes are considered to be more sensitive than the general public to poor air quality 

because the population groups associated with these uses have increased susceptibility to respiratory 

distress. Parks and playgrounds are considered moderately sensitive to poor air quality because 

persons engaged in strenuous work or exercise also have increased sensitivity to poor air quality; 
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however, exposure times are generally far shorter in parks and playgrounds than in residential 

locations and schools, which typically lessens overall exposure to pollutants. Residential areas are 

considered more sensitive to air pollution conditions compared with commercial and industrial areas 

because people generally spend longer periods of time at their residences, with associated greater 

exposure to ambient air pollution conditions. Sensitive receptors within the project area include 

on-site staff and recreational users, specifically the elderly and the young, within developed areas of 

the Merced River corridor, including Yosemite Valley, Wawona, and El Portal. In addition to human 

sensitive receptors described above, there are also sensitive ecological receptors in the Yosemite 

National Park, such as pine and lichen AQRVs, which are susceptible to adverse effects from elevated 

ozone exposure and nitrogen deposition, respectively. 

Environmental Consequences Methodology 

Local sources of emissions would have minimal effect on regional emissions, particularly during the 

summer season when regional emissions meet or exceed federal and state standards. The exceptions 

would be wildland and prescribed fires, which can result in regionally significant emissions on a given 

day. Other local emissions sources include stationary, area, and mobile sources. The air quality impact 

assessment involves the identification and qualitative description of the types of actions under the 

various alternatives that could affect air quality, sensitive receptors and AQRVs, corresponding 

emissions sources and pollutants, and relative source strengths. In addition, quantitative criteria 

pollutant emission estimates were developed for on-road vehicular traffic for each Alternative. Based 

on the relative source strengths, an assessment was performed to determine the potential for higher 

pollutant emissions or concentrations, taking into account the frequency, magnitude, duration, 

location, and reversibility of the potential impact. Regional pollutant transport issues were evaluated in 

the context of regional cumulative impacts. The criteria that follow are used to determine these 

impacts. 

 Context. The context of the impact considers whether the impact would be local or regional. 

For the purposes of this analysis, local impacts would be those that occur in a specific area 

within a segment of the Merced River corridor. Regional impacts would be those related to the 

Mountain Counties Air Basin (MCAB) and San Joaquin Valley Air Basin (SJVAB). With respect 

to air quality issues, both local and regional perspectives are relevant. 

 Intensity. The intensity of the impact considers whether the impact would be negligible, 

minor, moderate, or major. Negligible impacts would be effects considered not detectable and 

would have no discernible effect on air quality (assumed to be 1% or less of threshold). Minor 

impacts would be those that are present, but not expected to have an overall effect on those 

conditions (assumed to occur up to 50% of the applicable threshold). Moderate impacts 

would be clearly detectable and could have an appreciable effect (assumed to occur at 

emissions levels greater than 50% but not exceed the applicable threshold). Major impacts 

would have a substantial, highly noticeable influence on local or regional air quality (assumed 

to occur when emissions exceed applicable threshold). 

Quantitative thresholds that would apply to each river segment within the project area’s 

respective air basins (i.e., MCAB and SJVAB) are described below. Notably, a major impact 

would occur if emissions exceed these thresholds. 

Actions that would occur in the Mariposa County portion of the MCAB would be subject to: 
Analysis Topics: Natural Resources 

Air Quality 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-707

Federal General Conformity Rule de minimis thresholds: 

- 50 tons per year VOC or ROG 

- 100 tons per year NOx 

Actions that would occur in the Madera County portion of the SJVAB would be subject to: 

Federal General Conformity Rule de minimis thresholds: 

- 10 tons per year VOC or ROG 

- 10 tons per year NOx 

- 100 tons per year PM2.5 

Notably, only one action — reroute Triple Peak Fork Trail upland where possible — in 

Segment 1, which is common to Alternatives 2–6, would occur in Madera County. 

 Duration. The duration of the impact considers whether the impact would occur in the short 

term or the long term. A short-term impact would be temporary in duration and would be 

associated with transitional types of impacts. A long-term impact would have a permanent 

effect on air quality. 

 Type of Impact. Impacts are evaluated in terms of whether they would be beneficial or 

adverse to air quality. Beneficial air quality impacts would reduce emissions or lower 

concentrations, and adverse impacts would have the opposite effect. 

Environmental Consequences of Alternative 1 (No Action) 

Under Alternative 1 (No Action), no policies that protect or enhance air quality in the corridor would 

be developed. Policies and actions that protect and enhance air quality in the corridor arise not from 

the Wild and Scenic Rivers Act but from such laws as the federal Clean Air Act. Alternative 1 would 

continue the current management direction and level of management intensity in the Merced River 

corridor. Lodging, camping, infrastructure, and parking would continue in the same locations, 

configurations, and at the same level of development. There would be no comprehensive approach to 

protect and enhance river values. 

Under Alternative 1, air quality in the Merced River corridor would continue to be influenced by local 

pollution sources within the park and by regional sources upwind of the park. Local emissions sources 

include stationary, area, and mobile sources. Local air quality varies based on temperature, humidity, 

wind speed, elevation, topography, and other environmental factors, such as regionwide conditions. 

Generally, the effects of local emissions sources would be most intense in those areas where the 

sources are concentrated and can be compounded by inversions, such as in the Yosemite Valley. 

Analysis of effects is qualitative, and professional judgment was applied to reach reasonable 

conclusions as to the context, intensity, and duration of potential impacts. 

All River Segments 

Impacts of wildland and prescribed fires would continue to be controlled through implementation of 

smoke management policies in the 2004 Fire Management Plan/EIS. These policies are intended to 

minimize impacts on air quality from prescribed burning within the park and region. It should be 

noted that while wildland fire drives the largest and most intense exceedances of particulate matter 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-708 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

standards in the Merced River corridor, as is the case in Yosemite Valley, the baseline levels of 

particulate emissions are already high. Several assumptions were integrated into this assessment. 

 Alternative 1 (No Action) would not affect the smoke management policies in the Fire 

Management Plan/EIS. 

 Alternative 1 would not create campfire regulations specific to the project area. 

 The NPS would continue to ensure that all stationary emissions sources under its control or 

under the control of its concessioners comply with applicable air district rules and regulations. 

 The NPS would continue to participate in the regional air quality planning processes for ozone 

and visibility impairment and would continue to review applications for new or modified 

major stationary sources upwind of the park, pursuant to the Prevention of Significant 

Deterioration regulations. 

 The NPS would comply with the EPA’s general conformity rule for any future actions that 

would occur within Mariposa and Madera counties, which are part of MCAB and SJVAB, 

respectively. 

In accordance with the 2009 Settlement Agreement, no new structures would be constructed in the 

Merced River corridor, except for minor structures that are small, temporary, easily removed, not 

habitable; designed to support existing uses, systems, and programs; located within the existing 

building footprint; and not created solely for commercial purposes. Temporary housing for employees 

displaced by the 2008 rockfall would continue as needed at Huff House, Lost Arrow, Yosemite Lodge, 

Ahwahnee Dorm, Boys Town, and El Portal Trailer Village, and for NatureBridge students at Curry 

Village. Housing for NPS employees and park partner staff would remain in current locations and at 

current levels. 

Alternative 1 accounts for 3% growth in visitation following recent trends. It is expected that more 

days during the peak season would receive the visitation currently experienced during the busiest days. 

Visitation could also increase in the off-peak seasons. Consequently, traffic congestion and associated 

air pollutant emissions during those nonpeak periods could approximate current congestion during 

peak periods. Increases in visitation during peak periods could also occur, and to the degree that such 

increases do happen, traffic congestion and air pollutant emissions would marginally increase. These 

local mobile sources would continue to include automobiles, trucks, and buses, and would remain 

subject to state and federal emissions control standards and programs. For the foreseeable future, 

motor vehicle fleet turnover, cleaner burning fuels, improved technologies, and stricter state and 

federal standards would be expected to decrease emissions per vehicle-mile-traveled (VMT). Thus, 

the overall impact of mobile source exhaust emissions would remain approximately the same as under 

existing conditions. Regional AQRV impacts (such as pine injury from ozone and visibility) would also 

be approximately the same as under existing conditions. However, in contrast to the ozone precursors, 

most of the particulate matter associated with vehicle use is related to entrainment of road dust rather 

than to exhaust. Emissions from vehicle entrainment of road dust would continue to affect air quality, 

particularly in winter and early spring, when drying road surfaces expose sand deposited for traction 

to vehicle entrainment into the atmosphere. However, even with the anticipated annual increase in 

visitation, the effect would be negligible. Were visitation to increase, road dust would be expected to 

increase in rough proportion to VMT within the park, as would those emissions associated with traffic 
Analysis Topics: Natural Resources 

Air Quality – Alternative 1 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-709

congestion and delays that would accompany such increases. Under the latter scenario, the effect on 

local air pollution conditions would be long term, minor, and adverse. 

Park management has implemented temporary access restrictions for use when traffic and parking 

conditions in Yosemite Valley are overly congested. This has the effect of reducing the number of 

incoming vehicles and their related emissions until the traffic volume and parking demand in Yosemite 

Valley decrease sufficiently (as departing visitors leave the Valley) to stabilize traffic conditions. These 

access restrictions occur when traffic in Yosemite Valley is at maximum capacity, and thus associated 

vehicle pollutant emissions would also be at peak levels. In addition, the Yosemite Area Regional 

Transportation System (YARTS) would continue to reduce the number of individual vehicles operated 

within the park. In 2011, YARTS transported 300,979 passengers into Yosemite National Park (NPS, 

2012i). The intent of YARTS is to provide an attractive alternative to private vehicles by expanding the 

range of travel options for visitors to Yosemite Valley and to other primary park destinations, and for 

employees commuting to work in the park. 

Local area pollution sources would continue to include regular maintenance activities, consumer 

products, natural gas combustion for heating/cooling and campfires. Most of these sources would 

continue in the same manner and extent as under existing conditions. However, potential future 

increases in visitor use levels would cause these sources to increase in relative proportion. Daily, 

routine, and intermittent operational maintenance intended to stabilize and protect park facilities, 

address visitor health and safety issues, and protect natural and cultural resources would continue, 

such as campground maintenance, road and trail maintenance, building and grounds maintenance, 

and utility system repair and maintenance throughout Segments 1–8. Trail and road maintenance 

would preserve the existing character, so that parking areas or trails that are currently unpaved remain 

so. Park facilities themselves — roads, parking spaces, bridge crossings, and overnight 

accommodations — would remain as they were in 2010. Campfires would continue to be subject to 

park regulations, and related emissions could increase in proportion to the increased visitation, 

especially during nonpeak periods. 

Segments 1, 5, 6, and 8: Merced River Above Nevada Fall, South Fork Merced River Above 

and Below Wawona, and Wawona Impoundment 

Wilderness and impoundment Segments 1, 5, 6, and 8 would be minimally affected by local emissions 

sources, with the exception of wildland and prescribed fires, or the occasional campfire from 

overnight visitors. Impacts from prescribed burning would continue to be controlled through 

implementation of smoke management policies in the Fire Management Plan/EIS. Although there are 

no transportation facilities in Segments 1, 5, 6, or 8, and none are proposed under Alternative 1, 

incidental future increases in traffic within the Merced River corridor would affect these segments by 

pollutant drift. In addition, impacts from in-park emissions, such as vehicles, would be more apparent 

in areas near road corridors and concentrations of visitor and administrative services. The overall 

effect on regional air pollution conditions would be long term, minor, and adverse. 

Segments 1, 5, 6, & 8 Impact Summary: Implementation of Alternative 1 (No Action) would result in 

local, long-term, minor, adverse air quality impacts within these segments. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-710 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Segment 2: Yosemite Valley 

As described above, for Segments 1–8 there could be adverse air quality impacts associated with 

transportation conditions under Alternative 1. Specific to Segment 2, there would likely continue to be 

local, minor, long-term, adverse air quality impacts associated with traffic congestion and delays that 

would continue to occur at busy intersections in Yosemite Valley and possibly increase should 

visitation levels increase in the future. Traffic emissions, as a source of nitrogen deposition, are also 

correlated to lichen AQRVs and would also likely result in long-term local, minor, adverse air quality 

impacts. Park management may continue to implement temporary access restrictions in Yosemite 

Valley when westbound traffic is backed up from Lower Yosemite Fall to the Curry Village four-way 

intersection or when all of the day parking spaces have been filled. 

The effect on air quality from existing stationary sources, such as fuel storage systems and generators, 

would be greatest immediately adjacent to the emission source, including employee housing areas, 

visitor facilities, and lodging. Emissions from stationary sources would continue to be regulated, as 

appropriate, through applicable MCAPCD regulations. In the long term, the replacement of dated 

equipment (e.g., generators) with newer, more energy-efficient models to meet NPS sustainability 

goals would result in regional and local long-term, negligible, beneficial impacts. 

Area emissions would continue to affect air quality and visibility within the Yosemite Valley under 

certain meteorological conditions. For example, particulate matter resulting from burning wood could 

remain near ground level during temperature inversions. Area sources of particulate matter in the 

Valley are the most important driver for the PM10 nonattainment status due to the strength and 

frequency of inversions. The majority of overnight visitor accommodations, and their associated 

campfires and other sources of evening smoke, are located within Segment 2. Campfires would 

continue to be subject to park regulations, and related emissions could increase in proportion to the 

increased visitation, especially during nonpeak periods. Campfires or other evening sources of smoke 

would continue to affect local air quality at levels that may be unhealthy for sensitive groups, including 

individuals with pulmonary or cardiovascular diseases, the elderly, and children. Since wood smoke 

can currently contribute enough local emissions to create unhealthy pollutant levels for sensitive 

groups, especially through many wood-burning sources operating under stable atmospheric 

conditions, the expected increase in the usage of campfires under Alternative 1 would have a 

potentially long-term, moderate, adverse impact on sensitive receptors within Segment 2. Increased 

usage of campfires would also result in a potentially long-term, local, moderate, adverse impact if the 

usage results in increased PM10 measurements above the ambient air quality standard at the Yosemite 

Valley Visitor Center monitoring site. 

Segment 2 Impact Summary: Implementation of Alternative 1 (No Action) would result in local, 

long-term, minor, adverse air quality impacts associated with vehicle emissions. Air quality within the 

segment would also experience long-term, moderate, adverse impacts from campfires and other 

evening sources of smoke. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 1 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-711

Segments 3 and 4: Merced River Gorge and El Portal 

Segments 3 and 4 would continue to be affected by local and regional sources of air pollutants, as 

described above for Segments 1–8. There are no NPS overnight accommodations along Segments 3 

and 4, and thus few campfires or other visitor-related evening sources of smoke. As described above, 

were visitation to increase, road dust would be expected to increase in rough proportion to VMT 

within the park, as would those emissions associated with traffic congestion, which would result in 

long-term, local, minor, adverse impacts. 

Segments 3 & 4 Impact Summary: Implementation of Alternative 1 (No Action) would result in local, 

long-term, minor, adverse air quality impacts within Segments 3 & 4. 

Segment 7: Wawona 

As described above for Segments 1–8, there could be regional, long-term, minor, adverse air quality 

impacts associated with transportation conditions under Alternative 1. Specific to Segment 7, there 

could be local, long-term, minor, adverse air quality impacts associated with traffic congestion and 

delays that would continue to occur at busy intersections in Wawona, and possibly increase should 

visitation levels increase in the future. Traffic emissions, as a source of nitrogen deposition, are also 

correlated to lichen AQRV impacts and would also likely result in local, long-term, minor, adverse air 

quality impacts. Park management may continue to implement temporary access restrictions in 

Wawona when all of the day parking spaces have been filled. 

The effect on air quality from existing stationary sources, such as fuel storage systems and generators, 

would be greatest immediately adjacent to the emission source, including the Wawona Store and 

Wawona Hotel. Emissions from stationary sources would continue to be regulated, as appropriate, 

through applicable MCAPCD regulations. In the long term, the replacement of dated equipment (e.g., 

generators) with newer, more energy-efficient models to meet NPS sustainability goals would result in 

regional and local, long-term, negligible, beneficial impacts. 

Campfires would continue to be subject to park regulations, and related emissions could increase in 

proportion to the increased visitation, especially during nonpeak periods. Since wood smoke can 

currently contribute enough local emissions to create unhealthy pollutant levels for sensitive groups, 

especially through many wood-burning sources operating under stable atmospheric conditions, the 

expected increase in the usage of campfires under Alternative 1 would have a potentially long-term, 

local, moderate, adverse impact on sensitive receptors. 

Segment 7 Impact Summary: Implementation of Alternative 1 (No Action) would result in local, 

long-term, minor, adverse air quality impacts associated with vehicle emissions. Air quality within the 

segment would also experience long-term, moderate, adverse impacts from campfires and other 

evening sources of smoke. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-712 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Summary of Alternative 1 (No Action) Impacts 

Under Alternative 1, air quality in the Merced River corridor would continue to be influenced by local 

pollution sources within the park and by regional sources upwind of the park. The relative importance 

of local and regional sources would continue to vary by season, diurnally, and by pollutant. 

Furthermore, nonwilderness portions of the corridor would be affected by local emissions sources to a 

much greater extent than wilderness portions. Local stationary sources would continue to be regulated 

under the MCAPCD rules and regulations, some local area sources would continue to be subject to 

park regulations, and mobile sources would continue to be subject to state and federal tailpipe 

emissions standards. With respect to ozone precursors, overall local emissions under Alternative 1 

would be similar to existing conditions. AQRV impacts (such as pine injury from ozone, visibility, and 

lichen sensitivity to nitrogen deposition) would also be approximately the same as under existing 

conditions. With no increase in visitation or VMT within the corridor, the effect of particulate matter 

on air quality would be negligible. However, should VMT increase by 3%, the long-term impacts 

would be minor and adverse. 

Cumulative Impacts of Alternative 1 (No Action) 

Cumulative effects on air quality discussed herein are based on analysis of past, present, and 

reasonably foreseeable actions in the Yosemite region in combination with potential effects of 

Alternative 1. The projects identified below include only those that could affect air quality within the 

study area or that could be affected by air pollutant sources within the Merced River corridor. 

Past Actions 

Past actions have resulted in both adverse and beneficial impacts on air quality. The majority of past 

projects listed in Appendix C (Cumulative Actions) had short-term, regional and local adverse impacts 

on air quality resulting from temporary construction activities (i.e., associated with ozone precursors 

from equipment and motor vehicle exhaust, as well as fugitive dust from ground-disturbing activities 

and vehicular travel over paved and unpaved roads), which have no net adverse or beneficial impacts 

on current or future air pollution conditions. The following past projects had long-term, minor, 

beneficial impacts on transportation and associated regional and local air pollution conditions, which 

would continue under Alternatives 2–6. 

The Yosemite Area Regional Transportation System is a regional transportation system, established 

in 2000, whose intent is to provide an alternative to private vehicles by expanding the range of travel 

options for visitors to Yosemite Valley and to other primary park destinations, and for employees 

commuting to work in the park. It also provides a means for visitors to travel to Yosemite Valley when 

restricted access measures are implemented for private vehicles during times of severe congestion. In 

2011, YARTS transported 300,979 passengers into Yosemite National Park (NPS, 2012i). This regional 

transportation system has a regional and local, long-term, negligible beneficial impact by reducing the 

number of day visitors arriving in private vehicles. 

Housing Projects (i.e., Curry Village Employee Housing, Curry Village Huff House Temporary 

Housing, Yosemite Valley Lost Arrow Temporary Employee Housing, and Yosemite Valley Ahwahnee 
Analysis Topics: Natural Resources 

Air Quality – Alternative 1 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-713

Temporary Employee Housing) included the construction of housing and related facilities to 

accommodate concessioner employees. The housing units replaced concessioner housing lost in the 

January 1997 flood and the rockfall events at Curry Village in October 2008, and were developed in 

consultation with litigants as part of a settlement agreement concerning the 2005 Merced Wild and Scenic 

River Comprehensive Management Plan. These actions provide temporary lodging for concessioner 

employees, and are needed to help meet immediate short-term housing needs for the park concessioner 

until permanent employee housing is available. Construction was completed between 2007 and 2009. 

Construction of housing units resulted in regional and local, short-term, minor, adverse impacts. Over 

the long-term, since the housing replaced lost units to maintain capacity, there would no net adverse or 

beneficial impacts on current or future air pollution conditions. 

Yosemite Valley Shuttle Bus Stop Improvements involved the preparation of preliminary design 

plans, environmental compliance documents, and construction drawings; the construction of six 

10-foot by 80-foot concrete braking pads; the rehabilitation or replacement of 94,000 square feet of 

asphalt road approaches; and the construction of bus stop shelters. Construction was completed in 

2010. These improvements support shuttle bus service in Yosemite Valley, a local, long-term, minor, 

beneficial impact. 

Hybrid Electric-Diesel Shuttle Bus Procurement consisted of the purchase of diesel hybrid transit 

buses by the NPS. Hybrid bus operations result in regional and local long-term, negligible benefits 

related to fuel usage and air pollutant emissions compared with diesel-only buses (NPS 2005C). 

Present Actions 

Present actions proposed in the region are separated below into four general categories: (1) projects 

anticipated to have a net beneficial impact, (2) projects anticipated to have both beneficial and adverse 

impacts, (3) projects anticipated to have adverse impacts, and (4) projects anticipated to have a no-net 

adverse or beneficial impact. 

Present projects that could have a corridorwide, long-term, minor, beneficial, cumulative impact on air 

quality include: 

 2004 Fire Management Plan/EIS smoke management policies

 The following projects would individually, and in combination, encourage travel to the park 

by alternative (nonprivate vehicle) modes, and would manage traffic and parking to reduce 

congestion and associated air pollutant emissions: 

- Increased Yosemite Area Regional Transportation System services 

- Changeable electronic signs in Mariposa, Midpines, and El Portal, alerting drivers to 

traffic conditions in Yosemite Valley 

- Computer-aided Dispatch/Automatic Vehicle Locator 

- Software design and purchase to process raw data from vehicle counters to produce 

useful information for visitors on parking and traffic conditions 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-714 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Restricted access measures would continue to control the volume of incoming vehicles when traffic and 

parking conditions in Yosemite Valley are overly congested. The YARTS would continue to provide an 

alternative to individual private vehicles operated within the park. 

Present projects that could have a short-term, adverse impact due to construction activities, but a longterm, beneficial, cumulative impact on traffic-related air quality include 

 South Park Intelligent Transportation System: electronic signs and automatic vehicle counters 

at entrance stations and parking lots to know when parking lots are full 

 Parking alternative option at the El Portal Maintenance Facility 

 Parkwide Communication Data Network (CDN) infrastructure upgrade 

Although the above projects would have some site-specific, short-term, adverse impacts (e.g., 

construction-related air pollution), the general goal of each of these projects is to improve 

transportation circulation, which would also improve the associated air quality. 

Present projects that could have a short-term, adverse impact on air quality include all projects not 

mentioned above that include some temporary construction activities. There would be no net, longterm, adverse or beneficial impacts on air quality from these projects. 

Reasonably Foreseeable Future Actions 

Similar to past actions, reasonably foreseeable future actions would result in both adverse and 

beneficial impacts on air quality. Reasonably foreseeable future projects that could have a long-term, 

beneficial, cumulative impact on air quality include: 

 Transit Passenger Information System 

Other beneficial impacts for reasonably foreseeable future actions are similar to those discussed for 

past and present actions (i.e., the restricted access measures and increased Yosemite Area Regional 

Transportation System services). Reducing traffic congestion and encouraging travel to the park by 

alternative (nonprivate vehicle) modes would have regional and local, long-term, negligible beneficial 

impacts on air quality. 

Reasonably foreseeable future actions that could have a short-term, adverse impact on air quality 

include all projects that include some temporary construction activities. There would be no-net, longterm, adverse or beneficial impacts on air quality from these projects. 

Human activities (e.g., suburban growth, industry, transportation, farming and ranching) in the 

San Joaquin Valley, San Francisco Bay Area, and Sierra foothills continue to create air quality impacts 

that occasionally violate federal standards, particularly for ozone and for particulates. Some of these 

pollutants disperse into the Yosemite area, affecting the park’s air quality and visibility. These adverse 

impacts are expected to continue for the foreseeable future with anticipated population growth. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 1 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-715

Overall Cumulative Impact 

Because Alternative 1 would not involve substantial construction projects, it is not anticipated to 

contribute to short-term, adverse impacts on air quality resulting from construction activities. 

Continued management of traffic and encouragement of alternative forms of transportation would 

have regional and local, long-term, negligible to minor beneficial impacts on air quality. 

Over the long term, with respect to ozone, conditions in the Merced River corridor would be determined 

almost entirely by regional emissions trends instead of by local emissions sources under Alternative 1. 

The regional, long-term impact would most likely be minor and beneficial, owing to the emissions 

reductions expected to occur with implementation of ongoing state and federal mobile-source control 

programs. With respect to particulate matter, conditions in the corridor would be determined by both 

regional sources and local sources, and the relative influence of these two types of sources would vary 

from day to day and season to season. Under Alternative 1, with visitation assumed to remain constant, 

impacts from particulate matter would be negligible. However, if visitation or VMT within the corridor 

were to increase, particulate matter would be expected to increase in rough proportion to VMT (owing 

to entrainment of dust), which would have a local, long-term, minor, adverse impact on air pollution 

conditions. The increased usage of campfires would result in a long-term, local, moderate, adverse 

impact on air pollution conditions. 

Environmental Consequences of Actions Common to Alternatives 2–6 

For Alternatives 2–6, as described above for Alternative 1 (No Action), emissions from wildland and 

prescribed fires would continue to be controlled through implementation of smoke management 

policies in the Fire Management Plan/EIS. These policies are intended to minimize impacts on air 

quality from prescribed burning within the park and region. Several assumptions were integrated into 

this assessment. 

 Alternatives 2–6 would not affect the smoke management policies in the Fire Management 

Plan/EIS. 

 Alternatives 2–6 would not create campfire regulations specific to the project area. 

 The NPS would continue to ensure that all stationary emissions sources under its control or 

under the control of its concessioners comply with applicable air district rules and regulations. 

 The NPS would continue to participate in the regional air quality planning processes for ozone 

and visibility impairment and would continue to review applications for new or modified 

major stationary sources upwind of the park, pursuant to the Prevention of Significant 

Deterioration regulations. 

 The NPS would comply with the EPA general conformity rule for any future actions that 

would occur within Mariposa and Madera counties, which are part of MCAB and SJVAB, 

respectively. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-716 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

All River Segments 

Impacts of Actions to Protect and Enhance River Values 

Corridorwide actions to protect and enhance river values that would occur across Alternatives 2–6 

involve restoration and protection of the channel itself, meadow and riparian habitats, and upland 

vegetation. These include restoration of six miles of informal trails, removal of abandoned 

underground infrastructure, improvement of river access points, management of large wood, and the 

removal of riprap, among other activities. Such actions would involve temporary emissions of air 

pollutants, which would likely include ozone precursors from equipment and motor vehicle exhaust, 

as well as fugitive dust from ground-disturbing activities and vehicular travel over paved and unpaved 

roads. Pollutant emissions would vary based on the intensity of construction (i.e., type and quantity of 

equipment, number of workers and trucks, area disturbed), time of day (due to inversions during the 

night and mixing during days), and duration of construction activities. Construction activities for each 

segment are assumed to be similar to those generally described herein, just with differing intensities. 

Compliance with the dust abatement and exhaust mitigation measures MM-AIR-1 and -2, which 

would reduce particulate emissions and NOx during construction (included in Appendix C), for 

applicable actions would reduce potential regional and local short-term, negligible to moderate 

impacts associated with construction emissions to the extent feasible.

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur across all segments under Alternatives 2-6 include 

removing 3,400 feet of riprap from the river bank and revegetating with riparian species, and replacing 

an additional 2,300 feet of riprap with bioengineered riverbank stabilization devices. This work would 

require the use of heavy equipment, including loaders and dump trucks. The removal, transport, 

disposal, restoration, and monitoring work associated with these actions would require several weeks 

of park staff time to implement, but would not substantially disrupt other ongoing construction, 

demolition, and restoration activities in the Valley and beyond. As a result, these actions would result 

in short-term regional and local, negligible to moderate, adverse impacts on air quality, even after 

implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with parking and housing facilities would 

involve temporary emissions of air pollutants, which would likely include ozone precursors from 

equipment and motor vehicle exhaust, as well as fugitive dust from ground-disturbing activities and 

vehicular travel over paved and unpaved roads. Pollutant emissions would vary based on the intensity 

of construction (i.e., type and quantity of equipment, number of workers and trucks, area disturbed), 

time of day (due to inversions during the night and mixing during days), and duration of construction 

activities. Compliance with the dust abatement and exhaust mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Long-term Impacts of Actions to Manage User Capacities, Land Use, and Facilities would primarily be 

associated with on-road vehicles (visitors and employees) and local area pollution sources. Local 
Analysis Topics: Natural Resources 

Air Quality – Common to Alternatives 2-6 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-717

mobile sources would include automobiles, trucks, and buses and would remain subject to state and 

federal emissions control standards and programs, which are expected to lead to a continuing decrease 

in emissions per VMT for the foreseeable future, which would likely be regionally minor and 

beneficial. VOC and NOx are precursor compounds associated with ozone formation. However, in 

contrast to the ozone precursors, most of the particulate matter associated with vehicle use is related 

to entrainment of road dust rather than to exhaust, which would likely be local, negligible, and 

adverse. 

In general, local area pollution sources would include regular maintenance activities, consumer 

products, natural gas combustion for heating/cooling, and campfires. Daily, routine, and intermittent 

operational maintenance intended to stabilize and protect park facilities, address visitor health and 

safety issues, and protect natural and cultural resources include campground maintenance, road and 

trail maintenance, building and grounds maintenance, and utility system repair and maintenance 

throughout Segments 1–8. Visitors and employees may use consumer products, such as hair spray, that 

emit VOC. Natural gas combustion may be used for water heaters or other facility systems, which emit 

ozone precursors and particulates. Campfires emit particulate matter and would continue to be subject 

to park regulations. Impacts of these local sources would likely be regional and local, negligible, and 

adverse. 

Segment 2: Yosemite Valley 

Impacts of Actions to Protect and Enhance River Values 

Actions to protect and enhance river values that would occur in Yosemite Valley under Alternatives 2-6 

involve removal of abandoned infrastructure and other development affecting the Merced River’s 

hydrologic function, extensive meadow restoration, and management of high visitor-use areas to address 

associated impacts on riparian habitats and sensitive cultural resources. Removal of abandoned or 

obsolete infrastructures would reduce ongoing impacts on meadow hydrology and lessen channel scour. 

Upland restoration activities, including removal of informal trails, roadbeds, and parking areas, would 

improve meadow health. The demolition, removal, transport, disposal, restoration would require the use 

of heavy equipment over a period of several weeks. As a result, these actions would result in short-term 

regional and local, negligible to minor, adverse impacts on air quality, even after implementation of 

mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 2 under Alternatives 2-6 include: restoring 4.5 acres of riparian 

habitat in the area of Yosemite Lodge and 20 acres in the area of the Former Upper Pines Loop 

Campground; restoring impacted areas of Ahwahnee Meadow, including through removal of tennis 

courts; improving access and removing infrastructure from riparian areas at Cathedral Beach, 

Housekeeping Camp, and Bridalveil; constructing a boardwalk extension to reduce Sentinel Meadow 

trampling; fencing and vegetation management at Stoneman Meadow, restoring floodplain habitat at 

Devil’s Elbow, removing one and paving and formalizing five other roadside pullouts along El Portal 

Road, and filling ditches not serving current operational needs. This work would require the use of 

heavy equipment, including excavators, skid steers, loaders, and dump trucks. The demolition, 

removal, transport, disposal, restoration, and monitoring work associated with these actions would 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-718 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

require more than one year of park staff time to implement. As a result, these actions would result in 

short-term regional and local, negligible to moderate, adverse impacts on air quality, even after 

implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur within Segment 2 under Alternatives 2-6 include: 

placing engineered logjams in the channel between Clarks and Sentinel Bridges; and removing the 

abandoned gauging station at Pohono Bridge, removing the footings and former river gauge base at 

Happy Isles, and restoring these areas to natural conditions. This work would involve the use of heavy 

equipment, including excavators, a skid steer, and dump trucks, and require approximately more than 

17 weeks to implement. As a result, these actions would result in short-term regional and local, minor 

to moderate, adverse impacts on air quality, even after implementation of mitigation measures 

MM-AIR-1 and -2 (included in Appendix C). 

Cultural Resource Actions. Specific projects to protect and enhance the river’s cultural values that 

would occur within Segment 2 under Alternatives 2-6 include rehabilitation of informal trails and 

parking in the vicinity rock art and rock shelters in the area of Bridalveil Falls, fencing and/or 

restricting access to the archeologically significant large bedrock mortar (pounding rock) next to 

Yosemite Falls Trail, restoration of impacted portions of Ahwahnee Meadow, and removal of 

abandoned infrastructure from the Bridalveil sewer plant to enhance oak recruitment. With the 

exception of abandoned infrastructure removal, the majority of this work would be completed 

through the use of hand tools. As such, the impact on air quality would be regional and local, shortterm, negligible to minor, and adverse. 

Scenic Resource Actions. Specific projects to protect and enhance the river’s scenic values that would 

occur within Segment 2 under Alternatives 2-6 include: selective thinning of conifers and other 

vegetation in the vicinities of The Ahwahnee and Meadow, Bridalveil Falls and West Valley, Cooks and 

Sentinel Meadows, Curry Village, El Capitan, Housekeeping Camp, Yosemite Lodge, and other areas 

of the Valley; restoring grassland and oak habitat in the areas of Bridalveil Straight; repairing riverbank 

erosion at Clark’s Bridge; and addressing informal trails and trampling at the east end of El Capitan 

Meadow. Much of this work would be accomplished through the use of hand tools, but could also 

involve heavy equipment for various handling, transport, and restoration activities. This work would 

occur over the course of several years. As a result, these actions would result in short-term regional 

and local, negligible to moderate, adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Actions to manage visitor use and facilities within Segment 2 that would occur under Alternatives 2-6 

involve substantial changes to campsites, visitor and administrative facilities, employee housing, and 

transportation. The construction, demolition, transport, and disposal activities associated with this 

work would contribute to a short-term, regional and local, moderate, adverse impact on air quality, 

even after implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). These 

actions would have a long-term, local, minor, beneficial impact on air quality within Segment 2, as 

vehicle traffic and visitation would be reduced as a result. 
Analysis Topics: Natural Resources 

Air Quality – Common to Alternatives 2-6 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-719

Curry Village and Campgrounds. The park would remove the Happy Isles Snack Stand at Curry 

Village. At The Ahwahnee, the park would remove the swimming pool and tennis courts; redesign, 

formalize, and improve drainage within the existing parking lot; and construct a new 50 parking space 

lot east of the current parking area. These actions would require the use of heavy equipment and 

demolition activities. As such, the impact on local air quality would be short-term, minor, and adverse. 

The addition of parking would provide access to the valley for a greater number of private vehicles, 

resulting in a local, long-term, negligible, adverse air quality impact. 

Camp 6 and Yosemite Village. The park would remove from Yosemite Village the Concessioner 

General Office, Concessioner Garage, and the Arts and Activities Center (Bank Building), and 

repurpose the Village Sports Shop for public use. It would also construct a new maintenance building 

near the Government Utility Building. The park would remove roadside parking along Sentinel Drive 

and expand Camp 6 parking into the footprint of the Concessioner Garage. To improve visitor access 

between the Camp 6 area and Village, the park would construct a pathway connecting the new Camp 6 

parking lot with the repurposed Village Sports Shop. These actions would require the use of heavy 

equipment and demolition activities. As such, the impact on local air quality would be short-term, 

minor, and adverse. 

West Yosemite Valley. The park would remove the NPS Volunteer Office, post office, swimming 

pool, and snack stand. It would also remove old and temporary employee housing (Thousands Cabins 

and Highland Court) and replace it with new housing. In addition, the park would relocate the 

Yosemite Lodge maintenance and housekeeping facilities and repurpose the food court. These actions 

would require the use of heavy equipment and demolition activities. As such, the impact on local air 

quality would be short-term, minor, and adverse. 

Segment 2 Impact Summary: Actions to protect and enhance river values would result in regional and 

local, short-term, adverse impacts on air quality, ranging from negligible to moderate. No long-term 

impacts would be expected. Actions to manage user capacities, land use, and facilities within 

Segment 2 would have regional and local, short-term, negligible adverse impacts. Over the long-term, 

the impacts of these actions would be local, long-term, minor, and beneficial. 

Segments 3 and 4: Merced River Gorge and El Portal 

Impacts of Actions to Protect and Enhance River Values 

To protect and enhance river values within the Merced River gorge and El Portal, the park would 

remove informal trails, nonessential roads, fill materials, and abandoned infrastructure throughout 

Segments 3 and 4. The demolition, removal, transport, and disposal of waste materials; and restoration 

of these areas would have a short-term, regional and local, negligible to minor adverse impact on air 

quality within Segments 3 and 4. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 4 under Alternatives 2-6 include removing development, asphalt, and 

imported fill from the Abbieville and Trailer Village areas and recontouring and revegetating the 

150-foot riparian buffer. The project would require the use of a skid steer and dump truck, and take 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-720 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

several weeks to complete. Accordingly, this action would result in short-term regional and local, 

negligible, adverse impacts on air quality. 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic resource values include restoring the Greenemeyer Sand Pit to natural 

conditions. The work would require the use of heavy equipment over a period of several weeks. 

Accordingly, this action would result in short-term regional and local, negligible, adverse impacts on 

air quality. 

Scenic Resource Actions. Specific projects to protect and enhance the river’s scenic values that would 

occur within Segment 3 under Alternatives 2-6 include: selective thinning of conifers in the area of the 

Cascade Falls viewpoint. Much of this work would be accomplished through the use of hand tools, but 

could also involve heavy equipment for various handling, transport, and restoration activities. This 

work would occur over the course of a few days and would not be expected to disrupt other 

restoration activities. Accordingly, this action would result in short-term regional and local, negligible, 

adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Under each alternative, the park would construct infill housing in El Portal Village Center. The park 

would also construct a restroom for visitor use in Old El Portal. The work would require the use of 

heavy equipment throughout the construction process. As such, the projects would have a short-term, 

regional and local, negligible to minor, adverse impact on air quality within Segment 4. Over the longterm, occupation of the new residential units would contribute to a local, negligible, adverse impact on 

air quality within Segment 4. 

Segments 3 & 4 Impact Summary: Actions to protect and enhance river values would have a shortterm, regional and local, negligible to minor adverse impact on air quality within Segments 3 and 4. 

These actions would not be expected to have a long-term air quality impact. Actions to manage user 

capacities, land use, and facilities within Segments 3 & 4 would have local, long-term, minor, adverse 

air quality impacts. 

Segments 6 and 7: Wawona and Wawona Impoundment 

Impacts of Actions to Protect and Enhance River Values 

The park would improve Wawona Campground wastewater and refuse management and facilities, 

remove abandoned infrastructure, and undertake numerous site-specific management measures to 

counteract or minimize ongoing impacts on cultural resources. These actions would have a short-term, 

regional and local, negligible, adverse impact on air quality within Segment 7.

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic values that would occur within Segment 7 under Alternatives 2-6 include developing a waste 

water collection system, including the construction of a pump station above the Wawona Campground. 

This work would require the use of heavy equipment, including an excavator, skid steer, loader, and 
Analysis Topics: Natural Resources 

Air Quality – Common to Alternatives 2-6 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-721

dump truck. This effort would require approximately one month of crew time to complete. Accordingly, 

this action would result in short-term regional and local, negligible, adverse impacts on air quality. 

Cultural Resource Actions. Specific projects to protect and enhance the river’s cultural values that 

would occur within Segment 7 under Alternatives 2-6 include removing and relocating campsites that 

cause potential impacts to sensitive archeological resources. This work could require the use of heavy 

equipment, including an excavator, skid steer, loader, and dump truck. This effort would require 

approximately one week of staff time to complete. Accordingly, this action would result in short-term 

regional and local, negligible, adverse impacts on air quality. Over the long-term, reduced campsites 

would result in reduced campfires, which would be a local, negligible, beneficial impact. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

To improve operational efficiency, the park would construct new facilities to house maintenance 

operations and a new wildland fire station within Segment 7. The park would also remove staged 

materials, abandoned utilities, vehicles, and a parking lot from the riparian buffer at the Wawona 

Maintenance Yard and restore the area’s native ecosystem, and remove roadside parking between the 

Wawona Store and Chilnualna Falls Road. The construction and restoration activities associated with 

these projects would involve the use of heavy equipment and occur over a period of several months. 

The resulting impact on Segment 7 air quality would be regional and local, short-term, minor to 

moderate, and adverse, even after implementation of mitigation measures MM-AIR-1 and -2. 

Wawona. The park would redesign the bus stop at the Wawona Store to accommodate increased 

visitor use. This work would be completed largely with hand tools and some power tools. As a result, 

the air quality impact would be local, short-term, negligible, and adverse. 

Segment 7 Impact Summary: Actions to protect and enhance river values within Segments 6 & 7 

would have a local, negligible, beneficial air quality impact. Actions to manage user capacities, land use, 

and facilities would not be expected to have a long-term air quality impact. 

Summary of Impacts Common to Alternatives 2–6 

Air quality in the Merced River corridor would continue to be influenced by local pollution sources 

within the park and by regional sources upwind of the park. The relative importance of local and 

regional sources would continue to vary by season and by pollutant. Furthermore, nonwilderness 

portions of the corridor would be affected by local emissions sources to a much greater extent than 

wilderness portions. Local stationary sources would continue to be regulated under the applicable air 

district rules and regulations, some local area sources would continue to be subject to park regulations, 

and mobile sources would continue to be subject to state and federal tailpipe emissions standards. 

Many of the action items would involve varying degrees of short-term construction activities that would 

result in short-term, negligible to moderate (depending on action item construction phasing/activity 

overlap) impacts with regard to ozone precursors and particulate emissions from equipment and 

vehicular exhaust and fugitive dust. Compliance with mitigation measures MM-AIR-1 and -2 (included 

in Appendix C) for applicable actions would reduce these potential short-term, adverse impacts 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-722 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

associated with construction emissions to the extent feasible. Even after mitigation, regional and local 

short-term, negligible to moderate, adverse impacts from construction would be expected. 

Environmental Consequences of Alternative 2: Self-reliant Visitor Experiences and 

Extensive Floodplain Restoration 

All River Segments 

Impacts of Actions to Protect and Enhance River Values 

Impacts associated with implementation of Alternative 2 would be similar to those described above for 

the analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local 

short-term, negligible to moderate impacts associated with construction emissions to the extent 

feasible. 

With regard to regional, long-term impacts associated with the reduced visitor capacity under 

Alternative 2, on-road mobile emissions were quantified using the California Air Resources Board’s 

emissions factors model (EMFAC2007) and compared to the Federal General Conformity thresholds. 

The results are shown in table 9-134, below. Although bus operations are projected to increase under 

Alternative 2, the reduction in total daily visitor and administrative use and capacity would result in a 

regional and local long-term, minor, beneficial impact owing to reduced on-road vehicles in the park, 

as depicted in the table. Regional and local impacts to AQRVs (such as pine injury from ozone, 

visibility, and lichen sensitivity to nitrogen deposition) would also be long-term, minor, and beneficial. 

Other local, long-term operational impacts of Alternative 2 are described below for each segment. 

Segments 1, 5, 6, and 8: Merced River Above Nevada Fall, South Fork Merced River Above 

and Below Wawona, and Wawona Impoundment 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the analysis 

common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance River Values 

under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 (included in 

Appendix C) for applicable actions would reduce potential regional and local short-term, negligible to 

moderate impacts associated with construction emissions to the extent feasible. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 2 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-723

TABLE 9-134: ON-ROAD VEHICLE CRITERIA AIR POLLUTANT EMISSIONS (tons/year)a

Scenario NOx ROG 

Alternative 2 Emissions 18 20 

Alternative 1 (No Action) Emissions 22 26 

Incremental Changeb (4) (6) 

Federal General Conformity Thresholdc 100 50 

Impact Intensity, Type?d Minor, Beneficial Minor, Beneficial 

a Emissions were calculated using EMFAC2007 factors and assume 2.4 visitors per car with 

approximately 22 VMT per vehicle (calibrated based on annual VMT projected for Alternative 1 

assuming 240 days/year peak and shoulder seasons) and bus trip VMT from Supporting Information: 

A Life-Cycle Greenhouse Gas Inventory for Yosemite National Park (Villalba et al 2012b). User 

capacities included in chapter 7 were totaled for each alternative to determine the regional air 

pollutant emissions. Specific assumptions and emission factors incorporated into the calculations are 

included in Appendix G. b Values in (parentheses) are net reductions with respect to Alternative 1 (No Action) emissions. 

c

 Federal General Conformity thresholds for the Mariposa County portion of the MCAB. 

d Negligible impacts would be effects considered not detectable and would have no discernible effect 

on air quality (assumed to be 1% or less of threshold). Minor impacts would be those that are 

present but not expected to have an overall effect on those conditions (assumed to occur up to 50% 

of the applicable threshold). Moderate impacts are clearly detectable and could have an appreciable 

effect (assumed to occur at emissions levels greater than 50% but does not exceed the applicable 

threshold). Major impacts would have a substantial, highly noticeable influence on local or regional 

air quality (assumed to occur when emissions exceed applicable threshold). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to the Merced Lake 

Backpackers Camp, Merced Lake High Sierra Camp, and Little Yosemite Valley would be similar to 

those described above for the analysis common to Alternatives 2–6 (see discussion of Impacts of 

Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). Compliance 

with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable actions would 

reduce potential regional and local short-term, negligible to moderate impacts associated with 

construction emissions to the extent feasible. 

Wilderness areas would be minimally affected by local emissions sources, with the exception of 

wildland and prescribed fires, or the occasional campfire from overnight visitors. Impacts from 

prescribed burning would continue to be controlled through implementation of smoke management 

policies in the Fire Management Plan/EIS. In addition, impacts from in-park emissions, such as 

vehicles, would be more apparent in areas close to roads and concentrations of visitor and 

administrative services. With fewer on-road vehicles in the vicinity under Alternative 2, the overall 

effect on local air pollution conditions would be long term, minor, and beneficial. 

Merced Lake High Sierra Camp. The park would close the Merced Lake High Sierra Camp and 

remove all associated infrastructure, convert the area to designated Wilderness, and expand dispersed 

camping at Merced Lake Backpackers Camping Area into the former High Sierra Camp footprint. 

These actions would primarily involve the use of hand tools and a limited amount of power 

equipment. However, removal of these facilities would likely require several helicopter trips. As such, 

the impact on local air quality would be short-term, negligible, and adverse. The reduction in lodging 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-724 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

units would reduce total overnight visitation and energy required to run the facility, resulting in a local, 

long-term, negligible, beneficial air quality impact. 

Segments 1, 5, 6, & 8 Impact Summary: Actions to manage user capacities, land use, and facilities 

within Segments 1, 5, 6, and 8 would have long-term, minor, beneficial impacts on air quality within 

these segments. 

Segment 2: Yosemite Valley 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 2 under Alternative 2 include: rerouting trails at Ahwahnee 

Meadows; removing and restoring a portion of Northside Drive (900 feet) and rerouting the bike path; 

removing 1,335 feet of Southside Drive, re-alignment of the road, reconfiguring Curry Orchard 

parking lot, and extending the Stoneman Meadow boardwalk; removing development, asphalt, and fill 

material, and restoring 35.6 acres of floodplain at the former Upper and Lower River campgrounds; 

removing campsites and infrastructure from the 100-year floodplain and restoring an additional 

25.1 acres of floodplain and riparian habitat; and removing informal trails and informal parking at 

El Capitan Meadow. This work would require the use of heavy equipment, including excavators, skid 

steers, loaders, and dump trucks. The demolition, transport, disposal, and restoration work would 

require approximately 65 weeks of crew and equipment time over a period of three years. The 

resulting impact on regional and local air quality would be short-term, negligible to moderate, and 

adverse, even after implementation of mitigation measures MM-AIR-1 and -2. 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur within Segment 2 under Alternative 2 include: 

relocating unimproved Camp 6 parking and rerouting a portion of Northside Drive; removing the 

Stoneman, Ahwahnee and Sugar Pine Bridges; and restoring these areas to natural conditions. This 

work would require the use of heavy equipment, including excavators, skid steers, loaders, and dump 

trucks. The demolition, transport, disposal, and revegetation activities associated with this work would 

require approximately 30 weeks of crew and equipment time. The resulting impact on regional and 

local air quality would be short-term, negligible to moderate, and adverse, even after implementation 

of mitigation measures MM-AIR-1 and -2. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping, lodging, parking, 

circulation, employee housing, and service facilities would be similar to those described above for the 
Analysis Topics: Natural Resources 

Air Quality – Alternative 2 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-725

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local 

short-term, negligible to moderate impacts associated with construction emissions to the extent 

feasible. 

Overnight visitation and total daily use levels would be 26% and 33% less, respectively, than under 

Alternative 1. With fewer on-road vehicles under Alternative 3, the effect on local air pollution 

conditions would be long term, minor, and beneficial. However, the majority of campsites and their 

associated campfires and other sources of evening smoke are located within Segment 2. These sources 

of smoke would continue to affect local air quality at levels that may be unhealthy for sensitive groups, 

including individuals with pulmonary or cardiovascular diseases, the elderly, and children. Wood 

smoke can contribute enough local emissions currently to create unhealthy pollutant levels for 

sensitive groups, especially many wood burning sources operating under stable atmospheric 

conditions. Reduced campsites along this segment (estimated at 450 versus 466 for Alternative 1) 

would result in a proportional reduction in campfire emissions, which would be a local, long-term, 

minor beneficial impact. With fewer on-road vehicles and potential for wood smoke under Alternative 2, 

the overall effect on local air pollution conditions would be long term, minor, and beneficial. 

Curry Village and Campground. The park would construct 78 new hard-sided units in Boys Town, 

bringing the total number of new and retained units at Curry Village to 433. The park would remove 

campsites from lower Pines (32), North Pines (86), and Upper Pines (24). In addition, the park would 

discontinue commercial day rides from the Curry Village Stables. These actions would require the use 

of heavy equipment and demolition activities. As such, the impact on local air quality would be shortterm, minor, and adverse. The reduction in overnight accommodations would reduce total overnight 

visitation and number of campfires, resulting in a local, long-term, minor, beneficial air quality impact. 

Camp 6 and Yosemite Village. The park would reroute Northside Drive to the south of the Yosemite 

Village day-use parking area, reconfigure the lot to accommodate a total of 550 parking spaces north of 

the road, and install walkways leading to Yosemite Village. These actions would require the use of 

heavy equipment and demolition activities. As such, the impact on local air quality would be shortterm, minor, and adverse. 

Camp 4 and Yosemite Lodge. The park would move on-grade pedestrian crossing Camp 4 and 

Yosemite Lodge. The park would convert the Highland Court area to a walk-in campground; 

reconfigure pedestrian crossing of Northside Drive and Yosemite Lodge Drive, and redevelop an area 

west of Yosemite Lodge to provide an additional parking for 150 automobiles and 15 tour busses. 

These actions would require the use of heavy equipment and demolition activities. As such, the impact 

on local air quality would be short-term, minor, and adverse. The addition of parking would provide 

access to the valley for a greater number of private and commercial vehicles, resulting in a local, longterm, minor, adverse air quality impact. 

Segment 2 Impact Summary: Actions to protect and enhance river values within Segment 2 would 

have local, short-term, adverse impacts ranging from negligible to moderate. These actions would not 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-726 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

be expected to have a long-term impact on air quality. Actions to manage user capacities, land use, and 

facilities within Segment 2 would have local, long-term, minor, beneficial impacts on air quality. 

Segments 3 and 4: Merced River Gorge and El Portal 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping and employee 

housing facilities would be similar to those described above for the analysis common to Alternatives 2–6 

(see discussion of Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All 

River Segments). Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) 

for applicable actions would reduce potential regional and local short-term, negligible to moderate 

impacts associated with construction emissions to the extent feasible. 

There are no NPS overnight accommodations along Segments 3 and 4, and thus few campfires or other 

visitor-related evening sources of smoke. Also, as described in the Alternatives chapter, total daily use 

levels would be less than under Alternative 1. With fewer on-road vehicles under Alternative 1, the 

overall effect on local air pollution conditions would be long-term, minor, and beneficial. 

Segments 3 & 4 Impact Summary: Actions to protect and enhance river values would have a shortterm, regional and local, negligible to minor adverse impact on air quality within Segments 3 and 4. 

These actions would not be expected to have a long-term air quality impact. Actions to manage user 

capacities, land use, and facilities within Segments 3 & 4 would have local, long-term, minor, beneficial 

air quality impacts. 

Segment 7: Wawona 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 7 under Alternative 2 include the relocation of stock use campsites 
Analysis Topics: Natural Resources 

Air Quality – Alternative 2 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-727

from sensitive resource areas to Wawona Stables. This work could require the use of heavy equipment 

and would require approximately one week to implement. Accordingly, this action would result in 

short-term regional and local, negligible, adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to service facilities would be 

similar to those described above for the analysis common to Alternatives 2–6 (see discussion of 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). 

Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable 

actions would reduce potential regional and local short-term, negligible to moderate impacts 

associated with construction emissions to the extent feasible. 

Wawona Campground: Under Alternative 2, the park would reduce the size of the Wawona 

Campground. Thirty-two campsites, or 33% of all campsites within Wawona, would be removed from 

the floodplain. There would be a proportional reduction in campfire emissions. This would result in a 

long-term, local, minor, beneficial impact on air quality. 

Segment 7 Impact Summary: Actions to protect and enhance river values within Segments 6 & 7 

would have regional and local, short-term, negligible to minor, adverse air quality impacts. Over the 

long-term, these actions would contribute to a local, negligible, beneficial impact. Actions to manage 

user capacities, land use, and facilities within Segment 7 would have local, long-term, minor, beneficial 

impacts on air quality. 

Summary of Impacts from Alternative 2: Self-reliant Visitor Experiences and Extensive 

Floodplain Restoration 

Impacts associated with implementation of Alternative 2 would be similar to those described above for 

the analysis common to Alternatives 2–6. In summary, compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential short-term adverse 

impacts associated with construction emissions to the extent feasible. Even after mitigation, shortterm, negligible to moderate, adverse impacts from construction would be anticipated. With regard to 

long-term operations, reduced housing, campsites, or lodging would result in a proportional reduction 

in area source emissions (e.g., from consumer products, maintenance/landscaping, natural gas 

combustion for heating/cooling) and campfire emissions. In addition, reducing the overall visitor 

capacity would result in a regional and local, long-term, minor, beneficial impact on the air quality 

environment by reducing pollutant emissions associated with on-road vehicles and campfires in 

Yosemite Valley. Regional and local, impacts to AQRVs (such as pine injury from ozone, visibility, and 

lichen sensitivity to nitrogen deposition) would also be long-term, minor, and beneficial. 

Cumulative Impacts from Alternative 2: Self-reliant Visitor Experiences and Extensive 

Floodplain Restoration 

The past, present, and reasonably foreseeable future actions in the Yosemite region considered for the 

following air quality analysis are the same as those identified for Alternative 1. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-728 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Overall Cumulative Impact from Alternative 2: Self-reliant Visitor Experiences and Extensive 

Floodplain Restoration 

Because management action under Alternative 2 and actions common to Alternatives 2-6 involve 

substantial construction activity, it would be expected to contribute to regional and local, short-term, 

adverse impacts on air quality resulting from construction activities. 

Over the long term, with respect to ozone, conditions in the Merced River corridor would continue to be 

determined almost entirely by regional emissions trends instead of by local emissions sources. The 

regional, long-term impact would most likely be beneficial, owing to the emissions reductions expected 

to occur with implementation of ongoing state and federal mobile-source control programs. In addition, 

with reduced visitor capacity and campsites, Alternative 2 would result in a long-term, cumulatively 

beneficial impact on air quality from reduced VMT (ozone and particulate emissions) and campfire 

usage (particulate emissions). The continued management of traffic and encouragement of alternative 

forms of transportation would have regional and local, long-term, negligible to minor, beneficial impacts 

on air quality. 

Environmental Consequences of Alternative 3: Dispersed Visitor Experiences and 

Extensive Riverbank Restoration 

All River Segments 

Impacts of Actions to Protect and Enhance River Values 

Impacts associated with implementation of Alternative 3 would be similar to those described above for 

the analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the analysis 

common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, Land Use, 

and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

With regard to regional, long-term impacts associated with the reduced visitor capacity under 

Alternative 3, on-road mobile emissions were quantified using EMFAC2007 emission factors and 

compared to the Federal General Conformity thresholds. The results are shown in table 9-135, below. 

Although bus operations are projected to increase under Alternative 3, the reduction in total daily 

visitor and administrative use and capacity would result in a regional and local, long-term, minor, 

beneficial impact owing to reduced on-road vehicles in the park, as depicted in the table. Regional and 

local impacts to AQRVs (such as pine injury from ozone, visibility, and lichen sensitivity to nitrogen 

deposition) would also be long-term, minor, and beneficial. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 3 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-729

TABLE 9-135: ON-ROAD VEHICLE CRITERIA AIR POLLUTANT EMISSIONS (tons/year)a

Scenario NOx ROG 

Alternative 3 Emissions 17 19 

Alternative 1 (No Action) Emissions 22 26 

Incremental Changeb (5) (7) 

Federal General Conformity Thresholdc 100 50 

Impact Intensity, Type?d Minor, Beneficial Minor, Beneficial 

a Emissions were calculated using EMFAC2007 factors and assume 2.4 visitors per car with 

approximately 22 VMT per vehicle (calibrated based on annual VMT projected for Alternative 1 

assuming 240 days/year peak and shoulder seasons) and bus trip VMT from Supporting Information: 

A Life-Cycle Greenhouse Gas Inventory for Yosemite National Park (Villalba et al 2012b). User 

capacities included in chapter 7 were totaled for each alternative to determine the regional air pollutant 

emissions. Specific assumptions and emission factors incorporated into the calculations are included in 

Appendix G. b Values in (parentheses) are net reductions with respect to Alternative 1 (No Action) emissions. 

c

 Federal General Conformity thresholds for the Mariposa County portion of the MCAB. 

d Negligible impacts would be effects considered not detectable and would have no discernible effect 

on air quality (assumed to be 1% or less of threshold). Minor impacts would be those that are 

present but not expected to have an overall effect on those conditions (assumed to occur up to 50% 

of applicable threshold). Moderate impacts are clearly detectable and could have an appreciable 

effect (assumed to occur at emissions levels greater than 50% but does not exceed the applicable 

threshold). Major impacts would have a substantial, highly noticeable influence on local or regional 

air quality (assumed to occur when emissions exceed applicable threshold). 

Other local, long-term, operational impacts of Alternative 3 are described below for each segment. 

Segments 1, 5, 6, and 8: Merced River Above Nevada Fall, South Fork Merced River Above 

and Below Wawona, and Wawona Impoundment 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping facilities would be 

similar to those described above for the analysis common to Alternatives 2–6 (see discussion of 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). 

Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable 

actions would reduce potential regional and local short-term, negligible to moderate impacts 

associated with construction emissions to the extent feasible. 

Impacts from in-park emissions, such as vehicles, would be more apparent in areas close to roads and 

concentrations of visitor and administrative services. With fewer on-road vehicles in the vicinity under 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-730 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Alternative 3, the overall effect on local air pollution conditions would be long term, minor, and 

beneficial. 

Merced Lake High Sierra Camp. The park would close the Merced Lake High Sierra Camp and 

removal all infrastructure, convert the area to designated Wilderness, and use the former camp area for 

a temporary stock camp. These actions would primarily involve the use of hand tools and a limited 

amount of power equipment. However, removal of these facilities would likely require several 

helicopter trips. As such, the impact on local air quality would be short-term, negligible, and adverse. 

The reduction in lodging units would reduce total overnight visitation and energy required to run the 

facility, resulting in a local, long-term, negligible, beneficial air quality impact. 

Segments 1, 5, 6, & 8 Impact Summary: Actions to manage user capacities, land use, and facilities 

within Segments 1, 5, 6, and 8 would have long-term, minor, beneficial impacts on air quality within 

these segments. 

Segment 2: Yosemite Valley 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values that 

would occur within Segment 2 under Alternative 3 include: rerouting trails at Ahwahnee Meadows; 

removing and restoring a portion of Northside Drive (900 feet) and rerouting the bike path; removing 

1,335 feet of Southside Drive, re-alignment of the road, reconfiguring Curry Orchard parking lot, and 

extending the Stoneman Meadow boardwalk; removing development, asphalt, and fill material, and 

restoring 35.6 acres of floodplain at the former Upper and Lower River campgrounds; removing 

campsites and infrastructure from within 150 feet of the river and restoring an additional 12 acres of 

floodplain and riparian habitat; and removing informal trails and installing signage and fencing to 

redirect visitor traffic at El Capitan Meadow. This work would require the use of heavy equipment, 

including excavators, skid steers, loaders, and dump trucks. The demolition, transport, disposal, and 

restoration work would require approximately 50 weeks of crew and equipment time over a period of 

two years. The resulting impact on regional and local air quality would be short-term, negligible to 

moderate, and adverse, even after implementation of mitigation measures MM-AIR-1 and -2. 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur within Segment 2 under Alternative 3 include: 

relocating unimproved Camp 6 parking; removing the Stoneman, Ahwahnee and Sugar Pine Bridges; 

and restoring these areas to natural conditions. This work would require the use of heavy equipment, 

including excavators, skid steers, loaders, and dump trucks. The demolition, transport, disposal, and 

revegetation activities associated with this work would require approximately 30 weeks of crew and 
Analysis Topics: Natural Resources 

Air Quality – Alternative 3 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-731

equipment time over a period of two years. The resulting impact on regional and local air quality 

would be short-term, negligible to moderate, and adverse, even after implementation of mitigation 

measures MM-AIR-1 and -2 (included in Appendix C). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping, lodging, parking, 

circulation, employee housing, and service facilities would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local 

short-term, negligible to moderate impacts associated with construction emissions to the extent 

feasible. 

Overnight visitation and total daily use levels would be 23% and 37% less, respectively, than under 

Alternative 1. With fewer on-road vehicles under Alternative 3, the effect on local air pollution 

conditions would be long term, minor, and beneficial. However, the majority of campsites, and their 

associated campfires and other sources of evening smoke, are located within Segment 2. Campfires 

would continue to be subject to park regulations, and related emissions could increase in proportion 

to the increased campsites. Campfires or other evening sources of smoke would continue to affect 

local air quality at levels that may be unhealthy for sensitive groups, including individuals with 

pulmonary or cardiovascular diseases, the elderly, and children. Since wood smoke can contribute 

enough local emissions currently to create unhealthy pollutant levels for sensitive groups, especially 

many wood burning sources operating under stable atmospheric conditions, the expected increase in 

the usage of campfires under Alternative 3 would have a potentially local, long-term, moderate, 

adverse impact on sensitive receptors. Increased usage of campfires would also result in a potentially 

local, long-term, moderate, adverse impact if the usage results in increased PM10 measurements above 

the ambient air quality standard at the monitoring site at the Yosemite Valley Visitor Center. 

Curry Village and Campground. The park would retain 355 guest units at Curry Village. The park 

would remove campsites from lower Pines (15), North Pines (34), and Upper Pines (2). In addition, the 

park would discontinue commercial day rides from the Curry Village Stables. These actions would 

require the use of heavy equipment and demolition activities. As such, the impact on local air quality 

would be short-term, minor, and adverse. The reduction in overnight accommodations would reduce 

total overnight visitation and number of campfires, resulting in a local, long-term, minor, beneficial air 

quality impact. 

Camp 6 and Yosemite Village. The park would reroute Northside Drive to the south of the Yosemite 

Village day-use parking area, reconfigure the lot to accommodate a total of 550 parking spaces north of 

the road, and install walkways leading to Yosemite Village. These actions would require the use of 

heavy equipment and demolition activities. As such, the impact on local air quality would be shortterm, minor, and adverse. 

Camp 4 and Yosemite Lodge. The park would move on-grade pedestrian crossing to west of the 

Northside Drive and Yosemite Lodge Drive, relocate the existing bus drop-off area to the Highland 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-732 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Court area to accommodate loading/unloading for 3 busses, and redevelop an area west of Yosemite 

Lodge to provide an additional parking for 150 automobiles and 15 tour busses. These actions would 

require the use of heavy equipment and demolition activities. As such, the impact on local air quality 

would be short-term, minor, and adverse. The addition of parking would provide access to the valley 

for a greater number of private and commercial vehicles, resulting in a local, long-term, minor, adverse 

air quality impact. 

Segment 2 Impact Summary: Actions to protect and enhance river values within Segment 2 would 

have local, short-term, adverse impacts ranging from negligible to moderate. These actions would not 

be expected to have a long-term impact on air quality. Actions to manage user capacities, land use, and 

facilities within Segment 2 would have local, long-term, minor, beneficial air quality impacts associated 

with vehicle emissions; but would also result in a local, long-term, moderate, adverse air quality impact 

from increased numbers of campfires. 

Segments 3 and 4: Merced River Gorge and El Portal 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to employee housing facilities 

would be similar to those described above for the analysis common to Alternatives 2–6 (see discussion 

of Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). 

Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable 

actions would reduce potential regional and local short-term, negligible to moderate impacts 

associated with construction emissions to the extent feasible. 

There are no NPS overnight accommodations along Segments 3 and 4, and thus few campfires or other 

visitor-related evening sources of smoke. Also, as described in the Alternatives chapter, total daily use 

levels would be less than under the Alternative 1. With fewer on-road vehicles under Alternative 3, the 

overall effect on local air pollution conditions would be long term, minor, and beneficial. 

Segments 3 & 4 Impact Summary: Actions to protect and enhance river values would have a shortterm, regional and local, negligible to minor adverse impact on air quality within Segments 3 & 4. 

These actions would not be expected to have a long-term air quality impact. Actions to manage user 

capacities, land use, and facilities within Segments 3 & 4 would have local, long-term, minor, beneficial 

air quality impacts. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 3 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-733

Segment 7: Wawona 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 7 under Alternative 3 include the relocation of stock use campsites 

from sensitive resource areas to Wawona Stables. This work could require the use of heavy equipment 

and would require approximately one week to complete. Accordingly, this action would result in 

short-term regional and local, negligible, adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to service facilities would be 

similar to those described above for the analysis common to Alternatives 2–6 (see discussion of 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). 

Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable 

actions would reduce potential regional and local short-term, negligible to moderate impacts 

associated with construction emissions to the extent feasible. 

Wawona Campground. Under Alternative 3, the park would reduce the size of the Wawona 

Campground. Twenty seven campsites, or 28% of all campsites within Wawona, would be removed 

from the floodplain. There would be a proportional reduction in campfire emissions. This would 

result in a long-term, local, minor, beneficial impact on air quality. 

Segment 7 Impact Summary: Actions to protect and enhance river values within Segments 6 & 7 

would have regional and local, short-term, negligible to minor, adverse air quality impacts. Over the 

long-term, these actions would contribute to a local, negligible, beneficial impact. Actions to manage 

user capacities, land use, and facilities within Segment 7 would have local, long-term, minor, beneficial 

impacts on air quality. 

Summary of Impacts from Alternative 3: Dispersed Visitor Experiences and Extensive 

Riverbank Restoration 

Impacts associated with implementation of Alternative 3 would be similar to those described above for 

the analysis common to Alternatives 2–6. In summary, compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local, 

short-term, adverse impacts associated with construction emissions to the extent feasible. Even after 

mitigation, regional and local, short-term, negligible to moderate, adverse impacts from construction 

would be anticipated. With regard to long-term operations, increased campsites and associated 

campfires in Yosemite Valley could result in a local, moderate, adverse impact. Reduced housing or 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-734 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

lodging would result in a proportional reduction in area source emissions (e.g., from consumer products, 

maintenance/landscaping, natural gas combustion for heating/cooling). In addition, reducing the overall 

visitor capacity would result in a regional and local, long-term, minor, beneficial impact on air quality 

within the Merced River corridor by reducing pollutant emissions associated with on-road vehicles and 

campfires in Yosemite Valley. Regional and local, impacts to AQRVs (such as pine injury from ozone, 

visibility, and lichen sensitivity to nitrogen deposition) would also be long-term, minor, and beneficial. 

Cumulative Impacts from Alternative 3: Dispersed Visitor Experiences and Extensive 

Riverbank Restoration 

The past, present, and reasonably foreseeable future actions in the Yosemite region considered for the 

following air quality analysis are the same as those identified for Alternative 1. 

Overall Cumulative Impact from Alternative 3: Dispersed Visitor Experiences and Extensive 

Riverbank Restoration 

Because management action under Alternative 3 and actions common to Alternatives 2-6 involve 

substantial construction activity, it would be expected to contribute to short-term, adverse impacts on 

air quality resulting from construction activities. 

Over the long term, with respect to ozone, conditions in the Merced River corridor would continue to 

be determined almost entirely by regional emissions trends instead of by local emissions sources. The 

regional, long-term impact would most likely be beneficial, owing to the emissions reductions 

expected to occur with implementation of ongoing state and federal mobile-source control programs. 

In addition, with reduced visitor capacity, Alternative 3 would result in a long-term, cumulatively 

beneficial impact on air quality from reduced VMT (ozone and particulate emissions). Regarding 

potential particulate emissions, since campsites would increase in Yosemite Valley, campfire usage 

(particulate emissions) would increase proportionately which would result in a local, long-term, 

moderate adverse impact. The continued management of traffic and encouragement of alternative 

forms of transportation would have regional and local, long-term, negligible to minor beneficial 

impacts on air quality. 

Environmental Consequences of Alternative 4: Resource-based Visitor Experiences 

and Targeted Riverbank Restoration 

All River Segments 

Impacts of Actions to Protect and Enhance River Values 

Impacts associated with implementation of Alternative 4 would be similar to those described above for 

the analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 4 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-735

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local 

short-term, negligible to moderate impacts associated with construction emissions to the extent 

feasible. 

With regard to regional, long-term impacts associated with the reduced visitor capacity under 

Alternative 4, on-road mobile emissions were quantified using EMFAC2007 emission factors and 

compared to the Federal General Conformity thresholds. The results are shown in table 9-136, below. 

Although bus operations are projected to increase under Alternative 4, the reduction in total daily 

visitor and administrative use and capacity would result in a regional and local, long-term, minor, 

beneficial impact owing to reduced on-road vehicles in the park, as depicted in the table. Regional and 

local, impacts to AQRVs (such as pine injury from ozone, visibility, and lichen sensitivity to nitrogen 

deposition) would also be long-term, minor, and beneficial. 

TABLE 9-136: ON-ROAD VEHICLE CRITERIA AIR POLLUTANT EMISSIONS (tons/year)a

Scenario NOx ROG 

Alternative 4 Emissions 20 22 

Alternative 1 (No Action) Emissions 22 26 

Incremental Changeb (2) (4) 

Federal General Conformity Thresholdc 100 50 

Impact Intensity, Type?d Minor, Beneficial Minor, Beneficial 

a Emissions were calculated using EMFAC2007 factors and assume 2.4 visitors per car with 

approximately 22 VMT per vehicle (calibrated based on annual VMT projected for Alternative 1 

assuming 240 days/year peak and shoulder seasons) and bus trip VMT from Supporting Information: 

A Life-Cycle Greenhouse Gas Inventory for Yosemite National Park (Villalba et al 2012b). User 

capacities included in chapter 7 were totaled for each alternative to determine the regional air pollutant 

emissions. Specific assumptions and emission factors incorporated into the calculations are included in 

Appendix G. b Values in (parentheses) are net reductions with respect to Alternative 1 (No Action) emissions. 

c

 Federal General Conformity thresholds for the Mariposa County portion of the MCAB. 

d Negligible impacts would be effects considered not detectable and would have no discernible effect 

on air quality (assumed to be 1% or less of threshold). Minor impacts would be those that are 

present but not expected to have an overall effect on those conditions (assumed to occur up to 50% 

of applicable threshold). Moderate impacts are clearly detectable and could have an appreciable 

effect (assumed to occur at emissions levels greater than 50% but does not exceed the applicable 

threshold). Major impacts would have a substantial, highly noticeable influence on local or regional 

air quality (assumed to occur when emissions exceed applicable threshold). 

Other local, long-term, operational impacts of Alternative 4 are described below for each segment. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-736 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Segments 1, 5, 6, and 8: Merced River Above Nevada Fall, South Fork Merced River Above 

and Below Wawona, and Wawona Impoundment 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping facilities would be 

similar to those described above for the analysis common to Alternatives 2–6 (see discussion of Impacts 

of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). Compliance 

with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable actions would 

reduce potential regional and local short-term, negligible to moderate impacts associated with 

construction emissions to the extent feasible. 

Impacts from in-park emissions, such as vehicles, would be more apparent in areas close to roads and 

concentrations of visitor and administrative services. With fewer on-road vehicles in the vicinity under 

Alternative 4, the overall effect on air pollution conditions would be local, long term, minor, and 

beneficial. 

Merced Lake High Sierra Camp. The park would close the Merced Lake High Sierra Camp and 

removal all infrastructure, convert the area to designated Wilderness, and restoration of the former 

camp area to natural conditions. These actions would primarily involve the use of hand tools and a 

limited amount of power equipment. However, removal of these facilities would likely require several 

helicopter trips. As such, the impact on local air quality would be short-term, negligible, and adverse. 

The reduction in lodging units would reduce total overnight visitation and energy required to operate 

the facility, resulting in a local, long-term, negligible, beneficial air quality impact. 

Segments 1, 5, 6, & 8 Impact Summary: Actions to manage user capacities, land use, and facilities 

within Segments 1, 5, 6, and 8 would have long-term, minor, beneficial impacts on air quality within 

these segments. 

Segment 2: Yosemite Valley 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 4 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-737

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 2 under Alternative 4 include: removing fill and constructing a 

boardwalk over meadow and wet areas at Ahwahnee Meadows; installing culverts beneath Northside 

Drive; removing 1,335 feet of Southside Drive, re-alignment of the road, reconfiguring Curry Orchard 

parking lot, and extending the Stoneman Meadow boardwalk; removing asphalt and fill material, 

restoring topography of 19.7 acres of floodplain, and installation of box culverts or other similar 

design components at the former Upper and Lower River campgrounds; removing campsites and 

infrastructure from within 150 feet of the river and restoring an additional 12 acres of floodplain and 

riparian habitat; and erecting fencing, signage, and boardwalks to redirect visitor traffic, and removing 

informal trails at El Capitan Meadow. This work would require the use of heavy equipment, including 

excavators, skid steers, loaders, and dump trucks. The demolition, transport, disposal, and restoration 

work would require at least 20 weeks of crew and equipment time over a period of at least two years. 

The resulting impact on regional and local air quality would be short-term, negligible to moderate, and 

adverse, even after implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur within Segment 2 under Alternative 4 include: 

relocating unimproved Camp 6 parking; placing large wood and engineered logjams along the base of 

Stoneman Bridge; removing the Ahwahnee and Sugar Pine Bridges; and restoring these areas to natural 

conditions. This work would require the use of heavy equipment, including excavators, skid steers, 

loaders, and dump trucks. The demolition, transport, disposal, and revegetation activities associated 

with this work would require approximately 30 weeks of crew and equipment time over a period of 

two years, during which other restoration and maintenance activities would be disrupted. The 

resulting impact on regional and local air quality would be short-term, negligible to moderate, and 

adverse, even after implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping, lodging, parking, 

circulation, employee housing, and service facilities would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local shortterm, negligible to moderate impacts associated with construction emissions to the extent feasible. 

Overnight visitation and total daily use levels would be 7% greater and 19% less, respectively, than 

under Alternative 1. With fewer on-road vehicles under Alternative 4, the overall effect on local air 

pollution conditions along roadways would be long term, minor, and beneficial. However, the majority 

of campsites, and their associated campfires and other sources of evening smoke, are located within 

Segment 2. Campfires would continue to be subject to park regulations, and related emissions could 

increase in proportion to the increased campsites (701 sites versus 466 sites for Alternative 1). 

Campfires or other evening sources of smoke would continue to affect local air quality at levels that 

may be unhealthy for sensitive groups, including individuals with pulmonary or cardiovascular 

diseases, the elderly, and children. Since wood smoke can contribute enough local emissions currently 

to create unhealthy pollutant levels for sensitive groups, especially many wood-burning sources 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-738 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

operating under stable atmospheric conditions, the expected increase in the usage of campfires under 

Alternative 4 would have a potentially local, long-term, moderate, adverse impact on sensitive 

receivers. Increased usage of campfires would also result in a potentially local, long-term, moderate, 

adverse impact if the usage results in increased PM10 measurements above the ambient air quality 

standard at the monitoring site at the Yosemite Valley Visitor Center. 

Curry Village and Campground. The park would retain 355 guest units and construct a new 40 site 

campground at Curry Village. The park would remove campsites from lower Pines (15), North Pines 

(34), and Upper Pines (2). In addition, the park would discontinue commercial day rides from the 

Curry Village Stables. These actions would require the use of heavy equipment and demolition 

activities. As such, the impact on local air quality would be short-term, minor, and adverse. The 

reduction in overnight accommodations would reduce total overnight visitation and number of 

campfires, resulting in a local, long-term, minor, beneficial air quality impact. 

Camp 6 and Yosemite Village. The park would improve the configuration of and on-grade 

pedestrian crossing at the Northside Drive-Yosemite Village Drive intersection, shift the parking area 

north and redevelop a portion of the former administrative footprint to accommodate 750 parking 

spaces, and install a new three-way intersection connecting the parking lot to Sentinel Drive. These 

actions would require the use of heavy equipment and demolition activities. As such, the impact on 

local air quality would be short-term, minor, and adverse. The addition of parking would provide 

access to the valley for a greater number of private and commercial vehicles, resulting in a local, longterm, minor, adverse air quality impact. 

Camp 4 and Yosemite Lodge. The park would design a pedestrian underpass, relocate the existing 

bus drop-off area to the Highland Court area to accommodate loading/unloading for 3 busses, and 

redevelop an area west of Yosemite Lodge to provide an additional parking for 150 automobiles and 

15 tour busses. These actions would require the use of heavy equipment and demolition activities. As 

such, the impact on local air quality would be short-term, minor, and adverse. The addition of parking 

would provide access to the valley for a greater number of private and commercial vehicles, resulting 

in a local, long-term, minor, adverse air quality impact. 

Segment 2 Impact Summary: Actions to protect and enhance river values within Segment 2 would 

have local, short-term, adverse impacts ranging from negligible to moderate. These actions would not 

be expected to have a long-term impact on air quality. Actions to manage user capacities, land use, and 

facilities within Segment 2 would have local, long-term, minor, beneficial air quality impacts associated 

with vehicle emissions; but a local, long-term, moderate, adverse air quality impact from increased 

numbers of campfires.

Segments 3 and 4: Merced River Gorge and El Portal

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 
Analysis Topics: Natural Resources 

Air Quality – Alternative 4 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-739

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to parking and employee 

housing facilities would be similar to those described above for the analysis common to Alternatives 2–6 

(see discussion of Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All 

River Segments). Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) 

for applicable actions would reduce potential regional and local short-term, negligible to moderate 

impacts associated with construction emissions to the extent feasible. 

There are no NPS overnight accommodations along Segments 3 and 4, and thus few campfires or other 

visitor-related evening sources of smoke. Also, as described in the alternatives chapter, total daily use 

levels would be less than under Alternative 1. With fewer on-road vehicles under Alternative 4, the 

overall effect on local air pollution conditions would be long term, minor, and beneficial. 

Segments 3 & 4 Impact Summary: Actions to protect and enhance river values would have a shortterm, regional and local, negligible to minor adverse impact on air quality within Segments 3 & 4. 

These actions would not be expected to have a long-term air quality impact. Actions to manage user 

capacities, land use, and facilities within Segments 3 & 4 would have short-term, regional and local, 

negligible to minor, adverse impacts on air quality within Segment 4. Over the long-term, these actions 

would have minor, beneficial air quality impacts. 

Segment 7: Wawona 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 7 under Alternative 4 include the relocation of stock use campsites 

from sensitive resource areas to Wawona Stables. This work could require the use of heavy equipment 

and would require approximately one week of crew and equipment time. Accordingly, this action 

would result in short-term regional and local, negligible, adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-740 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local 

short-term, negligible to moderate impacts associated with construction emissions to the extent 

feasible.

Wawona Campground. Under Alternative 4, the park would reduce the size of the Wawona 

Campground. Twenty-seven campsites, or 28% of all campsites within Wawona, would be removed 

from the floodplain. There would also be a proportional reduction in campfire emissions. This would 

result in a long-term, local, minor, beneficial impact on air quality. 

Segment 7 Impact Summary: Actions to protect and enhance river values within Segments 6 & 7 

would have regional and local, short-term, negligible to minor, adverse air quality impacts. Over the 

long-term, these actions would contribute to a local, negligible, beneficial impact. Actions to manage 

user capacities, land use, and facilities within Segment 7 would have local, long-term, minor, beneficial 

impacts on air quality. 

Summary of Impacts from Alternative 4: Resource-based Visitor Experiences and Targeted 

Riverbank Restoration 

Impacts associated with implementation of Alternative 4 would be similar to those described above for 

the analysis common to Alternatives 2–6. In summary, compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential short-term adverse 

impacts associated with construction emissions to the extent feasible. Even after mitigation, regional 

and local, short-term, negligible to moderate, adverse impacts from construction would be anticipated. 

With regard to long-term operations, reduced housing or lodging would result in a proportional 

reduction in area source emissions (e.g., from consumer products, maintenance/landscaping, natural 

gas combustion for heating/cooling). In addition, reducing the overall visitor capacity would result in a 

regional and local, long-term, minor, beneficial impact on the air quality environment by reducing 

pollutant emissions associated with on-road vehicles. Regional and local, impacts to AQRVs (such as 

pine injury from ozone, visibility, and lichen sensitivity to nitrogen deposition) would also be longterm, minor, and beneficial. A greater number of potential campfires associated with increased 

campsites in Yosemite Valley, however, would result in a potentially local, long-term, moderate, 

adverse impact owing to particulate emissions. 

Cumulative Impacts from Alternative 4: Resource-based Visitor Experiences and Targeted 

Riverbank Restoration 

The past, present, and reasonably foreseeable future actions in the Yosemite region considered for the 

following air quality analysis are the same as those identified for Alternative 1. 

Overall Cumulative Impact from Alternative 4: Resource-based Visitor Experiences and Targeted 

Riverbank Restoration 

Because management action under Alternative 4 and actions common to Alternatives 2-6 involve 

substantial construction activity, it would be expected to contribute to regional and local, short-term, 

negligible to moderate, adverse impacts on air quality resulting from construction activities. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 4 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-741

Over the long term, with respect to ozone, conditions in the Merced River corridor would continue to 

be determined almost entirely by regional emissions trends instead of by local emissions sources. The 

regional, long-term impact would most likely be beneficial, owing to the emissions reductions 

expected to occur with implementation of ongoing state and federal mobile-source control programs. 

In addition, with reduced overall visitor capacity, Alternative 4 would result in a regional and local, 

long-term, minor cumulatively beneficial impact on air quality from reduced VMT (ozone and 

particulate emissions). However, increased campsites could result in a local, moderate, adverse impact 

from increased campfire usage (particulate emissions). The continued management of traffic and 

encouragement of alternative forms of transportation would have regional and local, long-term, 

negligible to minor beneficial impacts on air quality. 

Environmental Consequences of Alternative 5: Enhanced Visitor Experiences and 

Essential Riverbank Restoration 

All River Segments 

Impacts of Actions to Protect and Enhance River Values 

Impacts associated with implementation of Alternative 5 would be similar to those described above for 

the analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the analysis 

common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, Land 

Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 and -

2 (included in Appendix C) for applicable actions would reduce potential regional and local shortterm, negligible to moderate impacts associated with construction emissions to the extent feasible. 

With regard to regional, long-term impacts associated with the reduced visitor capacity under 

Alternative 5, on-road mobile emissions were quantified using EMFAC2007 emission factors and 

compared to the Federal General Conformity thresholds. The results are shown in table 9-137, below. 

As depicted in the table, the reduction in total daily visitor and administrative use and capacity would 

result in a regional and local, long-term, minor, beneficial impact for ROG emissions owing to reduced 

on-road vehicles in the park. However, with the increased bus operations under Alternative 5, NOx 

emissions would be a regional and local, long-term, negligible adverse impact. Regional impacts to 

AQRVs (such as pine injury from ozone and visibility) would be similar to existing conditions, but the 

local impact to lichen along roadways would be long-term, negligible, and adverse due to increased 

nitrogen deposition. 

Other local, long-term, operational impacts of Alternative 5 are described below for each segment.
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-742 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

TABLE 9-137: ON-ROAD VEHICLE CRITERIA AIR POLLUTANT EMISSIONS (tons/year)a

Scenario NOx ROG 

Alternative 5 Emissions 23 25 

Alternative 1 (No Action) Emissions 22 26 

Incremental Changeb 1 (1) 

Federal General Conformity Thresholdc 100 50 

Impact Intensity, Type?d Negligible, Adverse Minor, Beneficial 

a Emissions were calculated using EMFAC2007 factors and assume 2.4 visitors per car with 

approximately 22 VMT per vehicle (calibrated based on annual VMT projected for Alternative 1 

assuming 240 days/year peak and shoulder seasons) and bus trip VMT from Supporting Information: 

A Life-Cycle Greenhouse Gas Inventory for Yosemite National Park (Villalba et al 2012b). User 

capacities included in chapter 7 were totaled for each alternative to determine the regional air pollutant 

emissions. Specific assumptions and emission factors incorporated into the calculations are included in 

Appendix G. b Values in (parentheses) are net reductions with respect to Alternative 1 (No Action) emissions. 

c

 Federal General Conformity thresholds for the Mariposa County portion of the MCAB. 

d Negligible impacts would be effects considered not detectable and would have no discernible effect 

on air quality (assumed to be 1% or less of threshold). Minor impacts would be those that are 

present but not expected to have an overall effect on those conditions (assumed to occur up to 50% 

of applicable threshold). Moderate impacts are clearly detectable and could have an appreciable 

effect (assumed to occur at emissions levels greater than 50% but does not exceed the applicable 

threshold). Major impacts would have a substantial, highly noticeable influence on local or regional 

air quality (assumed to occur when emissions exceed applicable threshold). 

Segments 1, 5, 6, and 8: Merced River Above Nevada Fall, South Fork Merced River Above 

and Below Wawona, and Wawona Impoundment 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping facilities would be 

similar to those described above for the analysis common to Alternatives 2–6 (see discussion of 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). 

Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable 

actions would reduce potential regional and local short-term, negligible to moderate impacts 

associated with construction emissions to the extent feasible. 

Impacts from in-park emissions, such as vehicles, would be more apparent in areas close to roads and 

concentrations of visitor and administrative services. With fewer on-road vehicles in the vicinity under 

Alternative 5, the overall effect on air pollution conditions would be long term, minor, and beneficial. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 5 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-743

Merced Lake High Sierra Camp. The park would reduce the capacity of the Merced Lake High 

Sierra Camp to 42 beds and replace the flush toilets with composting toilets. These actions would 

primarily involve the use of hand tools and a limited amount of power equipment. However, removal 

of these facilities could require one or more helicopter trips. As such, the impact on local air quality 

would be short-term, negligible, and adverse. The reduction in lodging units would reduce total 

overnight visitation and energy required to run the facility, resulting in a local, long-term, negligible, 

beneficial air quality impact. 

Segments 1, 5, 6, & 8 Impact Summary: Actions to manage user capacities, land use, and facilities 

within Segments 1, 5, 6, and 8 would have long-term, minor, beneficial impacts on air quality within 

these segments. 

Segment 2: Yosemite Valley 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values that 

would occur within Segment 2 under Alternatives 5 include: removing asphalt and fill material, restoring 

topography of 35.6 acres of floodplain, and installation of box culverts or other similar design 

components at the former Upper and Lower River campgrounds; removing campsites and infrastructure 

from within 100 feet of the river and restoring an additional 6.5 acres of floodplain and riparian habitat; 

removing fill and constructing a boardwalk over meadow and wet areas at Ahwahnee Meadows; 

installing culverts beneath Northside Drive; reconfiguring the Curry Orchard parking lot; removing 

informal trails and erecting fencing, signage, and boardwalks to redirect visitor traffic, and selectively 

removing conifers to improve views at El Capitan Meadow. This work would require the use of heavy 

equipment, including excavators, skid steers, loaders, and dump trucks. The demolition, transport, 

disposal, and restoration work would require at least 40 weeks of crew and equipment time over a period 

of two years. The resulting impact on regional and local air quality would be short-term, negligible to 

moderate, and adverse, even after implementation of mitigation measures MM-AIR-1 and -2 (included 

in Appendix C). 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur within Segment 2 under Alternative 5 include: 

relocating unimproved Camp 6 parking; removing the Sugar Pine Bridge; placing large wood and 

engineered logjams along the base of Stoneman Bridge; and improving trail connectivity and routing in 

the vicinity of the Ahwahnee Bridge. This work would require the use of heavy equipment, including 

excavators, skid steers, loaders, and dump trucks. The demolition, transport, disposal, and revegetation 

activities associated with this work would require at least 16 weeks of crew and equipment time over a 

period of two years, during which other restoration and maintenance activities could be disrupted. The 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-744 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

resulting impact on regional and local air quality would be short-term, negligible to moderate, and 

adverse, even after implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping, lodging, visitor 

services, parking, circulation, employee housing, and service facilities would be similar to those 

described above for the analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to 

Manage User Capacities, Land Use, and Facilities under All River Segments). Compliance with 

mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable actions would reduce 

potential regional and local short-term, negligible to moderate impacts associated with construction 

emissions to the extent feasible. 

Overnight visitation and total daily use levels would be 16% greater and 5% less, respectively, than 

under Alternative 1. With fewer on-road vehicles and potential for wood smoke under Alternative 5, the 

overall effect on local air pollution conditions would be long term, minor, and beneficial. However, the 

majority of campsites, and their associated campfires and other sources of evening smoke, are located 

within Segment 2. Campfires would continue to be subject to park regulations, and related emissions 

could increase in proportion to the increased campsites (640 sites versus 466 sites for Alternative 1). 

Campfires or other evening sources of smoke would continue to affect local air quality at levels that 

may be unhealthy for sensitive groups, including individuals with pulmonary or cardiovascular 

diseases, the elderly, and children. Since wood smoke can contribute enough local emissions currently 

to create unhealthy pollutant levels for sensitive groups, especially many wood-burning sources 

operating under stable atmospheric conditions, the expected increase in the usage of campfires under 

Alternative 5 would have a potentially local, long-term, moderate, adverse impact on sensitive 

receivers. Increased usage of campfires would also result in a potentially local, long-term, moderate, 

adverse impact if the usage results in increased PM10 measurements above the ambient air quality 

standard at the monitoring site at the Yosemite Valley Visitor Center. 

Curry Village and Campground. The park would construct 98 hard-sided units at Boys Town, 

bringing the total number of new and retained units at Curry Village to 453. The park would remove 

campsites from lower Pines (5), North Pines (14), and Upper Pines (2). In addition, the park would 

discontinue commercial day rides from the Curry Village Stables. These actions would require the use 

of heavy equipment and demolition activities. As such, the impact on local air quality would be shortterm, minor, and adverse. The addition of overnight accommodations would increase total overnight 

visitation and related vehicle emissions, while the reduction in campsites would decrease the number 

of valley campfires and associated emissions. The resulting air quality impact would be local, longterm, negligible, and adverse. 

Camp 6 and Yosemite Village. The park would construct a pedestrian underpass and a traffic circle at 

the intersection of Northside and Yosemite Village Drives, shift the parking area north and redevelop 

a portion of the former administrative footprint to accommodate 850 parking spaces, and install a new 

three-way intersection connecting the parking lot to Sentinel Drive. These actions would require the 

use of heavy equipment and demolition activities. As such, the impact on local air quality would be 

short-term, minor, and adverse. The traffic circle and underpass would reduce emissions through 
Analysis Topics: Natural Resources 

Air Quality – Alternative 5 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-745

reducing intersection delays. However, addition of parking would provide access to the valley for a 

greater number of private vehicles. The net air quality effect would be local, long-term, minor, and 

adverse. 

Camp 4 and Yosemite Lodge. The park would design a pedestrian underpass, relocate the existing 

bus drop-off area to the Highland Court area to accommodate loading/unloading for 3 busses, and 

redevelop an area west of Yosemite Lodge to provide an additional parking for 300 automobiles and 

15 tour busses. These actions would require the use of heavy equipment and demolition activities. As 

such, the impact on local air quality would be short-term, minor, and adverse. The addition of parking 

would provide access to the valley for a greater number of private and commercial vehicles, resulting 

in a local, long-term, minor, adverse air quality impact. 

Segment 2 Impact Summary: Actions to protect and enhance river values within Segment 2 would 

have local, short-term, adverse impacts ranging from negligible to moderate. These actions would not 

be expected to have a long-term impact on air quality. Actions to manage user capacities, land use, and 

facilities within Segment 2 would have local, long-term, minor, beneficial air quality impacts associated 

with vehicle emissions; but a local, long-term, moderate, adverse air quality impact from increased 

numbers of campfires. 

Segments 3 and 4: Merced River Gorge and El Portal 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to parking and employee 

housing facilities would be similar to those described above for the analysis common to Alternatives 2–6 

(see discussion of Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All 

River Segments). Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) 

for applicable actions would reduce potential regional and local short-term, negligible to moderate 

impacts associated with construction emissions to the extent feasible. 

There are no NPS overnight accommodations along Segments 3 and 4, and thus few campfires or other 

visitor-related evening sources of smoke. Also, as described in the alternatives chapter, total daily use 

levels would be less than under Alternative 1. With fewer on-road vehicles under Alternative 5, the 

overall effect on local air pollution conditions would be long term, minor, and beneficial. 

Segments 3 & 4 Impact Summary: Actions to protect and enhance river values would have a shortterm, regional and local, negligible to minor adverse impact on air quality within Segments 3 & 4. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-746 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

These actions would not be expected to have a long-term air quality impact. Actions to manage user 

capacities, land use, and facilities within Segments 3 & 4 would have short-term, regional and local, 

negligible to minor, adverse impacts on air quality within Segment 4. Over the long-term, these actions 

would have minor, beneficial air quality impacts. 

Segment 7: Wawona 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the analysis 

common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance River Values 

under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 (included in 

Appendix C) for applicable actions would reduce potential regional and local short-term, negligible to 

moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values that 

would occur within Segment 7 under Alternative 3 include the relocation of stock use campsites from 

sensitive resource areas to the Wawona Maintenance Yard. This work could require the use of heavy 

equipment and would require approximately one week of crew and equipment time. Accordingly, this 

action would result in short-term regional and local, negligible, adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local 

short-term, negligible to moderate impacts associated with construction emissions to the extent 

feasible.

Wawona Campground. Under Alternative 5, the park would reduce the size of the Wawona 

Campground. Thirteen campsites, or 13% of all campsites within Wawona, would be removed from 

the floodplain. There would also be a proportional reduction in campfire emissions. This would result 

in a long-term, local, minor, beneficial impact on air quality. 

Segment 7 Impact Summary: Actions to protect and enhance river values within Segments 6 & 7 

would have regional and local, short-term, negligible to minor, adverse air quality impacts. Over the 

long-term, these actions would contribute to a local, negligible, beneficial impact. Actions to manage 

user capacities, land use, and facilities within Segment 7 would have local, long-term, minor, beneficial 

impacts on air quality. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 5 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-747

Summary of Impacts from Alternative 5: Enhanced Visitor Experiences and Essential 

Riverbank Restoration 

Impacts associated with implementation of Alternative 5 would be similar to those described above for 

the analysis common to Alternatives 2–6. In summary, compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential short-term, adverse 

impacts associated with construction emissions to the extent feasible. Even after mitigation, shortterm, negligible to moderate, adverse impacts from construction would be anticipated. With regard to 

long-term operations, reduced housing or lodging would result in a proportional reduction in area 

source emissions (e.g., from consumer products, maintenance/landscaping, natural gas combustion for 

heating/cooling). In addition, the reduction in total daily visitor and administrative use and capacity 

and would result in a regional and local, long-term, minor, beneficial impact for ROG emissions owing 

to reduced on-road vehicles in the park. However, with the increased bus operations under 

Alternative 5, NOx emissions would be a regional and local, long-term, negligible adverse impact. 

Regional impacts to AQRVs (such as pine injury from ozone and visibility) would be similar to existing 

conditions, but the local impact to lichen along roadways would be long-term, negligible, and adverse 

due to increased nitrogen deposition. A greater number of potential campfires associated with 

increased campsites in Yosemite Valley, however, would result in a potentially local, long-term, 

moderate, adverse impact owing to particulate emissions. 

Cumulative Impacts from Alternative 5: Enhanced Visitor Experiences and Essential 

Riverbank Restoration 

The past, present, and reasonably foreseeable future actions in the Yosemite region considered for the 

following air quality analysis are the same as those identified for Alternative 1. 

Overall Cumulative Impact from Alternative 5: Enhanced Visitor Experiences and Essential 

Riverbank Restoration 

Because management action under Alternative 5 and actions common to Alternatives 2-6 involve 

substantial construction activity, it would be expected to contribute to regional and local, short-term, 

negligible to moderate, adverse impacts on air quality resulting from construction activities. 

Over the long term, with respect to ozone, conditions in the Merced River corridor would continue to 

be determined almost entirely by regional emissions trends instead of by local emissions sources. The 

regional, long-term impact would most likely be beneficial, owing to the emissions reductions 

expected to occur with implementation of ongoing state and federal mobile-source control programs. 

In addition, with reduced overall visitor capacity, would result in a regional and local, long-term, 

minor, beneficial impact for ROG emissions. However, with the increased bus operations under 

Alternative 5, NOx emissions would be a regional and local, long-term, negligible adverse impact. 

Increased campsites could result in a local moderate, adverse impact from increased campfire usage 

(particulate emissions).The continued management of traffic and encouragement of alternative forms 

of transportation would have regional and local, long-term, negligible to minor beneficial impacts on 

air quality. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-748 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Environmental Consequences of Alternative 6: Diversified Visitor Experiences and 

Selective Riverbank Restoration 

All River Segments 

Impacts of Actions to Protect and Enhance River Values 

Impacts associated with implementation of Alternative 6 would be similar to those described above for 

the analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the analysis 

common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, Land 

Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 and -

2 (included in Appendix C) for applicable actions would reduce potential regional and local shortterm, negligible to moderate impacts associated with construction emissions to the extent feasible. 

With regard to regional, long-term impacts associated with the slightly increased visitor capacity under 

Alternative 6, on-road mobile emissions were quantified using EMFAC2007 emission factors and 

compared to the Federal General Conformity thresholds. The results are shown in table 9-138, below. 

As depicted in the table, the increase in total daily visitor and administrative use and capacity and bus 

operations would result in a regional and local, long-term, negligible to minor, adverse impact owing 

to increased on-road vehicles in the park. Regional and local, impacts to AQRVs (such as pine injury 

from ozone, visibility, and lichen sensitivity to nitrogen deposition) would also be long-term, negligible 

to minor, and adverse. 

Other local, long-term, operational impacts of Alternative 6 are described below for each segment.

Segments 1, 5, 6, and 8: Merced River Above Nevada Fall, South Fork Merced River Above 

and Below Wawona, and Wawona Impoundment 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 6 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-749

TABLE 9-138: ON-ROAD VEHICLE CRITERIA AIR POLLUTANT EMISSIONS (tons/year)a

Scenario NOx ROG 

Alternative 6 Emissions 25 26 

Alternative 1 (No Action) Emissions 22 26 

Incremental Changeb 3 0 

Federal General Conformity Thresholdc 100 50 

Impact Intensity, Type?d Minor, Adverse Negligible, Adverse 

a Emissions were calculated using EMFAC2007 factors and assume 2.4 visitors per car with 

approximately 22 VMT per vehicle (calibrated based on annual VMT projected for Alternative 1 

assuming 240 days/year peak and shoulder seasons) and bus trip VMT from Supporting Information: 

A Life-Cycle Greenhouse Gas Inventory for Yosemite National Park (Villalba et al 2012b). User 

capacities included in chapter 7 were totaled for each alternative to determine the regional air 

pollutant emissions. Specific assumptions and emission factors incorporated into the calculations are 

included in Appendix G. b Values in (parentheses) are net reductions with respect to Alternative 1 (No Action) emissions. 

c

 Federal General Conformity thresholds for the Mariposa County portion of the MCAB. 

d Negligible impacts would be effects considered not detectable and would have no discernible effect 

on air quality (assumed to be 1% or less of threshold). Minor impacts would be those that are 

present but not expected to have an overall effect on those conditions (assumed to occur up to 50% 

of applicable threshold). Moderate impacts are clearly detectable and could have an appreciable 

effect (assumed to occur at emissions levels greater than 50% but does not exceed the applicable 

threshold). Major impacts would have a substantial, highly noticeable influence on local or regional 

air quality (assumed to occur when emissions exceed applicable threshold). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping facilities would be 

similar to those described above for the analysis common to Alternatives 2–6 (see discussion of 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All River Segments). 

Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) for applicable 

actions would reduce potential regional and local short-term, negligible to moderate impacts 

associated with construction emissions to the extent feasible. 

Impacts from in-park emissions, such as vehicles, would be more apparent in areas close to roads and 

concentrations of visitor and administrative services. With more vehicles on park roads and in the 

vicinity of wilderness under Alternative 6, the overall effect on local, air pollution conditions would be 

long term, negligible, and adverse. 

Merced Lake High Sierra Camp. The park would retain the Merced Lake High Sierra Camp and 

replace the flush toilets with composting toilets. These actions would primarily involve the use of hand 

tools and a limited amount of power equipment. However, removal of these facilities would likely 

require one or more helicopter trips. As such, the impact on local air quality would be short-term, 

negligible, and adverse. 

Segments 1, 5, 6, & 8 Impact Summary: Actions to manage user capacities, land use, and facilities 

within Segments 1, 5, 6, and 8 would have long-term, negligible, adverse impacts on air quality within 

these segments. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-750 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Segment 2: Yosemite Valley 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values that 

would occur within Segment 2 under Alternative 6 include: removing asphalt and fill material, restoring 

topography of 19.7 acres of floodplain, and installation of box culverts or other similar design 

components at the former Upper and Lower River campgrounds; removing campsites and infrastructure 

from within 100 feet of the river and restoring an additional 6.5 acres of floodplain and riparian habitat; 

removing fill and constructing a boardwalk over meadow and wet areas at Ahwahnee Meadows; and 

removing informal trails, installing viewing platforms and boardwalks, and selectively removing conifers 

to improve views at El Capitan Meadow. This work would require the use of heavy equipment, including 

excavators, skid steers, loaders, and dump trucks. The demolition, transport, disposal, and restoration 

work would require at least 40 weeks of crew and equipment time over a period of at least two years. The 

resulting impact on regional and local air quality would be short-term, negligible to moderate, and 

adverse, even after implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Hydrologic/Geologic Resource Actions. Specific projects to protect and enhance the river’s 

hydrologic and geologic values that would occur within Segment 2 under Alternative 6 include: 

relocating unimproved Camp 6 parking and placing large wood and engineered logjams along the 

bases of Stoneman, Sugar Pine, and Ahwahnee Bridges. Under this alternative, Sugar Pine Bridge 

would be retained, engineered log jams and large wood installed at its base, and its condition 

monitored. Should long-term monitoring reveal mitigation measures are not sufficient, the park may 

undertake more aggressive management action, including removal of the bridge. Such action would 

require the use of heavy equipment and explosives to drop the bridge and dismantle the abutments. 

This work would require the use of heavy equipment, including excavators, skid steers, loaders, and 

dump trucks. The demolition, transport, disposal, and revegetation activities associated with this work 

would require approximately 16 weeks of crew and equipment time over a period of two years. The 

resulting impact on regional and local air quality would be short-term, negligible to moderate, and 

adverse, even after implementation of mitigation measures MM-AIR-1 and -2 (included in Appendix C). 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to camping, lodging, parking, 

circulation, employee housing, and service facilities would be similar to those described above for the 

analysis common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, 

Land Use, and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential regional and local shortterm, negligible to moderate impacts associated with construction emissions to the extent feasible. 
Analysis Topics: Natural Resources 

Air Quality – Alternative 6 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-751

Overnight visitation and total daily use levels would be 33% and 4% greater, respectively, than under 

Alternative 1. With more on-road vehicles under Alternative 6, the overall effect on local air pollution 

conditions along roadways would be long term, minor, and adverse. In addition, the majority of 

campsites, and their associated campfires and other sources of evening smoke, are located within 

Segment 2. Campfires would continue to be subject to park regulations, and related emissions could 

increase in proportion to the increased campsites (739 sites versus 466 sites for Alternative 1). 

Campfires or other evening sources of smoke would continue to affect local air quality at levels that 

may be unhealthy for sensitive groups, including individuals with pulmonary or cardiovascular 

diseases, the elderly, and children. Since wood smoke can contribute enough local emissions currently 

to create unhealthy pollutant levels for sensitive groups, especially many wood burning sources 

operating under stable atmospheric conditions, the expected increase in the usage of campfires under 

Alternative 6 would have a potentially local, long-term, moderate, adverse impact on sensitive 

receptors. Increased usage of campfires would also result in a potentially local long-term, major, 

adverse impact if the usage results in increased PM10 measurements above the ambient air quality 

standard at the monitoring site at the Yosemite Valley Visitor Center. 

Curry Village and Campground. The park would construct 98 hard-sided units at Boys Town, 

bringing the total number of new and retained units at Curry Village to 453. The park would remove 

campsites from lower Pines (5), North Pines (14), and Upper Pines (2). In addition, the park would 

discontinue commercial day rides from the Curry Village Stables. These actions would require the use 

of heavy equipment and demolition activities. As such, the impact on local air quality would be shortterm, minor, and adverse. The addition of overnight accommodations would increase total overnight 

visitation and related vehicle emissions, while the reduction in campsites would decrease the number 

of valley campfires and associated emissions. The resulting air quality impact would be local, longterm, negligible, and adverse. 

Camp 6 and Yosemite Village. The park would expand the Concessioner Warehouse Building to 

accommodate Concessioner General Office functions, construct a pedestrian underpass and two 

roundabouts, shift the parking area north and redevelop a portion of the former administrative 

footprint to accommodate 850 parking spaces, and install a new three-way intersection connecting the 

parking lot to Sentinel Drive. These actions would require the use of heavy equipment and demolition 

activities. As such, the impact on local air quality would be short-term, minor, and adverse. The 

roundabout and underpass would reduce emissions through reducing intersection delays. However, 

addition of parking would provide access to the valley for a greater number of private vehicles. The net 

air quality effect would be local, long-term, minor, and adverse. 

Camp 4 and Yosemite Lodge. The park would design a pedestrian underpass, relocate the existing 

bus drop-off area to the Highland Court area to accommodate loading/unloading for 3 busses, and 

redevelop an area west of Yosemite Lodge to provide an additional parking for 300 automobiles and 

15 tour busses. These actions would require the use of heavy equipment and demolition activities. As 

such, the impact on local air quality would be short-term, minor, and adverse. The addition of parking 

would provide access to the valley for a greater number of private and commercial vehicles, resulting 

in a local, long-term, minor, adverse air quality impact. 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-752 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

Segment 2 Impact Summary: Actions to protect and enhance river values within Segment 2 would 

have local, short-term, adverse impacts ranging from negligible to moderate. These actions would not 

be expected to have a long-term impact on air quality. Actions to manage user capacities, land use, and 

facilities within Segment 2 would have local, long-term, negligible to minor, adverse air quality impacts 

associated with vehicle emissions; but a local, long-term, moderate, adverse air quality impact from 

increased numbers of campfires. 

Segments 3 and 4: Merced River Gorge and El Portal 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts associated with changes to parking and employee 

housing facilities would be similar to those described above for the analysis common to Alternatives 2–6 

(see discussion of Impacts of Actions to Manage User Capacities, Land Use, and Facilities under All 

River Segments). Compliance with mitigation measures MM-AIR-1 and -2 (included in Appendix C) 

for applicable actions would reduce potential regional and local short-term, negligible to moderate 

impacts associated with construction emissions to the extent feasible. 

There are no NPS overnight accommodations along Segments 3 and 4, and thus few campfires or other 

visitor-related evening sources of smoke. Also, as described in the alternatives chapter, total daily use 

levels would be greater than under Alternative 1. With more on-road vehicles under Alternative 6, the 

overall effect on local air pollution conditions would be regional and local, long term, negligible, and 

adverse. 

Segments 3 & 4 Impact Summary: Actions to protect and enhance river values would have a shortterm, regional and local, negligible to minor adverse impact on air quality within Segments 3 & 4. 

These actions would not be expected to have a long-term air quality impact. Actions to manage user 

capacities, land use, and facilities within Segments 3 & 4 would have short-term, regional and local, 

negligible to minor, adverse impacts on air quality within Segment 4. Over the long-term, these actions 

would have minor, beneficial air quality impacts. 

Segment 7: Wawona 

Impacts of Actions to Protect and Enhance River Values 

Short-term construction activities and impacts would be similar to those described above for the 

analysis common to Alternatives 2-6 (see discussion of Impacts of Actions to Protect and Enhance 
Analysis Topics: Natural Resources 

Air Quality – Alternative 6 

Merced Wild and Scenic River Comprehensive Management Plan / DEIS 9-753

River Values under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

Biological Resource Actions. Specific projects to protect and enhance the river’s biological values 

that would occur within Segment 7 under Alternative 6 include the relocation of stock use campsites 

from sensitive resource areas to Wawona Stables. This work could require the use of heavy equipment 

and would require approximately one week of crew and equipment time. Accordingly, this action 

would result in short-term regional and local, negligible, adverse impacts on air quality. 

Impacts of Actions to Manage User Capacities, Land Use, and Facilities 

Short-term construction activities and impacts would be similar to those described above for the analysis 

common to Alternatives 2–6 (see discussion of Impacts of Actions to Manage User Capacities, Land Use, 

and Facilities under All River Segments). Compliance with mitigation measures MM-AIR-1 and -2 

(included in Appendix C) for applicable actions would reduce potential regional and local short-term, 

negligible to moderate impacts associated with construction emissions to the extent feasible. 

As described in the alternatives chapter, total daily use levels would not change and maximum overnight 

capacity would be 5% less than under Alternative 1. Since campsites would be reduced along this 

segment (estimated at 83 and one group site versus 96 and one group site for Alternative 1), there would 

also be a proportional reduction in campfire emissions, which would be a local, long-term, minor, 

beneficial impact. 

Wawona Campground. Under Alternative 6, the park would reduce the size of the Wawona 

Campground. Thirteen campsites, or 13% of all campsites within Wawona, would be removed from 

the floodplain. This would result in a long-term, local, minor, beneficial impact on air quality. 

Segment 7 Impact Summary: Actions to protect and enhance river values within Segments 6 & 7 

would have regional and local, short-term, negligible to minor, adverse air quality impacts. Over the 

long-term, these actions would contribute to a local, negligible, beneficial impact. Actions to manage 

user capacities, land use, and facilities within Segment 7 would have local, long-term, minor, beneficial 

impacts on air quality. 

Summary of Impacts from Alternative 6: Diversified Visitor Experiences and Selective 

Riverbank Restoration 

Impacts associated with implementation of Alternative 6 would be similar to those described above for 

the analysis common to Alternatives 2–6. In summary, compliance with mitigation measures MM-AIR-1 

and -2 (included in Appendix C) for applicable actions would reduce potential short-term adverse 

impacts associated with construction emissions to the extent feasible. Even after mitigation, regional and 

local, short-term, negligible to moderate, adverse impacts from construction would be anticipated. With 

regard to long-term operations, increased housing, campsites, or lodging would result in a proportional 

increase in area source emissions (e.g., from consumer products, maintenance/landscaping, natural gas 

combustion for heating/cooling) and campfire emissions. In addition, increasing the overall visitor 

capacity would result in a regional and local, long-term, negligible to minor, adverse impact on the air 
AFFECTED ENVIRONMENT AND ENVIRONMENTAL CONSEQUENCES

9-754 Merced Wild and Scenic River Comprehensive Management Plan / DEIS

quality environment associated with on-road vehicles. Regional and local, impacts to AQRVs (such as 

pine injury from ozone, visibility, and lichen sensitivity to nitrogen deposition) would also be long-term, 

negligible to minor, and adverse. A greater number of potential campfires associated with increased 

overnight accommodations in Yosemite Valley would result in a potentially local, long-term, moderate, 

adverse impact owing to particulate emissions. 

Cumulative Impacts from Alternative 6: Diversified Visitor Experiences and Selective 

Riverbank Restoration 

The past, present, and reasonably foreseeable future actions in the Yosemite region considered for the 

following air quality analysis are the same as those identified for Alternative 1. 

Overall Cumulative Impact from Alternative 6: Diversified Visitor Experiences and Selective 

Riverbank Restoration 

Because management action under Alternative 6 and actions common to Alternatives 2-6 involve 

substantial construction activity, it would be expected to contribute to regional and local, short-term, 

negligible to moderate adverse impacts on air quality resulting from construction activities. 

Over the long term, with respect to ozone, conditions in the Merced River corridor would continue to 

be determined almost entirely by regional emissions trends instead of by local emissions sources. The 

regional, long-term impact would most likely be beneficial, owing to the emissions reductions 

expected to occur with implementation of ongoing state and federal mobile-source control programs. 

However, with increased overall visitor capacity, Alternative 6 would result in a regional and local, 

long-term, negligible to minor cumulatively adverse impact on air quality from increased VMT (ozone 

and particulate emissions) and increased campfire usage (particulate emissions). The continued 

management of traffic and encouragement of alternative forms of transportation would have regional 

and local, long-term, negligible to minor beneficial impacts on air quality.