This chapter describes the probable consequences (or impacts) of each alternative on the resources described in Vol. Ia, Chapter 3. In addition, the effects to historic properties are considered in accordance with the National Historic Preservation Act (NHPA). This chapter begins with a description of the methodologies and assumptions for each topic (the rationale for the topics presented is located in Vol. Ia, Chapter 3). The analysis for each impact topic includes the identification of impacts of the various actions comprising the alternative; characterization of the impacts, including duration and intensity of the impact; applicable mitigation measures and their effect on reducing impacts; and a conclusion, followed by an assessment of cumulative impacts.

As required by the National Environmental Policy Act (NEPA), direct, indirect, and cumulative impacts are identified and characterized in the impact analysis for each alternative. A key tool in analyzing impacts to resources is the graphic portrayal of new development and redevelopment areas (see Vol. Ic). Direct impacts were analyzed in part by overlaying areas of new development and redevelopment on top of mapped resources and evaluating the implications. Due to limitations of map scale and the fact that precise locations of new development or redevelopment are as yet undetermined, graphics illustrating potential disturbance areas are generalized. Thus, delineation of an entire area for new development and redevelopment does not necessarily mean that the entire area colored purple or orange, respectively, would be disturbed. Rather, it may be that a facility would be placed somewhere within the colored area, with the precise location to be determined during detailed facilities design. However, for purposes of this impact analysis, impacts to vegetation, wildlife habitat, wetlands, and other resources were assessed assuming the entire area delineated would be disturbed. The National Park Service (NPS) draft National Environmental Policy Act guidelines (NPS 1997d) suggest an approach to identifying the intensity (or magnitude) and duration of impacts, and that approach has been implemented. Indicators of the intensity of an impact, whether it be negligible, minor, moderate, or major, are included in the impact analysis and specifically defined by topic area in the methodology section that follows. The duration of an impact is noted as either short-term or long-term and defined in a range of years. Where duration is not noted in the impact analysis, it is assumed to be long-term. Mitigating actions listed in Vol. Ia, Chapter 2 would be taken during implementation of the alternatives. With the exception of the cultural resource analysis, all impacts have been assessed assuming that mitigating measures already have been implemented. Section 106 of the National Historic Preservation Act requires a federal agency to take into account the effects of its undertaking on properties included, or eligible for inclusion, in the National Register of Historic Places, and provide the Advisory Council on Historic Preservation a reasonable opportunity to comment. This also applies to properties not formally determined to be eligible, but that are considered to meet eligibility criteria. Cultural resource impact analysis in this environmental impact statement is described in terminology consistent with the regulations of the Council on Environmental Quality (CEQ) and will comply with requirements of both National Environmental Policy Act and Section 106 of the National Historic Preservation Act. The determination of effect for the undertaking (implementation of the alternative) required by the Yosemite National Park Programmatic Agreement is included in the "conclusion" section of each alternative.

A cumulative impact is described in the Council on Environmental Quality regulations (1508.7) as follows: "Cumulative impact" is the impact on the environment which results from the incremental impact of the action when added to other past, present, and reasonably foreseeable future actions regardless of what agency (federal or non-federal) or person undertakes such other actions. Cumulative impacts can result from individually minor but collectively significant actions taking place over a period of time. To assist in evaluating potential cumulative impacts, reasonably foreseeable future projects within the region surrounding Yosemite National Park were identified. The region or assessment area included eight surrounding counties (Mariposa, Madera, Fresno, Merced, Stanislaus, Tuolumne, Inyo, and Mono), four National Forests (Sierra, Stanislaus, Inyo, and Humbolt/Toiyabe), nearby lands administered by the Bureau of Land Management, and lands administered by the National Park Service within Yosemite National Park and the El Portal Administrative Site. Projects occurring within the jurisdictional areas of five city governments in the region (Oakdale, Fresno, Merced, Modesto, and San Francisco-Hetch Hetchy Water and Power) and two utilities (Pacific Bell and Pacific Gas and Electric) were also identified. Projects were identified through correspondence and phone calls with county and city governments and federal land managers. Reasonably foreseeable future projects include any planning or development activity that was currently being implemented or would be implemented in the reasonably foreseeable future. A comprehensive list of reasonably foreseeable future actions is provided in Vol. II, Appendix H. These actions are evaluated in the cumulative impact analysis in conjunction with the impacts of each alternative to assess whether they have any additive effects on a particular environmental, cultural, or social resource. Because most of these cumulative actions are in the early planning stages, the evaluation of cumulative impacts has been based on a general description of the project.

Descriptions of the methodologies and assumptions applied to the evaluation of potential impacts for each topic chosen for analysis are described below.

Impacts of the actions of each alternative have been assessed to three aspects of water resources: hydrology, floodplain values, and water quality. Hydrology refers to hydrologic processes such as flooding, erosion and deposition, and channel movement, and particular attention is given to alterations or restoration of water flow (e.g., facilities in the Merced River channel). Floodplain values refers to the importance to natural resources of flooding, and particular attention is given to alterations or restoration of the floodplain (e.g., facilities in the Merced River floodplain). Water quality refers to the suitability of surface water for recreational use and wildlife habitat, particularly the enhancement or degradation of water quality. Since flooding is an important hydrologic process, the hydrology discussion will occasionally include flooding and floodplain values. The National Park Service Freshwater Resource Management Guidelines (found in NPS-77) requires the National Park Service to "maintain, rehabilitate, and perpetuate the inherent integrity of water resources and aquatic ecosystems." The Clean Water Act requires the National Park Service to "comply with all Federal, State, interstate, and local requirements, administrative authority, and process and sanctions respecting the control and abatement of water pollution. Particular consideration has been given to those actions with the potential to affect the natural hydrology and surface water quality of the Merced River. To provide a relative comparison of the environmental consequences to hydrology and water quality, the impacts of each action alternative were contrasted with impacts of Alternative 1, the No Action Alternative.

DURATION OF IMPACT

Short-term impacts occur during the alternative’s implementation and are usually less than 2 years in duration (e.g. construction projects). Long-term impacts remain after the alternative has been implemented and are usually longer than two years in duration. Since the full implementation of an alternative would take place over a number of years, this section frequently assesses the duration of individual actions of the alternative (e.g., removal of a bridge, restoration of a campground, construction of lodging units) instead of full implementation of the alternative.

INTENSITY OF IMPACT

Negligible impacts would be imperceptible or not detectable. Minor impacts would be slightly perceptible and localized, without the potential to expand if left alone. Moderate impacts would be apparent and have the potential to become larger. Major impacts would be substantial, highly noticeable, and may be permanent.

TYPE OF IMPACT

Adverse impacts alter natural hydrologic conditions (e.g., impede flood flows, cause unnatural erosion or deposition, etc.) or degrade water quality (e.g., increase pollution or bacteria levels from recreational use). Beneficial impacts are those that restore natural hydrologic conditions (e.g., remove impediments to flood flows, stabilize riverbanks, etc.) or improve water quality (e.g., reduce non-point source pollution).

CONTEXT OF IMPACT

Localized impacts would occur in the immediate vicinity of an action (e.g., bridge removal, bank restoration, parking facility construction) or in a nearby area indirectly affected by the action (e.g., radiating impacts of concentrated visitor use). Regional impacts would occur over a large area, such as the Merced River watershed, Yosemite National Park, or the Sierra Nevada. Many water quality impacts are regional because an action could potentially affect water quality downstream.

The National Park Service manages floodplains in accordance with Executive Order 11988, Floodplain Management, and the National Park Service Special Directive 93-4, (Floodplain Management Guideline [NPS 1993c]). In brief, National Park Service policy is to protect natural floodplain values and functions and to minimize risk to life or property by avoiding the use of the regulatory floodplain whenever there is a feasible alternative location. Evaluation of impacts of the alternatives as related to floodplains is based on avoiding the loss of life and property during major floods. The Water Resources section of Chapter 4 addresses potential impacts on floodplain values and hydrology. The regulatory floodplain is defined as the 100-year, 500-year, or maximum possible flood depending on the type of activity and the amount of risk inherent in the nature of flooding at a location. Generally, the regulatory flood is the 100-year flood for most park functions in non-flash flood environments like Yosemite Valley. For critical actions (as defined in the Floodplain Management Guideline) such as schools, hospitals, and large fuel storage facilities, the regulatory floodplains is defined as the 500-year floodplain in non-flash flood areas. Some facilities such as picnic areas and day-visitor parking are exempt from the National Park Service guidelines because they are often located near water for the enjoyment of visitors and do not involve overnight occupation. Campgrounds are also exempt from the National Park Service guidelines provided that an evaluation of alternative sites has indicated that there is no aesthetically comparable, flood-safe location available, and that evacuation and safety plans are in place. When there is no practicable alternative to placement of facilities in a floodplain location, National Park Service policy permits the use of the floodplain when there are compelling reasons for doing so, when the level of impact to natural floodplain processes is acceptable, and when mitigation is provided to protect human life and property. In this case, a statement of findings must be written documenting the decision to use a floodplain location. Although Merced River floods typically rise slowly enough to present little hazard to humans, the National Park Service can best minimize the risk to human life by limiting the number of people inhabiting the 100-year floodplain. This objective complements other floodplain management goals: to protect park facilities and to preserve/restore natural floodplain processes. In contrast to Yosemite Valley, the steeper gradient in El Portal and Wawona allows the water in the Merced River and the South Fork to gain greater amounts of energy during flood events. During a 100-year or larger flood event, the Merced River may alter its course by eroding its banks, becoming a threat to buildings that are not currently in the 100-year floodplain. In this rare situation, there would be sufficient time for evacuation, making the risk to humans low, but the risk to structures would be somewhat higher than in other lower-energy environments.

DURATION OF IMPACT

Short-term impacts would be those that occur over a period of less than 1 year. Long-term impacts would be those occurring for more than 1 year. All the impacts evaluated would be considered long term. The risk posed to construction personnel working in the floodplain (short-term) was considered too small to warrant evaluation.

INTENSITY OF IMPACT

Beneficial and adverse impacts of individual actions in each alternative were assigned intensities as they relate to effects on life/safety and property in the floodplain. Definitions of impact intensities are provided in table 4-1, below.

TYPE OF IMPACT

In the context of evaluating impacts of each alternative by evaluating risk to human life and property, removing structures from the 100-year floodplain was considered a beneficial impact to human life or property. Development of new Class I or Class II actions (non-exempted facilities) in the 100-year floodplain was considered an adverse impact to human life or property.

The National Park Service is committed to minimizing wetland loss. The wetland protection mechanisms used by the National Park Service include Executive Order 11990, Protection of Wetlands; Director’s Order #77-1, Wetland Protection, and its accompanying Procedural Manual #77-1; Clean Water Act Section 404; and the "no net loss" goal outlined by the White House Office on Environmental Policy in 1993. Executive Order 11990 requires that leadership be provided by involved agencies to minimize the destruction, loss, or degradation of wetlands. National Park Service’s Director’s Order #77-1 and Procedural Manual #77-1 provide specific procedures for carrying out the Executive Order. Section 10 of the Rivers and Harbors Act and Section 404 of the Clean Water Act authorize the U.S. Army Corps of Engineers to grant permits for construction and disposal of dredged material in waters of the United States. In Yosemite Valley, wetland impacts were estimated using National Wetlands Inventory information (USFWS 1995), supplemented with information from a vegetation map of the Valley (NPS 1994e). An assumption was made that all meadow and riparian communities on the vegetation map were likely to be classified as wetlands in future site-specific wetland delineation (see Vol. Ia, Chapter 3, Wetlands). This information provided a conservative and broad estimate of potential wetlands in Yosemite Valley. More specific wetland delineations have been completed through various studies for portions of the park, including the campground and former campground areas in east Yosemite Valley (Kleinfelder 1998). In the early 1990s, vegetation in Yosemite Valley was surveyed in the field and delineated on color infrared photographs (at a scale of 1:12,000). These data were transferred to an ortho-rectified satellite image of Yosemite Valley (10 to 20m resolution). The resulting vegetation map was transferred to a geographic information system. The numbers of acres of new development and redevelopment impact on vegetation and wetlands were estimated with these geographic information system data. The numbers of acres of proposed restoration were calculated based on expected or target vegetation for each proposed restoration site (see Vol. II, Appendix F).

DURATION OF IMPACT

A short-term impact has been defined as lasting less than 20 years following the implementation of an alternative. A long-term impact has been defined as lasting longer than 20 years after implementation of an alternative.

INTENSITY OF IMPACT

Three primary measures were used to evaluate the intensity of impacts on wetlands: the size and type of the wetland, the integrity of the wetland, and the connectivity of the wetland to adjacent habitats. The greater the size of a wetland and the strength of its linkages with neighboring communities, the more valuable a wetland is for the integrity and maintenance of biotic processes. The intensity of impacts has been described as negligible, minor, moderate, or major. Negligible impacts would be imperceptible or not detectable. Minor impacts would be slightly detectable, localized within a small area, and would not affect the overall viability of wetlands in the park. Moderate impacts would be apparent and have the potential to become major impacts. Major impacts would be substantial, highly noticeable, and could be permanent.

TYPE OF IMPACT

Adverse impacts are those that would degrade the size, integrity, or connectivity of wetlands. Conversely, beneficial impacts would enlarge or enhance the integrity and connectivity of wetlands.

Information regarding soil types, descriptions, locations, and management limitations for soil units within Yosemite Valley was developed by the Natural Resources Conservation Service (formerly the Soil Conservation Service) and published in the Soil Survey of Yosemite Valley, Yosemite National Park — Interim Report, completed in 1991. This soil survey identified soil names and descriptions, locations, composition, characteristics, soil formation processes, and observed management concerns. Additional management concerns, related to site-specific project activity, were identified by Yosemite National Park resources management personnel. Information regarding soils outside Yosemite Valley was collected and provided by Natural Resources Conservation Service staff during a parkwide soil survey that began in 1995. This survey is expected to be completed in 2003. Data provided from this survey were considered provisional. Soil mapping units have not yet been developed, and at times park staff have extrapolated data from existing mapped soil units nearby to examine affected areas. Other soil data were obtained from the following soil surveys: (1) Soil Survey of Sierra National Forest Area, California (USFS 1993), (2) Soil Survey of Mariposa County Area, California (Soil Conservation Service 1974), (3) Soil Survey of Tuolumne Meadows Study Area, Yosemite National Park (NRCS 1995a) and (4) Soil Survey of High Sierra Area, California (NRCS 1995b). These soil information sources have been used as the basis to evaluate potential impacts to soils that may result from implementation of any alternatives. Hydric soils are soils with legally designated protection since they commonly form in wetlands and can be associated with rare, threatened, or endangered plants. Hydric soils usually form under sufficiently wet conditions to develop anaerobic conditions and support hydrophytic vegetation. Aquandic Humaquepts and Terric Medisaprists are examples of hydric soils found in riparian and active floodplain areas along the Merced River and Tenaya Creek. Hydric soils are protected by wetland protection policies such as Director’s Order #77-1, Wetland Protection. Highly valued resource soils include those soils found in or adjacent to, meadows and riparian areas, hydric soils, and soils associated with lateral or terminal moraines. Soils in and along riparian and meadow areas often support overlapping ecosystems that are especially rich in vegetative and wildlife diversity. Highly valued resource soils are typically more susceptible to development impacts; they lack the structure to readily support building weight and erode more easily than a resilient soil type. Conversely, a highly valued resource soil is very suitable for restoration. The Leidig fine sandy loam found in and around Leidig Meadow is an example of a highly valued resource soil. Resilient soils are more capable of withstanding alteration without permanent deformation. These soils tend to be able to recover more quickly from alteration. Generally, these soils do not have major use limitations or severely restrictive physical attributes. The Sentinel loam soil type is an example of a resilient soil. Soils classified as "other" include those that are not identified as highly valued resource or resilient soils. Generally, these soils have more limitations on use because of steep slopes or other physical attributes. They may require more intensive management or engineered mitigation measures for development, as compared to resilient soils. Other soils do not fit into the highly valued resource soil resource category because they are generally more abundant or do not support plant communities that are rare or especially diverse. The Half Dome soil complex is an example of another soil resource. The different types of soil impacts that may occur as a result of project implementation include soil removal, soil profile mixing, soil compaction, soil erosion, soil contamination, and soil restoration and revegetation activities. Activities that may result in soil impacts include the construction of buildings, parking areas, roads, campgrounds, trails, and picnic areas. Soil Removal — Paving activities and building construction remove and cover the soil surface and result in significant changes to the basic soil properties of the topsoil. Excavation and removal of the soil surface would result in a long-term impact because the basic soil properties, which have taken thousands of years to develop, would have been removed. Capping the surface reduces water movement and minimizes the opportunity for the normal processes of physical transport and chemical transformations, such as illuviation, eluviation and nutrient cycling. Soil Profile Mixing — Soil excavation and redistribution results in removal or mixing of the soil profile and disrupts soil structural characteristics, interrupting the chemical, physical, and biological processes that naturally occur in the soil. The level of change is dependent on the level of the alteration. It may be many years before the soil profile would redevelop. Soil Compaction — Soil compaction may occur as a result of construction activities or in areas of intensive use such as trails, campgrounds and picnic areas. Highly valued resource soils associated with meadows are most susceptible to compaction effects. Soil compaction reduces infiltration rates, thereby increasing surface runoff and the potential for erosion. Deep compaction of soils may impede subsurface flow. In turn, these effects could alter soil chemical processes such as nutrient transfer, biological processes such as root development and microbial patterns, and physical processes such as soil structure. Vegetation growth on compacted soils is often limited due to low infiltration and poor root penetration. Soil Erosion — Removal of vegetation through grading activities or pedestrian use may result in accelerated erosion of the soil surface. Soils on steep slopes and along watercourses are especially susceptible to erosion. Soil Contamination — The addition of chemical constituents into the soils as a result of pavement installation, untreated runoff from paved surfaces, or from incidental spills, may alter micro- or macro-organism populations, diversity, and dynamics. Machinery involved with construction activities may deposit small amounts of natural and synthetic petrohydrocarbons onto soils through equipment failure or normal operations. Soil Restoration — Restoration activities may have both adverse and beneficial effects on soil properties. Adverse effects may occur during site restoration activities where construction equipment may compact soils, temporarily eliminate groundcover vegetation, and cause potential erosion from surface water runoff over the exposed soils. Beneficial effects may include the removal of asphalt and buildings that would allow natural physical, chemical, and biological processes to resume. Revegetation would minimize erosion potential and increase organic matter in the soil, providing an essential element for biological activity.

DURATION OF IMPACT

The duration of the potential impacts may be characterized as short-term or long-term. Short-term impacts would be those that could be restored when project construction is completed and are considered to last 20 years or less. Long-term impacts would be considered to last over 20 years.

INTENSITY OF IMPACT

Impact intensity has been characterized as negligible, minor, moderate, or major. Definitions of impact intensities for various soil types are provided in table 4-2, below.

TYPE OF IMPACT

Beneficial impacts to soils would be those that contribute to protecting or restoring natural soil conditions including abiotic and biotic components, soil structure, and moisture. Adverse impacts would result in degradation of chemical, physical, abiotic, or biotic soil components.

Vegetation in Yosemite Valley was surveyed in 1990 and the resulting vegetation map (NPS 1994e) was transferred to a geographic information system database to measure the acreage of each plant community. The sizes of plant communities and proposed new development within the Valley were measured using the geographic information system database. To measure proposed development, sites lines were drawn around the perimeters of the sites. The acreage calculated includes the entire area inside the perimeter. Vegetation within and immediately adjacent to proposed actions within each of the out-of-Valley areas was surveyed for species composition in the fall of 1999.

The numerous plant communities within the Valley considered in this analysis were grouped into five general vegetation types for ease of discussion: California black oak, meadow, riparian, upland, and other, the first three of which are considered highly valued resource vegetation (see Vol. Ia, Chapter 2). Out-of-Valley vegetation types differ from these five types and are described independently. Impacts to vegetation types were estimated using best available knowledge, through reviews of literature, and geographic information system analysis.

Developed sites have less ecological integrity than undeveloped sites in terms of the diversity and abundance of species present and in terms of non-native plant encroachment. Development limits the size of plant communities and fragments and disassociates communities from one another. The greater the size of a community and the stronger its link to neighboring communities, the more valuable it is to the integrity and maintenance of ecosystem processes.

Impacts on vegetation communities have been assessed in terms of duration, type, and intensity in site-specific, parkwide, and regional contexts. Two primary parameters were used to evaluate the intensity of impacts on vegetation: (1) the size and continuity of the plant community, and (2) the natural structure, productivity, and diversity (integrity) of the plant community. Highly valued resource designations have also been factored into this analysis.

The relative extent of a plant community is determined by comparing its size to that of other similar communities within a defined area. Larger areas of intact vegetation create larger areas for wildlife and for ecosystem function. Therefore, new areas of development, however small, within otherwise intact and undisturbed areas constitute a greater impact to the overall vegetation of the area than the direct impact to that particular acreage. In the same vein, small areas of restoration surrounded by existing or new development constitute a lesser beneficial impact on restoring overall vegetative integrity and ecosystem health in an area than does restoration of a small area adjacent to a larger intact community or restoration of large areas with little to no surrounding impact. Radiating impacts (impacts resulting from human use spreading out beyond developments, including parking, camping, lodging, and housing areas) can affect plant community size and continuity. Radiating impacts create disturbed/compacted soils, increase the potential for non-native species introduction and establishment, and trampling native vegetation cover.

The natural structure of a plant community is measured by the presence or absence of non-native species, the opportunity for natural processes to occur such as fire and flood, and the presence or absence of natural structural layers, or strata. Biotic integrity can be defined as the ability to support and maintain a balanced, integrated, adaptive community of organisms having species composition, diversity, and functional organization comparable to that of a natural habitat of the region. Diversity and productivity are important for vegetation communities as a whole because the interaction of species and presence of different components provides for ecosystem health and habitat for other species.

The measure of these parameters includes the ability to control, eradicate, or prevent the establishment of non-native plant species, and the ability to manage vegetation with a full range of management options to maintain natural structure and diversity. For example, the presence of non-native species decreases the value of any particular area of vegetation by altering the contribution the vegetation makes towards habitat (food, shelter, etc.) for wildlife and other organisms. Non-native species also alter the effects of natural processes such as flooding or fire by changing the physical characteristics (e.g., surface roughness, fuel loads) of the plant community. Developed areas have varying degrees of potential non-native plant establishment. Landscaped areas can sometimes control the encroachment of non-native species, but housing areas and campgrounds where trampling and ground disturbance occur on a regular and unconfined basis are much more likely to be invaded and overrun by invasive non-native species.

Management tools available to the National Park Service include removal of trees that are considered to be hazardous to visitors and staff (hazard trees), modifications to hydrology that affect species composition, and the use of controlled burning (prescribed fire). Although the applicability of controlled burning is outside the scope of the Yosemite Valley Plan, it is a valid management tool that will continue as set forth in the 1990 Fire Management Plan, the 1993 Resources Management Plan, and the 1997 Vegetation Management Plan. Mechanical methods of vegetation control are used when the use of prescribed burning will not meet environmental conditions such as safety, minimization of smoke, and visitor disturbance. Site-specific prescriptions are developed for these mechanical removal projects, similar to prescriptions followed during prescribed burns. Livestock grazing is not used as a management tool because it is not allowed according to the National Park Service’s enabling (1890 and 1906). Management tools also are available to benefit Yosemite Valley’s oak woodlands, meadows, and riparian communities.

Yosemite Valley’s California black oak woodlands are recognized as critical contributors to the Valley’s natural ecosystem as well as to the cultural landscape. The decline of this vegetation type has been recorded over the years through such studies as Gibbons and Heady (1964) and Heady and Zinke (1978). According to the latter report, "The openness of the forest and the dominance by the two species [California black oak and ponderosa pine] probably resulted from periodic fires and the efforts of Indians to maintain orchards of California black oak for acorns. Both these factors have been greatly reduced for over 100 years." Other actions that have further reduced stands of California black oaks include development of housing, roads, and visitor and administrative areas. These actions and activities have also deterred California black oaks from reproducing, both because of heavy use levels and/or pavement in developed zones, and competition by native and non-native plants in areas no longer maintained by fire. California black oaks in other areas of the Valley that do not receive these stresses are reproducing at natural rates, resulting in variably aged stands of seedlings, saplings, and overstory trees in distinctive age classes. In developed or impacted stands, all oaks are mature trees, with no seedlings and saplings to replace mature trees as they die.

Because of their significance as both cultural and natural resources, the National Park Service has focused on protecting existing stands of California black oaks, restoring impacted stands, and avoiding impacts to these long-lived trees in areas with development. In the Final Yosemite Valley Plan/SEIS, the California black oaks are also designated as one of the highly valued resource vegetation types, and have been used (in conjunction with the other highly valued resources) to guide land-use planning decisions during the development of alternatives.

Other not-so-visible impacts (such as encoachment of meadows by non-native species) would continue to be managed by vegetation management staff in conjunction with fire management and other National Park Service programs involved in the protection and long-term management of the park’s vegetative resources.

The River Protection Overlay in the Merced River Plan provides for the protection of resources that connect to the Merced River system, which includes most meadow and riparian resources in Yosemite Valley. The width of the River Protection Overlay is based on the area needed to encompass riparian and adjacent upland vegetation and habitat and to allow for a large enough area for natural processes to prevail–one of the five primary goals of the 1980 General Management Plan. Implementation of the River Protection Overlay would result in long-term benefits to the river system and the vegetation communities to which it is linked.

DURATION OF IMPACT

Long-term impacts have been defined as those that can be detected for longer than 20 years. Short-term impacts have been defined as those lasting less than 20 years.

INTENSITY OF IMPACT

Negligible impacts would have no measurable or perceptible changes in plant community size, integrity, or continuity. Minor impacts would be measurable or perceptible and localized within a relatively small area. This means the overall viability of the plant community would not be affected. Moderate impacts would cause a change in the plant community (e.g., size, integrity, and continuity); however, the impact would remain localized. The change would be measurable and perceptible, but could be reversed. Major impacts would be substantial, highly noticeable, and could be permanent in their effect on plant community size, integrity, continuity, productivity, and structure.

TYPE OF IMPACT

Impacts were classified as adverse if they would reduce the size, continuity, or integrity of a plant community. Conversely, impacts were classified as beneficial if they would increase the size, continuity, or integrity of a plant community.

This section addresses the effects of alternatives on wildlife and their habitat. Nearly all wildlife concerns can be addressed by considering the effects of alternatives on wildlife habitat as represented by general vegetation types. The correlation of how the vegetation impacts would affect wildlife is described within this section.

In general, adverse effects on wildlife can be minimized by reducing and limiting habitat fragmentation; that is, by preserving and restoring large areas of habitat, patches of habitat, and maintaining connections within and among habitat types. Larger patches of habitat tend to support higher numbers and diversity of wildlife species than smaller ones, and connections between habitat patches enable the movement of wildlife between areas, enhancing reproduction and survival. Small patches of habitat can serve as stepping stones for wildlife moving between larger blocks.

The value of habitat patches for wildlife is also affected by adjacent human activities and development. Severe disruption of habitat between patches can impede wildlife movements. Impacts radiating into habitat patches (referred to in the analysis as radiating impacts), such as light, noise, non-native species, and human use, can affect habitat quality. This impact is less severe in larger habitat patches because the ratio of volume to edge is greater than in smaller patches, and wildlife preserve a core of habitat that is more isolated from radiating impacts. These same factors of radiating impact also increase the effect of new development beyond the boundaries of the habitat directly affected by removal and/or modification.

Ultimately, the value of a restored area or the impact of a developed area to wildlife is determined by the characteristics of the species affected. Home range size, tolerance of human disturbance, and life-history characteristics determine whether a species reoccupies a restored area or abandons a disturbed area.

Impacts on wildlife have been assessed in terms of changes in the amount and distribution of wildlife habitat, the size and connectivity of habitat, the integrity of the site (including past disturbance), the potential for habituation of wildlife to humans, and the relative importance of habitats.

Habitat types with high value to wildlife were identified through a combination of evaluation methods. Habitat types were evaluated using the California Wildlife Habitat Relationships System based upon the number of species unique to each habitat type, the number of special status species expected in each type, and the scarcity of the habitat in Yosemite Valley. This model indicated that changes to two rare habitat types in Yosemite Valley (fresh emergent wetland and lacustrine) would have the most effect on wildlife (Chow et al. 1994). This evaluation was broadened by an overview of habitat types in Yosemite Valley and the Sierra Nevada that have a recognized high value to wildlife and have undergone extensive reduction and degradation. Such habitats include meadows, riparian, and California black oak woodland (NPS 1994e; UC Davis 1996b) Overlaying this evaluation of habitat types, however, was an assessment of the degree to which actions increased or decreased habitat fragmentation (the size of the area affected, its relationship and connection to other habitat areas, and the level of human disturbance that would continue to affect its quality). The home ranges of those species and their tolerance of human disturbance also affect the value of habitat areas to individual species. For instance, the restoration of a 10-acre area would increase habitat for small rodents, but probably would not substantially benefit black bears or mountain lions.

Actions were also assessed as to their potential for causing human/wildlife conflicts resulting from the introduction of unnatural food sources. Such impacts can lead to changes in animal behavior, increased mortality, and altered habitat use.

DURATION OF IMPACT

Long-term impacts have been defined as those lasting 20 years or longer. Short-term impacts would be expected to last for less than 20 years. All short-term impacts to wildlife and habitat from implementation of the alternative would relate to construction activities and their immediate effects on wildlife. These impacts end with cessation of construction activity, or soon thereafter, and include:

• Noise, dust, and light emanating from construction sites could affect the use of surrounding habitats by wildlife.

• Vegetation removed, trampled, or run-over during temporary use of some habitat as areas for staging of machinery or materials would affect wildlife until such areas could be restored after the project.

• Diversion of water flows during construction would result in unnatural drying or wetting of habitats adjacent to sites.

• Wildlife could be killed by traffic or machinery associated with construction.

• Pits and trenches could entrap wildlife, resulting in their death.

• Spills of fuel, oil, hydraulic fluid, antifreeze, and other toxic chemicals could affect wildlife, especially those in aquatic environments.

• Construction personnel, at in-park residences or at work sites, could provide a source of human food to wildlife, resulting in conditioning of wildlife and in human/wildlife conflicts.

Subsequent impact analyses focused primarily on long-term effects of implementation of the alternatives.

INTENSITY OF IMPACT

Negligible impacts are impacts that would not be measurable or perceptible. Minor impacts would be measurable or perceptible and would be localized within a relatively small area; however, the overall viability of the resource would not be affected. Without further impacts, negative effects would be reversed, and the resource would recover. Moderate impacts would be sufficient to cause a change in the resource (e.g., abundance, distribution, quantity, or quality); however, the impact would remain localized. The change would be measurable and perceptible, but negative effects could be reversed. Major impacts would be substantial, highly noticeable, and could be permanent.

TYPE OF IMPACT

Impacts were classified as adverse if they would negatively affect the size, continuity, or integrity of wildlife habitat. Conversely, impacts were classified as beneficial if they would positively affect the size, continuity, or integrity of wildlife habitat.

WILDLIFE

The impact evaluation for special-status wildlife species for each alternative was based on the following: (1) the possibility of a species or its preferred habitat types occurring in areas expected to be affected; (2) the direct loss of habitat; (3) the partial loss of habitat from its modification; and (4) the species’ sensitivity to disturbance from human activities that may cause it to abandon currently occupied habitat or deter it from occupying suitable habitat.

Habitat fragmentation is also a critical factor for special-status species. Restored blocks of habitat should be large enough to support viable populations, and intact habitat should not be reduced or affected to the point that it would no longer support viable populations. A more detailed discussion of impact duration, intensity, and type is included in the preceding Wildlife section.

VEGETATION

The assessment of potential impacts to federal species of concern, state-listed rare, and park rare plant species is based on comparisons between the No Action Alternative and the four action alternatives. Impacts have been evaluated considering species’ sensitivity to impacts (based on rarity, resilience, size of population, and extent of species throughout the park); location of species in proximity to new disturbance and mitigation measures applied as appropriate for the species and the site (see Chapter 2, Alternatives).

DURATION OF IMPACT

The expected duration of impacts is described as long-term or short-term. Long-term impacts would be defined as those lasting 20 years or longer, and short-term impacts as those lasting less than 20 years.

INTENSITY OF IMPACT

The intensity and magnitude of impacts on special-status vegetation and wildlife species have been described as negligible, minor, moderate, or major. Negligible impacts would be imperceptible or not detectable. Minor impacts would be slightly detectable, localized within a relatively small area, and would not affect the overall viability of resources in the park; without further impacts, adverse effects would be reversed, and the resource would recover. Moderate impacts would be sufficient to cause a change in the resource (e.g., abundance, distribution, quantity, or quality), but would remain localized; they would be readily apparent. Major impacts would be substantial, highly noticeable, and affect larger areas.

TYPE OF IMPACT

Impacts were classified as adverse if they would negatively affect the species population size, or habitat size, continuity, or integrity. Conversely, impacts were classified as beneficial if they would positively affect population size, or the size, continuity, or integrity of habitat.

Air Quality

The air quality impact analysis for each alternative quantifies air emissions associated with the estimated vehicles operating in the park, and emissions associated with construction and demolition activities.

The air quality analysis also provides a comparative evaluation of the impact of the alternatives relative to each other. This comparison was based on quantifying mass air emissions from vehicles and construction activities. For example, although these include volatile organic compound and nitrogen oxide emissions, which are precursors to the formation of ozone, they do not include ozone itself. Also, although mass emissions are provided for comparative purposes, the impact of an individual alternative on the ambient air quality standard in the region was not quantified for several reasons. The creation of pollutants resulting from the implementation of an alternative can contribute to an impact on air quality; however, air quality is a regional issue that is influenced by factors outside the immediate area. For example, the California Environmental Protection Agency (EPA) concluded that 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 Air Basin.

For this analysis, vehicle emissions were first quantified for each criteria pollutant to provide a comparison of mass emissions associated with each alternative. Mass emissions of carbon monoxide and particulate matter less than 10 microns in diameter were then used to conduct air dispersion modeling to estimate ambient air concentrations of carbon monoxide and PM₁₀ at heavily used road segments in the Valley. Although this is not predictive of impacts on air quality standards over time, it does provide comparative concentrations of these two pollutants at peak travel hours at the most congested areas in the Valley.

The methodology for performing the analysis of air quality impacts resulting from traffic in the Valley consisted of characterizing and quantifying emissions from existing and future visitor vehicle, park and concessioner employee commuter traffic volumes, and operations of National Park Service and Yosemite Concession Services Corporation vehicles in the Valley. A period encompassing calendar years 2000 through 2015 was chosen for consistency with previous air quality analyses performed for the Draft Yosemite Valley Implementation Plan/SEIS. Table 4-3 illustrates the source of each type of vehicle-generated pollutant.

U = Source of each type of vehicle-generated pollutants.
CO = carbon monoxide
NO_x = nitrogen oxides
PM = particulate matter
SO₂ = sulfur dioxide
VOC = volatile organic compounds

Vehicle traffic emissions were characterized and quantified using the California Air Resources Board computer model titled "EMFAC." EMFAC, which is derived from the abbreviation for "Emission Factor," is a model that estimates calendar year-specific, on-road motor vehicle emission factors for the California vehicle population. EMFAC emission factors were generated for the following pollutants: total organic gases, carbon monoxide, nitrogen oxides, and PM₁₀. Volatile organic compound emissions were estimated by adjusting the total organic gases emissions using factors from another California Air Resources Board computer model, BURDEN. Sulfur dioxide emissions were developed separately based on vehicle fuel consumption values estimated by EMFAC and BURDEN and fuel sulfur contents derived from the technical literature.

The particulate emissions calculated by the EMFAC model were associated with exhaust emissions and tire and brake lining wear. Additional particulate emissions (or road dust) from vehicles operating on paved roads in the Valley were also calculated using a California EPA emission factor equation:

California-specific roadway silt loading (sL = 0.32 g/m²) and average vehicle weight (W = 2.4 tons) data were used as inputs. The EPA factor k for PM₁₀ emissions in terms of pounds per vehicle miles traveled is 0.016. The resultant emission factor, E, was applied to the total annual vehicle miles traveled estimated for each alternative, as shown in table 4-4.

1. Vehicle miles traveled are the same for each year that was modeled and include travel within the Valley as well as travel from park entrances to the Valley.

Air dispersion modeling was also conducted to estimate ambient air concentrations of several pollutants at a "hot spot," which is a heavily used intersection or area where many idling vehicles concentrate air pollutants. To estimate these ambient concentrations, an air dispersion model titled CALINE3 was used. The model, which was originally developed by the California Department of Transportation, is based on the Gaussian diffusion equation and employs a mixing zone concept to characterize pollutant dispersion over the roadway.

The purpose of the CALINE3 model was to assess air quality impacts of emissions from vehicles operating in a microscale region. Inputs to the model included meteorology, site geometry, site characteristics, and source strength, estimated from the EMFAC model emission factors and traffic population. Using these data, the model predicted carbon monoxide and particulate matter concentrations for receptors located within approximately 500 feet of the roadway. A more detailed discussion of the model, roadway link selection, and modeling parameters is provided in Vol. II, Appendix I.

A noteworthy assumption of the EMFAC model is that older vehicles in the current fleet would be replaced over time by newer vehicles with more advanced emission control technology. This results in a reduction of total emissions over time for a given vehicle population.

The emission factors in grams per mile for all pollutants were then applied to estimated vehicle miles traveled under each of the five alternatives to derive overall traffic-related mass emission estimates. Table 4-4 summarizes the total vehicle miles traveled estimated for each alternative for the years of interest. Total vehicle miles traveled includes travel by visitors’ private automobiles; regional, tour, and shuttle buses; National Park Service and concessioner employee commuter vehicles; and National Park Service and concessioner maintenance and administrative vehicles.

The analysis also included alternative-fuel vehicles, including compressed natural gas, propane, and fuel cells, for the visitor shuttle buses in the later years (2005-2015).

In general, construction emissions are generated by (1) earth movement, brush clearing, rock blasting, and roadway construction/demolition activities; (2) non-road (construction) vehicle exhaust emissions; and (3) hot mix asphalt plant operations. The U.S. EPA has published an emission factor from heavy construction activities based on field measurements of total suspended particulate concentrations surrounding construction projects. This factor, 1.2 tons/acre/month of activity, assumes medium activity level, moderate silt content, and a semiarid climate. The PM₁₀ and PM_2.5 (particulate matter less than 10 and 2.5 microns in diameter, respectively) fractions of this total particulate matter emission factor are estimated to be 0.6 and 0.12 tons/acre/month, respectively, based on size fractions from the California Emission Inventory Development and Reporting System. These factors have also been adjusted to reflect a construction intensity level or percentage of site development.

As the particulate matter emission factor suggests, a key assumption to estimating particulate matter emissions from construction and demolition activities is the total acreage associated with the construction or demolition activities. For purposes of this analysis, it was assumed that parking lot densities are 90 vehicles per acre, and a housing density of 6.24 units per acre was assumed for the new employee housing units in El Portal and Wawona. Estimated disturbed acreage for other projects, such as new headquarter facilities in El Portal, were derived from previous Yosemite Valley planning studies.

For the purpose of developing particulate matter emissions for the construction and demolition activities in and out of the Valley, it was assumed that road/parking lot/site disturbances would be equally distributed throughout the construction period. For example, it was assumed that only 1.67 acres per month (15 acres over 12 months) would be disturbed during construction operations at Taft Toe for Alternative 4. In addition, because road construction activities along Southside Drive would primarily consist of repaving and minor road reconstruction, the emission factor was reduced by a factor of 10 to more accurately reflect actual particulate matter emissions.

Non-road or construction vehicle exhaust emissions were estimated using U.S. EPA’s NONROAD emissions inventory model. This model, which updates previous AP-42 factors (compilation of emission factors) for heavy-duty construction equipment, allows the user to estimate construction vehicle emissions based on an actual or assumed gasoline- and diesel-powered vehicle mix and equipment rates. The model assumes a California non-road equipment inventory for emissions calculation. Estimates of duration (6 to 24 months), vehicle type, and daily operating schedule (six days a week and 10 hours per day) for the construction projects were used to develop emissions for PM₁₀, volatile organic compounds, carbon monoxide, nitrogen oxides, and sulfur dioxide.

Due to the size of the construction efforts and remoteness of the park, it is envisioned that a portable batch hot mix asphalt plant would be required to provide the asphalt necessary for day visitor parking lot and road construction. Batch hot mix asphalt plants typically involve aggregate storage and handling, rotary drying (typically oil-fired), screening, and mixing, and emit particulate matter, carbon monoxide, nitrogen oxides, sulfur dioxide, and volatile organic compounds. Estimates of the amount of asphalt needed for each of the various roadway construction projects were developed based on paved area, road width, and asphalt thickness. Asphalt thickness was assumed to be 4 inches for surfacing operations. U.S. EPA emission factors for hot mix asphalt plant operations were applied to the amount of asphalt needed for each operation to calculate emissions.

Additional construction activities that are common to all the alternatives, except Alternative 1, involve constructing new housing units in El Portal and/or Wawona and new lodging rooms in the Yosemite Lodge area. Using the methodology and assumptions presented earlier, total particulate matter emissions were calculated for housing construction activities for each alternative. Non-road or construction vehicle exhaust emissions also were calculated using the U.S. EPA NONROAD emissions inventory model.

Air quality impacts were evaluated in terms of intensity and duration and whether the impacts were considered beneficial or adverse. Cumulative effects on air quality were also considered based on past, present, and reasonably foreseeable future actions occurring in the Yosemite National Park region, in combination with the potential air quality effects of each alternative.

DURATION OF IMPACT

The duration of the impact was considered whether the impact occurs in the short term or long term. For this analysis, short-term impacts would be associated with construction and demolition activities that are temporary in nature, while vehicle emissions were quantified for the 15-year (2000-2015) time period and assumed to continue beyond 2015.

INTENSITY OF IMPACT

The intensity of an impact considers whether the impact is judged to be negligible, minor, moderate, or major relative to Alternative 1. For this analysis, negligible impacts are those which increase or decrease air emissions or pollutant concentrations by 5% or less; minor impacts by 5% to 20%; moderate impacts by 21% to 50%; and major impacts by more than 50%.

TYPE OF IMPACT

Impacts were considered to be beneficial or adverse to air quality. Beneficial air quality impacts would reduce emissions or lower pollutant concentrations, while adverse impacts would increase emissions or raise pollutant concentrations.

For purposes of analysis, geologic hazards have been evaluated only in regard to rockfall risks to visitors, staff, and developed areas. Areas with evidence of past rockfall deposits were used to evaluate those areas most likely to be impacted by future events. The evaluation was using the location of the base of talus, in conjunction with the location of the rockfall shadow line, using the concept of a minimum shadow angle. (The definitions for terms used are presented in the Glossary.)

Recent documentation of talus slope and shadow line zones in Yosemite Valley as defined by the United States Geological Survey (USGS) has allowed the National Park Service to develop the Yosemite Valley Geologic Hazard Guidelines (see Vol. II, Appendix C). The Yosemite Valley Geologic Hazard Guidelines in conjunction with the National Park Service Draft Management Policies (January 2000) were used to evaluate the placement and uses of facilities within the Valley. The guidelines allow natural processes to occur unimpeded. Although the magnitude and timing of rockfall incidents would likely remain difficult to forecast, the National Park Service would strive to more clearly understand potential hazards, and minimize their potential consequences on visitors, staff, and developed areas.

The Yosemite Valley Geologic Hazard Guidelines prohibit placement, within the talus slope and shadow line zones, of any facilities with expected occupancy of more than 300 people (special occupancy), or facilities that support emergency services unless there is not a practicable alternative. The Yosemite Valley Geologic Hazard Guidelines also recommends that standard occupancy facilities should be constructed outside the talus slope zone. Miscellaneous structures may be placed in any area when no practicable alternative exists after considering the potential hazards, and following other National Park Service policies and guidelines.

Under the Yosemite Valley Geologic Hazard Guidelines, historic structures remaining in one of these zones, and all other structures remaining in the talus slope zone, would be adapted for more appropriate uses. The existing structures in the talus slope zone with occupancy greater than 300 should be considered for removal. After careful evaluation regarding hazard potential, and where no practicable alternative exists, these structures may remain in the talus slope zone.

The geologic hazards analysis was completed only for those areas currently within the talus slope and shadow line zones in the Valley. Out-of-Valley areas were not included in this analysis, because the relative risk of rockfall in these areas would be negligible due to the lack of evidence of past rockfall events.

DURATION OF IMPACT

Rockfall hazards would likely be long-term and permanent. The potential for rockfall is ongoing, as this natural process continues to occur in Yosemite Valley.

INTENSITY OF IMPACT

The intensity of an impact was based on its location within the Valley. The intensity of the impact would be negligible if facilities of any kind are located outside geologic hazard zones. The intensity of the impact would be considered a minor risk if standard occupancy and miscellaneous facilities are within the shadow line zone. The intensity of the impact would be moderate if essential, hazardous, and special occupancy facilities are within the shadow line zone, or standard occupancy and miscellaneous facilities are within the talus slope zone. The intensity of the impact would be considered major if essential, hazardous, and special occupancy facilities are within the talus slope zone.

TYPE OF IMPACT

All rockfall events are potentially hazardous. The type of impact is related to risk, and it is difficult to estimate risk involving natural events. In general, reducing risk is considered a beneficial impact. The type of impact would be considered beneficial if there would be a decrease in both the density of individuals and facilities from the talus slope zone; this includes moving them into the shadow line zone, a zone of lower risk. It would also be considered beneficial if there would be a decrease in both the density of individuals and facilities from the shadow line zone.

Generally, maintaining facilities within or moving facilities into a zone of higher risk or exposing people to greater levels of risk was considered adverse. Specifically, the type of impact would be considered adverse if (1) essential and hazardous occupancy facilities remain in or are placed in the talus slope and shadow line zones; or (2) special occupancy facilities remain or are placed in the talus slope zone.

The assessment of potential impacts to scenic resources was based on comparisons between the No Action Alternative and the four action alternatives. The effects of each alternative were evaluated by analyzing potential impacts both on the physical component of the landscape (quantitative) and how the change may be experienced (qualitative).

In its current configuration, Yosemite Valley has 406 acres of development (note: all acreages are rounded to the nearest whole acre). This baseline figure is presented in Alternative 1, the No Action Alternative, and is the basis for comparison of changes that would result from implementation of any of the action alternatives. Potential impacts related to the physical component of the landscape were evaluated by analyzing the change in acreage of development within the scenic resource categories. The scenic analysis map, created for the 1980 General Management Plan, was used as a base map for comparison (see Vol. Ic, plate F). The park’s geographic information system (GIS) was used to identify and quantify change between the alternatives. The scenic resources are categorized as follows:

A Scenic — Areas included in scenic views commonly chosen by eminent early photographers and painters, or included in the most significant scenic views that exist today (includes all meadows and the Merced River).

B Scenic — Areas included in scenic views less commonly chosen by historic photographers and painters or that compose less significant modern views.

C Scenic — Areas of minor scenic quality and areas that can accept visual intrusion without detracting from either A Scenic or B Scenic views.

A quantitative analysis of impacts to scenic resources is based on this categorization. In addition to this analysis, a qualitative analysis considered both the effects on principal scenic features and the effects on the views from particular vantage points.

The analysis developed in the 1980 General Management Plan identified 11 highly important features viewed from Yosemite Valley: Half Dome, Yosemite Falls, El Capitan, Bridalveil Fall, Three Brothers, Cathedral Rocks and Spires, Sentinel Rock, Glacier Point, North Dome, Washington Column, and Royal Arches. These 11 sites were given special consideration during the assessment of impacts to scenic resources for the following reasons: (1) these features have become cultural icons of the American landscape, and (2) these icons are viewed by millions of visitors.

The 1980 General Management Plan and further analysis also identified 15 important vantage points designed for or providing specific opportunities for viewing the Valley’s magnificent scenery: Tunnel View, Bridalveil Fall turnout along Southside Drive, Valley View, Dewey Point, Taft Point, Upper Yosemite Fall, Sentinel Dome, Glacier Point, El Capitan Meadow, Sentinel Meadow turnout along Southside Drive, Sentinel Bridge, Four Mile Trailhead, Columbia Point, Lower Yosemite Fall view, and Cook’s Meadow.

Potential impacts to landscape views are determined by analyzing whether there would be a visual improvement in the foreground, intermediate ground, or background from a particular vantage point.

For locations out-of-Valley (which were not categorized in the General Management Plan analysis), the underlying assumption is that natural appearing conditions are aesthetically pleasing, and that constructed facilities would decrease the amount of undeveloped area and the sense of naturalness.

DURATION OF IMPACT

The duration of the impacts considers whether the impact would be short-term or long-term. A short-term impact would be short-lived or temporary due to construction, restoration, or demolition activities, and a long-term impact would be permanent and continual.

INTENSITY OF IMPACT

The magnitude of impacts to the scenery within the view from specific vantage points and to specific scenic features is described as negligible, minor, moderate, or major as described below.

• Negligible impacts would be imperceptible or not detectable.

• For the A Scenic category, minor impacts would be slightly detectable or localized within a relatively small area. For the B Scenic category, minor impacts would be slightly detectable, localized within a relatively small area, or readily apparent.

• For the A Scenic category, moderate impacts would be those that are readily apparent. For the B Scenic category, moderate impacts would be substantial, highly noticeable, and/or result in changing the character of the landscape.

• For the A Scenic category, major impacts would be substantial, highly noticeable, and/or result in changing the character of the landscape. For the B Scenic category, major impacts would be substantial, highly noticeable, and/or result in changing the character of the landscape by adding human-made features to a mostly undisturbed area or by removing most human-made features from a developed area.

Analysis of impacts to the Merced Wild and Scenic River’s scenic Outstandingly Remarkable Values can be found in the Merced Wild and Scenic River section of this chapter.

TYPE OF IMPACT

All actions proposed in each alternative were analyzed using geographic information system to evaluate the net change in each of the scenic categories (A, B, and C). This approach assesses the acreage of scenic categories A, B, and C that would be improved by the removal of development and restoration to natural communities, or impacted by new development. Impacts were considered beneficial if they decreased the number of acres disturbed within A and B Scenic resource categories, and considered adverse if actions within each alternative increased the number of human-caused visual intrusions in these categories. Impacts were also considered beneficial if the quality of the visual experience would be improved, and adverse if the visual quality would be degraded. No C Scenic resources would be altered by any of the alternatives.

This impact analysis methodology applies to four basic types of cultural resources: archeological sites, ethnographic resources, cultural landscape resources (including individually significant historic structures), and museum collections.

Section 106 of the National Historic Preservation Act requires a federal agency to take into account the effects of its undertakings on properties included in, eligible for inclusion in, or potentially eligible for inclusion in the National Register of Historic Places, and provide the Advisory Council on Historic Preservation the reasonable opportunity to comment. A Programmatic Agreement was developed among the National Park Service at Yosemite, the California State Historic Preservation Officer, and the Advisory Council on Historic Preservation, in consultation with American Indian tribes and the public, to take into account the effects of park planning and operations on historic properties (see Vol. II, Appendix D, Programmatic Agreement).

The methodology for assessing impacts to historic resources is based on stipulations of the Programmatic Agreement. This includes: (1) identifying areas that could be impacted; (2) assessing the information regarding historic properties within this area and conducting any necessary inventories and resource evaluations; (3) comparing the location of the impact area with that of resources listed, eligible, or potentially eligible for listing in the National Register of Historic Places; (4) identifying the extent and type of effects; (5) assessing those effects according to procedures established in the Advisory Council on Historic Preservation’s regulations; and (6) considering ways to avoid, reduce, or mitigate adverse effects.

Cultural resource impacts in this document are described in terminology consistent with the regulations of the Council on Environmental Quality, and in compliance with the requirements of both the National Environmental Policy Act and Section 106 of the National Historic Preservation Act. The Section 106 determination of effect for the undertaking (implementation of the alternative), required by the Programmatic Agreement, is included in the "Section 106 Summary" for each alternative, presented later in this chapter.

DURATION OF IMPACT

Impacts to historic properties (cultural resources) could be of short term, long term, or permanent duration. Analysis of the duration of impacts is required under National Environmental Policy Act, but is not required and is not usually considered in assessing effects in terms of National Historic Preservation Act.

TYPE OF IMPACT

Impacts are considered to be either adverse or beneficial to historic properties (cultural resources) when analyzed under the National Environmental Policy Act. However, impact type is not viewed this way when conducting analysis under Section 106 of the National Historic Preservation Act. For the purposes of assessing effects to historic properties under the National Historic Preservation Act, effects are either adverse or not adverse. Effects under both the National Environmental Policy Act and the National Historic Preservation Act are considered adverse when they diminish the significant characteristics of a historic property.

Impacts can be either direct or indirect. Direct impacts result from specific actions, such as demolition of historic structures. Indirect impacts generally occur after project completion, and are a result of changes in visitor-use patterns or management of resources fostered by implementation of an action.

INTENSITY OF IMPACT

The intensity of an impact on a cultural resource can be defined as negligible, minor, moderate, or major. Negligible impacts would be barely perceptible changes in significant characteristics of a historic property. Minor impacts would be perceptible and noticeable, but would remain localized and confined to a single element or significant characteristic of a historic property (such as a single archeological site containing low data potential within a larger archeological district, or a single contributing element of a larger historic district). Moderate impacts would be sufficient to cause a noticeable but not substantial change in significant characteristics of a historic property (such as an archeological site with moderate data potential or a small group of contributing elements within a larger historic district). Major impacts would result in substantial and highly noticeable changes in significant characteristics of a historic property (such as an archeological site with high data potential or a large group of contributing elements within a larger historic district).

MITIGATION OF IMPACT

The National Environmental Policy Act also calls for a discussion of the "appropriateness" of mitigation, and an analysis of the effectiveness of mitigation. A reduction in intensity of impact from mitigation is an estimate of the effectiveness of this mitigation under the National Environmental Policy Act. It does not suggest that the level of effect, as defined by implementing regulations for Section 106 of the National Historic Preservation Act, is similarly reduced. Although adverse effects under Section 106 may be mitigated, the effects remain adverse.

Mitigation in this document is based on the Programmatic Agreement and includes the avoidance of adverse effects or the application of one or more standard mitigation measures as described in stipulations VII (C) and VIII of the Programmatic Agreement. Avoidance strategies may include the application of the Secretary of the Interior’s Standards and Guidelines for Archeology and Historic Preservation (Secretary’s Standards; USDOI 1983), design methods such as vegetation screening when placing new facilities in a historic district, and the development of guidelines to ensure compatibility between new and existing facilities. Stipulation VIII of the Programmatic Agreement requires the National Park Service notify the State Historic Preservation Officer, American Indian tribes, and certain members of the public of its decision to implement standard mitigation measures as described in Stipulation VIII (A) for individual actions having an adverse effect on historic properties.

Presented below are the specific discussions of duration, intensity, and type of impacts to cultural resources, and a description of typical mitigation measures.

Archeological Resources

Archeological resources are typically considered eligible for inclusion in the National Register of Historic Places because of the information they have or may be likely to yield.

Any change in the physical attributes of an archeological site is irreparable and considered adverse and of permanent duration. Adverse impacts to archeological resources most often occur as a result of earthmoving activities within an archeological site area, soil compaction or increased erosion, unauthorized surface collection, or vandalism. Beneficial impacts to archeological resources can occur when patterns of visitor use or management action are changed in the vicinity of archeological resources such that an ongoing impact, which would otherwise continue to degrade archeological resources, is reduced or arrested. Direct impacts can occur as a result of grading, trenching, or other activities that damage the structure of an archeological site. Indirect impacts can occur as a result of increasing visitor activity or management action in the vicinity of an archeological site, leading to things such as artifact collection, accelerated soil compaction, and erosion.

The intensity of impact to an archeological resource would depend upon the potential of the resource to yield important information, as well as the extent of the physical disturbance or degradation. For example, major earthmoving at an archeological site with low data potential might result in a minor, adverse impact. Negligible impacts would be barely perceptible and not measurable, and would usually be confined to archeological sites with low data potential. Minor impacts would be perceptible and measurable, and would remain localized and confined to archeological site(s) with low to moderate data potential. Moderate impacts would be sufficient to cause a noticeable change, and would generally involve one or more archeological sites with moderate to high data potential. Major impacts would result in substantial and highly noticeable changes, involving archeological site(s) with high data potential.

For archeological resources, mitigation includes avoidance of sites through project design, or recovery of information that makes sites eligible for inclusion in the National Register of Historic Places. According to Stipulation VII (C) of the Programmatic Agreement, impacts to archeological resources are considered not adverse for purposes of Section 106 of the National Historic Preservation Act if data recovery is carried out in accordance with the Archeological Synthesis and Research Design (Hull and Moratto 1999).

Ethnographic Resources

Ethnographic resources are considered eligible for inclusion in the National Register of Historic Places as traditional cultural properties when: 1) they are rooted in a community’s history and are important for maintaining the continuing cultural identity of the community; and 2) they meet National Register criteria for significance and integrity.

Impacts to ethnographic resources occur as a result of changes in the physical characteristics, access to, or use of resources, such that the cultural traditions associated with those resources are changed or lost. Beneficial impacts can occur when intrusive facilities, or visitor or management activities are removed from a traditional use area; when ecological conditions are improved at a gathering area such that the traditionally used resource is enhanced; or when access for American Indian people is enhanced. Adverse impacts occur when physical changes to a traditionally used resource or its setting degrade the resource itself, or degrade access to or use of a resource.

Impacts are considered short term if they represent a temporary change in important vegetation or temporarily restrict access to an important resource, and do not disrupt the cultural traditions associated with that resource for a noticeable period of time. They are considered long term if they involve a change in important vegetation or cultural feature, or addition of a new facility or visitor use that would change the physical character of or access to a resource for a noticeable period of time. This period of time would vary by resource type and traditional practitioners. These long-term changes would disrupt cultural tradition(s) associated with the affected resource, but the disruption would not alter traditional activities to the extent that the important cultural traditions associated with the resource are lost. Permanent impacts to ethnographic resources would involve irreversible changes in important resources such that the ongoing cultural traditions associated with those resources are lost.

The intensity of impacts to an ethnographic resource would depend on the importance of the resource to an ongoing cultural tradition, as well as the extent of physical damage or change. Negligible impacts would be barely perceptible and not measurable, and would be confined to a small area or single contributing element of a larger National Register district (such as the ethnographic landscape in Yosemite Valley). Minor impacts would be perceptible and measurable, and would remain localized and confined to a single contributing element of a larger National Register district. Moderate impacts would be sufficient to cause a change in a significant characteristic of a National Register district or property, and/or would generally involve a small group of contributing elements in a larger National Register district. Major impacts would result in substantial and highly noticeable changes in significant characteristics of a National Register district or property, and/or would involve a large group of contributing elements in a larger National Register district and/or an individually significant property.

The National Park Service would continue to consult with culturally associated American Indian tribes according to stipulations of the Programmatic Agreement, as well as specific agreements such as the October 17, 1997 "Agreement Between the National Park Service, Yosemite National Park, and the American Indian Council of Mariposa County, Inc. for Conducting Traditional Activities," to develop appropriate strategies to mitigate impacts on ethnographic resources. Such strategies could include identification of and assistance in providing access to alternative resource gathering areas, continuing to provide access to traditional use or spiritual areas, and screening new development from traditional use areas.

Cultural Landscape Resources, Including Individually Significant Historic Sites and Structures

Impacts to cultural landscape resources result from physical changes to significant characteristics of a resource or its setting. Beneficial impacts can occur as a result of restoration or rehabilitation of resources, or removal of incompatible or noncontributing facilities. Direct, adverse impacts generally occur as a result of modifying a significant characteristic of a historic structure or landscape resource; removal of a significant structure or landscape resource; or addition of new, incompatible facilities in proximity to a historic site or structure. Indirect adverse impacts can also occur following project completion. These impacts are generally associated with changes in historic vegetation, or continued deterioration of historic structures. They are considered indirect impacts as they are not directly associated with project construction, but rather result from increased visitor use or change in management of resources fostered by the completed plan.

Impacts to historic structures and cultural landscape resources are considered short term if they involve activities such as temporary removal of vegetation or other contributing resources, road closures, or prescribed burns, where the impacts are noticeable for a period of from one to five years. Other examples of short-term Impacts to historic structures include constructing scaffolding surrounding a building during rehabilitation work, or minor deterioration in historic fabric that is repairable as part of routine maintenance and upkeep. Impacts are considered long term if they involve a reversible change, lasting from five to twenty years, in a significant characteristic of a historic structure or landscape. These changes could include such actions as alteration of contributing resources or construction of an incompatible building addition or adjacent facility. Permanent impacts to a historic structure or landscape resources would include irreversible changes in significant characteristics, such as removal of contributing resources; restoration of natural systems and features; irreversible removal of historic fabric that changes the historic character of a property; or demolition of a historic structure.

Negligible impacts would be barely perceptible and not measurable and would be confined to small areas or a single contributing element of a larger National Register district. Minor impacts would be perceptible and measurable but remain localized and confined to a single contributing element of a larger National Register district. Moderate impacts would be sufficient to cause a change in a significant characteristic of an individually significant historic structure, or would generally involve a single or small group of contributing elements in a larger National Register district. Major impacts would result from substantial and highly noticeable changes in significant characteristics of an individually significant historic structure, or would involve a large group of contributing elements in a National Register district.

Mitigation measures for historic structures and cultural landscape resources include measures to avoid impacts, such as rehabilitation and adaptive reuse, designing new development to be compatible with surrounding historic resources, and screening new development from surrounding historic resources. In situations where a historic structure was proposed for removal, the National Park Service would first consider options for relocating the structure to another location in the park for adaptive reuse. Standard mitigation measures, as defined in the Programmatic Agreement, include documentation according to standards of the Historic American Buildings Survey/Historic American Engineering Record (HABS/HAER) as defined in the Re-Engineering Proposal (October 1, 1997). The level of this documentation, which includes photography and a narrative history, would depend on the significance of a resource (national, state, or local) and the nature of the resource (an individually significant structure, contributing elements in a cultural landscape or historic district, etc.). When a historic structure is slated for demolition, architectural elements and objects may be salvaged for reuse in rehabilitating similar structures, or they may be added to the park’s museum collection. In addition, the historical alteration of the human environment and reasons for that alteration would be interpreted to park visitors.

Museum Collection, Including Research Library and Archives

Museum collections are important for their historic, scientific, artistic, and interpretive value. In addition, ethnographic objects and records are of particular cultural value to American Indian people. For the purposes of this plan, impact analysis for the museum collection focusses on the storage and management of the collection. Treatment or management of individual objects within the collection is beyond the scope of the Yosemite Valley Plan. In this context, duration of impacts to museum collections are either short-term or long-term. Short-term impacts would involve reversible actions that last up to five years. Changes in museum collections that would result in short-term impacts include placement of objects into public exhibition under environmentally controlled conditions, or carefully controlled transportation of objects from one location to another. Long-term impacts include actions or conditions that place the collections at continued risk, lasting from five to twenty years, such as storing collections in a facility that does not meet National Park Service standards for security and environmental controls. Fragmenting the collection between several repositories, thus making effective management of the collection difficult, would also be considered a long-term impact.

Negligible impacts to museum collections would be barely perceptible, such as the placement of objects on public exhibit with appropriate lighting, security, and environmental controls. Minor impacts to the collection are measurable and perceptible, and would involve individual components of the collection (such as the archives or the research library). Moderate impacts are measurable, and would result in noticeable change involving several components of the collection. Major impacts would result in highly noticeable change in treatment or management of the entire collection.

Beneficial impacts occur when ongoing degradation of the collection is alleviated, or unsatisfactory conditions for managing the collection are remedied. These beneficial impacts can occur when the collection, which would otherwise continue to be stored in facilities that place it at risk, is placed into storage or exhibit facilities that adequately control security, lighting, temperature, and humidity. Adverse impacts can occur when the collection is subject to degradation as a result of inadequate security and environmental controls, or when management of the collection is hampered.

Mitigation measures related to museum collections consist of preventative conservation of a collection through proper storage, handling, and exhibit of objects.

This assessment is based on the Merced Wild and Scenic River Comprehensive Management Plan/Final Environmental Impact Statement (Merced River Plan), and the management elements of the Merced River Plan, including: Outstandingly Remarkable Values, boundaries, classifications, Wild and Scenic Rivers Act Section 7 determination process, River Protection Overlay, management zoning, and the Visitor Experience and Resource Protection process. The applicable Merced Wild and Scenic River segments are Segment 2 (Yosemite Valley), 3A and 3B (Impoundment and Gorge), 4 (El Portal), and 7 (Wawona). See Vol. Ia, Chapter 3, Affected Environment, for further discussion on the Merced River Plan management elements.

Alternatives have been assessed within a river segment with regard to their: (1) impacts on the Outstandingly Remarkable Values, the values for which the river was designated by Congress; (2) compatibility with classifications; (3) compatibility with the Wild and Scenic River Act Section 7 determination process; (4) consistency with the River Protection Overlay; and (5) consistency with management zoning. The Merced River Plan, which established the River Protection Overlay, management zoning, Wild and Scenic River Act Section 7 determination process, and the Visitor Experience and Resource Protection framework (within the wild and scenic river boundaries), is discussed as a cumulative project.

The Final Yosemite Valley Plan/SEIS alternatives are analyzed to be consistent with the Wild and Scenic River boundaries and Merced River Plan management zoning.

To provide a relative comparison of the environmental consequences, the impacts of each action alternative have been evaluated relative to the impacts of the No Action Alternative.

OUTSTANDINGLY REMARKABLE VALUES

Impacts to Outstandingly Remarkable Values are those actions that: (1) protect, enhance or degrade the Outstandingly Remarkable Values; or (2) substantially interfere with the public’s use and enjoyment of those values. This section analyzes impacts to Merced Wild and Scenic River Outstandingly Remarkable Values from actions that occur both inside and outside the Merced Wild and Scenic River boundaries.

CONCLUSION

It is not atypical for Outstandingly Remarkable Values to be in conflict with each other where an action (or the existing condition) has beneficial impacts with regard to one Outstandingly Remarkable Value and adverse impacts with regard to a different Outstandingly Remarkable Value. The Merced River Plan recognizes this situation, and in the section on Criteria and Considerations (Chapter II, page 3) states:

Actions must protect the Outstandingly Remarkable Values, regardless of where the Outstandingly Remarkable Value is located. When Outstandingly Remarkable Values lie within the boundary of the Wild and Scenic River, the Outstandingly Remarkable Value must be protected and enhanced. When Outstandingly Remarkable Values are in conflict with each other, the net effect to Outstandingly Remarkable Values must be beneficial.

As shown in Vol. II, Appendix B, table II-1, the Outstandingly Remarkable Values vary by Merced Wild and Scenic River segment. The segment-by-segment analysis considers impacts to the specific Outstandingly Remarkable Values of each segment. In evaluating potential environmental consequences, the following assumptions for each Outstandingly Remarkable Value have been made:

Scientific

The Scientific Outstandingly Remarkable Value is related to the Merced River’s value as a largely undisturbed watershed for scientific research. Analysis of the scientific Outstandingly Remarkable Value found that none of the alternatives would impact this Outstandingly Remarkable Value.

Scenic

Views of specific features are listed in the scenic Outstandingly Remarkable Value for each river segment, and potential impacts to views have been analyzed from the perspective of a person situated in the river and on its banks.

Geologic Processes/Conditions

The analysis gives primary consideration to those designated processes, and evidence of those processes (e.g., glaciation, granite domes, river processes, unique geologic features), that have been responsible for creating today’s geologic landscape. Impacts related to natural meandering of the Merced River in Yosemite Valley are considered under the hydrologic processes Outstandingly Remarkable Value.

Recreation

The analysis considers changes in opportunities to experience a spectrum of river-related recreational activities, and focuses on the diversity of recreational opportunities rather than the quantity.

Biological

The analysis gives consideration to river-related habitats such as riparian forests, meadows, and the aquatic environment of the river and associated special-status species.

Cultural

River-related cultural resources are important for their scenic, recreational, educational, and/or informational value. The analysis considers river-related cultural resources that are not intended to divert the free flow of the river, and that are either eligible for or listed on the National Register of Historic Places (for example, the Cascades Diversion Dam, while historic, is not a cultural Outstandingly Remarkable Value). The analysis does not focus on the specific criteria of effect and adverse effect specified under regulations for Section 106 of the National Historic Preservation Act (see the Cultural Resources section in this chapter for this analysis).

Hydrologic Processes

Because the character of the river varies greatly from segment to segment, the hydrologic processes Outstandingly Remarkable Resource varies greatly from segment to segment. For example, floodplains are well-developed in Yosemite Valley and flooding is an important hydrologic process. In the gorge, there is no floodplain due to the exceptionally steep gradient, and the exceptionally steep gradients is the hydrologic process Outstandingly Remarkable Value of this segment.

Additional analyses of resource impacts, particularly cultural resources, biological resources, and hydrological processes, can be found in other sections of this chapter.

CLASSIFICATIONS

Collective actions in each river segment have been assessed for their compatibility with the Merced Wild and Scenic River classification. The amount of development in the watershed, the amount of shoreline development, and accessibility by vehicles have also been considered in assessing classification compatibility.

WILD AND SCENIC RIVER ACT SECTION 7 DETERMINATION PROCESS

Pursuant to the Wild and Scenic River Act, the National Park Service must carry out a Section 7 determination on all proposed water resources projects to ensure that they do not directly and adversely impact the Outstandingly Remarkable Values for which the river was designated. The analysis will identify examples of potential water resources projects proposed in the Final Yosemite Valley Plan/SEIS alternatives that would undergo the Section 7 determination process.

RIVER PROTECTION OVERLAY

Actions proposed in the Final Yosemite Valley Plan/SEIS alternatives have been assessed for their consistency with the River Protection Overlay. The analysis includes consideration of whether an action is consistent with the River Protection Overlay prescriptions. Particular attention is paid to existing facilities that remain and to new facilities. The analysis will identify actions that are inconsistent with the River Protection Overlay.

MANAGEMENT ZONING

Actions proposed in the Final Yosemite Valley Plan/SEIS alternatives have been assessed for their consistency with the Merced River Plan management zoning and corresponding zone prescriptions. Particular attention is paid to facilities. The analysis will identify actions that are inconsistent with the management zoning.

CONTEXT OF IMPACT

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 within Yosemite National Park, or impacts specific to Yosemite Valley, Wawona, or the El Portal Administrative Site. Regional impacts would be those that occur within the greater Yosemite and Sierra Nevada region. Unless otherwise noted, the context of the impacts for the Merced Wild and Scenic River section would be local.

DURATION OF IMPACT

A short-term impact on Outstandingly Remarkable Values would occur in the period concurrent with the implementation of individual actions. A long-term impact would remain and continue even after full implementation of the individual actions.

INTENSITY OF IMPACT

A negligible impact on Outstandingly Remarkable Values would be imperceptible or not detectable. A minor impact would be slightly perceptible and would be localized to relatively small areas. A moderate impact would be apparent. A major impact would be substantial or highly noticeable.

For actions with adverse impacts, potential mitigation was identified and incorporated into the impact evaluation.

TYPE OF IMPACT

An adverse impact would degrade the river segment’s values or "interfere with the public’s use and enjoyment of the river’s outstandingly remarkable values" (as stated in Section 10 of the Wild and Scenic Rivers Act). A beneficial impact would protect and enhance the river segment’s values.

Impacts on visitor experience may occur as a result of changes to road circulation, interpretation facilities, campgrounds and lodging, trails, and other facilities and resources that contribute to the type and quality of the visit to Yosemite National Park. They may also occur from direct actions altering the availability of a specific experience or activity.

Visitor experience is also directly affected by actions influencing natural resources such as, air quality, scenic resources, and cultural resources. Though impacts to these resources are not repeated in the analysis of visitor experience, enhancement or degradation of these resources also enhances or degrades the quality of the visitor experience.

Impacts on visitor experience have been assessed using professional judgement to develop a qualitative analysis of the effects of actions on the activities of different visitor populations. These conclusions have been considered in combination with data on the proportion, when known, of visitors who participate in different activities while in the park.

Assumptions used in evaluating visitor experience impacts for the alternatives include the following:

• Existing facilities in Yosemite Valley have come into being in response to visitor demands and needs. This includes roads, trails, turnouts and viewpoints, and various visitor services and accommodations.

• Private vehicles are the preferred mode of travel for most visitors. However, most visitors would support use of a required transit system to bring about desired improvements in visitor experience (Gramann 1992).

• Those visitors who support these measures, and a large portion of those who have no preference and who do not support such measures, would still choose to participate in various Yosemite Valley activities.

• Visitor activities and opportunities in the Valley would continue to exist, even if changes were made in modes used for moving about Yosemite Valley, except as changed by the alternatives.

• Anticipated changes in visitor participation would represent an effect.

• Anticipated changes in trip quality would represent an effect.

• Anticipated changes in service level (such as reductions in accommodations or increase in services) would represent an effect.

DURATION OF IMPACT

A short-term impact on visitor experiences would be temporary in duration due to construction, restoration, or demolition activities. A long-term impact would have a permanent effect on the visitor experience.

INTENSITY OF IMPACT

The intensity of impacts has been defined as negligible, minor, moderate, and major. Negligible impacts would result in little noticeable change in visitor experience. Minor impacts would result in changes in desired experiences but without appreciably limiting or enhancing critical characteristics. (Critical characteristics are those elements of a recreational activity that are most important to those who pursue it; for example, it may be important to picnickers to be able to drive to a picnic site.) Moderate impacts would change the desired experience appreciably, (i.e., changes one or more critical characteristics, or appreciably reduces/increases number of participants). Major impacts would eliminate or greatly enhance multiple critical characteristics or greatly reduce/increase participation.

Size of user groups was defined based on a percentage of visitors who participate in an activity in Yosemite Valley:

• Small; less than 1% of visitors, unless Yosemite Valley is a principal destination for this activity that cannot be replaced at other destinations, which moves user group to moderate.

• Moderate; 1% to 5% of visitors

• Moderately large; 6% to 19% of visitors

• Large; 20% to 49% of visitors

• Majority; 50% to 74% of visitors

• Most; 75% or more of visitors to Yosemite Valley

Two additional areas of impact were evaluated relative to visitor experience: the reliability of the Valley transportation system, and the night sky. Each was evaluated based on the following methods.

TYPE OF IMPACT

Impacts were evaluated in terms of whether they would be beneficial or adverse to visitor experience. Beneficial impacts would enhance visitor participation, quality of visitor experience, and service level. Adverse impacts would be effects that reduce visitor participation, quality of visitor experience, and service level.

RELIABILITY OF THE YOSEMITE VALLEY TRANSPORTATION SYSTEM

The certainty that a visitor would be able to visit a particular Valley attraction at any given time throughout the day is defined as the reliability of the Valley transportation system. Factors that can limit access to an attraction include parking availability, Valley traffic congestion, transit waits, and travel times between attractions. These limiting factors are estimated in qualitative levels. Reliability is considered high when a visitor is relatively assured of having access to a given attraction. This is true when parking is plentiful at each attraction, congestion in the Valley is low, or transit frequency is high. Reliability is adversely affected by extended periods spent searching for available parking or waiting for the next available shuttle bus, periods of high vehicle congestion (poor circulation), and poor shuttle bus frequency.

The general reliability in being able to visit a given Valley attraction under each action alternative is qualitatively compared to the No Action Alternative in analyzing this impact topic.

Negligible impacts create no measurable or perceptible change in the level of reliability a visitor feels at being able to visit a particular attraction at any given time. A minor impact creates a perceptible change in reliability, but one that is expected to affect relatively few Valley visitors, and constitutes a relatively small change in the level of reliability held by Valley visitors. Moderate impacts create a change in reliability that affects a relatively moderate number of Valley visitors, and major impacts create a change in reliability that affects a relatively large number of Valley visitors.

Short-term impacts would last up to five years and would be the result of implementing a proposed action or program. A long-term impact would be one created through permanent disruption of Valley circulation patterns following the implementation of the alternative action.

Adverse impacts would result from decreased reliability of the transportation system, whereas beneficial impacts would result from increased reliability.

NIGHT SKY

Interior and exterior lighting of buildings and of certain infrastructure such as parking facilities are needed to accommodate visitors. This lighting has the potential to affect the ability to see the night sky and landscape. The draft "Yosemite National Park Exterior Lighting Guidelines" serve as an initial guide for preserving and restoring the night environment of the park as visitor service facilities are rehabilitated and new buildings and infrastructure are designed and built.

Potential impacts on the night sky (ability to see stars and the effect of the sky on the landscape) have been identified for the removal or addition of buildings and infrastructure for each alternative. All impacts are considered long-term. Where artificial lighting already exists within a complex, a substantial change in outdoor lighting is considered a minor long-term impact. Where artificial lighting would be substantially expanded beyond or reduced within an existing complex, the change is considered a long-term moderate impact. The addition of lighting to an area where no architectural lighting exists or removal of all architectural lighting from a distinct area is considered a long-term major impact.

The following general actions have been evaluated for their effect on the night sky environment:

• Removal or addition of vehicle parking infrastructure
• Employee housing
• Visitor lodging
• Food, retail, and other services
• Orientation and interpretation facilities
• Parking operation support facilities
• Implementation of exterior lighting guidelines and rehabilitating existing lighting

Implementation of the action alternatives would change the ways in which visitors and employees travel to and within Yosemite Valley and also change the numbers and types of vehicles that enter the Valley and circulate along Valley roads. Resulting transportation impacts would affect visitor access (travel to the Valley) and visitor circulation (travel within the Valley) in distinct ways. Impacts on visitor access were assessed using estimates of changes in the time that would be required to travel to the Valley and changes in the travel modes that would be used by visitors to reach the Valley. Impacts associated with visitor circulation were assessed using estimates of the number of vehicles and buses entering the east Valley, the total mileage traveled by vehicles in the Valley on an average peak season day, the changes in the mode of travel used by visitors to travel within the Valley, and the quality of traffic flow on selected road segments and at selected intersections. Methods used to estimate impacts are discussed in more detail below.

The assumptions used in evaluating transportation impacts include the following:

• Commercial tour buses would bring a constant share of day visitors and overnight guests to the Valley (13.5 %).
• The average occupancy of private vehicles bringing visitors into the Valley would continue to be 2.9 people.
• Out-of-Valley shuttle buses and Valley shuttle buses would operate as frequently as needed to meet the expected demand for travel (see Vol. II, Appendix G for more detail on how the operations of shuttle buses were planned).
• The existing temporal distribution of visitor arrivals during the day would remain unchanged across all alternatives.
• A visitor information and traffic management system would direct visitors to available parking in Alternatives 2, 3, 4, and 5. This system would manage the number of vehicles entering the east Valley to match the capacity of parking areas.
• The share of vehicles approaching the Valley from each entrance station would remain unchanged (see Vol. Ia, Chapter 3).
• Visitors would spend the same amount of time in the Valley as they do today, meaning that the time spent in the Valley would not be affected by the amount of time required to travel to the Valley.
• The Valley roads would retain their current width and general design characteristics, except that segments of road that would be converted to two-way operation would have wider lanes and shoulders where needed for safety.

CONDITIONS ON STATE HIGHWAYS OUTSIDE YOSEMITE NATIONAL PARK

The alternatives in the Final Yosemite Valley Plan/SEIS would potentially cause changes in travel conditions on Highways 120, 140, and 41 as a result of changes in visitation to Yosemite Valley. However, implementation of the Yosemite Valley Plan would not cause changes to visitation in other parts of Yosemite National Park or changes in travel through the park using state highways. The impacts of the alternatives on travel conditions on state highways outside the park were assessed by estimating the change in the volume of traffic associated with visitor travel to and from Yosemite Valley. A qualitative assessment of impacts on traffic flow was conducted on the basis of changes in vehicle travel to and from the Valley considering how these changes would affect overall traffic volumes on state highways.

VISITOR ACCESS TO THE VALLEY

Travel Times

The impact on travel time to reach Yosemite Valley was assessed by ascertaining the amount of time the average visitor would spend traveling to the Valley under each alternative. For the No Action alternative, the existing travel time by tour bus or regional bus and by private vehicle for each approach route to the park was estimated. For El Portal Road, which serves visitors approaching the Valley from the Arch Rock Entrance Station, the travel time from the entrance station to the Valley Visitor Center was estimated for buses and private vehicles. A weighted-average travel time was then calculated based on the share of visitors who travel by bus and the share of visitors who travel by private vehicle. The same procedure was used for visitors approaching the Valley along Wawona Road, using the South Entrance Station as the starting point for calculating travel time. Visitors who approach the Valley along Big Oak Flat Road include those entering the park at Tioga Pass and at the Big Oak Flat Entrance Station. The Big Oak Flat Entrance Station was used as the starting point for travel time for visitors entering there. The travel time starting point for visitors entering the park at the Tioga Pass Entrance was Crane Flat. An overall average travel time by bus and by private vehicle was calculated for visitors on the Big Oak Flat Road approach route to the Valley based on the share of visitors entering at each station served by the route. Then, similar to the other approach routes, an overall average travel time to the Valley was determined for the Big Oak Flat Road. Finally, the average travel time to the Valley Visitor Center for all Valley visitors was determined based on the share of visitors who travel to the Valley on each route.

For the action alternatives, the travel time to the Valley Visitor Center was determined in a similar manner to that described above for the No Action Alternative. If the alternative included out-of-Valley parking, the travel time to the Valley Visitor Center for visitors parking at out-of-Valley sites was determined by estimating the travel time to the out-of-Valley parking lot, the waiting time for an out-of-Valley shuttle bus, the riding time for the out-of-Valley shuttle bus, and the waiting and riding times for a Valley shuttle bus (if needed) to reach a location near the Valley Visitor Center. An overall average travel time for visitors on each approach route, including visitors traveling by tour bus or regional bus, by private vehicle, and by out-of-Valley shuttle bus, was determined based on the share of visitors who could be expected to travel to the Valley on each access mode. Similar to the No Action Alternative, an overall average travel time for Valley visitors was calculated based on the share of visitors traveling on each approach route.

Travel speeds were estimated for each of the Valley modes of access and remained constant by alternative. For this analysis, private vehicles were assumed to average 35 miles per hour (mph); out-of-Valley shuttle buses, 25 mph, Valley shuttle buses, 10 mph; and tour buses and regional transit buses, 30 mph.

DURATION OF IMPACT

A short-term impact is one that would be created during the implementation phase of the alternative action (e.g., temporary disruption of Valley access created during construction of facility improvements or during the implementation of policy changes) and would generally last between 0 and 5 years. A long-term impact would be created through the permanent disruption of Valley access expected following the implementation phase of the alternative action.

INTENSITY OF IMPACT

The intensities of impacts are defined as follows, (alternatives are compared to Alternative 1).

• A negligible impact would create no measurable or perceptible change in Valley access travel time.
• A minor impact would cause an increase in travel time of less than 20 minutes.
• A moderate impact would cause an increase in travel time of between 20 and 40 minutes.
• A major impact would cause an increase in travel time of greater than 40 minutes.

These intensities were assigned based on professional judgement regarding the inconvenience or improvement that would be perceived by visitors from changes in travel time. The ranges were also selected recognizing that the typical visit to the Valley is about 4.5 hours for day visitors and that the existing travel time to the Valley averages 41 minutes. As a result, a minor impact is associated with a 50% increase in travel time to the Valley, a moderate impact occurs when travel time is increased up to 100%, and a major impact occurs when travel time is more than doubled.

TYPE OF IMPACT

Impacts are considered in the context of being either beneficial or adverse. A travel time saving is considered a beneficial impact for the average peak-season Valley visitor; added travel time is considered an adverse impact.

Modes of Access

Each action alternative would shift a portion of the day visitors traveling to the Valley from private vehicles to buses. This shift was measured by the change in the share of visitors who must travel to the Valley by transit.

DURATION OF IMPACT

A short-term impact would last no longer than 5 years and would result from the implementation of a proposed action or program. A long-term impact would be a result of a permanent disruption of Valley access.

INTENSITY OF IMPACT

The intensities of impacts listed below were quantified for each action alternative based on the percentage of visitors who would access the Valley by transit, compared to the No Action Alternative, in which 86% of day visitors would travel by private vehicle.

• A negligible impact would create no measurable or perceptible change.

• A minor impact would create a change of 15% or less in Valley visitors arriving by transit.

• A moderate impact would create a change of 16% to 30% in visitors arriving by transit.

• A major impact would create a change of more than 30% in visitors arriving by transit.

These intensity levels were selected using professional judgment and recognizing that the existing share of day visitors traveling to the Valley by private vehicle is 86%. A 15% shift in access mode share towards buses would mean that about 1 in 6 visitors who are now traveling in private vehicles to the Valley would be shifted to buses. Measurable shifts in access mode share up to this level were judged to have minor impact intensity. The range of moderate impact intensity would result in between 1 in 6 and 1 in 3 people who are now in private vehicles shifting to buses. If more than 1 in 3 visitors now traveling in private vehicles were to be shifted to buses, the impact was judged to be major.

TYPE OF IMPACT

Shifts of day visitors from private vehicles to buses would not be inherently beneficial or adverse with respect to transportation. Consequently, impacts relative to modes of access are not classified as beneficial or adverse in discussion of the consequences relative to each alternative.

VISITOR CIRCULATION WITHIN THE VALLEY

Traffic Volume and Vehicle Miles Traveled

To evaluate the changes in traffic volumes that would be generated by each alternative, daily total inbound vehicle trips passing the Yosemite Chapel on Southside Drive and total daily vehicle miles traveled in Yosemite Valley were calculated for each alternative. Inbound vehicle trips passing the Yosemite Chapel represent the number of vehicles that enter the east Valley on a daily basis. Vehicle miles traveled were calculated by multiplying all vehicle trips (auto and bus) made on major roadway segments in the Valley by the average trip length for each trip type. Vehicle miles traveled by mode were summed to determine the total daily vehicle miles traveled for each alternative.

DURATION OF IMPACT

The effects would be similar over both the short and long term under all action alternatives.

INTENSITY OF IMPACT

Impact intensities are defined below:

• A negligible impact would be a change in total daily vehicle miles traveled of less than 10%.
• A minor impact would be a change in inbound vehicle trips or total daily vehicle miles traveled of between 10% and 30%.
• A moderate impact would be a change in inbound vehicle trips or total daily vehicle miles traveled of between 31% and 50%.
• A major impact would be a change in inbound vehicle trips or total daily vehicle miles traveled by more than 50%.

These intensity levels were selected using professional judgment regarding the ability of visitors to notice changes in traffic volume and the corresponding presence of vehicles in the Valley. The intensities also were selected with the recognition that traffic volumes vary from day to day and from hour to hour. For example, the average daily traffic entering the Valley in July was 6,166 vehicles in 1998 (National Park Service Traffic Counts). The traffic entering the Valley on the maximum day was 7,252 vehicles, a difference of about 18%. Thus, a traffic volume change similar to the difference between the average day and the peak day in July would have a minor impact. The ranges may be further illustrated by considering the average traffic volume in the Valley over the year is about 52% of the traffic volume on the typically busy day. As a result, a traffic volume change with a major impact would be equal to or greater than the traffic volume difference between the average day in the Valley and a typically busy day.

TYPE OF IMPACT

The change in daily vehicle miles traveled compared to the No Action Alternative was used as the standard by which to measure the impact of changes in the amount of vehicle travel in the Valley by alternative. A decrease in vehicle miles traveled would be a beneficial impact, and an increase in vehicle miles traveled would be an adverse impact.

Bus Volume on Roads

Bus volume on Valley roadways is a quantitative measure of the difference between the number of bus trips made on Valley roads under the No Action Alternative and the action alternatives. Travel by buses was considered in addition to travel by all vehicles because buses, being larger and creating more visual and noise impacts, may have associated consequences that are distinct from those caused by changes in the volume of general traffic. The number of bus trips on Valley roads was computed for each action alternative and estimated for the No Action Alternative. The number of bus trips that would be required to serve the estimated demand for each type of service was estimated for each alternative. Preliminary bus routes were also defined. Daily bus vehicle miles of travel were estimated for each alternative, using Pohono Bridge as the western boundary of Yosemite Valley.

DURATION OF IMPACT

Short-term impacts would last less than 5 years and would be created during the implementation phase of the alternative actions. A long-term impact would be a permanent change in visitor circulation following the implementation of an action.

INTENSITY OF IMPACT

The range of impact intensities for bus volumes on Valley roadways is listed below:

• With a negligible impact, there would be no measurable or perceptible change in the number of bus trips or bus vehicle miles traveled on Valley roadways.
• With a minor impact, the change in the number of bus trips or bus vehicle miles traveled on Valley roads would be less than 25%.
• With a moderate impact, the change in the number of bus trips or bus vehicle miles traveled on Valley roads would be between 26% and 75%.
• With a major impact, the change in the number of bus trip or bus vehicles miles traveled on Valley roads would be greater than 75%.

These ranges are higher than the ranges of impact intensity defined for all vehicle miles of travel.

TYPE OF IMPACT

Changes in the number of bus trips or bus vehicle miles traveled cannot be characterized as beneficial or adverse from a transportation perspective.

Level of Service

To evaluate the impacts of the various alternatives on the Yosemite Valley roadway system, nine locations were selected for analysis, including five roadway segments and four intersections. The roadway segments were analyzed using the procedures for two-lane roads in the Highway Capacity Manual (Transportation Research Board, 1994 and 1997). To facilitate the analysis, the Highway Capacity Software (version 3) was used. The Highway Capacity Manual identifies six levels of service to quantify the performance of a roadway section, from A (the best operating conditions) to F (the worst operating conditions).

The intersection analysis was conducted following the procedures for intersections without signals as outlined in the Highway Capacity Manual. In alternatives that maintain the existing intersection configuration, four-way stop control was assumed based on existing conditions. Where alternatives would eliminate a movement, thus changing the configuration to a T intersection, one-way stop control was assumed. Six levels of service (A through F) are defined for intersections in the Highway Capacity Manual, based on the average total delay to a motorist for an unsignalled intersection. An intersection characterized as level of service A has the lowest delay, while level of service F experiences the highest delay.

The chosen roadway segments and intersections, listed below, are among the more heavily traveled routes within the Valley.

Roadway Segments:

• Pohono Bridge
• El Capitan Bridge
• Southside Drive near the Chapel
• Northside Drive between Yosemite Lodge and park headquarters
• El Portal Road between Big Oak Flat Road and the Pohono Bridge

Intersections:

• Southside Drive and Sentinel Road
• Southside Drive and Northside Drive (near Curry Village)
• Northside Drive at the Village Store/Camp 6 intersection
• Northside Drive and Sentinel Road

DURATION OF IMPACT

Short-term impacts would last less than 5 years and would occur during the implementation phase of the alternative action. A long-term impact would be a permanent change in traffic flow following the implementation of an action.

INTENSITY OF IMPACT

The impact intensities associated with changes in level of service are listed below:

• With a negligible impact, the level of service for individual locations would remain the same.
• With a minor impact, the level of service would change by one or more categories at up to one-third of the locations and time periods analyzed.
• With a moderate impact, the level of service would change by one or more categories at between one-third and two-thirds of the locations and time periods analyzed.
• With a major impact, the level of service would change by one or more categories at more than two-thirds of the locations and time periods analyzed.

TYPE OF IMPACT

An improvement in level of service (i.e., from level of service C to level of service B) would be a beneficial impact; a deterioration in service (i.e., from level of service B to level of service C) would be an adverse impact.

Sound impacts may occur from both transportation-related actions and from nontransportation actions. Separate methods were used to estimate impacts from each type of noise source.

VEHICLE NOISE

The assumptions used in evaluating transportation sound impacts of the alternatives include the following:

• Sound levels produced by individual private vehicles and other traffic not related to transit and tour buses were assumed to remain similar to existing conditions. Changes in sound levels associated with traffic other than transit and tour buses are assumed to be caused only by changes in the volume of traffic.
• The number of vehicles of each type during the peak travel hours is assumed to be equal to the number reported in the Transportation section of this chapter.
• Traffic conditions on a typically busy day are assumed to represent typical conditions for the No Action Alternative. Sound impacts for alternatives are estimates of expected sound levels.
• The existing Valley shuttle bus fleet, over time, will be replaced with new buses. Current internal combustion engine technology, combined with possible use of alternative propulsion systems, would allow the sound emitted from in-Valley shuttle buses to be reduced. It is assumed that the new buses would have sound levels similar to the sound produced by the park’s existing electric shuttle buses.
• Other buses, such as commercial tour buses and the buses operated by the park concessioner for tours, are assumed to produce sound levels similar to existing tour buses.
• Buses used for out-of-Valley shuttle service and other buses entering the Valley (such as transit buses and commercial tour buses) are assumed to produce sound levels similar to those produced by newer tour buses currently operating in the Valley.
• The sound-attenuating impacts of topography and vegetation are not factored into this analysis.
• Noise impacts at out-of-Valley parking areas would be caused primarily by increases in noise events from out-of-Valley shuttle buses. Noise from visitor vehicles would be minimal because the vehicles would travel at low speeds and many of the vehicles would pass by the out-of-Valley parking sites under Alternative 1.

The methodology used to assess sound impacts associated with transportation actions was as follows:

• Estimates of hourly traffic and bus volumes during the peak inbound hour and the peak outbound hour were used for estimating sound levels at two selected locations where changes in sound levels would be expected. Sound levels are expressed as equivalent sound levels over the peak hour. The equivalent sound level for the peak hour is the constant sound level that would have the same sound energy as all of the individual sound events and background sound over the hour.
• Traffic volumes on Southside Drive west of Sentinel Bridge and on Northside Drive between Yosemite Village and Yosemite Lodge were used to represent the range of impacts on sound levels associated with traffic. Quantitative sound level impacts are presented for these roadways in Chapter 4, Environmental Consequences.
• Sound levels were calculated as a function of distance from the centerline of the roadway. Typically, the same sound levels would be experienced at points a constant distance from the centerline along each segment of road with constant traffic volume and speed.
• For roadways where mass transit vehicles operate, sound impact would be a result of the transient nature of the bus sound as well as the impact of other traffic. It is no longer a steady stream of car sound, but also includes discrete events. The impact of changes in the volume of bus traffic on the sound events experienced by a person are expressed in terms of the number of events and the relative sound level of the events compared to the ambient sound level, as measured February 22-26, 1999.
• Actual ambient sound levels would be influenced by the movement of water in the Merced River and its tributaries, by water flow in adjacent falls, and by wind conditions, in addition to sound created by visitor activities near a person listening to the sound events. Ambient sound levels during typically busy days are likely to be higher than those measured in February and presented in Chapter 2. The number of sound events that would be very noticeable within 200 feet of the roadway is estimated for each alternative. An event is considered very noticeable if it exceeds the L₁₀ sound level at 200 feet from the roadway by 3 dBA or more. (Definitions for these terms are provided in the Glossary included in Chapter 8.) Sound events with lower sound levels were also estimated for some roadway segments where shuttle bus trips with lower sound levels would increase by a large number. These sound events would be very noticeable 100 feet from the roadway centerline.

Only the impact of bus operations on the number of sound events is considered in this analysis. It is assumed that other traffic-related sound events (such as the passage of heavy trucks or other maintenance equipment) would be the same across all alternatives.

The California Department of Transportation (Cal Trans) Sound 32 traffic sound model with California noise emission factors was used to generate sound level estimates.

Duration of Impact

Short-term impacts would be impacts created through the implementation phase (0-5 years) of the alternative action (temporary disruption of Valley sound levels created during construction of facility improvements or during implementation of other actions).

Long-term impacts would be impacts created through permanent changes to Valley sound levels, and which are expected to prevail following implementation of the alternative action.

Intensity of Impact

The level of impact (negligible, minor, moderate, or major) of sound changes from the No Action Alternative to the action alternatives was evaluated using the following definitions.

A negligible impact indicates the change in Valley sound levels would not be perceptible, and would be less than 3 dBA. A minor impact indicates the change in Valley sound levels would be equal to 3 to 5 dBA. A moderate impact indicates the change in Valley sound levels would be equal to 6 to 9 dBA. A major impact indicates the change in Valley sound levels would be greater than 9 dBA.

The impact intensity of sound events is presented in table 4-5.

Type of Impact

Impact type was evaluated using the following definitions: beneficial impacts would be created through a reduction in decibels, and adverse impacts would be created through an increase in decibels.

NONVEHICLE NOISE

In the analysis of nonvehicle noise, the following definitions were used:

• Human-caused sounds are considered noise: heavy equipment (trash removal, snow removal, construction), service vehicles (custodial, guest services, stock trailers, etc.), sirens, idling service vehicles, vehicle fueling areas, music, generators, voices and barking dogs, etc.
• Naturally occurring sounds (i.e., natural quiet) are not considered noise: waterfalls, watercourses, wildlife, wind, ice fall, rock fall, etc.
• Ambient noise is the all-encompassing sound associated with a given environment, usually a composite of sound from many sources at many directions, near and far, including the specific sources of interest.

In addition, the following assumptions were used:

• There are two receptors of nonvehicle noise: visitors and residents (e.g., Yosemite Valley, Wawona, Foresta, and El Portal); all noise impacts are experienced by both receptors to some degree.
• Residential activity is not confined to residential areas, and visitor activity is not restricted from residential or operational areas.
• A reduction in the number of people (e.g., visitors, employees, or residents) in an area generally would result in a reduction in the amount of noise (fewer voices, fewer service vehicles, less trash removal, etc.), but not necessarily a reduction in peak noise levels.
• An increase in the number of people (e.g., visitors, employees, or residents) in an area generally would result in an increase in amount of noise (more voices, more service vehicles, more trash removal, etc.), but not necessarily an increase in peak noise levels.
• A reduction in facilities (e.g., buildings, campsites, parking areas, etc.) in an area generally would result in a reduction in amount of noise (fewer voices, less heavy equipment, less trash removal, etc), but a reduction in peak noise levels would be a function of which facilities were removed.
• An increase in facilities (e.g., buildings, campsites, parking areas, etc.) in an area would generally would result in an increase in amount of noise (more voices, more heavy equipment, more trash removal, etc), but the peak noises produced would be a function of the types of facilities introduced.
• Aircraft noise would not vary among the five alternatives (i.e., the aircraft noise of the No Action Alternative is the same as the aircraft noise of the four action alternatives).

A qualitative assessment of noise impacts is presented. The assessment of the action alternatives is relative to the No Action Alternative, and the following areas have been evaluated:

• Yosemite Valley (including west Yosemite Valley, Yosemite Lodge, Yosemite Village, Curry Village, and campgrounds)
• El Portal
• Wawona
• Foresta
• Hazel Green
• South Landing (including Crane Flat)
• Henness Ridge
• Badger Pass

• Entrance stations (South Entrance, Big Oak Flat Entrance, Arch Rock Entrance, and Tioga Pass Entrance Station)

The following types of noise associated with an activity or facility have been evaluated:

• Construction/deconstruction/restoration (voices, heavy equipment, tools, forestry, etc.)
• Housing (voices, service vehicles, trash removal, music, dogs, etc.)
• National Park Service and primary concessioner operations (voices, service vehicles, sirens, idling vehicles, fueling stations, snow removal, trash removal, etc.)
• Transit centers, day-visitor parking, and out-of-Valley parking (voices, service vehicles, trash removal, etc.)
• Lodging (voices, service vehicles, trash removal, etc.)
• Camping (voices, generators, music, trash removal, etc.)
• Picnic areas (voices, trash removal, etc.)
• Pedestrian, bicycle, and stock trails (voices, bicycles, etc.)

DURATION OF IMPACT

Long-term impacts have a permanent effect on the ambient noise environment (visitor and operational activity). Short-term impacts are temporary in duration and would be associated with transitional types of impacts (construction activity is usually a short-term impact).

INTENSITY OF IMPACT

Negligible impacts would not be detectable. Minor impacts would be slightly detectable in close proximity to the source, but are not expected to have an appreciable effect on ambient noise levels. Moderate impacts would be clearly detectable and could have an appreciable effect on ambient noise levels; moderate adverse impacts may include introduction of noise associated with an activity or facility into an area with little or no ambient noise.

Major impacts would be clearly audible against ambient noise levels; or would have a substantial, highly noticeable effect on ambient noise levels.

TYPE OF IMPACT

Beneficial impacts are those impacts that result in less noise, and adverse impacts are those impacts that result in more noise.

Analysis of social and economic impacts has been included in this Final Yosemite Valley Plan/SEIS to evaluate potential effects of the alternatives on communities, visitor population, revenues and expenditures, and concessioners and cooperators. Potential impacts for each of these subjects were evaluated using a method most appropriate to each. A summary description of methodology is shown in table 4-6, and a more comprehensive description is included in Appendix J.

Environmental consequences of implementing any of the alternatives were evaluated for each of the four subject areas identified above. Subjects were analyzed in the context of the alternatives and the effects of actions associated with each alternative on these social and economic topics have been projected within the affected region. Assessments of potential social and economic impacts were based on comparisons between the No Action Alternative and the four action alternatives. The significance of these impacts was evaluated in relation to the affected environment described in Vol. Ia, Chapter 3.

DURATION OF IMPACT

Evaluation of impacts also included an assessment of duration. Distinguishing between short-term and long-term duration was necessary to understand the extent of the identified effects. In general, short-term impacts are temporary in duration and typically are transitional effects associated with implementation of an action (e.g., related to construction activities). In contrast, long-term impacts have a permanent effect on the social and economic environments (e.g., operational activities).

INTENSITY OF IMPACT

The intensity of each impact was rated in terms of increasing severity, as negligible, minor, moderate, or major. Negligible impacts are effects considered not detectable and are expected to have no discernible effect on the social and economic environment. Minor impacts are slightly detectable and are not expected to have an overall effect on the character of the social and economic environment. Moderate impacts are detectable, without question, and could have an appreciable effect on the social and economic environment. Such impacts would have the potential to initiate an increasing influence on the social and economic environment (particularly if other factors have a contributing effect). Major impacts are considered to have a substantial, highly noticeable influence on the social and economic environments, and could be expected to alter those environments permanently. In addition, impacts are recognized as indeterminate if the intensity of their effects on the social and economic environment could not be readily identified (especially when compared with the potential influence of other social and economic factors and/or when data limitations exist).

There are no pertinent National Park Service, or Occupational Safety and Health Administration regulation, policies that specifically apply to the social environment of park housing. However, the General Management Plan includes two relevant objectives: (1) the rights, safety, and security of all visitors and employees would be protected, and (2) the services and amenities conducive to a community environment for employees would be provided.

The National Park Service analyzed available demographic information including information from the park’s primary concessioner on the employee population to project the future population and socioeconomic impacts of actions under consideration. Using the information from these surveys, potential impacts on the social characteristics of the environment were evaluated for each alternative, based on the locations chosen for housing and the number of employees that would be housed there. The impacts on the local economies and to county services were evaluated based on each alternative’s projected population changes and information obtained from National Park Service and Mariposa County staff. The economic impacts of the proposed construction spending were estimated using the IMPLAN input-output model.

Four variables were determined to be the most influential in their potential to affect the social environment: housing conditions, commuting distances and modes, amenities available to employees, and locale. The locale includes the general character of a particular community or housing site. Variables affecting the character include vegetation, climatic conditions, topography, and proximity to roads, the Merced River, and recreational opportunities.

TYPE OF IMPACT

Impacts were recognized as beneficial if they would improve upon characteristics of the existing social and economic environment, as it relates to:

• Local Communities
• Visitor Population
• Regional Economies
• Concessioners and Cooperators

Conversely, impacts were considered adverse if they would degrade or otherwise negatively alter the characteristics of the existing environment in these four areas.

Impacts for each action alternative were evaluated by assessing changes to operations that would be required to meet various operational requirements outlined in each of the action alternatives. Relative costs were generated, using staff estimates of the funding and labor required to implement these actions. These effects were compared to existing operations, staffing, and funding, which are described in Alternative 1.

Existing staffing levels were inventoried and assessments were made of current park operations. In addition, professional judgments by individuals who are most knowledgeable about various activities were used to anticipate the operational changes that would be needed under each action alternative. Estimates were made of the personnel required to: (1) provide various services to the public; (2) staff visitor centers and other facilities; (3) maintain utilities, infrastructure, grounds, and buildings; and (4) preserve and restore natural and cultural resources. These assessments were compared to existing staffing levels. It should be noted that in many cases, existing staffing levels are lower than knowledgeable staff believe necessary to support current operations. It should also be noted that staffing and funding impacts for the action alternatives are difficult to project until such time as final facility designs and operational planning are available. Thus, the estimates are intended to provide a general description of potential effects, considering the variability within the range of possible operational scenarios.

The discussions of impacts are for those operations that would be new, undergo major operational change, or show susceptibility to increases or decreases in operational activity. For example, increasing the number of visitor contact facilities would require increases in staffing for interpretive operations; thus, this impact is discussed in the analysis. For a majority of day-to-day and programmatic activities, the action alternatives would have negligible effects, i.e., there would not be a measurable change or difference in operations. These activities were generally not included in the analysis. For example, keeping an existing picnic area, at the same size, serving the same types of user groups, and with the same types of facilities, would have negligible effects on campground maintenance operations, and thus was not included in the analysis. Even in a case where a campground would be moved to a new location, the effects would be negligible, and are not discussed.

DURATION OF IMPACT

Short-term impacts would last only until all action items are completed. Long-term impacts would have a permanent effect on operations.

INTENSITY OF IMPACT

With negligible impacts, there would not be a measurable difference in costs from existing levels. With minor impacts, measurable additions or reductions in cost would be less than 15% of existing levels. With moderate impacts, additions or reductions in cost would be between 15% and 30% of existing levels. With major impacts, additions or reductions in cost would exceed 30% of existing levels.

TYPE OF IMPACT

Adverse impacts represent an increase in operating costs. Beneficial impacts represent a decrease in operating costs.

The implementing regulations of the National Environmental Policy Act (NEPA) require that environmental impact statements address the energy requirements and conservation potential of project alternatives. The National Park Service Management Policies require that all facilities be managed, operated, and maintained to minimize both energy consumption and development of nonrenewable fuels. The policies also require that new energy-efficient technologies be used where appropriate and cost effective. One of the General Management Plan’s management objectives for park operations is to provide facilities and utility systems that conserve energy; the plan also states that design techniques and application of new technology to reduce energy and water consumption should be emphasized in the design of new facilities.

For each of the action alternatives, energy impacts would result from changes in fossil fuel consumption associated with changes in housing space and water heating, vehicle fuel consumption for the additional employees commuting to job sites in the Valley, and vehicle fuel consumption for the various mix of visitor vehicles and shuttle buses traveling to the Valley. To analyze the impacts associated with the expanded shuttle system and the relocation of employee housing, estimates of the quantities of current propane heating-fuel consumption were analyzed. Table 4-7 summarizes the change in beds for each alternative.

Propane fuel consumption for the various alternatives was estimated by calculating the average propane fuel consumption per housing bed in the Valley, based on total 1998 propane fuel consumption. In reality, fuel utilization by individual housing beds would be a mix of propane, electricity, wood, fuel oil, and possibly renewable energy sources such as solar energy. However, since propane is the primary fuel used in the area, it served as the basis for comparison of home energy use between the alternatives. This average propane fuel consumption was then applied to changes in total proposed housing beds where applicable.

To estimate energy consumption associated with the proposed visitor transportation management plans, employee commuting patterns, and utilization of National Park Service and concessioner vehicles that operate in the Valley, a California Air Resources Board model, called BURDEN, was used to estimate fuel consumption for gasoline-powered automobiles, light-duty trucks, and medium-duty trucks. This model uses a carbon balance formula that uses carbon dioxide, carbon monoxide, and total organic gas emissions that were calculated using the emission factor (EMFAC) model. The carbon balance formula originates from the federal Corporate Average Fuel Economy standards and California Air Resources Board documentation.

Similar fuel consumption estimates for the other vehicle categories using this carbon balance approach were not possible, since EMFAC does not estimate carbon monoxide emissions for the three heavy truck categories, urban buses, shuttle buses, and motorcycles. Therefore, annual fuel consumption for these categories was derived from vehicle miles traveled estimates calculated as part of the air emission calculations and typical fuel economy values for these vehicles. The Corporate Average Fuel Economy values for each vehicle category were adjusted as necessary to better represent an average.

The energy impact analysis for each alternative quantified energy consumption associated with National Park Service and concessioner housing and the vehicles operating in the park. Energy impacts were evaluated in terms of their intensity and duration and whether the impacts were considered to be beneficial or adverse. Cumulative effects on energy were also considered based on past, present, and reasonably foreseeable future actions in the Yosemite National Park region, in combination with the potential energy effects of each alternative.

DURATION OF IMPACT

The duration of the impact considers whether the impact would occur in the short term or long term. Generally, short-term impacts are temporary in nature, whereas long-term impacts would have a continuing effect on energy consumption. For this analysis, vehicle emissions were quantified for the 15-year (2000-2015) time period and are assumed to continue beyond 2015.

INTENSITY OF IMPACT

The intensity of an impact considers whether the impact is judged to be negligible, minor, moderate, or major relative to Alternative 1. For this analysis, negligible impacts are those that increase or decrease energy consumption by 5% or less annually; minor impacts by 5% to 20% annually; moderate impacts by 21% to 50% annually; and major impacts by more than 50% annually.

TYPE OF IMPACT

Impacts were considered to be either beneficial or adverse with respect to energy consumption. Beneficial energy impacts would reduce energy consumption, whereas adverse impacts would increase energy consumption.

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