Impacts Common to All Alternatives

Components of air quality that may be impacted include visibility, air pollutant concentrations, and atmospheric deposition. Air quality impacts would primarily result from minerals development and production, and oil and gas production as potential emissions associated with these actions would substantially outweigh those produced from any other proposed activity.

Source: BLM 2010c

Air Quality

Mineral development and production would result in short-term air quality impacts from five sources: (1) combustive emissions (vehicle tailpipe and exhaust stack emissions) due to the operation of mobile and stationary source construction equipment; (2) fugitive dust emissions (PM₁₀) due to earthmoving activities and the operation of vehicles on unpaved surfaces; (3) NO_x and particulate emissions from blasting and oil and gas well construction activities and drilling rig equipment; (4) PM emissions from fire management; and (5) VOC and CO emissions associated with OHV use (all terrain vehicles, off-road motorcycles [dirt bikes], and snowmobiles), vehicular traffic and oil and gas well construction and production equipment. The primary PM_2.5, NO_x , and SO₂ emissions may result in the formation of secondary PM_2.5 and would affect total measured PM_2.5 concentrations. Increases in PM_2.5 would also affect visibility in the region. The VOC, NO_x , and CO emissions may affect the formation of ground-level ozone, a criteria pollutant. Ozone is a secondary pollutant not directly emitted, but rather formed in the lower atmosphere by a series of reactions involving ultra violet (UV) radiation and precursor emissions of NO_x, VOC, and CO. NO_x consists of nitric oxide (NO) and nitrogen dioxide (NO2), which are primarily emitted from anthropogenic sources. VOCs consist of thousands of individual hydrocarbon and oxygenated hydrocarbons emitted from both man-made and biogenic sources (trees). Ozone formation in the troposphere is affected by local weather conditions (winds, temperature, solar radiation, and horizontal and vertical dispersion characteristics), which influence precursor concentrations, reaction rates, formation, transport, and deposition.

In recent years in Sublette County, Wyoming (BLM Pinedale planning area), 8-hour average ozone concentrations that exceed the NAAQS have been measured during the winter months. This is a result of a unique set of topographic and atmospheric conditions that include high pressure, light winds, a strong radiation inversion, and adequate snow cover. The atmospheric conditions limit precursor dispersion while the snow cover increases albedo, resulting in much higher UV radiation and NO2 photolysis rates. In 2009, the Governor of Wyoming recommended the Sublette County area (and parts of two adjacent counties) be classified as an ozone nonattainment area. Because of the lack of monitoring, it is impossible to know whether the Bighorn Basin area also experiences wintertime ozone episodes such as those occurring in the Pinedale planning area. Air quality data from monitors located in nearby areas showed no exceedances of the 8-hour ozone standard in 2009. The lack of ozone monitors in the Bighorn Basin makes it difficult to speculate about the potential impacts of emissions from the various alternatives, including Alternative D, to future ozone air quality in 2015 and 2024.

Minerals production would generate long-term combustive and fugitive dust emissions from two sources: (1) stationary sources, such as natural gas flaring, natural gas-fired compressors, and minerals storage and handling equipment; and (2) mobile sources that access and service oil and gas facilities and extract and handle subsurface minerals, such as hard minerals. Minerals reclamation activities also would produce combustive emissions and fugitive dust.

Management actions and resource uses under each of the alternatives may impact air quality related values (AQRVs) within the federal Class I areas of Yellowstone National Park, and the North Absaroka, Washakie, Bridger, and Fitzpatrick NWAs. Although minerals development and production and oil and gas production would be the primary sources of emissions, other resource management actions that would produce combustive and/or fugitive dust emissions include the following: forestry production, fire and fuels management, road maintenance, ROWs, and OHV use (especially for CO and VOC emissions). This analysis assumes that the expected activity and resulting emissions for these other resource management actions would be the same for all alternatives for 2015 and 2024.

The Wyoming DEQ has the authority to implement emission controls for sources requiring air permits under Wyoming Air Quality Standards and Regulations and to ensure that these sources do not contribute to an exceedance of an ambient air quality standard. To facilitate this process, the BLM currently implements a program to share emission source information with the Wyoming DEQ and other government agencies. This program would continue under all alternatives. In addition, the BLM would require implementation of BMPs within its authority to minimize impacts, such as fugitive dust emissions in proximity to high use roadways, populated areas, and resource-sensitive areas. Prior to site-specific project approval, the BLM would conduct environmental analyses in compliance with the National Environmental Policy Act (NEPA).

Under all alternatives, site-specific hydrogen sulfide (H₂S) plans would be prepared for all oil and gas wells in compliance with the requirements of Occupational Safety and Health Administration and Onshore Order #6. These (H₂S) plans may include requirements to monitor wind speed, wind direction, and atmospheric stability, and to conduct dispersion modeling analyses for (H₂S). These requirements would apply to areas where public health and safety or important resource values are a concern, such as proposed well sites in proximity to residences. If the BLM determines after review of an (H₂S) plan that additional data or safety precautions are needed, the BLM may require these items as conditions of approval (COA). Section 4.8.3 Health and Safety discusses management and impacts of (H₂S).

Greenhouse Gases

Under all of the alternatives, a variety of activities in the Planning Area would generate greenhouse gas (GHG) emissions, including carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O). These activities include oil and gas and other minerals development, fire events, motorized vehicle use, livestock grazing, facilities development, and other surface-disturbing activities. The lack of scientific tools designed to predict climate change on regional or local scales limits the ability to quantify potential future impacts. Currently the BLM does not have an established mechanism to accurately predict the effect of resource management-level decision from this planning effort on global climate change. Since the Industrial Revolution, atmospheric concentrations of CO₂ have risen about 36 percent (IPCC 2007a), principally due to the combustion of fossil fuels. Fossil fuel combustion accounted for 94 percent of national CO₂ emissions in 2008 (EPA 2010). Activities that require fossil fuel-powered machinery, such as minerals development and motorized vehicle use, would comprise the majority of CO₂ emissions in the Planning Area under all of the alternatives. Wildland fires, including prescribed burns, would also result in CO₂ emissions. However, CO₂ from fires, particularly prescribed fires, is typically considered to be counterbalanced by the increased productivity of existing larger vegetation and new growth of vegetation post fire. Alternative C is projected to result in the most new oil and gas wells and locatable mineral development (the activities anticipated to result in the greatest CO₂ contributions during the planning cycle), resulting in the most CO₂ emissions, followed by alternatives D, A, and B respectively (see Tables and for CO₂ emissions by alternative measured in CO₂ equivalents).

CH₄ is more than 20 times as effective as CO₂ at trapping heat in the atmosphere and accounted for 8.2 percent of GHG emissions in 2008 (based on CO₂ equivalents) (EPA 2010). CO₂ equivalent is a measurement that allows an aggregate comparison of multiple GHGs (e.g., CH₄ and N₂O), created by multiplying the actual or anticipated emissions of each gas by its relative global warming potential. Oil, gas, and locatable mineral development and enteric fermentation from livestock (which accounted for 25 percent of total CH₄ emissions in 2008 [EPA 2010]) are the predominant source of CH₄ emissions in the Planning Area. As a result of higher levels of mineral development, CH₄ emissions are anticipated to be highest under Alternative C, followed by alternatives A, D, and B respectively. Animal Unit Month (AUM) projections under alternatives A, C, and D are similar, and therefore would result in similar CH₄ emissions. Alternative B would reduce AUMs by about 50 percent, resulting in a proportional reduction in CH₄ emissions from enteric fermentation.

N₂O emissions, which like CH₄ are also more effective heat trapping agents than CO₂, in the Planning Area would result predominantly from fuel combustion in motor vehicles that are likely to be greatest under Alternative C, followed by alternatives A, D, and B.

Under all alternatives, management actions would likely affect the level of carbon sequestration in the Planning Area. Management that conserves carbon sinks or provides for research and technology to store carbon that would otherwise be released into the atmosphere would reduce overall contributions of GHGs. Alternative B would result in the greatest preservation of biological carbon sinks including vegetation and soils, followed by alternatives D, A, and C. Forest management practices and silvicultural treatments that improve forest health and reduce the risk of catastrophic wildlife may increase or maintain carbon sequestration in forests and woodlands in the short term; however, altering the natural fire regime through forest management may lead to long-term impacts on forest health (e.g., infestation) that affect carbon sequestration in forests and woodlands. Alternative C includes the greatest number of silvicultural practices and other treatments to actively manage forests and woodlands, followed by alternatives D, A, and B. Allowing carbon sequestration research and projects under Alternative C and considering carbon sequestration research and projects under Alternative D would increase the potential for carbon sequestration projects and management that reduces atmospheric CO₂, compared to the alternatives.

Source: BLM 2010c

¹Carbon Dioxide Equivalent is a measurement that allows an aggregate comparison of multiple greenhouse gases, created by multiplying the emissions of each gas by its relative global warming potential. For this analysis however, metric tons of Carbon Dioxide Equivalent includes only carbon dioxide (CO₂) emissions.

Source: BLM 2010c

¹Carbon Dioxide Equivalent is a measurement that allows an aggregate comparison of multiple greenhouse gases, created by multiplying the emissions of each gas by its relative global warming potential. For this analysis however, metric tons of Carbon Dioxide Equivalent includes only carbon dioxide (CO₂) emissions.

Alternative A

Figure 4-1 presents a summary of annual emissions for the base year (2005) and for 2015 for each alternative. Figure 4–2 presents a summary of annual emissions for the base year and for 2024 for each alternative. Appendix U provides the details regarding the emission calculations and emission summary tables.

For Alternative A (current management), Figure 4-1 indicates that emission estimates for 2015 are greater than those for 2005 for PM₁₀ , PM_2.5 , and CO, and slightly lower for NO_x , SOX, VOC and HAPs. By 2024, emissions for all pollutants (except VOCs and HAPs) would be greater than in 2005, with the largest increase in PM₁₀ emissions, which are expected to increase by 173 tons per year (7 percent).

The Planning Area is a large, irregularly shaped region with an east-west extent of approximately 100 miles, a north-south extent of 105 miles, and a northwest-southeast extent of 150 miles. Given the generally good air quality in the region currently and the expected separation of sources within the Planning Area, it is unlikely emissions from Alternative A would contribute to an exceedance of NAAQS or WAAQS. There may be localized air quality impacts (potentially on local ozone) depending on the locations and emission levels of proposed sources in the area, the surrounding topographical characteristics, and the site-specific meteorology.

The impacts of these estimated future air emissions at the nearby federal Class I areas under Alternative A are difficult to quantify with any level of confidence without information on the specific locations and characteristics of projected sources in the Planning Area. As noted above, air quality modeling can be used to estimate these impacts, and this requires detailed information regarding source location/characteristics, topography/land use, and local and regional meteorology to accurately quantify the potential spatial and temporal aspects of air quality impacts from the various emission sources/activities. In addition, the Wyoming DEQ air-permitting processes would require larger development projects to identify the locations for specific emission sources to demonstrate with air quality modeling analyses that proposed emissions would not adversely affect ambient air quality and AQRVs in federal Class I areas.

[D]

Figure 4.1. Emissions Estimates for 2015 from BLM Activities in the Bighorn Basin Planning Area

Source: BLM 2010c

Figure 4.2. Emissions Estimates for 2024 from BLM Activities in the Bighorn Basin Planning Area

In addition to the proposed sources of HAPs within the Planning Area, there also may be emissions of (H₂S) in the area. These sources would include fossil fuel combustion, fugitive VOCs, and emissions due to oil and gas production. The accidental release of “sour” natural gas (rich in (H₂S)) poses the main risk under Alternative A. Another source of release of (H₂S) is at oil and gas fields where secondary recovery operations are occurring.

Under Alternative A, qualitative air quality analyses are performed for activities with expected effects to air resources and quantitative air quality modeling may be performed on a case-by-case basis. If an analysis shows that significant impacts are possible, mitigation measures within BLM authority would be implemented or applied to reduce potential adverse impacts to air quality. However, the Wyoming DEQ Air Quality Division has the authority to require demonstration of compliance with federal and state air quality regulations and standards for any substantial future development action under their jurisdiction, which may include quantitative analysis.

Alternative B

As shown in Figure 4–1 and Figure 4–2, Alternative B would result in the lowest emissions of any of the alternatives, for both 2015 and 2024. Compared to the base year 2005 estimates, Alternative B would result in lower emissions for all pollutants for both future years, except for CO in 2015 where a slight increase is expected. VOC emissions would drop by 759 tons or 35 percent in 2024 due to development constraints in Alternative B. This would result in the lowest natural gas production—one of the principal sources of VOC emissions—of all alternatives and the expected reductions in emissions from cleaner OHV engines, the other principal source of VOC emissions.

As a result, this alternative would likely result in similar or smaller impacts to AQRVs at the nearest federal Class I areas similar to base year conditions. In addition, given the generally good existing air quality in the region, the BLM would not expect emissions under Alternative B to contribute to an exceedance of NAAQS or WAAQS. Implementing the mitigation measures common to all alternatives also would reduce emissions and air quality impacts associated with Alternative B.

Alternative C

Emission estimates for Alternative C, reflecting more resource use in the Planning Area, show slight to moderate increases in emissions by 2024 compared to the base year (2005). The largest increase is for PM₁₀ emissions, with an expected increase of 668 tons (27 percent). The estimates for Alternative C are also consistently higher than those for Alternative A.

Because of the potential increases in emissions compared to Alternative A, it is possible that impacts under this alternative could contribute to exceedances of the NAAQS or WAAQS. Although the existing air quality in the region is considered good, limited measurements make it difficult to fully and comprehensively assess current conditions. Because of expected increases in emissions under this alternative, adverse impacts to AQRVs in the nearby Yellowstone National Park and other NWAs may occur. Implementing the mitigation measures common to all alternatives would reduce emissions and any air quality impacts associated with Alternative C.

Alternative D

As listed in Table 4–2 and depicted in Figures 4–1 and 4–2 , the emission estimates for Alternative D are generally similar to or lower than Alternative A, except for a negligible increase in CO emissions. Similar to the other alternatives, it is quite difficult to speculate whether emissions for this alternative would contribute to an exceedance of NAAQS or WAAQS or would adversely affect AQRVs in nearby Class I areas. This alternative may require the application of an air quality model to determine project-specific and cumulative air quality impacts on ozone, PM_2.5 , and visibility.