Chapter 8 Air Quality
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Chapter 8 Air Quality Introduction This section describes the affected environment for air quality and the potential impacts on air quality that would result from the Proposed Project and other alternatives. The major air quality issue related to the Proposed Project and other alternatives would be fugitive dust generated from winds over the exposed lakebed of Walker Lake and newly retired farmland in the Walker River Basin. Windblown dust in Mineral and Lyon County resulting from the implementation of the Proposed Project and other alternatives would represent an adverse impact on regional air quality. The degree of impact for each alternative depends on the level of funding for acquisitions. Sources of Information The key sources of data and information used in the preparation of this chapter are listed below. Full references can be found in Chapter 17, References. EPA, Region 9 Air Plan Actions (U.S. Environmental Protection Agency 2009) EPA Monitor Value Reports—Criteria Air Pollutants (U.S. Environmental Protection Agency 2008) Nevada Bureau of Air Quality Planning (2003) Great Basin Unified Air Pollution Control District (2008) Affected Environment This section describes the environmental setting related to air quality in the study area. Although the project area is the entire Nevada portion of the Walker River Basin (Chapter 1), the study area for the analysis of air quality impacts includes only Lyon and Mineral Counties in Nevada. However, because air pollution may cross county lines and there is no pollutant monitoring within the study area, background information is obtained from beyond the study area. Nevada Bureau of Air Quality Planning (BAQP) has jurisdiction over air quality issues in Nevada. It administers air quality regulations developed at the federal, state, and local levels. Applicable federal, state, and local air quality regulations are described in Appendix 1B. 8-1 Air Quality Local Meteorology and Climate Conditions Climate and weather affect air quality conditions. In particular, precipitation, temperature, and wind influence the potential formation of dust storms. According to historic climate information from the National Weather Service, there are weather monitoring stations in the study area, in Yerington and Hawthorne (Figure 8-1). There is also a weather monitoring station at Bridgeport, California. Precipitation and temperature data for the study area are presented in Chapter 15, Climate and Climate Change. Wind data are presented below. Wind Patterns Walker River Basin topography has a dominating effect on wind patterns. Winds tend to blow somewhat parallel to the valley and mountain range orientation. In spring and early summer, thermal low-pressure systems develop over the interior basins east of the Sierra Nevada, and the Pacific high pressure cells move northward. These developments and the study area topography produce the high incidence of relatively strong northwesterly winds in the spring and early summer (Lopes et al. 2007). Wind speed and direction data indicate that, during the summer, winds usually originate at the north end of the basin and flow southeasterly through the valleys. Wind speed and direction data indicate that, during the winter, winds occasionally originate from the west end of the basin and flow in a west-northwesterly direction. Steady winds are typical in the mountainous area. National Weather Service operates wind monitoring stations in Hawthorne and Yerington. The prevailing wind directions at Hawthorne are from the west- northwest and north, although the station does experience southerly winds during the spring and summer. The prevailing wind direction at Yerington is from the west-southwest. The average annual wind speeds at the Yerington and Hawthorne stations are 2.9 and 7.4 mph, respectively (Western Regional Climate Center 2008). Thermal inversions are a regular occurrence in the desert southwest. Inversions can occur on any given day but are most common in the winter, evenings, and mornings. Inversions are affected by dry weather, changing air temperature, and changing ground temperature. During 2008, the highest sustained wind speed at the Hawthorne Monitoring Station was recorded at 50 mph from the southwest, and the highest instantaneous wind gust speed of 71 mph was recorded from the west-southwest (Weather Underground 2009a). During 2008, the highest sustained wind speed at the Yerington Monitoring Station was 38.6 mph from the south-southeast, with a wind gust of 52.5 mph from the south. The prevailing wind direction over the entire year was from the west-northwest for Hawthorne and from the southwest for Yerington. Wind speeds are typically light, with most of the measurements below 10 mph. Data from the Yerington Mine site indicate that winds tend to 8-2 STOREY WASHOE CHURCHILL LYON CARSON W CITY al ke r R i ve r nm Yerington !. y Walker River e l l Schurz Indian Reservation a V !. n o DOUGLAS s a M y e l l a V E a h t i s t m S r W e v a i l R k Smith e !. r r e k R l iv a e W r t We s MINERAL W a l k e r L a k e y e l l a V e p o l e nm t n Hawthorne A Army Hawthorne !. Depot ) 9 0 - 5 0 - 6 0 ( S S D X M . E T A L P M E T _ S N O I T A T S _ R E H Legend T A Owner E W Weather _ R Bureau of Land Management E nm Monitoring Stations K L A !. W Cities / Towns Lakes / Reservoirs _ 1 _ 8 _ G Rivers I U.S. Department of Defense F \ C O Study Area Tribal Land N D P E A C V M \ County Boundaries A A State of Nevada Lands 7 !! !! !! ! L D ! 0 ! ! _ I A 6 ! F ! ! ! ! ! ! 1 ! ! ! Project Area 5 Private O 0 0 R \ Toiyabe National R U.S. Forest Service N N I U Forest Boundary A \ S T C E J O R ESMERALDA P \ Source: ICF Jones and Stokes 2008 : Q 0 3 6 9 12 Figure 8-1 Miles Weather Monitoring Stations within the Study Area an ICF International Company ± Air Quality blow from the southwest or northeast, with a predominant southwest wind during high wind episodes (Atlantic Richfield Company 2008). Table 8-1 presents a summary of wind speed and wind direction during 2008 for both the Walker Lake-Hawthorne Monitoring Site, located in Hawthorne at U.S. Highway 95 and operated by MesoWest under contract with the State of Nevada Department of Transportation; and the Yerington Monitoring Site, located north of U.S. Highway 95 on the Alpaca Mining Company property. Table 8-2 presents the summary of wind speed occurrence at both sites (Weather Underground 2009b). Table 8-1. Wind Speeds and Direction in Study Area for 2008 Maximum Wind Maximum Wind Speed (mph) Gust (mph) Average Wind Prevailing Location (Wind Direction) (Wind Direction) Speed (mph) Wind Direction Hawthorne 50.0 (SW) 71.0 (WSW) 6.8 WNW Yerington 38.6 (SSE) 52.5 (S) 2.9 SW Source: Weather Station Histories for MWLKNV station (Weather Underground 2009a) and KNVYERIN2 station (Weather Underground 2009b). Table 8-2. Wind Speed Frequencies in Study Area Walker Lake – Hawthorne Yerington – Lyon County Wind Speed Value 2008 Data 2007 Data 2008 Data Category (mph) (days) (days) (days) < 10 148 81 56 11–15 100 124 120 16–21 60 67 118 22–29 45 27 44 30–49 9 13 18 > 50 3 1 1 Source: Weather Station Histories for MWLKNV station (Weather Underground 2009a) and KNVYERIN2 station (Weather Underground 2009b). Note: Walker Lake-Hawthorne wind data only available for 2008. 8-3 Air Quality Windblown dust in the Great Basin area is a significant air pollution concern. Long-term water diversions have led the alkaline, and now almost dry, Owens Lake to become the largest single source of windblown dust in the United States. Winds in the area often exceed 40 mph at a 33-foot height, which has led to particulate matter greater than 10 microns in size (PM10) concentrations often 80 times higher than NAAQS), and the highest concentrations are up to 133 times the NAAQS. Annual PM10 emissions caused by wind erosion of the Owens Lake bed are estimated at 76,000 tons per year (Great Basin Unified Air Pollution Control District 2008). Similarly, water diversion has led to similar wind erosion problems from Mono Lake, which has had 33 PM10 violations since 2005 (California Air Resources Board 2008). Walker Lake elevations have declined 150 feet over the past 126 years, and the receding lake elevation has exposed outer portions of the lakebed making them susceptible to windblown dust. The drying of the shoreline at Walker Lake mimics the wind erosion and dust emissions conditions described above for Owens and Mono Lakes. Soil Conditions Because of the relatively low precipitation in the Walker River Basin, particularly in the lower elevations, direct precipitation contributes only sporadically to soil moisture. Groundwater conditions, agricultural irrigation, and proximity to surface water are the dominant influences on soil and sediment moisture conditions. The generally warm to hot air temperatures, along with low humidity and moderate winds, mean that soil surfaces are typically dry. Soils determine the susceptibility of land to wind erosion (Western Regional Air Partnership 2006). For Lyon County, Table 8-3 shows the major soil associations that occur on irrigated lands in Mason Valley, Smith Valley, and East Walker Valley. Figure 8-2 shows the distribution of soil associations in the area. Most of the soil associations in Lyon County contain at least one soil series with high susceptibility to wind erosion. Table 8-3.