Great Basin Unified Air Pollution Control District (GBUAPCD): State Implementation Plan for the Coso Junction PM-10 Planning Area

The Coso Junction PM₁₀ Planning Area is located in Eastern California in the southern portion of Inyo County (Figure 1). It is an arid desert area that receives less than 5 inches of rain per year. The area is rural in nature and sparsely populated. The principle PM₁₀ monitor site is located at Coso Junction in the Rose Valley. This valley is flanked by the Sierra Nevada and Coso mountain ranges.

Air pollution in the Coso Junction Planning Area (CJPA) is dominated by wind blown dust transported from Owens Lake, which is located outside the planning area . Air pollution sources within the CJPA boundaries have not been found to have a significant impact on PM₁₀ concentrations. These sources include the Coso geothermal power operations, military operations at the China Lake Naval Air Weapons Station, and volcanic cinder and pumice mining operations. Although high PM₁₀ readings were documented in 1990 due to wind blown dust from abandoned agricultural land, this land became naturally stabilized with vegetation in 1991. Since that time no agricultural activities have taken place in the CJPA.

2. Clean Air Act Regulatory History

The Coso Junction area was initially designated as a PM₁₀ nonattainment area in 1987 along with the Indian Wells Valley and Trona. Together they comprised the Searles Valley PM₁₀ nonattainment area as shown in Figure 1. The Great Basin Unified Air Pollution Control District adopted a State Implementation Plan (SIP) for the Coso Junction portion of the Searles Valley PM₁₀ nonattainment area in November 1991 (GBUAPCD, 1991). This was followed by air quality plans for the Indian Wells Valley and Trona, which were regulated by the Kern County and the San Bernardino County Air Pollution Control Districts (now called the Mojave Desert Air Quality Management District), respectively.

In August 2002, the US Environmental Protection Agency (EPA) redesignated the Searles Valley into three separate PM₁₀ nonattainment areas. Under this regulatory action, Coso Junction and the Indian Wells Valley were classified as moderate PM₁₀ nonattainment areas, and a finding of attainment was made for Trona (Federal Register, 2002a & 2002b). In 2003, Indian Wells Valley was reclassified to attainment with US EPA’s approval of the Moderate Area SIP and Maintenance SIP. Trona’s reclassification to attainment and proposed SIP revision are currently pending approval. (Federal Register, 2003a and 2003b) This SIP revision is intended to update the air quality plan for the Coso Junction planning area, and provide a demonstration that the area will attain the National Ambient Air Quality Standard (NAAQS) for PM₁₀ by December 31, 2006.

Figure 1. The Searles Valley PM₁₀ Nonattainment Area was reclassified into three separate planning areas in 2002. Coso Junction and Indian Wells Valley are moderate PM₁₀ nonattainment areas and Trona is in attainment with the PM₁₀ standard.

3. Air Quality

Fifteen exceedances of the federal 24-hour PM₁₀ standard have been monitored at Coso Junction since 1985. Thirteen of the 15 exceedances were caused by dust from Owens Lake. High northerly winds and high PM₁₀ concentrations near Owens Lake are good indicators for wind blown dust to be transported from the exposed lake bed at Owens Lake to the CJPA.

To document the Owens Lake dust impact at Coso Junction and other downwind sites, a special-purpose monitoring network was operated from 1993 to 1996. The monitoring network shown in Figure 2 measured Owens Lake dust impacts at five downwind sites and found exceedances of the standard as far as 50 miles from Owens Lake. PM₁₀ monitors at Coso Junction, Navy I, and Pearsonville are within the CJPA boundaries. Sites north of Coso Junction are in the Owens Valley PM₁₀ planning area and the monitor sites in Ridgecrest and Inyokern are in the Indian Wells PM₁₀ planning area.

Table 1 shows a summary of the PM₁₀ exceedances monitored in the CJPA and the levels measured at other sites in the network. Table 2 shows PM₁₀ concentrations, wind speed and directions in the Owens Lake area for these exceedance days. As previously mentioned, 13 of the 15 exceedances in the CJPA were caused by dust from Owens Lake. The exceptions to this are two events measured at Coso Junction on 4/23/90 and 7/25/02.

Table 3 shows the annual average PM₁₀ concentrations for the Coso Junction site. The annual average over 3 years is used to determine compliance with the annual PM₁₀ NAAQS of 50 µg/m³ . In 2003, the 3-year annual average was 18.8 µg/m³ , which demonstrates compliance with the NAAQS. Table 3 also includes the number of monitored exceedances per year, and the expected number of exceedances per year based on the monitoring frequency. Except for monitoring performed as part of the Owens Lake transport study, samples were normally collected on a once every sixth-day, or once every third-day schedule. A listing of all the PM₁₀ monitor data for Coso Junction and other nearby sites is included in Appendix A.

Figure 2. PM₁₀ monitor locations in and near the Coso Junction Planning Area.

Table 1. Summary of the PM₁₀ exceedances monitored over 150 µg/m³ in the Coso Junction Planning Area and concentrations at other sites on the same day.

Table 2. Except for two days, all the exceedances shown in Table 1 for the Coso Junction Planning Area were associated with wind blown dust from Owens Lake.

Table 3. Annual average PM₁₀ concentrations in the Coso Junction Planning Area meet the NAAQS set at 50 µg/m³ .

4. Emission Inventory

PM₁₀ emissions generated in the CJPA are primarily from stationary sources, and re-entrained dust from paved and unpaved roadways. Figure 3 shows a pie chart of the relative contributions of these sources to the annual PM₁₀ emission inventory, which is estimated at about 460 tons per year. A listing of the industrial facilities and emissions from mobile and area sources is shown in Table 4. In comparison, the total PM₁₀ emissions generated in the planning area are less than 1% of the wind blown dust emissions from nearby Owens Lake, which the District has determined is the primary cause of the air quality violations at Coso Junction. Owens Lake emissions were estimated at 80,398 tons per year prior to the implementation of dust control measures on the lakebed. Emission estimates are shown for 2002. (GBUAPCD, 2003)

The following information and assumptions were used to estimate emissions and to forecast emission changes.

Mobile Sources. PM₁₀ tailpipe emissions from on-road motor vehicles are based on ARB’s emission estimates for Inyo County in 2003 and pro-rated for the proportion of traffic in the CJPA (5.1%). The mobile source emissions are not expected to change in future years.

Figure 3. The annual PM₁₀ emission inventory is primarily associated with stationary sources and unpaved roads. Total PM₁₀ emissions are about 460 tons per year, which is less than 1% of the emissions caused by wind blown dust from Owens Lake.

Table 4. Annual PM₁₀ emission inventory for the Coso Junction Planning Area.

Stationary Sources	Tons/year
California Lightweight Pumice	32.1
China Lake Naval Air Weapons Station	22.9
Coso Operating Company	106.7
Halliburton Services	10.9
Twin Mountain Rock	60.8
Valley Sand & Gravel	26.0
Area Sources
Unpaved Road Dust	182.5
Paved Road Dust	16.4
Mobile Sources
On-Road Motor Vehicles	0.6

Total Annual PM₁₀ Emissions	458.9

5. Control Strategy

As discussed in the Air Quality section of this SIP, PM₁₀ violations in the CJPA are primarily due to the transport of wind blown dust from the Owens Lake area. Therefore, achieving emission reductions at Owens Lake is the primary control strategy for reaching attainment in the CJPA. The US EPA classified the Owens Valley as a serious PM₁₀ nonattainment area in 1993 and required that a SIP be developed to achieve compliance with the PM₁₀ NAAQS. A SIP was adopted in 1998 and approved by the US EPA for the Owens Valley with an interim control strategy that required dust controls on 16.5 square miles of the lakebed. Under the Owens Valley SIP, the City of Los Angeles is responsible for mitigating the dust generated from Owens Lake in order to bring the area into attainment with the NAAQS. The Owens Valley SIP was revised in 2003 to require controls on 30 square miles of lakebed, and additional areas if necessary. The 2003 Owens Valley SIP control strategy is expected to bring the Owens Valley into attainment with the NAAQS by December 31, 2006. Dust mitigation measures at Owens Lake include shallow flooding and managed vegetation dust control measures, which will both achieve 99% emission reductions. (GBUAPCD, 2003)

Other sources of PM₁₀ that may be found in the future to cause or significantly contribute to PM₁₀ violations in the CJPA can be controlled through existing District rules and regulations, which are listed in Table 5. These regulations address emissions from new facilities, fugitive dust sources, open burning, and projects associated with federal actions that must comply with Transportation and General Conformity requirements.

Figure 4 shows the Reasonable Further Progress emission trend anticipated with the implementation of the 2003 Owens Valley SIP. As seen on this graph, significant emission reductions were achieved in 2002 and 2003, as the result of dust control measures that were implemented on about 20 square miles of the lakebed. About 30 square miles of the lakebed will need to be controlled to meet the requirements of the 2003 Owens Valley SIP. With the full implementation of the SIP, the Owens Valley is expected to attain the PM₁₀ standard by December 31, 2006. (GBUAPCD, 2003) Since quantifiable emission reductions are not anticipated in the Coso Junction Planning Area, the Owens Valley emission reduction trend will be used to evaluate Reasonable Further Progress toward attainment in the CJPA.

Table 5. Existing District rules and regulations to control sources of PM₁₀

Rule	Description
209-A	Requires new sources with PM₁₀ emissions greater than 250 pounds per day of total suspended particulates, or facility modifications of greater than 15 tons per year of PM₁₀ to apply Best Available Control Technology to control PM emissions.
400	Limits visible emissions from any source, except those exempted under Rule 405, to less than Ringelmann 1 or 20% opacity.
401	Requires that reasonable precautions be taken to prevent visible particulate emissions from crossing the property boundary.
402	Prohibits sources of air pollution from causing a nuisance to the public or endangering public health and safety.
408	Limits agricultural burning operations to designated burn days and requires a burn permit.
409	Limits range improvement burning to designated burn days and requires that a burn plan be approved by the APCO.
410	Limits forest management burning to designated burn days and requires that a burn plan be approved by the APCO.
411	Limits wildland management burning to designated burn days and requires that a burn plan be approved by the APCO.
Reg. XII	Requires that federal actions and federally funded transportation-related projects conform to SIP rules and that they do not interfere with efforts to attain federal air quality standards.
Reg. XIII	Requires that federal actions and federally funded projects conform to SIP rules and that they do not interfere with efforts to attain federal air quality standards.

Figure 4. Reasonable Further Progress trend for Owens Lake emission reductions.

Figure 5. The dispersion modeling domain was expanded from the Owens Lake modeling area. The map shows the meteorological stations, land use and terrain contours (meters) and USGS land use categories.

6. Air Quality Modeling and Attainment Demonstration

A dispersion modeling study was performed to examine PM₁₀ concentrations at the boundary of the Owens Valley and Coso Junction planning areas, and at the Coso Junction monitoring site. Model receptors were placed on this planning area boundary since they were expected to have the highest PM₁₀ impacts from Owens Lake dust in the CJPA. The CALPUFF modeling system was used following the method developed to model the attainment demonstration for the 2003 Owens Valley SIP. In this case, the modeling domain was expanded to include the northern portion of the CJPA (Figure 5). The model simulations were performed using meteorological and wind blown dust emission information for the period from January 2000 through June 2002. The model simulation for this attainment demonstration assumed that dust source areas on Owens Lake would be controlled as specified in the 2003 Owens Valley SIP. (GBUAPCD, 2003)

The model results show that after control measures are implemented at Owens Lake PM₁₀ concentrations due to wind blown dust from the Owens Valley will no longer cause or contribute to exceedances of the PM₁₀ NAAQS in the CJPA. After controls, the predicted 3 rd highest PM₁₀ concentration was 25.4 µg/m³ at a receptor on the boundary of the two planning areas. Note that the 3 rd highest value is used for the model design day for attainment demonstration purposes, since the 24-hour PM₁₀ NAAQS allows one statistical exceedance per year and the modeling period was two and a half years. Figure 6 shows the 3 rd highest PM₁₀ concentrations during the modeling period for the boundary receptors and the Coso Junction monitor site. Since the model assumed a background PM₁₀ concentration of 20 µg/m³, this shows that the maximum contribution to the CJPA from Owens Lake is about 5 µg/m³ after dust control measures are implemented. More information about the modeling method and results are included in Appendix B.

7. References

Federal Register, 2002a. Clean Air Act Redesignation and Reclassification, Searles Valley Nonattainment Area; Designation of Coso Junction, Indian Wells Valley, and Trona Nonattainment Areas; California; Determination of Attainment of the PM-10 Standards for the Coso Junction Area; Particulate Matter of 10 microns or less (PM-10), Federal Register, Vol. 67, no. 151, pp. 50805-50808, August 6, 2002.

Federal Register, 2002b. Clean Air Act Redesignation and Reclassification, Searles Valley Nonattainment Area; Correction; Federal Register, Vol. 67, no. 182, pp. 59005-59006, September 19, 2002.

Federal Register, 2003a. Approval and Promulgation of Implementation Plans and Designation of Areas; California - Indian Wells Valley PM-10 Nonattainment Area; Federal Register, Vol. 68, no. 88, pp. 24368-24370, May 7, 2003.

Federal Register, 2003b. Correction of Designation of Areas for Aire Quality Planing Purposes; California – PM-10 Nonattainment Areas; Federal Register, Vol. 68, no. 120, pp. 37090-37091, June 23, 2003.

GBUAPCD, 1991. Great Basin Unified Air Pollution Control District, PM10 State Implementation Plan for the Searles Valley Planning Area, GBUAPCD, Bishop, California, November 1991.

GBUAPCD, 2003. Great Basin Unified Air Pollution Control District, Owens Valley PM₁₀ Planning Area Demonstration of Attainment State Implementation Plan 2003 Revision, GBUAPCD, Bishop, California, November 13, 2003.

Wilderness Society, 2003. Wilderness Society, Summary of the McNally Fire, California: July 21-August 29, 2002, Science & Policy Brief, Wilderness Society, Ecology and Economics Research Department, Washington, DC, No. 10, March 2003.

State Implementation Plan for the Coso Junction PM₁₀ Planning Area

November 1, 2004

1. Planning Area

2. Clean Air Act Regulatory History

3. Air Quality

4. Emission Inventory

5. Control Strategy

6. Air Quality Modeling and Attainment Demonstration

7. References

State Implementation Plan for the Coso Junction PM10 Planning Area

November 1, 2004

1. Planning Area

2. Clean Air Act Regulatory History

3. Air Quality

4. Emission Inventory

5. Control Strategy

6. Air Quality Modeling and Attainment Demonstration

7. References

State Implementation Plan for the Coso Junction PM₁₀ Planning Area