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2010 Coso Junction PM10 Maintenance Plan

EXECUTIVE SUMMARY

This document is a revision to the 2004 PM10 State Implementation Plan (SIP) for the Coso Junction PM10 Planning Area. It includes 1) a request to redesignate the area from nonattainment for the National Ambient Air Quality Standard for PM10 (federal standard) to attainment based on monitoring data and a modeling analysis, and 2) a maintenance plan that contains requirements to ensure the federal PM10 standard will not be violated in the future. As required to redesignate the area to attainment, the enclosed monitoring data and modeling analysis show the Coso Junction Planning Area (CJPA) had less than or equal to 1.0 average annual exceedances of the federal PM10 standard (150 µg/m3 for a 24-hour average) during the 3-year period from January 2007 through December 2009.

The 2004 State Implementation Plan for the Coso Junction Planning Area examined the PM10 problem during the period from 1985 to 2003. During that period, 15 violations of the federal 24-hour PM10 standard were monitored at the Coso Junction rest area on Highway US 395. Thirteen of those violations were found to have been caused by windblown dust from the dry lake bed of Owens Lake that is 14 miles outside (to the north) of the Coso Junction Planning Area. In November 2004, the District adopted a SIP for the CJPA to explain how the area would be brought into attainment. Since PM10 violations at Coso Junction were primarily caused by windblown dust from Owens Lake, the Coso Junction attainment demonstration relied on implementing dust controls outside of the planning area. Under the 2003 Owens Valley PM10 SIP, windblown dust from 29.8 square miles of the dry lake bed at Owens Lake were required to be controlled by December 2006. A dispersion modeling analysis showed these dust mitigation efforts would be adequate to bring the Coso Junction Planning Area into attainment.

A review of daily ambient monitoring data from Coso Junction showed three monitored exceedances of the federal 24-hour PM10 standard (150 micrograms per cubic meter, µg/m3) during the 3-year period from January 2007 through December 2009. The federal 24-hour PM10 standard allows no more than an average of 1.0 expected exceedances per year over a 3-year period. Since daily PM10 monitor data showed the monitor site had an average of 1.0 exceedances per year, PM10 levels near the monitor site can be considered to be in attainment with the federal standard.

A closer examination of the three exceedances found that two exceedances in 2007 (6/5/2007, 217 µg/m3; 12/6/2007, 283 µg/m3) were caused by windblown dust from an unpaved truck parking area west of the PM10 monitor site. The owner of the unpaved parking area was notified and the area was graveled in 2008 and surfaced with asphalt in 2009 to control fugitive dust. The third monitored exceedance (12/22/2009, 168 µg/m3) was caused by windblown dust from Owens Lake. During that event, dust source areas at Owens Lake that were not previously identified in the 2003 Owens Valley SIP contributed to the exceedance at Coso Junction. A revision to the Owens Valley SIP in 2008 included the majority of these dust source areas as part of an additional 9.8 square miles of the lake bed that was controlled using shallow flooding in April 2010. Another 3.5 square miles of the lake bed are expected to be controlled by October 2010. Therefore, dust control measures were implemented to mitigate the causes of dust for all three PM10 exceedances at Coso Junction that took place during the 3-year attainment demonstration period.

Although daily PM10 monitor data collected at the Coso Junction rest area showed the area could be considered to be in attainment with the federal standard, higher PM10 levels are likely to have occurred at locations closer to Owens Lake, since this is the primary source of windblown dust that caused Coso Junction to be designated nonattainment. The monitor site at the Coso Junction rest area is about 18 miles south of Owens Lake, while the northern boundary of the CJPA is closer at 14 miles from Owens Lake. To determine if windblown dust from Owens Lake caused PM10 violations at the northern boundary or at other locations in the CJPA, a dispersion model was run to analyze windblown dust impacts for the 3-year period from July 2006 through June 2009. To evaluate attainment through a modeling analysis, the fourth highest value over a 3-year period must be below 150 µg/m3 at all locations. The District used the CALPUFF dispersion model, which is a guideline model recommended by the United States Environmental Protection Agency (US EPA) for long-range transport and situations where complex winds influence dispersion. As expected, the CALPUFF model showed the highest PM10 concentrations were at the northern boundary of the CJPA. The highest site had two days with modeled impacts above 150 µg/m3 and a third high concentration of 150 µg/m3. Since 150 µg/m3 is not an exceedance of the PM10 standard there were only two modeled exceedances at the highest receptor site in the CJPA. The fourth highest modeled value at the same site for the 3-year period was 137 µg/m3. Therefore, the CALPUFF model analysis demonstrated it is reasonable to believe that attainment of the standard was achieved at all locations in the planning area.

As a result of our evaluation of monitoring data and a CALPUFF modeling analysis, the District recommends through the adoption of this SIP revision that the California Air Resources Board request the US EPA redesignate the Coso Junction Planning Area from nonattainment to attainment for the federal PM10 standard.

To ensure compliance with the federal PM10 standard is maintained in future years, the District evaluated future activities that could affect PM10 levels in the planning area and the adequacy of existing rules, policies and emission control requirements to control emissions from those sources and activities. District staff found that existing rules for fugitive dust and new source review were adequate to control potential new sources within the Coso Junction Planning Area. For PM10 sources outside the planning area, the major concern is for windblown dust from Owens Lake. District staff believes the control strategy and contingency requirements in the 2008 Owens Valley PM10 SIP are adequate to protect air quality in the Coso Junction area. Therefore, no additional contingency measures will be needed to ensure future compliance with the federal PM10 standard in the Coso Junction Planning Area.

Tables from FINAL 2010 PM10 Maintenance Plan and Redesignation Request for the Coso Junction Planning Area below:

Table 1. Summary of PM10 exceedances monitored over 150 μg/m3 in the Coso Junction Planning
Area and concentrations at other sites on the same day. See Table 2 for causes of exceedances
in the CJPA for the dates shown below and Appendix B for hourly meteorological data for these
events.

Table 2. Over the last 25 years, violations of the federal PM10 standard in the Coso Junction
Planning Area were primarily caused by dust from the Owens Lake area. See Table 1 for PM10
concentrations on the dates shown below and Appendix B for hourly meteorological data for
these events.

Table 3. The expected number of exceedances per year has decreased since dust control
measures were implemented on 29.8 square miles of the Owens Lake bed in December 2006.

Table 4. Daily PM10 emissions inventory for the Coso Junction Planning Area for 2008 through
2025. For the purpose of the maintenance plan, no significant growth is expected in the
emissions inventory through the year 2025.

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