State of California 

Staff Report 

Analysis of the Coso Junction 

PM10 Redesignation Request and 

Maintenance Plan 

Release Date: June 7, 2010 

Scheduled for Consideration: June 24, 2010 

 

California Environmental Protection Agency 

AIR RESOURCES BOARD 
 

This document has been reviewed by the staff of the California Air Resources Board 

and approved for publication. Approval does not signify that the contents necessarily 

reflect the views and policies of the Air Resources Board, nor does the mention of trade 

names or commercial products constitute endorsement or recommendation for use. 
 

TABLE OF CONTENTS 

I. BACKGROUND...................................................................................................... 1

II. REDESIGNATION REQUIREMENTS .................................................................... 1

III. EVALUATION OF THE COSO JUNCTION PLAN ................................................. 2

A. Coso Junction Attains the 24-Hour PM10 Standard.......................................... 2 

B. The State Has Met Applicable Act Requirements.......................................3

C. Improvement in Coso Junction’s PM10 Air Quality is Due to Permanent and 

Enforceable Reductions in Emissions ............................................................... 3

D. Maintenance Plan.............................................................................................. 4

1. Attainment Emission Inventory...................................................................... 4

2. Maintenance Demonstration.......................................................................... 5

3. PM10 Monitoring Network ............................................................................. 5

4. Verification of Continued Attainment ............................................................. 5

5. Contingency Plan .......................................................................................... 5

IV. STAFF RECOMMENDATION ................................................................................ 6
1 

I. BACKGROUND 

The Coso Junction Planning Area (Coso Junction) was initially designated as a PM10 

nonattainment area in 1987 along with the Indian Wells Valley and Trona areas. 

Together they comprised the Searles Valley PM10 nonattainment area. The Great 

Basin Unified Air Pollution Control District (District) adopted the first PM10 attainment 

plan for the Coso Junction portion of the Searles Valley PM10 nonattainment area in 

November 1991. The Coso Junction attainment demonstration was based on controlling 

dust from Owens Lake. In August 2002, the US Environmental Protection Agency 

(U.S. EPA) redesignated the Searles Valley into three separate PM10 nonattainment 

areas; Coso Junction, Indian Wells Valley, and Trona. 

On May 19, 2010, the U.S. EPA finalized its determination in the Federal Register that 

Coso Junction attained the 24-hour PM10 standard. Based on their clean data finding, 

U.S. EPA has determined that certain nonattainment area requirements do not apply, 

including those for reasonable further progress (RFP), an attainment demonstration, 

reasonably available control measures (RACM), and contingency measures, because 

these provision’s sole purpose is to achieve attainment of the standard. On May 17, 

2010, the District adopted the PM10 Redesignation Request and Maintenance Plan 

(Plan) for Coso Junction. The Plan officially requests that this area be redesignated to 

attainment for the PM10 standard and charts the course for continued maintenance of 

the standard. The concerted adoption of controls on Owens Lake resulted in the Coso 

Junction attaining the 24-hour PM10 standard based on 2007-2009 PM10 data. 

II. REDESIGNATION REQUIREMENTS 

Air Resources Board (ARB) staff reviewed the Coso Junction PM10 Maintenance Plan 

within the context of the Clean Air Act (Act), which identifies the following requirements 

an area must meet to be redesignated to attainment:

A. The PM10 standard has been attained; 

B. The District has an approved State Implementation Plan (SIP) and the State has 

met all applicable Act requirements for PM10 in the nonattainment area; 

C. The improvement in PM10 air quality is due to permanent and enforceable 

emission reductions; and 

D. U.S. EPA has approved a maintenance plan. 

The Act also sets the general framework for maintenance plans1

. Each PM10 

maintenance plan must provide for continued maintenance of the PM10 standard for 

ten years after redesignation and includes the following components: 

1. Attainment emission inventory; 

 

1

 Calcagni, John, Memorandum, Procedures for Processing Requests to Redesignate Areas to 

Attainment, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina, 

September 4, 1992. http://www.epa.gov/ttn/oarpg/t5/memoranda/redesignmem090492.pdf
2 

2. Maintenance demonstration; 

3. Commitment to continue the monitoring network operation; 

4. Commitment for verification of continued attainment; and 

5. Contingency plan to promptly correct any violation of the PM10 standard that 

occurs after the area has been redesignated. 

III. EVALUATION OF THE COSO JUNCTION PLAN 

Based on review of the Coso Junction PM10 Maintenance Plan and the District’s 

supporting technical analysis, ARB staff concurs that the Plan meets the Act’s 

requirements. The following sections describe the major elements of the Plan and the 

redesignation request. 

A. Coso Junction Attains the 24-Hour PM10 Standard 

PM10 is measured at one monitoring station in Coso Junction (Figure 1). A TEOM 

(tapered element oscillating microbalance) collects hourly PM10 samples at this site. 

The 24-hour standard is met when the estimated number of exceedances measured 

over a three year period averages one or less per year. Daily PM10 monitoring data 

collected at Coso Junction over the last 3 years has shown on average no more than 1 

exceedance of the PM10 standard per year as required to demonstrate attainment of 

the federal standard. Figure 1 illustrates the Coso Junction PM10 nonattainment area, 

monitor locations, and the area’s close proximity to Owens Lake. 

Figure 1. PM10 Monitoring Stations in Coso Junction 
3 

On three days over the 2007 to 2009 period, the 24-hour standard was exceeded due to 

high wind conditions that suspended fugitive dust from an unpaved parking area and 

from Owens Lake. 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. Table 1 

shows the maximum 24-hour concentration at the Coso Junction site between 2007 and 

2009 and average exceedance days, demonstrating attainment. 

Table 1. Coso Junction PM10 Data from 2007 to 2009 

Monitoring 

Station 

Observed Maximum 24-hour 

Concentration (μg/m3)

24-Hour 

Exceedance Days 

3-year Average 

Exceedance Days 

2007 2008 2009 2007-2009 2007-2009 

Coso Junction 283 137 168 3 1 

B. The State Has Met Applicable Act Requirements 

ARB and the District have met all of the Act requirements applicable for a moderate 

PM10 nonattainment area to be considered for redesignation. Due to the clean data 

finding, this Plan will serve as meeting the requirement of an approved SIP. 

C. Improvement in Coso Junction’s PM10 Air Quality is Due to Permanent and 

Enforceable Reductions in Emissions 

Coso Junction is an isolated area with a population of roughly 100 people. The main 

source of PM10 pollution in Coso Junction is transport of fugitive dust from the Owens 

Valley. In 1998, the Owens Valley SIP was adopted and approved by the U.S. EPA 

including a 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 PM10 standard. (GBUAPCD, 1998) The Owens Valley SIP was 

revised in 2003 to expand dust controls to 29.8 square miles of the lake bed by 

December 31, 2006. The City of Los Angeles successfully implemented these control 

measures by the required deadline. 

In 2008, the Owens Valley SIP was amended to expand control requirements to a total 

of 43.1 square miles of the Owens Lake bed. The City of Los Angeles is expected to 

have dust control measures implemented on 39.6 square miles of the lakebed by 

April 1, 2010, and then to expand the control area to 43.1 square miles by 

October 1, 2010. Overall, PM10 emissions from the Owens Lake bed have been 

reduced by 90% since 2000 when the City of Los Angeles initiated efforts to control 

windblown dust at Owens Lake. Thus, the improvement in Coso Junction is due to 

permanent and enforceable reductions.
4 

D. Maintenance Plan 

The Coso Junction PM10 Maintenance Plan includes the following components: 

emission inventory; commitment to continue monitoring network operation; commitment 

for verification of continued attainment; and contingency plan. 

1. Attainment Emission Inventory 

An emission inventory is a critical tool used to support evaluation, control, and mitigation 

of air pollution which is comprised of a systematic listing of the sources of air pollutants 

along with the amount of pollutants emitted from each source or category over a given 

period of time. Emission inventories are estimates of the air pollutant emissions 

released into the environment – they are not direct ambient concentration 

measurements. To determine the expected emissions in future years, emission 

inventories incorporate the effects of growth and existing regulations (baseline 

inventories). An attainment inventory identifies the level of emissions during the period 

when air quality data show attainment. 

The Coso Junction PM10 Maintenance Plan presents an updated 2009 attainment 

inventory of direct PM10 emissions split by source subcategory. Inventory updates 

include the latest point, area, and mobile source emissions for the Coso Junction. Total 

PM10 emissions are estimated at 1,427 pounds per day for the Coso Junction, which is 

less than 0.1% of the emissions caused by windblown dust from Owens Lake. In 

addition to the 2009 adjusted baseline PM10 emissions, the Coso Junction PM10 

Maintenance Plan provides emission projections out to 2025. No significant growth or 

changes in the emission inventory are expected for Coso Junction through the year 

2025. 

Table 2. Coso Junction PM10 Emissions Inventory 

Daily PM10 Emissions for 2009 through 2025 

Stationary Sources Pounds/day

California Lightweight Pumice 167 

China Lake Naval Air Weapons Station 84 

Coso Operating Company 953 

Halliburton Services 20 

Twin Mountain Rock 58 

Area Sources 

Unpaved Roads 33 

Paved Roads 101 

Mobile Sources 

On Road Motor Vehicles 12 

 

Total PM10 (pounds per day) 1,427 
5 

2. Maintenance Demonstration 

Coso Junction is projected to maintain attainment with the PM10 standards due to ARB, 

District, and other State and local control measures already in place. No significant 

growth or changes in the emission inventory are expected for Coso Junction through the 

year 2025. Thus, Coso Junction is expected to maintain the PM10 standard. In addition, 

regional PM10 emissions are projected to decrease even further in the future as a result 

of the additional controls on Owens Lake. 

3. PM10 Monitoring Network 

The District commits to continue PM10 monitoring to verify continued attainment of the 

PM10 standard. The existing PM10 monitoring network in Coso Junction includes a 

PM10 TEOM monitor located at the Highway 395 rest area in Coso Junction (Figure 1). 

Federal regulations require daily sampling at the site reporting peak PM10 

concentrations. This real-time PM10 monitor meets this daily monitoring requirement. 

4. Verification of Continued Attainment 

To verify continued attainment of the PM10 standard, the District commits to continue 

daily PM10 monitoring at the Coso Junction rest area to help ensure new sources of 

PM10 are identified and controlled, if necessary. 

5. Contingency Plan 

The Act requires the maintenance plan to include contingency provisions for prompt 

correction of any PM10 standard violation that might occur after the area has been 

redesignated to attainment. The maintenance plan is not required to contain fully 

adopted contingency measures that will go into effect without further state action as is 

required in attainment SIPs. Instead, for maintenance plans, the area must have a plan 

to ensure that contingency measures are adopted once they are triggered. 

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 Coso Junction. 
6 

IV. STAFF RECOMMENDATION 

ARB staff has reviewed the PM10 Redesignation Request and Maintenance Plan for 

Coso Junction and consulted with District staff during this review. ARB staff finds that 

the Coso Junction PM10 Maintenance Plan meets all applicable Act requirements. ARB 

staff believes that implementation of this Plan will continue to maintain PM10 levels 

below the national air quality standard in Coso Junction. Therefore, we recommend that 

the Board adopt the Coso Junction PM10 Maintenance Plan as a revision to the 

California SIP for submittal to U.S. EPA. In addition, ARB staff recommends that the 

Board approve the District’s request that Coso Junction be redesignated from 

nonattainment to attainment for the national PM10 standard.