State of California

AIR RESOURCES BOARD



## Status Report on Imperial County Air Quality and Approval of the State Implementation Plan Revision for PM 10

Release Date: April 26, 2010This report is available for downloading from the A ir Resources Board’s Internet site at

http://www.arb.ca.gov/planning/sip/sip.htm . In addition, written copies may be obtained from the Board’s Public Information Office, 1001 I Street, 1 st Floor, Environmental Services Center, Sacramento, California 95814, (916 ) 322-2990.

If you are a person with a disability and desire to obtain this document in an alternative format, please contact the Americans with Disabilit ies Act Coordinator at (916) 323-4916, or TDD (916) 324-9531, or (800) 700 -8326 for TDD calls from outside

the Sacramento area.

This document has been reviewed by the staff of the California Air Resources Board and approved for publication. Approval does not si gnify 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. IMPERIAL COUNTY AIR QUALITY

A. Profile of the Imperial County.................

................................................... ....1 B. Historical Air Quality....................................................................... .2

1. PM 10 ..................................................................................... 2

2. PM 2.5

................................................. ................................. ... 4

3. Ozone....................

.................. ................................................5

II. IMPERIAL COUNTY PM10 STATE IMPLEMENTATION PLAN

A. Planning Requirements....................................................................6

1. Moderate Area PM 10 Attainment Plan.......................................... .6

2. Serious Area PM 10 Attainment Plan............................................. 6

III. PLAN EVALUATION

A. Air Quality Assessment................................................. .........................7

1. High Wind Natural Events.................. ........................................7 2. International Transport Events....................................... ............8 3. Specific Attainment Demonstration Provisio ns..............................8 B. Emission Inventory........................................................................ .9 C. District Control Strategy.........................................................

......... 9 D. Other Clean Air Act Requirements............... ....................................11

1. Transportation Conformity Budgets........................ ..................11

IV. STAFF RECOMMENDATIONS...............................................................12

APPENDIX A1

I. Imperial County Air Quality

A. Profile of Imperial County

Imperial County is located in the southeast corner of California. As shown in Figure 1, the County extends over 4,597 square miles, borderi ng Mexico to the south, Riverside County to the north, San Diego County to the west, and Arizona to the east. With a population of approximately 170,000, the principal industries in Imperial County are year-round irrigated farming and retail trade. Few stationary sources are located in the region. Most of the population, farming, and retai l trade exists in a narrow band of land in the central portion of the county. This region comprises on average less than 1/4 th

the width of the county and stretches from the sout h shore of the Salton Sea to the Mexican border. The remaining land in Imperial Cou nty consists of large expanses of open desert, primarily managed by the federal gover nment, including some of the largest sand dunes in the State. This arid region receives less than 3 inches of rainfall a

year.

Imperial County faces additional air quality challe nges due to its proximity to the large international city of Mexicali, Mexico. Mexicali h as a population of over one million people and is located just across the international border from Calexico. As shown in Table 1, NOx and VOC emissions in the city of Mexic ali are twice those of the entire county of Imperial, and SOx emissions are more than 10 times higher. Several major border crossings are also located in Calexico.

Figure 1. Map of Imperial County2

Table 1. Imperial County/Mexicali 2005 Emissions in tons per day (tpd)

SOx NOx ROG/VOC

Source Type City of

Mexicali Imperial

County City of

Mexicali Imperial

County City of

Mexicali Imperial

County
Stationary 12.7 0.2 39.38 3.56 2.0 1.31

Area 0.5 0.1 3.3 0.9 41.92 17.08

Mobile 0.6 0.6 35.77 27.31 26.13 14.98

Total 13.8 0.9 78.45 31.77 70.05 33.37

B. Historical Air Quality

Despite the unique challenges that Imperial County’ s geography, climatology, and proximity to Mexico pose for air quality, the combi ned efforts of State and local control programs have resulted in improving air quality in the region. The following sections characterize the nature of current particulate matt er and ozone conditions and provide an overview of progress.

1. Coarse Particulate Matter (PM 10 )

Because Imperial County is an arid, desert region, PM 10 concentrations are dominated by fugitive dust, but are generally quite low. As shown in Figure 2, more than 70% of

the PM 10 concentrations measured between 2005 and 2008 were less than 50 ug/m3, and more than 95% were below 100 ug/m3. Concentrat ions exceed the federal 24-hour

PM 10 standard of 150 ug/m3 on average once or twice a y ear at any given location. These infrequent occurrences are due to two distinc t types of conditions – transport of emissions from Mexico, or naturally occurring high winds.

Figure 2. Distribution of PM 10 Concentrations in Imperial County (2005-2008)

0 100 200 300 400 500 600 700 800

<25 26-50 51-75 76-100 101-125 126-150 150<

PM 10 Concentration (ug/m 3 )Number of measurements3

The impact of transport from Mexico is seen primari ly at monitors in Calexico that are near the international border. These transport-rel ated exceedances occur during the winter months when conditions are stagnant, and emi ssions from Mexicali accumulate

near the border. Research into PM 10 concentration differences between Mexicali and Calexico showed that average cross border transport of PM 10 from Mexico was three times higher than from the U.S., and that concentra tions in Mexico were almost double those at Calexico (Chow. et. al., 2000). Increased residential trash and wood burning and charbroiling in Mexicali, often associated with cultural activities during holiday periods, are believed to be the primary cause of th e transport exceedances at Calexico. Figure 3 is an image from the Mexicali newspaper La Cronica that illustrates reduced air quality on January 1, 2009.

Figure 3. Photo of the Pollution on January 1, 2009 in Mexicali

The second type of condition that causes elevated P M 10 levels in Imperial County is high winds. These high winds events typically occu r once or twice a year, usually between the months of April and September. Because of the large amount of open desert land, coupled with the limited rainfall, ele vated wind speeds can loft and disperse large amounts of fugitive dust throughout the Count y. Figure 4 is a photograph taken in the western portion of Imperial County on April 15, 2008 that shows the impact of wind-generated dust. Evaluation of data between 20 04 and 2008 found that after identifying exceedances due to international transp ort, all remaining exceedances occurred only once wind speeds exceeded 20 miles pe r hour (mph), with most occurring under conditions when winds reached over 30 mph. R ecognizing that these types of naturally occurring high wind conditions are not co ntrollable, United States Environmental Protection Agency (U.S. EPA) regulati ons allow areas to identify natural events such as high wind days and exclude them from use in determinations of a region’s air quality.4 Figure 4. Photo of Windblown Dust on April 15, 2008

2. Fine Particulate Matter (PM 2.5 )

Unlike PM 10 , the fine portion of particulate matter (PM 2.5 ) reflects greater contributions from combustion related sources, with less influenc e from fugitive dust. As a result, the

nature of PM 2.5 in Imperial County differs from PM 10 . In 1997, U.S. EPA established

new PM 2.5 standards to protect against both 24-hour and annua l average exposures. The 24-hour standard was further tightened in 2006, lowering from 65 ug/m3 to 35 ug/m3. PM 2.5 levels throughout Imperial County have been below t he annual standard of 15 ug/m3 since 2003. While Imperial Co unty was recently designated as nonattainment for the revised 24-hour standard, con siderable improvement has occurred since 2001. Figure 4 compares 24-hour con centrations at Imperial’s three monitoring locations in 2001 and 2008. In 2001, PM 2.5 levels throughout Imperial County were considered unhealthy. Today, violation s of the 24-hour standard are limited to the border site of Calexico, and the sta ndard is exceeded by only 1 ug/m3.

Similar to PM 10 , these elevated levels at Calexico occur during De cember and January, and are due to transport of emissions from the neig hboring city of Mexicali.5

Figure 5. Imperial County PM 2.5 24-hour Design Values (2001-2008)

0 10 20 30 40 50 60

Calexico Brawley El CentroDesign Value concentration (ug/m3)

2001 2008

3. Ozone

Ozone air quality has also improved significantly i n Imperial County in recent years.

Both concentrations and the number of exceedance da ys have decreased between 1997 and 2009. The number of exceedances days drop ped from approximately 50 in 1997, to less than 2 in 2009. Imperial County atta ined the 1997 8-hour ozone standard of 0.08 ppm in 2008. However, the U.S. EPA is in t he process of strengthening the 8-hour ozone standard. This new standard is expecte d to be promulgated in August 2010, in a range of 0.060 and 0.070 ppm. As a result, we expect that Imperial County will be designated as nonattainment for the new standard.

Meeting this more stringent standard in Imperial Co unty will rely heavily on emission reductions in neighboring areas. Ozone levels in I mperial County are affected by transport from several other regions. Typically, tr ansport impacts vary from day-to-day, depending on variations in wind patterns. However, Mexicali has an overwhelming impact on almost all Calexico exceedance days. In t he northern area of the County, El Centro and Westmorland ozone levels are impacted by transport from both Mexicali and the South Coast region, as well as from San Die go County in the west.6

II. Imperial County PM 10 State Implementation Plan

Imperial County has been designated as nonattainmen t for the federal 24-hour PM 10 standard. In order to meet Clean Air Act requireme nts for nonattainment areas, the Imperial County Air Pollution Control District (Dis trict) developed a State Implementation Plan (SIP) in 2009.

A. Planning Requirements

In 1987, U.S. EPA replaced its standard for total s uspended particulates with standards that focused solely on PM 10 . The 1990 Clean Air Act Amendments (Act) subseque ntly

established moderate and serious classifications fo r PM 10 nonattainment areas, with planning requirements applicable to each classifica tion.

1. Moderate Area PM 10 Attainment Plan

Imperial County was originally classified as a mode rate PM 10 nonattainment area which required reasonably available control measures (RAC M), and set an attainment deadline of December 31, 1994. The District adopte d RACM rules prior to being designated nonattainment. In October 9, 2001, U.S. EPA found that Imperial County

attained the PM10 standard “but for” the emissions from outside the United States. However, on December 18, 2001, Earthjustice sued U. S. EPA regarding this determination. Subsequently, on August 3, 2004, U. S. EPA reclassified the Imperial Valley from a moderate to a "serious" PM 10 nonattainment area. On December 11, 2007, U.S. EPA determined that the Imp erial Valley failed to attain

the PM 10 standard by the required serious area deadline of December 31, 2001. In response to this finding, a SIP revision was requir ed that provided for attainment of the

PM 10 standard in the Imperial Valley area as expeditiou sly as practicable.

2. Serious Area PM 10 Attainment Plan

Imperial County developed the 2009 PM 10 SIP revision with the following required

elements:

1) Air Quality Assessment; 2) Emission Inventory; 3) Best Available Control Measures (BACM) and Best Available Control Technologies (BACT); 4) Transportation Conformity Budgets;7

III. PLAN EVALUATION

The following sections provide the ARB staff evalua tion of the 2009 PM 10 SIP with respect to meeting the requirements of the Act.

A. Air Quality Assessment

The central requirement of an attainment SIP is to demonstrate how a region will meet the applicable air quality standard by the federal deadline. Traditionally, the first step in developing an attainment plan is the evaluation of recent air quality data and a determination of the peak concentration around whic h the control strategy must be designed to reduce concentrations to the level of t he standard. This is known as the design value. For PM 10 , it generally represents the highest measured conc entration over a three year period. As part of the developme nt of the 2009 PM 10 SIP, District staff

evaluated all exceedances that occurred between 200 6 and 2008. During this period there were five days which exceeded the standard at various locations within the District. Based upon extensive technical analysis, the District determined that each of the five exceedance days were due to either interna tional transport or high wind natural

events.

1. High Wind Natural Events

Imperial County experienced three high wind natural events between 2006 and 2008. Table 3 lists the natural event dates along with th e affected monitors, the 24-hour average PM 10 levels and the maximum resultant wind speed.

Table 3. Imperial County High Wind Exceptional Even ts (2006-2008)

Date Location and Concentration Max wind speed

September 2, 2006 ● Calexico-Ethel 164 μg/m 3 , FRM

● Calexico-Grant 233 μg/m 3 , FRM

● Westmorland 167 μg/m 3 , FRM 23 mph

April 12, 2007 ● Brawley 291 μg/m 3 , FRM

● Westmorland 155 μg/m 3 , FRM 34 mph

June 5, 2007 ● Brawley 281 μg/m 3 , FRM

● Calexico-Ethel 282 μg/m 3 , FRM

● El Centro 200 μg/m 3 , FRM

● Niland 162 μg/m 3 , FRM

● Westmorland 226 μg/m 3 , FRM 34 mph

On September 2, 2006, the high PM 10 levels were primarily the result of wind-entrained dust carried up into the atmosphere by high winds a ssociated with a large thunderstorm system that impacted the southwestern United States and northwestern Mexico. Strong
winds were observed on the east, southeast, northea st, and northwest borders of Imperial County, with wind gusts up to 47 mph at th e Blythe, Yuma, and Thermal Airports. Air quality monitoring showed that this n atural event also influenced PM 10 air quality in Yuma, Arizona, and in the Coachella Vall ey.

On April 12, 2007, strong winds from the west with gusts of 30 mph over the8

Anza Borrego Desert entrained dust into the atmosph ere and caused two areas in Imperial County to record concentrations in excess of the federal 24-Hour PM 10 standard. According to the Imperial Valley Press, winds were so high on April 12, 2007 that they overturned a big-rig, toppled trees, and the Energy Department was put on alert due to wind incidents in Brawley, Imperial, a nd El Centro. In addition, the California Highway Patrol issued a wind advisory warning motor ists to slow down and drive cautiously. This natural event also impacted PM 10 air quality in the Mojave Desert and

the South Coast.

Similarly, on June 5, 2007, strong winds from the w est with gusts of 33 mph over the Anza Borrego Desert entrained dust into the atmosph ere and caused all five Imperial County monitors to record concentrations i n excess of the federal 24-hour PM 10 standard. Gusts as high as 47 mph were recorded at the Imperial Airport. High wind speeds and wind gusts were also recorded at the Bly the, Yuma and Thermal Airports, all of which are in close proximity to the Imperial Valley.

In 2007, U.S. EPA adopted the Exceptional Events Ru le (Rule). The Rule recognizes that that there are certain naturally occurring, un controllable events such as high winds

and wildfires that can result in exceedances of fed eral standards for which it is not appropriate to apply the normal planning process. The Rule therefore allows appropriately documented events to be removed from consideration of a region’s attainment status. District staff developed extensi ve technical documentation for the

three wind events that occurred in 2006 and 2007. ARB staff concurred with this analysis and submitted the documentation to U.S. EP A.

2. International Transport Events

Between 2006 and 2008 the remaining two exceedance days at the Calexico monitoring sites were due to international transport - Decembe r 21, 2006 and December 25, 2006. The District provided significant documentation in the 2009 PM 10 SIP demonstrating the impact of transport and that the PM 10 standard would not have been exceeded “but for” emissions from Mexico. The Act contains a specific provision (179B) for areas that are affected by international transport. While exceeda nces that occur due to international transport are still considered violations of the st andard, the Act does not require a State to develop an attainment strategy addressing pollut ion that stems from international

sources.

3. Specific Attainment Demonstration Provisions

In summary, three of the five exceedances days are considered high wind natural events which should be excluded from attainment pla nning because they are neither controllable nor preventable within the scope of th e Act’s planning process. The remaining two exceedance days would not have occurr ed in the absence of contributions from international transport. As dis cussed previously, the Act does not require an attainment demonstration for these types of events under the international transport provisions of 179B. Therefore, Imperial County is considered to have met the

federal PM 10 standard “but-for” these events and no attainment demonstration is required. U.S. EPA policy also states that the req uirements for reasonable further9

progress, a five percent yearly reduction in emissi ons, and contingency measures are not applicable since their sole purpose is to bring an area into attainment of the
standard. Nevertheless, in the 2009 PM 10 SIP, Imperial County addressed contingency measures to provide additional assurance that PM 10 levels will remain below the standard. These contingency measures reflect reduct ions from adopted regulations beyond those required for a serious nonattainment a rea.

B. Emission Inventory

Emission inventories are fundamental elements of an y air quality plan, incorporating the effects of growth and existing regulations to deter mine the expected emissions in future years. The District selected 2005 as the baseline y ear for the emission inventory and worked closely with ARB staff to improve the emissi on inventory for Imperial County. To determine the estimated emissions beyond 2005, s taff prepared projections that used the baseline emission inventory, expected grow th trends, and reductions from rules and regulations. External adjustments and imp rovements were made to certain source categories in the emission inventory. These adjustments and improvements are

discussed in more detail in the 2009 PM 10 SIP.

Table 2 presents the updated baseline and projected emission inventory for direct PM 10 emissions in the County split by main source catego ry for 2006 through 2010. In 2006, 72 percent (196 tpd) of the total emission inventor y was from windblown dust. Area wide dust sources include fugitive dust from paved and unpaved roads, construction, and farming. The other area wide category includes waste burning, residential fuel combustion, and cooking. Stationary sources reflec ts fuel combustion and other industrial processes. Finally, mobile sources incl ude emissions from both on- and off-road vehicles and equipment. While emission in ventories are a required SIP element, it is important to note that understanding the nature of a region’s PM10 problem is best characterized by what constituents are measured at the monitors. Analysis of Imperial County data has shown that fug itive dust is the dominant component of PM10.

Table 2. Imperial County PM 10 Annual Average Emission inventory in 2006-2010 (tpd)

Source Category 2006 2007 2008 2009 2010

Area Wide Dust Sources 70 69 68 68 67

Other Area Wide Sources 3 3 3 3 3 Stationary Sources 3 3 3 3 3

Mobile Sources 2 2 2 2 2

Subtotal 78 77 76 76 75

Windblown Dust 196 196 196 196 196 Total emissions including windblown 274 273 272 272 271

C. District Control Strategy

The Act requires serious areas PM 10 plans to implement Best Available Control Measures (BACM) for area sources and Best Available Control Technologies (BACT) for major stationary sources. According to the 200 5 stationary source emission10

inventory, there is only one PM 10 major stationary source that operates in Imperial County. This source manufactures gypsum wallboard a nd related products, and is located approximately 20 miles west of the nearest PM 10 monitoring site in Plaster City. This source is currently at BACT levels.

BACM is required for all area source categories tha t are considered significant

contributors to violations of the federal PM 10 standard. A source category is considered to be significant if its estimated contribution is 5 ug/m3 or higher to the total concentration. The significant source analysis outl ined in the Imperial County’s 2009

PM 10 SIP determined that there were only two significan t source categories in Imperial County, agricultural tilling and unpaved road dust.

Although only two source categories required BACM, in 2005 the District developed a comprehensive set of fugitive dust rules collective ly known as Regulation VIII, addressing all fugitive dust categories in the inve ntory. The categories covered include:

• Construction and Earthmoving Activities

• Bulk Materials

• Carry-Out and Track-Out

• Open Areas

• Paved and Unpaved Roads

• Agricultural Conservation Management Practices

The two significant BACM sources are specifically c ontrolled under rules 806 (Agricultural Conservation Management Practices) an d 805 (Paved and Unpaved Roads). The selection of control approaches was b ased upon an assessment of rules

in other PM 10 nonattainment areas and their specific applicabili ty to Imperial County. The adopted controls include watering or chemical s tabilization of unpaved roads, cleaning up dust from paved roads, preventing track -out from construction sites, requiring dust control plans for federal lands, and application of dust reducing conservation management practices such as providing cover crops or reduced tillage on agricultural lands. The fugitive dust rules are ex pected to reduce PM 10 emissions by over 16 tpd by 2015. In addition to these reductio ns, the Bureau of Land Management implements additional controls for windblown dust a nd the Imperial Irrigation District’s Fallowing Program reduces dust from fallow fields.

These rules were developed through a public process that included representatives of the agricultural community, private industry, Coali tion of Labor and Business, Farm Bureau, Bureau of Land Management, Border Patrol, I mperial Irrigation District, County Public Works Department, ARB, and U.S. EPA. The Dis trict held six public workshops

to solicit comments. ARB staff reviewed the rules at that time and supported the District’s adoption of these rules as BACM. In add ition, at the Imperial County Board hearing, U.S. EPA staff testified that they believe d that the Imperial County fugitive dust rules represented BACM level controls. Subsequent to their adoption, ARB staff submitted the rules to U.S. EPA in 2006 for adoptio n into the SIP. No action was taken by U.S. EPA until February 2010, at which time U.S. EPA proposed a partial approval of the rules, but also identified several rule compone nts which they believed required11

additional analysis in order to demonstrate BACM le vel equivalence. When evaluating BACM, U.S. EPA does not have specific defined crite ria, but rather the analysis is done on a case by case basis, reflecting the nature of t he sources in the region, and considering cost-effectiveness. Because of this, A RB staff believes that given the specific nature of sources in Imperial County, the rules continue to reflect an appropriate

BACM level of control.

However, the District continues to look for cost-ef fective rule improvements that would further improve air quality. As discussed in the l etter contained in Appendix A, the District has committed to additional rule improveme nts that would represent a strengthening of the SIP for Imperial County. These changes include more specific controls for off-highway vehicles, revising the con servation management practices application forms to be more specific on the requir ed controls and frequency, narrowing the exemption and specifying dust control measures required for Border Patrol unpaved roads, and adding windblown dust controls for fallo wed land. In a separate effort Imperial County is also in the process of updating their Smoke Management Plan to enhance public outreach and include a “good neighbo r policy” to alert nearby residents of an upcoming burn. ARB staff support these effor ts for the purpose of further improving public health in the region.

D. Other Clean Air Act Requirements

1. Transportation Conformity Budgets

The 2009 PM 10 SIP establishes on-road motor vehicle emissions bu dgets for the years 2010, 2020, 2030, and 2035. The new emissions budge ts for PM 10 are shown in Table 4. The budgets are derived with EMFAC2007 pro jections and matched to activity data reported by the South Coast Association of Gov ernments (SCAG). The new budgets will become applicable when U.S. EPA finds the budgets adequate. The conformity budgets are based on the average annual daily emissions for the Imperial County nonattainment area. The emissions budgets e stablished in this Plan fulfill the requirements of the Act and U.S. EPA regulations to ensure that transportation activities support progress and attainment of the PM 10 standards.

Table 4. Motor Vehicle Emission Budgets for PM 10 * Imperial County, Annual Average, Tons per Day

2010 2020 2030 2035

EMFAC Output* 0.8 0.7 0.8 0.9

Paved Road Dust 3.9 6.5 7.9 8.5

Unpaved Road Dust 24.5 24.5 24.5 24.5

Road Construction Dust 0.5 0.4 1.4 1.9

Reductions from District Rules ** 4.5 8.8 9.1 9.2

Total 25.1 23.3 25.5 26.5

Motor Vehicle Emission Budgets 26 24 26 27
(rounded up to the nearest ton)

* EMFAC 2007 with Imperial County activity provided by SCAG April 2009.

** Reductions from Imperial County APCD rules 801, 803 and 805.12

IV. STAFF RECOMMENDATIONS

ARB staff has reviewed Imperial County’s 2009 PM 10 SIP and finds that the SIP meets all applicable CAA requirements. Therefore, we rec ommend that the Board adopt the Imperial County 2009 PM 10 SIP, including updated transportation conformity b udgets, and emission inventory, as a revision to the Califo rnia SIP for submittal to U.S. EPA.13 APPENDIX A