Off-Highway Vehicle (OHV) Area 

Best Available Control Measures 

(BACM) Assessment

Prepared for:

Imperial County Air Pollution Control District

El Centro, CA

Prepared by:

ENVIRON International Corporation

Los Angeles, California

Date:

October 2012

Project Number:

05-21191A
Contents ii ENVIRON

Contents

Page

1 History 1

2 Emissions from OHV-related Open Areas 2

2.1 Windblown Emissions 2

2.2 Entrained OHV Emissions 3

2.2.1 OR Event Entrained Emissions 3

2.3 Summary 4

3 Potential Control Measures 4

3.1 RACM Guidance Summary (April 28, 1992 57 FR 18072) 4

3.1.1 Restrict OHV Activity Locations 4

3.1.2 Require Use of Permits 4

3.1.3 Restrict OHV times (an activity ban on OHV-approved lands) 5

3.2 Potential BACM and other measures 5

4 BACM Comparative Analysis 5

4.1 Restrict OHV Locations 6

4.2 Require Use of Permits 6

4.3 Restrict OHV times (an activity ban on lands on OHV Recreational Use Areas) 7

4.4 Potential BACM and other measures 7

5 Feasibility and Impact Analysis 8

List of Figures

Figure 1: Federal and State Lands in Imperial County (2009 PM10 SIP)

Figure 2: Maricopa Land Ownership Distribution

Figure 3 Imperial Sand Dunes Recreation Area

List of Appendices

Appendix A: PM10 Nonattainment Areas: Selected Comparisons

P:\I\Imperial\2012-2013\OHV BACM analysis 2012\121003 OHV BACM Analysis -Final.docx
History 1 ENVIRON

Executive Summary

This report is the latest Best Available Control Measures (BACM) assessment for Off-Highway 

Vehicle (OHV) areas. It was prepared at the request of the Imperial County Air Pollution Control 

District (ICAPCD or District) in support of its proposed amendments to Regulation VIII, Fugitive 

Dust Rules (in particular, Rule 800 open area requirements). Open areas are non-urban, nonagricultural undeveloped lands. Regulation 800 and the proposed OHV-related open area 

amendments are described in Section II.B of the ICAPCD Staff Report for the BACM 

Amendments to Regulation VIII, Fugitive Dust Rules. In general, the OHV-related open area 

amendments include new or revised definitions, clarification of applicability, and revised OHVrelated requirements (dust control plan contents, explicit list of certain BACM control measures, 

etc.) In this report, we present:

• The history of ICAPCD BACM assessments for open areas and recent regulatory actions.

Those assessments are included, by reference, in this report.

• The emissions from open areas in Imperial County, with a focus on OHV areas and 

activities. In this section, other serious PM10 non-attainment areas that have appreciable 

OHV activity (areas within Maricopa and Clark County counties) and OHV requirements are 

also described to facilitate the comparative analysis.

• Potential control measures (including Reasonably Available Control Measures (RACM) 

described in federal guidance and BACM measures in serious non-attainment areas). 

• BACM comparative analysis of OHV-related measures in serious non-attainment areas.

• Feasibility and impact analysis of proposed Rule 800 OHV-related amendments.

Based on this assessment, Rule 800 and the proposed Rule 800 amendments are at least as 

stringent as open area OHV requirements in other serious PM10 non-attainment areas.

1 History

On August 11, 2004 the United States Environmental Protection Agency (EPA) issued a finding 

that Imperial County failed to attain PM10 National Ambient Air Quality Standard (NAAQS) by 

December 21, 1994. Therefore, under CAA Section 189(b)(1)(B), all Best Available Control 

Measures (BACM) were required to be implemented by September 10, 2008 and a PM10

attainment plan was required by December 2008. 

On November 8, 2005, the Air District adopted its fugitive dust BACM rules in anticipation of its 

PM10 Attainment Plan to expedite emission reductions and document high wind events 

according to the EPA’s Exceptional Events Rule. The Regulation VIII rules impose stringent 

requirements to reduce the amount of PM10 entrained in the ambient air as a result of emissions 

generated from anthropogenic fugitive dust sources, which include agriculture, construction, 

recreational off-highway vehicles and unpaved roads. The 2005 BACM Technical Assessment 

was prepared and approved by ICAPCD. The rules were submitted to EPA on June 16, 2006. 

ICAPCD and CARB also submitted documentation for three high-wind days in 2006 and 2007 

demonstrating that the PM10 exceedances were caused by exceptional events. On August 
Emissions from OHV-related Open Areas 2 ENVIRON

2009, ICAPCD adopted its 2009 Imperial County PM10 State Implementation Plan (2009 PM10

SIP), which included an attainment demonstration based, in part, on the exclusion of the 

exceptional events. A revised BACM assessment was also included in the 2009 PM10 SIP. On 

July 8, 2010, EPA granted limited approval/disapproval to Regulation VIII based on rejection of 

the 2006 and 2007 exceedences. The Air District filed a petition with the Ninth Circuit for review 

of EPA’s limited disapproval. After hearing oral arguments from the parties, the Ninth Circuit 

ordered them to mediation. 

The mediation was settled by all parties after multiple sessions. As part of the settlement, the 

Air District agreed to amend some of the Regulation VIII rules to further enhance BACM 

requirements. The District is proposing to revise rule 800 to include specific BACM 

requirements to reduce fugitive dust emissions from OHV recreational areas. 

2 Emissions from OHV-related Open Areas

As detailed in the 2009 PM10 SIP (c.f.., Appendix III.B.1, first sentence), most of the areas in the 

District’s jurisdiction are open areas, of which 77% of the total land area is state/federally 

managed or owned (see Appendix A “PM10 Nonattainment Areas: Selected Comparisons” of 

this report for a summary). The rest of the land is mainly agriculture (20%), urban areas (~2%) 

and less than one percent is vacant, developable land. Figure 1 shows the Imperial County and 

federal/state lands. Both Imperial County and the Maricopa County serious PM10 non-attainment 

area (Maricopa nonattainment area) have appreciable OHV open areas and OHV regulations. 

(The Clark County serious non-attainment area includes mostly the populated greater Las 

Vegas area and has more limited OHV open areas).1

 Key differences between Imperial County 

and the Maricopa nonattainment area, particularly open lands within those areas, are important 

in the discussion of OHV-related emissions and the control measure comparative analysis. 

Those differences will be referenced below; a more detailed discussion of those differences can 

be found in Appendix A (PM10 Nonattainment Areas: Selected Comparisons). This report 

considers 1) windblown emissions from lands where there has been OHV activity and 2) 

entrained dust emissions from OHV travel. 

2.1 Windblown Emissions

Windblown emissions from open areas are the largest emission inventory contributor in Imperial 

County. Based on the 2009 PM10 SIP analysis of windblown dust emissions from vacant lands 

(Appendix III.B), all open areas produce 157 tons of windblown PM10 per day (tons/day), which 

are mostly from the 1.9 million acres of state/federal lands. State and federal OHV areas (the 

164,000 acres where OHV activity is not restricted) produce 8.8 tons/day of the total 157 

tons/day. Analysis results demonstrate that private lands have negligible windblown dust 

emissions (see Appendix A and the 2009 PM10 SIP Appendix III.B). Figure III.B.6 of the 2009

PM10 SIP (Appendix III-B, also in Appendix A, Figure 7) shows spatial distribution of open area 

 1 As discussed in Appendix A in more detail, “The Imperial Valley nonattainment area includes almost all of Imperial 

County, CA; thus, Imperial Valley and Imperial County are used interchangeably in this Report. The Maricopa 

nonattainment area includes only about 31% of Maricopa County. The Maricopa nonattainment area is heavily 

populated; only the central portion of the Imperial Valley nonattainment area is populated (and that lightly).” 

Similarly, the Clark County nonattainment area is only a small portion of Clark County as a whole.
Emissions from OHV-related Open Areas 3 ENVIRON

windblown dust and OHV-allowed areas. As noted directly above, less than 6% of the open 

area windblown dust emissions come from federal/state areas that are open to OHVs. At the 

request of EPA shortly before the 2009 PM10 SIP adoption hearing, a more conservative 

estimate assuming greater levels of soil disturbance was prepared that showed an additional 0 

to 12 tons/day of windblown emissions could potentially be emitted based on differing 

assumptions about soil disturbance; ICAPCD does not believe that there are appreciable 

additional emissions but included this analysis in the final 2009 PM10 SIP (Appendix III.B). 

2.2 Entrained OHV Emissions

The motion of an OHV over an open area can entrain dust from the ground into the air – these 

emissions are a function of the weight and speed of the OHV, as well as other parameters. Due 

to the small user population within day-trip driving range, no activity data are available. 

However, an estimate of these emissions can be made based on Maricopa nonattainment area 

emissions (see Appendix A of this report for details on the methodology and results). The 

Maricopa non-attainment area OHV entrained emissions are 6.02 tons/day; the population ratio 

of Imperial County to Maricopa is 175,000:4,297,000. The population ratio of Maricopa to 

Imperial County is a reasonable metric since the activity in both locations is driven by the 

number of riders. In the Arizona Trails 2010 Report2

, Maricopa records that 1,027,000 or 22% 

of its population has general riders of which 511,000 or 10.7% of them are self-described core 

riders. The core Maricopa riders are almost three times the whole Imperial County population. 

Using the population to emission ratio, Imperial County’s OHV emissions would be <0.25 

tons/day based on an annual average day. Based on the socioeconomic distribution in the 

population, actual emissions are expected to be lower.3

 It is reasonable to expect near-zero 

emissions on wind event days and the hottest days because the number of these riders would 

be negligible. 

2.2.1 OR Event Entrained Emissions

Off-road (OR) events differ from OHV events because they can attract riders from outside of 

Imperial County. Large OR events only occur on state and/or BLM-approved OHV areas. In 

addition, large OR events must receive a permit from the land manager and abide by several 

regulations and requirements, including those related to Rule 800. 

For state lands, specific OHV areas (such as Ocotillo Wells SRVA) make up 28% of the state 

lands in Imperial County. Generally, these areas have low OHV speed events (geocaching, 

church groups, etc.) of small groups of 20-100 people; however, some holidays can draw more 

than 250 attendees. These OR events generally occur on the weekends or holidays and are 

typically rescheduled if the conditions are either too hot and/or windy. 

For federal lands under the jurisdiction of the Bureau of Land Management (BLM), specific 

OHV-allowed areas are approximately 11% of those lands (OHV ban on over 90% of BLMmanaged lands). Large-scale OHV events occur five to ten times per year; the largest events 

 2 http://azstateparks.com/publications/downloads/2009_Trails_2010_Final_c.pdf. 3 From the US Census (http://quickfacts.census.gov/qfd/states/00000.html) for 2006-2010: Imperial County median 

household income ($36,685) compared to Maricopa County ($55,054). Unemployment rate in Imperial County was 

21.4% compared to 13.9% in Maricopa. 
Potential Control Measures 4 ENVIRON

are in the Imperial Dune area on large sand dunes east (and generally downwind) of populated 

areas. Such large OR events are not held in high wind and/or high heat conditions because of 

safety, including low visibility and heat-related illnesses, and other concerns. Such large-scale 

OR events have not occurred during any documented exceptional event and thus, direct OR 

entrained dust emissions have not contributed to any exceedance. 

2.3 Summary

Relying on the exceptional events determinations by ICAPCD and CARB, the 2009 PM10 SIP 

concluded that windblown dust, including from open areas, was not a significant source. Based 

on EPA’s rejection of those event determinations, EPA does consider open area windblown dust 

emissions to be significant. Regardless, the 2008 PM10 SIP calculated that of the 157 tons/day 

of annual average emissions from open areas, approximately 9 tons/day of emissions come 

from areas where OHV activity and OR events are allowed. (Different soil disturbance 

assumptions could yield from 0 tons/day to 12 tons/day of additional windblown emissions.)

Large-scale OR events are expected to have zero or negligible entrained dust emissions on 

potential exceedence days because those OR events are not held during days when potential 

exceedence-day conditions occur. 

Other (non-event) OHV entrained dust emissions are estimated to be de minimis (<0.25 

tons/day or less than 0.1% of the annual average inventory). These emissions are expected to 

be near zero on potential exceedence days because of the conditions associated with those 

days (i.e., high winds resulting in low visibility and high temperatures). 

3 Potential Control Measures

3.1 RACM Guidance Summary (April 28, 1992 57 FR 18072) 

EPA issued Reasonably Available Control Measure (RACM) guidance in 1992 (April 28, 1992 

FR 18072, Appendix C1). The three RACM listed in the Guidance were: 1) confine operations to 

specific areas; 2) require use permits; and 3) ban OHV activity (for specific locations/times). 

3.1.1 Restrict OHV Activity Locations

BLM restricts OHV activity to four areas (Imperial Sand Dunes, Plaster City, Superstition 

Mountains, Arroyo Salado) of the BLM land. Only 136,000 acres (or 11% of the total 1.26 million 

acres) of BLM land are currently open to OHV activity. More restrictions are applied to State 

parks, which are 100,000 acres. The State (Department of Parks and Recreation) restricts OHV 

activity to two areas, Ocotillo Wells SVRA and Heber Dunes SVRA; only 28,000 acres (or 28% 

of 100,000 acres of state lands in Imperial County) are open to OHVs. Thus, OHV activity is 

restricted to 164,000 acres. Thus, only ~9% of state/federal lands (164,000 acres out of 

1,360,000 acres) allow OHV activities. As noted in Section 4 below, both Maricopa and Clark 

counties also restrict OHV activities to certain areas.

3.1.2 Require Use of Permits

OHV permits are required by the State of California and large scale OR events require special 

approvals by state/federal authorities. From www.dmv.ca.gov/vr/ohvredgreen.htm:
BACM Comparative Analysis 5 ENVIRON

California Air Resources Board (ARB) established regulations to limit the use of Off-Highway 

Vehicles (OHVs) that do not meet emission standards applicable for California OHV riding areas. 

After the regulations were established, ARB and DMV worked together to develop criteria for 

identifying non-complying OHVs. OHVs are registered by the Department of Motor Vehicles 

(DMV). A red or green sticker is issued depending upon certain criteria. 

Green stickers are issued for all California OHVs year model 2002 and older, including those 

that were previously issued a red sticker, and to 2003 and newer complying vehicles. Green 

stickers are issued to OHVs for year round use at all California OHV riding areas. 

Red stickers are issued to 2003 year model and newer OHVs that are not certified to California 

OHV emission standards. If your OHV has a "3" or "C" in the eighth position of the vehicle 

identification number (VIN) then your vehicle will be issued a red sticker. Red stickers are issued 

to OHVs that can use California OHV riding areas for seasonal use only. 

BLM4 requires Special Recreation Permit (SRPs) for competitive use and organized group 

activity and event use to “manage visitor use [and] protect natural and cultural resources.”

These are discussed in more detail in Section 4.2.

3.1.3 Restrict OHV times (an activity ban on OHV-approved lands)

Permit restrictions on times when areas where OHV activity is allowed would only affect 

entrained dust-related emissions because the area is already disturbed. As noted in Section 2 

above, entrained emissions from other OHV activities on these lands is de minimis and OR 

events do not occur during exceedence conditions; thus, entrained dust-related emissions are 

not significant contributors to high-wind event PM levels and do not contribute to exceedences

in Imperial County. 

3.2 Potential BACM and other measures

ICAPCD Rule 800 includes measures that minimize OHV-related dust emissions (c.f. Rule 800 

F.5). These requirements were based on Maricopa and Clark County regulations at the time of 

Regulation adoption (2005). These measures include dust control plans with stipulations, OHV 

area descriptions, and PM10 control measures (including on unpaved roads, parking and open 

areas). Maricopa and Clark Counties describe control measures (e.g., Clark County 90.1 in 

nonattainment area only and Maricopa AZ 49-457.03 that prohibits OHV activity on high 

pollution advisory days except for events with dust abatement measures) that are similar to 

those in Rule 800 and proposed amendments to Rule 800 that would enhance dust control plan 

requirements and include explicit BACM as dust abatement measures. 

4 BACM Comparative Analysis 

This section compares the OHV-related control measures in ICAPCD Rule 800 and proposed

amendments to similar measures in other serious PM10 nonattainment areas with appreciable 

OHV activity (e.g., Maricopa County and Clark County nonattainment areas). In comparing 

 4 From BLM web site (www.blm.gov/ca/st/en/prog/recreation/recpermit.html): Competitive Use means any organized, 

sanctioned, or structured use, event, or activity on public land in which two or more contestants compete and 

either (1) participants register, enter, or complete an application for the event, or (2) a predetermined course or 

area is designated.” “Organized group/event permits are for noncommercial and noncompetitive group activities 

and recreation events.”
BACM Comparative Analysis 6 ENVIRON

control measures among the serious PM10 nonattainment areas with appreciable OHV activity, it 

is important to remember the key differences among these areas (see Appendix A and Figures 

1 and 2). 

4.1 Restrict OHV Locations

Maricopa Rule 9-500.27 states the following in regards to OHV activity: “city or town shall adopt, 

implement and enforce an ordinance that prohibits the operation of any vehicle, including an off 

highway vehicle, an all-terrain vehicle or an off-road recreational motor vehicle, on a unpaved 

surface that is not public or private road, street or lawful easement and that is closed by the 

landowner by the rule or regulation of a federal agency, this state, a county of municipality”. 

Note that OHV activity can occur on lands under state or federal agency jurisdiction. Clark 

County, Section 90 states that OHV are prohibited, by fencing or other barriers, in nonattainment areas unless control measures are used to establish a stabilized surface afterwards. 

Clark County has essentially banned OHV activity, but only in non-attainment areas near Las 

Vegas (and not in OHV areas outside the non-attainment area). Both Maricopa and Imperial 

County, through federal and state land managers, have restricted OHV activity to specific 

locations. Even within Imperial County recreational areas, OHVs are restricted to certain 

locations, such as Imperial Sand Dunes (see Figure 3). Proposed amended Rule 800 would 

add specific requirements for any new recreational OHV areas to incorporate mitigation 

measures and demonstrate that any new emissions will not create new violations or delay 

attainment of the federal PM10 standard.

Further restriction of OHV areas would not be effective. OHV areas are established to minimize 

OHV activity in other areas, particularly where there are natural resources being protected. 

BLM and State Parks officials believe that further limiting the size of OHV areas would have the 

effect of increasing illegal OHV activity on non-travelled lands. Potential environmental effects 

include use in new areas and/or on private property, use in areas not managed for OHV 

recreation, trespass on closed areas and economic effects of job loss and business closure on 

Imperial County. This would have the inadvertent effect of increasing the potential for windblown 

dust emissions, rather than reducing them. 

4.2 Require Use of Permits

Persons using OHVs in Imperial County are required to have a state permit. Similar permitting 

requirements are also in effect in Maricopa and Clark counties. BLM5 requires Special 

Recreation Permits for competitive use and organized group activity and event use to “manage 

visitor use [and] protect natural and cultural resources.” As noted at 

ww.blm.gov/ca/st/en/prog/recreation/recpermit.html:

Objectives of the BLM recreation permitting system are to satisfy recreational demand within 

allowable use levels in an equitable, safe, and enjoyable manner while minimizing adverse 

resource impacts and user conflicts. In issuing recreation permits to recreational users of public 

 5 From BLM web site (www.blm.gov/ca/st/en/prog/recreation/recpermit.html): Competitive Use means any organized, 

sanctioned, or structured use, event, or activity on public land in which two or more contestants compete and 

either (1) participants register, enter, or complete an application for the event, or (2) a predetermined course or 

area is designated.” “Organized group/event permits are for noncommercial and noncompetitive group activities 

and recreation events.”
BACM Comparative Analysis 7 ENVIRON

lands, the BLM authorizes permittees use of the lands and/or related waters for permitted 

purposes. This represents a privilege to use public lands and/or related waters which is subject 

to the terms and conditions of the permits. Recreation permits are managed in a manner which is 

consistent with management objectives determined in resource management plans, recreation 

area management plans, or in their absence, through recreation management objectives resulting 

from analysis of resources and visitor use for each area.

From the BLM SRP Handbook6:

All SRP applications must include the following: a) the current Special Recreation Permit 

application typed or printed in ink and completely filled out, b) a map produced using Global 

Positioning Systems with transferable compatible data to the BLM computer systems, c) 

operating/business plan or other information the BLM requests, d) advance payment of estimated 

fees (if cost recovery is required), and e) copies of other licenses and permits from state, local, 

and/or federal agencies (if applicable).

ICAPCD requirements are discussed in Section 4.4 below.

4.3 Restrict OHV times (an activity ban on lands on OHV Recreational Use 

Areas)

Comparative BACM analysis was also conducted on OHV activities during specific times. 

Maricopa County only allows OR events on pollution alert days if there is dust abatement for 

staging areas, parking areas and entrances. ICAPCD Rule 800 requires dust abatement during 

OR events regardless of air quality conditions. The proposed amendments to Rule 800 would 

make these abatement requirements more specific. ICAPCD is proposing amendments to Rule 

800 (new F.5.g) that include restrictions on OR events during summer months, as well as clarify 

OHV-related definitions and unpaved road/traffic area requirements. 

Maricopa County prohibits OHV activity on pollution advisory days, except for authorized OR 

events with dust abatement measures, business, or government travel, and/or abated closed 

course. Entrained dust emissions from OHV activities are de minimis in Imperial County, 0.25 

tons/day (<0.1% of inventory); the Maricopa nonattainment area has 6 tpd of entrained OHVrelated emissions, which is 4% of that area’s total inventory. Further activity-related restrictions 

would not result in any appreciable emission reduction on potential exceedence days, high wind 

days in particular. 

4.4 Potential BACM and other measures 

In addition to the requirements described above, ICAPCD Rule 800 includes measures that 

minimize OHV-related dust emissions (c.f. Rule 800 F.5). Many of these requirements were 

based on Maricopa and Clark County regulations at the time Regulation VIII was initially 

adopted in 2005. These measures include dust control plans with stipulations, OHV area 

descriptions, and PM10 control measures (including on unpaved roads, parking and open areas). 

Amendments to Rule 800 that clarify definitions and requirements (particularly for specific 

unpaved road/traffic area control measures) are proposed that meet EPA recommendations. 

 6 www.blm.gov/pgdata/etc/medialib/blm/ca/pdf/caso/publications.Par.23962.File.dat/SpecialRecreationPermit.pdf
Feasibility and Impact Analysis 8 ENVIRON 

Certain amendments to Rule 800 include additional requirements if new recreational OHV use 

areas are designated (c.f., Section F.7); these proposed requirements are not found in any other 

jurisdiction. 

Maricopa’s rule effectiveness amendments pertained to Rule 310.01 and specifically to the 

100,000+ vacant lots in Maricopa County. Rule 804 already applies to these lands. In addition, 

less than 1% of open lands are urban vacant areas in Imperial County (compared to 52% of 

Maricopa’s nonattainment area open lands that are private/developable vacant lands). Thus, 

increased rule effectiveness on these minimal areas would not appreciably affect emissions. 

5 Feasibility and Impact Analysis 

In the feasibility and impact analysis in ICAPCD’s 2005 BACM assessment (Chapter 5) and 

ICAPCD’s 2009 PM10 SIP (Chapter 5), the control effectiveness and costs/cost effectiveness of 

the 2005 Rule 800 were assessed. In this analysis, certain additional measures (such as further 

restricting OHV-permitted areas) were analyzed and determined to be ineffective and/or 

infeasible. OHV activity has been increasingly restricted on public lands; it is currently restricted 

to less than 9% of all federal/state land. Federal and state land managers believe that further 

restriction of the land approved as OHV recreational areas would be ineffective, and perhaps 

counter-effective, because activity would move to non-permitted areas that do not have dust 

control plans. This would potentially increase windblown emissions if those areas are 

significantly more disturbed as a result of this new activity. 

The proposed amended Rule 800 contains additional changes to enhance BACM for open 

areas (see Staff Report for more details). The proposed amended Rule 800 clarifies and/or 

strengthens the requirements and does not interfere or lessen any existing BACM requirements. 

DPR, BLM and/or users of their lands will incur costs related to the preparation of new or 

revised Dust Control Plans (per Rule 800 Section F.5), meeting new requirements (if any) for 

large-scale off-road events and high-trafficked unpaved roads/parking areas, and any Rule 800 

F.7.b determinations and related interagency consultation. At this time, such costs cannot be 

quantified, although it is expected that the cost-effectiveness and cost of such actions would be 

consistent with those described in the 2005 BACM assessment for similar actions.
ENVIRON

Figures
ENVIRON

Figure 1: Federal and State Managed Lands in Imperial County (2009 PM10 SIP) 

Figure 2: Maricopa Land Ownership distribution (Passive/Restricted areas are federal/state 

managed)
ENVIRON

Figure 3: Imperial Sand Dunes Recreation Area (note restrictions on OHV 

activity, including outside the ISDRA, military bombing areas, 

wilderness areas, and vehicle closure areas)
ENVIRON
ENVIRON

Appendix A

PM10 Nonattainment Areas: Selected Comparisons

PM10 Nonattainment Areas:

Selected Comparisons

Prepared for:

Imperial County 

Air Pollution Control District

El Centro, California

Prepared by:

ENVIRON International Corporation

Los Angeles, California

Date:

September 2012

Project Number:

05-21191A
PM10 Nonattainment Areas:

Selected Comparisons

Contents i

Contents

Page

Executive Summary

1 Nonattainment Area Land and Population Comparison 1

2 Nonattainment Area Emission Comparison 3

List of Tables

Table 1: Land Area, Population and Population Density Comparison

Table 2: Major Open Areas

Table 3: Area and Emissions Related to Wind Erosion in Imperial County

List of Figures

Figure 1: Imperial County

Figure 2: Maricopa County and Maricopa Nonattainment Area

Figure 3: Imperial County Nonattainment Area

Figure 4: Maricopa County and Nonattainment Area

Figure 5: Maricopa and Imperial County Areas

Figure 6: Federal and State Managed Lands in Imperial County

Figure 7: Windblown Dust Emissions in Imperial County

List of Acronyms

ICAPCD Imperial County Air Pollution Control District

mi2 square miles

PM Particulate Matter

PM10; PM-10 Particulate Matter less than 10 microns in aerodynamic diameter

SIP State Implementation Plan

P:\I\Imperial\2012-2013\OHV BACM analysis 2012\App A Nonattainment area comparison final.docx
PM10 Nonattainment Areas: 

Selected Comparisons

Executive Summary ES-1

Executive Summary

This Report has been prepared to provide a comparison of the Imperial Valley serious PM10

nonattainment area (Imperial Valley nonattainment area) with the Maricopa County serious 

PM10 nonattainment area (Maricopa nonattainment area). These two nonattainment areas differ 

in many ways, but this Report focusses on two of the main differences:

• Differences in the scope and character of the non-attainment areas

• Differences in the contribution of open-area windblown dust emissions to the 

non-attainment area emission inventory

The Imperial Valley nonattainment area includes almost all of Imperial County, CA; thus, 

Imperial Valley and Imperial County are used interchangeably in this Report. The Maricopa 

nonattainment area includes only about 31% of Maricopa County. The Maricopa nonattainment 

area is heavily populated; only the central portion of the Imperial Valley nonattainment area is 

populated (and that lightly). The Report notes that in comparison to the Maricopa 

nonattainment area, the Imperial Valley PM10 serious nonattainment area, which includes 

almost all of Imperial County, has:

• a 45% larger land area (4,200 mi2 vs. 2,880 mi2);

• 96% less population (175,000 vs. 4,297,000); and

• an over 97% lower population density (42 people/mi2 vs. 1,492 people/mi2).

Federal and state managed lands cover almost 77% of the land area in Imperial County. 

Windblown dust from these remote desert areas accounts for 54% of the emissions on an 

annual average day. In contrast, only about 11% of the Maricopa nonattainment area annual 

average day emissions come from “other” windblown sources, including private and public 

vacant lands. During the windiest month of the year in Imperial County (April in this analysis), 

these state and federally managed remote desert areas can account for over 72% of the 

month’s average day emissions. The percentage would be even higher on the highest wind 

days. Unlike in Imperial County, the majority of these types of lands in Maricopa County are not 

even in the Maricopa nonattainment area; emissions from those lands are not in the 

anthropogenic inventory for the Maricopa non-attainment area and sources there are not subject 

to serious nonattainment area requirements. 

These are two of the important differences between the Imperial Valley and Maricopa 

nonattainment areas that can be taken into consideration when evaluating inventories, best 

available control measures, exceptional events, and other serious PM10 nonattainment area 

Clean Air Act requirements in these areas. 
PM10 Nonattainment Areas: 

Selected Comparisons

Nonattainment Area Land and Population Comparison 1

1 Nonattainment Area Land and Population Comparison

Most of Imperial County falls within the Imperial Valley Planning Area (Imperial Valley) (40 CFR 

part 81). Thus, Imperial Valley and Imperial County are used interchangeably in this Report. 

The Maricopa non-attainment area includes only about 31% of Maricopa County. 

Figure 1 shows Imperial County and its monitoring stations.1

 The county covers 4,597 mi2; the 

land portion covers 4,200 mi2

. Almost 77% of the county land area are state or federally 

managed lands (3,244 mi2

). Only the central area, which is extensively covered by agricultural 

lands (~870 mi2

), is populated, and that sparsely.

Figure 2 shows the Maricopa non-attainment area.2

 As noted above, the Maricopa 

nonattainment area only covers a portion of Maricopa County. Densely populated urban areas 

cover much of the central area of the nonattainment area. Large remote areas of the county are 

not included in the nonattainment area. 

Table 1 compares the land area, population, and population density of the two nonattainment 

areas. 

Table 1: Land Area, Population and Population Density Comparison

Nonattainment Area Area (mi2) Population Population 

Density Notes

Imperial Valley 

(essentially Imperial County) 4,200 175,000 42 State- and/or federal-managed lands: 3,244 mi2 (~ 77% of land area)

Maricopa non-attainment area

(partial county) 2,880 4,297,000 1,492

Maricopa County (9,223 mi2):

essentially 100% of the population in 

the nonattainment area

Data Sources:

2009 Imperial County PM10 SIP: 

www.co.imperial.ca.us/airpollution/attainment%20plans/final%20ic%202009%20pm10%20sip%20document.pdf

Maricopa Association of Governments 2012 Draft 5% Plan: www.azmag.gov/Projects/Project.asp?CMSID=1120

 1 From 2009 Imperial County PM10 SIP: Figure 2.1. 2 From March 2012 DRAFT Maricopa Association of Governments Five Percent Plan for PM-10 for the Maricopa 

County Nonattainment Area: Figure 2-1
PM10 Nonattainment Areas: 

Selected Comparisons

Nonattainment Area Land and Population Comparison 2

Table 2 compares the major land use categories subject to wind erosion. 

Table 2: Major Open Lands (in mi2 and % of Total Major)

Nonattainment Area Agricultural 

Areas

Vacant 

(developable)

Non-Private 

Open Space Total of Major Open Lands

Imperial Valley 

(essentially Imperial County)

873

(21%)

63

(1%)

3,244

(78%)

4,180

(100%)

Maricopa non-attainment area

(partial county)

203

(14%)

739

(52%)

473

(33%)

1,416

(100%)

Maricopa County 463

(6%)

3,481

(45%)

3,709

(48%)

7,653

(100%)

Data Sources:

2009 Imperial County PM10 SIP: 

www.co.imperial.ca.us/airpollution/attainment%20plans/final%20ic%202009%20pm10%20sip%20document.pdf

Maricopa Association of Governments 2012 Draft 5% Plan: www.azmag.gov/Projects/Project.asp?CMSID=1120 ; 

Appendix A, Table 1.5-2.

These metrics are relevant because they are related to emissions. Greater land area provides 

more locations for anthropogenic activity and/or open areas susceptible to producing windblown 

dust. Generally, the greater the population and population density, the greater the 

anthropogenic activity that can generate emissions (e.g., residential fuel combustion, vehicle 

miles travelled). In the case of the Maricopa nonattainment area, it was defined to include only 

the populated area of Maricopa County; the remote, sparsely populated areas of the county 

(~69% of the county) are not included in the nonattainment area. In contrast, all of Imperial 

County is essentially in the nonattainment area, including remote, sparsely populated areas of 

the county that account for over 77% of its land area.

Figures 3 and 4 show satellite photographs of Imperial County and the Maricopa 

County/Maricopa nonattainment area, respectively. These photographs pictorially present the 

land use and population metrics described above. The central populated area, which is 

predominantly agricultural, occupies about 23% of Imperial County land area (Figure 3). The 

Maricopa nonattainment area occupies about 31% of Maricopa County (Figure 4). Figure 5 

gives a relative comparison of the Maricopa nonattainment area and the populated portion of 

Imperial County. These areas encompass the area of the majority of human activity. However, 

the Imperial Valley nonattainment area (Figure 3) also includes remote, sparsely populated 

areas that are excluded from the Maricopa non-attainment area (but are within Maricopa 

County). Almost all of the remote, non-populated area within Imperial County is under state or 

federal management. 
PM10 Nonattainment Areas: 

Selected Comparisons

Nonattainment Area Emission Comparison 3

2 Nonattainment Area Emission Comparison

Federal and state managed lands cover about 77% of the land area in Imperial County. 

Figure 6 shows federal and state managed lands in Imperial County.3

 Figure 7 shows the 

annual windblown dust emissions in Imperial County;

4 the highest windblown emissions are 

from remote, non-populated federal and state lands. 

Table 3 compares the area and emissions from area sources subject to wind erosion. 

Table 3: Area and PM10 Emissions Related to Wind Erosion in Imperial County

Agriculture Urban open 

areas

Other (remote 

state and 

federal)

Remaining 

inventory

% Windblown 

from remote state 

and federal lands

Area (1000s of acres) 559 40 2076 -- --

Windblown emissions 

(average day –

tons/day)

11 <0.1

158

(94% of 

windblown dust)

125 54% 

(out of 294)

Windblown emissions

(windiest month 

average day –

tons/day)

28 <0.0 406 125 72% 

(out of 556)

Data Sources: 

2009 Imperial County PM10 SIP: 

www.co.imperial.ca.us/airpollution/attainment%20plans/final%20ic%202009%20pm10%20sip%20document.

pdf

Windblown dust from these remote desert areas accounts for 54% of the emissions on an 

annual average day. In contrast, non-agricultural windblown dust accounts for about 11% of the 

Maricopa non-attainment area annual average day emissions5 and a fair portion of these 

emissions come from private vacant (developable) land. During the windiest month (April, as 

identified in the Imperial Valley windblown dust studies6

), windblown dust from these areas can 

account for 72% of that month’s average day emissions. It would be expected that on the 

windiest days that this percentage would be even larger.

 3 From 2009 Imperial County PM10 SIP: Appendix III.B, Figure III.B.1. 4 From 2009 Imperial County PM10 SIP: Appendix III.B, Figure III.B.6. 5 From March 2012 DRAFT Maricopa Association of Governments Five Percent Plan for PM-10 for the Maricopa 

County Nonattainment Area: Table ES-1. 6 ENVIRON, 2004. Final Report – Development of a Wind Blown Fugitive Dust Model and Inventory for Imperial 

County, California. See also ENVIRON 2005 Technical Memorandum (2005 BACM Report Appendix A).
PM10 Nonattainment Areas: 

Selected Comparisons

Figures
PM10 Nonattainment Areas: 

Selected Comparisons

Figure 1: Imperial County 

(From Figure 2.1 of the 2009 Imperial County PM10 SIP. 

Nonattainment area includes most of Imperial County.)

Figure 2: Maricopa County and Maricopa Nonattainment Area

(From Figure 2-1 of the March 2012 Draft Maricopa 5% PM-10 Plan)

Niland

Westmorland

Brawley

El Centro

C. Ethel

C. Grant
PM10 Nonattainment Areas: 

Selected Comparisons

Figure 6: Federal and State Managed Lands in Imperial County (2009 PM10 SIP)

Figure 7: Windblown Dust Emissions in Imperial County (2009 PM10 SIP)