State of California

Staff Report

Town of Mammoth Lakes

PM10 Maintenance Plan and 

Redesignation Request

Release Date: August 18, 2014

Scheduled for Consideration: September 18, 2014

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 .................................................................... 2

III. EVALUATION OF THE MAINTENANCE PLAN/REDESIGNATION REQUEST ... 3

A. Attainment of the Standard................................................................................ 3

B. Fully Approved SIP............................................................................................ 5

C. Attainment Results from Permanent and Enforceable Emission Reductions .... 5

D. Maintenance Plan Provides for Continuing Attainment ..................................... 6

1. Attainment Year Emission Inventory............................................................ 6

2. Maintenance Demonstration........................................................................ 7

3. PM10 Monitoring Network............................................................................. 8

4. Verification of Continued Attainment ........................................................... 8

5. Contingency Plan ........................................................................................ 8

E. Motor Vehicle Emission Budgets....................................................................... 9

IV. STAFF RECOMMENDATION .............................................................................. 10
I. BACKGROUND

The Town of Mammoth Lakes (Mammoth Lakes), referred to as the Mammoth Lakes

Planning Area in U.S. Environmental Protection Agency (U.S. EPA) rulemaking, was 

designated as nonattainment for the 24-hour particulate matter less than 10 microns 

(PM10) National Ambient Air Quality Standard (standard) on November 15, 1990. The 

nonattainment area covers approximately 68 square miles within the Great Basin 

Unified Air Pollution Control District (District) and encompasses almost all of the 

incorporated portion of Mammoth Lakes and a portion of unincorporated Mono County. 

The unincorporated portion of the nonattainment area includes the Mammoth Yosemite 

Airport. Figure 1 shows the boundaries of the nonattainment area and the incorporated 

portion of Mammoth Lakes.

The District and Mammoth Lakes adopted an Air Quality Management Plan (1990 Plan) 

to attain the 24-hour PM10 standard in November 1990. The 1990 Plan focused 

emission control requirements on two area source categories that were determined 

during earlier air quality monitoring and analysis to be primarily responsible for 

exceedances of the standard in the winter: residential wood combustion and road 

sanding with volcanic cinders (road cinders). The 1990 Plan committed to long-term 

PM10 monitoring at a location found to be significantly impacted by emissions from both 

of these area sources. Since 1984, the site chosen for monitoring has been situated in

a commercial area (Gateway Center) near the western edge of town. This site has 

hosted Federal Reference Method (FRM) monitors and Federal Equivalent Method 

(FEM) monitors continuously except for a two year period from 1998 to 2000 when the 

roof upon which the station was installed was replaced during building remodeling. 

Currently, the District maintains one FRM filter-based monitor and one non-certified 

continuous PM10 monitor at the Gateway Center site. 

The 2014 Update to the Air Quality Maintenance Plan and Redesignation Request for 

the Town of Mammoth Lakes (Maintenance Plan/Redesignation Request) adopted by 

the District Board on May 5, 2014, reports that no exceedances of the 24-hour PM10

standard of 150 μg/m3 have been recorded at the site since 1993. Analysis of air quality 

data accessed through U.S. EPA’s Air Quality System shows that the number of 

exceedances per year during the 2010-2012 averaging period to be less than 1.0. 

Although two exceedances of the standard were recorded in 2013, these occurred 

during the height of the Aspen Fire near Fresno that pushed smoke into the Mammoth 

Lakes area. Regardless, these two exceedances did not cause Mammoth Lakes to 

violate the PM10 standard under U.S. EPA regulations. These regulations trigger a 

violation of the PM10 standard when four or more exceedances are recorded in a three 

calendar year period.

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Figure 1. Map of the Mammoth Lakes Planning Area PM10 Nonattainment Area

II. REDESIGNATION REQUIREMENTS 

The federal Clean Air Act (Act) authorizes the U.S. EPA to redesignate an area from 

nonattainment to attainment if a number of requirements are satisfied. These 

requirements, as listed in Section 107(d)(3)(E) of the Act, are:

1. The area has attained the standard;

2. The applicable implementation plan for the area is fully approved under Section 

110(k) of the Act;

3. The improvements in air quality are due to permanent and enforceable emission 

reductions resulting from implementation of the applicable implementation plan;

4. The area has a fully approved maintenance plan satisfying the requirements of 

Section 175A of the Act; and

5. The state in which the area is located has met all applicable requirements under 

Section 110 and Part D of the Act.

U.S. EPA guidance further explains the redesignation requirements including the 

required elements of approvable maintenance plans1

. Each PM10 maintenance plan 

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

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must provide for continued maintenance of the PM10 standard for twenty years after 

redesignation and include the following components:

1. Attainment emission inventory; 

2. Maintenance demonstration;

3. Commitment to continued operation of the monitoring network;

4. Commitment to 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 MAINTENANCE PLAN/REDESIGNATION REQUEST

Based on review of the District Maintenance Plan/Redesignation Request and 

supporting technical analysis, ARB staff concurs that the Maintenance 

Plan/Redesignation Request meets the Act’s requirements. The following sections 

summarize ARB staff findings and conclusions with respect to the required elements of 

the Maintenance Plan/Redesignation Request.

A. Attainment of the Standard

As shown in Table 1, PM10 air quality improved significantly over the first few years of 

implementation of the 1990 Plan in Mammoth Lakes. PM10 is measured at a single 

monitoring station at the Gateway Center. The Gateway Center site lies downslope 

from most residential areas and adjacent to the intersection of Main Street and County 

Road 203. Air within the ground-level mixing layer on cold, still winter nights in 

mountainous terrain tends to cool through ground contact more than air aloft, resulting 

in downhill flows that behave somewhat like water in surface runoff flows but with flow 

depths measured in tens of meters. These air “surface runoff flows” entrain wood

smoke and, in the absence of vertical mixing, transport the smoke and its PM10 load

downhill to pool in areas of level terrain. The Gateway Center monitoring site lies at the 

toe of Mammoth Mountain and the edge of the Long Valley Caldera, a flat, wide bowl to 

the east of Mammoth Lakes. PM10 concentrations from vehicle-entrained road cinders 

are typically highest adjacent to heavily-traveled arterial streets. Both of these 

phenomena make the Gateway Center site a good candidate for sampling the highest 

PM10 impacts from residential wood combustion and road sanding in the community.

Table 1 lists PM10 monitoring data using several metrics for tracking PM10 air quality 

year by year. These metrics include the highest 24-hour average PM10 concentration 

recorded during each year, the estimated number of exceedance days per year for the 

24-hour PM10 standard, and the 3-year average of estimated numbers of exceedance 

days per year for use in determining attainment of the 24-hour PM10 standard. The 24-

hour PM10 standard is met when the estimated number of exceedance days recorded 

over a three-year period average one or less per year.

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Table 1. Peak 24-Hour Average PM10 Per Year and Estimated PM10 Exceedance 

Days Per Year and Per Three-Year Average

Year

Peak 24-Hour PM10

Concentration

(μg/m3

)

Estimated 

Exceedances Days

Per Year

3-Year Average of 

Estimated 

Exceedance Days

Per Year

1988 166 6.2

1989 163 7.1

1990 161 12.0 8.4

1991 134 0 6.4

1992 138 0 4.0

1993 178 6.4 2.1

1994 92 0 2.1

1995 122 0 2.1

1996 74 0 0

1997 112 0 0

19981 106 * *

19991 -

2 * *

20001 70 * *

2001 134 * *

20021 129 * *

20031 74 * *

2004 86 0 *

2005 85 0 *

2006 78 0 0

2007 67 0 0

2008 138 * *

2009 116 0 *

2010 100 0 *

2011 101 0 0

2012 56 * *

(1) Monitoring data for these years do not meet U.S. EPA completeness standards

(2) Monitoring discontinued during building remodeling.

PM10 monitoring has been conducted at the Gateway Center site for more than the

duration needed to determine air quality status as specified by U.S. EPA regulation 

defining the PM10 standard. PM10 monitoring began at this location on April 17, 1988,

with 1-in-6 day filter sampling. Monitoring was suspended between August 23, 1998, 

and September 10, 2000, while the roof upon which the station is mounted was 

replaced during building remodeling. The frequency of PM10 filter monitoring was 

increased from a 1-in-6 day schedule to a 1-in-3 day schedule in 2001, and continuous 

monitoring commenced in 2008 at this site.

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The last three year period during which the 24-hour PM10 standard was violated was 

1993-1995 at Mammoth Lakes. As Table 1 indicates, peak 24-hour PM10

concentrations have remained below the 150 μg/m3 standard since monitoring 

recommenced in 2000 and below 100 μg/m3 for more than 50 percent of the years with 

adequate datasets in the past decade. U.S. EPA regulation defines a violation of the 

24.hour PM10 standard as 4 or more exceedances recorded in a three year period.

B. Fully Approved SIP

The 1990 Plan is a fully approved portion of the California SIP. The 1990 Plan was 

submitted to U.S. EPA on September 11, 1991, and subsequent amendments, primarily 

of an administrative nature, were forwarded to U.S. EPA on January 9, 1992. In a 

Direct Final Rule Notice published in the June 24, 1996, Federal Register, U.S. EPA 

fully approved the 1990 Plan as amended.2

C. Attainment Results from Permanent and Enforceable Emission Reductions

The substantial decline in peak winter day PM10 concentration shown in Table 1

between 1991 and 1995 is due to the implementation of control measures contained in 

the 1990 Air Quality Management Plan. Studies conducted prior to development and 

adoption of the 1990 Plan estimated that up to 93 percent of ambient PM10 on some 

exceedance days was generated by fireplaces and woodstoves, and that up to 44

percent on other exceedance days was produced by the entrainment of pulverized road 

sanding agents (road cinders) after roads became free of ice.

Mammoth Lakes ordinances adopted to implement the 1990 Plan reduced residential 

wood-burning emissions by requiring permanent replacement of non-U.S. EPA- certified 

woodstoves with certified units upon property resale, requiring the removal of some 

wood-burning devices by limiting the number of devices per residence to one, and by 

instituting no burn days when calm or stagnant meteorological conditions were 

forecasted in winter months.

Data collected and analyzed by the District and Mammoth Lakes between 1990 and 

1994 demonstrated measureable reductions in the PM10 wood smoke emission 

inventory for the nonattainment area. Over this time span, the total number of woodburning devices declined from 5,946 to 5,749, and the fraction of these that were 

U.S. EPA-certified rose from 1 percent to 35 percent.

3

 In December 2006, Mammoth 

Lakes amended these ordinances to eliminate the operational exemption from no burn 

day requirements originally granted to U.S. EPA-certified devices. Starting in 2007, all 

wood-burning devices in the nonattainment area are required to be shut down on no 

2 Federal Register, Vol. 61, No. 122, June 24, 1996, pp. 32341-32345

3 Taylor, Bill, Town of Mammoth Lakes, Letter to Duane Ono, Great Basin Unified APCD, March 2, 1995

5

 
burn days. Emission inventories compiled by the District report that PM10 emissions 

from residential wood-burning declined by 54 percent between 1990 and 2012.

Also due to the 1990 Plan, PM10 emissions from the re-entrainment of road cinders 

were controlled in Mammoth Lakes ordinances adopted in 1990 by requiring the use of 

high-efficiency vacuum street sweepers for cinder removal and the enforcement of a 

traffic volume limit within the boundaries of the incorporated area through VMTreduction permit conditions on new development. 

Prior to 1989, Mammoth Lakes did not remove road cinders from public streets and 

roads (as indicated by the 1990 Plan emission inventory calculations), but instead 

allowed cinders to be pulverized and removed by entrainment and transport of road 

surfaces by passing vehicles. Applicable emission control guidelines published prior to 

1990 estimated the control efficiency of vacuum street sweepers to be 34 percent, 

which – at the time – was believed to the most effective control technology for reducing 

PM10 emissions from public streets with high loadings of sand and silt.4

 This control 

efficiency was used in the attainment demonstration of the 1990 plan, based on 

Mammoth Lakes’ commitments to purchase and use these sweepers in a program of 

early road cinder removal as sanded roads became free of ice. After the high efficiency 

vacuum street sweepers were purchased, a test of the effectiveness of the vacuum 

street sweeper program in the winter of 1993-1994 revealed that road cinder emissions 

were reduced by 68 percent, resulting in greater control of emissions and lower residual 

impacts on air quality than had been estimated in the 1990 Plan.5

D. Maintenance Plan Provides for Continuing Attainment

Section 175A of the Act establishes the required elements of a maintenance plan for 

areas seeking redesignation from nonattainment to attainment. Using an attainment

year inventory and future inventory projections, plans must demonstrate continued 

attainment through the first 10-year maintenance period. Comprehensive inventories 

were developed in this Plan for the representative attainment year (2012) and for the 

projected full build-out year (2030) when peak winter day PM10 emissions will reach a 

maximum level.

1. Attainment Year Emission Inventory

As the standard being addressed in the Maintenance Plan/Redesignation Request is 

the 24-hour PM10 standard, and as all historical exceedances of this standard occurred 

during winter months, the emission inventories contained in this Plan all report peak 

winter day PM10 emissions. PM10 monitoring data from Mammoth Lakes demonstrates 

4 Control of Open Fugitive Dust Sources; prepared by Chatten Cowherd et. al. for U.S. Environmental 

Protection Agency; U.S. EPA-450/3-88-008; September 1988 5 Street Sweeper Efficiency Study for the Town of Mammoth Lakes; prepared by Charles Satterfield, 

Satterfield & Associates, for the Town of Mammoth Lakes; June 13, 1994

6

 
that the last violation of the standard occurred in 1993, and that peak winter day 

concentrations each year have not varied substantially between 2005 and 2012. As a 

result, the starting point for inventory tracking in the plan is 2012, the most recent year 

of complete data at the time that drafting of the plan commenced.

A series of analyses determining the speciation of peak winter day PM10 also 

demonstrated that two sources – residential wood combustion and road sanding –

accounted for more than 95 percent of ambient PM10 on these days in 1990, and more 

than 90 percent in 2012. These findings are supported by the dominance of PM10

emissions from these two sources in the emission inventories. Although PM10

emissions from residential wood combustion and road sanding have each decreased by 

approximately 33 percent since 1990 - according to the emission inventory - the 

magnitudes of emissions from these sources continue to overwhelm all other sources in 

2012. The result of this dominance is that emission inventory analysis reported in the 

Maintenance Plan/Redesignation Request continues to focus on these two sources. A 

tabulation of peak winter day PM10 emissions by source category and milestone year 

that quantifies the dominance discussed above is shown in Table 2.

.

Table 2. Peak 24-hour PM10 Emissions (kg/winter day)

Source Category 2012 2030

Residential Wood Combustion 850 802

Road Dust and Vehicle Emissions 3,466 4,319

Industrial Sources 8 8

TOTAL 4,324 5,129

Note: ARB customarily reports emission inventory in pounds or tons per day or year. The 

Maintenance Plan/Redesignation Request reported this inventory in kilograms per day.

2. Maintenance Demonstration

In order to demonstrate maintenance of the PM10 24-hour standard through the year 

2024, the District compiled an emission inventory for an attainment year (2012) and 

formulated projections for the build-out year (2030) of the Mammoth Lakes 2007 

General Plan. The attainment year and projected inventories represent winter 

emissions which reflect the nature of the PM10 problem in the area. The Maintenance 

Plan/Redesignation Request states that residential wood combustion and resuspended

road dust comprise almost all of the PM10 emissions during winter days. This statement 

is supported by chemical mass balance (CMB) analyses that were conducted in 1990 

and 2012. 

The District used the recent CMB analyses in conjunction with recent high winter days 

to determine if the PM10 standard would be maintained through the 10-year 

maintenance period. Despite the increases in road dust and vehicle emissions forecast, 

the Maintenance Plan/Redesignation Request demonstrates that the PM10 standard will 

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be maintained through 2030. The 2030 timeframe provides ample time for the 

U.S. EPA approval process and still allows for a 10-year maintenance period.

3. PM10 Monitoring Network

The existing PM10 monitoring network in Mammoth Lakes consists of the single station 

located at the Gateway Center commercial cluster. The District commits in the 

Maintenance Plan/Redesignation Request to continue daily PM10 monitoring for the 

twenty year term required of an approvable maintenance plan. Daily PM10 monitoring 

using a continuous method is also a critical element in the Mammoth Lakes’ residential 

wood combustion tracking and control program.

 

4. Verification of Continued Attainment

The District commits in the Maintenance Plan/Redesignation Request to verify 

continued attainment through the compilation and submittal of progress reports to U.S. 

U.S. EPA every third year starting in 2017. The progress reports will contain emission 

inventory updates, air quality trend assessments, modeling performance re-evaluations, 

and additional information that may be relevant to the air quality program of Mammoth 

Lakes. Eight years after designation to attainment, the District also commits to revisiting 

the SIP to address the second 10-year maintenance cycle. 

5. Contingency Plan

The Act requires a 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. If a violation of the standard occurs, the District will 

determine whether the violation was due to an exceptional event or a controllable 

source. If the violation was due to a controllable source, within 18 months, the District 

and Mammoth Lakes will adopt additional control measures related to residential wood 

smoke or volcanic cinders. The District believes that the need to exercise contingency 

measures is small given the ample attainment margin demonstrated by the ambient air 

quality monitoring data collected since 2003 showing peak winter 24-hour PM10

concentrations generally hovering between 90 and 110 μg/m3

.

In addition, while not needed to show maintenance, the Maintenance 

Plan/Redesignation Request incorporates several amendments to District Rule 431 

(Particulate Emissions) that increase the stringency of the Mammoth Lakes residential 

wood combustion requirements that will further reduce emissions by eliminating 

exemptions for burning on no burn days, prohibit wood-burning devices in new 

commercial buildings, and allow only pellet stoves in new multi-family structures. These 

amendments will cause the currently flat-lined peak winter day PM10 concentrations to 

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begin dropping, potentially resulting in larger compliance margins and further reducing 

the potential for use of contingency measures.

E. Motor Vehicle Emission Budgets

The Act requires that transportation plans, programs, and projects receiving federal 

funding or requiring federal approval must be found to be fully consistent with the 

applicable SIP. The federal Transportation Conformity Rule requires SIPs to specify onroad motor vehicle emission budgets (transportation conformity budgets) that are 

consistent with the attainment and maintenance demonstrations in the SIP.6 The 

conformity regulation requires departments of transportation to demonstrate that 

emissions from applicable portions of regional transportation plans and programs do not 

exceed these emissions budgets.

The transportation conformity budgets in PM10 SIPs must include emissions from 

several categories of sources that are integral components of on-road infrastructure 

construction, maintenance, and use. These source categories are identified in the 

Maintenance Plan/Redesignation Request as vehicle exhaust, vehicle wear (e.g., 

abrasive generation of particles from brake linings, tire surfaces, etc.), re-entrained road 

dust, and re-entrained traction agents (road cinders). Under U.S. EPA regulation, road 

construction fugitive dust may be excluded from conformity budgets if the applicable SIP 

does not identify this source as being significant.7 PM10 emissions from source 

categories included in the budgets must be reported in the units of measure upon which 

the SIP emission inventories are based. For the Maintenance Plan/Redesignation 

Request, this unit is kilograms (kg) per peak winter day.

Table 3 shows the District-adopted transportation conformity budgets for PM10 peak 

winter day emissions for the Mammoth Lakes Planning Area. If U.S. EPA determines 

these budgets to be adequate, future transportation plan amendments and updates in 

Mammoth Lakes will need to conform to these budgets. Mammoth Lakes must ensure 

that the aggregate peak winter day transportation PM10 emissions in the Planning Area 

do not exceed these levels when approving new transportation plans and transportation 

programs, even if the mix of projects changes or growth increases. These budgets will 

remain in effect until other budgets are found adequate through approval by U.S. EPA.

During the 30-day public comment period prior to District Board adoption of the 

Maintenance Plan/Redesignation Request, District staff modified the motor vehicle 

emission budgets to respond to comments from U.S. EPA. As a result, the version of 

Maintenance Plan/Redesignation Request considered and adopted by the District Board 

was not the version released to the general public at the commencement of the public 

comment period. To fully comply with the requirements for public hearings on SIP 

revisions in U.S. EPA regulations8

, ARB is providing a full 30-day comment period and 

6 The Transportation Conformity Regulation is found at 40 CFR Parts 51 and 93.

7 40 CFR 93.122(e)(1)

8 40 CFR 50.102(a) (Public Hearings)

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public hearing on the District-adopted version of the Maintenance Plan/Redesignation 

Request.

Table 3. Motor Vehicle Emission Budgets for Maintenance of the 24-hour PM10 

NAAQS

Motor Vehicle Emissions (kg/peak winter day) Year

2012 2030

Road Dust & Vehicle Emissions (Incorporated Portion) 2,531 3,154

Road Dust & Vehicle Emissions (Unincorporated Portion) 935 1,165

Total 3,466 4,319

IV. STAFF RECOMMENDATION

ARB staff has reviewed the Maintenance Plan/Redesignation Request for Mammoth 

Lakes and consulted with District staff during this review. ARB staff finds that the 

Maintenance Plan/Redesignation Request meets all applicable Act requirements. The 

monitoring data shows that the area attained the 24-hour PM10 standard in 1994, and 

the maintenance demonstration shows that the standard will be maintained for ten 

years. 

Therefore, staff recommends that the Board adopt the 2014 Update to the Air Quality 

Maintenance Plan and Redesignation Request for the Town of Mammoth Lakes as a 

revision to the California SIP for submittal to U.S. EPA.

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