Cache Valley Idaho 

PM2.5 Nonattainment Area 

State Implementation Plan Amendment 

State of Idaho 

Department of Environmental Quality 

December 2014 
Printed on recycled paper, DEQ, December 2014,

PID CVSP, CA 61215. Costs associated with this 

publication are available from the State of Idaho 

Department of Environmental Quality in accordance 

with Section 60-202, Idaho Code.
Cache Valley Idaho 

PM2.5 Nonattainment Area 

State Implementation Plan Amendment 

December 2014 

Prepared by 

Idaho Department of Environmental Quality 

Pocatello Regional Office 

444 Hospital Way, #300 

Pocatello, Idaho 83201
This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

iii

Table of Contents 

Acronyms, Abbreviations, and Symbols ........................................................................................ v

1 Introduction .............................................................................................................................. 1

2 Air Quality Data ...................................................................................................................... 2

2.1 Idaho and Utah Summary ................................................................................................. 2

2.2 Design Value Determination- 24-Hour Standard ............................................................. 4

3 Meteorological Discussion ...................................................................................................... 4

4 Emissions and Attainment Year Inventories ........................................................................... 6

5 Modeled Attainment Test and Attainment Date ...................................................................... 6

6 Control Strategies .................................................................................................................... 7

6.1 Reasonably Available Control Measures ......................................................................... 8

6.2 Reasonably Available Control Technology ...................................................................... 8

6.3 Additional Emissions Reductions (Woodstove Change Out) .......................................... 8

6.4 Voluntary Measure—Dairy Rule ..................................................................................... 9

7 Conclusion ............................................................................................................................... 9

8 References .............................................................................................................................. 10

Appendix A. Meteorological Discussion of the January 2013 Stagnation Episode ................... A-1

Appendix B. Updated Road Sanding Agreements ...................................................................... B-1

Appendix C. Woodstove Change Outs ....................................................................................... C-1

Appendix D. Public Involvement ............................................................................................... D-1

List of Figures 

Figure 1. The 98th percentile of Franklin County, Idaho, 24-hour PM2.5 values from 2004–

2013. ................................................................................................................................. 3

Figure 2. The 98th percentile of Cache County, Utah, 24-hour PM2.5 values from 2004–2013. .... 3

Figure 3. Cache County (Logan monitor) running 24-hour PM2.5 design values. .......................... 4

Figure 4. Cache County, Utah, emissions inventory and annual exceedances (UDAQ 2014). ...... 5

Figure 5. Model results for the Cache Valley nonattainment area, Logan monitor. ....................... 7

List of Tables 

Table 1. Cache Valley emissions inventory (tons per day) for the 2010 base year and 2015 

attainment year for PM2.5, NOx, VOC, NH3, and SO2; emissions shown are for Utah 

and Idaho. ......................................................................................................................... 6

Table 2. Modeled concentrations for the Cache Valley nonattainment area. ................................ 7

Table 3. Emissions reductions due to the woodstove change outs. ................................................ 8
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

iv

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

v 

Acronyms, Abbreviations, and Symbols 

μg/m3 micrograms per cubic meter 

ADT average daily traffic

ATR automatic traffic counters 

BMP best management practice 

CAA Clean Air Act 

CFR Code of Federal Regulations

CMAQ community multiscale air quality model 

CO carbon monoxide

CVNAA Cache Valley nonattainment area 

DEQ Idaho Department of Environmental Quality 

DSL deep stable layer 

DV design value 

EPA US Environmental Protection Agency 

FR Federal Register 

HDD heating degree days

IDAPA Idaho Administrative Procedures Act 

MATS Model Attainment Test Software 

MOVES motor vehicle emission simulator 

NAA nonattainment area 

NAAQS National Ambient Air Quality Standards 

NH3 ammonia 

NOx nitrogen oxides 

PBR permit by rule 

PM particulate matter 

PM2.5 particulate matter under 2.5 microns in size 

PM10 particulate matter under 10 microns in size 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

vi

RWC residential wood combustion 

SIP state implementation plan 

SO2 sulfur dioxide

tpd tons per day 

tpy tons per year

UDAQ Utah Division of Air Quality 

VOC volatile organic compounds 

VMT vehicle miles traveled 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

1 

1 Introduction 

The purpose of this amendment is to revise the Cache Valley Idaho PM2.5 Nonattainment Area

State Implementation Plan (DEQ 2012) to address the Clean Air Act (CAA) Title I, Part D, 

Subpart 4 requirements. In amending the state implementation plan (SIP), the following changes 

occurred: 

 Revised model attainment test 

 Revised attainment date 

 Shifted model base year to 2010 

 Added emissions reductions through additional woodstove change outs

 Strengthened the existing road sanding agreements 

 Provided a voluntary control measure: permit by rule (PBR) for dairies, IDAPA 

58.01.01.760–764, prescribing best management practices (BMPs) to control ammonia 

(NH3) and volatile organic compounds (VOCs).

This amendment demonstrates that the Cache Valley 2012 particulate matter 2.5 (PM2.5) SIP

satisfies federal PM2.5 SIP requirements under CAA, Title I, Part D, Subpart 4, attaining the 

standard by 2015. 

Background 

The Idaho Department of Environmental Quality (DEQ) completed a PM2.5 SIP for the Idaho 

side of Cache Valley, which is part of the Cache Valley nonattainment area (CVNAA) (Logan 

UT-ID NAA), and submitted it to the US Environmental Protection Agency (EPA) in December 

2012. This plan satisfied requirements from EPA’s 2007 Fine Particle Implementation Rule,

which was grounded in the CAA, Title I, Part D, Subpart 1. 

On January 4, 2013, the District of Columbia Circuit Court found that EPA incorrectly 

interpreted the CAA when determining how to implement the National Ambient Air Quality 

Standards (NAAQS) for PM2.5. The court ruling held that the EPA should have implemented the 

PM2.5 NAAQS based on both CAA, Title I, Part D “Plan Requirements for Nonattainment 

Areas,” Subpart 1 “Nonattainment Areas in General” and Subpart 4 “Additional Provisions for 

Particulate Matter Nonattainment.” Therefore, as of January 4, 2013, Subpart 4 also applies. 

Under CAA Subpart 4, nonattainment areas (NAAs) for particulate matter may carry the 

classification of either moderate or serious. Subpart 4 address the attainment dates and planning 

provisions for both moderate and serious particulate matter NAAs. The Logan UT-ID NAA is 

classified as a moderate PM2.5 NAA.

Since its submission in December 2012, EPA acted on two portions of the Cache Valley, Idaho,

PM2.5 SIP (DEQ 2012). In March 2014, EPA issued a Federal Register (FR) notice finalizing a 

limited approval of PM2.5 control measures contained in the December 2012 submittal because 

incorporation of these measures strengthen the Idaho SIP and reduce sources of PM2.5 emissions 

in Franklin County that contribute to violations of the 2006 PM2.5 standard on the Idaho side of 

the Logan UT-ID NAA (79 FR 16201 [March 25, 2014]). In July 2014, EPA issued an FR notice 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

2 

approving the baseline emissions inventory contained in DEQ’s submittal as meeting the 

requirement to submit a comprehensive, accurate, and current inventory of direct PM2.5 and 

PM2.5 precursor emissions in Franklin County (79 FR 41904 [July 18, 2014]).

The amendment addressing Subpart 4 is required to be submitted by December 31, 2014, and 

demonstrate attainment by December 31, 2015. 

For additional information, refer to the Cache Valley Idaho PM2.5 Nonattainment Area State 

Implementation Plan” (DEQ 2012), which is available at www.deq.idaho.gov/media/930589-

cache_valley_pm2_5_nonattainment_state_implementation_plan_1212.pdf. The SIP appendices 

are available at www.deq.idaho.gov/media/930593-cache-valley-pm2-5-sip-appendices-1212.pdf.

2 Air Quality Data 

PM2.5 standards are based on averaging air quality measurements both annually and on a 24-hour 

basis. The 24-hour standard is designed to provide an appropriate level of protection from shortterm exposures to PM2.5. The 24-hour standard for PM2.5 is met whenever the 3-year average of 

the annual 98th percentile of values at designated monitoring sites in an area is less than or equal 

to 35 micrograms per cubic meter (μg/m3). The analysis of the PM2.5 data for the monitoring sites 

across the valley show violations of the 24-hour PM2.5 NAAQS on both the Utah and Idaho sides 

of the CVNAA. 

2.1 Idaho and Utah Summary 

Figure 1 details the 98th percentile monitoring data for the Franklin County, Idaho, air quality 

monitor from 2004 through 2013. The 2010 data should not be considered representative of the 

area; due to upgrades to the Franklin sewage lagoons, the area was without power for a 

considerable portion of the year. During 2010, none of the quarters for data collection met EPA 

criteria for data completeness. Figure 2 details the 98th percentile monitoring data for the Cache 

County, Utah air quality monitor. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

3 

Figure 1. The 98th percentile of Franklin County, Idaho, 24-hour PM2.5 values from 2004–2013. 

Figure 2. The 98th percentile of Cache County, Utah, 24-hour PM2.5 values from 2004–2013. 

0

20

40

60

80

100

120

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

concentration

(micrograms per cubic meter)

year

98th Percentile of Franklin County

24-hr PM2.5 Values

*

0

20

40

60

80

100

120

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

concentration

(micrograms per cubic meter)

year

98th Percentile of Cache County

24-hr PM2.5 Values
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

4 

2.2 Design Value Determination—24-Hour Standard 

Design values are the metrics that are compared to the NAAQS to determine compliance. For the 

24-hour standard, the design value is the 3-year average of annual 98th percentile, 24-hour 

average values. The 24-hour PM2.5 NAAQS is met when the design value is less than or equal to 

35 μg/m3. 

EPA recommends an average of three such 3-year averages that straddle the baseline inventory 

be used to calculate the monitored baseline value. The year 2010 represents the baseline 

inventory. Therefore, the 3-year running average of 98th percentile values collected from 2008–

2010 would be averaged together with the 3-year averages from 2009–2011 and 2010–2012 to 

arrive at the site-specific monitored baseline design value. 

For this SIP, the baseline design value concentration for the Utah side of Cache Valley is 

40.7 μg/m3

. The SIP demonstration will be based on the Utah design value because it is the 

highest in the CVNAA. The 24-hour PM2.5 design values for the Cache County (Logan) monitor 

are shown in Figure 3. 

Figure 3. Cache County (Logan monitor) running 24-hour PM2.5 design values. 

3 Meteorological Discussion 

The 2012 Cache Valley UT-ID SIP was projected to achieve compliance with the PM2.5 24-hour 

NAAQS by the end of 2014. Projected emissions levels and the number of measured 

exceedances were trending downward, as indicated in Figure 4 (UDAQ 2014) and the attainment 

plan appeared to be on track. In 2013, especially in January, the number of exceedances 

0

10

20

30

40

50

60

70

2004-2006 2005-2007 2006-2008 2007-2009 2008-2010 2009-2011 2010-2012

24-hour Design Value

(micrograms per cubic meter)

Years

Cache County (Logan monitor)
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

5 

increased dramatically. DEQ analyzed the January–February stagnation episodes in an effort to 

determine whether this was due to suddenly increasing emissions or strictly an unusual weather 

pattern. 

The DEQ analysis, provided in Appendix A, found the following: 

 An unusually strong and persistent high-pressure system occurred in 2013 producing the 

coldest January in over 62 years. 

 Baseline source activity related to population and traffic remained approximately flat 

from the SIP baseline year, 2010 through 2013.

 The cold temperatures alone probably exacerbated the emissions by increasing heating 

loads and vehicle emission rates (but not source activity). 

 The PM2.5 concentrations in Cache Valley and other locations in the northwest such as 

Boise, Idaho, reached extreme levels as a result not so much of the strength of the 

inversion, but its persistence, or more specifically the number of consecutive days when 

the lower stable layer (< 500 meters) did not break up in the afternoon, allowing PM2.5 

and its precursors to accumulate from day to day. 

The duration of the January accumulation period was longer than any in at least the past decade. 

As a result of this analysis, DEQ concluded that the increased exceedances resulted solely from 

this extreme meteorological event. 

Figure 4. Cache County, Utah, emissions inventory and annual exceedances (UDAQ 2014). 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

6 

4 Emissions and Attainment Year Inventories 

A detailed emissions inventory using the best information available was prepared for the Cache 

Valley airshed to assess direct PM2.5 emissions as well as emissions of precursors to secondary 

PM2.5 formation. In July 2014, EPA issued an FR notice approving the baseline emissions 

inventory contained in DEQ’s submittal as meeting the requirement to submit a comprehensive, 

accurate, and current inventory of direct PM2.5 and PM2.5 precursor emissions in Franklin County 

(79 FR 41904 [July 18, 2014]).

Table 1 lists total daily winter emissions (for both Utah and Idaho) for the 2010 base year as well 

as the 2015 attainment year. The attainment year totals include projections concerning growth in 

population, vehicle miles traveled, and the economy. The totals also include the effects of 

emissions control strategies that are either already promulgated or were required as part of the 

Utah SIP. 

Table 1. Cache Valley emissions inventory (tons per day) for the 2010 base year and 2015 

attainment year for PM2.5, NOx, VOC, NH3, and SO2; emissions shown are for Utah and Idaho. 

Notes: particulate matter 2.5 (PM2.5); nitrogen oxides (NOx); volatile organic compounds (VOC); ammonia (NH3); 

sulfur dioxide (SO2); tons per day (tpd). 

5 Modeled Attainment Test and Attainment Date 

The Utah Division of Air Quality (UDAQ) used the Model Attainment Test Software (MATS) 

for the modeled attainment test at grid cells near monitors. MATS results for future year 

modeling at the Logan monitor site are presented in Figure 5. The future year design value is 

presented for 2015, the attainment year, along with the MATS future year design values for 

modeling simulation that include control strategies. For comparison purposes, the monitored 

design value is also presented for the base year, 2010. Table 2 presents the same information in 

tabular form and also includes data from the monitoring location in Franklin, Idaho. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

7 

Figure 5. Model results for the Cache Valley nonattainment area, Logan monitor. 

Table 2. Modeled concentrations for the Cache Valley nonattainment area. 

2010 2015

Observed

(μg/m3)

Business-As-Usual

(μg/m3)

Control Basket

(μg/m3)

Logan 41 37 34

Franklin 39 34 32

The attainment date for this moderate PM2.5 NAA is December 31, 2015. As shown in the 

modeled attainment test, the emissions reductions achievable in 2015 allow for a demonstration 

that the CVNAA can attain the 24-hour PM2.5 NAAQS by the attainment date. 

6 Control Strategies 

The overall strategy for improving air quality throughout the Cache Valley consists of many 

different components across the multistate NAA. Collectively, these components are responsible 

for reducing PM2.5 emissions in the CVNAA and have contributed to the demonstration of 

attainment with the NAAQS by December 31, 2015. Both sides of the Cache Valley (Utah and 

Idaho) dealt separately with various control measures, due to both jurisdictional authority and 

differences in the emissions inventory. Details concerning the control measures used on the Utah 

side of the Cache Valley are found in the PM2.5 SIP and technical support document developed 

41

37

34

0

5

10

15

20

25

30

35

40

45

2010 base year 2015, no

additional

controls

2015, with Utah

control

strategies

micrograms per cubic meter

Logan Monitor
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

8 

by UDAQ (2014). The following subsections deal directly with any updates to the existing 

controls and applicability to CAA, Subpart 4. 

6.1 Reasonably Available Control Measures 

Reasonably available control measures, which refers to measures of any type that may be 

applicable to a wide range of sources (mobile, area, or stationary), was addressed in the original 

SIP submission with road sanding agreements and residential wood combustion ordinances. The 

original road sanding agreements lacked a measure of enforceability. This amendment contains 

updated road sanding agreements (Appendix B), which are now tied to the IDAPA rules and 

have a new measure of enforceability. 

6.2 Reasonably Available Control Technology 

Reasonably available control technology refers to measures specifically designed for stationary 

sources. In developing the emissions inventories underlying the SIP, the criteria of 40 CFR 51 

for air emissions reporting requirements was used to establish a 100 tons per year (tpy) threshold 

for identifying stationary point sources. For the CVNAA, there are no point sources with the 

potential to emit 100 tpy of PM2.5 or any PM2.5 plan precursor. 

6.3 Additional Emissions Reductions (Woodstove Change Out) 

DEQ has operated three woodstove change-out programs on the Idaho side of the CVNAA 

(2006–2007, 2011–2012, and 2013–2014), changing out a total of 209 uncertified residential 

wood combustion devices. The original SIP submission claimed credit for the first two change 

outs (152 woodstoves). DEQ is claiming credit for the additional 57 woodstoves, as well as an 

additional 39 uncertified woodstoves that were recycled in accordance with Idaho’s Alternative 

Energy Device tax deduction. This program allows Idaho citizens to deduct all, or most, of the 

cost to acquire and install a certified appliance (wood/pellet/gas). Table 3 lists the emissions 

reductions due to all of the woodstove change outs. Supporting documentation is found in 

Appendix C. In addition to reductions in particulate matter, the woodstove change-out program 

has also led to the reduction in air toxics, such as formaldehyde, Acrolein, and benzo(a)pyrene, 

which are generated as by-products of combustion. 

Table 3. Emissions reductions due to the woodstove change outs. 

Pollutant Old Woodstove to Certified Wood 

or Gas Stove (tpy)

Old Woodstove to Pellet

Stove (tpy)

Total (tpy)

CO 46.64 15.72 62.36

SO2 0.05 0.01 0.06

NOX 0.45 0.02 0.47

VOC 14.79 3.79 18.57

PM2.5 primary 6.00 2.04 8.04

PM10 primary 6.00 2.04 8.04

Notes: tons per year (tpy), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen oxides (NOx), volatile organic 

compounds (VOC), particulate matter (PM2.5, 10).
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

9 

6.4 Voluntary Measure—Dairy Rule 

DEQ has added an additional voluntary control measure to this SIP amendment to address the 

control of ammonia emissions in Idaho. Rules for the control of ammonia from dairy farms,

IDAPA 58.01.01.760–764, sets forth BMPs for dairy farms of a certain size licensed by the 

Idaho State Department of Agriculture through a PBR. The PBR applies to dairy farms with a 

capacity to produce 100 or more tons of ammonia emissions per year. Dairy farms with fewer 

than the specified number of animal units or mature cows may opt into the PBR program as well. 

These rules derived from negotiations amongst the dairy industry, Idaho Department of 

Agriculture, Idaho Conservation League, and DEQ as part of a settlement of a lawsuit. The 

stakeholders agreed these rules would not be submitted to EPA for SIP approval. These rules are 

considered “State Only” rules and are not enforceable by the federal government.

The capacity to produce is based on the number of animal units or mature cows and the type of 

manure collection system. It requires dairy farms above specified threshold numbers of cows or 

animal units to register with DEQ and to implement industry BMPs to control ammonia 

emissions. The BMPs also have the added benefit of controlling VOC emissions. The rules 

prescribe various BMPs to control ammonia emissions, such as installing certain types of waste 

storage and treatment systems, implementing composting practices, and exporting manure. A 

point value is assigned to each BMP. Dairy farms must employ BMPs totaling 27 points. 

While model runs have shown that significant reductions in the NH3 inventories have little to no 

effect on predicted PM2.5 concentrations, it was determined that VOCs do play a role in the 

secondary aerosol formation. This amendment provides for a voluntary control measure: PBR for 

dairies, IDAPA 58.01.01.760–765, prescribing BMPs to control NH3 and VOCs. The reduction 

in NH3 will likely have no effect on the PM2.5 formation, but the reduction in VOC is an added 

benefit that will help to reduce PM2.5 secondary aerosol formation. 

7 Conclusion 

This SIP amendment demonstrates that the Logan, UT-ID NAA will achieve attainment with the 

24-hour PM2.5 NAAQS by December 2015. Utah and Idaho have worked cooperatively with 

each other, EPA, and citizens to develop control strategies in keeping with the inventories on 

both sides of the valley. The State of Idaho will continue to monitor PM2.5 concentrations in 

Franklin County. If exceedances occur, Idaho will determine the cause(s) and adjust the 

appropriate control measures to ensure prompt corrective action is taken. 

This plan fulfills the requirements of the CAA as they pertain to SIPs. Input received from the 

public comment period is provided in Appendix D. DEQ requests that EPA approve this 

attainment plan in accordance with CAA Section 110 and Subpart 4. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

10

8 References 

DEQ (Idaho Department of Environmental Quality). 2012. Cache Valley PM2.5 Nonattainment 

Area State Implementation Plan. Pocatello, ID: DEQ. 

FR (Federal Register). 2014. “Revision to the Idaho State Implementation Plan: Approval of 

Fine Particulate Matter Control Measures; Franklin County.” 79 FR 16201.

FR (Federal Register). 2014. “Approval and Promulgation of Implementation Plans; Idaho 

Franklin County Portion of the Logan Nonattainment Area; Fine Particulate Matter 

Emissions Inventory.” 79 FR 41904.

IDAPA. 2014. “Rules for the Control of Air Pollution in Idaho.” Idaho Administrative Code 

IDAPA 58.01.01.

US Congress. 1970. Clean Air Act. 42 USC § 7401 et seq. 

UDAQ (Utah Division of Air Quality). 2014. PM2.5 State Implementation Plan, Weight of 

Evidence in the Model Attainment Test. Salt Lake City, UT: UDAQ. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-1 

Appendix A. Meteorological Discussion of the January 2013 

Stagnation Episode 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-2 

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-3 

Meteorological Discussion of the January 2013 

Stagnation Episode 

1 Introduction 

The 2012 Cache Valley Utah-Idaho state implementation plan (SIP) demonstrated that a number 

of control measures should bring the 24-hour averaged particulate matter 2.5 (PM2.5) design 

value (DV) concentration under 35 micrograms per cubic meter (μg/m3) and thereby into 

compliance with the National Ambient Air Quality Standard (NAAQS) by 2015 (DEQ 2012). 

Emissions were projected to decline and by 2012, there were no exceedances recorded in either 

Franklin or Cache Counties. However, in 2013, there were numerous exceedances, and the 98th

percentile values were 68 μg/m3in Cache County and 55 μg/m3 in Franklin County. An 

unusually persistent series of cold temperatures occurred in January–February 2013, resulting in 

a sharp increase in the DV, defined as the 95th percentile 24-hour concentration value averaged 

over 3 years. 

The purpose of this analysis is to show that the 2013 increase in PM2.5, particularly in January, 

resulted from an extreme weather pattern and does not represent a sudden reversal of the 

downward trending emissions rates produced by source control measures as demonstrated in the 

SIP. To be clear, stagnation events cannot be excluded under the Exceptional Events Rule and 

such a demonstration is not proposed here, nevertheless, it is of value to understand that the 

increased 2013 PM2.5 was strictly the result of an extreme meteorological phenomenon and does 

not indicate that sources are increasing or that the SIP control measures are not working. 

The analyses in the following sections will show that: 

Section 2. An unusually strong and persistent high pressure ridge remained in place for most of 

January leading to a very long period of cold air pooling and temperature inversions that 

persisted throughout each afternoon. 

Section 3. Baseline source activity, at least for the major categories related to population and 

traffic, did not suddenly increase in January 2013.

Section 4. While emissions activity (related to population and traffic) itself did not increase, and 

wood-burning curtailment was in effect for 20 days in January 2013, the coldest January in 62 

years probably led to higher than normal home heating emissions and vehicle emission, which 

contributed to the PM2.5 buildup. 

Section 5. While the inversion conditions were strong, the unusually high PM2.5 levels resulted 

primarily from the duration of the event, or more specifically to the number of days that the lowlevel inversions persisted in the afternoon without breakup. This caused a consistent day-to-day 

accumulation of PM2.5 concentrations around 13 μg/m3per day. The duration of the continuous 

low stable layer (LSL) period was the longest in at least the past 10 years. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-4 

2 Unusually Strong and Persistent High Pressure System 

Affected the Region 

While no strong direct relationship exists between PM2.5 levels and the strength of an upper level 

ridge pattern, the weather characteristics typical to a long-duration upper level ridge event 

typically enhance PM2.5 levels. Large-scale synoptic (O: 1,000 kilometer) blocking patterns can 

be identified by viewing upper level atmospheric observational data as shown in Figure 1. 

Additional 500 millibar (mb) charts for the most severe inversion days are shown in 

Attachment A. Blocking patterns—events that limit the zonal motion of passing waves through 

the atmosphere—are identified in the analysis below at the 500 mb level, which typically occurs 

at an elevation of 18,000 feet. The two meteorological parameters investigated are the 500 mb 

heights (the altitude at which 500 mb of pressure occurs) and the 500 mb temperature. 

Characteristically, the high pressure blocking patterns that occurred in the month of January 

2013 have warmer than normal temperatures and higher than normal heights. Both of these 

attributes occurred during the period of interest. Again, it must be stressed that while the values 

of these meteorological parameters share no significant direct relationship to PM2.5 levels, the 

weather associated with high pressure blocking patterns can cause increased levels of PM2.5 with 

increasing duration of blocking patterns. 

Upper air radiosonde profiles from weather balloons for Salt Lake City, Utah, and Boise, Idaho,

were obtained to investigate the January 2013 stagnation period in comparison to the 30-year 

climatology period of 1981–2010. Data presented in Table 1 and Table 2 verify that the 500 mb 

heights were at a statistically significantly higher altitude than climatology (1981–2010) for 

southern Idaho and northern Utah. Boise data during the time periods of January 1–6, 2013,

January 15–21, 2013, and January 15–26, 2013, were each statistically different than the 

climatological comparison period (Table 1). T-tests (computed with α = 0.05) are shown, such 

that any T-test value less than 0.05 indicates that the heights and temperatures are statistically 

different than the 30-year climatological record of 500 mb heights and temperature. As a result, 

Boise PM2.5 concentrations reached their three highest wintertime values since before 1999 on 

January 19, 22, and 25. This is further indication of the regional nature of the event and that it 

did not result from any local change in source activity. 

Furthermore, published literature has suggested that the heights experienced in the eastern 

Pacific Ocean and Pacific Northwest were higher than any recorded levels, further promoting the 

regional scale of this particular wintertime event; in fact, Swain et al. (2014) note that the largescale meteorological pattern over the northeastern Pacific led to observationally unprecedented 

geopotential heights (an altitude referenced to sea level) over a broad region and noted that this 

pattern was nicknamed the “Ridiculously Resilient Ridge.” Funk et al. (2014), Swain et al.

(2014), and Wang and Schubert (2014) all note the role of increasing global temperatures and the 

increase in frequency of such highly anomalous ridge events over the eastern Pacific and Pacific 

Northwest in the future. Finally, while noted for the relationship between geopotential height and 

precipitation, the probability of an event with such high anomalies was determined to be less 

than 1 in 126 years (with confidence > 95%). Although this relationship was discerned with 

precipitation in mind, it serves to indicate the general strength and anomalous nature of the 

January 2013 event. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-5 

Figure 1. The 500 mb height contours for January 2, 2013, showing a Rex block high pressure 

ridge over the Pacific Northwest. 

Table 1. Paired T-test values and anomalies for periods of interest for Boise, Idaho.a

Boise α=0.05 α=0.05

Height 

Anomaly (m)

Temperature 

Anomaly (o

Date C) T-test ValueHeight

T-test ValueTemp (oC)

Entire monthb0.26005 0.23740 29.26 29.26

January 1–6 0.00708 0.00335 91.02 3.63

January 15–21 0.00008 0.00027 155.90 4.78

January 15–26 <0.00001 <0.00001 137.99 5.10

a. Compared to 1981–2010 climatology.

b. January 30, 2013, values are averaged from January 29 and 31.

In Salt Lake City, the time periods of January 15–21, 2013, and January 15–26, 2013, are also 

significantly different than climatology for those dates (Table 2). One can see that the 500 mb 

heights were typically 90–150 meters higher than climatology at Boise and Salt Lake City for 

those time periods. As is typical with ridge patterns, the 500 mb temperature (oC) was also higher 

than climatology over the same times with the same events being statistically significant for 

Boise and Salt Lake City as with the 500 mb height. The 500 mb temperature anomalies varied 

from 3.5 oC to 5.1 oC higher than climatology. It is important to note that the data do not indicate 

the relative intensity or strength of the corresponding high or low pressure systems as the data 

are single-point values from two locations.
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-6 

Table 2. Paired T-test values and anomalies for periods of interest for Salt Lake City, Utah. 

Salt Lake City α=0.05 α=0.05 Height 

Anomaly 

(meters)

Temperature 

Anomaly (oC)

Date

T-test ValueHeightT-test ValueTemp (

oC)

Entire month 0.90839 0.99719 2.94 0.00

January 1–6 0.39089 0.23215 30.60 1.41

January 15–21 0.01859 0.00958 101.28 3.55

January 15–26 0.00021 0.00007 111.05 4.56

Note: Compared to 1981–2010 climatology.

3 Major Sources of PM2.5 and Precursor Emissions Did Not 

Increase in 2013 

When ambient concentrations of a pollutant increase, one must consider two contributing factors: 

(1) sources are increasing, or (2) weather is causing the pollutants to be more concentrated over 

more days. To evaluate the first factor, DEQ considered the largest source categories of PM2.5

and its precursors that cause increased PM2.5 formation in the Cache Valley atmosphere—area 

sources such as home heating and traffic. Both traffic and home heating, including residential 

wood combustion, are major sources of PM2.5 and PM2.5 precursors: nitrogen oxides (NOx) and 

volatile organic compounds (VOCs). (Ammonia is a PM2.5 precursor but is believed to be so 

abundant that moderate changes in ammonia levels have little effect in the Cache Valley 

wintertime atmosphere.) Population and traffic counts were selected to represent the source 

activity for home heating and other area sources, and for traffic. The changes from 2010, the 

baseline year of the Utah Division of Air Quality (UDAQ) SIP, and 2013 are shown in Table 3. 

3.1 Traffic 

Traffic counts for the four automatic traffic counters (ATRs) in Cache Valley on main roads and 

with a record back to 2004 were obtained from the Utah Department of Transportation (UDOT 

2014). A sum of the January weekday average daily traffic (ADT) counts at three primary ATRs 

in Cache County with a continuous record back to 2004, as well as the ATR on State Road 91 at 

the Idaho-Utah border, is shown in Figure 2 for the period from 2004 to 2013. The traffic sum in 

2013 is within 1% of the values in 2004 and represents a 2.7% decrease from 2010 (Table 3). 

Thus both the traffic activity (or vehicle miles traveled [VMT]) in Cache County, Utah, and that 

entering Cache County from Franklin County, Idaho, is generally flat and is clearly decreasing 

from 2010 to 2013. This finding only relates to VMT or traffic activity, however, it should be 

noted that vehicle emission rates (per VMT) are declining every year as a result of new car 

emission standards, and the inspection and maintenance program will begin to lower emission 

rates as well. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-7 

Figure 2. Weekday average daily traffic counts summed for 3 ATRs (363, 510, 511) in Cache 

County, and one ATR (303) on State Road-91 at the Utah-Idaho border showing a flat 10-year trend 

and slight reduction from the 2010 SIP baseline year to 2013. 

3.2 Population 

As shown in Table 3, the population in Cache County, Utah, grew only 3.8% from April 2010 to 

July 2013, while Franklin County, Idaho, grew only 0.5% (US Census Bureau 2014). Population 

represents a surrogate for most area sources, including wintertime home heating sources, a major 

contributor of NOx, VOCs, and PM2.5. Thus, we must conclude that the area source categories 

that vary with population, including residential wood combustion, other combustion home 

heating sources, residential outdoor burning, and consumer uses of VOC-containing products 

like solvents and paints do not appear to account for any significant increase in air pollution 

during January–February 2013. If the source activities cannot explain the increase in PM2.5 for 

this period, we must look to the weather to see if an explanation of the high pollution levels can 

be found. 

Table 3. Changes from 2010 to 2013 in area source activity, represented by population and traffic 

for Cache County, Utah, and Franklin County, Idaho, from 2010 to 2013. 

Cache County, Utah Franklin County, Idaho

Population 3.80% 0.50%

Traffic -2.7% -4.6%
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-8 

4 Unusually Cold Temperatures Exacerbated Heating and 

Vehicle Emissions 

The discussion about source activity levels in section 3 demonstrates that changes in the 

population and traffic activity levels were minor suggesting that residential home heating and 

traffic emissions alone could not explain the very large increase in concentration. In addition, 

mandatory curtailment burn bans were in effect on 20 of the inversion episode days in January 

2013, which should have lowered residential wood combustion and residential open burning 

activities significantly. Nevertheless, the cold temperatures alone probably enhanced emissions 

from heating and vehicles and may have negated some of the emission-lowering benefits of the 

burn bans. 

As a corollary to the extremely cold temperatures in Cache Valley during January 2013, the 

heating degree days (HDD) in January 2013 were the highest of any January in the previous 

62 years. The mean HDDs in Logan (WRCC 2014) are shown in Figure 3 along with their 95% 

confidence intervals, minimum and maximum values, and the 2013 values (green circles). Since 

residential wood combustion (and all other types of home heating) increase with increasing heat 

load and heat load is a direct function of HDD, any residential heating emissions not subject to, 

or compliant with the burn bans would have been at the highest January loads and emissions 

level since before 1951, with a heating load (HDD) 28% higher than the 62-year mean for 

January. 

In addition to the effect of temperature on heating load, colder temperatures also influence 

vehicle emissions. The motor vehicle emission simulator (MOVES) temperature sensitivity 

graphs shown in Figure 4 (Choi 2010) indicate that PM2.5 emissions as well as PM2.5 precursor 

emissions of VOC and NOx all increase as temperatures drop from the the 62-year average 

January temperature (24.0o

F) to the 2013 mean January temperature (14.4oF), an approximately 

10-degree departure from normal mean monthly temperatures for January. The emission 

increases are not large, but all species except the PM2.5 from diesel vehicles are shown to trend 

upward as the temperature drops from 24oF to 14oF. To be clear, source activities related to 

population and traffic are flat or declining, but the purely meteorological influence of colder 

temperatures causes higher emissions at the same time that the persistent inversion traps 

pollutants through the afternoon, causing many consecutive days of accumulation. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-9 

Figure 3. Logan, Utah, heating degree days in 2013 versus 1951–2013 period of record 

(WRCC 2014). 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-10

Gasoline Vehicles Diesel Vehicles

Figure 4. Temperature sensitivity for gasoline and diesel vehicles in the MOVES2010b model 

(Choi 2010). 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-11

5 Why Franklin County, Idaho, PM2.5 Was Higher in 2013 

The previous sections have shown that an extremely persistent high pressure system 

predominated in January 2013; source activity for major sources declined or remained flat 

throughout the month; and cold air by itself can contribute to increased emissions. The following 

analysis demonstrates that the key factor in producing extreme PM2.5 levels is not so much the 

strength or depth of the inversion, but rather the number of consecutive days that the afternoon 

lower stable layer persists without breakup, and that 2013 had the longest such period in the last 

decade. 

5.1 Assumptions 

1. Maximum 24-hour PM2.5 concentration increase rate (μg/m3

per day) in a strong 

stagnation episode is more or less constant assuming the constant emissions. 

2. Maximum 24-hour PM2.5 concentration increase rate (μg/m3per day) in a strong 

stagnation episode is positively correlated with emission level. 

3. A deep stable layer (DSL) with a thickness of 500 meters above ground level or more 

(12Z soundings) indicates a stagnation condition. A deep stable layer is defined as a 

condition in which 65% of the layer from 0 to 1,500 meters is stable. 

4. A low stable layer (LSL) of 50 meters or more above ground level (in the lowest 

500 meters, 0Z soundings) between two consecutive DSL days indicates a continuous 

DSL episode in which the PM2.5 concentration on one day will accumulate in the next 

day with a roughly constant rate. 

5. The maximum PM2.5 elevation in a severe stagnation episode can be conceptually

estimated by Equation 1: 

C = R (mixing height, emission rate) x N Equation 1. Conceptual model.

where: 

R (a function of mixing height and emission rate) is the concentration increase rate 

that can be estimated using the data from most recent episode. 

N is the number of days in the first stage (increasing PM2.5 stage) of the episode, 

which should be continuous without breakup, i.e., a LSL exists at 0Z, the afternoon 

sounding between any two consecutive DSL days. 

6. There could be brief breakups or relief during an episode, therefore, the above estimation 

is for the maximum level and the actual level is usually lower. 

7. There could be exceptional situations in which the PM2.5 level may increase extremely 

fast, such as 50 μg/m3

per day or more. This kind of extreme situation is not considered 

in this study. 

5.2 Conceptual Model 

While the PM2.5 formation and concentrations depend on complicated emission and weather 

patterns, experience has shown that pollutant levels could be estimated by relatively simple box 

models. During severe stagnation episodes, both vertical and horizontal dispersion are limited. In 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-12

the deep valleys, inversions establish early before dusk, and mixing height in afternoon may 

never reach the level that allows pollutants to disperse; as a result, pollutants will persistently 

increase for days. The conventional dispersion models and photochemistry models often fail to 

properly simulate this situation due to the lack of accurate meteorological information near the 

surface. An example of community multiscale air quality (CMAQ) modeling results are shown in 

Figure 5 (UDAQ 2014). It can be seen that the PM2.5 levels constantly increase at a linear rate 

during the episodes; the highest concentration is roughly proportional to the number of the days 

of the episode, as suggested in Equation 1. While the R in Equation 1 depends on the mixing 

height and emission rate, it is observed that R remains nearly constant over several episodes. The 

number of days without afternoon LSL breakup (N) is also relatively easy to predict from largescale weather forecasting. 

Figure 5. Examples of PM2.5 episodes in which PM2.5 concentrations accumulated at a nearly 

constant rate. 

Based on this consideration, R can be determined using the data from the most recent severe 

stagnation episodes and the number of days of an episode. N is the only parameter needed to 

estimate the potential maximum PM2.5 level. The longer the episode duration, the higher the 

potential maximum PM2.5 level could be. 

While the duration of episodes can be forecasted using the DSL method (Wolyn and McKee 

1968), and the DSL method was found to be applicable to the Boise, Idaho, airshed, the 

atmospheric stability with respect to trapping inversions in the Cache Valley is better defined 

using an LSL scheme because it is found that DSL thickness could vary in a great range, which 

results in uncertainties in determining the effect on the polluted layer. In other words, the layer 

above 500 meters may be deeply stable, but if the lower stable layer below 500 meters still 

breaks up in the afternoon, the accumulation is interrupted and PM2.5 levels drop or stop 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-13

accumulating. Figure 6 and Figure 7 clearly show that the PM2.5 events are defined by the 

existence of LSL. 

Figure 6. Salt Lake City, Utah, PM2.5 events defined by lower stable layer. PM2.5 and lower stable 

layer data are both from Salt Lake City. 

Figure 7. Franklin, Idaho, 2013 episode defined by lower stable layer. PM2.5 data are from Franklin 

County, Idaho, and lower stable layer data are from Salt Lake City, Utah, upper air soundings. 

0

1

0

10

20

30

40

50

60

70

80

LSL (Yes/No)

24hr PM2.5 (g/m3

)

Date

PM2.5 Levels and LSL

Salt Lake City

Daily Mean PM2.5 Concentration LSL

0

1

0

20

40

60

80

100

120

PM2.5 24 Concentration *(μg/m3

)

2013 Franklin PM2.5 Episode and LSL

24hrPM2.5

LSL
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-14

Data Analysis 

Two major PM2.5 events occurred in the past decade, early 2005 and early 2013, as shown in 

Figure 8 and Figure 9, respectively. The events in 2005 were shorter with the longest one about 

7–8 days. The valid LSL data are not available for 2005; however, it could be determined from 

the incomplete data that the 2005 episodes were much shorter and milder. 

From Figure 8, the R value estimated from the first event is about 18.7 μg/m3per day, and the R 

value estimated from the linear portion in the main episode in Figure 9, is about 13.7 μg/m3

per 

day. The episode during in 2013 is much longer than that in 2005, therefore the highest PM2.5

concentration in 2013 was much higher than in 2005, while the R value is lower in 2013 

probably reflecting lower emissions. 

Figure 8. PM2.5 events in Franklin, Idaho, early 2005. 

0

10

20

30

40

50

60

70

80

90

PM2.5 24-hr Concentration (μg/m3

)

Date

Franklin 24 hr PM2.5, 2005
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-15

Figure 9. PM2.5 events in Franklin County, Idaho, early 2013. 

The skew-T diagrams for 2013 and 2005 show that the stable system is much stronger in 2013, 

while the mixing heights in afternoon were similar (Figure 10 and Figure 11). The lower R value 

in 2013 can be partially explained by the reduced emission rate since 2005. The emission rate in 

2013 is about 80% of emissions in 2005 (UDAQ 2014), and the R value is about 70% in 2013 

compared to 2005. This supports the theory that R varies with emissions and suggests emissions 

are lower in 2013, in agreement with the emission inventory (UDAQ 2014). 

0

20

40

60

80

100

120

1/1/20131/3/20131/5/20131/7/20131/9/2013

1/11/20131/13/20131/15/20131/17/20131/19/20131/21/20131/23/20131/25/20131/27/20131/29/20131/31/2013

2/2/20132/4/20132/6/20132/8/2013

2/10/20132/12/20132/14/20132/16/20132/18/20132/20/20132/22/2013

PM2.5 24-hr concentration (μg/m3

)

Date

24hr PM2.5 Franklin ID, 2013
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-16

Figure 10. A skew-T diagram in a typical day in 2013 episode. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-17

Figure 11. A skew-T diagram in a typical day in 2005 episode. 

Figure 12 shows the consecutive LSL days of the longest episode in each year in the past decade. 

The January 2013 episode had the longest LSL event. While it is not the only factor affecting the 

severity of the pollution episode, it is clear that the meteorological conditions in the 2013 episode 

made it one of the worst in recent years and are responsible for the sharp upturn in days 

exceeding the 24-hour PM2.5 NAAQS.
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-18

Figure 12. Longest consecutive lower stable layer days in each year; the 2013 event had the 

longest duration in the past decade. 

In conclusion, PM2.5 accumulates during severe stagnation events. The accumulation rate 

depends on the average mixing height and emission rate. The average mixing height in a severe 

stagnation episode is assumed to be similar; therefore, the accumulation rate is largely dependent 

on the emission rate only. The stagnation episode in 2013 was the strongest and longest in the 

past decade, therefore, while the accumulation rate, R, is smaller than 10 years ago due to the 

reduced emission rate, the maximum PM2.5 concentration reached 102 μg/m3

due to the longer 

duration of the episode. 

0

2

4

6

8

10

12

2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Number of days of continuous LSL

Number of days of Longest 

Lower Stable Layer (LSL)-episode each year

in Salt Lake City 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-19

6 References 

DEQ (Idaho Department of Environmental Quality). 2012. Cache Valley PM2.5 Nonattainment 

Area State Implementation Plan. Pocatello, ID: DEQ. 

Choi, D., M. Beardsley, D. Brzezinski, J. Koupal, and J. Warila, 2010. “MOVES Sensitivity 

Analysis: The Impacts of Temperature and Humidity on Emissions.” Presented at the 

19th Annual International Emission Inventory Conference: Emissions Inventories - 

Informing Emerging Issues., San Antonio, TX.

Funk, C., A. Hoell, and D. Stone. 2014. "Examining the Contribution of the Observed Local 

Warming Trend to the California Droughts of 2012/12 and 2013/14." Bulletin of the 

American Meteorological Society. 95.9: S11–15.

Swain, D.L., M. Tsiang, M. Haugen, D. Singh, and A. Charland. 2014. "The Extraordinary 

California Drought of 2013/2014: Character, Context, and the Role of Climate Change." 

Bulletin of the American Meteorological Society. 95.9: S3–S7. 

Wang, H., and S. Schubert. 2014. "Causes of the Extreme Dry Conditions over California During 

Early 2013." Bulletin of the American Meteorological Society. 95.9: S7–S11. 

UDAQ (Utah Division of Air Quality). 2014. PM2.5 State Implementation Plan, Weight of 

Evidence in the Model Attainment Test. Salt Lake City, UT: UDAQ. 

UDOT (Utah Department of Transportation). 2014. “Traffic on Utah Highways (AADT).” 

Accessed October 2014. http://www.udot.utah.gov/main/f?p=100:pg:0::::V,T:,529.

US Census Bureau. 2014. “State & County Quick Facts.” Accessed September 2014. 

http://quickfacts.census.gov/qfd/states/16/16041.html.

Wolyn P.G. and T.B. McKee. 1968. “Deep Stable Layers in the Intermountain Western United 

States.” Monthly Weather Review. 117: 461–472.

WRCC (Western Regional Climate Center). 2014. “Cooperative Climatological Data 

Summaries.” Accessed October 2014. http://www.wrcc.dri.edu/summary/Climsmut.html.
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-20

Attachment A 

January 2: A Rex block has developed over the Pacific Coast. This forces the air to travel into 

Canada before entering Idaho. This promotes dry, cold transport into Idaho. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-21

January 3: The low pressure system responsible for the Rex block has devolved into an open 

wave but is still steering the winds in this same pattern while the high pressure system associated 

with the Rex block as shifted to the east putting southwestern Idaho directly along the ridge axis. 

This promotes stagnant, stable weather. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-22

January 5: Again, this ridge is evident with the ridge axis located directly along the 

Idaho/Oregon border. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-23
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-24
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-25

January 15–21: Offshore ridge of high pressure is strongly amplified and steering cold, dry, 

continental Canadian wind into Idaho. This pattern remains for a week. This pattern promotes a 

consistent northwest wind pattern that is typically quite dry. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-26
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-27

January 22–23: This ridge axis shifts to center directly over southwestern Idaho once more. 

Again, this promotes stagnant winds. The 20,000-foot wind speeds are at 10 miles per hour 

(mph) near the ridge axis on January 22, while accelerating to 35 mph on January 23. This image 

also allows the identification of a strong upper level low pressure system in the Gulf of Alaska 

with an elongated trough that is likely the cause of clearing for this particular stagnation event. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

A-28

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

B-1 

Appendix B. Updated Road Sanding Agreements 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

B-2 

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

B-3 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

B-4 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

B-5 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

B-6 

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

C-1 

Appendix C. Woodstove Change Outs 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

C-2 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

C-3 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

C-4 

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-1 

Appendix D. Public Involvement 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-2 

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-3 

Proof of Publication 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-4 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-5 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-6 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-7 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-8 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-9 

Sign-In Roster 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-10

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-11

Official Public Hearing Transcript 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-12
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-13
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-14
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-15
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-16
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-17
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-18
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-19
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-20
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-21
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-22
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-23
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-24

This page intentionally left blank for correct double-sided printing. 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-25

Response to Public Comments

The Idaho Department of Environmental Quality (DEQ) received one written comment and one 

oral comment at the public hearing held on December 10, 2014. None of the comments received 

raised substantive issues requiring modification to the proposed Cache Valley Idaho PM2.5

Nonattainment Area State Implementation Plan Amendment. The following details both the 

comments and DEQ’s response to those comments.

Comments from the Public Hearing 

Comment 1—Dirk Bowles: I just wanted to comment that the education that I’ve received over 

the last five years, I think, that we’ve been meeting with the DEQ and with Melissa has been 

very important to me personally just to understand what these different – what all the acronyms 

mean, for one thing, but also just the importance of the SIP agreement and how dedicated they 

have been in working through that with us to make it most cost effective for us to try to come 

into compliance. As an elected official, I just really appreciate the many trips down here and the 

patience they’ve had with us in answering our questions and helping us, hopefully get this passed 

and get through the process so that we will really get the air quality that we desire and what is 

necessary for use to have the quality of life we want. But that’s all.

Response to Comment 1—No response is necessary. 

Comments from E-mail 

Comment 2—Trent Gudmundsen: The EPA currently allows masonry heaters (defined as sitebuilt and weighing more than 800kg). After researching what that means, I found that masonry 

heaters are much cleaner-burning, and use far less fuel wood, than most EPA-certified 

woodstoves; the conclusion being that the best alternative is not even mentioned as a viable 

option in the current amendment. 

Pellet stoves are specifically mentioned, and yet masonry heaters are not. Even if masonry 

heaters are not mentioned, I strongly encourage the mention of "EPA-exempted" options. And on 

a more personal and local level, I strongly encourage those who are unfamiliar with this 

technology (as I was until recently) to research the efficiency and other benefits of masonry 

heaters. There is much information that can easily be found online regarding the superior 

efficiency of masonry heaters. 

One fear I have is that such things may inadvertently be outlawed (or at least frowned-upon) due 

to lack of specific exemption or allowance in amendments such as that being discussed for the 

Cache Valley, ID area. Another fear I have is that specific local businesses who sell 

manufactured woodstoves (including pellet stoves) will unfairly benefit while those wishing to 

site-build, or have constructed on site, a masonry heater will be unfairly disadvantaged by not 

being mentioned as a viable alternative. 

If those who write the laws in Idaho will be open to lesser-known clean-burning options such as 

the masonry heater, I believe we could quickly become known as a forward thinking and 

environmentally minded area of the country, and could be instrumental in helping to orchestrate 

a paradigm shift in thinking. It is my hope, therefore, that masonry heaters will not only be 
Cache Valley Idaho PM2.5 Nonattainment Area SIP Amendment 

D-26

specifically exempted from being regulated in Idaho ("exempt" being the EPA's wording), but 

also be specifically allowed, and the education about such be encouraged. 

Response to Comment 2—The comment is outside the scope of the amendment; no changes or 

modifications to the local residential wood combustion ordinances were part of this amendment, 

and therefore no comment is necessary.