UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

REGION 8 

Ref: 8P-AR 

Bryce Bird, Director 

Utah Division of Air Quality 

P.O. Box 144820 

Salt Lake City, Utah 84114-4820 

1595 Wynkoop Street 

DENVER, CO 80202-1129 

Phone 800-227-8917 

http://www. epa. gov/reg ion08 

FEB 1 2 2015 

RE: EPA Region 8 Comments on Utah's Proposed Rule R307-311 State Implementation Plan Revision 

and Draft Technical Support Document 

Dear Mr. Bird: 

Thank you for the opportunity to provide comments on the state of Utah's proposed Rule R307-311 and 

the proposed rule's associated draft Technical Support Document (TSD). The purpose of the proposed 

rule is to provide a State Implementation Plan (SIP) revision that will allow, as appropriate, trading 

between the PM10 and NOx Motor Vehicle Emissions Budgets (MVEB) that are part of the EPAapproved Utah County PM10 attainment plan element of the SIP (see: 67 FR 78181 , December 23, 

2002). 

The EPA was advised by the Utah Division of Air Quality (UDAQ) that the reason for a MVEB trading 

rule, which is allowed by 40 CFR 93 .124(b ), arose from the need to demonstrate transportation 

conformity while using one of EPA's currently approved motor vehicle emissions models, 

MOVES2010b or MOVES2014. Utah County's Mountainland Association of Governments (MAG), 

which is the area's Metropolitan Planning Organization, cannot demonstrate transportation conformity 

to the prior-approved NOx MVEB, which is based on EPA's older MOBILE6 model, contained in the 

Utah County PM10 attainment plan element ofthe SIP. It is our further understanding that should EPA 

be able to approve R307-311, and its supporting associated TSD, this would then facilitate MAG's 

ability to demonstrate transportation conformity using current EPA-approved models. 

We have completed our review ofthe proposed R307-311 and the draft TSD. Our comments are detailed 

in the enclosure to this Jetter. We note that these comments are preliminary; we will not reach any final 

conclusions until the state provides a formal submittal of the R307-311 Utah County MVEB trading rule 

SIP revision and after we conduct our own notice and comment rulemaking. 

1 
We will provide any assistance needed by the UDAQ to resolve the issues and concerns that we have 

identified and look forward to working with you and your staff. If you have any questions, please 

contact me at (303) 312-6416, or have your staff contact Tim Russ at (303) 312-6479. 

Enclosure 

0:0cC) 

Carl 

Air Program 

Daly, Direct~ 

2 
ENCLOSURE 

EPA Region 8 Comments on the Proposed Rule R307-311 and the Associated Draft Technical 

Support Document 

A.) EPA Review and Comments Regarding the Proposed Rule R307-311: 

1.) EPA has compared the proposed rule R307-311 to the EPA-approved Salt Lake County (MVEB) 

trading rule R307-310. EPA does not have any comments regarding the proposed rule language in R307-

311 as the language is very similar to the PM10 MVEB trading rule (R307-31 0) that we approved in 

2002 for Salt Lake County. For reference, please see the Salt Lake County MVEB trading rule Federal 

Register final rule action; see 67 FR 44065, July 1, 2002. 

B.) EPA Review and Comments Regarding the Proposed R307-311's Draft TSD: 

EPA offers the following comments with respect to the draft TSD: 

1.) Please refer to page one ofthe draft TSD under the heading "What Fraction of the NOx Emissions 

Convert to PMlO?": EPA acknowledges and understands that the method the UDAQ used to establish 

the PM10 to NOx trading ratio would be conservative and follows the approach for the EPA-approved 

Salt Lake County trading rule (R307-31 0). This understanding is with respect to the 1 to 1 trading ratio 

and the single direction; with only available PM10 (which includes PM2.s) reductions being used to 

compensate for increases in NOx. 

2.) EPA notes a concern on page one ofthe draft TSD under the heading "What Fraction of the NOx 

Emissions Convert to PMlO?" regarding the justification for the PM10 for NOx MVEB trading. Our 

concern is that UDAQ continues to only rely on preamble language regarding interpollutant trading for 

New Source Review (NSR) offsets in the EPA's 1996 proposed rule for "Prevention of Significant 

Deterioration (PSD) and Nonattainment New Source Review (NSR)"; see 61 FR 38250, July 23, 1996. 

While EPA has also relied in part upon this language in our proposed rule and final rule for the Salt 

Lake County MVEB trading rule R307-310 (67 FR 21607, July 1, 2002), we note there is more recent 

interpollutant information available that UDAQ should evaluate and reference. 

EPA issued guidance on July 21 , 2011 regarding the appropriate technical demonstration for 

interpollutant trading, again in the context ofNSR offsets, with reference to PM2.s. Our July 21,2011 

guidance document (copy attached) is entitled "Revised Policy to Address Reconsideration of 

Interpollutant Trading Provisions for Fine Particles (P M2.5)." We recommend that UDAQ review the 

guidance with specific attention to the four steps for developing trading ratios located on pages four and 

five. We believe there may be information in this guidance that could lend additional support and 

correlation to the PM10 and NOx MVEB trading that would be allowed by R307-311 . In addition, we 

believe that additional support and correlating information may be available from the data/modeling 

contained in the Utah's recently submitted (December 16, 2014) Utah County PM2.s nonattainment 

impracticability demonstration SIP revision 1

• 

1 The "Utah State Implementation Plan Control Measures for Area and Point Sources, Fine Particulate Matter, 

PM2.5 SIP for the Provo, UT Nonattainment Area Section IX. Part A.22" as adopted by the Utah Air Quality 

Board (UAQB) on December 3, 2014 and submitted to EPA on December 16, 2014. 

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3.) On page two of the draft TSD under the heading "Consistency with the Approved Utah County 

PMlO SIP", second and third paragraphs: The UDAQ makes reference to the 2013 Utah County PM2.s 

SIP revision. The third paragraph notes that PM2.s and NOx modeling was done as part of a SIP revision 

that was" ... submitted to EPA in 2013." EPA has concerns with UDAQ's reference and use of this 

information from the 2013 Utah County 24-hour PM2.s SIP revision as justification in the draft R307-

311 TSD. 

We note that at this point in time the modeling and data from the Utah County PM2.s 2014 

impracticability demonstration is the more appropriate reference to use in support of the draft TSD. EPA 

recommends that UDAQ use this updated emissions information, data, modeling, and derivation of 

PM2.s to NOx ratios to support the information and conclusions in the draft TSD. 

Our reasons for the above recommendation are: (1) EPA never took action on the Utah County PM2.s 

2013 SIP revision submittal; and (2) with the December 16, 2014 Governor's letter submitting the final 

Clean Air Act (CAA) subpart 1 and subpart 4 PM2.s SIPs (including the impracticability demonstration 

for Utah County), the Governor also officially withdrew the 2013 PM2.s SIP submittals. With the 

Governor's withdrawal of the 2013 Utah County PM2.s SIP revision, the information, modeling, and 

data from that particular SIP revision are no longer available for EPA to reference should we determine 

that we can propose approval of R3 07-311 and its TSD. Therefore, any references or information 

derived from the 2013 SIP submittal should be deleted from the draft TSD. 

4.) On page two, and continuing into page three, of the draft TSD under the heading "Consistency with 

the Approved Utah County PMlO SIP": EPA does not have concerns with the UDAQ's information 

with regard to its understanding of the relationship between NOx and the formation ofPM10 and PM2.s in 

the Utah County airshed. However, we have two issues with this particular section of the draft TSD: (1) 

the reliance on sensitivity modeling from the 2013 PM2.s SIP revision submittal; and (2) the statement 

regarding the PM2.s component ofPMto in Utah County: 

a.) With regard to the sensitivity modeling from Utah's 2013 PM2.s SIP revision submittal, EPA 

notes in our comment #3 above that this 2013 SIP revision was withdrawn with the Governor's 

December 16, 2014 submittal of the Utah County PM2.s impracticability demonstration. We 

recommend that similar information and data be extracted from the Utah County PM2.s 20 14 

impracticability demonstration rather than from the withdrawn 2013 SIP submittal. The 

referenced information from the PM2.s 2014 impracticability demonstration could then be used to 

document and support the statement in the draft TSD that reducing primary PM2.s is more 

beneficial to improving Utah County's air quality than reducing NOx. 

b.) We also note the statement which appears at the bottom of page two of the draft TSD: " 

PM10 in Utah County consists mainly ofPM2.5 during wintertime inversion events." This 

statement needs additional supporting information as it is important with regard to the UDAQ's 

CAA section 11 0(1) demonstration that the proposed R307-311 will not impair the attainment of 

the 24-hour PM2.s National Ambient Air Quality Standard (NAAQS) in Utah County. We 

suggest that UDAQ consider evaluating information contained in the Utah County PM2.s 2014 

impracticability demonstration SIP revision for potential references to support this statement in 

the draft TSD. 

5.) On page three of the draft TSD under the heading "Impact of the Combined Budget Program on 

Other Pollutants": EPA questions the relevance ofUDAQ's write-up regarding the interim emissions 

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conformity test for PM2.s as it relates to emissions in 2008. This type of transportation conformity test is 

only applicable to the Utah County PM2.s SIP and considers emissions in calendar year 2008 as relevant 

at the time of the PM2.s nonattainment designations (74 FR 58688, November 13, 2009). For PM10 

specifically, MAG's transportation conformity evaluation for its Regional Transportation Plan (RTP) 

will take place in 2015 and will use MAG's latest planning assumptions and motor vehicle emissions 

modeling tools. Therefore, EPA recommends that UDAQ consider using the 2015 mobile sources NOx 

emission inventory data in the Utah County 2014 PM2.s impracticability demonstration to facilitate a 

comparison between the potential increases in NOx emissions due to PM10 MVEB emissions trading and 

the Utah County PM2.s SIP's NOx emissions. 

6.) On page three of the draft TSD under the heading "Impact of the Combined Budget Program on 

Other Pollutants" EPA notes incorrect references to possible ozone MVEBs for Utah County. See 

"Like ozone, the CO maintenance has its own CO budget ... " and "Nothing in this proposal changes this 

budget, and as with ozone, the MPO ... "We note that Utah County is designated as 

unclassifiable/attainment for the 2008 8-hour ozone NAAQS and there are no NOx and VOC MVEBs as 

part of an ozone plan. 

7.) On page three of the draft TSD under the heading "Impact of the Combined Budget Program on 

Other Pollutants" EPA recommends this section address the requirements of section 11 0(1) of the 

CAA. Section 11 0(1) states that a SIP revision cannot be approved by EPA if the revision would 

interfere with any applicable requirement concerning attainment and reasonable further progress towards 

attainment of a NAAQS, or any other applicable requirement ofthe CAA. The draft TSD needs to 

provide a CAA section 11 0(1) demonstration to justify the approval ofR307-311 into the Utah SIP. 

The CAA section 11 0(1) demonstration should address not only PM10, PM2.s, and CO, but also other 

potentially impacted NAAQS including ozone and N02. Supporting information for PM10 may involve 

the most recent three years of ambient air quality monitoring data. For PM2.s, the same ambient 

monitoring data years should be considered in addition to information and data excerpted from the Utah 

County PM2.s 2014 impracticability demonstration. Components of the demonstration for ozone and 

N02 could involve a qualitative analysis that discusses the relevance ofNOx emissions for these 

NAAQS and would also consider the most recent three years of ambient air quality monitoring data. 

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JUL 21 2011 

MEMORANDUM 

SUBJECT: Revised Policy to Address Reconsideration of Interpollutant Trading Provisions for Fine 

Particles (PM2.s) 

FROM: 

TO: Regional Au Division Directors, Regions 1-10 

The purpose of this memorandum is to announce a change in the policy that the U.S. Environmental 

Protection Agency originally set forth in the 2008 PM2.s New Source Review Implementations Rule (the 

2008 final rule) concerning the development and adoption of interpollutant trading (offset) provisions 

for PM2.s under state nonattainment area New Source Review (NA NSR) programs for PM2.5• As a result 

of our reconsideration of the policy, we no longer support the ratios provided in the preamble to the 

2008 final rule as presumptively approvable ratios for adoption in state implementation plan (SIPs) 

containing NA NSR programs for PM2.S· This revised policy does not affect the EPA rule provisions that 

allow states to adopt as part of their NA NSR programs for PM2.s appropriately supported interpollutant 

offset provisions involving PM2.5 precursors. 

In sum, the new policy is that any ratio involving PM2.5 precursors submitted to EPA for approval for 

use in a state's interpollutant offset program for PM2.5 nonattainment areas must be accompanied by a 

technical demonstration that shows the net air quality benefits of such ratio for the PM2.5 nonattainment 

area in which it will be applied. 

Background: 

The 2008 final rule authorizes states to adopt provisions in their NA NSR rules that would allow major 

stationary sources and major modifications locating in areas designated nonattainment for PM2.

5 to 

offset emissions increases of direct PM2.5 emissions or PM2.5 precursors with reductions of either direct 

PM2.5 emissions or PM2.5 precursors in accordance with offset ratios contained in the approved SIP for 

the applicable nonattainment area. The inclusion, in whole or in part, of the interpollutant offset 

provisions for PM2.5 is discretionary on the part of the states. 

In the preamble to the 2008 final rule, the EPA included preferred or presumptive offset ratios, 

applicable to specific PM2.5 precursors that states may adopt in conjunction with the new interpollutant 

offset provisions for PM2.5, and for which the state could rely on the EPA's technical work to 
2 

demonstrate the adequacy of the ratios for use in any PM2.s nonattainment area. Alternatively, the 

preamble indicated that states may adopt their own ratios, subject to the EPA's approval, that would 

have to be substantiated by modeling or other technical demonstrations of the net air quality benefit for 

ambient PM2.

5 concentrations. The preferred ratios were subsequently the subject of a petition for 

reconsideration, which the Administrator granted. This memo is a result of that reconsideration and, as 

stated above, we no longer support the ratios provided in the preamble to the 2008 final rule as 

presumptively approvable ratios for adoption in SIPs containing NA NSR programs for PM2.sAdditional Background: 

Section 173 of the Clean Air Act (CAA) sets forth certain requirements for obtaining a preconstruction 

permit for major stationary sources that are located, or propose to locate, in an area designated 

nonattainment for a NAAQS. One such requirement is that the proposed major stationary sources and 

major modifications must obtain emissions reductions of the affected nonattainment pollutant from the 

same source or other sources in the area to offset the proposed emissions increase. CAA § 173( c). The 

2008 final rule included a provision in the nonattainment NSR regulations at 40 CFR § 51.165 and 40 

CFR Part 51, Appendix S that provided an option for meeting the offset requirement for PM2.s with 

interpollutant (precursor) offsets. Under the provision, states could allow reductions in direct PM2.5 

emissions to offset precursor emissions increases, emissions reductions of one precursor to offset 

emissions increases of another precursor, and reductions in precursor emissions to offset direct PM2.s 

emissions increases. The provision further stipulates that the use of a PM2.

5 precursor offset must 

"comply with the interprecursor trading hierarchy and ratio established in the approved plan for a 

particular nonattainment area." 40 CFR § 51.165(a)(ll ). 

In the preamble to the 2008 final rule, the EPA issued "preferred" offset ratios that it recommended 

states use as part of an interpollutant offset provision in their NSR rules. As part of its policy authorizing 

states to implement the new PM2.5 offset provision within their approved NSR SIPs, the EPA provided a 

hierarchy and "preferred" ratios involving two PM2.5 precursors--sulfur dioxide (S02) and nitrogen 

oxides (NOx). Implementation of the New Source Review (NSR) Program for Particulate Matter Less 

Than 2.5 Micrometers (PM25), 73 Fed. Reg. 28321,28339-40 (May 16, 2008). We indicated that the 

preferred ratios were the result of a technical assessment that we conducted to support use of the ratios. 

(The preamble clearly indicated that such ratios were for purposes of offsets only and not applicable to 

source netting for applicability purposes.) The technical assessment, with details on data and modeling 

inputs, was fully described in a technical memo entitled "Details on Technical Assessment to Develop 

Interpollutant Trading Ratios for PM2.s Offsets," which was placed in the docket to the 2008 final rule. 

We recommended that states use the EPA-preferred ratios in .their PM2.5 SIPs for PM2.

5 nonattainment 

areas, and that we would approve such ratios based on our own technical demonstration, "absent a 

credible showing that the EPA's trading ratios are not appropriate for that location." We further stated 

that if any states chose to develop their own hierarchies and ratios, then such states would have to 

"substantiate by modeling and/or other technical demonstrations of [sic] the net air quality benefit for 

PM2.s ambient concentrations, and such trading programs will have to be approved by EPA." Ibid. 

In 2009, portions of the 2008 final rule, including the preferred interpollutant offset ratios for PM2.

5 

precursors, were the subject of a Petition for Reconsideration filed by Earthjustice on behalf ofNRDC 

and Sierra Club. On April 24, 2009, the Administrator signed a letter granting the Petition for 
3 

Reconsideration and agreed to reconsider portions of the 2008 final rule, including the preferred offset 

ratios discussed in the preamble. The reconsideration proceedings for the Interpollutant Trading Policy 

have resulted, in part, in the issuance of this policy memorandum. 

Revised Policy on Preferred Ratios: 

We continue to support the basic policy that sources may offset increases in emissions of direct PM2.

5 or 

of any PM2.s precursor in a PM2.s nonattainment area with actual emissions reductions in direct PM2.5 or 

PM2.s precursors in accordance with offset ratios as approved in the SIP for the applicable nonattainment 

area. However, we will no longer consider the preferred ratios set forth in the preamble to the 2008 final 

rule for PM2.s NSR implementation to be presumptively approvable. Instead, any ratio involving PM2.

5 

precursors adopted by the state for use in the interpollutant offset program for PM2.5 nonattainment areas 

must be accompanied by a technical demonstration that shows the net air quality benefits of such ratio 

for the PM2.5 nonattainment area in which it will be applied. 

We have revised the policy based on our re-evaluation of the "preferred" ratios. We have reached 

several key conclusions. First, upon re-examination of the original data, we believe that the original 

preferred ratios are not sufficiently representative of conditions in all areas of the country. Any preferred 

ratios would need to be considerably more conservative to be applied nationwide and to account for the 

inherent differences in the nature of PM2.5 ambient concentrations across nonattainment areas and the 

associated variability in responsiveness to direct and precursor emissions changes. We believe that the 

2008 preferred precursor offset ratios for PM2.5 are not sufficiently conservative to ensure the net air 

quality benefit for PM2.5 ambient concentrations across all areas of the country and, thus, to serve as 

presumptively approvable ratios for the EPA's general SIP approval in state PM2.5 NA NSR programs. 

The EPA's original technical assessment only reflected nine urban areas in detail and therefore did not 

sufficiently account for the full spectrum of differences across all nonattainment areas. As a result, the 

technical assessment did not adequately identify the offset ratios that would be needed to be considered 

presumptively approvable ratios. 

Second, we have determined that the ratios defmed in the 2008 preamble are generally not suitable for 

application to offsets that address violations of the 24-hour primary PM2.s NAAQS. The 2008 preamble 

did not distinguish between the annual and daily averaging periods to defme applicable offset ratios. 

One could have assumed that the offset ratios provided in the 2008 final rule would apply with respect to 

offsets for any averaging period. However, we have determined that those ratios are not adequate for 

addressing the precursor relationship for PM2.5 for the short-term averaging period, because the 

modeling setup that we used to develop the original preferred ratios does not adequately capture the 

local and seasonal nature of the short-term PM2.5 responsiveness to direct and precursor emissions 

changes. Daily PM2.5 concentrations in the air are highly dependent on both source and meteorological 

factors and are widely variable across and within urban and rural areas. Accordingly, states will be 

expected to develop separate PM2.5 precursor offset ratios that are demonstrated to be suitable for 

addressing the particular precursor's relationship with ambient PM25 concentrations for 24-hour 

averaging period(s) that are causing violations in that nonattainment area. 
4 

As stated above, under the EPA's revised policy, the ratios contained in the preamble to the 2008 final 

rule will no longer carry a presumptive approval status. While we believe that our original modeling 

analysis is valid and demonstrates the technical capability and approach to develop such ratios for areas 

across the country, states wishing to adopt any of those ratios contained in the 2008 preamble must treat 

them as any other ratios that they may choose, such that each ratio will need to be supported by 

modeling or other technical demonstration to show that such ratio is suitable for the particular PM2.5 

nonattainment area(s) of concern, and will be subject to the EPA's evaluation prior to approval in the 

state plan. For the nine urban areas included in the EPA's original technical assessment, that assessment 

may already contain the kind of information that a state needs to support the ratios of their choosing. 

General Guidance for Developing Case-specific Offset Ratios for PM2.s Precursors: 

The July 23, 2007 technical analysis entitled "Details on Technical Assessment to Develop 

Interpollutant Trading Ratios for PM2.s Offsets," provides details on the method used to establish the 

original "preferred" precursor offset ratios. We do not expect that the specific results from the EPA's 

2007 technical assessment could be used generally by a state as part of their demonstration without 

additional technical demonstration specific to the area(s) within which the ratios would be applied, 

unless the area(s) is among the nine areas in the 2007 assessment. We expect EPA regional offices, with 

assistance from the EPA's Office of Air Quality Planning and Standards, to assist states, as necessary, to 

structure appropriate technical demonstrations leading to the development of area-specific ratios for 

PM2.s nonattainment areas. We do not, however, plan to develop new EPA-preferred or presumptive 

ratios. We believe any presumptively approvable ratios at the national level that we might ultimately 

develop for use across the different PM2.5 nonattainrnent areas would need to be considerably more 

conservative, such that they likely would be considered undesirable by most states and permit applicants 

for use in many, if not most, nonattainrnent areas' permitting scenarios. 

We expect existing models and techniques to be adequate for states to conduct local demonstrations 

leading to the development of area-specific ratios for PM2.5 nonattainrnent areas. The general framework 

for such developmental efforts would include the following steps: 

1) Define the geographic area(s) in which offsets between emission sources are allowed, i.e., 

nonattainrnent area( s). 

2) Conduct a series of sensitivity runs with appropriate air quality models to develop a database 

of modeled PM2.s concentration changes associated with reductions of direct PM2.5 emissions 

and PM2.s precursor emissions (e.g., S02 and NOx) from anthropogen.ic point sources within 

the area of interest. For precursor emissions, a photochemical model (e.g., CMAQ, CAMx) at 

grid resolution of 12 kilometers (km) or less is recommended to predict changes in PM2.5 

concentrations. For direct PM2.5 emissions, a dispersion model (e.g., AERMOD) or 

photochemical model at grid resolution of 4 km or less is recommended to predict changes in 

PM2.s concentrations. 

3) Calculate the interpollutant offset ratios for PM2.s between direct PM2.s emissions and 

precursor emissions in a manner similar to the EPA's 2007 technical assessment, i.e., the 

ratio of impact metrics from step 3, above . 
5 

4) Conduct quality assurance of the resulting ratios and evaluate their interpretation and 

appropriateness given the nature of PM2.s sources and formation in the area of interest. This 

evaluation will likely require emissions inventory data and observed ambient data for PM2.5 

and its component species. 

If there are questions about applying these steps we encourage states to contact their Regional Office 

modeling contact for further technical consultation. 

Effects of This Revised Policy: 

This document is intended as a general statement ofthe EPA's policy with respect to the review and 

approval of interpollutant offset ratios to meet offset requirements for PM2.5 in accordance with 40 CFR 

§ 51.165(a)(ll) and 40 CFR Part 51, Appendix S(IV)(G)(5). The preferred offset ratios described in the 

preamble to the 2008 final rule were not promulgated in the Code of Federal Regulations, were not 

outlined in the proposed rule, and were not subject to public review and comment. The description of the 

preferred offset ratios in the preamble did not impose binding, enforceable requirements on the states, 

but rather provided a statement of the EPA's policy. The 2008 preamble described how the EPA 

intended to exercise its discretion in reviewing ratios submitted to the EPA for approval in accordance 

with 40 CFR § 51.165 and 40 CFR Part 51 , Appendix S. 

This memorandum reflects the EPA's reasoned reconsideration of that policy position. This document 

does not substitute for the statutory provisions or regulations, nor is it a regulation itself. Since each 

proposal to allow interpollutant offsets under a SIP or in accordance with 40 CFR Part 51, Appendix S 

will be considered on a case-by-case basis, this policy statement does not limit or restrict any particular 

approach states may take to set appropriate interpollutant offset hierarchies and ratios. Thus, the policies 

set forth in this paper are intended solely as guidance, do not represent final agency action, and cannot 

be relied upon to create any rights or obligations enforceable by any party. 

cc: Steve Page 

Anna Wood 

Scott Mathias 

Raj Rao 

Dan DeRoeck 

Tyler Fox 

Richard Wayland 

Brian Doster 

Stephanie Hogan