E6-7032. Approval and Promulgation of Implementation Plans; Las Vegas Valley Carbon Monoxide Attainment Plan

AGENCY:

Environmental Protection Agency (EPA).

ACTION:

Proposed rule.

SUMMARY:

EPA proposes to approve a revised attainment plan for the Las Vegas Valley carbon monoxide nonattainment area on the condition that Clark County and the State of Nevada withdraw the 2030 motor vehicle emission budget, or, in the alternative, to disapprove the plan. This plan has been submitted to the Agency by the State of Nevada as a revision to the Nevada state implementation plan. The revised attainment plan includes revised base year and future year emissions inventories and a revised demonstration of continued attainment of the carbon monoxide national ambient air quality standard in Las Vegas Valley through 2030 based on the most recent emissions models and planning assumptions and establishes new motor vehicle emissions budgets. EPA is proposing this action under section 110(k) of the Clean Air Act, which obligates the Agency to take action on State submittals of revisions to state implementation plans. The intended effect of this proposed approval action is to update the carbon monoxide motor vehicle emissions budgets in the Las Vegas area and thereby make them available for the purposes of transportation conformity, and the intended effect of this proposed disapproval action is to retain the previously-approved budgets.

DATES:

Any comments on this proposal must arrive by June 8, 2006. Public comments on this action are requested and will be considered before taking final action.

ADDRESSES:

Submit comments, identified by docket number EPA-R09-OAR-2006-0322, by one of the following methods:

1. http://www.regulations.gov: Follow the on-line instructions for submitting comments.

2. E-mail: [e-mail].

3. Mail or deliver: Karina O'Connor (AIR-2), U.S. Environmental Protection Agency Region IX, 75 Hawthorne Street, San Francisco, CA 94105-3901.

Instructions: Direct your comments to EPA-R09-OAR-2006-0322. EPA's policy is that all comments received will be included in the public docket without change and may be made available online at http://www.regulations.gov,, including any personal information provided, unless the comment includes information claimed to be Confidential Business Information (CBI) or other information whose disclosure is restricted by statute. Do not submit information that you consider to be CBI or otherwise protected through http://www.regulations.gov or e-mail. The http://www.regulations.gov,, Web site is an “anonymous access” system, which means EPA will not know your identity or contact information unless you provide it in the body of your comment. If you send an e-mail comment directly to EPA without going through http://www.regulations.gov, your e-mail address will be automatically captured and included as part of the comment that is placed in the public docket and made available on the Internet. If you submit an electronic comment, EPA recommends that you include your name and other contact information in the body of your comment and with any disk or CD-ROM you submit. If EPA cannot read your comment due to technical difficulties and cannot contact you for clarification, EPA may not be able to consider your comment. Electronic files should avoid the use of special characters, any form of encryption, and be free of any defects or viruses.

Docket: All documents in the electronic docket are listed in the http://www.regulations.gov index. Although listed in the index, some information is not publicly available, e.g., CBI or other information whose disclosure is restricted by statute. Certain other information, such as copyrighted material, will be publicly available only in hard copy. Publicly available docket materials are available either electronically in http://www.regulations.gov or in hard copy at EPA Region IX, 75 Hawthorne Street, San Francisco, California. To inspect the hard copy materials, please schedule an appointment during normal business hours with the contact listed in the FOR FURTHER INFORMATION CONTACT section.

FOR FURTHER INFORMATION CONTACT:

Karina O'Connor, EPA Region IX, telephone number: [phone]; fax number: [phone]; e-mail address: [e-mail].

SUPPLEMENTARY INFORMATION:

Throughout this document, “we,” “us” and “our” refer to EPA.

Table of Contents

I. Summary of Action

II. Introduction

A. What Is the Purpose of this Proposed Rulemaking?

B. What Did the State Submit To EPA?

C. What Is a SIP and How Is it Revised From Time to Time?

D. What Is the Background of Today's Action?

E. What Are MOBILE6 And MOBILE6.2?

F. What Is the Current Status of CO Levels in Las Vegas Valley and how do the Levels Compare With the Federal Standards?

III. Review of the Las Vegas Valley 2005 CO Plan Submittal

A. What Is the Purpose and Content of Nevada's Submittal?

B. How Is EPA Evaluating This Submittal?

C. How Have Emissions of Carbon Monoxide in Las Vegas Valley Changed?

D. How Has the Attainment Demonstration Changed?

E. Are Las Vegas Valley's Motor Vehicle Emissions Budgets Approvable?

F. How Does This Action Affect Transportation Conformity?

IV. Proposed Action and Request for Public Comment

V. Statutory and Executive Order Reviews

I. Summary of Action

Under section 110(k) of the Clean Air Act (CAA or Act), EPA proposes to approve a revised attainment plan for the Las Vegas Valley carbon monoxide (CO) nonattainment area on the condition that Clark County and the State of Nevada withdraw the 2030 motor vehicle emission budget, or, in the alternative, to disapprove the plan.

This plan has been submitted to EPA by the Nevada Division of Environmental Protection (NDEP) as a revision to the Nevada state implementation plan (SIP). The revised attainment plan includes revised base year and future year emissions inventories and a revised demonstration of continued attainment of the carbon monoxide national ambient air quality standard in Las Vegas Valley through 2030 based on the most recent emissions models and planning assumptions and establishes new motor vehicle emissions budgets. The intended effect of this proposed approval action is to update the carbon monoxide motor vehicle emissions budgets in the Las Vegas area and thereby make them available for the purposes of transportation conformity, and the intended effect of this proposed disapproval action is to retain the previously-approved budgets. The currently approved attainment plan did not include 2030 budgets, therefore we do not need 2030 budgets to be able to approve the remaining budgets in the revised plan.

II. Introduction

A. What Is the Purpose of this Proposed Rulemaking?

The purpose of this proposed rulemaking is to present our evaluation and conclusions with respect to a submittal of a revision to the Nevada SIP, identified below, that includes a revised attainment plan for the Las Vegas CO nonattainment area. The revised plan includes updated emissions inventories and dispersion modeling in support of new motor vehicle emissions budgets.

B. What Did the State Submit to EPA?

Under a letter dated February 14, 2006, NDEP submitted the Carbon Monoxide State Implementation Plan Revision, Las Vegas Valley Nonattainment Area, Clark County, Nevada (October 2005) (“2005 CO plan”), to EPA as a revision to the Nevada SIP following the plan's adoption by the Clark County Board of Commissioners on October 4, 2005. Prepared by the Clark County Department of Air Quality and Environmental Management (DAQEM), the 2005 CO plan includes a revised emissions inventory, a revised modeling demonstration of continued attainment, and revised motor vehicle emissions budgets. The inventories and modeling demonstration included in the 2005 CO plan relate to analysis years 1996, 2006, 2010, 2015, 2020 and 2030. The plan allocates almost all of the estimated safety margins ^[1] in years 2006, 2010, 2015, 2020, and 2030 to the on-road motor vehicle emissions category.

Also submitted by NDEP on February 14, 2006 is a report entitled, “Supplement to the Carbon Monoxide State Implementation Plan Revision,” which was prepared by DAQEM in response to comments raised by EPA subsequent to the Clark County Board of Commissioners' adoption of the 2005 CO plan. This supplemental report presents an air quality trends analysis in further support for the plan's forecast of continued attainment through 2030 with the plan's proposed motor vehicle emissions budgets.

C. What is a SIP and How Is it Revised From Time to Time?

The Clean Air Act requires States to attain and maintain ambient air quality equal to or better than standards that provide an adequate margin of safety for public health and welfare. These ambient air quality standards are established by EPA and are known as the National Ambient Air Quality Standards (NAAQS). Carbon monoxide (CO) is one of the pollutants for which EPA has established NAAQS.

The State's plan for attaining and maintaining the NAAQS are outlined in the SIP for that state. The SIP is a planning document that, when implemented, is designed to ensure the achievement of the NAAQS. Each State currently has a SIP in place, and the Act requires that States make SIP revisions periodically as necessary to provide continued compliance with the standards. The State of Nevada's SIP is identified at title 40, part 52, subpart DD of the Code of Federal Regulations (40 CFR part 52, subpart DD).

SIPs may include, among other things, the following: (1) An inventory of emission sources; (2) statutes and regulations adopted by the State legislature and executive agencies; (3) air quality analyses that include demonstrations that adequate controls are in place to meet the NAAQS; and (4) contingency measures to be undertaken if an area fails to attain the standard or make reasonable progress toward attainment by the required date. The State must make the SIP available for public review and comment through a public hearing before it is adopted by the State and submitted to EPA by the Governor or his appointed designee. When EPA takes Federal action to approve the SIP submittal, the rules and regulations become federally enforceable.

For an area designated as nonattainment for a given NAAQS, the State first submits a plan with emissions reduction measures to bring the area into attainment. Once the area has attained the standard based on monitored air quality, the State then submits a redesignation request to attainment and a maintenance plan demonstrating that the area will continue to maintain the standard for at least 10 years after the redesignation into attainment.

D. What Is the Background of Today's Action?

Based on CO monitoring data from the mid-1970's, EPA designated Las Vegas Valley ^[2] as a CO nonattainment area under the Clean Air Act, as amended in 1977. See 43 FR 8962, 9012 (March 3, 1978). In response, Clark County and the State of Nevada adopted and implemented various air quality plans and programs, including a vehicle inspection and maintenance (I/M) program, to reduce CO levels in Las Vegas Valley, but the CO NAAQS was not attained by the then-applicable 1987 attainment date.

The Clean Air Act was significantly amended by Congress in 1990 to establish new attainment dates and planning and control requirements for areas that had failed to attain the NAAQS under the 1977 Amendments. Under the 1990 Amended Act, Las Vegas Valley was classified as a “moderate” nonattainment area for CO with a new attainment date of December 31, 1995 and subject to the specific requirements for such areas. EPA later extended the attainment date to December 31, 1996, but given monitoring data from that period showing continued CO NAAQS violations, EPA reclassified Las Vegas Valley in 1997 as a “serious” CO nonattainment area with an attainment date of December 31, 2000 and subject to the additional requirements applicable to such areas. See 62 FR 51604 (October 2, 1997).

In response to the “moderate”, and then “serious,” nonattainment classification and related CAA requirements, Clark County and the State of Nevada adopted and implemented new air quality plans and programs, including wintertime gasoline specifications for oxygen content and Reid Vapor Pressure(RVP), enhancement to the vehicle I/M program and a “serious” area attainment plan, the Carbon Monoxide State Implementation Plan, Las Vegas Valley Nonattainment Area, Clark County, Nevada (August 2000) (“2000 CO plan”). The 2000 CO plan included a base year (1996) emission inventory, future-year emissions projections, an attainment demonstration, and additional control measures, including additional wintertime gasoline specifications for sulfur and aromatics (referred to as “cleaner burning gasoline”), an alternative fuels program for government vehicles, and a transportation control measure program. The plan also established motor vehicle emissions budgets and provided modeling documentation showing that the CO standard would continue to be attained beyond the attainment deadline of 2000 through the 2020 analysis year. In 1998, we approved the wintertime gasoline specification for oxygen content (i.e. oxygenated fuel program) (64 FR 29573, June 2, 1999), and in 2004, we approved the revised vehicle I/M program, the wintertime gasoline specification for RVP, and all of the elements of the 2000 CO plan (except for the contingency provisions ^[3] , including the new control measures (e.g., cleaner burning gasoline rule), emissions inventories, attainment demonstration, and motor vehicle emissions budgets (69 FR 56351, September 21, 2004).

The 2000 CO plan established motor vehicle emission budgets for years 2000, 2010, and 2020. These budgets were developed using MOBILE5b, which was the latest EPA-approved motor vehicle emission factor model at that time. EPA officially released a new version of motor vehicle emissions model, MOBILE6, on January 29, 2002 (67 FR 4254). All SIPs and SIP revisions that are developed after that date must use the new model to estimate motor vehicle emissions. The release of MOBILE6 also began a 24-month grace period for conformity. All conformity determinations that are initiated after January 29, 2004 must use MOBILE6. As discussed in the following section of this notice, MOBILE6 has now been revised with the release of MOBILE6.2. Besides the release of updated emissions models, another circumstance that has changed since adoption of the 2000 CO plan is the change in the expected rate of population growth in Las Vegas Valley. The most recent forecasts show population growth outpacing the corresponding projections used for the 2000 CO plan.

In response to these changes, DAQEM, in consultation with the Regional Transportation Commission of Southern Nevada (RTC), undertook a comprehensive air quality planning effort to review and update the 2000 CO plan and the associated motor vehicle emission budgets to maintain consistency for future conformity findings. The planning efforts included detailed technical analyses, such as preparation of new base and future year emissions inventories and regional and hotspot dispersion modeling, and culminated in the preparation, adoption and submittal of the 2005 CO plan, which is the subject of today's proposed action.

E. What Are MOBILE6 and MOBILE6.2?

MOBILE is an EPA emissions factor model for estimating pollution from on-road motor vehicles in states except for California. MOBILE calculates emissions of volatile organic compounds (VOCs), nitrogen oxides (NO_X) and carbon monoxide (CO) from passenger cars, motorcycles, buses, and light-duty and heavy-duty trucks. The model accounts for the emission impacts of factors such as changes in vehicle emission standards, changes in vehicle populations and activity, and variation in local conditions such as temperature, humidity, fuel quality, and air quality programs.

MOBILE is used to calculate current and future inventories of motor vehicle emissions at the national and local level. These inventories are used to make decisions about air pollution policies and programs at the federal, state and local level. Inventories based on MOBILE are also used to meet the Federal Clean Air Act's SIP and transportation conformity requirements.

The MOBILE model was first developed in 1978. It has been updated many times to reflect changes in the vehicle fleet and fuels, to incorporate EPA's growing understanding of vehicle emissions, and to cover new emissions regulations and modeling needs. Although some minor updates were made in 1996 with the release of MOBILE5b, MOBILE6 was the first major revision to MOBILE since MOBILE5a was released in 1993. Released in 2002 (67 FR 4254, January 29, 2002), MOBILE6 incorporates new and improved vehicle and emissions data and a new understanding of vehicle emissions processes.

In 2004 (69 FR 28830), MOBILE6 was updated with the release of MOBILE6.2, which adds the capability to generate direct particulate matter emission factors and emission factors for particulate precursors. MOBILE6.2 also corrects some minor coding errors in MOBILE6 and incorporates some revisions to CO emission factors for cars and light-duty trucks that meet national low emission vehicle (NLEV), low emission vehicle (LEV), and Tier 2 vehicle standards. MOBILE6.2 is now the latest emission model released by EPA and should be used by all areas for SIP and conformity analyses. Further details on MOBILE models can be found at http://www.epa.gov/​otaq/​mobile6.htm.

F. What Is the Current Status of CO Levels in Las Vegas Valley and How Do the Levels Compare With the Federal Standards?

The national 8-hour CO ambient standard is attained when the highest 8-hour CO concentration of 9 parts per million (ppm) is exceeded no more than one time in a calendar year. Since the initial operation of CO monitors in Las Vegas Valley in the 1970's, exceedances of the CO standard occurred relatively frequently during the winter months, but, with the implementation of various State and local CO control measures (e.g., fuel specifications and vehicle I/M program) and also the implementation of the Federal motor vehicle control program (e.g., exhaust emission standards for new light-duty vehicles, light-duty trucks, and heavy-duty trucks), CO levels trended downward in Las Vegas Valley despite large increases in population and VMT through the 1980's and 1990's.

By the late-1990's, ambient CO conditions had improved to such an extent that exceedances were no longer recorded at any of the CO monitoring stations. The last exceedances of the 8-hour CO standard in Las Vegas Valley were recorded in 1998, and based on the record of clean data during the 1999-2000 period, we determined that Las Vegas Valley attained the CO NAAQS by the applicable “serious” area attainment date of December 31, 2000. See 70 FR 31353 (June 1, 2005). Since 2000, and through year 2005, the highest 8-hour CO concentration measured by the CO monitoring network in Las Vegas Valley was 7 ppm (measured at the Sunrise Acres monitoring site), which is well below the CO standard of 9 ppm. Thus, after attaining the CO standard in 2000, Las Vegas Valley has continued to attain the standard up to the present time.

III. Review of Las Vegas Valley 2005 CO Plan Submittal

A. What Is the Purpose and Content of Nevada's Submittal?

DAQEM's purpose in preparing the 2005 CO plan is to update the CO motor vehicle emissions budgets from the 2000 CO plan for use in transportation conformity determinations.

The 2005 CO plan generally follows the outline of the 2000 CO plan and provides expanded discussion of the plan elements for which new information is available or for which circumstances have changed since adoption of the previous plan. First, the 2005 CO plan discusses the changes to the CO monitoring network and ambient CO level trends since 2000, as well as the results of the CO saturation study, which was completed in January 2002. See chapter 2 and appendix B of the 2005 CO plan. The 2005 CO plan then provides a comprehensive revision to the base year (1996) emissions inventory and future year emissions projections reflecting updated underlying data, such as population and VMT forecasts, and also updated methods, such as MOBILE6.2 and NONROAD2004 for on-road and nonroad sources, respectively. The 2005 CO plan summarizes the control measures that have contributed to attainment of the CO NAAQS in Las Vegas Valley and that are being counted on for continued attainment of the standard but neither repeals nor modifies any such measure. The remainder of the 2005 CO plan provides updated dispersion modeling results reflecting the updated emissions estimates and extends the showing of continued attainment from 2020 (as provided for in the 2000 CO plan) to 2030, and supporting the establishment of new motor vehicle emissions budgets.

Included with the 2005 CO plan are technical appendices which include a technical support document for the emission inventory and dispersion modeling, the carbon monoxide monitoring saturation study, a study on the effectiveness of the area's vehicle I/M program, airport modeling studies, a support letter from the area's Metropolitan Planning Organization (i.e., the RTC) and documentation of the public review process for the plan.

Enclosed with the 2005 CO plan, NDEP also submitted a report entitled, “Supplement to the Carbon Monoxide State Implementation Plan Revision,” which was prepared by DAQEM in response to comments raised by EPA after adoption of the 2005 CO plan on October 4, 2005. The supplemental report presents an air quality trends analysis in further support for the plan's forecast of continued attainment through 2030 with the plan's proposed motor vehicle emissions budgets.

B. How Is EPA Evaluating This Submittal?

Section 110(l) of the Clean Air Act requires SIP revisions to be subject to reasonable notice and public hearing prior to adoption by the applicable State or local agency and submittal to EPA. In this instance, the Clark County Board of Commissioners adopted the 2005 CO plan on October 4, 2005, following a 30-day comment period and a public hearing, properly noticed in a newspaper of general circulation in Las Vegas Valley. NDEP, the Governor's designee for SIP submittals in Nevada, then submitted the 2005 CO plan to EPA as a revision to the Nevada SIP on February 14, 2006. Thus, we find that the procedural requirements for SIP submittals under CAA section 110(l) have been satisfied.

Section 110(l) also prohibits EPA from approving any SIP revision that would interfere with any applicable requirement concerning attainment and reasonable further progress or any other applicable requirement of the Act. In this instance, the SIP revision involves an update to emissions inventories, dispersion modeling, and motor vehicle emissions budgets previously approved by EPA.

We review emissions inventories to ensure they are comprehensive and accurate and are based on the latest planning assumptions and emissions models. We review modeling demonstrations to ensure they are consistent with the underlying emissions estimates and reflect reasonable methods and assumptions. We review motor vehicle emissions budgets to ensure that the budgets are clearly related to the emissions inventory and the control measures in the applicable plan and that the budgets, when considered together with all other emissions sources, are consistent with applicable requirements for reasonable further progress, attainment, or maintenance.

As described in the following sections of this notice, we conclude that, for the base year (1996) through 2020, the models and methods used to revise the emissions inventories and dispersion modeling are acceptable and that the motor vehicle emissions budgets are clearly related to the revised inventories and EPA-approved CO control measures for Las Vegas Valley and that the budgets are consistent with continued attainment of the CO NAAQS in Las Vegas Valley through 2030 and thus approvable under CAA section 110(l). However, the 2005 CO plan fails to demonstrate continued attainment in the horizon year of 2030 because the micro-scale modeling for Clark County airports extends only through 2020. Based on these conclusions, we are proposing to approve the Las Vegas Valley 2005 CO plan and related motor vehicle emissions budgets as a revision to the Nevada SIP on the condition that Clark County and the State of Nevada withdraw the 2030 motor vehicle emissions budgets, or to disapprove the plan in the alternative if no such withdrawal is made.

C. How Have Emissions of Carbon Monoxide in Las Vegas Valley Changed?

The emissions inventory is a list, by source, of the air contaminants directly emitted into the air within a given area. The data in the emissions inventory are based on calculations and are developed using emission factors, which convert source activity levels into an estimate of emissions contributions for those sources. For the 2000 CO plan, the Clark County Department of Air Quality, which performed the air quality planning functions now performed by DAQEM, developed a base case emissions inventory for the base year 1996 and then projected inventories for years 2000, 2010 and 2020. The general categories of CO sources included on-road motor vehicles, nonroad mobile sources, and stationary area and point sources, and the emissions estimates corresponded to an average day during the peak CO (i.e., winter) season.^[4]

For the 2005 CO plan, DAQEM developed updated estimates for the 1996 base year and for years 2010 and 2020 but also developed new estimates of emissions for certain interim years, 2006 and 2015, not previously quantified, and developed an emissions inventory for a new horizon year, 2030. The 2005 CO plan inventories cover the same basic source categories but adjust the emissions estimates to correspond to the second Sunday and second Monday in December consistent with the December 8-9, 1996 episode used for dispersion modeling purposes in the plan. The most significant changes in the emission inventories for the 2005 CO plan are in the on-road motor vehicle and nonroad mobile source categories.

The 2005 CO plan is based on the latest available forecasts of population. These updated forecasts reflect a higher rate of growth in population in Las Vegas Valley than had been assumed for the 2000 CO plan. For example, for years 2010 and 2020, the population forecasts used in the 2005 CO plan are 25 to 30% higher than the corresponding forecasts used in the 2000 CO plan.

The RTC used the updated population forecasts to provide updated travel demand forecasts for the purposes of emissions inventory preparation and dispersion modeling for the 2005 CO plan. To develop the travel demand forecasts for future years, RTC used the TransCAD travel demand model, a model that has replaced TRANPLAN, the older model that had been used for the 2000 CO plan. For the base year, the original TRANPLAN-derived data was used, but TransCAD-derived data was used for all future years. TransCAD incorporates a number of refinements as compared to TRANPLAN including more accurate temporal and spatial allocation of vehicle miles traveled (VMT). Further details regarding VMT processing are provided in chapter 2 of DAQEM's Technical Support Document, which is included as appendix A of the 2005 CO plan.

RTC's updated travel demand forecasts provided the basis for updated motor vehicle emissions estimates through application of MOBILE6.2 emissions factors. As noted above, MOBILE6.2 represents a significant revision of the previous model, MOBILE5b, which was used for the 2000 CO plan, is the latest EPA emissions factor model for estimating pollution from on-road motor vehicles, and incorporates the effects of national vehicle control programs and, with the appropriate input controls, the effects of local control programs such as the State's alternate “low” enhanced vehicle I/M program and the wintertime gasoline specifications for RVP, sulfur and oxygen.

The MOBILE6.2-derived emissions factors for the 2005 CO plan reflect an assumed vehicle I/M effectiveness of 100% instead of 50% as assumed for the 2000 CO plan. To provide support for this change, DAQEM commissioned a study of the effectiveness of the decentralized (i.e., privately owned and operated as opposed to state-run or “centralized”) network of I/M testing stations in Las Vegas Valley that concluded that the “test-and-repair” stations are equally as effective as “test-only” stations at reducing emissions. We note that Nevada I/M regulations allow “test-only ^[5] ” stations to perform certain types of automotive services (e.g., change of oil; and replacement of oil, air, or fuel filters) that “test-only” stations as defined in EPA's I/M regulations are not allowed to perform. See 40 CFR 51.353(a).

However, we also note that, based on information contained in the DAQEM study cited above, only 25% of the “test-only” stations in Las Vegas Valley actually offer these limited services and 75% only perform emissions testing. Thus, the presumptive equivalency (to centralized test-only stations), i.e., assumption of 100% I/M effectiveness, allowed under 40 CFR 51.353(a) is not unreasonable with respect to the “test-only” stations in Las Vegas Valley. Furthermore, given the results of the DAQEM study cited above that the “test-and-repair” stations are equally as effective as the “test-only” stations, the assumption of 100% effectiveness for the overall I/M program in Las Vegas Valley is also not unreasonable. DAQEM included a copy of the study of I/M effectiveness as appendix C of the 2005 CO plan.

With respect to nonroad mobile sources, the 2005 CO plan incorporates updated information concerning airport and railroad operations and activities, and reflects use of an emissions model (NONROAD) ^[6] for the other types of nonroad sources. NONROAD was not available at the time when the 2000 CO plan was being prepared and represents a significant refinement in the method for estimating emissions from nonroad sources as compared to the 1991 EPA study that was used for the 2000 CO plan. Clark County land use/land cover data were used as inputs to the NONROAD model to estimate revised emissions for these categories in both the base and future year inventories.

For the 2005 CO plan, stationary area and point sources are largely consistent with the corresponding emissions estimates for these source categories in the 2000 CO plan except for seven specific point sources for which the future-year projections in the 2005 CO plan incorporate potentials to emit (rather than projected actual emissions) plus a 70 tons per year additional buffer.

Tables 1 and 2 summarize the emissions estimates contained in the 2005 CO plan. Table 1 represents the second Sunday in December and table 2 represents the second Monday in December. The inventories were prepared for these particular conditions because the dispersion modeling demonstration of continued attainment is predicated on the December 8-9, 1996 episode.

As shown in these two tables, on-road motor vehicles continue to represent the most significant source category for CO emissions in Las Vegas Valley, but the contribution from on-road sources is expected to decrease from roughly 70 to 75% of the total CO inventory under existing conditions to 65 to 70% by 2030. Nonroad mobile source account for 20 to 25% of the total inventory under existing conditions but the relative contribution from this source category is expected to increase to 25 to 30% by 2030. The 2005 CO plan estimates that stationary area and point sources account for 5 to 10% of the CO inventory both now and in the future.

Table 1.—Las Vegas Valley CO Nonattainment Area Emissions, December Sunday (Tons) by Source Category

Source category	1996	2006	2010	2015	2020	2030
On-road motor vehicle	329	275	287	276	273	296
Nonroad mobile	102	89	99	109	121	143
Stationary area	9	13	14	16	18	22
Point	3	16	16	16	16	16
Total	445	392	415	418	428	477

Table 2.—Las Vegas Valley CO Nonattainment Area Emissions, December Monday (Tons) by Source Category

Source category	1996	2006	2010	2015	2020	2030
On-road motor vehicle	511	441	464	451	447	486
Nonroad mobile	138	111	123	136	150	178
Stationary area	10	13	15	17	19	23
Point	3	16	16	16	16	16
Total	662	581	617	619	631	702
Source: Derived from 2005 CO plan, Table 3-12.

Based on our review of the documentation provided in the 2005 CO plan as summarized above, we find that the revised base year and future year CO emissions inventories reflect the latest planning assumptions and emissions models and provide a comprehensive and accurate assessment of CO emissions in Las Vegas Valley for the various impact analysis years. Furthermore, we find that the revised inventories provide a reasonable basis upon which to update the dispersion modeling analysis, as discussed in the following section of this notice.

D. How Has the Attainment Demonstration Changed?

The 2000 CO plan's attainment demonstration included both an areawide and a hot-spot modeling analysis at heavily-traveled intersections, and the revised demonstration in the 2005 CO plan also includes both the regional and micro-scale modeling analyses. As in the previous attainment demonstration, areawide analysis was conducted using the Urban Airshed Model (UAM), according to our “Guidance for Application of Urban Areawide Models for CO Attainment Demonstrations” (1992).

The 2000 CO plan provided a modeling demonstration of attainment from the nonattainment conditions in 1996 for the applicable attainment date of 2000 through implementation of new control measures. The 2000 CO plan also demonstrated continued attainment beyond 2000 by developing CO level estimates for impact analysis years 2010 and 2020. Since Las Vegas Valley has already attained the CO NAAQS, the 2005 CO plan does not need to demonstrate attainment per se but must demonstrate continued attainment of the standard, and it does so for the following impact analysis years: 2006, 2010, 2015, 2020 and 2030.

For the 2005 CO plan, the UAM analysis uses the same December 8-9, 1996 episode as in the previous demonstration, but with the revised emission inventory information described in the previous section of this notice. Overall, the spatial pattern of predicted 8-hour maximum CO agrees with the previous modeling in the 2000 CO plan and with the distribution of observed CO for this period. Unlike the modeling documented in the 2000 CO plan, no external scaling was needed for the UAM results in the new modeling runs. The maximum CO concentration predicted for the base case 1996 episode was 11.4 ppm which is close to the 11.2 ppm predicted in the 2000 CO plan, along Las Vegas Boulevard near the intersection with Spring Mountain Road. Model performance for the base year UAM simulation is within our acceptable range of accuracy: +19 percent for the unpaired peak prediction, -15% percent for the paired peak prediction, and 1 hour for the timing error. See the 2005 CO plan, page 5-2. Once the model performance was verified, the 1996 base case emission inventory was projected into the future and then these projected emission inventories were used with the 1996 meteorological conditions to simulate the impact of emission changes in the future.

The simulations showed that emissions in future years with controls would continue to support peak concentrations well below the 9 ppm 8-hour CO standard. Concentrations for the 8-hour average are shown for the maximum concentration predicted over the modeling domain. The predicted regional maximum 8-hour average CO concentration is 8.0 ppm in the year 2030, assuming continued implementation of all previously adopted control measures (e.g., the vehicle I/M program and the wintertime gasoline specifications). Results for all future years modeled are shown in table 3.

Table 3.—UAM Results for Future Year Scenarios

Year	Concentrations (ppm)
2006	7.37
2010	7.17
2015	6.47
2020	6.74
2030	7.96
Source: 2005 CO plan, Table 6-3.

The UAM analysis thus shows attainment with a margin of safety based on continued implementation of fully adopted control measures. However, an additional model, CAL3QHC must be used to determine the maximum CO levels in the area. CAL3QHC is needed to predict the micro-scale impacts of vehicles operating at congested intersections. Vehicles operating within congested conditions spend more time in idle modes that can contribute to high levels of CO near the roadways. As in the 2000 CO plan, micro-scale modeling was completed for three intersections (1) Charleston Blvd./Eastern Avenue, (2) Charleston Blvd./Fremont Street and (3) Eastern Avenue/Fremont Street. These three intersections comprise the “5 points” area, which is near the Sunrise Acres CO monitoring station. For years 2006, 2010, 2015, 2020 and 2030, traffic data from the roadways were combined with emission factors from MOBILE6.2 and meteorological data to predict local hotspot concentrations. These hourly results from the micro-scale model were then combined with hourly concentrations from the background UAM grid cell to compute maximum running 8-hour concentrations. The combined results of the CAL3QHC and UAM results are shown in Table 4 below.

Table 4.—Intersection Maximum Predicted Combined 8-Hour CO Levels

[ppm]

Intersection	2006	2010	2015	2020	2030
Charleston/Eastern	6.14	5.61	4.97	4.67	4.83
Charleston/Fremont	5.09	4.81	4.31	4.07	4.20
Eastern/Fremont	5.66	5.32	4.76	4.48	4.58
Source: 2005 CO plan, Table 6-5.

As in the 2000 CO plan, in addition to roadway intersections modeling, the 2005 CO plan includes an analysis of CO levels at airports in Las Vegas Valley. To model the impact of airport sources, the Emissions and Dispersion Modeling System (EDMS) model was again used. This model was developed for evaluating the specific emission sources typically located at airports. The hotspot results from EDMS must be combined with the results of the UAM analysis to predict the concentrations at receptors around the airports. The 2005 CO plan presents the results of the combined UAM and EDMS models for the all future years in table 4-5 of appendix A. No values were modeled above the 9.0 ppm CO standard at any publicly accessible receptor location. The peak combined concentration at McCarran International Airport for future years is 8.45 ppm for 2020. We note however that the micro-scale analysis for the airports' environs does not extend beyond year 2020, and thus that analysis demonstrates continued attainment through 2020, but not in year 2030.

Based on our review of the documentation provided in the 2005 CO plan as summarized above, we find that the revised modeling results are consistent with the underlying emission estimates and reflect reasonable methods and assumptions. Further, we find that the revised modeling results demonstrate continued attainment of the CO NAAQS in Las Vegas Valley through 2020 but that the plan fails to demonstrate continued attainment in 2030 because of the lack of micro-scale analysis in the environs of the Clark County airports in that year.

E. Are Las Vegas Valley's Motor Vehicle Emissions Budgets Approvable?

The CO motor vehicle emissions budgets from the EPA-approved 2000 CO plan are 310.2, 329.5, and 457.4 tons of CO per average (December) day for years 2000, 2010, and 2020, respectively. Conformity determinations must be made using the latest planning assumptions and emissions models. In light of updated population forecasts for Las Vegas Valley that show higher levels of growth than expected in the 2000 CO plan as well as the significant differences between the MOBILE6.2 and MOBILE5b emissions model, DAQEM, in consultation with the RTC, developed the 2005 CO plan to replace the budgets from the 2000 CO plan, which are based on outdated population forecasts and MOBILE5b, with new budgets reflecting the latest planning assumptions and MOBILE6.2 and thereby provide for consistency between the CO attainment planning in Las Vegas Valley and future conformity determinations.

During the course of preparing the 2005 CO plan, DAQEM recognized, from the revised dispersion modeling analysis discussed above, the possibility that the reduction in CO emissions factors over time due to the implementation of new Federal motor vehicle standards, the area's I/M program and wintertime gasoline specifications, would offset the higher level of expected population growth and keep the area in attainment of the CO NAAQS with some margin of safety. Therefore, as part of this SIP revision, DAQEM explored scaling up emissions to determine how much more the area's emissions estimate could grow while still keeping the area in attainment.

DAQEM conducted several sensitivity analyses to determine the impacts of scaling up emissions in the modeling domain. In the first test runs, the modeling domain was split into a central urban core and an outer domain. Total emissions for all sources were doubled in the outer domain. The resulting UAM predicted concentrations for all future years modeled are shown in table 5. A comparison of the results in table 5 with the results in table 3 shows that CO concentrations only increase slightly with the doubling of outer domain CO emissions.

Table 5.—UAM Results for Future Year Scenarios With Doubled Outer Domain Emissions

Year	Concentrations (ppm)
2006	7.41
2010	7.24
2015	6.54
2020	6.80
2030	8.03
Source: 2005 CO plan, Table 6-3.

In the next sensitivity analysis, on-road motor vehicle emissions were scaled up from the base case over the entire modeling domain until the modeled UAM concentrations reached 8.9 ppm. Then, motor vehicle emissions in the outer domain were increased an additional 70%. The final revised emissions for this sensitivity analysis are shown in table 6.^[7]

Table 6.—Base and Scaled On-Road Emissions For the Final Sensitivity Analysis

[Tons per December weekday]

Year	Base			Scaled
	Urban	Outer	Total	Urban	Outer	Total
2006	345	96	441	427	196	623
2010	347	117	464	438	252	690
2015	320	131	451	453	315	768
2020	309	138	447	463	354	817
2030	318	167	485	464	417	881
Source: Derived from 2005 CO plan, Table 6-4.

The final scaled revised emissions were then input into UAM to determine the resulting peak UAM concentrations. Then, to assess the micro-scale impacts of increased numbers of vehicles operating at congested intersections, the UAM results in the appropriate grid cells were combined with additional CAL3QHC modeling of increased traffic. Those combined results, and the maximum modeled UAM CO concentrations are presented in table 7.

Increased UAM concentrations in grid cells around the airports were also examined with the combined EDMS modeling. Again, no values were modeled above the 9.0 ppm standard in any publicly accessible receptor locations. The peak combined concentration at McCarran International Airport for future years is 8.98 ppm for 2020. However, as noted in the previous section of this notice, the micro-scale analysis for the airports' environs does not extend beyond 2020.

Table 7.—UAM and CAL3QHC Maximum Predicted 8-hour CO Levels

[ppm]

Modeled cell or intersection	2006	2010	2015	2020	2030
Peak UAM Grid Cell (Domain-wide):	8.96	8.98	8.98	8.97	8.97
Peak Combined UAM (for applicable grid cell) & CAL3QHC:
Charleston/Eastern	7.45	6.97	6.85	6.78	6.84
Charleston/Fremont	6.17	5.99	5.93	5.88	5.91
Eastern/Fremont	6.85	6.61	6.54	6.48	6.45
Source: 2005 CO plan, Appendix A: Tables 5-5 and Table 5-6.

Since the maximum modeled concentrations for this final sensitivity test resulted in concentrations close to the standard, to account for modeling uncertainty, DAQEM also completed an air quality trend analysis for the ten year period from 1996 to 2005 to provide additional support for the modeling demonstration. DAQEM prepared this additional analysis in response to EPA comments after adoption of the 2005 CO plan by the Clark County Board of Commissioners, and NDEP enclosed this analysis, entitled “Supplement to the Carbon Monoxide State Implementation Plan Revision,” with the February 14, 2006 SIP revision containing the 2005 CO plan.

DAQEM conducted the trend analysis based on meteorological and monitoring data collected at the Sunrise monitoring station for each day from November 1st though January 31st (CO season), because the 8-hour maximum CO concentrations are typically recorded at this site. After normalization, linear regression analysis and a multivariate linear regression analysis was performed to predict trends at the site. The results of the analysis show a continued downward trend of maximum CO concentrations for future years, independent of meteorology, and suggest that event if CO emissions were increased by 80%, that future emissions would still be below 9.0 ppm, i.e., in attainment with the CO NAAQS.

The 2005 CO plan establishes the emissions shown in the final scaled on-road motor vehicle emissions table (see the far-right column in table 6, above) as the new motor vehicle emissions budgets for Las Vegas Valley. The budgets are also summarized below in table 8. These budgets reflect allocations of the safety margin to the motor vehicle source category varying from approximately 180 tons per year in 2006 to nearly 400 tons per day in 2030. Based on the scaled modeling results in the 2005 CO plan and the supplemental trend analysis prepared by DAQEM, we find that, with the exception of the 2030 budget, replacement of the current budgets with the motor vehicle emissions budgets in the 2005 CO plan would not interfere with continued attainment of the CO NAAQS in Las Vegas Valley and are therefore approvable. However, we cannot find that establishment of the 2030 budget would not interfere with continued attainment because the micro-scale analysis in the environs of the County airports does not extend to that year.

Table 8.—On-Road Motor Vehicle Emissions Budgets

[Tons per December weekday]

Year	Budget
2006	623
2010	690
2015	768
2020	817
2030	881
Source: 2005 CO plan, Table 7-1.

F. How Does This Action Affect Transportation Conformity?

Under section 176(c) of the Act, transportation plans, programs, and projects in nonattainment or maintenance areas that are funded or approved under 23 U.S.C or Federal Transit Laws, must conform to the applicable SIPs. In short, a transportation plan is deemed to conform to the applicable SIP if the emissions resulting from implementation of that transportation plan are less than or equal to the motor vehicle emissions budget established in the SIP for the attainment year and other analysis years. If the condition is met on our proposed approval (i.e., Clark County and the State of Nevada withdraw the 2030 budget) and our action is otherwise finalized as proposed here today, the CO motor vehicle emissions budgets shown in table 8 above (minus the 2030 budget) must be used by U.S. Department of Transportation and the Regional Transportation Commission of Southern Nevada for transportation conformity determinations made after the effective date of our final rule.

IV. Proposed Action and Request for Public Comment

Pursuant to section 110(k) of the Act, we propose to approve the Carbon Monoxide State Implementation Plan Revision, Las Vegas Valley Nonattainment Area, Clark County, Nevada (October 2005), which was adopted by the Clark County Board of Commissioners on October 4, 2005 and submitted to EPA by NDEP on February 14, 2006, as a revision to the Nevada SIP on the condition that Clark County and the State of Nevada withdraw the 2030 motor vehicle emission budget, or, in the alternative, we propose to disapprove the plan. The plan disapproval will not trigger any Clean Air Act 179(b) sanctions.

Our proposed approval is based on our evaluation of the plan submittal and determination that the plan's revised base year and projected emission inventories and modeling demonstration of continued attainment of the CO standard through 2020 reflect acceptable methods and the most recent models and planning assumptions. Our proposed disapproval is based on our finding that the plan does not demonstrate continued attainment in year 2030 because it lacks micro-scale modeling analysis for the environs of the County's airports in that year.

Furthermore, we find that, with the exception of the 2030 budget, the new motor vehicle emissions budgets established in the plan and reflecting scaled inventories are also consistent with continued attainment of the CO NAAQS in Las Vegas Valley. Thus, we propose to approve the following motor vehicle emissions budgets from the 2005 CO plan as meeting the purposes of section 176(c)(1) and the transportation conformity rule at 40 CFR part 93, subpart A contingent upon the withdrawal of the 2030 budget by Clark County and the State of Nevada, and to disapprove the submitted budgets in the 2005 CO plan, in the alternative, if no such withdrawal is made:

CO Motor Vehicle Emissions Budget

[December weekday]

Year	Tons per day
2006	623
2010	690
2015	768
2020	817

Our action in approving the submitted plan revision and related motor vehicle emissions budgets, if the county and state withdraw the 2030 budget and if this action is otherwise finalized as proposed, would have the effect of replacing the existing CO motor vehicle emissions budgets from the Las Vegas Valley 2000 CO plan for the purposes of transportation conformity. EPA is soliciting public comment on the issues discussed in this document. These comments will be considered before taking final action.

V. Statutory and Executive Order Reviews

Under Executive Order 12866 (58 FR 51735, October 4, 1993), this proposed action is not a “significant regulatory action” and therefore is not subject to review by the Office of Management and Budget. For this reason, this proposed action is also not subject to Executive Order 13211, “Actions Concerning Regulations That Significantly Affect Energy Supply, Distribution, or Use” (66 FR 28355, May 22, 2001). This proposed action merely approves an air quality plan as meeting Federal requirements or disapproves the plan in the alternative and imposes no additional requirements beyond those imposed by state law. Accordingly, the Administrator certifies that this proposed rule will not have a significant economic impact on a substantial number of small entities under the Regulatory Flexibility Act (5 U.S.C. 601 et seq.). Because this proposed rule approves or disapproves in the alternative pre-existing requirements under state law and does not impose any additional enforceable duty beyond that required by state law, it does not contain any unfunded mandate or significantly or uniquely affect small governments, as described in the Unfunded Mandates Reform Act of 1995 (Pub. L. 104-4).

This proposed rule also does not have tribal implications because it will not have a substantial direct effect on one or more Indian tribes, on the relationship between the Federal Government and Indian tribes, or on the distribution of power and responsibilities between the Federal Government and Indian tribes, as specified by Executive Order 13175 (65 FR 67249, November 9, 2000). This proposed action also does not have Federalism implications because it does not have substantial direct effects on the States, on the relationship between the national government and the States, or on the distribution of power and responsibilities among the various levels of government, as specified in Executive Order 13132 (64 FR 43255, August 10, 1999). This proposed action merely approves a state plan implementing a Federal standard or disapproves the plan in the alternative, and does not alter the relationship or the distribution of power and responsibilities established in the Clean Air Act. This proposed rule also is not subject to Executive Order 13045, “Protection of Children from Environmental Health Risks and Safety Risks” (62 FR 19885, April 23, 1997), because it is not economically significant.

In reviewing SIP submissions, EPA's role is to approve state choices, provided that they meet the criteria of the Clean Air Act. In this context, in the absence of a prior existing requirement for the State to use voluntary consensus standards (VCS), EPA has no authority to disapprove a SIP submission for failure to use VCS. It would thus be inconsistent with applicable law for EPA, when it reviews a SIP submission, to use VCS in place of a SIP submission that otherwise satisfies the provisions of the Clean Air Act. Thus, the requirements of section 12(d) of the National Technology Transfer and Advancement Act of 1995 (15 U.S.C. 272 note) do not apply. This proposed rule does not impose an information collection burden under the provisions of the Paperwork Reduction Act of 1995 (44 U.S.C. 3501 et seq.).

List of Subjects in 40 CFR Part 52

• Environmental protection
• Air pollution control
• Carbon monoxide
• Intergovernmental relations
• Reporting and recordkeeping requirements

Dated: May 1, 2006.

Wayne Nastri,

Regional Administrator, Region IX.

Footnotes

1.  The term “safety margin” refers to the amount by which the total projected emissions from all sources of a given pollutant are less than the total emissions that would satisfy the applicable requirement for reasonable further progress, attainment or maintenance. See 40 CFR 93.101. The 2005 CO plan also allocates a small portion of the safety margins to certain point sources.

2.  The boundaries of the Las Vegas Valley CO nonattainment area are defined by reference to State hydrographic area #212, which covers the central portion of Clark County. See 40 CFR 81.329.

3.  Note that the contingency measure requirement was removed when EPA made a finding of attainment in June 2005 (See 70 FR 31353).

4.  That is, except for on-road motor vehicles, which reflect average daily conditions during the month of December.

5.  Vehicles are tested annually in a decentralized network that employs stations licensed as either test-only or test-and-repair.

6.  NONROAD is EPA's model for estimating emissions from nonroad vehicles such as construction equipment, lawn and garden equipment and recreational equipment. For the 2005 CO plan, DAQEM used the latest version of NONROAD (NONROAD2004) available at the time of plan preparation. NONROAD2004 has since been superseded by NONROAD2005, which is the final version of NONROAD. The previous versions, including NONROAD2004, were draft versions, but nonetheless represented the best method for calculating emissions from nonroad mobile sources, excluding commercial marine, locomotive, and aircraft, at the time of their release.

7.  Note that DAQEM has not submitted, and EPA is not acting on, sub-area motor vehicle emission budgets for the Las Vegas area. The modeling domain was split into urban and outer areas so that DAQEM could examine the sensitivity of the model to increases in emissions in the outer areas. For transportation conformity purposes, we are only acting on the total motor vehicle emissions budgets from both areas combined together.