Federal Register / Vol. 53, No. 163 / Tuesday, August 23, 1988 / Proposed Rules

authority inthe Federal Aviation Act of 1958, as amended (49U.S.C. 1301, et seq.),which statute is construed to preempt state law regulating the same subject. Thus, in accordance with Executive Order 12612, it is determined that such regulations do nothave federalism implications warranting the preparation ofa Federalism Assessment.

For these reasons, theFAA has determined that this document (1) involves a proposed regulation which is not majorunderExecutive Order 12291 and (2) is not a significant rule pursuant to theDepartment ofTransportation Regulatory Policies and Procedures (44 FR 11034; February 26, 1979); and it is further certified under the criteria ofthe Regulatory Flexibility Act that this proposed rule, ifpromulgated, willnot have a significant economic impact, positive or negative, on a substantial number ofsmall entities because few,if any, Model 727 airplanes are operated by small entities. A copy of a draft regulatory evaluation prepared for this action is contained in the regulatory docket.
Listof Subjects: 14 CFR Part 39

Aviation safety, Aircraft.
The Proposed Amendment

Accordingly, pursuant to the authority delegated to me by the Administrator, the Federal Aviation Administration proposes to amend Section 39.13 ofPart 39 oftheFederal Aviation Regulations (14 CFR 39.13) as follows:

PART 39--[AMENDED]

1. The authority citation for Part39 continues to read as follows:

Authority: 49 U.S.C. 1354(a), 1421 and 1423; 49 U.S.C. 106(g) (RevisedPub. L 97-449, January 12,1983); and 14 CFR 11.89.

2.By adding the following new airworthiness directive: Boeing: Applies to allModel 727series airplanes listedin Boeing Service Bulletin 727-53-149, Revision 2, dated March 20,1981, certificated in any category. Compliance required as indicated, unless previously accomplished.
To detectcracking ofthe mainlanding gear (MLG) wheel wellpressure floor adjacent to body stations (BS) 880,890,930. and 940, accomplish the following:

A. Prior tothe accumulation of30,000 flights orwithin thenext 2.500 flights, whichever occurs later,andthereafter at intervals not to exceed 4,000 flights, perform

a close visual, eddy current, ordye penetrant inspection forcracks in thepressure floor,in accordance with Boeing ServiceBulletin 727- 53-149,Revision 2, dated March 20,1981. B.Ifcracks are detected that do not exceed the limits listed inTable 11 in Section III of Boeing Service Bulletin 727-53-149, Revision 2,dated March 20,1981, prior to further flight, repair in accordance with the interimrepair described in paragraph C.ofSection I, or the permanent repair described in paragraph D. ofSection IIIofthe servicebulletin. The interim repair mustbereplaced within 600 flights with the permanent repair.

C.If cracks are found that exceed the limits listed inTable II, ofSection IIIofBoeing Service Bulletin727-53-149, Revision 2, dated March 20, 1981, prior to further flight, accomplish the permanent repair described in paragraph D. ofSection III ofthe service bulletin prior tofurther flight. Arepair accomplished usingblind fasteners mustbe reinspected at intervals not to exceed 2,000 flights until the blind fasteners are replaced with the fasteners specified inparagraph 4.of Section ImI ofthe service bulletin. D. Incorporation ofthe repairs in accordance with paragraph B. or C., above, terminates the repetitive inspection requirements ofparagraph A., above, forthat

area. Incorporation ofthe preventative modification in paragraph E. ofSection III of Boeing Service Bulletin 727-53-149, Revision 2, dated March 20, 1981, terminates the repetitive inspection requirement of paragraph A., above.

E. An alternate means ofcompliance or adjustment ofthe compliance time,which provides an acceptable level ofsafety,may be usedwhen approved by the Manager, Seattle Transport Airplane Office, FAA, Northwest Mountain Region.

Note.-The request shouldbe forwarded through an FAA Principal Maintenance Inspector (PMI), who may add any comments and then senditto theManager, Seattle Transport Airplane Office.

F. Special flightpermits maybe issuedin accordance with FAR21.197 and21.199 to operate airplanes to a base in order to complywith the requirements ofthis AD.

All persons affected by this directive who have not already received the appropriate service documents from the manufacturer may obtain copies upon request to Boeing Commercial Airplanes, P.O. Box 3707, Seattle, Washington 98124.These documents
may be examined at the FAA, NorthwestMountain Region, 17900 Pacific Highway South, Seattle, Washington, or Seattle Transport Airplane Office, FAA. Northwest Mountain Region, 9010 East Marginal Way South,Seattle, Washington.

Issued inWashington, DC, on August 16, 1988. Thomas B.McSweeny, ActingDirector, Officeof Airworthiness. [FR Doc. 68-19024Filed 8-22-88; 8:45am]

BILLING CODE 4910-1". ENVIRONMENTAL PROTECTION
AGENCY

40CFR Ch. I

(AD-FRL-3433-5; Docket No. A-88-041
Conference on AirQuality Modeling

AGENCY: U.S. Environmental Protection Agency (EPA).

ACTION: Notice ofconference.

SUMMARY: The EPA announces the Fourth Conference on Air Quality Modeling. Such a conference is required by section 320 of the Clean Air Act (CAA) to be held every 3 years. The
purpose ofthe fourth conference is to advise the public on new modeling techniques and to solicit comments to guideEPA's consideration of any rulemaking needed to revise the "Guideline onAir Quality Models (Revised)", EPA-450/2-78-027R (1986) and Supplement A (1987). A more detailed discussion ofthese new modeling techniques will be given by EPA during the conference. DATES: The fourth conference willbe
held on October 12 and 13, 1988, from 9:00 a.m. to 5:00 p.m. Requests to speak

at the conference must be submitted to the individuals listed below by October 3, 1988. All written comments must be submitted by December 15, 1988.
ADDRESSES: Conference: The conference will be held in the Thomas Jefferson Auditorium, South Agriculture Building, 14th Street and Independence Avenue, SW., Washington, DC.

Comments: Written statements or comments not presented at the conference should be submitted (in duplicate ifpossible) to: Central Docket Section (SouthConference Center, Room 4), Attention: Docket A-68-04, U.S. Environmental Protection Agency, 401 M Street, SW., Washington, DC 20460.
Documents referenced in this notice as well as comments received may also be inspected at this address. A reasonable fee may be charged for copying. This is

a new docket established for the conference and for consideration ofany further revision ofthe "Guideline on Air Quality Models (Revised)" and Supplement A. Priormaterial relevant to the development ofthe modeling guideline and Supplement A may be found in Docket A-80-46.
FOR FURTHER INFORMATION CONTACT. Joseph A. Tikvart. Chief,Source Receptor Analysis Branch (MD-14),
Office ofAir Quality Planning and Standards, U.S. Environmental Protection Agency, Research Triangle Park, North Carolina 27711; telephone I 

### 32M81Federal Register / Vol. 53, No. 163 / Tuesday, August 23, 1988 / Proposed Rules

(919) 541-5562 or Jawad S. Touma, telephone (919) 541-5381.
SUPPLEMENTARY INFORMATION:
Background

Section 320 ofthe CAA states that a conference on air quality modeling is to be held every 3 years to address appropriate air quality modeling
necessary for carrying out prevention of significant deterioration (PSD) requirements, thereby fostering the standardization ofair quality modeling practices. Such models are also used for evaluating State implementation plans forexisting sources, making new source reviews, and otherwise estimating

source receptor relationships. The first conference, held in December 1977, addressed EPA's proposed modeling guideline. The result was the "Guideline

on Air Quality Models" (EPA-450/2-78- 027) which provides guidance on the selection and application of air quality models. The second conference in August 1981 was an open forum to address model accuracy and the incorporation ofmodel uncertainty in regulatory decision-making. The third conference, held in January 1985, provided a forum for public review and

comment on proposed revisions to the modeling guideline. As a result of public
comment during that conference EPA issued the "Guideline on Air Quality (Revised)", EPA-450/2-78-027R, (51 FR 32176). Revisions responding to issues raised during that conference are included in Supplement A to the guideline (53 FR 392).

The Fourth Conference on Air Quality Modeling will address EPA's modeling guidance. Substantial new knowledge concerning modeling analyses has become available since the guideline and Supplement A were issued.Future revisions to the guideline are needed to improve the basis for air quality impact
assessments and to insure that it reflects the state-of-the-art with respect to air quality models and data bases. As a basis for possible revisions of the modeling guideline and forholding this fourth conference, EPAhas assembled a list ofrecent developments in modeling techniques and related methods developed by EPA, other Federal agencies, or the private sector. These techniques and related methods are briefly described below. Topics are arranged to coincide with the organization ofthe modeling guideline.

The EPA requests comments on the general issues oftechnical validity, relevant accuracy, merits and limitations ofthe models and methods listed here compared to current techniques in the modeling guideline, and comments on othermore specific issues listed below. Comments related
to air quality modeling ofgeneral interest to thepublic may also bemade. The issues raised at the conference and in the comment periodwill be considered in development of anotice proposing to revise the "Guideline on Air Quality Models (Revised)" and Supplement A. Modeling Activities
A. Complex TerrainDispersion Model (CTDM)

The EPA has completed theCTDM project, EPA/600/3-88/006 (DocketItem 11-1-2). Onemajor output is the development and evaluation of the CTDM. This is a refined air quality model for determining pollutant concentrations from sources in "complex terrain" areas (where the height of thenearby terrain exceeds the height ofthe source being modeled). The CTDM is designed for situations where plume impingement on the windward side of terrain features during stable to neutral atmospheric conditions is believed to cause air qualityproblems. The user's guide documenting the scientific assumptions used in CTDM is available as EPA/600/8-87/058a and 058b (DocketItem 11-l-1). Because CTDM wasdesigned for neutral to stable flow conditions, the model does notpredict concentrations during unstable atmospheric conditions when a plume is within the mixed layer.Thus, in order to adequately estimate concentrations during all averaging periods ofconcern forregulatory applications, it willbe necessary to merge the output fromCTDM with output from another model that can handle the convectively unstable atmospheric conditions. Other issues that need to be resolved for any regulatory application include meteorological data requirements, receptor grid spacing, the choice of model options, and a consistent approach to terrain characterization.

The EPAis currently studying the performance ofCTDM and has completed several additional model evaluation and sensitivity studies (DocketItems 11-1-3 and 4). The EPA solicits comments on: (1)Whether CTDM is a technically validmodel; (2) whether use ofan additional algorithm for modeling convective atmospheric conditions is suitable; (3)whether the validation and sensitivity studies warrant the adoption ofCTDM as a refined model in complex terrain; (4) how data requirements should be specified given that CTDM requires an extensive set ofmeteorological data inputnot routinely collected in most
current measurement programs; (5) whether EPA shouldrecommend the use ofCTDM in a screening mode with assumed "worst case" meteorological conditions ifmore sophisticated on-site data are not available; and (6) whether limitations should be placed on the use ofCTDM for regulatory applications.

The CTDM does not address all situations involving complex terrain where concentrations ofpossible

concern can occur, e.g., on the lee side ofhills. During the public comment period on the supplemental proposal (Docket A-80-46, Item VI-G-1), several
commenters suggested thathigh concentrations may result at such locations and that the highly conservative nature ofthe existing complex terrain screening models compensates to some extent fornot addressing any ofthese phenomena. The EPA solicits public comment on how to take such situations into account in setting emission limits for sources which

use CTDM.

B. OzonePrecursor PointSource Modeling

The EPA's regulations require a demonstration that a proposed source (ormodification) will not cause or contribute to a violation ofany National Ambient Air Quality Standards. The modeling guideline does not,however, recommend a technique forpredicting the impact on ambient ozone concentrations due to point sources of

ozone precursor emissions, i.e., volatile organic compounds ornitrogen oxides. The EPAhas developed a screening technique based on the Reactive Plume Model (RPM-II), (Docket Item 11-1-5) and solicits comments on the technical validity ofthis screening technique.

C.MobileSourceModelingat Signalized Intersections

The EPA is reviewing the most appropriate traffic and emissions components ofintersection models for air quality analyses because high carbon monoxide concentrations occur near signalized intersections. In addition, the EPA guidance contained inWorksheet 2 ofthe "Guideline for Air Quality Maintenance Planning and Analysis, Volume 9", EPA-450/4-75-01, cannot adequately model overcapacity situations at these intersections. The EPA has been working with the Federal Highway Administration (FHWA) to determine how an intersection analysis should be performed and what emissions/traffic model to use. As a result of thisjoint effort recommendations on these issues and a 

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## I Proposed Rules323

workplan foraccomplishing them have been developed (Docket Items 1-1-6 and 7). The EPA solicits comments on the adequacy of thetechnical approaches in therecommendations and workplan.

D. Emissionsand Dispersion Modeling SystemforAirports

TheU.S. AirForce and the FAA are jointly developing the Emissions and Dispersion Modeling System (EDMS) to provide an integrated assessment of pollution frommultiple sources (e.g., aircraft, motor vehicles, andpower plants) at airports and airbases.The model makes use ofa modern microcomputer database system through which an inexperienced layperson can enter data and initiate an emissions or dispersion modeling activity. This model has been submitted
to EPA in accordance with EPA provisions for soliciting new models (45 FR 20157). A description ofthe model and a User's Guide have been prepared (DocketItem 1-1-8).

TheEPA solicits comments on: (1) Whether EDMS is a technically valid model; (2)whether the performance evaluations warrant the adoption ofthis model as a preferred model to estimate pollutant concentrations at airports; and (3)whether any limitations should be placed on theuse ofthe EDMS model for regulatory applications.

E. Long-RangeTransport Models
The EPA has been evaluating the performance ofseveral long-range transport models. These models are needed to estimate pollutant concentrations at distances beyond about 50kin, the conventional limit for straightline Gaussian models. Estimates of concentrations at distances greater than 50 km may be required in certain applications, e.g., Class I PSD areas. Eight long-range transport models, submitted to EPA in accordance with EPA provisions for soliciting new models (45FR 20157), havebeen evaluated by testing themodels against
two sets of field data. The eightmodels submitted canbe used to predict shortterm averages (3to 24 hours) ofSO, and primary partculates over distances of 20-2,000 km from single or a cluster of multiple sources. The study is described in the document titled "Evaluation of Short-Term Long-Range Transport Models", Volumes I and 2, EPA-450/4- 86-016a and 016b (DocketItem 11-1-9). The American Meteorological Society has completed a peer review report for this study (DocketItem 11-1-10).

The EPA solicits comments on: (1) Whether EPA should adopt one ofthese eightmodels as a preferred long-range transport model; (2)whether any limitations should be placed on model

use forregulatory applications; (3) whether the model estimates are appropriate for averaging times and

source receptor distances ofregulatory
concern; (4)whether the model use shouldbe limited to concentrations of S02 and primary particulates; (5) whether consideration shouldbe given
to availability, complexity and the detail/content of input databases in determining which model is recommended; and (6) how data collection andprocessing requirements could be minimized.

Themodeling guideline currently
states that selection ofa long-range transport model is on a case-by-case basis.The EPA is developing an example guidance protocol to illustratehow to apply a long-range transport modelto regulatory problems. This document contains recommendations for model input and options and an example application (DocketItem H-I11). The EPA solicits comments on the technical approach used therein.

F.

ModelsforEstimatingVisibility Impactof SpecificSources
The modeling guideline lists two models which may be used on a caseby-case basis for refined analysis to estimate short-term impact assessment ofthe type ofvisibility impairment known as "plume blight" which can be attributed to a specific source. The EPA Office ofResearch and Development has provided recommendations of acceptable plume blight models (Docket Item 11--12). TheEPA solicits comments

on whether to adopt the recommendations ofthis document and whether any limitations shoud be placed

on the use of these models forregulatory applications.

The modeling guideline also references a document titled "Workbook forEstimating Visibility Impairment", EPA-450/4-80-031. A revision ofthis document has beenprepared to reflect
current technical information and experience (Docket Item 11-1-13]. It contains procedures and a visibility model that can be used for screening
purposes to estimate visibility impairment from specific sources. The EPA solicits comments on thetechnical validity of therevised visibility workbook, and whether to adopt the techniques in this document.

G. Model forShorelineDispersion
Themodeling guideline recommends the Offshore and Coastal Dispersion model for simulating plume dispersion and transport from offshore point

sources to receptors on land orwater. Themodeling guideline also indicates the need forpredicting plume dispersion and fumigation under theunique meteorological conditions that affect elevated sources located on the coastline. There, a convective boundary layer capped by an inversion,becomes established when winds are onshore and sufficient overland heatflux and land-water temperature differences exist.Although models have been developed to address this problem, previous evaluations were not sufficient
to allow EPA to recommend a specific technique. The EPA has not completed a performance evaluation entitled "Analysis and Evaluation ofStatistical Coastal Fumigation Models", EPA-450/ 4-87-002, (DocketItem 1-1-14). TheEPA has also developed a method to incorporate shoreline dispersion conditions in EPA regulatory models using readily available data (Docket Item 1-1-15).

The EPA solicits comment on: (1) Whether the performance evaluation study warrants the adoption ofa preferred model for predicting plume dispersion and fumigation for elevated

sources located on the coastline; (2) whether themethods to approximate certain inputparameters fromreadily available data are adequate; and (3) whether any limitations shouldbe placed on the use ofthemodel in regulatory applications.

H. ValleyStagnation

The modeling guideline addresses the issues ofwind stagnation but does not recommend any specific modeling techniques. Concerns about PMto violation violations in valley basins have ledmany State and local agencies
to request a simple modeling technique for simulating stagnation and wind recirculation conditions. Stagnation conditions tend to occur more frequently andpersist for a longer time in well defined valleys; however, periods of persistent very low winds can also

occur in broad shallow velleys. Simply Gaussian models arenot adequate during these conditions. The WYNDvalley model (developed by WYNDsoft, Inc.) appears to have technical merit and tobe relatively simple to apply. However, model evaluation results based on a comparison between model estimates and air quality data are limited (Docket Item 11--16).

TheEPA solicits comments on: (1) Whether WYNDvalley is a technically valid model; (2) whether additional data bases existto evaluate this model; (3) what guidance EPA should provide for

users ofthe model; (4)whether any limitations shouldbe placed on its use Federal Re ster / Vol 53 No. 163 / Tuesday, August 23, 1988 / Proposed Rules 32083Federal Register / Vol. 53, No. 163 / Tuesday, August 23, 1988 / Proposed Rules

forregulatory applications; and (5) whether there are any othermodels applicable to these stagnation conditions.

I. On-SiteMeteorological Program Guidance

The use ofon-site meteorological data to support air quality impact analyses has grown steadily over recent years. The EPAhas published a document titled "On-site Meteorological Program Guidance for Regulatory Modeling Applications", EPA-450/4-87-013 (Docket Item 11-1-17). The purpose of this document is to consolidate into a single document specific guidance on the collection and use ofon-site meteorological data for air quality modeling analyses. While this document has undergone extensive external peer review by State agencies, meteorological instrument manufacturers, and otherFederal agencies, it has not been subject to formal public comment. The EPA, therefore solicits comments on the onsite meteorological guidance document and on whether to adopt the recommendations ofthis document.

In response to the need for consistency in the processing ofon-site meteorological data, EPAhas developed

a Meteorological Processor for Regulatory Models (MPRM), Docket Item 11-1-18). This computer algorithm is designed to process on-site meteorological data following the procedures recommended in the on-site meteorological guidance document and produces output necessary to run the EPAregulatory dispersion models. The MPRM can also process National Weather Service surface and upper air data. It is designed to provide considerable flexibilityto users in terms ofimput data formats, and also is structured to be easily expanded to accommodate data requirements of future models. The EPA. therefore, also solicits comments on whether to adopt MPRM as the standard processor of meteorological data imput for modeling applications.

.Method forEvaluating Models
The modeling guideline describes a number ofactions tobe taken to allow a judgment to be made as to what model is most appropriate for a given application and specifically refers to the document titled "Interim Procedures for Evaluation Air Quality Models", EPA450/4-84-023. The Agency continues to work on refining these methods and has made advances in the statistical methodology needed for determining which modelperforms better than other competing models. With this newer methodology, it is feasible to combine results from different averaging periods and different data bases into a probabilistic framework. This methodology is described in an EPA report titled "Protocol for Determining the Best Performing Model" (Docket Item 11--19). An Appendix to this report provides examples ofapplying the protocol to compare the performance of two rural air quality models. The EPA solicits comments on the technical approach used in thisreport and whether to adopt the procedure in judging thebest performing models for regulatory applications.
K. OtherIssues

The modeling guideline references a document titled "Guidelines for Air Quality Maintenance Planning and Analysis, Volume 10 (Revised)", EPA450/4-77-001. This document has been revised to incorporate additions to the technical approach and changes so that the techniques now can easily be executed on an IBM-PC compatible microcomputer (DocketItem 11--20). The EPA solicits comments on the technical validity ofthese screening techniques.

The EPA has under development and evaluation two regional scale models: the Regional OxidantModel and the Regional Acid Deposition Model (Docket Items 11-1-21 and 22). These models can treat complex chemical interactions associated with emissions from a large number ofwidely distributed sources (e.g., a metropolitan area) and can account for comprehensive physical and chemical processes important in the transport, transformation, and deposition of pollutants on a regional scale. These models are designed to evaluate policy implications ofalternative control strategies forgroups ofsources encompassing a region.They are not designed to setemission limitsfor specific sources. TheEPA solicits comments on thepotential usefulness to regulatory programs ofregional scale models to assess transport, chemical interactions and dispersion ofmultiple pollutants.

Finally, air quality dispersionmodels

are taking on increasing importance as tools foranalyzing air emissions in connection with toxics and hazardous waste pollutants. The EPA solicits comments on what modeling techniques to consider in developing air pathway analyses for such pollutants.
Public Participation

The Fourth Conference on Air Quality Modeling willbe open to the public; no admission fee is charged. Themorning of the first day will include briefings by EPA officials and others onthe modeling issues discussed above. In the afternoon, the conference will continue with statements from representatives of APCA's Meteorology Committee, the American Meteorological Society, the National Academy of Sciences, appropriate Federal agencies including the National Science Foundation, the National Oceanic and Atmospheric Administration, the National Bureau of Standards, the FAA, and others.The day will conclude with statements by representatives of State and local air pollution control agencies.-On the second day, the conference will be opened to statements and comments from the general public.

Persons wishing to speak at the conference should contact EPA at the address given in the "FURTHER INFORMATION" section no later than 10 days priorto the conference date. Such persons shouldidentify the organization (ifany) on whose behalf they are speaking andthe length of presentation. If a presentation is projected to be longer than 15 minutes, the presenter should also state why a longer period is needed. Persons failing to submit awritten notice but desiring to speak at the conference shouldnotify the presiding officer immediately before the conference and willbe scheduled on
a time-available basis.

The conference will be conducted informally and chaired by an EPAofficial. There will beno sworn testimony or cross examination. A verbatim transcript ofthe conference proceedings will be made and placed in the docket. Speakers shouldbring extra copies oftheir presentation forinclusion in the docket, forthe convenience ofthe reporter and theAgency panel. Speakers willbe permitted to enter into the record any additional written comments that

are notpresented orally.Additional written statements orcomments should be sent to the Central Docket Section (see ADDRESSES section). A transcript ofthe proceedings and a copy ofall written comments will be maintained in Docket A-88-04 which will remain open for 60 days following the conference for the purpose ofreceiving additional comments.

Date: August 15, 1988.

Don R.Clay, ActingAssistant AdministratorforAir and Radiation.
[FRDoc. 88-18951 Filed8-22-88; 8:45 am]

BILLING CODE 6560-60-M I 32084