( 

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UNITED STATES ENVIRONME~TAL PROTECTION AGENCY 

Office of Air Quality Plan.ning and Standards 

Research Triangle Park, Nonh Carolina 2nll 

45EP 1992 

K£M01WIDUH 

SUBJECT: Procedures for processing 

to Attaimaent 

FROM: John Calcagni, Directo~~z=~ 

TO: 

Purpose 

Air Quality Hanagement 

Director, Air, Pestic' es 2n~ Toxies 

Division, Regions I and IV .. t 

Director, Air and WastB Management Division, . Reqion II 

Director, Air, Radiation and Toxics Division, 

Region III . Director, Air and Radiation Division, 

Region V 

Director, Air, Pesticides and Toxics Division, 

Region VI· 

Director, Ai:.: and Toxlcs Division, 

Regions VIi, VIII, IX, end X ~ 

The ottice of Air Quality Planning and Standards (OAQPS) 

expects that a number of redesignation requests will be submitted 

in the near future. Thus, Regions will need to have guidance on 

the applicable procedures for handling these requests, including maintenance plan provisions. This memorandum, therefore, 

consolidates the Environmental Protection Agency's (EPA's) 

guidance regarding the processing of requests for redesigl"1ation of nonattainment areas to attainment for ozone (OJ)' carbon 

monoxide (CO), particulate matter (PM-lO), sulfur dioxid~ (S02)' 

nitrogen dioxide (N02 ), "and lead (Pb). Regions should use th1s· 

guidance as a general framework for drafting Federal Register notices pertaining to redesiqnation requests. Special concerns 

for areas seeking redesignation from unclassifiable to attainment 

will be addressed on a case-by-case basis. 

Background 

Section l07(d)(J)(E) of the Clean Air Act, as amended, 

states that an area can be redesiqnated to attainment if the 

following conditions are met: 
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1. The EPA has determined that the national a~ient air 

quality standards '(NAAQS) hav~ been attained • 

2. 'The applicable iaple_entation plan has'been fully appr~ved hy EPA under section 110(k). 

3. The EPA has deter.ined that the iaprove.ent in air 

quality is due ito penaanent and enforceable reductions, in '" 

eaissions. . .' 

4. The State has met all applic~ble requirements for the 

area under . section 110 and Part D. . . 

5~ 'Tlie EPA. has fully approved a maintenaDce .. plan, includinq 

a contingency .' 'plan, for the area under section 175A. . 

Each of these criteria is discUssed in mora detail in ~e following paragraphs. Particular attention is given to 

maintenance plan provisions at the end of this document since 

maintenance p'lana constitute • ne. requirement under the amended 

Clean Air Act. ,Exceptions ,to the quidance wi~l'be considered on 

'a case-by-casa basis. ' 

1. Attainment Of the Standard 

The state must show that the araB is attaining the 

applicable NAAQS. There are two components involved in making this demonstration which should be considered interdependently. The first component relies upon aabient air quality data. The 

data that are used to de.onstrate attaimaent should be the 

product of ambient monitoring t~at'is representative of the area 

of highest.concentration. The.e aonitors a~ould remain at the saJDe~ location for the duration of -the aonitorinq'-period required for demonstrating attainment. The data should'be collected and 

quality-assured, in accordance with 40 CPR 58 and recorded in the 'Aeromet~io Inforwation'Retrieval Syatea (AIRS) in order for it to 

be availabl. to the public for review. Por purpose. of 

re4eaiqnation, the Reqional office.sbou~d verify that the 

integrity of the air quality aonitorinq network bas b.en ,pres~rved .. 

F~r.PM-IO, an area may be considered attaining the HAAQS if 

1:he. nUllber '.of expected. axc.adana •• per year, according to 40 eFR 

50.6, is leas than or equal to 1.0 •. For 03' the area ."at show 

that the average. ,annual nuaber of expected exceadancea,according 

.to 40 eFR 50.9, is les. than or equal to 1.0 based on data from 

all monitoring sites in the area or its affected downwind 

environs. In making this showing, both PM-10 and 03 must rely on 

J co .. plete·,~cons.cuti:ve,~ca·l.nclar: ~year •. :of,; .. qual~~y.-assured .. ,.i ..r. ...... " .. " ~ ..... 

quality aonitoring' data, coll.ected~ in accorda,hce with 40 eFR 50, 

Appendices Hand K. For CO,an are. aay be considered attaining the HAAQS if there are no violations, as determined in accordance 
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with 40 CFR 50.8, based on 2 complete, consecutive calendar ye~rs of quality-assured monitoring data. For S02' according to 40 CFR 

50.4, an. area must show no more than· one exeeedance annually and 

for Pb, ~ccording to section 50"12, an area may show no . II 

exceedanoss on a quarterly basis. 

The second component relies upon supplemental EPA-approved air quality m~eling. No such supplem6ntal modeling is requir+d forol nonattainment areas seeking redesignation. Modeling may be necessary to deternaine the representativene!!s of·-t~e .. monitoted 

data. For·pollutants such as s02 and CO; a small number ot l 

monitors typically is not representative of 'areawide air quality 

or areas of highest concentration. When dealing with s02' Pb'l 

PM-IO (except for a limited nUllber of initial moderate . ." 

nonattainment areas), and Co '(except moderate areas with design va~ues of 12.7 parts per million or lower at ·the time of passage of the Clea~ Air Act Amendments of 1990), dispersion modeling I 

will g~nerally be necessary to evaluate comprehensively sources I' 

impacts a~d to' determine the areas of expected high . '. 

concentrations based upon current conditions. Areas which were 

designated nonattainment based on modeling will generally not ~e 

redesignated to attainment unless an acceptable modeling analysis indicates attainment. Regions should consult with OAQPS foro. 

further guidance,addressing the need for modeling in specific circumstances. . . 

2. state Implementation Plan (SIP) Approyal 

Thf SIP for the ~rea must be fully approved under section 

110(k), and must satisfy all· requirements that apply·to the I 

area. It should be noted that approval action on SIP elements 

and the redesignation request may occur. simultaneously.. An area 

cannot be redesignated if a required element of' its plan is t.he· 

subject of a'disapproval; a finding of failure to 'submit or tOI 

implement the ·SIP: or -partial ,. conditional, or .limi ted approval. 

However, this does not mean that earlier issues with regard tol 

the SIP will be reopened. Regions should not reconsider those' 

things that have alr,eady been approved ~nd for which the Clean I 

Air Act Amendments did not alter what is required •. In contrast, 

to the extent the Amendments add a requirement or alter an i 

existin~ requirement so that it adds something more, Regions , should consider those issues. In addition, requests from areas 

known to be affected by dispersion techniques which are ! 

inconsistent with EPA guidance will continue to be considered I 

unapprovable under section 110 and will not qualify for ! 

redesiqnation. I 

'lsection 110(k) contains the requirements for EPA action on 

plan submissions~ It addresses completeness, deadlines, full and 

partial approval, conditional approval,'and disapproval. 
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3., Permanent and' Enforceable Improvement in Air Qual~ty 

The state'must be able t~ reasonably attribute<the ' 

improvement in air quality to emission reductions which are 

permanent and en force'able .2 Attainment resul tinq ,from temporary reductions in emission rates (e.g., 'reduced production or s~utdown due to temporary adverse economic.conditions) or . unusually favo,~abl. meteorology would not qual ify as an air 

quality improvement due to permanent and enforceable emission 

reductions,,' " " ;, .' .' .. - .... , . .., .. , In .makinq this showing, the'state shoul4 'estimate the 

percent ~eduction (from the year that was ,used to determine the 

desiqn value for designation' and classification) achieved,from' 

Federal -measures such as the Federal'Motor Vehicle COntrol 

Proqram and fuel volatility rules as well as control measures 

that have been adopted and i.pl •• ented by the' state. This , estimate should consider emission ratesi production capacities, and other related information to clearly show that· the air, ' 

quality improvements are the result of Impleaeneed controls. The 

analysis should assume that sources are operatinqat permitted . ~evels (or historic peak ,levels)· unless evidence is presented that such an assumption is unrealistic. ' 

" 

4. Section·11P and Part D Requirements 

For the purposes' of . r.designation, a' ,State must meet all 

requirements of se~tion 110 and Part D that were applicable prior 

to submittal of the complete redesignation reque~t. When ' 

evaluating a redesignation request; Regions should not consider , whether the state hae met requirements that come due und~r ~he 

Act, after submittal of'a cOllplete redesiqnation request •. 

2This is consistent" with EPA's existing policy on 

redesignations as ~tated in an April 21, 1983'memorandum titled 

"Section 107 Designation Policy SUJDJIlary. I. This memorandum states 

that in order for an area to be redesiqnated to attainment, the 

state must show that "actual enforceable emission reductions are 

responsible for the recent air quality improvement." This 

element of the policy retains its validity under the, amended Act 

pursuant to section 193. [Note: other aspects of the April 21~ 

1983 memorandum have since been superseded by sUbsequent memorandums:. interested parties should consult with OAQPS before 

relying on these aspects, e.g. those relating to required years of air quality data.] 

JUnder section 175A(c), however, the requirements of Part D 

remain·· in ,force: and. effect for.' the ·area unt-il"'such ·,time:' as' it-is" - redesignated. Upon redesiqnation to attainment, the requirements that became due under section 175A(C) after submittal of the 

complete redesignation request would no longer be applicable. 
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However, ,any requirements that came due prior to submittal of 

redesignation request must 'be fully approved into the plan at 

before the t1me EPA red~siqnates the area. ' 

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or 

TO avoid confusion. concerning what requirements will be 

applicable for purposes of· redesignation, Regions should 

encourage states to work closely with the appropriate Regianal Office early in the process. This will help to ensure that a 

redesignation request submitted by the state has a high ,. likelihoOd of being approved by EPA. Regions'sho~ld advise 

states of the practical planning ~onsequences if EPA d'i~approves 

the redesiqnatiQn request or if the request is invalidated . 1 

because af violations recorded during EPA's review. . Under such . circumStances, EPA does not have the discretion to ad just ~. 

schedules for implementing SIP requirements. As a result, an 

area may risk sanct:ions and/or Federal implementation plan implementation that could result frOID failure to meet SIP 

submittal or implementation requirements. 

a. section 110 Regyirements 

section 110(a)(2)- contains general requirements nonattainment plans. Most of the provisions of this 

the saae as those contained in the pre-amended ACi. 

provide quidance on these requirements"as neede~. 

b. Part D Beguirements 

for 

section are 

We will 

Part D consists of general requirements applicable to all 

areas which are designated nonattainment based on a violation of 

the NAAQS. The general requirements are followed by a series of 

subparts specific to each pollutant. ~e qeneral require~ents I 

appear in subpart 1. The requirements relating to 0 3 , CO, PM-10, 

S02' ~02' and Pb appear in subparts 2 through 5. In those I 

instances where an area is subject to bOth ,the qeneral 'nonattainment provisions in subpart 1 as well as one of the 

pollutant-specific subparts, the general provisions may-be 

subsumed within, or superseded by, the .orespecific requirements of subparts 2 through 5. , . 1 

If an area was not' classified under 'section 181 for"OJI orl 

section 186 for CO, then that area is only subject to the i 

provisions of subpart 1, "Monattainment Areas in General." In 1 

addition to relevant provisions in subpart 1~ an 0 3 and CO area~ 

which is classified, must meet all applicable requIrements in r 

subpart 2, "Additional Provisions for Ozone Monattainment Areas," 

and subpart 3, "Additional Provisions for Carbon Monoxide l 

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4General guidance regarding the requirements for SIP's may, 

be found in the "General Preamble to Title I of the 1990 Clean I 

Air Act Amendments," 57 FR 13498 (April 16, 1992). 
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Nonattainment.Areas," respectively, before the area lDay be 

rede~ignated tOt attainment. All PM-lO nonattainment areas 

(whether classified a~ moderate or serious) must similarly meet 

the applicable general provisions of subpart 1 and the specific 

PM-IO provisiqns in ~ubpar~ 4, ~Additional Provisions for 

Particulate Matter Nonattai~ent Areas." ~ikewise, S02' N02 , and 

Pb nonat~ainme~t areas are subject to the applicable qener,l nonattainment provisions in subpart 1 as well as the aore 

specific requirements in subpart 5, -Additional Provisions for 

Areas Desi~nated; Nonattainme,l~t for sul~ur oxides, . Nit~9gen ," 

Dioxide, and Lead. II " ' 

,i. 'section 172{c) geguirnents' : 

This' section con:t~ins g~neral,' requirements. (or nonatuimaent 

plans. A 1:;horough discussion Of ,these requirements may be found 

in the General Preamble to Title I [57 FR 13498 (April 16,' 

1992)]. Tbe EPA' anticipates that areas will already. have met 

most or all of these requirements to the extent that they are not 

superseded by m~re'spe~ific Part D requirements. The 

requirements for reasonable further progress, identification of 

certain emissions increases, and other measures needed for. 

attainment will not apply for redesiqnations because they only , have mean~n9 for areas not attaining the standard. The 

requirements for .. an e.lssio~ inventory wlll be. satisfied by the 

inventory requirements of the maintenance plan. The requirements of the Part D new source review program will be replaced by the, 

prevention of significant deterioration (PSD) p~ogram once the 

area has been redesignated. However, in order to ensure that the 

PSD program will becom~ fullY,~ffective immediately upon redesignation, either the state must,be delegated the Federal PSD 

program or the state must make any 'needed modifications to its 

rules to· have the approved PSD program apply to the affected area 

upon z:edesi9n~tion. .... . 

i i. ','CQnforJlli~ , . The state must work with EPA to show that its SIP 

provisions are consis'tent with section 116 (c) (4) confonai ty , requirements. The redesignation request should include conformf~y procedures, if the state already has these procedures in place. Additionally, we currently interpret the conformity' requirement to apply.to attainment areas. However, EPA has not 

yet issued its co~formity regulations specifying what areas are 

subject' to theconforaity requirement. Therefore, if a state 

does not have conformity proc~dures in place at the time that it, 

submits a redesi~ation request, the state' must 'commit to follow 

EPA'S conformity regulation upon issuance, as applicable. If the 

state subJDits 'the 'redesiqnation ~request' subse~ent' .. to' Ep~/;S' , 

issuance of the conformity regulations, and the conformity req~frement became appli~able to the area prior to submission, . 
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the state ~ust adopt the applicable conformity requi~~m~nts 

befote EPA can redesignate the ar~a. i . I 

Maintenance Pllns I 

Section l07(d)(3)(E) of 'the amended Act stipulates that for' 

5. 

an area to be redesignated, EPA must fully approve a ma~ntenance 

plan which meets the requirements of section 175A. A. State may submit both the redesignation request and the maintenance plan at ~he same time and rulemaking on both ,may ,proceed on a 'parallel- track. Maintenance plans may, ot course, be submitted and ' 

approved by EPA before a,redesignation is requested. However, 

according to section 175A(c), pending approval of 'the .aintena~ce 

~plan and 'redesigna~io~ request, all ,applicable'nonattainment area 

requirements shall remain 'in place. . . I 

section 175A defines the qeneral framework of a·maintenance 

plan. T~e maintenance plan will constitute a SIP revision and I 

must provide for maintenance of the relevant NAAQS'in the area' 

for at least 10 years after redesiqnation. Section 1751i further 

states that the plan shall contain such additional 'measures, 'i~ 

any, as'may be necessary to ensure such maintenance. Because the 

Act requires a' dem9ns.tration of maintenance for 10 years after Ian . area is redesiqnated (not 10 years after submittal of a 

redesignation request), the state should plan for some lead ti~e 

for EPA action on the request. In other Words, the aaintenance 

demonstration should project maintenanc~ for 10 years, beqinnirlg from a date which factors in the time necessary for EPA'reviewl 

and approval action on the redesigna~ion request. In determining 'the amoUilt of lead time to allow, states should consider that. I 

section l07(d)(l)(D) grants the Administrator up to 18 months 

from receipt of a complete ,submittal to process a redesignation " request. Th*, statute also requires 'the state to submit a j 

revision. of the SIP 8 years. 'after the,. original, redesignation I 

request ~s approved to prov1de for ma~ntenance,of the NAAQS fo~ 

an additional 10 years following the first lO-year period [see I 

section 175A(b)]. " 

, In addition, the maintenance plan shall contain such I 

contingency measures as the 'Administrator deems necessary to 

ensure prompt correction of any violation of the NAAQS [see 

section 115A(d)]. The Act provides tha~, at a minimum, the 

contingency measures must include a requIrement that the state; 

will implement all measures contained in the nonattainment SIP , prior to redesignation. Failure to maintain the NAAQS and 

triggering of the contingency plan will not necessitate a 

revision'ot the SIP unless required by the Administrator, as 

stated in section 175A(d). 

The. following is a list of core provisions that we 

anticipate will be necessary to ensure maintenance of the 

relevant NAAQS in an 'area seeking redesignation from 
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nonattainment to attainment.. We therefore recommend that States 

seeking redesignatfon of a' n~nattainment area consider these 

provisions. However, any final 'EPA determination regardinq tbe 

adequacy. of.a maintenance plan will be made following review of 

the plan submittal in light of the particular 'circumstances 

facing the area proposed for redesiqnation and based on all 

relevant information'available at the time. . ~ . ..;: ' " 

a. '. ittal.nment Inyentory 

. The sta'te should develop an' attainm.ent emfssions inventory 

to identify.the level of emissions in the area which is 

sufficient to attain the NMQS. 5, This inventory-'should be ~, 

",consistent with EP~'s most recent quid~nce on emission 

inventories for nona~tainment areas available at the time and sho~ld include the emissions during .the time6

period assoCiated 

with the monitoring data showing att.ioment. . . . ' 

.' . 

Source size thresholds are 100 tons/year for S02' NO , and PM~10 areas, and 5 tons/year for Pb based upon 40.CFR 51.iOO(k) 

,and 51.322, as well as ~stablished practice for AIRS data. The 

source size 'threshold for serious PH-IO areas is 70 .tons/yea~ 

5Where the state has made an adequate demonstration that air 

quality'has improved as a result of the SIP (as discussed 

previously), the attainment inventory will generally be th~ 

actual inventory at the t~.e the area attained ~he ~tandard. 

6The EPA's 'cu~rent guidance on the prepar~tion ofemissiaD 

inventorie, for 03 and CO nonattainment, areas is contained in the 

following docum~n~s:. "Procedures for the Preparation ot Emission 

Inventories for Carbon Monoxide and Precursors of Ozone: Volume 

I" (EPA-450/4-91':'Ol6 >" "Proce.dures for the Prepare'tion of 

Emission Inventories for Carbon Monoxide and Precursors of Ozone: 

Volume II" (EPA-450/4-91-014), ~Emission Inventory Requirements' for Ozone state Implementation Plans" (EPA-450/4-91-010), 

"Emission Inventory Requirements for Carbon Monoxide 

Implementation PlanaD (EPA-450/4-91-0l1), "Guideline for Requla~ory Application of the Urban Airshed Hodel" (EPA-450/4-91-

013), "Procedures for Emission Inventory Preparation: Volume' IV, 

Mobile Sources" (EPA-450/4-81-026d), and IIProcedures for 

preparing 'Emission, Inveneory Projections" (BPA-450/4-9l-019). 

The EPA does not currently hav.e. specific guidance on attainment 

emissions inventories'for S02*' In lieu tbereof, States are 

referred to ~he quidan~e on emissions data to be used as input to 

modeling demons,trations, contained in Table 9.1 of EPA's 

DGuideline on Air Quality Models (Revised)" (EPA-450/2-78-027R), 

July 1~87 ,.,.YO~gh. is. g~ne~ally applicable to~ all, criteria .. ,'. 

pollutants. Emission inventory procedures and requirements documents are currently being prepared by'OAQPS for PM~lO and Pb: 

these documents are due for release .by summer 1~92. 
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according to Clean Air: Act section 189(b)(J). However, the I 

inventory should include sources below these size thresholds i~ 

these smaller sources were included in the SIP attainment I 

demonstration. Where sources below the 100; 70, and 5 tons/yelr- size thresholds (e.g_, areas with smaller source size, . definitionsl are subject to a State's minor source permit j 

program, these ~ources need only be addressed in the agqreqate to 

the extent that: they res~lt in areawide growth., I 

- :.For 03 nonattain~ent. are~s, the inTJentory' should be based Ion 

actual "typical summer day" emissions of'Ol precursors- (volatile 

organic compounds and.nitrQqen oxides) durlng the attainment· 

year. This will generally correspond to one of the periodiC inventories required for nonattainment areas to reconcile 

milestones. For CO nonattainment areas, the 'inventory should be 

based on actual -"typical CO season day" e.is~ions for the . attainment ·year. This will generally correspond to one of the 

periodic inventor~es required for nonattainaent areas. 

b. Maintenance Demonstritian 

A state may generally demonstrate maintenance of the NAAQS 

by either sh~winq that future emissions of a poI~utant or its I 

precursors w~ll not exceed the level of the attainment inventor;y, 

or by modeling to show that the future mix 01 sourc~s and 

emission rates will not cause a v~olation of the NAAQS. Under 

the Clean Air Act, many areas are required to s~bmit ~odeled 

attainment demonstrations' to show that proposed reductions in ~ emissions will be sufficient to attain the applic::able NMQS. or 

these areas, the maintenance de.onstratio~ should be based upo . the same· level of modeling. In areas, where. no such modeling w~s 

required, the- state 'should be able to rely on the attainment I 

inventory approach. In both instances, the demonstration shou~d" 

be for· a period of ,10 ,year,;; following th~ rfi!desiqnation. I 

Where moaeling is relied upon to demonstrate maIntenance, I 

each plan should contain a suamary of the air quality .. ! 

concentrations expected to result from application of the control 

strategy. ,In'the process, the plan should identify and descri~ 

the dispersion model or other ai·E' quality model used to project! 'allbient concentrations (see 40 CFR 51.46). .", l" 

In either case, to satisfy the demonstration requirement the 

state should project' ellli.ssionsfor the lO-year period followinq redesignation, either for the purpose of showing that emissions! 

will not ~ncrease over the attainment inventory or for conductip9 modeling. The projected inventory should consider future : 

growth', including' population and industry I should be consistent: 

7Guidance for projecting emissions may be found in the 

emissions inventory guidance cited in footnote 6. 

.... r; ." 
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with the attainment inventory, and 'should doc~ment data inputs and assumptions. All elements of the demonstration ,(e.g_, 

emission projections, new source growth, and mwdeling) should be 

consistent with,current EPA modeling quidance. For 03 and CO, 

the proj.cted emis.~ions should reflect the expected actual 

emissions based on enforce~ble emission rates and typical' " producti~n rat~s. '~, . . 

For CO, a State should address the areawid~ component of the,' 

maintenance demonst,ration a1 ther by ,showing that future CO' 

emissions will not increase or by conducting ar.awide modeling_ Preferably, the State should carry o~t hot-spot.modeling that is 

consistent with the GuidelineoD Air 'Ouality Hodels (Revised), in 

order to demonstrate maintenance of the HAlQS. In particular, if 

the.nonattainment p~oble~ is related to a pattern of hot-spots then hot-spot aodeling sbould gener.ally be.conducted. However, 

hot-spot modeling is not 'automatically required_. For example, if 

the nonattainaent p~oble. was related solely to stationary point 

sources, or if highway i.proveaents have been implemented and the 

associated emission reduction. ,and travel charact.ristics can be 

qualitatively documented, then hot-spot modeling is not required. In such cases, adequate documentation as well as the'conourrence 

o! 'Head~arters is needed. ,r '.. '. ' 

. . Any. assumptions: concerning emission rates must reflect 

permanent, enf~r~eable measures. In other~words, a State 

generally can~ot take credit in the maintenance demonstration for 

reductions unless there are'reCJUla~ions in place requiring 'those 

;reductions or the reductio"sare-otherwise.shown to be permanent. Therefore, the state will be expected to maintain its implemented control strategy ~espite redesignaticn to attainment, unless such 

measures are shown to be unnecessary for maintenance or a~e , replaced with measures that achieve equivalent reductions (see additional discussion under ·contingency Plan"). ' Emission 

reductions from source shutdcwns can be considered permanent and 

enforceable to the extent, that those shutdowns have been 

reflected in t~eSIP and all applicable permits have been 

modified acqordingly. . 

.~odelin9 used to demonstrate attain~~nt may be. reli.d upon in the, maintenance demonstration wherethe'llodelinq conforms to 

current EPA guidance and where the state has' projected no 

significant chang~s in the·modeling inputs during the intervening time. Where the oriqinal attainment demonstration may no longer 

be relled upon, states will be expected to remodel using current 

8The EPA-approved modeling guidance may be found in the 

'following documents: "Guideline on Air Quality Models 

(Revised)," OAQPS, RTP, He (EPA-450/2-78-027R) ~ July 1986; 'and 

"PM-10 SIP Development Guideline," OAQPS, RTP, He (EPA-450/2-86-

001), June 1987. 
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EPA referenced techniques. 9 This may be necessary where, for , example, there has.~en a change i~ emissions or a.change.in tie. 

siting of new sources or modificatlons' such that alr quallty m y 

no longer be accurately represented by the existing modeling. 

c. Monitoring Network 

Once an area has been redesignated, the state should 

continue to operate an appropriate air quality monitoring network, in accordance with 40 CFR'Part 58, to.verify the at~ainment status'of the area. The maintenance plan should 

contain provisions for continued operation of air quality monitors .that will provide such verification. In cases where I 

measured mobile source parameters (e.g., vehicle Diles traveled 

conqestion) have changed over time, the state, may also need tal 

perform a saturation monitoring study to determine the need fo~, 

and location of, additional permanent monitors. 

d. VerIfication of Cgntinued Attainment 

Each state should ensure that it has' the legal authority to 

implement and enforce all measures necessary to attain and to I 

maintain theHAAQS •. sections 110(8)(2)(B) and (F) of the Clean 

Air Act, as amended, and r~ulations promulgated at 40 CPR 

51.110(k), suggest that one such'measure is the acquisition of 

ambient and source emission data t'o demonstrate attainment and 

maintenance. 

" 

Regardless of whether the maintenance demonstration is based 

on a showing that future emission inventories will not exceed the 

attainment inventory or on modeling, the state submittal should' 

indicate how the state will track the progress of the maintenance 

plan. ,'. This is necessary due to the fact that the emission. r 

projections made for the maintenanc,e demonstration depend on I 

assumptions of point and area source growth • 

. - One option for tracking the proqress of the maintenance ., 1 

demonstration, provided here as an example, would be for the' j 

state to periodically update the emissIons inventory. In this i 

case, the maintenance plan should specify the frequency of any 1 

planned inventory updates. Such an update could be based, in i 

part, 'on the annual AIRS update and could indicate new source ! I 

growth and other changes from the attainment inventory (e.g., changes in vehicle miles travelled or in traffic patterns). 'As 

an alternative to.a complete update of the inventory, the stat~ may choose to do a comprehensive review of the factors that were 

used in developing the attainment inventory to show no I 

significant change. If this review does show a significant change, the state should then perform an update of the inventory. 

9See references for modeling guidance cited in footnote 8. 
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Where the demonstration is based on modeling, an option for trackin9.~rogress would be for the State to periodically' (typically every 3 years) reevaluate the modeling assumptions and , input data. In any event, the state should monitor the 

indicators for triggering contingency measures Cas discussed 

below) • 

e. contingency Plan 

se~tion 175A of the·Act also requires that a'maintenance 

plan include contingency provisions, as necessary, to promptly 

correct any violation of the NAAQS ~hat occurs after . redesign"tion of the area. These c~ntinqency_ .••• sures are . distinguished from those generally required for nonattainment 

areas under· section 172(0)(.9) and those specificallY'required for 

o -·and co "nonattainment areas under sections 182(c)(9) and 

la7(a)(3), respective~y. For the purposes of section 175A, a 

state is not required to have fully'adopted contingency measures 

that will take effect without further action by the state in 

order'for-the maintenance plan to be approved. However, the 

.continqencyplan is. considered to be an enforceable part of the 

o'SIP . and should ensure that the contingency measures ara' adopted ~xpediently once they are tri9gered.The plan should cl~arly 

identify the measures to be adopted, a schedule and procedure for 

adoptioq and implementation, and a specific time limit for action 

by the state. . As a necessary pare of the plan, the State should 

also identify specific indicators, or triggers, which will be 

used to determine when the contingency measures need to be 

implemented. 

'Where ~he'maintenance demonstration is based on the 

inventory, "the state may, for example, identify an "action level" 

of emissions as the indicator. If later inventory updates show ~at the inventory has exceeded the action level, the State wquld take the necessary steps to implement the contingency measures., 

The indicators would allow a State to take early action to 

address P9tential violations of the NAAQS before they occur. By taking early action, states may be able to prevent any actual 

violations of the NAAQS and, therefore, eliminate the need on the 

part of ~PA to red~siqnate an area to nonattainment • 

. Other indicators to consider include monitored" or modeledviolations of ~he HAAQS (due to the inadequa~y of monitoring data 

in some situations). It is important to note that air quality data in exces~ of the NAAQS will not automatically necessitate a revisi~n of the SIP·whereimplementation of contingency measures 

is adequate to address the cause of the violation. The need for 

a SIP revisi~n is sUbject to the Administrator's discretion • • I 

- The EPA will review what constitutes a contingency plan on a 

case-by-case basis. At a mi~lmum, it must require that the state 

will implement all measures contained in the Part D nonattainment 
I 

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plan for the area prior to redesignation [s~e section 175A(d)].' 

This language suggests that a State may submit a SIP revision ~t the" time of its redesignation request to remove or reduce t.he I 

stringency of control measures. Such a revision can be ~pproved ' 

by EPA if ~t prov~des for ,compensating equivalent reductions. IA 

demonstrat10n that. lIeasurf#s are equivalent would have,to incluae 

appropriate modeling or an adequate justification. Altern~­

tively, a state might be able to demonstrate (through EPA-approved modeling) that the measures are not necessary for 

maintenance of the standard. In e1 ther c,B.se, the contingency plan would have to provide for implementation of any measures 

that were reduced or removed aft~r redesignation of the area. 

sym:mgry 

As stated previously, this memorandum consolidates EPA's 

redesignation and maintenance plan guidance and Regions shoul 

rely upon it as a general framework in drafting Federal BeSist.r 

notices. It 1s strongly suggested that the ,Regional Offices I 

share this document ,with the appropriate States. This should 

give the states ~ better understanding of .what is expected from a 

r.designat.ion request and maintenance plan undcar existinq poli'cy. Any necessary changes to existing Agency policy will be aade 

through our action on specific red,esignation requests and the 

review of section 175A maintenance plans for these particular 

areas, both of which are subject to notice and comment ~le.aking . procedures. Thus, in applying this memorandum to specific I 

circumstances in a rulemeking, Regions should consider the 

applicability of the underlyinq policies to the particular facts 

and to comments submitted by any person. If your staff membe~lls have questions which ~equire clarification, they may contact 

Sharon Reinders at (919).541-5284 for 0 3 - and CO~related issues, 

and Eric Ginsburg at (919) 541-0877 for S02-' PM-10-, and 

Pb-related issues. 

cc: Chief, Air Branch, Regions I-X 

J.ohn Cabaniss, OMS 

Denise Devoe, OAQPS 

Bill Laxton, TSD ' 

Rich Ossias, OGC 

John Rasnic, SSCD 

John seitz, OAQPS 

Mike Shapiro, OAR 

Lydia Weqman, OAQPS