## ( ,.

UNITEDSTATES**ENVIRONME~TAL**PROTECTIONAGENCY OfficeofAirQualityPlan.ningandStandards ResearchTrianglePark, NonhCarolina2nll 

# 45EP1992

K£M01WIDUH
SUBJECT: Procedures for processing to Attaimaent

FROM: 

### John Calcagni,**Directo~~z=~**

TO:



### Purpose Air QualityHanagement 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:

# .. 2
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 

### dueito 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.) 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.limited 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 CleanI 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.4 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 enforce'able.2 Attainment resultinq ,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 qualify 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 DRequirements
For the purposes'of

.r.designation, a',State must meet all requirements of**se~tion** 110 and Part Dthat 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 theApril**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.5 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. ' I I 

### I I the

I 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 adjust**~.** 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 DBeguirements for section are We will

Part Dconsists 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 03, 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 03 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

, , 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).6 Nonattainment.Areas," respectively, before the area lDay be**rede~ignated** tOtattainment. 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 nonattainmentprovisions 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 Drequirements. 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 Dnew 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 modificationsto its rules to·have the approved PSD program apply to the affected area upon**z:edesi9n~tion.** .... . ii.**','CQnforJlli~**

,

# . The state must work with EPA to show that its SIP provisions are consis'tent with section 116(c)(4) confonaity, 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,

.7 I
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 afterIan

.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)]. "

, I In addition, the maintenance plan shall contain such 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 from8
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 time6period 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.**

### I
! I 

### I 9 ,I ' I 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 basedIon 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
Astate 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 industryI should be consistent:

7Guidance for projecting emissions may be found in the emissions inventory guidance cited in footnote 6. ....r; ."10
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 a1ther 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 orderto 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

8T

# he 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.i



### I

I 

### I r .•

11 

## I
I 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 my 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 ithas'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 8.12
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 effectwithout 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 DnonattainmentI i I I



### I 13 

### I 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 e1ther 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 particularfacts 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 03- 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