MEMORANDUM UNITEDSTATES ENVIRONMENTALPROTECTIONAGE Off1ceofAir·OualityPlannmgandStaf)dards ResearchTrianglePark. NorthCarolma27711 

## 4SEP

# 1992

SUBJECT: Procedures for Processing to Attainment FROM:
TO:

Purpose John Calcagni,

**Directo~~~~** Air Quality Management Director, Air, Pestic' es and Toxics nt Division, Regions I and IV Director, Air and Waste Management Division, Region 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, Air and Toxics Division, Regions VII, VIII,.IX, and X Areas

The Office 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

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

# I· consolidates the Environmental ProtectionAgency's (EPA!s) guidance regarding the processing of requests for redesignation of nonattainment areas to attainment for ozone (03), carbon 

### I mc;moxide C<;:O)! particulate matter (PM-10).'

**~ulfur dioxid~** 

**(So ~,** 

**n~trogen d~ox~de**  (NO), and lead (Pb).

**Reg~ons** should use

**th~s** guidance as a



### genera~ framework for drafting Federal Register 

### I notices pertaining to redesignation requests. Special concerns for areas seeking redesignation from unclassifiable to attainment will be addressed on a case-by-case basis. Background Section 107(d)(3)(E) of the Clean AirAct·, as amended, states that an area can be redesignated to attainment if the following conditions are met:2 1. The EPA has determined that the national ambient air quality standards '(NMQS) have been attained. 2.' The applicable implementation plan has been fully approvedby EPA under section 110(k). 3. The EPA has determined that the improvement in air quality is due::to permanent and enforceable reductions in · emissions. 4. The State has met all applicable requirements for the area under section 110 and Part D. 5. The EPA has fully approved a maintenance

..plan, including a contingency plan, for the area under section 175A. Each of these criteria is

**di~cussed** in more detail in the following paragraphs. Particular attention is given to maintenance plan provisions at the end of this document since maintenance plans constitute a new requirement under the amended Clean Air Act. Exceptions to the guidance will.be consideredon a case-by-case basis. · 1. Attainment of the Standard The State must show that the area is attaining the applicable NAAQS. There are two components involved in making this demonstration which should be considered interdependently. The first component relies upon ambient air quality data. The data that are used to demonstrate attainment should be the product of ambient monitoringthat is representative of the area of highest concentration. These monitors should remain at the same location for the duration of_themonitoring··period required for demonstrating attainment. The data should be collected and quality-assured in accordancewith 40 CFR 58 and recorded in the Aerometric Information Retrieval system (AIRS) in order for itto be available to the public for review. For purposes of redesignation, the Regional Office.shouldverify thatthe integrity of the air qualitymonitoring network has been _preserved.- For PM-10, an area may be consideredattaining the NAAQS if 1:he_number of expected exceedances per year, according to 40 CFR 50.6, is less than or equal to l.0.

. For o3, the area must show that the average
__annual number of expected exceedances, according to 40 CFR 50.9, is less than or equal to 1.0 based on data from all monitoring sites in the area or its affected downwind· environs. Inmaking this showing, both PM-10 and

### o3 must rely on 3 complete,.,.consecutive.-,calendar,.years.!Of,.,quality.-assured

...al·r"··'"···--·· qualitymonitoringdata, collected·in accordance with 40 CFR 50, Appendices Hand K. For CO, an area may be considered attaining the NAAQS if there are no violations, as determined in accordance3 with 40 CFR 50.8, based on 2 complete, consecutive calendar

**ye~rs** of quality-assured monitoring data. For 502, according to 40 CFR 50.4; an area must show no more than-one exceedance annually and for Pb,

**~ccording** to section 50.12, an area may show no exceedances on a quarterly basis. The second component relies upon supplemental EPA-approved air quality modeling. No such supplemental modeling is required for o3 nonattainment areas seeking redesignation. Modeling may be necessary to determine the representativeness of·.the-monitared data. For pollutants such as 502 andCO; a small number of 

### I monitors typically is not representative of areawide air quality or areas.of highest concentration. When dealingwith so2, Pb,

### I PM-10 (except for a limited number of initial moderate

. nonattainment areas), and co (exceptmoderate areas with design values of 12.7 parts permillion or lower at the time of passage of the Clean Air Act Amendments of 1990), dispersion modeling 

## I will generallybe necessary to evaluate comprehensively sources' impacts and to·determine the areas of expectedhigh

. ·. j concentrations based upon current conditions. Areas which were designated nonattainmentbased on modelingwill generally not be redesignated to attainment unless an acceptable modeling analysis indicates attainment. Regions shouldconsult with OAQPS for· further guidance addressing the need for modeling in specific circumstances. · 2. state Implementation Plan CSIPl Approval Thr SIP for the area mustbe fully approvedunder section 110(k), andmust satisfy all requirements that applyto the area. It shouldbe noted that approval action on SIP elements andthe redesignationrequestmay occur simultaneously.. An area cannot be redesignated if a required element of its plan is the subject of a disapproval; a finding of failure to submit or tal implement the SIP; or-partial, conditional, or limited approval. However, this does not mean that earlier issues with regard to the SIP will be reopened. Regions shouldnot reconsider those things that have alreadybeen approved and for which the Clean AirActAmendments did not alterwhat is required. In contrast, to the extenttheAmendments add a requirement or alter an 

### I existing.requirement so that it adds somethingmore, Regions should consider those issues. In addition, requests from areas known to be affectedby dispersion techniques which are inconsistentwith EPA guidance will continue to be considered unapprovable under section 110 and will not qualify for redesignation.

1section 110(k) contains the requirements for EPA ac'tion on plan submissions; Itaddresses completeness, deadlines, full and partial approval, conditional approval,·anddisapproval.4 3

.. Permanent and· Enforceable Improvement in Air Quality The State must be able to reasonably attribute the · improvement in air quality to emission reductions which are permanent and enforceable.2 Attainment resulting from temporary reductions iri emission rates (e.g., reduced production or shutdown due to temporary adverse economic-conditions) or . unusually favorable meteorology wouldnotqualify as an air quality improvement due to permanent and enforceable emission r_eductions• , .. Inmaking this showing, the•State should'estimatethe percent reduction (from the year thatwasused to determine the design value for designation and classification) achieved.from Federal·measures suchas the Federal Motor Vehicle Control Program and fuel volatility rules as well as control measures thathave been adopted and implementedbythe'State. This

. estimate should consider emission rates, production capacities, and other related informationto clearly show that'the air. quality improvements are the result of implementedcontrols. The analysis should assume that sources are operating at permitted levels (or historic peak.levels)·unless evidence is presented that such an assumption is unrealistic. 4. Section·llO and Partp Requirements For the purposes of·redesignation, a·State must meet all requirements of section 110 and Part 0 that were applicable prior to submittal of the complete redesignation

**reque~t.** When evaluating a redesignationrequest, Regions should not consider ·whether the Statehas met requirements that come due

**und~r** the

Act after submittal of a complete redesignation request

.. 2This is consistent·withEPA's existing policy on redesignatians as .stated iri anApril 21, 1983 memorandum titled "Section 107 Designation Policy summary." This memorandum states that in order for an area tobe redesignated to attainment, the Statemust show that "actual enforceable emissionreductions are responsible for the recent air quality improvement." This element of the policyretains itsvalidityunder the.amended Act pursuant to section 193. [Nate: other aspects of theApril 21; 1983 memorandum have sincebeen supersededby subsequent

**memorandums~.interested** parties should consultwith OAQPS before relying on these aspects, e.g. those relating torequired years of air quality data.] 3under section 175A(c), however, the requirements of PartD

**remain·~**in.force

..and

..effect.for.·the area unt-il'such"time'·as it·is· redesignated. Upon redesignation to attainment, the requirements thatbecame due under section 175A(c) after submittal of the · complete redesignatianrequestwouldno longerbe applicable.

## ;-i~:i~;~-~

..

**:~o.** 5 However, any requirements that came due priorto submittal of the redesignation request mustbe fully approved into the plan at

**o~** before the time EPA redesignates the area. To avoid confusion concerningwhat requirements will be applicable for purposes of redesignation, Regions should encourage States to work closely with the appropriate RegiQnal Office early in the process. Thiswill 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 consequences if EPA disapproves the redesignation request or if the request is invalidated

. 

### I because of 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 couldresult from failure to meet SIP submittal or implementation requirements.
a. Section 110Reguirements Section 110(a)(2) contains general requirements nonattainment plans. Most of the provisions of this the same as those contained in the pre-amended Act. provide guidance on these requirements-as needed.4 b. Part p Reguirements for section We will are

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 specificto eachpollutant. Thegeneral requirem.ents

## I appear in subpart 1. The requirements relating to o3, CO, PM-10, so2, N02, and Pb appear in subparts 2 through 5. In those instances where an area is subjectto boththe general nonattainment provisions in subpart 1 as well as one of the pollutant-specific subparts, the general provisions may-be subsumedwithin, or supersededby, themore specific requirements of subparts 2 through 5. · If an area was not-classifiedunder ·section 181 for-o3, or section 186for co, then that area is only subjectto the provisions of subpart 1, "NonattainmentAreas in General." In addition to relevant provisions in subpart

**1~** an o3 and co area, which is classified, mustmeet all applicablerequ1rements in 

### r subpart 2, "Additional Provisions for Ozone Nonattainment Areas," and subpart 3, "Additional Provisions for Carbon Monoxide 4General guidance regarding the requirements for SIP'smay be found inthe "General Preamble to Title I of the 1990 Clean Air Act Amendments," 57 FR 13498 (April 16, 1992).6 Nonattainment"Areas," respectively, before the area may be

**rede~ignated** to,attainment. All PM-10 nonattainment areas (whether classified

**a~** moderate or serious) must similarlymeet the applicable general provisions of subpart 1 and the specific PM-10 provisions in subpart 4, '"'Additional Provisions for Particulate Matter Nonattainment Areas." Likewise, so2, N02, and Pb nonat'tainment areas are subject to the applicable

**gener~1** nonattainment"provisions in subpart 1 as well as the more specific requirements in subpart 5, "Additional Provisions for Areas DesignatedNonattainme,Ht for SulfurOxides,"Nitrogen Dioxide, and Lead."

. " i. Section 172Ccl Requirements' This section contains general requirements.for nonat:tainment plans. Athorough discussion of.these requirements may be found in the General Preamble to Title I (57 FR 13498 (April 16, 1992)]. The EPA anticipates that areas will already havemet most or all of these requirements to the extentthat they are not superseded bymore specific Part Drequirements. The requirements for reasonable further progress, identification of certain emissions increases, and other measures needed for. attainment will not apply for redesignations because they only have meaning for areas not attaining the standard. The requirements for.an emission inventorywill be"satisfied by the inventory requirements of themaintenance plan. The requirements of the Part Dnew source review program will be replaced by the prevention of significant deterioration (PSD) programonce the area has been redesignated. However, in order to ensure that the PSD programwill become fully.effective immediately upon redesignation, eitherthe State must be delegatedthe Federal PSD program or the statemust make any neededmodifications-to its rules to have the approved PSD program apply to the .affected area upon r:ed.esignation. ". ii. ".conformity The Statemust workwith EPA to showthat·its SIP provisions are consistentwith section 176(c)(4) conformity" requirements. The redesignation request should include conformity procedures, ifthe State already has these procedures in place: Additionally, we currently interpretthe conformity " requirement to apply to attainment areas. However, EPA has not yet issued its conformityregulations specifyingwhat areas are subject"to the conformityrequirement. Therefore, if a state does not have conformity

**proc~dures** in place at the time that it" submits a

**redesig~ation** request, the state"must commit to follow EPA'!> conformityregulation upon issuance, as applicable. If the State submits the"redesignation request·subsequent·to EPI\'s·" issuance of the conformityregulations, and the conformity requirement became applicable to the area prior to submission,

. '

**~** .7 the state must adopt the applicable conformity requirements before EPA can redesignate the area. 5. Maintenance Plans Section 107(d)(J)(E) of'the amended Act stipulates that for an area to be redesignated, EPA must fully approve a maintenance plan which meets the requirements of section 1'75A. AState

**rna~** submit both the redesignation request and the maintenance plan at the same time and rulemaking on both may proceed on a parallel- track. Maintenance plans may, of course, be submitted and approved by EPA before a redesignation is requested. However, according to section 175A(c), pending approval of the maintenance _plan andredesignation request, all_applicable·nonattainment ar'ea requirements shall remain inplace.

. 

### I section 175A defines the general framework of a-maintenance plan. The maintenance plan wil.l constitute a SIP revisi-on arid

### I must provide for maintenance of the relevant NAAQS in the area · for at least 10 years after redesignation. Section 175A further states that the plan shall contain such additional measures, 

### ii any, as may be necessary to ensure such maintenance. Because the Act requires a demonstration of maintenance for 10 years afterian area is redesignated (not 10 years after Submittal of a redesignation request), the State should plan for some lead time for EPA action on the request. In other words, the maintenance demonstration should projectmaintenance for 10 years, beginning from a date which factors in the time necessary for EPA reviewj and approval action on the redesignation request. In determining the amount of lead time to allow, States should consider that 

### I section 107(d)(J)(D) grants the Administrator up to 18 months from receipt of a complete.submittal to process a redesignation request. The statute also requires the State to submit a 

### I revision of the SIP 8 years after the original redesignation request is approved to provide for maintenance.of the NAAQS foz:; an additional 10 years following the first 10-yearperiod [see section 175A(b)]. In addition, the maintenance plan shall contain such contingencymeasures as the-Administratordeems necessary to ensure prompt correction of any violation of the NAAQS [see section 175A(d)]. The Act provides that, 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 contingencyplan will notnecessitate a revision·of 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 seekingredesignation from8 nonattainment to attainment.. We

**th~refore** recommend that States seeking redesignation of a· nonattainment area consider these provisions. However, any final 'EPA determination regarding the 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 redesignationand based on all relevant information available at the time. I

.

a.·. Attainment Inventory The State should develop an attainment emissions inventory to identify.the level of emissigns in the area which is ' sufficient to attain the NAAQS. · This inventory.'should be

.. ·consistent·with EPA's most recent guidanceon emission

inventories for nonattainment areas available at the time and should include the emissions during the time period associated with the monitoring data showing attainment.6

. '. Source size thresholds are 100 tonsjyear for SO , N02, and PM-10 areas, and 5 tonsjyear for Pbbasedupon



### 40.CF~ 51.100(k) and 51.322, as well as establishedpractice for AIRS data. The source size threshold for serious PM-10 areas is 70.tons/year 5where the Statehas made an adequate demonstration that air quality has improved as a result of the SIP (as discussed previously), the attainment inventory will generally

**beth~** actual inventory at the time the area attained the standard. 6The EPA's current guidance on the



### prepar~tion of emission inventories for o3 and co nonattainment.areas is contained in the following documents:. "Procedures for the Preparation of Emission Inventories for CarbonMonoxide and Precursors of ozone: Volume I" (EPA-450/4-91.:.016). "Procedures for the Prepara.tionof

. Emission Inventories for CarbonMonoxide and Precursors of Ozone: Volume II" (EPA-450/4-91-014), "Emission InventoryRequirements for Ozone State Implementation Plans" (EPA-450/4-91-010), "Emission Inventory Requirements for carbonMonoxide Implementation Plans" (EPA-450/4-91-011), "Guideline for Regulatory Application of the Urban AirshedModel" (EPA-450/4-91- 013), "Procedures for Emission Inventory Preparation: Volume IV, Mobile Sources" (EPA-450/4-81-026d), and "Procedures for Preparing·Emission.Inventory Projections" (EPA-450/4-91-019). The EPA does not currentlyhave specific guidance on attainment emissions inventories.for

# so2•. In lieu thereof, States are referred to the guidance on emissions data to be used as input to modeling demonstrations, contained in Table 9.1 of EPA's "Guideline onAir QualityModels (Revised)" (EPA-450/2-78-027R), July 1987,.J•7hJc;:his.generally applicable to,all.criteria

..... pollutants. Emission inventory procedures and requirements documents are currentlybeingpreparedby·OAQPS·forPM-.10 and Pb; these documents are due for releaseby summer 19.92., ....



### '#:~%: 9 according to Clean Air'Act section 189(b)(3). Howe"er, the inventory should include sources below these size thresholds i these smaller sources were included in the SIP attainment demonstration. Where sources below the 100; 70, and 5 tonsjye r- size thresholds (e.g., areas with smaller source size definitions) are subject to a State'sminor source permit program, these sources need onlybe addressed in the aggregate to the extent tha.t'they result in areawide growth.

**~-For** 03 nonattainment areas, the invento).-yshouldbe based on actual "typical summer day" emissions of·o3 precursors (volatile organic compounds and.nitrogen oxides) dur).ng the attainment · year. This will generally correspond to one of the periodic inventoriesrequired for nonattainment areas to reconcile milestones. Forco nonattainment areas, the inventory shouldbe based on actual "typical co season day" emissions for the attainment year. This will generally correspond to one of the periodic inventories required for nonattainment areas. b. Maintenance Demonstration AStatemay generallydemonstratemaintenance of the NAAQS by either showing that future emissions of a pollutant or its I precursors will not exceedthe level of the attainment inventory, or by modeling to show that the future mix 

### ofsources and emission rates will not cause a violationof the NAAQS. Under the Clean Air Act, many areas are required to submitnodeled attainment demonstrations to show that proposed-reductions in emissions will be sufficientto attain the applicable NAAQS.

**~or** these areas, the maintenancedemonstration should be basedupon the same level of modeling. In areas where no such modeling wa!s · required, the state shouldbe able to relyon the attainment 

### I inventory approach. In both instances, the demonstration shouldbe for·a period of 10years following the redesignation.

. c::: Where modeling is relied upon to demonstrate maintenance, each plan should contain a summary of the airquality concentrations expected to result from application of the control strategy. In the process, the plan should identify and descritJe the dispersion model or other air qualitymodel used to

**projec~** ambient concentrations (see 40 CFR 51.46)• · ·· 

# I'
In either case, to satisfythe demonstration requirement



### t~e State shouldproject emissio_ns for the 10-yearperiod following! redesignation, either for the purpose of showing that emissions will not

**~ncrease** over the attainment inventoryor for conducting modeling. The projected inventory should consider fUture growth, including-population and industry, shouldbe consistent 7Guidance for projecting emissions may be found in the emissions inventory guidance cited in footnote 6. 

# .. )"

**~.**10 with the attainment inventory, and·should doCument data inputs and assumptions. All elements of the demonstration (e.g.-, emission projections, new source growth, and

**m~deling)** shouldbe consistent with current EPA modeling guidance. For o3 and co, the projected emissions should reflect the expected actual emissions based on

**enforce~ble** emission rates and typical· production

**rat~s.** For CO, a State should address the areawide component of themaintenance demonstration eitherby showing that future co· emissions will not increase orby conducting areawide modeling. Preferably, the State should carry otit hot-spot.modeling that is consistent with the Guideline on Air QualityModels (Revised), in orderto demonstrate maintenance of the NAAQS. In particular, if the_nonattainment problem is related to a pattern of hot-spots then hot-spotmodeling shouldgenerally be.conducted. However, hot-spotmodeling is not automatically required._ For example, if the nonattainment problemwas related solely to stationarypoint sources, or if highway improvements have been implemented and the associated emission reductions,and travel characteristics canbe qualitatively documented, then hot-spot modeling is not required. In such cases, adequate documentation as well as the concurrence of Headquarters is needed.

.. ._, Any assumptions concerning emission rates must reflect permanent, enforceablemeasures. In otherwords, a State generally cannot'take credit in the maintenance demonstration for reductions unless there are-regulations inplace requiring those ,reductions or the reductions are-otherwise.shown to be permanent. Therefore, the State will be expected tomaintain its implemented control strategy despite redesignation to attainment, unless such measures are shown to be unnecessary for maintenance or

**a~e** _ replacedwith measures that achieve equivalent reductions (see additional discussion under "ContingencyPlan"). Emission reductions from source shutdowns can be considered permanent and enforceable to the extent.that those shutdowns have been reflected in

**t~e** SIP and all applicable permits have been modified accordingly. Modeling used to demonstrate attainm!!nt may be.relied upon in themaintenance demonstration where themodeling conforms to current EPA guidance and where the Statehas projected no significant changes in the-modeling inputs during the intervening time. Where the original attainment demonstration may no longer be relied upon, States willbe expected to remodel using current 8The EPA-approved modeling guidance may be found in the ·followingdocuments: "Guideline onAir QualityModels (Revised)," OAQPS, RTP, NC (EPA-450/2-78-027R); July 1986; ·and "PM-10 SIP Development Guideline," OAQPS, RTP, NC (EPA-450/2-86- 001), June 1987.11 EPA referenced techniques.9 This may be necessary where, for example, there has been a change in emissions or a change in t e siting of new sources or modifications·such that air quality 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 qualitymonitoring network, Jn accordance with 40 CFR'Part 58, to verify the attainment status·of the area. The maintenance plan should contain provisions for continued operation of air quality monitors thatwill provide such verification. In cases where measured'mobile source parameters (e.g., vehicle miles traveled congestion) have changed over time, the Statemay also need toj perform a saturationmonitoring study to determine the need for, and location of, additional permanentmonitors. d. Verification of Continued Attainment Each state should ensure that ithas the legal authority to implement and enforce all measures necessary to attain and to I maintain the NAAQS•. Sections 110(a)(2)(B) and (F) of the Clean Air Act, as amended, and regulations promulgated at 40 CFR 51.110(k), suggest that one such measure is the acquisition of ambient and source emission data to demonstrate attainment and maintenance. Regardless of whether the maintenance demonstration is based on a showing that future emission inventories will not exceedthe attainment inventory or onmodeling, the State submittal should indicate how the statewill track the progress of the maintenance plan.

-This is necessary due to the fact that the emission projections made for the maintenance demonstration depend on assumptions of point and area source growth•

.. One option for tracking the progress of the maintenance demonstration, provided here as an example, wouldbe for the State to periodicallyupdate the emissions inventory. In this case, the maintenance plan should specifythe frequency of any plaril'led inventory updates. Such an update could be based, in part,·on the annual AIRS update and could indicate new source growth and other changes from the attainment inventory (e.g., changes in vehicle miles travelled or in traffic patterns). As an alternative to a completeupdate of the inventory, the State! may choose to do. a comprehensiv. e review of the factors thatwez!le used in developingthe attainment inventoryto show no significant charige. If this reviewdoes show a significant change, the state should thenperforman update of the inventory. 9see references for modeling guidance cited in footnote

### a.12 Where the demonstration is based on modeling, an option for tracking.'progress 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 contingencymeasures (as discussed below).
e. Contingency Plan Section 175A of the-Act also requires that a

**maintenanc~** plan include contingency provisions, as necessary, to promptly correct any violation of the NAAQS

**~hat** occurs after redesignation of the area. These contingencymeasures are distinguished from those generally required for nonattainment areas under section 172(c)(9) and those specifically·required for 0 ·and co nonattainment areas under sections 182(c)(9) and



### 1~7(a)(3), respectively. For the purposes of section 175A, a state is not required to have fully-adopted contingency measures tha_t will take effect-without further action by the state in order for the maintenance plan to be approved. However, the .-contingencyplan is.considered tobe an enforceable part of the 'SIP-and should ensure that the contingencymeasures are·adopted expediently once they are triggered. The plan should clearly identify the measures to be adopted, a schedule and procedure for adoption and implementation, and a specific time limit for action by the State. As a necessary part of the plan, the State should also identify specific indicators, or triggers, which will be used to determine when the contingencymeasures need to be implemented. Where the maintenance demonstration is based on the inventory,.the Statemay, for example, identify an "action level" of emissions as the indicator. If later inventory updates show that the inventory has exceeded the action level, the State would take the necessary steps to implementthe contingencymeasures.- The indicators would allowa Stateto take early action to address potential violations of the NAAQS before they occur. By taking early action, States may be able to prevent anyactual violations of the NAAQS and, therefore, eliminate the need on the part of EPA to redesignate an area to nonattainment. ·Other indicators to consider include monitored or modeled· violations of the NAAQS (due to the inadequacyof monitoring data in some situations). It is important to note that air quality data in excess of the NAAQS will not automatically necessitate a revision of the SIP-where implementation of contingency measures is adequate to address the cause of the violation. The need for a SIPrevision is subjectto the Administrator's discretion•



### . ' The EPA will reviewwhat constitutes a contingencyplan on a case-by-case basis. At a minimum, itmust require that the State will implement all measures contained in the Part Dnonattainment13 plan for the area prior to redesignation [see section 175A(d)]. This language suggests that a Statemay submit a SIP revision kt thetime of its redesignation request to remove or reduce the I stringency of control measures. such a revision can be approved by EPA if itprovides for.compensating equivalent reductions. 

### IA demonstration that measurE!s are equivalent would have.to include appropriate modeling or an adequate justification.

**Altern~­** tively, a Statemight be able to demonstrate (through EPA-approved modeling) that the measures are not necessary for maintenance of the standard. In either case, the contingency planwould have to provide for implementation of any measures thatwere reduced orremoved after redesignation of the area. summary As stated previously, this memorandum consolidates EPA's redesignation and maintenance plan guidance and Regions should rely upon it as a general framework in drafting Federal Regist'er notices. It is strongly suggested that the Regional Offices 

### I share this document with the appropriate States. This should give the States a betterunderstanding of.what is expected from a redesignation request and maintenance plan under existingpoli'cy. Any necessary changes to existingAgency policy will be made through our action on specific redesignation requests and the review of section 175A maintenance plans for these particular areas, both of which are subject to notice and comment rulemaking· procedures. Thus, in applying this memorandum to specific 

### I circumstances in a rulemaking, Regions should consider the applicability of the underlying policies to the particular'facts '

. I and to comments

**subm~tted** by any person. If your staff

**membe~js** have questions which require clarification, theymay contact Sharon Reinders at (919) 541-5284 for o3- and

**co~related** issues, and Eric Ginsburg at (919) 541-0877 for so2-, PM-10-, and Ph-related issues.

cc: Chief, Air Branch, Regions I-X John Cabaniss, OMS Denise Devoe, OAQPS Bill Laxton, TSD Rich ossias, OGC John Rasnic, SSCD John Seitz, OAQPS Mike Shapiro, OAR LydiaWegman, OAQPS