I,

UNITEDSTATES ENVIRONMENTALPROTECTION AGE OfficeofAirQualityPlanningand Standards ResearchTrianglePark, NorthCarolina27711 

## 4SEP

## 1992

MEMORANDUM iURl'BOGRAMSBRAHCl

## ~J?nnf1

SUBJECT: Procedures for Processing to Attainment

FROM:

TO:

Purpose John Calcagni,**Directo~~z==** 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 ofAir Quality PlannIng and Standards (OAQPS) expects that a number ofredesignation 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 ProtectionAgency's (EPA's) guidance regarding the processing ofrequests for redesignation of nonattainment areas to attainment for ozone (03)' carbon monoxide (CO), particulate matter (PM-lO), sulfur dioxide (S02)' nitrogen dioxide (N02), and lead (Pb). Regions should use th1s guidance as a general framework for drafting Federal Register notices pertaining to redesignation requests. Special concerns for areas seeking redesignation from unclassifiable to attainment will be addressed on a**c~se-by-case** basis.
Background

section l07(d)(3)(E) ofthe Clean AirAct, as amended, states that an area canbe redesignated to attainment ifthe following conditions are met:.,,-... 2

1. The EPAhas determined that the national ambient air quality standards (NAAQS) have been attained.

2. The applicable implementation plan has been fully approved by EPA under section 110(k).

3. The EPAhas determined thatthe improvement in air quality is**du~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 ofthese criteria is discussed in more detail in the following paragraphs. Particular attention is given to maintenance plan provisions at the end ofthis document since maintenance plans constitute a new requirement under the amended Clean Air Act. Exceptions to the guidance will be considered on
a case-by-case basis.

1. Attainment ofthe Standard

The state must show thatthe area is attaining the applicable NAAQS. There are two components involved in making this demonstration which shouldbe considered interdependently. The first component relies upon ambient air quality data. The data that are used to demonstrate attainment shouldbe the product of ambientmonitoring that is representative ofthe area ofhighest concentration. These monitors shouldremain at the

same location for the duration ofthe monitoring period required for demonstrating attainment. The data shouldbe collected and quality-assured in accordance with 40 CFR 58 and recorded inthe Aerometric InformationRetrieval System (AIRS) in order for it to be available to the public for review. For purposes of redesignation, the Regional Office shouldverify thatthe integrity ofthe air quality monitoring networkhas been preserved.

For PM-10, an areamaybe considered attaining the NAAQS if the number ofexpected exceedances per year, according to 40 CFR 50.6, is less than or equal to 1.0. For03, the areamust show that the average annual number of expectedexceedances, 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. In making this showing, both PM-10and03 must rely on 3 complete, consecutive calendaryears ofquality-assured air quality monitoring data, collected in accordance with 40 CFR 50, Appendices Hand K. ForCO, an areamay be considered attaining the NAAQS ifthere are no violations, as determined in accordancer'

..**~,** 3

with 40 CPR 50.8, based on 2 complete, consecutive calendaryears of quality-assuredmonitoring data. For 502' according to 40 CFR 50.4, an area must show no more than one exceedance annually and for Pb, according to section 50.12, an area may show no exceedances on a quarterly basis.

The second component relies upon supplemental EPA-approved air quality**m~deling.** No such supplemental modeling is required for 03 nonattainment areas seeking redesignation. Modelingmay be necessary to determine the representativeness ofthe monitored data. Forpollutants such as s02 and CO; a small number of monitors typically is notrepresentative ofareawide air quality

or areas.ofhighest concentration. Whendealing with s02' Pb, 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 ofpassage of the Clean Air ActAmendments of 1990), dispersion modeling will generally be necessary to evaluate comprehensively sources' impacts and to determine the areas ofexpected high concentrations based upon current conditions. Areas which were designated nonattainmentbased on modelingwill generally notbe redesignated to attainmentunless an acceptable modeling analysis indicates attainment. Regions should consult with OAQPS for further guidance addressing the need for modeling in specific circumstances.

2. state Implementation Plan (SIP) Approval

The SIP for the areamustbe fUlly approvedunder section 110(k),1 and must satisfy all requirements that apply to the

area. It shouldbe noted that approval action on SIP elements and the redesignation requestmay occur simUltaneously.. Anarea cannotbe redesignated ifa required element of its plan is the sUbject of a disapproval; a finding of failure to submit or to implement the SIP; or partial, conditional, or limited approval. However, this does notmean that earlier issues with regard to the SIP will be reopened. Regions shouldnot reconsider those things thathave already been approved and for which the Clean AirActAmendments did not alterwhat is required. In contrast, to the extentthe Amendments add a requirement or alter an existing requirement so that it adds somethingmore, Regions should consider those issues. In addition, requests from areas known to be affected by 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 action on plan submissions. It addresses completeness, deadlines, full and partial approval, conditional approval, anddisapproval.3. 4

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 in emission rates (e.g., reduced production or shutdown due to temporary adverse economic conditions) or unusually**fav~rable** meteorologywould notqualify as an air quality improvement due to permanent and enforceable emission reductions.

In making this showing, the state should estimate the percent**~eduction** (fromthe year thatwas used to determine the design value for designation and classification) achieved from Federal measures such as 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 implemented controls. 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·110 and Part 0 Requirements

For the purposes ofredesignation, a state mustmeet all requirements of section 110 and Part 0 thatwere applicable prior to submittal ofthe complete redesignation**reque~t.** When evaluating a redesignation request, Regions should not consider whether the state has metrequirements that come due under the Act after submittal of a complete redesignation request.3

2T his is consistentwith EPA's existing policy on redesignations as stated in an April 21, 1983 memorandum titled "Section 107 Designation Policy Summary." This memorandum states that in order for an areato be redesignated to attainment, the Statemust show that "actual enforceable emission reductions are responsible for the recent air quality improvement." This element ofthe policy retains its validity under the amendedAct pursuant to section 193. [Note: other aspects ofthe April 21, 1983 memorandum have since been supersededby subsequent memorandums; interestedparties should consultwith QAQPS before relying on these aspects, e.g. those relating to required years of air quality data.]

3under section 175A(c), however, the requirements of Part 0 remain in force and effect for the area until suchtime as it is redesignated. Upon redesignation to attainment, the requirements thatbecame due under section 175A(c) after submittal ofthe complete redesignation requestwould no longerbe applicable

.



## ..5

-- However, any requirements that came due prior to submittal ofthe redesignation request must be fully approved into the plan at or before the time EPA redesignates the area.

To avoid confusion concerningwhat requirements will be applicable for purposes ofredesignation, Regions should encourage**State~** to work closely with the appropriate Regiqnal Office early irrthe process. This will help to ensure that a redesignation request submittedby the state has a high likelihood ofbeing approvedby EPA. Regions should advise states ofthe practical planning consequences ifEPA disapproves the redesignation request or ifthe request is invalidated because ofviolations recorded during EPA's review. Under such circumstances, EPA does nothave the discretion to adjust schedules for implementing SIP requirements. As a result, an
area mayrisk sanctions and/or Federal implementation plan implementation that couldresult from failure to meet SIP submittal or implementation requirements.

a. Section 110 Requirements

section 110(a)(2) contains general requirements nonattainment plans. Most ofthe provisions ofthis the same as those contained in the pre-amendedAct. provide guidance on these requirements as needed.4 for section are We will

b. Part DRequirements

Part Dconsists ofgeneral 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. The general requirements appear in subpart 1. The requirements relating to 03' CO, PM-10, S02' N0 2, and Pb appear in subparts 2through 5. In those instances where an area is sUbjectto both the general nonattainment provisions in subpart 1 as well as one ofthe pollutant-specific subparts, the general provisions maybe subsumedwithin, or supersededby, the more specific requirements of subparts 2 through 5.

If an area was not classifiedunder section 181 for 03' or section 186 for CO, then that area is only subject to the provisions of subpart 1, "NonattainmentAreas in General." In addition to relevant provisions in subpart 1, an 03 and CO area, which is classified, mustmeet all applicable**requ~rements** in subpart 2, "Additional Provisions for Ozone NonattainmentAreas," and subpart 3, "Additional Provisions for CarbonMonoxide

4General guidance regarding the requirements for SIP's may be found in the "General Preamble to Title I ofthe 1990 Clean AirActAmendments," 57 FR13498 (April 16, 1992).6

NonattainmentAreas," respectively, before the area maybe redesignated to attainment. All PM-I0 nonattainment areas (Whether classified as moderate or serious) must similarly meet the applicable general provisions of SUbpart 1 and the specific PM-I0 provisions in subpart 4, "Additional Provisions for Particulate Matter NonattainmentAreas." Likewise, S02' N02, and Pb**nonattainme~t** areas are subjectto the applicable generql nonattainmentprovisions in SUbpart 1 as well as the more specific requirements in subpart 5, "Additional Provisions for Areas DesignatedNonattainment for Sulfur Oxides,Nitrogen Dioxide, andLead."

i. Section 172(c) Reguirements

This section contains general requirements for nonattainment plans. Athorough discussion ofthese requirements maybe found in the General Preamble to Title I [57 FR13498 (April 16, 1992)]. The EPA anticipates that areas will already have met most or all ofthese requirements to the extentthat they are not superseded by more specific Part Drequirements. The requirements for reasonable further progress, identification of certain emissions increases, and othermeasures needed for attainmentwill not apply for redesignations because they only have meaning for areas not attaining the standard. The requirements for an emission inventory will be satisfiedby the inventory requirements ofthe maintenance plan. The requirements ofthe Part D new source review programwill be replacedby the prevention of significant deterioration (PSD) programonce the

area has been redesignated. However, in orderto ensure that the PSD programwill become fully effective immediately upon redesignation, eitherthe State mustbe delegated the Federal PSD programor the State mustmake any neededmodifications to its rules to have the approved PSD program apply to the affected area upon redesignation.

ii. Conformity

The State mustworkwith 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, wecurrently interpretthe conformity requirementto apply to attainment areas. However, EPAhas not yet issued its conformityregulations specifyingwhat areas are SUbject to the conformity requirement. Therefore, ifa State does not have conformityprocedures in place at the time that it submits a redesignation request, the Statemust committo follow EPA'S conformity regulation upon issuance, as applicable. Ifthe State submits the redesignation request subsequentto EPA'S issuance ofthe conformity regulations, andthe conformity requirementbecame applicable to the area priorto submission,7

the state must adopt the applicable conformity requirements before EPA can redesignate the area.

5. Maintenance Plans

section 107(d)(3)(E) ofthe amended Act stipulates that for

an area to be redesignated, EPA must fully approve a maintenance plan which**mee~s** the requirements ofsection 175A. AState may submit both the redesignation request and the maintenance plan at the same time and rulemaking on bothmayproceed on a parallel track. Maintenance plans may, ofcourse, be submitted and approved by EPAbefore a redesignation is requested. However, according to section 175A(c), pending approval ofthe maintenance plan and'redesignation request, all applicable nonattainment area requirements shall remain in place.

section l75A defines the general framework of a maintenance plan. The maintenance plan will constitute a SIP revision and must provide for maintenance ofthe relevant NAAQS in the area for at least 10 years after redesignation. section 175A further states that the plan shall contain such additional measures, if any, as maybe necessary to ensure such maintenance. Because the Act requires a demonstration ofmaintenance for 10 years after an
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 EPAreview and approval action on the redesignation request. In determining the amount of leadtime to allow, states should considerthat section 107(d)(3)(D) grants the Administratorup to 18 months from receipt of a complete submittal to process a redesignation request. The statute also requires the state to submit a revision of the SIP 8 years after the original redesignation request is approved to provide for maintenance ofthe NAAQS for

an additional 10 years following the first 10-yearperiod [see section 175A(b)].

In addition, the maintenance plan shall contain such contingencymeasures as the Administrator deems necessary to

ensure prompt correction of any violation ofthe NAAQS [see section 175A(d}]. The Actprovides 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 ofthe contingency plan will notnecessitate a revision ofthe SIPunless requiredby 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 ofthe**~~** relevant NAAQS in an area seeking redesignation from8

nonattainment to attainment. We therefore 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 ofthe particular circumstances facing the area proposed for redesignation and based on all relevant information available at the time.

a. Attainment Inventory

The state should develop an attainment emissions inventory to identify the level ofemissions in the area which is sufficient to attain the NAAQS.5 This inventory shouldbe consistentwith EPA's most recent guidance on emission inventories for nonattainment areas available atthe time and should include the emissions during the time period associated with the monitoring data showing attainment.6

Source size thresholds are 100 tons/year for so , N02, and PM-10 areas, and 5 tons/year 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 State has made an adequate demonstration that air quality has improved as a result ofthe SIP (as discussed previously), the attainment inventory will generally be the actual inventory at the time the area attained the standard.

6The EPA's current guidance onthe preparation ofemission inventories for 0 and CO nonattainment areas is contained in the following documenfs: "Procedures for the Preparation

### ot Emission Inventories for CarbonMonoxide andPrecursors ofOzone: Volume I" (EPA-450/4-91-016), "Procedures for the Preparation of Emission Inventories for CarbonMonoxide and Precursors ofOzone: Volume II" (EPA-450/4-91-014), "Emission Inventory Requirements 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 ofthe UrbanAirshedModel" (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 EPAdoes not currently have specific guidance on attainment emissions inventories for S02. In lieu thereof, states are referred to the guidance on emissions datato be used as input to modeling demonstrations, contained inTable 9.1 of EPA's "Guideline onAir Quality Models (Revised)" (EPA-450/2-78-027R), July 1987, Which is generally applicable to all criteria pollutants. Emission inventory procedures and requirements documents are currentlybeing preparedbyOAQPS for PM-10 and Pb;

.,-- these documents are due for release by summer 1992.9

-- according to Clean Air Act section l89(b)(3). However, the inventory should include sources below these size thresholds if these smaller sources were included in the SIP attainment demonstration. Where sources below the 100, 70, and 5 tons/yearsize thresholds (e.g., areas with smaller source size definitions) are sUbject to a State's minor source permit program, these**~ources** need only be addressed in the aggre9ate to the extent that:they result in areawide growth.

For 03 nonattainment areas, the inventory shouldbe based on actual "typical summer day" emissions of-03 precursors (volatile organic compounds and nitrogen oxides) dur1ng the attainment year. This will generally correspond to one ofthe periodic inventories required for nonattainment areas to reconcile milestones. For CO nonattainment areas, the inventory shouldbe based on actual "typical CO season day" emissions for the attainment year. This will generally correspond to one ofthe periodic inventories required for nonattainment areas.

b. Maintenance Demonstration

AState maygenerally demonstrate maintenance ofthe NAAQS by either showing that future emissions ofa pollutant or its precursors will not exceed the level ofthe attainment inventory,

or by modeling to show that the future mix of sources and emission rates will not cause a violation ofthe NAAQS. Under the CleanAir Act, many areas are required to submitmodeled attainment demonstrations to show thatproposedreductions in emissions will be sufficientto attain the applicable NAAQS. For these areas, the maintenance demonstration shouldbe basedupon the same level ofmodeling. In areas where no suchmodeling was required, the State shouldbe able to rely onthe attainment inventory approach. In both instances, the demonstration should be for a period of 10 years following the**r~esignation.** c=-

- Where modeling is relied upon to demonstrate maintenance, eachplan should contain a summary ofthe airquality concentrations expected to result from application ofthe control strategy. In the process, the plan should identify and describe the dispersion model or other airqualitymodel used to project ambient concentrations (see 40 CFR 51.46).

In either case, to satisfy the demonstration requirement the state should projectemissions for the 10-yearperiod following redesignation, either for the purpose of showing that emissions will not**~ncrease** overthe attainment inventory or for conducting modeling. The projected inventory should consider future growth, including population and industry, shouldbe consistent

7G uidance for projecting emissions maybe 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, andmodeling) shouldbe consistentwith current EPAmodeling guidance.8 For 03 and CO, the projected emissions shouldreflect the expected actual emissions based on enforceable emission rates and typical production**rat~s.** For CO, a state should address the areawide component ofthe maintenance demonstration either by showing that future CO emissions will not increase orby conducting areawide modeling. Preferably, the state shouldcarry out hot-spot modeling that is consistentwith the Guideline onAir QualityModels (Revised), in order to demonstrate maintenance ofthe NAAQS. In particular, if the nonattainment problem is relatedto a pattern ofhot-spots then hot-spotmodeling shouldgenerally be conducted. However, hot-spot modeling is not automatically required. For example, if the nonattainment problemwas related solely to stationary point
sources, or ifhighway improvements have been implemented and the associated emission reductions and travel characteristics can be qualitatively documented, then hot-spot modeling is not required. In such cases, adequate documentation as well as the concurrence ofHeadquarters is needed.
Any assumptions concerning emission rates must reflect permanent, enforceable measures. 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 to maintain its implemented control strategy despite redesignation to attainment, unless such

measures are shown to be unnecessary for maintenance or are replaced with measures that achieve equivalent reductions (see additional discussion under "Contingency Plan"). Emission reductions from source shutdowns canbe consideredpermanent and enforceable to the extentthat those shutdowns have been reflected in the SIP and all applicable permits have been modified accordingly.
Modeling used to demonstrate attainmentmaybe reliedupon in the maintenance demonstration where the modeling conforms to current EPA guidance and where the state has projected no significant changes in the modeling inputs during the intervening time. Where the original attainmentdemonstration may no longer be reliedupon, States will be expected to remodel using current

8The EPA-approved modeling guidance maybe found in the following documents: "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 maybe necessary where, for example, there has been a change in emissions or a change in the siting ofnew sources ormodifications such that air quality may
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 attainment status ofthe 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 overtime, the State may also need to perform a saturation monitoring study to determine the need for, and location of, additional permanentmonitors.

d. verification of continuedAttainment



# - Each State should ensure that ithas the legal authority to implement and enforce all measures necessary to attain andto maintain the NAAQS. sections 110(a)(2){B) and (F) ofthe 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 exceed the attainment inventory or on modeling, the state submittal should indicate howthe state will trackthe progress ofthe maintenance plan. This is necessary due to the fact that the emission projections made for the maintenance demonstration depend on assumptions ofpoint and area source growth.

One option for tracking the progress ofthe maintenance demonstration, provided here as an example, wouldbe for the state to periodicallyupdate the emissions inventory. In this
case, the maintenance plan should specify the frequency of any planned inventory updates. Such an update couldbe based, in part, on the annual AIRSupdate 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 maychoose to do a comprehensive review ofthe factors thatwere used in developing the attainment inventory to show no significant change. Ifthis review does show a significant change, the State shouldthen perform an update ofthe inventory.

9s ee references for modeling guidance cited in footnote 8.



# ------...,,--------_.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 contingency measures (as discussed below)

.

e. contingency Plan

section 175A ofthe Act also requires that a maintenance plan include contingency provisions, as necessary, to promptly correct any violation ofthe NAAQS that occurs after**redesign~tion** ofthe area. These contingencymeasures are distinguished from those generally required for nonattainment

areas under section 172(c)(9) and those specifically required for

o and co nonattainment areas under sections 182(c)(9) and 1a7(a)(3), respectively. For the purposes of section 175A, a state is not required to have fully adopted contingency measures thatwill take effectwithout further action by the state in order for the maintenance plan to be approved. However, the contingency plan is considered to be an enforceable part ofthe 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 andprocedure for adoption and implementation, and a specific time limit for action by the State. As a necessary part ofthe plan, the State should also identify specific indicators, or triggers, whichwill be used to determine when the contingencymeasures need to be implemented.

Where the 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 that the inventory has exceeded the action level, the State would take the necessary steps to implement the contingencymeasures. The indicators would allow a State to take early action to address potential violations ofthe NAAQS before they occur. By taking early action, states maybe able to prevent any actual violations ofthe NAAQS and, therefore, eliminate the need on the part of EPAto redesignate an area to nonattainment.

other indicators to consider include monitored ormodeled violations ofthe NAAQS (due to the inadequacy ofmonitoring data in some situations). It is important to note that air quality data in excess ofthe NAAQS will not automatically necessitate a revision ofthe SIPwhere implementation ofcontingency measures is adequate to address the cause ofthe violation. The need for

a SIP revision is sUbject to the Administrator's discretion.

The EPAwill review whatconstitutes a contingency plan on a case-by-case basis. At a minimum, itmustrequire that the State will implement all measures contained inthe Part 0 nonattainment**-------,~-~,~_._---**,"

13
plan for the area prior to redesignation [see section 175A(d)]. This language suggests that a state may submit a SIP revision at the time of its redesignation request to remove or reduce the stringency of control measures. Such a revision can be approved by EPA ifit provides for compensating equivalent reductions. A demonstration that measures are equivalent would have to include appropriate modeling or an adequate justification. Alternptively, a state might be able to demonstrate (through EPA-approvedmodeling) that the measures are not necessary for maintenance ofthe standard. In either case, the contingency plan would have to provide for implementation of any measures that were reduced or removed 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 Register notices. It is strongly suggested that the Regional Offices share this document with the appropriate states. This should give the States a betterunderstanding ofwhat is expected from a redesignation request and maintenance plan under existing policy. Any necessary changes to existing Agency policy will be made through our action on specific redesignation requests and the review of section 175Amaintenance plans for these particular
areas, both ofwhich are subject to notice and comment rulemaking procedures. Thus, in applying this memorandum to specific circumstances in a rulemaking, Regions should consider the applicability ofthe underlying policies to the particular facts and to comments submittedby any person. Ifyour staffmembers have questions which require clarification, they maycontact Sharon Reinders at (919) 541-5284 for 03- and CO-related issues, and Eric Ginsburg at (919) 541-0877 for S02-' PM-I0-, and Pb-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 Lydia Wegman, OAQPS