MEMORANDUM 

UNITED STATES ENVIRONMENTAL PROTECTION AGE 

Office of Air·Ouality Planning and Staf)dards 

Research Triangle Park. North Carolina 27711 

4 SEP 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 Protection Agency'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)., i;;ulfur dioxid~ (So ~, 

nitrogen dioxide (NO), and lead (Pb). Regions should use this 

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 Air Act·, 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 

approved by EPA under section llO(k). 

3. The EPA has determined that the improvement in air 

quality is due i: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 dii;;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 wi11· be considered on 

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 monitoring that is representative of the area 

of highest concentration. These monitors s_hould remain at the 

same location for the duration of. the monitoring·· period required 

for demonstrating attainment. The data should be collected and 

quality-assured in accordance with 40 CFR 58 and recorded in the 

Aerometric Information Retrieval system (AIRS) in order for it to 

be available to the public for review. For purposes of 

redesignation, the Regional Office.should verify that the 

integrity of the air quality monitoring network has been 

_preserved.-

For PM-10, an area may be considered attaining the NAAQS if 

1:he_number of expected exceedances per year, according to 40 CFR 

50.6, is less than or equal to l.O •. 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. In making this showing, both PM-10 and o3 must rely on 

3 complete ,.,.consecutive .. ,calendar, .years. 1of1 .. quality.-assured ... ai·r" '"· · ·--·· quality monitoring data, coll.ected· in accordance with 40 CFR 50, 

Appendices H and K. For CO, an area may be considered attaining 

the NAAQS if there are no violations, as determined in accordance 
3 

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 o 3 nonattainment areas seeking redesignation. Modeling may be necessary to determine the representativeness of-.the.monitored 

data. For pollutants such as 502 and CO; a small number of I 

monitors typically is not representative of areawide air quality 

or areas .of highest concentration. When dealing with so2 , Pb, I 

PM-10 (except for a limited number of initial moderate . nonattainment areas), and co (except moderate areas with design 

values of 12.7 parts per million or lower at the time of passage 

of the Clean Air Act Amendments of 1990), dispersion modeling I 

will generally be necessary to evaluate comprehensively sources' 

impacts and to· determine the areas of expected high . ·. j 

concentrations based upon current conditions. Areas which were 

designated nonattainment based on modeling will generally not be 

redesignated to attainment unless 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 CSIPl Approval 

Thr SIP for the area must be fully approved under section 

llO(k), and must satisfy all requirements that applyto the 

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 the 

subject of a disapproval; a finding of failure to submit or tol 

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 should not reconsider those 

things that have already been approved and for which the Clean 

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

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

existing. 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 

unapprovable under section 110 and will not qualify for 

redesignation. 

1section llO(k) contains the requirements for EPA ac'tion on 

plan submissions; It addresses completeness, deadlines, full and 

partial approval, conditional approval,·and disapproval. 
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 favo.rable meteorology would not qualify as an air 

quality improvement due to permanent and enforceable emission 

r_eductions • , .. 

In making this showing, the,State should'estimate the 

percent reduction (from the year that was 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 

that have been adopted and implemented by the· State. This . estimate should consider emission rates, production capacities, 

and other related information to 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 p 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 request. When 

evaluating a redesignation request, Regions should not consider · whether the State has met requirements that come due und~r the 

Act after submittal of a complete redesignation request .. 

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

redesignatians as .stated iri an April 21, 1983 memorandum titled 

"Section 107 Designation Policy summary." This memorandum states 

that in order for an area ta be redesignated to attainment, the 

State must show that "actual enf arceable 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. [Nate: other aspects of the April 21; 

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

relying on these aspects, e.g. those relating to required years 

of air quality data.] 

3under section 175A(c), however, the requirements of Part o remain-~in. force .. and .. effect .for.- the area until' such "time'· as it ·is · redesignated. Upon redesignation to attainment, the requirements 

that became due under section 175A(c) after submittal of the · complete redesignatian request would no longer be applicable. 
;-i~:1~;~-~ .. :~o. 

5 

However, any requirements that came due prior to submittal of the 

redesignation request must be fully approved into the plan at o~ 

before the time EPA redesignates the area. 

To avoid confusion concerning what requirements will be 

applicable for purposes of redesignation, Regions should 

encourage States to work closely with the appropriate RegiQnal 

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 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 could result from failure to meet SIP 

submittal or implementation requirements. 

a. Section 110 Reguirements 

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 D consists of general requirements applicable to all 

areas which are designated nonattainment based on a violation of 

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

subparts specific to each pollutant. The general requirem.ents I 

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

so2 , N02 , and Pb appear in subparts 2 through 5. In those 

instances where an area is subject to both the general 

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 more specific requirements of subparts 2 through 5. · 

If an area was not.classified under ·section 181 for-o3, or 

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

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

addition to relevant provisions in subpart 1~ an o3 and co area, 

which is classified, must meet all applicable requirements in r 

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

and subpart J, "Additional Provisions for Carbon Monoxide 

4General guidance regarding the requirements for SIP's may 

be found in the "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 similarly meet 

the applicable general provisions of subpart 1 and the specific PM-10 provisions in s.ubpart 4, "Additional Provisions for 

Particulate Matter Nonattainment Areas." Likewise, so2 , N02 , and 

Pb nonat'tainmen.t areas are subject to the applicable gener~l 

nonattainment .provisions in subpart 1 as well as the more 

specific requirements in subpart 5, "Additional Provisions for 

Areas DesignatedNonattainme,1tt for Sulfur Oxides, ·Nitrogen Dioxide' and Lead. II ' . 

i. Section 172Ccl Requirements' 

This section contains general requirements. for nonat:tainment 

plans. A thorough 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 have met 

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

superseded by mo.re specific Part D requirements. 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. inventory will be. satisfied by the 

inventory requirements of the maintenance plan. The requirements 

of the Part D new source review program will be replaced by the 

prevention of significant deterioration (PSD) program once the 

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

PSD program will become fully_effective immediately upon 

redesignation, either the State must be delegated the Federal PSD 

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

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

upon i::ed.es ignation. . .-

ii. ·. conformity 

The State must work with EPA to show that· its SIP 

provisions are consistent with section 176(c)(4) conformity. 

requirements. The redesignation request should include 

conformity 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 conformity regulations specifying what areas are 

subject· to the conformity requirement. 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'!> conformity regulation upon issuance, as applicable. If the 

State submits the ·redesignation request· subsequent· to EP/\ 1 s· · issuance of the conformity regulations, 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. A State ma~ 

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 and redesignation request, all _applicable · nonattainment ar'ea 

requirements shall remain in place. . 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 after Ian 

area is redesignated (not 10 years after sμbmittal 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 project maintenance 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 foi:; 

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

section 175A(b)]. 

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 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 contingency plan will not necessitate 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 seeking redesignation from 
8 

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 redesignation and 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 .. · consisterit ·with EPA's most recent guidance on 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 tons/year for SO , N02 , and 

PM-10 areas, and 5 tons/year for Pb based upon 40.CF~ 51.lOO(k) 

and 51.322, as well as established practice 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 of the SIP (as discussed 

previously), the attainment inventory will generally be th~ 

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 Carbon Monoxide and Precursors of ozone: Volume 

I" ( EPA-450/4-91.:.016), "Procedures for the Prepara.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 Plans" (EPA-450/4-91-011), "Guideline for 

Regulatory Application of the Urban Airshed Model" (EPA-450/4-91-

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

Mobile Sources" (EPA-450/4-Sl-026d), and "Procedures for 

Preparing ·Emission. Inventory Projections" (EPA-450/4-91-019). 

The EPA does not currently have specific guidance on attainment 

emissions inventories.for so2 •. In lieu thereof, States are 

referred to t.he guidance on emissions data to be used as input to 

modeling demonstrations, contained in Table 9.1 of EPA's 

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

July 1987, .J•7hJ<;:h is. g~nerally applicable to, all. criteria ..... pollutants. Emission inventory procedures and requirements 

documents are currently being prepared by.OAQPS 'for PM-.10 and Pb; 

these documents are due for release .bY summer 19.92. 
, .... 

'f~;,~s 

9 

according to Clean Air• Act section 189(b)(3). Howe'1er, 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 tons/ye rsize thresholds (e.g., areas with smaller source size 

definitions) are subject to a State's minor source permit 

program, these sources need only be addressed in the aggregate to 

the extent that' they result in areawide growth. 

~.For o 3 nonattainment areas, the inventoi·y should be based on 

actual "typical summer day" emissions of·o3 precursors (volatile 

organic compounds and.nitrogen oxides) during 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" emissions for the 

attainment year. This will generally correspond to one of the 

periodic inventories required for nonattainment areas. 

b. Maintenance Demonstration 

A State may generally demonstrate maintenance of the NAAQS 

by either showing that future emissions of a pollutant or its I 

precursors will not exceed the level of the attainment inventory, 

or by modeling to show that the future mix of sources and 

emission rates will not cause a violation of the NAAQS. Under 

the Clean Air Act, many areas are required to submit -modeled 

attainment demonstrations to show that proposed-reductions in 

emissions will be sufficient to attain the applicable NAAQS. ~or 

these areas, the maintenance demonstration should be based upon 

the same level of modeling. In areas where no such modeling wa!s · required, the state should be able to rely on the attainment I 

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

Where modeling is relied upon to demonstrate maintenance, 

each plan should contain a summary of the air quality 

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 quality model used to projec~ 

ambient concentrations (see 40 CFR 51. 46) • · -· iIn either case, to satisfy the demonstration requirement t~e State should project emissio. ns for the 10-year period followinql redesignation, either for the purpose of showing that emissions 

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

growth, including.population and industry, should be consistent 

7Guidance for projecting emissions may be found in the 

emissions inventory guidance cited in footnote 6. 

.. )" ~. 
10 

with the attainment inventory, and ·should doc:iument data inputs and assumptions. All elements of the demonstration (e.g.-, 

emission projections, new source growth, and m~deling) should be 

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 the - maintenance demonstration either by showing that future co· 

emissions will not increase or by conducting areawide modeling. 

Preferably, the State should carry otit hot-spot .modeling that is 

consistent with the Guideline on Air Quality Models (Revised), in 

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

the_nonattainment problem is related to a pattern of hot-spots 

then hot-spot modeling should generally be.conducted. However, 

hot-spot modeling is not automatically required._ For example, if 

the nonattainment problem was related solely to stationary point 

sources, or if highway 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 

of Headquarters is needed. . . ._, 

Any assumptions concerning emission rates must reflect 

permanent, enforceable measures. In other words, a State 

generally cannot'take credit in the maintenance demonstration for 

reductions unless there are-regulations in place 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 a~e _ replaced with measures that achieve equivalent reductions (see 

additional discussion under "Contingency Plan"). 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 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 attainment demonstration may no longer 

be relied upon, States will be expected to remodel using current 

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

-following documents: "Guideline on Air Quality Models 

(Revised)'" OAQPS, RTP' 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 quality monitoring 

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 that will provide such verification. In cases where 

measured ·mobile source parameters (e.g., vehicle miles traveled 

congestion) have changed over time, the State may also need toj 

perform a saturation monitoring study to determine the need for, 

and location of, additional permanent monitors. 

d. Verification of Continued httaironent 

Each state should ensure that it has 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.llO(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 how the state will 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, would be for the 

State to periodically update the emissions inventory. In this 

case, the maintenance plan should specify the 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 complete update of the inventory, the State! 

may choose to do. a comprehensiv. e review of the factors that wez!le 

used in developing the attainment inventory to show no 

significant charige. If this review does show a significant 

change, the state should then perform an update of the inventoJ:iY. 

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 contingency measures (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 contingency measures 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 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 .. contingency plan is. considered to be an enforceable part of the 

'SIP.and should ensure that the contingency measures 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 contingency measures 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 contingency measures .. The indicators would allow a State to take early action to 

address potential 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 EPA to redesignate an area to nonattainment. 

·Other indicators to consider include monitored or modeled· 

violations of the NAAQS (due to the inadequacy of 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 SIP revision is subject to the Administrator's discretion • . ' 

The EPA will review what constitutes a contingency plan on a 

case-by-case basis. At a minimum, it must require that the State 

will implement all measures contained in the Part D nonattainment 
13 

plan for the area prior to redesignation [see section 175A(d)]. 

This language suggests that a State may 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 it provides for .compensating equivalent reductions. I A 

demonstration that measurE!s are equivalent would have.to include 

appropriate modeling or an adequate justification. Altern~-

ti vely, a State might be able to demonstrate (through 

EPA-approved modeling) that the measures are not necessary for 

maintenance of the 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 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 better understanding of .what is expected from a 

redesignation request and maintenance plan under existing poli'cy. 

Any necessary changes to existing Agency 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 submitted by any person. If your staff membe~js 

have questions which require clarification, they may contact 

Sharon Reinders at (919) 541-5284 for o 3- and co~related issues, 

and Eric Ginsburg at (919) 541-0877 for so2-, PM-10-, and 

Pb-related issues. 

cc: Chief, Air Branch, Regions I-X 

John Cabaniss, OMS 

Denise Devoe, OAQPS 

Bill Laxton, TSO 

Rich ossias, OGC 

John Rasnic, ssco 

John Seitz, OAQPS 

Mike Shapiro, OAR 

Lydia Wegman, OAQPS