UNITED STATES ENVIRONMENTAL PROTECTION AGENCY 

RESEARCH TRIANGLE PARK. NC 277 1'1 

OFFICE OF 

October 6, 1995 AIR QUALITY PLANNING 

AND STANDARDS 

MEMORANDUM 

SUBJECT: 

FROM: 

TO: 

Limited Maintenance Plan Option for Nonclassifiable CO 

Nonattainment Areas . . 

Joseph~- Paisie, Group Leader ~~ ft 

Integrated Policy and Strategies~Gtoup (MD-15) 

Air Branch Chiefs, Regions I-X 

On November 16, 1994, EPA issued guidance regarding a 

limited maintenance plan option for nonclassifiable ozone 

nonattainment areas in a memorandum from Sally L . Shaver, 

Director, Air Quality Strategies and Standards Division, to 

Regional Air Division Directors. EPA believes that such an 

option is also appropriate for nonclassifiable CO nonattainment 

areas and the f ollowing questions and answers set ·forth EPA's 

. guidance regarding the availability of this option for such 

areas. As this is guidance; final and binding determinations 

regarding the eligibility of areas for the limited maintenance 

plan option will only be made in the context of notice and 

comment rulemaking actions regarding specific redesignation 

requests. 

If there are any questions concerning the limited 

maintenance plan option for nonclassifiable CO areas, please 

contact me at (919) 541- 5556 or Larry Wallace at (919) 541-0906. 

Attachment 

cc: E. Cummings, OMS 

K. McLean, OGC 

c. Oldham 

L. Wallace Received: 

in the Air Quality Branch 
', 

10/6/95 

Limited Mai n tenance Plan Option for Nonclassifiable CO 

Nonattainment areas 

1. Question: 

What requirements must . CO nonclassifiable areas, which are 

attaining the co NAAQS with a design value that is 

signific antly below the NAAQS, meet in order to have an 

approvable maintenance plan under section 175A of the Act? 

Answer: 

Nonclassifiable CO nonattainment areas seeking redesignation 

to attainment whose design values are at or below 7 . 65ppm 

(85 percent of exceedance levels of the CO NAAQS) at the 

time of redesignation may choose to submit a less rigorous 

maintenance plan than was formerly re~ired. This new 

option is being termed a limited maintenance plan. 

Nonclassifiable co areas with design values greater than 

7.65ppm will continue to be subject to full maintenance plan 

requirements described in the September 4, 1992 memorandum, 11Procedures for Processing Requests to Redesignate Areas to 

Attainment," £rom John Calcagni, former Director of the 

OAQPS Air Quality Management Division to the Regional Air 

Division Directors. 

The EPA now believes that it is j 'ustifiable and appropriate 

to apply a different set of maintenance plan requirements to 

a nonclassifiable CO nonattainment areas whose monitored air 

quality is equal to or less than 85 percent of exceedance 

·levels of the ozone NAAQS . The EPA does not believe that 

the full maintenance plan requirements need be applied to 

these areas because ·they have achieved . air quality levels 

well below the standard without the application of control 

measures required by the Act for moderate and serious 

nonattainment areas. Also, these areas do not have either a 

recent histor¥ of monitored violation of the CO NAAQS or a 

long prior history of monitored air quality problems. The 

EPA believes that the continued applicability of prevention 

of significant deterioration (PSD) requirements, any control 

measures already in the SIP, and Federal measures (such as 

the Federal motor vehicle control program) should provide 

adequate assurance of maintenance for these areas. 
·,_ 

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2. Question: 

Besides having a design value that is equal to or less than 

85% of the CO NAAQS what other requirements are necessary 

for a _nonclassifiable CO nonattainment area to qualify for 

the limited maintenance plan option? 

Answer: 

To qualify for the limited maintenance plan option, the CO 

design value for the area, based on the 8 consecutive 

quarters (2 years of data) used to demonstrate .attainment, 

must be at or below 7.65ppm (85 .percent of exceedance levels 

of the ozone NAAQS). Additionally, the design value for the 

area must continue to be at or below 7 . 65ppm until the time 

of final EPA action on the redesignation. The method for 

calculating design valries is pr~sented in th~ June 18, 1990 

memorandum, "Ozone and Carbon Monoxide Design Value 

Calculations," from William G. Laxton, former Director of 

the OAQPS Technical Support Division to Regional Air 

·Directors. The memorandum foquses primarily on determining 

design values for nonattainment areas in order to classify 

the areas as moderate or serious for co. Therefore, the 

document discusses determining the design value for an area 

based on the monitors which are exceeding the standard. In 

the case of a nonattainment area seeking redesignation to 

attainment, all monitors must be meeting the standar d. To 

assess. whether a nonclassifiable area meets the 

applicability cutoff for the limited maintenance plan, a 

separate design value must be developed for every monitoring 

·site. The highest of these design values is the design 

value for the whole area . If the area .design value ' is ·at or 

below 7.65ppm, the State may select the limited maintenance 

plan option for the first 10-year maintenance period under 

section 175A. If the design value for the area exceeds 

7.65ppm prior to final EPA action on the redesignation, the 

area no longer qualifies for the limited maintenance plan 

and must instead submit a full maintenance plan, as 

indicated in the September 4, 1992 memorandum. 
·, 

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3. Question: 

What elements must be contained in a section 175A 

maintenance plan for nonclassifiable CO areas which qualify 

for t~e limi ted maintenance plan option? 

Answer: 

Following is a list of core provisions which should be 

included in the limited maintenance plan for CO 

nonclassifiable areas. Any final ~PA determination 

regarding the adequacy of a limited 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 available 

information. 

a. Attainment I n ventory 

~ .. 

The State should develop an attainment emissions inventory 

to identify a level of emissions -in the area which is 

sufficient to attain the NAAQS. This inventory should be 

consistent with EPA's most recent guidance1 on emissions 

inventories ·for nonattainment areas available at the time 

and should represent emissions during the time period 

associated with the monitoring data· showing attainment. The 

inventory should be based on actual "typical winter day" 

emissions of CO. 

b. Maintena n ce Demonstration 

The maintenance demonstration requirement is considered to 

be satisfied for nonclassifiable areas .if the monitoring 

data show that the area is meeting the air quality criteria 

for limited maintenance areas (7.65ppm or. 85% of the CO 

NAAQS) . There is no requirement to project emissions over 

the maintenance period. The EPA- believes if the area begins 

the maintenance period at or below 85 percent of exceedance 

levels, the air quality along with the continued 

applicability of PSD requirements, any control measures 

already in the SIP, and Federal measures, should provide -

·adequate assurance of maintenance over the initial 10-year 

1The EPA's current guidance on the preparation of emissions 

inventories for ozone 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) , . "Emission Inventory ' Requirements for Ozone State 

Implementation Plans" (EPA-450/4-91 -010) , and "Procedures for 

Emission Inventory Preparation: Volume IV, Mobile Sources" (EPA450/4-8l-026d). 
4 

maintenance period. 

When EPA approves a limited maintenance plan, EPA is 

c on c luding that an emissions budget may be treated as 

essentially not constraining for the length of the 

maintenance period because it is unreasonable to expect that 

such an area will experience so much growth in that period 

that a violation of the co NAAQS would result . · 

c. Monitoring Network/Verification of Continued Attainment 

To verify the attainment status of :the area over the 

maintenance period, the maintenance plan should contain 

provisions for continued operation of an appropriate, EPAapproved air quality monitoring network, in accordance with 

40 CFR part 58. This is particularly important for areas 

u sing a limited maintenance plan because there will be no 

cap on emissions. 

d . Contingency Plan 

·-. Section 1 75A of the Act requires that a maintenance plan 

include contingency provisions, as necessary, to promp tly 

correct any violation of the NAAQS that occurs after 

redesignation of the area. These contingency measures do 

not have to be fully adopted at the time of redesignation. 

However, . the contingency plan is considered to be an 

enforceabl~ part of the SIP and should .ensure that the 

contingency measures are adopted expeditiousl y once they are 

triggered by a specified event. The contingency plan should 

identify the measures to be promptly adopted and provide a 

dule and procedure for adoption and implementation of 

the measures. The State should also identify specific 

indicators, or triggers, which will be used to determine 

when the contingency measures need to be implemented. While 

a violation of the NAAQS is an acceptable trigger, States 

may wish to choose a pre- violation action level as a 

trigger, such as an exceedance of the NAAQS. By taking 

early action, a State may be able to prevent any actual 

violation of the NAAQS and, therefore, eliminate any need on 

the part of EPA to redesignate an area back to 

nonattainment. 

e. Conformity Determinat'ions Under · Limited Maintenance 

Plans 

The transportation conformity rule (58 FR 62188; 

November 24, 1993) and the general conformity rule (58 FR 

63214; November 30, 1993) apply to nonattainment areas and 

main-tenance areas operating under maintenance plans. Under 

e i ther rule, one means of demonstrating confo rmity of 

Federal actions is to indicate th~t expected· emissions from 
5 

planned actions are consistent with the emissions budget for 

the area. Emissions budgets in limited maintenance plan 

areas may be treated as essentially not constraining for the 

length of the initial maintenance period because it is 

unreasonable to expect that such an area will experience so 

much growth i~ that period that a violation of the CO NAAQS 

would result. In other words, EPA would be concluding that 

emissions need not be capped for the maintenance period. 

Therefore, in areas with approved limited maintenance plans, 

Federal actions reqUiring conformity determinations. under 

the transportation conformity rule could be considered to 

satisfy the "budget test" required· in sections 93.118, 

93.119, and 93.120 of the rule. · Similarly, in these areas, 

Federal actions subject to the general conformity rule could 

be considered to satisfy the "budget test" specified in 

section 93 . 158(a) (5} (i} (A} of the rule.