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October 6, 1995 

MEMORANDUM 

SUBJECT: Limited Maintenance Plan Option for Nonclassifiable CO Nonattainment Areas 

FROM: Joseph W. Paisie, Group Leader 

Integrated Policy and Strategies Group (MD-15) 

TO: 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 following 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 

eligibiliry 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 
AQSSD:IPSG:LW ALLACE:vwyatt:x5628:MD-12: 10-6-95 

WALLA CE: A:\JOE.ABC 
1. Question: 

1016195 

Limited Maintenance Plan Option for Nonclassifiable CO 

Nonattainment areas 

What requirements must CO nonclassifiable areas, which are attaining the CO NAAQS 

with a design value that is significantly below the NAAQS, meet in order to have an 

approvable maintenance plan under section l75A 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 Jess rigorous maintenance 

plan than was formerly required. 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, "Procedures for Processing Requests to Redesignate Areas to Attainment," 

from John Calcagni, former Director of the OAQPS Air Quality Management Division to 

the Regional Air Division Directors. 

The EPA now believes that it is justifiable 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 history 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 nonelassifiable 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 

values is presented in the 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 focuses 

primarily on determining design values for nonattaioment areas in order to classify the 

areas a.~ 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 standard. 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 IO-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 I 75A maintenance plan for nonelassifiable 

CO areas which qualify for the limited 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 EPA detennination regarding 

the adequacy of a limited maintenance plan will be made following review of the plan 

submittal in light of lhe particular circumstances facing lhe area proposed for 

redesignation and based on all relevant available infonnation. 

a. Attainment Inventory 

The State should develop an attainment emissions inventory to identify a level of 

emissions in the area which is sufficient lo 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. Maintenance Demonstcatjon 

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 

qunlity 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 maintenance period. 

Whe n EPA approves a limited maintenance plan, EPA is concluding that an emissions 

budget may be treated as essentially not constraining for the length of the maintenance 

'The 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• 

(EPA-450/4-81- 026d). 
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period because it is unreasonable to expect that such an area will experience so much 

growth in that period that a violation or the CO NAAQS would result. 

c. Monitoring NetworkNerification 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, EPA-approved 

air quality monitoring network, in accordance with 40 CFR part 58. This is particularly 

important for areas using a limited maintenance plan because there will be no cap on 

emissions. 

d. Contingency Plan 

Section l 75A of the Act requires that a maintenance plan include contingency provisions, 

as necessary, to promptly 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 redcsignation. However, the contingency plan is considered to be an 

enforceable part of the SIP and should ensure that the contingency measures are adopted 

expeditiously once they are triggered by a specified event. The contingency plan should 

identify the measures to be promptly adopted and provide a schedule 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 DeteCIDinations 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 

maintenance areas operating under maintenance plans. Under either rule, one means of 

demonstrating conformity of Federal actions is to indicate that expected emissions from 

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 in 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 Lhe "budget test" 
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specified in section 93.158(a)(5)(i)(A) of the rule.