values, e.g., expressway, arterial, collector, and local.

(x) "Time period" means any period of time designated by hour, month, season, calendar year, averaging time, or other suitable characteristics, for which ambient air quality is estimated.

(y) "Variance" means the temporary deferral of a final compliance date for an individual source subject to an approved regulation, or a temporary change to an approved regulation as it applies to an individual source.

(z) "Emission limitation" and "emission standard” mean a requirement established by a State, local government, or the Administrator which limits the quantity, rate, or concentration of emissions of air pollutants on a continuous basis, including any requirements which limit the level of opacity, prescribe equipment, set fuel specifications, or prescribe operation or maintenance procedures for a source to assure continuous emission reduction.

(aa) "Capacity factor" means the ratio of the average load on a machine or equipment for the period of time considered to the capacity rating of the machine or equipment.

(bb) "Excess emissions" means emissions of an air pollutant in excess of an emission standard.

(cc) "Nitric acid plant" means any facility producing nitric acid 30 to 70 percent in strength by either the pressure or atmospheric pressure process.

(dd) "Sulfuric acid plant" means any facility producing sulfuric acid by the contact process by burning elemental sulfur, alkylation acid, hydrogen sulfide, or acid sludge, but does not include facilities where conversion to sulfuric acid is utilized primarily as a means of preventing emissions to the atmosphere of sulfur dioxide or other sulfur compounds.

(ee) "Fossil fuel-fired steam generator" means a furnace or boiler used in the process of burning fossil fuel for the primary purpose of producing steam by heat transfer.

(ff) "Stack" means any point in a source designed to emit solids, liquids, or gases into the air, including a pipe or duct but not including flares.

(gg) "A stack in existence" means that the owner or operator had (1) begun, or caused to begin, a continu

ous program of physical on-site construction of the stack or (2) entered into binding agreements or contractual obligations, which could not be cancelled or modified without substantial loss to the owner or operator, to undertake a program of construction of the stack to be completed in a reasonable time.

(hh) "Dispersion technique" means any technique which attempts to affect the concentration of a pollutant in the ambient air by using that portion of a stack which exceeds good engineering practice stack height, varying the rate of emission of a pollutant according to atmospheric conditions or ambient concentrations of that pollutant, or by addition of a fan or reheater to obtain a less stringent emission limitation. The preceding sentence does not include: (1) The reheating of a gas stream, following use of a pollution control system, for the purpose of returning the gas to the temperature at which it was originally discharged from the facility generating the gas stream; (2) the use of smoke management in agricultural or silvicultural programs; or (3) combining the exhaust gases from several stacks into one stack.

good engineering practice stack height, measured from the ground-level elevation at the base of the stack,

H-height of nearby structure(s) measured from the ground-level elevation at the base of the stack,

L= lesser dimension (height or projected width) of nearby structure(s);

(3) The height demonstrated by a fluid model or a field study approved by the reviewing agency, which ensures that the emissions from a stack do not result in excessive concentrations of any air pollutant as a result of atmospheric downwash, wakes, or

eddy effects created by the source itself, structures, or terrain obstacles.

(jj) "Nearby" as used in § 51.1(ii)(2) is that distance up to five times the lesser of the height or the width dimension of a structure but not greater than 0.8 km (one-half mile). The height of the structure is measured from the ground-level elevation at the base of the stack.

(kk) "Excessive concentrations" for the purpose of determining good engineering practice stack height in a fluid model or field study means a maximum concentration due to downwash wakes, or eddy effects produced by structures or terrain features which is at least 40 percent in excess of the maximum concentration experienced in the absence of such downwash, wakes, or eddy effects.

(11) "Plume impaction" means concentrations measured or predicted to occur when the plume interacts with elevated terrain.

(mm) "Elevated terrain" means terrain which exceeds the elevation of the good engineering practice stack as calculated under paragraph (ii) of this section.

(Secs. 110, 123, 301(a), Clean Air Act as amended (42 U.S.C. 7410, 7423, 7601))

[36 FR 22398, Nov. 25, 1971, as amended at 37 FR 26311, Dec. 9, 1972; 38 FR 15195, June 8, 1973; 40 FR 7043, Feb. 18, 1975; 40 FR 46247, Oct. 6, 1975; 41 FR 18511, May 5, 1976; 43 FR 46269, Oct. 5, 1978; 47 FR 5868, Feb. 8, 1982]

§ 51.2 Stipulations.

Nothing in this part shall be construed in any manner:

(a) To encourage a State to prepare, adopt, or submit a plan which does not provide for the protection and enhancement of air quality so as to promote the public health and welfare and productive capacity.

(b) To encourage a State to adopt any particular control strategy without taking into consideration the costeffectiveness of such control strategy in relation to that of alternative control strategies.

(c) To preclude a State from employing techniques other than those specified in this part for purposes of estimating air quality or demonstrating the adequacy of a control strategy, provided that such other techniques

are shown to be adequate and appropriate for such purposes.

(d) To encourage a State to prepare, adopt, or submit a plan without taking into consideration the social and economic impact of the control strategy set forth in such plan, including, but not limited to, impact on availability of fuels, energy, transportation, and employment.

(e) To preclude a State from preparing, adopting, or submitting a plan which provides for attainment and maintenance of a national standard through the application of a control strategy not specifically identified or described in this part.

(f) To preclude a State or political subdivision thereof from adopting or enforcing any emission limitations or other measures or combinations thereof to attain and maintain air quality better than that required by a national standard.

(g) To encourage a State to adopt a control strategy uniformly applicable throughout a region unless there is no satisfactory alternative way of providing for attainment and maintenance of a national standard throughout such region.

§ 51.3 Classification of regions.

This section establishes a classification system to categorize regions for purposes of plan development and evaluation. The requirements of this part vary according to the classification of each region, in order that the time and resources to be expended in developing the plan for that region, as well as the substantive content of the plan, will be commensurate with the complexity of the air pollution problem. The classification will be based upon measured ambient air quality, where known, or, where not known, estimated air quality in the area of maximum pollutant concentration. All regions will be classified by the Administrator after consultation with State agencies. Each region will be classified separately with respect to each of the following pollutants: Sulfur oxides, particulate matter, carbon monoxide, nitrogen dioxide, and ozone.

(ii) The more restrictive classification will be chosen where there is a difference between the maximum value(s) and the annual averages e.g., if a region is Priority I with respect to an annual average and Priority II with respect to a 24-hour maximum value, the classification will be Priority I.

(2) Procedures which may be used, where appropriate, to estimate air quality in regions where no measured data or inadequate data exist are described in Appendix A to this part.

(b) For carbon monoxide, nitrogen dioxide, and ozone, each region will be classified into one of two categories defined as Priority I or Priority III.

(1) Ambient concentration limits which define the classification system are:

(i) Carbon monoxide: Priority I: Equal to or above 55 milligrams per cubic meter (48 p.p.m.), 1-hour maximum, or 14 milligrams per cubic meter (12 p.p.m.), 8-hour maximum; Priority III: Below such values.

(ii) Nitrogen dioxide: Priority I: Equal to or above 110 micrograms per cubic meter (0.06 p.p.m.) annual arithmetic mean; Priority III: Below such value.

(iii) Ozone: Priority I: Equal to or above 195 micrograms per cubic meter (0.10 p.p.m.), 1-hour maximum; Priority III: Below such value.

(2) In the absence of measured data to the contrary, classification with respect to carbon monoxide, ozone and nitrogen dioxide will be based on the following estimate of the relationship

100 (0.04) 455 (0.17)

60-100 (0.02-0.04) 260-455 (0.10-0.17) 1-1,300 (0.50)

60 (C 02: 260 (0.10) 1,300 (0.50)

95

60-95 150-325

60 150

325

between these pollutants and population: Any region containing an area whose 1970 "urban place" population, as defined in the U.S. Bureau of Census, exceeds 200,000 will be classified Priority I. All other regions will be classified Priority III.

(3) Where a region is classified Priority I on the basis of population, the air quality data requirements of § 51.14(e)(1) shall apply. If these data indicate the pollutant concentrations are below the values stipulated in paragraph (b)(1) of this section, the region will be reclassified Priority III. (4) Classifications with respect to hydrocarbons will be the same as the classifications with respect to ozone.

(c) Where a region is classified Priority I on the basis of measured or estimated air quality levels reflecting emissions predominantly from a single point source, it shall be further classified Priority IA. The requirements applicable to Priority IA regions shall be the same as those for other Priority I regions, except that the requirements applicable to Priority II regions under § 51.16 shall apply. A procedure for estimating air quality levels reflecting emissions from a single point source is described in Appendix A to this part.

(Secs. 110, 301(a), 313, 319, Clean Air Act (42 U.S.C. 7410, 7601(a), 7613, 7619))

[36 FR 22398, Nov. 25, 1971, as amended at 44 FR 27569, May 10, 1979]

(a) (1) Except as otherwise provided in paragraph (a)(2) of this section, the State shall, prior to the adoption of any plan or any revision thereof required by § 51.6(a) or prior to the submission to the Administrator of any individual compliance schedule pursuant to § 51.15(a) or any revision pursuant to § 51.6(d), conduct one or more public hearings on such plan, schedule, or revision. Separate hearings may be held for plans to implement primary and secondary standards.

(2) No hearing shall be required for any change to an increment of progress in an approved individual compliance schedule unless such change is likely to cause the source to be unable to comply with the final compliance date in the schedule. The requirements of §§ 51.6 and 51.8 shall be applicable to such schedules, however.

(b) Any hearing required by paragraph (a) of this section shall be held only after reasonable notice, which shall be considered to include, at least 30 days prior to the date of such hearing(s):

(1) Notice given to the public by prominent advertisement in the region affected announcing the date(s), time(s), and place(s) of such hearing(s);

(2) Availability of each proposed plan or revision for public inspection in at least one location in each region to which it will apply, and the availability of each compliance schedule for public inspection in at least one location in the region in which the affected source is located;

(3) Notification to the Administrator (through the appropriate Regional Office);

(4) Notification to each local air pollution control agency in each region to which the plan, schedule, or revision will apply;

(5) In the case of an interstate region, notification to any other States included, in whole or in part, in the region; and

(6) In the case of hearings on AQMA plans:

(i) Notification to the chief executives of affected local governments, planning agencies, transportation agencies, environmental control agen

cies, economic development agencies, and any other affected States, and

(ii) Public notice of alternative analysis and plan development procedures approved under § 51.63.

(c) The State shall prepare and retain, for inspection by the Administrator upon his request, a record of each hearing. The record shall contain, as a minimum, a list of witnesses together with the text of each presentation.

(d) The State shall submit with the plan, revision, or schedule a certification that the hearing required by paragraph (a) of this section was held in accordance with the notice required by paragraph (b) of this section.

(e) Upon written application by a State agency (through the appropriate Regional Office), the Administrator may approve State procedures designed to insure public participation in the matters for which hearings are required, and public notification of the opportunity to participate if in the judgment of the Administrator, such procedures, although different from the requirements of this part, in fact provide for adequate notice to and participation of the public. The Administrator may impose any conditions on his approval as he deems necessary. Procedures approved pursuant to this section shall be deemed to satisfy the requirements of this part regarding public hearings.

(f) The State shall, prior to adoption of transportation control measures, conduct one or more public hearings as required in paragraphs (a) through (d) of this section.

[37 FR 26311, Dec. 9, 1972, as amended at 38 FR 15195, June 8, 1973; 41 FR 18387, May 3, 1976]

§ 51.5 Submission of plans; preliminary review of plans.

(a) Submission to the Administrator shall be accomplished by delivering five copies of the plan to the appropriate Regional Office and a letter to the Administrator notifying him of such action. Plans shall be adopted by the State and submitted to the Administrator by the Governor as follows:

(1) For any primary standard, within 9 months after promulgation of such standard.

NOTE: The State of Illinois shall, not later than September 9, 1974, submit to the Administrator a demonstration that the control strategy approved by the Administrator for the Metropolitan Chicago Air Quality Control Region is adequate to attain and maintain the national standard for nitrogen dioxide.

(2) For any secondary standard, within 9 months after promulgation of such secondary standard or by such later date prescribed by the Administrator pursuant to Subpart C of this part.

(3) For compliance with the requirements of §§ 51.11(a)(4) and 51.18, no later than August 15, 1973.

(b) Plans for different regions within a State may be submitted as a single document or as separate documents.

(c) Upon request of a State, the Administrator will provide preliminary review of a plan or portion thereof submitted in advance of the date such plan is due. Such requests shall be made in writing to the appropriate Regional Office and shall be accompanied by five copies of the materials to be reviewed. Requests for preliminary review shall not operate to relieve a State of the responsibility of adopting and submitting plans in accordance with prescribed due dates.

(d) Submission to the Administrator shall be accomplished by delivering 10 copies of the transportation control portions of the plan to the appropriate regional office. Such portions shall be adopted by the State and submitted by the Governor.

(e) Upon request of a State, the Administrator will provide preliminary review of the draft transportation control measures or portions thereof in advance of the date such measures are due. Such requests shall be made as provided in paragraph (c) of this section and shall not operate to relieve a State of its responsibility for adopting and submitting transportation control measures in accordance with prescribed due dates.

[36 FR 22398, Nov. 25, 1971, as amended at 38 FR 15195, June 8, 1973; 38 FR 15836, June 18, 1973; 39 FR 16122, May 7, 1974]

(a) The plan shall be revised from time to time, as may be necessary, to take account of:

(1) Revisions of national standards,

(2) The availability of improved or more expeditious methods of attaining such standards, such as improved technology or emission charges or taxes, or

(3) A finding by the Administrator that the plan is substantially inadequate to attain or maintain the national standard which it implements.

(b) The plan shall be revised within 60 days following notification by the Administrator under paragraph (a) of this section, or by such later date prescribed by the Administrator after consultation with the State.

(c) The plan may be revised from time to time consistent with the requirements applicable to implementation plans under this part.

(d) Any revision of any regulation or any compliance schedule pursuant to paragraph (c) of this section shall be submitted to the Administrator no later than 60 days after its adoption.

(e) Revisions other than those covered by paragraphs (a) and (d) of this section must be identified and described in the next annual report required by § 51.321.

(f) Any revision shall be submitted only after any applicable hearing requirements of § 51.4 have been satisfied.

(Secs. 110, 301(a), 313, 319, Clean Air Act (42 U.S.C. 7410, 7601(a), 7613, 7619))

[36 FR 22398, Nov. 25, 1971, as amended at 37 FR 26312, Dec. 9, 1972; 44 FR 27569, May 10, 1979]

$51.7 [Reserved]

§ 51.8 Approval of plans.

The Administrator shall approve any plan, or portion thereof, or any revision of such plan, or portion thereof, if he determines that it meets the requirements of the Act. Revisions of a plan, or any portion thereof, shall not be considered part of an applicable plan until such revisions have been approved by the Administrator in accordance with this part.