5900 Federal Register / Vol. 56, No. 30 / Wednesday, February 13,' i991 I Proposed Rules

ENVIRONMENTAL PROTECTION

AGENCY

40 CFR Parts 51 and 52

[AH-FRL-3820-7, Docket No. A-88-041

RIN 2060-AC43

Requirements for Preparation,

Adoption, and Submittal of

Implementation Plans

AGENCY: U.S. Environmental Protection

Agency (EPA).

ACTION: Notice of proposed rulemaking.

SUMMARY: The "Guideline on Air

Quality Models (Revised)", EPA-450/2-

78-027R (1986), and supplement A

(1987), hereinafter referred to as the

"Guideline", list air quality models for

estimating ambient air concentrations

due to sources of air pollutants. The

Guideline is presently incorporated by

reference into the prevention of

significant deterioration (PSD)

regulations under the Clean Air Act at

40 CFR 51.166 and 52.21. EPA here

proposes to augment that Guideline with

several new modeling techniques. The

purpose is to provide models for

situations where specific procedures

were not previously available and to

improve several previously adopted

techniques. In addition, revisions are

proposed that make the guidance and

model requirements consistent with

regulatory programs that have been

formalized or changed since the last

major Guideline revision in 1986 (51 FR

32176). EPA is proposing to establish

these additions and changes as

supplement B to the Guideline. EPA is

also proposing to amend 40 CFR 51.166

and 52.21 to incorporate supplement B,

and to amend 40 CFR 51.46, 51.63, 51.112,

51.117, 51.150, and 51.160 to codify the

Guideline as the basis by which air

quality models are to be used for

demonstrations associated with SIP

(State Implementation Plan) revisions,

AQMA (Air Quality Maintenance Area)

analyses, regional classifications for

episode planning, and new source

review I in general (not just PSD). The

proposal, in part, is based on public

comments received at the Fourth

Conference on Air Quality Modeling, the

purpose of which was to advise the

public on these new techniques and to

facilitate further technical review.

Adoption of the new modeling

techniques should significantly improve

the technical basis for impact

assessment of air pollution sources.

DATES: A public hearing on the proposed

I New source review includes that of modified

sources.

changes will be held March 19, 1991

(Tuesday), from 9 a.m. to 5 p.m. As

needed to allow for presentation of all

verbal comments, the hearing may be

extended to noon of the next day. The

period for comment on these proposed

changes closes May 6, 1991.

ADDRESSES: Comments: Written

comments should be submitted (in

duplicate if possible) to: Air Docket (LE131), room M-1500, Waterside Mall,

attention: Docket A-88-04, U.S.

Environmental Protection Agency, 401 M

Street SW., Washington, DC 20460 (also

see "Public Hearing").

Copies of supplement B (draft) to the

"Guideline on Air Quality Models

(Revised)" may be obtained by writing

or calling Joseph A. Tikvart, Source

Receptor Analysis Branch, MD-14, U.S.

Environmental Protection Agency,

Research Triangle Park, NC 27711,

phone (919) 541-5561. Supplement B

(draft) is also available to registered

users of the Support Center for

Regulatory Air Models Bulletin Board

System by downloading the appropriate

file. To register or access this electronic

bulletin board, users with a personal

computer should dial (919) 541-5742.

Public Hearing: GSA Auditorium,

GSA National Capitol Region Building,

7th and D Streets SW., Washington, DC.

Docket: Copies of reports referenced

herein, public statements and comments

made in relation to the Fourth

Conference on Air Quality Modeling,

and public comments made on this

Notice of proposed rulemaking are

maintained at Docket A-88-04. The

docket is available for public inspection

and copying between 8 a.m. and 4 p.m.,

Monday through Friday, at the address

above. A reasonable fee may be charged

for copying.

FOR FURTHER INFORMATION CONTACT.

Joseph A. Tikvart, Chief, Source

Receptor Analysis Branch, Office of Air

Quality Planning and Standards, U.S.

Environmental Protection Agency;

Research Triangle Park, NC 27711;

telephone (919) 541-5561 or (FTS) 629-

5561.

SUPPLEMENTARY INFORMATION:

Background

- The "Guideline on Air Quality

Models" ("Guideline") was originally

published in April 1978. It was

incorporated by reference in the

regulations for the Prevention of

Significant Deterioration of Air Quality

in June 1978 (43 FR 26380). The purpose

of the Guideline is to promote

consistency in the use of modeling

within the air management process.

Such consistency is fostered by sections

110(a)(2), 165(e), 172 (a) and (b), 173,

301(a)(1) and 320 of the 1977 Clean Air

Act Amendments, 2 42 U.S.C. 7410(a)(2),

7475(e), 7502 (a) and (b), 7503, 7601(a)(1)

and 7620, respectively. The Guideline

provides model users with a common

basis for estimating pollution

concentrations, assessing control

strategies and specifying emission

limits.

.In December 1984, EPA proposed

revising the Guideline to incorporate

knowledge concerning modeling

analyses that had been developed since

the original guidance was issued. Final

revisions to the Guideline were

promulgated in September 1986 (51 FR

32176) and, as a result of public

comment, changes concerning four

additional modeling techniques were

simultaneously proposed. They were: (1)

addition of a specific version of the

Rough Terrain Diffusion Model (RTDM),

(2) modification of the downwash

algorithm in the Industrial Source

Complex (ISC) model, (3) addition to the

Offshore and Coastal Dispersion (OCD)

model to EPA's list of preferred models,

and (4) addition of the AVACTA II

model as an alternative model in the

Guideline. In January 1988, EPA

promulgated the four techniques as

Supplement A to the Guideline (53 FR

392). The "Guideline on Air Quality

Models (Revised)" (1986) and

supplement A (1987) have been

incorporated by reference into the PSD

regulations at 40 CFR 51.166 and 52.21.

Codification of the Guideline in 40

CFR parts 51 and 52 has heretofore been

for purposes of compliance with PSD

regulations. However, as stated in the

Introduction, the Guideline describes

".air quality modeling techniques that

should be applied to State

Implementation Plan (SIP) revisions for

existing sources and to new source

review * * *", and this has always been

EPA policy. Use of air quality models for

such purposes is required at 51.112

(Demonstration of Adequacy) and at

51.117 (Additional Provisions for Lead).

Use of air quality models is also

required: For Air Quality Maintenance

Area (AQMA) analyses at 51.46

(Projection of Air Quality

Concentrations); for classification of

regions for episode plans at 51.150

(Prevention of Air Pollution Emergency

Episodes); and for new source review at

2 On November 15, 1990, the Clean Air Act

Amendments of 1990 ("Amendments"), Public Law

101-549. were enacted. As amended, the Clean Air

Act provides continued authority for the revisions

to the Guideline and the Code of Federal

Regulations contained in this proposal. That

authority Includes but is not limited to, the following

provisions, some of which may have been modified

by the Amendments: Clean Air Act sections

110(a)(2). 165(e). 172 (a) and (c), 173, 301(a), and 320.
Federal Register / Vol. 56, No. 30 / Wednesday, February 13, 1991 / Proposed Rules

51.160 (Review of New Sources and

Modifications). EPA believes that its

proposed incorporation by reference of

the Guideline into these provisions is

consistent with the authority granted by

sections 110(a)(2), 165(e), 172 (a) and (b),

173, 301(a)(1) and 320 of the 1977 Clean

Air Act Amendments (see footnote 2), 42

U.S.C. 7410(a)(2), 7475(e), 7502 (a) and

(b), 7503, 7601(a)(1) and 7620,

respectively.

To support the process of developing

and revising the Guideline during the

period 1977-1988, the First, Second and

Third Conferences on Air Quality

Modeling were held as required by

section 320 of the Clean Air Act to help

standardize modeling procedures. These

modeling conferences provided EPA

with comments on the Guideline and

associated revisions, thereby facilitating

introduction of improved modeling

techniques into the regulatory process.

In October 1988. the Fourth

Conference on Air Quality Modeling

was held. Its purpose was to advise the

public on new modeling techniques and

to solicit comments to guide EPA's

consideration of any rulemaking needed

to further revise the Guideline. The new

models provide techniques for situations

where specific procedures had not

previously been available, and also

improve several previously adopted

techniques. These new techniques and

the guidance discussed at the modeling

conference are:

Complex Terrain Dispersion Model,

Ozone precursor point source

modeling,

Mobile source modeling at signalized

intersections,

Emissions and dispersion modeling

system for airports,

Long-range transport models.

Models for estimating visibility impact

of specific sources. Model for shoreline dispersion.

Valley stagnation,

On-site meteorological program

guidance.

Method for evaluating models,

General screening techniques,

Regional scale models,

Modeling techniques for air pathway

analyses.

In general. EPA solicited comments on

(1) whether the techniques are sound, (2)

whether they should be adopted for

regulatory application, and (3) whether

limitations on use, including data base

requirements, should be specified.

All comments presented at the fourth

modeling conference and/or submitted

to Docket A-&-04 are encompassed in

Docket Items II-D, II-E, and II-G. Also,

a verbatim transcript of the conference

proceedings is available as Docket Item

I-G-3a and b. EPA has summarized

these comments, developed responses,

and drawn conclusions on appropriate

actions for this Notice of Proposed

Rulemaking in the document "Summary

of Public Comments and EPA Responses

on the Fourth Conference on Air Quality

Modeling-October 1988" (Docket Item

II-0-1).

The following are hereby proposed as

models or analysis procedures

recommended for inclusion in the

Guideline: Complex Terrain Dispersion

Model (refined model, accompanied by

CTSCREEN and modifications in the use

of other screening models); CAL3QHC

(carbon monoxide estimates at

signalized intersections); modeling for

air pathway analysis of toxic/hazardous

pollutants (consistent multimedia use of

ISC and other models); EDMS (modeling

system for airports); on-site

meteorological program guidance

(expansion of current guidance); general

screening techniques and VISCREEN

(updates and computerization of current

screening techniques); method for

evaluating models (enhancement of

current guidance). For the most part,

these models and analysis procedures

are designed for operation bn or to be

compatible with a personal computer.

The following are being proposed for

addition to Appendix B of the Guideline

with an indication that they are

available for application in the unique

circumstances to which they apply on a

case-by-case basis: Shoreline Dispersion

Model (sea/lake breeze fumigation) and

WYNDvalley (valley stagnation). Two

models falling in a similar category that

are already in appendix B are:

MESOPUFF-Il (long-range transport)

and PLUVUE-Il (visibility).

Besides adding new techniques, EPA

is also proposing to clarify and update

portions of the Guideline to make it

consistent with current regulatory

programs that have been established

through other Agency activities.

Specified proposed actions on models,

analysis procedures, and Guidelines

modifications are discussed in the

following section. Codes, user's guides,

and other documents or guidance

pertinent to specific modeling

techniques are identified as individual

Docket Items. These models and other

changes will be adopted in the

Guidelines on Air Quality Models

(Revised) through supplement B (Draft)

(Docket Item rn-B-); see the

ADAESS Section of this notice for

general availability. Of the techniques

considered at the fourth modeling

conference, only two are not being

proposed for further action at this time;

they are point source modeling for ozone

precursors and regional scale models.

Proposed Action

A. Complex Terrain Models

1. Refined Model

The Complex Terrain Dispersion

Model (CTDM) (Docket Item I-I-ib) is

the result of a major development and

evaluation effort. It should fill a

significant void in the Guideline by

providing a refined technique for

determining pollutant concentrations

due to plume impingement on the

windward side of terrain features during

stable and neutral atmospheric

conditions. Public comments generally

support EPA's view that the model is

technically sound, represents the best

theoretical approach, and should be

adopted for regulatory application as a

refined model.

One concern had been the ability to

estimate concentrations during unstable

conditions. Public comments discussed

several ways of coping with this matter,

but in the meantime, EPA has elected to

deal directly with the problem by

augmenting CTDM with a module for

unstable conditions based on current

scientific theory. The new model is

known as CTDMPLUS and has

undergone sensitivity analysis and

evaluation (Docket Items 11--30,11-1--

31). The user's guide documenting the

scientific assumptions, Input and

operating requirements, model options

and defaults, and the code is available

as EPA-600/8-89/041 (NTIS No. PB 89-

181424).

Other concerns related to limitations

of the model or its data base

requirements. Based on those comments,

EPA is limiting application of

CTDMPLUS to the windward side of

terrain features and makes no attempt at

this time to recommend techniques for

lee side effects or other complex terrain

phenomena. However, CTDMPLUS is

applicable to all terrain receptors above

stack height; thus, for applications of

this model the "intermediate-terrain"

problem that has bothered many users

of complex terrain models is eliminated.

(Other regulatory models in the

Guideline are currently recommended

for receptors at or below stack height).

With regard to data base

requirements, commenters would like

these to be set forth as specifically as

possible. However, due to the intense

data requirements of the model (Docket

Items Il4-lo-d) and limited experience

with its use for regulatory applications,

these specifications must remain

somewhat general in the Guideline.

Meteorological inputs to CTDMPLUS

should be based on multi-level wind

speed and direction data obtained up to

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Federal Register I Vol. 56, No. 30 /, Wednesday,, February 13, 1991 / Proposed Rules

representative plume height; SODAR

data may be appropriate. Direct

turbulence measurements and vertical

potential temperature gradient should be

obtained for at least three measurement

levels with the topmost level as close to

plume height as practical: generally,

data up to 15Dm above stack base on an

instrumented tower should be adequate.

Elements of the on-site meteorological

measurement program, and development

of a receptor network, should be

developed on a case-by-case basis with

the concurrence of the EPA Regional

Office.

2. Screening Techniques

EPA has also received varied

comment on the advisability of

establishing a screening technique

derived from CTDM; such a model

would have a better scientific basis than

currently available screening

techniques. Some commenters recognize

the desirability of such a technique,

while others express concerns about the

actual need and difficulty of establishing

a standard set of meteorological

conditions for the screening technique.

EPA has elected a screening technique

entitled CTSCREEN, EPA-600/8-90/

XXX (Docket Item I-J-7). This

technique is essentially CTDMPLUS

with a predetermined range of

meteorological conditions that are

thought to bracket the highest

concentrations for most source-terrain

configurations. The preparation of this

technique is justified by the improved

scientific basis derived from the

CTDMPLUS code. It will be allowed as

an alternate screening technique.

3. Sensitivity Analysis

Adoption of a new model can affect

the design concentrations on which

emission limits are based, thus,

sensitivity analyses for CTDMPLUS as a

refined model were conducted (Docket

Item II-I-28a-l). These analyses

compared design concentrations from

CTDMPLUS to those from available

complex terrain screening techniques for

a variety of source-terrain

configurations. The expectation was

that the screening techniques would

provide generally higher design

concentrations than CTDMPLUS; by

intent, the screening techniques should

be more conservative than this refined

technique which has also been

established as the most accurate of all

complex terrain techniques considered

(Docket Item 1-1-2 and 11-1-3). This

expectation was satisfied in most cases

so that CTDMPLUS provides less

stringent and more appropriate emission

limitations than previously possible with

the conservative screening techniques in

use. The degree of conservatism, though,

among the screening models was not

always consistent within the present

hierarchical structure of such

techniques. The addition of CTSCREEN

further complicates the situation and, in

combination with findings of the

sensitivity analyses, places in doubt the

merits of such a hierarchical structure.

Thus, the structure will be dropped so

that any acceptable screening technique

may be used consistent with the needs,

resources, and available data of the

user.

In a few cases, the screening

techniques (RTDM more so than other

models) have the potential to provide

less stringent design concentrations than

does CTDMPLUS and may not be acting

effectively as conservative screening

techniques. However, for several

reasons the limited findings cited here

are not thought to be a significant

enough matter to justify any further

changes in the use of these models. For

instance: (1) Recent evaluations with the

current version of RTDM-default show

the model to provide conservative

estimates compared to measured data;

(2) the experience with CTDMPLUS in

relation to screening models is

insufficient to draw conclusions with

any confidence; (3) the extent to which

RTDM might underestimate

concentrations is not unequivocally

delineated in the various analyses; (4)

estimates lower than those of

CTDMPLUS occasionally occur with

other screening models, although rarely;

and (5) since RTDM is the most refined

of the screening models, it is expected to

provide the most realistic of the

conservative estimates and occasional

crossover to lower estimates than those

derived from CTDMPLUS might not

indicate significant inaccuracy.

Nevertheless, screening models should

generally function as conservative

estimators of ambient concentrations,

and EPA seeks public comment on

limited exceptions like those noted here.

As additional information becomes

available and experience with

CTDMPLUS is gained over the next few

years, it may be necessary to further

consider this matter.

4. Conclusion

EPA is proposing to identify

CTDMPLUS in chapter 5 of the

Guideline as a recommended refined

model for complex terrain with a

minimum set of requirements for data

used in the model. More detailed

elements of the meteorological

measurement program and the selection

of receptor sites are to be developed on

a case-by-case basis with concurrence

of the EPA Regional Office. The model

will be included in appendix A of the

Guideline. CTSCREEN will be added as

an acceptable technique in chapter 5.

The hierarchical structure of acceptable

screening techniques is proposed to be

dropped, allowing discretion of the user

and the EPA Regional Office or

reviewing authority as to which

technique is most useful for a given

application.

B. Mobile Source Modeling at

Signalized Intersections

Public comment indicates concern

that current guidance on modeling

carbon monoxide concentrations for

intersections (Worksheet 2 of the

"Guideline for Air Quality Maintenance

Planning and Analysis", Volume 9, EPA450/4-75-001) is difficult to use,

outdated, and cannot adequately model

over-capacity situations. In response,

EPA developed a program to review

traffic and emissions components of

intersection models and has consulted

with the Federal Highway

Administration (FHWA) on such

analyses. A plan for conducting these

analyses and developing an improved

intersection model was presented at the

fourth modeling conference. Public

comments supported the need for an

improved modeling technique and more

specifically the program that EPA

proposed.

As a result of this program, EPA has

completed development of the

CAL3QHC intersection model which has

improved traffic and emissions

components; it incorporates CALINE3

which is the recommended Guideline

dispersion model for roadway sources.

Documentation for the code and user's

guide is available as Docket Item II-J--8.

CAL3QHC and a related screening

technique appear to be suitable to

replace Worksheet 2 for refined

analyses and the Hot Spot Guidelines

for screening analyses in estimating CO

concentrations. Since this is the first

public view of the complete model, no

restrictions on use were identified in the

public comments other than restrictions

to roadways at intersections. EPA has

also prepared "Guideline for Modeling

Carbon Monoxide from Roadway

Intersections" (Docket Item 11-J-9) and

solicits comments regarding it.

Performance evaluation of CAL3QHC

(Docket Item 11-1-32) indicates that this

is among the most accurate of several

models tested for signalized

intersections. A sensitivity analysis

(Docket Item 11-1-29) was also

performed to determine the impact of

CAL3QHC on design concentrations

relative to the other available

techniques. Contrary to expectations, it

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Federal Register / Vol. 56, No. 30 / Wednesday, February 13, 1991 / Proposed Rules

was found that CAL3QHC produced

higher estimates and the need for more

stringent controls than did Worksheet 2

and some other techniques for the

intersection scenarios considered. This

indicates that EPA's existing guidance

on modeling for roadway intersections

up until this time may tend to lead to

underestimates of highest ambient

concentrations.

Conclusion: EPA is proposing to

include CAL3QHC and a related

screening technique as the

recommended models for roadway

intersections in Section 6.2 of the

Guideline. They would replace

Worksheet 2 for refined analyses and

the Hot Spot Guidelines for screening

analyses. CALINE3 remains the

recommended dispersion model in

appendix A for roadways.

C. Emissions and Dispersion Modeling

System for Airports

The Federal Aviation Administration

and the U.S. Air Force have jointly

developed the Emissions and Dispersion

Modeling System (EDMS} to provide an

integrated assessment of pollution from

multiple sources (e.g., aircraft, motor

vehicles, and power plants) at airports

and air bases. These agencies have

requested that EPA adopt this modeling

system to fill the void in the Guideline

which does not contain any models or

recommendations oriented specifically

to these operations. While the emissions

components of EDMS are a unique new

application, the dispersion components

are consistent with models already

recommended in the Guideline and

contained in appendix A. A user's guide

and code for the EDMS model are

contained in Docket Item 11-1-8.

The public comments on this model

were mixed and appeared to confuse the

identified model with an earlier version.

Nevertheless, given the apparent need

for such a model and the fact that

dispersion components are consistent

with techniques already recommended

in the Guideline, EPA believes that

EDMS should be considered for

inclusion in appendix A of the

Guideline. However, it is appropriate to

restrict the regulatory application of

EDMS to those impact assessments

which contain or have as a major focus

changes in aircraft operations which

will result in a significant change in

emission and pollutant concentration

patterns. For example, if a combustion

unit at an airport requires a PSD permit

by itself, independent of aircraft

operations or mobile source peripheral

to, but off airport property, then a model

recommended in the Guideline for these

specific applications should be used in

such an analysis.

Conclusion. EPA is proposing to

include EDMS as the recommended

model for, but limited to, airport

operations as identified in section 7.2.8

of the Guideline. The model will be

included in appendix A of the Guideline.

D. Modeling for Air Pathway Analyses

At the fourth modeling conference,

EPA sought comment on techniques for

developing air pathway analyses of

toxic and hazardous waste pollutants.

Modeling for these pollutants is done

across a number of the EPA offices with

varying levels of detail in the analysis

performed. While the public comments

did not give as much attention to this

matter as had been expected, there was

general support for uniform modeling

guidance and standardized models both

through direct availability of models and

through improved guidance in specific

areas. The comments have already been

satisfied in part, since ISC is the model

that serves as the basis for most air

pathway analyses of continuous

pollutant emissions. In addition, the

"Workbook of Screening Techniques for

Assessing Impacts of Toxic Air

Pollutants", EPA-450/4-88-009 (NTIS

No. PB 89-134340) provides the basis for

obtaining preliminary estimates of shortterm concentrations due to a wide range

of toxic/hazardous pollutant release

scenarios. Also, DEGADIS 2.1 is

available as a refined model for treating

releases of heavier-than-air gases over

time periods of limited duration, EPA450/4-89-019 (NTIS No. PB 90-213893).

Conclusion: EPA proposes to amend

sections of the Guideline appropriate to

air toxics to discuss several items. For

instance, the ISC model will be

identified in section 7.2.7 and in

appendix A as the recommended air

quality model for analyses of toxics/

hazardous pollutants, especially those

that involve continuous releases.

Screening techniques contained in the

"Workbook of Screening Techniques for

Assessing Impacts of Toxic Air

Pollutants" will be identified as

available for air toxics analyses.

References in section 12 will be

expanded to identify guidance

developed by other EPA programs

which, in general, heavily rely on the

ISC model, and to provide more

information on toxic chemical

properties. In addition, DEGADIS 2.1

will be added to appendix B as a refined

model for dense gases that may be used.

as appropriate, on a case-by-case basis.

E. On-Site Meteorological Program

Guidance

The use of on-site meteorological data

to support air quality impact analyses

has grown steadily over recent years.

EPA has published a document titled

"On-site Meteorological Program

Guidance for Regulatory Modeling

Applications", EPA-450/4-87-013

(Docket Item 11-1-17]. The purpose of

this document is to supplement the

limited guidance on this subject

currently in chapter 9 of the Guideline. It

also consolidates into a single document

specific guidance on the collection and

use of on-site meteorological data for air

quality modeling analyses. This

document had undergone extensive

external peer review by State agencies,

meteorological instrument

manufacturers, and other Federal

agencies prior to the fourth modeling

conference.

Also, in response to the need for

consistency in the processing of on-site

meteorological data, EPA has developed

a Meteorological Processor for

Regulatory Models (MPRM), EPA-600/

3-88/043 (Docket Item 11-1-18). This

computer algorithm is designed to

process on-site meteorological data

following the procedures recommended

in the on-site meteorological program

guidance document, and produces

output necessary to run the EPA

regulatory dispersion models. It is

designed to provide considerable

flexibility to users in terms of input data

formats, and may be easily expanded to

accommodate the data requirements of

future models.

Public comments generally supported

the basis for and adoption of the on-site

meteorological guidance document and

MPRM in the Guideline. In addition, a

variety of minor technical points were

made about both. EPA has assessed

these technical points individually and

finds It unnecessary or inappropriate (as

documented in the response to

comments document) to act on most of

them for this proposal. However, EPA

agrees with comments suggesting a

revised stability classification scheme.

EPA developed a scheme and conducted

a sensitivity analysis (Docket Item 11-j12). The scheme is included in an

addendum (Docket Item 11-1-14) to the

guidance document, the Guideline and

MPRM. I

Conclusion: EPA proposes to

reference the document "On-Site

Meteorological Program Guidance for

Regulatory Modeling Applications" in

section 9.3.3 as the primary source of

supplementary guidance on the

collection and use of on-site

meteorological data. The hierarchy of

stability classification schemes in that

document will be changed to the

preferred scheme that is based on solar

radiation and temperature difference

measurements, but the use of other

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5904 Federal Register / Vo1. 56, No. 30 / WednesdAy, Febitary 13, 1991 / Proposed Rules

techniques prior to a year following

promulgation will be exempt from this

provision. As part of incorporation of

the on-site guidance document, MPRM

will be identified as the standard

processor of on-site meteorological data

input for regulatory model applications.

F. General Screening Techniques

The Guideline references Volume

10(R), EPA-450/4-77-001, as the basis of

recommended screening techniques for

stationary point sources. This document

has been revised to incorporate

additions to the technical approach and

changes so that the techniques may

easily be executed on a personal

microcomputer. The revised document is

"Screening Procedures for Estimating

the Air Quality Impact of Stationary

Sources", EPA-450/4-88-010 (Docket

Item 11-1-20), including an addendum

(Docket Item lI-I-20a). The Guideline

also references a visibility workbook,

EPA-450/4-80-031. A revision of the

document, "Workbook for Plume Visual

Impact Screening and Analysis", EPA450/4-88-015 (Docket Item 11-1-13), has

been prepared to reflect current

technical information and experience.

This revised document contains

procedures and a visibility model that

can be used for screening purposes to

estimate visibility impairment from

specific sources. Both of these revised

documents were discussed at the fourth

modeling conference.

Comments on the two sets of

screening techniques were mixed,

although EPA believes that these new

personal computer based techniques are

an improvement over the existing handcalculation techniques. EPA has

addressed a variety of criticisms and

suggested changes in the response to

comments document, where it is noted

that many of these comments are either

inappropriate or misinterpret the intent

and basis of the guidance. Therefore,

since there has been time for the public

to gain additional experience with these

techniques, their attributes will be more

apparent and their basis relative to prior

screening techniques better understood.

These computerized techniques are not

intended to be inherently different or

more conservative, but are instead

meant to better organize and ease the

computational burden.

Conclusion: EPA proposes to identify

"Screening Procedures for Estimating

the Air Quality Impact of Stationary

Sources" with the SCREEN model as the

recommended screening technique in

section 4.2 of the Guideline. It also

proposes to identify "Workbook for

Plume Visual Impact Screening and

Analysis" with the VISCREEN model as

the recommended screening technique

for visibility assessments in section

7.2.4.

G. Method for Evaluating Models

The Guideline refers to "Interim

Procedures for Evaluating Air Quality

Models", EPA-450/4-84-023 as the basis

for determining which of two or more

models is most appropriate for a given

application. However, EPA has recently

refined these methods and advanced the

statistical methodology for determining

which model is better suited to a

particular situation. With this newer

methodology, it is feasible to combine

results from different averaging periods

and different data bases into a

probabilistic framework. This

methodology is described in an EPA

report titled "Protocol for Determining

the Best Performing Model" (Docket

Item 11-1-19) with an appendix that

provides examples of a protocol

comparing the performance of two rural

air quality models. The method is now

also documented in a user's guide

(Docket Item 11--33).

The public comments were cautious in

their support of this improved

methodology. Concerns primarily

addressed flexibility of the techniques

and limitations in experience with their

use. Nevertheless, EPA believes that

these techniques may be exercised with

great flexibility: The example presented

is not intended to be the only set of

statistical comparisons. When used with

this built-in flexibility, these techniques

should enhance the ability to assess the

relative merits of the available models

for a given application.

Conclusion: EPA proposes to include

the "Protocol for Determining the Best

Performing Model" as an adjunct to the

"Interim Procedures" when the use of an

alternative model is being justified for a

site specific application. This analysis

procedure will be referenced in sections

3.2 and 10.1 of the Guideline.

H. Alternate Models in Appendix B

At the Fourth Conference on Air

Quality Modeling, EPA identified four

additional models that have unique

applications for which there is currently

no recommended model. Those models

(and their applications) are: Shoreline

Dispersion Model (SDM) (sea/lake

breeze fumigation), WYNDvalley (valley

stagnation), MESOPUFF-1I (long-range

transport), and PLUVUE-1I (visibility).

Actually no one long range transport

model was specifically referenced, but

from the limited statistical data

available MESOPUFF-I appears to be

the most accurate of the models

identified in EPA's performance

evaluation. MESOPUFF-II is also the

model for which EPA prepared an

example protocol.

The public comments on these four

models were mixed, but no fatal flaws

were identified. However, there was

general comment directed toward these

models with which EPA basically

agrees: that is, the performance

evaluation of these models may be of

limited utility due to sparse data bases.

As a result, information on the

performance of these models is either

inadequate to justify recommending

generic use or the evaluation has

identified limitations which need to be

further investigated before a

recommendation may be issued.

Information on the user's guides, codes

and accuracy of these models beyond

that information already in the

Guideline follows:

SDM

User's Guide to SDM-A Shoreline

Dispersion Model, EPA-450/4--88-017

(Docket Item 11-1-15).

Analysis and Evaluation of Statistical

Coastal Fumigation Models, EPA-450/4-

87-002 (Docket Item 11-1-14).

WYNDvalley

A User's Guide to WYNDvalley 3.11

(Docket Item II-I-16a-c).

MESOPUFF II

Evaluation of Short-Term, Long Range

Transport Models, Volumes I and 2,

EPA-450/4-86--016a and 016b (Docket

Item lI-I-9a and 9b).

Review of Short-Term Long Range

Transport Models (Docket Item 11-1-10).

A Modeling Protocol for Applying

MESOPUFF-I1 to Long Range Transport

Problems (Docket lI-I-11).

Also see the Guideline.

PLUVUE II

See the Guideline.

Even with the limitations identified

above and in the public comments, EPA

finds that these models fill a unique void

in available modeling applications and

that they may be at least as accurate,

under appropriate conditions, as other

available techniques.

Conclusion: EPA is proposing to add

SDM and WYNDvalley to appendix B of

the Guideline. In addition, these models

along with MESOPUFF-II and PLUVUEII will be identified as models available

for unique applications on a case-bycase basis in the following respective

sections of the Guideline, sections 8.2.9,

8.2.10, 7.2.6, and 7.2.4.

L Supplementary Changes

Besides the addition of new models,

EPA is also proposing revisions to make
Federal Register / Vol. 56, No. 30 / Wednesday, February 13, 1991 / Proposed Rules

the Guideline consistent with regulatory

programs that have been formalized or

changed since the last major Guideline

revision in 1986 (51 FR 32176).

In addition to minor wording changes,

the following procedural changes/

additions to the Guideline are worthy of

note:

1. A recommendation for consultation

with the Regional Office on complex

issues concerning VOC/NO. point

source remodeling (section 6.2.1);

2. Clarification of modeling

requirements applicable to prevention of

significant deterioration for NOa (section

6.2.3);

3. Changing references to particulate

matter, i.e., PM-10 replacing TSP

(sections 7.2.2 and 11.2.3);

4. Clarification on the use of emissions

data for NAAQS analyses associated

with prevention of significant

deterioration (PSD) compliance

demonstrations (Table 9-2), in

particular, estimating emissions in a

manner which more closely reflects the

allowable rather than the actual

emissions for background sourcesS;

5. Deletion of the ERTAQ and MPSDM

models from Appendix B at the request

of the model developer since these

models will no longer be supported and

they have not been widely used;

6. Updates to the Offshore and

Coastal Dispersion (OCD) model to

reflect recent improvements prepared by

the Minerals Management Service

which has funded development of this

model (appendix A),

7. Updates to the Urban Airshed

Model and to EKMA (OZIPP) to include

the latest chemical mechanism (CB-4)

and to reflect improved and updated

guidance (section 6.2.1 and appendix A).

The CB-4 mechanism is being

substituted because it Is a clearly

superior technique. It has been the

subject of scientific and evaluation

studies (Docket Item 11--27) and the

scientific community has generally

found this chemical mechanism to be

technically sound and to accurately

represent detailed smog chamber

findings (Docket Item 11-1-26). Also,

results from a study of St. Louis, where

comparison between estimates and

observations for CB-4 vs. CB-2 is

possible, indicate more accurate ozone

estimates and less underprediction with

CB-4 (Docket Item 114-34).

EPA has also reviewed the definition

of model calibration in section 8.2.11 of

Thi . crifcation does not app y when

calculating increment consumption under the PSI)

program, since the regulatlon applicable to that

analysis require, e apy optate. actual (vs. allowable) mInkme. Sea 4 CFR 52.mb}(1J3Xi/ 45

FR 52717-2M Agu*4 7. 29M

the Guideline to determine if

unacceptable practices are clearly and

precisely identified and prohibited. This

was done in response to a report by the

General Accounting Office that

addressed, in part, the consistent use of

air quality models in regulatory

decisions (Docket Item II-F-1). Upon

review, EPA has found the Guideline to

be clear and appropriately definitive; it

states in part that "model calibration is

unacceptable". Past experience has

indicated that this guidance is

unambiguous; further detail applied to

prohibiting calibration of these complex

mathematical tools could confuse and

create the appearance of "loopholes".

No further action on calibration or

changes to section 8.2.11 are here

proposed.

This Notice also proposes to amend 40

CFR part 51 to give regulatory status to

long-standing EPA policy regarding the

use of air quality models for purposes of

control strategy development, AQMA

analyses, classification of regions for

episode plans, and new source review,

thereby clarifying and codifying that the

Guideline is applicable for those

purposes. In addition to explicit

reference to regulatory modeling in

section 166 (as well as § 52.21), the

introduction to the Guideline makes

clear that its "air quality modeling

techniques * * * should be applied to

State Implementation Plan (SIP)

revisions for existing sources and to

new source reviews * * ". Therefore,

because use of air quality models is

required in J § 51.46 (Projection of Air

Quality Concentrations) for projections

associated with AQMA analyses, 51.112

(Demonstration of Adequacy) for SIP

revisions, 51.117 (Additional Provisions

for Lead) for analysis of lead

concentrations, 51.150 (Prevention of Air

Pollution Emergency Episodes) for

classification of regions for episode

planning, and 51.160 (Review of New

Sources and Modifications) for new

source review, this amendment to 40

CFR part 51 will serve to close a gap not

addressed in previous rulemakings. Note

that with respect to the proposed

revision of 40 CFR 51.160, it is intended

that the Guideline apply to the entire

subpart, including but not limited to new

and modified source review under

§ § 51.165 (a) and (b) and 51.166(1).

J. Public Comments an Other Topics

At the Fourth Conference on Air

Quality Modeling, EPA solicited

comments on (1) the technical validity of

a screening technique for point sources

of ozone precursors and (2) the

usefulness of regional scale models to

regulatory programs. Public comments

on the screening technique found them

inappropriate, too conservative, and

requiring further research and testing.

Based on these comments, EPA does not

intend to propose these screening

techniques for inclusion in the Guideline

at this time.

With regard to regional scale models,

commenters supported the need for and

use of these models. However. it was

felt that they are too computationally

complex and costly in terms of computer

and human resources to include in the

Guideline-at this time. EPA agrees that

further testing and experience with

these models is needed for regulatory

application, and no recommendations on

their use are being made at this time.

In addition, a variety of public

comments were provided on subjects for

which EPA did not seek input; most

prominent were the variable emissions

for SO2 and the Industrial Source

Complex (ISC model. Commenters

urged use of the expected exceedances

method for estimating SO2

concentrations and an expanded use of

the multi-point rollback method (46 FR

58101, November 30, 1981). However,

EPA does not intend to modify general

provisions of the Guideline to include

these methods. With the current

deterministic form of the SO2 NAAQS,

the expected exceedances method

would provide no assurance that the

NAAQS would be attained and

maintained. Also, EPA does not

generally endorse multi-point rollback

and has limited its use to a few cases for

a single source type. Also, comments on

ISC identified operating problems and

concerns about limitations of the model.

EPA has corrected the problems and is

actively working to keep the model

current. There Is an ancillary ongoing

program to upgrade the model to make it

easier to use and maintain.

Other comments considered: (1) Issues

which have been addressed elsewhere

in EPA policy memoranda outside the

scope of the Guideline; (2) issues that

were previously resolved in prior

Guideline revisions subjected to public

comment; (3) narrow technical issues

which are premature to address; and (4)

issues upon which EPA has already

acted, e.g.. implementation of an

electronic bulletin board. For obvious

reasons, EPA plans no further action on

these matters, as discussed in the

response to comments document.

E.O. 12291

Under Executive Order 12291, EPA

must decide whether a rule is "major"

and therefore subject to the requirement

of a Regulatory Impact Analysis. The

Administrator finds this proposed rule

not major because it will not have an

5905
Federal Register / Vol: 56, No. -30 / Wednesday, February 13.,- 1991 ,/ Proposed Rules

annual effect on the economy of $100

million or more; it will not result in a

major increase in costs or prices; and

there will be no significant adverse

effects on competition, employment,

investment, productivity, innovation or

on the ability of U.S.-based enterprises

to compete with foreign-based

enterprises in domestic or export

markets. This regulation will result in no

significant environmental or energy

impacts. Thus, no Regulatory Impact

Analysis was conducted.

Regulatory Flexibility Act

Pursuant to the provisions of 5 U.S.C.

605(b), I hereby certify that the attached

proposed rule will not have a significant

impact on a substantial number of small

entities. This rule merely updates

existing technical requirements for air

quality modeling analyses required by

other Clean Air Act programs (e.g.,

prevention of significant deterioration,

new source review, SIP revisions) and

imposes no new regulatory burdens.

Economic Impact Assessment

The requirement for performing an

economic impact assessment in section

317 of the Act, 42 U.S.C. 7617, does not

apply to this proposed action since the

revisions included do not constitute a

substantial change in the regulatory

burden imposed by the regulation.

Paperwork Reduction Act

This proposed rule does not contain

any information collection requirements

subject to review by the Office of

Management and Budget (OMB) under

the Paperwork Reduction Act of 1980,

U.S.C. 3501 et seq. EPA has submitted

this regulation to the OMB for review

under Executive Order 12291 and their

written comments on the revisions and

any EPA responses have been placed in

the docket for this proceeding.

List of Subjects

40 CFR Part 51

Administrative practice and

procedure, Air pollution control, Carbon

monoxide, Hydrocarbons,

Intergovernmental relations, Lead,

Nitrogen dioxide, Ozone, Particulate

matter, Reporting and recordkeeping

requirements, Sulfur oxides.

40 CFR Part 52

Air pollution control, Lead, Nitrogen

dioxide, Ozone, Sulfur oxides.

Authority- This Notice of Proposed Rulemaking is issued under the authority

granted by sections 110(a)(2), 165(e), 172 (a) &

(b), 173, 301(a)(1) and 320 of the 1977 Clean

Air Act Amendments, 42 U.S.C. 7410(a)(2),

7475(e). 7502 (a) & (b). 7503, 7601(a)(1) and

7620, respectively (see Footnote 2 under

"SUPPLEMENTARY INFORMATION").

Dated: February 5, 1991.

William K. Reilly,

Administrator.

It is proposed to amend part 51,

chapter I, title 40 of the Code of Federal

Regulations as follows:

PART 51-REQUIREMENTS FOR

PREPARATION, ADOPTION, AND

SUBMITTAL OF IMPLEMENTATION

PLANS

1. The authority citation for part 51 is

revised to read as follows:

Authority: 42 U.S.C. 7410(a)(2), 7475(e), 7502

(a) and (b), 7503, 7601(a)(1) and 7620.

2. Section 51.46 is amended by

revising paragraph (b) and removing

paragraph (c) to read as follows:

§ 51.46 AOMA analysis: Projection of air

quality concentrations.

Such concentrations shall be

projected using techniques consistent

with the requirements in § 51.112(a).

§51.63 [Amended]

3. In § 51.63, paragraph (a) is amended

by removing "51.46,".

4. In § 51.112, paragraph (a) is

amended by removing the second

sentence and adding paragraphs (a)(1)

and (a)(2) to read as follows:

§ 51.112 Demonstration of adequacy.

(a) * * *

(1) The adequacy of a control strategy

shall be demonstrated by means of

applicable air quality models, data

bases, and other requirements specified

in the "Guideline on Air Quality Models

(Revised)" (1986), supplement A (1987)

and supplement B (1990), which are

incorporated by reference. The

Guideline and its Supplements (EPA

Publication No. 450/2-78-027R) are for

sale from the U.S. Department of

Commerce, National Technical

Information Service, 5825 Port Royal

Road, Springfield, VA 22161. They are

also available for inspection at the

Office of the Federal Register, room

8301, 1100 L Street NW., Washington,

DC. These materials are incorporated as

they exist on the date of approval and a

notice of any change will be published

in the Federal Register.

(2) Where an air quality model

specified in the "Guideline on Air

Quality Models (Revised)" (1986),

supplement A (1987) and supplement B

(1990) is inappropriate, the model may

be modified or another model

substituted. Such a modification or

substitution of a model may be made on

a case-by-case basis or, where

appropriate, on a generic basis for a

specific state program. Written approval

of the Administrator must be obtained

for any modification or substitution. In

addition, use of a modified or

substituted model must be subject to

notice and opportunity for public

comment under procedures and set forth

in § 51.102.

§ 51.117 [Amended]

5. In § 51.117, paragraph (c)(1) is

amended by adding the phrase ",

consistent with requirements contained

in § 51.112(a)" immediately after ".* *

if desired". Paragraph (c)(2) is amended

by adding the phrase ", consistent with

requirements contained in § 51.112(a)"

immediately after " * *for

demonstration of attainment".

Paragraph (c)(3) is amended by adding

the phrase ", consistent with

requirements contained in § 51.112(a)"

immediately after " *..for the

demonstration of attainment".

§ 51.150 [Amended]

6. In § 51.150, paragraph (e) is

amended by adding the phrase ",

consistent with the requirements

contained in § 51.112(a)" immediately

after " * * of this section" in the first

sentence, and by removing the second

sentence.

7. In § 51.160, is amended by adding

paragraphs (f)(1) and (f)(2) to read as

follows:

§ 51.160 Legally enforceable procedures. * * * * *

(1) All applications of air quality

modeling involved in this subpart shall

be based on the applicable models, data

bases, and other requirements specified

in the "Guideline on Air Quality Models

(Revised)" (1986), supplement A (1987)

and supplement B (1990), which are

incorporated by reference. The

Guideline and its Supplements (EPA

Publication No. 450/2-78-027R) are for

sale from the U.S. Department of

Commerce, National Technical

Information Service, 5825 Port Royal

Road, Springfield, VA, 22161. They are

also available for inspection at the

Office of the Federal Register, room

8301, 1100 L Street, NW., Washington,

DC. These materials are incorporated as

they exist on the date of approval and a

notice of any change will be published

in the Federal Register.

(2) Where an air quality model

specified in the "Guideline on Air

Quality Models (Revised)" (1986).

,,,506
Federal Register / Vol. 56, No. 3 Wednesday, February 13, 1991 / Propdsed Rules

supplement A (1987) and supplement B

(1990) is inappropriate, the model may

be modified or another model

substituted. Such a modification or

substitution of a model may be made on

a case-by-case basis or, where

appropriate, on a generic basis for a

specific state program. Written approval

of the Administrator must be obtained

for any modification or substitution. In

addition, use of a modified or

substituted model must be subject to

notice and opportunity for public

comment under procedures set forth in

§ 51.102.

§ 51.166 [Amended]

8. In § 51.166, paragraph (1)(1) and

(1)(2) are amended by removing "and

supplement A (1987)" and by adding ",

supplement A (1987) and supplement B

(1990)".

It is proposed to amend part 52,

chapter I of title 40 of the Code of

Federal Regulations as follows:

PART 52-APPROVAL AND

PROMULGATION OF

IMPLEMENTATION PLANS

1. The authority citation for part 52

continues to read as follows:

Authority: 42 U.S.C. 7401-7642.

§ 52.21 [Amended]

2. In § 52.21, paragraph (1)(1) and (1)(21

are amended by removing "and

supplement A (1987)" and by adding ",

supplement A (1987) and supplement B

(1990)".

[FR Doc. 91-3448 Filed 2-12-91; 8:45 am]

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