Air Quality Modeling Guidelines

Prepared by

New Source Review Permits Division

RG-25 (Revised)
February 1999

iii

Contents

Summary of Significant Changes .............................................. viii

Glossary of Acronyms and Symbols .............................................. x

Definitions ............................................................... xiv

1.0 Introduction .......................................................... 1

1.1 What Is Air Dispersion Modeling? ................................... 1

1.2 Authority for Modeling ............................................ 1

1.3 Guidance Philosophy ............................................. 2

1.4 Use of Monitoring Data in State Permit Review ......................... 3

2.0 The Air Quality Analysis Process .......................................... 5

2.1 Permit Engineer Coordination ....................................... 5

2.2 Coordination with Other TNRCC Staff ................................ 5

2.3 ADMT Responsibilities ............................................ 6

2.4 Modeling Request ............................................... 6

2.5 Guidance Meetings, Protocols, and Checklists .......................... 7

3.0 Conducting the Air Quality Analysis ........................................ 9

3.1 Levels of Modeling Used in the Air Quality Analysis ...................... 9

3.1.1 Screening Modeling ........................................ 9

3.1.2 Refined Modeling .......................................... 9

3.2 Types of Air Quality Analyses ..................................... 10

3.3 Modeling Emissions Inventory ..................................... 10

3.3.1 Ratio Techniques ......................................... 11

3.3.2 Collocation of Emission Points .............................. 11

3.4 Preliminary Impact Determination ................................... 12

3.5 State Property Line Analysis ....................................... 15

3.6 State NAAQS Analysis ........................................... 17

3.7 State Effects Evaluation Analysis ................................... 19

3.7.1 Tier I Effects Analysis ...................................... 20

3.7.2 Tier II Effects Analysis ..................................... 21

3.7.3 Tier III Effects Analysis .................................... 22

3.7.4 Modeling Postprocessing Requirements ........................ 22

3.7.5 Baseline Date for Effects Reviews ............................. 23

3.8 State Disaster Review ............................................ 23

3.9 PSD NAAQS Analysis ........................................... 23

3.10 PSD Monitoring Analysis and Exemptions ............................ 26

3.10.1 Monitor Siting and Monitoring Quality Assurance Plan ............. 28
iv

3.11 PSD Increment Analysis .......................................... 28

3.12 PSD Ozone Ambient Impact Analysis ................................ 32

3.13 PSD Additional Impacts Analyses ................................... 33

3.14 PSD Class I Impact Area Analysis .................................. 33

3.15 RCRA Combustion Permits Analysis ................................ 34

3.15.1 BIF Demonstration ........................................ 34

3.15.2 Multipathway Risk Assessment ............................... 35

4.0 Acceptable Dispersion Models ........................................... 37

4.1 Distance Limitations ............................................. 39

4.2 Modification of Models .......................................... 39

4.3 Use of Data Entry Software ....................................... 39

5.0 Basic Model Input Data Requirements .................................... 41

5.1 Urban versus Rural Dispersion Options ............................... 41

5.1.1 Simplified Auer Land-Use Analysis ............................ 41

5.1.2 Multiple Modeling Technique ................................ 43

5.2 Digital Elevation Model .......................................... 44

5.3 Variable Emission Rate Option ..................................... 45

5.4 Building Wake Effects (Downwash) ................................. 45

5.5 Receptor Grid .................................................. 47

5.5.1 Receptor Grid Design ...................................... 47

5.5.2 Coordinate System ........................................ 48

5.5.3 Receptor Elevations ....................................... 48

5.5.4 Receptor Spacing ......................................... 50

5.5.5 Special Receptor Spacing ................................... 50

5.5.6 Cavity Calculations ........................................ 51

5.5.7 Concentration Maps ....................................... 51

5.6 Meteorological Data ............................................. 51

5.6.1 Short-Term Meteorological Data ............................. 52

5.6.2 Long-Term Meteorological Data .............................. 52

5.6.3 Anemometer Height ....................................... 52

5.6.4 Replacement of Meteorological Data .......................... 53

5.6.5 Replacement of Low Mixing Heights .......................... 53

5.6.6 Gravitational Settling and Deposition Modeling .................. 53

6.0 Guidance for Determining Nonpoint Source Characterization .................... 55

6.1 Pseudo-Point .................................................. 55

6.2 Volume ...................................................... 55

6.3 Area ......................................................... 56

6.4 Open Pit ..................................................... 57

6.5 Flares ........................................................ 57

6.6 Road Emissions ................................................ 58

6.6.1 When to Exclude from Modeling .............................. 58
v

6.6.2 Modeling Road Emissions ................................... 59

6.7 Wind-Generated Particulate Emissions ............................... 60

7.0 Reporting Requirements ................................................ 63

8.0 Transmittal of the Air Quality Analysis Report ............................... 65

8.1 Request for ADMT Technical Review ............................... 65

8.2 Modeling Technical Review Process ................................ 65

9.0 Common Shortfalls in Modeling Reports ................................... 67

9.1 Modeling Emissions Inventory ..................................... 67

9.2 Plot Plans or Area Maps .......................................... 67

9.3 Building Wake Effects (Downwash) ................................. 68

9.4 Receptor Grid .................................................. 68

9.5 Auer Land-Use Analysis .......................................... 69

9.6 Omitted or Incomplete Data ....................................... 69

9.7 Meteorological Data ............................................. 69

10.0 References .......................................................... 71

Appendix A Values for Comparison with Modeling Results ........................ A-1

Appendix B Screening Factors and Ratio Techniques ............................. B-1

Appendix C Meteorological Stations by County ................................. C-1

Appendix D Protocol and Permit Modeling Guidance Requirements .................. D-1

Appendix E Permit Modeling Guidance Checklist ............................... E-1

Appendix F Air Quality Analysis Reporting Guidance ............................ F-1

Appendix G PSD NAAQS and Increment Analyses Summary Sheets ................. G-1

Appendix H Point Source Data Base Retrievals ................................. H-1

Appendix I Increment Minor Source Baseline Dates ............................. I-1

Appendix J Attainment/Nonattaiment Areas ................................... J-1

vii

Summary of Significant Changes

Main Document

General: Permit Modeling Unit (PMU) changed to Air Dispersion Modeling Team (ADMT).

1.1 Clarifies the use of modeled predictions in the technical review process.

1.3 Adds Internet addresses for modeling information.

1.4 Provides information on the use of ambient air monitoring data in state permit review.

2.4 Adds Internet e-mail address for the ADMT.

2.5 Reorganizes guidance on meetings, protocols, and checklists.

3.1 Adds the EPA Internet address for the Support Center for Regulatory Air Models

(SCRAM).

3.2 Adds types of air quality analyses for RCRA combustion strategy permits.

3.4 Clarifies procedures for preliminary impact determination.

3.5 Removes requirement to evaluate any constituents under 30 TAC Chapter 113. Adds

rationale for use of 1-hour modeled concentrations for 30-minute standards.

3.6 Adds procedure to streamline state NAAQS analysis. Adds procedure to determine

background concentrations for state NAAQS analysis.

3.7 Updates effects evaluation procedures to reflect guidance in the Modeling and Effects

Review Applicability technical guidance package. Outlines TARA’s tiered technical

review process. Introduces concept of various types of sensitive receptors. Introduces

concept of baseline date.

3.9 Advises that the old form of the PM10 standard will be used to determine compliance with

the new form of the PM standard and the new PM standards until EPA develops 10 2.5

procedures for the new technical reviews. Adds procedure to determine background

concentrations for PSD NAAQS analysis.

3.10 Makes ozone preconstruction monitoring case-by-case until EPA develops new

procedures for the 8-hour ozone standard.

3.11 Clarifies procedures for PSD increment calculation. Adds definitions for major source

baseline date, trigger date, minor source baseline date, actual emissions at baseline date,

and actual emissions at modeling date.

3.12 Provides a surrogate procedure to determine for ozone ambient impact because of the

change to the ozone standard and the revocation of the 1-hour standard in attainment and

unclassifiable areas until EPA develops new procedures.

3.13 Clarifies when a growth analysis would be required. Eliminates requirement for Class II

visibility impairment analysis.
viii

3.15 Adds requirement for RCRA combustion permit analyses: boiler and industrial furnace

demonstration and multipathway risk assessment.

4.0 Indicates ADMT preference of ISCST for long-term predictions. Announces possibility of

a new regulatory model: AERMOD.

4.3 Adds requirement for the applicant to submit data entry software to ADMT.

5.2 Replaces terrain section with information on Digital Elevation Model.

5.5 Reformat of previous version. 

5.5.1 Modifies suggested distance for tight receptors. 

5.5.2 Adds requirement to provide datum used to determine UTM coordinates. 

5.5.3 Adds requirement to include receptors on highest terrain. Addresses the use of USGS

DEM data. Changes procedure to set elevation height for receptors below stack base.

5.5.4 Modifies suggested distance for tight receptors. 

5.5.5 Changes suggested distance for special receptor spacing. Adds caveat for isolated terrain. 

5.5.6 Requires use of ISC-PRIME for cavity calculations.

5.6 Adds Internet address for meteorological data.

5.6.1 Requires submittal of ASCII files for preprocessed meteorological files.

5.6.6 Changes header. Adds requirement to submit supplementary meteorological data.

5.5.7 Clarifies use of isopleths in place of gridded concentration maps.

6.1 Changes parameters for pseudo-point source characterization.

6.2 Clarifies development of volume source characterization parameters.

6.4 Clarifies development of open pit parameters.

6.6 Updates guidance for modeling road emissions.

7.0 Adds the ftp URL for incoming data.

8.0 Removes requirement to send any supporting documentation to EPA Region 6.

9.1 Adds guidance concerning rotation of coordinates.

9.3 Adds guidance concerning rotation of coordinates.

Appendixes

A Updates previous version.

B Clarifies guidance on Ambient Ratio Method.

D Clarifies and updates guidance.

E Clarifies and updates guidance.

F Clarifies and updates guidance.

G Modifies concentration rank.

H Modifies search option, area sources.

I New. Adds increment baseline dates.

J New. Adds attainment/nonattainment counties.
ix

Glossary of Acronyms and Symbols

A attainment

ADMT Air Dispersion Modeling Team

AERMOD AMS/EPA Regulatory Model

AIRS Aerometric Information Retrieval System

AMS American Meteorological Society

AOI area of impact

AP-42 EPA’s Compilation of Air Pollutant Emission Factors

AQCR Air Quality Control Region

AQRV Air quality related value

BACT Best Available Control Technology

BIF boiler and industrial furnace

BPIP EPA’s Building Profile Input Program

CAS Chemical Abstract Service

CFR Code of Federal Regulations

CO carbon monoxide

DEM digital elevation model

DF dilution factor

EPA Environmental Protection Agency

EPN emission point number

ESL effects screening level

FCAA Federal Clean Air Act

FTP file transfer protocol

GAQM EPA’s Guideline on Air Quality Models

GEP good engineering practice

GLC ground-level concentration 

GLCmax maximum ground-level concentration

GLCr ground-level concentration at a sensitive receptor, r

HAP hazardous air pollutant

H building height b

HSC Texas Health and Safety Code

HTTP hypertext transfer protocol 

IDLH immediately dangerous to life and health

ISC EPA’s Industrial Source Complex model

ISCLT ISC long-term model
x

ISCST ISC short-term model

ISC-PRIME ISC-plume rise model enhancements model

L lesser of the building height or maximum projected width

MEI maximum exposed individual

MSA metropolitan statistical area

MSDS material safety data sheet

m/s meters per second

μg/m micrograms per cubic meter 3

μm micron

MW molecular weight

NAA nonattainment area

NAAQS National Ambient Air Quality Standard(s)

NAMS national air monitoring station(s)

NCDC National Climatic Data Center

NWS National Weather Service

NO nitrogen oxides x

NO2 nitrogen dioxide

NSRPD New Source Review Permits Division

O3 ozone

Pb lead

PC personal computer

PM particulate matter with an aerodynamic diameter of 10 microns or less 10

PM particulate matter with an aerodynamic diameter of 2.5 microns or less 2.5

ppb parts per billion

ppm parts per million

PSD Prevention of Significant Deterioration

PSDB Point Source Data Base

q gross heat release

RAC reference air concentration for noncarcinogens

RAM three-letter designation for a gaussian-plume, multiple-source model

RAMMET meteorological preprocessor developed for the RAM model

RCRA Resource Conservation Recovery Act

RSD risk-specific dose for carcinogens

Fy0 initial horizontal sigma or dimension

Fz0 initial vertical sigma or dimension

SCRAM EPA’s Support Center for Regulatory Air Models 
xi

SLAMS state or local air monitoring station(s)

SPMS special purpose monitoring station(s)

SO2 sulfur dioxide

STAR stability array

TAC Texas Administrative Code

TARA Toxicology and Risk Assessment Section, Chief Engineer’s Office 

TNRCC Texas Natural Resource Conservation Commission

TOXST EPA’s toxic modeling system short-term model

tpy tons per year

U unclassifiable

URL uniform resource locator

USGS United States Geological Survey

UTM Universal Transverse Mercator projection

§ section

xiii

Definitions

Note: The following explanations of terms are included solely for the readers’ convenience;

they do not take the place of any full, formal definition in state or federal laws, rules, or

regulations. All section references are to 30 TAC unless specified otherwise. 

Account. For sources required to be permitted under 20 TAC 122, an account means all

sources that are aggregated as a site. For all other sources, an account means any combination

of sources, under common ownership or control and located on one or more contiguous

properties, or properties contiguous except for intervening roads, railroads, rights-of-way,

waterways or similar divisions (§101.1). 

Air contaminant. Particulate matter, radioactive materials, dust fumes, gas, mist, smoke,

vapor, or odor, including any combination of those items, produced by processes other than

natural (HSC§382.003). May also be referred to by the staff as constituent, chemical,

compound, or pollutant.

Air pollution. One or more air contaminants in such concentration and of such duration that

they could cause injury; adversely affect human health or welfare, animal life, vegetation, or

property; or interfere with the normal use and enjoyment of animal life, vegetation, or

property (HSC§382.003).

Air quality-related value. A term used by the National Park Service that includes visibility,

odor, flora, fauna; geological resources; archeological, historical, and other cultural resources;

and soil and water resources.

Ambient air. That portion of the atmosphere, external to buildings, to which the general

public has access (§101.1).

Anthropogenic heat flux. Heat energy generated by human activity. Can usually be ignored

outside highly urbanized locations.

Application site. The site where the meteorological data will be applied.

Attainment. Any area that meets the national primary or secondary ambient air quality standard

for an applicable criteria pollutant. 
xiv

Background. Constituent concentrations present in the ambient air that are not attributed to the

source or site being evaluated. 

Baseline date (State Effects Review). The date the most recent sitewide modeling or ambient

monitoring was used in a permit review. In the absence of sitewide modeling or ambient

monitoring, the baseline date is July 12, 1993.

Bowen ratio. A measure of the amount of moisture at the earth’s surface. The presence of

moisture at the earth's surface alters the energy balance, which in turn alters the sensible heat flux

and Monin-Obukhov length.

Class I area. An area defined by Congress that is afforded the greatest degree of air quality

protection. Class I areas are deemed to have special natural, scenic, or historic value. The PSD

regulations provide special protection for Class I areas. Little deterioration of air quality is

allowed.

Class II area. An area defined by Congress where moderate deterioration of air quality associated

with well-managed industrial growth is allowed.

Constituent. A general term that refers to an individual contaminant, chemical, chemical

compound, pollutant, or particulate matter.

Criteria pollutant. A pollutant for which a national ambient air quality standard has been defined.

De minimis impact. A change in ground-level concentration below a specified amount. The de

minimis concentration varies with the type of permit review and associated standards or

guidelines.

Digital elevation model (DEM). An array of elevations, usually at regularly spaced intervals, for

a number of ground positions.

Dilution Factor (DF). Based on a unit emission rate of one gram per second (1 g/s) and

expressed in terms of micrograms per cubic meter per gram per second (Fg/m /g/s). Required to 3

support the RCRA BIF modeling demonstration and the emission limits on which the

demonstration was based. 
xv

Effects screening level (ESL). Guideline concentrations derived by TARA and used to evaluate

ambient air concentrations of constituents. Based on a constituent’s potential to cause adverse

health effects, odor nuisances, vegetation effects, or materials damage. Health-based screening

levels are set at levels lower than those reported to produce adverse health effects, and are set to

protect the general public, including sensitive subgroups such as children, the elderly, or people

with existing respiratory conditions. If an air concentration of a constituent is below the screening

level, adverse effects are not expected. If an air concentration of a constituent is above the

screening level, it is not indicative that an adverse effect will occur, but rather that further

evaluation is warranted. (See Attachment C of RG-324, Modeling and Effects Review

Applicability).

Exceedance. In excess of a pre-established comparison level.

Emission point. Point of constituent emissions release into the air.

Emission point number (EPN). An alphanumeric identifier used to identify an emission point.

Each EPN is unique for an individual account.

Facility. A discrete or identifiable structure, device, item, equipment, or enclosure that constitutes

or contains a stationary source, including appurtenances other than emission control equipment. A

mine, quarry, well test, or road is not considered to be a facility (§116.10). For the purpose of

emissions inventory, the term does not refer to the entire site but to individual process units at the

site.

Fraction of radiation absorbed at the ground. The flux of heat into the ground during the

daytime is characterized as a fraction of the net radiation.

Frequency of exceedance. The number of times a predicted ground-level concentration exceeds

an ESL at a receptor. 

Fugitive dust. Dust discharged to the atmosphere in an unconfined flow stream such

as that from unpaved roads, storage piles, and heavy construction operations. (GAQM).

Grandfathered facility. A facility constructed before the permit requirements of Chapter 116

(§116.10). Must be constructed and operated as it was before September 1, 1971.
xvi

Greenfield site. A contiguous area under common control that is an undeveloped site (§116.15).

Ground-level concentration (GLC). The concentration in micrograms per cubic meter (Fg/m )

3

as predicted by modeling. May also be observed by ambient air monitoring.

Ground-level concentration—maximum (GLCmax). The maximum predicted off-property

ground-level concentration at any receptor.

Ground-level concentration—receptor (GLCr). The predicted ground-level concentration at

the maximally affected sensitive receptor, r.

Hazardous air pollutant (HAP). Any pollutant subject to a standard promulgated under FCAA,

§112 (relating to hazardous air pollutants).

Isopleth. A line on a map connecting points at which a given variable has a specified constant

value. 

Major. The term major may refer to the total emissions at a stationary source or to a specific

facility. For PSD review, once a site or project is major for one pollutant, all other pollutant’s

emissions are compared to significance levels in 40 CFR 52.21(b)(23).

! A named major source is any source belonging to a list of 28 source categories in 40 CFR

52.21(b)(1) which emits or has the potential to emit 100 tons-per-year (tpy) or more of

any pollutant regulated by the Federal Clean Air Act.

! A major stationary source is any source not belonging to the 28 named source categories

which emits or has the potential to emit such pollutants in amounts of 250 tpy or more.

! A major source is any source that emits 10 tpy or more of any single HAP or 25 tpy or

more of any combination of HAPs under FCAA §112(b).

Major modified stationary source or facility. Used in the context of a PSD or Nonattainment

permit application, the phrase major modified stationary source or facility refers to a change in

operation that results in a significant net increase of emissions for any pollutant for which a

NAAQS has been issued. New sources at an existing major stationary source are treated as

modifications to the major stationary source.
xvii

Major source baseline date. For particulate matter and sulfur dioxide, January 6, 1975. For

nitrogen dioxide, February 8, 1988. [40 CFR 52.21(b)].

Maximum exposed individual (MEI). Used in the RCRA BIF analysis. The MEI is a

hypothetical person assumed to reside at the location of the maximum, off-property concentration

(unless people routinely reside on-property).

Measurement site. The site at which the raw meteorological parameters were measured, such as

a National Weather Service observing site.

Minor. The term minor may refer to the total emissions at a stationary source or to a specific

facility. To be minor for PSD review, the emissions must be less than 250 tpy. To be minor for

Nonattainment review, the emissions must be less than the major source emission thresholds in 30

TAC Chapter 116. To be minor for HAPs review, the emissions must be less than 10 tpy for a

single HAP or 25 tpy for multiple HAPs.

Minor source baseline date. The earliest date after the trigger date on which a major stationary

source or a major modification subject to PSD regulations submits a complete application. [40

CFR 52.21(b)].

Modified stationary source or facility

! When used in the context of modeling, the phrase modified stationary source or facility

refers to a change in the location or stack parameters of an emission point, including

emission rate.

! When used in the context of a permit application, the phrase modified stationary source or

facility refers to a proposed change that results in an increase of emissions.

Monin-Obukhov length. A measure of atmospheric stability. It is negative during the day when

surface heating results in an unstable atmosphere and positive at night when the surface cools

(stable atmosphere).

Model. A quantitative or mathematical representation or simulation that attempts to describe the

characteristics or relationships of physical events. (GAQM).
xviii

National Ambient Air Quality Standards (NAAQS). Levels of air quality to protect the public

health and welfare. (40 CFR §50.2).

National Geodetic Vertical Datum of 1929. Reference surface established by the U.S. Coast

and Geodetic Survey in 1929 as the datum to which relief features and elevation data are

referenced in the conterminous United States; formerly called "mean sea level 1929." 

New facility. A facility for which is construction started after August 30, 1971, and no contract

for construction was executed on or before August 30, 1971, and that contract specified a

beginning construction date on or before February 29, 1972 (§116.10).

New source. Any stationary source, the construction or modification of which is started after

March 5, 1972 (§116.10).

! When used in the context of modeling, the phrase new source refers to a proposed

emission point.

! When used in the context of a permit application, the term new source refers to a

stationary source that was constructed or modified after March 5, 1972. (§116.10).

! When used in the context of a PSD or Nonattainment permit application, the term new

source refers to the total proposed emissions for a greenfield site when the increase in

emissions will be major. Or, new source refers to emissions at a minor stationary source

when the increase in emissions will be major.

Noon-time albedo. The fraction of the incoming solar radiation that is reflected from the ground

when the sun is directly overhead.

Nonattainment. Any area that does not meet (or that contributes to ambient air quality in a

nearby area that does not meet) the national primary or secondary ambient air quality standard for

a criteria pollutant.

North American Datum of 1927 (NAD27). NAD27 is defined with an initial point at Meads

Ranch, Kansas, and by the parameters of the Clarke 1866 ellipsoid. The location of features on

USGS topographic maps, including the definition of 7.5-minute quadrangle corners, are

referenced to the NAD27. 
xix

North American Datum of 1983 (NAD83). NAD83 is an Earth-centered datum and uses the

Geodetic Reference System 1980 (GRS 80) ellipsoid, unlike NAD27, which is based on an initial

point (Meads Ranch, Kansas). Using recent measurements with modern geodetic, gravimetric,

astrodynamic, and astronomic instruments, the GRS 80 ellipsoid has been defined as a best fit to

the worldwide geoid. Because the NAD83 surface deviates from the NAD27 surface, the position

of a point based on the two reference datums will be different.

Profile. One method of making DEMs is commonly referred to as profiling. In this technique a

stereo pair of photographs is set up in a photogrammetric instrument and referenced to the

ground using ground control points. After this process is completed the instrument automatically

moves a computer cursor across the stereo model. As the cursor is being driven across the model,

the operator controls the motion of the cursor while a recording device captures the elevation

figures. Each swath across the stereo model is called a profile. 

Project. An operational and/or physical change that may affect air emission rates at a site.

Projection. Orderly system of lines on a plane representing a corresponding system of imaginary

lines on an adopted terrestrial or celestial datum surface. Also, the mathematical concept of such a

system. For maps of the Earth, a projection consists of (1) a graticule of lines representing

parallels of latitude and meridians of longitude or (2) a grid. 

Property. All land under common control or ownership coupled with all improvements on such

land, and all fixed or movable objects on such land, or any vessel on the waters of this state

(§101.1).

Receptor. A location where the public could be exposed to an air contaminant (or constituent) in

the ambient air. For the effects evaluation process, receptors are classified as industrial or

sensitive.

Reference air concentration (RAC). Used in the RCRA BIF analysis for noncarcinogens. A

RAC is a reference concentration converted from a reference dose and is used to predict health

impacts.

Refined model. An analytical technique that provides a detailed treatment of physical and

chemical atmospheric processes and requires detailed and precise input data. Specialized estimates

are calculated that are useful for evaluating source impact relative to air quality standards and
xx

allowable increments. The estimates are more accurate than those obtained from conservative

screening techniques. (GAQM).

Risk-specific dose (RSD). Used in the RCRA BIF analysis for carcinogens. The RSD is a

reference concentration based on a cancer risk of one cancer incident per 100,000 people and is

used to predict health impacts.

Screening technique. A relatively simple analysis technique to determine whether a given source

is likely to pose a threat to air quality. Concentration estimates from screening techniques are

conservative. (GAQM).

Sensitive receptor. A nonindustrial receptor such as a school, residence, recreational area,

commercial or business office, land used for agriculture, hospital, day-care center, or church.

Other types include roads, railroads, rights-of-way, waterways, or the like; public exposure at

these other types of receptors is less likely than at other sensitive receptors. 

Site. The area that encompasses all emission sources of constituents. Includes all facilities and

other emission sources within the TNRCC account number. See 30 TAC §122.10 for the

operating permit definition.

Sitewide modeling. Modeling (refined or screening) of all emission points on a contiguous

property or TNRCC account number. Synonymous with plantwide modeling. Includes

grandfathered sources and sources exempt from the permitting process pursuant to 30 TAC 106.

Source

! A point of origin of air contaminants, whether privately or publicly owned or operated.

(§116.10). Upon request of a source owner, the executive director shall determine

whether multiple processes emitting air contaminants from a single point of emission will

be treated as a single source or as multiple sources. (§101.1). For PSD and Nonattainment

permits, source may refer to all emission points on a site or to a facility.

! When used in the context of modeling, the term source refers to the release point of

emissions. On the Table 1(a) submitted with the permit application (see TNRCC Air

Quality Permit Application Instructions, PI-1 Form) and in the Point Source Data Base

(see Appendix H), the EPN identifies the release point of the source of emissions. 
xxi

Stationary source

! When used in the context of modeling, the term stationary source refers to emission

points that are fixed and not mobile. For example, exhaust from a stack or baghouse is

from a fixed point, and exhaust from a car is from a mobile source because the exhaust

moves as the car does.

! When used in the context of PSD and Nonattainment permit applications, the term

stationary source refers to any building, structure, facility, or installation that emits or may

emit any air pollutant subject to regulation under the Federal Clean Air Act. (§116.12).

Also see modified stationary source or facility and major modified stationary source or facility.

Surface roughness length. A measure of the height of obstacles to the wind flow. This length is

not equal to the physical dimensions of the obstacles, but is generally proportional to them.

Surrogate constituent. A substitute constituent.

Unclassifiable. Any area that cannot be classified on the basis of available information as meeting

or not meeting the national primary or secondary ambient air quality standard for the pollutant. 

Trigger date. The date after which the minor source baseline date may be established. For

particulate matter and sulfur dioxide, August 7, 1977. For nitrogen dioxide, February 8, 1988. [40

CFR 52.21(b)].

Universal Transverse Mercator projection (UTM). UTM is a widely used map projection that

employs a series of identical projections around the world in the mid-latitude areas, each spanning

six degrees of longitude and oriented to a meridian. This projection preserves angular

relationships and scale plus it easily allows a rectangular grid to be superimposed on it. Many

worldwide topographic and planimetric maps at scales ranging between 1:24,000 and 1:250,000

use this projection. 

World Geodetic System 1972 (WGS 72). The definition of Defense Mapping Agency (DMA)

DEMs, as presently stored in the USGS database, references the WGS 72 datum. WGS 72 is an

Earth-centered datum. The WGS 72 datum was the result of an extensive effort extending over

approximately three years to collect selected satellite, surface gravity, and astrogeodetic data

available throughout 1972. These data were combined using a unified WGS solution (a large-scale
xxii

least squares adjustment). 

World Geodetic System 1984 (WGS 84). The WGS 84 datum was developed as a replacement

for WGS 72 by the military mapping community as a result of new and more accurate

instrumentation and a more comprehensive control network of ground stations. The newly

developed satellite radar altimeter was used to deduce geoid heights from oceanic regions

between 70 degrees north and south latitude. Geoid heights were also deduced from

ground-based Doppler and ground-based laser satellite-tracking data, as well as surface gravity

data. This system is described in "World Geodetic System 1984," DOD DMA TR8350.2

September 1987. New and more extensive data sets and improved software were used in the

development. 
1

1.0 Introduction

The Office of Air Quality's Air Dispersion Modeling Team (ADMT) developed this guideline to

document the TNRCC air quality analyses procedures. This publication replaces the previous

edition of the Air Quality Modeling Guidelines, April 1997. Significant changes are identified in

the “Summary of Significant Changes” section. References included in the main portion of the

document are identified by the originator, year of publication, and sequence in a series. Section 10

lists the full references.

This document focuses on the application of air dispersion models and general procedures to meet

air permitting requirements of the TNRCC. It is assumed that the reader has a basic knowledge of 

modeling theory and techniques. In addition, the format of the text assumes that the reader is an

air dispersion modeler, unless indicated otherwise.

Apply these guidelines as applicable to each individual project. They suggest a minimum level of

analysis so that modeling results clearly demonstrate that the public's health, general welfare, and

physical property are protected. In addition, these guidelines provide consistency in the selection

and application of air models to ensure a common basis for estimating pollutant concentrations,

assessing control strategies, and specifying emission limits—without compromising accuracy. 

General procedures are updated as required. The applicant is responsible for determining current

modeling procedures between formal publications of this document. See Section 1.3.

1.1 What Is Air Dispersion Modeling?

Air dispersion modeling is a tool to predict concentrations from one or more sources of air

pollution. Equations and algorithms representing atmospheric processes are incorporated into

various computer models. Agency personnel use the results from these models in their review of

permit applications. A modeled prediction alone does not mean that there will be a condition of

air pollution but is one of many indicators that the staff considers in the technical review process.

However, a modeled prediction of an exceedance of a standard or guideline value may be used as

the basis to modify permit allowable emission rates, stack parameters or operating conditions, or

to require a state implementation plan review for criteria pollutants.

1.2 Authority for Modeling

The authority for air dispersion modeling is contained in TNRCC 30 TAC Chapter 116 (TNRCC,

1998b), which states that modeling may be required by the TNRCC New Source Review Permits

Division (NSRPD) to determine the air quality impacts from a proposed new facility or source
2

modification. In some cases, such as for federal permits, modeling analyses are mandatory. In

addition, modeling may be required for other permitting purposes, such as modeling for permit

renewals, commission orders, etc.

1.3 Guidance Philosophy 

This document is a guide to typical air dispersion modeling techniques and procedures and

generally expands on modeling procedures contained in the EPA Guideline on Air Quality

Models (GAQM) (EPA, 1995a) or model user’s guides. The ADMT's goal is to use worst-case

assumptions and conditions to conduct the minimum amount of modeling necessary to

demonstrate that the modeled sources should not cause or contribute to a condition of air

pollution. 

If additional refinement is needed, then only the level of refinement necessary to achieve the

modeling demonstration's goal is required. However, conduct the most refined analysis possible if

one of the purposes of the modeling demonstration is to determine baseline concentrations for an

entire site.

If the modeler can demonstrate that techniques other than those recommended in this document

are more appropriate, the ADMT may approve their use. Discuss this demonstration with the

ADMT and document it in the air quality analysis. 

Periodically, the ADMT develops new techniques or changes procedures to reflect improvements

in regulatory models, to correct deficiencies that have been discovered, or to be consistent with

requirements of other regulatory agencies. These changes to standard practices and other useful

information will be placed on the ADMT Internet page. The http and ftp URLs are

! http://www.tnrcc.state.tx.us/air/nsr_permits and click on the link to the Air Dispersion

Modeling Team, and

! ftp://ftp.tnrcc.state.tx.us/pub/AirQuality/NewSourceReviewPermits/Modeling. Note that

this URL has mixed cases. 

In addition, interested parties can contact the ADMT via the Internet at the following address:

! admt@tnrcc.state.tx.us. 

1.4 Use of Monitoring Data in State Permit Review 
3

Occasionally, modeling predictions may not clearly indicate whether emissions from a site or

individual source could cause or contribute to a condition of air pollution. In those cases, the use

of ambient monitoring data in the technical review process may be an option to supplement

modeled predictions. With few exceptions, the monitoring demonstration must be conducted

before a permit is issued to ensure that permit conditions and allowable emissions are protective.

See Section 3.10 for monitoring guidance for federal permits.

If the use of monitored data is an option, the applicant should contact the permit engineer to

arrange a meeting. The engineer will convene a team consisting of representatives from ADMT,

TARA, Monitoring Operations, the applicable region, and any other applicable agency staff. The

staff will help the applicant determine whether monitored data from an existing network can be

used in the permitting process. Or, if a network does not exist, the staff will help the applicant

determine whether monitoring is technically feasible for the constituent of concern. If it is, the

applicant should consider the following issues, at a minimum, to develop a monitoring strategy:

! Amount and type of monitoring. This is decided on a case-by-case basis and would depend

on such factors as air constituent; types and locations of sources; source parameters and

operating hours; meteorology; location of sensitive receptors; and location of other

sources of the constituent. For example, several weeks of data may by sufficient for

evaluating the impact of short-term emissions of an acute toxicant, but several months to a

year of data may be necessary for evaluating long-term exposure levels to a chronic

toxicant.

! Monitoring method. The method must be an approved method or a generally accepted

alternate or modified method. In addition, the applicant must keep track of production and

operations during the monitoring period and note any unusual occurrences that would

invalidate the data, such as truck traffic within the exclusionary boundary around a

particulate monitor.

! Siting of monitors. Monitors must be sited to obtain concentrations and meteorological

data that are representative. To be representative, the concentrations obtained must result

from significant sources emitting at near maximum operating conditions and under near

worst-case meteorological conditions. More than one ambient and meteorological monitor

may be required.
4

" Significant sources. These sources are the ones that cause the highest

concentrations or cause high concentrations frequently. In certain cases, there may

be many sources on the site but only one or two whose resulting concentrations

drive the effects review. That is, they either have the largest emissions; stack

parameters that cause the highest concentrations or the most frequent exceedances

of the ESL; or are located near a property line or sensitive receptor. Therefore, it

is these sources that the applicant should ensure are sampled. In addition, if

significant sources are separated by more than about 100 meters, representative

samples should be obtained from each source or source grouping as applicable.

" Determination of significant sources. Significant sources can be determined by

engineering judgment or by a culpability analysis using the ISC model. An analysis

based on modeling results can identify such information as culpable sources;

magnitude of concentrations; frequency of occurrence at different multiples of an

ESL; location of worst-case concentrations; and meteorological parameters by

time of day. 

" Upwind and downwind ambient air monitors. Multiple monitors may be needed

for property line and effects review if there are other sources of the constituent in

the local area. In addition, upwind and downwind meteorological monitors may be

needed to account for changes in wind speed and direction in cases where there are

large distances between emission points and property lines; for large distances

from emission points to the monitor; or for geographic features that could affect

air flow.

The monitoring plan must be in accordance with EPA Requirements for Quality Assurance

Project Plans for Environmental Data Operations (QA/R5) (EPA, 1993b), and be designed to

acquire monitoring data that represents, as closely as possible, worst-case operating conditions.

The staff will consider siting limitations, such as power and security constraints, as well as the

location of sensitive receptors and off-property sources of the same constituent during the review

of the monitoring plan.
5

2.0 The Air Quality Analysis Process

The air quality analysis is an evaluation of the potential impact of a new facility or source

modification on the environment [§116.111(9)]. Analyses are conducted for state permits and

federal permits; analyses for federal permits are usually more detailed than those for state permits.

Because there are several terms, such as the term source, that have different state, federal, and

modeling usage definitions, the process could be confusing. Misunderstanding of terms could lead

to an incomplete analysis. Therefore, applicants and staff should ensure that when using these

terms the context of usage is understood. See the “Definitions” section.

The air quality analysis process may involve a number of TNRCC staff, depending on the

complexity of the application and the potential impact of the associated facility or source on air

quality. The permit engineer determines the need for modeling and the scope of involvement of

other TNRCC staff. Therefore, the applicant should contact the permit engineer for guidance

before involving other TNRCC staff in the air quality analysis process. 

2.1 Permit Engineer Coordination

The applicant should provide sufficient information to the permit engineers so that they are able to

determine the need for regulatory modeling. Regulatory modeling is any air dispersion modeling

requested by the permit engineer that is used in the permitting process.

2.2 Coordination with Other TNRCC Staff

Individual members of the public who wish to inquire about the information contained in permit

public notices or to inquire about other agency permit applications or permitting processes, should

call the TNRCC Office of Public Assistance, toll free, at 1-800-687-4040. Applicants should not

contact the Office of Public Assistance but should work with the NSRPD. 

Other staff that may be involved in the permitting process include, but are not limited to, the

following:

! Toxicology and Risk Assessment Section (TARA), Chief Engineer’s Office: for effects

screening levels and other information required for a toxicological review.

! Customer Reports & Services, Information Resources Division: for PSDB retrievals.

! Emissions Inventory Section, Air Quality Planning Division: for correction of errors,

found in the PSDB.
6

! Data Management and Analysis Section, Monitoring Operations Division: for ambient air

quality monitoring data and county attainment status. 

! Quality Assurance Section, Monitoring Operations Division: for review of monitoring

quality assurance plans.

! Industrial & Hazardous Waste Permits Section, Permits Division: for RCRA combustion

permits.

! Legal Division: for legal opinions about interpretation of regulations, control of property,

ambient air, and other points.

2.3 ADMT Responsibilities

! Provide technical guidance for the modeling process to staff, applicants, and the public. 

! Review modeling performed by permit engineers or perform modeling in support of a

permit application.

! Evaluate the technical quality of air quality analyses submitted by applicants. Ensure that

predicted concentrations accurately represent potential impacts, demonstrate compliance

with federal and state regulations and guidelines, and can be used by the staff in the

technical review process.

! Help small business applicants meet modeling requirements needed to obtain a permit, or

perform modeling for them as necessary.

! Provide modeling support for other agency needs such as enforcement, pollution

prevention, or superfund activities, as directed.

2.4 Modeling Request

The permit engineer determines the need for air dispersion modeling and advises the applicant by

letter to contact the ADMT team leader to discuss the project and pre-modeling requirements.

Contact may be made by phone at (512) 239-1508 or by e-mail at admt@tnrcc.state.tx.us. At a

minimum, include a name, phone number, and a short message.

2.5 Guidance Meetings, Protocols, and Checklists
7

Guidance Meetings: Guidance meetings are optional and may be combined for state, PSD, and

RCRA BIF permit applications.

! To schedule a meeting. Contact the ADMT team leader to schedule a modeling guidance

meeting (see Section 2.4). The meeting may be conducted in-person with modelers,

engineers, and other applicable staff; or, for simple projects, by phone between a member

of the ADMT and the applicant's modeler. The team leader collects the required

information and assigns the project to one of the staff, who will provide detailed guidance

for the project.

! ADMT staff responsibility. The staff member coordinates with the permit engineer and

contacts the applicant to set up a time for a guidance meeting. The staff will respond to

the applicant either by phone or via e-mail.

Protocols and Checklists: Protocols and modeling guidance checklists serve as outlines of how

modeling analyses should be conducted—they are not mandatory. A protocol or checklist may be

helpful to an inexperienced permit modeler, or if the permit modeler is proposing new modeling

techniques or changes to normal modeling practices. A protocol contains more detail than a

checklist. The checklist contains similar data but prompts the modeler rather than providing

detailed instructions. The ADMT encourages applicants to submit protocols instead of checklists

for PSD and complex state permit modeling and RCRA BIF projects. In addition, the ADMT

suggests that no regulatory modeling be conducted before staff comments are received.

! To develop a protocol or checklist without a meeting. Applicants may submit a protocol

or checklist to the ADMT team leader without participating in a face-to-face meeting. If 

applicants determine that they require a protocol or checklist for a project, they should

follow the guidance in Appendix D to develop it. Since a protocol is a more formal

presentation and contains more detail than a modeling checklist, applicants should submit

a protocol by letter.

! To develop a protocol and have a meeting. If applicants want to meet and then submit a

protocol, they should prepare to discuss the project and address the items in Appendix D

at the meeting. After the meeting they should submit a protocol for ADMT review.

! To develop a checklist and have a meeting. If applicants want to meet and want the

guidance in the meeting documented by using a checklist, they should prepare the
8

modeling guidance checklist—or obtain as much information required to complete the

checklist as possible—before the meeting (see Appendixes D and E). The checklist can be

sent to ADMT via e-mail before a meeting. At the guidance meeting, an ADMT modeler

signs the checklist if it is complete or assists the applicant with the final checklist, which

the applicant should include in the air quality analysis report. 

! Protocol or checklist review. The team leader assigns the protocol or checklist to one of

the staff to review and provide comments to the applicant.
9

3.0 Conducting the Air Quality Analysis

The air quality analysis is an evaluation of the impact on the environment of increased emissions

from a new facility or modified source based on the predicted concentrations obtained through

modeling. [§116.111(1), (6), (9)].

3.1 Levels of Modeling Used in the Air Quality Analysis

There are two levels of modeling sophistication used in the air quality analysis process: screening

and refined. Modeling results from either level, as appropriate, may be used to demonstrate

compliance with standards or guidelines.

3.1.1 Screening Modeling

The first level of sophistication involves the use of screening procedures or models. Screening

models use simple algorithms and conservative techniques to indicate whether more detailed

modeling is necessary. 

Screening models are usually designed to evaluate a single source or sources that can be

collocated (Section 3.3.2). Multiple sources can be modeled individually and then the maximum

concentration from each source summed for an overall estimate of the sitewide maximum

concentration. This technique is conservative since the concentrations from each source are added

without regard to distance. Appendix B contains factors to convert one-hour concentrations to

other averaging periods. 

The permit engineer generally conducts an initial screening analysis using EPA’s SCREEN model,

or the staff may ask the applicant to conduct an analysis. The screening analysis should be

consistent with guidance contained in the GAQM (EPA, 1995a), and appropriate screening

modeling guidance documents, such as the Screening Procedures for Estimating the Air Quality

Impact of Stationary Sources (EPA, 1992b). The SCREEN model is available for download from

the EPA's SCRAM Internet page at http://www.epa.gov/scram001.

3.1.2 Refined Modeling

The permit engineer may determine that refined modeling is necessary if the screening analysis

results indicate that predicted concentrations from the evaluated sources could exceed a standard,

guideline (such as an effects screening level), a de minimis amount, or a staff-identified percentage

of a standard or guideline. It is usually the applicant's responsibility to perform refined modeling.

However, the permit engineer may ask the ADMT to perform this type of modeling under certain
10

circumstances, such as for small businesses that cannot afford the costs associated with refined

modeling. 

This second level of modeling requires more detailed and precise input data and more complex

models in order to provide refined concentration estimates. The primary model used is the EPA’s

Industrial Source Complex (ISC) model, which is available for download from the EPA's SCRAM

Internet page.

3.2 Types of Air Quality Analyses

The type of air quality analysis depends on the category of permit and pollutants to be evaluated.

There are two general categories of permits: state and federal. State permit types of analyses are

property line, NAAQS, effects evaluation, and disaster review. Federal permits are known as PSD

or RCRA combustion permits and may include several analyses. For PSD: NAAQS, increment,

monitoring, ozone ambient impact, additional impacts, and Class I area impacts. And for RCRA:

BIF and multipathway risk assessment. Note that several types of analyses could be required for

a single permit. Before conducting any analysis, a modeling emissions inventory must be

developed.

3.3 Modeling Emissions Inventory

The modeling emissions inventory consists of the emission points of the sources to be permitted,

as well as other applicable on- and off-property emission points, including exempt and

grandfathered points. These points are identified by emission point numbers (EPNs) but are

usually referred to as sources in air dispersion model guidance documents. Modeling parameters

for off-property sources can be obtained from the agency's PSDB (see Appendix H).

The PSDB is a computerized database containing information about point and area sources of air

pollutants, as defined by TNRCC permit and exemption activities and emission inventory surveys.

Standard retrievals have been developed to obtain required source information. Include all known

sources in the modeling demonstrations, even if they are not found in the PSDB.

If errors are found in the PSDB retrieval (for example, incorrect stack parameters), notify the

Emissions Inventory staff and the ADMT. Provide the needed corrections for any of the

applicant's sources, if applicable.
11

M = hs V T s

 _______

 Q

3.3.1 Ratio Techniques

Since predicted ambient air quality impacts from a source are proportional to its emission rate, it

may be appropriate to use a ratio technique to simplify the evaluation of on-property sources

and/or to reduce the number of pollutants requiring individual refined modeling runs to a

manageable number. Please refer to Appendix B for a description of two ratio techniques. Other

techniques may be approved on a case-by-case basis. Document in the modeling checklist or

protocol, and in the air quality analysis, the rationale for the choice of ratio technique.

3.3.2 Collocation of Emission Points 

Regulatory modeling should reflect the actual characteristics of the proposed or existing emission

points. Therefore, emission points should not be collocated except in well-justified circumstances.

For example, collocation may be appropriate when the number of points at a large site exceeds the

capability of the model. Modeling convenience or the desire to reduce model run time are not, by

themselves, acceptable justifications.

Collocating fugitive emission points may be appropriate for a screening analysis. If so, collocate

all emissions at the point located nearest to the property line, or fence line for PSD analyses.

Collocating stacks may be appropriate for both screening and refined analyses if the individual

emission points emit the same pollutant(s); have stack heights, volumetric flow rates, or stack gas

exit temperatures that do not differ by more than about 20 percent; and are within about 100

meters of each other.

Use the following equation (EPA, 1992b) to determine the worst-case stack:

where

M = a parameter that accounts for the relative influence of stack height, plume rise, and

emission rate on concentrations;

h = the physical stack height in meters; s

V = ( /4) d v = stack gas flow rate in cubic meters per second; s s

2 
12

d = inside stack diameter in meters; s

v = stack gas exit velocity in meters per second; s

T = the stack gas exit temperature in Kelvin; and, s

Q = pollutant emission rate in grams per second.

The stack that has the lowest value of M is used as a representative stack. The sum of the

emissions from all stacks is assumed to be emitted from the representative stack; that is, the stack

whose parameters resulted in the lowest value of M.

3.4 Preliminary Impact Determination

The following air quality analyses begin with a preliminary impact determination: State Property

Line, State NAAQS, PSD NAAQS, PSD Monitoring, and PSD Increment. The purpose is to

determine whether a new source, modification of an existing source, or a combination of the two

could cause a significant off-property impact. Petitions for single property designation (§101.2)

do not apply to federal permits. 

The general procedure for preliminary impact determination involves five steps. Either screening

or refined modeling can be used as appropriate. 

Step 1: Identify All Sources of Emissions. Include emissions from all new equipment, even if the

emissions are released through existing emission points.

Step 2: Determine Whether There Is a Net Emissions Increase. If there is a net increase,

conduct the preliminary impact determination. See the Modification of Existing Facilities under

Senate Bill 1126 guidance package for projects that qualify for consideration under that bill.

! State permits, except those for effects evaluation. Evaluate emissions of new sources and

emissions increases and decreases directly associated with the permit application or

project.

! PSD permits.

" For a major source, evaluate emissions from new sources and emissions increases

and decreases at any source sitewide over a contemporaneous five-year period to
13

determine whether there is a net emissions increase. If emissions decreases are

used in the netting calculations, they cannot be used in future PSD applications,

and cannot be banked. (30 TAC §116.160).

" For a minor source, evaluate emissions from new sources. For a Minor Source,

with a project that is considered to be major, netting is not allowed.

Step 3: Evaluate Modifications to Existing Sources. Carry out this step even if there is no net

increase in emission. For both state and PSD modeling, include these sources in the preliminary

impact determination if there is a change in operating hours or stack parameters, and previous

modeling demonstrations were limited to those hours or parameters—that is, the permit

conditions were based on those limits.

Step 4: Develop the Emission Inventory. Include all sources identified in the previous steps.

Both new and modified sources can be included in a single determination. Some of the possible

modeling combinations for the preliminary impact follow

! New source: 

" State: Use the proposed allowable emission rate.

" PSD: Use the proposed allowable emission rate.

! Modified source:

" State: Applies to the sources directly related to the permit application or project,

and those identified in Step 3 with a change in operating hours or stack

parameters. 

— If there is no change in location or stack parameters, use the difference

between the proposed allowable emission rate and the existing allowable

emission rate. 

— If there is a change in location or stack parameters, include the source in

the model twice, once at the current location or with current stack

parameters, and once at the proposed location or with proposed stack
 This definition of “actual” is different from the one used for increment analyses. 1

14

parameters. Enter an allowable emission rate increase as a positive number

and an allowable emission rate decrease as a negative number. Include

sources that will be shut down permanently and sources that will not be

operating or operating at a reduced rate during operating scenarios

specified in the permit.

" PSD: Applies to all sources used in the netting calculations, and those identified in

Step 3 with a change in operating hours or stack parameters. Actual emissions 1

are based on a representative two-year average for both short- and long-term rates. 

— If there is no change in location or stack parameters, use the difference

between the proposed allowable emission rate and the existing actual

emission rate for the source. Or for decreases in emissions, use the

difference between the existing actual emission rate for the source and the

proposed allowable emission rate.

— If there is a change in location or stack parameters, include the source in

the model twice, once at the existing location or with current stack

parameters, and once at the proposed location or with proposed stack

parameters. Enter an allowable emission rate increase as a positive number

and an actual emission rate decrease as a negative number. Include sources

that will be shut down permanently and sources that will not be operating

or operating at a reduced rate during operating scenarios specified in the

permit.

Step 5: Conduct Modeling. Carry out the preliminary impact determination modeling as indicated

for the applicable modeling analysis (3.5 through 3.7, 3.9 through 3.11). If there is a significant

impact, model all sources on site as they will operate after the permit is issued using allowable

emission rates. Model off-site sources as applicable using allowable emission rates as well.

3.5 State Property Line Analysis
15

The purpose of the property line analysis (also referred to as state regulation analyses) is to

demonstrate compliance with state standards for net ground-level concentrations. These analyses

are performed for particulate matter [30 TAC Chapter 111 (TNRCC, 1996)] and sulfur

compounds [30 TAC Chapter 112 (TNRCC, 1997a)].

This analysis must demonstrate that resulting air concentrations from all on-property sources that

emit the regulated pollutant should not exceed the applicable standard. Although all on-property

sources should be modeled, in many cases the proposed emissions or changes in emissions may

not be substantial when compared to the total emissions from the site. The basic procedure

involves four steps, described in the following paragraphs.

Property Line Step 1: Determine whether monitoring data has shown that a standard for the

pollutant under review has been exceeded nearby (within 8-10 kilometers of the property line);

whether previous modeling has shown that the standard could be exceeded; or whether the

engineer has any concerns about air quality.

! If yes, sitewide modeling is usually required. Go to Step 2. 

! If not, model allowable emission rates for all new and modified sources that emit the

regulated pollutant (Section 3.4).

" Use 1-hour modeled predictions to compare with 30-minute standards. This is a

conservative technique since the model’s dispersion coefficients were derived

based on sampling times of much less than 1 hour but are held constant during a

modeled hour. Also, if an hour was divided into segments based on the time 

for which a coefficient was derived, the results obtained would be equal for

each segment, since all other data are constant throughout the hour. For

example, if the coefficients were derived based on 10-minute sampling periods,

results from each of the six periods that comprise a modeled hour, or from each

of the three periods that comprise 30 minutes, would be equal, and the

corresponding period averages would be equal as well.

" If the predicted concentration—at or beyond the property line—is less than about

2 percent of the standard, the demonstration is complete. If not, sitewide

modeling maybe required by the permit engineer after the evaluation of such

factors as previous modeling results or monitoring data. Go to Step 2.
16

Property Line Step 2: If sitewide modeling is required, model the allowable emission rates for all

sources on the applicant's property that emit the regulated pollutant. Determine rates for

grandfathered and exempted facilities in consultation with the permit engineer.

Property Line Step 3: Compare predicted concentrations to the appropriate state standard (see

Appendix A and Appendix G). If the concentrations are less than the standard, the demonstration

is complete. If not, additional modeling, technical analyses, or monitoring may be appropriate. Go

to Step 4.

Property Line Step 4: Determine whether one of the following four options could apply to the

project. The applicant may propose other approaches for consideration as well.

! Option 1: modeling. Conduct additional modeling to reflect actual operating conditions,

such as batch operations, or special provisions such as limits to hours of operation or

bubble allowable emission rate limits.

! Option 2: air quality improvement. Demonstrate that air quality could be improved by

issuance of the permit. For example, air quality could be improved by replacing existing

control technology at a facility with Best Available Control Technology (BACT) that

would reduce sitewide emissions.

! Option 3: technical analyses. Two approaches are summarized below:

" Evaluate existing, representative monitoring data for the site to demonstrate that

the predicted maximum concentrations from a proposed source when added to

monitored concentrations would not exceed a standard. 

" Determine whether the concentration aligns with the form of the standard. Some 

standards are based on a fixed ambient temperature. Use the ideal gas law to

convert parts per million (or billion) to micrograms per cubic meter based on the

modeled ambient temperature for the exceedance. For example, the 1021

micrograms per cubic meter (μg/m ) concentration standard for sulfur dioxide 3

(SO ) is based on the conversion of the 0.4 parts per million standard at an ambient 2

temperature of 90 degrees Fahrenheit. At a lower temperature, the equivalent

concentration in μg/m would be higher, and the standard might not be exceeded. 3
17

! Option 4: monitoring. If monitoring is an alternative, the TNRCC staff will help the

applicant develop a monitoring plan. In most cases, the monitoring demonstration must be

conducted before a permit is issued, to ensure that permit conditions and allowable

emissions are protective.

3.6 State NAAQS Analysis

The purpose of the State NAAQS analysis is to demonstrate that emissions of criteria pollutants

from a new source or from a modification of an existing source that does not trigger PSD will not

cause or contribute to an exceedance of the NAAQS. The criteria pollutants of concern are

carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO 2 ) [surrogate is nitrogen

oxides (NO )], lead (Pb), and particulate matter with an aerodynamic diameter of 10 microns or x

less (PM ). Compliance with the pre-1997 form of the PM NAAQS will be the surrogate for 10 10

compliance with the 1997 form of the PM 10 NAAQS, and the new PM 2.5 NAAQS, until EPA

publishes new technical review procedures. The ADMT will post the new procedures on the

ADMT Internet page when they are effective. Compliance with any NAAQS is based upon the

total estimated air quality, which is the sum of the maximum modeled concentration plus a

background concentration. The basic procedure consists of nine steps, described in the following

paragraphs.

State NAAQS Step 1: Conduct a preliminary impact determination to predict whether the

proposed source(s) could make a significant impact on existing air quality—that is, equal or

exceed a NAAQS de minimis. (Section 3.4).

! Model all new and modified sources. Compare the predicted high concentration at or

beyond the property line for each pollutant and each averaging time to the appropriate

NAAQS de minimis level in Appendix A. If the sources do not make a significant impact

for a pollutant of concern, the demonstration is over. If they do, an area of impact (AOI)

is defined, and a full NAAQS analysis may be required. Go to Step 2.

State NAAQS Step 2: Obtain a screening background concentration from the ADMT Internet

page. Add the background concentration to the modeled concentration. If the total concentration

is less than 90 percent of the NAAQS, the demonstration is complete. If the concentration is 90

percent or more, go to Step 3.

State NAAQS Step 3: Determine the radius of impact for the AOI for each pollutant and

averaging period subject to the NAAQS analysis. 
Area sources in the PSDB must be manually entered into the model at this time. 2

18

! The radius is the farthest distance from the sources under review to the location where

concentrations are predicted to equal or exceed de minimis for each applicable averaging

time and pollutant. 

! Use the largest radius for each pollutant, regardless of averaging period, for the rest of the

analysis. This radius is limited to the actual distance or 50 kilometers (km), whichever is

less.

State NAAQS Step 4: Obtain a retrieval using the secondary radius search option from the PSDB

(Appendix H). This retrieval identifies point and area sources within the radius of impact and

other point and area sources outside the radius of impact that should be evaluated with the

sources in the permit application.

State NAAQS Step 5: Determine predicted concentrations over the AOI—at and beyond the

property line—from all retrieved sources and sources to be permitted. 2

! Model allowable emission rates for all sources that emit the regulated pollutant. Offproperty sources may be eliminated from the modeling demonstration if screening

modeling indicates that the sources' contributions would not equal or exceed the

applicable de minimis within the AOI. If any sources are omitted from the modeling

demonstration, explain in the air quality analysis why they were omitted. 

State NAAQS Step 6: Determine the background concentration. As defined by the EPA,

background air quality includes pollutant concentrations due to natural sources, nearby sources

other than the one(s) under consideration, and unidentified sources. 

! Obtain the data from the EPA AIRSWEB at the following URL:

http/www.epa.gov/airsweb/monreps.htm, or by contacting the ADMT or the Data

Management and Analysis Section, Monitoring Operations Division.

State NAAQS Step 7: Compare the predicted concentration plus background concentration for

each pollutant to the appropriate NAAQS (Appendix A, Appendix G). This concentration should

be conservative since both nearby and distant background point sources are included in both the

predicted and background concentrations. If the maximum concentrations are below the NAAQS,
19

the demonstration is complete. If not, determine whether the background concentrations are

representative. If they are conservative for the project, then attempt to refine them.

State NAAQS Step 8: Refine the background concentration to remove or limit the contributions

from the background point sources. Contact the ADMT for assistance as necessary or check the

ADMT Internet page. Several methods are suggested. The goal is to obtain a background

concentration with the least amount of time and effort. Therefore, the options do not need to be

followed in sequence.

State NAAQS Step 9: Conduct additional modeling if a predicted concentration will exceed a

NAAQS and the permitted sources are predicted to make a significant impact at the same time

and location of a NAAQS exceedance (EPA, 1990, TNRCC, 1998b).

3.7 State Effects Evaluation Analysis

The purpose of the effects evaluation analysis (also known as health effects reviews or effects

reviews) is to demonstrate that the public health and welfare are protected. Perform this analysis 

for noncriteria pollutants following the procedures in TNRCC’s RG-324, Modeling and Effects

Review Applicability technical guidance package (TNRCC, 1998a). 

Agency toxicologists use a three-tiered approach to evaluate the effects of emissions on a

constituent-by-constituent basis. The objectives of the analysis are to:

! establish off-property ground-level air concentrations (GLCs) of constituents resulting

from proposed emissions, and

! evaluate these GLCs for their potential to cause adverse health or welfare effects.

TARA staff compare the GLC to an effects screening level (ESL) An ESL is a guideline—not a

standard. This format provides the flexibility required to easily revise the value to incorporate the

newest toxicity data. TARA publishes a list of ESLs annually, which can be obtained from TARA

or the NSRP Internet page at http://www.tnrcc.state.tx.us/air/nsr_permits. Consult with a

toxicologist to ensure that the most recent ESL list is used; to obtain additional information

concerning the basis for ESLs; or to obtain ESLs for constituents not on the published list. For

constituents not on the published list, provide the chemical abstract service registry number and a

material safety data sheet to the staff so that they can positively identify the constituent and derive

an ESL.
20

The two primary averaging periods are 1-hour (due to short-term emissions) and annual (due to

average annual emissions). Occasionally, other short-term periods (such as 8-hour or 24-hour) are

of interest. In those cases, toxicologists will provide the appropriate ESL to use. 

If a review of long-term impacts is required along with short-term impacts, long-term

concentrations do not need to be obtained separately if the maximum short-term concentration is

lower than the corresponding long-term ESL. For example, no long-term modeling would be

required if the pollutant’s short- and long-term ESLs were 10 and 1 microgram per cubic meter

(Fg/m ), respectively, and the maximum short-term concentration was less than 1 Fg/m .

3 3

Subsections 3.7.1 through 3.7.5 summarize the effects evaluation analysis process. 

3.7.1 Tier I Effects Analysis

Use the flowchart in the Modeling and Effects Review Applicability guidance package. 

The following comments refer to steps in the flowchart.

! If Step 3 applies, refined modeling may be required after TARA’s review.

! For Step 4, netting does not apply. If the project includes both increases and decreases,

Step 7 offers an assessment of whether the reductions are sufficient to determine

acceptable impacts.

! If Step 4B applies, refined modeling may be required after TARA’s review.

! If the project’s emissions cannot pass Step 5, Step 6, or Step 7, sitewide modeling is

required by Step 8.

! For Step 8, design a receptor grid, select appropriate averaging periods, and use maximum

allowable emission rates, or applicable emission increases, for all applicable on-property

sources associated with the project.

" Compare the maximum off-property concentration (GLCmax)—at or beyond the

property line—to the applicable ESL. If the concentration is below 10 percent of

the ESL for the project, and cumulative concentrations from this and previous

projects are less than 25 percent of the ESL, the demonstration is complete. If not,
21

and the increased emissions cannot pass Step 10, or Step 11B is not an option,

then sitewide modeling is required for Step 11A.

! For Step 11A, design a receptor grid, select appropriate averaging periods, and use

maximum allowable emission rates for all on-property sources. ADMT suggests that

discrete receptors be included in this tier even though they are not required. This may save

time if exceedances of the ESL are predicted. In addition, select model output options to

ensure that gridded data plots can be created. 

" Compare the GLCmax—at or beyond the property line—to the applicable ESL. If

the concentration is below the ESL, the demonstration is complete. If not, go to

Tier II.

3.7.2 Tier II Effects Analysis

In the Tier II effects analysis, the evaluation focuses on potential exposure based on the type of

receptor where the ESL exceedance occurs. There are two types of receptors: industrial and

sensitive. Examples of sensitive receptors are residences, schools, hospitals, churches, businesses,

lakes, rivers, waterways, and roads. In addition, if land that is zoned industrial is leased for

another purpose such as cattle grazing or farming, treat the industrial area as sensitive. Contact

TARA to discuss the types and locations of sensitive receptors. Additional model runs may be

needed if sensitive receptors were not included in the original receptor grid.

! Determine the type of receptor if an exceedance of an ESL is predicted in Tier I. In order

to pass Tier II, the GLCmax must be no higher than twice the ESL at an industrial

receptor; and, the GLC at the maximally affected sensitive receptor (GLCr) must not

exceed the ESL. If both conditions are met, the demonstration is over. If not, go to Tier

III.

3.7.3 Tier III Effects Analysis

While the first two tiers are based on predicted concentrations, the third tier incorporates casespecific factors which bear on the exposure scenario. The factors considered include surrounding

land use; magnitude of exceedance; frequency of exceedance; existing levels of the same

constituent; type of toxic effect caused by the constituent; margin of safety between the ESL and

known effects levels; degree of confidence in the toxicity database; and acceptable reductions

from existing concentrations. Additional model runs may be needed to generate files needed to
22

create frequency of exceedance plots for various magnitudes of exceedance; such as 2, 4, or 10

times the ESL.

! Provide case-specific factors to TARA. In addition, provide the toxicological staff as

much modeling diagnostic information as possible concerning the production process or

operating conditions. For example, the culpable sources; the type of operation, limited or

continuous; an evaluation of the potential for multiple sources to operate at the same time.

! Design model output options to obtain the data TARA requests

! Provide results to the permit engineer and to TARA.

3.7.4 Modeling Postprocessing Requirements

Provide the following data if requested by the toxicologists to assist them with their Tier II and

Tier III evaluations. Include gridded maps in the air quality analysis that depict:

! maximum concentrations at each receptor on the grid;

! the magnitude of the ESL exceedance (concentration divided by ESL) at each receptor

with a predicted exceedance; 

! the number of times the ESL is predicted to be exceeded at each receptor, with a

predicted exceedance; and

! the location of sensitive receptors.

Before conducting additional modeling or postprocessing the modeling data, contact TARA to

discuss the appropriate format to use to present modeled results to meet the objectives of the Tier

III analysis. 

3.7.5 Baseline Date for Effects Reviews

Sitewide modeling establishes baseline concentrations for effects reviews that can be used in

future evaluations. To assist the staff and to shorten the evaluation process for future permitting

actions, provide the maximum concentration predicted for each source in the sitewide modeling

demonstration. This can be done by modeling each source as a separate source group. With these

results, the staff may be able to evaluate the change in overall impact resulting from an increase in
23

emissions of an existing source or addition of a new source without the need to require additional

sitewide modeling.

3.8 State Disaster Review

The purpose of a disaster review is to demonstrate that the public health and welfare are protected

from sources with a potential for catastrophic release of a chemical of concern. Disaster review

guidelines are included in TNRCC Air Quality Permit Application Instructions PI-1 Form.

Permit applications involving certain chemicals require additional information necessary to assess

disaster potential. If the permit engineer identifies a potential for a catastrophic release of any

applicable chemical, then conduct a disaster review, which could include modeling. The engineer

determines the need for disaster modeling and reviews the release scenarios and associated

emission rates to be modeled on a case-by-case basis. Agency toxicologists will compare modeled

concentrations to ESLs and to concentrations immediately dangerous to life and health (IDLH)

for each chemical. Coordinate with ADMT before conducting the modeling demonstration.

This disaster review is not a substitute for the risk management plan required under Section

112(r) of Title III of the Clean Air Act. However, modeling performed to demonstrate compliance

with this section may be used as applicable for the state disaster review. Numerous disaster

models are available; several are on the EPA’s SCRAM Internet site.

3.9 PSD NAAQS Analysis

The purpose of the PSD NAAQS analysis is to demonstrate that emissions of criteria

pollutants—and selected noncriteria pollutants—from a new major source or major modification

of an existing major source will not cause or contribute to an exceedance of the NAAQS—or

other health guidelines in the case of the noncriteria pollutants. The criteria pollutants of concern

are carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO 2 ) [surrogate is nitrogen

oxides (NO )], lead (Pb), and particulate matter with an aerodynamic diameter of 10 microns or x

less (PM ). Compliance with the pre-1997 form of the PM NAAQS will be the surrogate for 10 10

compliance with the 1997 form of the PM 10 NAAQS and the new PM 2.5 NAAQS. The ADMT

will post the new procedures on the ADMT Internet page when they are effective. The noncriteria

pollutants that could be considered for a modeling analysis are sulfuric acid mist, total reduced

sulfur (TRS), reduced sulfur compounds (RSC), and fluorides (Fl) not including hydrogen

fluoride.
24

The PSD NAAQS analysis is similar to the state NAAQS analysis, but there are differences. For

example, selected noncriteria pollutants must be reviewed. However, since there are no federal de

minimis concentration levels for noncriteria pollutants, ADMT uses appropriate de minimis or

threshold concentrations for state property line or effects evaluation analyses to develop impact

analysis requirements, including the definition of the AOI. 

More detailed guidance for PSD NAAQS analyses is contained in the EPA Draft New Source

Review Workshop Manual (EPA, 1990). Note that the term de minimis (TNRCC, 1998b) and the

phrase significance level (EPA, 1990) are synonymous.

Compliance with any NAAQS is based upon the total estimated air quality, which is the sum of

the maximum modeled concentration plus a background concentration. The basic procedure

involves eight steps described in the following paragraphs.

PSD NAAQS Step 1: Conduct a preliminary impact determination to predict whether the

proposed source(s) could make a significant impact on existing air quality—that is, equal or

exceed a NAAQS de minimis. (Section 3.4).

! Model all new and modified sources. Compare the predicted high concentration at or

beyond the fence line for each pollutant and each averaging time to the appropriate

NAAQS de minimis level in Appendix A. If the sources do not make a significant impact

for a pollutant of concern, the demonstration is over. If they do, an AOI is defined and a

full NAAQS analysis is required. Go to Step 2.

PSD NAAQS Step 2: Determine the radius of impact for the AOI for each pollutant and

averaging period subject to the NAAQS analysis. 

! The radius is the farthest distance from the sources under review to the location where

concentrations are predicted to equal or exceed de minimis for each applicable averaging

time and pollutant. 

! Use the largest radius for each pollutant, regardless of averaging period, for the rest of the

analysis. This radius is limited to the actual distance or 50 kilometers (km), whichever is

less.
25

PSD NAAQS Step 3: Obtain a retrieval using the primary radius search option from the PSDB

(Appendix H). The primary retrieval is made for the radius of impact plus 50 km (31 miles) and

identifies point and fugitive sources that could cause a significant impact within the AOI. This

retrieval identifies all point and area sources within the radius of impact that should be evaluated

in addition to sources in the permit application. Since the maximum AOI is limited to a radius of

50 km, the maximum retrieval radius of impact is 100 km.

PSD NAAQS Step 4: Predict concentrations at and beyond the fence line over the AOI from all

retrieved sources and sources to be permitted. 

! Model allowable emission rates for all sources that emit the regulated pollutant. Offproperty sources may be eliminated from the modeling demonstration if screening

modeling indicates that the sources' contributions would not equal or exceed the

applicable de minimis within the AOI. If any sources are omitted from the modeling

demonstration, explain in the air quality analysis why they were omitted. 

PSD NAAQS Step 5: Determine the background concentration (see the memo on the ADMT

Internet page.) As defined by the EPA, background air quality includes pollutant concentrations

due to natural sources, nearby sources other than the one(s) under consideration, and unidentified

sources. 

! Obtain the data from the EPA AIRSWEB at the following URL:

http/www.epa.gov/airsweb/monreps.htm, or by contacting the ADMT or the Data

Management and Analysis Section, Monitoring Operations Division.

PSD NAAQS Step 6: Compare the predicted concentration plus background concentration for

each pollutant to the appropriate NAAQS (Appendix A, Appendix G). This concentration should

be conservative since both nearby and distant background point sources are included in both the

predicted and background concentrations. If the maximum concentrations are below the NAAQS,

the demonstration is complete. If not, determine whether the background concentrations are

representative. If they are conservative for the project, then attempt to refine them.

PSD NAAQS Step 7: Refine the background concentration to remove or limit the contributions

from the background point sources. Contact the ADMT for assistance as necessary or check the

ADMT Internet page. Several methods are suggested. The goal is to obtain a background
26

concentration with the least amount of time and effort. Therefore, the options do not need to be

followed in sequence.

PSD NAAQS Step 8: Conduct additional modeling if a predicted concentration will exceed a

NAAQS and the permitted sources are predicted to make a significant impact at the same time

and location as a NAAQS exceedance (EPA, 1990, TNRCC, 1998b).

3.10 PSD Monitoring Analysis and Exemptions 

The purpose of the PSD monitoring analysis is to determine whether preconstruction monitoring

may be required to evaluate existing air quality before the permit is issued. Note that

preconstruction and postconstruction monitoring could be required if a potential threat to the

NAAQS is identified by modeling predictions. A threat is defined, in the Ambient Monitoring

Guidelines for Prevention of Significant Deterioration (PSD) (EPA 1987a), as 90 percent of the

NAAQS or PSD increment.

Use the following procedure to determine whether preconstruction monitoring is required.

PSD Monitoring Step 1: Compare the pollutant concentration obtained from the applicable

preliminary impact determination to the preconstruction monitoring significance level in Appendix

A.

PSD Monitoring Step 1a:. For criteria pollutants except ozone, compare the concentrations

obtained from the NAAQS AOI modeling demonstration to the monitoring significance level for

the pollutant of interest. If the maximum concentration does not exceed the preconstruction

monitoring significance level, the demonstration is complete. If not, go to Step 2.

PSD Monitoring Step 1b:. For ozone, emissions of 100 tpy or more of volatile organic

compounds (VOCs) are the surrogate for ozone and were used as a trigger for the pre-1997 form

of the NAAQS. However, the pre-1997 standard has been repealed for all counties in Texas

except those in nonattainment for the 1-hour ozone standard, and the 1997 8-hour form of the

standard is not compatible with the 100 tpy threshold. Therefore, preconstruction monitoring for

ozone will be required on a case-by-case basis until EPA develops an appropriate technique.

PSD Monitoring Step 1c: For noncriteria pollutants, use the preliminary impact determination

results from the appropriate state regulation or effects review demonstration. If the maximum
27

concentration does not exceed the preconstruction monitoring significance level, the

demonstration is complete. If not, go to Step 2b.

PSD Monitoring Step 2: The permit engineer, in coordination with ADMT, has discretionary

authority to exempt an applicant from the preconstruction monitoring requirement under the

following conditions:

PSD Monitoring Step 2a: For criteria pollutants, 

! Determine whether the predicted concentration from background point sources is below

the monitoring significance level. Obtain a NAAQS primary retrieval from the PSDB

(Appendix H). Multiple retrievals are not required. The primary retrieval for the NAAQS

analysis (see Section 3.9) can be used for this demonstration. 

Evaluate all sources identified in the retrieval over the area where the sources under

review make a significant impact, the same AOI as defined in the NAAQS analysis (see

Section 3.9). Do not include the sources in the permit application. If the predicted

concentration is below the monitoring significance level, an exemption can be granted.

! Determine whether a representative monitored concentration is below the monitoring

significance level. Obtain data from an existing monitoring network as was done

previously (see Section 3.9, PSD NAAQS Step 4). If this concentration is below the

monitoring significance level, an exemption can be granted.

PSD Monitoring Step 2b: For noncriteria pollutants, coordinate with applicable agency staff to

determine whether there is an environmental concern. If there is no concern, an exemption can be

granted.

3.10.1 Monitor Siting and Monitoring Quality Assurance Plan

If existing data are not available, or are judged not to be representative, then the applicant should

establish a site-specific monitoring network. The applicant should follow the guidance in the

Ambient Monitoring Guidelines for Prevention of Significant Deterioration (PSD) (EPA, 1987a)

and the On-Site Meteorological Program Guidance for Regulatory Modeling Applications,

(EPA, 1987b) to determine potential locations for monitoring sites. Before implementing any

plan, the applicant should consult with the permit engineer, the ADMT, and the Monitoring

Operations staff. In addition, the applicant should contact the Quality Assurance Section,
28

Monitoring Operations Division for assistance in the preparation of a monitoring quality assurance

plan.

3.11 PSD Increment Analysis

The purpose of the PSD increment analysis is to demonstrate that emissions of SO2, PM10, or NO 2

(NO is used as a surrogate) from a new major source or major modification of an existing major X

source will not cause or contribute to an exceedance of an increment. The PSD increment is the

maximum allowable increase in concentration that is allowed to occur above a baseline

concentration for a pollutant. 

Baseline and Trigger Dates. There are several dates that are used in the increment analysis:

! Major source baseline date. January 6, 1975, for PM and SO , and February 8, 1988, for 10 2

NO . This is the date after which actual emissions associated with physical changes or 2

changes in the method of operation at a major stationary source affect the available

increment. Changes in actual emissions occurring at any source after this date do not

affect the increment, but instead contribute to the baseline concentration until the minor

source baseline date is established.

! Trigger date. August 7, 1977, for PM10 and SO 2, and February 8, 1988, for NO 2. The date

after which the minor source baseline date may be established.

! Minor source baseline date. This is the earliest date after the trigger date on which a PSD

application for a new major source or modification to a major source is considered

complete for a particular Air Quality Control Region (AQCR).

The baseline concentration means the ambient concentration level that existed in the baseline area

at the time of the applicable minor source baseline date, hereafter referred to as the baseline date.

The baseline concentration is the reference point for determining air quality deterioration in an

area, and is based on concentrations from the calendar year prior to the baseline date.

Baseline dates have been established for SO and PM for all counties in Texas by AQCR. 2 10

Baseline dates for NO2 have been established but have not been identified for all regions; use

February 8, 1988 as the default date (see Appendix I). Contact the ADMT to obtain a conversion

from AQCR to TNRCC region. 
29

Increment Calculation Terms. The amount of PSD increment that has been consumed in an

attainment or unclassified area is determined from the emissions increases and decreases that have

occurred from sources in operation since the applicable baseline date. An applicant does not need

to obtain the baseline ambient concentration—if one exists—to determine the amount of PSD

increment consumed or the amount of increment available. Instead, modeled increment

consumption calculations reflect the change in ambient pollutant concentration attributable to

increment-affecting emissions. Increment consumption (or expansion) calculations are determined

by evaluating the difference between the actual emissions at the baseline date (ActualBD) and

actual emissions as of the date of the modeling demonstration (ActualMD) .

ActualBD is defined as the representative two-year average for long-term rates, or the maximum

short-term rate in the same two-year period immediately before the applicable baseline date. If

little or no operating data are available, as in the case of permitted sources not yet in operation at

the time of the baseline date, the permit allowable emission rate as of the baseline date must be

used.

ActualMD is defined as the most recent, representative two-year average for long-term rates, or the

maximum short-term rate in the same two-year period immediately before the modeling

demonstration. If little or no operating data are available, as in the case of permitted sources not

yet in operation at the time of the increment analysis, the permit allowable emission rate must be

used.

The ADMT suggests a tiered approach to this analysis to limit the amount of research needed to

determine actual emission rates. The basic five-step procedure is described in the following

paragraphs.

PSD Increment Step 1: Determine whether the predicted concentration (excluding background

concentration) for NO2, SO2, or PM 10 obtained in the PSD NAAQS analysis is below the

applicable increment. If yes, the demonstration is complete because all sources were modeled at

allowable emission rates. If not, go to Step 2.

PSD Increment Step 2: Determine the radius of impact for each pollutant that had an AOI

defined in the NAAQS analysis (see Section 3.9). The radius of impact will be the same one used

in the PSD NAAQS analysis. 
30

PSD Increment Step 3: Obtain a retrieval using the primary radius search option from the PSDB

(Appendix H). The primary retrieval is made for the radius of impact plus 50 km (31 miles) and

identifies sources that could affect the increment within the AOI. Since the maximum AOI is

limited to a radius of 50 km , the maximum retrieval radius of impact is 100 km. This retrieval

identifies all increment-affecting sources within the radius of impact that should be evaluated

along with the sources in the permit application. 

PSD Increment Step 4: Adjust the emission inventory.

! For all sources, including grandfathered and exempted sources, use allowable emission

rates from the PSDB; these rates are provided in the electronic copy of the retrieval. Do

not use the actual emission rates indicated in the paper copy of the retrieval unless they

meet EPA criteria. Ensure all of the applicant’s sources are included in the modeling

inventory.

! Omit any source from the inventory that has a negative emission rate unless the source

existed and was in operation at the baseline date. Also, omit any source that was permitted

but not placed into operation.

! For proposed sources, use proposed allowable emission rates. 

Note: A source must have existed and been in operation on or before the baseline date to be

considered for increment expansion. The source must be shut down as part of the project or have

lower actual emissions to expand the increment. That is, there is no credit for contemporaneous

shutdowns or for sources permitted after the baseline date that have reduced emissions, have been

shut down, or will be shut down as part of the current project, since modeling is used to

determine the amount of increment consumed or expanded. Therefore, a source that did not

exist—or was not operating—on the baseline date would not have contributed to the air quality at

that time, and there would be no need to model the source with an emission rate of zero. Omit

these sources from the inventory.

PSD Increment Step 5: Conduct the modeling demonstration using the following tiered

approach, as applicable.

Increment Modeling Tier I. Model all sources using their allowable emission rates, as adjusted in

Step 3. This approach is conservative since the difference in increment is the entire allowable
31

emission rate. Compare the predicted concentration to the appropriate increment (Appendix A,

Appendix H). If the increment is not exceeded, the demonstration is complete. Otherwise, go to

Tier II

Increment Modeling Tier II. Model selected sources with ActualMD emission rates and all other

sources at allowable emission rates. The selected sources are usually the applicant’s, since actual

emission rates may be difficult to obtain for off-property sources. This process assumes that the

difference in increment for the selected sources is the entire actual emission rate. If the increment

is not exceeded, the demonstration is complete. Otherwise, go to Tier III.

Increment Modeling Tier III. Model selected sources that existed and were in operation at the

baseline date with the difference between ActualMD and Actual .

 BD

! For major sources permitted at or after the major source baseline date but not in operation

as of the minor source baseline date, use the difference between ActualMD and the

allowable emission rate.

! For sources that existed at the baseline date, where a change in actual emission rates

involved a change in stack parameters, use the emission rates associated with both the

baseline date and the existing situation. That is, enter the Actual as negative numbers BD

along with the baseline source parameters, and enter ActualMD for the same source as

positive numbers along with the existing source parameters.

! Model grandfathered and exempted sources as the difference between ActualMD and

Actual . BD

! Use emission rates found in Tier I or II for other sources, as applicable. 

If the increment is not exceeded, the demonstration is complete. Otherwise, continue to refine

increment emission rates or demonstrate that the project’s impact will not be significant (EPA,

1990).

3.12 PSD Ozone Ambient Impact Analysis

The purpose of the ozone ambient impact analysis is to demonstrate that a new major source or

major modification of an existing major source that could emit 100 tpy or more of VOCs would

not cause or contribute to a violation of the 1-hour ozone standard in attainment or unclassifiable
32

areas. However, this standard has been repealed for all counties in Texas except those in

nonattainment for the 1-hour ozone standard, and the 1997, 8-hour form of the standard is not

compatible with the 100 tpy threshold. 

The 1-hour standard was exceedance based; that is, the NAAQS could not be exceeded more than

once per year at an ambient air monitoring site. A violation of the NAAQS occurred only if there

were four or more exceedances within a 3-year period—one exceedance per year at the same

ambient air monitoring site. The 8-hour standard is not exceedance based. The NAAQS is

violated only if the 3-year average of the fourth highest 8-hour averages for each year at the same

ambient air monitoring site is 85 ppb or higher—EPA convention is to round down for

concentrations of 4.9 ppb or less. It is not readily apparent at this time whether a single project

could significantly affect an 8-hour average concentration over a 3-year period to such a degree

that the NAAQS would be violated.

Therefore, ADMT will use the procedures developed to evaluate a project’s impact on the 1-hour

ozone standard as a surrogate for its impact on the 8-hour standard until EPA develops an

appropriate evaluation technique for the new standard.

! For VOC-dominated sources. Use the VOC/NO Point Source Screening Tables X

developed by Richard Scheffe (Scheffe, 1998) if the methane-normalized VOC to NOX

ratio is about 2:1. Another alternative would be to assume that all the project’s VOC

emissions (or the site’s VOC emissions, as applicable) were ozone emissions and use the

ISC model to predict a maximum 1-hour concentration This concentration would be

added to a 1-hour background concentration and the result compared to the 1-hour ozone

standard.

! For NO -dominated sources. If the methane-normalized VOC to NO ratio is 2:1 or less, X X

no significant increase of ozone would be expected.

3.13 PSD Additional Impacts Analyses

The purpose of the additional impacts analyses is to provide an assessment of the project’s effect

on the overall environment. There are three types of analyses: growth, soil and vegetation, and

visibility impairment.

The growth analysis evaluates the impact associated with the project on the general commercial,

residential, and industrial growth within the AOI. An in-depth growth analysis would only be
33

required if the project would result in a significant shift of population and associated activity into

an area—that is, a population increase on the order of thousands of people.

The soils and vegetation analysis evaluates the impact associated with the project on soils and

vegetation within the AOI. Modeling results from the NAAQS analysis can usually be used for

this analysis.

The visibility impairment analysis evaluates the impact associated with the project on the

visibility within the AOI (usually within a Class II area), and upon any Class I areas within 100 km

of the project. The applicant can meet the requirement for the Class II visibility analysis by

acknowledging compliance with the visibility and opacity requirements in 30 TAC Chapter 111.

However, additional modeling for a Class I visibility impairment analysis, if required, should

follow EPA’s Workbook for Plume Visual Impact Screening and Analysis (EPA, 1992c) or

User’s Manual for the Plume Visibility Model (PLUVUE II) (EPA, 1992d) as applicable. 

3.14 PSD Class I Impact Area Analysis

Class I analyses involve the federal land manager as a participant in the permit review process. A

Class I analysis is required for PSD sources that locate within 10 km of a Class I area whose

emissions of any regulated pollutant would have a 24-hour average impact of 1 Fg/m or greater. 3

In addition, a Class I analysis is required for PSD sources that locate within 100 km of a Class I

area whose emissions exceed applicable significance levels; this analysis could be required if the

sources will be located more than 100 km away, if there is a concern that the emissions could

adversely affect the Class I area. The only Class I areas in Texas are Big Bend National Park and

Guadalupe Mountains National Park. However, other Class I areas in adjacent states, for

example, Carlsbad Caverns National Park, New Mexico, could trigger a Class I analysis. 

The air dispersion modeling requirements for Class I areas include more stringent PSD

increments, air quality-related values, and a visibility impairment analysis. Due to the fact that

PSD Class I analyses are rare in Texas, refer to the Draft New Source Review Workshop Manual

(EPA, 1990) Chapter E for procedural and technical guidance, as well as the applicable Class I

increments.

3.15 RCRA Combustion Permits Analysis 

The purpose of the RCRA combustion permits analysis is to determine waste feed limits or

allowable emissions that will protect public health from emissions from sources burning hazardous

waste or from associated sources in hazardous waste service. Two modeling demonstrations are
34

required for these permits under the TNRCC’s combustion strategy: boiler and industrial furnace

(BIF) and multipathway risk assessment. The applicant must conduct the BIF demonstration, and

the TNRCC staff conducts the risk assessment. Waste feed limits or emission rates will be based

on the results of both demonstrations.

3.15.1 BIF Demonstration

The BIF demonstration follows the guidance in 40 CFR §266.103–04, 40 CFR §266.106–09, and

EPA 530-R-92-011, Technical Implementation Document for EPA’s Boiler and Industrial

Furnace Regulations (EPA, 1992a). Refined modeling may be required if the facility does not

qualify for screening techniques. The maximum predicted annual average off-property groundlevel concentration due to emissions from all BIF sources within a facility is used to determine

compliance for each constituent. This concentration is commonly referred to as the maximum

exposed individual (MEI) concentration. Note: The on-property concentration must be used if a

person resides on the property and the concentration is the MEI concentration. The following

items should be evaluated and included in the modeling demonstration, as applicable.

! For noncarcinogenic metals, HCl, and Cl . The predicted MEI concentration must not 2

exceed the reference air concentration (RAC) specified in Appendix IV of the BIF

guidance document.

! For carcinogenic constituents. The MEI concentration must not exceed the risk-specific

doses (RSDs) specified in Appendix V of the BIF guidance document.

! For carcinogenic constituents. In addition to the RSD evaluation, the sum of the ratios of

predicted maximum concentrations to their respective RSDs must not exceed 1.0. 

! For constituents not listed in Appendixes IV or V. The default MEI concentration cannot

exceed 0.1 Fg/m .

3

! For dioxins and furans. The ratio of the MEI concentration to the RSD for 2,3,7,8-TCDD

must not exceed 1.0.

! Dilution factor (DF). Required to support the modeling demonstration and the emission

limits on which the demonstration was based. The DF is source-specific and pertains to

the maximum predicted air concentration for each constituent. The model calculates a DF

concentration based on an emission rate of 1 g/s that is expressed in units of Fg/m /g/s. 3
35

3.15.2 Multipathway Risk Assessment

The multipathway risk assessment evaluates the potential cancer risk from hazardous waste

combustion sources and from noncombustion emission sources (fugitive and point) in hazardous

waste service. The ADMT provides concentration and deposition values for on- and off-property

receptors to TARA to determine an overall health risk. The receptors include watersheds and

water bodies and specified sensitive receptors, such as dairy and beef farms and locations where

people fish.

37

4.0 Acceptable Dispersion Models

In general, use the models and follow the modeling procedures identified in the GAQM (EPA,

1995a). Although the GAQM was developed to address PSD and State Implementation Plan

modeling issues, the ADMT applies the general guidance contained in the GAQM to other

modeling demonstrations in order to maintain a consistent approach for all projects.

Appendix A of the GAQM lists preferred air quality models, and Appendix B lists models that

may be considered on a case-by-case basis. Occasionally, it may be appropriate to use models that

are not specified in the GAQM; for example, some disaster models and other models, such as the

Toxic Modeling System Short-Term model. To use these models, demonstrate that no GAQM

Appendix A model is appropriate for the required modeling analysis. Use the most recent version

of each model in all cases. Guidance on demonstrating the need for non-Appendix A or nonGAQM models is found in Section 3.2.2 of the GAQM.

The ISCST and SCREEN models are the most commonly used models for state and PSD

modeling in Texas. These models can be used to assess the impacts from point, area, and volume

sources, and can incorporate the effects of building wakes upon plumes (building downwash).

EPA is evaluating the AMS/EPA Regulatory Model (AERMOD) for regulatory use. Check the

ADMT Internet page for guidance on the use of AERMOD after its release. Much of the

following discussion applies to ISCST, since it is the most commonly used model at this time.

The ISCST model can be used to obtain short-term concentrations for multiple averaging periods

simultaneously, if worst-case stack parameters and emission rate for any averaging period are

used. Short-term is defined as any time period less than or equal to 24 hours. This approach is

conservative if worst-case stack parameters are used, since the emission rate for the shortest time

period will equal or exceed emission rates for subsequent time periods. For example, the 1-hour

emission rate can be used to predict 3- and 24-hour concentrations. 

The ISCST model can be used to obtain long-term concentrations as well, and the ADMT prefers

its use instead of ISCLT. The general procedure follows:

! If a State NAAQS or effects review is required for SO , PM , or constituents with ESLs, 2 10

use the appropriate time-averaging option to obtain annual average concentrations. This is

a conservative approach if worst-case stack parameters are used since short-term emission

rates can be equal to but are usually higher than long-term emission rates. 
38

! If a State NAAQS review is required for NO2, select the appropriate time-averaging option

and run the ISCST model with the appropriate state year of meteorological data. If the

maximum predicted concentration is less than 75 percent of the appropriate de minimis or

standard, no further modeling is needed. Otherwise, run the model for each of five years of

meteorological data to ensure that a representative maximum concentration is identified

(Section 5.6.1). The ambient ratio method outlined in Appendix B may be used.

! If a PSD review is required for NO2, select the appropriate time-averaging option and run

the ISCST model separately for each of five years of meteorological data (Section 5.6.1).

The ambient ratio method outlined in Appendix B may be used.

! If a multiple-year, concatenated meteorological data set is used, do not select the annual

option because the model will provide a multiple-year average instead of a single-year

average. 

These approaches may not be applicable in cases where the worst-case short-term emission rate

results in unrepresentative concentrations for some averaging periods. In those cases, the shortterm model may be used with the appropriate emission rate for the period being evaluated. 

For example, the ISCST model may be run separately with the maximum 1-hour emission rate to

obtain 1-hour concentrations, and run again with the annualized average hourly emission rate

based on the maximum ton-per-year rate to obtain annual concentrations. 

The GAQM suggests that the ISCLT model should be used for modeling evaluations conducted

for pollutants that have only long-term standards. However, there is no reason to require the use

of ISCLT. The main difference between ISCST and ISCLT is the form of the meteorological data

files. The meteorological data for ISCLT are based on climatological data (Section 5.6.2) and

cannot be used in conjunction with gravitational settling or deposition. In addition, EPA does not

allow climatological data to be averaged. For example, meteorological data must be developed for

each quarter of the year (for Pb) or year (for NO2), and each quarter or year must be evaluated

separately.

Acceptable models for complex terrain are discussed in the GAQM Section 5.0. These are

essentially screening models. The Valley model is incorporated into the SCREEN model, and the

Complex I model is incorporated into the ISCST model. Use of screening models is sufficient

unless exceedances of a standard or increment are predicted; then a refined model may be used.
39

Use of a refined complex terrain model, such as CTDMPLUS, requires extensive meteorological

information, which must be collected over a one-year period. Contact the ADMT to discuss

complex terrain modeling as applicable.

4.1 Distance Limitations

The GAQM indicates that the useful distance for guideline models is 50 km (31 miles).

Occasionally, some sources may be located beyond 50 km from portions of the AOI. When this

occurs, include these sources in the demonstration unless their contribution would be insignificant.

Modeled impacts from sources beyond 50 km are conservative estimates that may provide an

indication of a threat to the NAAQS.

4.2 Modification of Models

The EPA has established procedures to request changes to model algorithms. Applicants should

submit requests with suggested changes to model source codes to EPA with a copy to the

ADMT. 

The internal source codes for regulatory models should not be modified in a manner that would

change the basic algorithms used by the model to calculate ground-level concentrations without

ADMT review and comment. Minor changes unrelated to model algorithms, such as

re-dimensioning of source or receptor arrays, do not require ADMT coordination. 

Document and submit substantial preprocessor or postprocessor programs or subroutines to the

ADMT. For example, a program used to calculate downwash parameters for entry into the ISC

models is a substantial preprocessor program. An example of a substantial postprocessor 

program would be one that is used to count the number of exceedances at each receptor for the

appropriate averaging period.

4.3 Use of Data Entry Software

There are several consultants who have developed more user-friendly computer programs to

assist with data entry for EPA dispersion models as well as some preprocessing programs. If these

programs are used, submit the software and program documentation to assist the ADMT in the

technical review process, unless the ADMT has the software and documentation. Check with

ADMT to determine the software the staff maintains.

41

5.0 Basic Model Input Data Requirements 

Always select the regulatory default option, unless the ADMT approves the use of other model

options. This option is defined in the User's Guide for the Industrial Source Complex (ISC3)

Dispersion Models (EPA, 1995d) (ISC User's Guide) and other GAQM Appendix A model user's

guides. 

5.1 Urban versus Rural Dispersion Options

The classification of the land use in the vicinity of sources of air pollution is needed because

dispersion rates differ between urban and rural areas. In general, urban areas cause greater rates

of dispersion because of increased turbulent mixing and buoyancy-induced mixing. This mixing is

due to the combination of greater surface roughness caused by more buildings and structures and

greater amounts of heat released from concrete and similar surfaces.

EPA guidance provides two procedures to determine whether the character of an area is

predominantly urban or rural. One procedure is based on land-use typing and the other is based on

population density. Both procedures require an evaluation of characteristics within a 3-km radius

from a source. The land-use typing method is based on the work of August Auer (Auer, 1978)

and is preferred because it is more directly related to the surface characteristics of the evaluated

area that affect dispersion rates.

While the Auer land-use typing method is more direct, it can be labor-intensive to apply. A

simplified technique referred to in the hazardous waste combustion screening approach contained

in the Title 40 Code of Federal Regulations, Part 266 (40 CFR 266), Appendix IX, Section 6.0

can be used as a screening tool. If the land-use designation is clear—that is, about 70 percent or

more of the total land use is either urban or rural—then further refinement is not required.

5.1.1 Simplified Auer Land-Use Analysis

The Auer land-use approach considers four primary land-use types: Industrial (I), Commercial

(C), Residential (R), and Agricultural (A). Within these primary types, subtypes are identified in

Table 5-1.
42

 Table 5-1. Land-Use Types

 and Corresponding Dispersion Classification

Type Description Class

I1 Heavy Industrial Urban

I2 Light/Moderate Industrial Urban

C1 Commercial Urban

R1 Common Residential (Normal Easements) Rural

R2 Compact Residential (Single Family) Urban

R3 Compact Residential (Multi-Family) Urban

R4 Estate Residential (Multi-Acre) Rural

A1 Metropolitan Natural Rural

A2 Agricultural Rural

A3 Undeveloped (Grasses/Weeds) Rural

A4 Undeveloped (Heavily Wooded) Rural

A5 Water Surfaces Rural

The goal in a land-use analysis is to estimate the percentage of the area within a 3-km radius of

the source to be evaluated that is either urban or rural. Both types do not need to be evaluated

since the type that has the greatest percentage will be the representative type.

The most difficult evaluation involves the residential types depicted in the table. The degree of

resolution between subtypes for residential areas often cannot be determined without conducting a

site area inspection and referring to zoning maps and aerial photographs. The Auer land-use

typing process can require extensive analysis, which—for many applications—can be greatly

streamlined without sacrificing confidence in the selection of a representative land-use type.

The primary assumption for the simplified procedure is based on the premise that many facilities

should have clear-cut urban or rural designations; that is, the percentage of the primary

designation should be greater than about 70 percent. The color coding on United States

Geological Survey (USGS) 7.5-minute topographic maps provides an effective means of

simplifying the typing scheme. The suggested typing designations for the color codes found on the

maps are:
43

! Blue—water (rural)

! Green—wooded areas (rural);

! White—parks, unwooded, nondensely packed structures (rural);

! White—industrial; identified by the large buildings, tanks, sewage disposal or filtration 

plants, rail yards, roadways, intersections (urban);

! Pink—densely packed structures (urban); and,

! Red—roadways, intersections (urban).

Use the simplifying approach if the topographic map is within three years old, or is older but still

considered representative, and the land-use designation represents about 70 percent of the total.

If the land-use designation represents less than 70 percent of the total, supplement the

topographic map analysis with a current aerial photograph of the area surrounding the permitted

sources or with a detailed drive-through summary, to support the land-use designation to be used

in the modeling demonstration.

5.1.2 Multiple Modeling Technique

Alternatively, consider using the following screening modeling technique in place of the land-use

analysis.

Step 1. Run the screening model twice, once for each dispersion option, and use the higher of the

two modeled results. If refined modeling is required, go to Step 2.

Step 2. Run the refined model twice, once for each dispersion option, and use the higher of the

two modeled results.

! If predicted concentrations from both refined model runs are below the value of concern

for the modeling demonstration, the demonstration is complete. If not,

! Conduct an Auer land-use analysis, and use the appropriate dispersion option. This extra

detail would be needed if predicted concentrations exceed the value of concern from either

refined model run, or if the location, frequency, and magnitude of an exceedance is

needed. Depending upon the source configuration and dispersion coefficient selected, the

dispersion pattern and predicted concentrations could be significantly different and

adversely affect the staff’s technical review.
44

5.2 Digital Elevation Model

A digital elevation model (DEM) is a digital file consisting of terrain elevations for ground

positions at regularly spaced intervals. The USGS distributes two digital elevation data products

in the standard DEM tape format that could be used in state and federal air dispersion modeling

demonstrations in Texas: large-scale and small-scale.

Large Scale: USGS-produced 7.5-minute DEMs that correspond to standard USGS

1:24,000-scale 7.5- by 7.5-minute quadrangles. 

! The data are produced in 7.5- by 7.5-minute blocks either from map contour overlays that

have been digitized or from automated or manual scanning of photographs usually taken at

an average height of 40,000 feet (1:80,000-scale). 

! The data are processed to produce a DEM with a 30-meter sampling interval. Each 7.5-

minute unit of DEM coverage consists of a regular array of elevations referenced

horizontally in the UTM projection coordinate system. These horizontally referenced data

may be in the North American Datum (NAD) 27 or NAD83 for the continental U.S.

Elevation units are in meters or feet relative to the National Geodetic Vertical Datum of

1929 (NGVD29).

Small Scale: Defense Mapping Agency-produced 1-degree DEMs that correspond in coverage to

1-degree by 1-degree blocks (one-half of standard 1:250,000-scale 1-degree by 2-degree

quadrangles). 

! The data are produced by interpolating elevations at intervals of 3 arc-seconds from

contours, ridge lines, and drains digitized from 1:250,000-scale topographic maps. Three

seconds of arc represents approximately 90 meters in the north-south axis and a variable

dimension (approximately 90 meters at the equator to 60 meters at 50 degrees latitude) in

the east-west axis due to convergence of the meridians. The area of each map is divided

into an east half and a west half to accommodate the large volume of data required to

cover the 1-degree by 2-degree topographic map. 

! The 1-degree DEM consists of a regular array of elevations referenced horizontally on the

geographic coordinate system of the World Geodetic System (WGS) 72, which was

converted to WGS84. Elevations are in meters relative to NGVD29 in the continental US. 
45

The 7.5-minute and 1-degree DEM data files are identical in logical data structure but differ in

sampling interval, geographic reference system, areas covered, and accuracy of data. USGS

7.5-minute DEM data are available for selected quadrangles in the United States; DMA 1-degree

DEM data are available for most of the United States.

Keep in mind that the UTM is just one of many map projections used to represent locations on a

flat surface. Also, be aware that there are several horizontal data coordinate systems or datum

(NAD27, WGS72, NAD83, and WGS84) that are used to represent locations on the earth’s

surface in geographic coordinates (latitude and longitude). Spatial data (Global Positioning

System output, digitized maps, DEMs, etc.) used to obtain receptor, building, and source

locations can be in any one of these systems.

When representing receptor, building, and source locations in UTM coordinates, make certain

that all of the coordinates originated in, or are converted to, the same horizontal datum. There are

many free and commercial computer programs available to convert from geographic coordinates

to UTM coordinates; however, not all of these programs are appropriate for conversion between

horizontal data coordinate systems. For example, programs that do not prompt the user for a

specific horizontal datum are not appropriate.

5.3 Variable Emission Rate Option

When sources can operate only during specified hours, the variable emission rate option may be

used to restrict the modeling analysis to the hours of operation only. If this option is used, permit

conditions should restrict the operation of the permitted source to the time period modeled.

The variable emission rate option may also be used to simulate other operating scenarios as

necessary to design permit conditions.

5.4 Building Wake Effects (Downwash)

Modeling of point sources with stack heights that are less than good engineering practice (GEP)

stack height should consider the impacts associated with building wake effects (also referred to as

downwash). Building wake effects are not considered for area or volume sources.
46

As defined by the Guideline for Determination of Good Engineering Practice Stack Height

(Technical Support Document for the Stack Height Regulations) (EPA, 1985), GEP height is

calculated as:

GEP = H + 1.5L, b

where 

H = the building height; and b

 L = the lesser of the building height or the greatest crosswind distance of the 

 building—also known as maximum projected width. 

This formula defines the stack height above which building wake effects on the stack gas exhaust

may be considered insignificant. 

Region of Influence: A building or structure is considered sufficiently close to a stack to cause

wake effects when the minimum distance between the stack and the building is less than or equal

to five times the lesser of the height or projected width of the building (5L). This distance is

commonly referred to as the building's region of influence. If the source is located near more than

one building, assess each building and stack configuration separately.

Apparent Width: If a building's projected width is used to determine 5L, determine the apparent

width of the building. The apparent width is the width as seen from the source looking towards

either the wind direction or the direction of interest. For example, for short-term modeling, the

ISCST model requires the apparent building widths (and also heights) for every 10 degrees of

azimuth around each source.

To account for downwash, the SCREEN model requires the entry of a building or structure

height and the respective maximum and minimum horizontal dimensions. Generally, include the

building with dimensions that result in the highest GEP stack height for that source, to evaluate

the greatest downwash effects.

Be aware that when screening tanks, the tank diameter should not be used. The SCREEN model

uses the square root of the sum of the individual squares of both the width and length for a

structure in order to calculate the projected width. Because most tanks are round, the projected

width is constant for all flow vectors. However, using the actual tank diameter for both width and

length will result in a projected width that is too large. Therefore, when screening tanks, a

modeler should divide the diameter of the tank by the square root of 2.
47

The ISC models also contain algorithms for determining the impact of downwash on ambient

concentration; use them to determine refined concentrations estimates. Methods and procedures

to determine the appropriate entries to account for downwash are discussed in the EPA’s GEP

guidance document (EPA, 1985).

Due to the complexity of GEP guidance, the EPA has developed a computer program for

calculating downwash parameters for use with the ISC models. This program is called the BPIP

(EPA, 1993a), and it is available from the EPA SCRAM Internet page. Use the most current

version of the BPIP to determine downwash parameters for use with the ISC models.

5.5 Receptor Grid

Place receptors to determine the maximum ground-level concentration in an off-property area or

an area not controlled by the applicant. If an AOI has been defined, receptors should cover the

entire area of de minimis impact.

5.5.1 Receptor Grid Design 

Design the receptor grid by considering such factors as the results of screening analyses; a

source's release height; the proximity of emission points, fugitive areas, and other sources to the

property line; the location of nearest residents and other sensitive receptors and monitors; as well

as topography, climatology, and other relevant factors. Generally, the spacing of receptors

increases with distance from the sources being evaluated.

In general, do not use coarse-grid spacing to determine a hot spot, the suspected area of the

maximum concentration, followed by the use of a tighter grid spacing to zero in on the maximum

concentration. For example, if the highest concentration was predicted to occur to the east of a

source and the next highest concentration to the west, it would not be appropriate to ignore the

area to the west. However, if an area has predicted concentrations several orders of magnitude

higher than any other areas, it may be appropriate to focus on that area.

Tight receptors should cover a large enough area to demonstrate that the maximum predicted

concentration has been located. Determine the extent of the tight receptor grid on a case-by-case

basis. Usually tight receptors may be required as far as about 200-300 meters from the sources

being evaluated, depending upon the emission release heights and property or fence line location.

However, extend the tight receptors if the concentrations are increasing or are within

approximately 75 percent of a standard, guideline, or staff-identified threshold.
48

When multiple sources are modeled, use the most restrictive of the suggested types of spacing in

order to determine representative concentrations from each source type. For example, in order to

determine the overall maximum predicted concentration and location for a mix of tall and short

sources, it may be necessary to extend the grid several kilometers away from the property line to

identify concentrations related to tall stacks. It is appropriate to use a smaller receptor spacing

located close to the property line to identify concentrations caused by short stacks or fugitive

sources.

In addition, the location of ambient air receptors should guide the design of the receptor grid.

Ambient air for state modeling starts at the applicant's property line. However, for PSD modeling,

ambient air starts at the applicant's fence line or other physical barrier to public access. Also, no

receptors are required on the applicant's property because the air over an applicant's property is

not ambient; therefore, in a regulatory sense, applicants cannot cause a condition of air pollution

on their property from their own sources.

5.5.2 Coordinate System

Enter receptor locations into dispersion models in UTM coordinates, in order to be consistent

with on- and off-property emission point locations represented in the Table 1(a) contained in the

permit application and PSDB, and other reference material, such as USGS topographic maps.

Provide the datum used for UTM coordinates (Section 5.2). Applicable UTM zones in Texas are

either 13 (from the west border to 102 degrees longitude), 14 (between 102 and 96 degrees

longitude), or 15 (east of 96 degrees longitude to the east border). Please do not use coordinate

systems based on plant coordinates or other applicant-developed coordinate systems. Also, polar

grids should not be used unless the ADMT suggests their use.

5.5.3 Receptor Elevations

Much of Texas can be characterized as having relatively flat terrain; however, some areas of the

state have simple-to-complex terrain. The ADMT defines flat terrain as terrain equal to the

elevation of the stack base; simple terrain as terrain lower than the height of the stack top; and,

complex terrain as terrain above the height of the plume center line. (For screening modeling,

complex terrain is terrain above the height of the stack top). Terrain above the height of the stack

top but below the height of the plume center line is known as intermediate terrain. Evaluate the

geography near each facility to determine how terrain elevations should be addressed. Use USGS

7.5-minute topographic maps or their digital equivalents to determine the terrain in the area

surrounding the facility.
49

For refined modeling with the ISCST model, use both the simple and complex terrain calculation

options if other than flat terrain applies. That is, if terrain elevations for receptors are used,

activate both simple and complex options. In cases where multiple sources with varying heights of

emissions must be evaluated, use the ISCST model rather than the SCREEN model. Since the

SCREEN model can only evaluate one source at a time, combined results for sources in

intermediate-to-complex terrain might not be representative. 

If other than flat terrain is modeled, use appropriate receptor elevations. Ensure that the higher

terrain is always included in any direction from the source, not just the highest terrain. For

example, if the highest terrain is to the north of the property, but the second highest terrain is to

the south, include receptors at and in the general vicinity of each location. Conservative options

may be used though to reduce the effort of determining specific receptor heights for dense grid

networks. For example:

! Omit terrain if only ground-level fugitive sources are modeled. Terrain is generally not a

consideration when modeling releases from fugitive sources. Releases from these sources

are typically neutrally buoyant and are essentially at ground level. Maximum

concentrations from fugitive releases are thus expected to occur at the nearest downwind

receptor location. However, include terrain near a property or fence line for elevated

fugitive releases, or if nonfugitive point sources are included in the modeling

demonstration.

! Use the highest elevation of any receptor in the grid for all receptors in the grid, only if the

plume depletion option is not used. 

! Set receptors to the stack base elevation, if some elevations are below stack base.

! If the terrain is all below stack base, choose the FLAT terrain height option keyword in

the Control Pathway of the ISC model, which will cause the model to ignore terrain

heights. Note: do not select the elevated terrain height option without including receptor

elevations in the Source Pathway.

If worst-case terrain heights are used with coarse grids, and more refined heights are used on

progressively denser grids (medium, fine, tight), the modeled concentrations could decrease as the

heights decrease.
50

If 7.5-minute DEM data are not available for the entire receptor grid, use 7.5-minute DEM data

for receptors within approximately 3–5 km of the property line and 1-degree or mixed scale DEM

data for other receptors. In addition, ensure that ridges or small terrain features that may be

missing from either the 7.5-minute, 1-degree, or mixed scale DEM data are included in the

receptor grid.

If there are significant problems with the resolution of the data, that is, a mix of scales that could

result in the omission of terrain features or significant changes in elevation, the applicant may need

to add discrete receptors with appropriate elevations obtained from 7.5-minute data sources.

5.5.4 Receptor Spacing 

Use one or more of the following sets of receptors.

Tight receptors—spaced 25 meters apart. Tight receptors could extend up to 200–300 meters

from the sources being evaluated. Consider the distance between the source and the property or

fence line. For example, if a low-level fugitive source is located more than 200–300 meters from

the property line, it is unlikely that a 25-meter receptor spacing would be required. However,

receptors would be required along the property boundary at the next appropriate grid spacing. In

general, use a receptor spacing of 25 meters in the following cases:

! sources with heights less than 15 meters and not affected by building downwash;

! sources with heights less than 50 meters and affected by building downwash.

Fine receptors—spaced 100 meters apart. Fine receptors could extend 1 km from each source

being modeled.

Medium receptors—spaced 500 meters apart. Medium receptors could cover the area that lies

between 1 and 5 km from each source.

Coarse receptors—spaced 1 km apart. This spacing could cover the area that lies beyond the

medium receptors out to 50 km.

5.5.5 Special Receptor Spacing

Conduct additional modeling in the vicinity of each receptor when a predicted concentration

exceeds 75 percent of an applicable standard or guideline. Use the next lower receptor set
51

spacing. For example, use fine spacing if medium spacing was used initially. This guidance does

not apply for predictions at individual discrete receptors that represent a known location, such as

a residence or business. In addition, this approach would not apply if the predicted concentration

occurred at a receptor with the highest terrain elevation.

5.5.6 Cavity Calculations

In August, 1998, the EPA proposed changes to the ISC model to incorporate the Plume Rise

Model Enhancements (PRIME) model; the integrated model will be called ISC-PRIME. This

model can compute concentrations in a cavity region. Therefore, use ISC-PRIME to resolve any

cavity issues resulting from the use of ISC. Do not use the draft ISC-CAV model.

5.5.7 Concentration Maps

Include gridded concentration maps demonstrating that the maximum predicted concentration has

been found in the air quality analysis. Use isopleths rather than actual concentration plots only if

the presentation shows that concentrations are clearly decreasing away from the sources being

modeled and comparisons with de minimis or significance levels, or ESL exceedances or

frequencies of exceedance are not an issue. When isopleths are used, the maximum off-property

concentration must be clearly identified in the report and modeling output files. 

5.6 Meteorological Data

The ADMT has prepared meteorological data sets for state modeling analyses. These data sets are

available for download from the ADMT Internet page. The http and ftp URLs are

! http://www.tnrcc.state.tx.us/air/nsr_permits and click on the link to the Air Dispersion

Modeling Team; and

! ftp://ftp.tnrcc.state.tx.us/pub/AirQuality/NewSourceReviewPermits/Modeling (note that

this URL has mixed cases). 

The ADMT’s goal is to obtain and process meteorological data sets for PSD modeling analyses.

The staff will place these sets on the ADMT Internet page as they are completed. The applicant is

responsible for obtaining and preparing any required meteorological data not available from the

ADMT. 

For PSD permit applications, some unprocessed meteorological data are available on the EPA's

SCRAM Internet page. The SCRAM address is http://www.epa.gov/scram001.
52

Data not available on the SCRAM may be obtained from the National Climatic Data Center.

Process the data using the PCRAMMET (EPA, 1998) program. In addition, on-site

meteorological data may be used if appropriate and if obtained in accordance with EPA guidance

(EPA, 1987b). Certain complex terrain models, such as CTDMPLUS, require on-site

meteorological data.

For the commonly used ISC models, the ADMT can provide guidance on meteorological data

processing and input options including mixing height, temperature, and anemometer height. 

5.6.1 Short-Term Meteorological Data 

Short-term meteorological data include standard hourly surface and upper-air observations. These

observations must be processed before they can be used in the ISCST model (EPA, 1996; EPA,

1998). For state permit applications, use data for 1988 or 1989 as specified in Appendix C. For

PSD demonstrations, process and use the most recent, readily available five years of data available

on the SCRAM Internet page, unless the ADMT has placed processed data sets on the ADMT

Internet page. Provide an ASCII version of the data with the modeling submittal. 

5.6.2 Long-Term Meteorological Data

Long-term meteorological data are used in the ISCLT model. These data—known as STAR

summaries—are obtained by processing hourly surface observations (EPA, 1996; EPA, 1998) and

include joint frequency distributions of wind speed class, by wind direction sector, by stability

category.

For state permit applications, use STAR summaries for each of five years as specified in Appendix

C. For PSD permit applications, create a STAR summary for each of the most recent, readily

available five years of data (EPA, 1998) unless the ADMT has placed processed data sets on the

ADMT Internet page. The meteorological data period used to determine PSD compliance can

also be used for any associated state permit modeling.

5.6.3 Anemometer Height

Use the actual height of the anemometer that measured the wind speed observations at the surface

station used in the modeling demonstration. Anemometer heights for selected surface stations in

Texas are available from the ADMT and also on the ADMT Internet page.
53

5.6.4 Replacement of Meteorological Data

Replace missing meteorological data before processing them for dispersion modeling. Follow the

guidance in Procedures for Substituting Values for Missing NWS Meteorological Data for Use in

Regulatory Air Quality Models (Atkinson, 1992) to replace missing values.

Replacement of missing data must follow standard procedures. Document and submit all

occurrences of missing data and proposed replacement values for the ADMT’s approval for any

meteorological data that are not available on the SCRAM Internet page or data that are available

on the SCRAM Internet page but not complete. Do this before performing any modeling.

5.6.5 Replacement of Low Mixing Heights

Occasionally, the PCRAMMET program will generate low hourly mixing heights. These low

heights may cause a model to predict unrealistically high concentrations for ground-based and

other sources with low release heights. To mitigate this effect, the ADMT has developed a

procedure to replace low mixing heights to provide more representative concentrations. The

procedure is documented in a memo on the ADMT Internet page.

For state modeling, the ADMT has adjusted all short-term meteorological data sets and placed

them on the ADMT Internet page. However, for PSD modeling, the ADMT should approve

changes to any data set before a modeler uses it.

5.6.6 Gravitational Settling and Deposition Modeling

Contact the ADMT for assistance in developing the additional parameters required to process

data sets to support gravitational settling and deposition modeling. Also, ADMT should review

the sets and all the data used to develop the specific meteorological parameters required by the

PCRAMMET program before these sets are used. Provide the following information:

! Surface and upper-air data. Provide how the data were obtained (NCDC, SCRAM, or

other source) and station pressure, precipitation amounts, and present weather with

precipitation type.

! The procedure used to determine minimum Monin-Obukhov length; anemometer height;

surface roughness length at both the measurement and application sites; noontime albedo;

Bowen ratio; anthropogenic heat flux; and fraction of net radiation absorbed at the

ground. Note: All parameters are determined for the measurement site except for surface

roughness length.

55

6.0 Guidance for Determining 

Nonpoint Source Characterization

The guidance discussed in this section addresses some, but not all, possible ways to model certain

types of nonpoint, nontraditional sources. Discuss new procedures with the ADMT before final

modeling is conducted. In addition, include a complete description of how a source is

characterized and how the applicable modeling parameters were developed in the air quality

analysis report.

6.1 Pseudo-Point

If the permit engineer determines it is necessary to model emissions from fugitive sources, and if a

pseudo-point characterization is appropriate, then use the following modeling parameters:

! stack exit velocity = 0.001 meter per second;

! stack exit diameter = 0.001 meter;

! stack exit temperature = 0 Kelvin (causes the ISC model to use the ambient temperature

as the exit temperature); and

! actual release height.

In addition, there are a number of sources that do not release to the atmosphere through standard

stacks. Examples are stacks or vents with rain caps, and stacks or vents that release emissions

horizontally. Model these release points using pseudo-point parameters as well. 

Other approaches may be taken. Show that the nonstandard point sources being modeled have

buoyancy or momentum flux and that their suggested modeling parameters will provide

representative impacts.

6.2 Volume

Use the volume source characterization to simulate emissions that initially disperse in three

dimensions with little or no plume rise, such as emissions from vents on building roof; multiple

vents from a building; and fugitive emissions from pipes, conveyor belts, and roads. Parameters

needed are the emission rate, the release height, and the initial horizontal and vertical dimensions

of the volume.
56

The release height is the center of the volume above the ground. Determine the initial horizontal

(Fy0) and vertical ( Fz0) dimensions—also known as the initial sigmas—for the volume source

based on the characterization of the source. That is, first define the height, width, and depth of the

release and then use these limiting dimensions to calculate the initial horizontal and vertical

dispersion dimensions.

For example, if the length and width of a piping structure is 10 meters and the piping extends

from the surface to 20 meters, and the emissions could come from multiple locations throughout

the entire structure, then Fy0 would be 10 meters divided by 4.3, 

 Fz0 would be 20 meters divided

by 2.15, and the height of release would be 10 meters. However, if emissions could only come

from the upper portions of the piping, for example 10 to 20 meters, then F would be 10 meters y0

divided by 4.3, Fz0 would be 10 meters divided by 4.3, and the height of release would be 15

meters.

General guidance for developing F and F is contained in the ISC User’s Guide (EPA, 1995d). y0 z0

The ADMT can provide additional ways to characterize emissions from sources such as roads and

tanks. 

The base of the volume source must be square. If the base is not square, model the source as a

series of adjacent volume sources, each with a square base. For relatively uniform sources,

determine an equivalent square by taking the square root of the area of the length and width of the

volume base.

6.3 Area

Use the area source characterization to simulate emissions that initially disperse in two dimensions

with little or no plume rise, such as ground-level or low-level emissions from a storage pile, slag

dump, landfill, or holding pond. The area source may be characterized as a rectangle, irregularly

shaped polygon, or circle. The model integrates over the portion of the area that is upwind of a

receptor so receptors may be placed within the area and at the edge of the area. The model does

not integrate for portions of the area that are closer than 1 meter upwind of a receptor. Use an

emission rate per unit area instead of total emissions; that is, divide the total emissions in grams

per second by the total area in square meters. Detailed guidance is contained in the ISC User’s

Guide (EPA, 1995d). 
57

6.4 Open Pit 

Use the open pit source characterization to simulate emissions that initially disperse in three

dimensions with little or no plume rise, such as a surface coal mine or rock quarry. Parameters

needed are the open pit emission rate, the average release height, the initial lengths of the X and Y

sides of the open pit, the volume of the open pit, and the orientation angle in degrees from 360

degrees (north). While detailed guidance is contained in the ISC User’s Guide (EPA, 1995d),

some factors to consider follow.

! As with the area source, an emission rate per unit area is used; that is, the total emissions

in grams per second divided by the total area in square meters.

! The release height above the base of the open pit cannot exceed the pit’s effective depth,

which is calculated by the model based on the pit’s length, width, and volume. A release

height of zero indicates emissions that are released from the base of the pit.

! The length-to-width aspect ratio for open pit sources should be less than 10 to 1. Unlike

the area source, the open pit cannot be subdivided because the assumption used to

develop the algorithm is that the emissions are mixed throughout the pit before being

dispersed. Characterize irregularly shaped pit areas by a rectangular shape of equal area.

! Unlike the area source, receptors cannot be placed within the boundaries of the pit.

6.5 Flares

Flares are a special type of elevated source that may be modeled as a point source. The technique

to calculate buoyancy flux for flares generally follows the technique described in the SCREEN3

Model User's Guide (EPA, 1995b). 

Use the following parameters:

! effective stack exit velocity = 20 meters per second;

! effective stack exit temperature = 1273 Kelvin;

! actual height of the flare tip; and

! effective stack exit diameter. 
D' (10&6

qn) qn

'q(1&0.048 MW)

58

and

The effective stack diameter (D) in meters is calculated using the following equations:

where

q = gross heat release in cal/sec;

qn= net heat release in cal/sec; and

MW = weighted (by volume) average molecular weight of the compound being flared. 

Note that enclosed vapor combustion units should not be modeled with the preceding parameters

but instead with stack parameters that reflect the physical characteristics of the unit.

6.6 Road Emissions

The permit engineer will evaluate fugitive dust from road emissions as part of the technical review

of the permit as applicable; however, road emissions should only be included in the modeling

analysis in limited circumstances.

6.6.1 When to Exclude from Modeling

In general,

! Do not include road emissions in permit modeling analyses for short-term averaging

periods—periods less than annual. 

! Do not include road emissions in permit modeling analyses for an annual averaging period

if:

" they cannot be accurately quantified; or

" they will not be generated in association with the transport, storage, or transfer of

materials (raw, intermediate, and waste), including sand, gravel, caliche, or other

road-base aggregates; and

" the engineer omits them from the modeling demonstration because the applicant

will use best management practices to control them.
59

Rationale: This guidance is based on the process developed to quantify an emission rate for

fugitive dust generated by vehicle traffic over roads. Calculations to determine emissions from

roads involve a number of parameters, most of which cannot be accurately estimated unless they

are measured at a specific site. In addition, the values for these parameters can vary over a wide

range and in many cases depend upon recent meteorological events, such as rainfall. The

Compilation of Air Pollutant Emission Factors (AP-42) (EPA, 1995c) indicates that unless

site-specific information is used, lower confidence levels are placed upon emission estimates based

on time periods of less than one year. 

However, even with higher confidence levels, unrepresentative predictions of concentrations from

road emissions are likely due to the modeling process. The modeling process is based on the

assumption that emissions are continuous. The amount of road emissions is directly related to the

type and amount of road traffic, which is usually not continuous or uniform. Combined with

worst-case operating scenarios, the modeling tool will overpredict concentrations, particularly in

the vicinity of the source, and may incorrectly identify road emissions as the major cause of air

pollution at a site. Often the use of control measures and best management practices are the most

effective means to address off-property impacts from road sources. In addition, road emissions

must meet the opacity limits in 30 TAC Chapter 111 [§111.111(a)(8)] and the nuisance provision

in 30 TAC Chapter 101 (§101.4).

6.6.2 Modeling Road Emissions

If road emissions must be modeled, the emissions can be represented as volume sources, as

suggested in the ISC User's Guide (EPA, 1995d). A procedure to develop model input parameters

follows. The applicant can use other procedures on a case-by-case basis but must demonstrate

that those procedures would be appropriate. 

Volume Source Characterization: Follow the eight steps described in the following paragraphs.

Volume Step 1: Determine the adjusted width of the road. The adjusted width is the actual width

of the road plus 6 meters. The additional width represents turbulence caused by the vehicle as it

moves along the road. This width will represent a side of the base of the volume.

Volume Step 2: Determine the number of volume sources, N. Divide the length of the road by the

adjusted width. The result is the maximum number of volume sources that could be used to

represent the road.
60

Volume Step 3: Determine the height of the volume. The height will be equal to twice the height

of the vehicle generating the emissions—round to the nearest meter.

Volume Step 4: Determine the initial horizontal sigma for each volume.

! If the road is represented by a single volume, divide the adjusted width by 4.3.

! If the road is represented by adjacent volumes, divide the adjusted width by 2.15. 

! If the road is represented by alternating volumes, divide twice the adjusted

width—measured from the center point of the first volume to the center point of the next

represented volume—by 2.15. Start with the volume nearest to the property line. This

representation is often used for long roads.

Volume Step 5: Determine the initial vertical sigma. Divide the height of the volume determined in

Step 3 by 2.15.

Volume Step 6: Determine the release point. Divide the height of the volume by two. This point is

in the center of the volume. 

Volume Step 7: Determine the emission rate for each volume used to calculate the initial

horizontal sigma in Step 4. Divide the total emission rate equally among the individual volumes

used to represent the road, unless there is a known spatial variation in emissions.

Volume Step 8: Determine the UTM coordinate for the release point. The release point location is

in the center of the base of the volume. This location must be at least one meter from the nearest

receptor.

6.7 Wind-Generated Particulate Emissions

Wind-generated particulate emissions from drop operations and working storage piles depend

upon the wind speed, with the emission rate normally calculated based upon an average wind

speed. Additionally, the fastest-mile wind speed is used to determine the threshold friction

velocity in order to estimate windblown emissions from standing storage piles (EPA, 1995c). 
61

The predicted concentrations from these sources may be too conservative, since wind speeds will

vary in the model—but the emission rates are based on a fixed wind speed. Adjust the screening

or refined analysis to compensate for this effect. The following paragraphs give examples.

Case 1: Average Wind Speed; Screening Analysis; SCREEN Model: Use the wind speed

nearest to the speed used to determine the emission rate with each applicable stability class

according to Table 2 in the SCREEN user’s guide (EPA, 1995b). For example, if the wind speed

were 11 meters/second (m/s), run the model twice: once for a wind speed of 10 m/s and stability

class C, and again for stability class D. Use the highest predicted concentration.

Case 1: Average Wind Speed; Refined Analysis; ISCST Model: Use the appropriate emissionrate scalar for each wind-speed category that contains wind speeds less than the average wind

speed used to determine the emission rate. Calculate the scalar based on the ratio of each

applicable wind-speed category upper-bound value to the average wind speed used to determine

the emission rate. The upper bounds of the wind-speed categories 1 through 6 are 1.54

meters/second (m/s) 3.09 m/s, 5.14 m/s, 8.23 m/s, 10.8 m/s, and unlimited, respectively. Raise the

ratio to the 1.3 power and use the resulting scalar for each applicable wind-speed category. Enter

a one (1) for all wind-speed categories equal to or greater than the average wind speed.

For example, assume the average wind speed used to calculate the emission rate is 5.36 m/s. To

determine the scalar for the first wind-speed category, divide the upper bound of the first category

by the average wind speed and raise the result to the 1.3 power, or (1.54 m/s ÷ 5.36 m/s) =

1.3 

0.198. The scalar for the second and third wind-speed categories would be 0.489 and 0.947,

respectively. The scalars for the remaining wind-speed categories would be 1.

Case 2: Fastest-Mile Wind Speed; Screening Analysis; SCREEN Model: Determine the lowest

fastest-mile wind speed applicable for the project. Determine the threshold friction velocity.

Determine the lowest 10-meter wind speed that would result in an exceedance of the threshold

friction velocity. Find the corresponding wind speed if the wind were measured at a height less

than 10 meters. Use the lowest wind speed or corresponding wind speed nearest to the wind

speed that would result in an exceedance of the threshold friction velocity with each applicable

stability class according to Table 2 in the SCREEN user’s guide (EPA, 1995b). Use the

appropriate anemometer height. 

For example, if the wind speed were 9 m/s, run the model twice: once for a wind speed of 9 m/s

and stability class C, and again for stability class D. Use the highest predicted concentration.
62

Case 2: Fastest-Mile Wind Speed; Refined Analysis; ISCST Model: Determine the lowest

fastest-mile wind speed applicable for the project. Determine the threshold friction velocity.

Determine the lowest 10-meter wind speed that would result in an exceedance of the threshold

friction velocity. Find the corresponding wind speed if the speed were measured at a height less

than 10 meters. Enter a zero (0) in each wind-speed category whose upper bound is less than the

corresponding wind speed. Enter a one (1) for all wind-speed categories that equal or exceed the

10-meter or corresponding wind speed.

There may be other approaches. Obtain ADMT review and comment on any approach before

using it.
63

7.0 Reporting Requirements

Include in the air quality analysis report a written discussion covering the project, the modeling

performed, and the results. This analysis should contain at least the items in Appendix F.

The air quality analysis report is a stand-alone document. Results from the report should be

sufficient to make a decision without input from other reports. Do not refer to other documents or

reports for data required to be in the report. In addition, do not exclude items without

coordination with the ADMT, unless the items are clearly not applicable to the project. Follow the

reporting requirements to expedite the technical review of the air quality analysis and to eliminate

unnecessary modeling.

Occasionally, the staff may ask for additional data files. An efficient way to transmit them is via

the New Source Review Permits ftp site. The ftp URL for incoming data is 

! ftp://ftp.tnrcc.state.tx.us/incoming/AirQuality/NewSourceReviewPermits/Modeling. Note

that this URL has mixed cases. 

65

8.0 Transmittal of the Air Quality Analysis Report

Send the air quality analysis report to the permit engineer that requested the analysis. In addition,

for PSD applications send a copy of the report—with no disks or paper copies of the modeling

and downwash files—to EPA Region 6 at the following address: 

U.S. Environmental Protection Agency Region 6

New Source Review Section (6PD-R) 

1445 Ross Avenue, Suite 1200 

Dallas, Texas 75202-2733 

The permit engineer reviews the report and determines the need for a technical review, or audit,

by the ADMT.

8.1 Request for ADMT Technical Review

Frequently, the permit engineer requests that the ADMT conduct a technical review, or audit, of

an air quality analysis. The purpose of the review is to ensure that the procedure used to

demonstrate compliance with applicable standards or guidelines was technically correct and that

the predicted concentrations can be used in the technical review process.

If a review is required, the permit engineer sends an audit request to the ADMT team leader, who

then assigns the project to one of the staff.

Normal turnaround time is from two to four weeks depending on overall unit workload,

complexity of the project, completeness of the submittal, and deficiencies that must be evaluated.

8.2 Modeling Technical Review Process 

Before the technical review begins, the ADMT modeler contacts the applicant’s modeler to advise

that he or she will review the air quality analysis. The review is done to ensure that the modeling

output is technically representative and sufficient and that any deviations from guidance do not

significantly affect the compliance demonstration. As the review progresses, the ADMT provides

the status of the review as appropriate to the applicant’s modeler and the permit engineer.

To assist the ADMT, follow reporting requirements and provide clear documentation of how the

modeling was done and what assumptions were made. In addition, include in the air quality

analysis any calculations that were necessary to develop the input data required to run the selected

model.
66

If the ADMT staff finds errors or discrepancies, they attempt to evaluate them and determine

whether they would cause a significant change in the magnitude or location of predicted

concentrations—that is, whether the concentrations would be technically representative and

usable by the staff to determine whether the permit should be issued. The ADMT will work

closely with the permit engineer and the applicant’s modeler to resolve omissions, unclear

documentation, or other problems.

If the ADMT cannot resolve a modeling deficiency, then the modeling submittal is not accepted,

and recommended corrective actions are forwarded to the permit engineer. 
67

9.0 Common Shortfalls in Modeling Reports

Evaluating or correcting modeling shortfalls during the modeling technical review process takes

time, which lengthens the overall permitting process. The ADMT routinely finds similar errors,

discrepancies, or omissions in modeling reports. The staff believes that modelers can identify and

correct most shortfalls during the quality control process if they understand the audit process and

can recognize them. Therefore, some specific examples of potential shortfall areas follow.

9.1 Modeling Emissions Inventory

The modeling emissions inventory is one of the most important parts of the modeling

demonstration. Ensure that the data entered into the modeling files match the data represented in

the body of the report. For example: 

! Ensure that emission rates, source locations, or stack parameters entered into the

modeling input files agree with corresponding parameters listed on the Table 1(a) of the

permit application or other data represented in the report. Table 1(a) data are

representations in the permit application, and the modeling should reflect these data.

! Match emission point identifiers used in the Table 1(a) with those used in the modeling

input files. That is, the nomenclature or emission point identification scheme used in the

modeling should be the same as the one used in the permit application or air quality

analysis.

! Include in the modeling demonstration all emission points represented in the permit

application.

! Do not rotate source coordinates to align them with true north if they were converted

from a plant coordinate system to the UTM projection.

9.2 Plot Plans or Area Maps

The plot plans and area maps submitted with the permit application do not normally need the

detail required for a modeling demonstration. However, once the permit engineer requests that

modeling be conducted, annotate the plans and maps as necessary to conduct modeling or audit

the modeling process. That is, ensure that plot plans or area maps have enough information to

accurately determine the location of emission points; locations and dimensions of downwash

structures (length, width, and height); property lines; locations of sensitive receptors; and terrain

elevations.
68

9.3 Building Wake Effects (Downwash)

Downwash can significantly affect dispersion. Use the BPIP to determine downwash parameters.

Ensure that the data entered into the BPIP match the data represented in the body of the report.

For example:

! Ensure matching among data listed in downwash input files, Table 1(a) of the permit

application, plot plan, and modeling input files. These data include source location, source

base elevation, source height, and source identifiers referred to in the Modeling Emissions

Inventory Section (9.1).

! On the plot plan or in a supplemental table, annotate the base elevations and dimensions

(length, width, and height) of the structures used in the BPIP.

! Include all structures indicated on the plot plan in the BPIP unless they clearly could not

be downwash structures for the stacks being modeled. 

! Consider all potential downwash structures. While wake effects are commonly referred to

as building downwash, tanks and permanent land features could also be “structures.”

! Do not rotate building or structure coordinates to align them with true north if they were

converted from a plant coordinate system to the UTM projection.

9.4 Receptor Grid

The number of receptors in a grid is one of the key factors modelers consider when determining

computer run time. However, ensure that time or cost considerations do not adversely affect the

completeness of the modeling demonstration. For example: 

! Design grids with receptors spaced close enough to each other and that extend far enough

from the emission point to demonstrate that the maximum concentration was found. If

receptors are spaced too far apart, predicted concentrations could be significantly lower

than they would be if intermediate receptors were added. In addition, extend the grid far

enough to show that concentrations are decreasing. More receptors are needed if

concentrations increase at the edge of the grid. 

! Design grids to completely define the AOI. Extend the grid far enough to demonstrate that

concentrations have decreased below the applicable de minimis.
69

! Avoid using a hot-spot technique. That is, do not place fine or tight grids only near the

highest concentration found on the coarse receptor grid. Evaluate concentrations slightly

below the maximum concentration that may be predicted in other areas.

! Use receptor elevations in simple-to-complex terrain. Predicted concentrations can

increase significantly if the terrain in the vicinity of the sources is near or above the height

of the sources.

9.5 Auer Land-Use Analysis

The selection of dispersion coefficients is an important part of the modeling process. The primary

method to determine these coefficients is the Auer land-use analysis. This analysis should have

enough detail to justify the selection of the coefficient. If the land-use designation represents less

than 70 percent of the total, supplement the analysis as discussed in Section 5.1.

9.6 Omitted or Incomplete Data

Ensure that all required concentration maps, modeling and downwash input and output files,

boundary files, plot files, and other required data are complete and submitted with the modeling

report. Most data can be submitted on a diskette rather than in paper format. This saves paper yet

gives the ADMT access to the data as required during the technical review process. In addition, if

the ADMT finds an error, access to all the input files can be useful to determine whether the error

would cause a significant change in the magnitude or location of the predicted concentrations. 

9.7 Meteorological Data

Several years ago the National Weather Service (NWS) had a goal to standardize anemometer

heights at 10 meters. Consequently, most models, including the ISC models, have default

anemometer heights set at 10 meters. Unfortunately, the NWS program was delayed. Since

surface meteorological data may have been obtained from anemometers at various heights, ensure

that the proper anemometer height is used in the modeling demonstration. Heights are available

on the ADMT Internet page.

71

10.0 References

Atkinson, Dennis and Russell F. Lee, 1992: Procedures for Substituting Values for Missing NWS

Meteorological Data for Use in Regulatory Air Quality Models.

Auer, A.H., 1978: Correlation of Land Use and Cover with Meteorological Anomalies, Journal of

Applied Meteorology, 17:636-643.

EPA, 1985: Guideline for Determination of Good Engineering Practice Stack Height (Technical

Support Document for the Stack Height Regulations), (Revised), EPA-450/4-80-023R, June,

1985. U.S. Environmental Protection Agency, Office of Air and Radiation, Office of Air Quality

Planning and Standards, Research Triangle Park, NC.

EPA, 1987a: Ambient Monitoring Guidelines for Prevention of Significant Deterioration (PSD),

EPA-450/4-87-007, May, 1987. U.S. Environmental Protection Agency, Research Triangle Park,

NC.

EPA, 1987b: On-Site Meteorological Program Guidance for Regulatory Modeling Applications,

EPA-450/4-87-013, June, 1987. U.S. Environmental Protection Agency, Research Triangle Park,

NC.

EPA, 1990: Draft New Source Review Workshop Manual, Draft, October, 1990. U.S.

Environmental Protection Agency, Office of Air Quality Planning and Standards, Research

Triangle Park, NC. 

EPA, 1992a: Technical Implementation Document for EPA’s Boiler and Industrial Furnace

Regulations, EPA 530-R-92-011, March, 1992. U.S. Environmental Protection Agency, Office of

Solid Waste, Washington DC.

EPA, 1992b: Screening Procedures for Estimating the Air Quality Impact of Stationary Sources,

Revised, EPA-450/R-92-019, October, 1992. U.S. Environmental Protection Agency, Office of

Air and Radiation, Office of Air Quality Planning and Standards, Research Triangle Park, NC.
72

EPA, 1992c: Workbook for Plume Visual Impact Screening and Analysis, EPA-454/R-92-023,

October, 1992. U.S. Environmental Protection Agency, Office of Air and Radiation, Office of Air

Quality Planning and Standards, Research Triangle Park, NC.

EPA, 1992d: User’s Manual for the Plume Visibility Model (PLUVUE II), (Revised), EPA454/B-92-008, September, 1992. U.S. Environmental Protection Agency, Office of Air Quality

Planning and Standards, Technical Support Division, Research Triangle Park, NC.

EPA, 1993a: User’s Guide to the Building Profile Input Program, October, 1993. U.S.

Environmental Protection Agency, Office of Air Quality Planning and Standards, Technical

Support Division, Research Triangle Park, NC.

EPA, 1993b: Requirements for Quality Assurance Project Plans for Environmental Data

Operations (QA/R5) July, 1993. U.S. Environmental Protection Agency, Quality Assurance and

Management Staff, Washington, DC.

EPA, 1995a: Guideline on Air Quality Models, (Revised), EPA-450/2-78-027R-C August, 1995.

U.S. Environmental Protection Agency, Office of Air and Radiation, Office of Air Quality

Planning and Standards, Research Triangle Park, NC.

EPA, 1995b: SCREEN3 Model User’s Guide, EPA-454/B-95-004, September, 1995. U.S.

Environmental Protection Agency, Office of Air Quality Planning and Standards, Emissions,

Monitoring, and Analysis Division, Research Triangle Park, NC.

EPA, 1995c: Compilation of Air Pollutant Emission Factors, AP-42, January, 1995. U.S.

Environmental Protection Agency, Office of Air Quality Planning and Standards, Research

Triangle Park, NC.

EPA, 1995d: User’s Guide for the Industrial Source Complex (ISC3) Dispersion Models, EPA454/B-95-003a, September, 1995. U.S. Environmental Protection Agency, Office of Air Quality

Planning and Standards, Emissions, Monitoring, and Analysis Division, Research Triangle Park,

NC.

EPA, 1996: Meteorological Processor for Regulatory Models (MPRM) User’s Guide, EPA454/B-96-002, August, 1996. U.S. Environmental Protection Agency, Office of Air Quality

Planning and Standards, Technical Support Division, Research Triangle Park, NC.
73

EPA, 1998: PCRAMMET User’s Guide, August, 1998. U.S. Environmental Protection Agency,

Office of Air Quality Planning and Standards, Emissions, Monitoring, and Analysis Division,

Research Triangle Park, NC.

Scheffe Richard D., 1988: VOC/NOx Point Source Screening Tables, draft.

TNRCC, 1996: 30 TAC Chapter 111, Control of Air Pollution from Visible Emissions and

Particulate Matter, September, 1996.

TNRCC, 1997a 30 TAC Chapter 112, Control of Air Pollution from Sulfur Compounds, July,

1997.

TNRCC, 1997b: 30 TAC Chapter 101, General Rules, December, 1997.

TNRCC, 1998a: Modeling and Effects Review Applicability technical guidance package, RG324, August, 1998.

TNRCC, 1998b: 30 TAC Chapter 116, Control of Air Pollution by Permits for New Construction

or Modification, December, 1998.

40 CFR, 51: Code of Federal Regulations, Title 40 (Protection of Environment), Part 51. Office

of the Federal Register National Archives and Records Administration.

 40 CFR, 52: Code of Federal Regulations, Title 40 (Protection of Environment), Part 52. Office

of the Federal Register National Archives and Records Administration.

40 CFR, 266: Code of Federal Regulations, Title 40 (Protection of Environment), Part 266.

Office of the Federal Register National Archives and Records Administration.

A-1

Appendix A

Values for Comparison with Modeling Results

Table A-1. Values for Comparison with Modeling Results

Air Constituent Averaging NAAQS NAAQS TNRCC PSD De Minimis PSD

Time Primary Secondary Regulation Monitoring (μg/m ) Increment

(μg/m ) (μg/m ) Standard Significance Class II Area 3 3

(μg/m ) (μg/m )

3

3

3

Sulfur 30-min. --- --- 0.4 ppm --- --- ---

Dioxide (1021 μg/m )

a

3-hr. --- 1300 --- --- 25 512

24-hr. 365 --- --- 13 5 91

Annual 80 --- --- --- 1 20 

b

3

Hydrogen 30-min. --- --- 0.08 ppm --- --- ---

Sulfide (108 μg/m )

a

30-min. --- --- 0.12 ppm --- --- ---

a

c

3

d

162 μg/m3

Sulfuric 1-hr. --- --- 50 μg/m --- --- ---

Acid

24-hr. --- --- 15 μg/m --- --- ---

3

3

Total Reduced Sulfur 1-hr. --- --- --- 10 --- ---

e

Reduced Sulfur 1-hr. --- --- --- 10 --- ---

Compounds

e

Particulate Matter 1-hr. --- --- 400 μg/m --- --- ---

(PM)

3-hr. --- --- 200 μg/m --- --- ---

3

3

Inhalable Particulate 24-hr. 150 150 --- 10 5 30

Matter (PM ) 10

f

Annual 50 50 --- --- 1 17

Fine Particulate Matter 24-hr. 65 65 --- --- --- ---

(PM ) 2.5

g

Annual 15 15 --- --- --- ---

Nitrogen Dioxide Annual 100 100 --- 14 1 25 

Carbon Monoxide 1-hr. 40,000 --- --- 2,000 ---

8-hr. 10,000 575 500 ---

--- ---

Lead (Elemental) 3-mo. 1.5 --- --- 0.1 --- --- 

(Calendar 

Quarter) 

Ozone 1-hr. 235 235 --- --- 100 tons ---

 h

8-hr. 80 80 VOC

Fluorides 24-hr. 0.25 I

Other Constituents 1-hr. --- --- j --- k ---

Annual --- --- j --- k ---
A-2

Notes to Table A-1

a Use the predicted 1-hour concentration to compare with 30-minute standards.

b Conversion from parts-per-million (ppm) to micrograms-per-cubic meter (μg/m assuming 3)

temperature = 90 degrees Fahrenheit (F) (TNRCC, 1997). Standard is 0.28 ppm (715

μg/m3) for Galveston and Harris Counties and 0.32 ppm (817 μg/m3) (net ground level

concentration from all sources on-property) for Jefferson and Orange Counties.

c Conversion from ppm to μg/m assuming temperature = 90 degrees F (TNRCC, 1997). 3

Use this standard if property downwind is used for residential, recreational, business or

commercial purposes. 

d Conversion from ppm to μg/m assuming temperature = 90 degrees F (TNRCC, 1997). 3

Use this standard if property downwind is used for other than residential, recreational,

business or commercial purposes. 

e 40 CFR 52.21 (I)(8)(I). Acceptable monitoring techniques may not be available at this

time (40 CFR, 52).

f There was no change to the numerical value of the standards or increment; however, the

form of the 1997 24-hour standard changed. Both pre-1997 and 1997 standards apply to

both attainment and unclassified areas until revoked by EPA. 

g Implementation procedures under development by EPA.

h The 1-hour standard applies to nonattainment areas. The 8-hour standard applies

everywhere else.

I Does not include hydrogen fluoride.

j Not defined in a specific regulation but determined on a case-by-case basis. See the NSRP

Internet page or contact the Toxicology and Risk Assessment Section to obtain current

ESLs.

k See the Modeling and Effects Review Applicability guidance package for values that may

be applicable on a project-by-project basis (TNRCC, 1998b).
B-1

Appendix B

Screening Factors and Ratio Techniques

Screening Factors. For averaging times greater than one hour, the maximum concentration will

generally be less than the 1-hour value. Use the factors in Table B-1 to convert point and volume

source related concentrations (EPA, 1992a and ADMT memo on the ADMT Internet page for

lead modeling). Do not use the multiplying factors to obtain concentrations from area sources for

averaging times greater than one hour. Concentrations close to an area source will not vary as

much as those for point and volume sources in response to varying wind directions, and the

meteorological conditions which are likely to give maximum 1-hour concentration can persist for

several hours. Therefore, to be conservative, ADMT recommends that the maximum 1-hour

concentrations for area sources be assumed to apply for averaging periods out to 24 hours.

 Table B - 1. Multiplying Factors 

to Convert 1-Hour Point and Volume Source 

 Concentrations to Other Averaging Times 

Averaging Time Multiplying Factor

3-Hour 0.9

8-Hour 0.7

24-Hour 0.4*

Quarterly 0.2*

Annual 0.08*

* Can be used for area sources.

Ratio Technique 1. This technique uses a unit emission rate (1 pound per hour or 1 gram per

second) to determine if the maximum contribution from each permitted source when added

together, independent of time and space, could exceed a standard or ESL. This is a conservative

procedure since the maximum concentration from all sources modeled concurrently cannot be

more than the sum of the maximum concentration from each source modeled separately.

Each source is evaluated separately with a unit emission rate, such as 1 pound per hour or 1 gram

per second; the source's actual location; and the source's proposed stack parameters represented

in the permit application. In the ISC models this is done by setting up a separate source group for
B-2

each source. The SCREEN model can also be used for this demonstration with a separate

SCREEN model run for each source.

The maximum predicted concentration for each source is then multiplied by the appropriate

emission rate factor for each source and for each pollutant. The emission rate factor is the ratio of

the approved emission rate divided by the unit emission rate. 

The sum of the maximum concentrations (for each pollutant, independent of time and space) is

then compared with the threshold of concern for each pollutant. If the sum for any pollutant is

greater than that value, then refined modeling may be required and if so, enter the emission rate

for each source for this pollutant into the model for additional evaluation so that time and space

are considered. 

Determining individual source contributions to the ALL source group maximum concentration in

the ISC model is not appropriate unless there is only one source or the pollutants are emitted in

exactly the same amount for all sources, or pollutants are emitted in exactly the same ratio for all

sources.

Ratio Technique 2. One pollutant is modeled for all sources with TNRCC approved emission

rates and stack parameters. Other TNRCC approved pollutant emission rates are then compared

with the modeled pollutant emission rate to determine the source which has the maximum ratio.

This maximum ratio is then multiplied by the predicted maximum off-property concentration for

the pollutant modeled. If the resulting maximum concentration exceeds a value of concern, then

additional refined modeling may be needed and, if so, enter the emission rate for each source of

this pollutant into the model.

Ambient Ratio Method. The EPA adopted a new method to predict annual NO concentrations 2

[GAQM, Section 6.2.3 (EPA, 1995a)] that can be applied during screening modeling or refined

modeling. This method consists of two approaches. One approach applies a conversion factor to

the emission rate, and the other applies a conversion factor to the predicted concentration. The

process is outlined in the following steps that do not need to be applied in sequence.

Step 1: Assume total conversion of NO to NO . Use the NO emission rate as a surrogate for X 2 X

the NO emission rate. Conduct screening or refined modeling, as applicable. This approach is 2

conservative but is not realistic. If the concentration exceeds the de minimis or NAAQS (with

background concentration added), go to Step 2.
B-3

Step 2: Apply a conversion factor to the predicted concentration.

Step 2a: Assume limited conversion of NO X to NO 2. Multiply the predicted annual NO X

concentration by the national default of 0.75. This approach is conservative. If additional

refinement is needed, go to Step 2b if applicable. 

Step 2b: Obtain a representative factor for conversion of NO X to NO 2. Multiply the predicted

annual NO concentration by a measured NO / NO ratio obtained from a site-specific or X 2 X

representative regional air monitor.

Step 3: Apply a conversion factor to the emission rate.

Step 3a: Assume limited conversion of NO X to NO 2. Multiply the NO X emission rate by the

national default of 0.75. This approach is conservative. Conduct screening or refined modeling, as

applicable. If additional refinement is needed, go to Step 3b, if applicable. 

Step 3b: Obtain a representative factor for conversion of NO X to NO 

 2

. Multiply the emission rate

by a measured NO / NO ratio obtained from a site-specific or representative regional monitor. 2 X

Conduct screening or refined modeling, as applicable.

C-1

Appendix C

Meteorological Stations by County

Table C-1 contains a composite listing of meteorological stations and counties to standardize the

selection of meteorological data for Texas permit applications. Suggested NWS surface,

upper-air, and STAR stations are specified for each county. A modeler may suggest other data

sets if they would be more representative for the source location. Table C-2 contains NWS

stations, call signs, and identification numbers. Table C-3 shows new NWS upper-air stations. The

relocation of these stations results in different upper-air stations for several counties for PSD

demonstrations. Of immediate interest are the counties that use Victoria upper-air station data, as

that station was moved to Corpus Christi and became operational in 1989, with 1990 as the first

year with usable data. 

The ADMT has preprocessed meteorological data sets for state modeling, but has not

preprocessed sets for PSD modeling yet. However, a staff goal is to provide all meteorological

data for both state and PSD modeling. The staff will place a notice on the ADMT Internet page as

data sets are created.

The required year for short-term state modeling is currently 1988 (or 1989 for Shreveport data

sets). The required years for long-term state modeling are currently 1985 through 1989 (1985-

1987, 1989-1990 for Shreveport). Required years for PSD modeling are the most recent, readily

available five years of data for both short-term and long-term modeling. Most recent, readily

available means that the data are available on the EPA SCRAM or the ADMT Internet page. For

example, for permit modeling in Anderson County:

! State Permit

Short term - Waco surface and Longview upper-air data from 1988;

Long term - Waco STAR data for each year of the five-year period from 1985 through

1989.

! PSD Permit

Short term - Waco surface and Longview upper-air data for each year of the appropriate

five-year period;

Long term - Waco STAR data for each year of the appropriate five-year period.
C-2

Table C-1. Meteorological Stations by County

County Surface Upper Air STAR

Anderson Waco Longview Waco

Andrews Midland Midland Midland

Angelina Shreveport Longview Shreveport

Aransas Corpus Christi Victoria Corpus Christi

Archer Wichita Falls Stephenville Wichita Falls

Armstrong Amarillo Amarillo Amarillo

Atascosa San Antonio Del Rio San Antonio

Austin Austin Victoria Austin

Bailey Lubbock Amarillo Lubbock

Bandera San Antonio Del Rio San Antonio

Bastrop Austin Victoria Austin

Baylor Wichita Falls Stephenville Wichita Falls

Bee Corpus Christi Victoria Corpus Christi

Bell Waco Stephenville Waco

Bexar San Antonio Del Rio San Antonio

Blanco Austin Del Rio Austin

Borden Midland Midland Midland

Bosque Waco Stephenville Waco

Bowie Shreveport Longview Shreveport

Brazoria Houston Intercontinental Lake Charles Houston Intercontinental

Brazos Austin Victoria Austin

Brewster El Paso El Paso El Paso

Briscoe Amarillo Amarillo Amarillo

Brooks Brownsville Brownsville Brownsville

Brown San Angelo Stephenville San Angelo

Burleson Austin Victoria Austin

Burnet San Angelo Stephenville San Angelo

Caldwell Austin Victoria Austin

Calhoun Victoria Victoria Victoria

Callahan Abilene Stephenville Abilene
C-3

County Surface Upper Air STAR

Cameron Brownsville Brownsville Brownsville

Camp Shreveport Longview Shreveport

Carson Amarillo Amarillo Amarillo

Cass Shreveport Longview Shreveport

Castro Amarillo Amarillo Amarillo

Chambers Houston Intercontinental Lake Charles Houston Intercontinental

Cherokee Shreveport Longview Shreveport

Childress Amarillo Amarillo Amarillo

Clay Wichita Falls Stephenville Wichita Falls

Cochran Lubbock Amarillo Lubbock

Coke San Angelo Midland San Angelo

Coleman San Angelo Stephenville San Angelo

Collin Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Collingsworth Amarillo Amarillo Amarillo

Colorado Victoria Victoria Victoria

Comal San Antonio Del Rio San Antonio

Comanche San Angelo Stephenville San Angelo

Concho San Angelo Stephenville San Angelo

Cooke Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Coryell Waco Stephenville Waco

Cottle Lubbock Amarillo Lubbock

Crane Midland Midland Midland

Crockett Midland Midland Midland

Crosby Lubbock Amarillo Lubbock

Culberson El Paso El Paso El Paso

Dallam Amarillo Amarillo Amarillo

Dallas Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Dawson Midland Midland Midland

Deaf Smith Amarillo Amarillo Amarillo

Delta Shreveport Longview Shreveport
C-4

County Surface Upper Air STAR

Denton Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

De Witt Victoria Victoria Victoria

Dickens Lubbock Amarillo Lubbock

Dimmit San Antonio Del Rio San Antonio

Donley Amarillo Amarillo Amarillo

Duval San Antonio Del Rio San Antonio

Eastland Abilene Stephenville Abilene

Ector Midland Midland Midland

Edwards San Antonio Del Rio San Antonio

Ellis Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

El Paso El Paso El Paso El Paso

Erath Abilene Stephenville Abilene

Falls Waco Stephenville Waco

Fannin Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Fayette Austin Victoria Austin

Fisher Abilene Stephenville Abilene

Floyd Lubbock Amarillo Lubbock

Foard Wichita Falls Stephenville Wichita Falls

Fort Bend Houston Intercontinental Lake Charles Houston Intercontinental

Franklin Shreveport Longview Shreveport

Freestone Waco Longview Waco

Frio San Antonio Del Rio San Antonio

Gaines Midland Midland Midland

Galveston Houston Intercontinental Lake Charles Houston Intercontinental

Garza Lubbock Amarillo Lubbock

Gillespie San Angelo Del Rio San Angelo

Glasscock Midland Midland Midland

Goliad Victoria Victoria Victoria

Gonzales San Antonio Victoria San Antonio

Gray Amarillo Amarillo Amarillo
C-5

County Surface Upper Air STAR

Grayson Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Gregg Shreveport Longview Shreveport

Grimes Houston Intercontinental Victoria Houston Intercontinental

Guadalupe San Antonio Victoria San Antonio

Hale Lubbock Amarillo Lubbock

Hall Amarillo Amarillo Amarillo

Hamilton San Angelo Stephenville San Angelo

Hansford Amarillo Amarillo Amarillo

Hardeman Wichita Falls Stephenville Wichita Falls

Hardin Beaumont Lake Charles Beaumont

Harris Houston Intercontinental Lake Charles Houston Intercontinental

Harrison Shreveport Longview Shreveport

Hartley Amarillo Amarillo Amarillo

Haskell Abilene Stephenville Abilene

Hays Austin Victoria Austin

Hemphill Amarillo Amarillo Amarillo

Henderson Waco Longview Waco

Hidalgo Brownsville Brownsville Brownsville

Hill Waco Stephenville Waco

Hockley Lubbock Amarillo Lubbock

Hood Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Hopkins Shreveport Longview Shreveport

Houston Waco Longview Waco

Howard Midland Midland Midland

Hudspeth El Paso El Paso El Paso

Hunt Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Hutchinson Amarillo Amarillo Amarillo

Irion San Angelo Midland San Angelo

Jack Abilene Stephenville Abilene

Jackson Victoria Victoria Victoria
C-6

County Surface Upper Air STAR

Jasper Shreveport Lake Charles Shreveport

Jeff Davis El Paso El Paso El Paso

Jefferson Beaumont Lake Charles Beaumont

Jim Hogg San Antonio Del Rio San Antonio

Jim Wells Corpus Christi Brownsville Corpus Christi

Johnson Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Jones Abilene Stephenville Abilene

Karnes San Antonio Victoria San Antonio

Kaufman Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Kendall San Antonio Del Rio San Antonio

Kenedy Brownsville Brownsville Brownsville

Kent Lubbock Amarillo Lubbock

Kerr San Antonio Del Rio San Antonio

Kimble San Angelo Del Rio San Angelo

King Lubbock Amarillo Lubbock

Kinney San Antonio Del Rio San Antonio

Kleberg Corpus Christi Brownsville Corpus Christi

Knox Wichita Falls Stephenville Wichita Falls

Lamar Shreveport Longview Shreveport

Lamb Lubbock Amarillo Lubbock

Lampasas San Angelo Stephenville San Angelo

La Salle San Antonio Del Rio San Antonio

Lavaca Victoria Victoria Victoria

Lee Austin Victoria Austin

Leon Waco Longview Waco

Liberty Houston Intercontinental Lake Charles Houston Intercontinental

Limestone Waco Stephenville Waco

Lipscomb Amarillo Amarillo Amarillo

Live Oak Corpus Christi Victoria Corpus Christi

Llano San Angelo Del Rio San Angelo
C-7

County Surface Upper Air STAR

Loving Midland Midland Midland

Lubbock Lubbock Amarillo Lubbock

Lynn Lubbock Amarillo Lubbock

Madison Waco Longview Waco

Marion Shreveport Longview Shreveport

Martin Midland Midland Midland

Mason San Angelo Del Rio San Angelo

Matagorda Victoria Victoria Victoria

Maverick San Antonio Del Rio San Antonio

McCulloch San Angelo Stephenville San Angelo

McLennan Waco Stephenville Waco

McMullen San Antonio Del Rio San Antonio

Medina San Antonio Del Rio San Antonio

Menard San Angelo Stephenville San Angelo

Midland Midland Midland Midland

Milam Austin Victoria Austin

Mills San Angelo Stephenville San Angelo

Mitchell Midland Midland Midland

Montague Wichita Falls Stephenville Wichita Falls

Montgomery Houston Intercontinental Lake Charles Houston Intercontinental

Moore Amarillo Amarillo Amarillo

Morris Shreveport Longview Shreveport

Motley Lubbock Amarillo Lubbock

Nacogdoches Shreveport Longview Shreveport

Navarro Waco Stephenville Waco

Newton Shreveport Lake Charles Shreveport

Nolan Abilene Stephenville Abilene

Nueces Corpus Christi Brownsville Corpus Christi

Ochiltree Amarillo Amarillo Amarillo

Oldham Amarillo Amarillo Amarillo
C-8

County Surface Upper Air STAR

Orange Beaumont Lake Charles Beaumont

Palo Pinto Abilene Stephenville Abilene

Panola Shreveport Longview Shreveport

Parker Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Parmer Amarillo Amarillo Amarillo

Pecos Midland Midland Midland

Polk Shreveport Lake Charles Shreveport

Potter Amarillo Amarillo Amarillo

Presidio El Paso El Paso El Paso

Rains Dallas/Ft. Worth Longview Dallas/Ft. Worth

Randall Amarillo Amarillo Amarillo

Reagan Midland Midland Midland

Real San Antonio Del Rio San Antonio

Red River Shreveport Longview Shreveport

Reeves Midland Midland Midland

Refugio Corpus Christi Victoria Corpus Christi

Roberts Amarillo Amarillo Amarillo

Robertson Waco Stephenville Waco

Rockwall Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Runnels San Angelo Stephenville San Angelo

Rusk Shreveport Longview Shreveport

Sabine Shreveport Longview Shreveport

San Augustine Shreveport Lake Charles Shreveport

San Jacinto Houston Intercontinental Longview Houston Intercontinental

San Patricio Corpus Christi Victoria Corpus Christi

San Saba San Angelo Stephenville San Angelo

Schleicher San Angelo Midland San Angelo

Scurry Midland Midland Midland

Shackleford Abilene Stephenville Abilene

Shelby Shreveport Longview Shreveport
C-9

County Surface Upper Air STAR

Sherman Amarillo Amarillo Amarillo

Smith Shreveport Longview Shreveport

Somervell Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Starr San Antonio Del Rio San Antonio

Stephens Abilene Stephenville Abilene

Sterling San Angelo Midland San Angelo

Stonewall Abilene Stephenville Abilene

Sutton San Angelo Del Rio San Angelo

Swisher Amarillo Amarillo Amarillo

Tarrant Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Taylor Abilene Stephenville Abilene

Terrell Midland Midland Midland

Terry Lubbock Amarillo Lubbock

Throckmorton Abilene Stephenville Abilene

Titus Shreveport Longview Shreveport

Tom Green San Angelo Midland San Angelo

Travis Austin Victoria Austin

Trinity Waco Longview Waco

Tyler Shreveport Lake Charles Shreveport

Upshur Shreveport Longview Shreveport

Upton Midland Midland Midland

Uvalde San Antonio Del Rio San Antonio

Val Verde San Antonio Del Rio San Antonio

Van Zandt Dallas/Ft. Worth Longview Dallas/Ft. Worth

Victoria Victoria Victoria Victoria

Walker Houston Intercontinental Longview Houston Intercontinental

Waller Houston Intercontinental Lake Charles Houston Intercontinental

Ward Midland Midland Midland

Washington Austin Victoria Austin
C-10

County Surface Upper Air STAR

Webb San Antonio Del Rio San Antonio

Wharton Victoria Victoria Victoria

Wheeler Amarillo Amarillo Amarillo

Wichita Wichita Falls Stephenville Wichita Falls

Wilbarger Wichita Falls Stephenville Wichita Falls

Willacy Brownsville Brownsville Brownsville

Williamson Austin Victoria Austin

Wilson San Antonio Victoria San Antonio

Winkler Midland Midland Midland

Wise Dallas/Ft. Worth Stephenville Dallas/Ft. Worth

Wood Shreveport Longview Shreveport

Yoakum Lubbock Amarillo Lubbock

Young Abilene Stephenville Abilene

Zapata San Antonio Del Rio San Antonio

Zavala San Antonio Del Rio San Antonio
C-11

Table C-2. National Weather Service Stations, 

 Call Signs, and Identification Numbers

Station Call Sign Number

Abilene ABI 13962

Amarillo AMA 23047

Austin AUS 13958

Beaumont/Pt. Arthur BPT 12917

Brownsville BRO 12919

Corpus Christi CRP 12924

Dallas/Ft. Worth DFW 03927

Del Rio DRT 22010

Fort Worth FWD 03990

El Paso ELP 23044

Houston Intercontinental IAH 12960

Lake Charles LCH 03937

Longview GGG 03951

Lubbock LBB 23042

Midland MAF 23023

San Angelo SJT 23034

San Antonio SAT 12921

Santa Theresa, NM EPZ 03020

Shreveport, LA SHV 13957

Stephenville SEP 13901

Victoria VCT 12912

Waco ACT 13959

Wichita Falls SPS 13966
C-12

 Table C-3. National Weather Service Upper-Air Station Changes

Old Station Moved Last Usable New Station First Usable

Year Year

El Paso 1995 1994 Santa Theresa, NM 1996

Longview 1995 1994 Shreveport, LA 1996

Stephenville 1994 1993 Fort Worth 1995

Victoria 1989 1988 Corpus Christi 1990
D-1

Appendix D

Protocol and Permit Modeling Guidance Requirements

A protocol or checklist serves as an outline of how to conduct a modeling analysis. Protocols are

more formal and more detailed than checklists. Protocols and checklists are not mandatory;

however the ADMT encourages the applicant to submit them for PSD and complex state permit

modeling and RCRA BIF projects. 

The applicant should follow the guidance in Table D-1 to develop protocols, or permit modeling

guidance checklists shown in Appendix E. Items in the table apply to all analyses unless noted

otherwise. Do not exclude items without prior coordination with the ADMT. Send the original

copy of a PSD or RCRA BIF protocol or a guidance checklist to the ADMT team leader with

copies to the permit engineer and other interested parties as appropriate. A PSD protocol does

not need to be sent to EPA Region 6.

Table D-1. Protocol and Permit Modeling Guidance

1.0 Project Identification Information

Provide the following information to clearly identify the analysis:

Applicant

Facility

Permit Application Number

Air Quality Account Number

Nearest City and County

Applicant's Modeler

2.0 Project Overview

Provide a brief discussion of the plant process(es), and types and locations of emissions under

consideration. For RCRA BIF, provide a brief discussion of each BIF unit and the nature of wastes being

generated or burned.

Attach additional data as applicable for project overview.

2.1 Type of Permit Review

Indicate the type of permit review required by the permit engineer. The State modeling demonstration can

be addressed separately from the PSD or RCRA BIF demonstration.

2.2 Constituents to be Evaluated 

List all constituents to be evaluated.
D-2

3.0 Plot Plan

Depending on the scope of the project, several plot plans may be needed to present all requested

information. Provide a plot plan that includes:

A clearly marked scale.

All property lines. For PSD, include fence lines.

A true-north arrow.

UTM coordinates along the vertical and horizontal borders (Please do not use plant or other coordinates).

Provide the datum of your coordinates.

Reference UTM coordinates and locations of all emission points including fugitive sources modeled.

Buildings and structures on-property or off-property which could cause downwash. Provide length, width,

and height.

An indication of the shortest distance to the property line from any of the sources in the facility to be

permitted.

4.0 Area Map (More than one map may be required.)

For State Analyses

Provide a copy of the area map submitted with the permit application. If the map is an extract, it should be

full scale (no reduction or enlargement) and cover the area within a 1.9-mile (3-kilometer) radius of the

facility if used for the Auer land-use analysis.

Add UTMs to the horizontal and vertical dimensions of the map section, as well as the date and title of the

map. Provide the datum of your coordinates.

Annotate schools within 3,000 feet of the sources nearest to the property line.

For Effects Review, also annotate the nearest sensitive receptors of any type and nearest residents. Be

prepared to identify and annotate other sensitive receptors if required by TARA.

For hazardous waste landfill or land treatment facility permits, or an areal expansion of an existing

facility. Also annotate locations of established churches, day care centers, surface water body used for a

public drinking water supply, or dedicated public parks. If any of these locations are within 1000 feet of

the facility or expansion boundary, no permit should be issued.

For commercial hazardous waste management facility permits, or an areal expansion of an existing

facility or unit of the facility. Also annotate locations of established churches, day care centers, surface

water body used for a public drinking water supply, or dedicated public parks. If any of these are within

2640 feet of the facility or expansion boundary, no permit should be issued. For amendments, distance

limits apply as of the date of the original permit.

For PSD Analyses

Provide a copy of the area map submitted with the permit application. If the map is an extract, it should be

full scale (no reduction or enlargement) and cover the area within a 1.9-mile (3-kilometer) radius of the

facility if used for the Auer land-use analysis.

Add UTMs to the horizontal and vertical dimensions of the map section, as well as the date and title of the

map. Provide the datum of your coordinates.

Provide maps that show the location of:

PSD Class I areas within 100 kilometers (km) (62 miles).
D-3

Urban areas, nonattainment areas, and topographic features within 50 km (31 miles) or the distance to

which the source has a significant impact, whichever is less.

Any on-site or local meteorological stations, both surface and upper-air.

State/local/on-site ambient air monitoring sites used for background concentrations within 50 km (31 miles)

or the distance to which the source has a significant impact, whichever is less.

For RCRA BIF Analyses

Provide a copy of the area map submitted with the permit application. If the map is an extract, it should be

full scale (no reduction or enlargement) and cover the area within a 1.9-mile (3-kilometer) radius of the

facility if used for the Auer land-use analysis.

Add UTMs to the horizontal and vertical dimensions of the map section, as well as the date and title of the

map. Provide the datum of your coordinates.

Annotate the location of any on-property residence. Include as a receptor in the analysis.

5.0 Air Quality Monitoring Data 

For State and PSD NAAQS

Discuss how ambient background concentrations will be obtained. That is, preconstruction monitoring or

state/local/on-site monitoring network. Ideally, conduct the monitoring analysis before a PSD permit

application is submitted, as monitoring could take as long as one year if representative monitored data are

not available.

Provide a summary of observations for each constituent and averaging time, if available. 

Discuss how concentrations will be adjusted, if all nearby and background point sources are modeled in

the vicinity of a monitor, if applicable.

For Effects Review, identify any on-site or local monitored data that could be used to supplement or

substitute for modeling. Demonstrate that the data represent near worst-case operational and meteorological

conditions.

6.0 Modeling Emissions Inventory

6.1 On-Property Sources to be Permitted

Provide a copy of the Table 1(a) that was submitted with the permit application. Note that if stack

parameters for any averaging period or load level are different, additional entries are required on the Table

1(a).

Identify special source types such as covered stacks, horizontal exhausts, fugitive sources, area sources,

open pit sources, volume sources, roads, stockpiles, and flares and how they will be modeled. 

Provide all assumptions and calculations used to determine as appropriate the size, sides, rotation angles,

heights of release, initial dispersion coefficients, effective stack diameter, gross heat release and weighted

(by volume) average molecular weight of the mixture being burned.

Specify particulate emissions as a function of particle size; mass fraction for each particle size category;

and particle density for each particle size category, as applicable. 

In addition, it would be helpful to provide a table with stack parameters converted to metric units.

6.2 Other On-Property and Off-Property Sources

Advise how other on- and off-property sources' modeling parameters will be obtained.
D-4

6.3 Table Correlating the Emission Inventory Source Name and EPN with the Source Number in the

Modeling Output

Provide a table that cross-references the source identification numbers used in the modeling if they are

different from the emission point numbers in the Table 1(a) or from any additional list of sources.

6.4 Stack Parameter Justification

Provide the basis for using the listed stack parameters (flow rates, temperatures, stack heights, velocities)

if known before the protocol is submitted. This should include calculations if necessary for justification.

Evaluate at least 25 percent, 50 percent, 75 percent and 100 percent production or load levels, if the source

could be operated at these reduced levels.

6.5 Scaling Factors

Discuss how emission scalars will be developed and used in the modeling, if applicable. 

7.0 Models Proposed and Modeling Techniques

Identify proposed models, model version numbers, and the model entry data options such as the regulatory

default option and the period option.

Discuss any proposed specialized modeling techniques such as screening, collocating sources, ratioing.

Provide assumptions and sample calculations as applicable.

8.0 Selection of Dispersion Option 

Submit an Auer land-use analysis, if required, for the area within 3 km of the sources being permitted. Base

the selection of urban or rural dispersion coefficients on the Auer land-use analysis; however, the

population density method could also be used but is not a preferred method.

Provide a color copy of the USGS map, if a USGS map was used in the analysis.

Supplement the topographic map analysis with a current aerial photograph of the area surrounding the

permitted sources, or with a detailed drive-through summary, to support a land-use designation, that

represents less than 70 percent of the total area evaluated.

9.0 Building Wake Effects (Downwash)

State whether the EPA's Building Profile Input Processor (BPIP) or a software package that employs the

BPIP algorithms will be used. Provide any computer assisted drawing files.

10.0 Receptor Grid—Terrain

Discuss if terrain should be considered and how the terrain for individual receptors will be determined.

Ensure that the higher terrain in any direction from the source is included in the modeling—not just the

highest.

DEM. Provide the datum of your coordinates. If 7.5-minute DEM data are not available for the entire

receptor grid, ensure 7.5-minute DEM data are used for receptors within approximately 3–5 km of the

property line/fence line.

11.0 Receptor Grid—Design

Discuss how the receptor grids will be determined for each type of analysis. 

Provide a diagram of each grid and include any reference labels or nomenclature, if available before the

protocol is submitted.

Provide the datum of your coordinates.
D-5

12.0 Meteorological Data

Indicate the surface station, surface station anemometer height, upper-air station, and period of record. (See

ADMT Internet page for anemometer height data.)

For PSD and RCRA BIF, five consecutive years of the most recent, readily available, hourly and annual

National Weather Service (NWS) data, or one or more years of on-site data.

Discuss how any meteorological data was determined or replaced, if done before the protocol is submitted.

ADMT should approve substitutions before modeling begins. In addition, submit all the supplementary data

used to develop the specific input meteorological parameters required by the PCRAMMET program.

13.0 Modeling Results

Discuss how the modeling results for each averaging period relative to applicable de minimis values,

standards, guidelines, reference air concentrations, risk-specific doses, or risk-specific dose ratios will be

presented. Tabulated results are preferred when several constituents are addressed.

For PSD, use Appendix G of the modeling guidelines format.

13.1 Additional Impacts Analysis (For PSD)

Discuss what methods will be used to evaluate each of the following: growth, and soils and vegetation

analyses, if any, for this project.

13.2 Class I Area Impacts Analysis (For PSD)

Discuss what methods will be used to evaluate Class I area impacts, if any, for this project.

13.3 Dilution Factor (For RCRA BIF)

Discuss how the dilution factor for each constituent will be calculated for this project.

E-1

Appendix E

Permit Modeling Guidance Checklist

A checklist is an abbreviated protocol for the modeling project; include the checklist in the air

quality analysis report. By using a checklist instead of a protocol, the ADMT assumes that the

applicant is aware of routine modeling practices and procedures. A checklist is less detailed than a

protocol and serves to prompt the applicant to consider certain items and procedures—as well as

to document them—and to assist in the conduct of the modeling demonstration. Table E-1

contains the Permit Modeling Guidance Checklist format. The table can be reproduced and filled

out by hand or electronically. 

Use the Table E-1 in conjunction with Table D-1, Protocol and Permit Modeling Guidance

Requirements, and Table F-1, Air Quality Analysis Reporting Guidance, as applicable. Enter

required information and mark all items that apply. Include any explanatory information and

deviations from standard practice or procedures in the checklist or attach additional pages as

necessary. Complete a project-specific checklist and send it to the ADMT before a guidance

meeting if possible.

Table E-1. Permit Modeling Guidance Checklist

1.0 Project Identification Information

Applicant/Facility:

Permit Application Number: Air Quality Account Number:

Nearest City: County:

Applicant's Modeler:

2.0 Project Overview

Plant process(es) and types and locations of emissions under consideration ___

For RCRA BIF, each BIF unit and the nature of wastes being generated or burned____

2.1 Type of Permit Review

State Property Line____ State NAAQS___ State Effects Review___ State Disaster Review___

PSD___ RCRA BIF______ Other_____

2.2 Constituents to be Evaluated

PM___ PM 10___ CO_____ NO 2___ Pb___

SO 2___ H 2 S____ H 2 S0 

 4___ TRS___
E-2

Speciated VOCs____ Speciated Metals ____ Other____

3.0 Plot Plan

Clearly marked scale_____ All property lines_____ For PSD, fence lines_____

A true-north arrow_____ UTM coordinates along the vertical and horizontal border _____

Datum of UTM coordinates? NAD27______ NAD83______ Other_____

Reference UTM coordinates and locations of all emission points including fugitive sources modeled_____

Buildings and structures on-property or off-property which could cause downwash with length, width, and

height identified____

4.0 Area Map (More than one map may be required)

For State Analyses

Full-scale (no reduction or enlargement)_____ Cover area within a 1.9-mile (3-kilometer) radius of the

facility for Auer land-use analysis _____

UTM coordinates along the vertical and horizontal borders ___ Date and title of the map____

Datum of UTM coordinates? NAD27______ NAD83______ Other_____

School within 3000 feet?_______ (Include as a sensitive receptor in the analysis.)

For Effects Review

Distance to nearest sensitive receptor other than a school_________

Distance to nearest residents_______

For hazardous waste landfill or land treatment facility permits, or an areal expansion of an existing

facility. Any churches, day care centers, surface water body used for a public drinking water supply, or

dedicated public parks within 1000 feet of the facility or expansion boundary? ____ If this is the case, no

permit should be issued. 

For commercial hazardous waste management facility permits, or an areal expansion of an existing

facility or unit of the facility. Any churches, day care centers, surface water body used for a public drinking

water supply, or dedicated public parks within 2640 feet? ___ If this is the case, no permit should be issued.

For amendments, distance limits apply as of the date of the original permit.

For PSD Analyses

Full-scale (no reduction or enlargement)_____ Cover area within a 1.9-mile (3-kilometer) radius of the

facility for Auer land-use analysis _____

UTM coordinates along the vertical and horizontal borders ___ Date and title of the map____

Datum of UTM coordinates? NAD27______ NAD83______ Other_____

Class I area within 10 km (6.2 miles)?______

Class I area within 100 km (62 miles)?______

Urban areas, nonattainment areas, and topographic features within 50 km (31 miles)? _____

On-site or local meteorological stations, both surface and upper-air?______

State/local/on-site ambient air monitoring sites within 50 km (31 miles)? ______

For RCRA BIF Analyses
E-3

Full-scale (no reduction or enlargement)_____ Cover area within a 1.9-mile (3-kilometer) radius of the

facility for Auer land-use analysis _____

UTM coordinates along the vertical and horizontal borders ___ Date and title of the map____

Datum of UTM coordinates? NAD27______ NAD83______ Other_____

On-property residence? _____ Include as a receptor in the analysis.

5.0 Air Quality Monitoring Data 

For State NAAQS and PSD, are monitoring data for background concentrations available? ____ If not, are

there regional data that could be used? _____

For Effects Review, identify any monitored data that could be used to supplement or substitute for modeling.

Demonstrate that the data represent near worst-case operational and meteorological conditions.

6.0 Modeling Emissions Inventory

6.1 On-Property Sources in the Permit Application

Stack parameters for any averaging period or load level different than Table 1(a)?_____

For gravitational settling applications (for each applicable source):

Particle size____ Mass fraction for each particle size category___

Particle Density for each particle size category ____

Special Source Types/Characterizations? ____

Fugitive source____ Covered stack____ Horizontal exhaust___

Tilted stack____ Area source____ Open pit_____ Volume source____

Flare____ Stockpile____ Road____ Other_____

Techniques to Model Special Sources? ____

Follow Air Quality Modeling Guidelines_____ ADMT Technical Memo_____

Other______ 

6.2 Other On-Property and Off-Property Sources

Sitewide modeling required? _______

6.3 Table Correlating the Emission Inventory Source Name and EPN with the Source Number in the

Modeling Output

Source identification numbers used in the modeling different from the emission point numbers in the Table

1(a) or from any additional list of sources? ______

6.4 Stack Parameter Justification

Basis/calculations for stack parameters (flow rates, temperatures, stack heights, velocities)? ______ 

Stack parameters for any averaging period different? ______ If yes, include on the Table 1(a).

Load evaluation required? _____ Evaluate at least 25 percent, 50 percent, 75 percent and 100 percent

production or load levels, if the source could be operated at these levels.

Any stack parameters for any averaging period different for maximum load? ___
E-4

6.5 Scaling Factors

Scaling factors applicable?____ 

7.0 Models Proposed and Modeling Techniques

Model (Version Number)

ISCST (________) ___ SCREEN (_________) ___ OTHER _________ (_________)

Specialized Techniques? ____

Collocated Sources_____ Ratio______ Other___

8.0 Selection of Dispersion Coefficients

Urban ____ Rural ____ How determined? 

 Auer land-use analysis____ Supplemented Auer land-use analysis____ Population___

9.0 Building Wake Effects (Downwash)

EPA BPIP ______ Version _______

or

Software package that employs BPIP algorithms?_____ 

10.0 Receptor Grid—Terrain

Flat___ Simple___ Complex___

Elevated receptors? _____

(Ensure that the higher terrain in any direction is included in the modeling—not just the highest.)

DEMs Used? 7.5-Minute ___ 1-Degree ___ Mixed ____

Datum of UTM coordinates? NAD27________ NAD83______ Other________

7.5-minute DEM data available for the entire receptor grid? _____ If not, use 7.5-minute DEM data for

receptors within approximately 3-5 km of the property/fence line.

11.0 Receptor Grid—Design

Datum of UTM coordinates? NAD27________ NAD83______ Other________

12.0 Meteorological Data

Surface/Upper-Air Data Set (Five Years For PSD, RCRA BIF)?

Set(s)_________________________ Year(s)_____________________

Anemometer Height? _______

13.0 Modeling Results

Compare results for each averaging period to applicable de minimis values, standards, guidelines, reference

air concentrations, risk-specific doses, or risk-specific dose ratios____.

For PSD, use Appendix G of the modeling guidelines format _____

For Effects Review, separate results for sensitive receptors______

13.1 Additional Impacts Analysis (For PSD)

Additional impacts analysis for growth, and soils and vegetation, as applicable____
E-5

13.2 Class I Area Impacts Analysis (For PSD)

Class I area impacts analysis, as applicable_____

13.3 Dilution Factor (For RCRA BIF)

Dilution factor for each constituent for this project_____

14.0 Modeling Runs and Hard Copy Output

Output per constituent showing emission point numbers, locations, base elevation, and stack

parameters_______ 

Table of selected model options and any selected data such as meteorological stations and period of record,

roughness heights, scalars _____

Gridded maps showing the maximum predicted ground-level concentration for each modeled receptor for

each type of analysis required_____

Property lines on each map ____ For PSD, fence lines on each map_____

For Effects Review, gridded maps for each constituent's concentration that exceeds an ESL___

Exceedances and magnitude of exceedance at each receptor____ Property lines on each map______

15.0 Disks (Model Input/Output and Associated Computer or Electronic Files) Provide:

All input and output files for each dispersion model run, including data, grid and plot file____

All files produced by a software entry program_____

All automated downwash program input and output files and any computer assisted drawing files ____

All meteorological data files in ASCII format_____

Boundary files—including computer assisted drawing files—specifying coordinates for property lines_____

For PSD, boundary files—including computer assisted drawing files—specifying coordinates for fence

lines_____

All spreadsheet files used for comparison of predicted concentrations with standards or guidelines______

(This includes spreadsheet files used for ratio techniques.)

16.0 Meeting Record

Date:

Participants / Affiliation / Telephone #s: 

17.0 Remarks

18.0 TNRCC ADMT Staff Signature

________________________________________________________

Date:

F-1

Appendix F

Air Quality Analysis Reporting Guidance

The air quality analysis submitted to the TNRCC in support of a state, PSD, or RCRA BIF permit

application becomes an addendum to the permit application. The analysis should include the items

in Table F-1 as appropriate. Items apply to all analyses unless otherwise noted. Items should not

be excluded without prior coordination with the ADMT. 

Send the original copy of the air quality analysis report to the permit engineer that requested the

modeling. The engineer will review the report and determine if an evaluation by ADMT is needed.

Table F-1. Air Quality Analysis Reporting Guidance

1.0 Project Identification Information

Provide the following information to clearly identify the analysis:

Applicant

Facility

Permit Application Number

Air Quality Account Number

Nearest City and County 

Applicant's Modeler

2.0 Project Overview

Include a brief discussion of the plant process(es), and types and locations of emissions under consideration.

For RCRA BIF, include a brief discussion of each BIF unit and the nature of wastes being generated or

burned.

2.1 Type of Permit Review

Indicate the type of permit review required by the permit engineer. 

2.2 Constituents Evaluated

List all constituents that were evaluated.

3.0 Plot Plan

Depending on the scope of the project, several plot plans may be needed to present all requested information.

Include a plot plan that includes:

A clearly marked scale.

All property lines. For PSD, include fence lines.

A true-north arrow.

UTM coordinates along the vertical and horizontal borders. Please do not use plant or other coordinates.

Include the datum of your coordinates.
F-2

Reference UTM coordinates and locations of all emission points including fugitive sources modeled.

Labels and coordinates given emission points on the plot plan should correlate with the information contained

in the air quality analysis.

Buildings and structures on-property or off-property which could cause downwash. Include length, width, and

height.

4.0 Area Map

4.1 For State Analyses

Include a copy of the area map submitted with the permit application. If the map is an extract, it should be

full scale (no reduction or enlargement) and cover the area within a 1.9-mile (3-kilometer) radius of the

facility if used for the Auer land-use analysis.

Add UTMs to the horizontal and vertical dimensions of the map section, as well as the date and title of the

map. Include the datum of your coordinates.

Annotate schools within 3,000 feet of the sources nearest to the property line.

For Effects Review, annotate the nearest sensitive receptor of any type and nearest residents. Include any

additional sensitive receptors required by TARA. 

For hazardous waste landfill or land treatment facility permits, or an areal expansion of an existing

facility. Also annotate locations of established churches, day care centers, surface water body used for a

public drinking water supply, or dedicated public parks. If any of these locations are within 1000 feet of the

facility or expansion boundary, no permit should be issued.

For commercial hazardous waste management facility permits, or an areal expansion of an existing

facility or unit of the facility. Also annotate locations of established churches, day care centers, surface

water body used for a public drinking water supply, or dedicated public parks. If any of these are within 2640

feet of the facility or expansion boundary, no permit should be issued. For amendments, distance limits apply

as of the date of the original permit.

4.2 For PSD Analyses

Include a copy of the area map submitted with the permit application. If the map is an extract, it should be

full scale (no reduction or enlargement) and cover the area within a 1.9-mile (3-kilometer) radius of the

facility if used for the Auer land-use analysis.

Add UTMs to the horizontal and vertical dimensions of the map section, as well as the date and title of the

map. Include the datum of your coordinates.

Include maps that show the location of:

PSD Class I areas within 10 kilometers (km) (6.2 miles) or 100 km (62 km).

Urban areas, nonattainment areas, and topographic features within 50 km (31 miles) or the distance to which

the source has a significant impact, whichever is less.

All NAAQS and increment consuming sources within 50 km which have a significant impact within the AOI

if exceedances of a NAAQS or increment are predicted.

Any on-site or local meteorological stations, both surface and upper air.

State/local/on-site ambient air monitoring sites used for background concentrations within 50 km (31 miles)

or the distance to which the sources have a significant impact, whichever is less.

4.3 For RCRA BIF Analyses
F-3

Include a copy of the area map submitted with the permit application. If the map is an extract, it should be

full scale (no reduction or enlargement) and cover the area within a 1.9-mile (3-kilometer) radius of the

facility if used for the Auer land-use analysis.

Add UTMs to the horizontal and vertical dimensions of the map section, as well as the date and title of the

map. Include the datum of your coordinates.

Annotate the location of any on-property residence.

5.0 Air Quality Monitoring Data

For State NAAQS and PSD

Discuss how ambient background concentrations were obtained. That is, preconstruction monitoring or from

a state/local/on-site monitoring network.

Include a summary of observations for each constituent and averaging time, if available. 

If all nearby and background point sources were modeled how was double-counting of monitored background

values addressed, if applicable?

For Effects Review, identify monitored data that was used to supplement or substitute for modeling.

Demonstrate that the data represent near worst-case operational and meteorological conditions.

6.0 Modeling Emissions Inventory

6.1 On-Property Sources to be Permitted

Include a copy of the Table 1(a) that was submitted with the permit application and subsequently approved

by the permit engineer. Ensure additional entries are provided on the Table 1(a) if stack parameters for any

averaging period or load level could be different.

Identify special source types or characterizations such as covered stacks, horizontal exhausts, fugitive sources,

area sources, open pit sources, volume sources, roads, stockpiles, and flares. 

Include all assumptions and calculations used to determine as appropriate the size, sides, rotation angles,

heights of release, initial dispersion coefficients, effective stack diameter, gross heat release and weighted (by

volume) average molecular weight of the mixture being burned.

Specify particulate emissions as a function of particle size; mass fraction for each particle size category; and

particle density for each particle size category, as applicable. 

In addition, it would be helpful to have a table with stack parameters converted to metric units.

6.2 Other On-Property and Off-Property Sources

Include a paper copy of the PSDB retrieval for each constituent. 

Include an additional list for each constituent for any sources modeled but were not included in the PSDB

retrieval. This list should contain all the information required by the Table 1(a). 

For PSD, include a list of secondary emissions, if applicable. Secondary emissions occur from any facility

that is not a part of the facility being reviewed, that would only be constructed or would have an increase of

emissions as a result of the permitted project.

6.3 Table Correlating the Emission Inventory Source Name and EPN with the Source Number in the

Modeling Output

Include a table that cross-references the source identification numbers used in the modeling if they are

different from the emission point numbers in the Table 1(a) or from any additional list of sources.
F-4

6.4 Stack Parameter Justification

Include the basis for using the listed stack parameters (flow rates, temperatures, stack heights, velocities).

This should include the calculations used to determine the parameters.

If the production or load levels could be less than 100 percent, demonstrate how the modeled emission rates

and stack parameters were obtained to produce the worst-case impacts (in certain cases lower production

levels may result in higher predicted impacts).

Include at least 25 percent, 50 percent, 75 percent and 100 percent production or load levels analyses, if the

source could be operated at these reduced levels.

6.5 Scaling Factors

Discuss how emission scalars were developed and used in the modeling demonstration. In addition, identify

those scalars that should be included in an enforceable permit provision, such as restricted hours of operation.

7.0 Models Proposed and Modeling Techniques

Include a detailed discussion of the models that were used, model version numbers, and the model entry data

options such as the regulatory default option and the period option.

Discuss any specialized modeling techniques such as screening, collocating sources, and ratioing. 

Include assumptions and sample calculations.

8.0 Selection of Dispersion Option

Submit an Auer land-use analysis for the area within 3 km of the sources being permitted. Base the selection

of urban or rural dispersion coefficients on the Auer land-use analysis; however, the population density

method could also be used but is not a preferred method.

Include a color copy of the USGS map, if a USGS map was used in the analysis.

Supplement the topographic map analysis with a current aerial photograph of the area surrounding the

permitted sources, or with a detailed drive-through summary, to support a land-use designation, that

represents less than 70 percent of the total area evaluated.

9.0 Building Wake Effects (Downwash)

Discuss how downwash structures were determined and Include applicable information required to use the

EPA's Building Profile Input Processor (BPIP). Submit all input files and files generated by the BPIP

program, and any computer assisted drawing files.

10.0 Receptor Grid—Terrain

Discuss if terrain was applicable. If so, discuss how terrain for individual receptors was determined.

Identify any discrete receptors used for locations of higher terrain.

If DEM files were used, discuss if the file contained 7.5-minute, 1-minute, or mixed data. If 7.5-minute DEM

data were not available for the entire receptor grid, was 7.5-minute DEM data used for receptors within

approximately 3–5 km of the property line/fence line? Include the datum of your coordinates.

11.0 Receptor Grid—Design

Discuss how the receptor grids were determined for each type of analysis. 

Include a diagram of each grid and include any reference labels or nomenclature.

Include the datum of your coordinates..

12.0 Meteorological Data

Indicate the surface station, surface station anemometer height, upper-air station, and period of record.

Include the meteorological data files used for all demonstrations if not obtained from the TNRCC. 
F-5

Discuss how meteorological data was determined or replaced. Include ADMT approval of replacement data.

In addition, submit all the supplementary data used to develop the specific input meteorological parameters

required by the PCRAMMET program.

13.0 Modeling Results

Summarize and compare the modeling results relative to all applicable de minimis values, standards,

guidelines, reference air concentrations, risk-specific doses or risk-specific dose ratios. Tabulated results are

preferred when several constituents are addressed.

For Effects Review, present the maximum concentrations predicted for sensitive receptors separately and

include the location of the receptor.

For PSD, present tables for each analysis similar to the examples in Appendix G of the modeling guidelines.

13.1 Additional Impacts Analysis (For PSD)

Include the results of the additional impacts analysis for growth, and soils and vegetation, as applicable.

13.2 Class I Area Impacts Analysis (For PSD)

Include the results of the Class I area impacts analysis, as applicable.

13.3 Dilution Factor (For RCRA BIF)

Include the dilution factor for each constituent and demonstrate how the dilution factor was calculated for this

project.

14.0 Modeling Runs and Hard Copy Output

Include model output for each constituent showing emission point numbers, locations, base elevation, and

stack parameters. These entries should correlate with the Table 1(a), PSDB retrieval, and any other list of

sources modeled. 

Include a table of selected model options and any selected data such as meteorological stations and period of

record, roughness heights, or scalars. The summary page produced by the model can be used, if appropriate.

Include gridded maps showing the maximum predicted ground-level concentration for each modeled receptor

for each type of analysis required. For large modeling projects, with numerous constituents, maps for all

receptor grids may not be required if the modeler can demonstrate with the grids submitted that the maximum

concentrations have been found.

In addition, if predicted concentrations from a tight grid are less than about 50 percent of a threshold of

concern, only a map depicting the receptor grid—without concentrations—is necessary. 

For complex projects, concentration isopleths may be used if the concentration gradient can be clearly shown

to decrease, the maximum concentration has been found, and no standard or ESL has been exceeded. A mix

of grid point maps and isopleth maps may be used as appropriate. 

Depict property lines on each map. For PSD, depict fence lines on each map.

Include gridded maps for each constituent's concentration that exceeds an ESL showing the number of

exceedances and magnitude of exceedance at each receptor. Show property lines on each map.

 15.0 Disks (Model Input/Output and Associated Computer or Electronic Files) Include:

All input and output files for each dispersion model run, including data, grid and plot files.

All files produced by a software entry program.

All automated downwash program input and output files and any computer assisted drawing files.

All meteorological data files in ASCII format. 
F-6

All boundary files—including computer assisted drawing files—specifying coordinates for property lines.

For PSD, all boundary files—including computer assisted drawing files—specifying coordinates for fence

lines.

Include all spreadsheet files used for comparison of predicted concentrations with standards or guidelines.

This includes, but is not limited to, spreadsheet files used for ratio techniques.

16.0 Permit Modeling Guidance Checklist

The permit modeling checklist is optional. However, if a checklist was prepared include it with the air quality

analysis.
G-1

Appendix G

PSD NAAQS and Increment Analyses Summary Sheets

Each PSD AOI, NAAQS, or Increment analysis should contain a summary table of modeled

results similar to those in Tables G-1, G-2, and G-3, that addresses the following elements:

Constituent. Include a separate summary for each constituent; however, the summaries may be

combined if appropriate. For example, for multiple constituents emitted from a single stack and a

ratio technique used to obtain a unit concentration.

Averaging Time, Standard or De minimis. Provide the applicable averaging time and standard

or de minimis.

Grid Size. Identify the grid size (tight, fine, medium, coarse) used to locate the maximum impact

for the year evaluated.

Date, Time, and Location. Include these data for the maximum concentration for each year

evaluated.

Radius of Impact. Include the radius for the analysis, if applicable, for each time period and year

evaluated.

Concentration Rank. Indicate the rank of the reported concentration, such as high, first high

(H1H), high, second high (H2H) as applicable. The H1H is the highest concentration at any

receptor; that is, the highest concentration at each receptor has been tabulated and the highest

concentration of all the first highest concentrations is reported as the H1H. The H2H is the

second highest concentration at any receptor; that is, the highest concentration at each receptor

has been tabulated, then the second highest concentrations at each receptor has been tabulated,

and the highest of any second highest concentration is reported as the H2H. 

The AOI and state analyses use the H1H concentrations. PSD NAAQS and increment analyses

use the H2H concentrations for short-term standards and the highest average concentration at any

receptor for any year for long-term standards, with the exception of PM . The ADMT will 10

provide additional guidance when EPA publishes technical procedures for the 1997 24-hour PM10

NAAQS.
G-2

! For the pre-1997 24-hour PM10 NAAQS. Use the H6H concentration at any receptor for a

five-year evaluation period.

! For the annual PM10 NAAQS. Use the highest five-year average concentration at any

receptor.

Note that for any demonstration a higher concentration rank may be used to compare with a

standard or guideline. That is, the H1H concentration could be used instead of the H2H

concentration, since the H1H concentration would be higher and thus more conservative.

Maximum Concentration. Identify the applicable predicted maximum concentration from any of

the years evaluated. For example, the H1H and H2H.

Background Concentration. Identify the background concentration for NAAQS analyses.

Total Concentration. Provide the total concentration; that is, predicted maximum concentration

plus applicable background concentration. 

Tables G-1, G-2, and G-3 are on the following three pages.
G-3

Table G-1. Area of Impact Analysis Summary

Constituent: Grid:

Date/Time, Location, Averaging Time _______ Averaging Time _______ Averaging Time _______

H1H (μg/m )

3

De Minimis_______μg/m De Minimis _______μg/m De Minimis _______μg/m 3 3 3

First Year/ Day/Hour 

Receptor UTM Easting

Receptor UTM Northing

H1H Concentration

Radius of Impact (m)

Second Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing 

H1H Concentration

Radius of Impact (m)

Third Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

H1H Concentration

Radius of Impact (m)

Fourth Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

H1H Concentration

Radius of Impact (m)

Fifth Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

H1H Concentration

Radius of Impact (m)

Maximum Concentration

Maximum Radius of Impact (m)
G-4

Table G-2. NAAQS Analysis Summary

Constituent: Grid:

Rank:

Date/Time, Location, Averaging Time _______

Concentration (μg/m )

3

Standard ________μg/m3

Averaging Time _______ Averaging Time _______

Standard ________μg/m Standard ________μg/m3 3

First Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Second Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Third Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Fourth Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Fifth Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Overall Maximum Concentration

Background Concentration

Total Maximum Concentration
G-5

Table G-3. Increment Analysis Summary

Constituent: Grid:

Rank: 

Date/Time, Location, 3-Hour 24-Hour Annual

Concentration (μg/m )

3

Increment ________μg/m Increment________μg/m Increment_________μg/ 3 3

m3

First Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Second Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Third Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Fourth Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Fifth Year/ Day/Hour

Receptor UTM Easting

Receptor UTM Northing

Maximum Concentration 

Overall Maximum Concentration

H-1

Appendix H

Point Source Data Base Retrievals

Request PSDB retrieval information from the Customer Reports & Services, Information

Resources (IR) Division at (512) 239-DATA(3282). Written requests are required to obtain a

retrieval, and may be sent by fax to (512) 239-0888. Provide the following impact area parameters

with your PSDB request:

Constituent. Identify the constituent using one of the following designators: CO, NOx, SO2, TSP

( total suspended particulate matter, designated at PM in the permit), PM (particulate matter 10

with an aerodynamic diameter of 10 microns or less), Pb, VOC, or the specific 5-digit contam

(contaminant) code for noncriteria constituents. Contact the Emissions Inventory staff to obtain

the contam codes.

Type. Indicate the type of request: NAAQS or PSD Increment. The term NAAQS refers to both

criteria and noncriteria constituents. Therefore, a retrieval for benzene, for example, would also

be identified as a NAAQS retrieval.

! PSD Increment retrievals are available for NO , SO , and PM . x 2 10

Term. Indicate the term of interest: Short (used to determine concentrations of 24 hours or less)

or Long (used to determine concentrations of greater than 24 hours).

Search Option. Indicate the search option for the radius of impact: Primary (for PSD) or

Secondary (for State). 

! The Primary radius search option provides a report that includes all emission points

located within the circle defined by the designated radius of impact. This option is used for

PSD permit modeling retrievals.

! The Secondary radius search option provides a report that includes all emission points

located within the circle defined by the designated radius of impact. In addition, it causes

the retrieval program to search for points out to 60 km beyond the primary radius and

factor emissions against distance to determine if the emission points have potential impact.

If the emissions are found to be significant, they are included in the report.
H-2

UTM Zone. Provide the zone that the center point of the radius of impact is located in for each

search option. The retrieval program will automatically take care of any overlap from one zone to

another. Use either 13 (from the west border to 102 degrees longitude), 14 (between 102 and 96

degrees longitude), or 15 (east of 96 degrees longitude to the east border). 

Center Point of the Radius of Impact. Use UTM coordinates in meters to identify the center

point of the radius of impact: UTM East (meters) and UTM North (meters).

Radius of Impact. Provide the length of the radius of impact in meters. The maximum length is

9,999,999 meters. There is no minimum length; however, a minimum length of 1,000 meters is

suggested. 

! For PSD modeling projects, add 50,000 meters to the modeled radius of impact and

provide the resultant value as the length. For example, if the modeled radius of impact is

1,000 meters, add 50,000 meters and request a retrieval for a radius of impact of 51,000

meters.

This information is used by the retrieval program to locate all sources for the given constituent

which are within the radius of impact or sources which could have a significant impact within the

radius of impact. For the requested constituent, the program generates a written report that

includes for each source: the source identification, the TNRCC permit number or the TNRCC

account number, source parameters needed for modeling, and the location of the source. IR staff

can provide a computer diskette with all sources—except area sources—found in the retrieval

with the modeling parameters placed in the proper format for use with certain EPA models. Enter

area source data manually into the model. 
I-1

Appendix I

Increment Minor Source Baseline Dates

The following table contains the minor source baseline dates for SO2 and PM 10. Use 02/08/88 as a

default for NO2. To determine the actual baseline date for NO 2, the applicant must identify the

first complete PSD application for the AQCR. ADMT can assist with the conversion of the

current TNRCC Region to the old Texas Air Control Board (TACB) Region.

 Table I-1. Minor Source Baseline Date For SO2, PM, and NO 2

TACB Region AQCR Constituent Baseline Date

1 210 SO2 08/04/78

PM10 05/16/80

2 211 SO2 11/04/77

PM10 11/04/77

3 212 SO2 10/17/77

PM10 10/17/77

4 213 SO2 03/17/80

PM10 03/17/80

5 214 SO2 03/30/78

PM10 03/30/78

6 218 SO2 08/04/78

PM10 07/17/80

7 216 SO2 08/03/78

PM10 08/03/78

8 215 SO2 11/17/77

PM10 11/17/77

9 217 SO2 11/30/77

PM10 11/30/77

10 106 SO2 11/03/77

PM10 11/03/77

11 153 SO2 07/25/80

PM10 07/25/80

12 022 SO2 09/12/77

PM10 09/12/77

J-1

Appendix J

Attainment/Nonattaiment Areas

The list in this appendix is for information only and is not official. That is, areas may be added or

deleted after the publication of this document. See 40 CFR Part 81 and pertinent Federal Register

notices for legal lists and boundaries.

Table J-1. List of Attainment/Unclassifiable and Nonattainment Counties by Constituent

Constituent MSA County Status (NAA or A/U)

Ozone (O3) Beaumont- Hardin NAA-Moderate

Port Arthur Jefferson (Proposed Serious)

Orange

Dallas-Fort Worth Collin NAA-Serious

Dallas 

Denton 

Tarrant

El Paso El Paso NAA-Serious

Houston-Galveston- Brazoria NAA-Severe-17

Brazoria Chambers

Fort Bend 

Galveston

Harris 

Liberty 

Montgomery 

Waller

All Others A/U

Particulate Matter (PM10) El Paso NAA-Moderate *

All Others A/U

Carbon Monoxide (CO) El Paso NAA-Moderate * 

All Others A/U

Sulfur Dioxide (SO2) All A/U

Nitrogen Dioxide (NO2) All A/U

Lead (Pb) Collin NAA * 

All Others A/U

* Only a portion of the county is designated nonattainment