GUIDELINE SERIES

OAQPS No. 1.2-035
            Office of Air and Waste Management
          Office of Air Quality Planning and Standards
         Research Triangle Park, North Carolina 27711

                              OAQPS No. 1.2-03S
         UNDER  ESECA
     Division of Stationary Source Enforcement
            Office of Enforcement
             Washington, D.C.

     Monitoring and Data Analysis Division and
      Strategies and Air Standards Division
    Office of Air Quality Planning and Standards
       Office of Air and Waste Management
      Research Triangle Park, N.C.  27711

              October 1975


                         TABLE OF CONTENTS
   I.  Introduction                                    1
  II.  Determination of Primary Standard Conditions    3
 III.  Data Base                   "                    3
  IV.  Estimating Source Impact                        5
   V.  Specification of PSC                            8
  VI.  Responsibility                                  8
 VII.  Monitoring Requirements                         9
VIII.  Modifications of PSC                           10
 Appendix A—Data Requirements
   I.  Source Data                                   A-l
  II.  Meteorological Data                           A-4
 III.  Air Quality Data                              A-6
 Appendix B--Atmospheric Simulation Models
   I.  Introduction                                  B-l
  II.  Critical  Dispersion Conditions                B-2
 III.  Special  Situations                            B-3
  IV.  Computerized Simulation Models                B-5
 Appendix C—Supplementary Control
 Systems as a Primary Standard
   I.  Background                                    C-2
  II.  Requirements for a Reliable                   C-2
       and Enforceable SCS
 III.  Follow-up                                     C-8
 References                                          D-l

I.  Introduction
     The purpose of this guideline is to provide the EPA Regional Offices
with information relevant to the determination of Primary Standard Conditions
(PSC).  Primary standard conditions are specified by EPA for the control
of Emissions from sources granted compliance date extensions (CDE) in
accordance with the provisions of the Energy Supply and Environmental
Coordination Act of 1974 (ESECA).  Primary standard conditions may be
expressed as:  emission limitations; requirements respecting pollution
characteristics of coal; or other enforceable measures (which may include
supplementary control systems (SCS)).  ESECA authorizes EPA to grant
compliance date extensions that temporarily suspend applicable fuel or
emission limitations to eligible sources (See 40 CFR Part 551) prohibited
by the Federal Energy Administration from burning natural gas or oil as
a primary fuel.
     ESECA requires EPA to prescribe PSC for each source granted a CDE.
The PSC must apply to the pollutant(s) to which the CDE applies and must
ensure that, during the period of the CDE, the burning of coal by such a
source will not result in emissions which cause or contribute to pollu-
tant concentrations which exceed national primary ambient air quality
standards (NPAAQS).  EPA must certify to FEA the earliest date by which
the source can comply with the PSC, and the effective date of FEA's
prohibition order cannot precede the EPA certified date.
     The conference committee report for ESECA provides insight into
Congressional intent pertinent to compliance date extensions and primary
standard conditions.  In discussing air pollution control requirements,
the report reads,


               "The committee believes that the priority
          effort of each source which is subject to Section 119(c)
          should be to obtain low sulfur coal.   If an adequate,
          long-term supply of low sulfur coal  is available to
          such a source, the Administrator should only approve
          a plan which requires its use (and thus compliance with
          air pollution requirements) as expeditiously as prac-
          ticable.  In such a case, the Administrator would have
          to disapprove a plan which proposed  to wait until
          January 1, 1979 before beginning to  burn low sulfur
          coal.  The committee believes that requiring priority
          consideration to the use of nonmetallurgical low sulfur
          coal will reduce the likelihood of extended violation
          of applicable emission standards."

     The determination of primary standard conditions requires the

application of an atmospheric dispersion model  to quantify the effect on

ambient air quality of the conversion from gas  or oil to coal.  This, in

turn, requires the collection and organization  of considerable information

on the source.  A source ordered to convert is  required by 40 CFR Part

55 to provide appropriate information to EPA and is permitted to propose

its own primary standard conditions.

     Sulfur oxides and particulate matter are  the pollutants of primary

concern.  While nitrogen dioxide should not be  excluded from considera-

tion, the effects of conversion on ambient concentrations should be

relatively minor because few areas are experiencing excessive concen-

trations and the NPAAQS is an annual average.   Concentrations of the

other criteria pollutants (carbon monoxide, hydrocarbons, and photo-

chemical oxidants) are not significantly affected by conversions of

combustion sources from gas or oil to coal.

     II.  Determination of Primary Standard Conditions
     A PSC should be determined in several steps which include:
     1.   establishing a data base;
     2.   selecting and applying dispersion models;
     3.   determining the degree of emission control  that will  ensure
          that NPAAQS are not exceeded; and
     4.   specifying the regulatory form of the PSC most appropriate to
          the particular power plant.
The first three of these steps are described in detail in this  guideline.
The fourth, guidance in determining the regulatory form of the  PSC, is
available from the Division of Stationary Source Enforcement, Office of
Enforcement, Washington, D. C.
     III. Data Base
     The first step toward determining the PSC is data acquisition.
Meteorological, air quality, and source data from the latest available
four quarters should be used as the data base year.  In addition, infor-
mation about present and future sources in the area around the  converting
plant should be included in the data base.  Appendix A outlines the
specific data needs.
     Experience indicates that major power plants acting either alone or
in conjunction with other sources may have a significant impact on
ground level pollutant concentrations outward to a distance of  20 kilometers.
Therefore, to account for other major sources which may affect  portions
of the same area, it is necessary to examine sources within 40  kilometers
of the converting plant.

     This distance is a recommendation which may be appropriately altered
since the area in which a source has a significant impact varies with source
configuration and emissions, the impact of emissions from other sources,
increases in emissions due to growth, and the topography and
meteorology of the area.
     All sources within 40 kilometers of the plant (including any non-
converting units at the source) should be included in this base year
inventory.  Source data should be estimated for the years, during which
the compliance date extension is effective, when pollutant emissions
from plants in the surrounding area are expected to have the greatest
impact on air quality.  Such data should include expected changes in
patterns of fuel use and fuel quality (percent sulfur, percent ash, heat
content, etc.), and planned modifications or expansions of existing and
projected new sources in the area.
     All air quality data in the vicinity of the source for the base
year, and other recent years of available data, should be obtained.
These data are required to ascertain existing air quality and
trends, the contribution from other sources in the area, and the natural
background levels.  If these data do not exist, estimates should be
obtained by modeling.
     Meteorological data for the base year and/or data representative of
anticipated critical dispersion conditions should be identified and
obtained.  These data should be used with source data in a dispersion
model to estimate 24-hour and annual pollutant concentrations for the

year of greatest projected emissions in the areas of the converting
     IV.  Estimating Source Impact
     Emphasis should be placed on the 24-hour analysis since a large
power plant usually presents a greater threat to short-term NPAAQS than  to
long-term standards.  Further, due to the complex interaction of
source parameters, meteorological conditions and terrain configurations,
high short-term concentrations may occur with a variety of situations
and at a variety of locations.  For this reason, it is important to use
a dispersion modeling procedure which takes into account variations in
the source, receptor, meteorology, and terrain.
     Some of the factors which should be considered are the following:
     1.   source—present emissions under various load conditions,
          including maximum load from individual converting units;
     2.   receptor—a wide range of locations in the area should be
          considered since the most stringent emission limitation may be
          derived from a receptor location where a relatively small
          contribution from the converting source would cause NPAAQS to
          be endangered;
     3.   meteorology—at least the critical dispersion conditions
          Appendix B; and,
     4.   terrain—local features which may effect dispersion.
In most cases, a computerized dispersion model  will probably be necessary
to adequately consider all of these factors.

     Finally, to determine the total concentration due to all  sources,
an estimate must be made of the level of contributions from other sources
in the area, including non-converting units at the power plant.   The PSC
should be determined with a consideration of area growth and expansion
of existing facilities based on new source review information or an
appropriate index of industrial growth.   Depending on the number of
other sources and their nature, additional point and/or multi-source
modeling may be necessary to estimate their impact.   At the least,
a careful estimate of the air quality impact of all  sources in the area
should be made based on knowledge of emissions, measured air quality data,
and consideration of meteorological conditions.
     Dispersion model estimates of source impact on  an annual  basis do
not require as detailed a procedure as that for the  24-hour estimates.
However, there are similar information requirements  for average source
and growth data, consideration of meteorological and topographic para-
meters and use of appropriate simulation models.
     With data on the air quality impact of individual power plant units
and the combined air quality impact of projected emissions from all
other sources in the area, the maximum allowable contribution from
converting units at the power plant that would assure compliance with
all NPAAQS can be estimated.  From this estimate, the allowable pollu-
tant emissions from the converting units at the plant can be determined.
To make this determination, the total estimated impact of (1) the maxi-
mum projected emissions from all other sources in the area, and (2)

natural background is subtracted from the applicable NPAAQS.  The remainder
is the contribution that the converted units may make to pollutant con-
centration.  The ratio of this remainder to the estimated contribution
from the converting units (before conversion to coal) is the change in
concentration impact which may be allowed for the converting units.  If
this ratio is greater than one, pollutant emissions from the convertino
units can be proportionately increased by conversion to coal
(see example below).   If the ratio is less than one, pollutant emissions
from converting units must be proportionately decreased for any conver-
sion to coal.
     If it is determined that a PSC should be more stringent than the
existing SIP and the power plant is not eligible for SCS, the Office of
Enforcement should be notified and procedures initiated for a revision
of the SIP.  These cases will then be handled on an individual  basis.
An amendment to ESECA has been proposed which would require the source
to meet the revised SIP as soon as practicable but no later than December
31, 1978.
     Example:  The estimated 24-hour impact from all other sources
(including background and non-converting units) is determined to be 165
yg/m3 of 502-  The allowable contribution is then,
     365 yg/m3 - 165  yg/m3 = 200 yg/m3.
If the current maximum impact of oil-fired units to be converted is
estimated from modeling to be 100 yg/m3, and the present emission rate
is four tons  S02/hour, the allowable emission after conversion  is
     200 yg/m3
     100 yg/m3
                X 4 ton/hour = 8 ton/hour

     It should be noted that a switch in fuel type could result in a
change in stack gas characteristics, e.g., volume flow rate or tempera-
ture, so that the distance to and magnitude of the maximum concentration
could be different from that indicated above.  Thus, to be certain that
the calculated emission rate is sufficiently stringent to avoid any
violations of NPAAQS, the model should be rerun using the estimated
allowable emission while burning coal.  If a violation is predicted, the
allowable emissions should be lowered and the calculation repeated.  By
this iterative technique, the appropriate emission rate can be deter-
     V.  Specification of PSC
     As mentioned in the introduction, a PSC may be specified in the
form of an emission limitation, requirements respecting the pollution
characteristics of the coal, or other enforceable measures, including
an SCS.  Guidance in determining the form of the PSC most appropriate to
a particular power plant is available from the Division of Stationary
Source Enforcement, Office of Enforcement, Washington, D. C.
     VI.   Responsibility
     ESECA requires the Administrator of the EPA to prescribe a PSC
after consultation with the state in which the source is located.
However,  the EPA Regional Offices (RO) will be primarily responsible for
specifying the PSC for a given plant.  Technical assistance will be
provided by the Office of Air Quality Planning and Standards (OAQPS),
Research Triangle Park, N. C., if desired.  At its discretion, the RO
may consider an analysis report submitted by a state agency or by the
source; however, in such cases the RO is responsible for judging the
acceptability of the analysis.

     In the case of a power plant which could potentially cause con-

travention of a NPAAQS in a state other than the one in which it is

located, all affected states and RO's should be involved in

determining the PSC.  However, the RO responsible for the area in which

the power plant is located is responsible for the final determination.

     VII.  Monitoring Requirements

     ESECA requires that EPA publish a summary in the Federal Register

semi-annually on the status of compliance by the source with the pre-

scribed PSC.  To ensure that PSC are met and that NPAAQS are adequately

protected during the period of compliance extension, monitoring is

required.  This includes monitoring of emissions, meteorological con-

ditions, and air quality.  Guidance for air quality monitoring to meet

the requirements of ESECA will be provided in Guidelines for Air Quality

Monitoring and Data Report for Sources under ESECA which is being prepared


     An SCS requires considerably more monitoring than an emission or

fuel limitation.  The special needs of this type of PSC are discussed in

Appendix C.

     Meteorological data should be collected which adequately describes

transport and dispersion in the vicinity of the source.  If such data

are not being collected, the source should be required to acquire such

data.   As a minimum, this should include data on wind direction and

speed,  and atmospheric stability that are representative of meteoro-

logical conditions.  Sufficient data concerning the impact of weather

conditions should also be available to analyze trends of air quality in
the area.
     Emission monitoring is also required of the source to insure that
PSC are being met.  This includes a routine survey of emissions both at
the source meeting PSC and at other sources in the area.  To ensure that
a PSC emission limit is met, it is recommended that continuous in-stack
monitoring be required of the converting source.  Where continuous in-
stack monitoring is not employed and there is a limit on the pollutant
content of the fuel, a method of sampling and analyzing the coal  should
be specified in the PSC.  It is strongly recommended that such sampling
and analysis be required on a 24-hour basis so that the quality of the
fuel burned in any 24-hour period can be ascertained.  In either case
monitored emissions and/or data on the pollutant content of the fuel
should be routinely reported to the Regional  Office.
     Monitoring of growth and expansion in the area, and of associated
increases in pollutant emissions is also necessary.  If unforeseen/uncon-
trollable growth or expansion occurs near a plant meeting the require-
ments of a PSC, it may be necessary to modify the PSC to ensure that
NPAAQS will not be exceeded.
     VIII.  Modifications of PSC
     All data collected and associated with PSC must be reviewed semi-
annually.  If a PSC is being met, no action is required.  If air quality
standards are exceeded, the violations must be reviewed and the cause

determined.  Such causes might include adverse meteorological conditions
which were not considered in the development of the PSC, increased
emissions from other sources in the area, failure of the source to meet
the PSC due to faulty or inadequate control systems or variability of
fuel quality.  The likelihood of the cause continuing or recurring must
be determined and appropriate changes in the PSC should then be made or,
if appropriate, more aggressive enforcement of an existing PSC under-
     Modifications of PSC should follow an orderly sequence.  The PSC
may need to be modified because of monitored air quality violations,
because control equipment used by the source is less efficient than
predicted, or because emissions from new sources exceed anticipated
levels.  It should be noted that states may petition the Administrator
for a modification of the PSC.  The source impact is then reanalyzed and
appropriate changes in PSC are determined.  After consultation with
appropriate state agencies and public hearings, the Administrator can
issue a new PSC and certify the earliest date that the source can meet
the new PSC.

                      Appendix A--Data Requirements
     Determination of the primary standard  condition  (PSC)  should  rely
on dispersion model procedures requiring specific, accurate data.   The
degree of detail  required of the data is determined by the  use  to  be
made of it, and time and resources available for  obtaining  the  data and
for the modeling.   In general, the source,  meteorological,  and  air
quality data required for dispersion modeling procedures  are listed
below.  The use of the data is described in Appendix  B and  the  references
cited in Appendix  B.
     I.  Source Data
     Data on design characteristics of the  source and operating levels
should be obtained for the following:
     1.   Plant layout—the connection scheme between boilers,  genera-
          tors, and stacks, and the distance and  direction  between
          stacks,  building parameters (length,  width, height, location
          and orientation relative to stacks) for plant structures which
          house boilers, control  equipment, etc.;
     2.   Stack parameters—for all  stacks, the stack height and diameter
          (in meters), and the temperature  (in  °K) and volume flow rate
          (in actual  cubic meters per second) or  exit gas velocity
          (meters  per second)  for operation at  100%,  75%, and 50%  load;
     3.   Boiler  size—for all boilers,  the associated megawatts and
          pounds  of steam per  hour,  and  the design and/or actual fuel
          consumption rate for 100 percent  load for coal  (tons/hr), oil
          (barrels/hr), and natural  gas  (thousand cubic feet/hr);

     4.   Boiler parameters—for all  boilers,  the  percent  excess air
          used, the boiler type (e.g.,  wet  bottom,  cyclone, etc.), and
          the type of firing (e.g.,  pulverized coal,  front firing,
     5.   Operating conditions—for  all  boilers, the  type  and amounts of
          fuel used for each month of the latest year for  which data are
          available, the total  hours  of boiler operation and the boiler
          capacity factor during the  year,  and the percent load for
          winter and summer peaks;
     6.   Pollution control equipment parameters—for each boiler  served
          and each pollutant affected,  the  type of emission control
          equipment, the year of its  installation,  its design efficiency
          and mass emission rate, the date  of  the  last test and the
          tested efficiency, the number of  hours of operation during the
          latest year, and the best  engineering estimate of its projected
          efficiency if used in conjunction with coal  combustion;  data
          for any anticipated modifications or additions;
     7.   Data for new boilers or stacks—for  all  new boilers and  stacks
          under construction and for  all planned modifications to  exist-
          ing boilers or stacks, the  scheduled date of completion, and
          the data or best estimates  available for items  1 through 6
          above following completion  of construction  or modification.
                                                          2 3
Sources for these data include the Federal  Power Commission  '  , National
Coal Association , OAQPS/Energy Strategies  Branch, and individual  contacts
with the power plants.

     Information on the location of the plant and the nearby topographic
features should be obtained in either latitude-longitude or Universal
Transverse Mercator (DIM) system coordinates.  Such features include:
     1.   Stacks
     2.   Significant terrain features, including valleys, hills and
         other elevated terrain features, major bodies of water, other
         large structures, etc., within 20 kilometers of the plant.
For ease of analysis, the location of the plant should be indicated on a
U.S. Geological Survey (USGS) topographic map of appropriate scale.
     It is recommended that all point and area sources within 40 kilometers
of the power plant be examined to determine their additive impact on air
quality.  (Experience has indicated that major sources may have an
impact on ground level pollution concentrations outward to a distance of
20 kilometers.  To account for other point and area sources which may
affect the same geographical area, it may be necessary to examine sources
within 40 kilometers of the converting plant.)  While this distance is a
useful rule of thumb, the actual area of significant impact will vary
with power plant configuration and emissions, the impact of emissions
from other sources, increases in emissions due to growth, and the topo-
graphy and meteorology of the area.  Locations of the major point and
area sources (in either latitude-longitude or UTM system coordinates)
should also be plotted.
     Data on the operating and design parameters of these sources and
their emission rates should be documented in the standard format estab-

lished for EPA's National  Emissions Data System (NEDS)  to facilitate
updating of this file.   Data already in NEDS should be  reviewed for
accuracy.  Sources of new or increased emissions resulting from area
growth or the expansion of existing facilities should also be identi-
fied.  Information on their projected operations and expected emissions
should be gathered into a format compatible with the model to be used.
     II.  Meteorological Data
     In the specification of PSC for particular plants  it is essential
that consideration be given to the meteorological parameters involved in
atmospheric dispersion.  The principal variables of concern are wind and
temperature.   An analysis of the wind field is necessary to determine
the area over which a plant's emissions have significant impact on
ground level  concentration and the probable direction(s) of the impact.
An analysis of the vertical temperature profile yields  information
regarding the presence of temperature inversions.  This information is
required to determine the horizontal and vertical dilution of pollutants
as they are transported by the wind.  Data on these variables can be
translated into stability, mixing height, ventilation,  and wind direc-
tion-speed relationships, which are commonly used in estimating the
transport and dispersion of pollutants.
     The level of detail required in these analyses is  largely dependent
on the complexity of the terrain in the vicinity of the plant in
question.  Unevenness of terrain often results in distortions of the
thermal and wind structure of the lower atmosphere.

     Before undertaking a massive local meteorological  data-gathering
program, sources of existing data such as nearby National  Weather Service
Offices, military installations, and universities should be investigated.
The surface data required (temperature, wind speed, and wind direction)
are among those routinely taken at any weather observation facility.
The required upper air data are regularly recorded at some 62 National
Weather Service sites across the country.  Summaries of existing data
are available in various formats from the National Climatic Center at
Asheville, North Carolina.
     The critical meteorological conditions conducive to high ground
level pollutant impact vary from plant to plant as a function of variables
such as stack height.  Even for a specified plant such critical  meteoro-
logical conditions may vary with the plant's mode of operation,  inasmuch
as the stack gas parameters are affected.
     Before an adequate dispersion model analysis can be conducted,
judgments should be made concerning:
     1.   The degree of detail  needed in the meteorological data base;
     2.   The extent to which necessary data are already available;
     3.   The necessity of conducting a measurement program to obtain
          additional data.  Such a program could vary from the simple
          surface observation of wind and temperature,  to the measure-
          ment of these variables aloft using quick-response instrumen-
          tation mounted on trackable balloons and/or aircraft.

Once the data base is assembled, the following steps are necessary:

     1.   Place the data in a form amenable to dispersion work;  develop

          stability-wind joint frequencies, average mixing-heights for

          certain times of the day and year, hourly variations in meteoro-

          logical conditions, and critical  meteorological conditions

          with regard to wind, stability and mixing;

     2.   Perform preliminary estimations of plant-impact and choose an

          appropriate simulation model for more detailed analysis as


     3.   Tailor the meteorological data as required in order to render

          it usable in the chosen model.

     III.  Air Quality Data

     Air quality monitoring data is needed to estimate either the natural

background of a pollutant or the contributions from other sources in the

area to ground level concentrations.  These steps should be taken:

     1.   Identify all air pollution monitoring sites which may provide

          information about the air quality in the vicinity of the

          source.  Monitors operated by EPA, state and local pollution

          control agencies, universities, or industry may be included.

          Monitoring site locations should be specified by either lati-

          tude-longitude or Universal Transverse Mercator (UTM)  system


     2.   Gather all available data from the identified monitors in a

          format compatible with EPA's Storage and Retrieval of Aerometric

          Data (SAROAD) system.

     3.   The available air quality data for the pollutants of concern
          should be examined with two goals in mind: (1) to determine
          the natural background, if any, or the background from distant
          sources, and (2) to determine the impact of all other sources
          in the area.  A monitor isolated from the influence of local
          sources of the pollutant could provide information on ambient
          background concentrations.  If no such monitor exists, an
          estimate must be made using the best knowledge of possible
          natural sources, measured air quality and emission sources
          from neighboring AQCR's, and meteorological information on the
          prevailing wind direction, etc.
     Determination of possible contributions to ambient concentrations
from sources other than the power plant will require careful examination
of air quality data and nearby source data.  If sufficient data are not
available, or if a complex interaction of many sources exists, appropriate
multi-source atmospheric simulation models ' '  may be employed to
assist in estimating air quality .
     If little or no air quality data are available for estimating
background and impact from other sources, the simulation models alone
may be used to estimate air quality.  However, future monitoring should
be required.  Such new monitors should be located in areas where the
modeling indicates the highest total concentrations and highest contri-
butions from the power plant in question might be expected to occur.

                Appendix B--Atmospheric Simulation Models
     I.  Introduction
     A key element in the determination of primary standard conditions
is an adequate methodology for relating pollutant emissions to ambient
air quality.  The most commonly used tool for relating emissions and air
quality is an atmospheric simulation or dispersion model.
     An atmospheric simulation model is a mathematical description of
the transport, dispersion and transformation processes that occur in
the atmosphere.  In its simplest form, such a model relates pollutant
concentrations (x) to pollutant emissions rates (Q) and a background
concentration (b),
     x = kQ + b.
The constant k is a function of atmospheric conditions and the spatial
relationship between source and receptor.  Atmospheric simulation models
are ultimately concerned with the variabilities of k and Q and their
impacts on pollutant concentrations.
     Simulation models esti .ate concentrations only for pollutants which
have identified sources, the emissions from which are inputs to the
models.  If pollutants occur naturally in the atmosphere or are the
result of unidentified distant pollutant sources, these pollutant con-
centrations must be accounted for and separately added to the dispersion
model estimates in order to approximate total ambient concentrations.
For example, it is commonly assumed that the natural background concen-
tration of total suspended particulate matter is 30-40 pg/m  over much
of the Eastern United States.10

     II.  Critical Dispersion Conditions

     Dispersion models should be used to simulate meteorological  condi-

tions conducive to high ground level  pollutant concentrations.   Generally,

the highest pollutant concentrations  from point sources with stacks are

experienced with one of four critical dispersion conditions: looping,

inversion breakup fumigation, high wind coning, or limited mixing.   The

looping and fumigation conditions are transient phenomena which generally

do not occur for periods long enough  to endanger a 24-hour standard.

                                              ll            12
However, as has been shown by Carpenter et.al.  , and Pooler  , high

concentrations may occur with high-wind coning and limited mixing conditions,

Because of the persistence of these meteorological conditions,  the 24-hour

standard may be endangered.

     The principal characteristics of two dispersion conditions,  which

may cause point sources to pose a threat to ground-level air quality,


     1.   High-Wind Coning.   High-wind goning occurs with neutral sta-
          bility conditions  (See Turner }; these conditions are gener-
          ally associated with cloudy, windy weather.  The effluent
          plume is shaped like a cone, with its axis roughly parallel to
          the ground,  The maximum ground-level concentration is  a
          function of the wind speed  and the source characteristics
          (stack height, gas volume,  gas temperature).   The wind speed
          strongly influences the plume rise, i.e., the height  above the
          stack at which the plume bends from the vertical toward the
          parallel  position mentioned above, which in turn influences
          the maximum ground level concentration and the distance from
          the stack at which this concentration will occur.

     2.   Limited Mixing.  Limited mixing or trapping occurs when the
          upward dispersion  of the plume is inhibited by a stable or
          inversion layer aloft and the plume is mixed uniformly between
          the ground and the stable layer.  Maximum concentrations are
          accompanied by light winds  and occur from 5-10 kilometers from
          the source.  The maximum concentration is primarily determined
          by the elevation and intensity of the stable layer aloft;
          stack height has a minor influence.

Reasonable rules-of-thumb are (1) the high-wind coning condition causes
highest ground-level concentrations from sources with relatively
short stacks (500 feet or less) and (2) the limited mixing situation
causes greatest ground-level concentrations from sources with tall
stacks (greater than 500 feet).  Mathematical models which simulate
these critical dispersion conditions are available from Turner  and
Volume 10 to Guidelines for Air Quality Maintenance Planning and Analysis .
It is suggested that the set of plume rise equations given by Briggs
be used in any dispersion estimates.
     Most dispersion models provide estimates of 1-hour average concen-
trations.  To estimate 24-hour concentrations from 1-hour concentrations
it is suggested that a 4:1 ratio of the l-to-24-hour concentrations be
assumed.  This accounts for the daily variability of weather conditions
by implicitly assuming that the wind direction prevails in one direction
for 6 of the 24 hours during the day on which the critical condition
occurs.  The suggested ratio of 4:1 is supported by substantial data
collected around power plants in the States of Kentucky   , Massachu-
setts   and Ohio  .   Wherever observed data are available, location-
specific estimates of the l-to-24-hour concentration ratios should be
     III.  Special Situations
     In addition to the critical dispersion conditions noted above,
special situations such as aerodynamic downwash of the plume and plume
impaction on prominent terrain features can cause high pollutant concen-
     In the case of emissions released from a short stack, e.g., one
which is less than 2 1/2 times the height of an adjacent building,

emissions can become trapped under some wind conditions in the turbulent
cavity immediately downwind of the adjacent building.   In this case, the
maximum concentration can be estimated by the use of simple volume
approximation  .   While such downwash is generally a short-lived phe-
nomenon, sources subject to downwash which encounter periods of per-
sistent high winds may cause substantial 24-hour pollutant concentra-
tions.  In such cases, downwash should be considered the critical con-
     If rough terrain is present, major differences in the height of the
source and the height of the significant receptor locations may be
accounted for by modifying the effective plume height as follows:
     h - H + Zs - Zr
     h = height of source plume with respect to the height of the
         critical location (meters)
    Z  = elevation of source (meters)
    Z  = elevation of critical location (meters)
The above correction procedure should be used only where major terrain
variations due to hills and valleys are present.  Negative and small
positive values of h, derived from this equation, should not be used in
the modeling equation.  In such cases it is recommended that a value of
h = 10 meters be used.  Estimates of the 1-hour concentrations developed
for these situations can be ratioed to 24-hour concentrations in a
manner similar to that for the coning and limited mixing models.

     While the simplified techniques noted above make reasonable assump-
tions about plume behavior in complex situations, they cannot consider
the impact of the plume in the detail which is desirable.  The use of
physical models in wind tunnels or water channels allows a more detailed
study of plume behavior.  Physical modeling is recommended for complex
terrain situations when feasible.
     IV.  Computerized Simulation Models
     Specific computer programs which provide a more detailed analysis
than the simplified mathematical models are available.  Computerized
models can consider a wide variety of meteorological conditions so that
both average and worst case conditions and their frequencies can be
                                                              10 I Q
determined.  Such point source models are available within EPA  '
which (1) estimate concentrations at numerous receptors for averaging
times of 1 hour, 24 hours and 1 year, and (2) simulate the impact of
sources on elevated terrain.
     It is also possible to use point source models in the UNAMAP
system to estimate concentrations for the high wind and limited mixing
situations or to repetitiously apply the models to hourly periods for a
long period of time.  To estimate annual average concentrations with
computerized dispersion models, the Air Quality Display Model , and the
Climatological Dispersion Model  are available.
     The models discussed in this appendix are applicable for estimating
concentrations of S02, particulate matter, and non-decaying pollutants.
In those cases where the impact of pollutants undergoing major atmos-
pheric transformations are of concern, e.g., between NO and N0?, no

widely accepted methods are available for determining pollutant concen-
trations.  In such cases, it is necessary to make assumptions concerning
the conversion rate of the pollutant and the chemical constituents of
resulting compounds before concentration estimates can be made.

             Appendix C--Supplementary Control  Systems as a
                       Primary Standard Condition

     ESECA makes clear that EPA may require the use of intermittent or

supplementary control strategies as a primary standard condition (PSC)

or as part of a PSC to assure the maintenance of the NPAAQS during the

period of a compliance date extension.  The conference report for ESECA

indicates that supplementary control  systems (SCS) may be used

for meeting the NPAAQS for S(L only.   This report also provides guidance

for determining the circumstances and time period for which SCS may be

applicable.  In discussing Section 119 of the Clean Air Act (added by

ESECA), the report reads,

               "The committee believes that the priority effort of
          each source which is subject to Section 119(c) should be
          to obtain low sulfur coal.   If an adequate, long-term
          supply of low sulfur coal is available to such a source,
          the Administrator should only approve a plan which requires
          its use (and thus compliance with air pollution require-
          ments) as expeditiously as practicable.  In such a case,
          the Administrator would have to disapprove a plan which
          proposed to wait until January 1, 1979, before beginning
          to burn low sulfur coal.  The committee believes that
          requiring priority consideration to the use of non-
          metallurgical low sulfur coal will reduce the likeli-
          hood of extended violation of applicable emission
     This appendix provides guidance to the regional office for deter-

mining whether this approach is appropriate, and in properly specifying

the conditions for the use of SCS as a PSC should this approach be


     I.   Background
     Supplementary control  systems employ a methodology whereby SCL may
be emitted by a source (usually up to a fixed maximum level)  during
favorable atmospheric conditions, but emissions are reduced during poor
atmospheric dispersion conditions in order to avoid ambient S02 con-
centrations in excess of primary ambient air quality standards. Ambient
air monitoring instruments  are placed at points where the highest S0?
concentrations are expected, and the information from these instruments
is correlated with meteorological data, weather forecasts,  and operating
parameters, including emissions rates.
     Each SCS must necessarily be tailored to the circumstances sur-
rounding each source.  Therefore, an SCS capable of reliably attaining
and maintaining primary standards must be highly sophisticated.  Regula-
tion, surveillance, and enforcement with respect to a source using an
SCS can be correspondingly  complex due to the large number  of interrelated
factors that must be continually analyzed and balanced.  Enforceable
requirements for an SCS which will assure the necessary degree of
sophistication are presented in detail below.  SCS may be used as a PSC
only by those sources that  can satisfy each of the conditions specified.
     II.  Requirements for  a Reliable and Enforceable SCS
     The conference report  for ESECA states:
          "The Administrator of EPA may require that the
     source use intermittent or alternative controls during
     such period of a compliance date extension if he
     determines that such measures are enforceable and
     will provide the necessary assurance pertaining to
     the attainment and maintenance of the national pri-
     mary air quality standards.  (Conference report
     for ESECA: H.R. No. 1085, 93d Cong., 2d Sess.,
     June 4, 1974, at page  33.)"

     Only one power plant has successfully operated an SCS for a mean-
ingful period of time (TVA Paradise Steam Generating Station).  Three
primary non-ferrous smelters have also used supplementary control systems
with varying degrees of success (ASARCO, Inc.,  at Glover, Missouri,
El Paso, Texas, and Tacoma, Washington).  Based on experience with these
operating systems, EPA developed regulations for the use of supplemen-
tary control systems, which were proposed as amendments to Part 51 of
the Federal Register on September 14, 1973, at  page 25697.  Although
there are no present plans to finalize these regulations, the concepts
contained therein have been applied in the development of federally-
promulgated SIP regulations for the control of  S0? at western primary
non-ferrous smelters.  One such smelter regulation was promulgated in
Part 52 of the Federal Register on February 6,  1975, at page 5508.
Seven more SCS regulations for individual smelters are nearing comple-
     Major requirements of current supplementary control systems are
that the system be reliable and enforceable.  Since an SCS as a primary
standard condition must also meet these requirements, the regional
office should ensure that the following conditions are met:
     1.  The regional office must be assured that the periodic curtail-
     ment actions of an SCS can be appropriately implemented at the
          (a)  If fuel switching is to be utilized,

          (i)   adequate supplies of clean fuels  must be available
     (in addition to coal,  gas or oil  is  acceptable under the
     provisions of FEA's ESECA regulations and the definition of
     "primary energy source"  therein at 10 CFR 303.2);
          (ii)  the source  must be capable of accomplishing  the
     necessary switching with sufficient  promptness;
          (iii)  the switching must not cause the  violation  of a
     regional  limitation or other federally enforceable requirement
     which has not been extended by the CDE,  (e.g., switching from
     high sulfur coal  to a  lower sulfur coal  may cause  an increase
     in particulate emissions); and
          (iv)  the date by which the  source  will  begin the  use  of
     coal must be clearly specified by the regional office.   That
     date must not precede  complete implementation of the SCS
     compliance schedule (item 11  below).
     (b)  If load switching is to be utilized, the regional  office
     must be assured that power needs  can be  met if the output of
     the facility is reduced  in accordance with  the requirements of
     the SCS.   As FEA is concerned that this  method of  SCS operation
     might result in impairment of service, that agency should be
     notified in the Letter of Certification  that  the source in-
     tends to utilize this  method of emission curtailment.
2.  Regardless of the method(s) chosen to reduce emissions --
(l(a) or (b) above) -- the  regional office should  specify an emission
limitation which reflects the lowest sulfur content coal reasonably

available to the source.  This will reduce the total  SOX emissions
from the source over a period of time, and is thus consistent with
Congress' intent to minimize the total atmospheric loading of
sulfur compounds.  This emission limitation will  also increase the
likelihood that the SCS will be effective in meeting  the primary
standards by minimizing the number of emission curtailments neces-
sary to meet standards.
3.  A "designated liability area" (DLA), must be clearly specified
for the source.  The designated liability area is defined as
that geographical area in which the amibient air quality is signi-
ficantly affected by post-conversion emissions from the source.
Unless a refined source-receptor analysis indicates that a different
area should be selected, it is suggested that the DLA be a
circular area defined by the appropriate radius taken from the
following table.
S02 Emission
tons per hour
16 or less
48 or more
grarrs per sec
4,000 or less
12,000 or more

Statute miles
4.  The regional office must be able to hold the source owner or
operator responsible for all primary ambient air quality standard
violations that occur within the designated liability area.  The
source must specifically agree, in writing, to be held responsible
in this matter before an SCS can be used as a PSC.

This requirement is necessary to ensure that SCS is used as a PSC
only at these isolated power plants that can and will  operate an
SCS with the diligence necessary to reliably meet the  standards.
5.  In-stack, meteorological, and ambient air monitoring instruments
must be operational during the period in which the source assumes
liability for maintaining the NPAAQS.  Data from such  instruments
must be available to the control agency.
6.  The source owner or operator must conduct at least a 4-month
field study, which encompasses the time period when NPAAQS are most
likely to be exceeded, in order to develop information necessary
for the day-to-day operation of the SCS.  This field study is to be
conducted prior to the time that the source assumes liability for
maintaining the NPAAQS.  The study must show that a SCS can be
operated reliably to attain the NPAAQS around the source, and the
results of the study must be submitted to EPA for approval.
7.  Using the information from Item 5, the source owner or operator
must develop and submit for EPA approval an operating  manual spelling
out the specific steps that will be taken when each of the SCS
emission curtailment criteria is met.  These steps must be shown to
be adequate to prevent such air quality violations from occurring.

8.  The source owner or operator must follow procedures contained
in the operating manual required by Item 6, and systematically
evaluate and improve the reliability of the SCS.  Each change in an
operating manual must be approved.  These requirements must be
specified in the PSC.
9.  Periodic reporting requirements, adequate for maintaining
surveillance of the operation and effectiveness of the SCS, must be
specified in the PSC.
10.  The PSC must clearly define the conditions by which the source
will be held in violation of an applicable requirement, and the
conditions by which permission to use an SCS will be withdrawn and the
PSC revoked.
11.  The source must develop and implement the SCS according to a
compliance schedule specifying, as a minimum, the following increments:
     (a)  Date of submittal to the Administrator of the sources's
     plan for developing and implementing a supplementary control
     (b)  Date by which all contracts and purchase order for stack
     extensions (if necessary), monitors, and other component parts
     to accomplish a supplementary control system will be awarded
     or issued;

          (c)  Date by which the construction of stack extension
          (if necessary) and the installation of monitors and other com-
          ponent parts will  be completed;
          (d)  Date of submittal to the Administrator of the study
          and operating manual for the supplementary control system (as
          required by Items  6 and 7);
          (e)  Date by which the periodic  emission curtailment proce-
          dures contained in the operating manual for the supplementary
          control system will be initiated on a continuing basis; and
          (f)  Date by which the source will  become responsible for all
          violations of the  primary ambient air quality standards in the
          designated liability area (as required by Item 3).
     III.  Follow-up
     The following guidance  material  on SCS is being prepared by EPA:
     A.  Guidelines for Evaluating Supplementary Control Systems
     (EPA-450/3-75-035, OAQPS No. 1.2-036).  This draft document is
being revised by the Monitoring and Data Analysis Division, OAQPS, RTP,
N.C.   It is is designed to help the responsible control agency evaluate
an SCS during the various stages of development in order to assure that
the SCS will be reliable.  It will provide information on evaluating the
results of the background study, including the source's plans for the
placement of ambient air, in-stack, and meteorological monitoring
instruments.  It also will provide guidance for evaluating the periodic
emission reduction procedures proposed by  the source in its operating

     B.  Guidelines for Enforcement and Surveillance of Supplementary
Control Systems.  This manual, now being developed by Division of Sta-
tionary Source Enforcement, is designed to provide assistance to the
responsible control agency in surveillance of the SCS and in enforcing
SCS regulations after the source has assumed responsibility for main-
taining the ambient air quality standard.  It will provide guidance in
detecting ambient air concentrations in excess of the national standards,
and in determining whether the source has adhered to the requirements
of the operational manual.  It also will provide inspection checklists, and
procedures for inspecting and calibrating the monitors associated with
the operation of an SCS.

1.   Code of Federal Regulations; Title 40, part 55.

2.   Federal Power Commission; "Steam-Electric Plant  Air and Water
     Quality Control Data, Form 67".   Federal  Power Commission,  Fuel  and
     Environmental Analysis Section,  Washington, D.C. 20426.  (Available
     in yearly editions since 1969.  Design parameters reported  in 1969
     only, unless modified in subsequent year.)

3.   National Coal Association; "Steam Electric Plant Factors",  1130
     Seventeenth Street, N.W., Washington,  D.C. 20036.  (Available in
     yearly editions.)

4.   Federal Power Commission; "Monthly Report of Cost and Quality of
     Fuels for Steam-Electric Plants, Form 423", Federal Power Commission,
     Fuel and Environmental Analysis  Section,  Washington, D.C. 20426.

5.   Turner, D.B., "Workbook of Atmospheric Dispersion Estimates".
     Office of Air Programs Publication No. AP-26.   Superintendent of
     Documents, Government Printing Office, Washington, D.C. 21402

6.   TRW Systems Group, "Air Quality  Display Model",  prepared for the
     National Air Pollution Control Administration  under Contract No.
     PH-22-68-60 (NTIS PB 189194) DHEW, U.S. Public Health Service,
     Washington, D.C. (November 1969).

7.   Busse, A.D. and Zimmerman, J.R.; "User's  Guide for the Climato-
     logical Dispersion Model", Environmental  Monitoring Series  EPA-R4-
     73-024 (NTIS PB 227346AS) NERC,  EPA, Research  Triangle Park, N.C.
     27711,-(December 1973).

8.   U.S. EPA, Office of Air Quality  Planning  and Standards, "Applying
     Atmospheric Simulation Models to Air Quality Maintenance Areas".
     Guidelines for Air Quality Maintenance Planning  and Analysis,
     Volume 12.Publication No.  EPA-450/4-74-013 (OAQPS No. 1.2-031).
     Air Pollution Technical Information Center, Research Triangle Park,
     N.C. 27711 (1974).

9.   U.S. EPA, Office of Air Quality  Planning  and Standards; "Reviewing
     New Stationary Sources", Guidelines for Air Quality Maintenance
     Planning and Analysis, Volume 10.  Publication No. EPA-450/4-74-011
     (OAQPS No. 1.2-029), Air Pollution Technical Information Center,
     Research Triangle Park, N.C. 27711 (1974).

10.  McCormick, R.A., "Air Pollution  Climatology" in  Air Pollution
     Volume 1, Edited by A. C. Stern, Academic Press, New York,  New
     York, 10003 (1968).

11.  Carpenter,  S.B.,  et.al.,  "Principal  Plume  Dispersion  Models; TVA
     Power Plants".   Air Pollution Control  Association  Journal,  Volume
     22, No.  8,  pp.  491-495,  (1971).

12.  Pooler,  F., "Potential  Dispersion  of Plumes  from Large  Power Plants".
     PHS Publication No. 999-AP-16,   Superintendent  of  Documents,
     Government  Printing Office,  Washington,  D.C.  20402 (1965).

13.  Briggs,  G.A.;  Plume Rise, U.S.  Atomic Energy Commission, Division
     of Technical  Information, Oak Ridge, Tennessee  (1969).

14.  Montgomery, T.L.; "The  Relationship  Between  Peak and  Mean S02
     Concentrations",  Conference  on  Air Pollution  Meteorology, American
     Meteorological  Society,  Boston,  Massachusetts 02108 (April  5-9,

15.  Mills,  M.T.;  "Comprehensive  Analysis of Time-Concentration  Rela-
     tionships and  the Validation of a  Single-Source Dispersion  Model";
     Final Report,  EPA Contract No.  68-02-1376  (Task Order No. 5);
     GCA/Technology Division,  Bedford,  Massachusetts 01730 (March 1975).

16.  Mills,  M.T.,  and Stern,  R.W.; "Validation  of a  Single-Source
     Dispersion-Model  for Sulfur  Dioxide  at the J. M. Stuart Power
     Plant",  Final  Interim Report -  Phase I, EPA  Contract  No.  19,
     GCA/Technology Division,  Bedford,  Massachusetts 01730 (July 1975).

17.  Smith,  M.E.,  "Recommended Guide for  the Prediction of the Disper-
     sion of Airborne Effluents", The American  Society  of  Mechanical
     Engineers,  New York, New York 10017  (1973).

18.  Hrenko,  J., Turner, D.B., and Zimmerman, J.,  "Interim User's Guide
     to a Computation Technique to Estimate Maximum  24-Hour  Concentra-
     tions 'from Single Sources",  Meteorology Laboratory, National
     Environmental  Research Center,  EPA,  Research Triangle Park, N.C.
     27711 (October 1972, Unpublished Manuscript).

19.  Burt, E., "Description of Terrain Model (C8M3D)",  Office of Air
     Quality Planning and Standards, EPA, Research Triangle  Park, N.C.
     27711,  (September 1971,  Unpublished  Manuscript).

20.  U.S. EPA, "User's Network for Applied Modeling  of  Air Pollution"
     (UNAMAP).  (Computer Programs on Tape for  Point Source  Models,
     HIWAY,  Climatological Dispersion Model and APRAC-iA)  NTIS  PB
     229771,  National Technical Information Service, Springfield,
     Virginia 22151 (1974).