&EPA
            United States
            Environmental Protection
            Agency
           Office of Air Quality
           Planning and Standards
           Research Triangle Park NC 27711
EPA-450/4-86-006
May 1986
            Air
Activities Of The
EPA Model
Clearinghouse
A Summary Report
FY81 - FY85

-------
                                    EPA-450/4-86-006
Activities of the EPA Model Clearinghouse
     A Summary Report: FY81  - FY85
              Chicago, ^

              U.S. ENVIRONMENTAL PROTECTION AGENCY
                Monitoring and Data Analysis Division
               Office of Air Quality Planning and Standards
              Research Triangle Park, North Carolina 27711

                       May 1986

-------
This report has been reviewed by The Office of Air Quality Planning and Standards, U.S. Environmental
Protection Agency, and has been approved for publication. Mention of trade names or commercial products is
not intended to constitute endorsement or recommendation for use.

-------
                             ACKNOWLEDGEMENTS
     This report was prepared by Dean Wilson  with contributions  from Joseph
Tikvart and James Dicke, all  from the Source  Receptor Analysis  Branch,
Monitoring and Data Analysis Division.

     Appreciation is extended to Stephen Perkins, Region  I;  Michael  Koerber,
Region V; Robert Wilson, Region X;  and  Sharon Reinders, Control  Programs
Operation Branch, for their helpful  comments  during  the review  process.   The
patience of Linda Johnson as she typed  this  report is also appreciated.
                                     i n

-------
IV

-------
                                 SUMMARY

     The activities of the EPA Model  Clearinghouse during  its  first  five
years of operation are summarized.   Included are a summary of  the  number  of
cases and the nature of issues reviewed by the Clearinghouse,  a  description
of major recurring and generic issues referred to the  Clearinghouse,  and  a
series of example cases illustrating  the various modes of  operation  of  the
Clearinghouse.
     A total of 306 significant issues were referred to the Model  Clearinghouse
by the ten EPA Regional Offices during the five-year period.   A  majority  of
the referrals involved the modeling of S02 and TSP emissions from  power
plants, power boilers and other large point sources for purposes of  setting
emission limits.  Many of the referrals involved the proposed  application of
nonguideline models in complex terrain.  An additional  217 proposed  Federal
Register actions containing modeling  analyses were reviewed by the Clearing-
house for completeness and adherence  to policy.
     Coordination of Clearinghouse  issues with the ten Regional  Offices was
accomplished through the preparation  of annual summary reports,  presentations
at annual meetings, visits to the Regional Offices, and the distribution  of
various memoranda and reports that  document Clearinghouse  opinions and
determinations.
     Major recurring or generic issues with which the  Clearinghouse  dealt
include performance evaluations, modeling of large numbers of  sources,  multi-
source modeling to determine net prevention of significant deterioration  (PSD)
increment consumption, and modeling the impacts of point sources on  tall
buildings.  The resolution of issues dealing with generic  modeling guidelines,
composite wind roses, long range transport, and  the effective  date of
modeling guidance was also undertaken.
                                      v

-------
     Four case examples illustrating several  procedures used  by  the Clearing-
house to resolve issues are described.   Three of the examples involved  a
Regional Office asking for an advance opinion on the use of a modeling
technique or data base for an impending  regulatory action.   The  fourth
example involved consideration of modeling issues inherent  in a  proposed
regulation that was undergoing internal  review before publication  in the
Federal Register.
                                     VI

-------
                             TABLE OF CONTENTS
                                                                        Page
ACKNOWLEDGEMENTS	  i 11
SUMMARY	    v
TABLE OF CONTENTS	  vii
LIST OF TABLES	vi i i
1 .0  INTRODUCTION	    1
     1.1   Background and Responsibilities of the Model  Clearinghouse....    1
     1.2  Scope of Report	    3
2.0  FY81-FY85 MODEL CLEARINGHOUSE ACTIVITIES	    5
     2.1   Summary of the Number and Nature of Clearinghouse Reviews	    5
     2.2  Coordination with Regional  Offices	   10
3.0  MODEL CLEARINGHOUSE RESPONSES TO RECURRING AND GENERIC ISSUES	   13
     3.1   Performance Evaluations	   13
     3.2  Modeling a Large Number of  Sources	   14
     3.3  PSD Increment Consumption Calculations	   16
     3.4  Concentration Estimates on  Tall  Buildings	   17
     3.5  Generic Modeling Guidelines	   18
     3.6  Use of Composite Wind Roses	   20
     3.7  Long Range Transport	   21
     3.8  Effective Date of Guidance	   22
4.0  EXAMPLES OF CLEARINGHOUSE ISSUES AND THEIR RESOLUTION	   25
     4.1   Use of the ISC Model  with the Deposition Option	   26
     4.2  Representativeness of National  Weather Service Data	   27
     4.3  Use of the SONDEL Model	   29
     4.4  Modeling a Power Plant in an Urban Area	   31
                                     VII

-------
5.0  CONCLUSIONS	   35

6.0  REFERENCES	   37

     APPENDIX--Description of EPA Model  Clearinghouse  	  A-l
                               LIST OF TABLES


Number                                                                   Page

  1               Clearinghouse Responses  by  Year	   5

  2              FY81-FY85 Clearinghouse  Reviews  by  Region	   6

  3              Summary of Common Issues Associated With 306  Model
                 Clearinghouse Referrals  and Actions During  FY31-FY85...,   7

-------
1.0  INTRODUCTION
     This report summarizes the operation of the EPA Model  Clearinghouse
during its first five years of existence, FY81-FY85.  The main purpose of
the report is to summarize the number of cases and the nature of issues
that the Clearinghouse reviewed during this time.  In addition, the report
describes and illustrates, through a series of examples,  how the Clearing-
house fulfills its major responsibility for review of specific proposed
actions which involve interpretation of modeling guidance,  deviations from
such guidance, and the use of options in the guidance.
     The information contained in this document regarding Clearinghouse
opinions on specific problems or classes of problems should not be  taken by
the reader as "new guidance" or precedents for treating similar problems.
Many of the issues have not yet been Completely resolved  within EPA;  further
information and policy decisions may have a bearing on final  resolution of
the problems.  Should a user be confronted with any problem similar to the
ones described, he should consult the appropriate State/Regional  Office
before proceeding.

     1.1   Background and Responsibilities of the Model Clearinghouse
          The Model  Clearinghouse was established in November 1980  when
the Regional  Offices were notified of its general  purposes, procedures and
limitations.   A detailed operational plan describing the  functions, structure,
procedures and schedule for implementation was issued in  February 1981.
          The "Model  Clearinghouse Operational  Plan" states that the  primary
purposes of the Clearinghouse are to provide:   (1)  a mechanism whereby the
proposed acceptance  by a Regional Office of a  nonguideline  model  or alterna-
tive techniques may  be reviewed for national  consistency  before final

-------
approval by the Regional  Administrator;  (2)  a  mechanism whereby  the in-depth
technical  evaluation and/or performance  evaluation  of  a proposed technique
may be reviewed by those  EPA personnel who are most familiar with the  types
of techniques to be employed;  and (3)  a  communication  outlet for EPA's
experience with the use of nonguideline  models, data bases  or other deviations
from current guidance.  To accomplish  these  purposes the Clearinghouse main-
tains awareness of EPA modeling policies,  develops  and maintains a historical
record of modeling decisions,  develops clarifications  of existing modeling
guidance for special situations, reviews proposed actions which  involve
interpretation of or deviation from modeling guidance  and communicates the
results of significant decisions to all  regulatory  users in  the  Agency.
          The Clearinghouse formally operates  in the Source  Receptor Analysis
Branch (SRAB) and in the  Co'ntrol Programs  Operations Branch (CPOB) of  the
Office of Air Quality Planning and Standards (OAQPS).   Regional  Office
requests for review of nonguideline models are sent directly to  SRAB.   CPOB
maintains responsibility  for review/approval  of proposed Federal  Register
actions submitted from the Regions. These packages often contain modeling
issues.  Close coordination is maintained  between the  two branches on  al"
Regional Office modeling  issues that come  to their  attention.
          Activities of the Model Clearinghouse during the  FY81-FY85 period
included:
          1.  Responding  to Regional Office requests for review  of nonguideline
models proposed for use.
          2.  Responding  to Regional Office requests for interpretation of
modeling guidance.
          3.  Reviewing Federal Register submittals.
          4.  Documenting Clearinghouse  decisions and  discussions.
                                     2

-------
          5.  Summarizing Clearinghouse activities at various internal  EPA
meetings.
          6.  Issuing, internally, annual  summary reports of activities.
          7.  Developing and issuing a report summarizing the Clearinghouse
experience in dealing with nonguideline model  evaluations.
          8.  Acquiring historical  information on the application  of models
in EPA.

     1.2  Scope of Report
          The remainder of this report is  divided into three sections.
Section 2 summarizes the number and nature of the Clearinghouse  reviews
during the five-year period.  Section 2 also summarizes the  various programs
of the Clearinghouse that are designed to  keep EPA users informed  of its
activities, referrals and opinions.  Section 3 describes the Clearinghouse
responses to several common or recurring technical/consistency issues.  Sec-
tion 4 illustrates, through a series of case examples, the nature  of and
mode of Clearinghouse operation.  Section  5 contains the conclusions.

-------

-------
2.0  FY81-FY85 MODEL CLEARINGHOUSE ACTIVITIES
     This section summarizes each of the eight activities of the Model
Clearinghouse listed at the end of Section 1.1.

     2.1  Summary of the Number and Nature of Clearinghouse Reviews
          The number of reviews conducted by the Clearinghouse during FY81-FY85
is summarized in Table 1.   The data in the table only include those issues
where a coordinated clarification of policy was required or an investigation
had to be undertaken by the Clearinghouse.  In addition, there were numerous
telephone inquiries to the Clearinghouse regarding procedures, technical
considerations and policies which were readily resolved or referred elsewhere.
          Note from the table that there were a total of 65 modeling issues
referred to the SRAB function in the Clearinghouse which required a written
response and 241 issues which were resolved orally.  In addition, CPOB
directly reviewed another 217 regulatory action  packages which contained
modeling analyses that followed guidance and required no further technical
review by SRAB.  Although there is some variation from year to year, on
average the Model Clearinghouse handles slightly over 100 cases per year.

                 Table 1.   Clearinghouse Responses by Year

Written ResponsesU)
Telephone/ Oral ResponsesU)
Federal Register Actions(2)

Total
FY81
12
18
65

95
FY82
12
24
43

79
FY83
19
46
71

136
FY84
11
82
26

119
FY85
11
71
12

94
Total
65
241
217

523
  (1)  Cases containing modeling issues requiring a technical  review and
       coordination between CPOB and SRAB
  (2)  Cases that followed current guidance; reviewed directly by  CPOB

-------
          Table 2 shows the distribution  of the  Clearinghouse  reviews  over
the five-year period by Region  of origin.   Note  that  requests  for  assistance,
either written or by telephone, came from all  the  Regional  Offices.  This;
suggests that there is an awareness and a desire for  Clearinghouse support
throughout the Agency.  The majority of the referrals came  from  the  five
Eastern Regions.  These referrals most often were  associated with  State
Implementation Plans (SIP's)  and SIP revisions.  The  referrals from  the
Western Regions were most often associated with  new sources and  Prevention
of Significant Deterioration (PSD) permits.

            Table 2.  FY81-FY85 Clearinghouse Reviews by  Region
Region
I
II
III
IV
V
VI
VII
VIII
IX
X
Total
Written
ResponseU)
6
8
9
16
8
2
3
4
3
6
65
Telephone/Oral
ResponseO)
25
29
43
36
28
12
15
19
19
15
241
Federal Register
Actions!2)
40
22
30
25
87
3
1
3
6
0
217
Total
71
59
82
77
123
17
19
26
28
21
523
   (1)  Cases containing modeling  issues requiring  a  technical  review ano
        coordination between CPOB  and SRAB
   (2)  Cases that followed current guidance;  reviewed  directly by  CPOB
     Table 3 contains a summary, by subject area,  of the  nature  of the
referrals and requests for assistance that came  to the Clearinghouse.

-------
!4
1
1
1
0
0
1
1
1
24
2
3
0
2
0
0
0
5
43
3
2
3
0
0
2
0
12
47
10
4
12
3
1
12
0
4
40
16
2
3
4
0
6
2
9
178
32
12
19
9
1
21
3
31
Table 3.  Summary of Common Issues Associated With 306  Model  Clearinghouse
          Referrals and Actions During FY81-FY85.


Subject Area                                 Number of  Referrals
                               FY81     FY82    FY83    FY84    FY85     Total

1.  By Pollutant

    S02
    TSP
    CO
    Pb
    NOX
    03
    More Than One Pollutant
    Noncriteria
    Not RelevantO)

2.  By Source Type

    Power Plant(2)               16       9      16      21      18       80
    Industrial  Boiler             4       3       6       7       6       26
    Smelter                       0       1       4      14       5       24
    Steel Facility                0       3       2       2       3       10
    Paper Mill                     1       2       4       0       6       13
    Aluminum Plant  .              00420         6
    Refinery                      00121         4
    Roadway                       1       2       2       4       1       10
    Other Sources                 2       8       3       3      16       32
    Multiple/Mixed                0       0       7      15      14       36
    Generic^)                     6       8      15       8       6       43
    Not RelevantO)               0       0       1      15       6       22

3.  Urban vs. Rural

    Urban Only                     2       4      11      19      12       48
    Rural Only                    23      24      46      47      61      201
    Both Urban  and Rural           5       3       4      16       4       32
    Not RelevantO)               0       5       4      11       5       25

4.  Type of Response

    Written                      12      12      19      11      11       65
    Oral                          18      24      46      82      71      241

-------
Table 3. (Continued)
                                             Number of Referrals
                               FY81     FY82    FY83    FY84    FY85    Total
5.  By Regulation
    New SIP                       5       4      10      26      16       61
    SIP Revision                 13      12      26      22      15       88
    PSD                           4      11      11      21      26       73
    Bubble                        0       2       4       2       7       15
    EIS                           210339
    Others                        4       0       2       2       9       17
    Generic(3)                    2       4      12      14       6       38
    Not RelevantO)                02030        5

6.  By Terrain Setting

    High Terrain (Above           5      12      17      21      22       77
      Stack Height)
    Low Terrain (Below           15       3      25       8       8       59
      Stack Height)
    Both High and Low Terrain     6       9       9      17      21       62
    Essentially Flat Terrain      2       9      14      27      20       72
    Not RelevantO)                2       3       0      20      11       36

7.  Nonguideline vs. Guideline
      Model

    Nonguideline                 16      23      34      27      36      136
    Appropriate Use  of a Guide-  14      11      30      66      46      167
      1ine Model
    Not RelevantU)                02100        3

8.  On-site vs. Off-site Data
      Used in Model

    On-site                       7      16      21      30      18       92
    Off-site                     21      12      32      57      52      174
    Not RelevantU)                2       8      12       6      12       40
Footnotes

    (1)  The issue referred to the Clearinghouse was independent of this
         specific subject area.

    (2)  Includes resource recovery facilities and gas turbines.

    (3)  Applicable to classes of sources or types of regulations.

-------
Briefly some highlights of the table are:
          1.  Pollutants.   The majority of the  cases involved  S02  and  TSP
as the pollutants.  When more than  one  pollutant  had to  be  considered  the
combination was most often TSP and  SC>2.  Because  of the  emphasis on  develop-
ing lead SIP's during FY84 and the  complicated  modeling  problems associated
with primary and secondary lead smelters,  there were a number  of referrals
for that pollutant in that year.
          2.  Source Types.  Many problems referred to the  Clearinghouse
involved power plants/power boilers but there were  also  numerous other
modeling problems associated with area-wide problems including State-wide
SIP's and SIP revisions, generic  modeling  guidelines and other generic
issues.  The significant number of  smelter cases  during  FY84 was primarily
due to lead SIP development issues.
          3.  Urban/Rural.  Most  modeling  analyses  referred to the Clearinghouse
were either clearly urban  or clearly rural  such that the choice of urban or
rural  dispersion coefficients was not in question.   However there  were also
a variety of problems, especially during FY84,  where sources and/or  receptors
were located in both urban and rural  areas.  Most of these  problems  were
resolved by citing the current guidance.
          4.  Type of Regulation.  Most regulatory  actions  referred  to the
Clearinghouse were for SIP relaxations  (primarily SC^) and  PSD. The significant
number of cases associated with new SIP's  during  FY84 is primarily associated
with the development of lead SIP's; however,  there  were  also several cases
where a State began development of  a SIP in areas where  no  SIP currently
existed.  The significant  number  of generic modeling problems  during FY83
and FY84 were most often associated with States developing/adopting  their
own modeling guidelines for PSD and bubble (emissions trading)  analyses.

-------
          5.  Terrain Setting.   Since the Guideline on  Air Quality  Models1
does not recommend any refined  models for use  in  complex  terrain, a large
percentage of the referrals to  the Model  Clearinghouse  involved  proposals;
for new complex terrain models/analysis techniques for  use on  specific
sources.  Many applications involved  receptors both above and  below stack
height, sometimes requiring the use of more  than  one model.
          6.  Use of Nonguideline Models. A large percentage  of the Model
Clearinghouse referrals proposed the  use of  nonguideline  models, often  for
complex terrain situations.  However, the majority of the issues involvec
appropriate choices among guideline models and/or associated data bases.
          7.  Use of On-site Data.  The majority  of the model  applications
referred to the Clearinghouse utilized off-site meteorological data (usuelly
National Weather Service data).  Those that  utilized on-site data often were
in complex terrain.  The "not relevant" category  was most often  associated
with screening techniques where no local  meteorological data input  was  required.

     2.2  Coordination with Regional  Offices
          During the five-year  period the Clearinghouse conducted or partici-
pated in a number of activities that  can be  categorized as coordination and
information exchanges with the  Regional Offices.   One such activity was to
prepare and distribute to the Regional Offices in October of each year, a
Clearinghouse report; this report served as  a  "newsletter" informing Clearing-
house users about the issues and responses which  occurred during the year1.
The report included statistical summaries of Clearinghouse activities,  similar
to Tables 1-3, summaries of major responses  by the Clearinghouse to Regional
Offices, descriptions of recurring consistency issues that were  common  tc
more than one Region, and a summary of issues  by  pollutant,  source  type, etc.
                                    10

-------
          Another periodic activity of the Clearinghouse was to discuss the
activities of and issues referred to the Clearinghouse at the annual  Regional
Office modeling workshop held in April/May of each year.  At such workshops
recent significant issues referred to the Clearinghouse were presented.
Several of the particularly complex and controversial  issues were discussed
in some detail at these workshops.
          As another communication function,  beginning in FY83, the  Clearing-
house sent copies of all of its written responses (along with the incoming
requests) to all  the Regional Offices.  In this way the Regional  Offices
were made aware,  in a timely fashion, of decisions made that may  affect
some of their modeling activities.
          A related activity that began in FY83 was to solicit advance
opinions from all the Regional  Offices on particularly ^sensitive  issues
with national implications.  When such cases  arose, the proposed  Clearing-
house response, containing a detailed description of the issue and  its
risks, was sent to all the Regions for comment before  the response was
finalized.
          As a means of communicating with the general  air pollution  modeling
community, the Clearinghouse participated in  the design and operation of
the EPA booth at  the 1984 and 1985 Air Pollution Control  Association  (APCA)
national meetings.  These booths included displays from the several  EPA
Clearinghouses, e.g. the Model  Clearinghouse, the BACT Clearinghouse, etc.
The APCA booth display contained brief statements about the users of  the
Model Clearinghouse, the information available, and the methods of disseminat-
ing that information.  In addition, a one page statement that describes the
                                    11

-------
operation of the Model  Clearinghouse was prepared  and  distributed  to interested
visitors at the booth.   A copy of this statement is provided  in  the Appendix.
          Pursuant to its responsibility to establish  a  historical  record
of modeling decisions,  personnel  from the Model  Clearinghouse visited  all
ten Regions during FY82.  The purpose of these meetings  was to gather  infor-
mation on the historical usage of models by Regional  Offices  and to identify
current/upcoming modeling problems which may come  to  the attention  of  the
Clearinghouse.  A secondary purpose was to communicate information  to  the
Regions on the current  and future operation of the Clearinghouse.   As  a
result of these very useful meetings, the Clearinghouse  was able to document
precedents that have been established for the use  of  certain  models and
data base considerations and the  circumstances associated with the  precedents.
In addition, a number of broader  modeling issues were  identified where the
Regions have adopted specific policies in areas  where  national  guidance is
lacking or is flexible.
          As noted in Section 2.1 the Model  Clearinghouse was frequently
involved in reviewing justifications for the use of nonguideline models.
Several of the more involved and  complicated justifications included
technical and performance evaluations of the proposed  model  pursuant to
guidance contained in the "Interim Procedures for  Evaluating  Air Quality
Models (Revised)."2  jn order to  share its experience  in reviewing  such
evaluations with the Regional Offices and other  users, the Model Clearinghouse
prepared and issued in  1985 a report "Interim Procedures for  Evaluating Air
Quality Models:  Experience with  Implementation"^.  This report summarizes
and intercompares the details of  five major regulatory cases  which  were
reviewed by the Clearinghouse, and for which the above cited  guidance  was
implemented as support for acceptance of the proposed  nonguideline  models.

                                     12

-------
3.0  MODEL CLEARINGHOUSE RESPONSES TO RECURRING AND GENERIC ISSUES
     There were several  Clearinghouse referrals over the five-year
period that contained common modeling problems or issues.   In  these cases
the Model Clearinghouse  ensured that each recommendation was in  harmony  with
previous recommendations involving the same or similar issues.   If the
recommendations were in  conflict with previous determinations,  then the
changed position was coordinated and a consensus agreed upon by  the Regions^.
     Summarized below are recommendations the Clearinghouse has  made on  the
major recurring issues.   Also included are a few issues that did not occur
all that often, but which are expected to recur at a future date.
     In contrast though, it should be noted that issues referred to the
Model Clearinghouse were generally very narrow, i.e., highly geared to the
specific aspects of the  individual model  application.  Although  the resolu-
tion of such issues may  set precedents for future modeling  of  a  like situa-
tion, such similar situations rarely occurred.
     Also, it should be  reemphasized here that the Clearinghouse determinations
on these recurring/generic issues do not constitute national  guidance.
Relevant facts in a particular situation may suggest a somewhat  different
interpretation.  However, the information in the following  subsections can
provide an indication of how EPA may view a particular modeling  application
where these issues are inherent.

     3.1  Performance Evaluations
          The most frequently recurring issue involved proposals for acceptance
of nonguideline models/techniques where the primary justification  for acceptance
of such techniques consisted of "favorable" comparisons of  model  estimates
with measured data.  In  reviewing such proposals, the Clearinghouse most
                                     13

-------
often used the guidance contained in the "Interim Procedures for Evaluating
Air Quality Models (Revised)"2 in judging whether the  performance  evaluation
was objective and sufficiently comprehensive,  given  the scope and nature of
the proposal.
          For major problems,  e.g., a large power plant located  in  complex
terrain where a model  significantly different  from the  recommended  model
was proposed, the Clearinghouse recommended full  implementation  of  the
Interim Procedures guidance.   This involved a  technical  evaluation  of  the
proposed model, a protocol  for the performance evaluation  agreed upon  by
the source and the regulatory  agencies,  and the acquisition  or identification
of an agreed-upon data base to be used in the  evaluation.  A review of five
major issues of this nature that were referred to the Clearinghouse is
contained in the "Interim Procedures for Evaluating  Air Quality  Models--
Experience with Implementation."3
          A variety of other  referrals to the  Model  Clearinghouse for  smaller
sources or more narrow situations also included performance  evaluations as
partial justification  for the  use of new or alternative modeling techniques.
In these cases the basic principles contained  in  the Interim Procedures
guidance were still used to judge the adequacy of the proposal,  but perhaps
a complete protocol was judged to be unnecessary.  However,  many of the
proposals still could  not be  accepted because  of  a dearth  in coverage  (spatial
or temporal) of field  data for the performance evaluation.  In some cases
fluid modeling in conjunction  with minimal  field  data was  accepted.  In a
few cases where the Guideline  on Air Quality Models did not  recommend  a
technique for the situation,  a technically sound  model  was accepted, with
minimal field justification.   For example, see Section  4.3 below.
                                     14

-------
          3.2  Modeling a Large Number of Sources
               A number of referrals to the Model Clearinghouse during the
five-year period involved proposed relaxations from strict interpretation
of guidance when the guidance implied that a large number of sources would
need to be modeled.  In these cases the resources required to model  all  of
the sources in harmony with the guidance would be large and sometimes prohi-
bitively expensive.
               One set of circumstances involved TSP SIP cases where it was
necessary to model  a large number of sources (-1200).  In these cases
the computer costs and logistics required to use the RAM,5 ISC6 and/or COM?
models with five years of meteorological data were prohibitive.  In  one case
the computer costs alone were estimated to be $1 Million.
               ,In each of these cases the respective Region wrote a  protocol
for modeling the area which was designed to reduce the amo'unt of computer
run time and yet still  be technically defensible.  Although the details of
each protocol were slightly different, in general each incorporated  the
following procedure.  For the annual  estimates all sources were included in
COM or ISCLT and five individual years of meteorological  data (STAR) summaries
were input.  Coarse grids were used; remodeling around hot spots with a
finer grid would be conducted, if judged necessary.
               For the short-term analysis, a judgment was first made as to
which of several sources, usually the large industrial complexes, were likely
to cause the largest air quality impacts.  Many of the individual sources
within these facilities were then combined and the appropriate model (RAM
or ISC, depending on the need to consider downwash, etc.) was run with five
years of hourly meteorological data.   The meteorological  year yielding the
                                     15

-------
highest short-term impacts was singled out, each of the large facilities
then disaggregated into individual  sources, and the model  rerun for that
year.  Several (~5) "worst case" days were identified and  the model(s)
run for these days using the entire emissions inventory for the area.
               The Clearinghouse agreed that, although these modeling
procedures were somewhat less than  rigorous since they involve some subjective
judgments, they were technically sound in these situations and a reasonable
compromise to achieve acceptable costs.*
               A somewhat related set of issues that were  referred to the
Model Clearinghouse involved Regions and States that were  often in a position
of having to determine the emission limit for a single source located in
the midst of many other sources.  In these cases it was frequently necessary
to model all of the sources over an extensive grid, using  five years of
meteorological data.  This was often a sizeable and sometimes expensive
project.
               One solution to this problem proposed to the Clearinghouse
by some Regions, involved first modeling only the source in question using
the five years of meteorological data.  Then the specific  meteorological
periods where the source had a "significant" impact were identified.  Finally,
all the sources in the area were modeled but only for the  specific receptors/
time periods identified as significant.
               Prior to FY85 at least two Regions had used the technique,
in principle, or some variation in  the technique.  For example, one Region
used the technique to help determine the acceptability of  emission limits
*Application of these procedures for future modeling would also need to be
 shown to be technically sound prior to acceptance by EPA.
                                      16

-------
for three small  TSP sources in a nonattainment area.   In this case,  the
24-hour Level  II bubble significance level  of 10 ug/m3 was used  to define
the days/receptors where all  sources needed to be modeled.   Another  Region
asked the Clearinghouse to approve a variation of the technique  for  use in
a PSD analysis.   In this case the PSD significance levels were used  to
identify receptors where the  incremental  impact of "surrounding" increment
consuming sources needed to be calculated.   However,  in this case, the
technique was limited to only defining the  area of significant impact and
all sources were modeled using the full  set of sequential meteorological
data.
               The Clearinghouse agreed  with the Regions that the proposed
method was acceptable for these applications but at the same time indicated
that for future  uses the technique (or variatjpns) should continue to be
accepted on a case-by-case basis only.

          3.3  PSD Increment  Consumption Calculation
               A number of discussions were held with the EPA Regional  Offices
during FY83 and  FY84 on the general question of how,  from a modeling stand-
point, short-term increment consumption  should be calculated when multiple
increment consuming sources (or source shutdowns which create increment)  were
involved.  One viewpoint supported by some  Regions was to model  short-term
increment consumption on both a spatially and temporally consistent  basis, a
procedure analogous to the method contained in a policy memorandum on Level
II bubble analyses, dated February 17, 1983.8  in this methodology,  the
maximum amount of PSD increment consumed must be determined by modeling the
net changes in emissions (between the baseline and future cases) sequentially
for each time period with at  least a year of meteorological  data.  The
                                     17

-------
resulting maximum impacts of this type of analysis  specify  the  maximum
amount of increment consumption  at each receptor.
               Another viewpoint was that the  model  calculations should  be
performed on a spatial basis only, i.e., the  second  highest short-term
modeled impacts of all sources at each receptor  were compared to the second
highest modeled baseline concentrations at those receptors  to determine  the
increment consumption.
          The Clearinghouse recommended that  EPA should  follow  the  methodology
of spatial  and temporal  modeling to determine  increment  consumption.

     3.4  Concentration Estimates on Tall  Buildings
          In recent years a number of issues  surfaced regarding concentration
estimates on balconies and rooftops of tall buildings.   While the Model
Clearinghouse was not directly involved in the issues regarding applicability
of NAAQS and PSD increments on buildings,  it  was involved  in a  technical
manner concerning how to make the estimates.   One option was to use the
MPTER.9 ISC or ValleylO models to make such estimates,  identical  to the  manner
in which estimates are made on elevated terrain. One problem with  this  tech-
nique is that the buildings are  then treated  as  terrain  features with full
reflection.  The Clearinghouse did not believe that  buildings should be
regarded as terrain features since they act more like "flagpoles" extending
into the plume.  Another problem with the above  mentioned  models was, at
that time, that they did not properly account for urban  dispersion
applicable to most problems where tall buildings are present.
          Consequently, the Clearinghouse advised Regional  Offices  that
the appropriate concept to use when modeling  receptors on  tall  buildings
was to treat these receptors as "flagpoles."   In most cases the RAM model
was appropriate as it has an option that handles flagpole  receptors.
                                     18

-------
     3.5  Generic Modeling Guidelines
          Over the years several  States and local  agencies developed/adopted
their own modeling guidelines for use in evaluating the impacts  of sources
within their jurisdiction.  In some instances these agencies proposed  to
EPA that the modeling guidelines  be incorporated into their SIP  such that
EPA would not have to review new  or revised emission limits for  sources but
that the State/local  agency could issue such permits directly.   The Model
Clearinghouse was involved in the review of these  modeling guidelines.  The
approvability of the  modeling guidelines as part of the SIP was  generally
governed by two factors:  (1)  whether or not the  regulatory program for
which the guidelines  apply had been or could be delegated  to the agency and,
(2)  the degree to which they utilized technically sound techniques and
were consistent with  national guidance.
          Regarding the first factor, it should be noted that the Clean Air
Act allows for the new source review (NSR) and PSD programs to be delegated
to the States.  Approvability of  the delegation depends in part  on whether
the agency had an acceptable modeling guideline or, as most agencies have
done, had adopted EPA's Guideline on Air Quality Models into their own
regulations.  Once approved, the  agencies can issue permits directly,  using
these techniques to demonstrate that the allowable emissions do  not violate
applicable ambient standards and  PSD increments.
          On the other hand, EPA  cannot delegate the authority to issue/revise
permits pursuant to Section 110 of the Clean Air Act pertaining  to SIP's.
These permits require a SIP revision in each case  and the  emission limits
must be reviewed by EPA.  However, EPA has taken the position that its  role
in review can be minimized or, in the case of generic bubble regulations
                                     19

-------
where there is no net increase in emissions,  eliminated provided the agency
agrees to use "replicable" techniques in determining the air quality impact
of the changed emission limits.   "Replicable" is intended to mean that the
modeling techniques to be used on any source  are restrictively defined such
that the application of the techniques by any modeler would yield the same
estimate.
          Given these procedural  restrictions, the Model  Clearinghouse
reviewed several proposed agency  modeling guidelines for technical  adequacy
and national consistency.  For NSR and PSD the Clearinghouse supported
proposed screening techniques that were at least as conservative as those
used by EPA and the use of refined EPA Guideline models.   For Section 110
SIP's it was clear that only techniques that  precisely defined which models,
which model options and which data bases would be used for every applicable
situation could be approved.  For these actions the Clearinghouse supported
several different replicable screening techniques that were more conservative
than EPA's.  The Clearinghouse also supported the use of certain EPA refined
models provided that the predefined data bases to be used were representative,
The applicability of the technique had to be  significantly restricted since
no judgments could be allowed.  This precluded, for example, complex terrain
situations and complex sources where source emission characterization was
required.

     3.6  Use of Composite Wind Roses
           In reviewing Federal Register packages during the FY81-FY83 period
the Clearinghouse noted that some of the annual modeling demonstrations
utilized 5-year "composite" stability wind roses as input, i.e. a single
                                     20

-------
stability wind rose based on five years of meteorological  data.   While no

specific modeling guidance on the subject existed at the time, the Clearing-

house was concerned that the associated 5-year average estimate  did not

technically ensure that the annual mean would never be exceeded, as required

by regulation.  The issue of the annual mean was primarily a procedural

problem rather than a real problem for the cases reviewed  since  the

emission limits necessary to attain short-term standards/increments generally

provided for an ample margin of safety on the annual mean.

          However, in FY84 the Clearinghouse began reviewing lead SIP demon-

strations, some of which utilized composite quarterly stability  wind roses as

model input.  Since the 5-year average quarterly concentration estimates

clearly did not demonstrate compliance with the lead standard, the Clearing-

house..recommended that these SIP's be remodeled, i.e. using 20 individual
                                                                       t
quarters.  All Regions were subsequently advised that when using a long term,

climatological model  for pollutants for which there is a long term standard,

i.e. TSP, S02, N0£ and Pb, the analysis should be done for individual  years/

quarters.



     3.7  Long Range  Transport

          The Clearinghouse was consulted on a number of occasions regarding

the use of modeling techniques beyond the normal 50 km range of  recommended

refined models.  These cases usually involved PSD sources  where  there was a

question about the possible adverse impacts on a distant Class I area.  In

such cases the Clearinghouse recommended that an applicable screening

technique such as the Valley model be used to make the requisite estimates

since it was believed that such estimates would be conservative.  This

approach resulted, in most cases, in a showing of no adverse impact.
                                     21

-------
     3.8  Effective Date of Guidance
          The basic document used by the Clearinghouse  to  determine whether
a proposed modeling technique is in  harmony  with  national  guidance  is  the
Guideline on Air Quality Models, published  in  1978.   However,  since 1978
EPA issued policy memoranda and reports which  interpret this guidance  and/or
specify its applicability to new regulatory  requirements,  e.g.  bubbles,  GEP
stack height regulations, lead SIP's,  etc.   The  issuance of  such interpretative
guidance sometimes caught regulatory packages  in  the  middle  of  development,
e.g. a regulatory package containing modeling  techniques that did  not  conform
to the new guidance may have already been completed and is undergoing  EPA
review.  In this situation it seems  clear that EPA should  complete  its review
and not require new modeling based solely on the  fact that the  modeling  did
not conform to current guidance.  It was not so  clear that regulatory  modeling
analyses that were started several years previously,  perhaps revised several
times, and finally submitted to EPA  should  be  entitled  to  use only  the
guidance that was in place at the time of the  initial  analysis.
          On several occasions the Model  Clearinghouse  was asked to concur
on regulatory modeling analyses that did not conform  to current guidance,  but
did conform to guidance that was in  place at some point in the  past.  In
each case the Clearinghouse tried to establish first  whether it was reasonable
to expect that the State/source had  ample opportunity to conform with  current
guidance without undue resource impacts and  second, whether  the deviation
clearly resulted in a technically deficient  analysis  or was  only a  question
of consistency.
                                     22

-------
          To eliminate confusion  and  promote  consistency the Clearinghouse
now judges the acceptability  of a "dated"  technique based on the following
criteria:  (1)  whether there is a  written protocol with a legal or regulatory
basis or (2) whether the  analysis is  complete and regulatory action is
imminent or underway.
                                    23

-------
24

-------
4.0  EXAMPLES OF CLEARINGHOUSE ISSUES AND THEIR RESOLUTION
     The following four examples are provided with the primary purpose to
illustrate how the Model Clearinghouse operates in response to modeling
issues that come to its attention.  As mentioned in Section 1.1, the Clearing-
house becomes involved in modeling issues through two different mechanisms.
In one set of circumstances a Region may contact the Clearinghouse prior to
taking a formal  position on a regulatory action to obtain an advance opinion
on its approvability, from a modeling standpoint.  This inquiry may come
directly to SRAB or may come through the CPOB arm of the Clearinghouse if
it involves procedural as well  as technical  issues.  The other set of circum-
stances involves the Regional Office submittal  of a regulatory package to
CPOB.  In this case the Regional Office position on modeling issues is
established but is reviewed at the time of formal submittal by the Clearing-
house.
     The first three examples described below serve to illustrate the first
set of circumstances, i.e. an advance opinion is sought by a Regional  Office
on a modeling issue.  Section 4.1 illustrates the resolution of a minor
issue through a series of telephone discussions; oral resolution of issues
is the most common mode of operation of the Clearinghouse.  Section 4.2
involves the informal resolution of an issue involving the utilization of a
data base; cases referred to the Clearinghouse that involve data base issues
occur frequently.   The third issue involves the choice of a nonguideline
model for CO estimates from a roadway.  It is provided to illustrate how
issues are handled when the Model Clearinghouse does not internally have
the technical expertise to evaluate the adequacy of a proposed technique
and such technical  support is sought from other personnel  in EPA.
                                     25

-------
     The last example is provided to illustrate the second  set of circumstances,
i.e. a SIP proposal  containing modeling issues is forwarded to CPOB for
concurrence and a Model  Clearinghouse review/opinion is required before
such concurrence can occur.

     4.1  Use of the ISC Model With the Deposition Option
          During FY85 the Model  Clearinghouse was contacted by a Region
regarding proposed modeling of particulate matter from an excavation/
drilling operation on Federal  land.  The site was located in complex terrain;
however, significant terrain features were outside of the boundaries of the
project property.  Preliminary modeling with ISC indicated  that allowable
PSD increments would be  exceeded at the boundary lines.   A  significant
portion of the particul'ate material released would consist  of heavier
particles.  It was expected that much of this material  would be deposited
on-site, thus reducing concentrations at the boundary line.  The applicable
model  for handling the deposition problem would normally  be the ISC model.
However the ISC users' manual  cautions against using the  deposition option
for sources located  in complex terrain.
          The Region, who was assisting another Federal Agency in preparation
of the EIS for the project, asked the Clearinghouse if the  deposition  option
could still be used  for  estimates at the boundary line,  since complex
terrain was beyond this  distance.  A check of the Clearinghouse files
revealed that a similar  issue had occurred before in another Region.  In
that case the Region had contacted the ISC model  developer  to discuss  the
possible use of the  model in complex terrain.  The result of this inquiry
was that the deposition  option is valid out to the distance where terrain
is first encountered.  Based on this finding the Clearinghouse informed the
                                     26

-------
Region that the deposition option would be valid for calculating TSP levels
at the boundary line.
               This particular case illustrates a very common mode of
operation of the Clearinghouse.  A call came from a Regional  Office asking
for an opinion on a position that may conflict with guidance.  The Clearing-
house checked the guidance, in this case the ISC users' manual, then checked
the Clearinghouse records for any precedents for the case.  In this case a
precedent was found and the details of the previous case were determined.
These findings enabled the Clearinghouse to confirm that the  Region's
position was technically sound and nationally consistent.

          4.2  Representativeness of National Weather Service Data
               During FY83 The Model Clearinghouse was asked  by a Regional
Office to resolve an issue where a source wanted to discard certain hours
of National Weather Service (NWS) meteorological data on the  grounds that
they were not temporally representative.
               In this case a conventional set of CRSTER model runs had been
made for the purpose of analyzing secondary standard attainment using six
years of NWS meteorological data.  The results showed a number of 3-hour
ambient standard violations.  Each of these violations were predicted to
occur under a typical "A" stability condition.  The source made the argument
that these periods of predicted violation should be ignored because of the
manner in which NWS makes wind direction observations.  That  is, rather
than constructing true hourly average wind directions, the NWS observer
reports instantaneous wind directions once every hour.  It is the hourly
average wind direction which is of interest in air dispersion modeling.
                                     27

-------
               The Model  Clearinghouse,  in  an  oral  response  to  the Region,
indicated that the source had correctly  summarized  a  deficiency in the  data
bases available from the NWS.  However there exists no  practical  way  to
correct these data bases.  This problem was well  understood  and carefully
considered in the early 1970's when EPA developed its policy to require the
use of NWS data in dispersion modeling.   The issue  before  the EPA was
whether the benefits of using these data sets  to  establish reasonable
regulations nation-wide outweighed  their inherent deficiencies.  It is
important to realize that all data  bases have  certain inherent  deficiencies
which may be impractical, if not impossible to resolve.
               It was EPA's opinion that the ready  availability,  overall
quality, length of historical record,  and spatial coverage of the NWS data
bases strongly outweigh the inherent deficiencies.   Also,  since the time
of the institution of this policy,  many major  utilities  throughout the
country have been regulated through the use of NWS  data.   Therefore,  in
order to change the present policy, a  new and  compelling  rationale would be
necessary.  Since the argument presented by the source  constituted neither
a new nor a compelling rationale,  policy on this  matter  was  not changed.
               The mode of operation of the Model Clearinghouse in this
case was similar to the case described in Section 4.1,  i.e.  a Regional  Office
sought an advance opinion on the approvability of a technique that was  in
conflict with guidance.  However,  the  outcome  in  this case was  different;
the Clearinghouse indicated that the proposal  could not  be supported.
While the proposal had some technical  merits,  the conflict with consistency
was of such serious magnitude as to cause a disruption  of  national programs.
                                     28

-------
          4.3  Use of the SONDEL Model
               During FY83 the Clearinghouse responded to a written request
from a Region to review the acceptability of the SONDEL11 model  for CO SIP
analyses in deep street canyons of a major city.  The model  was  designed
for application to deep street canyons with height to width ratios greater
than two.  This model differed significantly from the more commonly used
APRAC^2 street canyon model.  The major differences stemmed from the observa-
tion that flow patterns differ for deep canyons and shallow canyons.  Shallow
street canyons, those with height to width ratios in the order of one,
under crosswind conditions develop a vortex circulation which carries road-
way emissions to the lee side of the canyon.  Thus-maximum concentrations
occur on the upwind side of the street canyon.  As the canyon aspect ratio
(ratio of building height to street width) becomes larger or the Reynolds
number becomes lower, the vortex no longer develops in the canyon.  Under
these conditions the model  developer reasoned that it was not appropriate to
apply the APRAC model because nonvortex flows were often observed in deep
street canyons.  Measurements showed a strong tendency for flow  to be
channeled along the street direction, especially in deeper canyons.  Flow
perpendicular to the street canyon was never observed.
               The SONDEL model assumes channeled flow and dilution resulting
solely from turbulent diffusion.  This is a steady-state system  where the
total mass emitted from the top of the canyon equals the emissions generated
on the street.  The dependence on wind is implicit, as the level  of the
turbulence and turbulent diffusion are related directly to the wind speed.
The assumptions of steady-state conditions and uniform source strength in
                                     29

-------
the canyon restricts application of the model  to longer blocks where inter-
section factors do not seriously violate the  assumptions.   There  are three
zones defined in the street canyon:  (1) the  mechanical  mixing cell  (MMC)
where concentrations are assumed to be uniform,  (2)  the lower  canyon region
(LCR) where uniform diffusivity is assumed, and  (3)  the upper  canyon region
(UCR) where the diffusivity is assumed to be  exponentially  increasing.   The
shape of the MMC is defined as the upper half of an  ellipse having  the
semi-major axis along the ground and the semiminor axis vertical  above  the
center of the roadway.
               While the Clearinghouse understood the arguments favoring the
use of the model, it did not feel  that there  was sufficient expertise within
the Office of Air Quality Planning and Standards to  review  the detailed
technical aspects of the model.  The Clearinghouse also questioned  whether
it would be appropriate for the State to conduct a comparative technical  and
performance evaluation between SONDEL and APRAC, the model  that was at  that
time commonly used for street canyon analyses.   These questions were referred
to the Meteorology and Assessment Division, Office of Research and  Develop-
ment, for an opinion.
               Comments from the Meteorology  Division indicated that the
SONDEL model was an improvement over currently  available models.   Some  of
the input parameters may be difficult to define  and  require measurements
and experience in assigning values to them.   The Meteorology Division also
noted that SONDEL was the only model known that  is appropriate for  deep street
canyons.  Therefore, in any verification study  one would not be trying  to
choose the best model from a group, but rather  to demonstrate  that  the
physics of the model were an appropriate characterization of the  dynamics  in
                                     30

-------
the street canyon.  Secondly, a study should show that the concentration
estimates are reasonable.
               Based on the comments from the Meteorology Division, the
Clearinghouse recommended to the Region that SONDEL be accepted within its
stated limitations.  The approval  was conditioned subject to tests that the
model  was performing satisfactorily and refinements were made to the input
values for the turbulent diffusivity and the attenuation coefficient.
               This case is similar to those in Section 4.1  and 4.2 in that
a Regional Office requested an advance opinion on the approvability of a
nonguideline technique for use in  regulatory analyses.  However, it differs
in two important ways.  First, the request was written, entailing a more
complete documentation of the relevant facts and requiring a written response
from the Clearinghouse. ..Second, the case involved technical subject matter
of such a nature that the Clearinghouse needed an outside opinion on its
technical adequacy.  Such outside  opinions do not necessarily totally govern
the Clearinghouse response to the  Regional Office since the  Clearinghouse
is also responsible for ensuring that the endorsement of the proposed
technique does not create a consistency issue.  In the case  described above
there was no consistency issue since the model addressed a unique situation
for which national guidance was absent.
          4.4  Modeling of a Power Plant in an Urban Area
               During FY84 CPOB received from a Regional Office a proposed
Federal Register action to renew a variance to allow for the burning of
2.2% sulfur content fuel oil in a  boiler of a large power plant in an urban
area.   Model  Clearinghouse personnel  in CPOB reviewed the package and
identified several instances where the modeling used to support the SIP
                                     31

-------
revision apparently deviated from strict interpretation  of the current
modeling guidance.  These issues were then  referred  to the SRAB Model
Clearinghouse function for further review.
               SRAB personnel  found that most of the deviations from guidance
were of minor consequence, i.e., a strict application of guidance would  not
have resulted in a showing that the National  Ambient Air Quality Standards
(NAAQS) or PSD increments would have been violated as a  result of the  proposed
action.  One particular issue did entail  a  closer look at its technical  defen-
sibility and an examination of other Clearinghouse opinions for consistency.
In this case the problem entailed a combination  of modeling considerations
for which there was no single recommended model  available.  The Regional
Office made a judgment on which aspects of  the problem were most important
in terms of protection of the NAAQS and PSD increments and chose a model  that
would address those aspects.  Subsequent discussions within the Clearinghouse
and with the Regional  Office focussed on the  basis for that judgment.
               A check with the Clearinghouse and Federal  Register files
indicated that there were other cases, similar to this power plant, where
the same reasoning and choice of model has  been  used before.  Thus the
Clearinghouse deferred to the Regional Office and concurred with the modeling
used to support this SIP revision; it was technically defensible and not
inconsistent with similar actions.  The proposed and final rules governing
this SIP revision were eventually published in the Federal Register.
               Several aspects of the Model Clearinghouse operation are
illustrated by this example.  First it shows how a proposed regulatory action
containing modeling issues was reviewed and coordinated  by Clearinghouse
functions in both CPOB and SRAB.  The regulatory package was first reviewed
                                     32

-------
by CPOB and modeling issues were identified.   These  issues  were  then  addressed
by SRAB and comments provided to CPOB.   CPOB  then  used  these  comments as
inputs to the concurrence/nonconcurrence on the  regulatory  package.
               Second, this example  shows that the Clearinghouse  often
defers to the Regional Office on technical judgment  issues  where  there  is
not a clear indication of which technique is  more  appropriate.   The Regional
Office is "closer to the problem" and is aware of  more  technical  facts  and
other considerations relevant to the problem.
               Finally, this example again  illustrates  how  the Clearinghouse
checks previous determinations on like  issues to make  sure  that  there is no
conflict with precedents.
                                     33

-------
34

-------
5.0  CONCLUSIONS

     The Model Clearinghouse was created in November of 1980 with the dual

purpose of assisting the Regional Offices in their decisions on the accepta-

bility of nonguideline models, techniques and data bases and for reviewing

regulatory actions with modeling analyses as they are forwarded to CPOB.

Judging by the number (523)  and wide variety of issues referred to or

reviewed by the Clearinghouse, the demand for its services are high.

     While most cases referred to the Clearinghouse involved narrow sets  of

modeling issues, unique to each given application, there were also a signi-

ficant number of cases where the modeling issues were interrelated and a

coordinated and consistent response from the Clearinghouse was required.

Most notable were cases involving the use of ambient data to substantiate a

proposed technique and cases not covered by existing modeling guidance such
                                                  •
as estimates on tall buildings and long range transport.  Another class of

problems resolved by the Clearinghouse involved coordination between modeling

issues and broader scale air pollution control  policy.  These included PSD

increment consumption calculation, applicability of generic modeling guide-

lines and the effective date of modeling guidance.  A review of these major

recurring or generic modeling issues indicates that the Clearinghouse can

satisfactorily support Regional Office needs for technically defensible tech-

niques for complex situations.  At the same time the Clearinghouse ensures

national consistency within  the framework of the various regulatory policies

and the Guideline on Air Quality Models.

     The dual mode of Clearinghouse operation involving advance reviews of

proposed regulatory modeling techniques and coordinated SRAB/CPOB reviews

of proposed regulatory actions containing modeling issues has worked well.
                                     35

-------
The success of this program is primarily attributed to a continual, high
level  of coordination within the Clearinghouse and between the Clearinghouse
and the Regional  Offices.
                                     36

-------
 6.0  REFERENCES

 1.  Environmental  Protection Agency.   "Guideline  on  Air  Quality  Models,"
     EPA 450/2-78-027, Office of Air Quality  Planning and Standards,  Research
     Triangle Park, NC 27711, 1978.

 2.  Environmental  Protection Agency.   "Interim  Procedures for  Evaluating
     Air Quality Models (Revised),"  EPA 450/4-84-023, Office  of Air Quality
     Planning and Standards,  Research Triangle Park,  NC 27711,  1984.

 3.  Environmental  Protection Agency.   "Interim  Procedures for  Evaluating
     Air Quality Models:   Experience with Implementation," EPA  450/4-85-006,
     Office of Air Quality Planning  and Standards,  Research Triangle  Park,
     NC 27711, 1985

 4.  Environmental  Protection Agency.   "Regional Workshops on Air Quality
     Modeling: A Summary  Report," EPA 450/4-82-015, Office of Air Quality
     Planning and Standards,  Research Triangle Park,  NC 27711,  1981.

 5.  Turner, D. B., and J. H. Novak.  "User's Guide for RAM," EPA 600/8-78-016
     Vol a, b, U. S. Environmental  Protection Agency, Research  Triangle  Park,
     NC 27711, 1978.

 6.  Bowers, J. R., R. J. Bjorklund  and C.  S. Cheney.  "Industrial Source
     Complex (ISC)  Dispersion Model  User's  Guide,  Volumes 1 and 2," EPA
     450/4-79-030,  031, Office of Air Quality Planning and Standards, U. S.
     Environmental  Protection Agency,  Research Triangle Park, NC  27711,  1979.

 7.  Busse, A. D. and J.  R. Zimmerman.   "User's  Guide for the Climatological
     Dispersion Model," EPA R4-73-024,  U. S.   Environmental Protection Agency,
     Research Triangle Park,  NC 27711,  1973.

 8.  Meyers, S.  Memorandum of February 17  to Regional Office Air Management
     Division Directors,  "Emissions  Trading Policy Technical  Clarifications,"
     Office of Air, Noise and Radiation, U. S.  Environmental  Protection  Agency,
     Washington, DC 24060, 1983.

 9.  Pierce, T. D.  and D. B.  Turner.  "User's Guide for MPTER," EPA 600/8-80-
     016, U. S. Environmental Protection Agency, Research Triangle Park, NC
     27711, 1980.

10.  Burt, E. W.  "Valley Model  User's  Guide,"  EPA 450/2-77-018,  U. S.
     Environmental  Protection Agency,  Research Triangle Park, NC  27711,  1977.

11.  Del and, R.  "Final Report on Deep  Canyon Model:   SONDEL,"  Bureau of
     Science and Technology,  New York  City  Department of  Environmental
     Protection, New York, NY 10003, 1982.

12.  Simmon, P. B., R. M. Patterso-n, F. L.  Ludwig, and L.  B.  Jones.   "The
     APRAC-3/Mobile 1  Emissions and  Diffusion Modeling Package,"  EPA 909-9-81-
     002, Environmental Protection Agency,  Region  IX, San  Francisco, CA  94104,
     1981.
                                      37

-------
38

-------
                                  APPENDIX

                          EPA MODEL CLEARINGHOUSE
     The Model Clearinghouse was created in November 1980 as the single EPA
focal point for reviewing the use of dispersion modeling techniques in
specific regulatory applications.  The Clearinghouse also serves to compile
and periodically report for Regional Office benefit Agency decisions
concerning deviations from the requirements of the "Guideline on Air Quality
Models."

Need for the Model  Clearinghouse

     The guideline states that when a recommended model  or data base is not
used, the Regional  Administrator may approve the use of other techniques
that are demonstrated to be more appropriate.  There is also a need to
provide for a mechanism that promotes fairness and consistency in modeling
decisions among the various Regional Offices and the States.  The Model
Clearinghouse was created in order to promote this fairness and uniformity
and also to serve as a focal point for technical review of "nonguideline"
techniques proposed for use/approval by a Regional Administrator.

Functions of the Model Clearinghouse

     The major function of the Clearinghouse is to review specific proposed
actions which involve interpretation of modeling guidance, deviations  from
strict interpretation of such guidance and the use of options in the
guidance, e.g., Regional Office acceptance of nonguideline models and  data
bases.  This is handled in two ways:  (1) the Clearinghouse, on request
from the Regional Office, will review the Region's position on proposed
(specific case) use of a nonguideline model for technical soundness and
national consistency, and (2) the Clearinghouse will screen SIP submittals
for adherence to modeling policy and make recommendations for resolution of
any issues identified.

     A secondary purpose of the Model Clearinghouse is to communicate  to
regulatory model users in EPA significant decisions involving the interpreta-
tion of modeling guidance.  This is accomplished through an annual  newsletter
or "Clearinghouse report" which itemizes the significant decisions that
have been made and the circumstances involved.  This report serves to
improve consistency in future decisions and as a source of technical  infor-
mation for the Regional  Offices.

Structure of the Clearinghouse

     The Clearinghouse is formally located in the Source Receptor Analysis
Branch (SRAB) of OAQPS.   However, the Control Programs Operations Branch
(CPOB) also participates in Clearinghouse matters involving SIP attainment
strategies and other regulatory functions.
                                     A-l

-------
     The primary responsibility for managing the Clearinghouse and ensuring
that all of its functions are carried out is performed by a full-time person
from SRAB.  In addition CPOB supports the Clearinghouse wi'th one individual
who is also knowledgable in modeling policy.  This individual  is responsible
for screening SIP submittals and related documents, referring  issues to SRAB
through the Clearinghouse and documenting the final (and any significant
interim) decision on disposition of the issues.

Communication Chain

     The Model Clearinghouse functions within the organizational structure
of EPA.  As such the Clearinghouse serves the EPA Regional  Offices.  It
coordinates with and communicates decisions to the Regional Offices.  Any
coordination with State and local agencies and individual sources on Clearing-
house activities is a function of the EPA Regional Offices.
                                     A-2

-------
TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
ERA 450/4-86-006
2.
4. TITLE AND SUBTITLE
Activities of the EPA Model Clearinghouse,
A Summary Report: FY81-FY85
7. AUTHOR(S)
9. PERFORMING ORGANIZATION NAME Af^
Monitoring and Data Analys
Office of Air Quality Plan
U.S. Environmental Protect
Research Triangle Park, NC
JD ADDRESS
is Division
ning and Standards
ion Agency
27711
12. SPONSORING AGENCY NAME AND ADDRESS


3. RECIPIENT'S ACCESSION NO.
5. REPORT DATE
Mav 1986
6. PERFORMING ORGANIZATION CODE
8. PERFORMING ORGANIZATION R£POR~ NO
10. PROGRAM ELEMENT NO.
11. CONTRACT/GRANT NO.
13. TYPE OF REPORT AND PERIOD COVERED
14. SPONSORING AGENCY CODE
15. SUPPLEMENTARY NOTES
16. ABSTRACT

  This  report  summarizes  the  operation of the EPA Model  Clearinghouse during its first
  five  years of  existence,  FY81-FY85.   Included are a summary of the number of cases
  and the nature of  issues  reviewed  by the Clearinghouse and a description of major
  recurring and  generic  issues  referred to the Clearinghouse.  In addition, the report
  describes and  illustrates,  through a series of examples, how the Clearinghouse ful-
  fills  its major responsibility for review of specific proposed actions which involve
  interpretation of  modeling  guidance, deviations from such guidance, and the use of
  options in the guidance.
17. KEY WORDS AND DOCUMENT ANALYSIS
a. DESCRIPTORS
Air Pollution
Meteorology
Mathematical Models
18 DISTRIBUTION STATEMENT
Unl imi ted
b. IDENTIFIERS/OPEN ENDED TERMS
Model Clearinghouse
19. SECURITY CLASS (This Report}
Unclassified
20 SECURITY CLASS (This page )
Unclassified
c. COSATI Field/Group

21. NO OF PAGES
22. PRICE
EPA Form 2220-1 (Rev. 4-77)   PREVIOUS EDITION is OBSOLETE

-------
                                                         INSTRUCTIONS

   1.   REPORT NUMBER
       Insert the EPA report number as it appears on the cover of the publicat:on.

   2.   LEAVE BLANK

   3.   RECIPIENTS ACCESSION NUMBER
       Reserved for use by each report recipient.

       TITLE AND SUBTITLE
       "itle should indicate clearly and briefly the subject coverage of the report, and be displayed prominently.  Set subtitle, if used, m smaller
         •je or otherwise subordinate it to main title. When a report is prepared in more than one volume, repeat the primary title, add volume
         mber and include subtitle for the specific title.

   5.   REPORT DATE
       Each report shall carry a date indicating at least month and year  Indicate  the basis on which it was selected le g., date of issue, dare of
        n,  oval, date of preparation, etc.).

   6.   PERFORMING ORGANIZATION CODE
       Leave blank.

   7.   AUTHOR(S)
       Give name(s) in conventional order (John R. Doe, J. Robert Doe, etc. I.  List author's affiliation if it differs from the performing organi
       zation.

   8.   PERFORMING ORGANIZATION REPORT NUMBER
       Insert if performing organization wishes to assign this number.

   9.   PERFORMING ORGANIZATION NAME AND ADDRESS
       Give name, street, city, state, and ZIP code. List no more than two levels of an organizational hirearchy.

   10.  PROGRAM ELEMENT NUMBER
       Use the program element number under which the report was  prepared.  Subordinate numbers may be included in parentheses.

   11.  CONTRACT/GRANT NUMBER
       Insert contract or giant number under which report was prepared.

   12.  SPONSORING AGENCY NAME AND ADDRESS
       Include ZIP code.

   13.  TYPE OF REPORT AND PERIOD COVERED
       Indicate interim final, etc., and if applicable, dates covered.

   14.  SPONSORING AGENCY CODE
       Insert appropriate code.

   15.  SUPPLEMENTARY  NpTES
       Enter information not included elsewhere but useful, such as:  Prepared  in cooperation with, Translation of, Presented at conference of,
       To be published in, Supersedes, Supplements, etc.

   16.  ABSTRACT
       Include a brief ^200 words or less} factual summary of the most significant information contained in the report.  If the report Contains a
       significant bibliography or literature survey, mention it here.

   17.  KEY WORDS AND DOCUMENT ANALYSIS
       (a) DESCRIPTORS - Select from the Thesaurus of Engineering and Scientific Terms the proper authorized terms that identify the major
       concept of the research and are sufficiently specific and precise to be used as index entries for cataloging.

       (b) IDENTIFIERS AND OPEN-ENDED TERMS - Use identifiers for project names, code names, equipment designators, etc.  Use open-
       ended terms written in descriptor form  for those subjects for which no descriptor exists.

       (c) COSATI 1 IELD GROUP - Field and group assignments are to be taken from the 1965 COSATI Subject Category List. Since tne ma-
       jority of documents are multidisciplinary in nature, the Primary Field/Group assignment(s) will be  specific discipline, area of human
       endeavor, or type of physical object. The application(s) will be cross-referenced with secondary Field/Group assignments that will follow
       the primary postmg(s).

   18.  DISTRIBUTION STATEMENT
       Denote releasability to the public or limitation for reasons other than security for example "Release Unlimited."  Cite any availability to
       the public, with address and price.

   19. & 20.  SECURITY CLASSIFICATION
       DO NOT submit classified reports to the National Technical Information service.

   21.  NUMBER OF PAGES
       Insert the total number of pages, including this one and unnumbered pages, but exclude distribution list, if any.

   22.  PRICE
       Insert the price set by the National Technical Information Service or the Government Printing Office, if known.
EPA Form 2220-1  (Rev. 4-77) (Reverse)

-------