March 23, 1990
 
 

 
MEMORANDUM 
 
SUBJECT:  Mon Valley SO2 Study 
          Allegheny County, PA 
 
FROM:     Joseph A. Tikvart, Chief 
          Source Receptor Analysis Branch (MD-14) 
 
TO:       Marcia L. Spink, Chief 
          Air Programs Branch, Region III (#AM10) 
 
          In response to your request the Model clearinghouse has reviewed 
your proposal for completing the Mon Valley study and establishing SO2 
emission limits for Allegheny County, PA.  Based on the information
provided in your memorandum and subsequent discussions between our staffs,
it appears that your proposed approach is conservative in that it is
mindful of potential underprediction problems.  It is our understanding
that both the State and Allegheny County BAPC support the proposal.  It is
also our understanding that post-application monitoring will be undertaken
in the Clairton area to ensure that the uncertainties in emissions and
modeling do not result in any NAAQS violations.  With these understandings,
and subject to the condition described below, we support your proposal as
being technically reasonable.  
 
     A condition of our support is that you will be able to satisfactorily 
reconcile the basis for your action with modeling guidance at that point in
the future when formal regulatory action is taken.  As you may be aware,
the procedures in the Allegheny County study leading to the development and

evaluation of a nonguideline model, while perhaps technically logical,
would not meet our current regulatory guidelines which specify the
requisite procedures for justifying nonguideline models.  This was also the
case in 1986, when Region III last contacted the Model Clearinghouse
regarding the design of the study.  At that point in time we negotiated an
agreement with Region III (July 9, 1986 memorandum from me to J. Sydnor) on
how the study would be conducted to be consistent with the guidance in
place at that time.  The agreement included grandfather justifications for
certain directions that the study would take in order to take advantage of
existing data bases and prior agreements.  
 
     At the present time we have an "information gap" between the 1986 
agreement regarding the conduct of the study and the outcome of the study, 
namely the selection of MPMOD for use in one or more areas in Allegheny 
County.  If and when MPMOD is used to support emission limits contained in
a Federal Register package, this information gap will need to be filled in
as part of the reconciliation of the chosen use of the nonguideline model
with guidance.  My understanding, based on discussions between our staffs,
is that you believe that such reconciliation can be satisfactorily written
at the time that regulatory action is taken. 
 
   In summary, we support your proposed action on the Allegheny County SO2 
SIP, subject to the understandings and conditions detailed above.  If you
have any questions please contact me at 629-5562 or the appropriate
Clearinghouse contacts (Dean Wilson, TSD, 629-5683 or Doug Grano, AQMD,
629-5255).  
 
cc:  R. Bauman 
     E. Ginsburg 
     D. Grano 
     D. Wilson 

bcc:  Regional Modeling Contact, Regions I-X, (with copy of incoming 
memorandum and list of FY-90 Clearinghouse memoranda)