November 7, 1989
  
  

  
  
  
SUBJECT:  Interpretation of On-Site Meteorological Data  
          Requirements and the Use of RTDM for a PSD Source  
  
FROM:     Joseph A. Tikvart, Chief  
          Source Receptor Analysis Branch (MD-14)  
  
TO:       Raymond Werner, Chief  
          Impact Assessment Section, Region II  
  
  
     The following is the Model Clearinghouse opinion in response to your  
request for an interpretation of complex terrain modeling issues primarily 
associated with the proposed new Pfizer facility in Puerto Rico.
 
Use of Nearby Representative Meteorological Data in a Complex Terrain Model 

     We agree with your conclusion that it will be necessary for Pfizer to 
collect on-site meteorological data if they plan to use RTDM, Complex I or
any other complex terrain model that requires the input of sequential  
meteorological data.  While some persuasive technical arguments can be made 
that the Aguirre data might be representative, one can also take issue with 
this position since the data site is located on the bay whereas Pfizer is  
located inland a couple of miles in more rugged terrain.  However, the main 
reason for requiring on-site data is the precedent that was set with the   
May 29, 1987 memorandum to Region IV (attached) involving RTDM and the
Alabama SIP.  There we agreed, based on a consensus of the Regional
Meteorologists, that it was more important to maintain technical
credibility and consistency; thus the use of 60m meteorological data, in
lieu of 100m data, could not be accepted.  
  
Use of RTDM  
  
     We believe it is premature to deal with your several "what if" and  
generic questions regarding the future use of RTDM.  All of the Regions
will  be party to decisions on how we deal with the future of RTDM.  At the
present time the only advice that we have been giving to your Region and
others is that you should be cognizant that there is a potential problem
with RTDM and  you should try to factor in options on commitments to future
applications of  the model as much as possible.  We do recognize that if
the model is indeed removed from Guideline status it will be necessary to
entertain grandfathering for those cases where the model has already been
applied or where irrevocable commitments to its use have been made.  It
appears that your Halfmoon Power Plant application might be a candidate for
grandfathering.  Right now we believe that we would handle the
grandfathering on a case-by-case basis, similar to the procedure we used
with the faulty ISC code problem; for each case a short memorandum to the
Clearinghouse outlining the facts in the situation would be necessary.  
  
    If you have any questions, please contact Dean Wilson (FTS-629-5683) or
me (FTS-629-5562).  
  
Attachments  
  
cc:  D. DeRoeck, OAQPS (MD-15)   
     D. Grano, OAQPS (MD-15)      
     W. Laxton, OAQPS (MD-14)  
     D. Wilson, OAQPS (MD-14)  
  
                   
                            (Attachment Following) 
  
  
                                May 29, 1987
 
 
 
 
 
 
 
MEMORANDUM 
 
SUBJECT:  Alabama GEP SIP--Gaston Power Plant 
 
FROM:     Joseph A. Tikvart, Chief 
          Source Receptor Analysis Branch 
 
TO:       Lewis Nagler, Regional Meteorologist 
          Air Programs Branch, Region IV 
 
 
     As followup to Dean Wilson's November 5, 1986 memorandum, we discussed
the acceptability of RTDM and the use of 60m wind data for input to the
model to set the Gaston GEP emission limits and related issues at the
Regional/State Modelers Workshop, May 12-15, 1987.  In order to close the
loop on Gaston from a modeling standpoint, I would like to summarize the
Workshop discussion/con- clusions, as I understood them. 
 
     We discussed extensively the data input (wind speed and direction) 
required for RTDM.  The unanimous conclusion of the modelers is consistent 
with the regulatory work group recommendations.  This conclusion was that 
winds representative of wind flow conditions at stack top height should be 
used as input to RTDM.  This is also consistent with the prevailing
scientific opinion.  The use of measurements representative of wind flow at
stack top is superior, and in complex terrain these winds cannot be
established accurately from lower level measurements.  However, for stacks
greater than 100m, the measurement height may be limited to 100m in height
relative to stack base. The use of stack top winds is also consistent with
present modeling guideline recommendations to measure transport level wind
direction.  EPA's rationale for its recommendations is that the scientific
integrity of this model is enhanced with the input of these winds.  The
technical study of input winds performed by ECE, Inc. for the Gaston plant,
on the other hand, is incomplete.  And even if completed, there was a clear
consensus at the modelers workshop that the scientific integrity of RTDM is
not maintained by extending the wind profile theory, inherent in the ECE
analysis, below 100m for complex terrain applications.
 
     Thus, if RTDM is to be applied to set an emission limit at Gaston, 
representative wind data from the 100m level will be needed for model
input.  With regard to the next steps toward completion of the Alabama GEP
SIP, I suggest you discuss the alternatives with the Control Programs
Operation Branch. 

     It should be noted that the Agency encourages source owners to allow
for time necessary to (1) gather input data needed for new models such as
RTDM, (2) execute the model to determine the emission limit and (3) submit
the documentation to the State for rulemaking action.  If there is a
compelling regulatory reason why an immediate action on the Gaston plant
might be necessary, other screening techniques which are less demanding in
their input data requirements are available.  EPA's rationale for its
recommendation on winds has been known by industry since July 1985 and thus
there has been ample time to plan for, if not complete much of, the data
collection process. 
 
cc:  T. Helms 
     S. Reinders 
     R. Rhoads 
     D. Stonefield 
     D. Tyler