November 23, 1988







MEMORANDUM

SUBJECT:  Request for Use of ISCST and ISCLT Version 6.2 in Twin
          Oak Steam Electric Station PSD Application

FROM:     Dean A. Wilson, Meteorologist
          Techniques Evaluation Section, SRAB (MD-14)

TO:       James W. Yarbrough, Air Modeling Contact
          Region VI (6T-AN)


     In response to your request, the Model Clearinghouse concurs
with  your position that Change 2 of the ISC model in UNAMAP 6
may be used for the Twin Oak Steam Electric Station PSD analysis. 
As was the case in our previous concurrence for the five Texas
PSD sources (November 9, 1988 memorandum), we recommend that you
review the status of this permit when the necessary corrections
to ISC have been completed and are available.  If, at that point
in time, the analysis is not substantially underway, then this
source should be modeled with the corrected version of ISC.

     If you have any questions, please contact me.

cc:  D. deRoeck (MD-15)
     S. Reinders (MD-14)
     Regional Modeling Contact, Regions I-V, VII-X (with incoming
       memorandum and list of the FY-89 Clearinghouse memoranda)