February 23, 1993


MEMORANDUM

SUBJECT:  AES Guayama, Puerta Rico Proposal to Use the Rough                
          Terrain Dispersion Model with Off-Site Meteorological             
          Data

FROM:     Joseph A. Tikvart, Chief
          Source Receptor Analysis Branch (MD-14)

TO:       Kenneth Eng, Chief
          Air Compliance Branch, Region II (2AWM)


     In response to your request, the Model Clearinghouse has reviewed your
position requiring AES to collect on-site meteorological data at their
proposed plant site.  We agree with your rationale and conclusion.  Your
reasoning is sound and your conclusion is consistent with guidance and with
a number of precedents for similar situations, including the Pfizer
situation which you cite.

     In addition to Pfizer, there is also a more recent example of a
precedent in Region IX that is especially relevant.  In this case, which
also involved AES, the Company proposed to utilize nearby off-site
meteorological data for a Complex I analysis for a proposed plant in
Hawaii.  In this case, the Clearinghouse agreed with Region IX that use of
such data would be inappropriate.  A copy of that determination is
attached.

     If you have any further questions, please contact Dean Wilson at 919-
541-5683.

Attachment

cc:  W. Barrett
     A. Colecchia
     D. deRoeck
     S. Riva
     D. Wilson