September 17, 1991


MEMORANDUM

SUBJECT:  AES Ohana, Inc. PSD Permit Application

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

TO:       David Calkins, Chief
          Air Programs Branch, Region IX


     In response to your request, the Model Clearinghouse has
reviewed your position that AES Ohana needs to collect on-site
meteorological data for input to COMPLEX I.  The model will be
used in the ambient air quality analysis for their proposed power
plant at Barbers Point, Hawaii.  We agree with your position.  It
has been a long-standing EPA policy that when modeling in complex
terrain with a model requiring the input of hourly meteorological
data, such data need to be collected on-site in order to properly
characterize the transport and dispersion of the plume.

     It should be noted that, in addition to the anemometer
height problem that both you and the State of Hawaii have
identified with the off-site data, there is also an additional
consideration that makes the off-site data clearly inferior to
that of on-site data.  Whereas the wind direction and speed from
the off-site data result from "1-minute" dial readings taken once
per hour, the on-site data would represent true hourly averages
of 360 to 3600 samples. These data are clearly better for
characterizing plume transport and dispersion over an hourly
period, which is the basic time frame, or kernel, for all
concentration calculations in COMPLEX I.

     In summary, we support your conclusion that AES Ohana needs
to collect on-site meteorological data.  Numerous Model
Clearinghouse responses to issues similar to yours over the past
ten years have been consistent with this position.  Also, it
should be noted that, from a national perspective, we are aware
of contemporary projects in other Regions that could potentially
be compromised if a decision were made in this case to allow an
exception to our policy.

     If you have any questions please contact Dean Wilson at 
FTS 629-5683.

cc: D. Bailey
    D. deRoeck
    D. Wilson