November 18, 1993



MEMORANDUM

SUBJECT:  Buiding Wake Effects on Volume Sources at FMC
          Corporation

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

TO:       Robert B. Wilson, Regional Meteorologist
          Region X (ES-097)


     In response to your request, the Model Clearinghouse has reviewed your
proposal for treating building wake effects on volume sources.  We concur
with your proposed approach for modeling the FMC facility.

     Your application of area of influence considerations of buildings for
volume sources seems quite reasonable.  We note, also, that your recommend-
ed procedure is equivalent to the recommended formula for cases when the
volume source is larger than the building.  However, for cases when the
volume source is much smaller than the building, the initial sigmas do not 
approach values that would be calculated by the building downwash algorithm
in the Industrial Source Complex (ISC2) model.  For this reason, I would be
concerned about the use of your procedure when the size of the source is
substantially smaller than the size of the obstruction (building). 
Fortunately, this does not occur at the FMC facility.

     As you are aware, before this or any other procedure can be recommend-
ed for generic use, it must undergo a more intensive technical review, as
well as both peer and public reviews.

cc:  D. Wilson