July 28, 1994



SUBJECT:  Fluid Modeling Protocol
          Muscatine Iowa Area

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

TO:       Richard L. Daye, Regional Meteorologist
          Air Planning and Development Section - Region VII


     In response to your request, we have reviewed your comments
and position that a field study be conducted to supplement the
proposed wind tunnel demonstration.  In general, we concur with
your comments and position that a field study is needed in this
case.  The following are additional comments concerning the need
for such a study.

     As reflected in your comments, the wind tunnel study may
provide useful information to characterize the dispersion processes
in the area of the Grain Processing Corporation (GPC) and Muscatine
Power and Water (MPW) facilities.  Also, one apparent objective of
this  characterization according to the protocol is to assess the
adequacy of the Industrial Source Complex (ISC2) model to represent
the dispersion characteristics of the area (i.e, urban versus
rural).  To do this horizontal and vertical dispersion coefficients
will be estimated from the concentration distributions in the
tunnel and compared with those predicted with the ISC2 model. 
Another objective is to assess the adequacy of the ISC2 plume rise
algorithms for modeling the plumes from the GPC and MPW facilities. 
The wind tunnel observed plume rise will be compared with the ISC2
model transitional and final plume rise calculations.  It is not
clear from the protocol how this information will be used in the
air quality compliance demonstration for the GPC and MPW
facilities.  We recommend that this be clearly articulated in the
protocol.  

     Modeling techniques developed from the tunnel demonstration
that are stability dependent would need to be evaluated in a field
study under other than near neutral conditions.  It was indicated
in the protocol that the wind tunnel demonstration would simulate
near neutral conditions.  As noted in your comments, an important
aspect of the field study would be to confirm acceptable
performance of the alternative model for other than near neutral
conditions.  

     In a related issue, it was also stated in the protocol that,
if needed, stable conditions may be simulated in the tunnel.  In
previous discussions with EPA technical staff concerning this
topic, it was noted that there is considerable uncertainty
concerning wind tunnel capabilities to simulate stable
stratification and correspondingly plume dispersion.  It was
concluded that further research and experience is needed for
acceptance of other than near neutral wind tunnel results in
regulatory assessments.  

     The protocol described previous dispersion modeling studies in
which the site land use was classified as urban or rural dependent
on wind direction sectors (i.e., "mixed mode model").  It was also
noted that one objective of the wind tunnel study was to determine
whether the site has rural or urban dispersion characteristics for
various wind directions.  It is not clear whether this information
would be used subsequently in a mixed mode dispersion model for the
compliance demonstration analyses.  It is likely that application
of a mixed mode model would be considered use of an alternative
modeling technique and thus would be subject to the requirements of
Section 3.2 of the Guideline on Air Quality Models (Revised), Use
of Alternative Models.  Consequently, a model performance
evaluation using measured air quality data would be required.
     
     In summary, we agree with your position that a field study is
needed to confirm the performance of alternative modeling
techniques developed from the wind tunnel demonstration under other
than near neutral conditions.  Also, if a mixed mode model is
anticipated for use in the air quality compliance demonstration, a
model performance evaluation would be needed.  It is not clear from
the protocol how the air quality modeling will be done to derive
the emission limits for the GPC and MPW facilities to show
compliance with the SO2 National Ambient Air Quality Standards
(NAAQS) for the Iowa State Implementation Plan.  If so, a modeling
protocol would need to be developed describing how the developed,
tested and evaluated model will be used in the compliance
demonstration.  This modeling protocol should be part of the wind
tunnel protocol.

     If you have any further questions please do not hesitate to
contact me at (919) 541-5562 or Dennis Doll at (919) 541-5693.

cc:  D. Doll
     J. Irwin