March 15, 1991


MEMORANDUM

SUBJECT:  Use of CTDMPLUS in the Virgin Islands Water and Power  
          Authority PSD Application

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

TO:       Raymond Werner, Chief
          Impact Assessment Section, Region II


     In response to your memorandum of February 27, 1991, the
Model Clearinghouse has reviewed the protocol you attached and
offers the following comments.  As you know, the general outlines
of the protocol were discussed by the TTW-CTDM Work Group during
a conference call on February 28 in which Desmond Bailey and Jim
Dicke participated.  Our comments should complement what 
Annamaria Colecchia heard then.

     In general we believe the Work Group's main concern was that
the 100m tower might not be tall enough to provide the necessary
data at plume heights of concern.  The suggestion was made that
the source (VIWAPA) run CTSCREEN to determine the plume height(s)
associated with maximum impacts and use these results to deter-
mine the appropriate tower height.  In addition, it was implied
that, depending on the magnitude of the estimated concentrations,
it may not be necessary to run CTDMPLUS.  It was also unclear
whether the calculated final stable plume height of 151.7m for
the unit 16 gas turbine is representative of plume heights of
interest, i.e. associated with the important meteorological
conditions for this site; these should be determined using
CTSCREEN.  The Work Group also noted that cloud cover, a variable
needed by CTDMPLUS, is not mentioned in the protocol.  The
importance/necessity of observing this variable should be 
discussed with Steve Perry, ASMD.  With regard to the measure-
ments of delta-T, the Work Group suggested that the 10 to 
40-meter delta-T should be determined and archived along with the
delta-T's for 2 to 10-meters, 10 to 100-meters and 40 to 
100-meters.

     We concur with the Work Group's comments and add that some
"tightening" on QA/QC may be appropriate, e.g. page 10, line 4
from bottom should state that procedures from the QA Handbook
will be used whenever possible and deviations shall be 
documented/justified.  In addition, we strongly encourage VIWAPA
to use the solar radiation/delta-T (SRDT) method for determining
on-site stability as proposed in Supplement B and the Addendum to
the On-Site Meteorological Program Guidance document.  The SRDT
method is discussed very briefly on page 8 of the protocol.

     If you have questions regarding these comments, please
contact Jim Dicke at 629-5682.

cc:  D. Bailey
     J. Dicke
     S. Perry
     D. Wilson