November 15, 1988







MEMORANDUM

SUBJECT:  Information Regarding Refinery Tank Farms and Their    
          Rural/Urban Designation

FROM:     Dean A. Wilson, Meteorologist
          Techniques Evaluation Section, SRAB (MD-14)

TO:       James W. Yarbrough, Air Modeling Contact
          Region VI (6T-AN)


     The Model Clearinghouse has considered your concerns
regarding the urban/rural classification of areas characterized
by tank-farm land use.  We note from the Clearinghouse files that
there have been several cases in the last few years where there
has been an issue regarding the appropriate classification of an
area.  In most of these cases the land use was approximately 50
percent rural/50 percent urban and there were differences of
opinion as to which was the appropriate classification.  Such
differences of opinion are not surprising since, as Dr. Auer has
pointed out in the TENERA letter, there is an element of profes-
sional judgment involved in determining the land use.  We believe
that the tank-farm land use issue is another example of a dif-
ference of opinion that can be traced to professional judgment.

     In 1986 Region V, who had been facing a number of these
"differences in professional judgment" issues on urban/rural
classification, asked the Clearinghouse if it might not be
appropriate to consider other criteria in addition to the land
use in making the determination.  The Clearinghouse recommenda-
tion at that time was that we not modify our urban/rural guidance
but continue to entertain exceptions on a case-by-case basis.  In
particular, the Clearinghouse noted that a justification based on
a comparison between monitored data and model estimates would
probably be the most defensible.  Since that time, Region V has
used this monitored/modeled data comparison in some cases to
clarify the classification.

     We continue to believe that there is insufficient basis to
change, clarify, or tighten our guidance on urban/rural clas-
sification, at this time.  Thus, future issues such as your tank-
farm issue should be handled on a case-by-case basis as they
arise, perhaps clarifying any differences of opinion using some
of the criteria considered by Region V.  However, we are willing
to entertain a proposal to modify our guidance.  Accordingly, in
the process of drafting the next Regional Office/State Modelers
Workshop Agenda, we will call you to see if you would like to
take the lead in proposing "strawman" revised guidance at that
Workshop.  That strawman probably should not be narrowly limited
to the tank-farm issue but attempt to address the general problem
of tightening guidance to minimize the qualitative nature of the
urban/rural classification scheme.

     Finally, I would like to note that the Model Clearinghouse
disagrees with TENERA's (July 2, 1988) conclusion that Dr. Auer
completely agrees with the TENERA position that the tank-farm
area is rural.  This conclusion does not follow from Dr. Auer's
opinion that "good judgment and common sense" should be used in
making each determination.

     If you have any questions please contact me.

cc:  D. deRoeck (MD-15)
     D. Grano (MD-15)
     S. Reinders (MD-14)
     D. Wilson (MD-14)
     Regional Modeling Contact, Regions I-V, VII-X (with incoming 
       memorandum and list of FY-89 Clearinghouse Memoranda)