United States Environmental Protection Agency
          Office of Air Quality Planning and Standards
          Research Triangle Park, North Carolina 27711

                        December 1, 1986





MEMORANDUM

SUBJECT:  Grandfathering of Modeling Analyses

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

TO:       Michael Koerber
          Regional Meteorologist, Region V

    Thank you for providing the list of regulatory actions for
States in  Region V that contain modeling analyses subject to
decisions on "grandfathering" the use of previous modeling
guidance.  As we have discussed with you, we intend to use the
list for information purposes and agree with your proposal to
seek clarification or documentation from the State on each SIP
submittal.  We provided some guidance on which to base a decision
on grandfathering during the last Regional Modelers Workshop.

    With respect to your second issue, long standing actions of
the type you mention that include substantial periods of
inactivity should be reexamined on a case-by-case basis.  The
following factors directly apply to the case you raise: (1) seven
years have passed since the initial agreement; (2) major
evolution of our guidance has taken place; (3) there has not been
a mutually recognized protocol in effect since 1979, and (4)
there are no ongoing analyses that would be disrupted by
implementing our new guidance.  Base on these factors, we do not
believe grandfathering is appropriate for this case.  

    Please contact me if you have further questions.

cc:  T. Helms
     R. Rhoads
     S. Rothblatt
     D. Wilson