January 27, 1992


MEMORANDUM

SUBJECT:   East Helena Lead SIP - Protocols for Design Value
           Determination and Model "Verification"; Clarification
           of Model Clearinghouse Memorandum of December 23, 1991

FROM:      Tom Coulter, Environmental Scientist
           Techniques Evaluation Section, SRAB (MD-14)

           Dean Wilson, Meteorologist
           Techniques Evaluation Section, SRAB (MD-14)

TO:        Mindy Mohr, Lead SIP Coordinator
           SIP/Permit Section, Region VIII (8AT-AP)


      This transmittal is to clarify our December 23, 1991
memorandum to you, particularly the intent of the comments
(Attachment 1) on the Inter-model Comparison Protocol 
(December 2, 1991 Protocol).  While everything in the attachment
was accurate, its intention was not to undermine any ongoing
activities engaged by ASARCO or any agreements between ASARCO and
Region VIII.  While the attachment stated that ASARCO's intended
efforts described in Section 2.2 of the December 2, 1991 Protocol
were not rooted in any definitive Environmental Protection Agency
(EPA) guidance or policy (and therefore not amenable to standard
EPA evaluation), it was not intended to say that such efforts
were without value.  Indeed, such efforts, especially presented
as a "demonstration," may provide valuable insight into the
degree of uncertainty to be expected between the now reconciled
dispersion modeling estimates and receptor modeling results for
the 10 selected days at each site.  Demonstration exercises of
this nature using independent data are strongly encouraged in any
modeling endeavor.  And we applaud the foresight given to perform
such an effort.

      We hope this clarification is helpful and eliminates any
confusion that might be associated with our December 23, 1991
memorandum.  We also hope that any misunderstanding it may have
caused does not compromise the level of effort to be carried out
in the remainder of this activity.  If you have any questions,
please feel free to call one of us at FTS 629-5683.

Attachment

cc:   J. Irwin
      J. Tikvart