March 1, 1990  
  
  
  
  
  
  
  
MEMORANDUM  
  
SUBJECT:  East Helena Lead SIP  
  
FROM:     Joseph A. Tikvart, Chief  
          Source Receptor Analysis Branch (MD-14)  
  
          Robert Bauman, Chief  
          SO2/Particulate Matter Programs Branch (MD-15)  
  
TO:       Douglas M. Skie, Chief  
          Air Programs Branch, Region VIII (8AT-AP)  
  
          In response to your request we have reviewed the February 14,
1990 letter from ASARCO to you as well as your comments on the Company's
proposal concerning development of the SIP for lead (Pb).  We agree with
your position and your specific comments on the Company's proposal.  In
that regard, we would like to stress the importance of continuing the every
day sampling through the first two quarters of 1991, as mentioned in your
Comment 3.  We also agree that the schedule leading up to a February 1992
SIP submittal should be maintained.  
  
     Based on the historical monitored data we believe that it is
important, if at all possible within the schedule, to include ambient data,
based on every day sampling, from the first quarter of 1991 in the receptor
modeling analysis and reconciliation process.  The first and fourth
quarters seem to typically contain some of the higest Pb levels.  This
result is also consistent with meteorological considerations; Spring and
Summer are climatologically good dispersion seasons.  
  
     It is our belief that the biggest uncertainty in modeling the smelter 
lies in the emissions quantification and characterization (e.g. point,
area, volume sources) and not in the dispersion models themselves.  The 
reconciliation of receptor modeling with the dispersion modeling is
important in that it will foster the refinement of these emission
uncertainties.  Also  the collection of on-site meteorological data should
alleviate past uncertainties associated with the use of off-site data.  
  
     Thus it is our position that the ISCST model is the most appropriate
dispersion model for application to the simple terrain areas near the
smelter.  If the Company wishes to consider an alternative model to ISCST,
it will be necessary to conduct a formal comparative evaluation of such an
alternative model with the ISCST model.  Procedures for planning and
conducting such an evaluation are provided for in EPA guidance.  Please
note that EPA policy on model evaluation studies is that such studies may
not be used to postpone deadlines for SIP submittal where existing
guideline models are applicable. Thus, while we will consider the results
of any model evaluation submitted to us subsequently, we will continue to
expect a complete SIP revision to be submitted by February 1992.   
   
     As a final note, we wish to remind you that the source is subject to 
reevaluation under the 1985 stack height rules.  For purposes of 
reconciliation of dispersion and receptor models, actual stack height
should be used.  However, to set an emission limit, it must be shown that
the existing stack meets Good Engineering Practice (GEP) or the plant must
be modeled at a height equal to GEP. 
 
     If you have any questions please contact Dean Wilson at 629-5683.  
  
cc:  J. Calcagni  
     W. Laxton  
     M. Smith  
     D. Stonefield