January 16, 1990 
 
 
 
 
 
 
 
MEMORANDUM 
 
SUBJECT:  Refined Metals Lead Modeling Analysis 
 
FROM:     Joseph A. Tikvart, Chief 
          Source Receptor Analysis Branch (MD-14) 
 
TO:       Steve Rothblatt, Chief 
          Air and Radiation Branch, Region V (5AR-26) 
 
     In response to your request the Model Clearinghouse has examined
issues associated with particle size distributions, settling velocities and
surface reflection at Refined Metals.  We agree that the positions you take
on each of these issues are appropriate, given the guidance and the
case-specific information that appears to be available in this case.  The
modeling procedures used in Alabama are not relevant since the issues are
primarily those of source characterization, which must be established on a
case-by-case basis. 
 
     In specific answer to your questions, the use of the AP-42 size 
distributions is appropriate.  Lacking information to the contrary, we
believe that you could also justify your assumption that particles larger
than 15 um should be modeled at 15 um in order to produce a conservative
air concentration estimate.  With regard to the use of the settling
velocity equation in the ISC Users Guide, the Guide indicates that the
equation is valid for particle densities on the order of 1 g/cm3.  While it
might be argued that particles containing lead may be heavier than this, it
would be up to the Company to establish a more representative density,
specific to their plant, then establish that the Users Guide equation is
still valid and applicable for that density.  Lacking such information it
can be reasoned that your position is either realistic or conservative
since deposition will either be estimated correctly or slightly 
underestimated.  With regard to the reflection term, we agree that Figure
2-8 of the User's Guide would constitute guidance for determining the
reflection coefficient.  Assuming that you have properly interpreted that
figure for the deposition velocities applicable in this case, we agree with
your position. 
 
     If you have any questions, please contact Dean Wilson at 629-5683. 
 
cc:  D. deRoeck 
     M. Smith 
     D. Wilson