March 2, 1993


MEMORANDUM

SUBJECT:  E. Helena Lead SIP Attainment Demonstration

FROM:     Gary Blais, Environmental Protection Specialist
          SO2/Particulate Matter Programs Branch (MD-15)

          Dean Wilson, Meteorologist
          Source Receptor Analysis Branch (MD-14)

TO:       Laurie Ostrand, Environmental Engineer 
          Air Programs Branch, Region VIII (8ART-AP)

          Kevin Golden, Regional Meteorologist
          Technical Operations Branch 


     In response to the request of January 12, 1993, the Model
Clearinghouse has reviewed the identified issues relating to the E. Helena
Lead SIP attainment demonstration.  First, regarding the stack height
increase, gas stream merging, and tie-in questions, we believe that these
proposed changes are approvable and do not represent prohibited dispersion
techniques for the following reasons:

     1.  There will be a plant-wide net reduction in allowable lead
emissions.

     2.  "EPA believes that as long as at least one gas stream is being
controlled, the motivation for the stack [merger] is not likely to be
governed by a desire for dispersion credit." Response to Comments on the
November 9, 1984, Proposed Stack Height Rules.

     3.  It may be argued that the venting of source 9P to the new 200 foot
stack is being done for sound engineering reasons, since the original stack
for this source is only 18 feet tall and the new stack is already a part of
an overall plan to reduce emissions at the plant and is not above the good
engineering practice de minimis stack height (65 meters).

     4.  The stack height credit for tying-in source 17P to stack 7P is
approvable but should be limited to 65 meters.

     With regard to process weight restrictions/emissions limit averaging
times, this is a Regional decision and should probably be made based on
enforceability concerns.

     With regard to the time of day restrictions, we agree with your
position that since the restrictions are based on historical meteorological
data and not real-time data, they are approvable measures from a regulatory
standpoint.  From a technical standpoint, it is our understanding that
ASARCO's proposal to restrict emissions during the nighttime hours stems
from higher modeled impacts associated with low level fugitive emissions
during stable meteorological conditions when dispersive conditions are
minimal.  Following the procedures for which we currently determine
stability for modeling purposes, such conditions would only occur during
the nighttime hours.  We have discussed with you the issue of whether our
methods of determining stability for modeling purposes would capture all of
the cases of truly reduced dispersion leading to elevated ground level
concentrations from low level fugitive sources.  We agreed that because of
limitations in our ability to simulate the atmosphere in time and space,
there could be cases where low level fugitives would have an elevated
impact due to reduced dispersion outside of the nighttime hours.  On the
other hand, since lead is a quarterly standard, the impact of a few such
hours would be expected to be minimal on the quarterly average.

     With regard to the enforceability of time of day restrictions, we
agree that specific recordkeeping and reporting requirements must be
maintained, and how this will be done must be spelled out in the SIP. 
Also, periodic measurements of the lead content of the materials being
handled must be made and recorded.  We also agree that it would be wise to
do recordkeeping on a monthly basis.

     If you have further questions, please contact us.
     
cc:  D. Atkinson
     E. Ginsburg
     J. Paisie
     J. Tikvart