January 7, 1990 
 
 
 
 
 
MEMORANDUM 
 
SUBJECT:    Effect of Changing Stack Heights on Prevention of 
            Significant Deterioration (PSD) Modeling and Monitoring 
 
FROM:       John Calcagni, Director 
            Air Quality Management Division (MD 15) 
 
TO:         Bruce P. Miller, Chief 
            Air Programs Branch, Region IV 
 
 
      This is in response to your October 20, 1989 memorandum concerning  
whether and when the beneficial air quality impacts that result from
raising  an existing stack height at a source can be considered as part of
a proposed  PSD modification.  You asked for our comments on your draft
response to Mr. Richard Grusnick's (Alabama Department of Environmental
Management) September 11, 1989 letter on this issue.  I have reviewed your
draft response concerning the following specific examples provided by Mr.
Grusnick. 
 
      Example 1.  A baseline (non-increment consuming) unit raising its
stack (from 100 feet to 250 feet) at the time of a mill expansion.  The
reason for raising the stack is:  
 
            (a)  to produce enough air quality credit to reduce the        
                 ambient impact caused by the expansion; and 
 
            (b)  to prevent a nuisance to workers in a new 200-foot        
                 building. 
 
      Example 2.  An existing PSD increment-consuming unit raising its
stack (from 100 feet to 250 feet) in conjunction with a mill expansion to
avoid worker exposure inside a new 200-foot building. 
 
      Example 3.  An existing PSD increment-consuming unit (with a wet
scrubber and a 100-foot stack) whose emissions would be merged with new
emissions from a proposed new adjacent unit (with an ESP) with a 300-foot
stack.  
 
      I agree with your position that the reason why a source raises a
stack is not relevant in deciding whether the air quality benefit to be
derived from the stack increase can be considered in the PSD analysis. 
However, the maximum height creditable as the good engineering practice
(GEP) stack height without providing a demonstration is 65 meters
(approximately 213 feet).  For a height greater than 65 meters to be fully
creditable as the GEP stack height, it must be established in a manner
consistent with the stack height rules.   
 
        In response to the question of when the increase in a stack height
can be considered as part of a proposed modification, I believe that the
increase must be proposed in conjunction with the overall modification, but
need not be directly related to other physical changes or changes in the
method of operation being proposed by the source.  That is, the stack being
raised need not be physically tied to the emissions unit(s) being
constructed or modified.  Thus, when a stack height increase is proposed in
a PSD (modification) application, any creditable air quality improvements
resulting from the higher stack (whether or not any increase in emissions
resulting from the proposed modification are to be released through such
stack) should be considered in the preliminary modeling analysis to
determine whether further modeling or preconstruction monitoring would be
required.   
 
      In each of the examples provided by Mr. Grusnick, I would consider
the proposed stack height increase to be part of the proposed modification,
and such increase, in general, should therefore be used in the
determination of whether PSD modeling or preconstruction monitoring would
be required.  However, before any new stack exceeding 65 meters
(approximately 213 feet) could be fully creditable, it would have to be
verified as the GEP height in accordance with approved stack height rules. 
There are additional requirements with regard to the merging of exhaust gas
streams that should be carefully evaluated to determine the creditable
stack parameters in the third example. 
 
      If you have any questions concerning this response, please contact 
Dan deRoeck at 629-5593.        
 
cc:   J. Calcagni 
      E. Lillis 
      G. McCutchen 
      E. Ginsberg 
      Air Branch Chief, Regions I-III, V-X     
      NSR Contacts