October 8, 1992


MEMORANDUM

SUBJECT:  Response to Proposal to Allow Credit for a Stack Height
          Increase at the Dade County Resource Recovery Facility, Dade
          County, Florida

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

TO:       Lewis Nagler, Regional Meteorologist
          Air Enforcement Branch, Region IV 


Background

     The Dade County Resource Recovery Facility has submitted a prevention
of significant deterioration (PSD) application to add two new boilers and
to modify the existing four boilers.  The existing boilers (units 1-4) vent
through two 150-foot stacks.  Two new 250-foot stacks will be built with
dual liners (one per liner).  The current stacks must be removed in order
to replace the existing control equipment with more stringent control
devices.  In addition to the modifications to units 1-4, two new boilers
will be added which will vent through a third 250-foot dual liner stack. 
The building dimensions of the new boiler building will be 146 feet high by
141 feet long by 136 feet wide.  All stacks are within the influence of
this building.  The existing boiler building for units 1-4 is 118 feet high
and good engineering practice (GEP) for the existing stacks is 295 feet. 
The GEP for the new stacks will be 354 feet.  Total SO2 emissions for the
facility will be reduced by 117.4 tons per year after modifications and
additions are made.

Response

     In light of the June 29, 1992 memorandum from John Calcagni on credit
for stack height increases due to the siting of new nearby structures, you
have taken the position that the facility can be given credit for the
proposed increase up to 250 feet.  Before deciding to concur with your
position or not, we discussed this matter via a conference call with Eric
Ginsburg (Chief, SO2 Programs Section), Dean Wilson (Model Clearinghouse),
and Regional representatives.  Regions I-VI, VIII, and IX participated in
the call.  Pat Embrey (Office of General Counsel) was unable to participate
in the call but had been consulted beforehand.  

     This was done because there had been some concern raised over the
possibility that this change in policy could be seen by sources as an
opportunity to erect frivolous structures upwind of their stacks in order
to qualify for the exemption from fluid modeling demonstrations possible
under the Calcagni memorandum.

     While some Regions expressed concern over allowing credit for any
stack height increases for sources with short stacks, whatever their
justification, all of the Regions that took part in the discussions agree
that Region IV's interpretation of the Calcagni memorandum is appropriate. 
There was a consensus that it is highly unlikely that sources will attempt
to qualify for the exemption under the Calcagni memorandum by building
frivolous structures.  No other objections were raised by any other parties
on the call.  We too agree that your interpretation is appropriate and we
concur with your position.  However, protecting the national ambient air
quality standards (NAAQS) and PSD increments is still of paramount
importance.  Therefore, the facility must be modeled using the downwash
option of any approved model at the proposed height (250 feet) so that the
resulting emission limit is sufficient to ensure that the source will not
cause or contribute to a violation of the NAAQS or PSD increments.  If a
violation is predicted by the model, either the emission limit must be
lowered or the stacks increased, possibly all the way up to GEP height (354
feet) to eliminate the violation.

     Additionally, keep in mind that the facility's emission limit may have
to be revisited some time in the future if the remanded merged gas stream
issue is resolved.

     Finally, it is worth noting that the Calcagni memorandum also allows
both States and EPA to require fluid modeling to justify stack height
increases in those situations where they feel it is warranted.

     If you have any further questions on this or any other stack height
issue, please contact me at 919-541-3223 as I have taken over
responsibility for this area from Gwen Jacobs, who has left EPA.  

cc:  D. Atkinson
     E. Ginsburg
     J. Irwin
     J. Tikvart
     D. Wilson