October 17, 1989 
 
 

 
 
MEMORANDUM 
 
SUBJECT:  Ambient Air 
 
FROM:     Robert D. Bauman, Chief 
          SO2/Particulate Matter Programs Branch (MD-15) 
 
TO:       Gerald Fontenot, Chief 
          Air Programs Branch, Region VI (6T-A) 
      
     My staff and I have discussed the ambient air case outlined in the
August 24, 1989 memorandum from Jim Yarbrough of your staff to Doug Grano of
my staff.  Specifically, Region VI and the Texas Air Control Board propose
that prevention of significant deterioration (PSD) modeling for Mitsubishi 
Industries can discount the contribution of a background source to the 
predicted concentration as follows: 
 
     1.   Assume Mitsubishi and background plants B and C. 
 
     2.   Mitsubishi and plants B and C are modeled and total concentrations 
          are estimated. 
 
     3.   Where a receptor is located on plant B's nonambient air property, 
          the contribution from plant B (only) may be subtracted from the 
          total concentration. 
 
     This situation is similar to a case raised to OAQPS's attention in 1987 
by Region V.  Guidance on this case was provided by OAQPS to Region V in a 
memorandum dated April 30, 1987 (attached).  That guidance is consistent with
your proposed approach and, therefore, we agree with your position. 
 
     However, the State should be advised that, when modeling Mitsubishi, all
receptors off Mitsubishi property are in ambient air and that the ambient air
policy does not allow sources to excessively pollute their neighbors.  Note 
that a background source could, in the future, change their operation and
make portions of their property accessible to the public.  Care should be
taken to avoid situations that could result in undue exposure to excessive 
concentrations and which could result in adverse public health impacts.  
 
     In response to your position on issuance of the permit where Mitsubishi 
makes a significant contribution to predicted violations of either the 
national ambient air quality standards (NAAQS) or PSD increments, policy 
contained in the July 5, 1988 memorandum from OAQPS to Region 3 should be 
applied (attached).  For a new or existing NAAQS violation, the permit may
be granted under specific conditions.  However, for any increment violation
for which the proposed source has a significant impact, the permit should not
be approved unless the increment violation is corrected prior to operation of
the proposed source. 
 
     If you have any questions regarding this memorandum, please call Doug 
Grano at FTS-629-5255. 
 
Attachments 
 
cc:  Air Branch Chief, Regions I-V, VII-X 
     SO2 Contacts 
      
bcc:  John Calcagni 
      Dan deRoeck 
      Gary McCutchen 
      Joe Tikvart 
      Dean Wilson 
      Jim Yarbrough 
      Regional Modeling Contact, Regions I-X 
 


     (Attachments may be found in generic/recurring issues section on the
     BBS as AMA#2 under Ambient Air and SAQ#1 under Significant Air Quality
     Impacts)