United States Environmental Protection Agency
          Office of Air Quality Planning and Standards
          Research Triangle Park, North Carolina 27711

                        January 20, 1984






MEMORANDUM

SUBJECT:  PSD Increment Consumption Calculations

FROM:    John R. O'Connor, Acting Director  /s/
         Office of Air Quality Planning and Standards (MD-10)

TO:      Thomas W. Devine, Director
         Air and Waste Management Division, IV

     Your November 13, 1983, memorandum proposes that spatial and
temporal calculation of PSD increment consumption is the
appropriate methodology to be used in the ambient analysis for the
Alumax PSD permit.  This methodology is used by Region IV as well
as all States within Region IV.  We also understand (memorandum
from A. Smith to S. Meyers, dated May 3, 1983) that Region X is now
implementing this method for all of their PSD permit processing.

     We agree that the spatial and temporal calculation of PSD
increments is appropriate not only for Alumax but for all cases
where PSD increment consumption calculations need to be made.  This
methodology is consistent with the manner in which the total
concentration is calculated for comparison with ambient standards
and is consistent with the method used to calculate incremental
concentrations for Level II emission trades (memorandum from
Sheldon Meyers to the Director, AWMD/AMD, Regions I-X, dated
February 17, 1983).  This methodology is also consistent with our
interpretation of the Clean Air Act and definition of increment and
baseline concentrations in the PSD regulation.  

     If you have any questions concerning the use of this method
for tracking the use of PSD increments or you are aware of any
situations where it results in a significant impact on a past
decision, please contact me or Dean Wilson of my staff.  

Attachment

cc:  Director, Air & Waste Management Division, Regions II, III,
     VI-VIII, X
     Director, Air Management Division, Regions I, V, IX
     Chief , Air Programs Branch, Regions I-X
     Richard Rhoads
     Sara Schneeberg
     Mike Trutna
     Darryl Tyler