June 7, 1990 
 
 
 
 
MEMORANDUM 
 
SUBJECT:  Definition of Postapproval Monitoring 
 
FROM:     Ed Lillis, Chief 
          Noncriteria Pollutant Program Branch (MD-15) 
 
TO:       Marcia Spink, Chief 
          Air Programs Branch (3AM10) 

     This is in response to your April 30, 1990 request to clarify the 
definition of "postapproval monitoring" as the term is used in the
regulations for prevention of significant deterioration (PSD) at 40 CFR
51.166(m)(v).  As you know, the term is used to identify the time when
ambient ozone monitoring is to be undertaken when the normal PSD
requirement for preconstruction ozone monitoring is waived.  The correct
interpretation is that the postapproval period may begin any time after the
source receives its PSD permit.  This is explained in the Ambient
Monitoring Guidelines for Prevention of Significant Deterioration (PSD)
[EPA-450/4-87-007, May 1987], which further provides that "in no case
should the postapproval monitoring be started later than 2 years after the
start-up of the new source or modification." (See page A-19.) 
 
     Please give me or Dan deRoeck a call if you have any questions. 
 
cc:  Air Branch Chief, Regions I-X  
     NSR Contacts 
     Regional Modeling Contacts