April 6, 1989







MEMORANDUM

SUBJECT:  "Connecticut Ambient Impact Analysis Guideline"

FROM:     Joseph A. Tikvart, Chief
          Source Receptor Analysis Branch (MD-14)

TO        Stephen S. Perkins, Chief
          Technical and Program Support Branch, Region I


     In response to your request we have reviewed the subject
Guideline and Richard Burkhart's comments on that Guideline.  We
have no problem with Mr. Burkhart's comments.  We feel somewhat
handicapped in reviewing this Guideline in that we have not seen
the SIP revision or the Technical Support Document that describes
what role the Guideline has in regulatory decision making in
Connecticut.  We are making the assumption that the Guideline
will only be applicable to the State's NSR/PSD program, and not
to generic SIP's, BTU bubbles, or any other type of regulatory
action. Let us know if this is not the case.  We would eventually
like to see the SIP revision that describes how this Guideline
will be used.

     Attached are specific comments of the Model Clearinghouse on
the document.

     If you have any questions, please contact Dean Wilson at FTS
629-5683.

Attachment

cc:  D. deRoeck, NPPB (MD-15)
     D. Grano, SO2/PMPB (MD-15)
     S. Reinders, SRAB (MD-14)
     D. Wilson, SRAB (MD-14)






       Comments on "Connecticut Impact Analysis Guideline"

                     EPA Model Clearinghouse
                         March 30, 1989

Page 1-1  The CT Guideline should note that the EPA guideline and
          EPA models are occasionally revised or updated. 
          Therefore the applicant should check with DEP and
          incorporate any relevant changes.

Pages 2-1 We question why the Guideline needs to include
to 2-10   verbatim definitions established by the regulation. 
          Perhaps it should just reference them or paraphrase
          them to the extent needed.

Page 2-5  The definition of major modification does not appear to
          allow netting.  Yet, Definition 52 in the Guideline
          (and regulation) describes netting.

Page 3-2  In the last paragraph we suggest that they delete the
          word "much" in the first sentence and change nitrogen
          oxides to nitrogen dioxide in the second sentence.

Page 3-3  In Table 3-1 we suggest that a footnote be added to
          explain that the annual (arithmetic) mean value is an
          expected exceedance value.  Also, footnote 4 applies to
          the 24-hour PM10 standard instead of footnote 1. 
          However, footnote 4 could be better worded.  For
          modeling purposes this explanation does not mean very
          much.

Page 3-5  Explain that significant impacts are used to determine
          whether a source would cause or contribute to a
          violation of the NAAQS or increments (except Class I
          increments).  As it currently reads, the section does
          not explain what the modeled significant impact is to
          be used for.
 
Page 5-2  The GEP discussion may be misleading.  This discussion
          seems intended to require the applicant to identify
          sources with stack heights below GEP which therefore
          should be modeled for downwash.  However, the          
          discussion should also make clear that the lessor of
          actual or GEP stack height must be used for (other
          than downwash) modeling for each source.  Thus GEP
          information is needed for sources outside the "radius
          of significance."

Page 5-2  Building downwash effects on estimates can occur well
          beyond the immediate vicinity of the stack.  Thus,
          while a special receptor grid need not be set up in the
          vicinity of the source to detect maximum downwash 
          concentrations, it is still generally necessary to
          input the requisite building dimensions to ISC for
          calculation of impacts within the area of significance.

Page 5-7  (PSD Increment Tracking)  Technically speaking, there
          is no size cutoff for sources that consume increment;
          thus it may be necessary to model all minor sources 
          and "growth" emissions in some circumstances where 
          concentrations approaching the allowable increment are
          found by modeling only those sources identified in 
          Section II.  Also, the Guideline should require maximum
          actual 24-hour emission rates rather than average
          actual emissions based on annual actual emissions.

Page 5-8  For consistency with EPA policy, on-site data (one or
          more years, up to 5) are always preferable to 
          off-site data.  The CT Guideline should be changed to
          reflect that policy.

Page 5-11 (Section 5.4.3, last paragraph).  This discussion
          should be supplemented to indicate that receptors
          should be placed on neighboring company property, even
          if fenced.

Page 6-1  The most recent EPA guideline should be referenced.