January 13, 1992


MEMORANDUM

SUBJECT:  NHARD Modeling Guide

FROM:     Dean A. Wilson, Meteorologist
          Techniques Evaluation Section (MD-14)

TO:       Ian D. Cohen, Regional Meteorologist
          Region I


     In response to your request the Model Clearinghouse has
reviewed your position with respect to the New Hampshire Air
Resources Division (NHARD) Guideline.  We agree with your
position and your comments.  We have also attached some
additional comments of our own on the Guideline.

     It is a bit unclear to us what the role of the Guideline is
once it is incorporated by reference into the State
Implementation Plan (SIP).  For example, does that mean that the
State can use the Guideline as part of their Prevention of
Significant Deterioration (PSD) program, in place of adopting the
Guideline on Air Quality Models?  There is probably a need to
discuss this further with the regulatory people in your Region
and in OAQPS.  

     Also, we note that historically there have been fairly
frequent revisions to the NHARD Guideline.  How do future
revisions get handled with respect to their incorporation into
the SIP?

     If you have any questions, please contact me.

Attachment

cc:  D. Atkinson
     G. Blais
     D. deRoeck





Specific Comments on April 19, 1991 Version of NHARD Policy and
Procedure for Air Quality Impact Modeling.

Page 3, Item C.  By interactive modeling we assume that NHARD is
referring to the explicit modeling of background sources
according to the material in Section 9.1 of the Guideline on Air
Quality Models.  The guidance in Section 9.1 does not involve the
consideration of significant air quality impacts but instead a
significant concentration gradient.  The two concepts are very
different; we disagree with the rationale in Item C.  The same
comment applies to page 15, Item A8, page 16, Item B4 and Page
18, Item C13.

Page 6, Item B.2.
     The definition of simple terrain should read "any elevation
that exceeds stack base but is below stack height."  This
definition may necessitate the State also defining intermediate
terrain as "all receptors between stack height and plume height."

Page 11, Item F.
     It is not clear why the State refers to the EPA Guideline to
select models for visibility, reactive plumes and long-range
transport, since the Guideline does not make specific
recommendations for models to be used in such circumstances.
     It is not clear how ISCST is to be implemented in a
screening mode.  The normal use of the model requires the input
of at least one year of meteorological data.

Page 13.  ISW(27) and ISW(28) switch positions are in conflict
with EPA guidance.  EPA could not support analyses conducted with
these options.

Page 16, Items A9 and B5.  It is not clear why only two wind
directions would allow one to determine the maximum combined
concentration resulting from multiple sources.

Page 17, Item C.  The complex terrain screening is less
conservative than the EPA method described in the Screening
Procedures for Estimating the Air Quality Impact of Stationary
Sources.  It also does not address receptors between stack height
and plume height (intermediate terrain).

Appendix B.  As new ambient data is gathered, this Appendix
should be updated.

Appendix C, Page C-2, Step 3.  For long buildings, add an "="
sign to the relationship (Y/H > 2).  Also, add W = crosswind
building dimension (m), to definitions.

Appendix C, Page C-4.  
     It is questionable whether 5 m/s should be included with
stability class F as a worst case meteorological condition.