November 24, 1993




MEMORANDUM

SUBJECT:  CP&L Stack Height Increase

FROM:     Gary Blais, Environmental Protection Specialist
          SO2/Particulate Matter Programs Branch (MD-15)

          Dean A. Wilson, Meteorologist
          Source Receptor Analysis Branch, TSD (MD-14)

TO:       Brenda Johnson, Regional Modeling Contact
          Region IV


Background

     Carolina Power & Light Company (CP&L) plans to construct a replacement
stack at its Lee Steam Electric Plant (Lee) in Wayne County, NC.  The
existing stack at 200 feet serves Lee Unit Nos. 1 and 2 (Lee 1/2), is
approximately 41 years old and is structurally unsound.  Lee Unit No. 3
(Lee 3) is 300 feet tall and was built about 4 years after the Lee 1/2
stack.  For engineering reasons, the proposed new Lee 1/2 stack will be
moved approximately 160 feet east of the existing stack and raised to a
height of 300 feet.  This height is less than formula Good Engineering
Height (GEP) for Lee 1/2 (which is 350 feet), and while still under the
influence of Lee 3's stack, the new position and height of the Lee 1/2
stack will reduce wake and downwash effects caused by Lee 3.

Issue

     The source would like to take advantage of the policy contained in the
June 29, 1992 memorandum from John Calcagni to the Regional Offices.  The
policy states that "it will generally be reasonable for a source seeking
credit for additional stack height to recalculate its GEP formula height
due to the siting of a nearby structure, without the need to justify the
increase through fluid modeling."

Model Clearinghouse Recommendation

     In previous communications, the Clearinghouse had indicated to you
that it did appear reasonable to apply the Calcagni memo policy in this
case.  However, the fact that the Lee 1/2 stack was to be moved as well as
raised to a higher height was not known to either of us at that time.  The
recent further information we received from you, including the GEP
analysis, indicates that the new Lee 1/2 stack will still be under the
influence of Lee 3.  If this were not the case, we would be inclined to say
that raising the stack to avoid downwash is probably unnecessary and
therefore credit for increased stack height should not be granted without
justifying the increase through fluid modeling.  However, since in its new
location, the Lee 1/2 stack will still be under the influence of Lee 3, an
increase in stack height could still be presumed necessary to avoid wake
and downwash effects caused by Lee 3.  Therefore, since the other facts
have not changed, it is still the Clearinghouse opinion that credit for the
increased stack height can be granted without the need to justify the
increase through fluid modeling.

     As always, the State or the EPA Regional Office retains the authority
to require fluid modeling to justify such an increase if you or they
believe it is warranted.

cc:  P. Eckhoff