-------
151.100
the maximum concentration experi-
enced In the absence of such down-
wash, wakea. or eddy effect* and
which contribute* to a total concentra-
tion due to emissions from all source*
that Is greater than an ambient air
quality standard. For sources subject
to the prevention of significant dete-
rioration program (40 CFR 51.IM and
02.21 >. an excessive concentration al-
ternatively means a maximum around-
level concentration due to emissions
from a stack due In whole or part to
downwash. wake*, or eddy effect* pro-
duced by nearby structures or nearby
terrain feature* which Individually I*
at least 40 percent In excess of the
maximum concentration experienced
In the absence of such downwash.
wake*, or eddy effects and greater
than a prevention of significant dete-
rioration Increment. The allowable
emission rate to be used In making
demonstrations under this part shall
be prescribed by the new source per-
formance standard that I* applicable
to the source category unless the
owiiei or operator demonstrate* that
this emission rale I* Infeaalble. Where
such demonstration* are approved by
the authority administering the State
Implementation plan, an alternative
embwlon rate shall be established In
consultation with the source owner or
operator.
(I) for sources seeking credit after
October U. 1»«3. for Increase* In eitot-
tng stack height* up to the height* es-
tahllshed under I SI. 100(11X3). either
(I) a maximum ground-level concentra-
tion due In whole or part to down-
wa»h. wake* or eddy effect* a* provid-
ed In paragraph (kkMI > of this section,
except that the emission rate specified
hy any applicable State Implementa-
tion plan (or. In the absence of such a
limit, the actual emission rate) shall
be used, or (II) the actual presence of a
local nuisance caused by the existing
•tack, as determined by the authority
administering the State Implementa-
tion plan: and
(I) for sources seeking credit after
January 13. 1*79 for a stack height de-
termined under I 51KXMIIMJ) where
the authority administering the Slate
Implementation plan requires the use
of a field study or fluid model to verify
QEP slmrk helglil. lor sou ices seeking
40 CM Oi. I (7-l-M MM**)
stack height credit after November 0.
1984 based on the aerodynamic Influ-
ence of cooling towers, and for source*
seeking stack height credit after De-
cember 31. 1970 based on the aerody-
namic Influence of structure* not ade-
quately represented by the equations
In 161.IOOOIM2). a maximum ground-
level concentration due In whole or
part to downwash. wake* or eddy ef-
fect* that I* at least 40 percent In
exce** of the maximum concentration
experienced In the absence of such
downwash. wakes, or eddy effect*.
(UMmm) IRawrvedl
ie rate at which pollut-
ant* are emitted to the atmosphere ac-
cording to meteorological conditions
and/or ambient concentration* of the
pollutant. In order to prevent ground-
level concentration* In exceas of appli-
cable ambient air quality standards.
Such a dispersion technique to an ICB
whether used alone, used with other
dispersion techniques, or used a* a
supplement to continuous emission
control* (I.e.. used a* a supplemental
control system).
(oo) "Partlculate matter" mean* any
airborne finely divided solid or liquid
material with an aerodynamic diame-
ter smaller than 100 micrometer*.
(pp> "Partlculate matter emissions"
mean* all finely divided solid or liquid
material, other than uncomblned
water, emitted to the ambient air a*
measured by applicable reference
methods, or an equivalent or alterna-
tive method, specified In this chapter.
or by a teat method specified In an ap-
proved State Implementation plan.
(qq> "PM,." mean* partlculate
matter with an aerodynamic diameter
teas than or equal to a nominal 10 mi-
crometers a* measured by a reference
method baaed on Appendix J of Part
•0 of thto chapter and designated In
accordance with Part 63 of thto chap-
ter or by an equivalent method desig-
nated In accordance with Part S3 of
thto chapter.
(rr) "PM,. emissions" means finely
divided solid or liquid material, with
an aerodynamic diameter less than or
equal to a nominal 10 micrometer*
emitted to the ambient air as meas-
ured by an applicable reference
few*******!** Protect!** Af)»iKy
method, or an equivalent or alterna-
tive method, specified In thto chapter
or by a teat method specified In an ap-
proved State Implementation plan.
(as) "Total suspended partlculate"
mean* partlculate matter as measured
by the method described In Appendix
B of Part M of thto chapter.
1*1 FR 40*81. No*. 1. IM*. at smmdsd at M
PR Milt, July I. IMl)
• 6l.lt!
Nothing to thto part will be con-
strued to any manner.
(a) To encourage a State to prepare.
adopt, or submit a plan which does not
provide for the protection and en-
hancement of air quality so ss to pro-
mote the public health and welfare
and productive capacity.
(b) To encourage a State to adopt
any particular control strategy with-
out taking Into consideration the eost-
effectlveness of such control strategy
to relation to that of alternative con-
trol strategies.
(c) To preclude a Stale from employ-
tag techniques other than those speci-
fied to thto part for purposes of esti-
mating air quality or demonstrating
the adequacy of a control strategy.
provided that such other technique*
an shown to be adequate and appro-
priate for such purposes.
(d) To encourage a State to prepare.
adopt, or submit * pun without taking
toto consideration the social and eco-
nomic Impact of the control strategy
set forth to such plan. Including, but -
not limited to. Impact on availability
of fuels, energy, transportation, and
employment.
(e) To preclude a State from prepar-
ing, adopting, or submitting a {Man
which provides for attainment Mod
maintenance of a national stsJMfcrd
through the application of a ventral
strategy not specifically Identified or
described to thto part.
(f) To preclude a State or political
subdivision thereof from adopting or
enforcing any emission limitation* or
other measure* or combinations there1
of to attain and maintain ah- quality
better than that required by a nation-
al standard.
(g) To encourage a State to adopt a
control strategy uniformly applicable
throughout a region unless there to no
722
isi.ioa
satisfactory alternative way of provid-
ing for attainment and maintenance of
a national standard throughout such
region.
• 61.1*1 PiiMIc bearings.
(a) Except as otherwise provided to
paragraph (c> of thto section. Bute*
must conduct one or more public hear-
ing* on the following prior to adoption
and submission to EPA of:
(1) Any plan or revision of It re-
quired by | BM04(a).
(3) Any Individual compliance sched-
ule under (| 61.3*0).
(3) Any revision under 161.1O4(d>.
(b) Separate hearings may be held
for plans to Implement primary end
secondary standard*.
(c) No hearing will be required for
any change to an Increment of
piogiea* to an approved Individual
compliance schedule' unless such
change to likely to cause the source to
be unable to comply with the final
compliance date to the schedule. Tbe
requirements of 1161.104 and 81.106
will be applicable to such schedules,
however.
(d> Any hearing required by para-
graph (a) of thto section will be held
only after reasonable notice, which
will be considered to Include, at least
M days prior to the date of such
hearing**):
(I) Notice given to the pubuc by
prominent advertisement to the area
affected announcing the dateta).
time**), and placets) of such
hearing**);
(3) Availability of each proposed
plan or revision for public Inspection
to si least one location to each region
to which It will spply. and the avail-
ability of each compliance schedule
for public Inspection to si least one lo-
cation to the region to which the af-
fected source to located;
(3) Notification to the Administrator
(through the appropriate Regional
Office):
(4) Notification to each local ah- pol-
lution control agency which will be
significantly Impacted by such plan.
schedule or revision:
(B) In the case of an Interstate
region, notification to any other
States Included, In whole or In part. In
723
-------
Monday
July 8, 1985
Part II
Environmental
Protection Agency
40 CFR Part 51
Stack Height Regulation; Final Rute
-------
27892 Federal Regiatar / Vol. SO. No. 130 / Monday. July 8. 1985 / Rulei and Regulations
ENVIRONMENTAL PROTECTION
AGENCY
40CFRPtft51
technique.* K defines CEP. with respect
to stack hiBgaa as:
Stack Might Regulation
AOKMCY: Environmental Protection
Agency (EPA).
ACTXMC Final rulemaking. _
SUMMAMV: Section 123 of the Clean Air
Act. aa amended requires EPA to
promulgate regulation! to enaure that
the degree of emission limitation
required for the control of any air
pollutant under an applicable State
implementation plan (SIP) it not
affected by that portion of any stack
height which exceeds good engineering
practice (CEP) or by any other
dispersion technique. A regulation
implementing section 123 was
promulgated on February 8. 1982. at 47
FR SM4. Revisions to the regulation
were proposed on November 9. 1984. at
49 FR 44878. Today's action incorporates
changes to the proposal and adopta this
regulation in final form.
WMCMVI OATC This regulation
becomes effective on August 7, 198S.
fo* WSTTHSJI HSVOMMATIOM CONTACT-
Eric O. Cinaburg, MD-15, Office of Air
Quality Planning and Standards, EPA.
Research Triangle Pack. North Carolina
27711. Telephone (919) SO-*MaX
TAUT OtPOMMATIOSC
Docket StetsiMBl
Pertinent information concerning this
regulation is included in Docket Number
A-43-49. The docket is open for public
inspection botmei die BOW* of lets
a.m. and 4:00 p.m~ Monday through
Friday, at the EPA Central Docket
Section. Weat Tower Lobby. Gallery
One. 401 M Street SW.. Washington.
D.C. Background documents normally
available to the public, such aa Federal
Register notices and Congressional
reports, are not included in the docket
A reasonable fee may be charged for
copying documents.
Background
Statuta
Section 123. which was added to the
Clean Air Act by the 1977 Amendments.
regulates the manner in which
techniques for dispcrson of pollutants
from a source may be considered in
setting emission limitations. Specifically,
section 123 requires that the degree of
emission limitation shall not be affected
by that portion of a stack which exceeds
CEP or by "sny ether dispersion
the height necessary to insure that essJssions
from iht itsck do not result in excesetoe
concentrations of any air pollutant ia> KM
immediate vicinity of the source as a nsull ef
•tmotphenc downwash. eddies or weaas
which may be created by the source itaeat
nesrby structures or nesrby terrain aoatodos
. . . (Sectioa 123(c)|.
Section 123 further provides thai CEP
stack height shall not exceed two sava*
one-half times the height of the save*
(2.5H) unless a demonstration ia
performed showing that a higher stack •
needed to avoid "excessive
concentrations." Aa the legislative
history of section 123 makes clear, taaa)
reference to a two and one-half law*
teat reflects the established anonce of
using a formula for detennottaf tja> GaV
stack height needed to avoid exooooiue
downwash. Finally, tactic* 123 [
that the Administrator shal tcgaifaat
only stack height credits fto* rs. oat
portion of the stack height used la
calculating an emission limitation—
rather than actual stack heights*
With respect to "other disparate
techniques" for which emission
limitation credit la reatricted. the statute
is lesa specific It states only that *Jt*
term shall ioebsd* intermittent aval
supplemental control systems (ICS,
SCS), but otherwise leaves the definition
of that term to the discretion of the
Adnuntatra toe.
The* (fee statute deiegatea to aW
Administrator the responsibility tot
eWkMOf key phraves. including
'exxeoaiv* coaicentrations" and
"nearby," with reepect to both
atructuree and tsjcrain obstacles, and
"other dispersion techniques." The
ArirBJaietTalig nuat also define the
requirements of an adequate
demonstration justifying stack haagfct
credita in excess of the 2.5H forsnia,
RuItmoJung and Litigation
On February 8.1982 (47 FR MB*). EPA
promulgated final regulations lisaiting
stack height credits and other diapansoB
techniques. Information concerning tbe
development of the regulation wo»
included in Docket Number A-Tt-Ol and
is available for inspection at the EPA
Central Docket Section. This regulation
was challenged in the U.S. Court of
Appeals for the D.C. Circuit by the
Sierra Club Legal Defense Fund. lac; the
Natural Resources Defense Council, Inc4
and the Commonwealth of Peruwylvana
in Siena Club v. EPA. 719 F. 2d 438, Om
October 11.1983. the court issued Ha
decision ordering EPA to reconasrfer
portions of the stack height regulation.
reversing certain portions and uiifmsrling
other portions. Further discussicai of the
covt decision is provided later in this
BDtJCC.
Administrative Proceedings Subsequent
a» the Court Decision
On December 19.1983. EPA held a
public meeting to take comments to
ist the Agency in implementing the
ndate of the court. This meeting was
1 in the Federal Regiatar on
• 8.1963. at 48 FR 54999.
Comments received by EPA are
bduded in Docket Number A-43-49. On
February 28.1984. the electric power
aaduatry filed a petition for a writ of
esrtiorari with the U.S. Supreme Court.
Wkila the petition was pending before
the cassn the mandate from the U.S.
Court of Appeals was stayed. On July 2,
MM. the Supreme Court denied the
petition (104 S.Ct. 3571). and on July 18.
19M. the Court of Appeals' mandate
VSJB formally issued, implementing the
court's decision and requiring EPA to
promulgate revisions to the stack height
sofjilationa within 4 months. The
promulgation deadline was ultimately
extended to June 27.1985. in order to
provide additional opportunities for
potlic comment to allow EPA to hold s
pofalic hearing on January 8.1985. and to
provide additional time for EPA to
complete its analysis of nilemaking
alternatives,
Documents
SB conjunction with the 1982
leojotatson and this revision. EPA
developed several technical and
gaudance documents. These served as
background information for the
rapilation. and are included in Dockets
A-79-01 and A-83-49. The following
documents have been or will be placed
• the National Technical Information
Service (NTIS) system and may be
obtained by contacting NTIS at 5285
Part Royal Road. Springfield. Virginia
22161.
(1) "Guideline for Use of Fluid
Modeling to Determine Good
BBjineering Stack Height" July 1981.
EPA. Office of Air Quality Planning and
EPA-4SO/4-81-003 (NTIS
145327).
(2) "Guideline for Fluid Modeling of
Atmospheric Diffusion." Apnl 1981.
EPA. Environmental Sciences Research
Laboratory. EPA-oOO/8-41-009 (NTIS
PB81 201410).
(3) "Guidance for Determination of
Good Engineering Practice Stack Height
(Technical Support Document for the
Suck Height Regulation)." June 1985.
EPA. Office of Air Quality Planning and
"Isaileuts EPA-450/4-80-023R.
(4) "Determination of Good
Engineering Practice Stack Height—A
-------
Federal Register / Vol. 50. No. 130 / Monday. July 8. 1985 / Rules and Regulations 27893
Fluid Model Demonstration Study for a
Power Plant." April 1983. EPA.
Environmental Sciences Research
Laboratory. EPA-600/3-43-024 (NTIS
PB83 207407).
(5) "Fluid Modeling Demonstration of
Good-Engineenng-Practice Slack Height
m Complex Terrain.'' April 1965. EPA
Atmospheric Sciences Research
Laboratory. EPA/600/3-35/022 (NTIS
PB85 203107).
In addition, the following documents
are available in Docket A-43-49.
"Economic Impact Assessment for
Revisions to the EPA Stack Height
Regulation." fune 1985.
"Effect of Terrain-Induced Downwash
on Determination of Good-Enginering-
Prtctice Stack Height" fuly 1984.
Pretnm Overview
General
The problem of air pollution can be
approached in either of two ways:
through reliance on a technology-based
program that mandates specific control
requirements (either control equipment
or control efficiencies) irrespective of
ambient pollutant concentration*, or
through an air quality baaed system that
relies on ambient air quality levels to
determine the allowable rates of
emissions. The .Clean Air Act
incorporates both approaches, but the
SIP program under section 110 uses an
air quality-based approach to establish
emission limitations for sources.
implicitly, this approach acknowledges
and is based on the normal dispersion of
pollutants from their points of origin into
the atmosphere prior to measurements
of ambient concentrations at ground
level.
There are two general methods for
preventing violations of the national
ambient air quality standards (NAAQS)
and prevention of significant
deterioration (PSD) increments.
Continuous emission controls reduce on
a continuous basis the quantity, rate, or
concentrations of pollutants released
into the atmosphere from e source. In
contrast, dispersion techniques rely on
the dispersive effects of the atmosphere
to carry pollutant emissions awey from
the source m order to prevent high .
concentrations of pollutants near the
source. Section 123 of the Clean Air Act
limits the use of dispersion techniques
by pollution sources to meet the NAAQS
or PSD increments.
Tall stacks, manipulation of exhaust
gas parameters, and varying the rate of
emissions based on atmospheric
conditions (ICS and SCS) are the basic
types of dispersion techniques. Tall
stacks enhance dispersion by releasing
pollutants into the air at elevations high
above ground level, thereby providing
greater mixing of pollutants into the
atmosphere. The result is to dilute the
pollutant levels and reduce the
concentrations of the pollutant at ground
level, without reducing the total amount
of pollution released. Manipulation of
exhaust gas parameters increases the
plume rise from the source to achieve
similar result*. ICS and SCS vary a
source's rate of emissions to take
advantage of meteorologic conditions.
When conditions favor rapid dispersion.
the source emits pollutants at higher
rates, and when conditions are adverse.
emission rates are reduced. Use of
dispersion techniques in lieu of constant
emission controls results in additional
atmospheric loadings of pollutants and
can increase the possibility that
pollution will travel long distances
before reaching the ground.
Although overrtiiance on dispersion
techniques may produce advene affects.
some use of the dispersive properties of
the atmosphere has long been an
important factor in air pollution control.
For example, some stack height ia
needed to prevent excessive pollutant
concentrations near a source. When
wind meets an obstacle such aa a hill or
a building, a turbulent region of
downwash. wakes, and eddies ia
created downwind of the obstacle aa the
wind passes over and around it This
can force a plume rapidly to the ground
resulting in excessive concentrations of
pollutants near the source. Aa discussed.
previously, section 123 recognizes these
phenomena and responds by allowing
calculation of emission limitations with
explicit consideration of that portion of
a source's stack that ia needed to ensure
that excessive concentrations due to
downwash will not be created near the
source. This height ia called CEP stack
height
Summary of tht Court Decision
Petitions for review of EPA'a 1982
regulation were filed in the D.C Circuit
within the statutory tine period
following promulgation of the regulation.
On October It. 1983. the court issued its
decision ordering EPA to reconsider
portions of the stack height regulation.
reversing certain portions and upholding
others. The following is a summary of
the court decision.
The EPA 11982 rule provided three
waya to carerraine CEP stack height
One way was to calculate the height by
using a formula based on the
dimensions o^nearby structures. The
other two were a de mimmis height of AS
meters, and the height determined by a
fluid modeling demonstration or field
study. The court endorsed the formula
as a starting point to determine CEP
height However, it held that EPA has
not demonstrated that the formula was
an accurate predictor of the stack heigm
needed to avoid "excessive
concentrations of pollutants due to
downwash. Accordingly, the court
directed EPA to re-examine in three
ways the conditions under which
exceptions to the general rule of formula
reliance could be justified.
First the 1982 rule allowed a source to
justify raising its stack above formula
height by ahowing a 40-percent increase
in concentrations due to downwash.
wakes, or eddies, on the ground that this
was the percentage increase that the
formula avoided. The court found this
justification insufficient and remanded
the definition to EPA with instructions
to make it directly responsive to health
and welfare considerations.
Similarly, the 1982 rule allowed a
source that built a stack to less than
formula height to raise it to formula
height automatically. Once again, the
court required more justification that
such a step was needed to avoid
advene health or welfare effects.
Finally, the court directed EPA either
to allow the authorities administering
the stack height regulations to require
modeling by sources in other cases as a
check on possible error in the formula.
or explain why the accuracy of the
formula made such a step unnecessary
The 1982 rule provided two formulae
to calculate CEP stack height For
sources constructed on or before
January 12.1079. the date of initial
propoeaJ of the stack height regulations.
tile applicable formula was 2.3 times the
height of the source or other nearby
structure. For sources constructed after
that date, the rule specified a newer.
refined formula, the height of the source
or other nearby structure plus 1.5 times
the height or width of that structure.
whichever is leaa (H-M.SL). The EPA
baaed ita decision- to include two
formulae on the unfairness of applying
the new formula retroactively. In its
examination of this issue, the court
specified four factors that influence
whether an agency has a duty to apply s
rule retroactively. They are:
1. Whether the naw rule represents «n
abrupt departure from wail established
practice or manly attempts to fill a void man
unsettfed area of law.
2. The extent to which the party against
whom the new rule ia applied relied on tne
former rule.
J. Tha detTM of burden which a retroactive
order impoaas on a party, and
4. The statutory interest In apply'"* • new
rule dwpite the reliance of a perry on rfte nd
standard.
-------
27J94 Federal Regis*** / Vol 50. No. 13O / Monday. July B. 1965 / R«fe» and Regulations
719 fid at 48? (citation* omitted).
Applying this aoalyus. to the two
formulae. the court upheld EPA's bane
decision.
However, the court also held that
sources constructed on or before
January IZ 1973. should not be
automatically entitled to fuil credit
calculated under the Z.5H formula unless
they could demonstrate reliance on that
formula. The court remanded this
provision for revision to take actual
reliance on the 2.5H formal* otto
account.
The starate limits site* height eredtt
to that needed to avoid excemiv*
concentration* doe to downwaeik caused
by "nearby" strectune or terrain
festare*. Tee 19*2 reguiatfea defined
"nearby" far CEP formate sppKeatioM
as five tima* the lesser al erther fee
height or projected wtdta of the
structun caueina, dowowesk oat to
exceed HIM half nit*. Na such ejrtuc*
limitation waa placed aa structures or
terrain features waose effects wen
being considered in Ouid •~Wi«tt
demonstration* or field studios. Tb*
court held that section 123 explicitly
applies the "nearby" limitation to
demonstrations and studies aa weE aa
formula applications, and remanded the
rule to EPA to apply the limitation in
both contexts.
The 198T rule defined "dispersion
techniques" ae those techniques which
attempt to affect poflutant
concvfHrotioRS by using (act portfon of a
stack exceeding GEP. by varying
emission mtee accordia* tv atauepheik.
conditions or-pollutant eonceittretiens.
or by the oddltio* of e fan or refceeter tv
obtain e lees suingtiil eaueeiea
• limitation. The court found *is
definition too narrow because any
technique -si§r»*caittty motivated by a*
intent to gain enisaiona credit for
greater dispersion" should be bami
719 F.2d 462. As a result the comrt
directed EPA to develop ruts*
diMllowiaf credit for all saca diapersioa
technique* unless die Agency
adequately justified excapMaav oa the
basis of administrative nacsssrty or sot
rr:nimis result
Tbe CEP formulae estabtiafaed in the.
1962 rule do not consider pcsssa rue. «•
the ground that plume rise is not
significant under downwash conditions.
In its review of this, provision, the court
affirmed this judgment by EPA.
The 1982 rule addressed r^""'*T"
concentrations estimated to occur whan,
a plume impacts elevated temin by
auowmg. credit for stack height
necessary to avoid air qualify violations
.n such cases. However, the court ruled
that section 123 did not allow EPA to
grant credit for plume inspection in.
setting elusion uarfc. and reversed this
part of the regulation.
TaepraaaBbiete the 18U refukoon
provided a 22 south process for State
iBplsoentatioa of the regulation. The>
court found tfai» period to be> coatiwy to
secnan 406(d)(2} of the OMB Air Ad
and reversed it
The regulation. foUowinf the statute.
excluded stack* "i» exatance" oa or
before Oecanber 31. iva froet the- CEP
requirements. However, the reguiabaai
did not prohibit source* constructed
after December 31. 1970. freaai receiving
credit for tying into pre-1971 f*fuT
Although, the court upheld EPA's
defiaitioo of "is existence." it ao4e« tbe4
EP A had faaVad to addieaa tket tte-ia
issae. Acconisagly. the court resBead*4
this issue M EPA for juatifiaatieB.
One other proviatoa of the rafuieanai
waa challenged is the. Siena Ouo iuifc
The evduainsi of uarea froaa the
defiainon of "aUck."u»Ua review afthie
prmviaiao, the court held thM HP A h*si
acted properly.
Other pro vuMau of the stack heigiu
regulatiaa aucha« the, oeavmaMe stack
height eattbiisAed under I SLUiiHlK
were not challenged in Ik* suit aid th«*
remain in effect.
Summary oftti* ftovmint 9
fa Ae November 9k UBe. node*
responding to the court daoaioa, EPA
proposed to redefine a. amber of
gptcific tasma. 'T^'HP*^ "exceaai«a
techniquBe," "Bearby." aaatolha*
important, concept*, aad propoaari ta
modify SABA of tbe haaee, tot
itmtmrtnirtiwt^ Crf3* StaCkbei^L
foOowiig ia a auoaary of the i
that were proposed
The Court of Appeals held that EPA
erred Is defifiiflaj ^DSDeaat^^
concenoation*" erne taeawmwe«kvfai
purpoaee of justifying * stack gteetea
than formul* aeigak aa nothiic OMT*
thaa a «H>efcaat increaae, ia pnllnlaaX
coocaotratoca over waal weald occur
in the shsenre of dowvweaa, It
remaodedi uua. ieaua to EPA M ratal* tbs>
dafiaiao* to soau ebaokt* level of ear
pollutioa that couid be lateraeetad to
endanger health and welfare, aad thaa
to be "exraesiiia."
The EPA irapoeed twe- aisataalive
appnacaa* to deruunf "eacaaeive
concentranona," FitakEPA reojeeated
conimeni oo whether the 4A-Mroee*
appraeca adopted aa port oitk* MM
njjiiliitisi IB fsnpiiiisiia aawael Thai
danger* k> *-—"^ and welaare
enviaiosttd by Coocreee wkeat it'
sectioa 123. !• ta*ev«H thai s«di •
shovrmg caa£d not be made. EPA
proposed a two-part defiaftioo of
excessive coacemtranooe. reoamnf ths i
the dowmwatft, wakaa. or eddies
induced by nearby structuree or terrem
featune reaaft ia inaseses in grvud-
level polhttant concetilrarioae thai:
(*) Ceuee or cotrtribofe to an
exceedanee- of e rVAAQS or apptieathe
PSO mereffient end
(b) Are at least 40 percent in excess of
concentration* projected to occur in the
absence of such structures or terrain
features.
Definition of CEP Stack Hfigfit
EPA pnaoood to find tiuM the
traditional (ZSH} and refined (H-f.l.5L)
formulae remained proper methods for
calculating CEP stack height except EPA
proposed to revise its regulation to
allow EPA the State or local air
pollution control agency discretion to
require a farther demonstration using a
field study or fluid model to
demonstrate CEP stack height for a
source to a case when it waa believed
that the rbrnrda may not refiafiiy predict
CEP height Ia the case of structures that
are porous or sarodynamicaHy smoother
thaa block-shaped structures, it would
require a source to demonstrate the
downwash effects of suca structures
using a field study or fluid model before
receiving credit for stack height baaed
oa the structures. EPA also proposed
generally to aflow sources to raise
existing, stacks up to fbnaula CEP height
without ftirtnar damooatratioaa with the
excepttoo noted abort fat diacratianary
R» lionet on tht iSH Formula
Ia it» latZ nine. EPA aaowwi wore**
built eefere {aauary 12. MW, the date OB
which it proposed tbe reneed H-t-l^L
formulae, to calcalate their araMBioa
limit! hasaii oa tke> trarialanal X5H
forssula tkat aviated pMnouely. Toe
court approved taia distinctiaa, bw)
ruled that it sboald be Ueutoe to sowrcee
that "reaed" oa tae mdittaaas forauia.
nifljarriag, for axaa^iie. that sources
that bad ciaiaied creok for stacks far
taller thaa th*.iorawi« providosi cc«U
not be said, to haw* "relied" oa rt.
to response to tka coot deaawo. EPA
propoeed te reviaa rte ngeJeOoa «•
January It 1879. sources eaeaonetrete
that tberaetaalrf relied ca tbe 13H
foramss ia the daaiss> of taesr stacirs
before recernog cradM far taatleiaM »
proposei, EPA reeawssee) caaeaaeat en
whatitaaaaldi
i el anea reaaoee.
-------
F*d*r*J Ragbtar / Vol. 50. No. 130 / Monday. July 8. 1965 / Rules and Regulations
2789£
DtfinitiofofNfartry"
In iti 1982 rules. EPA allowed sourcaa
that modeled the effects of terrain
obstacles on downwash to include any
terrain features in their model without
limiting their distance from the stack.
The court though persuaded that this
was a sensible approach, since it
allowed the model to best approximate
reality, ruled that Congress had
intended a different result, namely that
terrain features beyond tt mile from the
stack should not be included in tha
model.
In response, EPA proposed to rtviae
i 5U(U)(3) o/itt regulation to limit the
consideration of dowawasa. wakes, aod
eddy effects of structure* aad tarraia
features to those feature* "'"-'"^ aa
being "nearby" as defiaed ia | Stlfjj).
Under this proposal structure* aad
terrain feature* would be considered to
be "n*arby"1f they occur within a
distance of not more than O4 km (V4
mile]; terrain feature* that extend
beyond U km could be considered it at
a distance of 041 km. they achieved a '
height greater than or equal to 40-
percent of the CEP stack height
calculated by applying the CEP formula
to actual nearby structures. la other
words, a terrain feature would be said to
"begin- within V4 mile if It reached at
leest the height of nearby buildings
within that *timtmtu^ ftvi^» features
be considered only out to
equal to 10 times the •••»•»«•» h*«jtit of
the feature, not to exceed 2 mile*.
The EPA proposed two options for
diitinguiabing between source*
constructed before aad aftar the date of
promuigattoa of the** revision*. The
first opted wodd treat both categoric*
of source* the same. The second option
would limit the cooaideradoo of tarraia
for new source* to only those portiooa of
terrain feature* that fall entuv/r within
0.8 km. thereby removing th* p inability
of indudiag features exteadiag beyoad
Finally. EPA proposed
alternatives for conductiaf fhrid
modeling to evaluate the <
effects or oaarby tetraia fe
altemativee d**cnb*d varioo*,w»ye of
limiting terrain in th* modal beyond the
proposed d'«*"f*« limitations.
To establish a baseline for
comparison, two alternative* would
initially model the stack on a flat plane
with no structure or terrain influences.
To analyze downwash effects, the first
approach would then ineert nearby
terrain, with ell terrain beyond th*
distance limit "cut off" horizontally The
second approach would gradually
•moot*) and slope the terrain beyond the
distance limit down to the elevation of
the base of the stack.
Th* third approach would proceed in
a somewhat different manner. A
baseline would be established by
modeling all terrain beyond the distance
limit smoothing and sloping nearby
terrain to minimise its influence. To
analyse downwash effects, the nearby
terrain would then be inserted into th*
model and the difference ia effect
measured to determine appropriate
downwash credit for stack height
Definition of "Ditptnioa Technique*"
Ia th* 19B2 rale*. EPA Identified two
practices, ia addition to stack* above
CEP aad ICS/SCS. a* having no pvrpoa*
otber than to obtaia • IMS stringaut
emtssioB iimitatto*, to so doing, it
allowad credit for any other practice
that had the remit o/increasing
dispersion. The court concluded that
Congress had intended, at a "»•"'"""•
to forbid any dispersion enhancement
practice that was significantly
motivated by aa intent to obtain
additional credit for greater dispersion.
and remanded the question to EPA for
reexamination.
The EPA proposed to revise It*
definition of "dispersion tsehaiqoes"
generally to Indod*. to sddMoa to ICS.
SCS. aad stack height* ia sneaee of CEP.
any terhniip** that hav* IB* effect of
Combining
alt
stacks it
can hav* each aa effect
ejeooftea
How*ver.
haws I
I b.«4IJk^*4«^ AJ^^^M|^»A|M
jimnmoon. Aoconangnr.
» *-m ' ** —
on neiiiniBj me
dii'istnlein*s andar wUcata*
combining of gas stream* sfcovU not b*
gy^^^fag^fl m jMafl^MH^M fM^MiM^A Mw4
proDOMo to allow source* as taw credit
in ensiessoei ozBttatioas ror soch ^fgtff
wherre facility we* origmafly designed
aad cowtrocted with 0j*rg*d gas
*)*M*BMBBS*1 A*l ~ •- --- •*-- ' -
*f leTWaBel Or WlffJIw Ukw UlVIgUa^ vfJdW
witkttw hwtallatiOB of additional
coatrois yi*idiag a B*t redaction ia total
emissions of tav affected poflntant The
EPA retained excrasioas from it*
definition of prohibited dispersion
technique* for smoke management ia
agneultnrar and stiviculturai prescribed
burcmg programs and also proposed to
exciude episodic restrictions oa
residential woodburning aad debris
New Sounm Tied into Prt-tan StocJu
Section 123 exempts stacks "la
existence" at the end of 1970 from its
requirements. EPA't general approach to
implementing this language was upheld
by the court However, in its 1982 nils
EPA had also allowed thir credit to
sources built after that date that had
tied into stacks built before that date.
EPA failed to respond to comments
objecting to this allowance, end 10 the
court remanded the question to EPA /or
the agency to addresa.
Upon reexamination. EPA saw no
convincing justificetion for granting
credit to these sources. Consequently.
for sources constructed after December
31.1970. with emissions ducted into
grandfathered stacks of greater than
CEP height and for sources constructed
before that date but for which major
modifications or reconstruction have
been carried out subsequently. EPA
proposed to limit stack height credit to
only so much of the actual suck height
as conforms to CEP. Sources
constructed prior to December 31.1970.
for which modifications are carried out
that are not classified es "major" under
40 CFR Sl.laXJ}(i). 5U4(8)(2J(i). snd
51-a(«H2Mi) would be allowed to retain
roll credit for their existing stack
heights.
Plutnt latpectiott
IB its 1982 rules. EPA allowed stack
height credit for "plume impart on." a
phenomenon met is distinct from
downwash. wakes aad eddies. The
court though sympathetic to EPA's
policy position, reversed this judgment
as beyond the scope of the statute.
Accordingly. EPA proposed to delete the
allowance of H"**"1 impacttoa credit
from.its regulation ia compliance with
the court d*rj»lnp However, EPA also
recogaicsd that aouca*tn complex
terram fee* additional analytical
.jifK'-iM— whan altemfCBBf to conduct
modciiat to d*t*emia* appscrist*
cauMioB liautationa. Coneaeoendy. EPA
request**! eoanMcrt on whether eny
allowance saoold b* mad* for
imoi*B*at*oon problem* that may
result from the application of reviaed
CEP stack height assumptions end. if so.
how such allowance should b* msde.
Statt UnpitoHtation flan Rt^utnatena
EPA's 1982 ndes geve states a total of
22 months to revise their rules and to
establish source emission limitation
based on new steck height credits. The
court found this. too. to go beyond the
language of the statute. In response.
EPA stated ia the propose! that States
would be required, pursuant to section
406(d)(2)(b) of the Clean Air Act. to
review their rde* end existing emission
limitations, reviaing them aa needed to
comply with the new regBiabM within 9
month* of tha date of its
-------
27896 Federal Register / Vol. 50. No. 130 / Monday. July 8. 1985 / Rules and Regulations
Response to Public Comments on the
Novembers. 1984. Proposal
The EPA received over 400 comment!
during the public comment period and at
the public hearing, addressing a number
of aspects of the proposed
regulation.These comments have been
consolidated according to the issues
raised and are discussed, along with
EPA's responses, in a 'Response to
Comments" document included in the
rulemaking docket Certain comments
can be characterized as "major" in that
they address issues that are
fundamental to the development of the
final regulation. These comments are
summarized below, along with EPA's
responses. Additional discussion of the
issues raised and further responses by
EPA can be found in the "Response to
Comments" document
I. Maximum Control of Emissions in Lieu
of Dispersion
A central legal and policy question
addressed in this rulemaking was raised
in the comments of the Natural
Resources Defense Council (NRDC) and
the Sierra Club. They contend that
section 123 requires all sources to install
the maximum feasible control
technology before receiving any credit
for the dispersive effects of a stack of
any height or for other practices that
may enhance pollutant dispersion.
The NRDC argument is summarized
fully in the Response to Comments
document together with EPA's response.
Very briefly, NRDC contends that
litigation prior to the 1977 Clean Air Act
Amendments had established that
dispersion can never be used as an
alternative to emission control and that
this understanding waa carried forward
and strengthened in the 1977 Clean Air
Act Amendments. Accordingly, no rule
that does not require full control of
emissions as a prerequisite to any stack
height credit would be consistent with.
Congressional intent
EPA disagrees. During the I yean
between 1977 and NRDCa comments, a
period covering two Administrations
and three Administrator*. NRDCs
position has never been either adopted
by EPA or seriously advocated before it
The pre-1977 cases cited by NRDC-do
not bar all stack credit but only credit
for stacks beyond the historical norm.
Finally, the text and legislative history
of section 123 contain essentially no
support for NRDCs "control first"
position.
II. Discussion of Other Major Issues
The EPA • position oa the "control
first" comments provides the necessary
background against which the remaimng
major issues in this rulemaking are
discussed. These issues are: the
definition of "excessive concentrations"
due to downwash. wakes, and eddies:
the definition of "nearby:" and the
definition of "dispersion technique." A
question that affects several of these
decisions, and that is addressed where
it arises, concerns the extent to which
any changes made in the stack heights
regulations should be applied
prospectively rather than retroactively.
This discussion of "excessive
concentrations" is in turn divided into a
discussion of the physical characteristics
of downwash. followed by a discussion
of the significance of those
characteristics as they pertain to the
CEP formulae, to stacks above formula
height to stacks being raised to formula
height and to stacks at formula height
being modeled at the choice of the
administering authorities.
Definition of "Excessive
Concentrations"
The Physical Nature of Downwash. A
number of commenten. including the
Utility Air Regulatory Croup (UARC).
have argued that the court decision doee
not obligate EPA to revise the definition
sdopted in the 1982 regulation, but only
directs EPA to ensure that the 40-
percent criterion protects again*
concentrations due to downwash that
could be related to health and welfare
concerns. They point oat that when
emissions from a source become trapped
in the wake region produced by the
source itself or upwind structures aad
terrain features, those MP^f'Tft are
brought rapidly to earth, with little
dilution. This, the comoentars argue.
can produce short-term peak
concentrations at groundlevoi that are
many times greater that the
concentration levels of the NAAQS.
Because their duration is relatively
short averaging these concentrations
over the times specified by the NAAQS
does not result in NAAQS violations.
Nonetheless, the- commenten argue that
these concentrations should be regarded
as nuisances that section 123 was
specifically enacted to avoid.
Accordingly, the commenten held that
EPA would be justified in retaining the
40-percent criterion without requiring
that such increases result in
exceedancas of the NAAQS
These same commenten argued that
seven hardships would result if EPA's
second proposed definition of
"excessive concentrations" is adopted.
and that by limiting stack height credit
to that just necessary to avoid
exceedance of NAAQS or PSD
increments, the definition would act to
limit sctual stack design and
construction in a way that would
increase the likelihood of NAAQS or
PSD exceedances. This would occur.
they argue, because, by building only so
tall a stack as they can receive credit
for. sources would be eliminating a
"margin of safety" that would normally
be provided otherwise. Furthermore, it
was argued that due to the changing
nature of background air quality.
inclusion of absolute concentrations
such as the NAAQS or PSD increments
in the definition would render
determinations of CEP stack height
constantly subject to change.
NRDC argued on the other hand that
only a violation of air quality standards
can be considered the type of
"excessive concentration" for which
downwash credit can be justified, the
EPA had failed to specify the health or
welfare significance of the short-term
peaks- that it might consider as meeting
this description, and mat in any event
UARG's attempt to show that short
stacks could cause a large number of
short-term peaks was technically flawed
in several different ways.
Response. Extensive discussion of the
downwash phenomenon, as well as the
aerodynamic effects of buildings and
terrain features on windfiow patterns
and turbulence, is contained in the
technical and guidance documents
previously listed in this notice. To
summarize briefly, numerous studies
have shown that the region of
turbulence created by obstacles to
windflow extends to a height of
approximately 2J times the height of the
obstacle. Pollutants emitted into this
region can be rapidly brought to the
ground, with limited dilution. Though
this tendency decreases the higher
vertically within the downwash region
that die plume la released, because of
the highly unpredictable nature of
downwaah and the lack of extensive
quantitative data, it is extremely
difficult to reliably predict plume
behavior within the downwash region.
As noted in the comments submitted.
the distinguishing features of downwash
do not show up well over an averaging
time aa long aa 1 hour or more. Pollutant
concentrations resulting from
downwash can arise and subside very
quickly aa meteorological conditions.
including wind speed and atmospheric
stability vary. This can result in »hon-
tenn peaks, lasting up to 2 minutes or so.
recurring intermittently for up to several
hours, that significantly exceed the
concentrations of the 3- and 24-hour
NAAQS. Little quantitative information
is available on the actual leveis of these
peaks, or on the frequency of taeu*
occurrence since mast itacks have been
-------
Federal Register / Vol. 50. No. 130 / Monday. July 8. 1985 / Rules and Regulations
designed to. a void downwash and
because downwash monitoring is not
typically conducted.
A number of modeling and monitoring
studies in the record assess the
significance of downwash when plumes
are released into the downwash region.
The most important of these are a
number of studies c:ted in the .Vovember
9 proposal showing that for sources with
sulfur dioxide (SOt) emission rate* of 4
to 3 rounds per million British Thermal
Units (Ib./mmBTU). stacks releasing the
plume into the downwash region can
significantly exceed the 0-hour NAAQS.
The utility industry submitted
monitoring results from four sites
showing that facilities with short stacka
(ranging from 23 to tt percent of formula
height) generated many short-term
peaks in the vicinity of the plant at
concentrations at least 2 times the
highest concentration of the 3-hour SOt
standard. i.a~ l ppm for up to 10
minutes. Those concentrations are the-
maximun that could be recorded by the
monitors used There is no way to
determine from these data the true peak
ground-level concentrations.
The NRDG la commenting on this
subject has argued that downwash- • •
related concentrations are largely
theoretical, since stacka have generally
been built to avoid downwash. and that
actual concentrations occur under other
meteorological conditions such as
"inversion breakup fumigations" and
"looping plums." that can equal these
"theoretical" concentrations predicted
under downwash.' The NRDC also
criticized the utility data on numerous
technical grounds.
EPA's studies indicate that, when
stacks are significantly leas than CEP
formula height high short-term
concentrations can indeed occur dm to
downwash that are in the range of the
values reported by the utility industry.
Concentrations produced by me other
conditions cited by NRDC though high.
may be lower by an order of magnitude.
and occur less frequently by as much as
two orders of magnitude, than those
produced by downwash.' As stack.'
' In mvtnion braaAup fumiaauon.' *• UIVOTM
liytr diiaipatti due 10 hMunc of tftf ground. lamas
the aoiiuiaruj that wtra trappad in it dncaod
luddtflly to ireund Itvtl. In "looping plumaa.* •
p.'umt ii brought down to tna> trouod cloo to th»
lourci in lha form of iniafnmtaw p*Jh under wry
unitablt atmoapnarie eondtMM.
1 Commtnti on Ptak Cround-Lcvtl
Concentration* Out to Buildinf Downwaab ftalauva
10 Pejk Conotnmnoni Undar Atmoaphane
D icenion Proctia**." Alan K Hubcr and Prancii
»oo!«r. fr JUM 10.1M.
height approaches the height determined
by the CEP formula, the expected
frequency and severity of short-term
peaks due to downwash becomes iasa
certain. This is to be expected, since it is
the purpose of a formula height stack to
avoid excessive downwaah. While it
might theoretically be possible for EPA
to revise the CEP formula downward
(e.g.. from H+UL to H+14EL or some
other value), such a revision would have
little purpose. By moving the release
point further into the downwash region.
such a change would increase the
probability of high downwash-caused
peaks. On the other hand such
relatively small changes in stack height
are not likely to appreciably affect the
emission limitation for the sourest Tola
is because emission limitations are
calculated based on physical stack
height and associsted plume rise under
atmospheric conditions )udg*d moat
contrr sg for the source. Increasing or
decre*i ..-if stack height by a email
fraction will not greatly change the rate
or extant of dispersion and thus will net
affect the ground-level concentration.
Moreover, ae EPA noted in its
November 9 proposal no data presently
exist on which to base a revision to the
formula.
The NRDC submitted data to EPA
which it believed to support the
conclusions that it urged EPA to adopt
concerning short-term peak
concentrations under other
meterological conditions.'However.
these data were not presented In e font
that could be nadir/ interpreted and
EPA has thus fa/ been anabJa to draw
any conclusions from then.'
In reviewing NRDC* comments on
building downwaaa, EPA agrees that
there is grant uncertainty about our
present understanding of this
phenomenon, and this is supported by
the rang* and variation of downwash
effects observed in recent stadias.
However, no information has beta
presented which would convince EPA to
abandon the present CEP formulae m
favor of any alternative.
The health and welfare significance of
downwaah concentrations that result in
violations of the ambient standards are
documented and acknowledged in the
standards themselves. The significance
of short-term peaks at the levels that
EPA's analyses predict is more
judgmental. However, a number of
studies cited in EPA's "Review of the
National Ambient Air Quality Standards
for Suiftir Oxides: Assessment of
Scientific and Technical Information
(EPA-WO/3-42-007. November 1967).
indicate that concentrations of one ppm
sustained for durations of 5 minutes or
more can produce bronchoconstriction
in asthmatics accompanied by
symptoms such as wheering snd
coughing. Such concentrations are well
within the range of concentrations that
can result from downwash. When
sources matt the ambient standards, the
frequency of occurrence for these
concentrations under the other
conditions cited by NRDC Is
substantially lower than for downwash
whan stacks are kss than CEP.
CEP Formula Stack Hmight, Some
commaotan, '"•'v^i-'g NRDC stated
that EPA cannot justify retention of the
traditional (Z5H) and refined (H+1.5L)
CEP formulae based simply on their
relaoonahip-to the 40-percent criterion.
and argued that the formulae provide
too much credit in many or moat cases.
This, they argue, results in allowing
sources to obtain unjustifiably lament
tfniteifjB limitations.
Other coauneoters argued that
rnngraas explicitly reaffirmed the
traditional CEP formula, and that EPA
should allow maximum reliance on it
(and by implication, on the refined
foranda that was subsequently denvted
from it).
Asseons*. The use of EPA's refined
formula as a starting point for
determining CEP was not called Into
question by any litigant m the Sittra
jCJub case. The court1 s opinion likewise
does not question toe use of the formula
as a starting point A detailed discussion
of the court's treatment of the formula.
showing how it endorsed the formula's
presumptive validity, is contained in the
Response to Comments document.
Despite this limited endorsement EPA
might need to revisit the formula on its
own if its nmamtnarton of the
"excessive concentration" and modeling
issues indicated that me formula cieariy
and typically misstated the degree of
stack height needed to avoid downwash
concentrations that causa sjMtiia or
welfare i
'Mtmofandum from Oavtd G. Hawkma. NRDC to
William F Ptdanan. jr. Offlca of Gtntnl Counaot
L'SEPA, Mar »• 1MB.
•Vtemonn4um from Aim H Hubar. ASM. M
David Slontfieifl. OAQP1 !
However, no such result baa emerged
froaa oar reexaminatioa. Stacka below
formula height are associated with
downwaah-relatad violations of the air
quality standards themselves where
emission rates significantly exceed the
levels specified by NSPS. Even where
emissions are low. downwash
conditions at stacks below formula
height can be expected unlike other
conditions, to ewerste numerous short-
term peeks of air pollution et high leve/»
-------
27896
Federal Register / Vol. 50. No. 130 / Monday. July a. 1985 / Rules and Reaulations
that raiM a real prospect of local health
or welfare impacts.
As EPA stated in the proposal, it is
impossible to rely primarily on fluid
modeling to implement the stack height
regulations, particularly under the
timetable established by the court. 49 FR
44883 (November 9.1964). No
conunenter other than NRDC even
suggested a different formula that in
their eyes would be better, and NRDCs
suggestions were premised on their
"control first" position, which EPA has
found inconsistent with the statute and
has rejected. EPA considers the refined
formula to be toe state-of-the-art for
determining necessary stack height
Given the degree of presumptive
validity the formula already poaaesaea
under the statute aad the court opinion.
we believe that this record amply
supports its reaffirmation.
Stadu Abovm CEP Formula Height.
The EPA's 1978 stack height guidelines
[cite] impoeed special conditions on
stacks above formula height—the
installation of control technology—that
were ne>t imposed on lower stacks.
Similarly. EPA's 1973 proposal had
made credit above formula height
•object to a vaguely defined "detailed
investigation" (38 FR 25700). The
legislative history of the 1077 dean Air
Act Amendments cautioned that credit
for stacks above formula height should
be granted only in rare cases, and the
Court of Appeals adopted this as one of
the keystones of its opinion. The court
also condaded that Congress
deliberately adopted very strict
requirements for sources locating in
hilly terrain.
For these reasons, EPA la requiring
sources seeking credit for stacks above
formula height and credit for any stack
height justified by terrain effects to
show by field studies or fluid modeling
that this height is needed to avoid a 40-
percent increase in concentrations due
to downwash and that such an increase
would result in exceedanee of air
quality standards or applicable PSD
increments. This will restrict stack
height credit in this context to cases
where the downwash avoided is at
levels specified by regulation or by ect
of Congress as possessing health or
welfare significance.
To conduct a demonstration to show
that an absolute air quality ___
concentration such as NAAQS or PSD
increment will be exceeded, it Is
necessary to specify an emission rate for
the source in question.' The EPA
believes that in cases where greater
than formula height may be needed to
prevent excessive concentrations.
sources should first attempt to eliminate
such concentrations by reducing their
emissions. For this reason EPA is
requiring that the emission rate to be
met by a source seeking to conduct a
demonstration to justify stack height
credit above the formula be equivalent
to the emission rate prescribed by NSPS
applicable to the industrial source
category. In doing this. EPA is making
the presumption that this limit can be
met by all sources seeking to justify
stack heights above formula height
Sources may rebut this presumption.
establishing an alternative emission
limitation, on a case-by-case basis, by
demonstrating to the reviewing
authority that the NSPS emission
limitation may sot feasibly be met given
the characteristics of the particular
source.'For example, it may be possible
for s source presently emitting SO» at a
rate of 1.8 Ib./mmBTU to show that
meeting the NSPS rate of 1.2 Jb./mmBTU
would be prohibitive in that it would
require scrapping existing scrubber
equipment for the purpose of '"«»fi['"g
higher efficiency scrubbers. Similarly, a
source may be able to show that due to
space constraints and plant
configuration, it is not possible? to install
the necessary equipment to meet the
NSPS •mission rate. In the event that a
source believes that downwasar will
continue to result in excessive
concentrations when the i
emission rate ia consistent with NSPS
requirements, additional stack height
credit may be justified through fluid
modeling at that emission rat*.
A source, of course, always remains
free to accept the •""frfrH* rate that ia
associated with a formula height stack
rather than relying on a demonstration
under the conditions described ban.
The third alternative mentioned in the
proposal" using the actual emission
limit for the source has been rejected
because, to the extent that limit relied
on greater than formula height it would
amount to using a tall stack to justify
itself.
The EPA's reliance on exceedancas.
rather than violations of the NAAQS
and PSD increments, is deliberate. Fluid
modeling demonstrations are extremely
complicated to design and cany out
even when the most simple
demonstration criteria—that is, a
percentage increase in concentrations.
• la CMWMC if tk* IMI at -
concfmnoaM" la»oK»a « «••!•
ina-MM. ib«r« «auk) b« ma •*•* to
fffllMIPB r*tl. tOlOt tlM IICTMM IB OOBCnntM*
OHM* by dovnwuk i» indcpadMt of mtaiM*
mm.
•Th* EPA will raly on It. Bni Avcibbto ftmoflt
TKfcaoMfjr GiudcHM IB rvruwiaf 4ay rabMUl*
tnd •Ittnuovt (OUMIOO UaiwnoiM.
with no consideration of absolute
values—are assumed. Adding
consideration of an absolute
concentration such ss a NAAQS or PSD
increment substantially complicates this
effort further and introduces the
scientific uncertainties associsted with
predicting an exceedanee of a 3-hour or
24-hour standard based on 1 hour or less
of modeling data. Using an hour or less
of modeling values, based on one set of
meteorological data, to draw the
distinction between only one
exceedanee of the standard during the
8760 hours in a year, and the two or
more that constitute s violation pushes
that uncertainty beyond reasonable
limits. EPA therefore does not find the
additional difficulties that would be
created by requiring violations instead
of exceedances to be warranted. That is
particularly so here, given that the
regulations require sources seeking
credit above the formula to be well-
controlled as a condition of obtaining
such credit
Use of an absolute concentration in
the test of "excessive concentrations"
can lead to problems of administering
the program, in that it can have a
"zoning" effect Since a source can only
get stack height credit to the extent that
it is needed to avoid a PSD Increment or
NAAQS exceedanee. an emissions
increase in the area of that source may
increase concentrations beyond the
controlling limit thereby making it
difficult for new sources to locate in the
area, or for sequential construction of
additional emitting units at the source in
question.
This effect cannot be avoided under
any test for "excessive concentrations"
that ia tied to absolute concentrations.
However; that effect will be mitigated
by the fact that the use of this approach
is voluntary and limited to sources
wishing to rely on fluid modeling to
justify stack height credit Moreover, the
effects of downwash tend to occur very
near the source, usually on fenced .
company property. Since concentrations
measured at such locations are not used
to evaluate NAAQS attainment or PSD
increment consumption, new sources
wishing to locate in the area are less
likely to be affected
Sources planning sequential
construction of new emitting units at
one location or contemplating future
expansion can reduce the uncertainties
noted above by initially obtaining
permits for the total number of units
anticipated and by planning for
expansion in the calculation of
necessary physical stack height. In the
latter instance, only the aflowable stack
height credit would be revised as
-------
Federal Register / Vol. 50. No. 130 / Monday. July g. 1985 / Rules and Regulations
27899
expansion is carried out—not actual
stack height
An additional theoretical
complication is presented when an
absolute concentration is wed where
meteorological conditions other than
downwash result in the highest
predicted ground-level concentrations in
the ambient air. In such cases, a source
that has established CEP at a particular
height, assuming a given emission rate.
may predict a NAAQS violation at that
stack height and emission rate under
some other condition, e.g.. atmospheric
stability Class 'A.' Reducing the
emission rate to eliminate the predicted
violation would result in stack height
credit greater than absolutely necessary
to avoid an excessive concentration
under downwash. However, reducing
stack height places the source back in
jeopardy of a NAAQS violation under
the other meteorological condition, and
so on. "ratcheting" stack height credit
and emission rates lower and lower. The
EPA has eliminated this "ratcheting"
potential in the CEP guideline by
providing that once CEP is established
for a source, adjusting the emission rate
to avoid a violation under other
conditions does not require
recalculation of a new CEP stack height
EPA is making this part of the
regulations retroactive to December 31.
1970. In the terms of the court's
retroactivity analysis, stack* greater
than formula height represent a situation
that Congress did affirmatively "intend
to alter" in section 123. Moreover. EPA
regulatory pronouncements since 1970
have placed a stricter burden on sources
raising stacks above formula height than
on others.
N.o source is precluded from building
a stack height greater than formula
height if such height is believed to be
needed to avoid excessive downwash.
However, the design and purpose of
section 123 prohibit SIP credit for that
effort unless a relatively rigorous
showing can be made.
Given the ability of sources to avoid
modeling and rely on validity of the CEP
formulae and requirement for further
control of emissions in conjunction with
stack heights in excess of formulae
height, the result predicted by UARG—
exceedances of the NAAQS or PSD
increments due to inadequate stack
height—is highly unlikely.
Tht potential effect of changes in
background air quality on stack height
credit is not substantially different from
the effect that such changes in
background can have on source
emission limitations in nonattainment
areas. In the first case, however, sources
may be able to address these effects
through greater stack height if such
changes affect the concentrations under
downwash. Moreover, the possibility
that shifting background air quality can
yield different calculation* of CEP is
significantly limited by the fact that
consideration of background in CEP '
calculation* is restricted to those cases
where credit for greater than formula
height is being sought or source* are
seening to raise stacks to avoid
excessive concentration*.
Raising Stada Btlow Formula Height
to Formula Htight. In response to EPA'*
proposal to allow automatic credit for
CEP formula height several commenters
have argued that EPA has failed to
adequately respond to the court's
directive to "reconsider whether, in light
of ita new understanding of 'exeeeaive
concentrations,' demonstration* are
necessary before stack height* may be
raised even if the final height will not
exceed formula height"
Attporut. F using a stack below
formula heigi to formula height is not
in EPA's judgment subject to the same
statutory reservations as building stack*
greater than formula height However.
as the court has cautioned it may still
be necessary for these sources to show
that raising stacks i* necessary to avoid
"excessive concentration*" that raiee
health or. welfare concern*.
For these reasons, source* wishing to
raise stack* subsequent to October 11.
1963. the date of the D.C Circuit
opinion. mu*t provide evidence that
additional height ie necessary to avoid
downwa*h-reiated concentration*
railing health and welfare concern*.
Theee rule* allow sources to do thi* in
twoweys.
The first wey I* to rebut the
presumption that the short stack was
built high enough to avoid dswnwaah
problem*: La. to show, by eite-epedflc
information such a* monitoring data or
dozen complaint*, that the short stack
had in fact caused a local nuisance and
muet be rai*ed for thi* reason. The EPA
believe* that both the historical
experience of the industry and the data
on short-term peak* discussed earlier
show that short stacks can cause local
nuisances due to downwash. However,
where e source has built a short stack
rather than one at formula height it ha*
created a presumption that thi* i* not
the cave. General data on saorMera
peak* may not be strong enough to
support by themselves and in the
abstract a conclusion that the stack
must be raised to-a void local adverse
effect*. Instead that proposition must be
demonstrated for each particular source
involved .
In the event that a source cannot
make such a showing, the second way to
justify raising a stack is to demonstrate
by fluid modeling or field study an
increase in concentrations due to
downwash that i* at least 40-percent in
excess of concentration* in the absence
of such downwesh and in exec** of the
applicable NAAQS or PSD increments.
In making thi* demonstration, the
emission rate in existence before the
•tack i* raited muet be used
Since raising stacks to formula height
i* not cubject to the same extraordinary
reservations expnceed by Congress and
the court with respect to stacks being
rai*ed above formula height EPA does
not believe that the use of presumptive
"well-controlled" emission rate is
appropriate here. A* discussed in EPA's
response to NRDC* "control first"
argument the basic purpose of section
123 we* to take sources a* it found them
and based on those circumstances, to
aaaure that they did not avoid control
requirements through additional
dispersion. Use of a source's actual
emission rate in thi* butane* i*
con*i*tent with that basic purpose and
absent special indications of a different
intent should be used in stack height
The EPA believe* that it is meet
unlikely that any source with a current
emission limitation ha* failed to claim
full formula credit for a stack of formula
height Accordingly, the question
whether a source can receive suck
height credit up to formula height will
involve only source* that want to
actually raise their physical stack not
sources that simply want to claim more
credit for a stack already in existence. A
source will presumably not go to the
trouble of railing an existing stack
without some reason. If a source cannot
•how that the reason was in fact the
desire to evoid a problem caused by
downwash. then the inference that it
we* inateed a desire for more dispersion
credit i* hard to evoid A nui*ance
caused by downwashed emissions could
include dtixen or employee complaints
or property damage. A source would be
expected to show that complaints of this
nature wen reasonably widespread
before getting credit under this section.
The EPA doe* not intend to make this
rule retroactive to stacks that
"commenced con*tructioei on
modification* that would raise them to
formula height prior to October It 1983.
Applying the court's retroactivity
analysis, it appears:
1. The new rule does depart from prior
practice. The EPA1* 1973 proposed rule
affirmatively encouraged sources with
shorter stack* to raise them to formula
-------
27900 Federal Regiatar / Vol. 50. No. 130 / Monday. )uly 8. 1965 / Rules and Regulations
height. 'Though EPA'i 1976 guideline
can be read aa imposing a "control Erst"
requirement oa some stack height
increase!, its general thrust gave
automatic credit for all stacks that met
the "2.5" times formula.' Automatic
permission was similarly set forth in the
1979 proposal, in the 1961 reproposal.
and in the 1982 final rule. Only a notice
published in 1980. but later withdrawn.
departs from this trend, requiring the use
of Raid studiea or fluid modeling
deaonamnooa to justify stack height
increases up to CEP formula height*
Even then, the notice would have made
thia policy prospective in its application.
2. Sources that raiacd stack* in
reliance on thia paat EPA guidance
assuming the availability of dispersion
credit cannot be rtisfinsiiishfl from the
source*, in the example approved by the
court that built atacka to the traditional
formula in aa identical expectation of
dispersion credit
3. It cannot be said that the raising of
stacks to formula height ia a practice
that Congreca "affirmatively sought to
end" It ia not mentioned in the text of
the statute or ita legislative history.
Further, aa the court has already noted,
the statute attributes a degree of
presumptive validity to the formula on
which sources that raise their atacka
will have relied.
Ditentiaii to flecum FhMMbdffinj.
Several commenten argued that EPA'a
proposal to allow ageaciee to require the
use of fluid •»~*»H»»J waa unnecessary.
since EPA had1 alnsurjr documented tha
validity of the GEP foramina.
Furthermore, these coaaaenten argot
that thia allowance would nuke find
modeling tha rale, rather than tha
exception. Thia would raeuiV tha
commanters state, because it waa their
expectation that agendas or
environmental groups would nearly
always call for fluid >*~<«ll"f
demonstrations during tha permit
application and review procaaa.
Other commentera stated that
providing the discretion to require fluid
modeling was appropriate. since EPA
had failed to demonstrate that the GEP
formulae represented tha
height necessary to avoid excessive
concentrations.
Rotpontf. The Court of Appeals -
directed EPA to reexamiae whether ita
rules should allow States, aa a matter of
discretion, to require even sources that
' "Th» UM of MM* hMftn «p • *• (•*•! of food
enginwnni pnctte* n cncaumpfd by OA • i
to *vo>dlocalBUMOCM.' (Mf*isnat
'41 m 7481 (Ftbnury IS, ISTSk "mrlrHr-
Scetton B.I. Clftt CJIZJ.
• U r* 42P9 nu* M. ISSOfc tftetKe tUmmo* W
nick taa*t o«* t* Miraonia *i *a«-».
planned to rely on tha formula to show
instead by fluid modeling that a stack
this high was required to avoid dangers
to health and welfare caused by
downwash. Tha court suggested that
EPA should include such a provision
unless it could find that the formula was
so accurate, or tended so much to err on
the low side, as to make discretionary
authority to adjust formula height
downward unnecessary.
The EPA believes that the court was
mistaken in its conclusion that a stack
at formula height ia likely to generate
downwash concentrations as greet as 40
percent only ia uncommon situations. In
fact EPA'a observations indicate that
whan stacks are built to CEP formula
height aa increase in concentrations
due to downwash can still be expected
to occur that ia between 20 and 80
percent greater than the concentration
that would occur in tha absence of
building influences. '•
Nevertheless, ia response to the
court's remand EPA is including in this
final rule a provision for the authority
•dminiatariag these rules to require field
studies or fluid modeling
demonstrations, even for stacks built to
formula height ia cases where it
believes that the formula may
significantly overstate the appropriate
stack height credit.11
While SPA believes the formula to a
reasonable rule of thumb indicating the
•tack height aeeded to avead soame
probability of a standarda violation and
a signincandy greater probability of a
given ease-may vary eaaanhnl based .
on specific circumstances. The EPA has
attempted to aunianxe this possibility
within the hmita of eveslabae data by
identifying two particular atraaooa* ia
which it believes mat the fonaaiae aaay
notberahabia mdtaetora of Ga» Poraea
rmaa'oo
which me roraaJae are besed"
tote
'"Qwti
SUMS an* MtSMit* M
whwioBiMrt to rauadtrt mount aliowWitoM*
for ecrwla upmd luvaunt «od cooUaa t
"GuuMfc» tar DMMMflM of Go* f
fimaOtf Stock rMsfet.- Wr 1SSS •» JS-a* SOT ft*
. B?A •Ul snmlbaMr «r mm far •*
itruenim IMI «r«r« aruud prior M NovcBftar-e,
1M4. Siaot EPA fiudiuwe h«* MMT IUNM4 oradll
for poroui tnenm. di* rn«eam In thl* rate tar
»udi uraatnm «o»*
31.1STEL
However. EPA acknowledges thai other
situations, of which the Agency is not
presently aware, may arise wherein the
formulae may not be adequate.
The EPA intends to "grandfather" any
source that relied on the formula in
building its stack before tha date of
EPA's 1079 proposal from the effect of
this discretionary ^examination
requirement
Only in that proposal did EPA first
suggest that such a discretionary
reexamination provision might be
included in the final rule. The
retroactivity analysis set out earlier
therefore supports exempting stacks
built in reliance on EPA guidance before
that data, from discretionary
reexamination. Indeed a failuca to
"grandfather" these sources would lead
to tha paradoxical result that a source
that had built a GEP stack under the
traditional EPA formula would have its
direct reliance intmets protected by the
"grandfather" provision previously
upheld by tha court but could then lose
that "graadfathered" credit through a
caaa specific daaaonstration requirement
showing that tha traditional formaia waa
somewhat inaccurate— the very mason
baattad tha change ia the formula
pioperiy faend nonretroactive by EPA
earner.
. Given this background EPA believes
that tae effect oa emissions of including
or oe eHBrBPfnsj a provision for
diacraniDoary determinations from tnis
rale ia likarjr to be vary small Building
stacks ebore formula height and raising
stacks below formaia height to formula
height, are covered by regulatory
provisions already discussed. The only
caaa left for flii^pTfT'^r^
determmations to address la the building
of stacks at formula height In the post-
197* period However, ail major sources
built since that time are already
controled to SOa emission rates no
greater than L2 IbVamBTU— and act
varioue
EPA regulations. Afl new power plants
on which construction "commenced"
since 1971 must meat EPA's NSPS
mandating an miisiHrn rate no greater
than thia level That standard was
tightened for afl power plants on which
construction "conaDanced" after 1979. la-
addition. all "ma^or" sources built smce
1977 ia,araaa subject to the Act's PSO
reqainanaata have had to install best
available control technology. That
technology atuet require the greatest
degree of emission control that ia
achievable coaatdeang technology.
econonucs, end energy impacts."
-------
Federal Register / Vol. 50. No. 130 / Monday. July a 1983 / Rules and Regulations 27901
If such sources had to show that use
of a formula height stack was needed to
avoid exceedances of the NAAQS or
PSD increments, that might prove
difficult for many of them. The
likelihood of such exceedances tends to
decrease as the emission rate for the
source decreases. By the same token.
the incremental emission reductions
available from the sources that are at
issue here tend to be small and among
the most expensive available. In terms
of emission reductions, little is at stake
where these sources are concerned.
Accordingly, the rules will require
such sources, if a reviewing authority
calls for a demonstration, to the rules
show that the use of a formula stack
height ia needed to avoid a 40-percent
increase in concentration* due to
downwash. This will provide a rough
check on whether the formula, a*
applied in the particular case at isiue.
produces the result it was designed to
produce.
The EPA ia not providing here for
sources to justify their formula height
stacks by arguing that the height in
excess of that needed to avoid NAAQS
violations ia needed to avoid a local
nuisance. The discretionary modeling
requirement ia designed for application
to stacks before they were built Beyond
that, there is no way to determine baaed
on the absence of a local nuisance that a
formula height stack ia not too tail in
the way that the pretence of a nuisance
shows that a stack under formula height
in fact ia too short Accordingly, there
will be no way. aa than waa with short
stacks being raised, to determine from
actual experience whether a local
nuisance would occur at a shorter stack
height Though avoiding local nuisance
is a legitimate purpose for which stacks
are built it would be very difficult to
show by modeling what stack height
was needed to avoid it
Some commenters have
misunderstood EPA s allowance of
discretion to require fluid modeling aa
requiring such modeling whenever any
individual or entity called foreuch e
demonstration. This discretion reels
explicitly with the reviewing agencies
who have always had the prerogative to
require more stringent analyses in thr
SIP process.-and no obligation is implied
for these agencies to require fluid
nadeiing simply because it has been
cabled for by some individual during the
permit review process. It is EPA's
expectation that technical decisions to
require such additional demonstrations
would be based on sound rationale and
vaiid data to show why the formulae
may not be adequate in a given
situation. In any case, given the burden
of reviewing a fluid modeling
demonstration, an agency ia not likely to
exercise this option abstnt sufficient
justification. Consequently. EPA
disagrees with the commenters'
contention that fluid modeling will
supplant the use of the CEP formulae.
except in what EPA believes will be
unusual instance*.
Reliance on the 2.5H Formula. In
limiting the applicability of the 2.SH
formula to those cases where the
formula was actually relied upon, the
November 9 proposal defined such
reliance in terms of stack design. A
number of comments indicated that
actual stack design and construction
may ultimately be control, not by the
Z-5H engineering rule, but by
construction materials specifications.
Consequently, while 2JH rule may have
provided an initial starting point in
stack design, the rule may not have
dictated final stack height In other
cases, it was argued that a number of
source owners may have constructed
their stacks in exceaa of what waa
determined to be minimum CEP for
precautionary reasons, for process
requirement*, or in anticipation of
additional growth in the art*
surrounding the facility, even though
emission limitations for these aourca*
would have been limited then, aa now.
to formula height Consequently. It waa
argued that EPA should allow source* to
demonstrate reliance on the formula in
the calculation of aaiaaion limita aa well
aa in tha daaiga of the stack.
In reeponae to EPA'a requeet far
comment* on what evidence should be
conaidered acceptable in determining
reliance on the 2JH formula, some
commenters urged EPA to conaider
reconstructed evidence, e.g.. affldavita
from decign engineers or copiee of
cormpondeace indicating past reliance
on EPA guidance. Other conunraten
stated that "reliance" should be very
strictly construed, that EPA should be
circumspect in its review of reliance
demonstrations, and that only
contemporaneous documentary
evidence, such as blueprints and facility
design plan*, be accepted aa evidence.
Rnponie. The EPA is in general
agreement with the view that reliance
should be conaidered in relation to the
emission limitation for the source, not
the design. Since section 123 specifically
prohibits EPA from regulating actual
stack heights and rather regulate* stack
height credit* used in setting emission
limitation*, it would be illogical to
require that sources demonstrate
reliance on the 2.5H formula for actual
stack design. Moreover, such an
approach would contradict principles of
•ound planning, in that it would penah:
thoae sources that have built taller
stacks in anticipation of facility
expansion or other growth in the area
that could influence CEP
determination*.
If a stack ha* been built taller than
2.5H formula provide*, while the
emiaaion limitation ha* been calculated
assuming 2.5H credit a convincing
demonstration ha* been made that the
source properly relied on the formula.
Conversely, if the eniaaion limitation for
the source is baaed on some other stack
height credit such as 2JH. 3.5H or some
other number, it would be difficult to
show that the CEP formula had in fact
been relied on.
In some caaea the emiaeion limit
information may be unavailable or
inconclusive. In such caaea. EPA will
allow reliance on reconatructed
evidence of conatruction intent
In comment* submitted during the
public comment period and in response
to quMtion* raised by EPA at the public
hearing held on January 8. 1985, industry
representative* repeatedly stated that
contemporaneou* evidence of reliance
on the 2JH formula, such a* facility
dealfn plan*, dated engineering
calculation*, or dediion record* are
rarely, if ever, retained for more than a
few year* after conatruction of the
facility la completed. Coaaequently. they
argued that meet caaea of legitimate
reliance would be denied If
coBtemporaneou* evidence were
required in order to retain for tha 2.5H
formula.
The EPA agree*. Additionally, credit
afforded by the 2JH formula in excess
of that resulting from the uae of the
H+1.5L derivative i* likely to be small
except when the building on which
•tack height credit ia baaed i*
substantially >•!!•> ^f it ia wide.
Finally. It ia EPA'a view that the court
did not intend that sources be subject to
a rigorous or overly •tringent of reliance.
but only mat they be accorded a
reasonable opportunity to show reliance
on the iSH formula. For these reasons.
EPA will allow the submission of
reconstructed. La, noncontemporaneous
documentary evidence to demonstrate
reliance on the 2JH formula.
Definition of "Nearby". Comments
were submitted by UAP.G and others.
arguing that effectively, no limitation
should be placed on the consideration of
terrain-induced downwaah.
Alternatively, some of the**
commenters argued that the court
decision require* that a limitation be
adopted that doe* not apply any
distance restriction of H mile in
modeling terrain effects such a* is
-------
27908 Federal Register / Vol. SO. No. 130 / Monday. July a. IMS / Rules and Regulations
applied to itcuctum in tht UM of CEP
formulae, but rather allows
consideration of aH terrain that'results
in the Mm* downwath affact u tboac
structures within tt mila of the stack.
Other commenters have argued that
the court decision and legislative history
preclude EPA from allowing
consideration of any terrain beyond a
distance of V* mile, regardless of where
it begins.
Response. For the reasons
summarized below. EPA does not accept
either the interpretation that the court
decision authorizes EPA to adopt a
definition beeed solely on effect or that
it limits consideration exclusively to
terrain features falling entirety within H
mile.
When Congreee dieeasaed the
allowance of credit for stack height to
addnsa dowawaah. it staled that the
term "nearby waa to be -strictly
construed.'' noting that If the tern
to bo amrpretad "to apply to ma.
strucrurea or ttrraitt ftetunt % to H
miia away front the sourcas or mote, the
result could be an opaa invitation to
raise stack heigfata to unreasonably high
elevation* and to defeat the basic
underlying committee infant" **
In iU opnuc*. thejxwrt held that EPA
could not ghre aniimitad credit whan
modeling terrain faatnrae because that
would confliet with the Congraaaaoaai
intention to impose artificial limits OB
that credit Tho cowl waa not presented
with, and did not adriraaa. the oueeooa
of what to do aboat tamia featuree thai
••bsejea" witbsa * auie aad extended
outside it The approach adopted by
EPA carried out tbia rim grass keul
purpose to impose aa artificial limit bat
at the eame time reflects tha real facts
more doaeiy than aa abaoluta % arik*
limitation.
Unlike man-made structures, turaia
feature* do not hava readily definable
Aimmnmiemp QthtT than height. FOT **^
reason. EPA has defined "nearby" aa
generally allowing •••"•fr'ftn of
consideration of terrain faaturea that faO
within a distance of Vs mila of the stack.
EPA's definition wiO psxaft
consideration of such tacrain that
extends beyond the H mile Omit if the
terrain begins within H mila. allowing
that portion within 10 time* the ,
maximum height of the feature, Hot to
exceed Z miles, as described In tha
proposal
To define when a terrain feature
"begins" within H mile, EPA has related
terrain height et the H mile distance to
the maximum stack height that could be
justified under the other two methods
for determining GEP. Accordingly. EPA
will require that terrain features reach a
height at tha Vfc mile 'ti«t or the
combining of exhaust gases from i everai
existing, stacks into one stack, with
several classes of exclusions. These
exclusions recognize the existence of
independent justifications based on
ring and/or economic factors.
include?
(1) Demonstration of original facility
design aad construction with merged
gas stream;
(2] Demonstration that merging after
July S, IMS ia part of a change in
operation that includes the installation
of pollution controia and results in i net
reduction m allowable emissions of the
pollutant for which credit is sought cr
-------
Fedejral Reggae- I Vol. 50. No. 130 / Monday. July a, 1988 / Rules end Relations
27902
(3) Demonstration that merging be/ore
July & 18*5 was part of • change ia
operation that included the installation
of control equipment or wat earned out
for sound economic or engineering
reasons. An allowable emissions
increase creates the .presumption that
the merging was not carried out for
sound economic or engineering
reasons."
Of these exclusions, the first is identical
to the proposal, and the second and
third are modifications of the second
exclusion included in the proposal with
a refinement based on prospective/
retroactive application.
The first exclusion was retained for
the reasons stated in the proposal After
reviewing the comments submitted. EPA
determined thai its previous
conclusion—that standard practice in
designing and constructing facilities
routinely includes venting emissions
from several units into a common or
multiflued stack—4s correct Sound
engineering and economic reasons,
based on costs of constructing and
maintaining separate stacks, availability
of land, and cost savings for pollution
control equipment support facility
design and construction considerations.
Even if air pollution requirements did
not exist at all sources would have
incentives to use as few stacks aa
possible.
Since iaenoting plume rise, rather
than plume rise itsait is a "dispersion
technique" and original design and
construction define the initial base, such
original design fn4 construction of
merged gas streams is not considered a
dispersion technique. Moreover, in
designing the facility, a source can
usually choose to build one larger unit
rather than several smaller units.
Therefore, prohibiting credit for original
design generally only effect the design
of units and not the phase rise.
Objections have been raised to
applying this logic to sources which are
constructed over a period of tana, but
use a single stack. However, the same
factual arguments just listed would
apply is the same, if the original design
included provision for the additional
units in the plans for the facility, and in
the design and construction of die stack.
In such a case, the later units merged .
into the stack would be included wtthta
the exclusion.
In addition, it would be logically very
di,*Sculf to apply a rale denying emttf to
o.-Hnal design stacks. EPA or the State
ld have to assume how many stacks
UaH txtmd for <
would have been built absent a desire
for dispersion credit where they would
have beta located and how high they
would have been. Since these
alternative stacks would be purely
hypothetical then would be no clear
way of answering these questions: the
answer would simply have to be
selected arbitrarily from the wide rang*
of possible answers. This problem is
absent when existing stacks have baa
combined.
In contrast EPA finds rhsnsss from
the original deaJga of a facility ia order
to include merged stacks to require a
narrower judgment The EPA concluded
that where prospective application is
concerned, the exclusion should be
available only to aoareas that combtae
stacks reduces allowable emissions of
the pollutant for which the credit is
grantee* Tnere are obvious ecoaoauc
advantage* ia «"»^'"^g stacks to
reduce the number of emiaaina control
units that nun be purchased. Ia
addition. * ***•*•*** n^g gf pfllhitiCTi
control for U» pollutant ia question
provides substantial assuraaos that thai
purpose of the combination ia not to
receive a more lenient emission ttatit
However, given past EPA f^-ft oa
merging of stacks. EPA has i
that retroactive application of this tear
would not be proper. The EPA guidance
documents uniformly took the view that
merging of separate stacks into a single
stack "Is generally not considered a
dispersion technique" absent other
factors such aa excessive use of fans or
other devices. '* Each
provided guidance to a source of a
Regional Office regarding the proper
treatment of merged stacks ia
i*mimi»tfnm emission limitations. •
Considering these statements. EPA must
consider the standards expressed by (he
coot as previously discussed ia this
notice, m Judging the propriety of a
differing standard for retroactive .
application. Given the nature and
applications of the guidance which It
issued in the past EPA judges the first
two criterie—that is. whether the new
rule represents an abrupt departure from
well-established practice, and whether
the parties against whom the new rule ia
applied relied on the former rale— to be
satisfied to addition, applying the
prospective criteria to past practice
would require significant changes ia niel
and/or control equipment for parties
whose emission limits were baaed oa
previous guidance. Finally, and
particularly where sources have not
been allowed to increase their previoa
emissions as a result of the combining
stacks. EPA don not judge the itstutor,
interest to be overriding in this instance.
since the role even in its retrospective
version only exempts sources that can
show a reasonable non-dispersion
enhancement ground for combining
stacks, and thereby implements the
"latent" test suggested by the court. On
the other hand EPA has never suggested
that combined stacks that cannot meet
such a te*t are proper. Sources whose
actual emissions are increased, or
whose emission limitations are relaxed
ia connection with the combining of
stacks create a strong presumption that
the combination waa carried out in
order to avoid toe installation of
controls. Such combinations would
Indeed run counter to the statutory
purpoee. and raB'uspsctivs application
of s test that rbrbid* them is therefore
proper.
Sxfmptfotu ftwn th» Definition of
Ditptnion Ttchmquu. The EPA
received numerous comments in
response to its request for input on what
consideration. If any. should be given to
excluding sources from the definition of
"Dispenses) Techniques" whose
*"*f***"f are below a specified level or
whew stacks an Jess than the dt
etadtnn height These commenters
anjaad mat cuinbining gar stresms in
particular ofhm had aa economic
justification independent of its effects
oa dUpetsean. and Ibererbn should not
be gaejanfly rororaden. Other comments
staled filet m ooastderiag any such
exduston. EPA should consider the
effect oa Mai atmospheric loadings,
(timitatios oa the
number of sources affected by the
definition at "dispersion techniques''
necessary tar EPA to carry out the stack
height program. There are currently
estimated la be over 2X000 sources of
SO* m toe United States win actual
emissions exceeding 100 tons per year. It
would aot be possible for EPA or States
to review the emission limits of even a
• igniflcant fraction of this number
within a reasonable time period
Twenty-fwo thousand of these sources
have emis*tons leu than 5.000 tons per
year and contribute a total of less than
13 percent of ta* total annual SO*
emissioa. "For (Bis reason, sad for
reasons of ednrinistrstive necessity
discussed earter. EPA is adopting sii
exemption from prohibitions on
manipulating plume rise for facilities
with allowable SO* emissions below
Stm Pirrri Tj-lw TT
RoihMfft A««K m It
fartar Inm Itumttt Ote Omtar e. ISB
D««d StmwMd »*•••* H*M. ftatff.
i fro* Me CiMbvt, OAQW '•>
. •SBMfleiMi of SO, Po«t
-------
27904 Fadarai Refistar / Vol. 50. No. 130 / Monday. July a. 1965 / Rules and Regulation
5.000 toai par year. The EPA believe*
the affect of this exemption on total SO»
emiuioBi to be da minions in nature.
Even if these sourcej were able to
increase their emission rates as the
result of an exemption from the
definition of dispersion techniques, their
combined effect would not be
significant Indeed, because these
sources are exempt on the basis of their
annual emissions, there exists an upper
limit to the extent to which they may
obtain relaxed emission limitations. i.e«
to maintain an,exemption. the annual
emissions of a source may never exceed
5.000 tone per year. For these reasons.
the 5.000 ton limit passes a r'f auiuaia
teat even more clearly than _* M-meter
limit included without challenge in the
prior version of this rule. Monovar. EPA
believes that a large majority of these
sources would not be inclined to seek
lesa stringent emission limitations. In
part because a substantial portion of
them an baited by State and local fuel
usemiea.
The- EPA believes at this time that a
drmmimii size exemption is justified
only for source* of SO» and that the
number of ssneJl sources for which
ealseimi limitations for other pollutants
an a f^gntflnrrt concern would not
support a similar exemption. The EPA
will mnrtmie to review the need for such
exssBpttona and. If deetaed appropriate.
will propose then for review and
consent at a tatar^data.
Phuu ZmpoctroA The EPA received »
number of comments requesting that
credit for plume iapactioa ba retained
on ^i^ grounds that eUnifnathv each
credit would have seven impacts oat
existing source*. Several approachee
wen offend for overcoming plume;
impactton effects in modeling to
determine emission limitations based on
CEP stack height Generally, theee ,
approaches focused on modifying the)
stack-terrain relationship represented to
the models. Several crnnmanters argued.
along theee Unas that the court
recognized and approweaYaf DtA's
attempt to avoid the eflptoaf phone
inspection, but only iflaajpyiiiisj of
EPA's regulatory nislhaa In sllnwliig
sources to avoid imr*"*4Tt Thee*
commenters argued that the court did
not preclude EPA from allowing credit
to avoid plume impactioa, bat esuf from
allowing credit for stack height la
excaae of CEP: this, it waa argued, could
be remedied in a way that waa
consistent with the court decision by
incorporating impaction avoidance)
within the definition of CEP. It wat*bo
snggeeted that EPA give its "Intent
approval" to the use of certain nfTienl'
complex terrain models, in particular the
Rough Terrain Display Model (RTDM).
to calculate emission limitations for
sources affected by changes to the stack
height regulation,
Response The.EPA agrees that the
court wu cognizant of the problem of
plume impaction and noted that then
waa much to recommend EPA's
allowance of credit for impaction
avoidance. However, the allowance of
credit for plume impaction waa not
remanded to EPA for revision or
reconsideration, but was reversed by
the court as exceeding EPA's authority.
The EPA does not agree that it would
be possible to redefine CEP in a manner
that allowed credit for evoiding
impaction. since CEP Is explicitly
denned in terms of preventing excessive
coflftrntr^^iy^ff doe to* uuwnwaen.
wakes, and eddies. Prom* impaction is a
phenomenon completely unrelated to
downwaah and, nther, la a consequence
of effluent gaaea being emitted at an
insufficient height to avoid their striking
downwind hillside* cliffs, or
mountainsides prior to dilution.
Manipulation or "adjustment" of
modeling parameters to avoid predicting
theontical plume impaction when
actual stadia have been constructed
above ^rKH would be tantamount to
granting the same impaction credit that
waa Invatidatad by the court
Furthermore. EPA believes that the
manipulation of modeling pareme tan
for no other naaon than to avoid ss
undertnblt result la tadnacafly
The EPA is in the
iti "Guideline oa Air
A number of
the guideline have eaojMsted that EPA
approve the uae of ma ODM model aa a
Jifir
of nvistas}
.. kaw^l.l. «
of this laeuecaabe found IB documents
associated with EPA's action oo tfaa
modeling guideline (Dockat Kb. A-ao-
<•). With nspact to the revised stack
height ngnlatiocu EPA has not rejected
the use of RTDM, To the extent that
appropriate and complete data bases
and utfbaaation on modal accuracy an
available. EPA may approve the uae of
RTDM oa a. caae-by-caas baaia when
executed m accordance with the
guideline nquinaaaats. Sponsors of
RTDM and presently developing Don
extensive support for broader
appUcatioaa of the modal When such
support la received and reviewed by
EPA. conaidantioo will be given to
allowing mere general use of RTDM in
regulatory activities such aa compliance
with the suck height rale.
Tlaiftobh for Stoat tapbatatatioa.
A number of comaentan stated that it
was not possible to conduct the
necessary analysea. prepare and submit
revised State rules and source-ipecif c
emission limitations within the 9-month
timaframa referred to in the November 9
proposal A variety of alternative
schedule* wan proposed by these
commenters for consideration by EPA
Re$poM*. As with EPA's previous
allowance of credit for plume impaction.
the timetable for preparation and
lubmittal of revised SIFs was not an
issue remanded by the court The EPA is
in agreement that these revisions to the
stack height regulation will require
significant efforts by State and local
agencies, individual emission source
owners and EPA Regional and
Headquarters offices in order to comply
within the 9-monm timafraae required
by section «6(d)(2J of the 1977 Clean
Air Act Amendments. It waa based on
ft^jf concern that EPA originally
pro video* e two-step process for States
to follow aa revising their plans and
submitting them to EPA for approval
However, the court found that this effort
waa explicitly contrary to section
«M(dX2f and ordered EPA to follow the
9-month schedule provided in the Clean
Air Act
Afar Stares* Tifd into Pn-lfTK
Stack*. As indicated earlier, in response
to die court opinion. EPA proposed to
deny "grandfathered" status to post'
1970 sources tying into pre-1971 stacks.
Some cnmreenters stated that EPA was
in no way prohibited from allowing
end*! far new sources ducted into pre-
1971 stacks exceeding CEP height
Rather, they indicated that EPA simply
had to provide justification for such
i Indicated general
support for EPA'a proposal with respect
to new sourcee tying into grandfathered
stacks, bat suggested that several
provided, meet notably that in addition
to new and ma for i
T"^>ir^i?Mt*T'f sourcee not be allowed
greater than CEP stack height oadit
when tying into greater than CEP stacks.
Aasponea. la further review of this
issue. EPA can Bad no convincing
rationale to allow saurces constructed
after December a, taTQ, to avoid CEP
"grand*
ply by dactiag their
stack
into a stack that I*
thend" under section US. On
the contrary, ta intent of section 123 to
limit credit for stack height in excess of.
CEP suggests that EPA should not allow
credit for such stack height except to
honor financial commitments made prior
to the end of 1970. Sources in existence
after that dale should be treated equally
under the regulation and not allowed to
avoid legitimate control requiremeeta
-------
Federal Repsur / VoL 50. No. 130 / Monday, fuly a. 1965 / Ruiet and Regulation*
27905
through tht UM of "grandftthered" alack
heights.
Sources undertaking major
modification, or reconstruction become
subject to additional control
requirements under the Clean Air Act
and are treated ai "new sources" for the
purpose of new source review aad PSD
requirements. EPA finds it appropriate
that CEP requirements should be
invoked at the tine that other
requirements for new. modified, or
reconstructed sources become
applicable.
Summary of Modifications to EPA 'i
Proposal Resulting from Public
Comment!
Based on comments received during
the public comment period, EPA ha*
made a number of revisions to ita
proposed regulation in addition to thoae
discussed above. These revtstons an
summarized below.
Stction SUfMXWBXii} of the
regulation has been clarified to require
sources merging gas streama after July a,
1983 to achieve a net reduction la
allowable emissions. This change was
made to make it dear that tat effects of
merging should not be need aa a way of
achieving compliance witft present
emission limits and to avoid penalizing,
sources who are presently emitting at
leu than allowable levels.
Sect/off SUCMMXBXiii) allow*
credit for a source that merged gas
streams in a change of operation at the
facility prior to Jury 8.1988 that induced
the installation of control equipment or
hed other sound engineering or
economic reason* Any increase in the
emission limitation, or in the previous
actual emissions where no emission
limitation existed created a presumption
that those sound reason* were not
present
Section 31.l(hh)(2)(E) has been added
to exclude from the definition of
prohibited "dispersion techniquea" the
use of techniques affecting final exhaust
gas plume rise where the resulting total
allowable emissions of SO* front the
facility do not exceed 5.000 ton* per
year.
Section 31.1(ii)(ll has been revised to
specify that the OS meter deminimis-'
height i« to be measured, as in other
determinations of CEP stack height
from '£e ground-level elevation at the
base s' the stack. This does not
represent a substantive change in the
rule " in its application relative to past
practices, but rather a simple
clarification.
Section St.l(ii)(2) has been revised to
require that source owners demonstrate
that the 2.5H formula we* relied on in
establishing the emission limitation.
Section 51.1(ii)(31 ha* been rtviaed aa
discussed elsewhere in this notice to
specify that aa emission rat* equivalent
to NSPS must be met before a source
may conduct fluid modeling to justify
stack height credit in excess of that
permitted by the CEP formulae.
Section 51.1(jj) now define* "nearby"
for purposes of conducting field studie*
or fluid modeling demonstrations a* (U
km (V* mile), but allows limited
consideration of terrain feature*
extending beyond that distance if neb
features "begin" within 04 km, aa
defined in the regulation.
Section Sl.l(ki) ha* been revised to
provide} separate diacaaaiona of
"excessive concentrations" for the
separate situations discussed earlier in
this preamble. As that discussion make*
dear. EPA believes that the differing
categories of eoarea* subject to this rale
are beet addressed by requirements that
vary somewhet with those
circumstances. This definition embodies
that approach.
Section Sl.lSflt) ha* beta coittcled to
provide that the provisions of 151.12(0
shall not apply to ttadc hoighti in
existence before December 311970. The
proposal had Incorrectly stated that
ISL12 shall not apply to ttodo
This regulation doee not limit the
physical stack height of any source, or
the actudw of dispersion tachniqnee
at a source, nor doee it require any
specific stack height for any i
Instead it sat* limit* on the i
credit for stack height and other
dispersion technique* to be used la
ambient air i^rWtg for the purpoee of
setting an emission limitation and
calculating the air quality impact of a
source. Source* are modeled at their
actual physical stack height unices that
height exceed* their CEP stack height
The regulation applies to all stack* in
existence and ail dispersion techniques
implemented since December 31. 1070.
State tmpleeaeotatioa Plan
Pursuant to section 406(dK2) of the
dean Air Act Amendments of 1977,
EPA i* requiring that all State* (1)
review and revise, a* necessary, their
SIP'S to include provisions that Unit
stack height credits and dispersion
techniques in accordance with this
regulation and (2) review all existing
emission limitations to determine
whether any of these limitations have
been affected by stack height credits
above CEP or by any other dispersion
technique*. For any limitation* that
have been so affected State* must
prepare revised limitations consistent
with their revised SIP'S. All SIP
revision* and revised emission
limitation* must be submitted to EPA
within 9 month* of promulgation of this
regulation.
Interim Guidance
In it* proposal EPA stated that it
would uae the proposed regulation to
govern stack height credits during the
period before promulgation of the final
regulation. The EPA further stated that
any stack height credits that are granted
based oa this interim guidance would be
subject to review against the final rules
and may need to be revised
Consequently, with theee final rules.
EPA is requiring that any actions that
were taken oa stack heights and stack
height credits during this interm period
be reviewed aad revised ae needed to
be nonaWem with this regulation.
Regulatory FIsadMBty Aaarrei*
Pursuant to the provision* of 5 U.S.C.
608(b), I hereby certify that the attacked
rule will aot have •fr"'*"*"* economic
JHiTMfti on a subetantial number of
•aull entities. Tata rule is structured to
apply only, to large) sources; La- those
with stack* above U meters (223 feet).
or wita aaaual SOi e&isaione in excess
of &000 teas, a* further noted in the rule.
Baaed on aa analysis of impacts, electric
utility plant* and several smelters and
pulp y**f paper *«*n« will be
significantly affected by this regulation.
Executive Order U2S1
Under Executive Order 12291. EPA
must fudge whether a regulation is
"major" and therefore subject to the
requirement of a regulatory impact
analysis. EPA'* analysis of economic
impacts predicts a potential coat to
emission source owner* aad operators
exceeding ROD million: therefore, this is
a major rule under Executive Order
12291. However, due to the promulgation
deadline Imposed by the court EPA did
not have sufficient time to develop s full
analyst* of coat* and ber.efits as
required by the Executive Order.
Consequently, it is not possible to judge
the annual effect of this rule on the
economy. A preliminary economic
impact analysis and *••!. sequent revision
were prepared and a.-' i .ie docket
For any fadliry, the * : ruliry and
economic impact of the suck height
regulation generally cVper. Js on the
extent to which the sc'Md.' stack st that
facility conforms to CEr < .*ck
-------
2790S Fedorai Register / VoL SO. No. 130 / Monday. July 8. 1963 / Rules and Regulation*
Thus, when the regulation ii applied to
large sources. ie~ thoae with stack
height greater than CEP and emissions
greater than 3.000 ton* per year, it will
have the potential for producing
emiuion reduction and increased
control cost*.
A preliminary evaluation of the
potential air quality impacts and a cost
analysis of the regulation was
performed at the time of proposal The
impacts identified were established in
isolation of other regulatory
requirements. The report predicted a
range of impacts, from a "low impact"
scenario that presumed that many
potentially affected sources would be
able to justify their existing stack
heights, configurations, aad emission
limitations to a "Ugh impact" scenario
which assumed that all of the potentially
affected sources would be required to
reduce their emissions to some degree.
In the development of its final
rulemaking action. EPA refined Its
evaluation of potential impacts,
producing revised estimates of the
probable costs of the changes to the
regulation and expected reductions in
SOi emissions. As a result of this
refinement EPA estimates that the rde
will yield reductions in SOi emissions of
approximately 1.7 million tons per year.
The aanualized cost of achieving these
reductions will be aproximately 1730
million, and the capital coat is expected
to be approximately STOP million.
This regulation waa reviewed by the
Office of Management and Budget, and
their written comments and any
responses are contained in Docket A-
KM8.
Judicial Review
The EPA believes that this rdi 1.
based on determinations of nationwide
scope and effect Nothing in section 123
limits its applicability to a particular
locality. State, or region. Rather, section
123 applies to sources wherever located.
Under section 307(b)(l) of die Clean Air
Act [42 U.S.C. r607(b)(l); judicial
review of the actiona taken by this
notice is available only by the filing of a
petition for review in the United States
Court of Appeals for the District of
Columbia and within 80 days of the date
of publication.
List of Subjects in 4t CFR Part 31
Air pollution control. Ozone. Sulfur
dioxide. Nitrogen dioxide. Lead.
Paniculate matter. Hydrocarbons.
Carbon monoxide.
Dated- June 27. »
Adminutmtor.
PA*T SI-ftEOUWEMCMTS FOP)
PREPARATION, ADOPTION. AND
SUBMITTAL OF IMPl£MCffTATION
PUNS
Part 31 of Chapter L Title 40 of the
Code of Federal Regulations is amended
as follows:
1. The authority citation for Part 51
continues to read as follows: j
Authority: Sec 110. Wife), and 129. OMB
Air Act as amended (42 U.S.C 7410. reoi(s)
and 7423).
2. Section S1.1 is amended by revising
paragraphs (ha), (ii). (Jfl. and (kk) as
follows:
111.1
(hh)(l) "Dispersion technique" i
any technique which attempts to affect
the concentration of a pollutant in the
ambient air by:
(i) Using that portion of a stack which
exceeds good engineering practice stack
height
(ii) Varying the rate of emission of a
pollutant according to atmospheric
that pollutant or
(ill) Increasing final exhaust gaa
plume rise by manipulating source
proceee parameters, exhaust gaa
parameters, stack parameters, or
combiniag exhaust gases froaa several •
existing stacks into MM stack: or other
selective handling of axhauat gaa
streams so aa to increase the exhaust .
gaa pliUM rise.
(2) The preceding sentence does not
include:
(i) The reheating of a gas stream.
following use of a pollution control
system, for the purpose of returning the
gaa to the temperature at which it waa
originally diacharged from the facility
generating die gaa stream:
(ii) The merging of exhaust jas
streams where:
(A) The source owner or operator.
demonstrates that the facility waa
originally designed and constructed with
such merged gas streams:
(B) After July 8.1963. such merging is
part of a change in operation at the
facility that includes die installation of
pollution controls and is accompanied
by a net reduction in the allowable
emissions of a poUutaaa, This exclusion
from the definition of "dispersion
.techniques" shall apply only to the
emission limitation for the pollutant
affected by such cbsnge m operation: or
(C) Be/ore July & i960, such merging
was part of a change in operation at the
facility that included the instsilation of
emissions control equipment or wss
carried out for sound economic or
engineering reasons. Where there w«i
an increase in the emission limitation 01
in the event diet no emission limitation
was in existence prior to the merging. «r
increase in the quantity of pollutants
actually emitted prior to the merging, the
reviewing agency shall presume that
merging was significantly motivated by
an intent to gain emissions credit for
greater dispersion. Absent s
demonstration by the source owner or
operator that merging was not
significantly motivated by such intent.
the reviewing agency shall deny credit
for the effects of such merging in
calculating the allowable emissions for
the source;
(ill) Smoke management in
agricultural or silviculture! prescribed
burning programs:
(iv) Episodic restrictions on
residential woodbuming and open
burning? e#
(v) Techniques under f 3l.lfhh)(l)(iii)
which increase final exhaust gas plume
rise where the resulting allowable
^fffffr^j of sulfur dioxide from the
facility do not exceed &000 tons per
year.
(ii) "Good engineering practice" (CEP)
stack height means the greater of:
(1) 68 meten, measured from the
ground-level elevation at the base of the
stack:
(2) (i) For stacks in existence on
JaooarytZ isn, and for which the
owner or operator had obtained all
applicable permits or approvals required
under 40 GFR Parts 51 and 32.
H.-JJH.
provided the owner or operator
producea evidence that this equation
waa actually relied on in establishing an
emiaeiao limitations
(ii) For all other stacks.
H.-M+1JL. •
H,«food eagmeerlni practice tuck height.
measured from the irouad-levei
elevation at the base et the *uck.
H-hmjht of aearby structured) measured
from the ground-level eievstion it the
boss of fap stack*
l«loeoor ^ <•>••»«<«'•> belgftt or projected
width, of oearby •tracmred)
provided that the EPA. State or local
control agency may require the use of s
field study or fluid modal to verify CEP
stack height for the source: or
(3) The height demonstrated by a fluid
model or a field study approved by the
EPA State or local control ag«ney. wnich
ensures that the emissions from s itsck
do not result in excessive
-------
Federal Register / Vol. 50. No. 130 / Monday. July 8. 1985 / Rules and Regulations
2790-
concentrations of any air polluttnt as a
rtsull of atmospheric downwwh. wakes,
or eddy affects created by the source
itself, nearby structures or nearby
terrain features.
(JJ) "Nearby" as used in f 5M(ii) of
this part is defined for a specific
structure or terrain feature and
(1J for purposes of applying the
formulae provided in f 51.1(ii)(2) meana
that distance up to five times the leaser
of the height or the width dimension of a
structure, but not greater than 0.8 km (H
mile), and
(2) for conducting demonstrations
under | 31.1(ii)(3) meana not greater '
than 04 km (Vt mile), except that the
portion of a terrain feature may be
considered to be nearby which falls
within a distance of up to 10 times the
maximum height (HJ of the feature* not
to exceed 2 mile* if such feature
achieves a height (HJ 04 km from the
stack that is at leeat 40 percent of the
CEP stack height determined by the
formulae provided in I 31.1(il)(2)(ii) of
this part or 28 meters, whichever is
greater, as measured Cram the ground-
level elevation at the baae of the stack.
The height of the structure or terrain
feature is measured from the ground-
level elevation at the baae of the stack.
(kk) "Excessive concentration" ia' *
defined for the purpose of determining
good engineering practice stack height
under f Sl.l(ii)O) and meana:
(1) for sources seeking credit for stack
height exceeding that established under
151.1(ii)(2). a maximum ground-level
concentration due to •miMiqnf from a
stack due in whole or part to downwaah.
wakes, and eddy effects produced by
nearby structures or nearby terrain
features which individually is at least 40
percent in excess of the maximum
concentration experienced in the
absence of such downwash. wake*, or
eddy effects and which contributes to a
total concentration due to emissions
from all sources that is greater than an
ambient air quality standard For
source* subject to the prevention of
significant deterioration program (40
CFR 51.24 and SZ21). an excessive
concentration alternatively meana a
maximum ground-level concentration
due to emission! from a stack due ia
whole or pert to downwash, wakes, or
eddy effects produced by nearby
structures or nearby terrain features
which individually is at least 40 percent
in excess of the maximum concentration
experienced in the absence of the
maximum concentration experienced In
the absence of such downwaah, wake*.
or eddy effects and greater than a
prevention of significant deterioration
increment The allowable emission rate
to be used in making demonatrationa
under thia part ahall be prescribed by
the new source performance standard
that ia applicable to the source category
unless the owner or operator
demonstrates that this emission rate ia
in/easible. When such demonstration*
era approved by the authority
administering the State implementation
plan, an alternative emiaaion rate ahall
be established in consultation with the
source owner or operator;
(2) for sources seeking credit a/tar
October 11983. for tncreeaee in existing
stack heights up to the height*
established under f 51.1(0X2). cither (1)
a •»•""""• ground'!*
atratic
due ia whole or pan to downwaah,
wakes or eddy effects aa provided hi
paragraph (kkMD of this section, except
that the emission rate specified by any
applicable State implementation plea
(or. ia the absence of such a limit the
•cruel emiaaioH rate) shall be used or
(ii) the actual presence of e local
nuisance caused by the exiating stack.
a* determined by the authority
admiaiateriag the State implementation.
plan: and
(3) for source* seeking credit after
January 12.1979 for a stack height
determiaeduader 15U(ii)(2) when the
enthority adminiateriag the State
implementation plan requires the use of
a field study or fluid model to verify
CEP suck height, for source* seeking
stack height credit after November 9.
1884 baaed on the aerodynamic
influence of cooling towers, and for
sources seeking stack height credit after
December 31.1970 based on the
aerodynamic influence of structures not
adequately represented by the equations
in | Sl.l(iJ)(2). a maximum ground-level
concentration due in whole or part to
downwaah. wake* or eddy effects that
ia at leeat 40 percent in excess of the
maximum concentration experienced in
the absence of such downwaah. wakes.
or eddy effects.
3. Section Sl.l ie further amended by
removing peragrapha (II) and (mm).
Mitt
4. Section 31.12 is amended by
removing paragraph (1).
5. Section 51.12(j) is amended by
removing "and (1)" from the first
ft. Section 91.12(k) is revised as
follow*:
(k) Toe provisions of f 51.12(j) shall
not apply to (1) stack heights in
existence, or dispersion technique*-
implemented on or before December 31.
1970, except when pollutants are being
emitted from such stacka or using such
dispersion technique* by sources, as
defined to section 111(*X3) of the Clean
Air Act which wen constructed, or
reconstructed, or for which major
modification*, as defined ia
II SL18fJXlX»X«). 3U4(bH2Xi) and
SX21(bK2XO. were carried out after
December 31.197ft or (2) coal-fired
steam electric generating unit* subject
to the prevision* of Section 118 of the
dean Air Act which commenced
operation before Jury 1.1987. and whoee
stack* wen eonaovcted under e
construction contract awarded before
February* 1974.
|lt18 It
7. Section 31.18(1) ia amended by
removing "and (I)" from the first
(Fit Dec aa-teOM filed 7-e-Sfc S.-43 «mj
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EPA-450/4-80-023R
Guideline for Determination of Good
Engineering Practice Stack Height
(Technical Support Document for the
Stack Height Regulations)
(Revised)
U.S. ENVIRONMENTAL PROTECTION AGENCY
Office of Air and Radiation
Office of Air Quality Planning and Standaros
Researcn Triangle Par*. NC 27711
June 19S5
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PN 123-85-10-28-009
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
j Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
OCT 2 8 198S
MEMORANDUM
SUBJECT: Implementation of Stack Height .Regulations - Presumptive NSPS
Emission Limit for Fluid Mod€Tl/»g StacK "Above Formula GEP Height
FROM: Darryl D. Tyler, Director
Control Programs Development Division (MD-15)
TO: Director, Air Management Division
Regions I-X
The following guidance is provided to explain the general emission
control requirements for sources conducting fluid modeling to justify stack
height in excess of that provided by the GEP formulae. While some of the
discussion and examples contained herein focus on utility sources, the
procedures outlined in this memorandum are generally applicable to all
stationary source categories. Please note that this 1s guidance. States
may present any other demonstrations that they may feel are warranted in
individual circumstances.
Background
.The revised stack height regulations published on July 8, 1985, define
three methods for determining good engineering practice (GEP) stack
height. These methods include:
1- a 65 meter de minimis GEP height;
2- the height determined by using an applicable formula based on the
dimensions of nearby buildings; and
3- the height necessary to avoid excessive concentrations due to
downwash as shown using a field study or fluid modeling
demonstration.
As the preamble to the regulations points out, the revised definition
of "excessive concentrations," a 40-percent Increase in concentrations
due to downwash resulting in a NAAQS or PSD increment exceedance,
necessitates that an emission rate be specified for purposes of evaluating
fluid modeling. The regulations require that a presumptive emission rate
equivalent to the new source performance standards (NSPS) be established
for the source in question before modeling may be conducted to determine
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stack height needed to avoid excessive concentrations due to downwash.*
This emission nte is described as "presumptive" because it is EPA's
presumption that all sources seeking to justify stack heights exceeding
those provided by the GEP formulae are capable of controlling their
emissions to NSPS levels. However,, the regulations also allow source
owners or operators to rebut this presumption, establishing an alternative
emission rate that represents the most stringent level of control that
can feasibly be met by that source in excess of the NSPS level. In the
preamble to the regulations, EPA Indicated that it will rely on the
"Guidelines for Determination of Best Available Retrofit Technology for
Coal-Fired Power Plants and other Existing Stationary Facilities,
EPA-450/3-80-009b" (SART Guidelines) whan reviewing these rebuttals.
If it is infeasible for a source to control Its emissions to NSPS
levels, then an alternative limit representing the lowest feasible emission
limit must be met before obtaining credit for stack height in excess of
GEP formula height. Sources may consider such factors as remaining plant
life and the cost of modifying existing equipment when determining NSPS
feasibility.
Procedures
The general procedure that is described in the BART Guidelines for
analyzing control alternatives should be followed to identify and evaluate
alternatives for sources seeking credit for stack heights In excess of
those produced by the applicable GEP formulae. Because the guidelines
were originally written to address visibility impairment, however, not all
of the analytical steps or applicability criteria—such as analysis of
visibility impairment or exemptions for power plants below 750 megawatts--
will be appropriate, and need not be addressed.
General steps in the analysis described 1n Section 2.0 of the
guidelines can be summarized as follows.
1. Identify a range of control alternatives, including both pre- and
post-combustion controls. In this regard, several fuel substitution and
alternative fuel blends should be considered, as well as technological
alternatives, such as coal cleaning and flue gas desulfurization.
2. Calculate t-.e cos", emissions, and other environmental and energy
impacts of the alternatives ^including those meeting NSPS objectives).
3. Select the alternative that represents the most stringent level
of emissions control feasible.
*Where the HS?S nas been subject to revision, and the source in
question is not subject to the revised NSPS, the earliest standard will be
applied; e.g., for po*er plants a rate of 1.2 Ib/mm3tu would be used.
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In perform.}ng these analyses, it Is Important to keep in mind that
EPA's presumption is that the NSPS emission limit is feasible unless
demonstrated otherwise. When carrying out evaluations, source owners or
operators may consider such factors as remaining useful plant life, the
remaining life of any equipment affected by revised emission rates
(including any control equipment), the cost of modifying boilers, control
equipment, and fuel handling facilities, and the cost of modifying or
cancelling existing fuel supply contracts (remaining useful plant life,
if a significant factor in determining NSPS feasibility, may necessitate
restrictions on the period of applicability of less stringent emission
limits). Finally, it is important to analyze, not only a range of alter-
native controls, but several combinations of alternatives, since such
combinations may yield a greater and more cost-effective degree of
emissions control.
Since determinations of the adequacy of any rebuttals of the NSPS
emission limit and the reasonableness of control alternatives considered
must be made on a case-by-case basis, and will be subject to public review
and comment during the rulemaking process, all technical and economic
analyses, as well as any claims of infeasibility, must be fully documented
and supported by any information that may be available.
If you have any questions regarding the application of this guidance
in a particular set of circumstances, please contact Eric Ginsburg at
(FTS) 629-5540 or Sharon Reinders at (FTS) 629-5526.
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Research Triangle Park, North Carolina 27711
APR 2
Mr. John P. Proctor
Bishop, Cook, Purcell and Reynolds
Law Offices
1400 L Street, N.W.
Washington, D.C. 20005-3502
Dear Mr. Proctor:
Your letter of February 23, 1989 to Administrator Reilly was
referred to me for response. The issues you describe were
previously raised to the attention of the Environmental
Protection Agency's (EPA's) Region III Office. You now question
Region Ill's rejection of your position that the best available
retrofit technology (BART) emission rate used in determining the
creditable stack height can be ignored for purposes of setting
the facility's operating rate as long as the operating rate is
consistent with the national ambient air quality standards
(NAAQS). The response provided to you by Region III on October
6, 1988 was extensively discussed with this office and with the
Office of General Counsel, and we fully endorse Region Ill's
conclusions and supporting rationale.
In your letter you stated that the sole basis for conducting
a fluid modeling study is to justify credit for stack height
above formula height, and that nothing requires States to rely on
the BART emission rate to determine the appropriate operating
rate. Actually, as noted by Region III, before such credit may
be considered, the preamble to the stack height regulation is
clear that the operating rate must be limited to the BART or new
source performance standards (NSPS) rate. The preamble to the
stack height regulation also notes that an emission limit more
stringent than BART/NSPS may be needed because the sources must
also meet the NAAQS and prevention of significant deterioration
requirements.
We agree with Region Ill's conclusion that NRDC v. Thomas.
838 F.2nd 1224 (D.C. Cir 1988), does not support your position.
In your February 23, 1989 letter to Administrator Reilly, you
raise a new argument not presented to Region III. You argue that
the court recognized that operating emission limitations are to
be determined after stack height credit has been calculated,
based on the court's acknowledgement that Congress imposed
technology-based limits in some situations, and EPA has authority
to mandate such limits for modeling demonstrations to determine
stack height credit. From this you conclude that a technology-
based emission rate used for fluid modeling is relevant only to
that modeiina.
-------
In response, we point out first that the court's discussion
of technology-based emission limitations (838 F.2d at 1241) was
in reference to NRDC's control-first position and not related to
fluid modeling as you suggest. We believe that the opinion
indicates clearly that the court regarded the presumptive NSPS
emission limit as a limit that must be complied with once the
fluid modeling was completed ("We find the attempt of industry to
bar control-first no stronger than NRDC's effort to require it in
the within-formula context." 838 F.2d at 1241; "... industry
petitioners assert that in order to use the NSPS presumption, EPA
must be able to point to substantial evidence that it is attain-
able by most of the affected sources. But as EPA allows any
source to use a higher emissions rate when NSPS is infeasible,
there is no need for any sort of generic demonstration that it is
normally so." id at 1242).
Second, in quoting EPA's statement about the significance of
fluid modeling demonstration the court was merely citing with
approval EPA's rationale for refusing to grandfather demonstra-
tions undertaken and approved prior to adoption of the 1985
regulations. This in no way implies a finding by the court that
the presumptive NSPS requirement (or higher BART limit) is not
the constraining limit. Neither of these references provides
support to your position.
In conclusion, we are in full agreement with the position
taken by Region III that sources seeking credit above formula
height must meet an emission rate consistent with BART/NSPS.
While final action as to any particular source would necessarily
await a State implementation plan revision, I hope the above
responds to your inquiry. Staff in our Region III Office are
available to assist you and your client, and I suggest that you
contact them directly if you have further questions.
Sincerely,
Gerald A. Emison
Director
Office of Air Quality Planning
and Standards
cc: Charles Carter. OGC
Thomas Maslany, Region III
Marcia Mulkey, Region III
bcc: Robert Bauman, AQMD Pat Embrey, OGC
Jesse Baskerville, Region III Eric Ginsburg, AQMD
John Calcagni, AQMD Doug Grano, AQMD
SDPMPB:DGrano:DataTech/PROCTOR2:PFinch:RTP(MD-15):629-5255:4-4-89
Control Number OAQPS-46- Due Date: 4-3-89
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BISHOP. COOK, PURCELL 6. REYNOLDS
WOO L STREET; N.W
WASHINGTON. D.C. 2OOO5-35O2
(202) 37I-570O
WOlTCR S OIBCCT DI»U 23, 1989 TELEX 44OS74 INTLAW Ul
TELECOPIER: Boa) 37I-59SO
William K. Reilly
Administrator
United States Environmental
Protection Agency
401 M Street, S.W.
Washington, D.C. 20460
Dear Mr. Reilly:
The purpose of this letter is to request EPA's
concurrence with a conclusion reached by this firm
pertaining to the setting of emission limitations for
existing sources that receive credit for stack height above
Good Engineering Practice ("GEP") stack height.
Specifically, I am seeking your concurrence with the
following conclusion: that a facility which uses a Best
Available Retrofit Technology ("BART") emission rate in a
fluid model to determine GEP stack height may ultimately
receive a different operating emission rate as long as that
rate is demonstrated by a dispersion model as being
consistent with the National Ambient Air Quality Standards
("NAAQS") .. EPA's consideration of this issue and response
is extremely important since the Agency's position will have
an immediate and long-term economic impact on one of our
client's operations. As pertinent here, our client must
make a major business decision regarding equipment
purchases, a possible shutdown of operations and technical
operating requirements. That decision is inextricably
linked to the stack height issues; it will be primarily
determined and affected by your response to this query.
For purposes of this discussion and request, I am
setting forth our analysis and position below as to what
legally appropriate procedures must be followed in
establishing operating emission rates pursuant to
Section 110 of the Clean Air Act for facilities receiving
credit for stack height above GEP formula height. In brief,
I believe this analysis supports our position that a
facility is not required to conduct a dispersion modeling
study that uses the same emission rate for a particular
pollutant that was used by the facility in justifying stack
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William X. Re illy
February 23, 1989
Page 2
height above GEP formula height; i.e., fluid and dispersion
modeling emission rates are to be developed and applied
independently. Thus, a state may authorize an emission rate
for a particular pollutant at a facility as long as the
emission rate is demonstrated by a dispersion model as being
consistent with the attainment and maintenance of the NAAQS.
Our analysis follows:
(a) In order to receive credit for stack height above
GEP formula height, a facility must conduct fluid modeling
studies to analyze the effects of terrain obstacles on
downwash, and to show that the additional height is needed
to avoid "excessive concentrations"; i.e., a 40 percent
increase in concentrations due to downwash that cause or
contribute to an increase or.an exceedance of air quality
standards or PSD increments.
(b) To complete the fluid modeling studies and to show
that there will be excessive concentrations, a facility must
obtain a BART emission rate from the applicable state agency
for each source. Although EPA's stack height regulations
initially require a source seeking to conduct a fluid
modeling study to use an emission rate equivalent to that
New Source Performance Standards ("NSPS") applicable to the
industrial source category ("presumptive NSPS emission
limit"), a source is permitted to rebut the applicability
of the presumptive NSPS emission limit.
(c) The sole basis for conducting a fluid modeling
study, and for obtaining an alternative emission rate to
complete the study, is to justify credit for stack height
above GEP formula height. The rate is but one aspect of
justifying stack height above GEP formula height, and GEP
stack height is but one aspect in determining an appropriate
operating emission rate. See Section 123(a)(1) of the Clean
Air Act, 42 U.s.C. § 7423(a)(1). In short, there is
nothing in either the Clean Air Act or the implementing
regulations that requires or advises the states to use or
rely upon the BART emission rate, used for a fluid modeling
!/ 40 C.F.R. § 51(kk).
2/ 50 Fed. Reg. 27892, 27898 (July 8, 1985).
3/ 50 Fed. Reg. 278P2, 27898 (July 8, 1985).
I/ In this section, Congress limits the degree to which tall
stacks may be considered in setting emission limitations. As
is apparent from the statutory language used in Section 123,
Congress intended to allow the states to consider other
factors, in addition to stack height, in setting emission
limitations.
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William K. Reilly
February 23, 1989
Page 3
study, in conducting a dispersion study to determine an
appropriate operating emission rate.
(d) States are required to ensure the attainment and
maintenance of the NAAQS by establishing emission
limitations for facilities within their boundaries.
Moreover, with respect to existing sources, states have the
discretionary authority to determine and enforce whatever
mix of emission limitations it deems best for these sources,
as long as the overall effect is compliance with the NAAQS.
Train v. N.R.D.C.. 421 U.S. 60,79 (1974).
We believe our analysis and conclusion are supported by
the District of Columbia Circuit Court of Appeals' recent
decision in N.R.D.C. Inc. v. Thomas. 838 F.2d 1224 (D.C.
Cir. 1988) in which the court reviewed EPA's stack height
regulations and the NRDC's argument that a source must apply
all available emission controls before it may justify a
stack height above GEP formula height. The Court of Appeals
rejected NRDC's "control-first" argument fid, at p. 1235)
because it recognized that BART (stack height) emission
rates and source-related emission limitations have
independent purposes: "Although the record does not allow
us to infer exactly the impact of the baseline emissions
rate on the emissions rate that would emerge (after the
stack height credit were calculated and then used to
determine the permissible emissions), all parties agree that
the impact is substantial. Indeed, that is what the issue
is all about. If Congress in Section 123 prescribed the use
of such a baseline emissions rate, with all its implications
for ultimate emission ceilings, it did so in a remarkably
cryptic way." Id. at p. 1236.
As is evident, the Court of Appeals recognized that
operating emission limitations are to be determined after
stack height credit has been calculated pursuant to
Section 123 of the Act. This conclusion is supported by the
Court's consideration of the following facts. First, the
Court observed that Congress imposed technology-based
emission limitations (including NSPS, BACT, LAER, RACT and
BART) in a variety of situations, and that EPA has the
authority to mandate a specific technology-based emission
limit (e.g., the presumptive NSPS limit) for GEP fluid
modeling demonstrations (id. at p. 1241) used for
calculating stack height credit. Second, the Court noted
that a "* * * * fluid modeling demonstration has no
significance apart from showing whether the source qualified
for credit under the stack height guidelines than in
effect.'" (emphasis in original). Id. at p. 1249. As
pertinent here, the Court's analysis supports the conclusion
that a specific technology-based emission rate used by a
facility in a fluid modeling demonstration is significant
only tc the extent that it demonstrates whether a source
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William K. Reilly
February 23, 1989
Page 4
should receive credit for stack height above GEP formula
height. A different conclusion; i.e., that the emission
rate used to calculate stack height (either a BART rate or
the presumptive NSPS rate) should be used by a facility,as
its operating emission rate, is contrary to the Court's
holding which rejected the "control-first" argument.
Please be advised that an EPA staff person, contacted by
our firm, appears to have reached a different conclusion.
Specifically, we have been advised by this staff member that
an existing source is required to operate at the lowest
emission rate resulting either from the stack height
demonstration or dispersion study — even though another
(i.e., higher) emission rate will assure compliance with the
NAAQS.
It is our opinion that this position is inconsistent
with Sections 110 and 123 of the Clean Air Act, the stack
height regulations, and existing case law. Therefore, we
are requesting EPA's analysis of this issue and official
agency position. We would appreciate your prompt review of
t.iis issue due to the impact that your response will have on
our client's operations and financial planning.
If you have any questions regarding this issue, please
feel free to contact me directly. Also, I have enclosed an
extra copy of this letter and a stamped, self-addressed
envelope. Would you please stamp this extra copy and return
it to me for our files.
Sincerely,
JPP:cas
John P. Proctor
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UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Research Triangle Park. North Carolina 27711
OCT 1 0 I9S5
MEMORANDUM
SUBJECT: Questions and Answers on Implementing the
Revised Stack Height Regulation
FROM: G. T. Helms, Chieff- L \W—*-
Control Programs Operations Branch (MD-15)
TO: Chief, A1r Branch, Regions I-X
A number of questions have arisen in several areas of the revised
stack height regulation since Its promulgation on July 8. The following
answers have been developed 1n response. The questions and answers are
arranged under the general topic headings of interpretation of the regula-
tion, State implementation plan (SIP) requirements, and modeling analyses.
Please continue to call Sharon Reinders at 629-5526 if you have further
comments or additional questions.
Interpretation of the Regulation
1. Q: What criteria should be used to determine when a stack was 'in
existence" with respect to the various grandfatherlng dates in the
regul at ion?
A: The recent promulgation of revisions to the stack height regulatio
did not change the definition of "in existence." The definition is provid
in 40 CFR 51.1(gg) and includes either the commencement of continuous
construction on the stack or entering Into a binding contract for stack
construction, the cancellation of which would result in "substantial
loss" to the source owner or operator. The definition of what constitutes
a "substantial loss" will be the subject of future guidance.
2. Q: What "source" definition should be used in determining whether tie
ins to grandfathered stacks should be permitted or prohibited?
A: The term "source" 1n this instance means a single emitting unit.
Thus, credit for tying a single post-1970 unit(s) Into a grandfathered
stack serving a number of old units is prohibited under the regulation.
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-2-
3. Q: What is meant in the regulation by "facility?
A: For purposes of this regulation, the definition contai-ned in
40 CFR 51.301(d) should be used. That definition essentially defines the
term as the entire complex of emitting activities on one property or
contiguous properties controlled by a single owner or designee.
4. Q: Must good engineering practice (GEP) stack height be established
separately for each pollutant? If not, how should it be determined?
A: It is not necessary to calculate a separate SEP stack height for
each pollutant. Since "SEP" is defined by Section 123 of the Clean Air
Act as the height necessary to ensure against excessive concentrations of
any air pollutant, it follows that SEP should be established for each
source based on the pollutant requiring the greatest height to avoid
excessive concentrations.
5. Q: How should "reliance" on the 2.5H formula be determined?
A: First, "reliance" on the 2.5H formula applies only to stacks 1n
existence before January 12, 1979. Credit for "reliance" on the 2.5H
formula, can be granted under the following cases: (a) Where the stack
was actually built to a height less than or equal to 2.5H; (b) Where the
stack was built taller than 2.5H and the emission limitation reflects th
use of 2.5H 1n the SIP modeling analysis; or (c) Where evidence 1s proviv. .
to show "reliance" as discussed in the following paragraph. If no modellnc
was used to set the emission limitation for the source, then it cannot be
argued that there was "reliance" on the formula, since EPA's guidance was
specifically aimed at using stack height credit in establishing emission
limitations. Once it is determined that the emission limitation was in
fact based on estimates of dispersion from the stack, then the source can
be said to have properly "relied" on the 2.5H formula. In the event that
it cannot be determined that the emission limit is based on "reliance" on
the 2.5H formula, then the refined H + 1.5L formula must be used.
Where a clear relationship between a 2.5H stack height and the
emission limitation cannot be shown, where the emission limitation was
not calculated based precisely on the 2.5H height, or where the stack
height used in modeling cannot be verified, then additional evidence will
be needed. Preferred would be written documentation, such as copies of
the original engineering calculations or correspondence between the State
or the emission source owner and EPA indicating that the 2.5H formula
should be used to derive the emission limitation. However, recognizing
that such evidence is often not retained for more than a few years,
"reconstructed" documentation may be considered, but should only be used
as a last resort. This evidence should include explanations by those
individuals who were involved in designing the facility, calculating
emission rates, and who represented the facility in dealings with the
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-3-
State and EPA on how the emission limit was derived, including a discussion
of how the formula was originally used in deriving the source emission
limitation, a discussion of the analytical method applied, and a listing
of any contacts or discussions with EPA during that period. This listing
will aid EPA in searching its own files to find any records of communication
or correspondence that may bear on the Issue.
In no case should a source be allowed after January 12, 1979, to
obtain a relaxation in the emission limitation by arguing that 1t "relied"
on past EPA guidance endorsing the 2.5H formula. In cases where a relaxation
based on GEP formula height is sought in the future, the refined H + 1.51
formula must be used.
6. Q: The preamble specifically discusses cooling towers as structures to
which the formula should not be applied. Will the Office of Air Quality
Planning and Standards be specifying other structures that are not well
represented by the formul a?
A: The discussion in the preamble and GEP guideline Is not intended to
be all-inclusive; judgment should be used 1n determining when fluid
modeling should be used to estimate the effects of structures with rounded,
domed, or tapered shapes. Water towers and storage tanks are additional
examples of such structures. As additional Information becomes available
on the aerodynamic effects of specific building shapes and configurations,
we will evaluate the need to revise the GEP guidance. 'However, at present,
there are no plans to Issue a "laundry list" of structures to which the
formulas do not apply.
SIP Requirements
7. Q: Should a compliance averaging-time be explicitly stated in a
SIP revision for sulfur dioxide (S02) emission limits that are revised to
meet the stack: height regulation?
A: A compliance averaging time need not be specified as an enforceable
SIP provision as long as a stack test compliance method is in place in the
underlying federally approved SIP. EPA's current national policy requires
that SIP's and permits contain enforceable "short-tern" emission limits
set to limit maximum emissions to a level which ensures protection of the
short-term national ambient air quality standards (NAAQS) and prevention
of significant deterioration (PSD) Increments. EPA relies upon a short-term
stack test provision in the SIP as the method of determining compliance
with the emission limits. In lieu of a stack test, EPA has accepted fuel
sampling and analysis and continuous emission in-stack monitors (CEM's).
When compliance is to be determined from information obtained by fuel
sampling and analysis and CEM's, short-tern averaging times should be
specified.
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-4-
8. Q: Are all States required to have "stack height regulations"?
A: Limitations on creditable stack height and dispersion techniques
impact the SIP program 1n two areas—SIP mission limits for existing
sources and SIP provisions covering new source review (NSR)/PSD permitting
procedures. For existing sources, State regulations limiting credit "for
stack height and other dispersion techniques (stack height regulations)
are not necessary as long as the SIP emission limits are not affected in
any manner by so much of the stack height as exceeds G£P, or any other
dispersion technique. Where a State has stack height regulations, those
regulations must be consistent with EPA's regulation. Where a SIP contains
regulations that are inconsistent with EPA's regulation, the State must
either adopt a stack height regulation that 1s consistent with EPA's or
Incorporate the EPA regulation by reference.
For the NSR/PSD programs, 1t is essential that the plan contain
limitations on the amount of creditable stack height and other dispersion
techniques. The following cases have been developed to illustrate what
action(s) may be required of the State since promulgation of the stack
height regul ation.
CASE All): A fully or partially delegated PSD program that references but
does not define GEP where the delegation agreement does not conta.,
a date to define which version of the PSD rule is being oeTegated,
ACTION: Notify the State that all permits issued henceforth must be
consistent with EPA's stack height regulation. AIT permits
previously issued must be reviewed and revised as necessary
within 9 months.
CASE A(2): A fully or partially delegated PSD program that references
but does not define GEP where the delegation agreement
does contain a date to define which version of the PSD rule
is being delegated.
ACTION: Update the delegation agreement to reflect agreement with EPA's
stack height regulation as of July 8, 1985. Notify the State
that all permits issued henceforth must be consistent with
EPA's stack height regulation. All permits previously Issued
must be reviewed and revised as necessary within 9 months.
CASE B: The current federally approved SIP for NSR/PSD does not
contain a reference to GEP or cispersion techniques, i.e.,
provisions assuring that emission limitations will not be
affected by stack height in excess of GEP or any prohibited
dispersion techniques do not exist in the current SIP.
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-5-
ACTION: Notify the State that such provisions must be adopted and
submitted as a SIP revision within 9 months. This can be
accomplished by adopting stack height regulations at the
State level or by adopting the appropriate reference and
commitment to comply with EPA's stack height regulation as
promulgated on July 8, 1985. Interim permitting should be
consistent with EPA's stack height regulation.**
CASE C: The current federally approved SIP for NSR/PSD contains
references to, but does not define, 6EP or dispersion techniques.
ACTION: Notify the State that a commitment to comply with EPA's stack
height regulation as promulgated on July 8, 1985, is required.
If a State 1s unable to make such a commitment, State regulations
must be revised to be consistent and submitted to EPA as a SIP
revision within 9 months and Interim permitting should be
consistent with EPA's stack height regulation. No "grace
period" will be allowed for sources receiving permits between
July 1985 and April 1986.**
CASE D; The current federally approved SIP for NSR/PSD contains stack
height regulations that are Inconsistent with EPA's regulation.
ACTION: Notify the State that such regulations must be revised to be
consistent and submitted as a SIP revision within 9 months
and that interim permitting should be consistent with EPA's
stack height regulation.**
CASE E(l): A SIP for NSR/PSD has been submitted to EPA, or will be
submitted to EPA before the due date for stack height revisions.
The submittal contains provisions that conflict with EPA's
stack heigot regulation.
ACTION: Notify the State that EPA cannot approve the submittal until
it is revised pursuant to EPA's July 8, 1985, regulation.
**
In the event that a State does not have legal authority to comply with
EPA's regulation in the interim (e.g., because 1t must enforce State
rules that are inconsistent with EPA's regulation) and is compelled to
issue a permit that does not meet the requirements of the EPA revised
stack height regulation, then EPA should notify the State that such
pern-its do iot constitute authority under the Clean A1r Act to commence
construction.
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-6-
CASE £(2): As in Case 1(1) t a SIP for NSR/PSD has been submitted to EPA
or will be submitted to EPA before the due date for stack
height revisions. The submittal is not Inconsistent with
EPA's stack height regulation, but portions of the existing
approved SIP that relate to the submittal are inconsistent.
ACTION: Approve the SIP submittal based on a commitnent by the State
to correct the inconsistencies in its existing SIP to comport
with EPA's July 8 regulation and submit the corrections as a
SIP revision within 9 months. Interim permitting should be
consistent with EPA's stack height regulation.** If the exist-
ing SIP is ambiguous, i.e., the SIP references but does not
define terms relating to SEP or dispersion techniques, the
action steps outlined in Case C above should be followed.
CASE F: In nonattainment areas, emission limits or permits do not always
Include modeling, but rather are based on lowest achievable
emission rate (LAER) and offsets.
ACTION: If no modeling is used 1n the Issuance of a permit, the emission
requirements for the source are not "affected" by stack heights
or dispersion techniques, and no action 1s needed. However, 1f
modeling was used 1n the process of preparing and issuing a
permit, such as cases where offsets were obtained offsite, that
modeling must be reviewed for consistency with the stack height
regul ation.
9. 0: What must all States do now that EPA's stack height regulation is
promulgated?
A: States must review and revise.their SIP's as necessary to include or
revise provisions to limit stack height credits and dispersion techniques
to comport with the revised regulations, and, in addition, review and
revise all mission limitations that are affected by stack height credit
above G£? or any other dispersion techniques. In accordance with Section
4Q6(d)(2) of the Clean A1r Act, States have 9 months from promulgation to
submit the revised SIP's and revised SIP emission limitations to EPA.
In an August 7, 1985, memo titled "Implementation of the Revised
Stack Height Regul ation-.Request for Inventory and Action Plan to Revise
SIP's," Regional Offices were requested to begin working with each of
their States to develop States' Action Plans. Each Action Plan should
include the following: (l) An inventory of (a) all stacks greater than
65 meters (m), (b) stacks at sources which exceed 5,000 tons per year
total allowable 563 emissions; and (2} A reasonable schedule of dates for
significant State actions to conform both State stack height rules and
emission limitations to EPA's stack height regulation. Schedules should
include increments of progress. Regional Offices should be satisfied
that each of tneir States provide schedules for completion of the tasks
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-7-
as outlined in the August memo and report the status of schedule commitments
to them on a monthly basis. Regional Offices have been asked to forward
monthly status reports to the Control Programs Development Division on
the States' progress to meet scheduled commitments and also report the
results of followup with the States on schedules that are not met. In
order to facilitate tracking the States monthly progress, guidance on a
standardized format will be issued shortly.
Modeling Analyses
10. Q: Is there any restriction or prohibition against, or demonstration
required for, raising an existing (or replacing) stack up to 65 m?
A: No, as Long as prohibited dispersion techniques are not employed.
11. Q: Are flares considered to be stacks?
A: No, flares are excluded from the regulation.
12. Q: What load should be used for a fluid modeling demonstration?
A:- One hundred percent load should generally be used unless there
is a compelling argument otherwise..
13. Q: Can new or modified sources who have agreed to a case-by-case
best available control technology (BACT) emission rate be required to use
this rate for fluid modeling rather than a less stringent new source
performance standard (NSPS) emission rate?
A: As set forth in 40 CFR 51.1 (kk), the allowable emission rate to
be used in making demonstrations under this part shall be prescribed by
the NSPS that is applicable to the source category unless the owner or
operator demonstrates that this emission rate is infeasible.
14. Q: Must the exceeddnce of NAAQS or PSD increment due to downwash, wakes,
or eddies occur at a location meeting the definition of ambient air?
A: No, the exceedance may occur at any location, including that to
which the general public does not have access.
15. Q: Is a source that meets NSPS or BACT emission Units subject to
restrictions on plume merging?
A: Yes. However, in a majority of such cases, there will be no practical
effect since BACT or NSPS limits will be sufficient to assure attainment
without credit for alume rise enhancement.
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-8-
Q: What stack parameters are to be used in modeling when the actual
stack neicnt is greater than G£P height?
A: Where it is necessary to reduce stack height credit below what is in
existence, for modeling purposes, use existing stack gas exit parameters—
temperature and flow rate—and existing stack top diameter and model at
GEP height.
17. Q: How should a stack that 1s less than GEP height be modeled when
dispersion techniques are employed?
A: In order to establish an appropriate emission limitation where a
source desires to construct less than a GEP stack but use dispersion
techniques to make up the difference in plume rise, two cases should be
tested. First, conduct a modeling analysis inputting the GEP stack
height without enhanced dispers* ?n parameters, then conduct a second
analysis inputting the less than GEP stack height with the increased
plume rise. The more stringent emission limitation resulting from each
of the two runs should be the one specified as the enforceable limitation.
18. Q: How are the effects of prohibited dispersion techniques to be excluded
for modeling purposes?
A: Where prohibited dispersion techniques have been used, modeling to
exclude their effects on the emission limitation will be accomplished by
using the temperature and flow rates as the gas stream enters the stack, and
recalculating stack parameters to exclude the prohibited techniques
(e.g., calculate stack diameter without restrictions in place, determine
exit gas temperatures before the use of prohibited reheaters, etc.).
19. Q: How are single flued merged stacks and multiflued stacks to be •
treated in a modeling analysis?
A: This is a multistep process. First, sources with allowable $03
emissions be'tow b,000 tons/year may be modeled accounting for any plume
merging that has been employed. For larger sources, multiflued stacks
are considered as prohibited dispersion techniques in the same way as
single flued merged gas streams unless one of the three allowable conditions
has been met; i.e., (1) the source owner or operator demonstrates that
the facility was originally designed and constructed with such merged gas
streams; (2) after date of promulgation, demonstrate that such merging is
associated with a change in operation at the facility that includes the
installation of pollution controls and results in a net reduction in the
allowable emissions of the pollutant for which credit 1s sought; or (3}
before date of promulgation, demonstrate that such merging did not result
in any increase in the allowable emissions (or, in the event that no
emission limit existed, actual emission level) and was associated with a
change in operation at the facility that Included the installation of
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-9-
enissi'ons control equipment or was carried out for sound economic or
engineering reasons, as demonstrated to EPA. Guidelines on what constitutes
sound economic or engineering justification will be issued shortly.
If plume merging from multiflued stacks is not allowable, then each
flue/liner must be modeled as a separate source and the combined impact
determined. For single flued merged stacks where credit is not allowed,
each unit should be modeled as a separate stack located at the same
point. The exit parameters, i.e. velocity and temperature, would be the
same as for the existing merged stack conditions and the volume flow rate
based on an apportionment of the flow from the Individual units.
20. Q: What stack height for point sources should be Input to air quality
dispersion modeling for the purpose of demonstrating protection of the
NAAQS and PSD increments?
A: A discussion of the maximum stack height credit to be used in modeling
analyses is provided in the "Guideline for Determination of Good Engineering
Practice Stack Height" and provides that the GEP stack height should be
used as input to the model assessment. If a source is operating with a
less than GEP stack height, then the actual stack height should be input
to the "model.
21. Q: What stack height should be used for background sources in
modeling analyses?
A: The GEP-stack height for each background source should
be input to the model assessment. If a background source is operating
with a less than GEP stack height, then the actual stack height should be
input to the model.
22. Q: Can credit for plume merging due to installation of control
equipment for total suspended paniculate (TSP) matter be allowed when
setting the SOj 1irait?
A: To state the question another way, the concern is what impact
the merging and installation of control equipment have on the emission
limit for another pollutant, and whether the merging occurred before or
after July 8, 1985. After July 8, 1985, any exclusion from the definition
of "dispersion techniques" applies only to the emission limitation for
the pollutant affected by such change in operation and 1s accompanied by
a net reduction in allowable emissions of the pollutant. For example, a
source tears down two old stacks and builds one new GEP stack with an
electrostatic precipitator (ESP). This results in a net reduction in TSP
emissions. This source could model using stack gas characteristics
resulting from merging tne two gas streams in setting the TS? emission
limit, but may not so nodel and receive the credit for stack merging when
evaluating the SC>2 emission limit.
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-10-
Before July 8, 1985, installation of TSP pollution control equipment
generally justifies the merging of the stacks for TSP. However, if a
source's emission limitation for SOj increased after the merging, then
credit would generally not be allowed since it is presumed that the
merging was to increase dispersion*
A source with no previous SOj emission limit that merges stacks and
installs an ESP for TSP control may consider the effects of merging on
compliance with the TSP NAAQS but may not use merging to justify setting
an S02 emission limit less stringent than its actual emission rate before
the merging.
23. Q: If, after determining GEP stack height by fluid modeling,
dispersion modeling under other than "downwash" meteorological conditions
shows that a lower emission limit than that from the fluid model GEP
analysis is necessary to meet ambient air quality constraints, should a
new stack height be defined for the source?
A: No. GEP stack height is set. Ambient air quality problems
predicted by dispersion modeling at the fluid modeled height means that a
more stringent emission limit is necessary.
24. Q: Does EPA intend to issue additional guidance on fluid modeling
demonstrations?
A: See the attached memo from Joseph A. Tikvart, Chief, Source
Receptor Analysis Branch, to David Stonefleld, Chief, Policy Development
Section, on guidance for a discussion of existing and additional guidance
on fluid model demonstrations.
Attachment
cc: Stack Height Contacts
Gerald Emison
Ron Campbell
B. J. Steigerwald
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PN 123-85-09-19-006
UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
Office of Air Quality Planning and Standards
Research Triangle Park. North Carolina 2771 1
September 19, 1985
MEMORANDUM
SUBJECT: Guidance ci Fluid Model Demonstrations for Detemining GEP
Stack Height in Complex Terrain
FROM: „ Joseph A. Tikvart, Chief
Source Receptor Analysis Branch, MDAD
TO: David Stonefield, Chief
Policy Developaent Section, CPDD
The recently promulgated stack, height regulation requires that a source
that wishes to receive credit for the effects of wakes, eddies and downwash
produced by nearby terrain for the purpose of calculating GEP stack height
must conduct a fluid model demonstration or a field study. Recent guidance
for fluid modeling these terrain effects is contained in Section 3.6 of the
"Guideline for Determination of GEP Stack Height (Revised)," EPA 450/4-80-023R,
June 1985, available from NTIS as PB 85-225-241. In addition, the report
"Fluid Modeling Determination of Good Engineering Practice Stack Height in
Complex Terrain," EPA 600/3-85-022, available from NTIS PB 85-203-107,
provides an actual case of how EPA conducted a GEP determination, abort of
performing the "excessive concentration" criteria teat. Requests to conduct
field studies in lieu of fluid modeling demonstrations" will be evaluated on
a case-by-case basis; refer to pp. 46-47 of' the GEP Guideline.
Previously, EPA published three documents which form the basis for
conducting fluid model demonstrations, particularly in flat terrain
situations: (1) "Guideline for Fluid Modeling of Atmospheric Diffusion,"
EPA 600/8-81-009, April 1981, available from NTIS aa PB 81-201-410; (2)
"Guideline for Use of Fluid Modeling to Determine Good Engineering Practice
Stack Height," EPA 450/4-81-003, July 1981, available from NTIS aa PB 82-145-
327; and (3) "Determination of Good-Engineering-Practiee Stack Height: A
Fluid Model Demonstration Study for a Power Plant," EPA 600/3-63-024, April
1983, available from NTIS aa PB 83-207407.
Lastly, EPA conducted a 4-day workshop on fluid modeling and GEP
determination at the Fluid Modeling Facility at RTF in February 1981,
attended by ataff from each Regional Office. Although some attendees are
no longer with the Agency, we believe at least one person in each Region
who attended is still "on board," except for Regions II and VIII, and could
serve as a resource person. At the Regional Workshop on the Stack Height
Regulation next month, we will poll the attendees concerning the need for
-------
another fluid modeling workshop for Regional Office and State technical
•taff. If a need is expressed and specific attendees can be identified, we
will request the Meteorology and Assessment Division, ASRL, to present such
a workshop at RIP within the next few months.
The above documents together with staff that have some knowledge of
fluid modeling should enable most Regions to provide initial technical
assistance to the States and enable the States to increase their own level
of expertise. Note that document (2) contains a report checklist in Section
5, outlining what a fluid model report should contain. Additional items
explicitly related to complex terrain studies may be required on a case-by-
case basis, especially after reviewing EPA's example study carefully. More
detailed procedures for implementing the excessive concentration criteria
calculations, using data from a fluid model demonstration, are being developed
and will be provided at the upcoming Regional Workshop.
Should technical questions arise regarding GEP determinations or fluid
model demonstrations, please contact Jim Dicke or Dean Wilson of my staff,
FTS 629-5681. We assume the Regional Office staffs will attempt a first-cut
resolution of technical issues before requesting our assistance.
cc: S. Reinders
R. R&oads
F. Scaleneier
D. Wilson
-------
United State*
{Environmental Protection
Agency
Office of Air Quality
Planning and Standards
Research Triangle Park NC 27711
EPA-450/4-B1-003
July 1981
Air
Guideline for Use of
Fluid Modeling to Determine
Good Engineering Practice
Stack Height
ENVIRONMENTAL PROTECTION
AGENCY
OCT 30 1981
UBftARY SERVICES OFFICE
-------
UMrtotf Statav Environmental SeiancM Raaaarcfi
•refaction Laboratory
Haaaarcn Triangle Park NC 27711
EPA-eoO/3-83-024
April 1983
Rtsaarch and Oavtlopmant
Determination of
Good-Engineering-
Practice Stack
Height
•
A Fluid Model
Demonstration
Study for a Power
Plant
-------
United States EPA-600/8-81-009
Environmental Protection April 1981
Agency
&ERA Research and
Development
OCT 3u 1981
Prepared for
Office of Air Quality
Planning and Standards
Prepared by
Environmental Sciences Research
Laboratory
Research Triangle Park NC 27711
ENVIRONMENTAL PROTECTION
AGENCY
Guideline for ^y^ sa^os OFFICE
Fluid Modeling of
Atmospheric Diffusion
-------
Protection
*»»«»reh Trwnvto Par* HC 2771 1
Fluid Modeling
Demonstration of
Good-Engineering-
Practice Stack
Height in Complex
Terrain
NATIONAL
INFORMATION
TIONAL TECHNICAL \ \
DRMATION SERVICE / S
•i ttufmn v cMmncf / ^
9*m**^ ^T ^
-------
REFERENCES FOR SECTION 5.7
-------
PN 123-85-10-28-008
,i if
° *
. UNITED STATES ENVIRONMENTAL PROTECTION AGENCY
3 Office of Air Quality Planning and Standards
* Research Triangle Park, North Carolina 2771 1
~*
CCT 2 * J98S
MEMORANDUM
SUBJECT: Implementation of Stack Helgjtf^Regulatljyis - Exceptions From
Restrictions on Credit for
FROM: Darryl D. iyler, Director
Control Programs Developm
TO: Director, A1r Management Division
Regions I-X
This guidance has been prepared to address two Issues pertaining to
credit for merged stacks prior to July 8, 1985. It establishes a procedure
that should be used to prepare and to review justifications for merging gas
streams for economic or engineering reasons, and to address the presumption
that merging was significantly motivated by an Intent to gain credit for
Increased dispersion. Please note that this 1s guidance; States may submit
alternative demonstrations 1n support of merged stack exemptions 1f they
feel the Individual circumstances warrant.
Background
Recent revisions to EPA's stack height regulations place certain
restrictions on the degree to which stationary sources may rely on the
effects of dispersion techniques when calculating allowable emissions.
One such restriction 1s provided for the merging of gas streams, or
combining of stacks. Several exemptions have been provided 1n the regula-
tion, however. More specifically, 40 CFR Part 5l.l(hh)(2)(11) allows
credit under circumstances where:
A. The source owner or operator demonstrates that the facility was
originally designed and constructed with such merged gas streams;
B. After July 8, 1985, such merging 1s part of a change 1n operation
at the facility that Includes the Installation of pollution controls and 1s
accompanied by a net reduction 1n the allowable emissions of a pollutant.
This exclusion from the definition of "dispersion techniques" shall apply
only to the emission limitation for the pollutant affected by such change
1n operation; or
C. Before July 8, 1985, such merging was part of a change 1n operation
at the facility that Included the Installation of emissions control equip-
ment or was carried out for sound economic or engineering reasons. Where
there was an Increase 1n the federally-approved emission limitation for any
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pollutant or, 1n the event that no emission limitation was 1n existence
prior to the merging, an Increase 1n the quantity of any pollutants actually
emitted from existing units prior to the merging, the reviewing agency
shall presume that merging was significantly motivated by an Intent to gain
emissions credit for greater dispersion. Absent a demonstration by the
source owner or operator that merging was not significantly motivated by
such an Intent, the reviewing agency shall deny credit for the effects of
such merging 1n calculating the allowable emissions for the source.
General Requirements
Figure 1 Illustrates a framework for evaluating claims for merged
stack credit. Because merged gas streams are generally regarded as prohibited
dispersion techniques under the regulations, 1t 1s Incumbent on the State
or the source owner or operator to demonstrate that such merging was conducted
for sound economic or engineering reasons, and was not significantly motivated
by an Intent to avoid emission controls. Consequently, the first step
should entail a review of State and EPA files to determine the existence of
any evidence of Intent on the part of the source owner or operator.
Information showing that merging was conducted specifically to Increase
final exhaust gas plume rise serves as a demonstration of dispersion Intent
that justifies a denial of credit for merged gas streams. Demonstrations that
merging was carried out for sound economic or engineering reasons are
expected to show that either the benefits of merging due to reduced
construction and maintenance costs outweigh the benefits relating to lower
emission control costs or that relevant engineering considerations showed
the merging to be clearly superior to other*conf1gurat1ons.
Demonstration Requirements
Several exemptions from prohibitions on gas stream merging are provided
for existing sources 1n the stack height regulations:
1- where sources constructed their stacks before December 31, 1970,
2- where the total facility-wide emissions from the source do not
exceed 5,000 tons per year,
3- where the facility was originally designed and constructed
with merged gas streams, and
4- where the merging was part of a change 1n facility operation that
Included the Installation of pollution control equipment and resulted 1n
no Increase 1n the allowable emissions of any pollutant.* Where there
was an Increase in emissions 1n conjunction with the merging and Installation
of control equipment, the regulations require that source owners also make
an affirmative demonstration that the merging was not motivated by dispersive
Intent.
*Where there was no federally-approved emission limit prior to merging
gas streams, there must be no Increase 1n the actual emissions of any
pollutant. Moreover, 1t 1s Incumbent on the State to demonstrate that there
was a logical relationship between the merging of existing gas streams and
the Installation of controls.
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Sources that are not covered under these criteria may still qualify for
exemption if they can show that merging was conducted for sound economic
or engineering reasons. Such demonstrations should Include justifications
for having replaced existing stacks. This may be done, for Instance, by
documenting through maintenance records, correspondence, or other
contemporaneous evidence, that the existing stacks had reached the end of
their useful life, were prematurely corroded, had sustained other damage
making them unservlcable, were of a height less than that regarded as
good engineering practice, thereby causing downwash problems, or that the
addition of new units at the facility necessitated additional stacks and
Insufficient land was available. The absence of any evidence supporting
the need for stack replacement creates a strong presumption that merging
was carried out specifically to avoid the Installation of pollution
controls, I.e., was "significantly motivated by an Intent to gain emissions
credit for Increased dispersion."
No Increase 1n Allowable Emissions
Once this Initial criterion 1s satisfied, demonstrations may show
that merging was based either on sound economic or sound engineering
reasons. Claims based on strict engineering justifications may be more
difficult to show, since the existence of more than one reasonable
engineering solution generally leads to a decision based on economics.
However, 1f 1t can be documented that the merged stack configuration was
clearly superior to other stack configurations for purely engineering
reasons, without consideration of cost, then credit for merging may be
granted.
In order to most reliably Implement the provisions of the regulations
regarding the merging of gas streams for sound economic reasons, 1t would
be necessary to ascertain the actual Intent of the source owner or operator
at the time the decision was made to merge gas streams. Recognizing that
the difficulty of doing so was the basis for EPA's rejection of an "Intent
test" 1n the rule, the following approach provides a surrogate demonstration
of Intent. This approach 1s summarized 1n Figure 2.
Because the potential savings attributable to the avoidance of
pollution controls can significantly Influence decisions to merge stacks,
one way to show the absence of dispersion Intent 1s to conduct an analysis
of the annual1zed capital and maintenance costs for merged stacks and for
Individual stacks, and compare the results to the compliance costs (fuel
and operation and maintenance of any control equipment) calculated based on
the emission limitations derived with and without merged stack credit. If,
when the difference 1n capital and maintenance costs 1s compared with the
difference 1n compliance costs over the period of capital amortization, the
capital and maintenance cost saving 1s greater than the compliance cost
saving, then merging can be accepted as having a sound economic basis.
In establishing this rule of thumb, we are aware that a benefit of as
little as 10-20 percent could be considered "significant" 1n the context of
the court's holding on this matter—I.e., such a benefit could have been
considered to be a relevant factor 1n decisions to construct merged stacks.
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However, recognizing that documentation of cost analyses after an extended
period of time— up to 15 years—Is likely to be limited, we believe that
the 50 percent test articulated above would constitute a more reasonable
basis for Initial determinations (that 1s, a level at which we believe that
there was likely a significant Incentive to merge stacks to avoid control
requirements).
Affirmative Demonstrations of Nond1spers1on Intent
In some Instances, a State or emission source owner may not be able to
make a demonstration as described above, or believe that sound economic
reasons existed for merging stacks, regardless of the relationship between
financial savings attributable to reduced emission control requirements
versus lower stack construction cost. In such cases, an opportunity should
be provided to affirmatively demonstrate that merged stacks were not
"significantly motivated by an Intent to obtain emissions credit for
Increased dispersion." The burden of proof rests solely with source owners
or operators attempting to make *i1s showing.
Demonstrations may rely on any relevant evidence, Including but not
limited to the following:
• construction permits, or permits to operate from pollution control
agencies
• correspondence between the source owner or operator and government
agencies
- engineering reports relating to the facility
- facility records
- affidavits
• any other relevant materials
For Instance, such a demonstration could be made by submitting
documentary or other evidence (e.g., Internal company memoranda presenting
the alternative construction opportunities available to the company) that
indicates the Intent of the source owner or operator and shows that
consideration of dispersion advantages was conspicuously absent.
Alternatively, 1t night be shown that either action by the State 1n
approving a revised emission limit followed actual merging sufficiently
later 1n time to suggest that dispersion credit was not considered by the
source at the time of merging or the State approved limit was unrelated to
the merging.
In attempting to make demonstrations, source owners or operators
should present as much evidence as can be located, with the understanding
that demonstrations based on any single category of evidence (such as
affidavits) presented 1n Isolation are less likely to constitute acceptable
showings than demonstrations based on cumulative bodies of evidence.
discussed below, affirmative showings will be required of sources
whose merged stacks were associated with an Increase 1n allowable emissions
as well as some sources whose mergers were not associated with such
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Increases. However, EPA expects sources whose emission limits Increased
subsequent to the merging to present stronger showings than those with no
Increase, since the regulatory definition of "dispersion technique" views
such increases as an explicit Indication that the merged stacks were
significantly motivated by an Intent to gain credit for Increased disper-
sion. Sources who do not Increase their emissions, but who have difficulty
making other demonstrations, such as the Installation of pollution controls,
or merging for sound economic or engineering reasons convey a more Implicit
Indication of dispersion Intent that must be rebutted; for such sources,
however, the presumption of Intent 1s not as compelling.
Increases 1n Allowable Emissions
As stated above, 1n cases where the allowable emissions of any
pollutant Increased 1n conjunction with the merging of gas streams, such
an Increase provides even stronger circumstantial evidence that merging
was not carried out for sound economic or engineering reasons, but was
"significantly motivated by an Intent to gain emissions credit for greater
dispersion." This presumption may be rebutted by making one of the
following demonstrations.
1- by showing that the cost savings associated with reduced compliance
costs for merged stacks are less than 50 percent of the total savings due to
merged stacks (I.e., annual compliance savings plus annual 1 zed capital
and maintenance savings), and by making an affirmative showing, as described
above, that there was no significant motivation to gain credit for the
Increased dispersion provided by merged stacks; or
2- by showing that alternatives to stack merging were reasonably
precluded strictly for engineering reasons, and by affirmatively demon-
strating the absence of significant dispersion Intent, as noted above.
In the absence of such a showing, 1t should be presumed that avoidance
of emissions control was a significant factor 1n the decision to merge gas
streams, and credit should be denied.
If you or your staff have any questions regarding the application of
this guidance 1n specific Instances, please contact Eric Glnsburg at
(FTS) 629-5540 or Sharon Relnders at (FTS) 629-5526.
Attachments
-------
FIGURE 1
GUI
Credit
Granted
fTeTl
Credit
Grantad
Pre- 7/8/85
Retrofit Merged Stacks
Record of Intent
for Dispersion
Pur oses
l"TeT
No
Credit
El
Installed
Pollution Controls
Increased
Emissions
Qes
Affirmative
Showlng
No
Reason to
Replace Stacks
run
Credit
E
R
nrn
Cng^
Rea«
No 1 Merg-
neerlng
sons make
Ing Clearly
Credit I No I Superior
ngl neerlng
easons for
Mergl ng
Increased
Emissions
rr<
t^^V
I
Economic
Reasons for
Merglng
See
Figure 2
No
Credit
Engineering Reasons
to Preclude Alternatives
Credit
Granted
Granted
Yes
LNOJ
ftffirmative
Showlng
No
Credit
No
No
Credit
-------
Figure 2
Economic Justification
for Merged Stacks
Savings due to Avoidance
of More Stringent
Emission Limit
Less than 50* of Total
Savings due to Merged
Stack Construction
Exceed 50% of Total
Savings due to Merged
Stack Construction
No Increase
In Emissions
Credit
Granted
Affirmative
Showing
Increase
In Emissions
Affirmative
Showing
No
Credit
-------
4* CM Ck. I (7-l-M MM**)
rAII SI—UQMUMINfS KM Plir-
AiAnoM, AoornoM, AND tuft-
MOTAl O» IMftlMfNTAflON
MANS
A-C-|*Uaer»*|-
II.M
AQUA Aauu.f si*
1141 AQUA analyala: Submit Ul dale.
11.41 AQHA analysis: Analysis period.
•I 41 AQMA analysis: Ouldallnas.
II 44 AQUA analysts: Projection at
II 4* AQMA analysis. Allocation of
IIM AQItA analysis: Projection a( ato-
ll 41 AQUA analysis: Description of data
II U AQItA analysis: Data bases.
II 4* AQMA analysts: Technique* •aterlp-
II H AQMA analysts: Accuracy factors.
Mil AQMA snsljraVj: Bubmtllslolcatoila-
AQMA FLU
III! AQMA plan: General.
•141 AQMA nkMt: Demrmetnllnn ol ads-
II M AQMA plan: MratesM*.
II M AQMA plan: UcaJ authority.
II M AQMA plan: PuUirsstreUde*.
II n AQMA paw Putun M«al sutborHy
IIM AQMA plan: UI*r«o**m*MaUI ca-
ll
II M AQMA plan: Resources
III! AQMA plan: aubasUlal formal.
IIII AQMA snslrsi* and «>*•«; OMa •*•!!-
•UIMy.
II •* AQMA UMly^i tod pteit AlUnuUi*
I *»!!»• U«I»>V«4I
II ion Ocllnltlom.
II 101 8tl|iuUUecUoni
•l.ll* DataavallabUlty
•1111 AddlUonal provWon* for toad.
II III Mtaek helcbt provUlon*.
•1.11* laiaraUtUot control ty.l IBM.
i«IAh
•I.IM
on of ractom for ipamd«
•1.111 •kmlitcant harm !•«•»*
•I IM CttnUrxenry plan*.
•I.IM lUnaluaUon of epUod* plan
HIM Admkttetr
HIM
•I. IN Puramli raqulrcmenta.
•I.IM PnvmUon of
niton of air ««iaUty.
proeeduna.
II 111 Transportation control i
•l.lll OnrtHnuTHSi emission ato
HIM RcqulremenU (or
II Ul UatilUkaUoa of le«*J *uUu>rlty.
•I HI ••ljTi»«Hi-ii HccuuTiOHa roa
PIKVKIITIUH or Aia PULLUTIUH Enaaoan
cv Cri«M»*
ArrcNBin M IKi&»viul
ArriHBix N KHIUIUM* RnoctioiM
AcHiivxif TMIUUBH ln»rumoii. M*m
TBH4MCC «HD RCTBOriT or UOHT DVT*
VKMICLU
ArruiMi O IHuu»u>l
ArravDii P MINIMUM CatiMioM Momroe
lav RK4uiau»nr*
ArwmicuQ- R-IRuBavavl
ArrsMii 8 EMIKIOM Omn Itrraran*-
TIV« RULIHO
ArrauMi T IRuuvavl
Armmi U -CLUH Aia ACT Bmmom 114
OUIMXIHU
AvnK»iTV Thl» rulemaklnc la promul
gated Hmier authority ol aecttona KKbKU.
III. IM-IM. Ill 111. and JOKal of Ihe
Clean Air Act 41 U8C. 14«libNl). 1411.
14W-141*. 1MI 1MM. and IMIlal.
SouacK M PH HIM. Nov. U. 1*11. unleai
other* Ue noted.
EaiToaiu. Nora: Nomenclature chance*
affectlni Part II appear at 44 PR IU1. Pck.
«. in* and H PR 4OMI. Nov. 1. IM«.
A C— (•
II 340 Rel fur 1 year edeiulon.
Booarc 41 PR HIM. May 1. ini. unleaa
oUterwUe noted.
• II.M Scope.
<•> Applicability The requlremenU
of Ihla lubpart apply to air quality
maintenance area* (AQUAa) Mentl-
lled under | M.IIMIl and to any areM
IdcnllCled under I ft 1.110(11.
-
Utlnc aource* and emlaalona aooclated
wllh protected irowlh and develop-
ment In area* Identified under para
•rapru and «l) of I SI 110 ThU
analysis U referred to In this subpart
as an AQMA analysis.
(c) AQHA Han Under this subpart.
the Administrator will require a rev!
slon to the State Implementation plan
for areas Identified under I M IKXDor
I SI 110(1) when ntrceBsary to prevent a
national ambient air quality ttanclard