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OAR Box 1778 

Prepped by Ollie Stewart 

Document Number: 

83) ll-C-25 

Docket Number: 

A-90-06 

Printed 10/28/2008 9:50:55 AM Sheet 83 of 276 
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II-C-25 

NOTE: Parts of this item are not legible. 

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Mr. Arearjit S. Gill 

Lnvironno^ntel/Rigulatory Plann. r 

Gas Turbine Products Division 

General Electric Con.]: any 

One River Road 

Schenectady, New York 12345 

Dear Mr. Gill: 

Your October 9, 1979 letter to Doug Bell of EPA's Standards 

Development Branch, has been forwarded to our office for 

response. You requested a determination as to whether a 

proposed new maintenance program t'er Rxisting gas turbines would 

cause the turbines to be considered irodified under 560.14. 

The special program would update certain turbines to 

improve reliability, efficiency and output. Under this program, 

you believe there will be an increase in NOx emissions when 

firing distillate fuel, end a greater decrease.' when firing 

natural gas. Although an increased use of natural gas is 

planned distillate fuel would still be fired part of the time. 

You have raised three questions concerning this situation, 

which are included with our accompanying determinations: 

'*" ' i) If, after the update, these gas turbines are flrefl part 

of "the time on natural gaa and the remainder of the time on 

distillate fuel, such that the yearly average VOx end 6O2 

emissions do not increase would this be considered a 

modification under 40 CFR 60.14? 

; Yearthis would be considered a mod if ication under $60.14, 

and the Modified turbines would be required to meet N8PS- • A' 

modification is defined at 560.14(a) as "any physical or 

operational change to an existing facility which results in an 

increase in the emission rate to the atmosphere of any pollutant 

to which a atandard applies". Certain exemptions are provided 

for under 560.14 (e) and (f), but these gas turbines are noteligible for any of these exenptions. 
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Even thouoh, accord ir.'-* to your d?tc, "•.he turbines will emit 

less over the course or. a yoar, vou feel there will be increases 

when distillate fuel is ured. lince r«o.1 if icet ion is based on 

increased emission rate, •->-*.(*. enission r.te under f-fiO.14(h), is 

expressed in terr.s of kq/hr, any increase in emission rate 

during the periods when distillate fuel is burned, will require 

the source be considered r.odified for NSPS purposes. 

This position is supported by a discussion in the preamble 

to the proposed provisions for NSPS modification, notification 

and reconstruction (39 FP 36946, October 15, 1974). The 

preamble states:- -"In the Act the phrase " Increase in emissions" 

ia not defined and therefore can be interpreted to mean any 

incre'a^g in emissions." 

Should there be subsequent disagreement between your 

company and the Ad^lnlstrctor as to whether an Increase in 

emission rate occurs, the procedures outlined under S6C.14(b) 

should be used to determine If a clear increase occurs, 

2) Does EPA consider on either a de minimis or administrative necessity basis that certain snail increases In the level 

of emissions would not require that the chanqes be classified as 

modifications? 

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There ia no specific de sr.lnlmis level or percent whereby 

increases below that level would not be considered modifications. If the Administrator determines that emission levels 

will increase, a modification will be deeded to have occurred. 

Emission rates can be determined, under 560.14(b)(1) and (2), 

from either Compilation of Air Pollutant Emission Pactora (BPA 

No. AP-42) or other emission factors if they demonstrate a clear 

increase or decrease. If these factors cannot so demonstrate, 

then material balance, continuous monitor data, or manual 

emission tests can be used. When the emission rate ia based on 

results from manual emission tests cr continuous monitoring. 

Appendix C (Student*8 t test) shall be used to determine if an 

increase or decrease has occurred. Thus, in this instance, a 

modification occurs only if the emission rate after the change 

Is statistically significantly higher than the rate before the 

change. 

3) Under USPS and PST") (proposed), le It correct that any 

available fuel suitable for use In operation of the equipment 

(aubject to any applicable permit limitation) may be used to 

determine "before" emissions, and any fuel with characteristics 

for which the operator is willing to accept enforceable permit 

conditions mav be used to determine the •after" emissions? 
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chanqe ar e rar.e.! or. -.ct.:... 1 i; 

t h e Droro. Cv' r>rovisic-. " v:. v 

i'. n vn t .£ h-for o ar..'1 a ft--•""- **• 

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or an c..]-***.i: taci l it-. 

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be an increase in 

sidcred d .f in i ;*»•** ' 

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'usoi^r ? . . . 

.t ion •• r-

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::*od if i r •*> t i on ther*-*1 "'.'-. t 

""'he Arlrin ir t r ato r con -

t.hot increase s in precon -

trolle r (notentiiil ) v:" i:;_. iu'.*.--. •. oul' " I'-* considere d rod i «" ic.it ions. 

However, th e pror'npr-' .: v- 0 i n i -_ i •: n of rod i f icst ion in lir.ito d t o 

increase s in actu.i l or irsi on:; in ')*..'. ..p inn wit h th e inten t of ** 311 

of controllin g faci l itio p -.-r.lv vhen the y cor. r-titut' . *_ new sourc e 

of emission" . 

Your interpretatio n of 

wit h roqarr. t o deterr.i n i:v* -r.-*-'/ 

potentia l eninsionr. CL the- -.cm 

*"•' >.-... • 7L1 (propose (proposedd f" ••-*•*• tenne r •*••, 1P79), 

ro d if ica t ii~riR , is correct . The 

e wo for e th e nod ificatio n should 

be based on any tvoe of fuel that 

firina. 

'e source v,"* ca.Pfthlo ot" 

he rem tv'.'.-e o: <',r 1" refers not to ?ulfur content 

but to e.c , gas, oil, coal. f'r.c^rceable porr.it conditions on 

the "type of fuel" conbnctcd will lirr.it the r-otent ..al emissions 

level. These conditions r-vst i*e enforcea'.:>le under th.e Clean Air 

Act. 

The nntontial enis_i.cn_ --fter tho r.odif ication should be 

deternined on tho ..arc t _•.•*. is: the dirtiest tvpe of fuel the 

source is capable of burn inn. ?«oain, enforceable rx.rr.it. 

conditions on the type or fool cor busted nay limit potential 

eniss icnj. 

T'he sulfur content o'*' tho fuel used in the calculation of 

pre-r-od If icstlon potential erir*sions should be tho aversie 

sulfur content used over tKe preceo inn one-to-two vear period if 

the source w<_!r. hern inc the sar.e typo of fuel to he used in the 

calculation. If the recc e had been burning a different type of 

fuel, the sulfur content to be used in the calculation shall be 

based on the most strinoent of the applicable PIP, any 

applicable NSPS, any Fir perrit, or any other enforceable 

requirement. 

Tor instance, er.suo.e that a source is capable of burnlna 

either oil or coal. For the past two years It has b<?en burning 

oil with c sulfur content of ?%, The applicable SIT specifies a 

2% sulfur Uni t for both oil and coal. The source now wants to 

adopt enforceable perrit conditions which would llrit It to 

burning oil. 

The source's pre-modification potential emissions may be 

based on the dirtiest fuel that could be acconnodated: coal. 

Pecacse the source has not burned coal over the n?-*t two years, 

the sulfur content user" in the calculation Fhall bo the 

applicable SIP limitation: 2» . 
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The source's post-modification en issions "ay be based on 

oil burninq, assunino thet the source has agreed to pern.it 

conditions enforceable unc or tho ("lean Air Act. "he sulfur 

content ui>ed to calculate potential omissions is the nominal 

sulfur content the source actoallv plans to use. 

If you have any questions concernino the MSPS aspects of 

this nod ification issue, please contact Pobert Myers of nv staff 

at (202) 75T-.-2564. Should you have any questions relating to 

the PSD aspect, please contact Libby Sconino at the sane number. 

,C 

^dward ?.. ^oich 

cc: Doug Bell, SDB 

Regional HSPS Contacts 

Regional PSC Contacts 

FN:BMyers:ncb:3202:l2/6/79