Ref: 8AT-AP 

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### UNITEDSTATESENVIRONMENTALPROTECTIONAGENCY REGIONVm 99918thSTREET-SUITE500 DENVER,COLORADO 80202-2405



### .APR19

### 1891

Ms. Diane P. Klancher Environmental 

### &Regulatory/ Loss Prevention Supervisor Mobil**Explorat~on** &Producing U.S. Inc. P.O. Box 633**~idland,** TX 79702-0633 Dear Ms. Klanchet: This letter is in response to your February 21, 1991 and February 22, 1991 letters to EPA, requesting changes to the Prevention of Significant Deterioration (PSD) permit that EPA .issued on October 22, 1987 for the McElmo Creek Unit Gas Plant. We have reviewed your requests to: (1) replace existing heating equipment with a waste heat:recovery unit, and (2) temporarily replace the existing gas turbine with an identical unit during**maintena~ce** overhaul of the turbine. Since these changes will not result in any emission increases, they can be approved as administrative changes to the EPApermit. OnMarch 14, 1991, we were informed by Mr. Worontsoff of your office that the second gas turbine approved for construction under the**October~2,** 1987 permit waS never installed. Please be aware that under federal regulation 40 CFR52.21(r)(2), approval to construct becomes invalidif construction is not commenced within 18 months after issuance of the PSDpermit, or if construction is discontinued for a period of 18 months or more, or if construction is not completed within a reasonable time. While construction deadlines may be extended by EPAupon a satisfactory showing by the permit applicant that an extension is justified, Mr. Worontsoff has informed us that Mobil currently has no plans to install the second turbine and is not requesting an extension. Therefore, we are rescinding approval ofthe second turbine at this time. ' In the event that Mobil wishes to install additional turbines or other equipment at some future date, and if facilitywide emissions resulting from those additions wili exceed the emission rates'used in dispersion**model~ng** for the October 22, 1987'permit, it will be necessary for Mobil to conduct new dispersion modeling to show that the PSD increments and the National Ambient Air Quality Standards will be protected. Mobil would also have to show that emission controls for the'additional eqUipment constitute Best Available Control Techtiology.We have also been informedbyMr. Worontsoff that the manufacturer's design capacity of the one**g~s** turbine installed thus .far under.the.-EPA.permit is4,390 horsepower at sea'level.--- The turbine is,therefore sUbject to the provisions of Subpart GG of the federal NewSource Performance Standards (40 CFR 60.330 through 60.335). NSPS Subpart GG applies to any stationary gas turbine larger than approximately 3985 horsepower (equal to 10.7 gigajoules perhour), constructed after October 3, 1977. A

.condition has therefore been added to the EPApermitto specify

that the turbine must comply with all relevant provisions of Subpart GG.

. The enclosed conditional permit replaces the October 22, 1987 permit. This permit shall become effective immediately unless you notify us, by the procedure described in Section IV of the permit, that you object to one or more of the permit conditions. In such event, construction and operation.ofthe modification would not be allowed until a revised permit acceptable to both EPAand Mobil is issued. Ifyou have any questions, please contact Mr. Michael Owens of my staff at (303) 293-1756. Sincerely,

# ~.~lR:~~;;;r Air &Toxics Division Enclosure
cc: Burnell Cordner, Director Utah Bureau ofAir Quality 1950 West North Temple Salt Lake City, UT 84116-069rr Louise Linkin, Environmental Coordinator ·Navajo Nation P.O. Box 308 Window Rock, AZ 86515

2CONDITIONAL PERMIT TO COMMENCE CONSTRUCTIONAND OPERATE 40 CFR52.21 Preventionof Significant Deterioration ofAir Quality

Mobil Exploration &Producing U.S. Inc. P.O. Box 633

. Midland, TX 79702-0633
I. INTRODUCTION Mobil Exploration 

### &Producing U.S. Inc. (hereinafter "the Applicant") proposes to construct and operate a modification to Mobil's McElmo Creek Unit on the Navajo Indian Reservation in San Juan County, Utah. On May 13, 1986, the Applicant submitted to the U.S. Environmental Protection Agency, Region VIII (hereinafter "EPA") a Prevention of Significant Deterioration (PSD) applicationto construct and operate three gas-fired reciprocating internal combustion (I.C.) engines, pursuant to 4DCFR52.21. The EPA issued a public notice on December 17, 1986, in the San Juan Record and the Salt Lake Tribune, newspapers of general circulation in the area. The notice proposed to approve the application and issue a conditional air quality permit for the source and provided opportunity for public comments during the ensuing 30 calendardays. The permit application, the proposed permit, and its supporting**~nalysis** were available for public inspection at the office of the San Juan County Clerk in Monticello, at the Utah Bureau ofAir Quality in Salt Lake City, and at the EPA office in Denver. The only comments concerning the permit were received fromthe Applicant and contained only minor clarifications. The conditional permit was issued on Februar¥ 2, 1987. On September 1, 1987, the·Applicant submitted a letter to EPA requesting that two gas turbines be approved, rather than**~he** three I.C. engines. Since this change did not represent an emission increase, and since the turbines were to utilize Best Available Control Technology, the EPAapprovedthe request as an administrative change to the PSDpermit. Arevised conditional permit was issued on October 22, 1987.OnFebruary 21 and 22, 1991, the Applicant submitted letters to EPArequesting approval to: (1) replace**eXist~n9** heating equipment

..w.itha..waste heat recoveryunit, and-(2)---temporarily-- replace the existing gas turbine with ari identical unit1during maintenance overhaul of the turbine. These changes do not represent an emission increase.

. . OnMarch 14, 1991, the Applicant informed EPAthat the second gas turbine was never installed and thatthe Applicant currently has no plans to install it. The Applicant also informed EPAthat the one gas turbine which was installed is rated at 4390 horsepower at sea level, rather than the 3216 horsepower listed in the October 22, 1987 permit. This exceeds the applicability cutoff size of 3985 horsepower (equivalent to 10.7 gigajoules per hour) for Subpart GG of the federal New Source Performance Standards.
II. FINDINGS Onthe basis of information in the administrative record, EPA has determined that: 1. The McElmo Creek Unit is a major stationary source and the modificationwhich has already been permitted by EPA (installation of two turbines) represents a significant net emission increase of oxides of nitrogen (NO x). The facility is therefore subject to PSD regulation. 2. The Applicant will meet all ofthe applicable requirements of the PSD regulations at 40 CFR 52.21. 3. Based on dispersion modeling, EPAhas good reason to believe that no ambient air quality standards or PSD increments will be violated asa result of the proposed facility modification. 4. EPAhas good reason to believe that the Applicant can comply with the conditions of this**permit~** If any of the conditions are not met bythe Applicant, EPAdoes not assume any risk or loss which maYoccur'as a result of the commencement of construction and operation by the Applicant.

2III. CONDITIONAL PERMIT TOCONSTRUCT AND OPERATE
On the basis of the findings set forth in II above, and

. pursuant to the authority of 40 CFR 52.21(i)(1), as delegated by the Administrator, EPAhereby conditionally authorizes the Applicant to construct and operate the modification described in the Applicant's permit application dated May 13, 1986, as amended by later communications on September 1,· 1987, February 21, 1991, February 22, 1991, SndMarch 14, 1991. ' This approval**~s** expressly conditioned as follows: 1. The Applicant shall abide by all representation, statements of intent, and agreements**conta~ned** in the permit**applic~tion** and in all additions**~nd** amendments thereto, as follows:

.. ,
a. May 13, 1986

--,PSDpermit application for the McElmo Creek Unit C02 Project, stage 2, to include installation of three·reciprocating internal combustion engines. b. September 2, 1986

-- Supplementary information related to NOx emission rates.
c. November 4, 1986

-- Supplementary information c:orrecting VOC emission rates. d. September 1,**1~B7** -- Letter requesting approval for two natural gas**fue~ed** turbines, rather than three reciprocating internal combustion engines.
e. February 21, 1991

-- Letter requesting approval for installation of waste heat recovery unit, to replace existing heating equipment. f. February 22, 1991**-~** Letter requesting approval to temporarily replace the existing gas turbine with an identical unit.during maintenance overhaul of the turbine. ' g. March 14, 1991

-- Information submitted verbally to EPA to correct the horsepower rating for the one gas turbine thus far installed, and to inf6rmEPAthat Mobil has no plans to install a secondgas turbine. 2.**Thi~** permit shall be considered invalid if the Applicant does not commence and complete construction of the permitted modification within the deadlines specified in 40 CFR 52.21(r)(2).
33. The Applicant shall operate no pollutant-emitting equipment at the McElmo Creek Unit other than that listed in Tables 1 --and-2 of-this-permit.---The-Applicant shall permanently--shut---

down the equipment listed in Table 2 prior to startup ofthe waste heat recovery unit. 4. The Applicant shall limit facilitywide emissions to those shown in Table 1, on a rolling 12-month basis. For demonstrating compliance with annual facilitywide emission limits, the Applicant shall, if requested by EPA, maintain a written record of rolling 12-month emission totals. 5. The Applicant shall comply with all applicable provisions of 40 CFR 60.7 for notification and recordkeeping relating to startup, shutdown and malfUnctions of the gas turbine. 6. The Applicant shall operate the gas turbine in accordance with th. operation and**mai~tenance** provisions of 40 CFR 60.11(d). Temporary installation of an identical gas turbine shall be allowedduring maintenance overhaul of the existing gas turbine, according to the procedure described in.the Applicant's letter to EPAdated February 22, 1991. 7. The Applicant shall comply with all applicable emission limits for thegas turbine which are specified in Subpart GG of federal New Source Performance Standards (NSPS), at 40 CFR 60.332 and 60.333.· In no event shall emissions of oxides of nitrogen (NO x) from the gas turbine exceed 150 parts per million by volume, at 15% oxygen on a dry basis. 8. The gas turbine shall be stacktested**a~cording** to the method(s) specified in NSPS Subpart GG, as amended by the test protocol submittedto EPAon November 5, 1990, and approved by EPAon February 7, 1991. Testing shall be scheduled and conducted.in-accordance with the deadlines and notification procedures**~ontained** in 40 CFR 60.8. Performance test results shall be submittedto EPAnot more than 45 days after the test. 9. At all times, including periods of startup, shutdown and equipment malfunction, the Applicant shall maLnt.afn and operate the overall McElmo Creek Unit in a manner consistent with good air pollution control practices for minimizing excess emissions. Determination of whether·acceptable operation and maintenance procedures are being used will be based on information available to the Administrator, which

.may include, but not be limited to, monitoring results,

review of operation and maintenance procedures, and EPA inspectionof the facility.

4

### 10. The Applicant shall notifyEPA as soon as possible, but in no event·more than 48 hours, afterdiscovery ofexcess

__emissions during periods-ofstartuPJ shutdownr-control equipmentmalfunction, orprocess upset. Nomorethan 10 days after discovery, all ofthe following shall beprovided to EPAin writing:
a. The identity ofthe stack or other emissionpointwhere excess emissions occurred. b. The identity ofthe equipment orprocess causingthe excess emissions andthe suspectedreason(s) for.the excess emissions.
c. The time, duration andmagnitude ofexcess emissions, expressed in terms ofpermit conditions. d. Corrective action taken during the excess emission incidentto minimize excess emissions, as 

### well as corrective action taken, or anticipatedtobetaken, to preventrecurrence of excess emissions. If EPAfinds thatthe information submittedunder Condition #10 ofthis permitdoes notprovide evidencethatthe excess .emissions wereunavoidable, orthe informationgives EPA reason to believe thatthe excess emissions 

### were the result of negligence, then the excess emissions shall be considered a violation ofthis permit. 11.

12. 

### EPAand its authorizedrepresentatives may inspectthe permitted facility during normalbusiness hours for purposes of ascertaining compliance with all conditions ofthis permit. Nothing in this approval shall relieve the Applicant from complyingwith all other applicable federal, state or local regulations.

(



### 5IV. GENERAL
This permit is issued in reliance upon the completeness and accuracy of the information set forth in the Applicant's application and subsequent correspondence to EPA for permission to modify the McElmo Creek Unit. Each and every condition of this permit is a material part hereof and is not severable. This permit is immediately effective and all conditions herein enforceable by EPA, unless the Applicant notifies EPAin

. writingthat any term or condition ofthis permit is rejected. Such notification must be postmarked not more than ten (10) days afterApplicant's receipt of this permit, must include the reason(s) for rejection, and must be addressed to: Mr. Michael Owens, Air Programs Branch (8AT-AP), U.S. EPA, 999 18th St., Suite 500, Denver, CO B0202-2405. Construction of the facility modification may not commence until the reasons for rejection are reviewed by EPA and a revised permit acceptable to EPAand the Applicant is issued.
UNITED STATES ENVIRONMENTAL PROTECTIONAGENCY, REGIONVIII

By: Irwin L. Dickstein, Director Air &Toxics Division



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# 1-/f-Zl Effective Date:

6

### 'l'able 1**-~-~---Pollutant-Emi** t.t.Lnq..

### Equipment Authorized under April 1991 EPAPermit for**Mob~l** 

### McElmo CreekUnit

Emission Point Size Emissions (tons per year) S02 NOx CO VOC T4500 Gas Turbine 4390 HP* 0.05 74.60 17.00 4.00 Ingersoll Rand Engine 491 HP 0.10 52.00 7.00 2.00
Fairbanks Morse Engine 1712 HP 0.10 72.00 35.00 7.00
Fairbanks Morse Engine 1712 HP 0.10 72.00 35.00 7

..00
Fairbanks MorseEngine 1848 HP 0.10 91.00 5.00 8.00
Fairbanks Morse Engine 1848 HP 0.10 91.00 5.00 8.00
DPC-540 Waste Heat Recovery Unit** 470 HP 0.10**11~0** 

### MMBTU/hr 0.10 18.20 4.10 3.88 0.77 1

### .40 O.

### 10

0.14 0.10 1.75 0.40 0.44 0.10**I"·------~'"** i O.

### 14) O. 10

.. -....._---------/ O.

### 10 O.

### 10· 0.10

0.10 0.10 0.10 0.14 1.0 MMBTU/hr 0.10 4.0 MMBTU/hr 0.10

-**0~33** 

### MMBTU/hrO.l0

0.33 MMBTU/hr '0.10 0.33 MMBTU/hr 0.10 HC Liquid Reboiler Heat Medium Heater

TEGReboiler TEGReboiler

TEG Reboiler Total facilitywide authorized emissions 1.25 477.29 109.67 38.00
FOOTNOTES:
* Sea-level ratingj at manufacturer's design capacity (used for NSPS Subpart GG applicability determination). Site rating is 3525 HP. ** - To replace**eq~ipment** 

### listed in Table 2 below.'Table'2 -Pollutant-EmittingEquipment:,

_ to be Shut Down Under April 1991 EPAPermit
Emissions (tons per year) Emission Point Size S02 

### NOx 

## eo voe Heat'Medium Heater 12.2 MMBTU/hr 0.10 7.40 1.90 0.15 TEGReboiler O."MMBTU/hr 0.10 0.10 0.10 0.10

Total emissions for equipment to be shut down 0.20 7.50 2.00 0.25

The above equipment will be replaced with the waste heat recovery unit listed in Table 1. Emissions of all pollutants are expected,to decrease as a reault.