### ( UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION IX 75 Hawthorne Street San Francisco, CA 94105-3901

Randy Cleaveland U.S. Production Manager ExxonMobil Production Company P.O. Box 4697 ' ' Houston, TX 77210-4697 ' May 22, 2006



### Re: Application for a Prevention ofSignificantDeterioration Permitfor ExxonMobil Corporation McElmo CreekUnit Oil Production FacilityMain Flare, Gas Compression Facility
DearMr. Cleaveland: This letter is in response to the submittal ofan application for a Prevention of Significant Deterioration (PSD) permit for the Main Flare at ExxonMobil's McElmo Creek gas compression facility. This application was received byEPA, Region 9 on November 13,2005. Upon review ofthe application in accordance with 40 CFR 

### § 124.3, EPA has determined that the application is administratively incomplete for PSD purposes with respect to emissions data, the BACT analysis, the Class I analysis, and the additional impact analysis. EPA is also unable to process the application without additional analysis ofpotential impacts to endangered species. Below please find a discussion ofeach of these areas, with EPA's expectations regarding what additional information is needed. You may find EPA's October 1990 Draft New Source Review Workshop Manual useful. See http://www.epa.gov/region7 /programs/artd/air/nsr/nsrmemos/1990wman.pdf You may also search for the document onEPA's NSRPolicy and Guidance Database, available at: http://www.epa.gov/Region7/programslartd/air/nsrl. In addition to the items requested below, we would also like to request that ExxonMobil provide us with the model name ofthe Zeeco flare, ifapplicable.
Emissions Data On page 3-1 ofthe application, ExxonMobillists the emission limits from the Consent Decree for Civil**A~tion** Case United States v. Mobil Exploration and Production U.S. Inc., for four criteria pollutants: sulfur dioxide (S02), carbon monoxide (CO), nitrogen oxides (NOx), and volatile organic compounds (VOC). However, for the application to be considered complete, ExxonMobil must provide information on actual and potential emissions. Pleaseprovide pre- and post-project actual emissions, as well as pre-project estimates ofthe potential to emit for all criteria pollutants, including particulate matter (PM10 and PM2.5) and lead. Please also include pre- and post-project

Printed on Recycled Papergas flow rates to the flare. Forpurposes ofthis application, pre-project means before the gas plant was dismantled in 1997, and post-project means after the gas plant was dismantled. Please include all calculations and the basis for all assumptions used in the emission estimates.
BACT Analysis Best available control technology (BACT) is defined in 40 CFR §52.21 as: An emissions limitation

...based onthe maximum degree ofreduction for each pollutant subject to regulation under [the Clean Air] Act which would be emitted from anyproposed major stationary source ormajor modification which the Administrator, 6n a case-by-case basis, taking into account energy, environmental,,and economic impacts and other costs, determines is achievable for such source ormodification through application ofproduction processes or available methods, systems, and techniques

...for control ofsuch pollutant..

..lfthe Administrator determines that technological or economic limitations on the application ofmeasurement methodology to a particular emissions unit would make the imposition ofan emissions standard infeasible, a design, equipment, work practice, operational standard, or combination thereof, may be prescribed

.... As noted in ExxonMobil's application, EPA specifies the use ofa "top-down" approach for determining BACT. This approach requires that all available control technologies be ranked in descending order ofcontrol effectiveness. Once that has been done, the most stringent alternative should be chosen as BACT unless the applicant demonstrates to the satisfaction ofthe permitting authority that technical considerations, or energy, environmental, or economic impactsjustifya conclusion that the most stringent option is not achievable. Ifthe most stringent technology is eliminated, then the next most stringent alternative is considered, and so on. ExxonMobil's application follows this approach, however the application fails to consider technologies, work practices, or operational standards that would limit the flow ofgases to the flare. To be considered complete, the application must address means to reduce the occurrence offlaring, notjustmeans to reduce emissions when flaring occurs. Please consider, among otherthings, methods to improve the efficiency, reliability, and/or capacity ofthe gas compressors (including replacing the compressors), and any other methods that mayreduce the frequency offlaring and the quantity ofgas flared. The application may incorporate byreference the operation and maintenance (O&M) plan from the afore-mentioned Consent Decree, butthe application must specifically analyze the O&Mplan according to the top-down BACTprinciples. For any options that are ruled out on the basis ofeconomic infeasibility, pleaseprovide a detailed costeffectiveness analysis.
Class I Analysis
Class I areas are areas ofspecial national orregional natural, scenic, recreational, orhistoric value for which the PSD regulations provide special protection. Forprojects 

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( that may affect a Class I area (most typically those sources located within 100 kilometers ofa Class I area), additional impact analyses mayberequired to ensure that air quality degradation is limited in these areas. One wayin which air quality degradation is limited in all Class I areas is by stringent limits defined bythe Class I increments for sulfur dioxide, particulate matter, and nitrogen dioxide, as well as visibilityprotection. In addition, the Federal Land Manager (FLM) ofeach Class I area- inthis case, the National Park Service- is charged with the affirmative responsibilityto protect that area's unique attributes, expressed generically as air qualityrelated values. According to ExxonMobil's application, the McElmo Creek Oil Production Facilityis located within 100 km ofthe following Class I areas: Canyonlands National Park and Mesa Verde**~ational** Park. However, the application is lacking any discussion or analysis ofClass I impacts. The applicant must contact the FLM, listed below, for guidance. After discussing the project with the FLM, the application must berevised to either include the appropriate air quality analyses, or, ifthe FLM determines that no impact is anticipated, to include a qualitative analysis designed to inform the general public oftherelative impact ofthe operations onthe Class I areas.
JohnBunyak Policy, Planning & Permit Review NPS-Air POBox 25287 Denver, CO 80225-0287 John_ Bunyak@nps.gov (303) 969-2818
Additional Impact Analysis John Notar Research and Monitoring NPS-Air POBox 25287 Denver, CO 80225-0287 John_ Notar@nps.gov (303) 969-2079

All PSD permit applicants must prepare an additional impacts analysis for each pollutant subject to regulation under the Clean Air Act. This analysis assesses the impacts ofair, ground, and waterpollution on soils, vegetation, and visibility caused by any increase in emissions ofanyregulated pollutant from the source ormodification under review, and from associated growth. The depth ofthe analysis generally will depend on existing air quality, the quantity ofemissions, and the sensitivity oflocal soils, vegetation, and visibility inthe source's impact area. Itis important that the analysis fully document all sources ofinformation, underlying assumptions, and any agreements made as a part ofthe analysis. Generally, small emissions increases in most areas will nothave adverse impacts on soils, vegetation, orvisibility. However, an additional impacts analysis still must be performed. Projected emissions from both the new source ormodification and emissions from associated residential, commercial, orindustrial growth are combined and modeled for the impacts assessment analysis. The additional impacts analysis generallyhas three parts, as follows:(A) growth; (B) soil and vegetation impacts; and (C) visibility impairment.
A. Growth Analysis
The elements ofthe growth analysis include (1) a projection ofthe associated industrial, commercial, and residential source growth that will occurin the area due to the source; and (2) an estimate ofthe air emissions generated bythe above associated industrial, commercial, and residential growth. ExxonMobil mustrevise its applicationto include an assessment :ofthe availability ofresidential, commercial, and industrial services existing inthe area, and a prediction ofhow much new growth is likelyto occur ' to support the source ormodification underreview.
Ifany new growth is expected, ExxonMobil should develop an estimate ofthe secondary air pollutant emissions that would likely result from this permanent residential, commercial, and industrial growth. ExxonMobil should then combine the secondary air pollutant emissions estimates for the associated growth with the estimates ofemissions that are expected to beproduced directlybythe proposed source ormodification. The combined estimate will serve as the input to the air quality modeling analysis, and the result is a prediction ofthe ground-level concentration ofpollutants generated by the source and any associated growth.
B. Soil and Vegetation Impacts Analysis Page 5-4 ofthe application discusses soils and vegetation in the project area in general terms; however the application shouldberevised to explicitly discuss the potential for impacts to soils and vegetation. The analysis ofsoil and vegetation air pollution impacts shouldbebased on an inventory ofthe soil and vegetation types found in the impact area. This inventory should include all vegetation with any commercial or recreational value, and maybe available from conservation groups, State agencies, and universities. Formost types ofsoil and vegetation, ambient concentrations ofcriteria pollutants below the secondary national ambient air quality standards (NAAQS) will not result in harmful effects. However, there are sensitive vegetation species (e

.g., soybeans and alfalfa) that maybe harmed bylong-term exposure to low ambient air concentrations ofregulated pollutants for which there are no NAAQS. Any discussion should reference the source ofinformation so that the conclusions inthe application canbe verified.
C. Visibility Impairment ExxonMobil's permit application contains no discussion ofvisibility impairment. The suggested components ofa good visibility impairment analysis are: · (1) A determination ofthe visual quality ofthe area; 

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( (2) An initial screening ofemission sources to assess the possibility of visibility impairment; and (3) Ifwarranted, a more in-depth analysis involving computer models.
ExxonMobil can start with a level 1 screeningprocedure, whichis a series of conservative calculations designed to identifythose emission sources that have little potential for adversely affecting visibility. The VISCREEN model is recommended for the level 1 screen. Calculated values relating source emissions to visibilityimpacts are compared to a standardized screening value. Ifpotential visibility impairments are indicated, then a level 2 analysis should be conducted. ' To successfullycomplete a visibility impairments analysis, the applicant is referred to an EPA document entitled "Workbook for Estimating Visibility Impairment," orits projectedreplacement, the "Workbook for PlumeVisual Impact Screening and Analysis." In this workbook, EPA outlines a screening procedure designed to expedite the analysis ofemissions impacts onthe visual quality ofan area. The workbook was designed for Class I area impacts, but the outlined procedures are generally applicable to other areas as well. Endangered Species Analysis
Section 7 ofthe Endangered Species Act of1973, as amended (16 U.S.C. 1531 et seq.) ("ESA"), directs all Federal agencies to use their existing authorities to conserve threatened and endangered species and, in consultation with the US Fish and Wildlife Service, to ensure that their actions do notjeopardize listed species ordestroy or adversely modify critical habitat. Section 7 applies to

. Federal actions that may affect listed species, including Federal approval ofprivate activities through the issuance of Federal permits, licenses, or other actions.
In processing ExxonMobil's PSD permit, EPAmust assure that listed species or their critical habitat will not bejeopardizedbythe changes at the McElmo Creek Gas Compression Facility. While the application does address threatened and endangered plant species (see page 5-4 ofthe application), endangered animal species have notbeen discussed in ExxonMobil's PSD permit application. Therefore, EPA is lacking information necessary to determine our obligations, ifany, under Section 7 ofthe ESA.
Pleaseprovide a list ofall endangered orthreatened plant and animal species and their critical habitat in the area ofthe proposed project; such a list maybe obtained from the Fish and Wildlife Service. Please contact: Henry Maddux US FWS

- Utah Field Office 2369 W. Orton Circle, suite 50 West Valley City, Utah 84119· Ifany endangered orthreatened species or critical habitat is in the area ofthe project, please provide a biological assessment ofthe impact construction or operation ofthe source mayhave on such species and their habitat. A biological assessment should discuss the proposed project in sufficient level ofdetail so that EPA can determine whether it is appropriate for the Agencyto initiate a section 7 consultationprocess with the U.S. Fish & Wildlife Service, and so that the biological assessment canbeutilized by EPA and the U.S. Fish & Wildlife Service ifa section 

### 7 consultation is needed. We can provide sample assessments ifneeded.
Should you have any questions concerning the review ofyour application, or if you would like to arrange for a meeting orconference call to discuss your application, please contact**Kathie~** Stewart ofmy staffat ( 415) 94 7-4119.

cc: Patrick Flynn, Resolute John Notar, NPS John Bunyak, NPS BudRolofson, USFS Scott Archer, BLM HenryMaddux, USFWS Sincerely, 

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Gerardo C. Rios Chief, Permits Office



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