UNITED STATES ENVIRONMENTAL PROTECTION AGENCY REGION IX 75 Hawthorne Street San Francisco, CA 94105·3901 January 10, 2008
Terrence O'Brien DeputyDirectorfor Energy Facility Siting CaliforniaEnergy Commission 1516 Ninth Street Sacramento, CA 95814-5512

Re: Request for U.S. EPA Concurrence Regarding Two Air Quality Amendment RequestsHigh DesertPowerProject (97-AFC-O 1)

DearMr. O'Brien:
This letteris in response to your recent letter, dated October 26,2007, regarding a request for revision of the High Desert PowerProject ("HDPP")permit, approved by the California Energy Commission ("CEC") on October 20, 2004, and a secondrevision request submitted by HDPP dated September 20, 2006.

EPA issued the initial Prevention ofSignificant Deterioration 

### CPSD") permit to HDPP
on February 15,2001. On July 30,2001, in response to a letter from HDPP, EPA issued a determination that reconfigurations and other specified changes to the powerplant design did not affect the terms and conditions of the initial EPA-issuedPSD permit. We acknowledge the time period for ourreview ofthe 2004 and 2006 permit modification requests has been extensive. At this time, we have reviewed the requested modifications and will propose the minorPSD permit modification for public review within the next several months. This letter addresses the two modifications described in your October 26, 2007 letter. Discussions regarding additional modifications requested by HDPP, but not addressed in your letter, will not be included here and will be discussed in the technical support document for the PSD permit modification.



### Startup and Shutdown Duration and Emission Limits

The CEC has approved the elimination of durational limits on startups and shutdowns 

### CS/S") while leaving all emission limits unchanged. Although not explicitly statedin your letter, the CEC approval, dated October 20, 2004, also allows the "perturbine" 

### SIS emission limits to be combinedfor all three turbines by multiplying the perturbine limit by three. TheEPA-issued PSD permit includes the durational limits for 

### SIS on a per turbine basis. These limits constitute the 

### SIS portion ofthe BestAvailable Control Technology 

### CBACT") determination for the HDPP PSD permit. As such, a requestedrelaxation of BACT must bejustifiedby HDPP. Although HDPP contends that this modification would provide flexibility during startup and would not change the air quality impact analyses from the initial PSD permit, HDPP has not provided adequatejustification to relax this BACTdetermination. Your letter states that CEC staffand staffat the Mojave Desert Air Quality Management District CDistrict") have

Printed on Recycled Paperdetermined that this modification would allow HDPP to start their turbines sequentially in order to minimize thermal stress on the combustion turbines and steam turbine.

HDPP is configured with three combustion turbines ("CT"), each with a dedicated heat recovery steam generator ("HRSG"). Each CT+HRSG unit feeds into one steam turbine generator ("STG"). Each unit has an individual 

### SIS limit based on pounds ("Ib") ofpollutant emitted per event, and an individual allowable startup duration depending on the condition of startup (i.e., cold, warm, hot start). Emission limits and durationallimits apply to each CT+HRSG unit individually; therefore, each unit is already permitted to startup sequentially. Becausethe requested modification relaxes an existing BACTdetermination, and the applicant has not supplied adequatejustification for removing the 

### SIS duration limits, we do not plan to act on this specific request.
On November 8, 2007, AnitaLee, ofmy staff, discussed the requested modifications with Jon Boyer, ofHDPP. Mr. Boyerraised an additional concern regarding the 

### SIS duration limits when the turbine "trips" during startup. This issue was not discussed in the 2004 or2006 PSD permit modification requests, however we will continue working with HDPP to address this
concern before proposing the PSD permit modification.



### NO! and CO Performance Test Frequency

Your letter additionally discusses a request from HDPP to extendthe frequency for oxides ofnitrogen ("NOx" ) and carbon monoxide ("CO") source testing from every yearto every five years. HDPPbelieves that the existing Continuous Emissions Monitoring Systems ("CEMs") for NOx and CO, andthe required annual Relative Accuracy Test Audits (RATA), wouldensure adequate determinations ofcompliance with the NOx and CO emission limits. EPA plans to act on this requested modification, and will include a condition that requires the source testing frequency for CO and/or NOxto return to every yearin the event ofa fai led RATA for the CO or NOx CEMS.

Ifyou have any questions or need additional information, please contact AnitaLee at (415) 972-3958, or at lee.anita@epa.gov. EPA will notify CEC, the District, and HDPP when the PSD permit modification for HDPP is proposed for public review.

Sincerely,



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Gerardo C. Rios Chief, Air Permits Office

Cc:	 Jon Boyer, High Desert PowerProject, LLC Alan De Salvio, Mojave Desert Air Quality Management District