AECOM 978.589.3000 tel 2 Technology Park Drive 978.589.3100 fax Westford, MA 01886-3140



## Memorandum

To enhance and sustain the world’s built, natural and social environments To: Scott Bohning Page 1

cc: Shirley Rivera
Subject: Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis
for PHPP

From: Richard Hamel

Date: October 7, 2010

On August 26, 2010, Mr. Scott Bohning of EPA Region 9 provided comments on the supplemental information provided in "Pal mdale Hybrid Power Project (PHPP) - Supplemental Information for the Application for PSD Permit", AECOM, July 21, 2010. The following information is provided in response to those comments. The comment is reproduced herein with the response following. Figures are provided at the end of this memo, and a modeling archive is attached.

1. There should be documentation on the representativeness of surface meteorological data for purposes of analyzing the 1-hr NO 2 impacts, including e.g. comparison of surface characteristics of the meteorological data station and facility site, with some reasoning about how they are sufficiently similar for the data to be representative, or about how modeling results using the data would expected to be
conservative.

The following information was included in the Class II Area Dispersion Modeling Protocol for the Proposed Palmdale Hybrid Power Project, Document 10855-002-040C2MP ( ENSR Corporation July, 2008), Sections 2.1.4 and 2.2.2:

The Palmdale Hybrid Power Project (PHPP or Project) modeling used a three-year sequential hourly meteorological data set, consistent with general practice for California Energy Commission projects. Three years (2002- 2004) of surface meteorological data from the Automatic Surface Observing System (ASOS) tower at nearby Palmdale Regional Airport were used in the application. Per discussion with Bret Banks of the Antelope Valley Air Quality Management District (AVAQMD), use of this tower was the preferred option if the data were suitable (from a data capture and availability perspective).AECOM 2

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPP Two other sources of meteorological data were considered as alternatives: The meteorological tower at the Division Street Monitoring Station in Lancaster, CA, and the tower at the William J. Fox Field located north of Lancaster. A data completeness study of these locations revealed that the data capture at each of the other towers was lower than the data collected at the Palmdale Regional Airport. Palmdale Regional Airport was therefore the best option for this analysis because of a) superior data capture, b) its close proximity to the Project site (the met tower is 2.5 km [1.5 miles] from the proposed turbine stack locations) c) the similarity in surface characteristi cs between the airport and the Project site, and d) AVAQMD’s recommendation that the Palmdale Regional Airport data are the most representative for this Project.

The location of the Palmdale Regional Airport meteorological tower relative to the proposed Project location is shown in Figure 1. It is clear from the figure that the proposed Project is very close to the meteorological data tower and that the land use at the meteorological tower site is consistent with that at the Project site. The wind rose shown in Figure 2 indicates that the predominant winds are from the sector between southerly and westerly winds, with a peak percentage of southwest winds. The upwind fetch from that direction at the airport meteorological site involves more urbanization than the area to the southwest of the Project site, but that area near the Project will become more consistent with the area near the meteorological tower site after the Project is built, with part of the 1-km circle to the southwest occupied by a solar turbine array.

A copy of the PHPP modeling protocol containing the technical details of the meteorological data processing is included in the electronic modeling archive attached to this memo.

2. There should also be some discussion of the representativeness of the upper air meteorological data used.

Four upper-air data sites were considered for the PHPP PSD application:

• Mercury-Desert Rock Airport in Mercury, NV;

• Edwards AFB near North Edwards, CA;

• Vandenberg AFB in Lompoc, CA; and,

• The Marine Corps Air Station in Miramar, CA, near San Diego.

Of these four sites, Edwards AFB is the closest. However, in reviewing the data from this site, it was discovered that the data capture at Edwards AFB is very limited, because data are only collected during specific United States Air Force activities. Therefore, Edwards AFB
was removed from consideration because it does not provide an adequate capture rate. Of the other three sites, Miramar and Vandenberg were eliminated as the data were not representative of Project site because both monitoring stations are close to the ocean and have upper air profiles representative of a coasta l air mass which is very dissimilar from the high-altitude, desert climate of Palmdale. The remaining site – the Desert Rock airport, offers very representative data because it is located in a desert setting with similarAECOM 3

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPP meteorological characteristics and an expected similar upper air profile to the Palmdale project area. Moreover, Desert Rock is typically the site of choice for air studies performed in the Mojave Desert region because of its similarity to the conditions present in that area. As a result, Mercury-Desert Rock Airport was used in this analysis.

We also note that the dominant emission source in the study was the PHPP’s emergency generator, a low-level source. Hence the upper air profile would have minimal impact on the modeling analysis regardless.

3. There should be additional detail in the assessment of the representativeness or conservatism of the background NO2 monitor with respect to background sources. The NO2 memo at p.6 raises the issue of background being "representative of allowable emission levels under the existing permits" for the background sources. A quantitative comparison of the amount of traffic near the monitor and near the project site should be part of the assessment.

The relative locations of the regionally representative Lancaster Division Street Monitor and the PHPP site are shown in Figure 3. The Division Street Monitor is approximately 4.1 km [2.5 miles] from the PHPP site, located well within the city limits of Lancaster and within 110 meters of the Sierra Highway and within 80 meters of the former Southern Pacific rail lines that are currently used by the Metrolink Commuter Rail. The Sierra Highway and Metrolink rail lines are both almost two kilometers [more than a mile] from the proposed PHPP site. The Antelope Valley Freeway (SR-14) is also only about half as far from the Division Street Monitor location as it is from the PHPP site (over 4 km [2.6 mile] from the site and about 2 km [1.2 mile] from the monitor).

The Antelope Valley Line of the Metrolink Commuter Rail Service, which passes directly by the Division Street Monitor and terminates at Lancaster Metrolink Station, runs 24 trains / day during weekdays, 12 trains / day on Saturdays, and 6 trains / day on Sunday 1 . Because of their significantly closer proximity, Metrolink tr ains passing just to the West of the monitor’s location will have a larger impact on the monitor than they would at the PHPP site.

According to the City of Lancaster Traffic Engineering Division, the daily traffic volume on the Sierra Highway is over 20,000 vehicles 2 . On an annual basis, this equates to over 5 million vehicles (counting only weekdays), and significantly exceeds EPA’s threshold of an annual average traffic count of 250,000 vehicles that triggers near-road monitoring 3 . The location of the monitor within about 50 meters of the Sierra Highway ensures that it is monitoring
localized elevated NO 2 concentrations that are higher (by approximately 30-100 percent) 3 than those to be expected near the PHPP site.

1 See http://www.metrolinktrains.com/docu ments/About/Fact_Sheet_2009_10_4Q.pdf

. 2 See http://www.cityoflancasterca.org/Modul es/ShowDocument.aspx?documentid=4370

. 3 See EPA’s NO 2 NAAQS fact sheet at http://www.epa.gov/air/nitr ogenoxides/pdfs/20090722fs.pdf

.AECOM 4

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPP The Division Street Monitor is located on the roof of the Antelope Valley Air Quality Management District (AVAQMD) office. In a telephone conversation with Chris Anderson of AVAQMD, on September 22 nd , 2010, Mr. Anderson stated that NO 2 concentrations recorded by the monitor visibly spike a few moments after a train passes by. Additionally, Mr. Anderson reported that traffic idling at the intersection of Division Street and Avenue K6 East, directly in front of the AVQAMD offices, causes daily spikes in recorded NO 2 levels during the morning and afternoon commutes.

Because of its closer proximity to sources of NO 2, such as the Sierra Highway and the Metrolink tracks, and the more urban setting around the monitor in general, the monitor experiences more local NO 2 impacts than the Project site and thus is a conservative representation of the ambient NO 2 in the area compared with the PHPP site. Furthermore, given the proximity of the monitor to the Project site, more distant sources of NO 2 can be expected to have similar contributions to the ambient NO 2 levels at both the monitor and Project site. Thus, the Division Street monitor provides a conservative background concentration representing both vehicle and train traffic in the local area and the
contributions of distant sources of NO 2 to the ambient concentration of NO 2 at the Project
site.

Although AECOM considers the monitored concentration to be conservative as background for this Project site, additional nearby sources at U.S. Air Force (USAF) Plant 42, as discussed in response to comment #4 below, were also included in the cumulative modeling analysis.

4. There does not appear to be any cumulative NO2 analysis including background sources, even though the project impact (56.8 ppb) is estimated to be well above the draft SIL of 4 ppb. Sources within 50 km beyond the 4 ppb circle around the source that result in a "significant concentration gradient in the vicinity of the source” should be included in the modeling. The emissions rates for those should reflect the recommendations in the Guideline on Air Quality models, section 8.1.2. Note that the NO2 memo states that the number of such sources is generally expected to be small.

To supplement the modeling provided in the Palmdale Hybrid Power Project PSD Application – Supplemental Information submitted in July, 2010, additional sources were included in a
revised cumulative 1-hour NO 2 modeling analysis in response to this comment. In a telephone conversation with Mr. Chris Anderson of AVAQMD, Mr. Anderson confirmed that the two nearby facilities were the only permitted NO 2 sources that should be considered for
cumulative NO 2 modeling: Lockheed Martin Aeronautics, and Northrop Grumman, both of which are located at USAF Plant 42, adjacent to the proposed PHPP site.

As was done with the cumulative PM2.5 modeling for the PHPP PSD application, the sources at these facilities included in the inventory provided by AVAQMD were reviewed and showed that there were a large number of sources, 284 in total, at these facilities. Further review showed that the vast majority had very small emissions. Given the large number of sources,AECOM

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPP 5

to simplify the modeling, the AVAQMD was contacted and the following procedure for representing the sources was agreed upon and implemented in the modeling:

• For each facility, all sources that emitted 5% or more of the total emissions of NO X were included in the model.

• The remaining source emissions were added to the source that emitted the highest percentage of the emissions.

• In the case where two sources had the highest emissions at the facility, the remaining emissions were added to the source closest to the Project site to be conservative.

This procedure produced a representative mix of source parameters and ensured that all NO 2 emissions from the two facilities were included in the modeling. Figure 4 shows the locations of the two facilities, their property boundaries 4 , and the sources that were included in the cumulative modeling. The emissions and source characteristics for each source included in the modeling are shown in Table 1.

The modeling was performed using the same methodology as discussed in section 3.0 of the PHPP Supplemental Information submittal, except that the Lockheed Martin and Northrop Grumman sources were included in addition to ambient background. Because emissions sources cannot contribute to an air quality standard violation on their own property, three runs were performed in order to correctly evaluate the modeled impacts:

1. All sources from PHPP, Lockheed, and Northrop, along with ambient background concentrations, on all receptors not located on either Lockheed or Northrop property.
2. All sources from PHPP and Lockheed, along with ambient background concentrations, on all receptors located on Northrop property.
3. All sources from PHPP and Northrop, along with ambient background concentrations, on all receptors located on Lockheed property.

The model was run for both the startup / shutdown and normal operations scenarios with the following assumptions:

a. The emergency generator will not be tested while the combustion turbines are in the startup or shutdown process.

b. The emergency generator and fire pump engine will not be tested simultaneously.

4 Figure 4 shows the boundaries of these two facilities, but we note that both facilities are located within the entire USAF Plant 42 area which is a fenced , secure area that is restricted to the public, and would not be considered to be “ambient air.”AECOM6Table 1: Lockheed Martin and Northrop Grumman Sources ParametersVolume Sources:Source IDFacilityUTMEasting(NAD27)UTMNorthing(NAD27)BaseElev.(m)Rel. Hgt.(m)Sigma-YSigma-ZNOX(lb/hr)NOX(g/s)S045Lockheed397820.63830906.0746.763.55235.0346.9792.08E-022.62E-3S046Lockheed400409.63833159.0746.762.30228.2686.9791.76E-022.22E-3S050Lockheed397820.63830906.0746.763.55235.0344.6522.13E-022.68E-3S051Lockheed400409.63833159.0746.762.28728.2684.6521.27E-021.60E-3S052Lockheed399963.63831599.0746.762.3024.2844.6522.87E-023.61E-3S158Northrop401777.93833322.0789.3012.1952.8415.6729.21E-021.16E-2Point Sources:Source IDFacilityUTMEasting(NAD27)UTMNorthing(NAD27)BaseElev.(m)StackHgt.(m)Temp(°K)ExitVel.(m/s)Exit.Diam.(m)NOX(lb/hr)NOX(g/s)S230Northrop402337.03833310.0789.3012.195299.8170.1023.0496.44E-028.11E-3Response to EPA Comments on AECOM 1-hour NO2NAAQS Analysis for PHPPAECOM 7

The results of the three modeling cases were then processed using the “Post-1hr” postprocessor created by AECOM and described in section 3.2 of the PHPP Supplemental Information submittal, and the worst case impact was compared to the standard. The results, as shown in Table 2, demonstrate that the worst case impact occurs during normal operations when the emergency diesel generator is being tested. The modeled impact of PHPP sources, Lockheed Martin and Northrop Grumman sources, and ambient background is 184.1 μg/m 3 . As this is below the 1-hour NAAQS for NO 2 (188 μg/m 3 ), compliance with the
standard is demonstrated.

All files associated with the cumulative 1-hour NO 2 modeling analysis are included in the
electronic files archive attached to this document.

Table 2: Cumulative 1-hour NO 2 Modeling Results

Modeled Concentrations ( μ g/m 3 )

Case All Sources Northrop Property Lockheed Property Max % of Standard
Normal Operations - 10% - No Emgen 115.2 108.7 112.2 115.2 61.3%
Normal Operations - 10% - No Fire Water Pump 184.1 123.1 176.2 184.1 97.9%
Startup/Shutdown - 40% - No Emgen 148.6 108.7 151.2 151.2 80.4%

5. It is not clear that the hour by hour addition of modeled to monitored values provides a conservative estimate of impacts that could occur, since in future years values may line up differently (e.g. the highest monitored and modeled values could occur simultaneously). The NO2 memo at p.5 states that "some level of temporal pairing of modeled and monitored values may be considered on a case-by-case basis, with adequate justification and documentation". There should be some showing that the hourly method used, along with choice of background site, results in a conservative estimate of total impacts relative to the NAAQS.

As discussed in the response to comment #3, the addition of ambient background data from the Lancaster Division Street monitor is a conservative measure for the following reasons:

• More urban location of the monitor.

• Closer proximity of the monitor to the Antelope Valley Freeway, Sierra Highway, Metrolink rail line, and commute related traffic congestion on Division Street, the latter two of which have an observed effect on background NO 2 concentrations according to Mr. Chris Anderson of the AVAQMD.

• The likelihood that some of the monitored background comes from Lockheed and Northrop emission sources, meaning that those emissions are being double counted in the modeling analysis.

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM 8

An additional level of conservatism to the modeling is the assumption of constant and concurrent emissions at the maximum potential to emit amongst all sources, Project and non-Project, included in the modeling.

The use of time matched backgrounds more accurately couples the amount of NO 2 in the atmosphere associated with the specific meteorological conditions occurring at the time. As Project impacts are derived from those same meteorological conditions in the modeling, the relative impacts of the Project and the ambient concentrations are representations of the specific meteorological conditions being modeled, and therefore are more accurately combined using time-matched background. Additionally, due to the large number of ongoing programs to lower NO 2 emissions, such as the tightening of the 1-hour NO 2 CAAQS in February, 2007, which post-dates the time matched ambient background used in this analysis, as well as the new Federal 1-hour NO 2 standard, local AVAQMD NOx control rules, and California and federal vehicle emission standards and air toxic control measures, future ambient background concentrations should continue to go down. A review of the maximum recorded concentrations at the Division Street Monitor shows that the ambient background concentrations have gone down every year since 2004, the last year included in this study. The maximum background concentration recorded in 2008, the last year currently available
on the EPA’s AIRS website 5 was 0.061 ppm, a value 40% lower than the 2004 maximum ambient concentration of 0.103 ppm. As a result, the use of background data from 2002- 2004 is another significant measure of conservatism build into the analysis.

6. The NO2 memo specifically notes at pages 3 and 9 that the there is no default instack NO2/NOx ratio for either the OLM or PVMRM methods for the 1-hr NO2 NAAQS. Rather (p.4), there should be a "case-by-case determination based on an assessment of the adequacy of the ozone titration mechanism utilized by these options to account for NOx chemistry within the AERMOD model based on 'the chemical environment into which the source’s plume is to be emitted' (Appendix W, Section 5.1.j)."

In the cumulative analysis performed in response to comment #4, a GE-supported in-stack
NO X / NO 2 ratio of 10% (consistent with the default value) was used for normal operations, while 40% was used for startup / shutdown. Both ratios are likely conservative representations of the true conv ersion rate as described below:

Normal Operations

In an email exchange on 9/20/10 with Andrew Dicke, HDGT Environmental Product Marketing Manager from GE Power and Water, Mr. Dicke indicated the following is GE’s recommended guidance regarding the in-stack ratio for GE7FA turbines during normal operations:

“Suggested NO2/NO emission assumptions:

• Assume NO2 ranges from approximately 10 to 15% of the total NOx when operating within the emission compliance range (approximately 50% to 100% of base load).

5 http://www.epa.gov/air/data/geosel.html

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM 9

• If there is an SCR, assume the NO2 is extremely low (<1% of total NOx). SCRs react with NO2 more rapidly than NO, as such the NO2 percentage is very low downstream
of the SCR.”

PHPP will use two GE7FA turbines, configured with GE’s Rapid Start Process (RSP). The turbines will be equipped with SCR. Although the above GE email indicates the ratio should be well below 10% when an SCR is used, 10% was used as the in-stack ratio for the two turbines for normal operations. Because the turbines will be using SCR during normal operations and GE has found the turbines will typically have an in-stack ratio at or below 1%, the use of 10% as the in-stack ratio is a conservative measure in the analysis.

Startup / Shutdown

As documented in the PSD application, the shutdown mode was determined to produce higher emissions than found during startup, and a shutdown was therefore used to represent the worst case startup / shutdown scenario. Mr. Dicke of GE did not provide a specific recommendation for an in-stack ratio during startup and shutdown, although he agreed that the ratio could be higher than during normal operations. The only other data found by AECOM for similar gas turbines was information determined during stack testing done at the Palomar Energy Center on May 3 rd , 4 th , 18 th , and 23 rd , 2006. Based on that data, the SanDiego County Air Pollution Control District (SDAPCD) recommended the use of a 40% instack ratio during startup. Additional testing performed later specifically during a cold-start
scenario determined the in-stack ratio of NO X to NO 2 to be 5% rather than 40%. SDAPCD chose to retain their conservative recommendation of 40% despite this result. Because additional data on the in-stack ratio during startup / shutdown is sparse, AECOM used the SDAPCD suggested value of 40% for the revised PHPP cumulative modeling. This assumption is very conservative for several reasons:

1. The Palomar Energy Center test specifically focused on startup showed a ratio of 5% during a worst case (cold start) scenario.
2. The PHPP will utilize RSP, in which the turbines will be brought to the normal operating temperatures (and hence stack tip ratios) much more quickly.
3. In the shutdown case being modeled for PHPP:

a. Unlike the beginning of startup, the turbines would be hot, and therefore the
ratio of NO X to NO 2 at the stack tip would be at or near the same value as for normal operations.
b. For at least some of the shutdown, the SCR will still be online, and even after it is offline, the residual ammonia continues to react with the NO 2

. c. Using 40% for the in-stack ratio assumes that the shutdown process takes the full hour. In reality, the shutdown process takes less than 30 minutes. During the other 30 minutes of the hour the turbines would be at normal operation levels (with a lower in-stack ratio) with SCR. As a result, using 40% for the whole hour is equivalent to an in-stack ratio of 70% or more during the actual shutdown period.
d. The in-stack ratio during the actual shutdown period itself would be transient: for the first portion of the shutdown, the in-stack ratio would be similar to normal operations because the turbine would still be hot and the SCR would

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM 10

still be operating. Only toward the end of the shutdown would the ratio of NO X to NO 2 potentially increase, when the NOx emission rate is trending toward zero. Thus, even the assumption of a higher in-stack ratio during the whole
duration of the actual shutdown is conservative.

e. The same stack parameters for low load operation were assumed to be constant during the hours, when they would actually be changing and the point of maximum impact would be moving throughout the hour.

For the reasons given above, the assumption of a 40% in-stack tip NO X to NO 2 ratio is conservative, perhaps to a large degree. Additionally, the modeling conservatively assumes that both turbines are being shutdown simultaneously, the worst case shutdown scenario.

As a result, not only are the selections of 10% and 40% NO X / NO 2 stack tip ratio likely conservative, there are several other significant levels of conservatism built into the modeling beyond the ratios assumed.

7. There should be some discussion of the representativeness of the Lancaster site for providing ozone data for use with OLM.

Ozone is largely a regional pollutant. Therefore the primary factor in deciding the representativeness of a monitor for use in a modeling analysis is its proximity to the Project site. Because the monitor is less than 2.5 km [1.5 miles] from the PHPP site, and because, as demonstrated in the response to comment #3, the monitor is located such that the recorded concentrations of pollutants should be as high or worse than at the project site, the Division Street monitor should be a representative, or potentially conservative, source of ozone data for the analysis.

8. If there is any missing data from the chosen ozone site, then the procedures used for filling in missing data should be described, and shown not to bias the modeling
results low.

Over the 3 years included in the modeling analysis (2002-2004), ozone data were available at the Lancaster Division Street Monitor for 24,113 hours out of a total of 26,304, or 91.7% of the total hours. The remaining hours were filled using the average ozone background over the available 24,113 hours, which was 38.8 ppb. Of the missing hours, 1096 occur atmidnight when the monitor is off line for auto-calibration. On many occasions autocalibration took two hours, accounting for the vast majority of the remaining 1095 missing hours. As night time levels of ozone are usually considerably lower than during the day, the use of the average ozone concentration to fill these values is a conservative measure, by up to as much as a factor of ten at times. In addition, the fact that the hours that are missing are those that would typically have the lowest concentrations artificially increases the average value used to fill the limited number of daytime missing hours upward. As a result, the use of 38.8 ppb to fill the missing hours is a conservative measure that thus should, if anything, bias the results higher rather than lower.

Please feel free to call me at 978-589-3275 if you have any questions or comments regarding this information.

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM 11

Figure 1: Relative Location of the PHPP Site and Meteorological Data Tower

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM 12

Figure 2: Wind Rose for Palmdale Regional Airport (2002-2004)

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM 13

Figure 3: Relative Location of the PHPP Site and the Division Street Monitor

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPPAECOM

Response to EPA Comments on AECOM 1-hour NO 2 NAAQS Analysis for PHPP 14

Figure 4: Location of Lockheed-Martin and Northrop-Grumman Sources and Property