AECOM 250 Apollo Drive, 978-905-2100 tel 250 Apollo Chelmsford, MA 01824 978-905-2101 fax



# Memorandum

To Scott Bohning Page 1

cc Shirley Rivera, Lisa Beckham, Sara Head Subject Justification of the use of the 3-year average 98 th percentile ambient background concentration for PHPP 1-hour NO 2 NAAQS Modeling.

From

Richard Hamel
Date July 21, 2011

I. Background

On June 27 th , 2011, representatives of AECOM, Inland Energy, an d the City of Palmdale met with EPA regarding outstanding issues still to be resolved r elated to the Prevention of Significant Deteriorati on (PSD) permit application for the Palmdale Hybrid Po wer Project (PHPP). One question that arose was whether the choice of the 3-year average of the 98 th percentile background value for 1-hour NO 2 was suitably conservative to satisfy the requirements o f the PSD program with regard to air dispersion modeling. The purpose of this memo is to clarify t he reasoning behind AECOM’s choice of this approach and to demonstrate that the 1st-Tier approach, as o utlined in the March 1 st , 2011 EPA Memo “ Additional Clarification Regarding the Application of Appendix W Modeling Guidance for the 1-hour NO 2 National Air Quality Standard

”, would be overly conservative as relates to the P HPP because of the monitor’s location and the localized NO 2 emissions that occur nearby. Much of the data pre sented in this memo has been included in previous submissions to EPA, but is rep roduced here so that all relevant data are located in one place.

II. NO 2 Emissions Sources Close to the Lancaster Division Street Monitor
The Lancaster Division Street Monitor is located ap proximately 4.1 kilometers from the PHPP site. The monitor is located in downtown Lancaster and has a number of NO 2 line sources in close proximity. The primary sources in the area are the Metrolink rail line, the Sierra Highway, the Antelope Valley Freew ay (SR-14), and commute related traffic on Division St reet. The locations of these line sources with res pect to PHPP and the monitor are shown in Figure 1. Tab le 1 shows the distance between these sources and the project site as compared to the monitor.

The maximum modeled 1-hour NO 2 impacts for normal operations, as well as startup / shutdown, occur on the eastern fence line of the PHPP. The distanc e from the line sources to the location of the maxi mum impacts would thus be slightly higher than the “Dis tance from PHPP” in Table 1 below. As can be seen inAECOM 2

the table, the monitor is much closer to all of the local line sources of NO 2 emissions than the Project and location of the maximum impacts. More importantly, these sources are generally north-south roadways and rail line that would be upwind of both the moni tor and PHPP (at different points along the line) d uring the meteorological conditions that lead to the maxi mum impact, so the distance is particularly relevan t.
Table 1: Distance from Project Site and Lancaster M onitor to Local Sources of NO 2

Emission Source Distance From Monitor Distance From PHPP Daily Volume (vehicles/day) Sierra Highway 110 meters ~2 km 20,000+ Southern Pacific Rail 80 meters ~2 km 24 trains / weekday 6-12 trains on weekends Antelope Valley Freeway 1 Just over 2 km Just over 4 km ~80,000 at Ave. L exit Division Street 2 50 meters About 3 km ~18,000 near the monitor Avenue K 0.6 km ~4.0 km 30,000 / 25,000 to the west / east of monitor Avenue L ~1.0 – 1.5 km ~3.5 km 30,000+ west of moni tor Avenue M ~2.5 – 3.0 km 0.5 km 18,500 in vicinity of PHPP 1. http://www.laalmanac.com/transport/tr26b.htm#14 2. This portion of Division Street ends at E Avenue L and starts again in Palmdale west of Sierra High way

The east-west streets present near PHPP have signif icantly less traffic than those near the monitor. East Avenue M, an east-west road that defines the northe rn boundary of the PHPP site, experiences traffic volumes of around 18,500 vehicles / day in the vici nity of the Project according to the City of Lancas ter Traffic Engineering Division 1 . Due to the extensive area covered by USAF Plant 42, there are no eastwest streets within 4 km south (upwind) of the PHPP power block that would have substantial traffic volumes (the closest is Avenue P/Rancho Vista Blvd) . The traffic volumes of the east-west streets nea r the monitor however are significantly higher: Avenu e K experiences traffic volumes of approximately 25,000 vehicles / day to the east of the monitor, a nd over 30,000 vehicles / day to the west. Avenue L experiences daily volumes well in excess of 30,000 vehicles / day to the southwest of the monitor, dir ectly upwind of the monitor in the predominant wind direc tion. There are also other streets (Avenue K6 and K8) that run east-west near and downwind of the mon itor.
Additionally, the monitor is significantly affected by commute traffic idling at the intersection in f ront of the building where the monitor is sighted. In a telepho ne conversation with Mr. Chris Anderson of the Antelope Valley Air Quality Management District (AV AQMD), on September 22nd, 2010, Mr. Anderson stated that NO 2 concentrations recorded by the monitor visibly spi ke a few moments after each train passes by. Additionally, Mr. Anderson reported tha t traffic idling at the intersection of Division St reet and Avenue K6 East, directly in front of the AVQAMD off ice where the monitor is located, causes daily spik es in recorded NO 2 levels during the morning and afternoon commutes. This scenario is borne out in reviewing the distribution of the background data b y hour and season, as shown in Table 2 below. As seen in the table, the hours with the highest maxim um recorded background combination occur from 5 am to 8 am, and 5 pm to 8 pm, corresponding closely to the daily commute, and the time at which the Metrolink commuter trains begin running from Lancas ter to Los Angeles each morning (commencing at

1 http://www.cityoflancasterca.org/Modules/ShowDocum ent.aspx?documentid=4370AECOM 3

3:58 am, then 4 more trains between 5 am and 7 am) 2 . Because this congestion does not occur at or near the PHPP site, the background values recorded during these hours, which constitute 33% of the total background data collected, significantly over state the ambient background concentration at the Project location.
Because of the much closer proximity of the vehicle and rail traffic sources to the monitor during the wind conditions that produced the highest modeled impact s, it can be assumed that the background concentrations during these periods are conservativ e compared to those occurring near the Project site during the worst case modeling scenario.
Table 2: Maximum Ambient Concentration by Hour and Season 2008-2010 (ppb)

Hour Starting Winter Spring Summer Fall Overall 0:00 38 45 20 40 45 1:00 33 32 25 39 39 2:00 30 28 24 35 35 3:00 33 43 42 41 43 4:00 32 47 49 47 49 5:00 42 53 65 56 65 6:00 45 54 61 57 61 7:00 49 53 45 47 53 8:00 45 36 34 46 46 9:00 43 27 19 41 43 10:00 38 20 11 28 38 11:00 29 16 10 21 29 12:00 27 14 18 16 27 13:00 25 14 11 16 25 14:00 23 15 13 16 23 15:00 32 15 12 23 32 16:00 42 17 12 40 42 17:00 47 23 14 62 62 18:00 51 36 16 56 56 19:00 47 42 24 50 50 20:00 45 41 33 49 49 21:00 47 47 30 47 47 22:00 41 42 25 43 43 23:00 1 29 ND ND ND 29 1. Most of the data from the hour beginning at 23:0 0 is missing from the dataset as the monitor is recalibrated nightly at that time. 2. Winter = Dec, Jan, Feb. Spring = Mar, Apr, May. Summer = Jun, Jul, Aug. Fall = Sep, Oct, Nov

2 http://www.metrolinktrains.com/schedules/pdf.php?i d=1041AECOM 4

III. NO 2 Emissions Sources Near the PHPP Site
The primary non-Project point sources contributing to the background at the PHPP site are the Lockheed

Martin and Northrop-Grumman facilities located on U .S. Air Force (USAF) Plant 42 property adjacent to the PHPP. Emissions from sources at these two faci lities are included in the cumulative NO 2 modeling. Since these sources are located about 4 km from the Lancaster monitoring station, they will also contribute to the ambient background, hence when us ing a background value that is not matched to the meteorological conditions will lead to some “double counting”. There are no other major point sources of NO 2 near (within 6 miles [10 km]) the PHPP (or the mon itor) beyond those that are explicitly included in the modeling.
The only potentially significant area source of NO 2 emissions closer to the Project site than the moni tor is air traffic at the Palmdale Regional Airport/USAF P lant 42. The airport is operated by Los Angeles Wo rld Airports (LAWA), but air traffic at the airport is minimal since no commercial airlines currently oper ate there. In a 1989 agreement with the Air Force, com mercial traffic is currently allowed up to 50 opera tions per day, with an operation being either a landing o r a takeoff 3 . There are provisions in the agreement, which is in place until 2017, that would increase t he allowed number to 400 should another commercial airline commence operations there. Eight airlines h ave attempted to establish a viable business at Palmdale Regional Airport since 1971, all of which have failed. In 2009, including military operation s, there were a total of 26,905 landing or take-off op erations, an average of 73.7 operations per day 4 . In 2007 and 2008, the average operations per day were 92.4 and 80.2. Because the runways are located to the south and southeast of the PHPP, these emission s should not impact the receptors showing the maximum modeled impacts at the same time as PHPP so urces, which occur when the winds are blowing from the west. Any long term contributions to the ambient background concentration should be picked u p by the Lancaster Division Street monitor, less than 4 kilometers away. No other significant sources o f NO 2 exist upwind of the highest modeled impacts that w ould contribute significantly to the modeled concentrations.
IV. Effect of Commute Related Sources on the Daily Maximum Monitored Concentrations.
When considering the appropriate 1-hour NO 2 background data to use for the PHPP PSD applicatio n modeling, the background data were sorted in a numb er of different ways: monthly, seasonal, hourly, et c. (see Table 2 for the seasonal and hourly results). All of this analysis showed that regardless of how the data were sorted, the impacts from commute-related background sources overwhelmed any other variation in the background concentrations. Furthe r analysis was then done to determine how the daily maxima correlated to commute related emissions. Ta ble 3 shows the breakdown, by hour, of the number of occurrences of the daily maximum background conc entrations from 2008-2010. As shown in the table, more than half of the days experience their maximum background concentration during the morning commute (5-8 am) time when traffic is at its height and commuter rail trains, both passing the monitor and idling at the station nearby, are most present. Wh en the data related to the evening commute hours (5 -8 pm) are added, that value increases to 70%.

3 http://www.jpbroker.com/pairport.html 4 http://www.city-data.com/airports/Palmdale-Regiona l-Usaf-Plant-42-Airport-Palmdale-California.html#PM DAECOM 5

Table 3: Occurrences of Daily Maximum Background Co ncentrations by Hour

Hour Beginning 2008 2009 2010 Total 0:00 19 22 19 60 1:00 3 5 4 12 2:00 0 3 4 7 3:00 8 6 3 17 4:00 24 17 21 62 5:00 84 94 93 271 6:00 73 83 66 222 7:00 28 23 16 67 8:00 5 7 6 18 9:00 4 0 3 7 10:00 1 2 0 3 11:00 1 1 0 2 12:00 1 2 1 4 13:00 2 1 1 4 14:00 2 2 1 5 15:00 0 1 1 2 16:00 1 4 0 5 17:00 19 21 20 60 18:00 22 17 36 75 19:00 15 9 14 38 20:00 14 12 7 33 21:00 12 10 10 32 22:00 27 17 23 67 23:00 0 0 0 0 % from 5-8 am: 50.7% 55.7% 51.9% 53.9% % from 5-8 pm: 15.3% 13.1% 20.1% 16.1% Total Commute: 66.0% 68.8% 71.9% 70.0%

V. Discussion and Recommendation of Appropriate Bac kground.

The March 1 st EPA memo describes the 1 st -tier determination of ambient background, which wo uld be accepted without further justification, as the 98th -percentile of the annual distribution of daily max imum 1-hour values averaged across the most recent three years of monitored data. Other approaches may be allowed on a case by case basis with appropriate ju stification. The 1 st -tier ambient background concentration is calculated as follows:



### 1. For each day included in the three years of data, d etermine the highest recorded 1-hour ambient NO 2 concentration, discarded the remaining 23 hours of data. 

### 2. For each of the three years, determine the 98 th percentile of the daily maxima calculated in step 1.AECOM 6



### 3. Average the 98 th percentile value determined for each of the three years together to determine the design ambient background concentration.

The 1 st -tier ambient background using the above calculatio ns for 2008 through 2010 would be 52 ppb (98.3 μ g/m 3 ). As shown in Tables 2 and 3, the ambient backgrou nd concentrations at the Lancaster Division Street Monitor are largely impacted by nea rby emission sources that do not exist at the PHPP or at the location of the maximum modeled 1-hour NO 2 impacts. The large majority of the daily maximum impacts in particular are driven by these commute r elated emissions. Because these commute emissions skew the data significantly (as shown above, by 33- 50%), the use of the daily maxima as the basis for developing a 98 th percentile background value as described above, is unrealistically conservative because it would be derived almost entirely from em issions that are neither present at the PHPP site, nor upwind of the modeled maxima such that they would c ontribute to those concentrations and in fact would result in an design background concentration that i s higher than the maximum ambient 1-hour NO 2 concentration recorded at the Lancaster monitor dur ing any non-commute hour over the entire 3 year period.
Because the use of the daily maxima would be unreal istically conservative, and in order to preserve th e probabilistic form of the standard, AECOM recommend s the use of the 3-year average of the 98 th percentile of all hours modeled. Table 4 shows thes e values in both ppb and μ g/m 3 from 2008-2010. By including all of the hours in the calculations, the high impact hours occurring during the daily commu te would still be included in the calculations, and th us the resulting 98 th percentile would still be conservative for the project site. The proposed ambient backgrou nd to be added in the 1-hour NO 2 NAAQS modeling, as shown in the table, is 39.3 ppb (74.0 μ g/m 3 ). Note that the background data for 2010 were not available when the updated 1-hour NO 2 modeling was performed. In that modeling, the thr ee year average of the 98 th percentile background from 2007-2009 of 41.0 ppb ( 77.1 μ g/m 3 ) was used. The 2010 data shows that the ambient background concentratio n of NO 2 in the Palmdale and Lancaster areas continues to diminish, as has been the trend since at least 2002.

Table 4: Lancaster Division Street Monitor 1-hour N O 2 Annual 98th Percentile Concentrations from 2008 – 2010

Units 2008 2009 2010 3-year Average ppb 41.0 39.0 38.0 39.3

μ g/m 3 77.1 73.4 71.5 74.0

Our prior memo dated March 30, 2011 contained updat ed cumulative NO 2 modeling results as shown in Table 5 below. The model was run for both the norm al operations and the startup / shutdown scenario with the following assumptions regarding the PHPP a ncillary equipment sources:

a. The PHPP emergency generator and fire water pump w ill not be tested while the combustion turbines are in the startup or shutdown process.

b. The PHPP emergency generator and fire water pump e ngine will not be tested simultaneously.
The EPA modeling guidance issued in March 2011 sugg ests that these intermittent sources do not need to be modeled at all, but in order to not redo the modeling again, we continued to include these sourc es in the modeling. In addition to the PHPP sources, the U.S. Air Force Plant 42 sources were also included

. We note that this modeling shows that even if the o verly conservative 1 st -tier background is used with the normal operations scenario and no emergency generat or testing, the total cumulative result is less tha n the 1-hour NO 2 NAAQS (88.2 μg/m 3 + 98.3 μg/m 3 = 186.5 μg/m 3 , which is less than 188 μg/m 3 ).AECOM 7

Table 5: Revised Cumulative 1-hour NO 2 NAAQS Modeling Results

Modeled Concentrations (μg/m 3 )

Modeling Scenario PHPP with updated USAF Plant 42 Sources and Receptors Background a Sum

Normal Operations - No PHPP Emergency generator 88.2 77.1 (74.0) 165.3 (162.2)
Normal Operations - No PHPP Fire Water Pump 108.2 77.1 (74.0) 185.3 (182.2)
Startup/Shutdown - No PHPP Emergency generator 109.7 77.1 (74.0) 186.9 (183.7)
a. Background based on 3-year average 98 th percentile background from 2007 – 2009 (or 2008 – 2010)

The other scenarios could arguably be excluded unde r the recent EPA guidance, as they involve intermittent sources or activities (emergency engin e testing or startup/shutdown events). These scenarios are also very conservative, as it was pre viously felt that the modeling was sufficiently conservative with the background approaches taken s uch that further refinement was not needed. For instance, the startup/shutdown scenario is actually a shutdown scenario where the plant stack parameters are assumed to remain constant throughou t the event, which will never be the case, as in actuality the stack temperature and flow rates are decreasing as the combustion turbine shuts down (an d would also be changing during startup). We note th at assuming that the maximum background concentrations (hours with values over 100 μg/m 3 only occur at the monitoring station about 2 perce nt of all hours) is in the first place representative, bu t then also occurs at the same time and under the s ame meteorological conditions as when the units are bei ng started or shutdown or engines are being tested, is very remote.
In conclusion, we offer two perspectives under whic h the impacts from the PHPP are determined to be acceptable: 1) EPA agrees that in this specific si tuation (a case by case determination) use of a 3 y ear average 98 th percentile value as background is sufficiently con servative as it reduces the influence of local mobile sources near the monitor but not near the Project; and/or 2) That intermittent sources or activities not be included in the modeling as allow ed by EPA guidance.

Please feel free to call Rich Hamel at 978-905-2231 (note the new phone number, our office has moved) or Sara Head at 805-388-3775 if you have any questi ons or comments regarding this information. The spreadsheets 2008-2010 Background Data Analysis .xlsx, 2008-2010 Daily Max Background Data Analysis.xlsx, and PHPP Impacts by Hour.xlsx are included as Attachment A to this memo for your review.AECOM 8



### Figure 1: Relative Location of the PHPP Power Block , Lancaster Monitor, and Significant Background Sources