October 4 , 2011

Mr. Ken Israels U.S. EPA Region 9
75 Hawthorne Street San Francisco, CA 94105

Re: Pechanga Ozone Monitor Data

Dear Mr. Isr a els:

On behalf of the Pechanga Band of Luiseno Indians (Pechanga or the Tribe), we are pleased to submit the following analysis related to the ambient ozone monitoring station located at the Pechanga Reservation.



### Background

On May 24, 2011

, a U.S. Environmental Protection Agency (EPA) contractor performed a scheduled audit of the Pechanga ozone monitor , a s required by EPA’s National Performance Audit Program (NPAP). The purpose of the NPAP audit is to provide quality assurance of monitoring data through independent assessments of the
monitors. Data quality is important because monitoring data are used to determine
attainment status for the National Ambient Air Quality Standards (NAAQS).

Pechanga’s monitor passed the NPAP audit on May 24, but subsequently the EPA

contractor conducted a side

- by

- side comparison with his device and found a problem
with the P echanga monitor that was causing it to show artificially low readi ngs when challenged with a side

- by

- side comparison with the EPA contractor’s analyzer

. Subsequently, on June 22, 2011, EPA provided the Pechanga Ozone Data Assessment memo, which gave a desc ription of the testing during the May 24 audit. The EPA

Assessment memo also compared the data from the Pechanga monitor to data from
three other California monitors , located at Eureka, Vandenberg, and Oceanside. Based

on these data, EPA concluded that t he problem with Pechanga’s monitor was likely related to the manifold system, and likely started in 2009

.

After conducting a site visit, reviewing the results of diagnostic experiments performed by the Tribe and its contractors, and receiving the EPA Asse ssment, Sierra performed a
separate analysis of the Pechanga monito r ing data, along with data from four other nearby monitors : Oceanside (Camp Pendleton), Lake Elsinore, Temecula 1 (Lake Skinner) , and the monitor operated by the Pala Tribe

. 2 Available d at a from all of these
monitors for the period of June 2008 to August 2011 were processed in accordance with

1 Data from the Temecula monitor were available only beginning in August 2010, when the monitor first became operational.

2 Data from the Pala monitor were available only from October 2008 to June 2009 on the EPA web site. 

## sierra research

1801 J Street Sacramento, CA 95811 Tel: (916) 444

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Ann Arbor, MI Tel: (734) 761

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- 6755Mr. Ken Israels

- 2

- October 4, 2011

the EPA Ozone Data Handling Guidance (December 1998)

. 3 The da ta from the Pechanga monitor were then compared to the data from the four nearby monitor s to analyze trends and relative ozone concentrations for the 1

- hour daily average, 1

- hour daily maximum, and 8

- hour daily maximum values.



### Analysis

For the scope of our analysis, monitors were selected for comparison based on specific
criteria: t he Oce anside (Camp Pendleton) monitor was chosen as the nearest coastal monitor, Lake Elsinore was chosen as the nearest long

- term inland monitor, and Temecula (Lake Skinner) and Pala were chosen for the close proximity to the
Reservation. Figure 1 shows the lo cation of the monitors used in this analysis

.

Figure 1
Monitor Location s

3 Available at http://www.epa.gov/ttn/oarpg/t1/memoranda/guidefin.pdf

.Mr. Ken Israels

- 3

- October 4, 2011

While EPA compare d the Pechanga data to data from the Oceanside, Vandenb e rg, and
Eureka monitors , we believe that the comparison to the Vandenb e rg monitor (a coastal

s ite in Central California ) was not necessary because the Oceanside monitor is also
located at a coastal site. In addition, a comparison with the Eureka monitor would yield

no relevant information since Eureka is the northernmost California monitor and Pechanga Reservation is in Southern California , which has markedly different topography and meteorology

.

Timing of Pechanga Monitor Issue

– The 1

- hour daily maximum ozone concentration s for the Pechanga and Oceanside monitors are shown in Figure 2

. As the figure shows, the ozone concentrations recorded at both monitors followed a similar pattern throughout the time period. The concentration recorded by the Oceanside monitor was consistently higher than the concentration recorded by the Pechanga monitor, but the

p eaks and valleys tend to coincide. In June 2009, both monitors had a noticeable drop in ozone concentration due to an unusual weather pattern in Southern California during that time. In May 2009, ambient temperatures in the area were beginning to warm, a s is normal for that time of year. However, the first week of June in 2009 brought an unusual span of cool weather, resulting in a dramatic decrease in ambient ozone concentration during that time. 4

Figure 2

4 When comparing the two

- week averages and maximums for June 1

- 14 for 2009 to th e same period for 2008 and 2010, temperatures for San Diego and Riverside County monitors were between 13° and 23° F cooler in 2009, as measured at the monitoring sites.Mr. Ken Israels

- 4

- October 4, 2011

F igure 3 shows the differences between the monthly

- averaged 1

- hour daily maximum ozone concentration readings from the four other monitors and the Pechanga monitor

. The Pechanga monitor readings were subtracted from each of the four monitor

m easurements and the r esults were averaged monthly to show a comparison of the difference between the Pechanga monitor and the other monitors

. 5

Figure 3

As shown in Figure 3, the differences between Pechanga and Lake Elsinore monitors
have a d efinite seasonality, with the difference being higher in summer than in winter, including in 2008, when EPA and Pechanga both believe that the Pechanga monitor was working properly (as verified by previous NPAP audits). The difference between the Pechanga and Oceanside monitors was fairly consistent, with less of a seasonal influence, with the exception of one specific dip in July 2008. The difference with the Temecula monitor actually decreases over the second half of 2010, which indicates the
monitors h ad readings coming closer together from August 2010 to February 2011. This information points to the fact that there is no clear point in time when a change took place that might indicate a problem with the Pechanga monitor. The consistent
seasonal varia tion in the Lake Elsinore plot shows that the difference in readings between Pechanga and Lake Elsinore has always been larger in the summer and smaller
in the winter.

As Figures 2 and 3 demonstrate , there is no clear point showing when the problems
be g an with the Pechanga monitor

— the only minor change that can be pointed to in the monitor differences is that the difference between the Pechanga and Oceanside monitors
increases slightly around January 2010, from approximately 0.02 ppm to 0.03 ppm on

avera ge. This slight difference is the only evidence that can be found as to when a problem might have occurred.

5 Note the gap in the figure for March

- May of 2011 due to Pechanga monitor downtime.

### Mr. Ken Israels -5- October 4,2011



### Conclusions

As discussed above, EPA has suggested that problems with the Pechanga monitor began

in 2009; however, based on the comparisons of the Pechanga monitor readings to readings from the four nearby monitors, we believe that the data do not clearly show a specific time when any problem with the Pechanga monitor may have begun. In addition, based on the comparisons with the nearby monitors, we believe that the problem with the monitor did not start prior to January 2010.

If you have any questions, please call me at (916) 273-5126.

Sincerely,

# 01ML~H.~ Gary Rubenstein

Senior Partner

cc: Colleen McKaughan, EPA Region 9

Jeff Wehling, EPA Region 9

Deborah Jordan, EPA Region 9

Meredith Kurpius, EPA Region 9