UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

REGION IX

75 Hawthorne Street

San Francisco, CA 94105

November 1, 2010

Mr. Eric Stevenson

Director of Technical Services

Bay Area Air Quality Management District

939 Ellis Street

San Francisco, CA 94109

Dear Mr. Stevenson:

Thank you for your submission of the 2009 Air Monitoring Network Review for the Bay 

Area Air Quality Management District (BAAQMD), July 1, 2010. We have reviewed the 

submitted document and have found that the plan is complete, informative, very detailed and 

meets all of the requirements for annual network plans as required by our regulations set forth 

under 40 CFR Part 58.10. We also approve the closure of the Fremont site as requested in 

BAAQMD’s September 22, 2010 letter. As discussed in the September correspondence, 

Fremont has not measured exceedances of the NAAQS over the past 5 years. The Livermore 

station, also in Alameda County, measures the same pollutants and shows similar or higher 

concentrations for all four pollutants. BAAQMD will still exceed minimum monitoring 

requirements even without Fremont. There is therefore no monitoring regulatory requirement for 

monitoring at Fremont, and EPA approves discontinuation of monitoring activities at Fremont. 

Additional future system modifications will require separate EPA approval, and we will continue 

to work with your district to review system changes as they proceed.

We also want to thank you for your timely submission of the 2010 Air Monitoring FiveYear Assessment for the Bay Area AQMD, as required under 40 CFR Part 58.10. We recognize 

that preparing the network assessment was a significant project and we appreciate your effort. 

We plan on providing feedback to all agencies on network assessments during the winter 2011.

If you have any questions regarding this letter or the enclosed comments, please feel free 

to contact me at (415) 972-3851 or Gwen Yoshimura at (415) 947-4134.

Sincerely,

/s/

Matthew Lakin, Manager

Air Quality Analysis Office

Air Division

Enclosure

cc: Glen Colwell, BAAQMD
Comments on 2009 Network Plan for Bay Area AQMD

Please update next year’s annual network plan to reflect the following comments:

- Minimum Monitoring Requirements: Minimum monitoring requirements per 40 CFR 58 

Appendix D are calculated based on MSA population and monitored values (design 

values, maximum monitored values) for the MSA. Future plans should show the highest 

monitored values for each MSA regardless of who operates the monitor, and list the 

resulting minimum monitoring requirements. Listing only monitoring data from 

monitors operated by BAAQMD results in confusion as to what minimum requirements 

apply. For example, Table 3 (page 12) lists Vallejo-Fairfield with a population of 

407,234, a design value of 67 ppb, and 2 required monitors. 40 CFR 58 Appendix D, 

Table D-2, indicates that areas with a population between 350,000 and 4 million require 1 

monitor if the design value is less than 68 ppb, and 2 monitors if the design value is equal 

to or greater than 68 ppb. It is unclear whether Bay Area has listed a higher number of 

required monitors because a Yolo-Solano-operated monitor has a design value of 68 or 

over, or if Vallejo-Fairfield in fact only requires 1 ozone monitor.

Performance Evaluations: Livermore’s last annual performance evaluation (gaseous) is 

listed as 7/29/2008 (page 42). Point Richmond’s last performance evaluation is listed as 

10/02/2008 (page 58). Please ensure that performance evaluations are conducted 

annually for all sites and that the most current information is reflected in the network 

plan.

Changes Within the Next 18 Months: Monitor information for San Pablo (page 77) states 

that there will be changes within the next 18 months. There is no change described in the 

narrative. Please contact EPA for approval of any future changes to be made at this site.

PM2.5 Monitor Sampling Frequencies: At sites such as Concord (page 30), the sampling 

frequency of the primary and collocated PM2.5 monitors varies according to the month, 

but the primary and collocated do not shift sampling frequency at the same time. Please 

explain why this is the case in your next network plan.

Monitoring Objective and Spatial Scale: Please explain why Oakland West (page 55) is 

described as source impact, urban scale, for SO2.