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Pacific Southwest, Region 9

Serving: Arizona, California, Hawaii, Nevada, Pacific Islands, Tribal Nations

PM-10 Actions in Imperial County, California

Note: EPA no longer updates this information, but it may be useful as a reference or resource.

August 6, 2001


Notice of Proposed Rulemaking to make:
Clean air Act Finding of Attainment Under 179B(d)
and Alternative Finding of Nonattainment
and Reclassification to Serious;
California-Imperial Valley Planning Area;
Particulate Matter of 10 microns or less (PM-10)

Today's Proposed Action

  • EPA is proposing to find that Imperial County has attained the PM-10 NAAQS by the applicable attainment date of December 31, 1994 but for the emissions from outside the U.S., i.e., Mexico. If finalized, this attainment finding would allow Imperial County to remain a moderate PM-10 nonattainment area and avoid a reclassification to serious. Imperial County is still required to submit a moderate area PM-10 control plan (State Implementation Plan or SIP) and is working with EPA and the State to develop an approvable plan with additional control measures.
  • Concurrently, EPA is taking public comment on an alternative proposal that Imperial County has failed to demonstrate that they have attained the PM-10 NAAQS and thus would be reclassified to serious. EPA is issuing this proposal in the event that public comment convinces EPA not to finalize the attainment finding discussed above. A final finding of failure to attain would cause Imperial County to be reclassified to serious leading to a requirement to develop a more comprehensive SIP including Best Available Control Measures.


  • Imperial County is located in the Southeastern portion of California and borders Mexicali, Mexico. The County often points out that its population of about 149,300 is much smaller than the Mexicali population of over 1 million. The principal industries in Imperial County are farming and retail trade. In Imperial County, elevated PM-10 levels can result from disturbance of soils by wind and human activity and from transport from Mexico. Likely PM-10 sources include unpaved roads, waste burning, agriculture, vacant lots, Immigration and Naturalization Service (Border Patrol) activities along the border and transport from Mexico.
  • Imperial County continues to violate the PM-10 or dust standard today. The area experiences the highest childhood asthma rate in the State.
  • Many scientific studies have linked breathing PM to a serious of significant health problems, include: aggravated asthma, increases in respiratory symptoms, difficult or painful breathing, chronic bronchitis, decreased lung function, and premature death. PM is also associated with increased hospital and emergency room visits for people with heart and lung disease, absences from work and school, and reduced visibility.
  • The Clean air Act has special provisions for areas which can demonstrate they are impacted by non-U.S. emissions. While EPA is finding that Imperial County would have attained the PM-10 NAAQS but for the emissions from Mexico, Imperial County is continuing to look for ways to reduce their local emissions to help improve public health.
  • EPA is also continuing to work with International, State and Local agencies to look for regional solutions to air quality problems along the border.

Opportunity for Public Comment on Today's Proposal

  • EPA will take public comment on this proposal for 30 days following publication in the Federal Register. Comments should be sent by mail or e-mail to the contact listed below.
  • After public comments are received and considered, EPA plans to finalize one of the alternative proposals.

Further Information

  • A copy of the proposal will be available in the air Programs section of EPA Region 9's website, within the next few days.
  • For more information, please contact Doris Lo, U.S. EPA Region 9, air Planning Office, at 415-744-1287; lo.doris@epa.gov.

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