By Marc Campopiano and Max Friedman

On March 6, 2015, the California Office of Environmental Health Hazard Assessment (OEHHA) updated its Guidance Manual for Preparation of Health Risk Assessments (HRAs) for the purpose of better characterizing exposure risks to children from air toxics.  Using the new Guidance Manual, HRAs are expected to estimate risks that are two to five times greater than HRAs using the former methodology—even assuming no changes in air toxics exposure.  As a result, once the updated Guidance Manual has been implemented by the various air districts, it likely will expand the notification and permitting requirements for many industrial uses that require air toxics permits and may require additional analysis and mitigation for development projects that trigger the California Environmental Quality Act (CEQA).

OEHHA is required to develop and periodically update guidelines for conducting HRAs under California’s Air Toxics Hot Spots Program.[i]  The Children’s Environmental Health Protection Act of 1999 also requires OEHHA to specifically consider risks to infants and children.[ii] The Guidance Manual was last updated in 2003.

Between 2007 and 2012, OEHHA developed three Technical Support Documents (TSDs) that primarily evaluated cancer and non-cancer risks in children, including the derivation of non-cancer reference exposure levels, [iii] cancer potency factors for early life stage exposure,[iv] and exposure assessment methodologies using stochastic risk assessment.[v]  These studies underwent public and peer review and were approved by California’s Scientific Review Panel on Toxic Air Contaminants.

OEHHA issued a draft version of the Guidance Manual on June 20, 2014, with the public comment period ending on August 18, 2014.  In November 2014, the Scientific Review Panel approved an updated version of the Guidance Manual that addressed public comments.  OEHHA then adopted the final Guidance Manual on March 6, 2015.

New Methodological Changes
The core revisions to the Guidance Manual involve estimating exposure of air toxics in children.  Key changes include:

  • Revising parameters relating to overall exposure, such as:
    • Increasing breathing rates typical among children and infants;
    • Adjusting time at home and duration of exposure, which differ among infants, children, and adults; and
    • Reducing exposure assumptions for affected non-children (e.g., workers).
  • Applying a “multiplier effect” (known as an Age Sensitivity Factor) for young children (in contrast, the former methodology treated an individual the same from birth through age 70):
    • Third trimester to age 2 – 10 times multiplier;
    • Age 2 to age 16 – 3 times multiplier; and
    • Age 16 to age 70 – no additional multiplier.
  • Establishing methods for evaluating short-term exposures from temporary impacts.

What’s Next
Although OEHHA has acted, additional steps are needed before the guidelines are fully implemented at the local level.  The California Air Resources Board and California Air Pollution Control Officers Association are expected to release Risk Management Guidelines in April 2015.  Subsequently, individual air districts will need to adopt new rules or policies to implement the guidelines into their permitting and CEQA programs.

Several air districts are already evaluating implementation options.  For example:

  • The South Coast Air Quality Management District is reviewing changes to existing rules and CEQA guidance for construction and operational project phases. Staff’s proposals are tentatively scheduled for May 2015.  Staff will host three public workshops and rulemaking will include a public process for stakeholder input.[vi]
  •  The Bay Area Air Quality Management District intends to initiate rule amendments in 2015, but a specific schedule has not been set.[vii]
  •  The San Joaquin Valley Air Pollution Control District held a public workshop on October 9, 2014 to consider raising its CEQA significance thresholds to account for the higher HRA results expected under the then-proposed guidelines.[viii]

After implementation by the air districts, the updated Guidance Manual may increase the regulatory burden on industrial uses that require air toxics permits and require additional analysis and mitigation for development projects that trigger CEQA:

  • For industrial uses that require air toxics permits, the updated Guidance Manual is expected to substantially increase the number of new and existing sources that trigger notification or modeling obligations under the AB 2588 “Hot Spots” program.[ix] Staff for the San Joaquin Valley Air Pollution Control District has expressed concern that the updated Guidance Manual will make it harder for many sources—including small sources such as gas stations—to obtain necessary permits in a timely manner.[x]
  • In-progress and future CEQA projects could be significantly affected if the CEQA lead agency requires the use of the updated Guidance Manual because HRAs using the new methodology are expected to estimate impacts that are two to five times greater (or more in some cases) than HRAs prepared using the prior methodology—even assuming no change in exposure.[xi] Because many CEQA documents use a ten-in-one-million risk level as the significance threshold, this multiplier effect could result in a finding of significant impact for a higher number of projects.[xii] Staff for the South Coast Air Quality Management District has also indicated that the updated Guidance Manual could mean that relatively small, temporary construction projects result in significant health risks.[xiii] This could require a greater number of projects to complete a full Environmental Impact Report and potentially include additional control measures.
  • Workload for air districts’ staff is also expected to increase, translating into longer delays in permitting and CEQA review.

[i]   Health and Safety Code Section 44360(b)(2).

[ii]  Health and Safety Code Section 39606.

[iii] Technical Support Document for the Derivation of Noncancer Reference Exposure Levels, 2008.

[iv] Technical Support Document for Cancer Potency Factors: Methodologies for derivation, listing of available values, and adjustments to allow for early life stage exposures, 2009.

[v]  Technical Support Document for Exposure Assessment and Stochastic Analysis, 2012.

[vi] Proposed Work Plan for Implementing the OEHHA’s Revised Air Toxics Hot Spots Program Risk Assessment Guidelines, available at

[vii] Health Risk Assessment (HRA) Guideline Revisions, available at default-source/Agendas/Governing-Board/2015/2015-mar6-026-presentation.pdf?sfvrsn=6.

[viii] See Leland Villalvazo, San Joaquin Valley Unified Air Pollution Control District Draft Staff Report: Proposed Update to District’s Risk Management Policy to Address OEHHA’s Revised Risk Assessment Guidance Document (Sept. 23, 2014) at 12, Workshops/postings/2014/10-09-14_OEHHA/Draft-Staff-Report-9-23-14.pdf.

[ix]  See id.

[x]   See id.

[xi]  See Proposed Work Plan for Implementing the OEHHA’s Revised Air Toxics Hot Spots Program Risk Assessment Guidelines, available at

[xii]  See Potential Impacts of New OEHHA Risk Guidelines on SCAQMD Programs, available at

[xiii]  See id.