Extension of Public Comment Period on Draft Air Toxics Hot Spots Program Guidance Manual for the Preparation of Risk Assessments

The Office of Environmental Health Hazard Assessment (OEHHA) released a draft document, Air Toxics Hot Spots Program Guidance Manual for the Preparation of Risk Assessments on June 20, 2014 for a 45-day public comment period, originally scheduled to end on August 4, 2014. We received a request from the California Chamber of Commerce on behalf of various business groups to extend the public comment period. This notice extends the comment period to August 18, 2014.  

This draft Guidance Manual has been developed by OEHHA, in conjunction with the Air Resources Board, for use in implementing the Air Toxics Hot Spots Program (Health and Safety Code Section 44360 et. seq.).  OEHHA is required to develop guidelines for conducting health risk assessments under Section 44360(b)(2). 

As stated in the original June 20, 2014 notice, we are seeking comment primarily on clarity of the guidance manual as it relates to implementing and integrating the risk assessment guidelines presented in three OEHHA Technical Support Documents (TSDs). These TSDs, completed in 2008, 2009 and 2012, describe non-cancer risk assessment, derivation of cancer potency factors, and exposure assessment methodology including stochastic risk assessment.  We are not seeking comments on the underlying scientific information that originally appeared in the TSDs, which have undergone public and peer review, approval by the Scientific Review Panel, and adoption by OEHHA.  However, we are seeking comments on specific items noted below that TSDs were silent on or that represent slight corrections.  As noted in the June 20 request for comment notice, these specific items are:

• Chapter 4

  • In Section 4.3.1 and 4.11.1.2, the text clarifies examples of “release types” for point, area, or volume sources and modeling selection related to screening or refined air dispersion modeling.
  • In Section 4.7.3, the text clarifies the method for spatial averaging at a fence line receptor when a portion of the grid is within the facility boundary.

• Chapter 5

  • In Section 5.3.2, the text clarifies that in Tier 1 assessments, for pathways involving dermal exposure to contaminated soil or soil ingestion, the concentration in soil reflects accumulation over 70 years.
  • In Section 5.3.4.4, we provide guidance on how to use the mother’s milk biotransfer coefficients shown in Table 5.5.
  • In Table 5.4, footnotes were added to clarify how to use intake point estimates for food animals in the food animal pathway.
  • In section 5.4.1.4 (and again in Chapter 8, Section 8.3.4), the text clarifies application of the 8-hour Reference Exposure Levels for offsite workers and residences, and for continuously emitting versus non-continuously emitting facilities.
  • In section 5.4.2.1, there is a small correction in the equation for calculating dermal dose. There was an extra parameter (year) in the equation in the 2012 TSD; it has now been removed.
  • In the 2012 TSD for Exposure Assessment, there were no equations shown to determine the weighted average dose used for calculating a chronic noncancer hazard quotient for the non-inhalation pathways of exposure. This needs to be done across age-groupings to estimate a chronic Hazard Quotient. Algorithms were added (pp. 5-40-42, 5-44-45, 5-47-48, 5-53-54, 5-57-58, 5-60-61) to make this clearer.

• Chapter 6

  • On page 6-7, we clarified that for determining Hazard Index by target organ system, reproductive and developmental toxicants are combined into one Hazard Index.

• Chapter 8

  • In section 8.2.7, we clarified that for estimating non-inhalation pathway cancer risk for the mother’s milk pathway, the exposure duration is one year in the 0 < 2yr age groups and 2 years for the other non-inhalation pathways.
  • In section 8.2.10, we included more detailed text regarding cancer risk assessment for short-term projects, relative to the description on page 61 in the May 2009 Technical Support Document for Cancer Potency Factors: Methodologies for derivation, listing of available values, and adjustments to allow for early life stage exposures. This issue is also discussed in Chapter 11, pages 11-17 and 11-18 of the Technical Support Document for Exposure Assessment and Stochastic Analysis.

• Appendix E

  • We added language on page E-2 regarding estimating noncancer impacts from unspeciated polychlorinated biphenyl mixtures.

OEHHA will review all relevant comments and revise the draft manual as appropriate.  The Scientific Review Panel will then review the document for clarity and its overall implementation and integration of the TSDs, including text related to the specific items cited above.  Please note that we cannot consider comments on regulatory impacts that may eventually result from efforts to reduce risks identified in future assessments conducted pursuant to the guidance manual.   These considerations are outside the jurisdiction of the guidance manual and OEHHA.  The California Air Resources Board and the state’s local air districts will consider regulatory impacts as part of their ongoing implementation of the Air Toxics Hot Spots Program.