BOARD MEETING DATE: June 3, 2005
AGENDA NO. 24

PROPOSAL:

Notification of Recent State-Approved Health Risk Values for New Source Review

SYNOPSIS:

On February 11, 2005, the state Office of Environmental Health Hazard Assessment (OEHHA) finalized a chronic risk value for respirable crystalline silica. The finalized chronic risk value for silica is based on PM₄ and no test method currently exists for measuring ambient PM₄ for environmental purposes. Since the chronic value for this compound would not be enforceable in the absence of a test method, staff recommends postponing amendments that would have added crystalline silica to Rule 1401 and subsequently postponing the analysis for Rule 1402 until 150 days after a test method has been developed and approved by CARB.

COMMITTEE:

Not Applicable

RECOMMENDED ACTION:

Approve staff’s recommendation to postpone amending Rule 1401 and analyzing Rule 1402 impacts until 150 days after a test method for measuring ambient PM₄ has been developed and approved by CARB.

Barry R. Wallerstein, D.Env.
Executive Officer

Background

Rule 1401 – New Source Review of Toxic Air Contaminants establishes permitting requirements for new, relocated and modified sources that emit one or more of the toxic air contaminants (TACs) listed in the rule.

The Office of Environmental Health Hazard Assessment (OEHHA) establishes risk values for TACs. The Scientific Review Panel (SRP) reviews and approves the methodologies used to develop these risk values, thereby finalizing these values for use by state and local agencies in assessing risk from exposures to TACs. This approval is considered final action by the state.

Rule 1401(e)(2) requires that, within 150 days of risk values for compounds not in Table I of Rule 1401 being finalized by OEHHA, staff will bring proposed amendments to this rule to the Governing Board to reflect changes to Table I. Rule 1402– Control of Toxic Air Contaminants from Existing Sources, requires prompt notification and a report to the Governing Board within 150 days of final action by OEHHA on the potential impacts of the changes before new or updated risk factors are used for risk assessments in Rule 1402.

Crystalline Silica

On November 30, 2004 the SRP approved a chronic reference exposure level (REL) risk value for crystalline silica (respirable). Crystalline silica was not previously listed in Rule 1401 as a toxic air compound. The final technical support documents were subsequently released by OEHHA on February 11, 2005. The REL for silica is based on particles of 4 microns and smaller (PM₄). The particle size is based on existing data studied for the SRP determination based on particles of this size collected with personal sampling devices. Particles of this size have been linked to the development of silicosis, which is a respiratory disease caused by the inhalation of silica dust that leads to inflammation and scarring of lung tissue. Therefore, the risk level is based on the measurement of PM₄ silica particles.

There are personal sampling devices which can be used to measure occupational exposure to silica dust in the PM₄ size range for an individual worker; however, there is currently no method for measuring PM₄ for ambient air sampling in the general environment. Devices for ambient air sampling measure particles in 2.5 or 10 micron size ranges (PM_2.5 and PM₁₀). While PM_2.5 and PM₁₀ measurements could be used as a screening mechanism, they cannot be used to determine compliance or non-compliance with a PM₄ standard. There is also no mathematical method of determining the portion of PM₁₀ silica particles which are in the PM₄ size range. This issue was discussed during a California Air Pollution Control Officers Association (CAPCOA) Toxics and Risk Managers Committee conference call on February 15, 2005. A CAPCOA subcommittee was formed to look into development of a test method; however, OEHHA and CARB have no imminent plans to develop a test method for measuring PM₄.

Rule 1401 and 1402 Impact Assessment

AQMD staff has been collecting data on crystalline silica emissions for several years from existing facilities; however the emissions are reported as total crystalline silica, not PM₄ crystalline silica. Based on the total crystalline silica emissions data, it is likely that four or fewer existing facilities will be affected by the new risk value. These facilities are sand and gravel operations and manufacturers of asphalt felts and coatings. Specific crystalline silica data has not been collected during permit evaluations for new facilities.

Specific crystalline silica data will be needed and further analysis for both Rule 1401 and 1402 impacts will be necessary once a testing methodology is developed. Consequently, an impact assessment cannot be completed as required by Rules 1401 and 1402 at this time.

Conclusion

At this time, staff is unable to complete the required impact assessment for Rules 1401 and 1402. In addition, actual permit evaluations and AB 2588 analysis cannot proceed because there is no ambient air sampling methodology for measuring crystalline silica PM₄. On this basis, staff recommends postponing the Rule 1401 amendment and Rule 1402 analysis until 150 days after a test method has been developed and approved by CARB.

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