19 August 1999

The California Air Resources Board (ARB) published a "Draft Conceptual Outline for the Risk Management Guidance for the Permitting of New and Modified Sources that Operate Stationary Diesel-Fueled Engines."

The document identifies "achievable performance levels" for particulate matter (PM) emissions from new and modified stationary diesel-fueled engines and provides guidance to air quality management districts in California in permitting stationary diesel engines.

Proposed achievable performance levels range from 0.2 g/bhp-hr PM for emergency stand-by engines, through 0.07 g/bhp-hr for low usage engines to 0.05 g/bhp-hr for high usage engines (> 500 hours per year). The performance levels for small engines below 50 hp were proposed at 0.2 - 0.45 g/bhp-hr.

All stationary engines would be divided into Tier 1 and Tier 2 categories. Air quality districts would determine which engine category a particular engine falls under, based on source-specific information. Engines designated as Tier 1 would have to meet the above PM emission limits to be granted an approval.

The Tier 2 category would include high-usage engines, engine located near schools, non-emergency engines installed where natural gas is available, or engines installed at sites designated as "significant risk facilities." Permitting of Tier 2 engines would require complex detailed analysis involving feasibility evaluation of using a natural gas engine, site-specific health risk assessment, and site-specific design considerations.

Release of Proposed Guidance for public review is scheduled for December 1999. ARB meeting on the Proposed Guidance is scheduled for Spring 2000.

The document has been prepared as part of the risk management process, conducted by the ARB after the identification of particulate emissions from diesel-fueled engines as toxic air contaminant (TAC). Once a substance is identified as a TAC, the ARB is required by law to determine if there is a need for further control.

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