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Toxic Air Contaminants Air quality regulations also focus on TACs. In general, for those TACs that may cause cancer,there is no concentration that does not present some risk. In other words,there is no threshold level below which adverse health impacts may not be expected to occur. This contrasts with the criteria air pollutants for which acceptable levels of exposure can be determined and for which the ambient standards have been established(Table 6-3). Instead, EPA and ARB regulate HAPS and TACs,respectively,through statutes and regulations that generally require the use of the maximum or best available control technology for toxics (MALT and BACT)to limit emissions. These in conjunction with additional rules set forth by SJVAPCD establish the regulatory framework for TACs. Federal Hazardous Air Pollutant Programs EPA has programs for identifying and regulating HAPS. Title III of the CAAA directed EPA to promulgate national emissions standards for HAPS(NESHAP). The NESHAP may differ for major sources than for area sources of HAPs. Major sources are defined as stationary sources with potential to emit more than 10 tons per year(tpy) of any HAP or more than 25 tpy of any combination of HAPs; all other sources are considered area sources. The CAAA called on EPA to promulgate emissions standards in two phases. In the first phase(1992- 2000),EPA developed technology-based emission standards designed to produce the maximum emission reduction achievable. These standards are generally referred to as requiring MALT. For area sources,the standards may be different,based on generally available control technology. In the second phase (2001-2008), EPA is required to promulgate health risk—based emissions standards where deemed necessary to address risks remaining after implementation of the technology-based NESHAP standards. The CAAA also required EPA to promulgate vehicle or fuel standards containing reasonable requirements that control toxic emissions, at a minimum to benzene and formaldehyde. Performance criteria were established to limit mobile-source emissions of toxics, including benzene, formaldehyde, and 1,3-butadiene. In addition, Section 219 of the CAAA required the use of reformulated gasoline in selected areas with the most severe ozone nonattainment conditions to further reduce mobile-source emissions. State and Local Toxic Air Contaminant Programs TACs in California are primarily regulated through the Tanner Air Toxics Act(AB 1807) and the Air Toxics Hot Spots Information and Assessment Act of 1987(AB 2588). AB 1807 sets forth a formal procedure for ARB to designate substances as TACs. Research,public participation, and scientific peer review must occur before ARB can designate a substance as a TAC. To date,ARB has identified more than 21 TACs and adopted EPA's list of HAPs as TACs. Most recently, diesel PM was added to the ARB list of TACs. Once a TAC is identified,ARB then adopts an Airborne Toxics Control Measure for sources that emit that particular TAC. If there is a safe threshold for a substance at which there is no toxic effect,the control measure must reduce exposure below that threshold. If there is no safe threshold,the measure must incorporate BACT to minimize emissions. The Hot Spots Act requires that existing facilities that emit toxic substances above a specified level prepare a toxic-emission inventory,prepare a risk assessment if emissions are significant,notify the public of significant risk levels, and prepare and implement risk reduction measures. ARB has adopted diesel-exhaust control measures and more stringent emission standards for various on-road mobile sources of emissions,including transit buses and off-road diesel equipment(e.g.,tractors, generators). In February 2000,ARB adopted a new public-transit bus fleet rule and emission standards for new urban buses. These new rules and standards provide for more stringent emission standards for some new urban bus engines, beginning with 2002 model year engines;zero-emission bus demonstration and purchase requirements applicable EDAW Manteca WQCF and Collection System Master Plans EIR Air Quality 4.3-16 City of Manteca