MACT NESHAP Standards

The first National Emission Standards for Hazardous Air Pollutants (NESHAPs) were originally required by the 1970 Clean Air Act (CAA). These standards were developed for sources and source categories that were determined to pose adverse risk to human health by the emission of HAPs. The EPA Administrator was directed to set the standard "at the level which in his judgment provides an ample margin of safety to protect the public health from such hazardous air pollutants." These risk-based NESHAPs are located in 40CFR61 and incorporated by reference in 45CSR34. The NESHAPs applies to all existing and new/modified sources.

45CSR34 incorporates by reference federal air toxics regulations promulgated under the NESHAP program.

Congress directed EPA to develop a program to develop further the regulation of HAPs in Section 112 of the 1990 Clean Air Act Amendments (CAAA). While the standards for major sources of HAPs developed per this section are also designated as NESHAPs, they are established according to Maximum Achievable Control Technology (MACT) requirements. MACT is a technology-based standard, as opposed to the original conception of NESHAPs as a risk-based standard. These technology-based NESHAPs are located at 40 CFR 63 and incorporated by reference in 45CSR34.

EPA has set MACT standards for over 100 source categories as specified under Section 112(d) . While these MACT standards typically apply to major sources (those at facilities with greater than 10 ton/yr of a single HAP, or greater than 25 ton/yr of aggregate HAPs), many MACTs also apply to area sources (sources with less than 10/25 ton/yr HAP thresholds); a few MACTs apply only to area sources. EPA has also begun to identify additional area sources of air toxics for regulation per its Integrated Urban Air Toxics Strategy as mandated by Section 112(k) of the CAAA. The definition of major source depends upon a facility's potential to emit not its actual emissions.

For new and reconstructed plants (those starting construction or reconstruction after EPA proposes the MACT standard for that type of facility), the MACT standard must be at least as stringent as the emission control achieved in practice by the single best controlled similar plant within the category or subcategory. Thus, a single plant's level of control appears to establish the "floor" for new sources, regardless of whether this control level can be met by other companies with different economic circumstances.

EPA's Air Toxics Website contains a wealth of information, including the text of promulgated, proposed, and upcoming MACT standards.

• EPA Technical Air Pollution Resources

There is a risk-based component to MACT standards that follows the initial technology-based MACT standard. Under the 1990 CAAA, EPA was mandated to set technology-based standards (based on Maximum Achievable Control Technology, MACT) for the source categories specified under 112(d). While these MACT standards typically apply to major sources (those at facilities with greater than 10 tpy of a single HAP, or greater than 25 tpy of aggregate HAPs), many MACTs also apply to area sources (sources with less than the 10/25 tpy HAP thresholds); a few MACTs apply only to area sources. Section 112(f) specifies that EPA determine whether or not to promulgate additional standards beyond the MACT within 8 years after promulgation of the MACT standard (but within 9 years after promulgation of the 2-year MACT source categories).

Thus, EPA is required to evaluate the NESHAPs developed according to the MACT standards for any "residual risk" with 8 years of promulgation. If the "residual risk" for a source category does not protect public health with "an ample margin of safety", then EPA must promulgate health-based standards for that source category to further reduce HAP emissions. EPA is required to set more stringent standards if necessary to prevent adverse environmental effects (considering energy, costs, and other relevant factors).

The chart, "National Emissions Standards for Hazardous Air Pollutants (NESHAPs) Applicability Determination", contains information which may be used as an aid in determining applicability with NESHAPs (contained in 45CSR15 or 45CSR34) and associated regulations.

EPA has also began to establish air toxic standards based on generally achievable control technology (GACT) for certain area (nonmajor) source categories.