Introduction

BACT is defined as

An emission limitation … based on the maximum degree of reduction for each pollutant … taking into account energy, environmental, and economic impacts and other costs … through application of production processes or available methods, systems, and techniques…

This section reviews the important elements in this definition and describes the approach that must be used to satisfy BACT requirements for a proposed new source or modification of an existing source.

There is a requirement for NSR and other air quality permits that new or modified sources be built with BACT. Because BACT is required for new or modified sources, it provides a substantial incentive for developers of control technologies to show that their product provides the maximum degree of reduction of pollutant emissions available better than competing products or at a lower cost. If a new technology can be shown to reduce emissions more than currently available equipment, taking into account energy, environmental, and economic impacts and other costs, BACT requires that it will be used. This kind of requirement, which persistently forces improved technologies on sources of air pollutant emissions, is termed technology forcing.

BACT is intended to include end‐of‐pipe controls, such as scrubbers or baghouses; process changes, such as changing from an organic solvent to a water‐based coating; and operations, such as inspection and maintenance of valves and flanges to reduce fugitive emissions. The intent is that there is no technology feasible to use that would result in lower emissions.

However, the definition also provides that the evaluation of BACT for a source will be on a case‐by‐case basis in which the characteristics and constraints of the source will be considered. The definition calls for evaluation of energy, environmental, and economic impacts and other costs that are specific to the source being considered. If these impacts are too great for a pollution control technology applied to a specific source, that technology is not considered BACT for that case. In another case, different conditions can lead to a different conclusion.

In the following sections, several additional definitions will be offered for terms that are similar to BACT but apply to special situations. Next, strategies for use in BACT determination for a proposed project are discussed. Then the “top‐down” approach to determine BACT is described. This is the approach required by most permitting agencies. Finally, several examples are given for determining BACT.

Control Technology Requirement Definitions

In addition to BACT, there are several other technology requirement terms that may be encountered in air quality permitting. All of them are conceptually similar to BACT – they define emission limits applicable to different source types, different pollutants, and/or different attainment status. They are determined in similar fashions and, in some cases, they may be more stringent. Several of them are discussed in the following:

THERE ARE SEVERAL DIFFERENT CONTROL TECHNOLOGY REQUIREMENTS

• RACT – Reasonably available control technology
• BACT – Best available control technology
• MACT – Maximum achievable control technology
• LAER – Lowest achievable emission rate
• GACT – Generally available control technology

Others include T‐BACT, BARCT, RACM, and BACM.

Reasonably Available Control Technology

RACT is the term that is applied when a State Implementation Plan (SIP) calls for reductions in emissions of existing sources in non‐attainment areas in order to progress toward attainment. Typically, RACT is implemented as a prohibitionary rule applicable to non‐attainment areas of a state or region. An example would be a limitation on NO _x emissions from a boiler larger than 50 000 Btu/h design capacity. An RACT rule would require that all boilers above this size have NO _x emissions less than 0.5 lb/MMBtu of heat input, and that existing boilers would have three years after the date of promulgation of the rule to comply. RACT requirements are never more stringent than BACT and are usually less stringent because they must be retrofitted to existing equipment. Since RACT applies to existing sources, it is not a requirement which must be addressed for new sources. However, it may become an issue when a new source is seeking offsets from an existing source being taken out of service.

Best Available Retrofit Control Technology

Best available retrofit control technology (BARCT) is a Californian term that refers to retrofit controls for existing sources in non‐attainment with California ambient air quality standards. It is defined in the California CAA. It is difficult to distinguish between RACT and BARCT. Both apply to existing sources. Both are only applicable in non‐attainment areas. BARCT is sometimes more stringent than RACT for a given source type. The California Air Resources Board periodically publishes technical memoranda identifying BARCT for particular source types. As with RACT, BARCT is implemented through prohibitionary rules within each of the 34 California air pollution control districts.

4.14.2.3 Maximum Achievable Control Technology

MACT is the control level for hazardous air pollutant emission sources required under the Clean Air Act Amendments of 1990 (CAAA). The definition in the Act is

… the maximum degree of reduction in emissions of hazardous air pollutants subject to [Section 112 of the Act] (including a prohibition on emissions, where achievable) that the Administrator, taking into consideration the cost of achieving such emission reductions, and any non‐air quality health and environmental impacts and energy requirements, determines is achievable for new or existing sources in the category or subcategory to which such emission standard applies.

MACT regulations are for major sources of HAPs, because HAPs are formed as by‐products of incomplete combustion source. A major source is defined as any facility that emits more than 10 T/Y of any HAP or more than 25 T/Y of all HAPs combined. Thus, all large industrial boilers, process furnaces, and stationary internal combustion engines are potential major sources. In addition to major sources like steel plants or petrochemical facilities, small area sources like dry cleaners, gas stations, and printers are also regulated in the United States. A MACT can include process changes, materials substitutions, or air pollution equipment. MACT is distanced in its definition from LAER, as it is not intended to ignore economic considerations.

LAER

LAER is the control technology that is required for non‐attainment pollutant sources. If an area is non‐attainment for ozone, LAER will be required for new or modified sources that emit the ozone precursors, nitrogen oxides (NO _x ) and VOCs. LAER is defined as follows:

For any source, that rate of emissions which reflects

1. the most stringent emission limitation which is contained in the implementation plan of any state for such class or category of source, unless the owner or operator of the proposed source demonstrates that such limitations are not achievable, or
2. the most stringent emission limitation which is achieved in practice by such class or category of source, whichever is more stringent.

The stringency of LAER is its absence of extenuating circumstances such as those contained in the definition of BACT. Although there is still a provision “unless the owner or operator of the proposed source demonstrates that such limitations are not achievable,” it only applies to controls identified in implementation plans, and any control “achieved in practice” must be adopted. The consequence of this language is that economic feasibility is not included, and a proposed source must install the most stringent control that has been “achieved in practice.” As applied, there has been some debate about whether “achieved in practice” counts if the “practice” is outside the United States (USEPA 1995c).

The LAER is used by the EPA to determine if emissions from a new or modified major stationary source are acceptable under SIP guidelines. LAER standards are required when a new stationary source is located in a non‐attainment air quality region. It is the most stringent air pollution standard above the best available control technology and reasonably available control technology standards, regardless of the cost of that control technology.

Generally Available Control Technology

GACT, like MACT, is a term that addresses hazardous air pollutant control. GACT is the control technology standard that is applied to nonmajor hazardous air pollutant sources. Since these sources emit smaller amounts of hazardous air pollutants, GACT may be less stringent than MACT, although for some hazardous air pollutant source categories for which MACT standards have been promulgated, the GACT standard has been the same.

Toxic Best Available Control Technology

Toxic best available control technology (T‐BACT) was coined by South Coast Air Quality Management District (SCAQMD) in California to identify technologies that were suitable for control of toxic air pollutants. The term was adopted by several other districts in California and applies to new sources of toxic air pollutants in those jurisdictions that have estimated health risk above a threshold value of 1 in 100 000 cases of cancer due to those emissions. In practice, T‐BACT control technologies are the same as technologies for control of PM, and VOC in almost every circumstance, so this term has not become widespread. For a more complete discussion of toxic air pollutants and health risk, refer to SCAQMD (1995) and CAPCOA (1993).

Reasonably Available Control Measures and Best Available Control Measures

Reasonably available control measures (RACM) and best available control measures (BACM) are control measure guidelines developed by EPA for inclusion in SIPs. Although these terms can be applied to any pollutant, they have been most commonly applied to PM₁₀ sources. The terms RACM and BACM address moderate and serious PM₁₀ non‐attainment areas respectively. RACM and BACM technical guidance was mandated under Section 190 of the CAAA of 1990 for three major PM₁₀ source categories: urban fugitive dust, residential wood combustion, and prescribed silvicultural and agricultural burning. These measures were developed to use as prohibitionary rules, similar to those implementing RACT, aimed at reducing PM₁₀ emissions with the goal of reaching attainment for those PM₁₀ non‐attainment areas. Measures identified as RACM and BACM will almost certainly be on the list of alternative technologies to be considered as possible BACT for sources of PM.