CAPCOA BACT Clearinghouse Resource Manual

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Control Technology Definitions
     A. Federal BACT
     B. LAER
     C. Summary of Differences between Federal BACT and LAER
     D. Control Technology Requirements of California Districts
     E. The Nature of "California BACT" Definitions
VIII. Control Technology Definitions

        A. Federal BACT

        Federal BACT applies to major sources that emit pollutants subject to the PSD program authorized under Part C, Title I of the federal Clean Air Act. It has also been used the permitting programs of some rural California districts which comply with all national ambient air quality standards. In addition, some districts have employed a BACT requirement in conjunction with a LAER requirement.1 In these districts, less stringent control technology requirements are used with lower net emission increase thresholds associated with larger minor sources or acceptable projected air quality impacts. Lower levels of net emission increase may trigger control technology requirements equivalent to federal BACT. Control technology requirements equivalent to LAER may be triggered by higher net emission increases likely to be associated with major source or unacceptable projected air quality impacts.

         Section 169(3) of the federal Clean Air Act defines BACT as follows:2

         The term "best available control technology" means an emission limitation based on the maximum degree of reduction of each pollutant subject to regulation under this Act emitted from or which results from any major emitting facility, which the permitting authority, on a case-by-case basis, taking into account energy, environmental, and economic impacts and other costs, determines is achievable for such facility through application of production processes and available methods, systems, and techniques, including fuel cleaning or treatment or innovative fuel combustion techniques for control of each such pollutant. In no event shall application of "best available control technology" result in emissions of any pollutant which will exceed the emissions allowed by any applicable standard established pursuant to section 111 or 112 of this Act. Emissions from any source utilizing clean fuels, or any other means, to comply with this paragraph shall not be allowed to increase above levels that would have been required under this paragraph as it existed prior to enactment of the federal Clean Air Act Amendments of 1990.

The definition states that BACT "means an emission limitation based on the maximum degree of reduction of each pollutant subject to regulation under this Act emitted from or which results from any major emitting facility." It is interesting to note that BACT is somewhat of a misnomer. The form of the requirement is defined as an emission limitation and not as an equipment standard. Therefore, one is constrained to assume that the emission limitation would, in many cases, correspond to the emission rate achieved with either basic or control equipment which would otherwise be determined to be an appropriate control technology requirement. In other words, BACT should be established as a performance requirement, not as an equipment requirement, on authorities to construct and permits to operate.

        By definition, Federal BACT is less stringent than LAER, and allows for consideration of "energy, environmental, and economic impacts and other costs." It also requires evaluation of alternative production processes and available methods, systems, and techniques, including fuel cleaning or treatment or innovative fuel combustion techniques. The definition also states a minimum requirement as "In no event shall application of best available control technology result in emissions of any pollutant which will exceed the emissions allowed by any applicable standard established pursuant to section 111 or 112 of this Act." Section 111 and 112 represent NSPS and NESHAP. Note, however, that BACT is not explicitly constrained to be as stringent as retrofit technologies labeled RACT.

        The encumbrance of so many considerations in the federal BACT definition creates some ambiguity regarding the implied procedure determining BACT requirements. Originally, the U.S. EPA suggested a sequential analysis referred to as "bottom-up" analysis. As a result, U.S. EPA has provided some guidance on the matter. This guidance is referred to as "the top-down approach," and is neither applicable to LAER nor California BACT definitions patterned after LAER. The guidance essentially dictates that the process of evaluation should include a ranking of candidate BACT alternatives, starting with evaluation of the most stringent candidate requirement with subsequent evaluations to cover decreasingly stringent alternatives in sequence. One cannot proceed down the list to a less-stringent BACT candidate unless the rejection of a more stringent candidate is justified. In setting the most stringent controls, one is not limited to those achieved in practice. In addition, any control previously required as LAER for the subject class or category or source should be included on the list.

        Another notable characteristic of the federal BACT definition is the direct authorization to consider alternative production processes and available methods, systems, and techniques, including fuel cleaning. As a result of this provision, BACT evaluations are not limited to add-on control technology and include pollution prevention measures as well as any other potentially feasible methods of reducing emissions. Even changes in basic equipment, fuels, and material substitutes can be considered.

        B. LAER

        The federal LAER is defined in Section 171(3) of the federal Clean Air Act.3 LAER focuses on requiring the most stringent emission limitation achieved in practice for such class or category of source, or which is contained in the SIP of any state for the same (i.e., RACT). There is relief provided from potentially stringent requirements originating from the SIPs if the applicant can demonstrate that such a limitation is not achievable. However, no requirement can be less stringent than federal NSPS.

         The term "lowest achievable emission rate" means for any source, that rate of emissions which reflects --
        (a) 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
        (b) the most stringent emission limitation which is achieved in practice by such class or category of source, whichever is more stringent.
         In no event shall the application of this term permit a proposed new or modified source to emit any pollutant in excess of the amount allowable under applicable new source standards of performance.

Explicit provisions for consideration of alternative basic equipment or fuels is not directly evident as in the definition for federal BACT. But neither does the language of the definition preclude the consideration of alternative basic equipment or fuels as a LAER requirement.

        There are several other notable differences between BACT and LAER. First of all, BACT is evaluated on a case-by-case basis, where LAER is more or less uniform for a class or category of source. This case-by-case evaluation of BACT has a large scope of concerns, including energy, environmental, and economic impacts. The LAER definition is very rigid and more narrow, allowing little argument in the decision other than what is "achieved in practice" and what is the class or category of source. As a result, highly similar sources can have different BACT requirements, but should not, in theory, have different LAER requirements.

        Part (a) of the LAER definition is largely self-evident. The most stringent emission limitation refers to any limit contained in a rule or regulations which has been adopted into an SIP. The applicant can be relieved of meeting such limitation upon demonstrating that that the limitation is not achievable. The degree to which an SIP limit can be challenged is addressed in U.S. EPA internal guidance:4

            There is, of course, a range of certainty in such a definition. The greatest certainty for a proposed LAER limit exists when that limits is actually being achieved by a source. However, a SIP limit, even if it has not yet been applied to a source, should be considered initially to be the product of careful investigation and , therefore, achievable. A SIP limit's credibility diminishes if a) no sources exist to which it applies; b) it is generally acknowledged that sources are unable to comply with the limit, and the state is in the process of changing the limit; or c) the State has relaxed the original SIP limit. Case- by-case evaluations need to be made in these situations to determine the SIP limit's credibility.
         The same logic applies to SIP limits to which sources are subject but with which they are not in compliance. Noncompliance by a source with a SIP limit, even if it is the only source subject to that specific limit, does not automatically constitute a demonstration that that limit is unachievable. The specific reasons noncompliance must be determined, and the ability of the source to comply assessed. However, such noncompliance may prove to be an indication of nonachievability, so the achievability of such a SIP limitation should be carefully studied before it is used as the basis of LAER determination

        The "achieved in practice" component of the LAER definition appears to be subject to some interpretation since it is not defined in the federal statues and regulations. As a result, there are few objective regulatory criteria to constrain the form of an achieved-in-practice evaluation. However, Region IX of the U.S. EPA has taken a position that the successful operation of a new control technology for six months constitutes achieved in practice."5 Prior to this assertion by the U.S. EPA, the air quality jurisdiction apparently had the latitude to interpret what was meant by "achieved in practice." In fact, there are some considerations that are tightly not defined, such as, what is considered successful operation.

        The "class or category of source" component of the definition is also a term that is largely subject to interpretation. As used in California, it is apparent that it could be as large as a group of basic equipment types that provide the same function, e.g., the combination of electric motors, turbines, and reciprocating engines to provide torsional drive. On the other hand, it could be set as a size segment or subtype within an equipment type, e.g., gas turbines over 33 MMBtu/hr heat input or lean-burn internal combustion engines, respectively. As a result, the use of this term in the LAER definition provides a lot of flexibility. Some California districts are using BACT guidelines which indicate what control requirements will be acceptable for California BACT, i.e., a "presumptive LAER."6 In the process, they are using their own home-generated lists of "class or category of source."

        In some cases a control technology achieved in practice for one class or category of source can be required for a different class or category of source. The U.S. EPA has established guidance for transferring LAER requirements across source categories, which they refer to informally as technology transfer. If basic equipment found in two different classes or categories of source have similar gas stream characteristics, the technology transfer policy dictates that achieved-in-practice add-on control technologies are transferrable between the two categories.7

        Finally, it is interesting to note that the definition of LAER does not contain explicit economic considerations. This is dissimilar to the federal BACT definition, which was largely concerned with the economic feasibility of a control technology as well as its energy and environmental impacts. The assumption is that if a given technology has been achieved in practice for a given (or comparable) industry, there is de facto evidence that the economic cost to the industry of that control technology is not prohibitive. In other words, the cost of the control could only be not achievable only if no new plants could be built in that industry due to an emission limitation proposed to meet the LAER definition. Otherwise, the technology must be economically feasible for that class or category of source.8

        C. Summary of Differences between Federal BACT and LAER

        The federal BACT definition is very clear in its intent to consider requirements for each source on a case-by-case basis. The decision is to include economic, energy, and environmental considerations. In contrast, the LAER definition is clearly more stricter, rigid, and objective by not allowing economic, energy, or environmental consideration, only considering the most stringent control achieved in practice for the category of source being considered. However, there is policy latitude in the chosen working definition of "achieved in practice" and a large amount of latitude in determining class or category of source.

        The above indicates that although federal BACT and LAER serve a similar purpose, the structures of both definitions and the process for establishing the control requirement are significantly different. As a result, if one were to establish policy or guidance regarding control technology requirements for new and modified sources, it would be advisable to make such guidance specific to either federal BACT or LAER, but not both. For instance, the U.S. EPA has implemented guidance on the use of a "top-down approach" in determining BACT. This "top-down approach" in essence requires that potential BACT options be considered in the order of their effectiveness. There is no such latitude in the LAER definition for considering less stringent requirements than that achieved in practice. Any other option used in the definition would have to be more stringent than achieved in practice. Some California BACT definitions include alternative provisions that allow the control officer to investigate the economic feasibility of technologically feasible measures, methods, controls, or limitations that have not yet been achieved in practice. A top-down approach in the review of alternative technologically feasible options would be appropriate under such circumstances.

        D. Control Technology Requirements of California Districts

        Most BACT definitions in California are more akin to LAER than federal BACT. Again, such definitions are often informally referred to as "California BACT." Although the forms of the definitions are usually quite similar, there are often slight differences between districts having "California BACT" definitions. "California BACT" definitions can be either more or less stringent than the federal LAER definition, depending on the selected district.

        Districts not having BACT definitions similar to federal LAER usually have both BACT and LAER definitions that are similar to their federal counterparts. The use of both requirements may seem confusing at first, since they are used in different federal programs (i.e., PSD and NSR, respectively). But the requirements are not applied simultaneously. Instead, BACT is normally required in projects where air quality standards are not projected to be violated, and LAER is required for projects with impacts that may exacerbate existing or create new violations of air quality standards. Districts with both BACT and LAER requirements are restricted to the Mountain Counties Air Basin. Exceptions include San Diego and Imperial County APCDs.

        Outside of districts with both BACT and LAER definitions, only a small minority of districts do not have either a BACT or a LAER definition that is not in some way similar to the federal LAER definition. These districts are restricted to the North Coast Air Basin. A comparison of district definitions is given in Table 9.

        E. The Nature of "California BACT" Definitions

        Usually, the definition is written so that "California BACT" is the more stringent of two to five possible alternative minimum requirements. Commonly, there are, in one form or another, three common minimum requirements. The first two of these minimum requirements, as listed in the generalized example definition below, parallel those found in the federal LAER definition. Various optional language used by districts is included in {} brackets, while potential additions of language often included by districts are included in [] brackets.9

         "Best Available Control Technology" (BACT) means for any {source, stationary source, emissions unit} the most stringent of:

         1.    The most {stringent, effective} {emission limitation, emission control} [or control technique] which the EPA {certifies, states} is contained in the implementation plan of any state approved under the Clean Air Act for {such category or class of source, the type of equipment comprising such a source}, unless the applicant demonstrates to the satisfaction of the Air Pollution Control Officer that such limitation is not achievable.


Table 9

Comparison of California District Control Technology Definitions with
Federal Definitions for best available control technology (BACT)
and Lowest Achievable Emission Rate (LAER)

District District Has
BACT Definition
Most Similar to
Federal BACT
Definition
District Has
LEAR Definition
Most Similar to
Federal LEAR
Definition
District Has
BACT Definition
Most Similar to
Federal LEAR
Definition
 
North Coast Air Basin  
Mendocino Co. AQMD *  
North Coast AQMD *  
Northern Sonoma Co. APCD *  
 
San Francisco Bay Area Air Basin
Bay Area AQMD   *
 
North Central Coast Air Basin  
Monterey Bay Unified APCD   *
 
South Central Coast Air Basin  
San Luis Obispo Co. APCD   *
Santa Barbara Co. APCD  
(PSD BACT definition) *  
(NSR LAER definition)   *
Ventura Co. APCD   *
 
South Coast Air Basin  
South Coast AQMD   *
 
San Diego Air Basin  
San Diego Co. APCD * *  
 
Northeast Plateau Air Basin  
Lassen Co.APCD   *
Modoc Co.APCD   *
Siskiyou Co.APCD   *
 
Sacramento Valley Air Basin  
Butte Co.AQMD   *
Colusa Co.APCD   *
Feather River AQMD   *
Glenn County APCD   *
Placer Co. APCD Portion   *
Sacramento Metropolitan AQMD   *
Shasta Co.AQMD   *
Tehama Co.APCD   *
Yolo-Solano Co. AQMD   *
 
San Joaquin Valley Air Basin  
San Joaquin Unified APCD   *
 
Great Basin Air Basin  
Great Basin Unified APCD   *
 
Southeast Desert Air Basin  
Imperial Co.APCD * *  
Kern Co.APCD   *
Mojave Desert AQMD   *
 
Mountain Counties Air Basin  
Amador Co.APCD * *  
Calaveras Co.APCD * *  
El Dorado Co. APCD Portion   *
Mariposa Co.APCD * *  
Northern Sierra AQMD * *  
Placer Co. APCD Portion   *
Tuolumne Co.APCD * *  
 
Lake County Air Basin  
Lake Co.AQMD   *
 
Lake Tahoe Air Basin  
El Dorado Co. APCD Portion * *  
Placer Co. APCD Portion   *


         2.    The most effective control device, technique, or emission limit which has been achieved in practice for such category or class of source.

         3.    Any other emission control technique [, alternative basic equipment, different fuel or process] found [after public hearing] by the Air Pollution Control Officer to be technologically feasible and cost effective for such class or category of sources [or for a specific source].

         Under no circumstances shall best available control technology be determined to be less stringent than the emission control required by any applicable provision of District, state, or federal laws or regulations, unless the applicant demonstrates to the satisfaction of the APCO that such limitations are not achievable.


        Table 10 shows which of the above alternative minimum requirements are contained in each of the district BACT definitions. Note that the table only addresses definitions considered to be "California BACT." The nuances of each minimum requirement are discussed below:

1.    The Most Stringent Limitation in any State Implementation Plan: This minimum requirement essentially states that the control technology requirement cannot be less stringent than reasonably available control technology (RACT). RACT essentially would be the most stringent control technology requirement that has been adopted as a retrofit control of existing sources by a state or local air pollution control agency and further incorporated into an SIP.

   The last provision of this minimum requirement, i.e., unless the applicant demonstrates to the satisfaction of the Air Pollution Control Officer that such limitation is not achievable, is also found in the federal LAER definition. However, the use of applicant versus owner or operator is probably a refinement, since the applicant is responsible for providing a complete application to the district.

2.    Most Effective Control Achieved in Practice: The wording of this minimum requirement can vary strongly by district. Three important elements are often varied, resulting in significant changes to the stringency of requirements. The first element refers to most effective control device, technique, or emission limit. Most districts at least include the most effective control device. Others will either include one or both of the technique or emission limit.

   The second element is achieved in practice. Unfortunately, there is no definition of achieved in practice. Therefore, the district has some latitude in defining achieved in practice. Some districts may use more prescriptive wording, such as, used or required. Used is a more stringent wording than achieved in practice, indicating that the technology does not have a "track record" of reliability. Required is even more stringent since the technology does not have to even be in use. It just has to already be determined to be technologically feasible and cost effective by some other air quality jurisdiction.

   The third element refers to the equipment type and scope of the equipment category. Some districts specify the equipment as emissions unit or permit unit. Others may use source or stationary source. Some districts may substitute type of equipment comprising such source for category or class of source. The category or class of source is a concept employed in federal LAER definitions as discussed earlier. The reason for using type of equipment comprising such source, instead, is not immediately clear. Category or class of source allows some latitude by the district to appropriately specify a subgrouping or supergrouping of source types for comparison purposes. The use of type of equipment does not immediately convey the ability of the district to specify a size category within a type of source.

Table 10

Comparison of Provisions Included in BACT Definitions for
California Districts with "California BACT" Definitions

District Alternative Minimum Requirements
Contained in District BACT Definitions

1
Most Stringent
Limitation
in any State
Implementation
Plan
2
Most
Effective
Control
Achieved
in Practice
3
Unproven Tech-
nologies Deemed
Technologically
and Economically
Feasible
 
San Francisco Bay Area Air Basin  
Bay Area AQMD * * A
 
North Central Coast Air Basin  
Monterey Bay Unified APCD   * *
 
South Central Coast Air Basin  
San Luis Obispo Co. APCD * * A
Santa Barbara Co. APCD (LAER def.) * * *
Ventura Co.APCD * * A
 
South Coast Air Basin  
South Coast AQMD * * A
Definition mandated by Health and Safety  
Code Section 40440.11(c)(1), i.e., Section 40405 * *  
 
Northeast Plateau Air Basin  
Lassen Co.APCD   * *
 
Sacramento Valley Air Basin  
Butte Co.AQMD   * A
Colusa Co.APCD   * A
Feather River AQMD   * A
Glenn County APCD   * A
Placer Co. APCD Portion * * A
Sacramento Metropolitan AQMD * * A
Shasta Co.AQMD   * A
Tehama Co.APCD   * A
Yolo-Solano Co. AQMD  
Modoc Co.APCD * * *
Siskiyou Co.APCD   * *
 
San Joaquin Valley Air Basin  
San Joaquin Unified APCD * * A
 
Great Basin Air Basin  
Great Basin Unified APCD * * *
 
Southeast Desert Air Basin  
Kern Co.APCD * * A
Mojave Desert AQMD * * *
 
Mountain Counties Air Basin  
El Dorado Co. APCD Portion   A
Placer Co. APCD Portion * * A
 
Lake County Air Basin  
Lake Co.AQMD  
 
Lake Tahoe Air Basin  
Placer Co. APCD Portion * * *


Symbol Key:    "*" indicates alternative minimum requirement is present in district BACT definition.
"A" indicates that in addition to alternative minimum requirement being present, the definition language explicitly mentions consideration of alternative basic equipment, processes, or fuels.

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        In some cases, districts have inserted language that allows relief from this alternative minimum requirement if the applicant demonstrates that the corresponding requirement is not achievable. This provision is usually similar to that found in the above alternative minimum requirement for RACT.

3.    Unproven Technologies Deemed Technologically and Economically Feasible: This minimum requirement allows the district to require unproven control technologies for a given category of source as BACT. Where present, it makes California BACT definitions more stringent than federal LAER definitions. Because of it, California districts can participate in advancing the stringency of "California BACT" requiring untried control technologies. It also allows for the transfer of control technology from one category of source to another when a proven technology in one category of source has not yet been required for a different category of source for a very similar situation.

   Fifteen districts explicitly consider alternative basic equipment, processes, and fuels to be considered in the scope of alternatives strategies for reducing emissions. This alternative is a relatively recent addition to California BACT definitions, starting with the South Coast AQMD and spreading rapidly to other districts. However, the South Coast AQMD has recently eliminated procedural provisions for considering alternative basic equipment. Furthermore, BACT procedures in the South Coast AQMD are undergoing radical changes in order to comply with constraining provisions of Health and Safety Code Section 40440.11.

        The final provision of the above generalized "California BACT" definition provides a "floor" for the scope of alternatives. Many rules have the last provision as stated in the generalized definition. Some others provide the following as minimum requirements for California BACT:

        a. In no event shall the emission rate reflected by the control technique or limitation exceed the amount allowable under applicable NSPSs.
        b. In no event shall the emission rate reflected by the control technique or limitation exceed the amount allowable under applicable NESHAPs.

        The language used in the last provision of the generalized definition is a potential problem. The language has a loophole that is not really a loophole. It implies, if not denotes, that BACT requirements may be less stringent than other local, state, or federal laws. However, district rules could not legitimately override the authority of state and federal laws. In addition, one would find it difficult to argue that the NSR rule of a district could override the authority of an applicable prohibitory rule.

        Even though the wording of a provision may be the same in two rules, they may be interpreted differently depending on the working definitions of such terms as "achieved in practice." A control technology that is "achieved in practice" may be considered a measure, method, or control that has been required elsewhere. On the other hand, the Bay Area AQMD formerly required a year of successful operation before a measure, method or control is achieved in practice. Some districts take the middle position of requiring a functioning application of candidate control technology for BACT.


1. For example, Imperial County APCD, San Diego Co. APCD, and some districts in the Mountain Counties Air Basin have both BACT and LAER definitions. Kern County APCD formerly used a combination of BACT and LAER definitions during the late 1970s and 1980s.

2. A slightly different form of the federal BACT definition can be found in 40 CFR 166(b)(12) and 52.21(b)(12). These provisions are located in two different sets of regulations for Prevention of Significant Deterioration of Air Quality.

3. Another form of the definition is contained in the federal regulations for new source review at 40 CFR 51.165(a)(1)(xiii).

4. U.S. EPA Memorandum from John Calcagni, Director of Air Quality Management Division, to David Kee, Director of Air and Radiation Division, Region V. The memorandum subject is "Guidance on Determining Lowest Achievable Emission Rate (LAER)."

5. This position was established in an August 25, 1997 letter from David Howekamp of U.S. EPA, Region IX to Mohsen Nazemi of SCAQMD.

6. Districts using "presumptive LAER" manuals include the South Coast AQMD, Bay Area AQMD, San Joaquin Valley Unified APCD, and Ventura County APCD.

7. This policy is documented in an August 29, 1988 memorandum from John Calcagni, Director of the Air Quality Management Division of the U.S. EPA, to David Kee, Director of the Air and Radiation Division of Region V of the U.S. EPA. The memorandum subject is "Transfer of Technology in Determining Lowest Achievable Emission Rate (LAER)."

8. More precise wording of this policy can be found in a February 28, 1989 memorandum from John Calcagni, Director of Air Quality Management Division of the U.S. EPA, to David Kee, Director of the Air and Radiation Division of Region V of the U.S. EPA. The memorandum subject is "Guidance on Determining Lowest Achievable Emission Rate (LAER)."

9. Although such a depiction as shown below was very applicable before 1993, district definitions continue to diverge from their common roots, making this composite definition less applicable as years go by.


Best Available Control Technology (BACT) Clearinghouse Program