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general provisions:
MACT Determinations - A Detailed look at the
mact analysis
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3 : 4 : 5 : 6 : 7
The purpose of this section is to provide state, local agencies and
sources of hazardous air pollutants with example methods for establishing
the case-by-case Maximum Achievable Control Technology (MACT.) As
with any guidance, this information does not impose legally binding
requirements for either the permitting authority or an owner or operator
put presents a possible process. It is provided to give a better
understanding of the National Emission Standards for Hazardous Air
Pollutants (NESHAP) for Source Categories.
Based on Guidelines for MACT Determinations
under Section 112(j) Requirements [PDF]
Tier I - Making a MACT floor finding
Step 1 - Identify the MACT affected emission unit(s) 
In accordance with the provisions established in 40 CFR 63.53,
the owner or operator is required to identify all HAP emission points
within the affected source. These emission points will be grouped
into emission units (MACT emission units) that will be subject to
a MACT determination by the permitting authority. When a relevant emission standard has been proposed, the scope
of the affected source and the emission units should be consistent
with the scope of the affected source and the emission units for
which MACT was determined in the proposed emission standard, unless
an alternative can be adequately supported. When no relevant emission
standard has been proposed, the MACT emission unit will be determined
on a case-by-case basis.
Step 2 - Make a MACT floor finding
Using the available information provided by the EPA, other permitting
authorities, and/or the permit applications, a level of HAP emission
control that is equal to the MACT floor for each type of emission
unit undergoing review should be calculated by the permitting authority
according to 40 CFR 63.55.
Three ways to establish a MACT floor include:
Using (1) State and local regulations, (2) control efficiencies,
and (3) emission reduction ratios. Use of any of these methodologies
to determine the floor depends on the format of available information.
It is possible that a hybrid of these approaches may be necessary,
or none of the methods may be appropriate given the format of
the available information. If the MACT floor cannot be determined
or if it is equal to "no control," the permitting authority
should proceed to Tier II of the analysis.
The MACT Analysis
Tier I – Making A MACT Floor Finding
(Permitting Authority)
- Identify the MACT emission unit
- Make a MACT floor finding
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Tier II - Considering All Control Technologies
Step 1 - List all available/reasonable applicable control technologies
Using available information, the permitting authority in consultation
with source owners/operators should develop a list of commercially
available control technologies that have been successfully demonstrated
in practice for similar emission units and that are reasonably
applicable to sources in the category or subcategory.
Step 2 - Eliminate technically infeasible control technologies
 All control technologies that could not be applied to the MACT
emission unit because of technical infeasibility should be eliminated
from the list. A technology is generally considered technically
infeasible if there are structural, design, physical or operational
constraints that prevent the application of the control technology
to the emission unit. A technology may also be eliminated if
the permitting authority deems it unreasonable. A technology
is considered unreasonable if the operational reliability and
performance have not been demonstrated by approved methods under
conditions representative of those applicable to the source for
which MACT is being determined.
Step 3 - Determine efficiency of applicable control technologies
The permitting authority should conduct a detailed analysis
of all of the available reasonably applicable control technologies.
The efficiency of each control technology in reducing overall
HAP emissions should be determined. Generally, MACT has been
selected based on an overall reduction of all HAP emissions.
However, a permitting authority may also select MACT based on
the degree of emission reductions achieved for one or more specific
HAPs when the risk to human health and the environment warrants
establishing MACT emission limitations specifically for these
HAPs. It should also be noted that the application of more than
one control technology may be necessary in order to address multiple
types of HAP emissions.
The MACT Analysis I
Tier I – Making A MACT Floor Finding
(Permitting Authority)
- Identify the MACT emission unit
- Make a MACT floor finding
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If floor can be determined |
Tier III – Identifying MACT
- Identify maximum emission control technology
- Conduct an impacts analysis
- Establish the MACT emission limitation
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Tier III - Identifying MACT
Step 1 - Identify the maximum emission reduction control technology
When a MACT floor finding is made, the permitting authority
will need to use available information to identify the control
technology(s) that reduce HAP emissions from the MACT emission
units to the maximum extent that is at least equal to or greater
than the MACT floor. As in Tier II, the permitting authority
should conduct an analysis to eliminate any technically infeasible
control technologies and to determine the efficiency of applicable
control technologies.
While the Clean Air Act establishes that MACT shall be no less
stringent than the MACT floor, in establishing MACT, the Administrator
must take into consideration “the cost of achieving such
emission reduction, and any non-air quality health and environmental
impacts and energy requirements.” In some cases, the EPA
has developed MACT standards that are more stringent than the
MACT floor when the following criteria are met:
- The economic impact and incremental cost-effectiveness are
not unreasonable;
- The standard would control emissions of high risk or highly
toxic pollutants, e.g., chromium; or
- The standard resulted from a negotiated rulemaking, e.g.,
the wood furniture NESHAP or the HON equipment leaks standard.
Step 2 - Conduct an impacts analysis
The control technology that achieves the maximum degree of HAP
emission reductions with consideration to costs, non-air quality
health and environmental impacts, and energy requirements is MACT.
The Act does not provide direction on the significance of one consideration
to another.
Step 3 - Establish the MACT emission limitation
The MACT emission limitation established by the permitting authority
is based on the degree of emission reduction that can be obtained
by the affected source if MACT is applied and is properly operated
and maintained.
The MACT Analysis II
Tier I – Making A MACT Floor Finding
(Permitting Authority)
- Identify the MACT emission unit
- Make a MACT floor finding:
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If floor cannot be determined |
Tier II – Considering All Control Technologies
(Permitting Authority and Applicant)
- List all available/reasonable applicable control technologies
- Eliminate technically infeasible control technologies
- Determine efficiency of applicable control technologies
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Tier III – Identifying MACT
- Identify maximum emission control technology
- Conduct an impact analysis
- Establish the MACT emission limitation
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Determining the MACT Emission Unit and "Affected Source"
In some cases available information is adequate to support a MACT
floor determination for the grouping of equipment and activities
comprising the affected source. However, in some cases the EPA
has found it necessary to evaluate smaller groupings of equipment
and activities for the purpose of the MACT floor and MACT determination.
This smaller grouping is referred to herein as a MACT emission
unit.
There are four basic principles to follow when designating the
MACT emission unit. The principles can be summarized as follows:
- When a relevant Section 112(d) or Section 112(h) standard has
been proposed, the permitting authority should refer to the relevant
standard to determine the MACT emission unit; or,
- The EPA's Office of Air Quality Planning and Standards should
be consulted to determine if a suggested method for grouping affected
emission points is available; or,
- When a specific piece of equipment is designated as a source
category or
subcategory on the source category or subcategory list, the MACT
emission unit is that piece of equipment or apparatus; or,
- Emission points should be combined into a single MACT emission
unit when the combination of points leads to a much more cost-effective
method of control, and achieves a greater degree of emission reductions
when compared to point-by-point compliance.
 A single emission point such as a storage tank could be considered
the MACT emission unit. By contrast, emission points from a distillation
column, a condenser and distillate receiver could be consolidated
into one emission unit. Larger groupings of emission points may
be appropriate when a single control technology can be used to
control the aggregation or when a pollution prevention or waste
reduction strategy is considered. For instance, the entire wastewater
treatment operation within the source category or subcategory could
be considered one emission unit. Collectively, a single steam-stripper
could be used at the beginning of the operation to remove HAPs
from the wastewater and prevent downstream emissions from occurring.
Another example is illustrated with a surface coating operation.
Rather than individually controlling the emissions from a spray
booth, flash-off area, and bake oven, switching to a water-based
paint could reduce emissions from all of these emission points.
Similar Emission Units
The permitting authority should evaluate control technologies used
by similar emission units in other source categories during Tier
II. Whether control technologies from
other source categories should be considered in the MACT analysis
depends on whether the emission unit is "similar". At
least two questions should be answered to determine if an emission
unit is similar:
- Do the two emission units have similar emission types, and
- Can the emission units be controlled with the same type of control
technology.
Subcategorization
When the source category list was developed, sources with some
common features were grouped together to form a "category".
During the standard-setting process, the EPA has found it appropriate
to combine several categories or to further divide a category into subcategories. The EPA chose to establish broad source
categories at the time the source category list was developed because
there was too little information to anticipate specific groupings
of similar sources that are appropriate for defining MACT floors
for the purpose of establishing emission standards.
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