National
Emission Standards for Hazardous Air Pollutants (NESHAP) and Maximum
Achievable Control Technology (MACT)
The 1990 Clean Air Act Amendments:
A "Technology First, Then Risk" Approach
Prior to the 1990 Clean Air Act Amendments, EPA used a chemical-by-chemical
decision framework, based solely on risk, for establishing National
Emission Standards for Hazardous Air Pollutants, better known
by the acronym, NESHAP. However, this risk-based
approach did not work as envisioned. Due to gaps in scientific
and analytical information, EPA had issued less than ten NESHAPs over
a thirteen year period .
It was this lack of progress that lead Congress to adopt a new strategy
in 1990 and mandate that EPA take a more practical approach to reducing
emissions of toxic air pollutants. Moving away from the risk-based strategy,
new standards would be developed based on control technologies used
by source categories or industries. The resulting regulations
from EPA's mandate are known as Maximum Achievable Control Technology,
or MACT, standards.
The MACT approach had three components. In the first phase, EPA developed a
list of 188 hazardous air pollutants (HAPS) and the industries
or source categories emitting those pollutants were determined. This
created a matrix
of 174 different source categories covering major emitters of the
188 HAPS. EPA also designated a list of seven carcinogenic
or persistent bioaccumulative toxins (PBTs) which would be regulated.
Next, EPA began developing regulations—MACT standards—for these pollutant-source
combinations. The MACT standards required sources to meet specific
emissions limits that are based on emissions levels already being achieved
by similar sources in the country. To do this, EPA surveyed a source
category or industry and determined the top 12% best controlled facilities. For
categories with fewer than 30 sources, EPA looked at the top five, best
controlled facilities. From this information, EPA developed emission
standards based on the control technologies or operational practices
utilized by the "top" sources.
In its final phase, EPA will return to its risk-based approach to assess
how these technology-based emissions limits are reducing health and
environmental risks. Based on this assessment, EPA may implement additional
standards to address any significant remaining, or residual, health
or environmental risks. Click on the link to Emerging
Issues for more information about residual risk.
MACT standards generally apply to major
sources of hazardous air pollutants and some smaller sources,
also known as area sources. For a complete
list of MACT standards, Federal Register citations and compliance
dates, visit EPA's website at http://www.epa.gov/ttn/atw/mactfnlalph.html.
For information about NESHAP, MACT standards and their
applicability to your business, contact Lisa Higgins at (207)287-7023, Lisa.Higgins@Maine.gov.
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Useful Links
- Clean Air Act Rules and Implementation - U.S. EPA (http://www.epa.gov/ttn/atw/eparules.html)
A compendium of links to all EPA's websites related to air toxics,
NESHAP, MACTs, and implementation tools.
- Taking Toxics Out of The Air - U.S. EPA (http://www.epa.gov/oar/oaqps/takingtoxics/)
This document describes what air toxics are, where they come from,
and how they can impact people and the environment. It also
describes the steps being taken by the U.S. EPA to reduce emission
of air toxics from major industrial sources, such as chemical manufacturing
plants, petroleum refineries, and steel manufacturing plants.
- Air Toxics Risk Assessment Library - U.S. EPA (http://www.epa.gov/ttn/fera/risk_atra_main.html)
EPA is currently developing an air toxics risk assessment (ATRA)
reference library for conducting air toxics analyses at the facility
and community-scale. This three volume effort will provide information
on the fundamental principles of risk-based assessment for air toxics
and how to apply those principles in different settings as well as
strategies for reducing risk at the local level. Volumes 1 and 2
are completed and Volume 3 is currently being developed and is expected
to be available in late 2005.
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