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Frequently Asked Questions: National Emission Standards for Hazardous Air Pollutants (NESHAP)

The U.S. EPA issues National Emission Standards for Hazardous Air Pollutants (NESHAPs) that are categorized as either MACT or GACT. For general information about NESHAPs, visit our air toxics page.

HAP = hazardous air pollutant
MACT = maximum achievable control technology
GACT = generally available control technology

How do I determine if any NESHAPs apply to a facility?

Visit EPA's MACT schedule [exit DNR] periodically to stay informed about MACT standards. The website includes proposed rule dates and promulgation dates listed alphabetically by MACT category. MACT standards generally apply to major sources of the federally regulated HAPs. Similarly, for area sources visit EPA's Area Source Standards [exit DNR] to learn about the GACT standards. Area sources are those with emissions below the major source level.

How do I determine if a facility is a major source of HAPs?

A major source has the potential to emit more than 10 tons per year of any single HAP or 25 tons per year of any combination of HAPs. Note that "potential to emit" is the theoretical maximum emissions from the facility operating at full capacity 24 hours per day, seven days per week. For assistance determining if a facility is a major source of HAPs, please contact the Small Business Environmental Assistance Program, the DNR compliance engineer or enlist the help of a private consultant.

When must sources comply with a NESHAP?

Existing sources typically must comply within three years of the date the EPA issues the standard. Three years are provided for the source to explore compliance options. An existing NESHAP-affected source must usually submit an initial notification to the DNR within 120 days of the date the EPA issues the standard. New sources need to comply at startup.

Each NESHAP requires an affected source to submit an initial notification to the regulating agency to indicate that they are affected. Other notifications are often required as well, including an initial Notification of Compliance Status and in some cases annual notifications of compliance. Most of the NESHAP now require that notifications are submitted through EPA's Electronic Reporting Tool (ERT) [exit DNR]. To check whether the NESHAP affecting a facility requires reporting to ERT, please refer to EPA's Electronic Data Reporting [exit DNR], and look in the column under 40 CFR Part 63 for the Subpart title for the affected NESHAP.

In addition, for some older NESHAP the delegation for the general provisions of 40 CFR Part 63 (which includes reporting for notifications) was delegated to the DNR through NR 460, Wis. Adm. Code [PDF exit DNR].

If a facility has NESHAP requirements in a permit OR is affected by a NESHAP that was final prior to May 2007 (that has not yet made it into the permit via revision or renewal), the facility should also submit a paper copy of the notification to:

Wisconsin DNR
Air Management Program - AM/7
ATTN: MACT Notifications
PO Box 7921
Madison WI 53707-7921

Do MACTs offer emission control options?

MACTs typically offer several emission control options, and each option includes extensive testing, monitoring, record keeping and reporting requirements. Emission reductions may be achieved through measures that:

  • require a process change, a substitution of material or the reuse or recycling of material;
  • specify design, equipment, work practice or operational methods;
  • require operator training; or
  • require collection, capture and treatment of pollutants emitted by a process.

Affected source operators may also comply by changing or limiting their operations so that the MACT would not apply to their revised operations, with some qualifications:

  • The change or limit in operation must be completed before the MACT compliance date; otherwise, EPA's "Once-In-Always-In" policy applies and the source is required to comply with the MACT. (See EPA's guidance on when a major source can become an area source.)
  • Sources that change or limit their operations must have this limit written into a federally enforceable document (typically an operation permit under Chapter NR 407, Wis. Adm. Code) that is issued before the MACT compliance date. Please remember that it takes time to process a permit or other enforceable document that would establish limits to allow a source to avoid a MACT. For example, Federally Enforceable State Operation Permits (FESOPs) require a 30-day public review and may be subject to public hearing requests.
Where can I find more information on the EPA's "Once-In-Always-In" policy?

The EPA issued a guidance memo in 1995, referred to as the "Once-In-Always-In" policy, which offers guidance on MACT standard applicability. This guidance was recently reversed in a new EPA guidance memo dated Jan. 25, 2018 [PDF exit DNR].

The following fact sheet provides more information on EPA's "Once-In-Always-In" policy and EPA's recent guidance memo.

How are operation permits handled under MACT?

The federal operation permit program under Title V of the Clean Air Act establishes that air pollution control requirements, such as MACT standards are to be incorporated as conditions of a facility's operation permit. If a source already has an operation permit and is subject to a MACT that was finalized after the permit was issued, the MACT requirements would be added to their operation permit as part of their five-year permit renewal.

Sources that want to take emission limits to avoid a MACT should submit a permit application to the DNR or amend their application requesting the emission limits at least six months before the MACT compliance date.

Can a facility avoid a MACT with a compliance date that comes before the source's permit renewal date?

Yes. The source can ask the DNR for a permit revision/renewal before the MACT compliance date. This revision/renewal would contain emission limits the source agrees to meet in order to avoid the MACT. The source should allow at least six months for the DNR to process the revision/renewal.

Sources that do not have an operation permit yet and want to take limits to avoid a MACT may need to amend their permit application to indicate their desire to take limits to avoid the MACT. The permit application should indicate that the source wants their permit issued before the MACT compliance date and specify the appropriate date.

What is the status of residual risk assessments?

The Clean Air Act directs the EPA to conduct risk assessments on each source category subject to MACT standards and to determine if additional standards are needed to reduce risk. The EPA has released the results of the risk review for many of the MACT standards and will be developing additional standards as needed to protect public health over the next few years. They have also changed the name for this activity from "Residual Risk" to Risk and Technology Review (RTR) [exit DNR].