Clean Air Act Compliance: MACT and NSPS

The Clean Air Act (CAA) establishes the framework for protecting and improving air quality in the United States. It authorizes the U.S. Environmental Protection Agency (EPA) to set national standards that limit emissions from a wide range of sources—protecting public health, safeguarding the environment, and ensuring a level playing field across industries. Two programs most relevant to industrial facilities are the National Emission Standards for Hazardous Air Pollutants (NESHAP)—which include Maximum Achievable Control Technology (MACT) standards—and the New Source Performance Standards (NSPS).

MACT (Maximum Achievable Control Technology)

Under Section 112 of the Clean Air Act, the EPA regulates emissions of hazardous air pollutants (HAPs)—a group of 188 chemicals, including substances such as benzene and n-hexane, that are known to cause serious risks to human health and the environment. Facilities that emit 10 tons per year or more of a single HAP or 25 tons per year or more of combined HAPs are considered “major sources” and are required to comply with MACT standards.

MACT standards were introduced in the 1990 Clean Air Act Amendments to accelerate the reduction of HAPs by focusing on what the best-performing facilities in each industry were already achieving. The program was designed in two phases:

• Phase 1 – Technology-Based Standards: Initial requirements based on emission levels already being achieved by well-controlled, low-emitting facilities.
• Phase 2 – Residual Risk & Technology Review (RTR): Conducted periodically to determine whether more stringent, health-protective standards are needed to provide an ample margin of safety and to reflect advances in control technology.

Over the past decade, the RTR process has resulted in significant updates to several major MACT rules—including the Refinery Sector Rule (RSR), Ethylene MACT (EMACT), Miscellaneous Organic NESHAP (MON), and Hazardous Organic NESHAP (HON). These revisions have created new compliance obligations for facilities, from flare monitoring requirements and fenceline benzene monitoring to updated work practices for startup, shutdown, and malfunction (SSM) events.

Implementing a facility-specific MACT program can be complex. New and revised provisions often affect procedures, controls, monitoring, staffing, and budgeting. For example, the elimination of startup, shutdown, and malfunction (SSM) exemptions has required many operators to update procedures, add controls/monitoring, and plan for additional resources to maintain compliance.

TRICORD has helped many petroleum refineries, petrochemical plants, chemical facilities, and bulk gasoline terminals develop and implement compliance programs for the Refinery Sector Rule (RSR), Ethylene MACT (EMACT), Miscellaneous Organic NESHAP (MON), Hazardous Organic NESHAP (HON), and NESHAP R and BBBBBB (Subpart R & 6B).

Highlights from key NESHAP/MACT rule revisions we support:

• RSR
  • New/expanded controls for flares, DCUs, CRUs, storage tanks, and MPVs
  • No SSM exemptions for FCCUs/SRUs; alternative SSM limits for some sources
  • HCN and PM testing for FCCUs; flare combustion efficiency requirements
  • PRD and flaring minimization, event RCFA requirements
  • CPMS Monitoring Plans and Flare Management Plans (FMPs)
  • Refinery fenceline benzene monitoring and added work practice standards
• EMACT
  • Work practices tied to loss of SSM exemptions (e.g., furnace decoking, PRD management, maintenance vents)
  • Heat-exchanger/cooling water monitoring
  • Degassing standards for controlled storage vessels
  • Bypass prohibitions/monitoring for vent controls
  • New flare provisions, including alignment with RSR monitoring, CPMS plans, and EMACT-specific FMPs
• MON
  • Ethylene oxide (EtO) controls for process vents, tanks, and equipment “in EtO service”
  • SSM-related work practices (closed-vent bypasses, atmospheric PRDs, maintenance vents)
  • Heat-exchanger/cooling water monitoring and degassing standards for controlled tanks
  • Revised fugitive monitoring
  • Direct application (with clarifications) of RSR flare requirements for certain EtO/MCPU scenarios
  • Electronic reporting additions
• HON
  • Focused requirements for equipment “in EtO or chloroprene service”
  • SSM-related work practices (closed-vent bypasses, atmospheric PRDs, maintenance vents)
  • Enhanced fugitive monitoring for EtO service
  • Fenceline monitoring for specified toxics (e.g., benzene, 1,3-butadiene, chloroprene, EDC, vinyl chloride, EtO)
  • Updated process vent definition (TRE calculation no longer required for process vents)
  • Alignment with RSR flare monitoring and expanded electronic reporting
• Subpart R & 6B
  • New LDAR program equipment leak detection requirements using Method 21 or Optical Gas Imaging (OGI)
  • Fitting controls on gasoline storage vessels
  • Internal floating roof LEL monitoring

Other NESHAP/MACT subparts we commonly support:

• HH (onshore/offshore oil & gas production)
• HHH (natural gas transmission and storage facilities)
• YYYY (turbines)
• ZZZZ (engines)
• DDDDD (boilers)

NSPS (New Source Performance Standards)

Under Section 111 of the Clean Air Act, the EPA developed the New Source Performance Standards (NSPS) program to ensure that new, reconstructed, and modified sources in specific industries incorporate modern, proven emission controls from the outset. Unlike MACT, which targets hazardous air pollutants, NSPS generally applies to non-hazardous regulated pollutants such as particulate matter, sulfur dioxide, nitrogen oxides, and volatile organic compounds.

The standards are based on the performance of the best system of emission reduction that has been adequately demonstrated, taking into account both cost and feasibility. This “best demonstrated technology” approach allows NSPS to drive continuous improvement in pollution control while providing flexibility for industry.

Importantly, Section 111(d) extends EPA’s authority to regulate certain existing sources of “designated pollutants”—those that are neither hazardous air pollutants (HAPs) nor criteria pollutants covered by the National Ambient Air Quality Standards. This gives EPA a mechanism to address pollutants that otherwise fall between the cracks of existing regulatory programs.

For industry, NSPS represents a forward-looking compliance obligation. Any new construction, equipment replacement, or facility modification can trigger applicability, meaning that early planning is critical. Identifying which NSPS subparts apply and integrating those requirements into design, permitting, and operational decisions helps avoid costly compliance issues later.

At TRICORD, we work with clients across a wide range of NSPS categories—including steam generating units, petroleum refineries, storage tanks, equipment leaks, engines, and oil and gas facilities—to evaluate applicability, develop compliance strategies, and ensure facilities stay aligned with the most current requirements.

Common NSPS subparts we support:

• D-series (steam generating units)
• J/JJ/Ja-series (petroleum refineries)
• K/Ka/Kb-series (storage tanks)
• VV / GGG-series (equipment leaks in SOCMI/refining)
• XX/XXa (bulk gasoline terminals)
• NNN / RRR-series (SOCMI distillation/reactors)
• IIII / JJJJ (engines)
• OOOO/OOOOa/OOOOb/OOOOc (oil & gas)

TRICORD is available to help your facility evaluate existing compliance and update your program to meet the most current requirements of these regulations.

Check out our Services page for a more comprehensive list of service offerings or email one of our MACT and NSPS service leaders below.