In one of its few major Clean Air Act (CAA) rulemaking actions that is not deregulatory, the Trump EPA is proposing to add significant requirements to its existing National Emissions Standards for Hazardous Air Pollutants (NESHAP) for the Miscellaneous Organic Chemical Manufacturing source category. Called the MON, the existing rule covers an estimated 201 facilities that manufacture a wide range of chemicals and products not subject to another NESHAP. Probably the most consequential part of the proposal would impose new obligations on eight facilities that process ethylene oxide. The rule is part of an EPA strategy to reduce human exposure to ethylene oxide; in 2016, the Agency said it agreed with research that found that the cancer risk to people exposed to ethylene oxide emissions was far higher than previously believed.

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Residual risk and technology review

Promulgated in 2003 (and amended in 2005 and 2006), the initial MON set emissions limits for miscellaneous organic chemical manufacturing process units (MCPUs)—for regulatory purposes, MCPUs include any assigned storage tanks and transfer racks; equipment in open systems that convey or store water having the same concentration and flow characteristics as wastewater; and components such as pumps, compressors, agitators, pressure relief devices, sampling connection systems, open-ended valves or lines, valves, connectors, and instrumentation systems.

The CAA requires that the EPA review all existing NESHAPs to determine if they continue to protect human health and the environment with an ample margin of safety and to make revisions if, in the opinion of the administrator, that level of safety is not being achieved. The Agency must also review any new technological developments to determine if the NESHAP should adopt requirements based on those developments; the technology review must consider cost, energy requirements, and non-air quality health and environmental impacts.

Cancer risk unacceptably high

The basic NESHAP health standard is that no NESHAP may result in the most exposed individual having a lifetime maximum individual cancer risk (MICR) greater than 100 in 1 million. For the MON, the Agency’s risk assessment found the MICR posed by the source category is 2,000 in 1 million. According to the EPA, the MICR is “driven by ethylene oxide emissions from storage tanks (75 percent), equipment leaks (15 percent), and process vents (8 percent).” Approximately 18,000 individuals are exposed to cancer risks greater than 100 in 1 million for actual and allowable emissions from the MON source category.

Proposed amendments

To address the unacceptable risk, the EPA’s proposal includes the following amendments to the MON:

• Process vents. Either reduce emissions of ethylene oxide by (1) venting emissions through a closed-vent system to a control device that reduces ethylene oxide by greater than or equal to 99.9 percent by weight, or to a concentration less than 1 part per million by volume (ppmv) for each process vent, or to less than 5 pounds per year for all combined process vents; or (2) venting emissions through a closed-vent system to a flare meeting the proposed flare operating requirements.
• Storage tanks. Either reduce emissions of ethylene oxide by (1) venting emissions through a closed-vent system to a control device that reduces ethylene oxide by greater than or equal to 99.9 percent by weight or to a concentration less than 1 ppmv for each storage tank vent; or (2) venting emissions through a closed-vent system to a flare meeting the proposed flare operating requirements.
• Equipment leaks. Two compliance options are proposed. Option 1—all light liquid pumps in ethylene oxide service must be monitored monthly at a leak definition of 1,000 ppm, and when a leak is detected, it must be repaired as soon as practicable but not later than 15 calendar days after it is detected. Under Option 2, pumps in ethylene oxide service would be required to be leakless (i.e.,have zero emissions) and monitored annually to verify there are no emissions. Additionally, valves in ethylene oxide service would be required to either be leakless and monitored annually or not be leakless and be monitored quarterly. Option 2 applies to MON facilities that have been linked to an MICR exceeding 100 in 1 million.
• Flares. The proposal would amend the operating and monitoring requirements for a subset of flares used as air pollution control devices in MON facilities. This subset includes flares that either (1) control ethylene oxide emissions, (2) control emissions from processes that produce olefins, or (3) control emissions from processes that produce polyolefins. The Agency has determined that the current requirements for flares in this subset are not adequate to ensure the level of destruction efficiency needed to conform with the maximum achievable control technology (MACT) standards in the MON.

Other parts of the proposal correct and clarify regulatory provisions related to emissions during periods of startup, shutdown, and malfunction (SSM) and require facilities to electronically submit copies of notification of compliance status reports and copies of performance test results and reports.

Benefits and costs

The Agency estimates that the proposed amendments (not including potential excess emissions reductions from flares) would reduce hazardous air pollutant (HAP) emissions from the MON source category by 116 tons per year (tpy), including a reduction in ethylene oxide emissions by approximately 10 tpy. The proposed flare requirements would result in additional emissions reductions of 260 tpy of HAPs.

The EPA estimates the proposal would result in $42 million in capital costs and $12.6 million in annual costs for all MON-regulated sources.

All affected sources would be required to comply with all the amendments no later than 3 years after the effective date of a final rule, or upon start-up, whichever is later.