Since Maricopa County’s redesignation to serious nonattainment of the National Ambient Air Quality Standard (NAAQS) for ozone, the Maricopa County Air Quality Department (MCAQD) has been working to correct deficiencies in its regulation of volatile organic compounds (VOCs), which are a precursor to ozone formation. As part of this effort, MCAQD is ratcheting down on the requirements of VOC-containing solvent cleaners, which are contained in Adopted Rule 331. As discussed in Trinity’s eNews article from June 2023, MCAQD initiated a rulemaking process to make changes such as lowering the threshold for “low-VOC cleaners”, removing exemptions for halogenated solvent cleaners, and more.

In July 2024, MCAQD released a draft notice of final rulemaking, following its June 2024 notice of proposed rulemaking. Since this rulemaking process began in early 2023, there have been various changes to the proposed rule’s language, so even if you have previously read about the Rule 331 rulemaking, read on to be sure you are up to date. But first, below is a summary of the key changes for those who may be reading about these proposed updates for the first time.

Summary of Key Proposed Changes to Rule 331

• Lowering the threshold for “low-VOC cleaners” from 50 g/l VOC to 25 g/l VOC

Rule 331 contains a partial exemption for cleaners that meet the definition of “low-VOC”. These low-VOC cleaners are not required to meet certain standards related to:

• Covers
• Draining
• Spraying
• Agitation
• Ventilation
• Non-vapor cleaning machines
• Recordkeeping
• And more…

Many facilities are currently taking advantage of these myriad exemptions for their low-VOC cleaners but will no longer be exempt for any cleaners above 25 grams of VOC per liter six months after this rule is finalized. Facilities should be prepared to either replace cleaners with those that meet the new definition or update their processes and recordkeeping to meet the requirements for non-exempt solvents.

• Removal of the total categorical exemption for sources regulated by National Emission Standards for Hazardous Air Pollutants (NESHAP) Subpart T – Halogenated Solvent Cleaning

NESHAP Subpart T applies to certain solvent cleaning machines that use methylene chloride (MeCl) perchloroethylene (PCE), trichloroethylene (TCE), 1,1,1-trichloroethane, carbon tetrachloride, or chloroform, or any combination of these halogenated solvents, in concentrations higher than 5 percent by weight. Sources that have to comply with this rule have historically been exempt from complying with MCAQD Adopted Rule 331. That will no longer be the case, and facilities in Maricopa County regulated under NESHAP Subpart T should be prepared to begin complying with Rule 331.

• Updating administrative requirements related to emissions control systems (ECS)

Rule 331 requires the use of ECS in certain cases. This proposed rule update adds a timeline for complying with such requirements (18 months to submit a compliance schedule and permit application and 36 months from permit issuance to fully comply with ECS requirements). It also clarifies requirements for recordkeeping and the operation and maintenance plan (O&M) required for the ECS.

Summary of Key Updates Since June 2023 Stakeholder Workshop

If you were familiar with the changes to Rule 331 that have been proposed during the rulemaking process, here are some recent developments to be aware of.

• Retaining solvent cleaning requirements for semiconductor manufacturing only in Rule 338

MCAQD is also in the process of revising Rule 338, which regulates semiconductor manufacturing. As part of these rulemakings, MCAQD planned to migrate solvent cleaning requirements that existed in Rule 338 to Rule 331. After receiving numerous public comments noting concerns about that approach, MCAQD in conference with EPA decided not to implement those changes. This means that semiconductor manufacturers who were worried about proposed changes to solvent cleaning provisions related to semiconductor manufacturing in Rule 331 can rest easy, there will be no such updates. However, be sure to stay on top of the proposed changes to Rule 338 which directly affect semiconductor manufacturers.

• Removal of exemptions for certain regulated sources

Currently, Rule 331 lists certain sources that are explicitly exempt from the rule. The initial proposed rule retained this list updating only the names of the rules (since some had changed since Rule 331 was last updated):

• Petroleum Solvent Cleaning (Rule 333)
• Architectural Coatings (Rule 335)
• Graphic Arts (Rule 337)
• Semiconductor Manufacturing (Rule 338)
• Automotive Windshield Washer Fluid (Rule 344)

In the notice of final rulemaking, MCAQD removed this provision entirely. This means that industries/cleaning operations regulated by any of the rules listed above are no longer automatically exempt from Rule 331. However, it is important to note that the provision that exempts cleanup of coating-application equipment subject to other rules is still in place. That includes Rule 336 (Surface Coating Operations and Industrial Adhesive Application Processes), Rule 342 (Coating Wood Furniture and Fixtures), and Rule 346 (Coating Wood Millwork).

• Modify certain ECS recordkeeping provisions in Rule 331 to match Rule 330 and Rule 338

Based on a comment received, MCAQD revised the Section 502.3 ECS recordkeeping provision in the proposed rule to be consistent with Rule 330 and Rule 338. The revision is as follows:

“For each day or period the O&M Plan requires maintenance, the owner or operator shall make a permanent record of the maintenance actions taken within 24 hours 3 business days of the maintenance completion.”

Conclusion

This article is not intended to provide an exhaustive list of the initial or recent proposed changes to Rule 331. It should, however, provide an idea of the types of changes facilities should be prepared for. Keep in mind that while this rulemaking is nearing the end of the process and is expected to be finalized in September or October, changes can continue to occur throughout the regulatory proceedings. If you would like help navigating these changes or discussing how they may impact your facility and any future facilities, please email Trinity’s Phoenix office or call 602.274.2900.