Proposed Changes to Storage Tanks New Source Performance Standards

The U.S. Environmental Protection Agency (U.S. EPA) recently proposed changes to the “Standards of Performance for Volatile Organic Liquid Storage Vessels (Including Petroleum Storage Vessels).” These changes to the New Source Performance Standards (NSPS) include proposed revisions to 40 CFR Part 60, Subpart Kb, applicable to sources that commenced construction, reconstruction, or modification after July 23, 1984, and a new Subpart Kc that will apply to sources that commence construction, reconstruction, or modification after October 4, 2023. U.S. EPA packed a significant amount of information and changes into about 20 pages of a Federal Register notice. This article provides an overview of the proposed amendments.

Applicability

40 CFR Part 60, Subpart Kb applies to storage vessels above certain capacity thresholds that store volatile organic liquids (VOLs) above a maximum true vapor pressure threshold. Subpart Kb contains another set of thresholds for storage vessels that require control. For Subpart Kc, U.S. EPA is proposing to eliminate the use of a vapor pressure threshold for regulated storage vessels and instead determine applicability based solely on the size of the storage vessel. U.S. EPA is, however, proposing to retain the vapor pressure threshold concept to determine which storage vessels must install controls. The tables below present the proposed applicability and control criteria.

Comparison of Rule Applicability Criteria

Comparison of Control Requirement Thresholds

U.S. EPA is proposing to carry over most of the exemptions specified 40 CFR §60.110b(d) to the new Subpart Kc, with the exception of storage vessels subject to 40 CFR Part 63, Subpart GGGG (National Emission Standards for Hazardous Air Pollutants: Solvent Extraction for Vegetable Oil Production) on the basis that the proposed Subpart Kc improves upon Subpart GGGG. Consistent with Subpart Kb, the proposed definition of storage vessel in Subpart Kc does not include process tanks.

Control Requirements for Subpart Kc: Storage Vessels Containing VOL with a Maximum True Vapor Pressure less than 11.1 psia.

For new or reconstructed affected storage vessels that contain a VOL with a maximum true vapor pressure less than 11.1 psia, U.S. EPA is proposing to revise the existing Kb requirements in a new Subpart Kc such that an internal floating roof (IFR) must be equipped with either a liquid-mounted or mechanical shoe type primary seal and be equipped with a rim-mounted secondary seal. Gauge hatches and sample ports must be gasketed and guidepole configurations must incorporate the provisions outlined in the 2000 U.S. EPA Storage Tank Emissions Reduction Partnership program.

U.S. EPA is also proposing to update the requirements for an external floating roof (EFR) storage vessel used as an alternative to an IFR. U.S. EPA is proposing that:

• EFRs must have a primary and secondary seal as specified for IFRs, in addition to welded seams.
• If unslotted guidepoles are used, they must be equipped with gasketed sliding covers and pole wipers.
• If slotted guidepoles are used, a liquid mounted primary seal must be used and the slotted guidepoles must have a gasketed sliding cover, pole sleeve, and pole wiper.

Facilities that plan to use an EFR as an alternative compliance method should review the proposed Subpart Kc rule language for other equipment design requirements.

Similar to Subpart Kb, U.S. EPA is proposing to retain the option to use a closed vent system (CVS) and a control device as an alternative to using an IFR in Subpart Kc; however, the Agency is proposing to increase the required control efficiency from a 95% to a 98% reduction in emissions. Additionally, U.S. EPA is proposing requirements for design and operation of CVSs as detailed below for storage vessels that contain VOL with a maximum true vapor pressure of 11.1 psia or more.

New for Subpart Kc, a “modification” would include storing a VOL that has a higher maximum true vapor pressure than the VOL previously stored. This is contrary to U.S. EPA’s previous interpretation of the exemptions at 40 CFR §60.14(e)(4) that a change in the type of material stored was not a modification if the storage vessel was capable of accommodating the new material. There are sure to be numerous comments on this proposed change.

U.S. EPA is proposing that modified storage vessels that store a VOL with a maximum true vapor pressure less than 11.1 psia that do not have an EFR, or that do not route emissions to a control device, must meet the requirements for IFRs described above.  If the modified storage vessel has an existing internal or external floating roof, it can alternatively meet the requirements of Subpart Kb for IFRs or EFRs, as applicable.  If the modified storage vessel routes emissions to a control device, the source would be required to reduce inlet volatile organic compound (VOC) emissions by 98% or greater under Subpart Kc (Subpart Kb requires a reduction of 95%).

Control Requirements for NSPS Subpart Kc: Storage Vessels Containing VOL with a Maximum True Vapor Pressure of 11.1 psia or More.

For new, modified, or reconstructed storage vessels that contain a VOL with a maximum true vapor pressure of 11.1 psia or more, U.S. EPA is proposing that emissions must be routed through a CVS to a control device achieving at least 98% control, as opposed to 95% in Subpart Kb. Furthermore, U.S. EPA is proposing the following requirements for the storage vessels, CVSs, and control devices:

• The storage vessels must be designed and operated to have a gauge pressure no less than 1 psi greater than the maximum true vapor pressure of the VOL and anticipated back pressure.
• Vacuum breakers must have a close pressure of no less than 0.1 pounds per square inch gauge (psig) vacuum.
• Unless the CVS is operated under vacuum, the CVS must operate with “no detectable emissions” demonstrated by a leak definition of 500 parts per million by volume (ppmv) above background. U.S. EPA is proposing that sensory monitoring (e.g., visible, audible, olfactory inspection) be performed quarterly, and Method 21 monitoring be conducted at least annually.
• Bypasses of the CVS or control device must be monitored.
• Any pressure relief device must be equipped with a monitoring device to identify pressure releases, notify operators of a release, and record the time and duration of the release.
• If emissions are routed to a flare, U.S. EPA is proposing that the flare meet the requirements in 40 CFR §63.670 (i.e., the enhanced flare provisions in the refinery sector rule).

Monitoring Requirements for NSPS Subpart Kc

In addition to the monitoring requirements described above for CVSs, bypasses, and pressure relief devices, U.S. EPA is proposing several monitoring updates for Subpart Kc to ensure compliance with the emissions standards. These include monitoring the vapor concentration of the air space above IFRs against the lower explosive limit (LEL) annually to assess the condition of the IFR and closure systems. In addition, U.S. EPA is proposing that floating roofs be equipped with alarms to indicate when the roof is approaching the specified landing height. Other significant proposed updates to monitoring requirements include a requirement to repeat control device performance tests every 5 years and a requirement to establish and comply with operating parameter monitoring limits on a rolling 3-hour average basis.

Perhaps one of the most significant revisions to monitoring requirements compared to Subpart Kb is the proposed change to require periodic testing for liquid vapor pressure for all VOL of variable composition, instead of just waste mixtures, for tanks storing VOL that are subject to the rule, but not otherwise subject to control. As mentioned earlier in this article, U.S. EPA is proposing to eliminate the vapor pressure threshold criteria for Subpart Kc applicability. Thus, facilities storing VOL with very low vapor pressures but variable composition will be required to conduct physical testing for vapor pressure every 6 months.

Startup, Shutdown, and Malfunction Requirements for NSPS Subpart Kc

In addition to the changes described above, U.S. EPA is addressing startup and shutdown emissions through the application of degassing requirements for storage vessels complying with the CVS and control device option (or requirement), and for any vessel with a design capacity of 1 million gallons or more that contains a VOL with a maximum true vapor pressure of 1.5 psia or more. EPA is proposing that these storage vessels must be degassed to a control device that reduces VOC emissions by 98% or more.

U.S. EPA is not proposing any separate allowance or exemption for malfunction events. U.S. EPA explains in the preamble to the proposed rule that discretion will be used in the application of enforcement to malfunction events, and that sources are able to raise defenses in enforcement cases before a court.

Additional Changes and Compliance Dates

U.S. EPA is proposing additional changes for both Subparts Kb and Subpart Kc. These changes include updates to analytical methods and the use of electronic reporting. U.S. EPA is proposing the specified reports required under Subpart Kb be submitted as PDF documents to the Compliance and Emissions Data Reporting Interface (CEDRI). Under Subpart Kc, facilities would be required to use Microsoft Excel reporting templates to submit reports via CEDRI.

Additionally, in Subpart Kc U.S. EPA is proposing to supersede the semi-annual reporting requirements under 40 CFR §60.7. U.S. EPA is proposing separate semi-annual reporting requirements that include:

• Storage vessel and compliance option identification;
• Whether a storage vessel was inspected during the reporting period;
• Dates that storage vessels were last emptied and degassed;
• Identification and details regarding required inspections;
• Indications as to whether floating roofs were repaired, replaced, or taken out of service;
• Information related to landing of floating roofs;
• Inspections of CVSs and instances where a continuous monitoring system (CMS) indicates operation outside the range of an established monitoring parameter;
• Information on the operation of a flare used to control emissions; and
• Information on releases from pressure relief devices and bypasses.

These semi-annual reports would be due on a scheduled based on the date the storage vessel first becomes an affected source under Subpart Kc. This could potentially lead to multiple reporting timelines for facilities with more than one affected source, prompting facilities to consider using the procedures in 40 CFR §60.19 to adjust reporting deadlines.

U.S. EPA is proposing affected sources would be required to comply with the changes upon publication of the final rule. Comments on the proposed rule are due by November 20, 2023. The final rule should be signed by September 30, 2024.

What do the Proposed Changes Mean for You?

Although we’ve condensed them into a few paragraphs, there are numerous changes to the NSPS storage vessel requirements coming in the future. As described above, U.S. EPA is proposing the applicability of Subpart Kc would be triggered by the storage of a VOL with a higher vapor pressure than that currently stored; therefore, facilities should carefully read and understand the proposed requirements prior to changing their storage vessel service in case this requirement is finalized as proposed. Environmental professionals at facilities should communicate now with operations staff about the implication of such a service change to avoid being caught off-guard in the future.

Have questions about the new requirements? Or need help determining future permitting changes required as a result? Don’t hesitate to reach out to me, Philip Crawford at pcrawford@all4inc.com, or your ALL4 project manager for additional information.