Section 49.4173 - VOC emissions control requirements for storage vessels(a)Applicability. The VOC emissions control requirements of this section apply to storage vessels at an oil and natural gas source (as specified in § 49.4169(b) ) as follows:(1) For oil and natural gas sources that began operations before February 6, 2023, the VOC emissions control requirements of this section apply when the source-wide potential for VOC emissions from the collection of all storage vessels, glycol dehydrators, and pneumatic pumps is equal to or greater than 4 tpy, as determined according to this section. The potential for VOC emissions must be calculated using a generally accepted model or calculation methodology, based on the maximum average daily throughput determined for a 30-day period of production during the 12 months before the compliance deadline for the affected source under this rule. The determination may take into account requirements under a legally and practicably enforceable limit in an operating permit or other federally enforceable requirement. You must reevaluate the source-wide VOC emissions from the collection of all storage vessels, glycol dehydrators and pneumatic pumps for each modification to an existing source; or(2) For oil and natural gas sources that began operations on or after February 6, 2023, the VOC emissions control requirements of this section apply upon startup of operation.(3) Modification to an oil and natural gas source requires a re-evaluation of the source-wide VOC emissions from the collection of all storage vessels, glycol dehydrators and pneumatic pumps. Adding production from a new well or increasing production at an existing well is considered a modification of a well site. Increasing maximum throughput at a tank battery, compressor station or natural gas processing plant is considered a modification.(b)Exemptions.(1) This section does not apply to storage vessels located at an oil and natural gas source that are subject to the emissions control requirements for storage vessels in 40 CFR part 60, subparts OOOO or OOOOa, or 40 CFR part 63, subpart HH.(2) This section does not apply to an emergency storage vessel located at an oil and natural gas source, if it meets the following requirements:(i) The emergency storage vessel is not used as an active storage vessel;(ii) The owner or operator empties the emergency storage vessel no later than 15 days after receiving fluids;(iii) The emergency storage vessel is equipped with a liquid level gauge or equivalent device; and(iv) Records are kept of the usage of each emergency storage vessel as required in § 49.4183(a)(3) , including the date the vessel received fluids, the volume of fluids received in barrels, the date the vessel was emptied, and the volume of fluids emptied in barrels.(3) This section does not apply to storage vessels that are removed from service. If you remove a storage vessel from service, you must comply with paragraphs (b)(3)(i) through (iii) of this section.(i) For a storage vessel to be removed from service, you must comply with the requirements of paragraphs (b)(3)(i)(A) and (B) of this section. (A) You must completely empty and degas the storage vessel, such that the storage vessel no longer contains crude oil, condensate, intermediate hydrocarbon liquids or produced water. A storage vessel where liquid is left on walls, as bottom clingage, or in pools due to floor irregularity is considered to be completely empty.(B) You must keep records as required in § 49.4183(a)(4) , identifying each storage vessel removed from service and the date of its removal from service.(ii) If a storage vessel identified in paragraph (b)(3)(i)(B) of this section is returned to service, you must determine its applicability as provided in paragraph (a) of this section, and you must keep records as required in § 49.4183(a)(4) , identifying the storage vessel and the date of its return to service.(c)VOC emission control requirements. For each storage vessel, you must comply with the VOC emissions control requirements of paragraph (c)(1) or (c)(2) of this section.(1) You must reduce VOC emissions from each storage vessel by at least 95.0 percent on a continuous basis according to paragraph (c)(1)(i) or (ii) of this section. You must equip each storage vessel with a cover that meets the conditions specified in § 49.4176(c) , and must route all flashing, working, standing and breathing losses from the storage vessels through a closed-vent system that meets the conditions specified in § 49.4176(d) to: (i) An operating system designed to recover 100 percent of the emissions and recycle them for use in a process unit or incorporate them into a product; or(ii) An enclosed combustor or flare that is designed to reduce the mass content of VOC in the natural gas emissions vented to the device by at least 95.0 percent and that is operated as specified in § 49.4177 ;(2) You must maintain the source-wide uncontrolled actual VOC emissions from the collection of all storage vessels, glycol dehydrators, and pneumatic pumps at an oil and natural gas source at less than 4 tpy. Before using the uncontrolled actual VOC emission rate for compliance purposes, you must demonstrate that the uncontrolled actual VOC emissions have remained at less than 4 tpy, as determined monthly for 12 consecutive months. After such demonstration, you must determine the uncontrolled actual VOC emission rate each month. The uncontrolled actual VOC emissions must be calculated using a generally accepted model or calculation methodology. Monthly calculations must be based on the average throughput of the source for the month. Monthly calculations must be separated by at least 14 days. You must comply with paragraph (c)(1) of this section within 30 days of the monthly emissions determination required in this section if the determination indicates that VOC emissions from the collection of all storage vessels, glycol dehydrators, and pneumatic pumps at your oil and natural gas source increased to 4 tpy or greater.(3) Except as provided in paragraph (c)(4) of this section, if you use a control device to reduce emissions from your storage vessels, you must equip each storage vessel with a cover that meets the requirements of § 49.4176(c) .(4) If you use a floating roof to reduce emissions, you must meet the requirements of § 60.112b(a)(1) or (2) and the relevant monitoring, inspection, recordkeeping, and reporting requirements in 40 CFR part 60, subpart Kb.(5) After a minimum of 12 consecutive months of operation at a source that begins operation on or after February 6, 2023, controls may be removed if the source-wide uncontrolled actual VOC emissions from the collection of all storage vessels, glycol dehydrators, and pneumatic pumps has been maintained at a rate less than 4 tpy, as determined according to paragraph (c)(2) of this section.