1. (a) Compatibility -- Underground storage tank systems must be constructed of or lined with materials compatible with the stored hazardous substance. Materials used in construction or repairs must be compatible with the materials used to construct the underground storage tank system and must not be subject to deterioration due to contact with hazardous substances stored.

   1. (1) Owners or operators must demonstrate compatibility using the following documentation:

      1. (A) Primary containment and integral secondary containment:

         1. (i) An independent testing organization approval for compatibility with the hazardous substances stored; or
         2. (ii) An independent testing organization approval and a manufacturer's affirmative statement of compatibility with the hazardous substances if those substances are not listed by the independent testing organization.

      2. (B) Non-integral secondary containment:

         1. (i) An independent testing organization approval for compatibility with the hazardous substances stored;
         2. (ii) An independent testing organization approval and a manufacturer's affirmative statement of compatibility with the hazardous substances if those substances are not listed by the independent testing organization;
         3. (iii) An engineering specification approved by a California registered professional engineer demonstrating compatibility with the hazardous substances stored; or
         4. (iv) An industry code or engineering standard demonstrating compatibility with the hazardous substances stored.

      3. (C) Spill containment, overfill prevention equipment, and ancillary equipment:

         1. (i) An independent testing organization approval for compatibility with the hazardous substances stored;
         2. (ii) A manufacturer's affirmative statement of compatibility with the hazardous substances stored;
         3. (iii) Approval by a California registered professional engineer; or
         4. (iv) An industry code or engineering standard demonstrating compatibility with the hazardous substances stored.

      4. (D) Release detection equipment:

         1. (i) An independent third party approval for compatibility with the hazardous substances stored; or
         2. (ii) A manufacturer's affirmative statement of compatibility with the hazardous substances stored.
   2. (2) Documentation of the underground storage tank system's compatibility with the hazardous substance stored must be maintained for as long as the system is used to store the hazardous substance.
   3. (3) An affirmative statement of compatibility made by a manufacturer will no longer satisfy the compatibility requirements of paragraph (1) if it conflicts with a later determination by an independent testing organization or independent third party evaluation on the compatibility of the hazardous substance stored or to be stored.
   4. (4) At least 30 days before beginning to store or changing the hazardous substance currently stored, the owner or operator must demonstrate compliance with this section by notifying the Unified Program Agency in writing. The notification must identify the substance to be stored, the earliest date storage of the substance may begin, and include, for all components used to construct the underground storage tank system and which may come into contact with the hazardous substance, the documentation specified in paragraph (1).
   5. (5) Except as provided in paragraph (6), diesel containing up to 20 percent biodiesel meeting ASTM D7467, is recognized as equivalent to diesel for purposes of satisfying this subdivision; paragraphs (2), (3), and (4) of subdivision (b); and section 2651(c)(1) for all underground storage tank systems.
   6. (6) The exception in paragraph (5) may not be used for any material or component of the underground storage tank system which the applicable approver has determined not compatible with diesel containing up to 20 percent biodiesel meeting ASTM D7467.

2. (b) Containment -- Underground storage tanks must have primary and secondary containment that meets the requirements of this section.

   1. (1) Primary containment must be product tight. Secondary containment may be manufactured as an integral part of the primary containment or constructed as a separate containment system. Secondary containment must be designed and constructed such that the secondary containment can be monitored in accordance with sections 2651 and 2652, and tested in accordance with section 2666.
   2. (2) The design and construction of all primary containment, including any integral secondary containment and all other components used to construct the primary containment that may come into contact with the hazardous substance stored, such as special accessories, fittings, coatings or linings, must be approved by an independent testing organization.

   3. (3) Secondary containment which is not an integral part of primary containment must be constructed, operated, and maintained in accordance with an engineering specification approved by an independent testing organization or approval by a California registered professional engineer. The engineering specification must include the construction, testing, and maintenance procedures. Materials used to construct the secondary containment must have sufficient thickness, density, and corrosion resistance to prevent structural weakening or damage to the secondary containment as a result of contact with any released hazardous substance. The following requirements apply to non-integral secondary containment:

      1. (A) The secondary containment must be constructed to contain at least the following volumes:

         1. (i) One hundred percent of the usable capacity of the primary containment where only one primary container is within the secondary containment.
         2. (ii) In the case of multiple primary containers within a single secondary containment, the secondary containment must be large enough to contain 150 percent of the volume of the largest primary container within it, or 10 percent of the aggregate internal volume of all primary containers within the secondary containment, whichever is greater. When all primary containers are completely enclosed within the secondary containment, the restrictions of this subparagraph do not apply.
      2. (B) If the secondary containment is open to rainfall, it must be constructed, operated, and maintained to accommodate the volume of precipitation which could enter the secondary containment during a 24-hour, 25-year storm in addition to the volume specified in subparagraph (A).
      3. (C) If backfill material is placed in the secondary containment, the volumetric requirements for the pore space must be equal to the requirement in subparagraph (A). The available pore space in the secondary containment backfill must be determined using standard engineering methods and safety factors. The specific retention and specific yield of the backfill material, the location of any primary container within the secondary containment, and the proposed method of operation for the secondary containment must be considered in determining the available pore space.
      4. (D) The secondary containment must be equipped with a collection system to accumulate, temporarily store, and allow removal of any liquid within the system.
   4. (4) Secondary containment must be constructed, operated, and maintained so that any loss of liquid hazardous substance from the primary containment will be detected by an interstitial monitoring device or visual monitoring method and readily demonstrate continuity within a zone.
   5. (5) Underground storage tanks with integral secondary containment which satisfies the construction requirements of subdivision (b)(2) fulfill the volumetric requirements for secondary containment specified in subparagraph (b)(3)(A).
   6. (6) Laminated, coated, or clad materials are single-walled and do not fulfill the requirements of both primary and secondary containment.
   7. (7) Two or more primary containment systems must not use the same secondary containment if the primary containment systems store materials that in combination may cause a fire or explosion, or the production of a flammable, toxic, or poisonous gas, or the deterioration of any part of the primary or secondary containment.
   8. (8) An underground storage tank constructed with integral secondary containment must provide 100 percent secondary containment. The tank may be single-walled up to 12 inches away from the top center line of the tank if it is equipped with overfill prevention equipment such that the hazardous substance cannot contact any portion of the single-walled construction.
   9. (9) All piping secondary containment must be sloped so that all releases will flow to a containment sump located at the low point of the secondary containment.

   10. (10) All connected piping must be secondarily contained except unburied fuel delivery piping at marinas exempt pursuant to section 2612(n), unburied fuel piping connected to an emergency tank system exempt pursuant to section 2612(o), and the following:

       1. (A) Vent and tank riser piping attached to Type 1 underground storage tanks, provided the tank is equipped with overfill prevention equipment meeting the requirements specified in subparagraph (B) or (C) of subdivision (f)(1);
       2. (B) Vapor recovery piping attached to Type 1 underground storage tanks if constructed to not contain liquid-phase hazardous substance; and

       3. (C) Suction piping attached to Type 1 underground storage tanks that meets all the following:

          1. (i) The piping operates at less than atmospheric pressure;
          2. (ii) The piping is sloped so that the contents of the pipe will drain back into the tank if the suction is released;
          3. (iii) No valves or pumps are installed in the suction line other than one check valve located directly below and as close as practical to the suction pump; and
          4. (iv) An inspection has demonstrated, as approved by the Unified Program Agency, compliance with clauses (i) through (iii), and documentation of the inspection is maintained in accordance with section 2613. The inspection method must be configured such that compliance with clauses (i) through (iii) can be periodically demonstrated.
3. (c) Corrosion Protection -- The outer surface of an underground storage tank system constructed of steel must be protected from corrosion through cathodic protection or isolation from the backfill. Field-installed cathodic protection systems must be designed and certified as adequate by a corrosion specialist. Criteria used to determine that cathodic protection is adequate as required by this section must be in accordance with a code of practice developed in accordance with voluntary consensus standards.
4. (d) Striker Plates -- The primary containment of the tank must have wear plates (striker plates) installed, center to center, below all accessible openings. The plates must be made of steel or other appropriate material. The width of the plates must be at least eight inches on each side or must be equal to the area of the accessible opening or guide tube, whichever is larger. The thickness of the steel plates must be at least 1/8 inch and those made of other materials must be of sufficient thickness to provide equivalent protection. A drop tube-mounted bottom protector meets this requirement.

5. (e) Spill Containment -- Each tank fill point must be equipped with spill containment to collect any hazardous substances spilled and prevent the hazardous substance from escaping to the environment when the tank is filled. The spill containment must:

   1. (1) Be protected from galvanic corrosion;
   2. (2) Have a minimum capacity of five gallons (19 liters); and

   3. (3) Have a means to keep the spill containment empty.

      1. (A) Alert the transfer operator when the tank is at 90 percent of capacity by restricting the flow into the tank or activating an audible and visual alarm;
      2. (B) Restrict delivery of flow to the tank at least 30 minutes before the tank overfills, provided the restriction occurs when the tank is filled to no more than 95 percent of capacity; and alert the transfer operator by activating an audible alarm at least five minutes before the tank overfills;
      3. (C) Provide positive shut-off of flow to the tank when the tank is filled to no more than 95 percent of capacity; or
      4. (D) Provide positive shut-off of flow to the tank so that none of the fittings located on the top of the tank are exposed to hazardous substance due to overfilling.

      (f)(1) Overfill Prevention Equipment -- All underground storage tanks that do not meet paragraph (2) must be equipped with overfill prevention equipment that does not allow for manual override and meets one of the following requirements:

   4. (2) The Unified Program Agency may waive or modify the requirement for overfill prevention equipment where the tank inlet is located in an observable area, the tank is filled by transfers of no more than 25 gallons at one time, and the owner or operator is not utilizing the single-walled vent or tank riser piping exemption for Type 1 underground storage tanks in subdivision (b)(10)(A). The Unified Program Agency may revoke an exemption if the system fails to prevent overfills.
   5. (3) On or after October 1, 2018, flow restrictors on vent piping cannot be installed or repaired to meet the requirement of this subdivision.
6. (g) Manways -- All tank entries must be through a manway. If a manway must be installed, the manway must be installed in accordance with the tank manufacturer's written guidelines, an industry code, or an engineering standard.
7. (h) Under-dispenser containment -- All dispensers must be fitted with under-dispenser containment that is designed, constructed, and monitored pursuant to sections 2642(a), 2642(f), and 2652(a).

Note: Authority cited: Sections 25299.3 and 25299.7, Health and Safety Code. Reference: Sections 25284.1, 25290.1, 25290.2, 25291, 25292.1 and 25299, Health and Safety Code; and 40 CFR Sections 280.20, 280.32 and 280.40-280.45.

History

1. Amendment of article and section headings and Note, repealer of subsections (a)-(f), and adoption of subsections (a)-(c) filed 8-9-91 as an emergency; operative 8-9-91. Text remains in effect uninterrupted pursuant to Health and Safety Code section 25299.7 (Register 92, No. 14).

2. Editorial correction of printing errors in History 1 (Register 92, No. 43).

3. Amendment of section and Note filed 4-5-94; operative 5-5-94 (Register 94, No. 14).

4. Amendment of subsection (c), new subsections (e)-(e)(3) and amendment of Note filed 5-14-2001; operative 5-14-2001 pursuant to Government Code section 11343.4 (Register 2001, No. 20).

5. Amendment of subsections (e) and (e)(2)-(3) and amendment of Note filed 10-13-2016; operative 1-1-2017 (Register 2016, No. 42).

6. Amendment of subsections (d) and (e)(2)-(3) and amendment of Note filed 8-27-2018; operative 10-1-2018 (Register 2018, No. 35).

7. Repealer and new article 4 heading, section heading and section filed 10-28-2025; operative 1-1-2026 (Register 2025, No. 44).