Cal. Health and Safety Code § 25281.6

(a) A tank located in a below-grade structure and connected to an emergency tank system, as defined in subdivision (c) of Section 25281.5, is exempt from the requirements of this chapter if all of the following conditions are met: (1) The tank is situated above the surface of the floor in such a way that all of the surfaces of the tank can be visually inspected by either direct viewing, through the use of visual aids, including, but not limited to, mirrors, cameras, or video equipment, or monitored through the use of a continuous leak detection and alarm system capable of detecting unauthorized releases of hazardous substances. (2) For a single-walled tank, in addition to all the other requirements in this section, the structure, or a separate discrete secondary structure able to contain the entire contents of the liquid stored in the tank, is sealed with a material compatible with the stored product. (3) The owner or operator of the tank conducts a visual inspection of the tank each time the emergency tank system is operated, or at least once a month, and maintains a log of inspection dates for review by the local agency. (4) The tank or combination of tanks in the below-grade structure has a cumulative capacity of less than 1,320 gallons of diesel fuel. (b) Nothing in this section excludes an emergency tank system from other applicable laws, codes, and regulations. (c) The exclusion provided by this section does not apply if the board adopts regulations pursuant to Section 25299.3 that address the design, construction, upgrade, and monitoring of underground storage tanks contained in below-grade structures that are connected to emergency tank systems.