Cal. Health & Safety Code § 25290.2

(a) Notwithstanding subdivision (o) of Section 25281, for purposes of this section, “product tight” means impervious to the liquid and vapor of the substance that is contained, or is to be contained, so as to prevent the seepage of the substance from the containment.
(b) Notwithstanding Section 25291, every underground storage tank installed on or after July 1, 2003, and before July 1, 2004, shall meet the requirements of this section.
(c) The underground storage tank shall be designed and constructed to provide primary and secondary levels of containment of the hazardous substances stored in it in accordance with the following performance standards:
1. (1) Primary containment shall be product tight and compatible with stored product.
2. (2) Secondary containment shall be product tight and constructed to prevent structural weakening as a result of contact with any hazardous substances released from the primary containment, and also shall be capable of storing the hazardous substances for the maximum anticipated period of time necessary for the recovery of any released hazardous substance.
3. (3) Secondary containment shall be constructed to prevent any water intrusion into the system by precipitation, infiltration, or surface runoff.
4. (4) In the case of an installation with one primary tank, the secondary containment shall be large enough to contain at least 100 percent of the volume of the primary tank.
5. (5) In the case of multiple primary tanks, the secondary containment shall be large enough to contain 150 percent of the volume of the largest primary tank placed in it, or 10 percent of the aggregate internal volume of all primary tanks, whichever is greater.
(d) The underground tank system shall be designed and constructed with a continuous monitoring system capable of detecting the entry of the hazardous substance stored in the primary containment into the secondary containment and capable of detecting water intrusion into the secondary containment.
(e) The underground storage tank shall be provided with equipment to prevent spills and overfills from the primary tank.
(f) If different substances are stored in the same tank and in combination may cause a fire or explosion, or the production of flammable, toxic, or poisonous gas, or the deterioration of a primary or secondary container, those substances shall be separated in both the primary and secondary containment so as to avoid potential intermixing.
(g) Underground pressurized piping that conveys a hazardous substance shall be equipped with an automatic line leak detector and shall be tightness tested annually.
(h) Before the underground storage tank is covered, enclosed, or placed in use, the standard installation testing requirements for underground storage systems specified in Section 2.4 of the Flammable and Combustible Liquids Code, adopted by the National Fire Protection Association (NFPA 30), as amended and published in the respective edition of the Uniform Fire Code, shall be followed.
(i) Before the underground storage tank is placed in use, the underground storage tank shall be tested after installation using one of the following methods to demonstrate that the tank is product tight:
1. (1) Enhanced leak detection.
2. (2) An inert gas pressure test that has been certified by a third party and approved by the board.
3. (3) A test method deemed equivalent to enhanced leak detection or an inert gas pressure test by the board in regulations adopted pursuant to this chapter. An underground storage tank installed and tested in accordance with this subdivision is exempt from the requirements of Section 25292.5.
(j) Notwithstanding Section 25281.5, for any system installed to meet the requirements of this section, those portions of vent lines, vapor recovery lines, and fill pipes that are beneath the surface of the ground are “pipe” as the term is defined in subdivision (m) of Section 25281, and therefore part of the underground storage tank system.