Section 2647 - Vadose Zone Monitoring Requirements(a) Owners or operators of existing underground storage tanks who use vadose zone monitoring as part of a non-visual monitoring program shall comply with the requirements of this section. Vapor monitoring, soil-pore liquid monitoring, or a combination of these or other vadose zone monitoring methods may be used.(b) Vadose zone monitoring shall not be used as the sole release detection method of non-visual monitoring where the monitoring well cannot be located within the backfill surrounding the tank, or where the existing ground water level or the highest anticipated ground water level, including intermittent perched ground water, is less than 10 feet below the bottom of the tank. Ground water levels shall be determined in accordance with section 2649(c).(c) Vadose zone vapor monitoring shall be conducted continuously. Other vadose zone monitoring shall be conducted at least weekly. All manual sampling in the vadose zone shall be conducted in accordance with section 2649(g).(d) The number, location, and depths of vadose zone monitoring points shall be selected to achieve the objective specified in section 2641(a). Where possible, monitoring points shall be located within the excavation backfill surrounding the underground storage tank. The owner or operator shall determine the exact location of the underground storage tank and associated piping before attempting to install monitoring wells and/or devices pursuant to local agency approved.(e) Vadose zone vapor monitoring shall comply with the following minimum requirements: (1) The vapor characteristics of the stored product, or a tracer compound placed in the underground storage tank system, shall be sufficiently volatile to result in a vapor level that is detectable by the monitoring devices;(2) Backfill materials and soils surrounding monitoring points shall be sufficiently porous to readily allow diffusion of vapors;(3) The level of background contamination in the excavation zone and surrounding soils shall not interfere with the method used to detect releases from the underground storage tank;(4) The monitoring devices shall be designed and operated to detect any significant increase in concentration above the background of the hazardous substance stored in the underground storage tank, a component or components of that substance, or a tracer compound placed in the tank system;(5) The location and depth of each monitoring point shall be placed according to the most probable movement of vapor through the backfill or surrounding soil;(6) Vapor monitoring wells located in the backfill shall be constructed so that any unauthorized release that may pond at the horizontal interface between the backfill and natural soils can be detected in the vapor well; and(7) All vapor monitoring wells shall be installed, constructed, and sampled according to the requirements specified in sections 2649(b), (c), (e), and (f).(f) Soil-pore liquid monitoring and other forms of vadose zone monitoring shall comply with the following minimum requirements: (1) The stored substance shall be susceptible to detection by the proposed release detection method;(2) The stored substance shall not corrode or otherwise attack the materials from which the detection system is constructed or otherwise render the detection system inoperable or inaccurate; and(3) Site-specific conditions (e.g., precipitation, ground water, soil-moisture, background contamination) shall not interfere with the operability and accuracy of the release detection method.(g) Compliance with the requirements of subdivisions (e) and (f) above, shall be based on a site assessment including assessment of the underground storage tank excavation zone.(h) Site assessments conducted on and after October 1, 2018 in accordance with subdivision (g) above, shall be signed by a professional engineer, professional geologist, or equivalent licensed professional with experience in environmental engineering, hydrogeology, or other relevant technical discipline.Cal. Code Regs. Tit. 23, § 2647
1. Repealer and new section 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 filed 4-5-94; operative 5-5-94 (Register 94, No. 14).
4. Amendment of subsections (b) and (g), new subsection (h) and amendment of NOTE filed 8-27-2018; operative 10-1-2018 (Register 2018, No. 35). Note: Authority cited: Sections 25299.3 and 25299.7, Health and Safety Code. Reference: Section 25292, Health and Safety Code; and 40 CFR §§ 280.43 and 280.45.
1. Repealer and new section 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 filed 4-5-94; operative 5-5-94 (Register 94, No. 14).
4. Amendment of subsections (b) and (g), new subsection (h) and amendment of Note filed 8-27-2018; operative 10/1/2018 (Register 2018, No. 35).