Section 2648 - Ground Water Monitoring Requirements(a) Owners or operators of existing underground storage tanks who use ground water monitoring as part of a non-visual monitoring program shall comply with the requirements of this section. Ground water monitoring may be used in combination with other quantitative or qualitative release detection methods or, where permissible under this section, as the sole release detection method.(b) Ground water monitoring may be used as the sole release detection method of non-visual monitoring for existing underground tanks only where all of the following conditions exist: (1) The hazardous substance stored is immiscible with water and has a specific gravity of less than one;(2) Continuous monitoring devices or manual methods are used which are capable of detecting the presence of at least one-eighth of an inch of free product on top of the ground water in the monitoring wells. This capability shall be certified by an independent third party using an appropriate evaluation procedure. Examples of acceptable evaluation procedures are in Appendix IV;(3) The existing ground water level or the highest anticipated ground water level, including intermittent perched ground water, is less than 20 feet from the ground surface. These ground water levels shall be determined according to the requirements of section 2649(c);(4) The hydraulic conductivity of the soil(s) between the underground storage tank and the monitoring wells or devices is at least 0.01 centimeters per second (e.g., the soil consists of gravels, coarse to medium sands, or other permeable materials);(5) The ground water proposed for monitoring has no present beneficial uses (e.g., domestic, municipal, industrial, or agricultural supply) or is not hydraulically connected to ground or surface water which has actual beneficial uses; and(6) Monitoring wells or devices are located within the excavation zone or as close to the excavation zone as feasible.(c) Compliance with the conditions specified in subdivision (b) above, shall be based on a site assessment, including assessment of the areas within and immediately below the underground storage tank excavation zone. If ground water monitoring is approved as the sole release detection method of a non-visual monitoring program, the number and location of the monitoring wells and/or devices as approved by the local agency shall also be based on this site assessment with minimum requirements as follows: (1) Single tank - two wells, one at each end of the tank.(2) Two or three tanks - three wells equally spaced.(3) Four or more tanks - four wells, at least two of which shall be downgradient and the remainder equally spaced.(4) Pipelines - additional wells, if needed, as determined by the local agency.(d) Site assessments conducted on and after October 1, 2018 in accordance with subdivision (c) 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.(e) Ground water monitoring shall be conducted at least once every 30 days or continuously. Any continuous monitoring system shall be capable of detecting the presence of hazardous substance on top of the ground water in the monitoring well and shall allow periodic collection of samples. Ground water samples shall be analyzed by visual observation or field or laboratory analysis as approved by the local agency depending on the method of monitoring and the constituents being evaluated. The local agency may require periodic laboratory analysis where visual observation or field analysis does not provide an adequate degree of detection as compared to that of laboratory analysis. Sampling conducted which requires field or laboratory analysis shall comply with the minimum requirements of section 2649(g).(f) The number, location, and depths of ground water monitoring wells shall be selected to achieve the objective specified in section 2641(a). Monitoring wells shall be located as close as possible to the underground storage tank or the perimeter of the underground storage tank cluster, subject to the review and approval of the local agency.Cal. Code Regs. Tit. 23, § 2648
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)(4), (b)(5) and (c), new subsection (d), subsection relettering, amendment of newly designated subsection (e) 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)(4), (b)(5) and (c), new subsection (d), subsection relettering, amendment of newly designated subsection (e) and amendment of Note filed 8-27-2018; operative 10/1/2018 (Register 2018, No. 35).