California Code of Regulations › Title 23 - Waters › Division 3 - State Water Resources Control Board and Regional Water Quality Control Boards › Chapter 16 - Underground Tank Regulations › Article 4 - Existing Underground Storage Tank Monitoring Requirements › Section 2647 - Vadose Zone Monitoring Requirements

Current through Register 2024 Notice Reg. No. 28, July 12, 2024
(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).