Section 20925 - CIWMB -Perimeter Monitoring Network (California Code of Regulations)

§ 20925. CIWMB -Perimeter Monitoring Network

(a) Location

(1) Perimeter subsurface monitoring wells shall be installed around the waste disposal footprint but not within refuse. In some cases the installation of monitoring wells may not be necessary around the entire perimeter of the disposal site permitted facility boundary. In such a case, the operator shall demonstrate to the satisfaction of the EA that landfill gas migration could not occur due to geologic barriers and that no inhabitable structure or other property or land use, such as agricultural lands, within 1,000 feet of the disposal site permitted facility boundary is threatened by landfill gas migration.

(2) Perimeter monitoring wells shall be located at or near the disposal site permitted facility boundary. The operator may establish an alternate boundary closer to the waste disposal footprint based on a knowledge of the site factors in § 20923(a)(2). When compliance levels are exceeded at the alternate boundary, the operator shall install additional monitoring wells closer to the permitted facility boundary, pursuant to § 20937.

(b) Spacing

(1) The lateral spacing between adjacent monitoring wells shall not exceed 1,000 feet unless the operator demonstrates to the satisfaction of the EA and CIWMB, based on the factors specified in § 20923(a)(2), that there is no potential for adverse impacts on the public health and safety and the environment from such wider spacing.

(2) The spacing of monitoring wells shall be determined based upon, but not limited to: the nature of the structure to be protected and its proximity to the refuse. Wells shall be spaced to align with gas permeable structural or stratigraphic features, such as dry sand or gravel, off-site or on-site structures, and areas of dead or stressed vegetation that might be caused by landfill gas migration.

(3) Monitoring well spacing shall be reduced as necessary to protect persons and structures threatened by landfill gas migration.

(c) Depth

(1) The depth of the wellbore of all monitoring wells shall equal the maximum depth of waste. The number and depths of monitoring probes within the wellbore shall be installed in accordance with the following criteria, except as specified in ¶(c)(2) of this section.

(A) a shallow probe shall be installed 5 to 10 feet below the surface;

(B) an intermediate probe shall be installed at or near half the depth of the waste;

(C) a deep probe shall be set at or near the depth of the waste;

(D) the specified depths of monitoring probes within the wellbore shall be adjusted based on geologic data obtained during drilling, and probes shall be placed adjacent to soils which are most conducive to gas flow;

(E) All probes shall be installed above the permanent low seasonal water table, above and below perched ground water, and above bedrock; and

(F) When the depth of the waste does not exceed 30 feet, the operator may reduce the number of probes to two, with one probe located in the shallow zone as indicated above and the other located adjacent to permeable soils at or near the depth of the waste.

(2) Exclusions or modifications to the requirements specified in ¶(c)(1) of this section may be requested when conditions limit the practicality or do not warrant the installation depth criteria (e.g., filled pits, cut and trench, and canyon fills). In those cases, the operator shall propose an alternate system of equivalent probe depths. The proposal must demonstrate to the satisfaction of the EA and CIWMB that probes located at these depths are sufficient to detect migrating landfill gas and provide protection to public health and safety and the environment.

(3) The EA may require an increase in the number of monitoring wells or probes or the depth of the wellbore or modify the depths of monitoring probes within a wellbore to ensure compliance with § 20921(a). The operator is not precluded from utilizing existing gas monitoring wells of an alternate design when the operator demonstrates to the satisfaction of the EA and CIWMB that such wells have been installed in a manner that ensures the detection of landfill gas migrating from the disposal site.

(d) Monitoring Well Construction

(1) Monitoring wells shall be drilled by a licensed drilling contractor or by a drilling crew under the supervision of the design engineer or engineering geologist. Wells shall be logged during drilling by a geologist or geotechnical engineer. Soils shall be described using the ASTM Designation: D2488-84 method for visual classification, Standard Practice for Description and Identification of Soils (Visual-Manual Procedure), which is incorporated by reference. Rock units shall be described in a manner appropriate for geologic investigation.

(2) A record of each monitoring well shall be maintained by the operator and submitted to the EA upon request. The record shall include:

(A) a map of the disposal site drawn to a scale proposed by the design engineer or engineering geologist sufficient to show the location of all monitoring wells. Each well must be identified with a number that corresponds to the well log. Surface elevations at the wellheads shall be denoted on the map;

(B) well logs, including the names of the person(s) logging the hole; and

(C) an as-built description, including a well detail which indicates probe material and depth, extent and type of filter pack, thickness and material used for seals, extent and material used for backfill, size and interval of perforations, and a description of any shutoff valves or covers.

(3) To isolate monitored zones within the wellbore and prevent contamination of perched ground water and permanent ground water, the operator shall provide a minimum seal of five (5) feet of bentonite at the surface and between the monitored zones.

(1. New section filed 6-18-97; operative 7-18-97 (Register 97, No. 25). 2. Amendment of section heading, section and Notefiled 8-21-2007; operative 9-20-2007 (Register 2007, No. 34). 3. Editorial correction of subsection (d)(3) (Register 2007, No. 40).)

Note: Authority cited: Sections 40502 and 45020, Public Resources Code. Reference: Sections 43021 and 43103, Public Resources Code.

Disclaimer: Lawrina has made every attempt to ensure the information on this page is accurate, but we cannot guarantee that Section 20925 CIWMB -Perimeter Monitoring Network is a replica of the current official text. Please use the external links to official resources for the latest version.

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