(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.

(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.

(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.

(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.

(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:

(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.