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nuc uiiic�tt Page z of -i (b) Spacing (1)The lateral spacing between adjacent monitoring wells shall not exceed 1,000 feet, unless it can be established to the satisfaction of the EA, in�20923(a)(2). (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 due to gas migration. (3)Probe spacing shall be reduced as necessary to protect persons and structures threatened by landfill gas migration. (c)Depth (1)The depth of the wellbore shall equal the maximum depth of waste as measured within 1,000 feet of the monitoring point. The number and depths of monitoring probes within the wellbore shall be installed in accordance with the following criteria, except as specified in 1(c)(2). (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 conductive 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 1(c)(1)may be requested for certain disposal sites(i.e.,filled pits, cut and trench, and canyon fills). When conditions limit the practicality or do not warrant the installation depth criteria,the operator shall propose an alternate system of equivalent probe depths. The proposal must demonstrate to the satisfaction of the EA, 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 probes,the depth of the wellbore, or modify the depths of monitoring probes within a wellbore to ensure compliance with§2_0921(a). The operator is not precluded from utilizing existing gas monitoring probes of an alternate design,when the operator demonstrates to the satisfaction of the EA, that such probes 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 where in-house drilling capability exists,by a drilling crew under the supervision of the design engineer or engineering geologist.Wells shall be logged during drilling by or 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 facility map drawn to a scale proposed by the design engineer or engineering geologist, http://ccr.oal.ca.gov/cgi-bin/om isapi.dll?clientlD=104287&infobase=ccr&softpage=Docu... 3/10/2005