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Ll <br />4.4.1.6 Air Infiltration <br />11 <br />Air infiltration into the vertical LFG wells will be minimized by constructing vertical <br />LFG wells with solid pipe to a minimum depth of 20 feet below the intermediate or final <br />cover or, for horizontal wells, maintaining a minimum of 20 vertical feet between grade <br />and the well, a minimum of 75 feet from side slopes, and 50 feet from a canyon slope. <br />Bentonite seals and/or well bore seals will be installed around the vertical non -perforated <br />well connection pipe in vertical LFG extraction wells and non -perforated lateral pipes in <br />horizontal well connections where they penetrate the landfill. In addition, hydrated <br />bentonite seals will be installed at the end of the well perforations in horizontal and <br />vertical wells, around the solid LFG pipe. Further, air infiltration will be minimized <br />through periodic monitoring and adjustment of the GCCS in accordance with NSPS <br />requirements and maintenance of the landfill cover. If the GCCS does not meet the <br />operational standards, it will be adjusted or modified in accordance with NSPS <br />requirements. <br />4.4.2 Landfill Gas Extraction Component Installation <br />§611.759(b)(2) Vertical wells shall be placed so as not to endanger <br />underlying liners and shall address the occurrence of water within the <br />landfill. Holes and trenches constructed for piped wells and horizontal <br />collectors shall be of sufficient cross-section so as to allow for their <br />proper construction and completion including, for example, centering of <br />pipes and placement of gravel backfill. Collection devices shall be <br />designed so as not to allow indirect short-circuiting of air into the cover <br />or refuse into the collection system or gas into the air. Any gravel used <br />around pipe perforations should be of a dimension so as not to penetrate <br />or block perforations. <br />4.4.2.1 Component Placement <br />Vertical wells in lined modules will not extend to the base liners. Depths of refuse will <br />be determined based on the difference between the existing elevation of the landfill <br />surface and the base elevation of the landfill. LFG extraction wells will be designed to <br />extend from the landfill surface to within no less than 10 feet of the landfill base or base <br />liner, or to a maximum depth of 100 feet, whichever is shallower.. Installation of wells <br />deeper than 100 feet was determined to not be cost effective for meeting the site-specific <br />gas control objectives. <br />4.4.2.2 Water <br />The occurrence of water within the landfill will be addressed by the leachate and <br />condensate management systems as stated in Section 4.1.6 of this design plan. <br />Foothill Sanitary Landfill 13 Public Works/Solid Waste <br />LFG CS Design Plan County of San Joaquin - March 10, 2005 <br />