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C <br />Mr. Robert McClellon <br />ADDITIONAL INFORMATION REGARDING THE PROPOSED UPGRADE OF PERIMETER LFG <br />MIGRATION MONITORING WELLS AT SAN JOAQUIN COUNTY -OWNED LANDFILLS <br />Perforation spacing: For deeper probes with longer perforation lengths, the tube will be <br />perforated twice per foot. For shallow probes with less than six feet of perforated probe <br />pipe, the tube will be perforated every six inches or less, thereby providing the minimum <br />12 perforations total. <br />Appropriateness of proposed tube material: We propose to use polyethylene (PE) tube, <br />which is resistant to most acids, alkalis and solvents, and an excellent selection for this <br />use. <br />This material is the same as approved for the perimeter migration monitoring probes at <br />Foothill and North County Landfills for landfill liners and landfill gas systems. In fact, the <br />landfill gas pipes visible on the slopes of the North County and Foothill Landfill, and <br />buried at Corral Hollow and Harney Lane Landfills, are comprised of polyethylene. <br />Note that the environment of these tubes for migration monitoring would be milder than <br />LFG pipe applications. <br />Contingency in case of problems with the tube: The tubes can be easily removed from <br />the surface by one person using common hand tools, and easily replaced in the same <br />way. This feature is important in considering the possible need to insert a camera inside <br />the probe pipe. <br />Schedule of installation: After approval by your Department and other jurisdictional <br />agencies as appropriate, we intend to install the tubes for use in the second quarter <br />monitoring. Surface conditions should not be a consideration. However, we understand <br />that the wells must be accessible for this work. <br />With your approval and after the work is complete, we will insert this information into each of our <br />LFG migration monitoring plans as an addendum. <br />We understand also your desire that Environmental Health Department staff be present for the <br />insertion 'of these tubes. We will coordinate this work during normal EHD inspection hours. <br />Please contact me at 468-8504 with any questions. <br />Sincerely, <br />W. MICHAEL CARROLL, PE <br />Senior Civil Engineer <br />Attachments <br />W MC:Ij <br />NA2ModifyPerimProbes2011\RMcCIe11on02-Probe1mp2.dccx <br />LA 11458A, LA 21123, LA 31103E, LA 6310 <br />