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j 2.4.1 MONITORING WELL DESTRUCTION BY OVER-DRILLING Per .SJCEHD Well Standard requirements, wells located in an area of known or suspected contamination or that have laboratory data from the last sampling event that demonstrate the presence of any'contaminants of concern are to destroyed by removing all the contents of the well. Wells MW-1,MW-2,MW-5,MW-6, MW-8,and MW-10 meet these criteria. I For these wells, the well vaults will be removed, and the upper five feet of each location will be cleared for utilities using a vacuum truck assisted airknife. The wells will then be drilled out.to their original depths using the.same size auger originally used to install the well (Appendix A). The resulting boreholes :will be backfilled i:with neat cement grout through the augers from the bottom up to a depth of approximately one foot below grade (fbg). The upper one foot of the borehole will.be -filled_ with concrete or asphalt to match the surrounding grade. 2.4.2 MONITORING WELL DESTRUCTION BY PRESSURE GROUTING Per SJCEHD Well Standard requirements, wells that have laboratorydata from the last sampling event:that report non-detectable concentrations of contaminants of concern and with acceptable laboratory detection limits and are not in areas- of known of suspected soil.contamination, may be destroyed by pressure grouting from the bottom upward, while leaving the well in place. Wells MW-3, MW-4, MW-7, and MW-9 meet these criteria. i .. I For these wells, the well boxes will be removed, and the upper three feet of each well i location will be removed using a vacuum truck assisted airknife. Each resulting hole will be widened to approximately 22 inches in diameter (the original borehole diameter plus 12 inches) with the airknife, and the casing will be cut off to the depth of approximately 2.5 fbg. Cement grout will be added to the well casing from the bottom up using a tremie pipe until no additional grout will be accepted, and then 25 pounds per square inch of pressure will be applied to the casing for 5 minutes. The grout sealant will then be topped up and allowed lo spill out of the top of the well casing to forma mushroom cap seal with at least a 1 foot layer of neat cement grout.poured six inches above and six inches below the top of the cut-off casing. The upper 2 feet will be filled with concrete or asphalt to match the surrounding grade. I .r 241359(22) 2 CONESTOGA-ROVERS&ASSOCIATES l