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i + <br /> ASC <br /> � AECOM 909 579 3050 tel <br /> e <br /> � SCO 901 Via Piemonte-5t'Floor 909 579 3997 fax <br /> Ontario,California 91764 <br /> www.aecom.com <br /> WELL ABANDONMENT MEMORANDUM <br /> To: Copies: <br /> Vicki McCartney (1)via email <br /> San Joaquin County <br /> Environmental Health Department <br /> 1868 East Hazelton Avenue <br /> Stockton, California 95205-6232 <br /> From: Subject: <br /> Todd G. McFarland, AECOM Chevron Former Service Station No. 90557 <br /> 909-579-3975 139 South Center Street, Stockton, California <br /> Date: Supplier Project No: <br /> July 14, 2014 60315673; Task 15.06 <br /> AECOM has prepared this well abandonment memorandum to document the methods and materials <br /> proposed to abandon all site wells as requested by the San Joaquin County Environmental Health <br /> Department in correspondence dated June 30, 2014, see attached. AECOM intends to destroy all 12 site <br /> groundwater monitoring wells (7 on-site and 5 off-site), by over drilling or pressure grouting techniques, <br /> see attached for the logs of exploratory borings. A site plan showing the well locations is attached. <br /> AECOM proposes to abandon all on-site wells (MW-3, MW-14 through MW-17, MW-15D, and MW-18D2) <br /> by overdrilling each well to total depth using a truck-mounted hollow-stem auger drill rig to remove the <br /> entire casing, filter pack, sanitary seal, and well vault. The total depth of each well will be confirmed prior <br /> to abandonment. The borehole will be sealed with neat cement tremied from the bottom upward to 1 k <br /> approximately 5 feet below ground surface (ft bgs). The remaining borehole will be filled with hydrated y, . <br /> bentonite chips to 1 ft bgs and completed to match the existing surface. t <br /> AECOM proposes to abandon all off-site wells (MW-5 through MW-8, and MW-13) by pressure grouting, <br /> see attached table for the analytical results from the last groundwater monitoring event. For wells that will <br /> be pressure grouted, the well casing will be left in-place and neat cement will be forced through the <br /> perforated well casing interval and into the filter pack under a pressure of approximately 20 pounds per <br /> square inch for at least 5 minutes. Then, the top 3 feet of casing will be overdrilled with an auger at least <br /> one foot larger in diameter than the auger originally utilized to installed the well. An additional 6-inches of <br /> material will be removed from around the cut-off casing to form a mushroom cap seal. The mushroom <br /> cap seal will be completed by allowing the neat cement to spill out of the top of the well casing with at <br /> least 12-inches of the neat cement grout poured 6-inches above and 6-inches below the top of the cut-off <br /> casing. The remaining borehole will be filled with hydrated bentonite chips to 1 ft bgs and completed to r� <br /> match the existing surface. Surface completion for the wells located within the sidewalk will be completed -1 (� <br /> by replacing the entire concrete sidewalk panel that the well is located within, in accordance with City �+ <br /> requirements. <br /> In the event a utility line is identified in close proximity to and/or safety concerns are identified for an <br /> individual well proposed to be overdrilled,AECOM may propose that the abandonment method be <br /> changed to pressure grout. AECOM will notify SJCEHD prior to changing the abandonment method. <br /> Page: 1 <br />