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San Joaquin County Environmental Health Department DIRECTOR Donna Heran,REHS 1868 East Hazelton Avenue Stockton, California 95205-6232 PROGRAM COORDINATORS .. r. Robert McClellon,REHS Jeff Carruesco,REHS,RDI c •. P Kasey Foley,REHS Website: www.sjgov.org/ehd Linda Turkatte,REHS Phone: (209)468-3420 Fax: (209)464-0138 July 29, 2014 Perry Pineda Shell Oil Products US 20945 S. Wilmington Ave. Carson, CA 90810 Subject: Independent Shell-Branded Service Station 4315 Waterloo Road Stockton, CA 95215 The San Joaquin County Environmental Health Department (EHD) has received and reviewed Well Destruction Work Plan, dated 16 June 2014, prepared and submitted by your consulting firm, Conestoga-Rovers &Associates (CRA), on your behalf for the above-referenced site. In the work plan, CRA proposes to destroy monitoring wells MW-1, MW-2, MW-5, MW-6, MW-8, and MW-10 by over-drilling, and MW-3, MW-4, MW-7 and MW-9 by pressure grouting. For those wells proposed to be over-drilled, CRA proposes to remove the well vaults, clear the upper five feet using the airknife technique, and drill out the wells to their original depths using the same size auger originally used to install the wells. The resulting boreholes are proposed to be backfilled from the bottom up to approximately one foot below grade with neat cement through the augers. For those wells proposed -to be pressure-grouted, CRA proposes to remove the well boxes, clear the upper three feet using the airknife technique, widen each hole diameter to approximately 22 inches, cut off casing to a depth of approximately 2.5 feet below grade, add cement grout to the well casings through a tremie pipe from the bottom up, apply approximately twenty-five pounds per square inch (psi) of pressure to the cement grout for a period of five minutes during the pressure grouting process, and allow the formation of an at least one foot "mushroom cap" layer of neat cement grout. The EHD approves the work plan with the following conditions: • Use only potable water to make the grout; displaced groundwater may not be used to make grout or for any other purpose and must be disposed of properly; • Use a tremie pipe when backfilling over-drilled wells' resulting boreholes from the bottom up; • Apply at least 25 psi of liquid grout pressure for ten minutes when pressure grouting the wells; destroy the wells by over-drilling if the well casings are unable to withstand this pressure for this length of time;