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E51 �� til �v-�i AJ55•." /�:'.,1: ! San Joaquin County eT OP 1868 ::cc Environmental: Health DepartmnBY._ - IREcTOR G "- leriria Ffeta�i'RHS 1868 East Hazelton Avenue N. PROGRAM COORDINATORS � 5 Stockton., California 95205-6232 Roberl,McClellori,`REHS . - Jeff Carruesco,REHS,RDI Kasey foley.RENS �' • :P Website: www.sigov.org/Ghd Linda Turkatte..REHS Phone: (209)468-3420 Fax: (209).464-0138 June 12, 2012 Ms. Jennifer Sedlachek Mr. Pat and.Ms. Kathleen.Meeks ExxonMobil Environmental Services Company" 25355 Highway 99 4096 Piedmont Avenue#194 Acampo, California 95220 Oakland, California 94611 Subject: Former Mobil-Service Station 99ACA(former.Meeks RV) 25355 North Highway 99 Acampo, California 95220 . ` The San Joaquin County Environmental Health Department (EHD) has received and reviewed Work Plan for Well Destruction (work plan)., dated 24May 2012, prepared by Cardno ERI on your behalf for the above-referenced site. -In the work plan, Cardno ERI proposed to destroy the M five soil vapor wells by removing the well contents, including tubing, sand, and annular seal, using vacuum equipment or hand tools, then 'fill the boreholes with neat cement. Cardno-ERI proposed to destroy the.nine remaining monitoring'welis by pressure grouting. The EHD approves the destruction of the five soil vapor wells using either vacuum equipment or hand tools; .however, use a tremie pipe.when filling all boreholes with total depth exceeding thirty feetwith neat cement. The EHD has reviewed historical soil'and groundwater .analytical' -results for this site and approves monitoring wells MW-2, MW-5, MW-7 through MW9R and MW-10 to,be pressure grouted. Prior to destroying the wells, check:each one for obstructions and if found' remove the obstructions. The EHD directs that 25 pounds per square inch(psi) of liquid grout pressure be { applied for a minimum of ten minutes. Following the pressure grouting a hole at least one foot larger diameter than the originally drilled hole must be excavated around, round the outside of the well casing to a depth of three feet below surface-grade (bsg). The well casing must then be cutoff six inches above the bottom of the excavation and removed- The grout used to fill the well must ; then be allowed to spill over into the excavation and fill the hole for a thickness of one foot and form a cap which has a diameter at least one foot.greater than-the diameter of the originally. drilled hole. (If augers are used to excavate the top three feet, the augers must be at least " twenty inches in diameter for wells that were installed using eight-inch augers.) Since monitoring wells MW 1, MW73 and MW-4 reside in an area of known- residual I contamination,'or 1,2-dichloroethane (1,2-DCA)'was detected in groundwater collected..from ff these wells during their last sampling event, the EHD directs that these three wells be over- . I drilled to total depth and the well contents, including the well casing, screen, filter pack and i grout sealant, be removed; the cleared borehole is then to be sealed with neat cement by pressure grouting from the bottom upward to a depth of three to five feet bsg using a tremie 1 pipe.