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Y ARCADIS, US, Inc. 1i�INI' Former OCC Lathrop Site—Monitoring Well Management Plan Pry io ftatoMs,Inc. September 15,2011 Industrial Piaaess Controls Page 1 of I Monitorine Well Manaeement PSI will team with Cascade Drilling for the management effort of the monitoring wells. As required by the San Joaquin County, Environmental Health Department(SJCEHD), a permit will be obtained for the well management and Cascade will supply professional oversight of the well cut off/extension activities. Well management will consist of two portions - the first will be to remove the monitoring wells before the excavation and the second will be to re-attach/extend the wells at the end of the excavation. Before excavation begins, the three (3) monitoring wells (PW26-089, PW26-154, and PW26-199) located in the excavation area will be addressed by digging down an estimated eight (8) feet below ground surface (bgs) and removing the upper portion of the casing and capping the remaining portion. The grout will be removed from the cut casing and discarded. The cut well casing will then be moved to a safe location until the end of the project. During the excavation, great care will be exercised to avoid possible damage to the in- place portion of the monitoring well casing. If needed, wood supports will be installed to support the in-place well casing as the excavation area gets deeper. Close inspection of the in-place well casing will determine whether the supports are needed. Once the excavation is complete, at each of the 3 monitoring wells the cut casing will be re-attached to the in-place well casing using a polyvinyl chloride (PVC) coupler as the backfill process reaches the in-place monitoring well height. Off-site imported material which meets the Information Advisory—Clean Imported Fill Material, guidance prepared by the California Department of toxic Substances Control (DTSC)and dated October 2001 will be used for backfill. Prior to backfilling of the upper approximately 8 feet of the excavation, a Sonotube® form will be placed around the extended well casing as a conductor casing. Approximately 10 inch lifts of backfill will be compacted around the conductor casing to approximately four feet bgs. The top four feet will be backfilled using 8 inch lifts compacted to 92% the maximum dry density. Neat cement grout will be added around the well casing within the conductor casing following each lift to the height of backfill. The conductor casing will be retracted vertically as the neat cement grout is added as a tremie to fill the void space around the well casing and match the existing well installation specifications. Upon completion, the protective equipment will be re-installed at the surface. Industrial Process Controls Construction and Environmental Services ❖ Electrical Services ❖ Pipeline Inspection/Certification 290 Rickenbacker Circle,Suite 100,Livermore,CA 94551 a- (925)456-8400 Phone 40 (925)456-8404 Facsimile www.presidiosystems.com