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Stantec Further Assessment Work Plan Stockton Charter Way Commingled Plume February 15, 2011 2.0 Proposed Scope of Work 2.1 Well Decommissioning The current property owner plans to remodel the existing ARCO-branded gasoline service station [former Texaco (Shell)] according to the remodeling plan included as Appendix B. The remodeling plan is currently being reviewed by the City of Stockton and may be subject to change. According to the remodeling plan, a retail building will be constructed at the northwest corner of the Shell property in the vicinity of existing groundwater monitoring wells SMW-7, SMW-18-80, and SMW-18-120. To accommodate the remodeling, a total of three wells (SMW-7, SMW-18-80, and SMW-18-120) will be decommissioned according to the San Joaquin County Environmental Health Department (SJCEHD) Well Standards (SJCEHD, 2005) as described in Section 3.0 of this Work Plan. In addition to the wells listed above, Stantec proposes to decommission the following wells: AMW-10, AMW-12, CMW-1 through CMW-3, SLMW-1, SLMW-7S, SLMW-7D, SMW-1, SMW-4, SMW-5, SMW-6, SMW-9, SMW-10, SMW-11, SMW-13, and SMW-17 (17 wells). Based on the boring logs and the generalized cross-sections included in the SCM, these wells (except AMW- 10, AMW-12, and SLMW-7D) are screened across multiple water-bearing zones and some are located near contaminant sources. Well SLMW-7D is constructed in the same borehole as SLMW-7S. Based on the A zone groundwater isoconcentration map, the groundwater impacts are delineated towards the north side at the former ARCO Service Station No. 2168 with wells AMW-8, AMW-9, and AMW-11, and nearby wells AMW-10 and AMW-12 are no longer necessary. The following table lists the wells to be decommissioned and the rationale for each. The boring logs are included in Appendix C. Table 2.1: List of wells to be decommissioned Screen Well ID Zone Top Bottom Justification (ft bgs) (ft bgs) AMW-10 A 17 32 No longer necessary AMW-12 A 17 32 No longer necessary CMW-1 A & B 30 50 Cross-screened CMW-2 A 30 50 Screened in mostly clay between A and B CMW-3 A & B 30 50 Cross-screened SLMW-1 A & B 26 46 Cross-screened SLMW-7S B & C 55 63 Cross-screened, installed in tank pit Screen not at top of C zone, nested with SLMW-7D C 80 85 SLMW-7S, screen spans clay, installed in tank pit SMW-1 A & B 26 46 Cross-screened SMW-4 A & B 25 45 Cross-screened Stockton Charter Way Commingled Plume Further Assessment Work Plan.doc 3