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w .s' Work Plan for Installation of Monitoring Wells(CW-01,CW-02,and CW-03) Cargill,Port Road No.8 Facility,Stockton,CA Sierra-Pacific Project No.95-128.04 Unconsolidated sediment present within the uppermost saturated zone, 5 to 20 feet bgs, consists largely of poorly-graded, silty-sand with traces of smectite clay (USCS Classification, SM). A medium-grained filter sand will be used to pack the well screens (RMC Lonestar #2-12 or equivalent product). It is anticipated that at least 95 percent of the filter pack will be retained by the 0.010-inch slotted screens. Adjustments to the well design, screen size selection, and filter sand application may be made in the field if subsurface information indicates a need to modify this plan. The monitoring wells will be gently surged to consolidate the filter pack before placing the bentonite seal. Additional sand will be placed in the wells to compensate for settlement and wash-out during purging. The filter packs will be followed with three feet of Enviroplug bentonite chips. The remaining two feet of each open boring will then be filled with Portland cement concrete. A schematic drawing of the well design is shown on Figure 4. The wells will be completed by installing flush-mounted wellhead boxes in Portland cement concrete. The new wells will be developed by purging with a submersible pump for period sufficient to grade the filter pack and flush fine-grained sediments from the well. The wells will then be allowed to settle and equilibrate for at least 24 hours. 3.4 Quarterly Monitoring Water levels and ground water chemistry in each of the new wells will be monitored on a quarterly basis. A minimum of three wetted casing volumes of water will be removed from each well with a submersible pump or with a disposable polyethylene bailers. The casing volume for a 2-inch-diameter PVC casing is about 0.16 gallons per linear foot. Sierra-Pacific will monitor field parameters (pH, conductivity, and temperature) of the purged water until the parameters have stabilized such that consecutive readings vary less than 10 percent from previous readings before sampling the well (Appendix B). Sierra-Pacific Groundwater Consultants, Inc. 3