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• • • A 5-foot bentonite seal will be placed on top of the pack material. The bentonite seal will • be composed of high quality bentonite pellets, as manufactured by Volclay or equal. • Unchlorinated water will be added to ensure that the pellets expand to form a tight seal. • Properly wetted bentonite pellets are the most time-effective form of bentonite for this application. • • A bentonite-cement grout seal will extend from the top of the bentonite seal to the land • surface. Bentonite powder will be mixed with water before the cement is added to the • mix. Grout may be mixed at the well site by the contractor, or purchased from a ready mix supplier, provided that the supplier can provide current water quality analyses • showing the mix water to be free from VOC, chlorine, inorganics, or other sources of • contamination. The grout will be pumped into the annular space under pressure using a • tremie pipe placed at the top of the bentonite seal to ensure a continuous grout seal. The protective casing will be set in the grout. Grout will be left undisturbed for 24 hours after • placement. After the grout seal has set, it will be checked for settlement, and additional • grout of approved composition will be added to fill any depressions. • Grout will be composed by weight of 20 parts Portland cement to 1 part bentonite, with a • maximum of 10 gal of approved water per 94 lb bag of cement. Bentonite powder used • in the seal will be a commercially available product designed for well sealing. Overall, • the percentage of bentonite in the bentonite-cement grout will not exceed 5 percent by • volume, to prevent excessive shrinkage of the cement mix. • 3. Well Protection • Because the monitoring wells will be located within the pond berms, it is proposed that • they be constructed with above-ground completions to prevent entry of pond water. As • shown in Figure 5, above-ground completions will consist of an 8-inch protective casing • installed at the well. This protective casing will extend approximately 2 feet above the • ground surface and 3 feet into the well seal grout. The protective casing will be vented to the atmosphere by a lockable, hinged cap. The cap will prevent entry of water but will • not be airtight, so the well will be in open connection to the atmosphere to allow for • water level stabilization. The hinged cap will be locked with a heavy-duty padlock. The • top of the well casing will be a minimum of 4 inches below the protective casing cap. In addition, a '/4 inch diameter drainage port will be installed centered 1/8 inch above the • level of the concrete pad. Modifications may occur if required by local ordinance. A square concrete pad will be placed at the monitoring well site, with the well located at the center of the pad. The pad will measure 3 feet by 3 feet, and will be 6 inches thick. • The pad will contain welded wire fabric (No. 10 wire) at middle depth throughout. Four • 4-inch diameter, Schedule 40 steel posts will be installed around the monitoring well pad • to prevent damage to the well by vehicular operation. The posts will be installed a • minimum of 2'/2 feet into the ground and extend approximately 3%2 feet above ground surface. The posts will be anchored in concrete and painted fluorescent yellow or orange. • • The outside of the protective casing, hinges, and cover/cap will also be painted • fluorescent yellow or orange. Extra care will be taken to ensure that no paint or aerosol • Riverbank W WTP Workplan Nolte Associates,Inc. • March 2005 4 \\SasO\project\SA1542\mm_weIMew\gwmwiwp\wp.doc •